Can a tail pipe fire occur in cruise? If not, why not? I was reading the news for an incident where an A321 had to divert due to:

  the aircraft returned suspecting a tail pipe fire on the #1 engine, the crew did not receive any engine fire indication or other abnormal parameters, however, as a precaution discharged the fire extinguisher into the engine after it was shut down. There had been an engine tail pipe fire.

However, according to SKYbrary,

  A tailpipe fire will only occur on the ground and only during engine start or during engine shutdown.

Finding the latter source more reliable, I assume that either the report was wrong or the flight crew did not know that tail pipe fire is not possible in cruise.

My questions are:

Is a tail pipe fire really only possible on the ground?
Why is that? Are there not any situations (possibly abnormal, such as a flameout and attempted reignition) that could cause a tail pipe fire to occur in cruise?

It comes down to the definition of "tail pipe fire".  A tail pipe fire is normally what you might call a "static fire" of unburned fuel accumulating in the tail pipe with little to no airflow through the engine, and this is normally during ground operations especially during starts.

The tail pipe has an overboard drain for this purpose, but it needs time to let the fuel out.  This is why, during a start, the procedure may require the engine to be dry motored for a minimum time if the start is aborted.  This is to keep pushing air through the engine, to help dry it out you might say, and let whatever unburned fuel has pooled in the tail pipe drain overboard.  If you don't do this and try another start right away, you might end up lighting off the residual fuel in the tail pipe during the start... and a tail pipe fire.

Based on the Air India pics, that wasn't a "tail pipe fire" in that sense (pooled fuel), and was actually case of some kind of engine disruption or malfunction that let the flame move out of the burner can into the turbine section and tail pipe.  This drives the temperatures at the turbine and tailpipe through the roof.  You can see this by the melted turbine blades.  A fuel control problem or air flow disruption problem farther upstream would be the issue here.

You may not get a tail pipe overheat warning in this case because the overheat detection loop (sensing wire) is usually around the section of tailpipe within the cowling, and with the flame originating from the burner can and contained in the tail pipe itself with the airflow, the sensing loops on the outside of the hot section case probably didn't get hot enough.

What should have been obvious to the crew however, was Inter Turbine Temperature (ITT) (or whatever turbine section parameter that engine measures) spiking through the roof at the time the passenger was seeing the flames out the back.

So to question 1: Yes, a "tail pipe fire" is normally a fire from pooled fuel in the tail pipe and is normally only on the ground (but on some engines, could possibly happen during an in-flight relight as well).

For question 2: A tail pipe fire in that sense won't occur in cruise with the engine running.  What is described as a "tail pipe fire" in the article is actually an engine malfunction that caused the flame to move aft out from it's normal place in the burner can, into the hot section, but it doesn't involve fuel pooling in the tail pipe.  Bird ingestion, compressor section malfunction or compressor stall, fuel control going haywire (dumping in too much fuel).  See any videos of airliners ingesting birds on departure and that's exactly what you see.


What is the flap extension schedule on approach for an airliner? I understand that there are probably no set altitudes and speeds for flaps extensions, but can someone with insight provide a general guide for speeds, altitude and flaps for an ILS approach in good weather for a Boeing 777-300ER with a landing of Flaps 25 and $V_{ref}$ of 147 knots.

Something like this:

Alt: 5000 ft - Speed: 210 kts - Flaps 1
Alt: 4000 ft - Speed: 190 kts - Flaps 5...

(Boeing 777 manual.)

Substitute altitudes with position to runway. Near an airport an airliner usually flies at around 200 KIAS, this is when you select flaps 1.

Subsequent flap settings are also combined with selecting a lower speed as shown above. The speed tape makes it easy. Flaps 5 should be down by the final intercept path to the localizer or before turning base. Flaps 20 when established on the localizer. Then comes gear down and flaps 30 before the glide-slope is captured.

Initially you wrote PMDG, I recommend check their manuals, they are usually very informative.

For normal procedures on a Boeing 737, the flap settings 2, 10, and 25 are usually also skipped. So it's 1, 5, 15, and 30/40. Non-normal procedures differ.


What's Permaswage / Harrison tube repair? In modern aircraft, damage of hydraulic tubes can be repaired by Permaswage/Harrison provided by maintenance manuel. However, What is Permaswage / Harrison? It's a name of company?

A quick google for "Permaswage/Harrison" reveals that

  Permaswage is the technology leader in the fluid fitting industry providing proprietary and standard components, tooling, and training to all major aerospace companies globally.

"Harrison" seems to refer to a variety of internal swage fittings that are separable ridge tube end fittings commonly used in aerospace fluid transfer applications:

  They are also referred as “Harrison”, “Stanley Aviation” or “Sierracin” fittings, due to the history of the product.

From this, I would deduce that one can use these products to effect a repair to hydraulic lines with these methods/products because:

  Internal swaging is a mechanical method for the attachment of fittings to tubing. This is accomplished by forming tubing outward into grooves within the fitting.

--From the "Harrison" link


Which radio altimeter is the Boeing 737NG call outs based on? I'm wondering which of the two Radio Altimeters: Captain (left) or F/O (right), that the 737 does the RA callouts based on.

For instance, if the F/O's RA is slightly off, and passes 500ft before the captain's RA, does the aircraft call "500" when the first (in this case the F/O's RA) RA passes that altitude, or is it always based on the captain's RA?

Also, while on this topic, could someone confirm if the "Minimums" callout is always based on whatever is set on the Captain side, because to my knowledge, that is the case.

The FCOM (volume 2, 15.20.17) states:

  The GPWS provides height callouts based on altitude set by the
  Captain's Minimums selector.

According to the investigation of Turkish Airlines 1951, the captain's and FO's radio altimeter are feed independently, and the autopilot is wired to react to whatever is happening on the captain's side. This includes the aural warnings.

Curiously, I cannot locate anywhere in the FCOM, FCTM nor QRH what happens when the RAs disagree. The only related information I find is, to use the autopilot for landing you'd need both RAs to be functional. If one of them fails while the autopilot is in landing mode (i.e. glideslope and/or localizer mode), the autopilot disconnects.


Is it a common airline practice to base T/O speeds on the actual T/O weight when an assumed temp thrust is used? Let's say the current outside air temp is 15 C and you have decided to use 50 C as the today's assumed temperature for your takeoff. In this case, use of the T/O weight the assumed temp thrust supports gives you the balanced V1.

But our company rules are to use the T/O speeds of the "acutual" T/O weight instead of those that the T/O weight the assumed temp thrust applied provides. I assume this rule has been made to give a greater safety margin for a runway overrun in the event of a possible rejected takeoff at the expense of decreased obstacle clearance, since use of the actual takeoff weight invariably brings lower V1, Vr, and V2 speed than when the T/O weight of the assumed temp thrust is used. My question is: is it a common practice among commericial airlines to use the actual T/O weight instead of the assumed temp T/O weight?

You determine the t/o thrust as a function of t/o weight and runway length
Once the t/o thrust is determined you can select the assumed temperature on the thrust limit page on the CDU.

V1 is not the target primary parameter, it is a consequence of the calculation, on modern FMS your calculated value is cross checked with a range calculated by the FMS, that is your calculation could be rejected by the installed FMS unless you may force your value on some models.

A minimum rate of climb is necessary with a speed of V2+10, and at worst V2 with engine failure.

Backward of this Vr is computed.


What are the costs versus benefits of takeoff/landing on grass versus pavement in a light aircraft? This question stated that landing on pavement is hard on tires compared to grass, however I don't necessarily agree with that. Even if it is true the impact on the gear and other components may outweigh the benefits to the tires. This leads to the question of what is overall lower cost for takeoff and/or landing from a maintenance perspective, grass or pavement? If that cannot be determined what are the costs and benefits of each?

This question needs limits in order to avoid being too broad, so please assume these conditions:

A tricycle gear airplane that can use either surface like a PA-28, Cessna 152/172, not something like a Mooney which is less grass friendly
The grass surface is in reasonable shape
Accident/incident costs are out of scope for the question

Pretty simple.  Even a nicely rolled grass runway is nowhere as smooth as asphalt.

Tires on grass seem to last forever, but it wears out everything else in the gear out faster.  Oleos get worked more; they get dirtier, so it's much harder on the scrapers and seals (dust (silica particles) + hydraulic fluid on the chrome = wonderful lapping compound), etc and can be expected to start to leak sooner. Scissors linkage bushings  and wheel bearings wear faster.  Fairings and bits that flex with the gear will crack sooner.  All that sort of thing.  Impossible to quantify, although tires are cheaper than oleo overhauls.

I operate from a field with grass and pavement (actually macadam - gravel/tar) side by side and I almost always use the pavement, because on smooth grass I can feel the oleos getting worked hard and they just get a lot dirtier.

On the other hand - if it's an option, I always do my engine run up on grass, and I usually start the takeoff roll (an option where I am) on the grass about 50 ft short of the threshold.  These are propeller protection measures.  Even nice clean looking pavement will have lots of, at minimum, very small pretty much invisible stones, which are murder on your propeller when stationary or when rolling at low speed/high power.

Props make great vacuum cleaners when close to the ground and pavement is like vacuuming a tile floor while grass is like vacuuming carpet without the beater attachment doohickey.


Did old propeller aircraft begin takeoff off-center to counter p-factor? I have tried to ask this in chat and I have been invited to ask a full fledged question here.

Is it true that an old (say about between the two world wars) take-off technique, to compensate for the p-factor experienced at high throttle settings, was to put the aircraft misaligned to the runway and let the p-factor align the aircraft to the center-line?

Example: take an aircraft with a p-factor that makes it yaw to the left, the pilot would have placed the aircraft on the left side of the center-line, with the nose to the right (so, looking at the center-line).

Why ask in past tense? The Mü-23 motor glider has a central wheel and would need someone to hold a wingtip during take-off. Sometimes, a different technique is used: The aircraft is parked at a right angle to the (grass) runway, with the wingtip pointing into the intended take-off direction on the ground. When the pilot opens the throttle, he steps on the rudder, causing the aircraft to swerve into the desired direction and rotating into a horizontal attitude thanks to the centrifugal force.

Akaflieg München Mü-23 (picture source)


Can these vortices be dangerous? There is a question related to this one right here but I'm more interested in the danger of those vortices. Are they very dangerous to cause a wake turbulence for the aircraft that  comes behind this? Can it cause an accident or so?

Source

While @Peter Kämpf 's answer is great and sufficient to answer the question, I would like to add a clarification (which should be a posted as a comment, but is too long for this format).

In the image in the question, there are visible streams of condensed water vapor from the atmosphere. These streams are only present at the blade tips. The question seems to assume that these streams depict the wake from the propellers. They don't, or more accurately there are only a very small part of the wake volume.

1. Images of tip vortices from different devices

1a, tip vortex from a propeller

Source

Condensed water forms because the change of pressure is adiabatic, in simple terms it occurs with little exchange of heat with the neighboring regions. It occurs first where the pressure difference is large and the transition quick. (By the way, note the 8 rockets used to assist for takeoff.)

1b, tip vortex from a wing

Source

1c: tip vortex from a rotor

Source

There is not doubt the rotors spin in opposite direction.

1d, tip vortex from a wind turbine

Source

Notice: Actually after looking at oddities on this image (the direction of the wind), I realized that this is an experimental turbine used by the US DoE and the NREL to study winds. The white stream is actually smoke released from the blade. Probes are visible on the leading edge to measure speed at different locations of the blade. I keep the image as it's a good one.

2. Full wake turbulence

Contrary to the previous images, the ones below show the whole turbulence created by the same airfoils. While the tip vortices are materialized by condensed water vapor created by a transition from high to low pressure at the tip of the devices, the whole wake is visible only if air is not clear.

2a, turbulence from a propeller

Source
Principle (no photo found, do you have one?)

2b, turbulence from a wing

Source

2c: turbulence from a rotor

Source

2d, turbulence from a wind turbine

Source

3. Images where both effects are combined

Note that regardless of whether they are visible or not, both the tip vortices and full wake always exist. Their visibility greatly depends, like contrails, on the air moisture and temperature.

As explained by @Peter, the energy of the tip vortices is diluted in the energy of the actual wake turbulence:

Source

Source: What causes a plane's wing tips to leave a small white vapor trail?

4. Complexity of the wake

Wake from a wind turbine, mixing all sources of turbulence:

Source

The tip vortex is initially a very small part of the wake, created by the high pressure air escaping from the low side of the wing. The whole wake volume grows in length and diameter as the airfoil moves. The vertex diameter grows, until there is no more energy left and air stops moving (see images in §3):

Source

Source

See this question for details: How does an aircraft form wake turbulence?


What are all the squawk codes? I love aviation and I love learning new things about it.

I was wondering if anyone knew all of the squawk codes and in particular what squawk 7500 means.


Has a civil aviation accident ever involved more than two manned aircraft? Has a civil aviation accident ever involved more than two manned aircraft? Meaning, in one accident: more than two manned aircraft had fatalities or serious injuries or significant damage; or one or two manned aircraft had fatalities or serious injuries or significant damage, while other manned aircraft contributed to the accident, totaling three or more aircraft.
If military aircraft were involved, that would also be of interest, as long as at least one aircraft was civil aviation.

The Rammstein Airshow Disaster comes to mind, where one airplane of the Italian Air Force display team collided with 2 others during a display, so 3 airplanes were involved in the collision in the air. A medivac helicopter on the ground was also destroyed, which was manned at the time, fatally injuring the pilot.


Can manoeuvres like overbanking and high G braking be used in a single propeller aircraft? While watching this very interesting short movie:

I noticed that for some turns pilot uses overbanking like at 1:25. Basically in a turns more than 90 of bank is used.

Can you explain how it works and how to use it and what is the advantage compared with regular steep turns?

I have CPL but I was never thought such maneuvering. Can it be used in SEP aircraft or glider with just a couple of G?

At the end of the movie looks like 5G is used for slowing airplane for landing. 5G is pulled and jet instantly slows from 300 to 260. I don't know if brakes are extended though. Can it be used in SEP as well? Like dive to the runway pull some G, slowdown and land?

Can you explain how it works and how to use it and what is the advantage compared with regular steep turns?

He needs to turn and start to descent. Note, that the two moments he's overbanking he's flying over ridges and wants to descent to the valley behind.

Now when you want to lower the nose in a turn you need to bank more so you still have the desired lateral lift, but less vertical.

But he's so fast that he needs negative vertical lift component, and since the wings are producing positive lift to make the turn, he needs to bank more than 90° to get it.

  I have CPL but I was never thought such maneuvering. Can it be used in SEP aircraft or glider with just a couple of G?

It is a positive G manoeuvre and you can do the same with, say, 2G, so technically yes. However:

You have no use for it. He's flying 420–480 knots. At 420 knots, a 1G (meaning 1G lateral, so 1.41G total at 45° bank) turn will have rate 2.6°/s and radius 4759 m. But in a SEP you might be flying, say, 120 knots and then 1G turn will have rate 9.1°/s and radius 388 m. That, of course, applies to vertical turns as well. So where he needs to push -1G, and thus overbank, you would do with reducing to, say, 0.5G, and thus still normal side up.
You would probably loose spatial awareness rather quickly if you are not trained in aerobatics. The fighter pilots train a lot to be able to handle the plane at these high Gs and unusual attitudes. Without training, it will get confusing pretty quickly.
Your attitude indicator will likely tumble. The fighters have attitude indicators carefully designed not to, but your average mechanical one in something like C172 almost surely will. That is not a problem in itself—aerobatic pilots just cage it and fly purely on external references—but you need to be aware of it.
The fighter has a G-meter, but in a typical SEP plane you don't. But if you fly below $V_A$, the wing will stall before exceeding the structural limit, so you can do without.

During aerobatics, such, or similar manoeuvres may be performed. For example in Red Bull Air Race turns are usually executed at 90° bank (to use all the lift for the change of direction). The plane climbs a bit to store some speed in height, since turns are tighter at slower speed, then makes the hard turn, during which it has 0G vertical and the vertical speed decays and it changes from climb to descent and then it levels from the descent in the gate height and with all its speed back.

  At the end of the movie looks like 5G is used for slowing airplane for landing. 5G is pulled and jet instantly slows from 300 to 260.

The induced drag is proportional to coefficient of lift. So when the wings are requested to generate a lot of lift, they also generate a lot of drag. Especially since this might have been enough to pull the delta wings of the Typhoon to the vortex lift regime, where it generates even more drag.

I believe part of the reason to fly such sharp turn here is to fly the pattern at modest size despite the high speed and the deceleration is just a nice side-effect. The speed brake would be enough to slow down, and still needs to be used as 260 knots is still about twice the landing speed.


Can the big "X" sign be used for purposes other than runway closure? About last Sunday night in the dark I was departing LAX on a redeye.  We pulled away from the terminals (maybe 500m?), made a right. Looking back out the window I saw a BIG lighted X (maybe 20? 30? foot high - really bright!) flashing. I guess it was one of THESE but it had four rather than five per arm and REALLY bright.  (I grabbed a completely hopeless video; I'll try to add it later.)

Now, just the previous day there was that incident at LAX where an airliner hit a supply truck, and toppled over the truck (some people in the truck were hurt even I believe).

Can the sign be used on situations other than runway closure? For example:

almost certainly some drama, such as the mentioned truck-jumbo incident, or
is it actually just a normal control sign that goes on an off?  (Perhaps, to indicate "don't cross here, someone else is crossing" - or whatever.)

My impression was that it was at the "side" of a runway  or taxiway, that is to say, as if crossing it.  (Of course, my impression could be totally wrong.)  Would these Xs be used in that way, or, only at one end of a runway?

There are a couple of different NOTAM's stating runway closures at KLAX, including the below. Bear in mind that runways are closed regularly for maintainence (resurfacing) just like roads. No drama about that.

LAX 05/189 LAX RWY 07R/25L CLSD DLY 0800-1300 1705300800-1706011300
LAX 05/157 LAX RWY 07L/25R W 1300FT CLSD. DECLARED DIST: RWY 07L TORA 9665FT TODA 9665FT ASDA 9255FT LDA 0FT. RWY 25R TORA 10808FT TODA...
LAX 05/156 LAX RWY 07L CLSD TO LDG 1705252200-1708190659

There are also several closed taxiways.


Is it possible to recover dumped fuel? During emergencies pilots are authorised to dump fuel, but is there any way or method to recover the fuel that has been jettisoned?

In practical terms, no. If you wanted to save/recover the dumped fuel then you would have only two basic options: dump the fuel as usual and then recover it somehow from the air; or, pump the fuel in a controlled way into a container outside the aircraft.

The first option is probably impossible: how could you capture a huge cloud of fuel and fuel vapor mixed with the air? That would be like gathering water from clouds.

The second is theoretically possible, but for civil aviation at least it probably requires too much equipment and risk. You could pump the fuel into a drop tank then jettison it with a parachute for a soft landing. Or you could pump the fuel into another aircraft via a tube, in a kind of reverse air-to-air refuelling. Or if you're dumping fuel from a  helicopter (does that ever happen?) it could hover over a tank on the ground, pump out the fuel and then land.

But all of those suggestions are totally impractical (again, at least for civil aviation). Adding drop tanks or air-to-air hoses would add huge cost in materials and training and reduce the useful load of the aircraft significantly, all for a situation that rarely occurs. And for air-to-air pumping you would need an empty tanker aircraft to be available immediately, which is highly unlikely, plus there is the inherent danger of operating two aircraft very close together.

Since fuel dumping is an exceptional situation and many aircraft can't dump fuel anyway, it seems unlikely that investing in a recovery solution would be worthwhile.


Why is there a minimum altitude for at least some high-speed jet engine restarts? While reading this other question about envelope constraints for jet-engine restarts, I noticed something odd in the graph provided (of the relight envelope for the Honeywell HTF7000 medium-bypass turbofan):

(Image obtained from a post by wbeard52, original source unknown but presumed to be either wbeard52 or public-domain)

Notice how, although the airstart envelope extends right down to -1kft pressure altitude at speeds not exceeding 250KIAS, it suddenly jumps up to 5kft at speeds of 250-300KIAS, and then up to 8kft at even greater speeds.  At first blush, I thought that this had to do with the FAA prohibition on exceeding 250KIAS below 10kft, but, on closer examination, it's clear that this can't be the case, since, if that were the culprit, one would expect the lower boundary of the envelope to jump straight up to 10kft at 250KIAS.

The jump in the minimum relight altitude coincides with the minimum speed for a windmill start, indicating that there might be something about the process of windmill-starting an engine that would preclude a low-altitude relight - but, in that case, why doesn't the starter-only-relight envelope extend to higher speeds under the floor of the windmilling envelope?  Is this problem unique to the HTF7000, or do other jets have it too?  What causes it, anyway?

Generally when you see those kinds of limitations it means that the engine or airframe developer had trouble getting successful, repeatable relights outside of the published envelope during development flight testing and you do see it with other engines (the CF-34 that I am familiar with has a similar but much less extreme limitation).

In that case it is probably related to density/velocity of the air flow into the burner can during windmilling and I would imagine that there were issues with getting a successful lightoff every time, or excessive peak ITT during the start, or maybe surging problems or something like that.

You'd have to talk to a Honeywell person for those details.


What kind of planes are on this old photo? Not sure what kind of planes are on this old photo? Does anyone have any idea?

This is a formation of Curtiss-Wright AT-9s officially known as the Fledgling, but also known as the Jeep.

A high resolution version of the photo is available here: A formation of AT-9s over the Gulf of Mexico. USAF Photo

The National Museum of the US Air Force has restored an example painted to represent the aircraft in the foreground; more information can be found here: AT-9


How much does a passenger-to-freighter conversion cost? Transforming a passenger airliner to a freighter seems to be common. If I understand correctly (do not hesitate to correct me), it basically consists of removing many components (seats, galley, ...) as done in the first phases of a D-check, and then the handling equipment is added (as it should be done in the late phases of a D-check for freighters).

How much does the transformation cost compared to a D-check?

Related: How much does a D-check cost compared to a new aircraft? (Useful to have an idea of D-check costs.)

Companies converted 87 passenger jets in 2018 ... Direct conversion costs for the 87 aircraft totaled \$641.5 million ... The direct cost of converting a Boeing 767-300ER amounts to some \$14 million, compared with \$15 million for an A330-200 and \$16 million for an A330-300 ...

Source: Freighter Conversion Market Totaled Nearly \$1B in 2018: IBA, ainonline.com

2018's average is 7–8 million USD per conversion.

Based on this source, an A330-300's heavy (D) check costs 3.8 million USD (adjusted for inflation from 2010 to 2018), and given the quoted conversion for the A333, it's ~4 times as much to do the conversion.

  Source: Boeing 747-400 Passengers to Cargo Conversion, Israel Aerospace Industries, YouTube

Of the changes:

The fuselage is cut and reinforced to allow for the bigger door
The floor may require reinforcement
Passenger environmental control systems are removed
Cargo fire suppression is installed
A 9G crash net is installed.

More in this A330-300/-200 P2F brochure (PDF). And then there is certification.


What do you need to know to fly a Cessna? I've almost finished ground school and am about to start flight training.  I'd like to show up fully prepared, so am compiling a list of things I'll need to know to fly a C150.

I was hoping someone knowledgeable could point out anything I've missed.  One point specifically is checklists: I read a good article once by a military pilot who argued for completing all procedures from memory, then checking them using the checklist (hence the name checklist).  Is this a controversial approach?

The things I think I should know on day 1 are:

Vso, Vs, Vfe, Va, Vno, Vne; Vr, Vx, Vy
Procedures: Walk-around, pre-flight, emergency procedures, pre-landing
Airport: Taxiway layout, communications
Skills: Taxi, takeoff, turns, mushing, landing

Any other tips on how to best prepare myself before getting in the cockpit would be welcome.

Thank you.

You're on the right track, but let your instructor guide you along the path of righteousness or you'll end up thinking about all the stuff rattling around in your head instead of listening to what they're telling you while they're trying to show you how to fly. Day 1 is largely just familiarization - you're not going to need to know all that detail. They'll have a syllabus that will include everything you need to know, and they should be able to guide you on what'll be good to focus on for the upcoming lessons.  The private pilot practical test standards are a great preview of what will (eventually) be expected, and if your ground school works you should be through the written and aware of any weak academic areas soon enough to correct any knowledge deficiencies that may bear on your flight training.  Definitely read the POH cover to cover so you know what's in there (but you don't have to memorize it all!), and ask your instructor about anything that doesn't make sense.  Listening to the tower on a handheld or through LiveATC.net may be useful (you'll find they're probably doing the same thing over and over and over) to understand what to expect, and the Aeronautical Information Manual is full of useful information that may go beyond what was specifically covered in ground school or on the written.  ATIS and/or ASOS/AWOS broadcasts are usually available on the phone, so listen to them until you "get" it all.  That should save time in the airplane.

The instructor should also cover checklist procedures, and will know what local examiners expect you to do to pass.


Could Airbus resume production of the A380? Airbus is phasing out the production of their A380 superjumbo due to low demand from airlines. But what if (for the sake of argument) in the future Airbus' prediction of the need of a large aircraft to relieve congested hubs on popular route finally comes true and the need for a large aircraft comes up again? Could airbus resume production of the A380? They would probably have to upgrade the model to state-of-the-art technology (probably to an A380neo) to make it efficient enough to be attractive to airlines. What would Airbus need to do to put an A380 back on the market that would also satisfy the airlines' economic constraints (assuming there is demand for such a large aircraft)? Or would it be cheaper to develop a new model?

The ability to restart production depends on:

is the tooling still available? Aircraft production uses giant jigs for production of the fuselage and wings. Sometimes these are stored when production ends (I've been in a hangar full of stored Airbus jigs), but sometimes they are scrapped.
is production space available? An A380 needs lots of space in the factory. If Airbus can use this floorspace to produce 3 A350s or one A380 per month, the question becomes what is more profitable for Airbus
is the infrastructure still available? The A380 was built at several sites, then assembled at Toulouse. Roads were widened to enable transporting the wings to the factory. Special vehicles were used etc. The French authorities won't start digging up the roads immediately, but in 10 years?

As noted in the comments, the A380 production line is still open, so it's easy to take new orders now. When the line closes, it becomes more difficult.

if the factory has been repurposed for other aircraft, you need to move your existing production to accommodate new A380 orders.
a few years after end of production, practical knowledge starts getting lost. The drawings etc. are still there, but things like optimal assembly sequences, how to move the giant wings in the most efficient manner, have to be rediscovered. When you assemble an aircraft every month for several years, you develop a routine. Restarting production means this routine has to be rebuilt, so the first year or so assembly will take more time and cost more.
when you close the production line, all contracts with suppliers also end. So they start clearing out their A380-specific tooling too. And when you restart, they need to retool and relearn, etc..

So the longer you wait, the higher the cost of restarting production will be. Upgrades can make the aircraft more attractive to customers, but developing the upgrade also costs lots of money ($1B to develop the A320neo), all of which you have to recoup by selling aircraft.
So it all comes down to how many orders you expect to get. A few dozen won't make it worthwhile to restart production once it's been shut down. A few hundred might.
Airbus has already worked on improved A380 variants. In 2015, they were talking about the A380neo:

On 15 June 2015, Reuters reported that Airbus was discussing a stretched version of the A380 with at least six customers. This aircraft, which could also feature new engines, would accommodate an additional fifty passengers. Deliveries to customers were planned for sometime in 2020 or 2021.[293] On 19 July 2015, Airbus CEO Fabrice Brégier stated that the company will build a new version of the A380 featuring new improved wings and new engines.[294] Speculation about the development of a so-called A380neo ("neo" for "new engine option") had been going on for a few months after earlier press releases in 2014,[295] and in 2015 the company was considering whether to end production of the type prior to 2018[291] or develop a new A380 variant. Later it was revealed that Airbus was looking at both the possibility of a longer A380 in line of the previously planned A380-900[296] and a new engine version, i.e. A380neo. Brégier also revealed that the new variant would be ready to enter service by 2020.[297] The engine would most likely be one of a variety of all-new options from Rolls-Royce, ranging from derivatives of the A350's XWB-84/97 to the future Advance project due at around 2020.[298][299]
On 3 June 2016, Emirates President Tim Clark stated that talks between Emirates and Airbus on the A380neo have "lapsed".[300] On 12 June 2017, Fabrice Brégier confirmed that Airbus will not launch an A380neo, stating "...there is no business case to do that, this is absolutely clear."

In 2017, Airbus announced the A380Plus:

The A380Plus, which was announced ahead of the Paris Airshow, will boast a new wing design intended to improve aerodynamics.
Airbus also said the cabin had been optimised to allow up to 80 extra seats "with no compromise on comfort".
The European plane maker said the new version would burn up to 4% less fuel thanks to its new winglets, which are designed to reduce drag. It will also have an increased maximum take-off weight and need less regular maintenance checks. Airbus said that along with other enhancements, the plane would cut costs for airlines by 13% per seat.

The fact they cancelled the programme in February 2019 indicates the A380Plus didn't get enough interest to justify keeping the production line open.


What makes the left engine on a conventional twin-engine aircraft the critical one? I already know that this is because of P-factor. But I don't know how to draw a picture or explain this simply?

The "critical engine" (as it is called in this context) is based on the direction of propeller rotation and the "arm" length from the descending blade to the aircraft's center of gravity.

Here is a picture and explanation (source: Skybrary)


What are the "Static Ports" in a Boeing 767? Recently while I was on a flight, I've noticed this area near the front door on a Boeing 767 aircraft. I'm a total aviation noob, I just wonder what are these and what they are used for.

One of the standard instruments of an aircraft is a "Pitot tube". This instrument allows measurement of the forward air pressure as the aircraft moves through the air. By this measurement the instrument can estimate the relative air speed of the aircraft.

In order to make the measurement, the forward air pressure is compared to the side air pressure and the difference between the two is presumed to be due to the force of the aircraft moving through the air. Thus, the measurement is a relative one, comparing the forward air pressure to the air pressure on the side of the plane.

The "static ports" allow air into the instrument to provide the input for the air pressure on the side of the aircraft. They are called "static" ports because in general they take in air at the ambient pressure which does not change very much as compared to the pitot tube which takes in air as the plane rushes through it, thus frequently changing according to the speed of the plane. The pitot tube is usually located on the bottom of the plane and is pointed forwards.


Does form 337 need to be sent to the FAA prior or after the work has been performed? Is the Form 337 sent to the FAA prior to the work being performed? Meaning the mechanic awaits the FAAs reply and approval before actually beginning work on the aircraft? Or is the work performed, then documented, and sent to the FAA?

The regulations state that any work must be performed in accordance with either approved, acceptable or specified data on a type certified aircraft. An FAA 337 form is used to report Major Repairs or Alterations to either the Airframe, Engine, Propeller or Appliance. So to answer your question, no, you don't have to send in the 337 form before performing the work because it's purpose is to report the work that was already performed. The form has a conformity statement that must be signed, it states:

  "I certify that the repair and/or alteration made to the unit(s) identified in item 5 above and described on the reverse or attachments hereto
  have been made in accordance with the requirements of Part 43 of the U.S. Federal Aviation Regulations and that the information
  furnished herein is true and correct to the best of my knowledge."

You can view the 337 form here:

https://www.faa.gov/documentLibrary/media/Form/Form_337.pdf


Is it possible to define a "good landing" in terms of pitch angle and vertical speed? Is there a specific combination of pitch angle and vertical speed at touchdown that would be usually be considered a "good landing" in a B737NG?

A "good" landing with a 737NG as described in the Flight Crew Training Manual (FCTM) is flown with a pitch that has increased by 2 to 3 degrees during the flare. The resulting vertical speed is not specified, but will only depend on the airspeed at a given pitch increase. Remember, that a good landing requires a stabilized approach first, so you should cross the runway threshold at Vref + wind correction and at the correct height (usually 50 ft for typical glideslope).

Initiate the flare when the
main gear is approximately 20 feet above the runway by increasing pitch attitude
approximately 2° - 3°. This slows the rate of descent.
After the flare is initiated, smoothly retard the thrust levers to idle, and make small
pitch attitude adjustments to maintain the desired descent rate to the runway.
Ideally, main gear touchdown should occur simultaneously with thrust levers
reaching idle. [...]

Typically, the pitch attitude increases slightly during the actual landing, but avoid
over-rotating. Do not increase the pitch attitude after touchdown; this could lead
to a tail strike.
Shifting the visual sighting point down the runway assists in controlling the pitch
attitude during the flare. A smooth thrust reduction to idle also assists in
controlling the natural nose down pitch change associated with thrust reduction.
Hold sufficient back pressure on the control column to keep the pitch attitude
constant.
Avoid rapid control column movements during the flare. If the flare is too abrupt
and thrust is excessive near touchdown, the airplane tends to float in ground effect.
Do not allow the airplane to float; fly the airplane onto the runway. Do not extend
the flare by increasing pitch attitude in an attempt to achieve a perfectly smooth
touchdown. Do not attempt to hold the nose wheels off the runway.

(Boeing 737NG FCTM 6.10 - Landing, emphasis mine)
Typical touchdown vertical speeds are then between 60 and 180 ft/min as explained in this answer.


How could a failed left wing cause a roll to the right? The crash of Continental Express flight 2574 in 1991 (see also this question) was caused by faulty maintenance to the de-icing boot on the left horizontal stabilizer. This became detached in flight, leading to violent movements of the plane which caused the left wing to fail and the right wingtip to detach.  Ultimately, the horizontal part of the T-tail detached and the plane crashed.

The NTSB report says (page 34, with essentially the same statement repeated on page 37):

  The airplane then rolled to the right at a roll rate exceeding
  160 degrees per second. The Safety Board believes that the lift produced by the
  intact right wing produced the extreme roll.

The report also says that the initial failure of the left stabilizer caused a 10–15° roll to the right, which makes sense: the loss of downforce from the stabilizer meant the left side of the plane was generating more net lift than the right. But how would the subsequent failure of the left wing produce a roll to the right? The natural assumption would be that, with the right wing generating lift and the left wing not, the plane would roll to the left.

Possibly relevant is that the left wing failed but didn't detach from the plane: the plane crashed right-way-up with the left wing folded under the fuselage and the inboard portion of the right wing.

The following is how I would interpret the information given in the report - this is to some extent speculation, also because the FDR plots in the report don't seem to cover that part of the incident. I'm very intersted in how other people interpret the data.

The report states:

  The airframe remained intact (minus the leading edge), and the load
  factor fluctuated around -2 g, for approximately 6 l/2 seconds. [...] airplane heading moved 20 degrees nose left, and a 15 degree right roll attitude was reached at the end of this period.

The fact that the left leading edge of the stabilizer was lost and that the heading is moving left makes me believe that the aircraft was in some kind of a slip with the right wing further forward in the wind. The negative load factor of -2 g indicates a lot of negative load on both wings - apparently more than the structure tolerated. Both wings "stalled negatively"1 at this point. Now if one wing goes missing (aerodynamically, even if not physically), it can't provide the downforce any more and the total momentum will cause the side of the aircraft where there is still a functioning wing to rotate down.

Because the right wing was probably pointing slightly forward (even more so if the left wing produced a lot of drag while or after failing, which seems likely), a roll to the right would make the aircraft more or less tumble over its own wing, with the wing upper surface pointing increasingly towards the airflow around a 90° right roll position. The resulting drag explains a very fast roll to a ~180° position. Starting from "10 to 15 degrees right wing down"2, that's about 160°.

Short version: Because the wings had negative load and were primarily drag surfaces at this point, everything is reversed. The side of the aircraft with less drag rolled towards the incoming airflow. In a negative angle of attack attitude, that's up in the aircraft coordinate system, causing a roll to the right.

1 3.1: Findings; 7. p. 48 (56 in pdf)
2 p. 20 (28 in pdf)


last 747 flight path, was this hand flown? How was this communicated with ATC? Elal's last 747 flight made this nice path of a 747, how was this done?
Could this be entered into the computer and flown? or was this hand flown

The path looks quite neat

Also what is the ATC procedure for such a maneuver?

I don't believe anyone could hand fly something that precise.  A series of waypoints could be entered in the flight plan in a "connect the dot" manner, then the autopilot could be put in NAV mode to fly the pattern.  Nothing that difficult about it though, it would just take some time.

If they are at 10,000 feet this could be done under VFR, in which case no "ATC Procedure" is necessary.  I am pretty sure though, that the flight would have communicated their intentions with ATC.

I am curious about area just off the end of the pointed nose.  I am guessing that they flew past this point and made a reverse turn, effectively creating a loop in the depicted track that is cut off in the picture.  Do you have a full screen shot showing this?  Because if it isn't there, then this was either all photoshopped, or flown, then the loop edited out later.  A 747 can't just turn on a point...


How did NASA Langley end up with the first 737? This answer shows N515NA, CN/MSN: 19437 as an early 737, and mentions that it may be the first one.

Was this a special design built for NASA, or perhaps a prototype that nobody wanted for commercial use?

NASA has lots of cool aircraft. They get them sometimes when they get to the end of their life/retired, sometimes they are custom built trainers, and sometimes they are used to test research projects. You can find the full history of that particular 737 here

  NASA’s Boeing 737-100 Transport Systems Research Vehicle was the
  prototype 737, acquired by the Langley Research Center in 1974 to
  conduct research into advanced transport aircraft technologies.

  ...

  The Boeing
  737 was Langley's number one choice, however,
  since it had a slightly wider fuselage and an
  advanced, high-lift flap system. Money however, was extremely tight. The
  market value of a used 737 in 1972 was about $3.5 million, but the
  Boeing Company had one particular 737 that its sales people said they
  might be willing to sell for substantially less."

  ...

  Boeing had designated the prototype as PA-099: PA for Lufthansa, and
  099 as the last one in a block of 100 aircraft numbers Boeing had
  reserved for the airline. The prototype was never sold, however,
  because it was only certified for experimental use. With all the
  holes, wiring and other modifications that were made to the airplane
  for certification tests, bringing it up to the standards of a
  commercial transport airplane would have been too expensive. Boeing
  used the airplane for a few additional flight tests and then simply
  set it aside. '

In short, it was cheap, couldn't be used for commercial flight, and just what NASA needed. Chapter 2 in the above linked document covers the history in more depth and explains more of the nuances of the deal. To keep from copying the whole text I'll end it here.


Can pilots take multitools on board in Canada? Can pilots in other countries or Canada carry Swiss army knives onboard on commercial flights? Passengers are not allowed to do that in Canada.

pilots are never allowed to have any kind of weapon on board. when pilots go to work they have to go security just like the passengers.

there has been accidents because of this.
https://en.wikipedia.org/wiki/Federal_Express_Flight_705#Flight_crew_and_hijacker

its maybe allowed when the total length is smaller then your hand but i`m not sure if this rule applies to pilots.


What is the standard temperature used in this true altitude equation? The control tower of a certain airport with true altitude of 2000ft informs the pilot that QNH is 900hPa and the temperature at the airport is -10 degrees Celsius. The airplane is at FL300 (vertically above the airport) and the OAT measured by the airplane sensor is -30 degrees Celsius. What's the true altitude of the airplane?

The teacher gave us the following formula

$$Z_v=Z_{QNH}+(Z_{QNH}-Z_t)\frac{4(T_v-T_{Std})}{1000}$$

but the question is. We have the $Z_t$ (2000ft) and $T_v$ (-30 degrees Celsius), we can calculate the $Z_{QNH}$, but what is the $T_{Std}$ ? Is it the temperature at the flight level considering the ISA Atmosphere or do we need to start with -10 degrees Celsius and calculate the temperature at FL300?

Standard temperatures are based on the Standard atmosphere. A lapse rate, dry or wet depending on your environment, is used determine the standard temperature for a given altitude relative to the standard sea level temperature. The post, How does one calculate true altitude? may help you out here.


When a B-2 takes off, does it use some device to ionise the airflow in front it? At takeoff, does the B-2 use some sort of ionization device in the leading edges of its wings?

I have never heard of an ionization device being used on an aircraft, but when I searched Google for "Northrop B-2 ionization", I actually found a reference for this:

  Microwave frequencies emitted along the leading edge would readily ionize the approaching air and allow the B-2's high-voltage electric field to discharge a greater flux of positive ions. With increased ion currents, the B-2 would be able to generate a greater ion sheath space charge at a given velocity and thereby increase the electrogravitic and electrostatic thrust propelling the craft.

This quote is from the book Secrets of Antigravity Propulsion: Tesla, UFOs, and Classified Aerospace Technology by Paul A. LaViolette, which sounds a lot like pseudo-science and conspiracy theories. This page says about the author:

  In addition, Paul LaViolette has developed a new theory of gravity that replaces the deeply flawed theory of general relativity.  Predicted from subquantum kinetics, it accounts for the electrogravitic coupling phenomenon discovered by Townsend Brown and may explain the advanced aerospace propulsion technology utilized in the B-2 bomber.

Putting the conspiracy theories aside, how much energy would be needed to ionize the air in front of an aircraft? It requires 14.5eV to ionize a single nitrogen atom (main component in air) and air has an average molar density of 28.97 g/mol resulting in a required energy per gram of air of

$$ E = \frac{14.5 \, \mathrm{eV} \times N_A}{28.97 \, \mathrm{g}/\mathrm{mol}} \approx 3.014 \times 10^{23} \, \mathrm{eV}/\mathrm{g} \approx 48.3 \, \mathrm{kJ}/\mathrm{g} $$

For comparison, jet fuel has an energy density of around 43kJ/g. So you need to burn about the same mass of jet fuel as air passes over the wings in order to ionize it. It goes without saying that this is not done on the B-2, nor any other aircraft.


Is there any airport planning to install ILS CAT IIIc? I know that right now no airport has an ILS CAT IIIc, but is there any airport in the world planning to have one in a near future?

Otherwise why bother to have rules and specifications for something not even planned to be in future?

Landing is one thing, taxiing with no visibility whatsoever is another.
At the moment the answer is no. But new rules are in place that may one day allow it (or its equivalent). See this Rockwell Collins post: Worth the Wait — FAA’s New EFVS Rule FAR 91.176.

Main benefits to FAA’s new EFVS rule:

Enhances low-visibility flight and ground operations

(...)

Enables descent below Decision Altitude/Decision Height (DA/DH) or Minimum Descent Altitude (MDA) in low visibilities on a greater number of approach procedure types (precision, approach procedure with vertical guidance (APV) and non-precision)

It's still a new rule and thus the implementations are not clear yet.

RE: Why have specs and not use them?
The CAT IIIc definition may soon be removed:

[A] preview of proposed changes to the draft OpSpec and 14 CFR part 121 to date [was presented]. The definition of Cat IIIa, IIIb, and IIIc will be removed from the regulation. The FAA will continue to use the same definitions, however they will not be defined in 14 CFR. In the future, expect the NOS Charts to depict only one minima for Cat III.

It's unclear what that will entail. And what ICAO will do. So there's a chance the zero/zero definition will no longer be there.

Related: Is it true an ILS CAT IIIc can automatically taxi-in an aircraft?


Why did the DC-3 have wing sweep? When looking at the silhouette of a DC-3, one can clearly see that the wings are swept. This design is from 1935, before the high-speed research work on wing sweep was ever implemented, and the DC-3 was not very fast anyhow.

Leading edge sweep was 14 deg and trailing edge 0 deg, so the quarter chord wing sweep was 10.5 deg, not inconsiderable, and causing some of the ugly stall behaviour associated with wing sweep. A 1938 NACA video of a DC-3 stalling here, a bit lengthy but it illustrates the tip stalling first, then the aileron.

None of the benefits and some of the drawbacks - why did the DC-3 have wing sweep?

Image Source

The wing was swept to move the center of lift back, closer to the center of gravity. When the design of the DC-1 was advanced to a point where the center of gravity became clear, a redesign of the wing-fuselage intersection would had been more effort, so the outer wing panels were swept back a little.

From this website by Jeff Lucker:

  the unique and characteristic swept wing of the DC-3 was an attempt to
  keep the wing in its original location as the center of gravity moved
  toward the rear.

When Douglas produced new variants (DC-2 and DC-2 sleeper, a.k.a. DC-3), they kept the proven layout.


What is this very distinct humming noise coming from the IAE-V2500 engines of the A320 during taxi? So I am a huge fan of the A320, and in a less broader sense, the A320 with IAE-V2500 engines. Arguably the greatest engines in the industry with the greatest sound. However though, I've had a question that I just can't seem to have answered so I'll ask here. If you're sitting inside an A320 with IAE-V2500's and you're taxing out to the runway, you here a very distinct humming noise coming from the engines. What I find confusing about this noise is that it sounds very different on the outside as I have spotted the A320 with V2500's in person, and the idle/taxi sound outside of the aircraft sounds very different from the inside. You can find the sound I'm talking about at timeframe 7:42 until takeoff (taxi) in this provided YouTube video:

Thank you all so much! -Niko

I don't think there's anything particularly special causing that sound, it's just how the engines sound.

Inside the airplane you're heavily insulated from exterior sounds, so you're not going to hear much of the airflow and fan sounds from the engine.  You're mostly hearing engine sound that travels through the airframe itself, the turbines primarily.

Outside, the engine sound is dominated by the airflow and fan noise.


How can larger wingspan decrease the strength of wingtip vortices? In the last paragraph from the link below, it states that Vortex Strength is inversely proportional to Wingspan. Why is this?

http://avstop.com/ac/flighttrainghandbook/wingtipvortices.html

EDIT: From https://howthingsfly.si.edu/aerodynamics/vortex-drag: "The farther a vortex is from the main body of the wing, the less influence it has on the wing."
Again: why?

The strength of the wing tip vortices depends upon the pressure differential between the top surface and the bottom surface. In general larger heavier planes produce stronger vortices.

Now consider two planes with the same weight but one with shorter wing span and one with longer wing span. The pressure differential between the top and bottom surfaces of the wing for the plane with the longer wingspan will be less ( pressure=force/area). Thus the strength of the wing tip vortices for the plane with the longer wingspan will also be less.


How are CPDLC VHF messages transmitted between ATC and aircraft? I'm trying to read up on some of the new developments in ATC (ATN, FANS etc.) and I've come across CPDLC: Controller–Pilot Data Link Communications. In particular, I'm confused of how the VHF messages travel to and from Air Traffic Control and the aircraft.

For the oceanic/remote flying, transmitting messages over SatCom sounds entirely reasonable. But everything I can find on VHF seems to imply that they use a separate Datalink Service Provider, similar how ACARS functions.

I always thought ATC had a bunch of antennas on the tower roof to do voice VHF. If this is the case, what prevents ATC from having their own datalink transceiver and doing all of this stuff 'in-house', avoiding more parties and infrastructure?

For non-oceanic operations, aside from the tower radios, most ATC communications go through remote communications outlets (RCO) scattered around to get the necessary coverage.  most are co-located with VORs or other navigational aids.  The controllers are located in either a TRACON or Center facility that's often a long distance to the RCOs.

The problem is this equipment is these systems were designed for voice comm (double-side band AM radios).  For data link, the radios operate as a radio modem using VHF data link (VDL) Mode 2.  So three things have to happen: 1. the controller needs a data link enabled workstation, 2. there has to be a network connection to the RCOs, and 3. the radios need to support VDL mode 2.

So the real issue boils down to the two primary factors; time and money.  The implementation in the US is part of Nexgen.  To speed up the implementation, there is the alternative of leasing services of network providers such as ARINC and SITA.

BTW, the most comprehensive reference on data link is the Global Operational  Data Link Document.


What is the relation between aircraft descent rate and speed? I am an ATCO working in India. I am trying to understand why an aircraft's rate of descent increases, when its speed increases. I am particularly interested in how it relates to jet engine aircraft.

Is it the same for aircraft climb rate?

If the pilot commands a certain glide path angle, any change in airspeed will also change vertical speed, because both are connected by the glide path angle $\gamma$.

Note that the vertical speed is air speed$\cdot\sin\gamma$. Climbing or descending makes no difference; only the sign of $\gamma$ changes (positive $\gamma$ means the aircraft climbs). Also the type of propulsion will not affect this basic relationship.

Since descending reduces potential energy, some other energy will increase. If the aircraft speeds up, its kinetic energy increases until the increase in drag balances the energy gain. Reducing engine thrust or deploying spoilers will limit the speed increase, but for a steep descent, even with idling engines and full spoiler deflection the flight speed will increase.

  Is it the same for aircraft climb rate?

No. In a climb the potential energy must be increased, and the primary source of energy are the engines. Only now will the type of propulsion affect the result: Both the speeds for the steepest and the fastest climb for propeller aircraft are fairly low, so an increase in vertical speed will normally be accompanied by a reduction in flight speed, freeing up more excess energy for climbing.

Jets also need to fly slow for their steepest climb, but need to pick up speed for their fastest climb speed. This is the more pronounced the lower the bypass ratio of the engines is, so fighter jets need speed to climb quickly. Turbofan-powered airliners fall between propeller aircraft and fighter jets and prefer a moderate speed for their best climb performance.

This is all only true in stationary flight. In a pull-up, any aircraft can gain altitude quickly by trading kinetic for potential energy. But this is a transitionary effect - the high climb speed will only last while the aircraft has excess speed to spend.


Is a first class medical to be an airline pilot eventually possible? I have a history of ocd and a little depression when I was younger . Up until now I’ve taken a number of SSRIs and finally recently risperidone which I’m almost tapered off of for ocd.I have been symptom free for a while and believe I can be a pilot. I have a number of hours of flying time from over the years. The issue is I have a history of taking abilify and an SSRI and risperidone which is also an anti psychotic and cymbalta. I’ve never been diagnosed with psychosis but the risperidone (antipsychotic) can help with ocd. If I’ve been off of all of medicine and am stable is a first class medical eventually possible? They say it’s unacceptable to have a history of multi drug agent psychiatric drug used in conjunction with an SSRI. Is my airline pilot career not possible and has this ever been done. Thanks

The section

Decision Considerations - Aerospace Medical Dispositions
Item 47. Psychiatric Conditions

From the FAA's website has a lot of the information for you. This page on SSRI's specifically has even more info to read up on. If you burrow down you will find a lot of worksheets and AME advisory papers most of which ultimately state

  Requires FAA Decision/Submit to FAA for approval

This basically means that the AME can not make the decision and its up to the FAA directly. That being said there is hope and they do make a path pretty clear for you to take.

In any case if you are tapering off a drug it may be best to wait until you are off it completely to go see an AME. The FAA seems to be much more cut and dry on current usage and far more "case by case" on historical usage based on the way the regs are written.

You may also want to take a look at the regulations here


How to disable GPWS in a 737NG just like how the Airbus can? The Airbus planes have a feature where the GPWS can be disabled. But I cannot find any switch in the 737NG cockpit to disable the GPWS.

There is no way to totally inhibit GPWS on the B737 except by pulling the circuit breaker.

What you can do is inhibit specific modes of the GPWS. This is done via the following switches:

Source: Boeing Co.

The Below G/S switch (1) inhibits the below glide slope alerting.
Flap and Gear inhibit switches (4 and 5) allow inhibiting the "Too Low Flaps" and "Too Low Gear" alerts.
The TERR inhibit switch (6) inhibits the look-ahead terrain alerts and the terrain display on the ND.


Can I fly a UAS that weighs more than 55lbs if I'm on private property? Can I fly a UAS that weighs more than 55 pounds within my own private property if I stay below say, 200 feet? I do not have 333 exemption

TL;DR

According to the FAA Part 333 rules, all UA aircraft (> 55 lbs) must register with the FAA with an N-number before flight. As far as I can tell, the rules don't specify zones or altitudes where the regulations aren't in effect, so I think it is highly advisable to register.

My personal rationale

Being safe just in case is far better, at least in my mind, than choosing to avoid registration. I know people in my RC Quadcopter possee that fly sUAS aircraft but don't have Part 107 licenses. I have one, (I would rather be safe than sorry) but I could see how as long as you are careful, flying a small sUAS without a Part 107 license isn't such a terrible option.

In my mind, UA aircraft are an entirely different story, as they are inherently significantly larger than sUAS aircraft, and if something does go wrong, damages would be more severe. The risks (not to mention the responsibility) involved are far more substantial, and I would never consider flying a UA aircraft without a license even if I was only flying on my own property.


Identify this USAAF biplane I have been unable to match this USAAF biplane with a similar photo mainly due to the cockpit canopy. I've found no other like it.  I believe the photo was taken at Madison, WI or Chicago, IL in the 1930s.  Written on the photo was "Douglas Military Observation Plane." I am hoping to find out the make, model, version, and if possible the Military Unit.

That is a Douglas O-38E, with sliding cockpit windows and rounded tail.
The tail on the right of the picture is also a Douglas O-38, but another version (standard, B,C & F had such tails)

Source: wikimedia Photographer: USAF
It seems that the picture in the question is damaged; there are some stains covering the area below the horizontal tailplane and also the arms crest on the fuselage. It seems that the arms crest is a circle with a cross in it. This is the insignia of the 33rd division,  Illinois National Guard.
Some of their other O-38's are pictured here
A picture of possibly the same aircraft with the insignia clearly visible can be found on alamy.com


Can I charge for editing footage from a video that was taken during a flight as a private pilot in US? I am a private pilot, and I went with one of my friends to a skydiving trip in a rented Cessna 172 that we split the cost on pro-rata.
I also used my video making equipment to record the duration of the flight.
He wants entire video now; I know that I may legally ask him to pay the $100 that is his pro-rata share, but can I charge him for my time spent editing and making that video as well?

I'm assuming you didn't do the editing while you were sitting in the cockpit, flying the plane. Charge him whatever you want for your time sitting at home on the computer. It doesn't matter where the footage was filmed, if you're charging him to cut it up, edit it together, and render. Even an aerial photography company will itemize the charges and list digital editing services separately from the filming flight.
Just to be safe, though: Make sure he pays you separately for the pro rata cost-share of the flight. You don't want to take a lump sum and have to explain what part was for the flight and what part was for something else entirely.


What is the best pair selection algorithm? Distance Measuring Equipment selection criteria is said “those closest to the aircraft and which intersect at an angle between 30 degrees and 150 degrees" (also said one whose geometry is closest to 90 degrees") (Not sure range or angle is more important in operation)

So question is what should be the best pair selection algorithm for coding in operation?

When using a DME pair, the location of the receiver can be determined with some accuracy associated.

The time measurement is performed with some uncertainty leading to a slant range that is within a ring area (the double circles).

Observation

When looking at the intersection of the two rings with different positions of the DMEs:

The hatched area must be eliminated using some method
The blue area is reduced when the two DME bearings are at a right angle
As the width of a ring is proportional to the radius (the uncertainty is a percentage of the range), the smallest blue area is obtained with DME at right angle and the closest to the aircraft (last diagram).

Proposed algorithm

Divide the area around the aircraft into, say 8 sectors of 45° (the number of sectors impacts the accuracy but also the number of computations to be done, in an exponential way).

Look for the two closest stations, write down the sector(s) they belong to
Compute the intersection area
Find the next closest station D, note its sector S
If S is a sector already tested, ignore D, return to 3
Else within the already known sectors, find sector SP closest to 90° of S. Get station DC of this sector.
Compute intersection area for pair D-DC
If this area is smaller than the previous smallest area, keep it as new smallest
Repeat from step 3 until all sectors have been tested (one station per sector) or the radius has exceeded some predetermined limit.
Determine the new aircraft position using the best pair found.
Restart at step 1 using the new aircraft position (the time interval before restarting the cycle may be determined from the distance the aircraft moved. If the aircraft hasn't moved, then the next search for a pair is likely to find the same pair).

Example

Step 1: The two closest stations are in sectors S3 and S7 (fig A).
Step 2: Their intersection area is X (fig. A).
Step 3: The next closest is D3 in sector S2 (fig B).
Step 4: S2 has not yet been visited, so let's look at D3.
Step 5: In {S3, S7}, S7 is the sector closest to 90° of S2
Step 6: D3-D6 intersection area is Y (fig. B)
Step 7: Y is smaller than X, so our candidates are now D3-D6

Step 3: The next closest is D5 in sector S5 (fig C).
Step 4: S5 has not yet been visited, so let's look at D5.
Step 5: In {S2, S3, S7}, S3 and S7 are the sector closest to 90° of S5, we chose S3 because D4 is closer than D6.
Step 6: D4-D5 intersection area is Z.
Step 7: Z is smaller than Y, so our candidates are now D4-D5
Step 3: The next closest is D2 in sector S2
Step 4: S2 has already been visited, we ignore D2.
Step 3: The next closest is D1 in sector S1
Step 4: S1 has not yet been visited, so let's look at D1 (fig D).
Step 5: In {S2, S3, S5, S7}, S3 and S7 are the sector closest to 90° of S1, we chose S3 because D4 is closer than D6.
Step 6: D4-D5 intersection area is Z.
Step 7: Z is smaller than Y, so our candidates are now D4-D5
Step 3: The next closest is D1 in sector S1 (fig D).
Step 4: S1 has not yet been visited, so let's look at D1.
Step 5: In {S2, S3, S5, S7}, S3 and S7 are the sector closest to 90° of S1, we chose S3 because D4 is closer than D6.
Step 6: D1-D4 intersection area is T.
Step 7: T is larger than Z, so our candidates still D4-D5
Step 8: Our maximum radius has been reached, our pair is D4-D5


When do pilots disconnect the autopilot on an ILS approach? In clear weather, when do pilots disconnect the autopilot, if the plane is flying an ILS approach and the autopilot is in "approach" mode (tracking both localizer and glideslope)?

Would the answer differ significantly in different planes, for example Boeing 777 vs Airbus A320?

The decision to disconnect the autopilot is made by the pilot and can be made at any point as long as the operational limitations of the aircraft are satisfied (according to the type of ILS). The pilot also has to satisfy the applicable regulations and company SOPs (as @Sami already pointed out). Note that this depends on the pilot decision too- the pilot can fly the missed approach in autopilot if he decides so.
Usually, the aircrafts have minimum altitudes below which the autopilot has to be disconnected, which are given in the aircraft operating limitaions. For example, for Airbus A340,

CATEGORY II
If the crew performs an automatic approach without autoland, the autopilot must be disengaged no later than at 80 feet.

For Boeing 777:

Autopilot/Flight Director System
The autopilot must be disengaged before the airplane descends more than 50 feet below the MDA unless it is coupled to an ILS glideslope and localizer or in the go–around mode.
Without LAND 2 or LAND 3 annunciated, the autopilot must be disengaged
below 200 feet AGL.

For Boeing 787:

Autopilot/Flight Director System
Without LAND 2 or LAND 3 annunciated, the autopilot must be disengaged
below 100 feet AGL.

As an example in GA aircraft, for Cessna C172 G1000:

The autopilot must be disengaged below 200 feet AGL during approach operations..

As you can see, there is not much difference.


How can one approximately guesstimate wave drag? Wave drag is an especially high drag that affects supersonic vehicles above mach 1, but I've found it hard to find source materials to estimate wave drag. I'm looking at the transonic region till Mach 1.2 and so I'm looking to have an estimate about how I can design better for wave drag by estimating how it would affect my flight in the region mach 0.8 - 1.2.

Usually wave drag $c_{d_w}$ starts becoming relevant at the drag divergence Mach number $M_{DD}$, which is defined as

$$\frac{\partial c_{d_w}}{ \partial M}_{M=M_{DD}}=0.1 \tag{1}$$

Or in words, the Mach number at which the wave drag coefficient versus M has a gradient of 0.1

Lock$^1$ has derived an empirical formula that shows the development of $c_{d_w}$ after the critical Mach number, $M_{cr}$, which is the number at which the flow becomes locally supersonic on the wing:

$$c_{d_w} = 20(M-M_{cr})^4 \tag{2}$$

If we apply the definition of $(1)$ to $(2)$ we obtain:

$$M_{cr} = M_{DD} - \left(\frac{0.1}{80}\right)^{1/3} \tag{3}$$

As you can see, the value of $M_{DD}$, is a little bit higher than the value of $M_{cr}$. First you get local super sonic flow, but the drag does not increase rapidly, as you further increase the Mach number, the drag starts to increase significantly, and you reach $M_{DD}$. See this image, where $M_{DD}$ is denoted by $M_{CDR}$.

Source

The value of $M_{DD}$ can be estimated using:

$$ M_{DD} = \frac{K_A}{cos \Lambda} + \frac{t/c}{cos^2 \Lambda} +\frac{c_l}{cos ^3\Lambda} \tag{4}$$

With $\Lambda$ is the sweep angle, $t/c$ the relative thickness, $c_l$ the lift coefficient, and $K_A$ the airfoil technology factor (a correction factor denoting the quality of the airfoil).

So the workflow is as follows:

Estimate $M_{DD}$ using $(4)$
Derive $M_{cr}$ using $(3)$
Determine the development of $c_{d_w}$ using $(2)$.

For more info, see this link and this link

$^1$ Hilton, W.F., High Speed Aerodynamics, Longmans, Green & Co., London, 1952, pp. 47-49

Note, this method is only for estimating the wave drag coefficient around the drag divergence Mach number, I'm not sure to what Mach number it provides an accurate estimate


Why do the elliptical and the rectangular wing show different aerodynamic efficiency? I understand the elliptical planform is aerodynamically the most efficient type of wing planform and generates the greatest L/Dmax, but it's difficult for me to understand why.

What makes the elliptical shape of a wing aerodynamically more efficient, say, compared to the rectangular type of a wing?

It turns out, elliptical lift distribution is not the most efficient planform. It is, however, the most efficient planform in terms of L/D for any given span length, and the reason has to do with its constant span induced downwash (see For the elliptical wing, what is elliptical, and why is drag regularly distributed?).

If you relax the span length requirement and instead optimize with regards to root bending moments, the Bell-Shaped Lift Distribution is actually superior to elliptical (see derivation and NASA paper). For the same root bending moment and the same lift, the bell-shaped distribution has less induced drag.


Can the Safety Pilot log an approach if acting as PIC? Suppose you are acting as Safety Pilot and PIC on a flight in IMC. Further suppose that the pilot at the controls is instrument rated but his or her IFR currency has expired. If the other pilot acts as sole manipulator of the controls during an approach, can you, as the PIC, log that approach as well? Assume the approach is loggable given weather conditions, etc.

No, a pilot may not log an approach that he or she did not perform as the sole manipulator of the controls.

According to the FAA, in order for a pilot to have performed a loggable approach, that pilot must have performed that approach as the sole manipulator of the controls. A required SIC may not log an approach that the PIC flew, nor may a PIC log an approach that was flown by the SIC. Likewise, a safety pilot, though he or she may be a required crewmember for a flight, may not log an approach that was performed by the other pilot.

This hinges on the FAA considering the word "performed" in 14 CFR 61.57 (c) to mean fly the approach as the sole manipulator of the controls. See the FAA's leter of interpretation Carpenter (1999) which addresses this issue:

  As the SIC you have not "performed" the approach as contemplated by FAR 61.57(c) because you were not the sole manipulator of the controls during the approach.


What is the breakout by service branch for FAA ATC specialists with military backgrounds? For young people interested in air traffic control careers with the FAA and who view military service as providing a boost toward that goal, which branches are most and least likely to get them there? In other words, how do the branches of the U.S. armed forces compare by headcount of ATC specialists working for the FAA?

All military services in the US have Air Traffic Control MOS codes and training, except the Coast Guard. Army, Navy, Air Force and Marines all have it.

I don't know of any source of data that tells me if an ATC controller is a veteran, and of what branch of service. As far as I know, the FAA does not discriminate on the basis of which branch you were in when you were awarded the ATC MOS upon completion of training.


Can one make an electric-sailplane from transparent carbon fiber? Is it technically feasible to make a sailplane from transparent carbon fiber? I am looking for an answer based on the specifications' comparison of the 2 different fibers.

And can it be made self-launch capable with an electric motor ? ie. the difference in the design considerations while positioning and designing an electric motor for a normal glider vs a carbon fiber glider; Eg. Sparrowhawk.

As long as there are load-bearing structures beneath the fiber (I don't know how strong that fiber is so I will assume it is fabric-like), it will most likely fly if designed properly. If the fiber is smooth, it shouldn't be much different than regular fabric or other composite skins.

And yes, there are plenty of sailplanes that self launch with electric or gas motors. You would just have to take into account the weight and position of the motor when you add it in. This could mean that you need to lengthen the tail section for more tail down force, move the seats further back, place the engine in a more neutral CG position above the fuselage on a pylon, or any number of other methods. You might then also need to increase the wing surface area a bit, to lift the extra weight. Also take into account the weight and position of the batteries. The design effects and considerations are pretty straightforward, but dealing with them may or may not be complicated.

The Soviets tried in the 1930's to make an invisible spy plane (an AIR-6 I believe) by replacing the cloth skin with a cellophane-like material so that its entire was transparent. At just a few thousand feet the engine could be heard but the plane was almost completely invisible. Unfortunately the cellophane-like material would rapidly degrade after a few flights or several days out in the sun. It seems like your idea would be the modern version of that endeavor.


How have deep-seated cultural human factors (particularly in east Asia) in the cockpit been successfully managed in the past 20 years? This question is based on https://aviation.stackexchange.com/questions/27814/ and related to:

How does cultural difference impinge upon human factors in aviation industry safety?
To what extent have political (race, gender, social class) attitudes been implicated as human factors in the cockpit?

Successful management of cultural human factors

East Asian airlines used to have poor safety records, notably KAL and Chinese airlines, in part because of cultural human factors in the cockpit (hence the disquiet in Korea over the notorious nut rage incident in 2014).

The last two decades have seen considerable improvements in these safety records.

To the extent that the improvements have been related to better management of human factors (rather than say better technical resources and practices) what approaches have been successful in managing these cultural factors to improve safety (and to what extent)?

The commercial aviation world today emphasizes crew resource management (CRM) as an integral part of flying. The premise of effective CRM lies in the principle that any member of the flight crew, whether it's the captain or the first officer, is able to, and should express honest and valid concerns during the flight without worrying about being marginalized or ignored.

Before I start, I would like to point out that Asian airlines are not the only ones to exhibit poor crew management in the past. KLM 4805 (Tenerife), Eastern 401 (crew gets distracted on approach trying to replace a light bulb), and more recently, Air France 447 serve as some examples.

I think the reason why crew management-related accidents in Asia come under the spotlight much more than others (I still hear Asiana 214 jokes all the time, and it's getting really old...) is the fact that the very nature of East Asian culture counters the basic premise of effective CRM — that regardless of position or status in the cockpit, each crew member has a responsibility and a right to speak up. Instead, everybody has a clear-cut hierarchical position roughly based on age. Therefore, whereas accidents in the West are viewed as one-off mistakes made by individuals in an individual case, accidents in the East are viewed more as a natural consequence of the area's culture.

Now, Asian aviation has changed a lot since the '80s. CRM training is a big thing in the industry (just like how the western world has been doing it) and there has been a giant push in the general culture as a whole to create an environment where everyone is heard with equal weight. Change alright, but the roots of old culture remain despite these recent developments, and this is especially true in the corporate environment (including the cockpit). The give-it-to-me-straight-doc cockpit culture in the East still makes it very hard for the FO to speak up and sort of awkward for the captain to allow other crew members to cooperate, even if he or she is willing to make the most use of the crew body.

So, to wrap up my answer to the question, there have been numerous efforts to improve crew management/human factors in the East, but we haven't quite seen the full effects of such changes. Perhaps when the current generation of pilots go (most of them in their '40s and '50s, who were born before the rapid cultural changes in Asia) and the newer, younger generation sets in might we be able to better gage the true effects of changing culture in Asia.

There is no way to summarize this entire subject in a perfectly objective way and there will be people that disagree with some things I've noted. All my above observations were made as a Korean now living in the US. Hopefully my 2 cents help.


Are the GPWS callouts recorded with real people or computer generated? I absolutely love the tone of the GPWS callouts in the Boeing 737NG, and I was wondering whether the callouts where computer generated or a recording of a brilliant voice actor.

Since the callouts are "fixed" and don't change it's easier and cheaper to design, manufacture, and certify the system using recorded voices. For each one, the software just needs to play the appropriate audio file.

I used to work on TCAS and the callouts were all just .wav files. Sometimes companies will hire voice actors (or subcontract to a recording company). We had an employee record the files.

Computer generated voice is useful where the content is highly variable such as the D-ATIS. (I know, it's a ground system but the concept applies.)


Was there ever a supersonic flight in a non-pressurized plane, and what is/would it be like for the pilot? If you went supersonic in a plane that has no pressurized cockpit, would you be completely deaf (because of flying faster-than-sound)? Would it be dangerous to the pilot even if he/she was in an enclosed cockpit, and if so, is this the reason why we still don't have supersonic maglev trains? Did anyone ever attempt or conduct a supersonic flight in a non-pressurized plane?

When you're in the cockpit, the sound you are hearing is vibrations of the skin and canopy/windows induced by the outside flow, transmitted through the air within the cabin to your ears.  A very loud hiss/roar (even in a normal jet, if you speed up to near Vmo, say .85 M, the noise level in the flight deck gets unpleasantly loud.  Go faster, and it's the same hiss/roar but the more energy being imparted means the sound level transmitted to your ears goes up).
When Chuck Yeager was going supersonic in the X-1, he could only tell he was supersonic was by the Mach Meter, not by the noise level.
If the cockpit was unpressurized, this doesn't really change because it's still just noise transmitted from vibrations of the skins/windows transmitted through air that is stationary relative to objects it's in contact with, so you're still just hearing a hiss/roar of the outer airstream passing by, supersonic flow or not. Just way louder, I'm sure, because of less sealing and insulation.
Any other sounds originating outside you would also hear to the extent that the sound waves from that sound impacted that skin and caused a change in the sound character being transmitted through the stationary air in the cockpit.  If the wave was intense enough, you should hear a thump sound of some sort, whatever was the result the pressure wave of the sound origin changing the transmitted energy passing through the still air in the cockpit at the instant it reaches the fuselage.
The key part is that the air within the cockpit is not moving with any speed, so it will transmit any vibration from the skins, windows, engines, pumps, etc to your ears whether you are supersonic or not.


Why don't all new GA planes include a parachute system? When the Cirrus was first introduced, it included a Ballistic Recovery System, which shoots a parachute out the rear of the plane that can save a plane and its occupants when something goes wrong.

Seeing as how this technology has been honed over the past decades, why don't all new planes incorporate this feature?  I would think that any drawbacks outweigh the benefit of not losing one's life when something happens unexpectedly.

Airframe parachutes are becoming an increasingly popular option on newly-certificated aircraft, thanks in part to the track record of successful deployments on Cirrus aircraft.

If I had to speculate on why they're not showing up in older certificated designs (like the Piper PA-28 or the Cessna 172 & 182) I'd go with the reason I mentioned in my comment: "New" Pipers and Cessnas are basically extended manufacturing runs of very old designs - going on 50+ years. Changing an existing aircraft design to include the required hardpoints, breakaway panels, etc. for a parachute system would be a substantial change to the type certificate, and under Part 23 certification rules doing so would cost the manufacturer an equally-substantial sum of money for the design, engineering, and testing required.
Light GA aircraft sales at the moment are, shall we say, lackluster -- the additional costs for the engineering, the type certificate update, and the parachute itself would certainly not help matters, as that cost would need to be passed along to the eventual purchaser of parachute-equipped aircraft (which would probably mean putting a 50+ year old classic Piper or Cessna design in the same price category as a clean-sheet Cirrus SR20/SR22).

In addition to the mainly-financial reasons above Quantas 94 Heavy has a point regarding weight.  BRS (the premier airframe parachute company) makes a STC'd kit for some Cessna aircraft.
This kit costs about 80 pounds of useful load, and on many light GA aircraft the useful load is marginal enough that this added weight means you're effectively sacrificing a passenger to the installation. The Cessna retrofit kit also takes up a substantial amount of space in the baggage compartment as you can see from their installation white paper, which is certainly a negative factor as well. Were the chute to be incorporated into the design by Cessna it would likely be installed in a similar location (there just aren't many other places to put it) with a similar cost in weight and cargo space.


Is there any regulation that authorizes autopilot use when cleared for a visual approach? Is there any FAA reference that recommends or specifically allows for the use of a coupled approach (such as autoland) when the pilot is specifically cleared for a visual approach?

The general answer is no. A visual approach isn't considered an instrument approach according to ATC so there's no restriction - or direction, if you prefer - on how to fly one:

  A visual approach is an ATC authorization for an aircraft on an IFR
  flight plan to proceed visually to the airport of intended landing; it
  is not an instrument approach procedure. Also, there is no missed
  approach segment. An aircraft unable to complete a visual approach
  must be handled as any go-around and appropriate separation must be
  provided.

And from the AIM 5-5-11:

  The pilot must, at all times, have either the airport or the preceding
  aircraft in sight. After being cleared for a visual approach, proceed
  to the airport in a normal manner or follow the preceding aircraft.
  Remain clear of clouds while conducting a visual approach.

That means that when you're cleared for a visual approach it's entirely up to you how you approach and land, providing that you follow the rules mentioned in the AIM and  - in the case of airline operations - whatever procedures are detailed in your operations specification.

But if you're asking about autoland specifically (not general autopilot use) then the FAA does have a few relevant comments in their guidelines for CAT III operations:

  Autoland or HUD to touchdown operations are required for all CAT III
  operations, and many operators use autoland or HUD for CAT II, CAT I,
  and visual flight rules (VFR) operations as well. Part 121, §
  121.579(c); part 125, § 125.329(d); and part 135, § 135.93(d) prohibit the use of autoland or HUD to touchdown in any operation unless the
  operator is specifically authorized via OpSpecs.

And:

  Practice autoland or HUD to touchdown operations may be conducted at
  CAT I runways in CAT I or better weather conditions where the facility
  classification is unknown, because the flightcrew is monitoring system
  performance, visually verifying the position of the aircraft, and can
  determine whether to continue to a landing or execute a missed
  approach in CAT I or better weather conditions. Though it is not
  recommended, flightcrew monitoring and increased visibility also
  permits practice autoland or HUD to touchdown operations using an ILS
  classified as I/A, I/B, I/C, or I/T, provided the operation is
  performed in VFR conditions

I understand that to mean that autolanding is allowed in visual conditions (provided it's authorized via OpSpecs) for training/practice purposes, and since they mention autolanding use even under VFR I don't see why it wouldn't be allowed on a visual approach.


Is it ever allowed to list your destination airport as the IFR alternate too? Is it legal (in certain conditions) to have your primary airport of intended landing, also listed as the alternate?

You would never list your destination as an alternate (that wouldn't logically make sense), but there are situations where having an alternate is not required:

At least one destination alternate aerodrome must be designated and specified in the both operational and ATS flight plans if a flight under IFR is going to be made unless one of the following applies:

after taking all relevant factors into account, it is reasonably certain that VMC will prevail for the approach and landing and there is more than one independently useable runway available which can be expected to be useable at the ETA and at least one of those runways has an instrument approach procedure

the aerodrome is isolated, in which case a destination alternate is not required and instead additional fuel must be carried. a Point of No Return (PNR) must be determined and this must not be passed unless an assessment of the prevailing weather, traffic and other operational conditions indicates that a safe landing can be achieved at the ETA.

Source: https://www.skybrary.aero/index.php/Alternate_Aerodrome (ICAO Annex 6 Chapter 4)


Can I use the load factor to estimate the lift? If I have a fixed aircraft as the baseline, then I am not sure the specific flight condition, can I use the load factor to estimate the lift on the wing?

If you know where the CG is, and where the aerodynamic centers of the wing and the tail are (I am assuming a traditional configuration) so you know the distance from the aero center of the wing to the CG = d_wing, and similar for the tail, and you know the moment the wing generates (ignore the moment about the tail...it is small), and you know the load factor, then you can figure out the total lift generated by the wing. You have two equations:

Sum of moments about CG = 0 (constant pitch rate)

d_wing x liftWing + d_tail x liftTail + wingMoment = 0

Sum of lifts equals load factor times weight of aircraft

liftWing + liftTail = loadFactor x weight

Now solve for liftWing.


What are these strips on HAL Tejas? What are these strips on and below the tail of this HAL Tejas?

Fin and Tail formation lights.

Look up slime lights. When lit, they look like slimy green, hence the name. They are used for flying formation at night when it isn't possible to use visual clues such as wingtips, missiles, intakes, etc. Basically for dark/night visual pickup, formation keeping. They are for night operations and have visible and infrared modes (for use with NODs).


How should the pressure coefficient distribution from a wind tunnel experiment be interpreted? I'm doing a wind tunnel experiment and I'm trying to plot the pressure coefficient distribution for the upper and the lower surfaces of an airfoil based on experimental data. The airfoil chord is 150 mm.

I have the pressure static ports located at:

Upper static port #: 1    3    5     7     9     11    13    15     17     19
X-coord [mm]:        0.76 3.81 11.43 19.05 38.00 62.00 80.77 101.35 121.92 137.16

Lower static port #: 2    4    6     8     10    12    14    16    18     20
X-coord [mm]:        1.52 7.62 15.24 22.86 41.15 59.44 77.73 96.02 114.30 129.54

And the pressure readings for each static port are the following:

Static port #:     1      2      3      4      5      6      7      8      9     10    11     12     13    14     15     16    17   18     19     20
Pressure [kPa]:   -0.034 -0.113 -0.087 -0.172 -0.136 -0.168 -0.148 -0.17 -0.15 -0.156 -0.133 -0.15 -0.124 -0.139 -0.12 -0.13 -0.13 -0.13 -0.117 -0.12

I also have Pitot velocity reading: $U_\infty=12.26$ m/s, density: $\rho=1.225$ kg/$m^3$ and $p_\infty=101.3$ kPa.

I know that to compute the pressure coefficient for each static port, I have to use:
$$c_p(x,z(x)) = \dfrac{p(x,z(x))-p_\infty}{1/2\cdot \rho_\infty \cdot U_\infty^2 }$$

I coded a MATLAB script that allows me to compute this equation for the upper part of the airfoil using the odd static ports readings, and for the lower part of the airfoil by using the even static ports readings of pressure.

But I'm having two problems that are a bit strange,

Pressure coefficient must be dimensionless. I have the pressure values in "kPa" and the problem is that if I convert them into "Pa" by multiplying a 1000 factor. The pressure coefficients values will not be around 1, which is what I'm used to seeing in the Cp-chord graphs. How can I fix this? I'm not sure it's correct to use a dividing 1000 factor to compensate this effect.
When I plot the the result I obtain the following result, which is not very similar to the typical Cp-chord plots I have seen in experiments. Am I doing something wrong? Or is it a problem of the experiment in which I obtained bad data?

Could you help me solve my doubts by giving me a little help based on your experience? I'm not asking to get the problem solved, I just want to know how to do it properly.

First, your pressure values cannot be the measured pressure, because they are negative. This indicates that they are pressure differences.

Next, their magnitude is too low to be in Kilopascal. Could it be that you list already the pressure coefficient?

Third, when plotting the pressure coefficient, it is customary to invert the Y axis, so the most negative value is on top. This just makes the plot look more familiar.

If I do this with the tabulated values, this is what I get:

Plot of tabulated values (own work). I extended the Y axis down to +1 on purpose, because this is the stagnation pressure coefficient in in compressible flow. Your data looks like that of a very thin symmetrical airfoil at an angle of attack near 0°.

Now look at this computed plot of pressure coefficients of symmetrical airfoils at zero angle of attack (source):

Inviscid pressure distribution of symmetrical NACA airfoils. The black line looks like your data. Unfortunately you never mentioned which airfoil the measurement is from, but to me it looks awfully like a NACA 0006 (or even something thinner).


Why is YF22 designed with conventional rudders while YF23 with all-moving rudders? Are all-moving rudders more stealthy? If so, how come YF22 which is just as fixated with rear body stealthiness as the YF23 comes with conventional ones?

Also, all-moving rudders have fixed camber, which means they are far more efficient during supersonic flight, right? Another reason for an all-moving design.

As a general rule when you see an all-moving surface vs a fixed fin and control surface it's because you get more control authority per unit of surface area, so the surface itself can be smaller.  Better stealth, less drag.  You lose the passive weathervaning effect that provides basic yaw stability you get with a fixed fin, but with a fully active artificial stability system, that might be acceptable to the designer (although maybe not to the Air Force).

The 23 went with what amounts to a V tail, on top of all-moving surfaces, with the surfaces providing yaw and pitch authority at same time, and a fully active artificial stability system to make up for the lack of fixed surfaces.  This would have had much less drag than the regular horizontal and vertical surfaces, and probably a better radar signature to boot.

Why it lost out to the 22? According to Wikipedia, it was faster and had better stealth, as your would expect from the tail arrangement, but was less agile, so we know what the Air Force's priorities were. And there was probably a range of other factors that made the 22 a better choice overall (it could be that the 23 was just a bit too radical, which may have impacted maintainability, reliability, and cost factors in a way that made the 22 look like a safer bet).