When did the color orange enter flight test? When did the color orange enter flight test?  As early as the Bell X-1, pictured here, aircraft were painted orange to enhance visibility. Later, in 1959, a study was conducted that suggested the utility of orange markings on aircraft.  In 1968, the Society of Flight Test Engineers adopted a logo with "flight test orange" as its color.

There are, however, few references that explain the following:

When orange flight test equipment (wires, parts, LRUs, etc.) first appeared.  For example, I transcribed a 1977 article from the SFTE's Flight Test News that sets 1949, anecdotally, as the time/event that caused Douglas to use orange wire. But it also references a Mil Spec. (Does anyone know more about the Mil Spec referred to?
When orange flight suits first appeared?
When aircraft (in general) adopted orange paint schemes for flight test aircraft, as seen here?

They were originally used to allow ground spotters to better spot the aircraft from the ground for optical tracking during flight test.  Another use of painting wingtips, tailplanes and tailfins bright colors was to allow observers a better means to determine the aircraft’s orientation and attitude in flight.

Finally if it all went so wrong so fast, hi viz colors made it easier for SAR crews to locate the wreckage....and the remains of the pilot.....quickly.

I know the Navy and the USMC were using orange flight suits as early as the Korean War, not for their test pilots, but for fleet air crews to make it easier for SAR aircraft to locate then in the event of a ditching or bailout over open water.


What notification am I required to give when starting an engine? This question is related to a single-engined piston-powered airplane.

I was at a small airport. I noticed another plane parked behind mine. The pilot/owner was in the process of covering up his plane. I walked up to my plane, did some preflight checks, entered the cockpit, did my engine start checks, shouted as loudly as I could - PROP CLEAR - waited a few seconds and then started the engine. A few seconds later the other pilot walked up to me and was enraged that I had started the engine without notifying him. I told him that I shouted but he claims he didn't hear me.

What is the correct procedure/etiquette in this situation?
Was I supposed to walk up to him and notify him before starting the engine?

shouted as loudly as I could - PROP CLEAR - waited a few seconds and
  then started the engine.

Something to note here. While your shouting of PROP CLEAR was correct you need to Look Up and ensure no one is around when starting your engine. This is a common mistake, however you can bust a check ride for only shouting and not looking.

  Was I supposed to walk up to him and notify him before starting the engine?

According to the FAA handbook, yes you should have alerted him and/or waited for him to clear the area.

  Prior to engine start, the pilot must ensure that the ramp area
  surrounding the airplane is clear of persons, equipment, and other
  hazards from coming into contact with the airplane or the propeller.
  Also, an awareness of what is behind the airplane prior to engine
  start is standard practice. A propeller or other engine thrust can
  produce substantial velocities, result in damage to property, and
  injure those on the ground. The hazard of debris being blown into
  persons or property must be mitigated by the pilot. A


What is this stem on the underside of a Cessna 172R (1997)? There is a stem that is located on the underside of the airplane between the drain valves for the fuel strainer and reservoir tank. It looks like a small stem that is protruding.

I have noticed it leaks a small amount of fuel (1 drip per 5 seconds). I am going to talk t my instructor about it but wanted to know what it was called. I am not seeing it in the fuel system diagram.

Updates:
I believe it is a part of the electric auxiliary fuel pump, but want any input.

The aircraft is a Cessna 172R made in 1997.

It is 100LL that is dripping.

Here is the fluid dripping.... Not water.

Ok - got word from the local a&p that this stem is a part of the aux fuel pump. It drains the motor side of the pump of any fuel in case the seal that separates the motor from the pump fails. You wouldn't want fuel getting inside of where the motor has current and sparks, hence this "stem" is the safety backup. The entire pump had to be replaced because overhauling made less sense due to the age of the pump. Turns out it wasn't in the diagrams at all!


Do commercial aircraft have electrical outlets? As we see trains nowadays with sockets for you to plug your laptop into, as well as Wi-Fi on-board both trains and planes, I'm wondering why you don't see electrical outlets on planes?

Do any airlines have sockets in the cabin? How about in first class?

Several of the answers here seem to suggest that this only happens in first or business class. While that was historically true, it's not so true anymore. Airlines such as Cathay Pacific and Korean Air, for instance, have them at every seat in most (or all?) of their long-haul aircraft. Delta also has it in parts of economy on several of their long-haul configurations as well as in all of economy on their recently-acquired 717s and 737-900ERs. You can check with your specific airline or with sites like Seat Guru before booking to determine what is available on any given aircraft and at which seats.

As Lnafziger said, some airlines' systems require adapters, while others don't. At least from personal experience, it seems that most of the recent ones do not. On Korean Air, Cathay, and Delta, the plugs are designed to be able to fit any of the standard power plug types (e.g. North American, European, Asian, etc.) Since most new electronic devices use auto-switching power supplies, they should accept the 110V/60Hz supplied by most of these systems, even if they're designed for 220V/50Hz markets.

Here's a picture of one of the outlets in economy on the Delta 717s. Notice that the holes are cut such that any of the standard plug types will fit in it. The slot on the bottom is a USB power port.


Possible military aircraft ID, N. Carolina I was recently in Oak Island, NC and saw the following plane flying above. It was low-flying and much louder and larger than the other small prop planes flying out of nearby Cape Fear Regional Jetport. Based on the size of the propellers I suspected it was some kind of military aircraft but wasn't able to figure out what it was. I know this is a small, dark picture, but does this plane look familiar?

This looks like a V-22 Osprey.  Here is a photo.  (it happens to be refueling, so ignore the nose hose.)


How much knowledge/experience can be transferred between different categories/classes of certification? This question was originally going to be "Is it possible to earn an ATPL without also ending up with at least one airliner type rating?", but I thought I'd broaden it just a bit (hopefully not too broad).

Requirements for an ATPL in the United States include 1,500 hours total flight time with several minimums in various special conditions and as PIC, "applicable to the aircraft category and class". My question is basically, "what is the definition of 'applicable'?".

For instance, it is theoretically possible, and even useful, to obtain an ATPL in the ASEL class (so the answer to my original question is "yes"; you can earn the FAA's highest certification level without being signed off on anything close to the type of aircraft Southwest or Delta have in their fleet). You could get that license and fly Cessna singles for Ravn Alaska (formerly "Era Alaska" of Discovery Channel fame) or any of the other bush airlines around the country.

However, that represents a lot of flight time before you can even sit the written tests and fly the checkride; 1,500 hours total (250 as PIC), 500 of that XC (100 as PIC), 100 hours night (25 as PIC), and 75 hours real or simulated instrument time (no more than 25 hours in a flight simulator, 50 if you're training under Part 141), all in single-engine fixed-wings. If you then wanted to progress to multis and thus eventually become useful to a major U.S. domestic airline, you would have to start from scratch as a student pilot in the AMEL class.

... Or would you? That's the question; how much of your flight time and/or certification level in one class is "applicable" by FAA regs toward any other class of the same category at the same level of certification? It seems unfair for a pilot with a fairly high ASEL certification to have to start from scratch on flight hours just to fly a plane with floats, or more than one engine, or both. However, they are different classes for a reason; more, or at least different, knowledge and experience is required to taxi a float plane on a lake or to get a multi-engine plane off the flight line. So while there is definitely a lot of overlap between the four "Airplane" classes, it's not 100%.

How about applicability of flight time and certifications to other categories? I'm particularly interested in the "rotorcraft-gyroplane" class and the "powered lift" category, as these were developed as aircraft hybrids which AFAIK have a significant skills overlap with a fixed-wing aircraft. Does flight time in an autogyro count in any capacity towards flight time in a fixed-wing, or vice-versa? How about flying a Harrier? In 50 years when the Osprey makes its way to GA in come capacity, how would existing civilian airplane and/or helicopter pilots get rated to fly it (I hope not by amassing 1,500 hours in an Osprey)? How about something completely different? Even between a fixed-wing and a helicopter there's some overlap (though I'd imagine even the chief pilot of a major airline would be out of his depth in a B204).

The answers to your question lie in 14 CFR 61.159 for airplanes.  Your quoted times for the ATP in the airplane category are correct but some of that time is total time as a pilot, some is just in category and only a small fraction of it is in category and class.

For example, in your hypothetical situation, you have an ATP in ASEL category/class and wanted to add the get the ATP AMEL.  All you need to do (aside from any knowledge tests you may require) is 50 hours in AMEL.  Of the 1500 hrs TT in airplanes, only 50 are required in class.  This is the same to add ASES and AMES ATPs.  You could have a certificate with ASEL,ASES,AMEL and AMES all that ATP level all with only 1500 TT as long as you had at least 50 hours in each class.

The situation for rotorcraft/helicopter is similar and can be found in 14 CFR 61.161.  To get an ATP helicopter, you need 1200 hrs TT but the only hours that need to be in category and class are:

15 hours at night,
200 hours w/75 PIC, and
25 hrs in actual or simulated IMC

You could accomplish all of that within the 200 required hours.  The 200 hours needed in helicopter still count as total time and can be applied toward a fixed wing ATP.

ATP powered-lift requires 250 hours PIC in category with some sub-requirements out of that 250 hours

100 XC powered-lift
25 night powered-lift
75 instrument hours powered-lift

The FAA does not currently issue ATP in rotocraft/gyroplane so you are out of luck there.

If you wanted to min/max optimize the above requirements and get ATP in all of the above the hard category and class requirements boil down to:

50 hrs airplane single-engine land
50 hrs airplane single-engine sea
50 hrs airplane multi-engine land
50 hrs airplane multi-engine sea
200 hrs rotorcraft helicopter

15 hrs at night
75 hrs pilot in command
25 hrs actual or simulated IMC

250 hrs powered lift pilot in command

100 hrs cross country
25 hrs night
75 hrs actual or simulated IMC

At this point you would have:

650 hours TT
325 hours PIC
40 hours night
100 hours cross country
100 hours instrument

Now lets fly 400 hours XC in a single engine (slow and economical) with at least 60 of those hours at night and all of it PIC.

Now we have

1050 TT
725 PIC

400 hrs airplane (at least)
75 rotorcraft helicopter
250 powered-lift

500 XC

400 hrs in airplane
100 hrs in powered lift

100 night

60 hrs in airplane
15 in helicopter
25 in powered-lift

Unless I'm missing something, this is all of the requirements for the ATPs except total time.  Go fly anything for another 150 hours and then take the ATP helicopter checkride.  Then fly another 300 hours in anything and take all of the other ATP checkrides with 1500 TT.

It is also worth pointing out that type ratings and ATPs are different things.  A type rating can be added to a private pilot certificate (though the checkride will be conducted at ATP standards).  You can also earn your ATP in an airplane that doesn't require a type rating (e.g. getting an ATP AMEL in a Piper Seminole).


How does the autopilot act when it receives an obviously bad temperature value? Assuming the plane is on autopilot: for example, if a plane is flying high (over 20000 feet) and its autopilot receives a positive value of external temperature, which is clearly abnormal or impossible.

What will the autopilot do with such a obviously wrong information?

The autopilot does not receive information about the outside temperature, it has no (direct) relation to what the autopilot controls.

The autopilot receives aircraft state inputs like airspeed, Mach number, vertical speed, attitude, accelerations etc.


Why does the CRJ100/200’s FMS miscalculate temperatures at altitudes in excess of 36k feet? The CRJ100/200’s flight management system (FMS) apparently is not to be used to calculate engine thrust settings when the aircraft’s altitude exceeds 36,000 feet, due to internal calculation errors at altitudes this high:

The Pinnacle Airlines CRJ FCOM, volume 2, Performance, pages 50 through 52, dated June 2002, presented altitude and climb capability charts. Pilots were required to consult these charts anytime a flight was operating above 36,000 feet because of a flight management system (FMS) limitation above that altitude.77  [...]
[...]
77 FCOM volume 2, Operating Limitations, pages 30 and 31, dated June 2004, stated that “the FMS calculated thrust setting must not be used if the pressure altitude is greater than 36,000 feet.” The Bombardier chief pilot stated that the reason for the FMS limitation above 36,000 feet was because of the inaccurate calculations above that altitude. Further, according to Bombardier, at altitudes above 36,000 feet, the conversion from static air temperature to the International Standard Atmosphere (ISA) deviation is incorrect within the FMS, resulting in an error in the N1 indication at those altitudes.  [...]  Bombardier’s Flight Planning and Cruise Control Manual and Quick Reference Handbook contain charts that show the proper N1 indication for altitudes between 36,000 and 41,000 feet.  [NTSB/AAR-07/01, page 33 (page 45 of the PDF file); footnote numbering in original; my emphasis.]

Given that 36 kilofeet is well below the CRJ100/200’s maximum operating altitude,1 it seems surprising that the aircraft’s FMS was not programmed correctly for altitudes beyond 36k feet, that this wasn’t caught very early on, and that the FMS  software was not updated to correct this bug once it was discovered; why was the FMS misprogrammed in the first place, and why wasn’t it fixed?

1: The maximum operating altitude for first-generation CRJs is 41 kft, a full 5,000 feet higher.

The reason is that the tropopause is at 11 km (36 089 ft) in the International Standard Atmosphere. At the tropopause, the temperature lapse rate of the atmosphere (how temperature changes with altitude) has an abrupt change: the ISA value is -6.5°C / km (-1.98°C / 1000 ft) below and then suddenly changes to 0°C / km (meaning temperature suddenly stays constant).
The FMS probably converts SAT to ISA deviation based on a fixed lapse rate of -1.98°C / 1000 ft, which means the conversion is wrong above that altitude. Only a Bombardier engineer (or someone involved in the Collins FMS used on the CRJ) could tell you the exact reason why. Based on John K's comment, it seems to have been fixed after the accident.
Note that the actual tropopause altitude can vary (usually between 9 km at the poles and 17 km at the equator).


Are there full scale helicopters capable of sustaining inverted flight? Background

I'm a model aviation enthusiast and really enjoy seeing how far people can push the limits of aerobatics. Model aircraft are able to push the limits well beyond full scale due to their small size. I understand that this is only possible because models are small* so they can withstand forces that would kill any occupants in a manned craft. Also, model aircraft are typically overpowered when compared to full scale aircraft

For example, I don't have a model plane that isn't capable of a 30 degree climb, and it's quite common for aerobatic model airplanes to have thrust to weight ratios exceeding 1.5:1 or even 2:1.

Question

When I first saw some of what model helicopters were capable of I was blown away. Having also seen some full scale helicopter aerobatics (Red Bull Demonstration) I've been wondering just what full scale helicopters are capable of.

In the Red Bull Demonstration it looked like the helicopter might use some negative (or at least neutral) collective while rolling, however it did not appear that it would have enough to sustain an inverted hover or inverted flight. This got me wondering: has there been a full scale helicopter capable of sustaining inverted flight or an inverted hover (which takes even more power)? If there hasn't, would it be possible to purpose build a helicopter that would be capable of doing so?

Note

I'm just wondering about technical possibility of creating a machine capable of this maneuver. For the scope of this question, please ignore the regulatory, legal, and economical obstacles that would need to be overcome to attempt such a feat (not to mention finding a pilot willing to try).

Also, I'm only asking about full scale inverted flight. I understand physics get in the way very fast if someone were to try to design a full scale helicopter capable of all the aerobatics models do.

*some model airplanes and helicopters can be greater than 35% full scale, but that is still small when compared to full scale aircraft.

There is no real helicopter capable of sustained inverted flight and certainly not of hovering inverted.

The simple reason is that there is no operational need to do so.

Is it theoretically possible?  Yes, but you have a lot of engineering problems to overcome.  In addition to inverted fuel and oil systems, the rotor head will be much more complex than it needs to be.

When flying normally, the fuselage effectively hangs like a pendulum underneath the rotor with a large nut (OK, it's more complex than that) holding the rotor onto the rotor shaft hub.  The rotor pulls the fuselage up.

To fly inverted, the rotor must be able to push the fuselage up so the hub would have to be engineered to apply and withstand the appropriate forces in both directions.

Then, the rotating blade cuffs, and associated hinges, must be designed so that the blades can have negative pitch (as seen from the normal attitude) across the full range.  In turn, this means that the collective mechanism must be designed so that it is possible to set positive and negative pitch as required.

The blades would also need to be more rigid, so that they do not cone excessively and contact the fuselage.  This would add more forces to the head joints which would need to be strengthened.

Finally, you must "reverse" the cyclic controls so that the expected collective pressure, cyclic back; nose up; reduce speed; works in the opposite sense.

I've probably not considered other factors.

All of this would add significant complexity and weight which, given that there is no requirement for inverted flight, will not happen.

By the way, the power required to fly or hover inverted would be the same as for normal flight.  There is no intrinsic reason why inverted flight would need more power - blades rotating at a certain speed, with a particular angle of attack will generate the same amount of lift no matter which way they are pointing.

The reason model helicopters can do this is that the ratio of the weight of the rotor to the weight of the fuselage is much lower than for a real helicopter, and therefore requires a lot less power to produce the required lift, and models have a much higher power to weight ratio.

The reason real helicopters can go inverted for a short time in aerobatic manoeuvres is because the momentum on the fuselage is pulling away from the rotor so that the lift vector pointing up, toward the fuselage, is countered. Consider an outside loop, which would be impossible, since the momentum of the fuselage and the lift vector would combine.

You should be able to demonstrate this in a model with a normally designed rigid head.  Add some (secure) ballast in the fuselage until you must accelerate in ground effect to gain translational lift in order to be able to climb out.  Now try to fly inverted!


Are there different configurations of cabin crew seating arrangement for one aircraft model? In many airlines, cabin crew are shown to be sitting in different areas. Is it common for airlines to offer different seating configurations for a particular airline model? Also, are there any advantages of the same?

For example, in A320, you will find cabin crew seating in the aisle at the rear of the aircraft in some aircraft, near the toilet.

Crew seating is partly concerned with the regulations requiring a crew member next to certain exits. Airlines choose different combinations of seating based on class and galley/lavatory arrangements and this changes the number of required exits and crew required to sit next to the exits. Some long hall airlines require berths for crew rest and sleep - I imagine some airlines may have employee union requirements.

All this requires ongoing customized cabin arrangements. Airlines often change the seating during mandatory maintenance (a, b, and c checks) to accommodate different routes, cultural expectations and changing economy.

Interestingly, the cockpit itself may vary. According to FAA regulations large aircraft must have at least one observer seat (usually called a "jump seat"). But, I have seen cockpit options that vary the number and type of "jump seat" in the triple 7.

For example, one cockpit of a Boeing 777 offered two padded conventional seats or three fold down "bench" type seats. I guess one company wanted the FAA observer to fall asleep and another company wanted to discourage "observers".


Does anyone have a diagram of the HC-130J wing dimensions and fuel tank locations? Looking for a drawing of the HC-130J that includes fuel tank locations and wing dimension (more than just wingspan)

If you're looking for the technical data, i recommend you the "service news" material, that can be checked out here: https://www.lockheedmartin.com/content/dam/lockheed-martin/aero/documents/sustainment/csc/service-news/sn-mag-v1-v10/V6N4.pdf.

For an overview, there's a diagram:

(diagram link: https://airwingmedia.com/downloads/lockheed-c130-hercules/).


Could gliders be a clean, practical alternative to other forms of transport? Would it be possible to use pure gliders as an eco-friendly mode of transport?
From what I have read so far, gliders can travel at a speed of 100-170 km/h. That would not be able to compete with a jet plane, but it could easily be faster than a car, and possibly even a high-speed train, since it can fly directly and doesn't have to follow train tracks.
So, would it be possible to build a glider that fills this arbitrary set of requirements that would qualify it for regular travel:

It needs to be able to carry at least 30 people plus luggage. Otherwise the pilots are much too expensive.
It needs to be able to fly regularly, only being inhibited by severe weather.
It needs to qualify for international, commercial passenger service in all matters (safety equipment, radio, ...)
It doesn't need to be able to fly around the year, pre-plannable months without service are acceptable.
It doesn't need to work with current infrastructure, e.g. it would be acceptable if the plane needs special runways and/or launching mechanisms.

Would it theoretically be possible to build something like this?

There's one thing that will forever prevent an unpowered aircraft from entering commercial passenger service: the inability to make a second attempt at a landing.
Airliners, with all their instrumentation, very experienced pilots, and such don't make go-arounds frequently -- but especially during weather, they do make go-arounds.  A passenger sailplane absolutely can't make a go-around, so if it gets crossed up due to a crosswind gust low and slow, instead of advancing throttle and climbing out, all the pilot(s) can do is pick where and how hard to crash.
This complete lack of second chances, as much as any of the other objections raised in other answers, will ensure that unpowered aircraft will never see commercial service.  It can also lead to "landing out" where you wind up having to retrieve your passenger glider from a farmer's field, freeway, or worse, along with its payload and crew.
The other big issue is how to launch these immense sailplanes -- with a common sport glider or competition sailplane, you're towed into the air by either another airplane, a winch, or occasionally a car or truck.  The winch that could launch something the size of a 737 high enough to fly off in search of its first lift would be so big and expensive it would severely limit the number of airports that could service such craft.  The airplane that could do it would be at least as big as that 737.


How did the B707 and DC-8 fight stress at the windows? As it is evident from this  question, 4 (or 3) de Havilland Comets crashed because of stress building around the rectangular windows.
How did DC-8 and B707 fight this problem, especially as it is quite clear that both of them had rectangular windows as well?

No, the Boeing 707 and the DC-8 used radiused corners on all their windows to avoid the problems of stress concentration factors, plus additional pad ups around the openings in the skins for the Windows themselves.

(Source)


What is this number in the bypass ratio? Here is an example of a bypass ratio 9:6:1. 9kg goes around the core and 6kg goes into the core, but what is the 1 for.

It is 9.6:1  not 9:6:1.

9.6 parts air are bypassed for each part that goes through the core.


What is the fuel consumption of an aircraft in a holding pattern? I am doing a research about fuel cost when an aircraft is about to land. they may be asked to be hold due to the traffic congestion at the runway. consequently they consume extra fuel. My question is how I can estimate the cost per minute or second being late of their *target time. Where can I get more details on this?

*target time: As I noticed each aircraft has a target time to land which is the most economical time and speed for them.

My research is about aircraft landing scheduling during rush hours where there are several objective functions such as maximizing the runway utilization, minimizing total delay and fuel consumption to be considered. these objective functions are subject to some constraints like aircraft's time window (earliest landing time,latest possible landing time), minimum time separation, Constraint position shifting...
In the literature that I have read so far they considered a fix fuel cost as a function of delay. as an instance: "Vj denotes the cost per unit time of the extra fuel associated with lateness relative to ULTj , then the overall extra fuel cost is : summation of Vj * (Landing times - ULTj) " (Aircraft Runway optimization, Mesgarpour, 2012)
Since it is more mathematically issue no body really pay attention to the details of that fuel cost or any other cost caused by the delay.

The fuel rate while holding depends on elements such as weight, altitude, speed and aircraft configuration.

Airbus uses the concept of green dot which is the speed with minimum fuel consumption per time unit in clean configuration.

This table shows fuel needs for a A330/A340 at 170 tons and 1,500 ft:

Fuel flow vs. speed. Source

While the green dot speed is the one offering the best fuel rate while holding, it assumes no flap and no slat. This speed may not be practical for certain airports where slats or flaps are advisable due to the rate of turn in the holding pattern.

To provide the necessary flexibility, Airbus publishes the fuel rate for three other combinations of speed/configuration (S speed is the minimum speed for flaps retraction):

Fuel flow vs. weight for 4 configurations. Source

Altitude is also a factor preventing an optimal fuel flow. Example for the green dot speed:

Percentage added when departing from the optimal altitude. Source

The total fuel required to hold can be somehow minimized by not flying at cruise speed when it is known that a hold will be required at some point. Savings can be done by flying at green dot speed to the holding point:

Source

That means determining the fuel flow depends on airline operating procedures and holding pattern design (e.g. altitude), but a maximum can be roughly predicted by looking at the manufacturer published documentation.


Does the definition of visibility take object size into account? Overall, visibility is the distance at which objects may be discerned.

Does this definition take into account the size of the objects? Obviously large objects can be seen from farther away than small ones.

The FAA gives the definition for "Flight Visibility" in 14 CFR 1.1:

  Flight visibility means the average forward horizontal distance, from the cockpit of an aircraft in flight, at which prominent unlighted objects may be seen and identified by day and prominent lighted objects may be seen and identified by night.

According to that definition, any mountain, geographical feature, structure, road, or other object could qualify for day visibility measurements, regardless of size. To identify the object in a way that is meaningful for measuring visibility, the object must be identified to a degree that the distance can be positively identified. If I see a mountain and positively identify it as a mountain that is at 150 NM distance, I can correctly state that I have at least 150 NM of flight visibility. Likewise, if I see a windmill and positively identify it as a windmill that is at 1 NM distance, I can correctly state that I have at least 1 NM of flight visibility.

The FAA also gives the definition for "Ground Visibility" in 14 CFR 1.1:

  Ground visibility means prevailing horizontal visibility near the earth's surface as reported by the United States National Weather Service or an accredited observer.

The term "prevailing horizontal visibility" is indefinite as seen here, so additional clarification is needed. In this case, that clarification is provided by the National Weather Service itself:

  Prevailing visibility is the value reported in non-automated surface observations. A human observer determines it by identifying objects and landmarks at known distances in a full 360 degree circle around the observation point. The greatest visibility observed over 50% or more of the 360 degree area is the prevailing visibility. If there is a sector of the 360 degree area that is significantly different from the prevailing visibility, the system may add a remark reflecting that difference. Pilots must realize, however, that nearly half the area around an airport may have lower conditions than the reported prevailing visibility.

Automated visibility sensors—such as those used with the Automated Weather Observing System (AWOS)—do not measure visibility over a distance. Instead, these systems sample a very small area for clarity of the air and use an algorithm to convert this value to a usable representative visibility value. For more information on these systems see the National Weather Service's Visibility Page.


How is flight planning performed with short turnaround times? For low cost carrier short-haul flight such as Dortmund-London I have experienced multiple times that turnaround times are around 20-25 minutes. In such a short time what is included in the flight planning of the pilots. This time seems very short to perform flight planning, preparation etc. Is it generally the case that for repeating flight planning efforts and necessity are reduced by a significant amount?

The main reason why turnaround times can be that short is that pilots brief all flights of the day in the morning before the first flight.
This briefing is typically done in the crew room at the airport where the pilots are based. It typically starts about an hour or more before the first flight since there is a lot to cover:

Routes: the flight routes for all flights would already be planned by the dispatch department by this time. They are also filed with ATC by dispatch, so the flight crew only has to review it. This review involves discussing terrain and other possible threats as well as possible diversion airports in case of problems.

Fuel: the required fuel calculation is also done by dispatch, but the final amount of fuel to take is at the captains discretion, so the pilots would discuss possible reasons for taking more fuel (e.g. weather, expected delays at busy airports).
The final weight and balance is only known once the gate closes since passengers might not show up for a flight or additional passengers are booked onto the flight, which is not yet known in the morning. So this will be done during the turnaround.

Weather: the briefing package will contain the METAR (current weather) and TAF (forecast weather) for all airports visited during the day and all possible diversion airports. The crew will carefully review the expected weather at the expected times spent at each airport. The prevailing wind direction typically dictates which runways are in use for takeoff and landing. The crew would discuss which departure and arrival procedures they expect at each airport.
The crew will also discuss en-route weather, like e.g. thunderstorms (might require deviating from the planned route) or expected clear air turbulence (so they can brief the cabin crew about this).

Aircraft: since an aircraft can be dispatched with some items inoperative (Minimum Equipment List), the crew will review the information about the aircraft they are about to fly. This means they are aware of any missing or inoperative items and their consequences. Some airlines also have aircraft with different equipment or engines installed (e.g. A320ceo and A320neo) and the crew will brief the differences in operation (if any).

NOTAMs: these notices to airmen contain important information about the current situation at airports or for specific airspaces. This could be an airspace closed during a special event, it could be a taxiway closed for maintenance, it could be an unavailable approach because some equipment is broken, etc. The crew will go through all NOTAMs and discuss which ones are relevant for the flights today so they are already prepared.

Since all of these things are already taken care of, the actual turnaround can be pretty short. After shutting down the engines, one pilot will start loading the next flight plan into the flight management computer (FMC), which can usually be done via ACARS or loaded from a stored company route, and review that all waypoints and altitude/speed constraints are loaded correctly. In the meanwhile, the other pilot will do the external walk-around. Once that is done, the pilot flying will brief the pilot monitoring about expected taxi routes, the takeoff (including possible rejected takeoff) and the expected departure procedure (including possible return or diversion in case of an engine failure). An experienced crew can do this briefing in less than 5 minutes.
Once the gate is closed, the captain will get the final load sheet and will verify that everything is within limits. Now both pilots will independently do the takeoff performance calculation and compare the results. If they match, the values are entered into the FMC and you are good to go.
The limiting factor for turnaround times is usually the required time for disembarking, re-fueling and boarding. Regional airlines with short turnaround times do not load any trolleys for food and beverages during these turnarounds (they are all loaded in the morning) and only do a very superficial cabin cleaning (if any) to minimize time on the ground.
Aircraft manufacturers publish time estimates for these activities in their airport planning documents. Here is an example for an Airbus A320 without refueling (source):

They estimate 22 minutes without refueling, so anything shorter than that is really quite fast. With refueling of 20,000 litres (which is quite a lot, definitely more than you would need for a short haul flight), they estimate 44 minutes:


Where can I take my ultralight aircraft? I know many airports do not allow ultralight aircraft but can I take it to work, home, or to the bar? What is the limits of freedoms of travel in an ultralight?

Taken from a more specific answer by @Pondlife to a question about ultralights and National Parks:

  For ultralights specifically, the regulations are in 14 CFR 103 which has only a few very simple restrictions on where ultralights can operate. 103.15 says you can't operate over a congested area or a crowd of people and other restrictions are the obvious ones: don't fly near airports without ATC approval, don't enter restricted airspace, and do follow NOTAMs.


What is the difference between a barrel roll and an aileron roll? I was going through social media and I came across this GIF image that showed a plane doing some sort of roll.

It was labeled "Barrel Roll" but in the comments to the post, someone said that it was an "Aileron Roll". What is the difference between a barrel roll and an aileron roll?

The difference between an aileron roll and a barrel roll is that an aileron roll's centre of rotation is very close to or on the aircraft. A barrel roll has its centre of rotation around a point further away from the aircraft itself.

The difference can be appreciated in this image:

Image Source You can find out about the difference in feeling that these two manoeuvres have.

Having stated these things, the manoeuvre shown in the GIF is certainly an aileron roll.


Why is this exit indicator placed here? Some  Boeing 737s have this exit indicator in the cabin, attached in a seemingly odd position, next to the overhead bins, instead of in the middle.

Why is it placed here?

You dont have this tagged with a jurisdiction and the answer may vary a bit by country regulations but here in the US under the FAA the requirements do not explicitly state the sign must be in the middle of the aircraft:

  § 25.812 Emergency lighting.

  (b)Emergency exit signs -

  (1) For airplanes that have a passenger seating configuration, excluding pilot seats, of >10 seats or more must meet the following requirements:

  (i) Each passenger emergency exit locator sign required by § 25.811(d)(1) and each
  passenger emergency exit marking sign required by § 25.811(d)(2) must
  have red letters at least 1 1/2 inches high on an illuminated white
  background, and must have an area of at least 21 square inches
  excluding the letters. The lighted background-to-letter contrast must
  be at least 10:1. The letter height to stroke-width ratio may not be
  more than 7:1 nor less than 6:1. These signs must be internally
  electrically illuminated with a background brightness of at least 25
  foot-lamberts and a high-to-low background contrast no greater than
  3:1.

  (ii) Each passenger emergency exit sign required by § 25.811(d)(3)
  must have red letters at least 1 1/2 inches high on a white background
  having an area of at least 21 square inches excluding the letters.
  These signs must be internally electrically illuminated or
  self-illuminated by other than electrical means and must have an
  initial brightness of at least 400 microlamberts. The colors may be
  reversed in the case of a sign that is self-illuminated by other than
  electrical means.

So if its easier due to electronic cabling, head room, brackets, or any other factor manufacturers are free to mount the sign off center.


Why is ditching speed higher than stalling speed? I was looking for a checklist for the Cessna 182 and I stumbled upon this one. When I looked at the speed-table, I found an interesting entry. It says "Ditching" with a speed of 65 KIAS:

Everything I read and watched about ditching so far told me to ditch at the lowest speed possible.

Why should I ditch with 13 knots more than I could (Vso is 52 KIAS)? I can think of no reason I would like to do that.

As far as I'm aware - and maybe a seaplane pilot could give a better answer - one of the big issues with ditching is judging your height above the water. If you stall it in, you might get it wrong and lose control completely.

I checked the POH for a 182RG, which has a Vso of 39 KIAS and ditching speed of 60 KIAS. The ditching checklist gives descent rate as the primary consideration, not airspeed:

  Power -- ESTABLISH 300FT/MIN DESCENT at 60 KIAS

In the amplified procedures section, it says:

  Avoid a landing flare because of difficulty in judging height over a
  water surface

In other words, better to descend slowly under control until impact than stall it at an unknown height above the water. As Bob Hoover famously said, "If you're faced with a forced landing, fly the thing as far into the crash as possible".

I did a bit of Googling and found similar checklists for other aircraft, e.g. a Piper Arrow:

  Power--ESTABLISH 300 FPM DESCENT AT 90 MPH


If you were to fly an ILS in a knife edge would you receve GS and LOC be flipped? because LOC and GS work the same way, if you were to fly one at 90 degrees bank would your information be displayed on the wrong indicators?

No, the directional part of ILS is located at the ground. (Ground) transmitter creates lobes with specified frequency and modulation to mark the high, low, right and left areas.

LOC and GS signals are distinguished by the carrier frequency, deviation from the optimal approach by relative intensity of 90 Hz and 150 Hz modulation in the signal. These signals provides information about position relative to the airport regardless of airplane attitude.

So flying knife-edge LOC axis of the instrument still shows (correct) horizontal deviation and G/S axis correct vertical deviation.

Of course, display of the instrument is turned 90° together with the whole airplane, so its G/S axis now lines up with the green-blue boundary you see behind your windows (I hope you are not flying such maneuvers in IFR conditions :) ) but it is still the G/S axis and it shows vertical deviation from the optimal glideslope.

Only difference would be that airplane antenna won't match the transmitter polarization (ILS transmitters transmit in horizontal polarization and receiver is likely polarized in the same plane), so you loose some signal intensity and receiver can be more sensitive to reflected signals, therefore reducing maximal working range and possibly increasing probability of spurious signal detection.


Where can I find a flight log archive for commercial flights? I heard that commercial flight logs are publicly available from the FAA, including mechanical delay reasons, etc.  Is this true?  If so, where can this information be found?

Under the Freedom of Information Act you can request these records from the FAA. Please read more about doing so here:
http://www.faa.gov/foia/foia_request/


What is the minimum runway width for SSC Stratolaunch? What is the minimum runway width for the Scaled Composites Stratolaunch vehicle?

Is this determined by the separation between its fuselages (and thus undercarriages), or its outer engines (to stop blast kicking up soil, and causing FoD)?

A 200ft runway would likely be approved for Stratolaunch, but it would need special approval.

Minimum runway width is determined by both physical characteristics as well as flight performance of the aircraft. A pilot has to be able to safely land the aircraft in adverse weather, cross wind, etc. Since the flight characteristics of Stratolaunch have not been determined, it would not be approved for other than special use operation on any runway at any airport. Even runways that can accommodate such a large plane may not be approved if associated taxiways are not also suitable.

ICAO has a standard table used for determining minimum runway width based on aircraft reference field length, wing span and gear spacing. Stratolaunch is larger than the largest standard entry, so it would not qualify for even 60m/200ft width on that basis.

Looking at the A380 introduction there was interest is allowing operation from 150ft wide runways. FAA Engineering Brief 65A determined that an average pilot could safely operate an A380 on a 150ft wide runway. Its track width is 47ft, so a 50ft deviation on either side was deemed acceptable. If you assume that Stratolaunch is as controllable as an A380 (which I think would be extremely permissive) and given that its track width is just over 100ft, it would be borderline ok for a 200ft runway based on flight characteristics.

The A380 also had a requirement for a "stabilized shoulder", which was intended to prevent runway contamination by FOD. This requirement added a 50ft strip to each side of the runway. Since the span to outer engines is 168ft, the stabilized width was 40ft outside the engines. Stratolaunch engine span is 220ft, so adding 40*2 feet of stabilized surface makes total width 300ft. This is pretty standard for a 200ft runway.

It seems on the basis of this special approval for the A380, a 200ft runway would be approved for Stratolaunch.


When did pilots start making announcements to passengers? It's common practice now, and maybe required for most airlines. But I don't think that earlier pilots made the same announcements that they do today. When did pilots start making in-flight announcements to passengers? And all the announcements sound the same, is there a standard format for making announcements?

This varies by jurisdiction and air frame in question as the brief is usually specific to the air frame. Ill answer for the FAA.

What the pilot needs to say (by law) is governed by (follow link for full text),

  § 121.571 Briefing passengers before takeoff.

  (a) Each certificate holder operating a passenger-carrying airplane shall
  insure that all passengers are orally briefed by the appropriate
  crewmember as follows:

  (1) Before each takeoff, on each of the following:

  (i)Smoking. Each passenger shall be briefed on when, where, and under
  what conditions smoking is prohibited including...

  (ii) The location of emergency exits.

  (iii) The use of safety belts...

  (iv) The location and use of any required emergency flotation means.

  (v) On operations that do not use a flight attendant, the following
  additional information:

  (A) The placement of seat backs in an upright position before takeoff
  and landing.

  (B) Location of survival equipment.

  (C) If the flight involves operations above 12,000 MSL, the normal and
  emergency use of oxygen.

  (D) Location and operation of fire extinguisher.

  (2) After each takeoff, immediately before or immediately after
  turning the seat belt sign off, an announcement shall be made that
  passengers should keep their seat belts fastened, while seated, even
  when the seat belt sign is off.

  ....

FAR 121.571 comes off Doc. No. 2033, 30 FR 3206, Mar. 9, 1965 and was presumably added to the regulations in 1965.

Yes there is a standard. You can find more details in this Advisory Circular AC121-24C which covers what the oral brief needs to contain in more depth and outlines the standards. This AC has been in place since 2003 and replaces AC121-24B which took effect in 1999 I cant find the full text of that one so Im not sure what it replaced (presumably AC121-24A).

There is no direct regulation in the FAR's (or current AC) that require announcing things like route, altitude or temp.


Why is it hard to see G1000 with sunglasses? I got checked out in the G1000 172 at my flight school just so I could schedule to fly when the two steam gauge 172s were booked. I'm very impressed by the G1000, but I can't wear sunglasses when I fly the NAVIII. This is with the avionics dial on the lighting panel turned all the way up.

Does anyone else have this problem? Is it my sunglasses?

The screens are LCDs, which have a polarized filter layer over them. That layer is usually placed at a 45° so they are misaligned with your polarized sunglasses which are aligned vertically. You can confirm this is the problem by turning your sunglasses at different angles and see if the screen changes.


Why do we call it a ramp? Airport ramps are close to level, not inclined.

What is the history and etymology of this aviation term?

Ramp refers to the area in airport where the aircraft are parked. This term comes from the days of seaplanes. From this site:

  The term ‘Ramp‘ traces its roots back to the days of seaplanes when there literally was a ramp from the water to the terminal parking area.

In case of seaplanes, the area is actually an inclined plane between the shore and water. This is similar to the term boat ramp.

Note that this is used mainly in US. The ICAO (and FAA) terminology for the area is Apron.


How much energy is "wasted" in an aeroplane's descent? In descent, an aircraft must lose both potential energy (in order to get down to the ground) and kinetic energy (in order to land at a safe speed).

Weight and drag can take care of that. An unpowered plane will eventually slow down and sink. However, sometimes it won't happen fast enough without additional control input, and the pilot must act to make the plane less aerodynamically efficient, and dispose of some surplus energy that would otherwise be retained longer.

If a plane completed its descent from top to bottom without using the control surfaces to:

dump excess lift
bleed off excess speed along the way

until actually landing, that would mean no waste of this energy in descent: all of it was used productively to get the aircraft to its destination, and none of it needed to be thrown away to get the plane low enough and slow enough fast enough.

In a particular descent, would it be possible to calculate or estimate how much of that energy in practice does in fact get "wasted", i.e. needs to be deliberately thrown away?

A meaningful numeric value is going to be hard to calculate, because so much depends on the aircraft you're working with.  In practice, if I can pull off power at the calculated Top of Descent point, descend, meet any ATC crossing restrictions, fly the approach, configure as late as possible, and push up the power right at the point where I'm required to be stabilized for the approach, then I've flown an efficient approach & wasted none of the energy that I started with.

If I have to add power sooner than that, I started down too soon (or wasted energy in some way); if I have to deploy drag (which includes configuring early), then I started down too late & so I have excess energy that I need to dissipate.

I suppose "amount of time speedbrakes were up" would be one way to score how much energy had to be wasted; add to that how long flaps & gear were out before they were "needed" (given the requirement to be stabilized & configured at a given point in the approach).

Here's the complication, though.  If I see early on that I have too much energy, I can push the nose down & gain speed, which increases the parasite drag of the aircraft -- thus dissipating energy.  If you have enough time at the higher speed (not just push the nose down, gain speed, pull the nose up, lose speed -- that doesn't accomplish very much), then you can get rid of excess energy without having to deploy speedbrakes or configure early.  And the reverse, if my standard descent is at 280 knots (above 10,000', obviously) but I slow up to 250 knots early enough, I can "gain" some energy, since I'm losing less with less parasite drag.  How you could account for all of that in a "score" is beyond me.

In the ideal case, I can descend to glideslope intercept altitude, level off there, let the speed decay, then at the point when I need flaps to fly any slower, I extend the first increment of flaps, let the speed keep dropping off, start down the glideslope (speed decreases more slowly or if the aircraft is light enough, not at all), at about 500' above the "stabilized approach" gate I'll lower the landing gear & extend more flaps, so that as I approach that gate I'm extending the last increment of flaps, my speed reaches VTarget, and I add power.  No extra time with power above idle, a fuel-efficient approach.

ATC may not let me do that, though; they may keep me fast until close to the runway, in which case I'm extending flaps & gear closer to their maximum speeds so as to dissipate more energy more quickly and still be configured & stabilized at the appropriate point.  (The 737 dissipates speed pretty quickly fully configured at idle power, even descending on the glideslope.)  So did I "waste" some energy in that scenario?  Yes.  But keeping ATC happy so they can get efficient runway utilization is a worthy goal as well.


What is "clearance delivery" meant for? I was recently having a conversation where the term "clearance delivery" popped up, and was talking about his time flying into PHX, but in all of my time flying, I've never heard of the term before! Could someone explain to me what exactly is this for, and where would you find this?

"Clearance Delivery" is exactly what you've surmised it is - a frequency used on the ground to copy your initial clearance from ATC before you take off.
The idea behind using a dedicated frequency for this is that it avoids tying up the ground control frequency (used for authorizing ground movement on taxiways and such) with long clearances and readbacks.

Clearance Delivery is found at controlled fields. Pilots operating under Instrument Flight Rules will generally use it prior to each flight, and at airfields in class C or class B airspace it's used by VFR pilots as well (since they'll be talking to departure controllers very shortly after take off until clear of the controlled airspace).

At less busy fields Clearance Delivery is often staffed by the same controller working Ground (e.g. at Long Island / Mac Arthur it's usually the same controller working both positions), and at some airports clearances will be read over the ground control frequency when it's not busy. At busier airports clearance is usually its own position - possibly with multiple frequencies (e.g. at La Guardia there is a separate clearance frequency for helicopters).


Is there any alternative to isolating the vibration of an ultralight engine other than using engine mounts? Is there any alternative to isolating the vibration of an ultralight engine other than using engine mounts?

You can prevent engine vibrations from being transmitted to the airframe by motion cancellation techniques. Similar in principle to Active Noise Reduction headsets that generate an inverse pressure wave to cancel sound, motion cancellation generates an inverse displacement of a mass to cancel vibrations.

Sensors determine the vector(s) required, and electronics control the mass actuator(s). These can be added to any engine. Predictable, repetitive vibrations are most successfully treated. Actuators tend to be heavy, so better engine/prop balance and more effective isolators (mounts) are preferred.


Do I need a PPL license for a CPL license? Do I need a PPL license to get a CPL/ATPL license?

I could not find anything on the net regarding my question.

Yes, with a couple of exceptions. FAR 61.123 contains the requirements for a commercial certificate, while 61.153 contains the requirements for an ATP certificate.

FAR 61.123(h) states than an applicant must:

  Hold at least a private pilot certificate issued under this part or meet the requirements of §61.73

FAR 61.73 refers to the option for military pilots to apply for an FAA certificate based on their military qualifications. For non-military pilots, the commercial certificate can only be earned after obtaining the private pilot certificate.

FAR 61.153(d) includes the ability to use a foreign commercial or ATP certificate as a prerequisite. An applicant must:

  Meet at least one of the following requirements:

  (1) Holds a commercial pilot certificate with an instrument rating issued under this part;

  (2) Meet the military experience requirements under §61.73 of this part to qualify for a commercial pilot certificate, and an instrument rating if the person is a rated military pilot or former rated military pilot of an Armed Force of the United States; or

  (3) Holds either a foreign airline transport pilot license with instrument privileges, or a foreign commercial pilot license with an instrument rating, that—

    (i) Was issued by a contracting State to the Convention on International Civil Aviation; and

    (ii) Contains no geographical limitations.


Do biplanes need bigger tail volume coefficients than monoplanes? Do biplane ultralights need bigger tail volume coefficients than monoplane ultralights?

Horizontal Tail Volume Coefficient

I understand that biplanes don't need a larger horizontal tail coefficients vs a monoplane of the same total wing area and same wing span. This is because the chord is would be half of the monoplane, but there are two wings, so the "total chord" is the same, so the horizontal tail volume coefficient does not need to increase. I'm told a typical tail volume coefficient for light airplanes is 35%.

I understand that the horizontal tail volume may actually be lower than that of a monoplane if the wings are staggered, the wings acting like a reflex wing and reducing the wing moment, so a smaller horizontal tail volume may be used in this specific case.

Vertical Tail Volume Coefficient

I understand that the vertical tail volume coefficient on a biplane is twice as large  as that of a monoplane with the same span, as there are two sections of span that the vertical tail needs to control. I'm told a typical vertical tail volume coefficient is 3.5% for light aircraft.

Is this correct?

Tail volume is a measure for the ability of the tail to compensate for the destabilizing pitch moment created by the wing in case of the horizontal tail and for adverse yaw in case of the vertical tail. This pitch moment is proportional to the square of the wing chord (one factor comes from the area, the second from the lever arm), so if you compare two otherwise equal designs, one of which is a biplane and the other a monoplane of twice the chord, the dimensionful horizontal tail volume (expressed as tail surface times tail lever arm) of that monoplane needs to be twice that of the biplane. To counter adverse yaw, however, the dimensionful vertical tail volume is the same.

Tail volume is normally made dimensionless by referencing it to the wing area and the mean aerodynamic chord (for the horizontal) or wing span (for the vertical tail). Since the area of both designs is the same and the MAC of the monoplane twice as large as that of the biplane, both dimensionless horizontal and vertical tail volumes become equal even though the dimensionful horizontal tail volume of the monoplane is twice as large.

However, if you compare wings of the same aspect ratio (which might be a better basis), both the chord and the wing span of the monoplane are larger by a factor of √2 but there is only one wing to consider versus two in case of the biplane. Now the dimensionful horizontal and vertical tail volumes for the monoplane are larger by a factor of √2.

Only when you make the chord of both wings equal (doubling the span of the monoplane in the process) will the dimensionful horizontal tail volume of both designs be equal but now the vertical tail volume needs to be twice as large.

Wing stagger with the same incidence on both wings would move the biplane closer to the monoplane with twice the chord whereas a lower incidence on the rear wing would indeed create that reflex effect and reduce the instability of the wing. Still, you need control power to change angle of attack quickly enough for maneuvering, so I would be careful with any further reduction of tail volume even if the staggered biplane wing by itself is stable already.


What are these unsymmetrical parts at the tail of the Tupolev TU-144? On a recent trip to the Technikmuseum Sinsheim, I noticed that the back of the Tupolev TU-144 is not symmetric.
Please take a look at the picture I took to understand what I mean:

(Please don't mind the crane, the Tupolev was getting cleaned that day)

Those parts most likely serve some aerodynamic/stabilizing purpose, but what exactly do they do? Why aren't they the same on both sides?

The four parts you're referring to contain the actuation mechanism for the rudder, similar to the wing pods that contain the flap actuation mechanism.

The reason they are not arranged symmetrically is that the rudder has two sections (you can see the 'cut' in the middle in your image)- apparently to provide redundancy and improve safety. So,each section has two actuation mechanisms on the same side, with both of them in opposite sides.

The Concorde had a similar arrangement, albeit with only a single mechanism on either side, as can be seen below.

By Simon Boddy, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=31619795


What is the difference between buffeting and fluttering? As I understand, both are dynamic effects of aeroelasticity - however, what is the exact difference between buffeting and flutter?

The vernacular meaning is...

1) Flutter is un-commanded self perpetuating (positive feedback) destructive & adverse cyclic movement of any part of an aircraft. It most commonly occurs on a control surface but may be an entire wing, tail surface, or more rarely fuselage or other part or device. Flutter may be induced either mechanically or aerodynamically and may be sustained mechanically (i.e. engine or prop, landing gear or ground resonance of a helicopter skid) or aerodynamically by self perpetuating (positive feedback) force. Mechanical inception can be (but not limited to) brisk or pilot induced oscillation, weak, unsupported, or flimsy structures. Aerodynamic inception can be (but not limited to) undesirable cg, or aerodynamic forces on parts. Flutter is always undesirable, dangerous and a destructive force.

2) Buffeting is a turbulent stream of air striking any part of the airframe. The turbulent air may be completely external (weather) or created by the aircraft it self (prop, wing,etc). The most common form of buffeting is turbulent airflow over a wing (i.e. during a stall or wind gusts) striking the wing or horizontal tail. Buffeting is not usually considered self perpetuating with positive feedback, nor is it considered to be precisely cyclic or harmonic - though it may be repetitive. Buffeting is usually considered undesirable but benign and not a destructive force.


May time be logged for an aborted flight? Consider the case where the engine is started, aircraft taxies to the run-up area to do check, then it turns out that a magneto is bad, or there's a radio problem. The pilot wisely decides to abort the flight, and taxies back to parking. In the process, experience has been gained in taxiing, possibly ATC communication, the pre-flight, and good pilot judgement for the flight. There were no take-offs, landings or air time, but the aircraft was under the control of a PIC during taxi.

There's a long discussion about this on PPRuNe, with varying opinions either way.

According to 14 CFR 1.1:

  Flight time means:

  (1) Pilot time that commences when an aircraft moves under its own
  power for the purpose of flight and ends when the aircraft comes to
  rest after landing; or

  (2) For a glider without self-launch capability, pilot time that
  commences when the glider is towed for the purpose of flight and ends
  when the glider comes to rest after landing.

The key phrases seem to be for the purpose of flight (which seems to be satisfied - unless going for a VOR check, or moving the aircraft from one location to another), and after landing (which, doesn't apply, because there was no airborne time).

Have there been any FAA determinations, rulings or enforcement actions made in this regard?

Interesting question, I found myself in exactly that position a couple of months ago (more on that below).

First, I found an FAA clarification on this, which is a legal interpretation from 2007 and it partly answers your question. The questioner asked the FAA three questions about logging flight time (in a helicopter in this case); questions 1 and 2 are very close to yours. Question 1 is:

  May a pilot log as "flight time" to qualify for a certificate or rating under 14 CFR Part 61, or for purposes of qualifying under 14
  CFR 135.243(b)(2), that time accrued in a helicopter when the aircraft
  is sitting on the ground with the engine running and rotor blades
  turning, but the aircraft has not moved from its parking place and
  flight has not yet commenced?

Question 2 is almost the same, but it asks about logging time after parking but when the engine is still running. I know that this is slightly different from your scenario, because you're asking about logging time after the aircraft has moved from its parking place, but the FAA response says the following:

  [...] flight time [...] commences the moment that [the aircraft] moves under its
  own power away from its parking place for the purpose of flight -
  whether departure is commenced by lifting off or taxiing.

So according to that interpretation, you can start logging time as soon as you start taxiing but it goes on to say that you cannot log time after the aircraft lands. That means that your question is still a grey area, and if you want a definite answer then you should probably ask the FAA for your own interpretation. But my personal take is that the FAA is only concerned about people trying to cheat the system by sitting with the engine running, and for practical purposes you can log time as soon as you start taxiing.

And turning to the real-world situation, I don't think it matters at all. Every instructor and pilot I have ever met simply logs whatever time the Hobbs says, regardless of what happens in between. The FAA has absolutely no way to accurately verify what you're logging and there's a large degree of trust in the system.

In my case, the AI gyro didn't spin up and although I didn't need that instrument (the planned flight was VFR in CAVU conditions) I elected not to fly anyway: better safe than sorry, and if one thing is broken it may be a symptom of a bigger problem. I taxied back with 0.2 on the Hobbs: I didn't log it (and the FBO didn't charge me). My thinking was simply that I didn't really 'fly' and 0.2 is irrelevant for all practical purposes. I'm sure that someone somewhere has found themselves 0.1 short of what they needed for a rating and really wished that they had that extra time, but if you ever find yourself in that position, it's no big deal to do a couple of turns in the pattern.

Note: there is another FAA interpretation on this, but it looks like it only applies to part 121. They said yes, you can log it, but that's based on the assumption that after you taxi back to the gate, the airline finds a second aircraft and you fly that one to the original destination. They didn't say what happens if the flight is cancelled completely.


How to calculate your landing ground roll distance with this chart? Under these conditions:  Pressure altitude  5,000 ft, Headwind  Calm, Temperature   101 F
I have no idea how to even start

All else being equal, increased temperature increases density altitude, and thus true airspeed for a given indicated/calibrated airspeed. Increased landing speed will increase the landing roll distance.
In your exercise above, the primary relevant condition given is a runway at 5000'. This tells you which column of the table you'll be using, i.e. the one labeled "At 5000 feet & 41 °F". Note that the temperature given there is the "standard" temperature for that altitude.
But there are footnotes. The first footnote, discussing headwind, doesn't apply because there's no headwind. But the second one, discussing temperature does. Your given temperature is 101 °F, which is 60 °F higher than standard temperature for the given altitude of 5000'. The footnote says you need to add 10% to the distance for every 60 °F higher than standard, and there is exactly 60 °F higher temperature given in the conditions, so you need to add 10%.
The standard ground roll is 495', so adding 10% to that you get 544.5' (which you might round to 545').
Note that if the temperature was, for example, only 30 °F higher, that doesn't mean you can ignore the second footnote. You should interpolate based on the information there, adding 5% in that example to the landing roll instead of 10%. Likewise a temperature 90 °F higher would require increasing the landing roll figure by 15% (assuming you think it's even safe to operate the airplane at that temperature! at 131 °F, there are lots of other problems that might argue against flying at all, including failure of paved surfaces, overheating of the engine, pilot dehydration and fatigue, etc.)
You don't say whether the runway is unpaved. The table you're using assumes a "hard surface runway". If it's a grass runway, you'd also want to apply the third footnote. Note that the footnote there is for a "dry, grass runway". A grass runway that's wet, or a gravel runway, or a snowy/icy runway could produce different results. A wet, grass runway in particular could reduce the landing roll significantly, while an icy paved runway could increase it significantly, as compared to "standard" conditions. A gravel runway might perform very similarly to a hard surface, depending on the condition.
In other words, while it's clear from the round numbers (5000' is exactly the base altitude for the column you'll use from the table, while the 101 °F temperature is exactly one unit of the 60 °F difference used for the second footnote) that this is just an academic exercise, in the real world you may have other factors to take into account, including the pilot's skill in maintaining the required approach speed of 60 mph (an even slightly faster approach can greatly increase the ground roll) and in using the brakes at their maximum effectiveness, and of course the condition of the airplane itself, especially the tires and brakes, along with the various environmental factors mentioned in the table and those I mentioned above.


Why does the boeing 747-8 have less wing flex than the 787? If you know the 787 wing flex is much greater than the 747-8's wing why can't the 747-8 have a greater wing flex

The reason is twofold: The materials used and the high aspect ratio.

The 747-8 primarily uses advance aluminum alloys, while the 787 uses carbon composites.

The carbon composites flex more compared to the aluminum alloys. This can be achieved because the carbon fibers are anisotropic and their properties can be tailored in each direction.

The yield strain of the aluminum alloys used in aerospace is ~1%, while that of the carbon composites is about 50% higher, ~1.5%.

These material characteristics mean that the carbon spar can flex more compared to the aluminum one. This effect is magnified by the high aspect ratio of the Boeing 787.

The aspect ratio of the 787 is about 11 while that of the 747-8 is about 8.5. This means that the wings are more slender and flex more for the same load.

The 787 wings are able to take this flexing in part because of the excellent fatigue properties of the Carbon composites used. See this question for a very good discussion on the causes and effects of wing flexing in 787.


How much is airspeed reduced on an A10-Warthog when firing its cannon? I just read on reddit that you could use the recoil of the gun as the propelling force for the A-10 if pointed backwards. There is also a question here on Aviation.SE, saying that the gun has the same power as one single engine.

I'm now wondering how fast airspeed actually decreases when firing the gun.

Let's suppose the aircraft is in level flight with no acceleration in any direction. The gun is now being fired. What acceleration is being applied to the aircraft (In m/s or kt/s)?
Bonus question: If there was infinite ammo and nothing like gun overheat, how long would it take to slow the plane down to stall speed, if initial speed was a usual A-10 speed.

What acceleration is being applied to the aircraft (In m/s or kt/s)?

From XKCD we know that the gun

  produces almost five tons of recoil force

that is about 50000 newtons (round numbers for simplicity, they won't overly affect the results)

The acceleration is force divided by mass, and the A-10 has an empty mass of 11000 kg, and a MTOW of 23000 kg.

This gives an acceleration between $4.545\ \mathrm{m/s^2}$ and $2.174\ \mathrm{m/s^2}$.

The Wikipedia page about the GAU-8 mentions that

  While this recoil force is significant, in practice a cannon fire burst slows the aircraft only a few miles per hour in level flight.

and gives as a reference a book that I do not own, so I cannot verify.

  If there was infinite ammo and nothing like gun overheat, how long would it take to slow the plane down to stall speed, if initial speed was a usual A-10 speed.

With the additional assumption of thrust balancing only the aerodynamic drag, we can say the following: cruise speed is $155.6\ \mathrm{m/s}$, and stall speed is $61.11\ \mathrm{m/s}$ (see Wikipedia link above), so this means that it would take between ~34 and ~71 seconds to completely stop the aircraft; or between ~20 and ~43 seconds to stall it.

If instead we want to be more realistic, we have to assume that we have infinite fuel, that ammo and fuel do not factor in the weight computation, and that the yawing/pitching moments do not overcome actuator authority.

With all that in mind, we should start from firing the gun at strafe speed, not at cruise speed, since we want to hit a specific target on the ground, so we want to move as slowly as possible, to have the highest chances of hitting it. This means that our starting velocity would be above stall speed but not significantly, leading to a smaller margin of continuous fire before stalling, unless the throttle is opened (if possible) to counteract the extra "drag".

If we ignore the discussion about strafing and hitting the target, and we fire from cruise speed (and this is what is meant by "usual speed"), it is possible that stall is not achieved, since at lower speeds you will have more excess thrust (but we are still assuming that the firing only produces "drag" or a negligible amount of yawing/pitching moments). This means that we could settle at a lower speed, but the determination of the exact speed requires the knowledge of the exact drag and thrust characteristics of the aircraft, in addition to it being a function of the initial speed, see Koyovis' answer for some basic numbers.


Is there a triangle representation for the Canadian airspace? I'm looking for the following figure, except modified for Canadian airspace.
Does anybody have a copy, or can help me modify this one? I searched everywhere and could not find one.

I did not find a triangle representation, but this poster summarise the particularities of the Canadian airspace

https://www.tc.gc.ca/en/services/aviation/documents/TC-6010-AirspacePoster-E.pdf


Is a Compass Swing Platform part of a runway or taxiway? I am trying to work out if the compass swing platform is part of the runway or taxiway.

It could be on a taxiway, but it can also be outside the movement area (e.g. on the apron or ramp in the US). As far as I know, it is never on the runway.

There is a compass rose on a taxiway at Petaluma Municipal Airport (O69). You can see it on the following image (from Google Maps). It is painted in front of the hold short line of runway 11.

Most airports will however have a dedicated position for the compass rose. This image (taken from this question) shows an example at Ramona Airport (KRNM):

It is not part of the taxiway as indicated by the yellow line, which separates the non-movement area from the movement area.


What types of wood can be used for making propellers? Early propellers were made from wood and they still are on some vintage/classic aircraft and reproductions. What types of wood are typically used to make wooden propellers?

Historically, the following woods were used:

Mahogany
Walnut
Oak

Almost all wooden propellers are reinforced to add strength. Fabric or metal coverings can be added too.


What is the difference between "Bay" and "Stand"? When should we use the word Stand and when Bay for ATC taxi clearance?

The correct terminology for a place where aircraft park is stand or aircraft stand, where bay or parking bay is colloquial.

The official definition from the ICAO ANNEX 14/I Aerodromes is:

  Aircraft stand. A designated area on an apron intended to be used for parking an aircraft.

This can be either a stand at a gate or a remote parking stand.

The correct use of the word bay is for a holding bay as defined in ICAO ANNEX 14/I Aerodromes as:

  Holding bay. A defined area where aircraft can be held, or bypassed, to facilitate efficient surface movement of aircraft.

So you use the term stand for an area where aircraft park (i.e. shut down engines, load/unload cargo, (dis-)embark passengers, etc.) and you use the term bay for an area where an aircraft temporarily holds (typically with engines running).

There are some sources using the term bay for parking, but I would consider all of them more informal than the official ICAO definitions:

The ENAV (company providing air traffic control services in Italy) writes (emphasis mine):

  [...] which guides it right up to the parking bay.

on the English version of their website, but this could also be a wrong translation from the Italian original.
The Thales Group (French aerospace company) writes (emphasis mine):

  Tower ensures smooth and seamless aircraft control between TMA boundary and the parking bay.

which again might be result of incorrect terminology used by the translator.
This article by Qantas suggests that the term is actually used by Australian ATCs (emphasis mine):

  PILOT: “Qantas 635...we will arrive on blocks at 1500. Have 2 UMs, 2 WCHRs, 1 will need assistance to a taxi. Request a parking bay please.”

  MOCO: “Copy that Qantas 635. 2 UMs, 2 WCHRs. You are for parking bay 26...2...6. See you on the ground Qantas MEL.

The CAAS (Civil Aviation Authority of Singapore) is also using the term (emphasis mine):

  the aircraft was also assigned the shortest possible route from the runway to the parking bay to minimise fuel consumption.

Related:

What is the difference between a Stand and Gate in Airports? How do they differ ?
What are the correct names of the parking spaces for turn-around?


Was this a near collision or a normal procedure? I flew on a plane from UK to Spain a couple of days ago (FR7542, 15/01/19 16:30) and in the middle of the flight I could see another plane (a private jet much smaller) just flying underneath us.
From my point of view it was excessively close. And given that I came across recently an article in the news saying that two planes of the company I was flying with flew a hundred meters close to another aircraft of the same company. I was a bit worried for that. Just wanted to share this here and hopefully get some explanations.

There is only 1000 ft of separation between levels of traffic at the altitudes jets operate in (above 29000 ft) and when you see someone 1000 ft above or below it looks really close.  When you are sitting in the flight deck the first time on a busy airway and oncoming traffic passes above or below, you think they are passing only a few hundred feet away even though they are 1000 ft.  When you first notice an oncoming contrail, it looks like it's coming straight at you until it's a mile or two away.

The Traffic Collision and Avoidance System (TCAS) on each airplane tells the crew the proximity and relative altitude of nearby traffic and the system gives warnings with directions to climb or descend if someone is on a collision path. Plus ATC knows everybody's altitude and the ATC computers provide warnings to controllers if an airplane deviates from an assigned altitude by more than a couple hundred feet.

It takes a lot to go wrong for airplanes to come too close to each other, although nothing is perfect and it can still happen.  The systems in place keep the probability to an acceptably low level.


Why does a helicopter need cyclic control rather than just tilting the whole main rotor? Helicopters use a cyclic control to tilt each blade differently through the rotor's revolution. This is quite a complex mechanism. What is the advantage of this vs tilting the whole rotor plane? This seems to be a much more simple solution.

Tilting the rotor doesn't do much, in fact the body will be tilting more than the rotor. The gyroscopic effect will work against you.

The cyclic increases lift on one side of the rotor which will tilt the rotor. Which will then move the craft in the correct direction.

In other words the cyclic system gives a more direct response to input.


Is it possible to get access to flight logs of USAAC trainer planes from the 1930s? After answering this question on History.SE, I started to wonder if it would be possible to find out even more detail about the plane now that its serial number is known.

I have no idea what kind of flight records the US Army Air Corps kept, however. I know most flight logs today are kept by pilot, but I imagine there would be some way to trace what pilots flew a particular plane. I have no idea if this is possible for USAAC trainer planes in the 1930s.

Could I get access to these records? If so, how would I go about it?

I'm mostly interested in seeing if I can find out more information about where the plane flew, and maybe (if I'm lucky) who flew it when and for what purpose.

For serial number 31-35
 - Pilot seems to be Brookley, Wendell H
 - Homebase seems to have been Wright Field, Dayton, OH

See Link

For serial number 31-85
 - Pilot seems to be Larkin, James D.
 - Homebase seems to have been Boeing Field, Seattle, WA

See Link

It seems that you can order any of these Reports.


Can all airborne aircraft be stored at their origin or destination airport? With the progressing outbreak of the Corona Virus the IATA has recently changed its predictions about the losses to be suffered by the aviation industry

The losses originate from the reduced number of passengers and the subsequent grounding of aircraft for which there are no passengers.

The question is, can all the aircraft in the air be grounded at either their origin or destination airport. If not, where else can they be stored?

Short answer: Yes.

You need to distinguish between short-haul and long-haul fleets.

For example, when it is 4 a.m. in Central Europe, almost all the aircraft which fly short-haul routes throughout Europe during the day will be on the ground somewhere in Europe simultaneously and there must, therefore, be ample parking for all those aircraft (though not necessarily at gates). Similarly for other parts of the world: when it is 4 a.m. in the central U.S., all the short-haulers will be parked-up somewhere in the U.S.; when it is 4 a.m. in South East Asia, all the short-haulers will be parked-up somewhere in South East Asia, and so on. There must, therefore, be ample parking for all short-haulers globally.

For long-haul fleets, it is a different matter. Such aircraft spend up to 16 hours a day in the air, and therefore well over half the aircraft will usually be airborne at any one time, round the clock. It is highly abnormal to have all long-haulers on the ground simultaneously. If all those long-haulers need to suddenly be grounded, it can cause serious problems, as happened after 9/11 when the entire transatlantic and transpacific fleets suddenly stopped flying. However, even then, the airport operators did manage to find sufficient parking.


What does "storing an aircraft" technically mean? I have read on wikipedia about airline fleets and you sometimes see that they have aircraft which they declare that have been stored.

Technically what does this mean? How do you store and aircraft? Being the plane out in the open air and susceptible to weather, wouldn't delicate parts and even the fuselage degrade quite quickly?

Are stored airplanes then reused or resold in the future?

Wouldn't it be more feasible just to sell them instead of storing them for a period of time?

Here there are some nice considerations.
You can basically divide stored aircrafts in two main categories: short-term and long-term.

From the link, for long-term:

  When discussing parked or stored aircraft, it is safe to assume one is referring to an aircraft that is no longer in operation and has been placed by the owner, airline or lessor into a manufacturer-approved storage regime to preserve maintenance and asset value.

Instead, for short-term:

  However, some will also refer to stored aircraft as those that are between owners. [...] a transition [...] takes time and [...] As such, an aircraft will often be stored and out of revenue service for six to 12 weeks.

or

  Additional or unusually lengthy checks can delay the aircraft from revenue service for many months, during which time they are sometimes referred to as parked or stored.

but in the end, to answer why they are not sold:

  With the exception of these transitions, the majority of aircraft in storage are there because they are no longer economically viable to operate; it is cheaper to put the aircraft into a storage programme than to fly it.

You keep it safe so that you can scrap it.


How do CFIs typically determine proficiency for complex and high-performance endorsement? I'm working on getting checked out in our flying club's Arrow II. Our club's insurance requires 10 hours of instruction if you don't have any retractible time.

I've done a few hours with an instructor, and he signed off on my complex endorsement, which I also need from an FAA standpoint. So I'm FAA endorsed, but I need more time to satisfy club insurance.

§61.31.(d)(2)(e)(i) says:

  (i) Received and logged ground and flight training from an authorized instructor in a complex airplane, or in a flight simulator or flight training device that is representative of a complex airplane, and has been found proficient in the operation and systems of the airplane;

What defines "found proficient?" What is the list of things an instructor "ticks off" their list to be able to give that endorsement?

Same question for the high-performance endorsement?

This Advisory Circular describes what should be examined when transitioning (and ultimately endorsing) a pilot for complex operations.

  This publication is offered as a guide to the procedures and standards
  to be followed for a thorough and comprehensive checkout in these
  airplanes. The conscientious application and adherence to the scope of
  coverage recommended in the syllabus should result in a more
  competent, effective, and efficient pilot.

The document is fairly short and I suggest you look through it, for brevity I wont copy it here as its pretty much all relevant. Its important to note that this is simply what the FAA suggests (albeit strongly) and its not required all the described things be covered in a checkout. Although the instructor may be assuming some liability by signing you off without a proper checkout.


Why is there an ETOPS marking on the nosewheel door? What is the reason for painting ETOPS on the door of the nose gear?

"ETOPS" marking on a B737-800 (source)

Markings on the belly are supposed to be useful for ground handlers, what is it supposed to do here?

You're correct that it is for ground handlers; more importantly, it is for mechanics. It is important to identify the aircraft as ETOPS as the servicing and checking requirements are different for ETOPS and non-ETOPS aircraft. For ETOPS aircraft, two critical systems (like engines) should have differnt maintenance personnel to avoid them making the same mistakes in both of them.
From 14 CFR § 121.374 Continuous airworthiness maintenance program (CAMP) for two-engine ETOPS:

(c) Limitations on dual maintenance.
(1) Except as specified in paragraph (c)(2), the certificate holder may not perform scheduled or unscheduled dual maintenance during the same maintenance visit on the same or a substantially similar ETOPS Significant System listed in the ETOPS maintenance document, if the improper maintenance could result in the failure of an ETOPS Significant System.
(2) In the event dual maintenance as defined in paragraph (c)(1) of this section cannot be avoided, the certificate holder may perform maintenance provided:
(i) The maintenance action on each affected ETOPS Significant System is performed by a different technician, or
(ii) The maintenance action on each affected ETOPS Significant System is performed by the same technician under the direct supervision of a second qualified individual; and
(iii) For either paragraph (c)(2)(i) or (ii) of this section, a qualified individual conducts a ground verification test and any in-flight verification test required under the program developed pursuant to paragraph (d) of this section.

In the same vein, from Boeing:

Strategies for Avoiding Multi-Engine Maintenance Errors
After investigating several multi-engine maintenance events, Boeing identified a key strategy for avoiding multi-engine maintenance error: If possible, operators and repair stations should avoid performing maintenance on multiple engines using the same personnel during a single maintenance visit. Following this strategy should also minimize the potential that improper maintenance will occur on redundant or backup critical systems, such as flight controls, electrical generation and distribution, and hydraulics.

If the NLG doors have ETOPS written on them it would be easier for the technicians to identfy the aircraft and perform checks/maintenance as required, using two different operators, if required.


Was the unmanned flight and landing of the Buran spacecraft in 1988 exceptional? The Buran had a very sad fate. But in 1988 it has undertaken its first and last flight, which was unmanned and landed with a precision of three meters in a crosswind of 60 km per hour. It lost only 8 of its 38 000 thermal tiles.

What was the level of technology of automated flights in that times? Was it usual that airplanes landed automatically or was that flight of the Buran something like exceptional?

Here is an image of the Buran with Energija launch vehicle:

(source of the image)

Your question is very subjective, but I think there are two ways to look at it:

Building a working space plane is pretty exceptional.

or

There's really nothing it did that wasn't done by something else.

The NASA shuttle was flown in fully-automatic mode for launch, and most of reentry. It's also the vehicle which pioneered the thermal tiles, the reentry profile of a space plane, and the general concept of a shuttle. Buran could almost be thought of as an iteration on that design. The Soviets used some lessons learned and, in some respects, built a better shuttle. Does that in itself make the Buran exceptional? Probably not.

The only thing Buran really did that the NASA shuttle never did was fly unmanned, including an automatic landing. That seems to be at the heart of what you're asking, so I'll address that specifically.

Autoland had existed for decades before Buran, so it certainly wasn't the first airplane to land on autopilot. Although, it may have been the fastest autolanding to date, which could be an argument for exceptional.

I would note that even though there was only one orbital flight of Buran, there were atmospheric tests of prototype vehicles (some prototypes had jet engines), so there were opportunities to safely test the autopilot during the landing phase of flight prior to the orbital test. In fact, it would have been the only phase of the autopilot that saw real-world testing prior to launch. So once Buran got on approach, the fact that landed safely probably shouldn't be too much of a surprise.

Lastly, I've heard and read many times how amazing it is that Buran landed so close to centerline in such a dramatic crosswind (around 33 knots). I think that would indeed be pretty impressive... if it were true. However, I urge you to go look at video of Buran landing (example, mute recommended). Does that look like a 33 knot crosswind to any pilot? To me, it looks like about a 5-10 knot crosswind at most. You see the wings doing very little correcting, and the wheels touchdown at almost the same time, which is very much not indicative of a crosswind.

For comparison, take a look at STS-133 landing. Note the wing movement at 8:58 which is to correct for about a 12-knot crosswind gust, which looks about right to me. Notice how the upwind wheel hits the runway about a second before the downwind wheel hits - very indicative of a crosswind.

I have no idea where the crosswind number came from, but it was almost certainly exaggerated, either on accident (perhaps mistaking wind conditions on approach for surface wind), or intentionally exaggerated to show how great and superior Buran was. Either seems plausible to me.

I tend to be in the camp that says anything you build which successfully goes to space and comes back safely is pretty exceptional, but I wouldn't say Buran was a tremendous advancement over existing technology, and ultimately it's always going to be difficult to really assess a ship which only flew once.


What type of engine/motor is used in aircraft APU? Is the APU a mini-jet engine, or some other type of motor? I know its purpose is to provide power when the engines are off, but what kind of motor/engine is used to generate the power?

I assume this differs from one type of aircraft to the other, but for the purposes of narrowing down the responses - I would like to know specifically about Boeing's APUs lets say on the 737NG.

Since the only fuel available on an airliner is kerosene, the APU is a kerosene-powered jet. Using a different and maybe more efficient type of engine would require an independent fuel system, which does not make sense for the small savings possible.

From the 737.org page on APUs:

  There are many different APUs available for the 737. The most common
  is the Garrett GTCP (Gas Turbine Compressor [air] Power unit
  [electrics]) 85-129. This was standard for the series 1/200 but when
  the -300 was introduced it was found that two to three times the
  energy was needed to start the larger CFM56 engines. Garrett produced
  the 85-129[E] which had a stretched compressor, ie the impellers were
  lengthened and the tip diameters increased. When the 737-400 was
  introduced, even more output was required and Garrett produced the
  85-129[H]. This has an Electronic Temperature Control which limits hot
  section temperatures depending upon demand and ambient temperatures.
  By 1989 the 85-129[H] was the most standard APU in all 737 models,
  although there are actually 14 different models of the 85-129 in
  service with 737s.

To answer your question about the 737 NG, it continues:

  Other APUs available are the Garrett GTCP 36-280(B) and the
  Sundstrand APS 2000 on the 3/4/500; and the Allied Signal GTCP 131-9B
  for the NGs. The main difference between them is that the Garrett is
  hydro-mechanical whereas Sundstrand and Allied Signal are FADEC
  controlled.

Be sure to load the 737.org page, it has lots of pictures and data on the APUs.


How late can a landing clearance be given? I regularly fly VFR in an (EASA-) airport where the tower is sometimes rather busy and the frequency full which led a few times to me receiving landing clearances as late as 10-20ft AGL above the threshold.

I was wondering, if (EASA) regulations say anything about when you have to / should perform a go around on approach when you still didn’t get a clearance. I’m not asking about how to deal with those situations when flying, I’m just asking about what’s in the regulations about this.

Short answer: for visual approaches, it is not yet set in EASA regulations, but a draft recommends that the landing clearance be issued somewhere from downwind to short final (dashed line in the diagram below).

The relevant distance I found only applies to radar approaches:

8.9.6.1.7 Clearance to land or any alternative clearance received from the aerodrome controller or, when applicable, the procedural controller should normally be passed to the aircraft before it reaches a distance of 4 km (2 NM) from touchdown.$^1$

As for visual approaches it says:

7.10.1 (...) a landing aircraft will not normally be permitted to cross the runway threshold on its final approach until the preceding departing aircraft has crossed the end of the runway-in-use, or has started a turn, or until all preceding landing aircraft are clear of the runway-in-use.$^2$

Reference: EASA PANS ATM Checklist
$^1$ Transposed from ICAO Doc 4444 as GM3 to AMC2 ATS.TR.160(d)(3)
$^2$ Transposed from ICAO Doc 4444 in various AMCs to ATS.TR.210(c) and ATS.TR.220
A note on EASA regulations: Generally, for air traffic services EASA uses the text of ICAO Doc 4444 as Acceptable Means of Compliance (AMC) to the regulations, hence the transposition here.

A 2017 EASA draft (not yet regulation) discusses where you should ideally receive the landing clearance:

GM5 ATS.TR.210(a)(3) Operation of air traffic control service
DESIGNATED POSITIONS OF AIRCRAFT IN THE AERODROME TRAFFIC AND TAXI CIRCUIT IN RELATION TO AERODROME CONTROL TOWER CLEARANCES
The following positions of aircraft in the traffic and taxi circuits, as shown in Figure 1, are the positions where aircraft normally receive aerodrome control tower clearances. Aircraft should be watched closely as they approach these positions so that proper clearances may be issued without delay. Where practicable, all clearances should be issued without waiting for aircraft to initiate the call.
(...)
— Position 4. Clearance to land is issued here as practicable.
(...)