Why don't airlines install Faraday cages in their planes? Cell phones and other electronic devices can interfere with the pilot's comms and other crucial avionics, as well as cell towers on the ground, if the plane is low enough. Due to these issues, the FCC forbids using cell phones on planes, while the FAA allows airlines to choose when they may be used, once the plane is out of range of the ground cell towers.Source

The fact is, though, many people just don't put their phones on airplane mode. You can forbid it all you want, but without enforcing it (not feasible - too many ways to get around it), it doesn't do much.

Enter the Faraday cage.

Faraday shields are, in short, metallic surfaces that prevent the transfer of electromagnetic waves from one side to the other; Faraday cages are ones with holes in them, blocking waves of specific wavelengths while allowing all others through. You've surely seen Faraday cages before; they're in the doors of all microwaves.

This seems to be an easy (perhaps somewhat expensive) solution. Just put one up on every airplane, maybe with a wire going from one side to the other to allow the on-board Wi-Fi to still work. But it would block all outside communication, regardless of if you've got airplane mode turned on or not. If the cage is routed around/inside the sides of the planes and across the door between the cockpit and the cabin, the pilot would have no problem communicating with the outside world.

I feel like I'm overlooking something obvious, but I can't put my finger on it. Is there a hole (so to speak) in this theory?

Cell phones and other electronic devices can interfere with the pilot's comms and other crucial avionics

As far as I can tell, nobody ever demonstrated an actual case of this. At least as long as the electronic device is FCC compliant, but all the consumer electronics has to be.

Keep in mind that all the avionic systems already have to be shielded against interference originating outside the aircraft and this shielding works for that in the cabin too.

  Due to these issues, the FCC forbids using cell phones on planes

No. It is due to the issues with the network. Moving mobile clients introduce frequency shifts due to Doppler effect and timing shifts. The system is only designed to handle them for the speeds of cars, but not much higher, so mobile client in an aircraft will not only have unreliable connection, but will also cause problems for the other clients on the ground.

In part, it is also so they don't have to explain everybody over and over why the batteries drain so quickly.

  FAA allows airlines to choose when they may be used, once the plane is out of range of the ground cell towers.

The aircraft is never out of range of ground cell towers, since the range is 35 km and the cruise altitude is only 10–12 km.

FAA allows airlines to choose when they may be used as long as appropriate relay is provided so they actually do work.

  without enforcing it, it doesn't do much.

As long as only effect ever actually observed is that that phone's battery quickly drains and the phone turns off anyway, nobody cares anyway.


What does 'intercept final' exactly mean? I work as ATC in Korea. I have question about the exact meaning of the word 'intercept'.

In FAA order 7110.65, 5-9-1 vector to final approach course, "vector to intercept the final approach course", The Korean manual interprets the word of the sentence 'intercept' as "crossing".

I think the word 'intercept' means not 'crossing' but means the state just on the final, not exactly crossing but  just 'established'.

The reason why i have question about this is that in the PAR approach, for precision approach, the final controller can vector aircraft to be exactly on the final beyond the faf although he started control in the state aircraft is not exactly on final.

So I think 'intercept' doesn't mean "crossing" but something else... Because I'm not a native English speaker I want to know the exact meaning of the word 'intercept'.

You are correct. The verb intercept, as used by ATC and pilots means to track to and then turn onto a given course. In your given example, "vector to intercept the final approach course", a vector to intercept is a vector which will cross the final approach course and from which the pilot will be able to commence a turn to become established on the final approach course. To intercept the final approach course means to accomplish that turn onto the final approach course.

See this additional example from an excerpt from Section 4 of the Aeronautical Information Manual (AIM)

  5-4-3. b. 1.

  (c) The pilot is not expected to turn inbound on the final approach
  course unless an approach clearance has been issued. This clearance
  will normally be issued with the final vector for interception of
  the final approach course, and the vector will be such as to enable
  the pilot to establish the aircraft on the final approach course prior
  to reaching the final approach fix.


Could low pressure compressor blades be made of aluminum? With the compressor blades on a gas turbine, could the low pressure blades be made of aluminum, or would it be catastrophic?

Edit:
Like the 6061 alloy.

The answer is yes, and they have been, in the early days. The blade speed is lower than can be reached using titanium or steel, so more stages are required.


What the preparations and procedures to consider for circumnavigation? If one wants to circumnavigate the planet in a general aviation airplane, how can one do it and what are the important issues to consider?

Circumnavigating the planet Earth very popular hobby and a courageous endeavor. It is not an easy task and requires extensive preparation, planning and training.

What is circumnavigation?
Travelling around an island, a continent, or the entire world is called circumnavigation.

What is considered global circumnavigation?
Crossing all meridians is not considered global circumnavigation. If you  walk completely around either Pole, you have crossed all meridians, but this is not generally considered a circumnavigation.

A basic definition is a route which covers at least one great circle, and it passes through at least one pair of points of antipodal to each other.

What are requirements for circumnavigation by airplane?

The route should start and finish at the same point.
It should cross all meridians.
The course must be at least 22,858.729 miles (36,787.559 kilometers) long. This is length of Tropic of Cancer.
It must include set control points at latitudes outside the Arctic and Antarctic circles.

Do people do it?
Yes, a lot of people do it. Earth Rounders shares experiences of pilots who have flown around the world. It is categorized by engine types and solos etc.

What should I need to know?
A lot. Typically, people who flew around the world typically break their journey in 80-100 flights, or even more. It takes several months. Each flight of circumnavigation is significantly longer than a typical cross-country flight. It is much harder on many levels than an ordinary cross-country flight.

This website takes about the preparations thoroughly. It covers these section:

The Pilot
The Aircraft
Preparation
Survival equipment
The flight

Because of the longevity of this article, I am not duplicating it here as it contains all very useful information.

What are other people's experience?
There are many people who have thoroughly documented their journeys, the preparations, the hazards and difficulties they faced, and many pictures and videos. I am listing a few, which certainly are not the best ones, but give a decent idea about their trip.

Robert Gannon
Carol Ann Garratt
Flight Simulator X
Although this is in a simulation, but this trip is very thoroughly planned and it contains detailed path descriptions.


Why are student pilots' shirt tails cut after they complete their first solo? There's a standing tradition, at least in the USA, that a student pilot has their shirt cut, signed and dated by their instructor. What is the origin of this practice and what is its significance?

Supposedly, this is because in the early days of flight before intercoms were common instructors used to sit behind their students in a tandem aircraft and pull on their shirt tails to give directions. After successfully soloing, the student has shown that he doesn't need that direction any more and therefore doesn't need his shirt in one piece either.

This isn't a universal tradition: I had the end of my tie cut off to mark my first solo (in South Africa). I had to go out and buy a tie first!


Do vertical stabilizers create vortices like wingtips do? On a wing, a wing tip vortex is unavoidable no matter what configuration you use, but does a vertical stabilizer form a wing tip vortex? I noticed this picture and saw two vortices coming off of the vertical stabilizers, so was this a result of moving the rudder or does the vertical stabilizer generate lift just like an aircraft wing?

Source

In general, the vertical stabilizer and rudder create a symmetric airfoil. As there is no pressure difference between the two surfaces of the vertical stabilizer, vortices doesn't form, unlike the wing, which is designed to produce lift at normal angles of attack (it is usually cambered, producing lift at zero angle of attack).
You're correct that the vortices are generated due to the movement of rudder. Usually, vertical stabilizer doesn't create vortices unless rudder is deflected.
Note: Though I can't be sure, I think the F-22 is braking (the F-22 does not have a dedicated surface for braking like F-15 and uses the normal flight control surfaces). A similar thing happens in the following figure

Source: f-16.net
Only one F-22 (second from top) is using its control surfaces, probably for braking, resulting in vortices from the vertical stabilizer.


How do I renew/revalidate my lapsed JAR PPL? I obtained a JAR PPL in 2003 and flew regularly for a few years afterwards. My last flight as Pilot in Command was around 2006 and as I have not kept up the required number of hours per year since then I'm assuming my license will have lapsed.

What do I need to do to regain my PPL? Will I need to retake the exams, the radio telephony license, and the Skills Test?

I'll have a go at answering this.  It's confused by the UK's transition from the JAA to EASA licensing.

My JAR-PPL(A), issued in 2011, is valid for 5 years so yes, I assume yours will have expired.  My FRTOL is valid for 10 years so presumably yours will have expired too.

The requirements are hidden in CAP 804 ([Deep breath] Section 7, Part B (Schedule 7) Part C, Section 2, Paragraph 9-(1)(c)).  Renewing an expired licence (single-engined/single pilot aeroplane) seems to require meeting FCL.740.A of Part-FCL (type rating) and Appendix 9 to Part–FCL (skills test).

I believe this effectively means you'll have to undertake training to ensure you can pass the skills test, pass it and pay to have your licence reissued.  (Not forgetting the medical.)   You will end-up with a part-FCL PPL (which do not expire).

I'm not sure about having to retake the FRTOL tests, I think you may just have to re-sit the theory (PPL comms), fill out a form and pay but the answer is probably in CAP 804 somewhere!

The easiest/best thing to do would be to pop-in to your local friendly FTO and discuss with them...


How are individual rotor/stator blades identified during engine inspection for the CFM56? During the inspection of fan, compressor and turbine blades, what is the method of identification?
For example during borescope inspection, what is the mode of identification of stator and rotor stages? Is there any form of labeling on these blades?

I don't know specifically for a CFM56, but in general: fan blades are usually identified by a dimple on the spinner (blade #1 is next to the dimple and number from there). High pressure compressor blades can be identified by special "locking" blades, which will look different from the others. They will have screws in them to "lock" them into place.  These line up with a feature on the rotor, so they are always in the same place.  Locking blade will be #1 and number from there. I'm not sure how high pressure turbine blades are identified.  LPT blades are usually identified by finding the #1 fan blade and rotating it down to bottom dead center.  Then the LPT blade at bottom dead center is considered blade #1.


How long does a wind shear last? I've got a job interview next week and the interviewer asked my colleagues this question. I didn't find the answer online, I personally don't think that there is a certain duration for a wind shear because it's a sudden change in wind direction and speed. The question is annoying actually and I really want to know.

They want to know how deep is your general understanding of W/S.  My answer would be, "What kind of wind shear are you asking about?  Microburst from a thunderstorm cell? Descending through a nocturnal jet (large change in wind velocity at a few hundred feet at night)? Wind shadow shear just above the surface?" (it's not unusual in a jet to hit a little 5 to 10 knot shear at between 100-200 ft when landing, just from the effect of trees and buildings slowing down the surface layer of air) and go from there, based on the research I've down beforehand.

There is no time limit. Could be 5 seconds. Could be half a minute, the time it takes to cross a mile wide microburst at 120 kt.  Whatever. The key thing is to do some googling and read some articles on windshear so you can sound like you've taken the trouble to learn about the topic.

So don't just look up that specific answer.  Become knowledgeable on the phenomenon itself.  That's what they want to see.


How to make ourselves more visible to other aircraft? What are the best practices in air to help others see our aircraft?

Transponders, ADS-B (which, honestly, is pretty much just an outgrowth of transponders) and exterior lights have already been mentioned. I'd like to add one more thing: speak up!

You've probably got a microphone right in front of your mouth, which is ultimately connected to a radio transmitter which is hopefully tuned to a frequency monitored by nearby aircraft.

To help make yourself more visible to other aircraft, press the transmit button and give your location and intentions, to let them know at least one place where they should look.

As a real-world example, another pilot did this the other day as I was in the air, saying something like "XX Radio, SE-XXX on downwind 21, for touch and go". My instructor took the opportunity to quiz me about where they should be given that, and they were pretty much exactly where I expected them to be. Not only did we now know where they were (position and, by inferrence, approximate altitude), which we could have known by looking for other traffic, but we also knew what they were planning to do. In this case, there was no risk of a traffic conflict between us, but you never know who else is out there.

Unless the traffic situation is congested, or there's something like emergency traffic going on, the occasional radio call with your position and intentions can do little but help others.


Why is managing CG (centre of gravity) important? Why do people have to worry about CG? Is it primarily due to fuel penalty, or take-off and landing performance, or is it mostly just to keep the aircraft from tipping over during loading and unloading, or other?

As a bonus, does tipping over of aircraft actually occur these days due to improperly managed CG?

To balance the aircraft, the sum of the lift from all lifting surfaces has to be at the same position as the weight. If the c.g. is ahead of the center of lift, the aircraft will pitch down. The pilot can counteract this by pulling on the elevator, which in effect reduces lift at the tail and thus shifts the center of lift forward. As you can imagine, there is only so much lengthwise change which can be effected with the elevator. So the first limit for the c.g. position is given by controllability.
Another important consideration is stability. You want the airplane to return to the original flight attitude if it has been disturbed, say by jolt on the stick or yoke. This can be done by creating proportionally more lift with the forward surfaces (= the wing in a conventional configuration) than with the tail surfaces. Say the jolt pitches the aircraft up. Now the aerodynamic forces should change in a way which increases lift proportionally more on the tail surfaces, so the aircraft pitches down and returns to it's original attitude. By distributing lift the way I mentioned above, the same change in angle of attack on both wing and tail will create a proportionally higher lift increase on the tail, making the aircraft (statically) stable. Thus, the second important limit for c.g. location is stability.
As for tipping over …


Should "mayday" be preferred over "SOS" in an emergency? I was asked about the difference today. The only difference I know is that mayday doesn't appear in the exams ( like the SOS parts of the book, you get the joke? :) ). I also found the difference in the origin, but:

  What is used in aviation? Both are equivalent or there is actually a difference and the one should be preferred over the other?

SOS is a distress signal. In the context of aviation emergency calls it would be equivalent to a Mayday call, which is the standard voice signal for distress.

There is, as far as I'm aware, no standard equivalent for an "urgency" (pan-pan) situation in morse code.

As far as its use in aviation, most aviation communication today is by voice (radiotelephone), and "SOS" is not generally used in voice communication.
Its used by morse code stations is because it is a short and easily recognized pattern:
. . . - - - . . .

Its recognizability is part of the reason it replaced the old Marconi CQD general distress call code
- . - . - - . - . - . .
which was literally a general call to all stations (CQ) signaling "distress" (D).

I can't find a reference, but I would assume there's at least one case in history where the SOS code was used by an aircraft (back when morse stations were common on aircraft).

An SOS signal could of course be transmitted today using the unmodulated carrier from your radio by simply keying the microphone, but that would only be useful if the voice circuit of your radio has failed and you had no other means to communicate. Otherwise voice contact or setting your transponder to an appropriate code would generally be the preferred way to signal distress.


Is it normal for gliders not to have attitude indicators? This answer shows a picture of and describes a "modern" glider instrument panel, with two variometers, airspeed indicator, altimeter, compass, temperature gauge and radio controls.

Notably (at least to me) missing from this is an attitude indicator (or "artificial horizon"). I had the impression that an AI was one of the more important indicators in an aircraft.

Is it frequently left off on gliders? How about other aircraft? Is this related to always avoiding flight outside of VFR (visual flight rules)? Is an AI not very useful or not useful at all in VFR conditions?

Yes, it is normal. With very rare exceptions, gliders are not allowed to operate in IMC (instrument Meteorological Conditions) and must remain clear of clouds. There are also powered aircraft that do not have attitude indicators, mostly for the same reason (VFR, Visual Flight Rules only).


What's the difference between orientation and position? In INS (Inertial navigation system) sensors, is there a distinction between the following?

Orientation (heading, pitch and roll)
Position (latitude, longitude and altitude)

Is the orientation relative to a specific axis while the position is absolute? If yes, what is the axis?

Yes there is a distinction, pitch, roll and heading are angles [unit = radian] and latitude, longitude and altitude are linear distances [unit = meter].  Together, these six parameters define the six Degrees of Freedom that define the momentary state of a rigid object with reference to the earth.

All six are defined relative to earth axes. For the linear dimensions this is clear, we just need to define a suitable zero point. For the angles:

Pitch is the nose up/down angle relative to the gravity field of the earth.
Roll is the wingtip up/down angle relative to the gravity field of the earth.
Heading is the angle relative to a suitable earth reference, usually magnetic north or geographical north.

Conversion of aircraft axes into earth axes is a non-trivial matter and the cause of much confusion, for instance in questions comparing lift to weight: lift is always coupled to aircraft axes, weight to earth axes. The axes sets are defined as follows:

Aircraft axes

Origin: Centre of Gravity of aircraft
X-axis: in the symmetry plane of the aircraft, + = forward to the aircraft nose
Y-axis: in the span wise direction of the aircraft, + = to the right wingtip
Z-axis: perpendicular to the XOY-plane, + = down into the floor.

Earth axes

Origin: Centre of Gravity at the start of the response
X-axis: In the horizontal plane (relative to gravity), + = pointing north.
Y-axis: Perpendicular to XOZ-plane, + = pointing east.
Z-axis: Pointing to the centre of the earth = +

Edit

Yes navigation lat/lon is given in [degrees] - the INS sensor ultimately converts displacement into proper navigational definitions of course. But for measuring 3-D aircraft inertial effects the SI system is used, and displacement is internally treated as a linear motion, units [metres].


Where can I get a high-res photo of the RAT from an A320 Airbus? I'm working on a project regarding the hydraulics system of the A320 airbus.  I can't seem to find a clear Hi-resolution image of a grounded A320 with the RAT extended out.  Anyone know where I can find one? Or if you have one and don't mind me using it for my project, I'd be much obliged!! Thank you!

Airliners.net is the photo directory of aircraft on the internet, a quick search turns up this beauty :) You can also diversify your search to A318, A319 and A321 since it's in principle the same equipment.

Aidyn Iskakov - Almaty Spotting Club

http://www.airliners.net/photo/Air-Astana/Airbus-A320-232/2419974/

(source: airliners.net)


Why are flaps retracted when an aircraft is parked on ground? I found this question. One of the answer tell the flaps are generally retracted after landing. I assume this mean flaps are retracted when the airplane is on the ground between flights.

Flaps are extended for landing and then extended again for take off. Not taking care of their position while on ground (no need of them) and putting them in the required position before take off may save (few) flaps actions (something like putting them from landing to take-off position instead of landing position to fully retracted and then from retracted to take-off position).

Is there some good reason to retract the flaps on ground? Does this good reason varies from a type of aircraft to another?

A few different reasons:

Good pilots put the aircraft into a well-known (up) configuration after landing, so that the aircraft is ready for use on the next flight.
Flaps down during taxi was a signal to the tower that the aircraft had been hijacked.
Take-off flaps (10 degrees on my airplane) and landing flaps (45 degrees), are nearly always different, so leaving the flaps down after landing at, say, 45, doesn't save any steps for departure. If the pilots forgets to set flaps before takeoff, some aircraft (like mine) will make it almost impossible to depart and climb out on full flaps because of the induced drag, while takeoff with no flaps is possible.
Prevent trucks and people from hitting the flaps while the airplane is parked, especially in the full-down (landing) configuration.
Some pilots employ the practice of retracting the flaps during the rollout because it puts more weight on the wheels, reducing stopping distance.
Flaps down increases the amount of lift generated by the wing, so some aircraft might actually lift off the ground while parked with full flaps in high winds.


Why did the US Airways Flight 1549 passengers stay on the wings? Couldn't they use the overwing slides as flotation devices and stay on those instead?

Because they were told to evacuate there, if you take a look at the official audio transcript from the accident:

  place both arms through the straps and hug it to your chest. flight
  attendants are pointing out there are a total of eight exits on this
  aircraft, two door exits in front of the aircraft, four window exits
  over the wings, and two door exits in the rear of the aircraft. once
  again, two door exits at the front of the aircraft, four window exits
  over the wings, and two door exits in the rear of the aircraft. each
  door is equipped with an evacuation slide if directed to exit... the
  aircraft jump onto the slide and move away from the aircraft.

The rear exits were largely blocked by water making the forward exits the only ones with slides, those slides were utilized as evidenced by photos included in the report:

(source)

With only half of the slides available the wings also had to be used. The wing slides are intended only for ground landings and do not double as rafts, as per the accident report

  According to TSO C-69c, Type IV is a combination inflatable exit ramp
  and wing-to-ground slide. The off-wing ramp/slides were intended to be
  used in the event of a ground, not a water, evacuation.

As such the over wing slides could not be used in this case.


Why do some aircraft have multiple ailerons per wing? In a recent flight on an Airbus A380 I noticed that its ailerons are split into three segments which move independently.

What advantages does this design have? Do other aircraft have split ailerons (or other control surfaces)?

General Reasons

There are three main reasons for having multiple ailerons per wing on large aircraft:

Aileron Reversal

On a large aircraft, at high speeds a deflected aileron can twist the wing enough to cause a net roll torque opposite to the one intended.  The further out on the wing an aileron is, the more likely this problem is to arise.  For high-speed aircraft, this necessitates an outboard/inboard aileron, with the outboard being locked out at a certain speed limit. On the Airbus A380, the downwards motion of the outward aileron is locked out at 240 KIAS, and upward motion at 300 KIAS.

Systems Redundancy

Another issue is that on most large aircraft, it is simply infeasible to have cables running through the aircraft, so hydraulic systems are used instead. Having ailerons split would allow for more redundancy of system failures, allowing more controllability in these failure conditions.

Load Alleviation Function

Building on what Bret Copeland has already discussed in his answer, multiple ailerons can be used by fly-by-wire computers to flex the aircraft's wings in a specific manner to allow for less loading on the wing during cruise (counteracts the wing's natural tendency to flex upwards), as well as allowing for dynamic turbulence alleviation.

One of the examples of using this is in Airbus's Safety First magazine (July 2012), where they use the flexibility of having three ailerons to tune out lateral accelerations in the rear of the aircraft changing the gains of each of the controls. By being able to move the centre aileron a fraction after the inner aileron, they managed to avoid these initial shifts during flight testing of the A380.

Other Aircraft

The majority of airliners have multiple ailerons, however in some instances (such as the Airbus A310), there is no outboard aileron -- this function is replaced by spoilers.

Another example of using computers on multiple ailerons is the Boeing 747-8, with the use of the outboard aileron to fix issues relating to the development of flutter in certain extremes of the flight envelope, called the Outboard Aileron Modal Suppression (OAMS) system.


Are peer-to-peer communications feasible between aircraft? I have several questions regarding plane-to-plane communications (P2P), by which I mean air-to-ground communications where instead of a satellite, planes act as the intermediate nodes between a given plane and its controller on the ground. Or in other words, peer-to-peer communication.

Would P2P be a feasible model for communicating between ground and aircraft? For example, could ATC or other operational messages be routed to an aircraft using a P2P method? Is this already possible? Does communication with aircraft require a satellite or terrestrial endpoint, or could P2P work instead? How much data and power would be required for all the messages needed for a typical transatlantic flight?

Yes, this we could do this.

Actually, we already do it: If an airplane cannot be joined by ATC, ATC will ask planes in the neighbourhood to relay the message.

As for what you are actually asking, which is a P2P mesh network for data or ATC, without active pilots involvement, this could work but would be completely impractical:

Mesh networks are still an active research topic (i.e., not exactly production ready), and offer little to no advantage over a traditional communication (satellite, aircraft to ground) that nobody would bother implementing this.

Few of the downsides are:

What if there is no plane to relay the message ? You are back to P2G (Plane to Ground), so why not use P2G in the first place.
What if there is a broken/rogue airplane that blocks/modify/fake your messages ?


Is it possible that meteor could strike a commercial airliner? Is it possible? Are there some such accidents in human history? Is there any rules or systems design to protect airplanes?

Yes, it is possible, however unlikely!

The final report into the downing of MH17 investigated the possibility that the aeroplane was hit by "meteor or space debris"

  In section 3.5 a number of scenarios are analysed that relate to the possible source or sources of the object that perforated the aeroplane. These include meteor and space debris.

It was concluded that

  The chance of a meteor striking an aeroplane was calculated as being one event in 59,000 to 77,000 years. This value was obtained from the University of Pittsburgh's Department of Geology and Planetary Science and was originally part of the NTSB's investigation into the 1996 accident to TWA flight 800 (see NTSB Report AAR-00/03, dated 23 August 2000)


Is the autorotation in San Andreas movie realistic? San Andreas is an awful movie, but given how helicopter-centric its plot is I'm wondering if they even got the autorotation landing correct?  In the middle of the movie the hero is cruising in (I think) a Bell 412 when the engines fail.  He tells his passenger they're going to autorotate, and he proceeds to do the following maneuver three times: Precipitous pitch down, then after picking up a lot of speed, a flare.  (The final "landing" flare is attempted in a crowded parking lot where he tries a last-second evasive maneuver that destroys the helicopter.)

My understanding is that a proper autorotation always simply consists of pitching to a specified glide path and not changing pitch until the landing flare.  Do any conditions or rotary-wing vehicles call for a different autorotation maneuver?

Let's see how many things we can find wrong.

There's a bang, smoke starts coming from the exhaust.  Master caution comes on and his first response is to tap and check the 115v AC gauge!  The pilot takes his hand off the collective!
You hear the engine wind down and the rotor RPM drop.  He announces a gearbox failure.  So why did the engine wind down?  His passenger even asks if he switched the engine off.  If the gearbox had seized, the engine would have been destroyed or, the input shaft would shear and the engine RPM would increase leading to a very rapid overspeed.  There is no gearbox failure mode that results in the engine winding down.
He had a long think and a bit of a chat after the engine and RRPM wind down.  In a Bell 412, with the speed of that wind down, the blades would have stalled after 2 or 3 seconds if he hadn't dropped the collective.
He announces that he is going to autorotate.  His passenger asks "auto what?"  He says we're going to crash.  The whole point of autorotation is that you don't crash.
With the RPM already low (let's forget that he would have stalled by now), his first action is to dive and you hear the RRPM increase.  In reality, they would go even lower.  If he wasn't already stalled (which of course he would have been) he would now.
He was straight and level, with significant airspeed over level open ground.  At the first bang and sound of the engine winding down, he would have lowered the collective and flared to preserve RRPM. He would then look for a good place to land, not a shopping centre car park, and fly towards it.
Each time he flares, he pitches forward again and the RRPM drop rapidly.  Flaring like that in auto would cause a large increase in RRPM, possibly overspeeding and lowering the nose to the level would cause a small drop in RRPM.  Diving again would reduce the RRPM.  So why would you flare to increase, then dive to decrease?

In short, the sequence is complete nonsense.


What is an example of a system like MCAS? The related question "Is it common for automated control systems to use non-redundant sensors?" does not ask about a specific example, nor are specific examples provided in the answer.

The criteria for my question:

Activates on its own, or always active.
No light/text indication of it being active.
No specific disable switch.
Relies on 1 sensor when 2+ exist.
The system is not disabled when the 2+ sensors disagree.

As you can see, these properties are modeled after what is known about MCAS.

This question isn't about the 737 in particular but about any commercial (fly-by-wire or not) airplane, so eventually the answers should specify the model, and if possible the justification of the design.

Irrespective of 737 MAX MCAS, I haven't seen similar decision relying on a single sensor on 777 or on 757.

Similarly I found nothing similar on Airbus 320, 330, 340, 350, or 380. On these Airbuses, 3 sensors are used for critical decisions, thus the faulty sensor is isolated by voting the data. If the 3 sensors are diverging (no 2 sensors giving similar data), the system goes into safe degraded mode, and the pilots are informed by automatic displayed message.


What is the name for a flight crew that includes extra members for a longer flight? For short haul flights, airlines fly with BASIC CREW.
For long haul flights, the crew must be composed for another crew or "extra" crew members, less than a crew.

What's the designation of the crew, that comprises more than the minimum number required to operate the aeroplane?
For example: 2 captains and 2 FOs; 1 relief pilot; 2 captains and 1 FO.

A crew that consists of the basic required cockpit crew for the aircraft plus relief crew for long flights is called an "augmented flight crew." As far as I know, this designation is used by ICAO, the FAA, and the EASA (and likely others.)

This ICAO document defines augmented flight crew as:

  Augmented flight crew. A flight crew that comprises more than the minimum number required to operate the aeroplane and in which each flight crew member can leave his or her assigned post and be replaced by another appropriately qualified flight crew member for the purpose of in-flight rest.

The FAA's Federal Aviation Regulations define it nearly identically in 14 CFR 117.3:

  Augmented flightcrew means a flightcrew that has more than the minimum number of flightcrew members required by the airplane type certificate to operate the aircraft to allow a flightcrew member to be replaced by another qualified flightcrew member for in-flight rest.


Are there any regulations on who can sit next to emergency exits? Whenever I fly with Lufthansa, if I want to sit next to the emergency exits, I have to satisfy some criteria such as:

  Be able to communicate in German or English
  Be at least 16 years old
  Be able in good physical shape so as to be able to open the door(I don't recall the exact wording Lufthansa used)

Now this is not a full list, but it gives you an idea.
Later on I took a flight with another company (still an European company). This company was proposing to get those seats for an additional cost (as they have much more leg space), and with no criteria to satisfy. Upon boarding the plane, I noticed that the people sitting in those seats were above 60 y/o, so I doubt they would be able to open the door. So I wonder are there any regulations in EU?

I saw an answer for the FAA regulations over here: link, but I wonder how is it in EU.

EU No 965/2012 provides some direction.

  CAT.OP.MPA.165 Passenger seating

  The operator shall establish procedures to ensure that passengers are seated where, in the event that an emergency evacuation is required, they are able to assist and not hinder evacuation of the aircraft.

Further clarification can be found from Acceptable Means of Compliance
(AMC) and Guidance Material (GM) to Part-CAT.

  AMC2 CAT.OP.MPA.165 Passenger seating

  ACCESS TO EMERGENCY EXITS

  The following categories of passengers are among those who should not be allocated to, or directed to, seats that permit direct access to emergency exits:

  (a) passengers suffering from obvious physical or mental disability to the extent that they would have difficulty in moving quickly if asked to do so;

  (b) passengers who are either substantially blind or substantially deaf to the extent that they might not readily assimilate printed or verbal instructions given;

  (c) passengers who because of age or sickness are so frail that they have difficulty in moving quickly;

  (d) passengers who are so obese that they would have difficulty in moving quickly or reaching and passing through the adjacent emergency exit;

  (e) children (whether accompanied or not) and infants;

  (f) deportees, inadmissible passengers or persons in custody; and

  (g) passengers with animals.

Whether or not a person can sit in the emergency exit row may also depend on if the specific seat is designated as an emergency exit. For example, on narrow body aircraft, generally all seats in the emergency exit row are considered emergency exit seats and only persons who "able to assist" can sit in those locations. However, on some wide body aircraft, only seats on the window sides are considered emergency exit seats. On an aircraft with a 2-3-2 configuration, the 3 seats in the middle are not considered exit row seats and therefore do not have any further safety requirements.


Which one is more effective produce power of this two turbine's location? Consider we have the exactly same turbine which is possible to be mounted to the tail (left picture) and to the wing (right picture) as picture below. Which one will produce more power to the airplane? Need physics analysis.

The power will be the same. But the aircraft with wing mounted engines will have less drag. Contributing factors are:

Engines are heavy. Putting them aft means there is a big difference in centre of gravity between empty and loaded aircraft, so larger horizontal stabilizer is needed to keep it in trim over the range of centres of gravity. It is also needed for rotation on take-off with forward CoG, since the main gear must be behind the aft-most CoG position. That means more trim drag.
Putting something heavy, like engines, on the wing ahead of it reduces flutter, so the wing can be less stiff, and thus lighter. This means more payload, or less induced drag at the same payload.
Engines ahead of the wing fit nicely with the Whitcomb area rule. At the tail they add a lot of cross-section where it should be tapering off already, slightly worsening the transsonic performance.

So engines tend to be wing-mounted on all but small low-wing aircraft where they would have too little ground clearance.


Does a METAR report variable wind direction in a clockwise direction? Does the convention for reporting variable wind direction always use a clockwise (nautical) sense?

For example, if the wind varies between 340 degrees and 10 degrees, assuming a clockwise sense the METAR item would be 340V010, but is 010V340 also correct?

According to meteocentre.com variable wind directions are encoded in clockwise order:

  This group reports variations in wind direction. It is only included if during the 10 minute period preceding the observation the direction varies by 60 degrees or more, and the mean speed exceeds 3 knots. The two extreme directions are encoded in clockwise order.

(http://meteocentre.com/doc/metar.html)


Is it possible to have a fully electric airliner? Is it possible to have a fully electric airliner?

How much room would have to be sacrificed for a power bank in these aircraft to allow similar range to the current models (e.g., A320, 737, etc.)?

Would it shrink the passenger capacity by a lot? Or is the concern mainly having enough power to push such weight?

Well, to use the same airframe, you'd basically have to find a way to replace the fuel volume in the wings with battery volume, and batteries are somewhere around 15-20% of the power density of fuel, as the answers in this ASE post lay out pretty well.

So if you had an electric fan that made the required thrust, and somehow figured out how to replace all the fuel tanks with batteries, you'd probably have something, but only with about an hour's endurance, which wouldn't even make up the IFR reserve range requirements most of the time.  You would have to replace a lot of pax with batteries to get even a couple hours endurance, which would kind of kill the business case.

So that kind of concept is pretty much a dead end until battery power density starts to approach the level of kerosene, maybe 20 or 30 years from now unless some massive new development comes along.


When do pilots perform a CAT II/III autoland? If I understand correctly in good, visual weather get conditions airline pilots generally do ILS CAT I, when at some point they disconnect autopilot at some point and land manually. If the visibility is low, they do ILS of higher category (II/III)  with autoland.

My question is, what are the criteria that pilots decide they will be shooting autoland? Is it RVR below CAT I minima or below some higher limit, just to be sure? Also, does ceiling matter in making this decision? For example OVC001, or OVC002 with good RVR and visibility - is it then required to autoland?

CAT II / III operations depend on DH and RVR, not cloud layer. It will be based on "the most demanding" of the two.*

Extreme low visibility, say due to dense fog (which is a cloud type), can actually be considered OVC000, hence the use of RVR. RVR tells you how bad the fog is and how far you can see inside it.

Here's an example of such METAR for Charles de Gaulle Airport:

  LFPG 051100Z 13005KT 090V180 0350 R27L/0900U R09R/1500D R26R/0800N R08L/0750N R26L/0800U R08R/0650N R27R/1000U R09L/0800U FG OVC000 00/00 Q1033 NOSIG

The airport also needs to enforce low visibility procedures (LVP) and broadcast it on the ATIS, so the ILS' safety area is protected. By planning ahead and by checking the ATIS, the pilots will know which approach to expect based on their operator's established 'operating minima'.

There's more to it however than DH, RVR, and LVP, for further reading check the Airbus publication, 'Getting to grips with CAT II / CAT III operations'.

* ICAO Manual of All-Weather Operations

Re: comment:

    Can cat II/III only be done, when airport announced (ex. via ATIS) that LVP are in force?

Yes, the alternative is for the pilot to request from the tower/approach a CAT II / III approach, so the tower can enforce the safety area and verify the ILS equipment is working up to the CAT II / III standards.

    If the weather was like in your METAR - RVR0800, the pilot would have to use CAT I minima if no LVP is enforced, but he could use use Cat II/III only if LVP is in force to make sure he won't have to go around - is that correct?

Without checking the French authority's specifics, the METAR visibility (350 m) is already below CAT I (>800 m), so the airport should be operating in LVP.

    (...) after choosing CAT II/III he must auto land - is that correct?

It will be based on their operator's established 'operating minima', i.e., the airline procedures, which adhere to the regulations set by its national authority. CAT III B must be flown using auto land to touchdown incl. roll-out. CAT II and III A not necessarily.


Are VFR pilots required to avoid an isolated cumulus cloud like any other cloud? When flying VFR, pilots are to stay free of clouds, which includes a minimum of 3 miles visibility, and 2,000 feet laterally.

Yet, I've seen some youtube videos where it appears the pilot gets too close to a "cotton ball" (a small, isolated cloud) simply because it is along his flight path.

If it is a very small, very isolated cloud, and you can see all the way around it, and have had good visibility on it for awhile as you approach, you know its not a "threat", right?

I suppose the FAA could violate you if you approach a cotton ball, but other than that, is there any reason to deviate and go slaloming around the sky just to keep distance from FEW clouds?

I suppose the FAA could violate you if you approach a cotton ball, but other than that, is there any reason to deviate and go slaloming around the sky just to keep distance from FEW clouds?

Aside from the legal reasons, keeping a healthy distance away from clouds is a Good Thing because other aircraft, birds, or alien spacecraft may pop out of them. Mid-Air collisions are no fun for anyone.

As far as going "slaloming around the sky", there's generally no reason to do that to avoid clouds:
If you're respecting the cloud clearance requirements (or at least the intent behind them) you shouldn't be getting close enough to clouds that you have to aggressively maneuver to avoid them - you've got plenty of distance to decide what you want to do.

Remember too that you've got 3 dimensions to work with: If we're only talking about a "puffy cotton-ball" or two you can always climb above or descend below them and stay on-course, or if they're all lined up inconveniently right along your flight path just offset your track a little bit (no reason to keep zig-zagging if a mile left or right of course keeps you clear).


What are the most powerful airplanes that ever flew? This question What are the least powerful airplanes that ever flew? made me wonder what the most powerful manned airplanes are that ever flew. There are two sensible categories, I suppose:

Most thrust overall.
Best thrust-to-weight ratio.

EDIT in response to a comment by @ratchet freak:

Answers including rocket-powered aircraft are welcome, although I'm also interested in other propulsion systems. However, I'd like to exclude rockets by requiring the craft in question to be able to at least land on, if not start from a runway.

EDIT 2 in response to a comment by @Robin Bennett:

I'd like to restrict this to reusable craft, in the sense that they should be fine to go again with not much more than a refuel. So I guess that excludes the Space Shuttle.

Most thrust overall?

Well the most powerful aviation gas turbine to date is the GE90-115B, producing a whopping 115,000 lbs of thrust per engine at maximum static thrust settings.

Overall the aircraft with the greatest thrust to date has been the StratoLaunch.  With 6 PW5406 engines, each rated at 56,000 lbs of thrust, this gives it the highest takeoff thrust at slightly over 340,000 lbs.  For production aircraft, it’s the A380.  With 4 84,000 lb thrust class Trent 900s, it gave the jet a massive 336,000 lbs of thrust on takeoff.  This beats out even the AN-225 Myria, with its 6 Progress 6DT engines rated at 51,600 lbs each.

The most powerful turboprop still goes to the old dog - The Tu95 Bear.  With four Kuznetsov NK-12 turboprop engines, each rated at 15,000 shp, no other turbopropeller came close.

The honor for the highest powered piston driven aircraft goes to the Hughes H-4 Hercules.  The ‘Spruce Goose’ was driven by 8 Pratt & Whitney R-4350 Wasp Major engines at 3000 bhp, giving it 24,000 bhp at full throttle.  This is also a sobering demonstration of the huge power to weight advantage of gas turbines over reciprocating engines.  Consider that the Tu-95 mentioned above has half the number of engines yet still packs 2.5x the power of the Spruce Goose at full throttle.

The gas turbine powered airplane with highest thrust to weight ratio that I ever heard of was a stripped down Su-27 used by the Soviets in the 1980s for setting time to climb records, similar to the F-15 Streak Eagle program.  The plane had a thrust to weight ratio of nearly 2:1 and had to be held back by steel cables during run up to full power as its own brakes were insufficient to restrain it.

But the X-15 beat them all.  With a gross weight of 27,000 lbs and a Reaction Motors XLR99 Rocket Engine to give it a push at 70,000 lbs of thrust, it claimed a thrust to weight ratio of nearly 2.6:1!

Who knows?  Maybe there’s an Aurora driver at Area 51 reading this right now who’s getting quite a chuckle out of it as he knows something I don’t!


How are forces on the landing gear reduced or compensated for at touchdown? When an aircraft lands with the tires of the landing gear at rest, as soon as the the aircraft touches down, the landing gear experiences a large amount of wheel-spin up forces (because of the static friction involved between the stationary tires and the relatively moving runway at a very fast speed), which even cause it to vibrate at some frequency. This force is considered to be highly undesirable.

Are airplane manufacturers using any kind of measures to reduce these forces on the landing gear at touchdown? How are they compensated?

There are lots of forces acting on the gear at the point of landing. The best way to minimize loads on the gear is to land smooth (I know that sounds obvious).

For what it's worth you do not necessarily want to spin up the gear before landing for a few reasons. First off you would need to spin up the gear to precisely (or at least very close to) the speed that the plane was going to touch down at. If you spin the gear up faster you actually will create a problem by accelerating the plane when it touches down. Spinning the gear up can also have a serious gyroscopic effect (since you now have a fast rotating mass) (see here as well) that will affect the handling of the aircraft.

On top of that remember that in aviation it's often about cost. What are the costs to maintain a system that pre-spins the gear vs the cost of tires. Some times its actually cheaper and easier to make a part that wears out some what quickly and replace it often, then design a complex system that require maintenance and up keep.

It appears that some devices for spin up have been looked into but the rotational inertia problem seems to be more of a concern than wheal wear. I would imagine that unintentional side loads on gear are a bigger issue and bigger cause of wear on the landing assembly. Keep in mind that the addition of an assembly like this also adds weight to the aircraft, and no one likes weight that is not needed.

This is a great research paper on the topic that suggests (in their conclusion) a pre spin situation would see 1.07% of the wear of a static situation. They go on to state that that they used a simple linear approximation and only accounted for forces in one direction but it would seem that it is beneficial for the tire.

On a side note this article even suggests the tires can be remolded so even if the are replaced often it seems they are recycled a few times.

  an A340 will complete roughly 6,000 take-offs and landings, calling for about 25 sets of replacement tires, each 1.30 m high and weighing about 200 kg. The tires can be remolded several times before they are finally scrapped.

In general, it's the job of the pilot to reduce the forces on the landing gear when landing. One of the best descriptions I have ever heard of landing is that the goal is not to land but to "transition". In other words what you really want to do is transition the load from the wings to the landing gear as smooth as possible, this will reduce the load on the gear. In some cases (short runway heavy plane) your landing may see more force on the gear. I have never flown a 737, but I can tell you that I can put a Piper Warrior down on a 7000-foot strip with out ever feeling that you have touched the ground.


Why has the 777x been designed with folding wingtips? I recently visited the Boeing factory outside Seattle, WA and noted in the distance a new 777x being built with, what looked like very large winglets.

However, on closer inspection they're not - the ends of the wings are designed to fold up.

Source: aviation today

I didn't get a chance to ask our tour guide, so I was wondering if anyone here can explain why this aircraft has been designed with folding wingtips. I'm presuming this is only for ground operations, and my guess is something to do with size - but are they really so big that they need to fold up? I would have imagined that other large wide body jetliners would have similar dimensions.

Please note that I'm not asking about whether this should have winglets, or if winglets provide any benefits, I'm asking specifically why the ends of these wings fold up rather than just fixed as per previous 777 models.

The Boeing 777X website states that this is to enable a more efficient wing (read: wider span) while maintaining the airport gate and taxi footprint of the classic 777 (which ensures airlines can use the 777X on roughly the same airports and intermix operations with the classic fleet).


How to go about designing a custom airfoil? I am familiar with the NACA 4-digit and 5-digit airfoil design system where airfoils, but I was wondering if anyone had some good reference material or software for designing a completely custom airfoil.

From what I understand, many new aircraft use completely custom non-NACA airfoils, sometimes several different airfoils over the wingspan. I am curious about how the design process goes from specifications of the airflow (incidence angle, perhaps the sweep of the wing, air speed, density, reynolds number etc) to a new custom airfoil?

Wing sweep, incidence, and airfoil geometry will all have to be adjusted to achieve the best performance at a certain air speed, density, and Reynolds number.

The software that egid mentioned is a good place to start. While studying aerospace in college, XFOIL was used for basic airfoil analysis in our classes.

Another program used was AVL. This analyzes the aircraft as a whole and can model other things such as dynamic stability.

I'm glad that XPlane was also mentioned, even though I wouldn't consider it the most scientific tool for testing wing geometry. It is an interesting way to test configurations since it does use the airplane geometry to simulate the performance characteristics.

In order to consider more variables such as sweep, dihedral, and different airfoils over the wingspan, computational fluid dynamics (CFD) software is used. ANSYS Fluent is one example. There are many other packages out there, and anyone doing serious commercial airfoil design will have proprietary software and methods for this.

Of course, even in the days of supercomputers and CFD, wind tunnel testing is still very important. Scale models can be tested to validate the computer models and demonstrate performance.

As far as requirements, they can get very complicated. For aircraft, of course, the primary goal is to provide the lowest drag at cruise conditions. However, many other factors include:

Preventing flutter
Provide room for sufficient supporting structure
Provide room for fuel
Methods to manufacture the shape
Good stall characteristics
No bad aerodynamics with fuselage and engines
Enough lift with flaps for low landing speed
Able to accommodate flaps, slats, spoilers, and ailerons
Tip treatment like winglets/raked tips
Wingspan must fit into available space (airport, hangar, aircraft carrier, etc.)

And probably many more. Of course, the air speed and conditions will also affect the fuselage, empennage (tail) and its control surfaces, and engines, so this will also be taken into account.


Are crosswind landings performed using autoland or under manual control? I believe many people here have seen at least one of Cargospotter's videos of crosswind landings at Düsseldorf (DUS/EDDL).
There are several of them. I picked this one:

I think the pilots land their aircraft manually in case of such heavy crosswinds.
But is that true? Or do they lean back and watch the scene as the autolanding system does its job?

This somehow related question suggests the plane is operated manually.

Are there any regulations as to when using autolanding and when to do it manually? I know this might be
opinion-based, but could autoland even handle these crosswind situations?

The B777 is limited to a max crosswind component of 25 knots when using Autoland so it is most likely that it was a manual landing in the photo above.

The B777 has a "max demonstrated crosswind component" of 38 knots. Some companies will round this up to 40 knots for a company limit.

The "max demonstrated crosswind component" is not a limit. It just means the aircraft can land with that wind speed, in a crabbed configuration, without damage to the aircraft or landing gear.

Crosswind landings for certification are done in a crabbed configuration. Boeing has demonstrated landings for the B777 with a 38 knot crosswind, so that becomes the Demonstrated Crosswind Component.

If Boeing had tested with winds greater than 38 knots, AND it resulted in damage,  then the B777 would have a 38 knot Crosswind LIMIT.

Of course there was no damage at 38 knots and there is nothing preventing pilots from landing with crosswind components greater than 38 knots.

Since Boeing has not tested or demonstrated crabbed landings ABOVE 38 knots, we don’t know what the actual limit is when damage may occur due to side loading.

So when landing with a crosswind greater than 38 knots, it would be prudent to use a technique that would involve a slip and removal of any crab at touchdown so that excessive side loading is avoided.


On an IFR Low Altitude Chart what does this symbol mean? I read the information below in the aeronautical chart user's guide. I have several questions.

On the third line - Why is there an ICAO identifier for a U.S. & Alaska low altitude chart? I thought ICAO was for international flying?
On the fourth line it says '0' and '*' but there is no explanation. What do these two symbols mean?
On the fifth line it says there is a part time frequency, I assume because the tower is part time based on line three. So if this is the case, why does it need to say part time twice?

CITY - City

Airport Name - Airport Name

(APT) (ICAO) [D]* - Airport Identifier, ICAO Location Identifier, Class D airspace with far 93 special requirements operating part time

280 0* 43s - Airport elevation, unknown symbol, runway length (soft field)

(A) *109.8 - ATIS, Part Time Frequency

① - ICAO ID

As indicated, will be used for OCONUS airports only (overseas), e.g. Guam has a 4-letter ICAO designator:

② - Symbol with circle: Lighting

  An "L" following the elevation under the airport name means that
  runway lights are on during hours of darkness. A circle around the "L"
  indicates there is Pilot Controlled Lighting. A star beside the "L"
  means the lighting is less than continuous.

(Source)

This is part of the legend, but there is no lead line.

③ - ATIS available part-time

This is not the tower frequency (as your question seems to assume), but the ATIS frequency.

This information is not redundant, the ATIS may be available full time for an airfield open part-time. This is the case for Grand Junction Regional in the snapshot above.


How does a synchro resolver converter work? There are Synchro converters or transducers used on aircraft to measure angle of attack using 3 sinusoidal inputs. I could not understand where  these 3 inputs come from and what angle information is generated by the synchro converter on the basis of the input signals?

The angle of attack sensor turns the shaft on a synchro (or a resolver: they're essentially the same thing) which is a transformer whose outputs are uniquely related to that shaft angle. That's where your 3 inputs come from. There are lots of possibilities for what happens next. The shaft angle is not the same as the angle of attack. The synchro is not measuring. It's just conveying measurement information from the sensor to the flight crew and other aircraft systems.


Where is the inlet for the APU on a Fokker 70/100? I can see the exhaust for the APU on a Fokker jet, but where is the inlet?

You can check this report from the BFU.

I reproduced the image of page 12 of the report here

Obviously, the exhaust is in the middle of the picture and the inlet is on the top right part (trapezonidal shape)


Would an area-ruled fuselage improve the MiG-15/17's performance? The top speed range of these MiG 15-17 airplanes is in the transonic region, but, when they were first designed, the area rule was unknown.
Even if owning a jet fighter is not exactly 'Maintaining pilot's performance', thus hard to obtain or license, the change looks not too complex to implement; curiosity, experimenting, is the force behind Aviation progress. Salut +

In a word, yes. But that sort of depends on the definition of "performance". The top speed would likely be effected only in a minor fashion, but the transonic acceleration would likely improve, as would the fuel economy.

It is worth pointing out that, largely by luck, many of these aircraft got some of the benefits of the area rule without specifically designing it. The location of the cockpit behind the intake required the fuselage to become larger in that area, especially when one considers the canopy, which ends just in front of the wing. And then the tail begins near the end of the wing and the fuselage begins to narrow behind the engine as well.


Can another pilot act as my safety pilot for only part of a flight? Let's say I fly with my safety pilot while under IFR plan (I recently earned my IR). I cancel IFR in air since I can maintain VFR for the last, say, 20nm of the journey (assume there was just some weather necessitating the rating earlier on enroute).
In the VFR phase, I don my hood and conduct 1 or 2 practice instrument approaches at or near destination.
First of all, is this ok? Passenger (since right seat sits VFR only pilot) "evolves" into safety pilot?
Second, if legal, how would one log this flight for purposes of currency?

Yes. This is all perfectly in accordance with the regulations.
You personally conducted the IFR flying through IMC, as an instrument rated pilot on a filed IFR flight plan. Check.
You cancelled the IFR flight plan midflight with a plan to continue VFR. Check.
In VMC, your VFR-rated pilot friend assumes the responsibility of acting as safety pilot while you undertake practice IFR approaches in simulated IFR. Check.
When logging the time, you would log the total time as PIC for yourself. Your friend was acting as a necessary crew member, but NOT necessarily as PIC. Nevertheless, his name and certificate number should be logged in your book as well. You would record the portion of your flight that was through IMC as ‘actual IFR time’ and your time under the hood as ‘simulated IFR time’. You would record your practice approaches and count them toward your required six-in-six as long as they were performed according to the required standards.
I found this article at Pilot Workshops that can provide you with more detail.
Clear skies!


Are there differences in tool standards between aircraft manufacturers? As a follow up to "What is the measurement system used in the aviation industry?" which specified about measurement units during operations, another question that comes to my mind is: are there differences used in tools for maintenance and repairs for aircraft produced in different countries?

Although things have been standardized these days, in the automotive industry you still get differences in the types of tools that are required for repairs. For example, the old British cars such as Land Rover or MG used imperial spanners until not long ago (3/8, 5/16 etc) whereas other cars used more common metric spanners.

Does this apply also to aircraft? An example that comes into my mind would be the Avro RJ series.

According to a friend of mine that has worked as an aircraft mechanic for the last 30 years or so, it depends on the manufacturer.  For example:

American made aircraft, including Boeing, use SAE sized tools (US standard sizes)
Airbus uses metric tools
Hawker uses British Standard Whitworth tools
Dassault Falcon uses (believe it or not) a combination of SAE and metric.
Bombardier uses SAE


How much does it cost to give an airliner a fresh coat of paint? Just a random thought I had: the weather gives a jet's paint job a battering; meaning they need to be resprayed approximately once every 5-10 years. (See How often is a passenger jet aircraft painted?)

Roughly what might a paint job for a 777 like the one shown in the YouTube video below, cost an airline?

Bonus: I believe afterwards that the weight of the plane has to be recalculated, so as not to affect weight-and-balance. How is this calculation done?

According to WallStreetJournal article, Tom Horton stated in an interview that :

  A 777 paint job can cost  \$100,000 to  \$200,000, depending on the number of colors involved, and a smaller Airbus A320 can cost $50,000 or more.


Can a fighter jet be stolen? What (if any) sort of pilot authentication systems do fighter jets have?

Could anyone with the required skills simply take the aircraft or is a key or authorization code required?

Military aircraft rarely have any sort of keys or any sort of authentication systems, they rely on physical security measures to prevent people from getting to the airplanes in the first place, like fences, dogs, cameras, guards, and of course guns.

If there were no physical barriers then you have 3 major barriers to being able to steal a fighter jet:

Support: just about every military fighter aircraft has an assigned crew to prepare it for flight and help the pilot(s) get in it. Without this crew you'd have to get the airplane powered up, fueled up, and then you'd have to figure out how to get into it and get the ladder removed. There's a lot of knowledge you'd need to do all this, just knowing how to open the canopy isn't going to be immediately obvious
Starting: starting up a fighter isn't like starting a car, you don't hit a button and everything happens for you, there's fuel tanks and pumps, hydraulic systems, electrical systems, and engine management. You'd have to know where to find all of the switches, dials and levers, and the sequence in which to use them. This isn't something you'd be able to guess, you'd need knowledge of the particular airplane
Flying: high performance jets are challenging to fly, and by flying I mean aviating, navigating, and communicating. Although modern fighters have a lot of computers to help out with this the systems require a great deal of training to use, and if you don't know exactly what you are doing you are most likely going to dig a big hole in the ground

If you know how to start and fly the airplane there's nothing stopping you from doing it, provided you can solve the problems of prepping and getting in the airplane. In fact, it's been done when pilots defect with their airplanes, see the comments below for some great examples.


What are these boxes built into the tails of some fighters? In looking at European-designed fighters of the 4th and 4.5th generation, I keep seeing a common design feature; a box-like structure built into the tail, often in the top half or third. Some examples:

Saab Gripen

Mirage 2000 (this one's more complex and less box-like but the arrangement is very similar)

Rafale

Eurofighter Typhoon (this one looks markedly different, much lower and more like an intake)

Panavia Tornado (this one has two main protrusions from the tail, one much like the Typhoon's, the other more like the Gripens or Rafales)

SEPECAT Jaguar (you know what you're looking at by now)

What is this box? My best guess is some sort of avionics/sensor package, maybe RWR/missile warning. What's odd to me is that this box-in-tail arrangement is not seen on any relatively late-model U.S. or Soviet fighter; you'd think if the Europeans were onto something with this placement, the U.S. or Soviets would have tried it out at least once.

The F-15 has what I think is an RWR probe on top of the left tail, but the tail itself is pretty clean:

The F-16 does have a boxy construction flaring out at the top of the tail, but the front is clean:

The F/A-18 has some trailing-edge bulges but again very clean:

Su-27, ditto to the F-18 (it does have that big probe between the engines though):

MiG-29, same thing:

I could go on but you get the point, Soviet and U.S fighters seem to have passed on whatever this package is in the tail. So, what is it, why is the arrangement limited to European fighters (for the most part) and how do other regional designers accomplish whatever these do?

You're right. It's the ECM/EW antenna/equipment (fairing) in all the aircrafts except Typhoon.

This photo shows the details of EW/ECM suite in Gripen.

Source: www.w54.biz

In Typhoon, it is the engine bleed air heat exchanger. The part is in detail here.

Source: b-domke.de


Could passengers on an airline flight create an out-of-CG situation by moving around the airplane? I've often wondered if most passenger airliners have a CG envelope which would allow the CG of the airplane to be pushed outside the limits if enough passengers relocated to the front or back of the airplane.

If they do passengers might be surprised to know that if for some reason a lot of people got up and crammed into the back of the plane it might become uncontrollable.

If this is the case, the mental exercise could help illustrate how important an understanding of weight and balance is. It also highlights the importance of flight attendants as part of the air crew in their need to ultimately exert control over the crowd of passengers if the situation warrants it.

As a bit of background, I once wondered if Flight 93 during the September 11th attacks might have become uncontrollable because the CG shifted when passengers moved around the airplane. Although I once speculated that this could be the case, I am no longer speculating on the subject. I just want to mention that this is the scenario which made me wonder about the answer to the actual question. Since writing the original version of the question I learned about the CVR from Flight 93 and that it was intentionally flown into terrain by the hijackers.

I was on a flight in an SWA B737 that was mostly empty and the flight attendants moved us all toward the front. They told us it was for balance reasons.

I don't think this was a factor on flight 93. The CVR recorded the hijackers discussing what to do about the passengers. The hijacker piloting the plane asked 'Is that it? Shall we finish it off?' Another hijacker responded, 'No. Not yet. When they all come, we finish it off.' Then a few seconds later when it sounds as if the passengers are getting through the cockpit door he asks, "Is that it? I mean, shall we put it down?" The other responded, "Yes, put it in it, and pull it down." That's somewhat odd phrasing but those are translations from Arabic. It's clear that it was intentional.


What are the ICAO equipment codes for those Garmin units? What are the ICAO equipment codes for those Garmin units?

Garmin G500 / 750 / 650 WAAS navigators?

For the GTN 6XX/7XX and GNS 4XXW/5XXW they are:

A1/B2/C2/D2/L1/O2/S1/S2

Source: garmin.com — scroll down to the link that reads: "Garmin Flight Plan Information Excel file".


Why is paragliding not an old invention? Paraglider looks like a rather simple device for me. It does not have a complex engine that needs lots of technology to be built. It also does not need a powered aircraft just to be launched. Looking from the side I have an impression that it can cover serious distances along the ridge under right wind. While it is not convenient to have the airways bound to mountain ridges, it could still have had uses like patrolling borders or similar.

I am surprised, why the master that could build a bow, or possibly sails for the ship could not build a paraglider many years ago. What are the reasons why the paraglider is relatively recent invention? Is there something complex about is I am not aware of?

Paragliders as we know them depend on parawings with relatively high glide ratios and useful levels of steering.  Neither of these qualities were well represented in the round parachutes (even the so-called glide 'chutes) in common use before modern flat canopy glide parachutes came along (in the 1970s?).  Parawings as we know them were an outgrowth of these highly maneuverable parachutes, modified to have lower loading (for better sink rate) and optimized for horizontal flight, without the need to open in a near-vertical fall at terminal velocity.

If the knowledge had existed, parawings as we know them could have been built as early as the 1860s (when plain, round, uncontrollable silk parachutes came into use for stunt jumps from balloons).  The missing ingredient, as it were, was simply the knowledge that such a thing was useful and possible.


What separation and information does ATC provide in different airspace classes? I am busy studying radio for my PPL in South Africa, but I'm struggling to understand the ICAO definitions of the different airspace classes, and how ATC separates traffic in them.

I understand that the difference between airspace classes is based largely on which flights are "controlled" or "separated" by ATC, and which ones are only getting "traffic information". But I don't understand exactly what the difference is.

I fly a rotor-wing at a class D airport. Under VFR, we should only receive "traffic information", correct? But in reality, we still have to request ATC's permission to take off etc. and they can instruct us to hold, give way and so on. Doesn't that mean that we are in fact being "separated" from other traffic?

And theoretically, if IFR traffic is controlled by ATC in class D but VFR is not, and IFR is not separated from VFR, how should conflicting traffic avoid each other? If an IFR flight sees a VFR one in its way, who should do what? (Practically, the pilots will obviously maneuver to avoid each other, but what does the theory say?)

Finally, since IFR flights only get "traffic information" about VFR flights but not "separation", what happens if a VFR flight gets in front of an IFR one on final approach to land? Won't ATC tell the IFR flight to go around, or will they do nothing because they don't provide "separation"?

Different countries have different meanings to the classification of Airspace. I am only looking at the controlled airspace for ICAO.
Controlled airspace is an airspace that an aircraft would need a clearance to enter, this doesn't mean all aircraft need a clearance to enter just some aircraft.
Classes of Airspace
Class A is for IFR flights only, all aircraft are separated from all aircraft and are known to Air Traffic Control (ATC).
Class B is like Class A but with VFR. IFR and VFR are cleared to enter, all aircraft are separated from all aircraft and are known to ATC.
Class C is where the major confusion on separation usually begins. IFR and VFR are cleared to enter, all flights are provided an ATC service. IFR flights are separated from IFR and VFR flights, but VFR flights are only separated from IFR flights. VFR aircraft are only passed traffic on other VFR aircraft. All aircraft are known to ATC. I will go into what they do when they get in conflict at the end.
Class D both IFR and VFR are cleared to enter, all aircraft are provided an ATC service. IFR aircraft are separated from IFR and passed Traffic on VFR flight. VFR flights are only passed traffic on other aircraft. All aircraft are known to ATC.
Class E IFR are cleared to enter and VFR are permitted to enter, only IFR aircraft are provided with an ATC service. IFR aircraft are separated from IFR aircraft and passed traffic on known VFR aircraft. VFR aircraft do not need a clearance and are not usually known to the Air Traffic Controller.
Class F No one is given a clearance. IFR aircraft are given traffic on IFR Aircraft and known VFR. But all pilots are responsible for their own separation.
Class G No one is given a clearance. Traffic is only passed where it is requested, and only on known traffic. Only those requesting traffic or are seen on a radar are known to ATC.
Answers to Specific Questions

I fly a rotor-wing at a class D airport. Under VFR, we should only receive "traffic information", correct?

Yes, that is correct.

But in reality, we still have to request ATC's permission to take off etc. and they can instruct us to hold, give way and so on. Doesn't that mean that we are in fact being "separated" from other traffic?

When talking about Class D airspace: you are only separated from other aircraft when on the runway; when you are in the air you are not being separated. You instead will be passed Traffic Information on other flights. You however are still subject to the conditions of your clearance (Route, Level, Holding Instructions, etc.).

And theoretically, if IFR traffic is controlled by ATC in class D but VFR is not, and IFR is not separated from VFR, how should conflicting traffic avoid each other? If an IFR flight sees a VFR one in its way, who should do what? (Practically, the pilots will obviously maneuver to avoid each other, but what does the theory say?)
Finally, since IFR flights only get "traffic information" about VFR flights but not "separation", what happens if a VFR flight gets in front of an IFR one on final approach to land? Won't ATC tell the IFR flight to go around, or will they do nothing because they don't provide "separation"?

If one or both aircraft are under a clearance the cleared aircraft will request an amended clearance to avoid the traffic:
ABC request 10NM right of track due traffic

or
ABC request descent 4500 due traffic

If there is not enough time for the amended clearance the Pilot in Command (PIC) can just break their clearance to avoid the traffic; either passing the aircraft on the right or changing levels. The PIC in some countries will be considered to have broken their clearance but it is usually only a slap on the wrist for letting it get that bad that you couldn't request the clearance change.
Reality can sometimes be a very different scenario. Some controller unofficially will separate VFR from IFR, but no one knows. Don't trust that this will happen.
Also controllers may give suggested amended clearances like:
ABC traffic XFV PC12 crossing track left to right at time 23,
6500 is available advise.

or
ABC traffic unknown VFR 25NM oposite direction 500 ft below unverified,
higher available advise

If the aircraft is not subject to a clearance then they can just move to avoid the traffic under the Rules of the Air.
In uncontrolled airspace it really is see and avoid. Because the Air traffic Controller may not have all the aircraft that are traffic for you. This also includes Class E airspace where the controller doesn't know about all the VFR aircraft.
Duty of care means that the controller may intervene if they think the pilots aren't separating themselves.
I work with Class D and C Towers with lots of VFR traffic. Because the traffic are aware of each other they usually request amended clearances well before the traffic is a problem.


How can I get started on a winglet design for a small remote controlled aircraft? I'm a member of a student competition team, we design light aircraft (total airplane overhead area is limited to 0.9 m²) capable of carrying higher payload. The competition also limits the takeoff distance (this year's limit was 70 m).

Coming from the last event, we decided that winglets are probably a great introduction to the project, but we have no idea how to design one.

My question is basically: with this kind of aircraft (weighs about 2.3 kg empty, carries about 13 kg, wingspan is 2.8 m), what should we look for in a winglet design?

We are mostly in doubt about what kind of airfoil should we use. Should we look for less drag? More efficiency? How can we maximize the traction vector, and should we do that in first place?

We have been reading papers on the subject, but with little luck. We also don't think it would be wise to just randomly test things until we get right, so a little bit of direction would help a lot, even if it's an article that we should work around.

Thanks in advance!

For best results, put good flaps on the wing and forget using a winglet.

If you insist on bending the wing up at its end, just continue with the tip airfoil and select the incidence such that your circulation distribution over the wing and winglet will become elliptical when you plot it in a straight line. The small size of your airplane implies that you will not need to unload the tips to reduce root bending moment.


Does Nitrogen inside commercial airliner wheels prevent blowouts on touchdown? I just watched the first episode of Inside Mighty Machine where civil engineer-turned-host, Chad Zdenek, discussed innovations of the 747. One innovation he discussed was the increased number of wheels and trucks, along with this tidbit:

  When the 747 touches down, the wheels must accelerate from 0 to 150 mph in a heartbeat, making them skid before they start to spin. That's why they smoke on touchdown. That friction causes heat to build inside the wheel, creating the risk of an explosion, so the 747's tires are filled with nitrogen, an inert gas which, unlike oxygen, won't aid combustion. That helps protect the plane from blowouts and keep landings safe.

That seems like an oversimplification and backhandedly suggests that the alternative is to fill the tires with pure oxygen—a surefire recipe for combustion I would think.

So, (1) is nitrogen really "the thin line" between safe landings and blowouts on modern commercial airliners and (2) is nitrogen landing gear inflation a legitimate innovation of the 747?

Apart from the paragraph you quoted, here are a few more reasons.

Dry nitrogen is specified for aircraft use. I believe the rules say that any gas used cannot exceed 5% oxygen content. Because its dry it reduces corrosion.
Nitrogen moleculeas are slightly larger than oxygen and takes longer to escape.. hence tyres stay inflated longer.
But more importantly, nitrogen has a lower rate of expansion/contraction than normal air. An aircraft wheel has to live in sub-zero (at 40,000ft) and blistering hot (IIRC about 500deg C will trigger hot brakes warning). A gas with a low expansion rate cf temp is desirable. This trait has been put to good use by unscrupulous 'performance auto shops' which claim better handling with nitrogen in the tyres...


Will ICAO 24 bit addresses suffer the same fate of IPv4? As we know; both IP addresses and Mode S (ICAO) addresses are relatively short. With local networks and NAT (Network Address Translation), there is not an urgent need for transition to IPv6.

But how about Mode S addresses? With the increasing number of drones, I am assuming ADS-B Out would be mandatory in the near future for them too. Is there any discussion about the relatively short length of ICAO addresses and the problem of unique address assignment for every flying aircraft?

I don't think there will be an ADS-B mandate specifically for drones. Instead I expect ADS-B will be mandated for certain airspaces.

The US has taken this approach from the beginning, Australia has a combined airspace & flight rule approach (IFR in class A,B,C & E airspace). The EU so far has based the ADS-B mandate on aircraft weight (>5700 kg MTOM) or speed (>250 KTAS). That is likely to change in the future.

For drones operating outside this ADS-B mandatory airspace, no ADS-B will be necessary. I guess the number of drones inside mandatory airspace will be limited, since there is no efficient way to integrate them into the Air Traffic Control system. However, over time this will likely change.

The big problem I see is not so much the limited address space, but the overloading of the 1090MHz frequency that ADS-B will be working on. On the long term I see a need to rethink frequency allocation for surveillance and navigation (and while we are at it, communication too). The limited number of addresses should be dealt with at the same time. With so many investments in the current system, it is going to be very difficult to transition to a new system.


Flying coworkers with a commercial pilot's license (USA/FAA) I will soon have my commercial pilot's license, and work full-time in a company and role unrelated to aviation. As a private pilot under FAA part 61.113b, I know that I can fly myself to conferences or sales meetings while having my employer reimburse me for the aircraft rental because the flight is only incidental to my employment.

My boss asked if my new CPL will allow me to take coworkers on such a trip, and I don't know how to answer him. It would be incidental to my employment and for a common purpose (i.e. I am also attending the same meeting), and there is no holding out since it would only be employees of the same company for a common purpose. I am also salaried, so there is no additional direct pay for the flight (just logging time). I'm not sure how to answer, and there are 3 scenarios to further complicate this (assume all aircraft have had 100-hr inspections):

I rent the plane and submit for reimbursement along with my other ordinary business expenses.
The company seeks out and rents the plane without my input.
The company rents the plane from an FBO, but after asking me for a recommendation on where to find one.

Which of these are permitted with a CPL? I'm 99% sure that #2 is completely fine, but can't find regulations for or against the other scenarios.

Since you have a CPL, you can receive compensation for flying.

Your question and concern is over the means of reimbursement which may have implications beyond that of the FAA. That said, I'm not a lawyer and I would suggest your company consult with one and establish a policy. Most companies I've worked for prohibit personal flying incidental to the business specifically due to liability concerns.

To avoid confusion, I would stick with option 1) as that makes it clear it's your choice to fly and not that of the business. If the company rents the plane, it may expose the company to additional FAA regulation as well as liability and tax implications.

As a point of explanation; before I retired from the USAF it was not uncommon to use private aircraft to travel on TDY (Temporary Duty - the military version of a business trip). The rules under AF regs and the Joint Travel Regulations (DoD) allowed you to travel using a privately owned aircraft or a rented aircraft. IIRC the AF required a CPL/IR and a total of 200 hrs. The rules also specified what expenses were allowed and how they were to be reimbursed.

If you used your own aircraft, it was classified as POV (Personally Owned Vehicle) travel. That was no different than driving your own car on the trip. In that case you were reimbursed at the POV mileage rate. That rate when I was in was actually less than the IRS allowed mileage rate and wouldn't come close to covering the cost. It also didn't matter if anyone was travelling with you, be it a coworker or family member.

If you rented an aircraft, it was treated the same as if the company allowed you to rent a car to make the trip. You were reimbursed your actual rental cost (wet) up to the cost airfare for the trip for all persons travelling together. What that meant was that if you traveled alone, the reimbursement was typically less than the rental cost (say \$400 for airfare vs \$600 rental). If you had two or more travelers, the airfare typically exceeded the rental cost and the entire rental was covered. The limitation was that only coworkers on travel orders counted towards the reimbursement.


What items could you bring on-board to maximise your chance of survival in an emergency? A question on Travel (Are parachutes allowed on airplanes as cabin baggage?) got me to wondering: hypothetically, what items could the "über-paranoid" passenger or pilot bring on-board to potentially save their life in an emergency?

I.e. a parachute, oxygen, a portable smoke hood?

What are the technicalities? I.e. would a parachute be of any use above a certain altitude? What about with oxygen?

Most of the items you can bring with you to maximize your chances of surviving an in-flight emergency are items you're not going to be allowed to bring with you.
About the only things I could recommend bringing along on a commercial flight are your cellphone and a personal locator beacon (PLB) of some kind, but frankly if your airliner goes down ATC is going to know where you were when they lost contact, (and the plane has an Emergency Locator Transmitter already).

You should also wear sensible clothing -- natural fibers like wool or cotton are the order of the day if in-flight fire is a concern. Polyester or other synthetic fabrics will melt to your skin and cause you to have a Bad Time.

More directly addressing your question though, the items that spring immediately to my mind (and why you probably won't be taking them with you) are:

A parachute (what prompted your question)
Sure, you can bring your parachute. It's kind of a useless security blanket though.
From cruise flight you'd basically be executing a high-altitude jump (let's say a HALO jump, because you want to get down as quick as you can). You would require oxygen to remain conscious longer than about 30-45 seconds (though an automatic-opening chute may save you here), as well as protective clothing to survive the low temperatures while you're free-falling.
Those concerns aside, remember that airliner cabins are pressurized and the doors are typically "plug doors" that open inward. No human is strong enough to open that door with the cabin pressurized, and if you've lost cabin pressure for some reason you're better off putting on that little drop-down oxygen mask like the nice flight attendant told you to in the safety briefing. You're not going to save yourself if you pass out from hypoxia while putting on your chute and trying to get to the door.
An oxygen mask / smoke hood can be useful in a fire.

Most airlines are not going to let you carry an oxygen cylinder onto the plane (as others pointed out in comments, oxygen and in-flight fires can cause more problems than it solves).  That holds true for pretty much any kind of compressed gas because really, how do they know what's in that tank?
A smoke hood using a filter (or a sealed rebreather hood) with no compressed air supply may make it past security, but ask yourself honestly: "Am I proficient enough to use an emergency escape smoke hood in an in-flight emergency?" -- If you can't answer "yes" you're probably putting yourself (and others) in more danger wasting time donning the hood versus just getting out of the aircraft.

A life vest (if traveling over water)
This is overkill on an airliner (though those of us that fly little planes should seriously consider flotation devices when flying over water).
Your airline seat cushion really CAN be used as a flotation device. Those big yellow slides also detach from the plane and make marvelous floats. Frankly if you need any of these items you're in a situation where having your own Mae West isn't going to really enhance your chances of survival.
A utility knife capable of cutting your seatbelt
This is incredibly useful for a bunch of reasons, not just cutting your way out of your seatbelt. In fact I keep one in my plane. Sharp and/or pointy things make airport security nervous though - if you try to take such an item on an airline flight it will likely be taken away from you before you get anywhere near the plane.
Food and Water
Useful if you have to make an emergency landing in a remote area, but frankly airliners already have beverages (some may even still have food).
If you're carrying a light snack you're as set as you're going to be in this department.
Emergency Blankets
Nice to have, but most commercial aircraft already have shock blankets on board (and much like food/water, this is really only useful if you have an otherwise uneventful landing in a remote area).
If it makes you feel better to have your own blanket you can get pre-packed ones that can fit in basically any carry-on for about $5-10.
Signal flares
Again, mainly useful if you have an emergency landing in a remote area (and your PLB and the plane's ELT don't work for some reason). Flares are good both for signaling rescuers and for starting fires to keep warm.
I don't know if rescue flares are still routinely carried on commercial airliners, but I can say with reasonable certainty that you will not be allowed to carry on your own. They don't let you smoke on most airlines these days - they're certainly not going to let you carry on a self-igniting flare!


Where are "standard taxi" instructions published? Example: at KATL (Atlanta), the ground control sometimes gives taxi instructions as "standard taxi"; Where is that defined?

  Delta 2732 27-Right Lima Charlie "Standard Taxi."

In that case, from a south ramp, the aircraft is noticed taxiing on Lima to 27R at intersection LC.

The question is, how did the pilot know that "standard taxi" meant going on taxiway Lima? Where are "standard taxi" instructions defined/published?

You can find a nice article on standard taxi routes here. They are included in the NOTAMS, or on Jepp charts if you have access to them. The full standard for publishing them can be found here.

This is what they look like:

(source: own image)

As ymb1 points out in the comments you can access them here as well.


Is it true that high-bypass engines are inherently inefficient at higher speeds? Power consumption=Kinetic energy=$1/2mv^2$.
Thrust=momentum change=$mv$.

I keep being told that aircraft engines are most efficient when their exhaust velocity closely matches the freestream.

The second graph shows the propulsive efficiency vs exhaust/freestream velocity ratio

I can understand that higher bypass engines have greater intake losses than narrower ones. But the ratio of airspeed to exhaust speed being the defining factor, as opposed to the absolute difference?? I have only one way to justify this - as speed increases, mass flow rate through an engine of given cross sectional area also increases.

Research on propfans, and on supersonic through-flow turbofans calls into question the idea that lower bypass ALWAYS = higher high-speed efficiency. And the above equations don't help either.

What mistake am I making?

Power consumption=Kinetic energy=$1/2mv^2$.
  Thrust=momentum change=$mv$.

This is only true if the engine is perfectly efficient internally and the air is still relative to the aircraft.

If the air is moving relative to the aircraft (and the engine is still perfectly efficient internally) then.

Power consumption=Kinetic energy=$\frac{1}{2}mv_e^2 - \frac{1}{2}mv_a^2$ = $\frac{1} {2}m((v_a + v_\Delta)^2 - v_a^2) = \frac{1} {2}m(2v_av_\Delta + v_\Delta^2) $
Thrust=momentum change=$m(v_e-v_a) = mv_\Delta$

Where $v_a$ is the ambient velocity (relative to the aircraft), $v_e$ is the exhaust velocity (relative to the aircraft) and $v_\Delta$ is the difference between the ambient velocity and the exhaust velocity ($v_e - v_a$).

If the exhaust velocity (relative to the aircraft) is smaller than the ambient velocity (relative to the aircraft) then you have negative thrust (aka drag).

If the exhaust velocity (relative to the aircraft) is much larger than the ambient velocity (relative to the aircraft) then most of the power is wasted (the $v_\Delta^2$ term is larger than the $2v_av_\Delta$ term)

If the exhaust velocity is only slightly higher than the ambient velocity then most of the power goes into useful thrust (the $2v_av_\Delta$ term is larger than the $v_\Delta^2$ term)

What this means if that if the engine were perfectly efficient internally then the advantages of a higher bypass ratio would drop off with speed, but there would still be a slight advantage to the engine with higher bypass ratio.

But that is a big if, in particular we assume that all the energy in the intake stream is captured and returned to the exhaust stream.

Lets consider what happens if we instead assume that the energy in the intake stream is lost.

Our power consumption equation becomes.

Power consumption=Kinetic energy=$\frac{1}{2}mv_e^2$ = $\frac{1} {2}m(v_a + v_\Delta)^2) = \frac{1} {2}m(v_a^2 + 2v_av_\Delta + v_\Delta^2) $

For a given thrust $m$ is proportional to $\frac{1}{v_\Delta}$ so our goal is to minimise. $\frac{1}{v_\Delta}(v_a^2 + 2v_av_\Delta + v_\Delta^2)$ = $\frac{v_a^2}{v_\Delta} + 2v_a + v_\Delta$ differentiating with respect to v_\Delta and setting to 0 gives $-\frac{v_a^2}{v_\Delta^2} + 1$ which (given that v_\Delta must be positive) gives $v_a = v_\Delta$

Having considered an optimistic and a pessimitic case we can conclude that the optimal exhaust velocity for efficency is greater than the ambient velocity (otherwise you would not produce thurst) but probably less than twice the ambient velocity.