Is it possible to give an endorsement via text message or email? Is it possible to give an endorsement to student pilot via email or text message?
For example, I gave an endorsement to my student for a XC. However, he stuck at the destination airport after the weather gets bad. On the next day, the weather became good enough to come back. But, he needs another XC endorsement to fly solo.

How can he receive an endorsement to come back?
Is it possible to send an endorsement via text message or email?
Is it okay to receive an endorsement from somebody CFI at the destination airport? (Let's say they don't know each other.)

That would be great if someone could help me!

Easy, peasy. Fill out a label/sticker with the endorsement printed on it. Then, all you have to do is sign it and place your CFI number on it. You can then either scan it or take a photo of it. Your student can upload the scanned document or photo into an electronic logbook. If they do not have an electronic logbook, they can print out the endorsement at the FBO to put into their paper logbook. When you and the student are together again, you can place the actual label/sticker in their logbook. Alternatively, you can use regular paper. Then you can cut the endorsement into a manageable size and tape it into the logbook. Also, if you and your student use the same software for your electronic logbooks, many have a function to sign endorsements electronically even at a distance (through the internet).


Could atmospheric effects cause a PA-30 to break up? About a week ago, a Piper PA-30 crashed into a residential area just a few miles from where I live. An engine was found to have landed a 0.24 nm from the impact site. Sadly, the pilot of the aircraft was killed. Thankfully, however, in spite of the crash occurring in a crowded subdivision, nobody on the ground was injured.

Now, to the heart of my query:

The NTSB preliminary report indicated an in-flight breakup of the plane. There was not an active thunderstorm in the area, but with 30 minutes or so a small cell had developed (source: me, I do live nearby). Are smaller aircraft subject to atmospheric effects that could cause an in-flight breakup? If so, what sort of atmospheric conditions, assuming a skilled pilot who wouldn't purposefully fly into known bad conditions, would be necessary to cause such catastrophic damage to a small craft like a PA-30?

Atmospheric conditions do not cause aircraft to break up in flight.

Improper aircraft handling in response to bad weather can cause an aircraft to be overstressed and then breakup.

So can improper handling due to disorientation.


Can I preheat my C150 by placing a space heater in the cabin? I have a C150 in a hangar, but no jet heater.  I was planning on just putting a directional space heater (an FH-06B) in the footwell and opening the cabin heat to let the heat through to the engine.

I figured that running that for an hour or two would be better than 20-min with a jet heater and almost as good as a heated hangar.

Testing this out, the rudder pedals get very hot, but not so hot that you can't touch them.

Are there any flaws with this plan?

Almost no heat gets to the engine.  What hot air drifts through the heater SCAT hose  might warm the exhaust muff a bit.  Plus you have that fire hazard heater in the cabin.

Get some of that aluminum flexible ducting used for clothes dryers and form the end to fit over the heater, and tape it on with aluminum speed tape. Set the heater on the ground to the side with the duct stuck in the bottom of the cowl.  Put some foam in the cowl inlets. 30 minutes to an hour is all you need.

A lot of people just stick the heater itself under the cowl but it's way safer to duct the air in with the heater outside and works just as well.

Preheating is traditionally all about warming up thick oil and the galleries the oil has to flow through, not so much heating the metal itself for the sake of the metal (the cylinder doesn't much care if it warms to 350F starting out at 20F or 50F as long as oil is getting to the parts).

If the OAT is above 20F and you are using multi-grade oil like Aeroshell 5W50, the oil will flow fine at ambient temperature and there is really no need to preheat if the rise in oil pressure is not significantly delayed from warm weather starting. Not saying not to do it, but if I had no preheater and it was 20 degrees, and I was using multigrade oil, I wouldn't ground myself and would start the engine anyway.


Which "Power Available" graph is more correct? Trying to understand the drag and power required/available graphs for a piston + propeller airplane. Both graphs are from current book/website and while they are showing mostly the same thing, I noticed the shape of the power available curves are different.
If I have to guess I think the second graph make more sense, since power available from a piston engine should be almost the same throughout the entire speed range.
*If the above is true, can you please also explain why it's not a perfect horizontal line across? Ie: if the engine is rated for 150 BHP, then the line should be at 150 BHP, other things equal (density altitude)
I feel like I'm missing something fundamental here but can't seem to work this out.
Thanks

Power is work getting done over a period of time.
Work is force multiplied by distance.
So when you are sitting at the beginning of the runway, at full throttle and brakes on, while thrust available is very high, power available is 0, because no “work” is getting done.
Edit- basically you are applying a lot of force, or using a lot of thrust, but since distance traveled is 0, no work was actually done.
Which is why the power available is indeed 0 at a velocity of 0, and increasing rapidly.
Note- the second graph is exactly the same as the first, only it is showing the curve beginning at some point after the stall speed.


Is it correct that a jet fighter can be used as a non-lethal (sonic) weapon? Imagine you have a crowd of people, who want to go to a certain territory (e. g. close to the border). An airplane flies over them such that when it reaches supersonic speed, there is a loud bang. People hear it, it hurts, and for several days they are deaf. That noise scares them off, and after some time most of them recover (i. e. there is no permanent injury to their ears).

I heard this story from a source I don't trust.

Can this be true? Could you, in theory, protect the border of a country from intruding crowds by simply flying over them (provided the crowds can't down the plane)?

Sonic booms from low flying aircraft, while loud, don't seem to cause hearing damage, as this F-14 pilot demonstrates during a Tiger Cruise air wing demonstration.

Now military fighters will sometimes make a 'show of force' in the form of a low altitude, high speed pass against threat forces which don't have a substantial IADS capability in order to motivate them to disperse under threat of employing ordanance on them if they continue belligerence.

UPDATE:  I found this story about an F-16 2-ship over Iraq on a CAS patrol mission.  The pilots get a radio call from desperate SOCOM operators pinned down by enemy troops at night.  The pilots cannot get a IR strobe to track for bombing, so the lead Viper uses a sonic boom delivered from a dive to frighten off the combatants.


Pros and cons of a pull-push propeller configuration What are the pros and cons of a pull push propeller in comparison to a counter rotating propeller?

Pusher-puller multi engine vs single or multi engine contra rotating propellers:

Pros:

Ideal configuration for a multi engine aircraft as it eliminates thrust asymmetry in the event of an engine failure.
As a consequence, improves safety during takeoff, landing and low speed, low altitude flight.
Can be a useful arrangement for multi engine flying boats.
Does not require oppositely geared engines nor heavy gearboxes.

Cons:

Engine crankshaft on the A/C centerline requires a more unorthodox airframe to accommodate which can present additional design challenges.
Does not fully eliminate propeller slipstream yaw depending on the aircraft layout.
Does not eliminate or reduce yaw from P-Factor.
Can be noisier inside the cabin than a twin with wing mounted engines.
Aft mounted Engine can be more difficult to cool due to indirect ram airflow.
Disrupted airflow from fwd propeller reduces the efficiency of the aft propeller.


How does one deal with a UNICOM operator directing aircraft like at a towered airport? Seems like an odd scenario, however I have experienced this a few times now.  A non-towered airport will have someone on the radio directing traffic and reading out weather info like barometric pressure.

I find this to be extremely dangerous and unwanted as the times I have encountered this, the person on the radio has no reason or training to do this (among other things).

Question:  If faced with this scenario what would you do?  Would you report the airport?  Am I looking too much into this and should just let it go?

You're almost certainly talking about a UNICOM operator, who is just an airport (FBO) employee who gives information to pilots on their request. The FAA's Pilot Handbook says:

  UNICOM is a nongovernment air/ground radio communication station which
  may provide airport information at public use airports where there is
  no tower or FSS. On pilot request, UNICOM stations may provide pilots
  with weather information, wind direction, the recommended runway, or
  other necessary information. If the UNICOM frequency is designated as
  the CTAF, it will be identified in appropriate aeronautical
  publications.

The important point is that UNICOM is not ATC. A UNICOM operator cannot give you instructions, clearances or require you to do anything. He can only give you information, and as PIC it's up to you to decide how to use that information.

The article that Porcupine911 mentioned is a great example of that. A student pilot thought that UNICOM was telling him which runway to land on, whereas in fact the operator was only recommending a runway (presumably based on the prevailing wind or whatever). Unfortunately, the operator recommended the opposite runway to the one that was actually in use by other pilots.

Like pilots, UNICOM operators vary in their experience and competence. A good UNICOM operator (in my opinion) will give you the local wind and altimeter information, tell you if there are other aircraft in the pattern or nearby, tell you which runway is in use by those aircraft, and give you any essential safety information (like a closed runway). But as PIC, I'm still going to listen to CTAF and AWOS and look for other traffic before choosing a runway and joining the pattern. It's also common for no one to reply to a UNICOM call (because the operator is out fueling aircraft in his other role as lineman, for example), in which case you're going to have to sort things out without it anyway.

So there's no need to "report" anything: UNICOM operators are a well-known and official service, but you have to know how to use them and what their limitations are.


What weight and balance form should I use for my checkride? I am studying for private pilot checkride and saw this form in an Oral Exam. Can you tell me where I can get this form online? If not, is there a better form for expiration and W&B data?

Use the same form you use every other time you go fly with your instructor.

If you're at the point of preparing for a check-ride and you have never had a weight and balance form before, you may want to sue your flight instructor (...kidding, kind of).

If I approach a new trainer-airplane for the first time, I find out whether someone has made a weight and balance form for the plane yet and ask for a copy.  If not, one can be created using the data in the AFM in Excel or other spreadsheet program.

I like to make mine fully-automated as much as possible for day-to-day usage, but they can still be filled in manually for the purpose of demonstrating the understanding to an examiner.

If you use LibreOffice Calc, you can download the one I made for the plane I use.

If you try to open it with other software, it will look screwed up, but you can still get the idea.

The light blue shaded fields are the only ones that can have data entered into them.  The graph is created based on the weight data, and it automatically subtracts the fuel burn based on the flight duration.  So the two connected dots are the takeoff and landing C.G./Weight combinations.

This was all done from scratch using the AFM's data.  It takes some work, but it is worth it.  Your instructor should have something like this made already.


How turbercle wings could generate aerodynamic advantage? Recently it has been discovered that turbercles present in fins from whales are actually providing hydrodynamic benefit for them.

As well, it has been proposed that this effect will provide benefit for airplanes.

From my perspective I can see strong difficulties to see this design able to improve current leading edges, as well, is a design working in water, in a lower Reynolds environment.

My question is actually three:

What is the aerodyamic (or hydrodynamic) mechanism and benefit that these turbercle provide?
How applicable is that to the airplane industry as proposed in several publications? (first thing I see difficulties is the existance of high lift slats and compatibility with these turbercles, probably more applicable to tails).
Which are the potential drawbacks of this design?

No, please, not another revolution of how we build airplanes again!

The linked article mentions two guys who pose as the discoverers of humps on whale flipper leading edges. What precisely have generations of marine biologists overlooked before?

Now to the humps: They produce a 3D flow pattern close to the leading edge which will help the flow to transition to a turbulent boundary layer more quickly. This is helpful at high angle of attack at intermediate Reynolds numbers (around 1 Mio) and will make the whales more maneuverable.

This is not to say that it will help any existing aircraft. Had nature given the whales the opportunity to integrate slats and double-slotted flaps into their flippers, they sure would have done so. This will help much more to increase maximum lift. Also, typical aircraft Reynolds numbers are much higher than those on whale flippers, and there turbulent transition is very quick. Right now, most efforts center on delaying this transition to reduce friction drag.

Swept wings will see a massive drag increase if this sort of leading edge is used.

The "tubercles" are a very specific form of turbulators and optimized for a narrow application. In other words, don't invest in this WhalePower company!


What is my BHP if I open full throttle and how is it controlled? In my Cessna 152 POH it is written that the horsepower rating is 110BHP at 2550RPM. My question is: is it 100% of the power of my engine or, as someone told me, if I open full throttle I will get 75% BHP? If so, then why don't I get 100% BHP at 2550 RPM? And is there any relationship between the mixture setting and BHP?

Rated BHP is measured at sea-level on a standard day. For the Cessna 152 I'm guessing you have an O235-L2 which is rated at 110HP @ 2550 RPM.

Now to understand how mixture affects the power produced by the engine you need to understand that the mixture knob controls how much fuel enters the cylinders to be burned with the air. As a combustion engine sparks, the fuel ignites but there is the fire triangle, Air, Fuel, Heat. Too much or too little of any of those pieces means a reduction of power or no power at all.

No, depending on the fuel type there is an optimum stoichiometric ratio where the proper amount of air and fuel are burned such that there is no extra air or fuel left over. For gasoline engines this is about 15:1, so for every 15 units of air, 1 unit of fuel is required. Having a richer fuel mixture results in an incomplete burn and may cool the cylinder temperatures, reducing power.

On the flip side, having too little fuel for the air can cause hotter cylinder temperatures and hot-spots on the cylinders. This causes detonation or knocking and can damage an engine very quickly. This is especially apparent in engines that have a lot of cylinder carbon deposits where the carbon can heat up and detonate the mixture before the spark plug does. Its like hitting the piston with a sledge hammer as its still coming up.

I don't have a graph from an O-235L but I did find one from an O-235C, which shows the relationship between throttle and BHP:

So you can see that reducing power from 2500 RPM to 2400 RPM gives a 10% decrease in BHP produced by the engine. Running at 2350 RPM is a 75% power setting (and in this graph nicely matches up with ~75 BHP). You can also see that there is a sweet-spot with relation to fuel consumption and produced power right around the 75% mark, which is usually refered to as the "performance cruise" value (best speed for fuel), and at 65% for "economy cruise" (best fuel).

So the mixture control needs to be leaned out based on the amount of air entering the engine. The levels of oxygen decrease with altitude and therefore the mixture needs to be leaned out. Its not uncommon for operations out of high altitude fields to perform take-offs with the mixture leaned, especially on hot days.

So its important to remember that the power produced by the engine is not a straight linear calculation. When you did your comment:

  But why the RPM is more and the BHP is only 75%? If I consider 2500RPM =110BHP then at 2400 it should be 105.6BHP which is 96% of total BHP

You assumed that the engine can produce power at 10RPM, which just isn't true. Lets take a better example and say that at 1600 RPM it is producing 25HP and at 2600 it produces 100HP, we can do the math then.

Using a linear interpolation formula this gives us 85HP which the graph tells us is 80 HP. Remember though, the graph is curved, and linear interpolation is, well, linear.


Can helicopter or aircraft intro flight hours count towards a private pilot license? I'm trying to figure out whether I'd prefer to fly helicopters or fixed-wing aircraft and am taking a few intro flights where the other person lets me fly for a little bit.

Can these hours count towards my helicopter / aircraft private pilot certificate? If yes, do I need a logbook or what kind of proof do I need?

Yes, these hours can be counted towards PPL, if you fly with a flight instructor next to you, which is generally the case if you go to a flight school and ask for "introductory flights" anyway.

In my case, they provided me with a tiny logbook for free so I can log my hours.


Are there standard ground-tether systems for unpowered aircraft? Do grounding systems have any standards or conventions?  Is tethering specified in any way?

I can understand the engineering aspects of the question, but I am wondering about regulation or convention.

.....I have a suspicion that any kind of formal or experimental craft / flyer is probably not regulated, so long as it doesn't 'escape' and remain in the air while it drifts into a controlled airspace.

I've participated in many balloon flights, and have never seen anything specific with this, so I suspect the answer is too simple ('no') or that this question is otherwise not well formatted
this question may be too close to the history of experimental-craft
I would appreciate help with proposing tags for this question

In the United States moored balloons (or kites) are governed under Part 101 of the FARs (a much neglected and very short corner of the regulations that also covers amateur rocketry and "unmanned free balloons" -- looking at your profile it's probably a section you'd find very interesting!).

In this particular case you're probably looking for Subpart B - Moored Balloons and Kites.

The FAA is mum on the specific engineering requirements of mooring systems - I expect they anticipate you will work with structural and mechanical engineers to design a tethering system that can safely hold the loads your moored object will place on it (or just tie it to the biggest, most structurally secure thing you can find, with a nice heavy rope and a proper knot).

There are a few things they ARE pretty specific about though.

Some operating limitations (altitude, size, location, visibility).
The fact that you have to tell them about it in advance
(At least if it's more than 150 feet AGL, per 14CFR101.15)
Lighting and marking requirements for the tether(s)
(14CFR101.17, which basically says the mooring line must have pennants (daytime) and/or lights (nighttime) to ensure visibility)
What happens to Balloons if the tether breaks
(14CFR101.19, which basically says if the balloon breaks free of its moorings you need a "rapid deflation device" that gets it down in a hurry so it's not just wandering around up there).

Interestingly they don't seem to care so much if a kite escapes its moorings.


Is there an exact solution for induced velocity during vortex ring state? In plots such as these, the section between -2 and 0 has no exact solution. As shown in the first image, the other two formulas are known, but not during vortex ring state because, as seen in the second image where the functions continue, neither match the data. After a bit of analysis, I have found that the following function is a close fit to the approximation given in the first image:
$$f(x) = \sqrt{1-\frac{x^2}{4}} + \frac{x(x^2 + x - 1)}{2}+\frac{4x^3}{x^3-8}$$
But I am not aware of any way I could even go about proving this is or is not the exact solution.
Thanks

By its nature, VRS is not constant over time or location on the rotor disk. Any estimation of induced velocity in VRS is going to be time- and/or location-averaged, this way we can use the same expressions for rotor power and so forth. Well, also in momentum theory, induced velocity is sort of averaged over the rotor disk; there are factors that account for non-uniformities in induced velocity along the rotor radius, but these are relatively simple.
The unsteady nature of VRS changes rotor geometry and this renders any estimation for exact induced velocity invalid. The change/flex in rotor geometry is significant even for one-piece rotors (think multicopters); with hinged rotors, the rotor blade dynamics need to be at the center of any analysis on induced velocity in VRS.
In my experience with a case study with Eurocopter X3, estimations for VRS work OK for high-solidity and rigid rotors; such as fixed-wing propellers in reverse thrust and the X3's propeller generating reverse thrust when the aircraft is in slow forward flight.


Where can I get statistics on landing incidents? I sometimes have the feeling that Airbus with augmented control are more prone to landing incidents (hard landings and runway excursions) than other models of aircraft with conventional controls.

Is there anywhere I could find data to perhaps back see if this might be correct? Such as a list of all landing incidents in Europe or the United States?

NASA collects statistics on aviation incidents through its Aviation Safety Reporting System, and the ASRS database is searchable online.  You can specify criteria such as the flight phase and aircraft type in your search.


What are the triggers of the MD-80's takeoff configuration warnings? I'm helping develop sounds for a MD80 simulation and I've noticed the MD has up to 5 alarms that fire when you advance the throttle and the aircraft is not properly prepared for takeoff:

"Beep beep flaps": I assume when flaps < 11 degrees.
"Beep beep slats": (???) Don't slats move along with flaps? Isn't it redundant?
"Beep beep brakes": I assume you have parking brakes set.
"Beep beep spoilers": I assume you have spoilers in other than stowed condition.
"Beep beep stabilizer": (???) Stabilizer trim is off for takeoff? What is the correct setting?

There are 7 conditions, not 5. The two you are missing are:

AUTO BRAKE
This warning is when the auto brake system (ABS) has detected a fault, or the system is not activated.
AUTO SPOILER
This warning is when the spoilers are not armed when the ABS is set to takeoff.

What flap setting triggers the warning?

  Flaps lever position does not agree with selected position in computer window.

Why slats and flaps have separate warnings?

While the flaps/slats handle is the same, there could be a mechanical reason the slats failed to extend properly, or a circuit breaker is pulled. Also historically, the earlier DC-9 from which the MD-80 is developed, had a handle that could be physically separated.

What stabilizer setting triggers the warning?

Same as flaps, when the position disagrees from the selected one in the computer (it varies from flight to flight based on the different conditions).

Source: MD-80 FCOM Section 6 Pages 76–77


Why is the A380’s with-reversers stopping distance the same as its no-reversers stopping distance? Thrust reversers, found on almost all jetliners1 and on the larger propliners, redirect engine thrust forwards, helping to slow the aircraft in the event of a landing or rejected takeoff.2  This takes some of the load off the aircraft’s wheelbrakes, reducing brakepad wear and tyre overheating, and considerably increases the total braking force available, allowing the aircraft to stop in a shorter distance than it otherwise would...3
...unless, that is, your aircraft is an A380, in which case, your reversers (all two of them), although they do reduce brake wear, apparently do not decrease the aircraft’s stopping distance (my emphasis):

The two reversers do help slow the A380—but not by much. In fact, unlike the thrust reversers on most airliners, including the Boeing 747 jumbo, they do not stop the aircraft in a shorter distance than brakes and spoilers alone. They do, however, take some of the strain off the brakes and are useful if water or snow makes the runway slippery.

How is this possible?  Any increase in available braking force should shorten the aircraft’s stopping distance (even if only by a small amount), so, assuming that the A380’s reversers produce a nonzero amount of braking force, the stopping distance for a given A380 at a given weight on a given runway under given conditions using maximum wheelbraking, maximum aerobraking, and maximum reverse should still be less than the stopping distance for said A380 at said weight on said runway under said conditions using maximum wheelbraking and maximum aerobraking, but no reverse thrust.
Yet, apparently, it isn’t.
Would someone like to explain this?

1: The main exceptions being the Fokker F28 and BAe 146, as well as early Caravelles.
2: A few jetliners, such as the DC-8, Il-62, and Concorde, can also use reverse thrust in flight, to steepen the aircraft’s descent angle without increasing its speed; in essence, the reversers are used as blown airbrakes.
3: This is especially important when wheelbrake effectiveness is degraded, due to, for instance, landing on a contaminated runway4 (which severely limits the amount of force that can be applied to the wheelbrakes without them locking up), with inoperative spoilers (which severely decreases the amount of weight carried by the wheels, and, thus, the amount by which their brakes can slow the aircraft), with one or more blown tyres (which renders the brakes on those wheel(s) useless for slowing the aircraft), overweight (which forces the aircraft to land at a much higher speed, where the coefficient of friction between the tyres and the runway is much lower than at lower speeds), with inoperative flaps and/or slats (ditto), with accreted ice and/or wing-leading-edge damage (ditto numero dos), with inoperative antiskid (which requires that the pilot(s) brake manually, and severely limit the amount of braking force [especially at high speeds] to prevent the wheels from locking up), with one or more inoperative wheelbrakes (for obvious reasons), numerous other things that I haven’t thought of, or any combination of the above.
4: For instance, one that is flooded (hopefully with water, not Jet A-1) or covered in (usually water) ice.

In all Airbuses auto-braking system aims for specific deceleration. Once the design target has been reached, the system does not apply more brake pressure although there usually is more available. So, if you apply thrust reverser with autobrake selected it will apply less pressure on wheel brakes and as the target deceleration remains the same, the stopping distance remains unaffected.

On slippery runways the autobrakes apply brakes until anti-skid starts to limit the brake pressure so in those conditions reverser would shorten the stopping distance. This would also apply to rejected take-off where maximum braking is commanded.


What does it mean for a payload to be "caged"? If an aircraft has a movable payload (e.g. camera) attached to it, two of the status modes are caged and stowed.

Stowed indicates the payload is retracted and or in a locked position.

What is caged?  I have found reference to "caged" in a couple of resources online, but the do not explain the term.  In some documents about passenger aircraft, it refers to cages in the luggage compartment, but this is completely different.

For something like a movable camera in a gimbal, or even a gyroscopic attitude indicator, it means that it is physically locked into place so that it can't move. On the gimbals (such as the camera pod in a predator, or other ISR asset) that can mean the camera is rotated into a stowed position, and then a pin is mechanically moved into place to keep the payload from moving.  This is usually done to prevent damage.

For a gyroscopic attitude indicator, you can generally cage it by pulling out a knob, and rotating it to a specific setting.  Again, this physically locks it into place so that it doesn't move.  This is usually done prior to shutting down as the mechanisms keeping the gyros spinning are powered down.  This is to prevent damage as well as give it a safe position from which to start from when power is re, applied to the aircraft.


Why is an F22 slower than an F15? An F22 has a higher thrust to weight ratio. The F22 has around ~70,000lbf thrust from its F119 engines, where as the F15 has around ~48,000lbf thrust from its F100 engines.

But every metric I can find indicates that the top speed of the F15 is higher than the top speed of the F22 (though I have not found a concrete reliable source on either).

How is this the case?

Aerodynamic heating will damage or destroy the composite wing of the F-22, especially around the leading edge where compression heating is highest. See here for the temperatures which supersonic flight causes.

Therefore, the F-22 has been restricted to Mach 1.8 for short duration and Mach 1.6 for prolonged flight. More speed will not be needed, anyway.

The internal weapons storage of the F-22 makes it bulkier than the F-15 which causes more wave drag. Also, the engine intakes were not designed to operate at speeds above Mach 2, so pressure recovery in them drops at higher speed. These two factors will affect the top speed of the F-22 negatively, so I would not be surprised if the F-15 is faster even without restrictions on the F-22 speed.


Where to find information on weight breakdown for helicopters? I would be interested in information on the weight breakdown for the different components of a helicopter. How much of the maximum gross weight is related to the airframe, engine, gearboxes, transmissions, rotor systems, avionics, etc.

Could someone point me to a data source where i can find such information?

I already found a very reliable source on technical specification of helicopters in the Type Certificate Data Sheets published on the EASA website here:
EASA TCDS List

Helicopter Performance, Stability and Control by Ray Prouty has a section on weight estimates on page 663. A few of the equations, rest are in the book:

I'm afraid Mr. Prouty used imperial units.


Why do some Air Forces not allow Color Blind Pilots? Some Air forces (Like the Indian Air force) do not allow Color Blind pilots. Is this local only to the IAF or a global procedure? Also, are there any regulations regarding commercial pilots not being Color Blind?

In fact, most militaries don't take colorblind people into flight school.

Colorblindness can be a serious problem for a pilot, because in the interest of cost and/or simplicity, not all indicators in an aircraft cockpit are colorblind-accessible. It's really cheap to use a two-way red/green LED as a status indicator (and by quickly alternating the current through the LED you get amber); it's much more expensive in electro-mechanical systems to combine text and color so that the status can be deciphered by someone who is red-green colorblind. It becomes easier again in a glass cockpit, but that increases cost and there are still concerns like screen resolution to consider when designing text-and-color displays. While it's in the general interest of aviation manufacturers to design certain avionics with as many overlapping visual cues as possible, it's not always feasible to specifically design towards colorblind accessibility in every circumstance.

Here is a set of spectra simulating how various forms of colorblindness would change a person's perception of the normal color set:

Protanopia and deuteranopia are various forms of red-green colorblindness, the most common form of dichromia (protanopia is a deficiency in red cells, deuteranopia a deficiency in green; the results are similar because red and green are close in wavelength). Tritanopia is commonly called blue-yellow colorblindness and is less common, with full colorblindness (monochromia) being very rare.

From this chart, we can deduce the following basic difficulties for a red-green colorblind person attempting to operate a plane:

Red on brown, or any dark color, would have no contrast. That would make reading (and setting) this Cessna radio stack nearly impossible:

... as well as decreasing the contrast of red lines on high-elevation sectionals (like Charlie/Echo space boundaries, non-towered airports, NDB frequencies etc):

Green and yellow are practically indistinguishable. That would make discerning the borders of inhabited low-lying areas on sectionals difficult:

... as well as making the color-coding of this airspeed gauge much less useful at a glance:

Blue and magenta are indistinguishable, as are cyan and white. That makes your GPS useless over water; where's the magenta line?

While you could probably get around most of these difficulties (buy a nav stack with blue LED displays, trace the borders of your sectional charts in something, configure the GPS to give you a white line, etc etc) these are all images that people with full color vision would be able to discern at a glance, which in an emergency situation is often a life-or-death advantage.

That point is especially true for military pilots, who are typically subject to more rigorous medical screening and training including very high requirements for visual acuity (often better than 20/20 uncorrected vision). If you can't see extremely well in a combat situation, you will either fail to spot an enemy until he has gained a significant advantage over you, or you will fire on friendly forces; either way, you're a liability. Coupled with the fact that everyone and their brother grew up dreaming of being a fighter pilot, flight schools get to be picky. Therefore, military aircraft cockpits are typically designed with the assumption of full color spectrum perception, because the only people who will ever be in them will be able to tell red from green, blue from yellow.

Consider, just as one example, a hypothetical conflict in the Middle East involving the Turks and Iranians, where NATO and thus the USAF is also involved. Both of these countries still operate variants of the F-4 Phantom. With an ROE requiring visual confirmation of a hostile, if you are in a USAF F-22, in a visual-range tangle with an F-4 whose IFF is inconclusive (either non-functioning or malfunctioning) and you can't tell the difference between these two rondels...

... you are screwed. The fact the Phantom is maneuvering against you is what any pilot would do when approached by an aggressor aircraft; a Turkish pilot isn't just going to sit there and be shot down by friendly fire, he'll engage defensive, so you can either shoot and risk spending the rest of your life in Leavenworth for dereliction of duty, or break engagement, presenting your tailpipe to the other craft and hoping it's not hostile. Fifty-fifty shot either way with a hundred and fifty million dollar plane on the line, not to mention your life. Your first clue it's an Iranian would be a missile launch, and no matter how much more advanced USAF craft are now than in the era of the F-4, an aircraft that has successfully launched a short-range missile at you has you by the wrinkly ones.

In addition, ground lighting systems are often not differentiable either. For instance, there is an important difference between a heliport beacon flashing green-yellow-white versus white-green-red (the one including a red flash is a hospital helipad and off-limits to gen-av traffic even in an emergency), but a red-green colorblind person may well not be able to tell the difference. Runway end lights are either green or red, indicating traffic direction (though there's usually a secondary cue of the approach array lights sequencing toward or away from the runway edge). Similarly, to a person for whom red is indistinguishable from white, the red-over-white glide slope indicator at the end of the runway would be useless (this would typically happen only with full colorblindness). Blue-yellow colorblindness is the other major type of partial colorblindness, and it would cause other problems like decreasing readability of navigation charts (for instance, incorporated land areas are yellow on FAA sectionals, while Victor routes and class B/D airspace borders are different blues) and trouble negotiating taxiways as the blue taxiway lights would look the same as yellow-white indicator lights elsewhere on the tarmac.


Why do airlines split themselves into domestic and international subsidiaries? As an example, Air Canada operates its own brand for international flights, but has a subsidiary called Air Canada Rouge for domestic and US flights. What's the reason for creating such subsidiaries?

Sometimes it can be for the purpose of recruiting pilots and cabin crew at lower pay. The airline may have pay agreements, possibly union collective agreements or else just formal agreements with non-union "associations", which set pay, working hours, and other conditions. This can be a barrier to offering ultra-low-cost tickets on the discount brand. If they structure the low-cost brand as a nominally separate entity, those agreements won't extend to it. See, for example, this news story on Westjet's new low-cost brand.

But there are lots of other brand-management reasons they might do this. They may want the big brand associated with reliable, high-service business travel for which they can charge full fare; and the new brand associated with cheap fares at the expense of everything else. Look at how the car companies spawn different brands so they can focus their marketing on luxury (Infiniti) mass-market (Toyota) and fun-and-cheap (Scion, now rolled into Toyota).


Is there a checklist for lightning strike? Is there a specific checklist or procedure to follow, after a confirmed or suspected lightning strike on the aircraft?

Or is a basic scan around the cockpit (plane is flying, no warning lights, no circuit breakers popped) sufficient?

For the aircrew, at least in the aircraft that I've flown, there is no defined checklist.  You scan and then deal with anything that occurs (inoperative equipment, pressurization issues, whatever you get) with whatever checklists apply: if the lightning knocked out a hydraulic pump, run the checklist for the inop pump, etc.

Once you're on the ground, maintenance has a HUGE checklist to work through, essentially checking every surface of the aircraft for damage and verifying that every piece of equipment still works.  The more that the crew can tell them (i.e. radios & instruments unaffected, no equipment stopped working, pressurization normal, etc), the more of it they can sign off from the crew observation.  But even then, it's still pretty lengthy.


Can a commercial airliner be landed on a highway, e.g. Highway 405 in Los Angeles? In a famous sequence from the TV show 24, a Boeing 727 is forced to land on the 405 in Los Angeles. It is a well-known myth that the interstate highway system was set up as a series of airstrips. But would it be feasible to land a commercial airliner on the 405 highway from an aviation perspective, given that there were few if any cars on the road? (Of course, anyone who lives in LA will tell you that there is never a time of the day or night when the 405 is not busy - so this is purely theoretical.)

It's possible, assuming the section chosen has no streetlamps, signs, overpasses etc. The police can block the traffic easy enough.

However, there would be zero reason to do so. If a plane has enough control to reach the highway, and enough advance notice to find a suitable part and block the traffic then it has enough control and time to reach one of the many airports in the region. Much less fuss for all concerned, and a much better equipped crash service.

In the prairies one could set up a fighter or bomber base on a random road, but again there's no need to - there's nothing nearby that would require it, heavy bombers or commercial planes would quickly destroy a normal highway and fighters could use the many civil airstrips in the area.

In Europe the math is different - opponents are a short flight away and destroying the airbases on both sides would be a top priority in any European conflict. See "Highway strip" in the usual reference for more details.


Does the stability of a mass change if the center of gravity is above or below the point of thrust? I was wondering if it makes any difference if the mass is balanced above or below the point of thrust. See image below for clarification:

In the image you can see two configurations. The red arrow / point in both represents the force / location pushing against the mass (hull of craft). This force can be an impulse or prolonged force. the blue arrows in both represent the upwards force of the rotors. And the green arrow represents the gravity in both.
I would imagine that balancing (keep the craft hovering) would be easier with the mass below the rotors since then gravity helps pulling the center of mass back under the center of the rotors. While if the center of gravity would be above the rotors and it would be pushed to an offset gravity would help make this offset worse.
So does it makes any difference for the stability of the mass (center of gravity) is above or below the point of thrust?
just to be sure config A represents the mass and center of gravity being above the point of trust, and in config B it is below the point of trust.
I am have no engineering or physics background so please explain this as simple to me if possible :)
Let me know if this is not the right place to ask and maybe suggest me where to ask this then.

The most stable way to maintain a hover is center of mass below and center of drag above.
What confuses many people is how a "pendulum" reacts while being accelerated, and how it reacts when air drag stops acceleration.
Placing the center of drag above the CG is commonly seen on aircraft tails.  This is one reason why "classic" aircraft tails are "upright". Wing dihedral serves the same purpose,
to roll a side slipping plane back to level.
Once hover stability is achieved, one may reduce drag above or add drag below to reduce stability enough to allow controlled movement.
Leaving the Center of Gravity underneath will increase stability where when the object is not accelerating.  But "pendulum stability" is more properly called "pendulum  and drag stability", as in a parachute.
So, in your case, keep the triangle above with light materials., but have your weight below the rotors, and just use the rotors to lift and propel the aircraft.  But if you want a separate (red arrow) source of propulsion, try to put the center of horizontal drag and CG in the same spot, and push there.


PA/APV Glidepath Descent and Obstacle Clearance Slope's lowest point determination I am studying the US Terminal Instrument Procedures manual (TERPS) and as I was skimming through the guidelines about Sloping Obstacle Clearance Surface, I came across the image below from section 2-1-4 (the red circle remark is mine):

The problem is, I can not understand how the lowest point of the OCS, which I have marked with the red circle, is determined. It seems to be a point close to Departure End of Runway (DER), but where exactly?

The only things TERPS states is:

  Descending on a PA/APV glidepath. The obstacle evaluation method for descent on a glidepath is the application of a descending OCS below the glidepath. The vertical distance between the glidepath and the OCS is the ROC; thus ROC = (glidepath height) - (OCS height). The ROC decreases with distance from the precise final approach fix (PFAF) as the OCS and glidepath are converging towards the landing surface (see figure 2-1-3). The OCS slope and glidepath angle (GPA) values are interdependent:  OCS Slope = 102/GPA; or GPA = 102/OCS slope.

Could someone point me in the right direction?

EDIT: What I mean is, why (and how do I calculate the extra distance) does the first image apply, rather than the second?

I can't yet find where this is indicated in TERPS, but it appears that the OCS surface starts at the point before the threshold where the GP is 250 feet above the threshold height.

I'm inferring that from this document about calculating VNAV criteria.

It has the above diagram and says:

  The distance from the runway threshold where the OCS surface starts
  (Section 1) is defined by the formula D = (250-HATh)/.052407779

where HATh is the same as TCH, which is a standard 50', and the number .05240779 is the tangent of 3°. So far I'm unable to reference that back to any TERPS definition, but maybe you can find it.

There's an interesting article discussing how TCH is defined over at Code7700.com


Why do some helicopters have the tail rotor mounted higher than the tailboom? Why do some helicopters have the tail rotor mounted high above the tailboom, whereas others have it at the end of the tail boom?

Above the tailboom:

Wiki Commons

At the end of the tailboom:

Boeing.com

I know the reason for having tail rotors, that's not the question at all. I am just curious as to whether the heavier helicopters have different torque counter requirements than the lighter ones?

Generally I notice that the heavier ones have the tail rotor mounted higher up and the lighter ones have it on the boom.

In R/C almost all of the 3D  models have the tail rotor at the same level as the tailboom.

I've been thinking hard about this question, how to answer it and indeed, whether to answer it or not at all since the question itself is a good one but borders on "too broad".

The answer from aeroalias is good but doesn't offer any "whys". Tail rotor design is also a fiendishly complex subject and, like most things in aviation, is the result of many compromises and inter-dependencies.

As an example of how complex it is, there are two helicopter dynamics "bibles" by Ray Prouty and Walter Wagtendonk. Neither of them fully explain tail rotors and indeed, Prouty often says "for reasons I don't understand". If Prouty doesn't understand something, then you are on a safe bet to say that the majority of helicopter pilots don't understand it either. You need a Physics PhD to design helicopters, you don't need a PhD to fly one.

So this is from the understanding of a pilot without the PhD. I will leave out any mention of which way the main rotor rotates and on which side the tail rotor is mounted since it will needlessly complicate the already complex. I am also assuming a generic "standard" helicopter with a single main rotor and both vertical and horizontal stabilisers. Of course, there are designs that deviate from this but to cover all scenarios would need a book, not an answer on SE.

I'm deliberately ignoring a bunch of other dependencies such as "is the advancing blade of the tail rotor at the front or the rear?"; "is it a tractor or pusher tail rotor?"; the interactions between the main rotor down-wash and vortexes and wind and what happens in high yaw rate situations (fast pedal turns) and sideways flight. Yes, tail rotor design is probably the most complex subject in helicopter dynamics.

As you know, the tail rotor counters the torque applied to the fuselage by the rotation of the main rotor. Since the tail rotor generates lift in the horizontal axis, it also produces a force which will move the helicopter across the ground (tail rotor drift).

To offset this, the rotor disc is rigged such that it tilts in the direction of this movement to introduce a horizontal component of lift which opposes the tail rotor drift and keeps the helicopter steady in the hover. If not rigged to do this with the cyclic neutral, then the pilot will subconsciously hold a little lateral cyclic to hold a steady hover. It's subconscious because you do not hold attitude and position by positioning the cyclic. You position the cyclic to hold attitude and position.

So we now have two horizontal thrust components, one from the main rotor and one from the tail rotor. Now all forces act around the centre of gravity, and it is from there that all accelerations to the aircraft to move it are measured. Therefore, if the centres of these two forces are not inline with respect to the CoG, i.e. the same vertical distance from the CoG, then a rolling "couple" is created between them and the fuselage will roll until the opposing forces are equal and opposite. This is why many helicopters hover with one skid low.

As the aircraft moves into cruise flight, the vertical stabiliser increasingly offsets the main rotor torque so the power required by the tail rotor and the angle of attack needed to offset torque reduces, therefore the roll couple force reduces and the deck of the fuselage will roll back towards level. The horizontal stabiliser also generates lift which further counters the roll such that in cruise, you are using little, if any pedal.

This is our main compromise. If the horizontal components of the lift vectors are not aligned with each other, then you accept an uneven deck in the hover. If the design calls for long periods of hovering (police work, search and rescue etc), then your design is likely to be that both centres are aligned and are above the CoG (the main rotor thrust vector must always be above the CoG because of the engine and main rotor gearbox). It is my guess that the Apache has the tail rotor mounted high to align the centres to provide a level and stable deck which makes sense on a gun platform designed to hover for long periods.

If you look at a model where the tail rotor and main rotor vectors are not centred, for example the R22, then they do indeed hover with one skid significantly lower than the other. This also has the effect of adding a couple of feet to the safe hovering height since catching the skid on the ground whilst rotating or moving sideways is almost certainly a generator of Bad Days(TM).

The trade off is that to position that rotor at the top of the fin requires an additional gearbox and drive shaft at the base of the fin adding weight, complexity and maintenance requirements. Not a concern for the Apache; certainly is for the R22.

Why does the Comanche mount the tail rotor so low, at the end of the boom? Well, I'm not privy to the design decisions and I can't find any authoritative references to them so I am using guesses, which I hope are educated guesses.

One design goal of the Comanche which is not present in almost any other helicopter is stealth.

Rotor blades make great RADAR targets, especially the tail rotor. It's relatively short blades rotating at high speed and stuck way out there in the open provide a lot of strong RADAR returns. There's not much you can do about the main rotor except in the blade profiles and materials (the details of which I expect are classified) but by mounting the tail rotor closer to the main body at the end of the boom and in a fenestron, those RADAR returns will be significantly reduced.

The tail rotor air flows are also going to help to disturb and cool down the engine exhausts by blowing them sideways and mixing them more quickly with the cooler ambient atmosphere. If you look closely, you'll see that the tail rotor is mounted directly aft of the exhausts. I am further guessing that the tail rotor gearboxes are good sources of heat so removing one (by mounting the tail rotor low) also contributes to stealthiness. The added benefit of mounting in a fenestron is to protect the tail rotor from tree strikes and so on, always a concern in nap of the Earth flying.

Because that tail rotor is mounted so low, there is a strong rolling couple and indeed, the Comanche flew very much skid low.

(Source)

To reduce this tendency, the tail rotor is canted (all this from memory) by about 20 degrees which reduces the horizontal thrust vector component and produces around 1000 lbs of lift through the vertical component which offsets the tail low tendency produced by having the TR below the CoG. That high dual horizontal stabiliser is also going to produce lift to keep the tail up in the cruise as the TR power reduces.

From Peter Kämpf:

  The 20° canting of the whole vertical also removes a powerful RADAR reflector. Flying low, a perfectly vertical tail would return horizontally oriented radiation, while the 20° angle lets one side reflect RADAR energy into the ground and the other into space.

There is a lot more to all this but as I say, it really needs a book to start to fully address all the factors but hopefully, this answer walks through the main lines of thought.


What passenger airplane has the lowest fuel efficiency? What is the airplane with the lowest fuel efficiency? To set some parameters, let's limit it to the following:

Must be manufactured between 1960 and modern day.
Must be a non-military passenger airplane.
Must use liquid fuel (100LL, Jet-A, etc.)
Can be a commercial aircraft or GA airplane, but must be manned and have passenger seats. No helicopters!
Spacecraft don't count! (You know you were thinking of this)
Must be in the highest standard seat count configuration for the airplane. You cannot take a large jet like an A380, and remove all of the seats save for one!

Fuel efficiency is calculated in pmpg (Passenger miles per gallon), which is the total miles per gallon of the aircraft, divided by the maximum number of seated passengers. This does not include pilot, copilot, or any associated crew as passengers.

Please link back to credible sources, and show how you arrived at your pmpg in terms of mpg and passenger count.

TU-144 =  9.78 passenger mpg

TU-144 figures found on another forum, from an official flight planning document:
https://www.airliners.net/forum/viewtopic.php?t=1355819#p19483811

--

By comparison the TU-104A = 15.88 passenger mpg

From an old Aviation Week story on the TU-104:
http://aviationweek.com/blog/tupolev-104-harsh-proof-rapid-soviet-progress-1956

Using that article and assuming 0.8 l per kg and 20% reserve, imperial gallons. These figures (especially TU-104A) are rough and would vary by loading and flight profile.


How many hydraulic systems does the Boeing 757 series have? How many hydraulic systems does the B757 series have, does it have a Power Transfer Unit (PTU)?

What is the operating pressure of the hydraulics in the Boeing 757?

How big is the hydraulic reservoir?

The Boeing 757 has three fully independent hydraulic systems. The three systems are "Left," "Center," and "Right."

The left system is powered by an engine driven pump (EDP) on the left hand engine, an alternating circuit motor pump (ACMP) located in the wheel well, and a power transfer unit (PTU) powered by the right hydraulic system.
The center system is powered by two ACMPs located just aft of the wheel well in the wing to body fairings, the center system can also be powered by a ram air turbine in an emergency.
The right system is powered by an EDP on the right hand engine and an ACMP located in the wheel well.

All three systems operate at a nominal pressure of 3000 psi.

Each system has its own reservoir. The reservoirs are air-on-oil type reservoirs and use engine bleed air to pressurize the fluid to provide proper head pressure for the pumps. The left and right reservoirs have a full fluid capacity of 6.6 gallons (on the ground), while the center reservoir is 3.5 gallons (on the ground). The reservoir itself is larger than these full volumes (roughly 50% larger) to allow for various effects, like thermal expansion of the fluid and different exchange volumes in actuators.

In addition to the 2 EDPs, 4 ACMPs, 1 RAT, and 1 PTU, there are also two small electrical pumps in the left system that are used to unlock the uplocks on the landing gear for alternate extension. These pumps only function in flight when alternate extend is required, but they are also used to release the gear doors on the ground for maintenance using switches on the belly.

Any one hydraulic system can fully control the aircraft, and further any one pump on any one hydraulic system can fully control the aircraft.

The image below gives a good block diagram of the 757 hydraulic systems. Another good resource for learning about the configuration of hydraulic systems on commercial aircraft is SAE AIR5005 "Aerospace - Commercial Aircraft Hydraulic Systems."


Why do jet engines smoke? (YouTube video)

From the video linked above, I was wondering why the engines emit so much smoke? Has something gone wrong? Poor maintenance? Isn't it dangerous?

Smoke in jet engines is usually from unburnt or partially burnt fuel (or by water injection). Early jet engines used to create a lot of smoke due to these reasons (and due to lack of environmental regulations).

KC 135 engines creating smoke due to water injection By USAF Photographer - USAF photo, Public Domain, Link

Water injection, while cooling the engine, quenches the flames to an extent, resulting in unburnt fuel, which comes out as smoke. However, aircraft have moved away from water injection, reducing emissions.

Another reason for the smoke is inefficient combustion- older jet engines (turbojets in first aircraft and low bypass turbofans) were not as efficient as engines today, which premix the fuel with air and pre-vaporise it before combustion, rather than using droplet combustion- basically mixing fuel more evenly with air. Requirements of fuel efficiency along with stricter regulations mean that engines today have less emissions compared to their predecessors.

Smoke during Boeing 707 takeoff; image from nycaviation.com

In this case re-engining the aircraft with more efficient ones usually results in a reduction of smoke. For example, the USAF re-engined the KC-135s (from Pratt & Whitney J-57-P-59W turbojet to the CFM International CFM56 turbofan), which along with the elimination of water injection, reduced smoke.

On the top is KC-135s from an exercise in 1979; image from network54.com. Below that is KC-135Rs from Singapore Airforce; image from reddit.com


What is the real difference between aerospace and aeronautical? I see people using these two words interchangeably. But I feel there is a huge difference between the both.

Aeronautics is a subset of aerospace.

  Aerospace is the human effort in science, engineering, and business to fly in the atmosphere of Earth (aeronautics) and surrounding space (astronautics).
  source: https://en.wikipedia.org/wiki/Aerospace

They are, somewhat incorrectly, used interchangeably - to colloquially refer to the broad subject of "flight".


What do the different colors of weather stations indicate on SkyVector? In this particular map

from SkyVector, what are the meanings of the different colored circles, and for the different amounts of 'fill-in'?

It's obvious by hovering over them, that they are weather stations, as the weather info will pop-up, but there doesn't seem to be anything (to my untrained eye) about the weather pop up that would indicate a need for the different colors.
It's also obvious that the color doesn't indicate something permanent about the station, as last Friday, there were large swathes of different colors across the USA, while today almost everything is green.

Colors
At present1, they mean (image source):

For more details, please see this description.
Fill-ins
These are called sky/cloud coverage.

Image Source

1 From SkyVector:

The color is controversial because the FAA is making the NWS swap the
colors for VFR and MVFR. When the new aviationweather.gov becomes the
current aviationweather.gov, we'll change our colors to match.


What is your responsibility when a distraught pilot is on frequency? I found the recent SeaTac incident with a suicidal pilot frightening. I myself remember being in very bad places mentally, and it got me to wonder what I should do if someone is on frequency, making dangerous maneuvers, and clearly has lost all hope and interest in life.

I looked through FAA guidelines and ICAO standards prior to posting this, and the only conclusion I could make is there is only an IMSAFE for you, and not for others.

But in the age of very realistic flight simulators, aviation can seem like a simple, beautiful, fun, and quick way to end one's life. If I am witnessing this, audibly on frequency and / or visually, what do I do? IMSAFE, but how about them?

On frequency, if control is responding to the distressed aircraft you should stay quiet and let them work the problem. This would not be a great time to ask for flight following or traffic advisories and you should expect neither. You should be listening for instructions broadcast to all aircraft in the area and possibly an announcement to change frequencies.

A controller may try and hand some aircraft off if possible to ease their load.

Depending on your situation, and if possible, it may be warranted for you to fly out of the area, or avoid it if you are inbound. In some cases ATC will work to get the aircraft to stay in an altitude block if you can hear this assignment, you should stay clear of that block.

It's not really your responsibility to play chase plane but reporting things on frequency may be warranted if the channel is free, you are not stepping on a controllers attempt to contact anyone, and the information is pertinent to the situation. Perhaps you saw the aircraft crash site from the air; if you can provide a definitive location it may warrant reporting. Saying something like, "Hey I see that guy" is not really helpful especially considering today's radar (although coverage is far from perfect) and soon to be ADS-B systems.

It is unequivocally NOT your place to attempt to contact or otherwise interact with the distressed aircraft. This will only increase confusion and create a situation where you are potentially contradicting what ATC is saying. To address your specific situation, controllers on the ground have the ability to get the required people on the line to work the problem. If someone with suicidal intentions is on the frequency controllers will respond (and in this case did respond) in a proper manner. It is not your place to attempt to talk to them as you are likely unqualified to do so and will likely worsen matters.

As a slight caveat to the above statement, there is one instance in which you as a pilot should get involved. In some areas of the country (or the world for that matter) where facilities are far apart and radio coverage at low altitudes is limited you may be in a situation where you can relay important information to a station that is with in your range but out of range of the aircraft in distress. In this case it is important to know this is the case and that you are not simply in range of an aircraft but out of range of the facility they are communicating with. If the distressed aircraft is making repeated, uniform calls with no clear response you may consider contacting approach and asking if they are aware of the situation. This is a very specific case and should be handled as a one-off on a case-by-case basis.


How does ATC handle a controller with psychological trauma? I've finally got around to watching Breaking Bad, (spoiler alert) in the last episode of season 2 a bereaved ATC controller accidentally causes a mid-air collision.
I am not asking whether the actual collision scenario was realistic, my question is whether the scenario of a controller with a very recent tragic loss being alone at the console is realistic. How would FAA ATC management deal with a controller who'd recently suffered a bereavement like loss of a loved one or some other sort of psychological trauma? What is the route back to work: is there a mandatory off-work policy, psychological assessment or supervision period?
I've limited this to FAA in order to keep it from being overly broad, I'm sure practices vary widely.

To my knowledge there is no automatic loss of medical clearance following a death in the family. The relevant order is JO 3930.3, current version C. From Chapter 3 Section 1 Medical Status we have the following paragraph:

3. Interim Medical Condition of an ATCS. Illnesses, injuries, or other medical conditions that could affect the employee’s eligibility for medical clearance may occur between periodic examinations.
a. When an ATO Air Traffic management official becomes aware of an ATCS’s absence due to a medical condition, treatment, or drug/alcohol related incident, the Air Traffic management official must promptly inform the FS so that a determination may be made whether the illness or injury affects the ATCSs medical status.
b. An ATCS must report to the FS office the following as soon as he/she becomes aware of the condition, but in any event before performing safety-related duties:

Any assessment or treatment of injuries, illness or other medical conditions by a health professional, except for conditions as noted in Chapter 1 paragraph 9.e,
Any occupationally related injury or illness, and
Any conduct that represents a violation under a DOT or FAA Order such as DOT Order 3910.1 series.

c. Air Traffic management must inform the FS when an ATCS receives medical attention and may request an opinion from the FS regarding the medical status of the ATCS.
d. The FS evaluates available information, obtains additional data if needed, and arranges for examinations or further evaluations as required to make a medical status determination in accordance with this Order.

None of that explicitly accounts for grief but either the controller themselves or management could decide the controller's actions and mental state warrant reporting to the flight surgeon.
There are various ways for a controller to try to deal with grief and loss, for example the FAA contracts with Magellan Health as the agency's Employee Assistance Program provider (I believe up to eight counseling sessions per year are allowed for free), and NATCA (the controllers' union) provides a peer-to-peer service called CISM. The EAP is supposed to be confidential but can pass information to the agency if they suspect the employee has a substance abuse problem.
The collective bargaining agreement provides that up to ten days of annual leave or leave without pay shall be granted (at the discretion of the employee) if there is a death in the employee's family. So you get two weeks off guaranteed, if you want it, but that doesn't really pertain to your medical clearance.
The realistic answer is, if the controller really needs to talk to a therapist or counselor about what they're feeling, they have three options:

Keep it bottled up inside,
Visit an out-of-network therapist, pay out of pocket, and use a fake name if possible, or
Visit an in-network therapist, create an official record of the visit, report it to the flight surgeon (because they'll be really mad if you don't report it and they find out anyway) and hope you can successfully argue to get your medical back after it gets pulled.

If the medical never gets pulled, I don't think there is any additional supervision mandated. But the controller's coworkers will probably keep an eye on them, and if management is on the ball they probably will as well.
If the medical does get pulled, and it takes too long to get it back, the controller will first lose currency and then proficiency on the control positions they've been certified for, depending on how long since they last worked. If they lose currency they will need to re-take a "certification ride" where they control for a decent amount of time while a supervisor is plugged in with them to make sure they still know what they're doing. If they lose proficiency they will probably need to go through their facility's training process again.

In general the likelihood of someone being completely alone in the operational quarters is relatively small, at least at a larger facility like ABQ. Perhaps on the overnight shift there will be just one person in the tower cab and one in the radar room, but generally more than one control position will be open in each area, and higher-up management are generally strict about having a separate supervisory position open as well. (Each operational area needs a supervisor position at all times, but this position doesn't have to be a management supervisor—controllers who are so certified may work the supervisor's desk—and in times of low staffing the supervisor position may be combined with any given control position.)


Why do airlines outsource regional flying? The three major American airlines (American, United, and Delta) all have regional brands. These brands are actually operated by other airlines (ie: SkyWest). Air Canada has a similar regional brand called Air Canada Express.

Obviously, these flights are important for getting passengers to the airline's hubs. It also seems obvious that this type of flying is quite profitable because there are a number of regional airlines that are flying for these carriers. Why don't the big airlines just fly these routes themselves? Why have they all chosen the path of outsourcing?

This article breaks it down super nicely, and has most of the info you are looking for. The key quote from my reading of it is

  The simple answer is that using regional airlines saves major airlines
  money compared to them operating a flight themselves. Where do the
  cost savings come from? For one, employees are paid significantly
  less.

There are also some serious union and historical reasons for the setup, regional airlines code sharing with majors is in some regards a way to skirt around union negotiations

  The first reason is that it would likely eliminate the cost advantage.
  Most major carriers have negotiated with their unions that flights
  with fewer than “X” number of seats will be operated by regional
  airlines. You can bet that if the regional airlines became part of the
  major airline (even if a separate division), the major carriers’
  unions would be fighting for significantly better pay for those crews.

  ...

  Historically another reason the major carriers have contracted out to
  regional carriers is because it allows them to share some risk. Keep
  in mind that historically airlines are ridiculously unprofitable
  (though that has changed recently). So leased planes were almost a
  liability rather than an asset, given that they were losing money with
  just about each flight.

Here is another interesting paper on the subject and good info here.


Why are there no blended-wing passenger airplanes in operation? Blended wings are more beneficial when it comes to fuel efficiency increase and noise reduction. However, no manufacturer has decided to produce these airplanes for major airline operation so far. What are the inhibiting factors in the industry for not using this configuration?

From what I can guess:

It is a complete new configuration with low experience on it. High risk.
Aircraft will be in VLA sector (>500 passengers), a sector not very attractive nowadays.
The 90 seconds evacuation limit needs to be observed.

All studies which so far showed an advantage for blended-wing bodies (BWB) were flawed.

The trick mostly used is to compare an existing airliner with a hypothetical BWB which uses equally hypothetical engines of improved efficiency, like what could be expected 20 years into the future. This masks the inefficiency of the BWB concept and makes the combination come out ahead.

The BWB will always have more surface area than a comparable conventional design. This translates into more friction drag and more skin mass, which more than offsets any advantage given by the bigger wing root (which helps to reduce wing spar mass). If you like real data, use the Avro Vulcan as an early BWB and compare it to its contemporaries. Note that design attempts for an airliner based on the Vulcan (type 722 Atlantic) went nowhere.

Why are these BWB studies published? The author gets more attention when he/she claims a "revolutionary breakthrough" than when he/she is more honest and admits that the concept is a dud. Even Boeing or Airbus like to publish BWB studies, so the public gets the impression they are ahead of the competition. It is sickening to read such academically dishonest studies - you need to spend time to dig to the bottom of the thing and to unravel the plot; however, once you have done this a few times, they all become alike. But compared to studies made 60 or 80 years ago, where the author factually lists what he did and why it didn't work out (which is the only way you can learn something), those modern studies are a waste of time.


What is the rationale of a weight/passenger value for the ICAO TCAS requirement? What is the rationale for the figures 5,700 Kg and 19 passengers?

Excerpt from TCAS's Wikipedia entry page:

  It is a type of airborne collision avoidance system mandated by the
  International Civil Aviation Organization to be fitted to all aircraft
  with a maximum take-off mass (MTOM) of over 5,700 kg (12,600 lb) or
  authorized to carry more than 19 passengers.

The numbers aren't random, though at first glance the rationale may not be obvious.
Weight
5700 kilograms is (roughly) 12,500 pounds - This aligns with the FAA definition of a "large aircraft" (an aircraft with a maximum certificated takeoff weight of more than 12,500 pounds).
Large aircraft tend to be "working airplanes" in passenger or cargo service, and will be operating to/from busy terminals. They will therefore benefit substantially from TCAS, and the operators can theoretically afford to equip their fleets.
Seating Capacity
Carrying more than 19 passengers further includes aircraft which may not be "large aircraft" but might be used as "working airplanes" in regular airline/commuter service carrying passengers (and would therefore benefit from TCAS, and theoretically be producing revenue to offset the cost of equipping them).
This roughly aligns with FAR 121.391 flight attendant requirements (Even relatively small aircraft - maximum payload of 7,500 pounds or less - are required to have a flight attendant on board to assist in evacuation in the event of an emergency, so it logically follows that such aircraft should be equipped with TCAS to avoid at least one possible type of emergency (mid-air collision).

As Federico pointed out, this is largely a cost/benefit trade off (nobody would argue for a flight attendant on a Cessna 150, similarly the TCAS safety features would be overkill for most Cessna 150s in the world).


How is the airfoil of a fixed wing ultralight constructed? This is a good example of the type of ultralight I am trying to build:

(Source)

How might the airfoil be constructed in this plane?

My guess was that it's mostly created by the cables that suspend it, but then again, one like this:

(Source)

Doesn't have those cables, so how are the wings constructed?

wood?
a bag of helium?
something else?

If you could link me to some sort of visual it'd also be much appreciated.

There are various ways to build a wing like this. Ultimately you need something to shape the rigid form which you then pull fabric over. The cables do not provide the wing shape they provide support for the length of the wing. This goes back to the fairly early days of aircraft design for heavier than air flight,

  In 1909,Frenchman Louis Bleriot produced an aircraft with notable design
  differences. He built a successful mono-wing aircraft. The wings were
  still supported by wires, but a mast extending above the fuselage
  enabled the wings to be supported from above, as well as underneath.

Mast/cable wings fell out of popularity as spar supported wings became viable in the early days of heavier than air flight.

  As early as 1910, German Hugo Junkers was able to build an aircraft
  with metal truss construction and metal skin due to the availability
  of stronger powerplants to thrust the plane forward and into the sky.
  The use of metal instead of wood for the primary structure eliminated
  the need for external wing braces and wires

You can use wood like this. Or wood with a foam core.

(source)

You can also achieve the same goal with a metal rib assembly.

(source)

If you have the budget carbon fiber is also an option.

There are a few ways to cover the wing frame once its complete but ultimately the fabric must be pulled over the form and, in some capacity, shrunk to make it taught.

Fabric covered wings have lead to some of the most successful airplanes in history. There is quite a bit of info out there on how to work with fabric in relation to aircraft. The FAA has a nice handbook on it here and more info here.

If you intend on building something I would take a look at this site about building a Breezy. It looks like you can even get a full kit for one here.


What's the rattling noise on an A320? I recently flew on an A320, and during takeoff when the aircraft was rotating, I heard a loud rattling noise. If I had to guess I would say it came from the gear below but I can't be sure. I was sitting slightly behind the wings. The noise stopped when we lifted off the runway.

Edit: The noise sounded a bit like a stick shaker, a loud vibration.

Rattling that disappears after liftoff is normally associated with a vibrating tire transmitting vibrations up through the airframe, and causing some sort of interior panel that is a bit loose to rattle in sympathy.  On most airliners the brake system applies the main wheel brakes momentarily, once weight-off-wheels, to prevent the usual spin down vibrations during retraction (Nosewheels normally use a friction brake that contacts the tire when it's fully up for the same purpose).  So if the wheel is shaking and making other things shake it will stop as soon as you're airborne.

Airliner wheel assemblies are usually statically balanced vertically like motorcycle tires, not dynamically balanced on machines like car tires (I shudder to think of the cost of a dynamic balancer that can do wheels that big).  You can have a vibration mode that comes in at a certain tire RPM, so all of a sudden starts to shake, then you lift off and the brakes are tapped by the braking system to stop the  wheels, and the vibration stops.


Can cruise pilots/second officers go for years without doing a takeoff or landing? I was looking at the description of this role i.e. someone who provides cruise flight relief flying. As conceivably, someone could be bonded for multiple years because of the type rating being covered by the airline, it is possible they could 'fly' for multiple years and yet never actually do a real takeoff or landing?

Every airline pilot is required to maintain currency. In a 2nd officers case most of this will probably be in a full motion simulator.


Why are some taxiways named with two characters? The picture above is a diagram of the Taoyuan Airport, Taipei, and as you can see in the diagram, some taxiways are named with two characters like “NC, NP, WC.” My question is: Is there any good reason, if any, why some taxiways are named with two characters when, clearly, there are other single letters still available?

Coding the taxiways this way makes it easy to create mnemonics. Note that from northwest to southeast, the first letters are alphabetically increasing. From southwest to northeast the numbers are increasing.

The combination of a letter and a number gives a good indication of the location of the taxiway.

Every taxiway close to the northern runway (5L-23R) is named Nx, everything close the southern runway (5R-23L) is called Sx. Numbering is from southwest to northeast, so N1 is close to the northern runway, at the west end (5L); S10 is the southern runway close to the eastern end (23L).

Letters can also be combined:

The apron side of the N taxiway is where you park, and called NP.

You cross on the east of the terminal on the eastern crossing or EC, or you cross on the west side of the terminal on WC or W2.


Why do airliners have to file delays through their handlers? Often when listening to ATC (commonly Dublin), when an ATP requests push and start, the controller will reply, "You have missed your pushback window", and/or ask the pilot to call their company or handler to "file a delay" or "update your flight plan with your off-blocks time".

I have two questions about this but I expect the same answer answers both.

Why is it necessary to re-file the plan, rather than simply activating the flight plan with the actual departure time?
Why is it necessary for the pilot to change to the airline's frequency, chat them up, change back, and then wait for the electronic flight plan to be updated, rather than talking to the controller directly?

Since you mention Dublin, I am going to give an answer that describes the situation in Europe. Other parts of the world may have different procedures, although I believe they will be similar.

Usually a flight plan must be activated within a given time window to ensure that there is enough capacity (airspace, ATC staffing, departure & arrival airport constraints) along the route to handle the flight. If the flight is not departing with this 'slot' a new flight plan needs to be requested and approved by the Network Manager Operations Centre (NMOC) (Previously called Central Flow Management Unit (CFMU)).

The controller is not responsible for filing flight plans and cannot be tasked with doing the paperwork for the crew. The crew therefore needs to contact their handler or flight operation centre to refile a flight plan.

The NMOC will reassess the flight plan and verify that there is capacity along the planned route to handle the flight. If there isn't, the flight may need to be planned along another route or an additional slot delay will be given.


What is the full-form of ATA? I was going through FCOM of A320 and came to know that FCOM chapters are called as ATAs. So first of all what is its full- form and secondly why do we call the chapters ATAs ?

ATA stands for Air Transport Association (today called Airlines for America). The numbering standard is called ATA 100 and was widely used for various types of aviation documents and manuals from 1956 until 2015 according to Wikipedia:

ATA 100 contains the reference to the ATA numbering system which is a common referencing standard for commercial aircraft documentation. This commonality permits greater ease of learning and understanding for pilots, aircraft maintenance technicians, and engineers alike. The standard numbering system was published by the Air Transport Association on June 1, 1956. While the ATA 100 numbering system has been superseded, it continued to be widely used until it went out of date back in 2015, especially in documentation for general aviation aircraft, on aircraft Fault Messages (for Post Flight Troubleshooting and Repair) and the electronic and printed manuals.


Is "excess thrust" possible in a steady state vector diagram? Being recently very much sold on the lift-weight-thrust closed triangle (with weight forming the hypotenuse) model for climbing flight, I proceeded to put the logic through its paces (validation) and got stuck on one fairly basic concept:  excess thrust may be only transient.
Increasing throttle increases speed.  We can initiate a climb with more speed, thrust working against increased drag, and to hold the climb against the tilted lift vector by increasing the lift coefficient, by way of increasing AOA.
Note the with a GA aircraft (25% max thrust to lift), increasing AOA excessively leads to loss of airspeed.  In fact, this is how to stall an aircraft.
Pitch can never be transitioned into hover before stalling.
Can anyone confirm that, beyond applying throttle before the takeoff roll, "excess thrust" exists at all?

First, we must be clear on what exactly is "excess thrust". I will list two possible definitions, although many more may be possible.

Excess thrust is the component of the resultant force in the direction of the flight path. Using this definition, excess thrust and steady state flight are directly at odds (because any net force results in an acceleration). So in that case, no, excess thrust is not possible in steady state flight.
Excess thrust is thrust minus drag. It splits the big lumpy thing called 'thrust' in two numbers: one that is used to counter drag (which is always there), and another that can be used for useful things.

Since we already answered the first option, I will now produce the free-body diagrams for the second option.

On the left, we have level flight. We recognize the four fundamental forces of flight: lift (blue), weight (green), drag (red), thrust (orange). It is immediately clear that all forces cancel each other, and we will happily coast along.
In the middle, we have a steady state climb. All vectors, except the weight vector, are 'tilted' back and change magnitude. Lift has decreased slightly, and as a consequence, drag has also decreased minutely (although this doesn't really matter). The biggest change can be seen in thrust, which has almost doubled in magnitude!
On the right image, I have proven that despite all these changes, the net force is still zero. I have replaced the lift- and drag vector in purple by subtracting drag from thrust. But wait a second! That purple vector is exactly what I called 'excess thrust': thrust minus drag! So this purple vector gives us a nice indication of how much 'extra' thrust we are using to make sure the resultant force on the airplane is still zero.
The sometimes heard term, "max excess thrust available" is then an indication of how far we can 'tilt back' the blue lift vector. On the diagram on the right, it should be obvious that this 'stretches' the purple 'excess thrust' vector. Steepest climb is thus achieved when the excess thrust equals the max excess thrust available.
Glossary

Resultant force: also called net force. The sum of all forces that act on the aircraft.
Steady state flight: all acceleration (in Earth's reference frame) is zero. I.e., level flight, steady climb, steady descent. Due to $\vec{F}=m\vec{a}$, zero acceleration means zero resultant force.

Addendum I: From the comments, "A Piper Cub cannot take part of its thrust and apply it for lift." We see in the image above that sadly, that is exactly what a Piper Cub must be doing to climb at all. The excess thrust $T_e$ requirement $T_e = W \sin \beta$ with $W$ lift and $\beta$ the climb angle. If very little excess thrust is available, we had better keep $\beta$ small - exactly what you would expect for a little cub!
Addendum II: below, the same image but with excess thrust according to definition 1. The vectors are no longer a 'closed triangle', and the net force is not zero. The aircraft is now accelerating.

Images created using IPE.


Why do airplanes not have manual transmission? I have limited experience with flight simulators but I have never bumped into a plane with manual transmission while, on the contrary, it's very common for other means of transportation (like cars and bikes) that rely on engine with some form of transmission control.

First of all, I'd like to know if it's actually true that no airplane have (or had) manual transmission and, secondly, why that is so.

Aircraft have fixed gears (when they have gears at all)! However in a sense a variable-pitch propeller can be considered analogous to transmission in a car and it was manual in some aircraft.

The power transmitted by propeller is, within some reasonable range, proportional to its rotation rate. And so is, again within some reasonable range, the power produced by the engine. So for slow planes a fixed pitch propeller with connected by fixed gear does a decent job. As you open the throttle, the engine speed increases, so does the propeller and that's exactly what it needs to do to transmit the power. Simpler aircraft have no gears at all and propeller is mounted directly on the engine shaft, higher power engines often have 2:1 reduction gear as the engine rpm would be too high for a propeller.

Now at higher speed, the apparent propeller pitch is reduced as the air is already moving, so it would spin faster and faster and eventually too fast for the engine. To counter this, faster propeller-driven aircraft have variable pitch propeller. As speed increases, it is set to higher angle of attack (coarser) so it keeps delivering power without increasing rpm.

Early variable pitch propellers had manually controlled pitch, but quite quickly constant speed propellers were developed (many WWII aircraft had them already) where a weight-on-spring controls the propeller pitch so that constant rpm is maintained. The manually controlled units required a lot of attention and the constant-speed system is rather simple, so manual pitch control was quickly abandoned.

And that is kind of equivalent to perfect variable gear transmission. The pilot still has a throttle lever and a propeller pitch lever and selects power and rpm independently. Higher rpm allow higher power, but don't require it, so landing is usually done with low power, but max rpm so the engine reacts quickly if power is added (does not need to spin up). During cruise some more moderate value is selected (according to manufacturer recommendation) to reduce wear of the engine.

Turboprop engines always have constant-speed propellers, because in a turbine engine the difference between turbine speed at idle and at full power is not actually that big. Again the rpm limits maximum power, so landing is done with low power, but high rpm and the engine reacts quickly when power is added.

Last the turbojet/turbofan engines just turn the turbines and compressors as they need. It's not much different from the fixed propeller really, though the jet engines now usually have variable guide vanes in the stator (that are just linked to rpm).


What are those thin magenta lines on the Sectional / Terminal Area Chart near Death Valley? Due west of KLAS and Death Valley are a large number of MOAs and Restricted areas. On the sectional and terminal area charts, there are thin magenta lines snaking over some of the mountain tops.

What do those lines represent? They don't seem to be a mode C veil of any sort, and the legend doesn't otherwise mention a thin magenta line without spikes.

Those lines denote areas of the MOA which have altitude exclusions different from what is listed on the chart's MOA table. In this case:

  MOA Excludes Airspace 3000' AGL & Below

Notice the same style magenta lines are drawn in circles around airports in the MOA which also have the same style remark excluding a specific portion of the airspace.


How do airlines bring spare parts to aircraft stranded outside their main facilities? No professional relationship with aviation. Just an avid follower. I guess it depends on location/part availability, etc, but looking for what typically happens. For the purpose of the question, aircraft can not fly without repairs.

I see many instances where certain parts of the aircraft need to be replaced like this UPS instance where aircraft burst 4 tires and was stranded for many hours.

I don't know, but most likely aircraft is stuck in this scenario because new set of tires are not available or lack of repair facilities. On the other hand, I have read many incidents on same site where tires were replaced and aircraft was on its way in couple of hours.

How do airlines manage scenarios in such cases? For example, will the UPS fly in parts from their main facility or there are part distribution centers available across globe and they can order the parts from these centers? Can such parts be rented? Do airlines rent/buy parts from each other?

In some cases airlines will follow the "what goes around comes around" principle and will loan or sell parts, and consumables like tires, to another operator that is "AOG" (Aircraft On Ground) to the extent they can without jeopardizing their own operation.

What that means is, in an airline's spares inventory it will have a baseline minimum inventory requirement of components to cover its own AOG situations, things like spare actuators, servos, pumps and other odds and ends, called "AOG stock".  If someone on the airport is hard up and approaches you, and you have the part but it's part of your own AOG stock, you won't lend or sell it because of the risk of your own AOG situation arising before you can replace the AOG unit you loaned out or sold.

If it's part of your larger non-AOG spares inventory, and you can afford to part with it temporarily, you might do so, and you may agree to loan it or sell it.  That's if you operate the same airplanes and have similar parts stocks with the same part numbers.  And airlines that operate the same fleets do buy and sell spares from each other, wheeling and dealing from time to time.

What happens probably more often is the stranded operator will have the required parts shipped "AOG" from either its own spares stock, from an OEM's spares stock from the nearest depot (OEMs will normally maintain spares depots at key locations worldwide) or possibly from the supplier of the part itself (both the OEM and the larger parts suppliers will have their own AOG spares support).  Whoever is fastest (or cheapest if time is less critical).  Often if the part is fairly small, and will fit in a Lear or Citation, the airline (or the OEM if it's something under warranty, and the operator is an important customer) will charter a corporate jet to fly the part to where it's needed (this is done a lot in the corporate world).

In the case of that UPS flight, it's more than just the tire replacements; wheel unit fuse plugs, or the wheels themselves, probably had to be replaced and a number of special inspections had to be done, so even if there were tires on the spot, the airplane was probably stuck there overnight anyway.

For the tires, say they were Goodyears. UPS might have had a set shipped from the nearest Goodyear distributor, which is in Dubai, which for an AOG would have probably would have arrived that evening or overnight.  If there was another airline on the field with the same tires, UPS could have tried to buy a set from them, but they'd have to get lucky and find someone with the same PN tires that were surplus to their own AOG needs and willing to give them up.  Or UPS may have just put a set of tires from their own spares on the next UPS flight going to Delhi.  Or they may have had Boeing's AOG spares take care of it.  They probably would have done whatever was fastest under the circumstances at reasonable cost.

There are also 3rd party spares and logistics companies that some airlines contract to handle all that stuff for them, especially if they are smaller.  Like these guys.


If Boeing used two sensors instead of one simultaneously, wouldn’t they be in the same position today? this article states  that the original version of MCAS was suppose to rely on two sensors,

One sensor will detect a high angle of attack, therefore activating MCAS
The other sensor will detect a high G force and therefore activate MCAS.

But what I don’t understand, is why people use this as an argument against Boeing, as if they should have went with that idea? If the high g force sensor was faulty, wouldn’t it technically need a second sensor looking at a high g force, in order to compare the two?
So basically if they had stuck with that idea, we’d still be here today?

The problem is that there is no redundancy in the sensor input. The quote from the article is:

  This original version of MCAS, according to two people familiar with the details, was activated only if two distinct sensors indicated such an extreme maneuver: a high angle of attack and a high G-force.

So on the original design, MCAS activation required two sensors detecting an input over a certain threshold, and in itself this creates protection against false positives.

There are two major failure modes for sub-systems:

Zero output, where the sub-system simply stops outputting a signal.
Hard-Over failure, where the sub-system outputs a false positive. This is what happened with the AoA sensor in the two MCAS disasters.

With the original design, if one sensor would go hard-over, MCAS would not activate and the system would be protected against a single failure. But in the certified config, the activating input was not checked against any signal and MCAS repeatedly activated.

Further notes on the AoA sensors, from the final accident report page 45:

There are two AoA indicators on the B737Max, and only one was used for MCAS input.
There was an AOA disagree detection installed - as an option which Lion Air had not selected at the time of the accident:

  Accordingly, the software activated the AOA DISAGREE alert only if an airline opted for the AOA indicator. At the time of the accident, Boeing advised that the AOA indicator has been selected by approximately 20% of airlines.

  When the discrepancy between the AOA display requirements and the software was identified, Boeing determined that the absence of the AOA DISAGREE alert did not adversely impact aircraft safety or operation. Accordingly, Boeing concluded that the existing functionality was acceptable until the originally intended functionality could be implemented in a display system software upgrade, scheduled for the third quarter of 2020.

  Lion Air did not select the optional AOA indicator feature on the PFD of their 737- 8 (MAX) aircraft. As a result, the AOA DISAGREE did not appear on PK-LQP aircraft, even though the necessary conditions were met.

The safety analysis of the certified system has proven to be fatally incorrect, and this is what is so baffling. A single mode of failure was allowed to activate a flight critical system, by the most experienced aerospace company on earth. Plus: the incorrect safety analysis was accepted by the aviation authority whose function it is to protect us, the passengers.