Technical factors to consider for retrofitting aerial refueling for commericial aircraft What are the factor that need to be taken into account to retrofit and an airliner like an a330 or 777 or maybe even a business jet like a global 5000 to an aerial refuelable (receiving) aircraft. Is it even possible?

Yes, of course this is possible.

The main factor taken into account is pilot training. Mid-air refuelling puts the receiving aircraft into an unstable position which needs to be held manually for the duration of the operation. Without proper training, the refuelling operation will carry a high risk of being unsuccessful. Mechanically the modification is simple: Add some fuel lines, valves and the standard receptacle for the Air Force boom system of refuelling (at the fuel mass needed only the boom system would make sense).

The best example is a Boeing 747-200 B which has been converted as the US presidential transport. The fuel receptacle sits ahead of the cockpit on the upper side of the aircraft's forebody. From the linked site:

  Capable of refueling midair, Air Force One has unlimited range and can carry the President wherever he needs to travel.

modified Boeing 747-200 being refuelled by a KC-135 (picture source)

However, this capability has never been used with any US president on board and is likely to be deleted from the next version of the plane. From Popular Mechanics:

  As part of the effort to cut costs by $1 billion, aerial refueling was cut from the program as well, as reported by Defense One earlier this month. Proponents of the cut argue that aerial refueling is not necessary considering no president has ever used the capability, not even George W. Bush who loitered over the Gulf of Mexico in Air Force One for eight hours after the 9/11 attacks. Opponents of removing mid-air refueling say that the ability to take on fuel and fly for long periods of time, even days, is vital to ensure the government can continue operating in a crisis, including nuclear war.


Is there any emergency situation in which jet engines would not be shut down before passenger evacuation of a transport aircraft? A comment to this answer discusses the possibility of evacuating passengers risking ingestion into the engines if evacuating over the leading edge of the wing. That particular question discusses the Boeing 737. For example:

  "I always thought that the reason to go off the back of the wing was to avoid getting sucked into an engine."

and

  "I'd imagine on a land landing, the leading edge could bring a passenger dangerously close to being ingested, should the engines be rotating.."

However, I really can't see any valid situation that calls for the following sequence of events:

Emergency landing (either on land or on water)
Keep engines running
Begin evacuation of aircraft
Shut off engines (during or after evacuation)

Instead, the sequence of events would seem to be:

Emergency landing (either on land or on water)
Shut off engines
Begin evacuation of aircraft

in which case some unlucky individual might possibly hit (come into contact with) some external or exposed part of the engine or engine pylon, but I have a really hard time seeing how anything could be ingested into the engine at that point.

For the purposes of this question, I suppose "engine running" can be interpreted as "sufficient intake airflow for large foreign object ingestion to be a concern".

Is there any valid situation where post-emergency-landing evacuation would begin while the engines are still running? If there is, then please describe at least one situation which would call for that and describe why such a course of action would be necessary in that situation as opposed to waiting for the engine front intake fans to spin down.

It is possible for the engine to not respond to shutdown sequence, so you'd have to get the passengers off before dealing with the rogue engine.

In the Qantas Flight 32 one engine had an un-contained turbine failure in engine No. 2 leaving them unable to shutdown engine No. 1. This was due to a piece of debris severing all communication to the engine, essentially leaving it out of control and running.

This in turn made it impossible for the crew to activate any safety mechanisms for the engine. It was eventually shutdown by dousing it until flameout.

Report by Australian Transport Safety Bureau

Wikipedia Article on Qantas Flight 32

It should be noted that in this specific case they didn't evacuate immediately due to a fuel leakage and the overheated brakes, though when they did evacuate engine No. 1 was still running.

Another situation where immediate evacuation may be preferable is if the aircraft had a cabin fire, meaning the highest priority would be cabin evacuation, which could potentially happen simultaneously to the crew attempting engine shutdown.


Where are the microphones for the black box located in the cockpit? All modern commercial airliners have a CVR (Cockpit Voice Recorder) on-board to record what the pilots are saying during the duration for a flight. I feel that the location of the microphones is important because they should be in a place that can easily pick up the cockpit conversations but should also be discreet enough to avoid accidental damage or even intentional sabotage by hijackers/suicidal pilots.

So where are the recording devices or microphones located in the cockpit for this?

Moreover:

Is there more than one microphone in the cockpit to provide stereo sound?
If so, do investigators listen to the recording from each microphone?
Are there any pictures of these microphones in the cockpit?

The headsets worn by the pilots have a microphone arm. These audio channels are split and routed to the black box.

Additionally, there is at least one microphone embedded in the cockpit, usually overhead.

The black box can support recording of up to 4 audio channels, so each channel can be examined separately.

Since the headsets and overhead microphone are inside the cockpit, stereo audio is available.

Can't find any pictures for you, sorry!

Seethis sources:

Avstop

FAA (pdf)


What aircraft would have these tail numbers? Last night I was looking at a flight radar on my phone, and I saw two blips flying close to each other over Camden, NJ. They were heading northeast at around 250 knots, and the only information displayed was their registrations, listed as 1678c37 and 1678c38. A google search of these displayed no results. Are these military or other special aircraft?

I'm convinced this numbers were fligtradar-internal identifiers, nothing concerning the flights themselves. The following is not an answer, just what I know about flightradar data records and where to find data like yours.

The flightradar website on a computer updates its data by requesting this url, which contains coordinate bounds, filter settings and so on:

https://data-live.flightradar24.com/zones/fcgi/feed.js?bounds=40.19,39.78,-76.26,-74.03&faa=1&mlat=1&flarm=1&adsb=1&gnd=1&air=1&vehicles=1&estimated=1&maxage=7200&gliders=1&stats=1

I guess the mobile app is not different in this point.
The answer from the server is a JSON object like this:

{"full_count":14127,"version":4,
"b2fd160":["AD3C6B",39.9674,-75.9941,230,34000,368,"1306","T-MLAT2","MD88","N952DL",1475422448,"BDL","ATL","DL2457",0,0,"DAL2457",0],
"b2fe181":["A9FF54",39.9429,-75.9208,273,16860,378,"2347","T-MLAT2","B737","N743SW",1475422445,"PHL","PHX","WN601",0,1600,"SWA601",0],
"b2fc0bf":["",40.0910,-75.8714,230,39999,368,"1361","T-MLAT2","GLID","",1475422448,"","","",0,0,"GLID",0],
"b2fb3da":["A1A8DA",40.0949,-75.8623,98,8700,304,"3553","F-KPNE1","A320","N206FR",1475422446,"MKE","PHL","F91052",0,-896,"FFT1052",0]
...,
"stats":{"total":{"ads-":8655,"mlat":2916,"faa":1647,"flarm":346,"estimated":456},"visible":{"ads-b":6,"mlat":11,"faa":3,"flarm":0,"estimated":0}}
}

There is one line per aircraft, starting with a 7-digit, lowercase hex number, followed by any information about the flight in square brackets. (You can easily identify position, course, speed, registration, aircraft type and so on.)
From the structure of the file and from the fact that you can observe many subsequent hex numbers when you collect lots of data, it seems the first number is a flightradar-internal identifier, acting as counter. Whenever a new flight is detected, it gets the next number.

Within the square brackets, the first number seems to be the unique 6-digit hexadecimal (=24-bit) aircraft ID @JScarry mentioned (and the third entry, a glider, doesn't have one). But more interesting is that all data here is uppercase. (And according to this site, text messages from the aircraft like flight ID doesn't have upper/lower case)

Now, you have two subsequent, lowercase 7-digit hex numbers. This really looks like the flightradar-internal ID. So, maybe flighradar had a glitch, or it had absolutely no further information about that flights, and displayed the internal ID instead. What doesn't fit is the range, right now the numbers are about 164.000 (decimal) ahead. (EDIT: It can fit, they record 140.000-175.000 flights per day)

One can also retrieve data about flights with a certain internal ID from flightradar, but with your numbers, I get an empty record.

Yet, I think it was an internal ID, and you won't get the answer outside of flightradar.


Where can I find numeric maps of aerodromes? I desperately need a map of an airport aerodrome like the ones used for tracking the movements of aircraft similar to the picture below and I don't know where I can find these ones :

Airport Diagrams such as this one of KPNE

are published here on the FAA website as well as in in the airport facilities directory. These are up to date and considered legal for navigation as far as I know. If you are looking for them in another type of format that may be tough, you can try reaching out to the specific airports or the FAA directly.


How does one determine the freestream and ultimate slipstream velocities to estimate thrust? The task before me is estimating the thrust of a propulsion system (a ducted fan) using this equation for thrust (Eq. 2.1.1)1:

$$T = (mass\; flow\; rate)\;(slipstream\; velocity - freestream\; velocity) $$

I know what the ideal inlet and exit velocities of the system are, but how does one determine the freestream and slipsteam velocities so that estimated thrust may be calculated?

1 Warren F. Phillips, Mechanics Of Flight Second Edition, John Wiley & Sons, Inc., Hoboken, New Jersey, 2010, p.153

The free stream velocity can be measured with a calibrated air data system. This uses a pitot tube somewhere at the front, the readings of which have been compared to known speeds in previous flights. The difference between the total pressure and the static pressure gives the dynamic pressure which can be translated into the desired speed.

The speed in the slipstream must be measured across the full cross section to ensure that the full speed profile is known so the slipstream speed used for thrust calculation really is the mean of all the speeds in the slipstream. This is done by measuring the total pressure at several locations, for example by using a moveable rake.

Combined temperature and pressure rake (picture source)


Is it possible for a pressure loss in the cockpit to not extend to the cabin? I have done research into the question of pressure differences between the cabin and cockpit and the theoretical answer I receive the most is that the pressure difference would equalize almost instantly, as cockpit doors are not capable of an airtight seal — and it makes sense, but I recently came across an incident that happened a couple years ago: Sichuan Flight 8633.
On that flight, the windshield actually exploded, and based on the passenger recordings, the cabin seemed a little messy from objects flying around, but they could still hold onto their phones and the flight attendants were able to stand up.
The only comment I could find on that matter had to do with insulation and sealing that protected the passengers from the low temperature and pressure loss. So with that information in mind, is it possible for a cockpit to experience extreme loss of pressure while the cabin suffers minor loss of pressure as on Flight 8633 (an A319)?

The internal walls in an aircraft are not designed to withstand any significant pressure difference. Since the accidents of American Airlines flight 96 and Turkish Airlines Flight 981 where explosive decompression in the cargo hold caused the passenger cabin floor to partially collapse and damage the control cables running below it, the internal walls and floors are intentionally designed so that the pressure has a way to equalize without causing damage to any of them (with enough openings or loosely fitted panels that will blow out if needed). Therefore it is not possible for pressure loss in cockpit not to extend to the cabin, or the cargo hold.
The information I found about Sichuan Flight 8633 only says the passengers were not exposed to cold, nothing about pressure. During decompression, the air rushing out is not doing much work, so it does not lose much energy, and therefore only cools down a bit. What is going on is not an isentropic expansion, but something closer to free expansion. The air still has to do some work to push the outside air out of its way, but not as much as if it was expanded gradually from the 8,000 ft cabin altitude (in which case it would get down to similar temperature as outside).
The only reason for exposure to cold would be if the cold outside air was rushing into the cabin. Which the wall between the cabin and cockpit minimized, plus the engines were still running and supplying warm air.


Why battery voltage is lower than system/alternator voltage I’m a noob in electricity so pardon for my ignorance. Why the battery voltage is always lower than whole system and alternator voltage (considering light aircraft electrical system). E.g. In Cessna 150 system voltage is 14 V and battery voltage is 12 V, in C152 system and alternator voltage is 28 V and battery voltage is 24 V.

This is more of an Electrical Engineering question than Aviation, indeed the exact same thing can be asked about any automobile.
Both of the figures that you quote are 'nominal': The battery cannot be expected to put out a much higher voltage than 12v, so in reality, all systems will work fine down to about 10volts or so, though 'normal' voltage will be 12.5v for a reasonably new, modern battery in good condition.
Conversely, the battery itself requires a significantly higher voltage to charge itself, so the alternator needs to put out 13 to 14 volts, which gets rounded off to 14v for simplicity when talking "in general".
Nearly forgot - for some heavy duty systems, a 12v system is insufficient, so the battery is simply doubled up, so 12v nominal becomes 24 volt, etc., but with the same tolerances.


What is this strut in biplane rigging, attached only to wires, not bearing any load? A few biplanes like the Stearman have a strut parallel to the fuselage, halfway along the rigging's landing wires and flying wires, not fastened to the airframe, not bearing any obvious load.  One on each side.  What are they for?  What are they called?
I'd guess that because some of the Stearman's wires are doubled (also unusual?), the strut prevents them from banging into each other and chafing.  But that seems unlikely because their tension is 800 to 1400 pounds, according to page 24 of the Dec. 2007 issue of Vintage Airplane (p. 26 of the pdf).  Even if a maneuver temporarily halved that tension, deflecting one of those by two inches to hit its twin would take tons of force.

(image source: Wikimedia)

It's just a stick set between the flying and landing wires (the "wires" are actually solid stainless steel rods with an almond cross section for streamlining - they are VERY expensive).  Normally they are made from wooden dowel with notches for the wires to fit, retained in the notches by wraps of lockwire, or on fancier biplanes they may be made from aluminum tube with a bullet nose and pointed tail.
They are usually called "wire stays". Their main function is to stop the wires from vibrating in the airflow (they're more or less metal vocal cords), which can create a lot of noise (that's the traditional diving airplane sound effect from the movies, as you can hear hear here, at 1:50:30, in Hell's Angels, one of the earliest sound movies with airplanes). The noise is from the "Wind in the Wires" (the title of a book by WWI pilot Duncan Grinnell-Milne). More importantly, the vibration can also induce fatigue cracking of the streamlined rods over the long term. Linking them together changes the natural frequency of the wires to something much higher than an individual wire, and stops them from vibrating in the airplane's speed range.


Is it always required to calculate the fuel for an IFR alternate? I was asked to plan a cross country flight from KTMB (Miami Executive Airport) to KTPA (Tampa International Airport). After doing all the planning, I realized I needed to calculate the fuel for an alternate airport.

According to 14 CFR 91.167, fuel is required from departing airport to intended destination airport, plus from intended destination airport to alternate airport, and another 45 minutes of flying at normal cruising speed.

In 1-2-3, if weather forecasts tell that 1 hour before and 1 hour after the ETA, the ceilings would be less than 2,000 feet and less than 3 statute miles visibility, I need to file an alternate airport.

But if the forecasts tell that at KTPA, the weather conditions will be better than that, would I still be required to calculate the fuel for an alternate?

If the conditions are worse than that, then how would I calculate the fuel to my alternate, which I chose to be KSRQ (Sarasota–Bradenton International Airport). Do I need to do again the SID at KTPA, then enroute and then STAR and approach at KSRQ, or just a direct flight?

You only need an alternate if a) the weather is below the minimums you mentioned, or b) your destination has no instrument approach. That's in both 91.167 (IFR fuel requirements) and 91.169 (IFR flight plan requirements), e.g.:

  §91.167   Fuel requirements for flight in IFR conditions.

  (a) No person may operate a civil aircraft in IFR conditions unless it
  carries enough fuel (considering weather reports and forecasts and
  weather conditions) to—

  [...]

  (2) Except as provided in paragraph (b) of this section, fly from that
  airport to the alternate airport; and

  [...]

  (b) Paragraph (a)(2) of this section does not apply if:

  [...]

  (2) Appropriate weather reports or weather forecasts, or a combination
  of them, indicate the following:

  (i) For aircraft other than helicopters. For at least 1 hour before
  and for 1 hour after the estimated time of arrival, the ceiling will
  be at least 2,000 feet above the airport elevation and the visibility
  will be at least 3 statute miles.

As for how to calculate the fuel requirement to your alternate, I would just plan a direct route (or whatever you need to avoid restricted airspace etc.) and calculate your regular cruise fuel requirement. I don't see any point in trying to anticipate in detail what would happen if you actually have to divert because you just can't know that anyway.

IFR Magazine has a nice article on planning alternates that might help you with some of the practical details.


Can a commercial airliner be used for military purposes? Is it possible that in case of some very serious emergency, a commercial airliner such as the B777F could be used for dropping bombs or to serve some other fighting purpose?
 I am simply asking about this from a technical standpoint.

Retrofitting is (as the comments to your post have already stated) rather difficult and unusual. In addition, the quality of service from such an aircraft you could expect to get would most probably not be great. Analogy: Try changing your minibus for 9 people into minivan for freight and industrial work.

It is also worth mentioning that the difference in operation is substantial between bombers and commercial jets. You would be better off using something that is not that complicated, like a Cessna Caravan for instance.

I think that energy, time and money would be better spent on building more dedicated aircraft. Changing the commercial ones is also not trivial and will require engineered changes.

It is however fully possible to design a military derivative of a commercial jet. The Boeing P-8 Poseidon is an example of this, being based off the Boeing 737 with the necessary modifications.

The armament is also fairly extensive:

  5 internal and 6 external stations for AGM-84H/K SLAM-ER, AGM-84 Harpoon, Mark 54 torpedo, missiles, mines, torpedoes, bombs, and a High Altitude Anti-Submarine Warfare Weapon system[


Why are podded engines preferred over engines fitted inside the fuselage or wing? Given the fact that podded engines on the wings of airplanes cause much drag (and thereby contribute to a lot of loss of efficiency), why do airliners still prefer podded turbojet engines over turbojet engines fitted inside the fuselage (or inside the wing) ?
Edit
This question is not regarding "What is the role of Pylons in a podded jet engine", but this is about "Why podded engines in the first place?"

Most important factor affecting drag is frontal area. Almost all frontal area of the engine pod is the intake and it has to have the size it does to collect the air the engine needs. So there is not so much drag to be saved.

Beside that, embedding the engine in wing roots like De Havilland Comet did has many disadvantages, most of which also apply to the central engine of three-engined jets (B727, DC-10):

The wing root carries the weight of the aircraft, so weakening it by embedding the engine is design and construction complication.
Access for maintenance is difficult. Engines need a lot of maintenance and sometimes need to be replaced.
Uncontained failure is more dangerous (see UA232).
There is not much structure to damp vibration, so it is awfully noisy.
And last but not least, modern high-bypass turbofans are huge. They would not fit in the wing anyway.

And reasons for not attaching the engines directly to the fuselage or wing are already mentined in Why do we use pylons to mount the engines on jetliners?. Mainly, the inlet needs:

Free space around it from which it can draw air at slow speed.
Free space around it to which it can spill the excess air at high speed.

And the engines mounted forward of wing actually improve the distribution of cross-sectional area according to the Whitcomb area rule and they dampen flutter, so the wing can be slightly less stiff and thus slightly lighter.


What is the plane on the Home Bush Bay Funsaver EP cover? Found this CD I had in 1997 and just bought it again as it got lost.

There is an aircraft which I cannot identify:

the sticker on the propeller leads to a propeller manifacturer called Avia
guess its a double engine plane with retractable landing gears
the picture on the CDs are invertet so I inverted the colors
guess it's a combustion engine, not a jet
the vent slots are pretty similar to Zlin planes but could not find a model which fits to the pictures

Solved: it's an Let L-200 Morava, thanks for your answers!

I submit the Let L-200 Morava.

https://en.wikipedia.org/wiki/Let_L-200_Morava

Engine Nacelles:

Nacelles and Nose Gear:

Nose gear Higher resolution:


Why do jet engines take a long time to throttle down? Apparently jet engines can take several seconds, up to ten or fifteen seconds, to go from full power to idle.

Why is this? Can't a simple fuel valve shut off fuel flow? Or reduce it to whatever flow rate corresponds to idle? Either of these, if done with a valve, should happen almost instantly as far as I can tell.

This would surely cut thrust, regardless if the engine still spins for a while. Is there something dangerous about this idea? To me it seems like a fuel valve can close and open again as many times as it wants.

Note: I'm interested in turbojets and turbofans. And I care about throttling down only.

The simple answer is rotational inertia, once you get a heavy mass spinning fast that heavy mass will have a tendency to continue spinning fast unless something else is acted upon the object. Piston engines have a great deal of friction between the piston walls and pistons (how they hold the explosion in) this helps them slow down faster than a jet in which the turbine is made to easily handle this thus the joints are very well made and very free moving. While cutting fuel will keep the engine from continuing to generate thrust the turbine will continue to spin until a force causes it to stop (drag and friction really).


Why do some A320s have double-bogie landing gear? I believe this is actually a rare sighting, but why do some A320s such as the VT-ESD have double-bogie landing gear? Does Airbus have a specific reason for making such A320s?

Update: Found an image in the former Indian Airlines livery,

Air India is the only carrier with that kind of landing gear in the A320 due to India's low pavement classification number back when those A320s were ordered. In other words, more tires distribute the load over a larger area.


Why did narrowbody jetliners take so long to switch over to high-bypass engines? High-bypass turbofans were introduced into the airliner market around 1970, when the first widebody jetliners were released (the 747 was first, followed in rapid succession by the DC-10, L-1011, and A300); however, narrowbodies continued to rely on low-bypass turbofans (primarily the Pratt & Whitney JT8D) for considerably longer.  To the best of my knowledge, the first narrowbody powered by high-bypass engines was the DC-8-70 (a re-engining of the DC-8-60), which entered service in 1982; the first narrowbody built with high-bypass turbofans, the 757, did not enter service until 1983.  As for the other narrowbodies of the time:

707, 720, 1-11, F28: No high-bypass version ever became available (although high-bypass versions of the 707 and 1-11 were proposed, they never entered production).
727: The only 727s that ever flew with high-bypass engines were four 727-100s reengined and renamed 727-100QFs in 1992.
737: The first high-bypass version, the 737-300, was only introduced in 1984.
DC-9: Stubbornly held onto the JT8D into the mid-1990s, only switching to high-bypass engines with the DC-9-90.

What kept the narrowbodies from immediately, or almost immediately, taking advantage of the greater power and lesser fuel consumption and noise of high-bypass turbofans?

Early high-bypass engines were expensive and unreliable.

The effort in developing new technology and designs, plus the cost of building a larger fan add cost. Then all of the new technology is inherently less reliable than existing proven designs.

The JT9D was notoriously unreliable, causing major problems in the development of the 747. Development problems and spiraling costs from the RB211 bankrupted Rolls-Royce, had huge failure rates, nearly causing an accident (Eastern Airlines Flight 855), and ultimately killing the L1011. CF6 fan disk failures caused National Airlines 27, sucking a passenger out the window, and the fatal United Sioux City crash.

Even what we think of as the most reliable engine today, the CFM56, when new had a fan failure leading to a fatal crash (Kegsworth), combined with water ingestion issues that nearly lead to a crash (TACA 110).

When you have such compromised technology, you narrow it in the place that makes sense. High bypass engines brought high efficiency, reducing fuel burn. They also had more thrust, allowing heavier planes, carrying more fuel. Both advantages combine to enable long-haul direct flights which passengers like. These are flown with widebodies, so naturally these engines were used in widebodies.

Short-haul narrowbodies carry less fuel per flight, and can refuel frequently, so there wasn't an advantage here. Only as the compromises with high-bypass engines were solved, then did the technology trickle down.

You see a similar thing today with carbon fiber composite fuselages. They're expensive to build, expensive to fix, and there is uncertainty over long-term costs. But the weight savings opens up ultra-long-haul flights, hence the A350 and 787.


Is it safe to roll an airplane that isn't approved for it? I have heard of pilots rolling airplanes that aren't approved for it (Cessna 172, Learjets, etc.), and other than the obvious legal issues, are there any mechanical or safety reasons to avoid it?

DISCLAIMER
I do not advocate doing anything (like this) that is not legal, but am looking more for additional reasons that I can use to dissuade people from doing this when they say that it isn't hurting anyone or something along those lines.

There are a lot of good reasons not to roll such an airplane.

If the plane has gyroscopic instruments, you might tumble them (cause the spinning gyro to hit the inside of the instrument).  This can be expensive.

You might easily over-stress the air frame.  Normal category light aircraft are rated to -1.5 to +3.8Gs.  (That's for a new aircraft)  A botched roll can easily hit 4.5 or higher.

If you over stress the air frame, you might just put a lot of very expensive "wrinkles" in the skin that would be very hard to explain to the FBO, your boss, or the insurance company.  Trashing the gyros would be cheaper.
If you're not lucky, the wings fold up and you fall out of the sky.  It's a stupid way to die.

Non-aerobatic aircraft typically have limited elevator authority; once upside down, you might find it very difficult to keep the nose pushed up high enough to keep the roll going.  Turning a botched roll into a "split-S" is one of the worst "recovery" mistakes you can make, and you're setting yourself up for it.

Non-aerobatic aircraft often have gravity-feed fuel systems.  A little bit of 0 or negative "G" and it will get very very quiet in the plane.  Some people consider this silence detrimental to the continued safety of the flight.

Non-aerobatic aircraft rarely have inverted oil systems.  As the engine gets quiet, it also loses most of its lubrication.  Bare metal on metal friction can be detrimental to achieving TBO.

Having said all that, in the hands of an expert, it is technically possible to barrel roll most aircraft.
A good way to tell if you're an expert is to call your insurance company and tell them exactly what you plan to do.  If they'll quote you affordable coverage, you might be an expert.
Obligatory links because if I don't include them someone else will:

Tex Johnson rolling a 707.  I'm pretty sure he'd never get away with this today.
Bob Hoover pouring iced tea.  Bob Hoover is beyond expert.  Way, way, beyond expert.

If you want to roll an airplane, contact your local aerobatic club.  In the US and some countries, it's the [International Aerobatic Club][5].  Get some competent dual instruction in a suitably rated airplane.


Will flying cars fall under aviation regulations? As science and engineering keep inventing new technologies like flying cars http://www.iflscience.com/technology/are-flying-cars-finally-becoming-reality, air space may become heavily overcrowded. Will flying cars be considered "aviation" or are there (will there be) some rules like flying with particular altitude will be considered as aviation? (As the concept is becoming reality soon or later it has to be decided.)

Flying cars will need to be regulated by both the FAA and the DOT as per current laws here in the US. For what its worth flying cars are really more like road capable airplanes. When the car is airborne it will be subject to the regulations set fourth by the FAA for the airspaces it passes through and maneuvers it makes. When the car is on the road it will be subject to vehicular laws that any other car would see. That being said there is room for change here and who knows what rules may be passed in the future. There is also some grey area around things like landing in a parking lot, folding up your wings and driving away as well as the reverse case.

The rules that currently govern aviation are more than capable of handling flying cars, even if they start taking off from peoples driveways. The larger issue is licensing the pilots. A drivers license is pretty easy to come by here in the states while a PPL or sport pilots license takes quite a bit of time. Everyone that currently would want a flying car would need both a drivers license and a pilots license of some form.

As far as I know the FAA makes the rules for any and all altitudes. While some airspaces (class G) may be unregulated they are still considered from the ground up. There is no minimum altitude at which FAA regulations don't apply and its far from a free for all in the skys the way it is on the roads in a manner of speaking.

Flying cars could potentially cause an increase in air traffic however the advantage of a plane (over driving) is generally speed. Until someone can build a car that can do 80MPH consistently on the road and a formidable 130Kts (and thats the slow end of planes) through the air the use case is pretty small.

One of the biggest preventers in the whole flying car situation is the engine its self. Car engines fit quite a different role than aircraft engines. The similarities end basically at the fact they are both piston engines. Some car engines have been put in planes (Mooney/Porsche PFM 3200) and in the end they are generally not great planes. You can find a full discussion on this here. You also need to keep in mind that anyone who will be fixing these vehicles will need to be an A&P licensed mechanic.

There are a few companies with some cool animations of future products and even a few test rigs that have been built but to date the engineering is just not really there. Chances are it will be some time before flying cars are even on the road let alone creating major air traffic issues. For the 279,000 a Terrafugia will cost you, you could buy a Used Piper Arrow (in great shape) and a Porsche and still have 79,000 left over for a hanger to keep them in...


What does it mean when an aircraft engine is de-paired? What does it mean when an aircraft engine is de-paired? e.g. the PW1000g engines being de-paired because of issues in the LPT or the Rolls Royce Trent 1000 engines due to excessive corrosion on some of the turbine blades?

De-pairing means literally braking up pairs. In the case in question, it means that if an aircraft is equipped with engines of a certain specific type, one of the engines has to be replaced with a version that has been upgraded.

The reason for the de-pairing is to mitigate the risk of a dual engine failure: Having two engines that are both affected by the same issue considerably increases the risk of both engines failing on the same flight. At least RR Trent 1000 and P&W 1100G have been issued a de-pairing AD by EASA.

Article on RR Trent 1000 de-pairing AD on Airlineratings.com

Article on P&W 1100G de-pairing AD on samchui.com


Why not a second airbridge at the back? Airbridges slow boarding and disembarking because (normally) there's only one door in use. But... why?

Now the most obvious reason would be that it's very easy to have the aircraft pull forward until its door is roughly in line with the bridge, while it's not possible to do that at the back as well, given the differences in fuselage length.

Sure, but I suspect that 90% of all aircraft could be serviced from a set of two possible bridge locations and the existing bridge movement range.

And then one notes that the wing would be an issue, but that's only true if the bridge is in the air. One could just as easily build a "bridge" on the surface, or even underground (I saw a cross-section of the ramp at Pearson, it was like swiss cheese).

Of course that would mean walking down stairs, which is one of the reasons you use a bridge in the first place, but it would mean that anyone with normal capabilities could use it without exiting outside (did that at Pearson too, in the middle of winter).

Such a system would have the added advantage of allowing the Spanish Solution, with three waves, the middle being the cleaning crew.

It was tested at Denver airport by United for a few years ultimately the project was scraped due to jet bridge malfunction that lead to wing damage.

  The deciding factor arose out of an incident where one of the bridges
  malfunctioned and damaged the wing of Boeing 757, as ANN reported in
  March. United removed the section that failed, and stopped using the
  over-the-wing part on the other four bridges.

(source)

Side parked dual jet bridge terminals did exist in the early jet age but don't appear to be a great use of space and I cant find any evidence they allowed faster board speeds back then. Taxi in and out would always require quite a bit of bridge retraction and a careful tight turn.

(source)

In a lot of cases the rear of the aircraft is used to load on the new food and remove old garbage blocking the rear with exiting and entering passengers could get in the way of the operations during fast turn arounds.

(source)

As you note you could always go under the wing and come back up. In areas where inclement weather is common you would need the ability to keep the whole jetway enclosed. This could get in the way of the wing unless it was either very low or underground, you would then need some form of retractable stair on the end. All in all it could be built but thats a lot of complexity to add into an airport ramp. This means down time for the gate and money lost for the airport. Depending on arrangement the tunnel may also need to be strong enough to support what ever is above it (vehicles, aircraft etc).


How does pregnancy affect airline pilots operating under FAA regulations? Female airline pilots have an area of medical concern that male pilots don't deal with: reproductive issues. If a female airline pilot operating at an air carrier in the United States of America under the Federal Aviation Administration (FAA) were to become pregnant, how would this affect her standing with a first class medical and in general with operations at most airlines?

As long as the pilot is having a first class medical, her pregnancy should have no effect on the operations, at least legally, though the regulations differ from country to country.

I'm not aware of any FAA regulations that prohibit pilot ing during pregnancy. The closest it comes is in 14 CFR § 61.53 - Prohibition on operations during medical deficiency, which says (noting that pregnancy is not a medical deficiency in any way and the regulation is taken here in the widest sense) that:

(a) Operations that require a medical certificate. Except as provided for in paragraph (b) of this section, no person who holds a medical certificate issued under part 67 of this chapter may act as pilot in command, or in any other capacity as a required pilot flight crewmember, while that person:
(1) Knows or has reason to know of any medical condition that would make the person unable to meet the requirements for the medical certificate necessary for the pilot operation

As long as the pilot feels that she is medically fit and has a valid medical certificate, they can't be legally prevented from flying the aircraft.

In case of other regulattions (like EASA), pregnant women are not allowed to pilot after 26 weeks of pregnance. For example, UK Aviation Authority says:

(c) Pregnancy
(1) In the case of pregnancy, if the AeMC or AME considers that the licence holder is fit to exercise her privileges, he/she shall limit the validity period of the medical certificate to the end of the 26th week of gestation.  After this point, the certificate shall be suspended.  The suspension shall be lifted after full recovery following the end of the pregnancy.
(2) Holders of class 1 medical certificates shall only exercise the privileges of their licences until the 26th week of gestation with an OML.

There are a number of medical issues that the pilot should be aware of while pregnant, so that appropriate measures could be taken, like,

Ability to move the controls to their full extent.

Ability to wear seat belts.

Effect of high altitude operation on the foetus
among others. The airline policy will vary and they have to consider a number of other conditions- for example, the ability of flight crew to egress during a crash etc.


Why is the UH-60 tail rotor canted? The Sikorsky UH-60 (S-70) has a tail rotor that is canted 20 degrees upwards. Why is that?

Picture source

John K and Koyovis's answers are both correct. However, as a former pilot of the UH-60 and a mechanical engineer here is a simpler version.

A helicopter must be balanced. If the front is much heavier than the tail, then it can't fly safely as the nose is too low. If the tail it too heavy, then the same. The point of balance is called the center of gravity.

The tail boom on a helicopter is very long. If you were to add one pound to the tail vs one pound to the nose, the pound on the tail would more impact due to the length of the tail boom. In engineering this is called the "moment arm" By canting the tail boom, the tail rotor actually lifts the tail boom. There isn't that much lift, but since the tail boom is so long it has a pronounced effect. This gives the aircrew more latitude in loading the helicopter. With the extra lift provided by the tail rotor, we can put more load (troops, fuel, etc.) behind the rotor mast and still keep the center of gravity in acceptable limits.


How do I translate this propeller start procedure into English? I'm translating a documentary from Hungarian to English. There is a scene where the pilot of an aeroplane with a propeller is preparing for take-off.

He says (seemingly into a 2-way radio) two short sentences, literally: "Propeller pushing. Propeller free." Could anybody help me with info about what an English-speaking pilot would say in this situation. A million thanks in advance!

If the engine is already started, and if this is a turboprop with a constant speed propeller, it is most likely that the pilot is performing a pitch control check.  In this case the pilot would move the throttle into Beta, or reverse, which would momentarily cause the propeller to "push".  After this he would come back to idle, where if the propeller control lever was set to fine pitch or max RPM, the prop would spin "free".  The actual procedure and intercom voice calls will vary by aircraft and operator.

This answer presumes that he is not yelling out a window, or transmitting with aircraft callsign to a ground controller.  A video clip showing where he is on the ground, whether the prop is turning, and what his hands are doing at the time of the calls would confirm this.

If it is difficult to post a clip here, just watch what his right hand is doing:  If he appears to disengage a latch and pull the main power lever backwards, (you may hear an audible change in the engine sound as the propeller reverses pitch) and declares “propeller pushing”, then moves the lever back forward again and declares “propeller free” this would be pretty strong confirmation of my interpretation.

If that is the case, I might suggest a literal translation as you described in the question.  If you know the exact make and model of aircraft you could maybe narrow down what an English speaking pilot would say instead, but the literal translation wouldn’t necessarily be wrong either.


What are these parts on Super Etendard? I'm currently working on modelling a Super Etendard and just have a few questions on what are some small parts.

First of all, any ideas what this tube thing is on the right side of the exhaust? My best guess is a fuel dump nozzle but seems like a bit of an odd place?

Next, any ideas what this tube thing is, seems to have a hole in it so maybe some kinda sensor intake or something?

Will most likely have more questions as time goes on but would be good to know what are these things?

EDIT: Also any idea what these bits might be under the wings?

The two objects on the wings are the hooks for the launch bridle, which attaches the aircraft to the catapult shuttle for launching the plane from a carrier deck.


In an emergency situation just after take off, is fuel dumping useful? Imagine a hypothetical scenario where a jet heavily loaded with fuel experiences more than one engine failures after $V_{1}$. Then I suppose that losing some weight would be beneficial since the airplane is not designed to sustain climb with such limited thrust. In such a case a) how much would dumping fuel help in this emergency (i.e. is the rate of dumping fast enough?) and b) could the captain proceed to do it without ATC authorization if he/she considers it necessary?

You would not attempt this. Aircraft are certified to climb with engines inoperative after V1, they would just climb to a holding altitude and run the checklist. They would rather not attempt to any cruise altitude. Running the checklist you would determine if you are above the maximum landing weight (MLW) and decide to burn or if able, to dump fuel.

Dumping fuel during the takeoff/rotation phase is not advisable to be honest, as you would leave a contaminated runway behind. Sure, most of the fuel will evaporate, but there will be a contamination nonetheless.

I will quote Nate Eldredge's comment shamelessly for another item to consider:

  According to How is fuel dumped in aircraft? a 747 can dump 6000 pounds of fuel per minute. Given that (from what I found) it typically carries at least 200,000 pounds, and has an MTOW of over 800,000 pounds, it seems unlikely you'd dump enough fuel fast enough to make any difference.


What is the reason for the poor low-speed characteristics of sweptback wings? I know there are advantages of swept-back wings delaying shock-wave allowing a aircraft to fly faster. However, what are the disadvantages.
I know one of them is that they have very poor low speed characteristics, however I do not know the reason. Another disadvantage will be on the F-100 Super Sabre Dance, do not understand these either.

Can any kind soul explain the disadvantages?

Disadvantages of wing sweep

Lift curve slope is reduced by the cosine of the quarter chord sweep angle. This means more angle of attack for takeoff, which requires a longer take-off run and a longer landing gear to avoid a tail strike on rotation.
If you rotate the airplane, the tips of backward swept wings come down when the aircraft rotates for take-off. This also might drive the requirement for a longer landing gear.
Bending moments in the wing will become torsion moments when you change the sweep angle. And you will need to change it at least in the wing root where the wing connects to the fuselage. This translates into a heavier structure.
If your sweep angle and aspect ratio both are large enough, the wing will show nasty stall characteristics. The boundary layer is swept towards the tips and causes earlier separation when the wing stalls, and the airplane will pitch up or roll uncontrollably. Wing fences help, but cannot completely remedy this.
Wing sweep causes a yaw-induced rolling moment, so less dihedral is needed. On high wing airplanes this requires to use anhedral. Unfortunately, this rolling moment varies with lift coefficient, so your yaw-induced rolling moment on a swept aircraft is lower than ideal at high speed and higher at low speed.
For flying wings, sweep will let the aircraft center pitch up and down when the wing flexes. This creates a powerful interaction between the fast period mode (which is only moderately damped in flying wings) with the wing bending mode, resulting in flutter.

In short, when having a choice, the clever airplane designer avoids sweep whenever he/she can. But sweeping a wing back is still better than forward sweep.

Low Speed Characteristics

An airfoil initially accelerates the air which flows over its top surface and decelerates it again over its rear part. On swept wings, this acceleration-deceleration only affects the orthogonal speed component, so the speed component in span direction remains unaffected. This is the reason for the higher Mach capability of swept wings, but also causes the air to flow first inwards and then outwards while transversing the wing's upper surface.

On top, friction decelerates the air flowing around a body, such that a layer of decelerated air surrounds each surface of an airplane. The thickness of this boundary layer increases with flow length, and on a swept wing this friction will initially mostly affect the orthogonal flow component. At around mid chord you will find air which has been decelerated mostly in its orthogonal speed component (since this component was so high over the forward part) and now will be subject to more deceleration of the orthogonal component, so that only the spanwise component will be left over the rear part of the boundary layer. Now this boundary layer will only flow off in span direction, such that a massive increase of slow, low-energy air will be collecting towards the tips.

A thick boundary layer will cause early flow separation, so when the angle of attack is increased, the flow at the tips of a backward swept wing will separate first. This will cause lift loss, and since the tips are also the rearward part of the wing, will shift the aerodynamic center forward. This in turn will make the aircraft pitch up, which aggravates the stall condition. If the separation happens asymmetrically, the aircraft will roll in addition to pitching up. In case of the F-100, the tail surfaces were too small to stop the pitch-up, so once the aircraft crossed into the stall region, it would uncontrollably pitch up more and stall completely.

Modern swept-back aircraft have an angle-of-attack limiter which will prevent the aircraft from flying into the stall region. Also, wing fences help to keep the spanwise flow in check, and vortex generators help to energize the flow such that the early flow separation at the wing tips is sufficiently delayed to avoid the uncontrollable pitch-up. The F-100 lacked all those remedies.

Wing fences on a MiG-17 (picture source)

Vortex generators on a Boeing 737 wing (picture source)


Why is this equation for TAS only valid for subsonic flow? I came across the equation for calculating True airspeed (TAS) on Wikipedia:
$$ \text{TAS} = a_0 \sqrt{\frac{5 T}{T_0} \left[ \left( \frac{q_c}{P} + 1 \right)^{2 / 7} - 1 \right]} $$
But this equation is apparently valid for only subsonic flows.
Why is that? Does this have something to do with pressure?

Because you didn't read the text in the Wikipedia page above that equation ;-)
That equation works for subsonic flow only because you have replaced the Mach number of the original TAS formula:
$$ \text{TAS} = a_0 M \sqrt{\frac{T}{T_0}} $$
with the formula of Mach number for subsonic flow:
$$ M = \sqrt{\frac{2}{\gamma - 1} \left[ \left( \frac{q_c}{p} + 1 \right)^\frac{\gamma - 1}{\gamma} - 1 \right]} $$
which exploit the simple form of Bernoulli's formula, working only for incompressible flows, i.e., subsonic flows. Check the Mach number and the Bernoulli formula pages for further details.


Do I need to obtain a student pilot certificate to transition from Glider to Sport Pilot? I am a current Private Pilot Glider, and will soon begin training to obtain my Sport Pilot Licence. My question is about the requirement to obtain a student pilot certificate to solo in the training aircraft. I have heard that it is no longer the normal practice to record the solo endorsement on the student pilot certificate, but instead to record it in the logbook.

With that in mind and the fact that I already hold a Glider licence, do I need to obtain a student pilot certificate?

You can't get another student certificate because as a Private Pilot you don't need one (and can't get one). Rather, you're a Private Pilot adding to your existing certificate.

Private pilots already have sport privileges, but if the LSA is a new category/class for you then you still need an endorsement for it. The requirements are in 14 CFR 61.303 (and see AOPA's guide too). You can check the table yourself, but let's assume you're a Private Pilot and you have no medical but you do have a US driver's license. That means the sixth row in the table applies to you:

You must hold the endorsements required in 61.321 for the LSA's category and class
You must comply with the limitations in 61.315, except 61.315(c)(14) and, if a private pilot or higher, 61.315(c)(7)

61.321 requires a logbook endorsement from an instructor who's trained you in the areas listed in 61.309 and 61.311; a proficiency check from a different instructor; an application to the FAA; and a logbook endorsement from the check instructor. You also need a certain number of hours, depending on the category/class of the LSA; see 61.313.

I assume your glider experience already covers a lot of the knowledge and experience required, but your sport instructor will have to determine exactly what training you still need.

(This appears to be the opposite of this question, by the way.)


Why/How does a "Powerflow" exhaust increase horsepower? I've seen airplanes (typically Cessna 172s) with a "Powerflow" exhaust system and then claim to get several more horsepower, resulting in faster cruise speeds.  How does a Powerflow exhaust work, and why does it increase horsepower?

It has to do with resonance.  Think of a pipe organ - each pipe resonates at a certain frequency, which we hear as a note or tone.  The length of the pipe determines its note/tone/resonance frequency.  Your plane's exhaust system has a certain resonance frequency.

Your plane's engine has a certain note or tone, too.  That is largely determined by engine RPM.  A powerflow exhaust matches the exhaust resonance frequency with the engine's rpm at a typical high cruise setting.

On a micro level, here is what happens.  After a cylinder's power stroke, when the exhaust valve first opens, exhaust floods out into the exhaust system.  Soon the exhaust valve shuts and the inertia of the gasses moving down the exhaust system cause the exhaust gas to continue towards the exit, creating a lower pressure behind it (near the exhaust valve).  If the resonance frequency of the exhaust system matches the rpm, at that point the exhaust valve opens on the next cycle, and the lower pressure area in the exhaust assists in scavenging the exhaust out of the cylinder.  On the subsequent intake stroke, there is less residual pressure in the cylinder and it can "suck in" more fuel/air mixture.  More fuel/air, more power.

Another way to say this is that it takes power for the engine to force the exhaust out of the cylinder and through the exhaust system.  The Powerflow system reduces the power required to do this.


After passing a checkride, can I get the plastic certificate card by visiting the nearest FSDO? As you know, it takes more than 30 days for the plastic certificate card to be delivered. I know that right after passing check-ride, the temporary certificate is given but I need a plastic card to convert US pilot license to my country license. My government does not accept the temporary paper certificate. Is there any way to get a plastic certificate card from the nearest FSDO as fast as possible?

No, sorry. They don’t have the device at the FSDO that would produce a plastic card.

If you want to see the page that shows what date they are currently processing for, click here.

Unfortunately it’s typically around 6-8 weeks.


Why do some aircraft approach the runway with a long detour and others with a short one? I am currently analyzing flight data. For some flights landing at Frankfurt Airport.

As you can see in the graphic, some of the planes fly out about 100km to then fly again towards the runway. Some only fly out for a short distance. How can you explain that?

I assume that after the cruise phase,  the approach phase depends on factors such as traffic volume at the airport (how many want to land at my time (or in my 10min radius)) and take off?) How is the Operating direction at the airport and what kind planes want to land. Since I was told that the "plane
mix" is also relevant, for example 2x MEDIUM aircraft and 3x large.

Are there rules for such behavior? How does the ATC decide here?

As you can see in this question and its answers, whether an aircraft has to go north or south is decided by ATC, as you also mention.

And, as you have correctly heard, the separation is influenced by the kind of aircraft flying in front of you, particularly during landing, as detailed in this answer.

So, in the end, an aircraft might have to fly further out if they have to put more distance between them and the preceding aircraft, or if there are more aircraft in the queue. ATC will decide in base of the currently available runways, the current amount of traffic, and whether any aircraft has declared any kind of emergency.

Note also that the approach paths for the airport are slightly asymmetrical (left side of page 11 and 12 of the pdf respectively), with ~50km on the south west approach, and ~65km on the north east one.


What are the specific number of passengers and conditions required to select HI, NORM, or LOW on the pack flow knob? On the Airbus A320 there is a pack flow knob and you can either select HI(120%), NORM (100%), or LO (80%). You choose which one according to the number of passengers and ambient conditions. Obviously If you have a full flight and it is hot outside you would choose HI. Or if you have very little passengers and it is cold or even raining outside you would select LO. But is there a specific number of passengers when you would select HI or LO, or is there a specific temperature, or both?

From the A320 flight crew operating manual (FCOM):

The selector is kept to NORM in most conditions.

It can be turned to LO:

When the number of passengers is low. 115 passengers is indicative and there are local regulations about the quantity of air which must be delivered per passenger. Operators may have different instructions in their SOP.
When fuel is low for some reason. Using more bleed air increases fuel consumption.
It is also tempting for an operator to reduce fuel and maintenance costs by also reducing air flow. See this thread on PPRuNE.

Air flow can be increased to HI:

Automatically:

When the other pack is turned off.
When APU provides bleed air.

Manually:

When air is too wet due to perspiration and breathing. Dampness increases with the number of passengers.
Air in the aircraft contains smoke.
To intentionally increase tapping of bleed air from the engines, which increases compressor stall margin. This would be desirable while flying in a volcanic ash cloud.

Packs also provide air for pressurization purpose (PACK stands for pressurization and air-conditioning kit). In case of leakage, air flow can be increased. In emergency situations, bleed air can be replaced by ram air (ram air is normally only used for cooling bleed air, but doesn't enter into the pressurized sections of the aircraft).


Should I switch the transponder to STBY or not while changing codes? I´m now reading Bob Gardner’s book “Say again, please” and there is this instruction on page 54:

  Do not turn the transponder function switch to STBY while changing codes.

What is the reason for this? I’m a PPL student and my instructor told me the opposite.

The FAA started advocating not selecting standby for code changes after it was found that more often than one would expect, the transponder doesn't always come back on after standby.  Seems they uncovered a number of switch failures.

I figure that someone decided that for TCAS it was better to have a transponder squawking any code than not squawking.  But that is my own conjecture.

So for quite a few years the guidance has been to not turn to standby when selecting codes.

I have had the folks at Flight Safety lecture me after sim sessions, with pretty much the same story.

So I now teach students to just switch the codes, and not standby the transponder.  And I suggest caution when dialing through "7xxx" although controllers I have talked to say it's not a big deal.

So the idea is to keep the transponder squawking, even though numbers are being changed.  There is continuity in that they will continue to have returns while you are playing with the knobs. And if you ever have a switch failure, it will likely be on the ground.

Addendum: Also, with ADS-B, one is supposed to keep the transponder on at all times, when on the airport surface in a movement area. So I can see that the philosophy of managing the standby position will continue to change.

Also note that Bob Gardner's book was from the mid-1990's and things change. Both the transponder technology, the technology, such as ADS-B, TCAS (which also relies on transponders, as well as processing algorithms, which decide how to display transitioning codes.


What is a 'Wing Loop Fault' on an A320 series Aircraft? I was recently involved in a flight that had issues before take off. The plane was an Airbus 321.

It was explained to me as being a "wing loop fault". The problem was that the ECAM messages were displayed differently each time and were inconsistent. The flight was aborted just before take off (for safety reasons) but the problem was fixed soon after by replacing a part.

Can anyone explain this problem with the wing loop to me in more detail. What could have gone wrong and what was the likely fix.

Also, what maintenance and pre-flight checks should occur on the "wing loop"?

Sorry for any vagueness in my question, I didn't receive much information.

Edits

This was on aircraft G-OMYJ around the 24th August 2013
My route was (EMA) --> (DLM), flight TCX5894. But the fault may have occurred on the previous flight. The details are unfortunately hazy. Is there anyway of me finding the whereabouts of the plane in the days leading up to this incident?

My guess is that there was some circuitry that was playing up. While I'm not sure about 'Wing Loops' specifically, for what I think is a similar example the Airbus A320 series has fire loops in the engines.

There are two fire loops. If I'm right, it's got little thermal sensors along way, which disrupt the current if they get too hot (or if the wire is broken). Logic gates ensure that both loops must be 'high' for the fire warning to go off. If one is not working, it works from a single input.

Assuming both of these were working from the beginning, I think it throws a FIRE DET FAULT warning on the pilot information display if one triggers without setting off the other one. I'd imagine that maintenance either disabled the faulty loop within those allowed by the Minimum Equipment List or by changing the part. If it was quick, it was probably the first, but they're not going to go telling passengers that they disabled safety equipment :)


What makes a jet single pilot certified? Why are some small-ish jets (Embraer Phenom 300, Pilatus PC-24 for example) single-pilot certified? The pilot still has to fly+navigate+communicate. Why would a small jet be more manageable than a bigger jet? Or is it more the case that they would not kill as many people if things go belly up?

According to this blog:

Up until 1977, the FAA required all jets to be operated by two pilots. In ‘77, Cessna was given approval on a single-pilot variant of the Citation I, the Citation I-SP. The aircraft met the 12,500-pound maximum takeoff weight threshold for small aircraft, but that wasn’t the only single-pilot qualification. Cessna also had to convince the FAA that its pilot workload was low enough for one pilot to handle safely.
According to J. Mac McClellan with Flying Mag, in order for an aircraft to qualify for single-pilot certification in the 70s, “you had to have a boom microphone for hands-free communications-somewhat uncommon 30 years ago-and a fully functioning autopilot. There was also the quaint requirement for a transponder ident button to be mounted on the control wheel. In those days, we would ident on almost every controller handoff.”
One of the most important (and obvious) requirements for single-pilot certification of an aircraft is the fact that all gears and controls must be accessible from the left seat. The autopilot must be seamlessly integrated into the airplane’s navigation systems, and it must be functional for every flight operated by one pilot. The aircraft must have hands-free communication, as well. Aside from those concrete requirements, the rest is subjective.
After a series of test flights, the FAA’s test pilots must come to the conclusion that the aircraft is safe for a single pilot to fly. The design of the aircraft’s controls is one of the most important factors, as one pilot must be able to operate the throttle, the yoke, control wheel, and other flight controls easily from the left seat.

So, all of the aircraft's controls must be operable from the left seat, there must be hands-free communication, and an integrated autopilot.
Now, of course, there is also a single-pilot type pilot's certification, which a pilot can obtain to legally fly aircraft which meet all of the requirements above, yet are larger than the 12,500-pound maximum takeoff weight threshold.


How can a 777ER fly from the 9000 ft runway at Bologna (LIPE)? How can a 777ER be operated from the Bologna runway which is only 9000ft?

I recently took the Emirates flight and the aircraft was full. I suppose that it was close to max weight. According to wiki the required runway at max load is 10000ft so what is the trick behind this?

LIPE - OMDB is only around 4,500 KM (2,800 NM) according to Great Circle Mapper, which is nowhere close to the 773ER max range of 14,500 KM (7,830 NM), so one can make an educated guess that the aircraft wasn't at MTOW.


What devices measure EPR & RPM on a turbofan engine? What devices measure EPR & RPM on a turbofan engine?

RPM is measured by a device called a tachometer. In a jet engine often this will be an inductive proximity probe that is measuring a toothed wheel on the shaft.

EPR is measured by comparing two static pressure sensors, one at the inlet and one at the propelling nozzle discharge, and taking the ratio. There are many different types of these. Many common ones will have a flexible membrane or diaphragm of some kind. Under pressure the membrane deflections and then you use some kind of deflection measurement.

These types of sensors are very common in many applications besides just jet engines. A little research on the internet will show you lots of details about how they are constructed and how they work.


How could a light or buzzer on the ground be triggered from an aircraft? I work at a Skydiving company in New Zealand and we are looking for a light switch or buzzer that is triggered in the plane and can effectively alert the staff on the ground that the plane is 3 minutes away from dropping the Parachutes. The plane can not have any external alterations and the device has to be completely portable, we currently have a small wifi router inside the plane but it is very unreliable. I'm completely oblivious to the world of electrical engineering so any help would be greatly appreciated

People on the ground should have a radio tuned to listen to the local frequency. Then the pilot can simply radio a call to notify the people on ground (and any other planes that may be nearby) about the skydivers.

Having this radio also means that during emergency (like a jumper getting caught on the plane) there can be coordination between pilot and ground crew.


With radio not working, why it is more important to stay away from exactly class D airspace? The instructions how to land when the radio is no longer working state as the first item "stay away from the class D airspace".

Why is the class D specifically mentioned in these instructions? How it could be that A, B which "has the most stringent rules" and C are less a problem?

I think you are mis-interpreting the answer, you should remain outside Class-D until the flow of traffic can be acertained. If you lose comms outside of a Class-B or Class-C, you should not enter that airspace, instead divert to a Class-D or E airport if possible. If you are already inside the B/C airspace, continue, but don't enter. Class-A is different, as it is not surrounding airports and you can fly IFR after you've gotten your clearance with lost comms.

The original question links to the AIM, Chapter 4, Section 2-13, read that and see if it clears things up.


Maximum Flaps extended speed Vfe for full or partial flaps? I fly Piper Archer/Warriors and the POH states "Maximum Flaps Extended Speed (VFE) – Do not exceed this speed with the flaps extended."  I try not to but I occasionally may exceed Vfe with one notch of flaps during a descent.  Could there be structural damage to the flaps in time or do aircraft designers factor in such potential pilot errors?

Unless a different speed is explicitly noted for partial flap extension, Vfe pertains to extending the flaps any amount. (For example, the C-172RG has a Vfe of 130 KIAS to 10º flaps, 100 KIAS beyond 10º flaps. Not so for the PA28s.)


What is the difference between variable and transient bleed valves? What is the difference between variable bleed valves (VBVs) and transient bleed valves (TBVs)? What is their range of operations? Can they be used at all airspeeds?

Turbofan engines have two or three distinct spools made of some turbine stages driving compressor stages using a shaft. The turbine stages collect the energy from the fuel combustion hot gases and drive the compressor stages which feed the combustion chamber with air.

When the fuel rate changes due to throttle position being changed, a delay is needed for this spool system to adapt, the time their rotational speeds adjust for a new equilibrium. However a turbine engine compressor is a tricky system in which the compressor must never stop producing air for the fuel combustion, and indeed must never allow hot gases from the combustion chamber to return forward, else the air pump is drained, the turbine stops producing power to turn the compressor, and the compressor itself stops compressing air.

The role of the VBV and TBV, as well as other elements (variable stator vanes, active turbine blade clearance system...) is to maintain the engine in conditions which prevent it to stop. The position of all these mechanisms is determined by the engine controller, which today is electronic and digital, and comprised of the FADEC, the EEC/ECU and the HMU.

While the VBV deal with more general equilibrium, the TBV deals which very quick transient states found in engine accelerations. In both cases the device reroutes a given quantity of air in the core to another location.

Source

Shared characteristics:

On a CFM56, the Variable Bleed Valves (VBV) and the Transient Bleed Valve (TBV):

Are both part of the engine control.
Are actuated by the HMU under the control of the ECU (EEC).
Are used to maintain the compressor pressure within the optimal compression region when the rotational speed of the compressors (low and hight pressure spools) changes and a new equilibrium between spool speeds needs to be achieved.
Prevent stall.

The VBV:

12 VBV located between the booster and the HPC (within the fan frame).
One or two "master valves" which drive the other.
Reduce water and foreign object ingestion.
Open when the engine decelerates or at low speed.
Close when the engine accelerates or at high speed.
When open, air from the hot flow is discharged in the bypass flow.

Source

Source

TBV:

Single valve located between the HPC stage 9 (bleed air tap) and the LPT stage 1.
Is aimed to quickly react after transient HPC pressure changes.
Improve HPC stall margin during engine start and acceleration.
When open, air from the HPC is discharged in the cavity before the LP turbine.

Source

CFM56-7B, Source

More on this site:

What is the transient bleed valve in a gas turbine engine?
Why does the CF6/CFM56 Turbofan Fan Frame contain 12 circular holes between the primary and secondary flow?
How does the FADEC prevent compressor stall during rapidly increasing thrust demand?


What types of air traffic controllers are there? I've heard of many different types of controllers, but I'm not sure exactly what their responsibilities and interactions are.

Here are some examples:

En route controllers
Approach controllers
Ground controllers

What types of controllers exist and what aspects of a flight is each one responsible for?

In Canada (and I believe similarly in the United States), there are four ratings which can be applied to an Air Traffic Controller license:

Airport Control
Terminal Control
Area Control
Oceanic Control

Within each of those ratings, the responsibilities are sub-divided a bit based on operational needs. For example, controllers at a tower (with an 'Airport Control' rating) would tend to be qualified in all aspects of tower operations including:

Clearance Delivery (issuing IFR clearances or assigning transponder codes)
Ground Control (issuing clearances for aircraft to move to/from the apron and runway areas via a taxiway system
Air Control (issueing clearances to aircraft in the runway environment and in the vicinity of the airport)

Terminal Controllers (if a terminal control area exists around the airport in question) would be responsible for flights in the immediate vicinity of the airport to approximately 20-50 nautical miles. Their responsibilities may include multiple small airports, just a single large airport, or even just one specific operation at an airport (such as arrival control or departure control). These controllers are usually allowed to apply a smaller amount of lateral separation between aircraft due to the dense nature of the terminal environment and the specific nature of their role.

Once the aircraft leave the terminal (if one exists), the Area Controller-sometimes called enroute control-takes over. They are responsible for anywhere between several hundred square miles of airspace to over several thousand square miles in the case of sectors in northern Canada.

In the case of an aircraft transiting the ocean, a specific type of area controller called an Oceanic Controller takes over. They possess slightly different training in order to safely separate aircraft over the ocean in non-radar airspace.


Does angle of rotation during takeoff affect the g-force? (Original)

When an airplane banks 60° during row, 2 g of force is induced. When an airplane pitches 60° during takeoff, is 2 g induced on the airplane?

Is the angle of rotation during takeoff related to the amount of g-force made during takeoff?

The increase in g-force in a banked turn is due to centrifugal force. That's a completely different situation than the g-forces during takeoff.

The forces during take off will be due to acceleration from thrust and, at rotation, an upward acceleration due to lift (and part of the thrust). The pitch angle doesn't have a direct relationship to g-force as the roll angle has in a banked turn. During climb the pitch angle can be as high as 15°, but once you've established a steady climb and a steady airspeed the g-forces are just the 1g of gravity.


Did the Swiss Air Force assist Austria in self-defence during the Yugoslav War? I was told a story a story by a friend that went along the lines of:

On multiple occasions, eastern european military aircraft strayed into Austrian airspace during one of the Yugoslav wars.
Neutral Austria did not have air-to-air combat capability in their J35Ö Draken, so the Swiss Air Force F-5s helped them out instead.
On one occasion, the Swiss air force came in and swiftly destroyed the aircraft in question before returning to base.

Note that I'm not completely sure of the exact sequence of events. I cannot find any reference for this story. Other aircraft downing during the war, especially NATO ones, are well covered.

Did this actually happen?

Updates with a few notes:

This must have occurred before 1995 when the Austrian Air Force outfitted their aircraft with Sidewinders AAM.
There is one case of a MIG-21 Pilot deflecting to Austria. Even this event is very vaguely documented.
Several sources suggest neutral Austria was very shaken up and upset by the foreign fighter jets overflying their country.
Information seems to be generally patchy, as this was before the days of the internet and there appears to have been much confusion and disorder.
As much as Switzerland is perceived as neutral, Austria was also very much so since it was a small country sandwiched between the east and west during the cold war.
Perhaps there is an international law that the Swiss were obligated to help, but kept it quiet out of concern of negative media publicity?

I'm likely reading the same sources than you read. The chance of the event you are searching for ever occurred seems slim. As you wrote, Austria worked hard to maintain its neutrality policy.

From Wikipedia, it seems clear Austria was not using guided missiles before 1993, but indeed other weapons can be used to shoot down an enemy.

The article seems to be exhaustive for significant elements related to flights over the country by foreign aircraft, and still doesn't mention any destruction between 1970 and 1993.

There was a major incident in 1991 with Yugoslav MiG-21, but no mention of a shot down. This incident and the similar ones the same year led to the adoption of guided Sidewinder missiles by the air force two years later.

  From 1970, Austria purchased a total of 40 Saab 105 lightweight
  multi-role aircraft with the intention to deploy them in trainer,
  reconnaissance, interception and ground attack roles. As it became
  clear in the 1980s that the sub-sonic aircraft were inadequate for air
  combat and airspace interdiction, Austria purchased 24 reconditioned J
  35 Draken fighter aircraft to supersede the Saab 105 as the Austrian
  Air Force's main interceptor in 1988. The Saab 105 remained in service
  as a trainer/surveillance aircraft.

  Shortly after, the Draken saw their first major use in airspace interdiction starting 1991 during the Yugoslav Wars, when Yugoslav
  MiG-21 fighters crossed the Austrian border without permission. In one
  incident on 28 June a MiG-21 penetrated as far as Graz, causing
  widespread demands for action. Following repeated border crossings
  by armed aircraft of the Yugoslav People's Army, changes were
  suggested to the standing orders for aircraft armament.

  Since 1955, Austria's armed forces had been forbidden to operate any
  guided missile system, including Air-to-air missiles and
  surface-to-air missiles. In the post-Cold War environment, and with
  gun-armed aircraft a relic of a past age, the Austrian Parliament
  voted to amend this section of its state treaty and in January 1993
  modern AIM-9 Sidewinder missiles were ordered from Sweden to arm its
  fighter aircraft.

On the other assumption that Switzerland provided military assistance, again no mention of such cooperation until recent year, with the EU treaties.

It seems the overflights of Austria by non authorized aircrafts was quite intense --daily-- at the time of the Yugoslavia war.

You may be right when saying that Austria could be reluctant to disclose a shooting. The fact that it would have happened before the widespread use of Internet is not something that could prevent the event to be recounted online today.

Not relevant downing:

Jan. 1992: Two EU helicopters downed by Yugoslav MiG-21, Austria radars detected the downing.

Additional documentation:

The Austrian Air Force - In the Past and Today
Austrian Air Force
Austrian Air Force
A well documented list of interceptions over Austria
Austrian Draken's on high alert


Does leading-edge droop increase or decrease lift, other things being equal? Consider a conventional subsonic airfoil in level flight. Typically it is cambered and with a small positive incidence, both of which features contribute to lift.

Now droop the leading edge, as with say a plain leading-edge flap. This reduces the incidence, possibly even taking it negative, but increases the camber. Will the net lift increase or decrease, and why? Can the answer vary according to other flight conditions?

From this NASA study on LE flap/droop for a light general aviation wing:

Variations of lift are small up to $\alpha$ 10°, but the stall is delayed to a higher angle of attack (and $C_L$) for a full-span droop (see: How do droops help to avoid stalls?).

And from a NACA study published in 1954 (NACA-RM-SA54B16) on the Effect of a Leading-edge Flap upon the Lift, Drag, and Pitching Moment of an Airplane Employing a Thin, Unswept Wing:

The variations of lift with angle of attack and of pitching moment with lift near zero lift were not significantly affected.

In general at all test Mach numbers, the drag at zero lift increased with flap deflection.

The maximum lift-drag ratio was increased at subsonic speeds, and the increment in the maximum lift-drag ratio for a given flap deflection decreased as the Mach number approached unity. At supersonic speeds, flap deflection had no influence upon the maximum lift-drag ratio.

(Above plot shows the round leading edge data at Mach 0.6; left-to-right: $C_D$, $C_L$, and $C_m$.)
Note: The second study is on a thin airfoil, but the core premise (reduction of incidence and increase of camber) is covered here.


What qualifies as a major overhaul? I have an engine that took a prop strike (previous owner).  The engine was completely disassembled to check the crank, case, etc for damage.  It was reassembled with new parts, bearings, rings, etc., overhauled cylinders, and mags with fresh 500 hour inspection. The logbook entry says "0 SMOH Lower End."  What else would be required to list this engine as simply "0 SMOH?"  How should I track this in my log book?

"0 SMOH Lower End." means just what it says. The lower end was completely rebuilt but there wasn't a complete overhaul of the "top end". Some of the old top end parts must have been re-used without being overhauled.

I would suggest speaking to the person who did the overhaul to get more information on why the top end did not qualify for 0 SMOH as well.


What are the implications of no longer requiring a complex aircraft for the commercial/CFI checkride? Are there any other implications for flying Complex Airplane (getting endorsements, etc.) now that the CFI and Commercial Pilot Practical tests no longer require the applicant to provide a Complex Airplane for the exam (As of April 24, 2018)?

The official FAA Notice says

  There is no change to the complex airplane training and endorsement requirements of § 61.31(e) or to the commercial pilot aeronautical experience requirements of § 61.129(a)(3)(ii) or part 141 appendix D.

So the requirements haven't changed but how about becoming an authorized instructor in a complex airplane now that you could technically become an instructor without ever flying in a complex airplane?

Even though I am supportive of this change, a fundamental change like this usually means there are some unforeseen circumstances, and I'm wondering if there are any far-reaching changes that aren't immediately obvious.

First, as Ron pointed out (and as the FAA Notice you quoted says), you still need 10 hours complex (or turbine) training time for a commercial single-engine certificate. The only change is that you no longer need to do the checkride in a complex aircraft.

Your main question seems to be if it will eventually be possible to instruct in a complex aircraft without having any complex experience. That could indeed happen if the FAA ever implements a proposal to allow Technically Advanced Aircraft (TAA) time as an alternative to complex time for commercial single-engine. Then you could fly a Cirrus (or another fixed-gear TAA) instead of something complex and become a CFI with no complex experience. That proposal requires a change to the regulations so it's a bigger deal than just changing the ACS and it hasn't happened yet.

But, it's already the case today that instructors don't need to be endorsed in the aircraft they instruct in: if they aren't acting as PIC then they don't need to be qualified as PIC. (Whether doing that is a good idea or not is another issue.) So instructors without endorsements wouldn't be a new issue at all, although it might become a more important and common one.

However in reality, insurance often determines what an instructor can do, not the FAA. I fly a C182RG, which is a complex aircraft, and the insurance policy specifies the experience requirements for instructors who use it. In a hypothetical future where you can become a CFI with zero complex time, you simply wouldn't meet the insurance requirements to provide instruction in that aircraft. I know insurance isn't mandatory anyway, but for CFIs and other professionals it's often the deciding factor in what they can and can't do.

As for unintended consequences of this change, I have no idea and we can only speculate. For example, complex single-engine aircraft prices may fall as flight schools sell them off.


What are the properties of a good general aviation training aircraft? I've been told that the best kinds of planes to train in are very small ones, like Cessna 150s and 152s.  But I've never been clear as to why.  I know they are cheaper to operate, so is operation cost the only thing?  Or are there aerodynamic properties that 152s have that make them "easier"?  What makes for a good training aircraft?

Cost is certainly a primary factor in choosing smaller planes. It makes training much more accessible to people with less money to spend.

Small planes are also easier to fly for various reasons. They fly slower and respond more quickly than large aircraft, which gives the pilot much more margin for learning. Being more maneuverable can help them escape tricky situations.

These planes are also generally designed to be resistant to and recoverable from common aerodynamic disasters like stalls and spins. See this related question for more information. There are FAA requirements for single-engine planes in FAR 23.221.

Smaller planes generally also have fewer and less complex systems, which makes the necessary training easier to complete.

They can also operate from smaller airports, which gives a student more choices of where to do their training.

Of course, there are always exceptions to these qualities, and large planes can have similar ones, but they hold true in general.


Why and how can a fume event occur? « A fume event occurs when bleed air used for cabin pressurization and
  air conditioning in a pressurized aircraft is contaminated by fluids
  such as engine oil, hydraulic fluid, anti-icing fluid, and other
  potentially hazardous chemicals. » (source)

Wikipedia does not explain how and why a fume event can occur, but notes:

  « The cabin is pressurized with bleed air tapped from the jet engine's
  compressor sections, which are prior to the combustion sections. » (source)

Question:

(1) status quo
Given that bleed air is tapped at an early stage before coming into contact with fuel and thus cannot come into contact with fuel, why then can it come into contact with the other fluids quoted above ?

(2) solution?
To avoid any potential contact with these fluids, couldn't it be tapped an an even earlier stage (in the front section of the engine) or rerouted/transported differently from the engine into the cabin? Isn't there any solution (other than bleedless aircraft) to eliminate the potential for both fume events (acute exposure) and long-term health effects (chronic exposure) for the cabin-crew and frequent flyers due to long-term exposure to minimal doses ?

(1) How can can other fluids contaminate the bleed air?

Engine Oil:
The engine fan and compressor stages are rotating pieces of metal on metal and thus need lubrication. Engine oil is used for this purpose and could come into contact with the bleed air in case of a leakage (see mooveaviation.com for details).
Hydraulic Fluid: Some components of the engine, e.g. the thrust reversers, are hydraulically actuated. Again, a leakage in a pipe could lead to hydraulic fluid entering the engine.
De-Icing Fluid: When an aircraft is deiced on the ground, the crew needs to disable the bleeds during the deicing in order to avoid any contamination, see e.g. Boeing 737 NG FCOMv1 XP.16.8 (Supplementary Procedures - Adverse Weather):

  CAUTION: Operate the APU during de-icing only if necessary. If
  the APU is running, ingestion of de-icing fluid causes
  objectionable fumes and odors to enter the airplane.
  Ingestion of snow, slush, ice, or de-icing/anti-icing
  fluid can also cause damage to the APU.

  [...]

  Engine BLEED air switches ......................................OFF
  F/O

  Reduces the possibility of fumes entering the air conditioning
  system.

  APU BLEED air switch .............................................OFF
  F/O

  Reduces the possibility of fumes entering the air conditioning
  system.

Some of the deicing fluid might flow into the engine afterwards and if the bleeds are turned on to early, the fumes might get into the cabin.

(2) Could the bleed air be tapped at an earlier stage?

Bleed air needs to have a high enough pressure to be usable for pressurizing the aircraft at cruise altitudes. Moving to an earlier compressor stage would reduce the available pressure. Some engines have bleeds in both the low and high pressure compressor and will automatically use the appropriate one depending on engine thrust and pressure.


Can endplates be used to reduce chord length by up to 14%? Can endplates be used to reduce chord length by up to 14%?

I understand large endplates can change the lift distribution from an elliptical one to a uniform one, making the wing more efficient by increasing lift near the wing tips.

This increases the effective aerodynamic span by up to 16% ( see pic below ).

pic: Effect of large endplates on a short span wing, Source: Zenith

Can this be used to shorten the chord?

eg.

16' span, 2' chord, total wing area: 32 sq ft rectangular wing.

Use large end plate, h/b=20%.

revised effective aerodynamic wing span: 16' x 1.16= 18.5'

Revised chord: 32 sq ft / 18.5 = 1.7' chord.

Is this correct thinking?

It would be possible to do as you suggest.

However the short-chord wing would have to be either thinner and therefore heavier, or less streamlined and therefore less efficient causing higher form drag. Both effects increase induced drag.

The endplate would need to be roughly square in proportion, which would add drag of its own. Also its mass and side area would complicate the aircraft behaviour.

It is generally better to add a small winglet rather than a big flat plate and use it to reduce the wing tip vortex. But even there, a bit extra wing span with suitable washout is just as good.


What are ways to reduce drag and noise generated by the landing gear? Apart from using fairings, what ways are there, or have been studied, but not necessarily implemented in reducing drag and noise produced by the landing gear, mainly for commercial aircraft with retractable landing gear, but would also like to know about smaller aircraft, perhaps with non-retractable landing gear.

Is there a study or a design that has been done on landing gear to reduce drag and/or noise produced by the landing gear?

The biggest noise reduction is achieved by closing most of the landing gear doors again after extension is complete.

Of the factors that influence drag and noise, one is the distance between wheel and fuselage. The picture below is taken from S. Hoerner's book "Fluid Dynamic Drag", chapter XIII.5 of which deals with the drag of landing gears.

Another influence is the shape of the landing gear strut. Since most airliner landing gear legs are oleo struts, they are round for practical reasons. Fairing them would already help, as can be seen from the lower line in the plot above. Another improvement can be achieved by covering the wheel hubs. However, the reduction of the drag and noise caused by extended, retractable landing gears has been studied but few of the results have yet found their way into actual aircraft. According to this DLR report, a fully faired A320 landing gear would reduce noise by 10 dB while partially fairing the most noisy parts of an A340 landing gear would reduce noise by 5 dB. The picture below is taken from this report.

For fixed landing gears, I recommend NACA Technical Report 485 which contains results of full-scale tests on several gears. NACA Technical Report 518 contains results for partially retractable gears.


What material is used for the floor panels in the main cabin for Boeing 747-400? Just conducting some research into materials used in construction for Boeing 747-400 and Douglas DC-3.

I just found out that in a DC-3 the floor panels in the main cabin and companionway are of plywood.

As such, I tried to find the information with regards to Boeing 747-400, but was unsuccessful.

I was hoping someone could provide me with information with regards to the material of the floor panels in the main cabin and companionway of Boeing 747-400.

This illustration is earlier than a -400. Later ones might differ. There are two types: the normal one has aluminum skins bonded to a PVC core, for galleys/hold it is titanium skin bonded to a PVC core with greater strength/corrosion resistance.

747 cutaway view

Later a honeycomb sandwich was used, apparently two cross plied glass-epoxy prepreg skins bonded to phenolic coated nomex honeycomb core using an epoxy film adjesive. From:

  Handbook of Adhesives and Sealants: volume 1, 2005


Can a pilot with an ICAO Multi-Crew Pilot License fly an airliner into the U.S.? In the question How do non-US pilots get the hours necessary for an ATP?, the question was raised of whether we have 250 or 500 hour foreign pilots flying airliners into major U.S. airports. DeltaLima's answer mentioned the ICAO Multi-Crew Pilot License (MPL), which

  allows a pilot to exercise the privileges of a co-pilot in a commercial air transportation on multi-crew aeroplanes.

Of particular interest is the large gap in the minimum experience requirement between this license and an ATP license that would normally be required to fly an airliner in the U.S. While the FAA normally requires airline pilots to have at least 1,000 flight hours (or 1,500 if they don't have a degree in aviation,) the requirement for the ICAO MPL standard is much less. According to ICAO:

  The ICAO Standard for the MPL specifies 240 hours as the minimum number of actual and simulated flight hours performing the functions of the pilot flying and the pilot non-flying.

While the U.S. has no such pilot certificate, what I'm wondering is:

Is a pilot who receives an MPL from another country allowed by the FAA to fly an airliner on normal scheduled passenger service routes into major U.S. airports?
If so, are there any further restrictions on doing so? For instance:

Can they fly a route subject to ETOPS regulations into the U.S.?
Can they fly a 777 into the U.S. or are they limited to smaller aircraft (e.g. turboprops and the like?)

What is required for a pilot to fly in another country? and I have a European EASA license - what do I need to do to be allowed to fly in the US? cover some general points about the certification requirements to fly an aircraft in a country other than the one where the pilot obtained their license, but they don't address issues specific to flying airline routes.

Interestingly, ICAO seems to suggest that pilots with an MPL would indeed be able to fly in the right seat of an airliner into any ICAO country:

  International recognition of flight crew licenses

  The Convention on International Civil Aviation, often called the Chicago Convention, provides for worldwide recognition of flight crew licences issued by any member State of the International Civil Aviation Organization (ICAO) provided that:

    1.the licence meets or exceeds the ICAO licensing Standards of Annex 1 – Personnel Licensing to the Convention on International Civil Aviation; and

    2.the licence is used on an aircraft which is registered in the State which has issued or validated the licence.

  If the licence is to be used on an aircraft which is not registered in the issuing State, the licence holder must obtain a validation of the licence from the State of Registry or alternatively obtain a new licence issued by the State of Registry.

Can someone provide a reference to the FARs (or something of similar authority) or cite personal experience to confirm whether this is indeed allowed and, if so, what restrictions are placed on such operations?

The MPL doesn't allow the holder to fly as Pilot-in-Command, although in a pinch he probably could do it.  It's a basic ticket to allow a non-ATPL pilot to fly as a fully qualified crew-member of an aircraft that otherwise requires the full ATPL ticket.  Elsewhere the pilot would likely be accumulating only solo experience, and he won't be much use when transitioning to a multi-crew airplane.  The MPL only allows the holder to act as copilot, 2nd officer (flight engineer) or cruise pilot, not as PIC, on any flight including to the USA. Where it's used, the MPL holder will be granted his ATPL when he completes any additional regulatory requirements and has accumulated the required hours. The MPL pilot is entitled to fly in his aircraft as co-pilot from anywhere outside the USA into the USA, although not in a USA-registered aircraft. Some pilots start their MPL training after completing A PPL or CPL beforehand.