Is there a benefit to a pilot/aviator having an FCC GROL license? I am an avionics technician (c-130) in the USAF and plan on learning to fly helicopters when I separate in about a year.

I have debated whether or not to pursue a GROL or possibly A&P.  From what I know, these are generally intended for maintainers/technicians rather than aviators.

That said, would there be any benefit to having a GROL or related license for an aspiring helicopter pilot?

There's no tangible benefit to having a GROL in getting a pilots license of any kind as getting the license generally confers the right to use aircraft radios. In some places you need to get an RT license for aviation as a separate test, however that's pretty minimal. A GROL is only good for repairing, maintaining, and running certain types of radio stations.

An A&P will let you work on airplanes, but it also does not help get a license. An A&P will give you insights into how an airplane works, but you can get those insights without an A&P. Having an A&P and a pilots license might be a different story if you plan to work in remote locations where being able to fix your aircraft when it breaks is useful. It won't help you get a flying job in most places.


What is the significance of the 10,600 lbs MTOW limit? I recently noticed that several airplanes have MTOWs very near or exactly 10,600 lbs. That was an interesting phenomenon to me because I am familiar with the 12,500 lbs MTOW regulatory limit on certain types of small planes, and familiar with the 19,000 lbs MTOW regulatory limit on certain other "commuter" planes, but I couldn't find anything to support why so many airplanes would have MTOWs at 10,600 lbs.

As I tried to google for "10,600 lbs max takeoff limit" I found more planes that are at or very near that exact MTOW but couldn't find the basis for why this is.

Does it have to do with European regulations? Does it have to do with insurance considerations?

Airplanes with near or exactly 10,600 lbs MTOW

Cessna CitationJet / M2
Beechcraft King Air C90 / and derivatives
Embraer Phenom 100
HondaJet HA-420

EDIT: A Little More Info

I have noticed that 10,600 lbs is very close to 4,800 kg. So its possible that this regulation stems from something non-FAA, something that regulates in kg, but even still, I haven't had any more luck with Google trying to figure out what the derivation of a 4,800 kg limit might be. Yet again, all I found was yet more planes that have that same MTOW limit.

It's nothing more than playing catch up.

If company X managed to build an aircraft for a certain mission at the lowest ever MTOW. Company Y will try to get down to that MTOW to be able to compete. Lowest is good if the mission is the same.

Check the MTOW of the Airbus A320-100 and the Boeing 737-400, to save you time, they are 200 pounds apart. But the A320-100 didn't sell well, the A320-200 did. Guess what, the 737-800 matched that weight.

Here's why:

There's something called Weight Factor.
$$
\text{Weight Factor}=\sqrt{\frac{\text{(MTOW in kg)}}{5}}
$$

The Weight Factor determines the route charges.

  This charge takes into account the distance flown and, less than proportionately, the aircraft weight.

That's why it's vital for competitors to have similar MTOW's. So they can advertise similar operating costs. MTOW is also used in airport fees.

The only interesting thing about 10,600 lb / 4,800 kg is that the weight factor is kept a tad under 10.00 (two decimal places are used). Now, is there a higher charge for a plane with WF at or above 10? I scoured the internet, there doesn't seem to be WF brackets set that way, to my dismay.

Ryanair has part of their fleet tailor-made to an MTOW of 66,990 kg (WF ~36.60) for similar reasons apparently, or they're just being cheeky.

It's also why some airlines don't choose the Extended Range. The 777-200 airframe and its ER version are the same (no auxiliary fuel tanks).

The differences are extra certification for higher MTOW, and the same engines but certified for higher thrust. Airlines can request a conversion to ER if they open routes to farther destinations.


What does "out of trim" mean? Our flight was delayed from takeoff because the captain reported it to be "out of trim". What does this mean?

In this context, it would mean the aircraft is loaded in such a way that the Center of Gravity is too far forward or aft.  That's actually not the way we usually use the word "trim" in aviation but it's what it means in this case.


Are taxi-way routing details saved? I am currently working on taxi-way route optimization. Are there any systems that store the taxi routes taken by the aircraft either by hour or by day or by airplane?

Your best bet will be to listen to recordings of taxi clearances issued by Ground Control.
The chance that you can see replays of enough ASDE-X or other surface radar recordings to get a meaningful data set is probably about zero unless you can get agreements with whatever ATC facility you're interested in.
While it's possible that some facility may record the data that you're asking about, the general answer is that the ground controller simply issues the clearance over the radio and the aircraft complies.  If a conflict arises that requires something different, then the controller issues a revised clearance & the aircraft follows the new instruction.  But unless a particular facility is doing something special (an extra person in the tower cab recording clearances & routings in order to undertake some specific analysis, for instance, or maybe a facility doing an analysis of ASDE-X tapes for some project), there's no widespread banking of that sort of thing.
Thus the suggestion that you will need to build your database yourself by listening to something like Live ATC (dot net) and copying down the routings given.


Why are the strings on paramotors so long? I don't completely understand why the strings on paraglider/paramotors (connecting the vehicle/person to the parafoil) are so long. Couldn't they be made shorter to reduce the amount of space used? It just seems like an unnecessary feature. Sorry if I'm missing something elementary.

The answer to this is mechanical leverage.

For this, you must understand that the center of mass for a paramotor is usually just above the pilot's head, and that the center of lift is more upwards.

The shorter the strings on a paramotor, the harder that it is to climb, because the length of the effort arm is reduced, requiring a greater power to tilt the paramotor into a climb.

As the motor power increases, you don't actually go much faster. You tip backward, and maintain speed. This is what helps you climb, essentially comboing the wing with the elevator.

The long strings allow for slower, more efficient flight by increasing leverage. This is the same mechanics that are used in most trainer crafts (outside the military) to allow the learner a long, slow flight.


Can a non-A&P fabricate and install his own hydraulic lines? As a non-A&P, am I allowed to fabricate and install hydraulic fluid lines as part of preventive maintenance on an aircraft?

Generally speaking someone who does not hold a mechanic's certificate may not fabricate their own hardlines or hoses, nor may they replace hardlines. This work must be done by someone holding the appropriate Airframe and/or Powerplant mechanic rating.

An owner/operator with a private pilot certificate may install prefabricated flexible fluid carrying hoses (with the specific exception of hydraulic hoses) as preventive maintenance,as allowed under FAR 43 Appendix A.

There are three notable exceptions to the above general statements:

An owner of a Special Light Sport aircraft may acquire a repairman certificate, enabling them to perform this kind of work on their aircraft.
The builder of an Experimental Amateur-Built aircraft ("homebuilt") may perform this work on aircraft they have built, as FAR 43 does not govern maintenance on aircraft with an Experimental airworthiness certificate.
If working under the supervision of an A&P mechanic you are authorized to perform any work your supervisor is authorized for (per FAR 43.3 (d), and subject to some specific requirements).


What was the first aircraft that could fly inverted? I'm taking a guess and assuming the Wright Flyer was incapable of flying upside down.  I'm just guessing it probably lacked the power... ;)

So what was the first plane that could fly inverted for a sustained period of time (10sec+) with full power?  I'm assuming you would need an engine that was okay being upside down*, and had the power to get you high enough to make the maneuver safe.  Then you'd need an airfoil that worked inverted (some of the high early cambered wings may have had problems, for example) and controls that functioned in that environment as well.  Probably a seat belt would be useful too.

Anybody know what plane was the first one to have all of these, and then went ahead and flew upside down?

Bonus points: I also wouldn't mind knowing what plane was the first to simply fly inverted, even if for a brief moment...

*As Jan Hudec pointed out, the engine itself doesn't really care, but the fuel system might.  So really we should be asking when the first fuel system that could go upside down was produced...

Deliberate momentarily inverted flight
The first reported deliberately inverted flight was probably in a Blériot model XI.

Inverted flight was also being considered. Several pilots had inadvertently found themselves upside down as a result of wind gusts, but no one had yet attempted it intentionally. Adolphe Pegoud decided he would be the one to try.
Pegoud was one of the first true aerobatic pilots. An accomplished test pilot with the Bleriot team, he was also the first flyer to jump from a plane with a parachute. Both Pegoud and the aircraft landed, unharmed. Having decided to try upside-down flying, Pegoud first practiced in a hanger [sic] in a plane hung upside down from the ceiling. He correctly assumed the controls would have to be operated in a reverse manner and he wanted to get the feel of it before actually flying.
It must have worked. Shortly thereafter, Pegoud made the first public demonstration of inverted flight in September of 1913. During this flight, he was the first to perform a half roll to an inverted position--another aerobatic maneuver was born. The flight did point out one potential problem: While Pegoud was prepared to fly inverted, the aircraft was not. It proceeded to drench the flyer with fuel!

From The history of aerobatics
Deliberate sustained inverted flight
This would have to have been an aerobatic aircraft specially modified for inverted flight

flop tubes in the fuel tank?
fuel-injection not carburettor?
strengthened and/or braced to allow wings to support fuselage in inverted position?

1925
June 1925, No 32 Squadron did an air display demonstrating Flight-converging bombing at the R.A.F Display, Hendon. Scott was selected to do individual aerobatics in a brand-new Snipe which he was allowed to paint red, this pleased Scott greatly as it meant that he was also allowed to practice his aerobatics at a low altitude, rather than above 2000 feet which was R.A.F regulations at that time. In Scott's book he tells of how for his solo display he was allotted exactly seven minutes during the luncheon break, to complete his show but after just two minutes, a flying wire broke in the near edge of the port side, anxious not to cut his allotted seven minutes down too much he began to fly the aircraft upside down in an effort to reduce the strain on the flying wires, he continued flying in an inverted position for some time until he noticed a worrying quiver in the top plane and promptly landed slightly short of his seven minutes.
From Wikipedia
1933 record
In 1933, NC872H, a Boeing 100, was flown inverted for 4 hours 5 minutes and 22 seconds.

After its career with Pratt & Whitney, the Museum of Flight's aircraft was sold to Milo Burcham on September 27, 1933. He modified it for skywriting and air-show work, painted it blood red, added fuel and oil systems for inverted flight, and flew it upside down from Los Angeles to San Diego.

From Seattle Museum of Flight


How can I learn about unpublished VFR reporting points? I often hear "The Creek" used by pilot and ATC in the vicinity of Provo Municipal airport.  I've been flying in this area for over 20 years, and I don't know what they are talking about.  There are at least three rivers that empty into Utah lake in the vicinity of the airport, one of them is named "Hobble Creek", but it would seem presumptuous to assume that is the one that is meant.

I am interested to hear strategies for learning the locations of unpublished, but commonly used waypoints.

Wait until the frequency isn't terribly busy on one of your flights, then just:

"Unfamiliar with Creek waypoint, Request clarification"

You can reasonably expect them to either explain the waypoint, or if they're busy, potentially give you a phone number or other contact info to try from the ground.

You can also call an Airport Manager (801-852-6715) for questions.


Has color vision deficiency ever contributed to any incidents in aviation history? I would like to know if there are any official reports pointing Color Vision Deficiency (CVD) as a major contributing cause of an air accident/incident. Not only related to flying but also maintenance or ATC for instace.

So far, I have only come across with FedEx flight 1478, in which a CVD F/O misjudged the PAPI lights. However, the report does not point how severe was the F/O's deficiency (all crew survived the accident). And more important is that the Captain and Flight Engineer (with normal color vision) could neither detect the wrong glidepath.

My final goal is to research the topic of color-blindness in aviation with real case instances and hopefully draw some conclusions about the actual impact of this disease in aviation for candidate's medical certification.

In response to two NTSB safety recommendations, the FAA stated that it has only identified three accidents involving pilots with valid medical qualifications in which color vision deficiency (CVD) was cited as a contributing cause.

As you mention above, on July 26, 2002, a Federal Express Boeing 727-200F crashed during a visual approach to Tallahassee Regional Airport in nighttime visual meteorological conditions. The three crew members were seriously injured and the airplane was destroyed in the crash, which the NTSB attributed to “the captain’s and first officer’s failure to establish and maintain a proper glide path.” Because the first officer was flying the plane at the time of the crash, the NTSB cited as one of several contributing factors “the first officer’s color vision deficiency" which interfered with his ability to discern the red and white lights of the precision approach path indicator (PAPI).

On Aug. 29, 1992, an incident occurred in which the pilot of a Mooney 20F with “a waiver for partial color blindness to red and green” landed on a closed runway that was marked with orange crosses in the dirt 50 ft beyond each end. The pilot’s “limited ability to detect the orange-colored marking” was cited as a contributing factor.

One incident involved a Navy F4J lost on Aug. 5, 1980, “when a severely color deficient pilot failed to interpret correctly the colored navigation lights of other aircraft in the area, leading to the false impression of a collision.”

Regarding the severity of the FO's color blindness from FedEx flight 1478, records indicate that he passed all color vision tests during his 16 years as a U.S. Navy pilot but failed a test administered during an FAA medical evaluation in 1995. This failed test indicated that he had a mild red-green deficiency. The FAA issued a first-class medical certificate with a statement of demonstrated ability (SODA), based on his years as a Navy pilot and the results of his Navy color vision tests. He was issued this SODA on all subsequent medical examinations.
After the 2002 crash, the first officer passed the Farnsworth Lantern (FALANT) color vision test, which was designed to differentiate between those with mild red-green deficiencies, who pass the test, and others with more significant red-green deficiencies, who fail. He also passed a light-gun-signal test administered by an FAA medical examiner. However, he failed seven other red-green color vision tests and was determined to have a “severe congenital deuteranomaly” — a red-green deficiency that is the most common color vision defect.
Hope this helps.
References: Werfelman, L. (2008, December). Color deficient?[PDF] Aero Safety World, 38-41. Flight Safety Foundation. Retrieved from:http://www.flightsafety.org/asw/dec08/asw_dec08_p38-41.pdf


What is the meaning of "regular pitch" when applied to a propeller? I am looking at parameters of a propeller that looks like this:

  3 blade xx inch diameter (regular pitch)

What does "regular pitch" mean?

Ill assume you are asking the context of fixed pitch propellers. In which case "regular pitch" is either the standard pitch for the airframe in question or some mid range pitch to deliver average performance. There are usually various propeller options for a given aircraft:

  There are two types of fixed-pitch propellers: climb and cruise.
  Whether the airplane has a climb or cruise propeller installed depends
  upon its intended use. The climb propeller has a lower pitch,
  therefore less drag. Less drag results in higher rpm and more
  horsepower capability, which increases performance during takeoffs and
  climbs, but decreases performance during cruising flight.

You can read more here.


Does the expression "stall speed" have a definition? I read, not only on this site, that the stall speed of an airfoil doesn't exist, and I usually make the effort to stay away from this expression.

While an airfoil can stall at any airspeed, it's clear that the stall speed refers to the airspeed at which the stall occurs in an horizontal 1G flight.

Stall speeds for B747-200 (n=1). (Source).

This speed is the lowest one that can generate a vertical component of lift equal to the weight with the airfoil at its stall angle of attack.

I would compare this implicit assumption with the maximum airspeed of an aircraft: It's clear we are assuming at least an horizontal flight and a standard atmosphere, etc, else this speed can be anything too.

So what's wrong with this definition of the "stall speed"? Is the stall speed defined in the aerodynamics field?

Example of use: Stall Speed (Dr. Mustafa Cavcar).

Indeed, "the stall speed of an airfoil doesn't exist." But the stall speed of an airplane does exist, though it's dependent on the aircraft weight $W$, load factor $n_z$, configuration (e.g., flaps position) and the air density. This variability makes it disadvantageous (for pilots---even dangerous) to think of an airplane's stall in terms of a definite stall speed $v_{Stall}$, as if it were a constant characteristic of the type. What are (roughly) constant are the stall angle of attack and the stall lift coefficient $c_{L_{Stall}}$.

The equilibrium equation for the forces acting on the airplane In stall in its symmetry plane and perpendicular to its velocity is:

$$n_z\cdot W = \frac{1}{2}\cdot\rho\cdot v^2_{Stall}\cdot S_{ref}\cdot c_{L_{Stall}}$$

Doing the algebra, one can easily exspress the stall speed in terms of the remaining parameters ($\rho$ = density of air, $S_{ref}$ = reference area) The resulting expression will explain (i) that for an airplane, stall speed does exist; (ii) the nature of its dependences and (iii) that for an airfoil, to which force equilibrium does not apply, there is no "stall speed."


Can we use the term CONTAMINATED RUNWAY for other meanings, such as: oil spill or debris on the runway? Contaminated Runway is used to say that the runway surface area (25%) is covered by 3.0 mm or more of: water, slush, snow and ice. But is it also possible to use this term to say about: heavy rubber, oil spill, debris or other substances are on the runway surface?

From the FAA Pilot/Controllers Glossary Book:

  CONTAMINATED RUNWAY− A runway is
  considered contaminated whenever standing water,
  ice, snow, slush, frost in any form, heavy rubber, or
  other substances are present. A runway is contaminated
  with respect to rubber deposits or other
  friction-degrading substances when the average
  friction value for any 500-foot segment of the runway
  within the ALD fails below the recommended
  minimum friction level and the average friction value
  in the adjacent 500-foot segments falls below the
  maintenance planning friction level.

(See also ICAO Circular on Runway Surface Condition Assessment Measurement and Reporting) Thanks to mins.

So this covers rubber and oil, but not debris.

However, from searching the glossary there are no instances of the word "debris" in the document. Usually if debris or oil were noticed on a runway, ATC would close the runway (issue a NOTAM) and then use an alternate runway until the debris or oil were cleaned up.

From a pilots perspective, if you notice debris on the runway just tell ATC (provided you didn't hit it), and they will close the runway for a FOD (foreign object debris) check. My local airport does this usually twice a day or more, typically by running a car down the runway looking for debris.


Would a pure flying wing in straight and level flight have zero wing bending stress? In studying the NASA 247 foot wingspan solar powered Helios aircraft it seemed that evenly spacing the weight would help create a lower bending stress across its span when in flight, as gravity and lift forces would cancel each other out more evenly as compared to a single fuselage.

The Helios did have spaced pods slung underneath, but none at the ends.  The aircraft, in turbulence (perhaps an updraft) that caused its wingtips to bend upwards, started a pitch up/pitch down cycle until the wing failed.  Could more even spacing of weight on the wing reduce the possibility of this happening again?

Net wing loading (weight per unit lifting area) can't be zero in level flight.  Lift must equal weight, else the aircraft will accelerate in the direction of the net force.

The loading distribution on the Helios is designed to reduce flexing moment along the span, which is an entirely different thing.  As you note, that optimization wasn't perfect, although pitch oscillation wasn't necessarily related to the wing flex that shows in the video.


What measurement units are used in Boeing FDR readouts? I am working with FDR readout data and I am trying to find good resources about measurement units for those logs. The data seems to be a mix of SI and non-SI units and it can be quite difficult to work with data if you don't have correct units.

The data comes from Boeing 757, 767 and 737MAX aircraft but I am not sure what type the FDR equipment is installed (will find out at some point).

Does anyone have a good resource on this?

I am using this data to create graphs and measurements in Elasticsearch and Kibana, focusing on fuel efficiency. It is quite interesting to see how fuel flow is different between engines and how altitude affects fuel consumption.

According to the provisions in ICAO Annex 6 - Operation of Aircraft, Vol 1 and Vol. III, a Type I FDR shall record the parameters required to determine accurately the aeroplane flight path, speed, attitude, engine power, configuration and operation. Types II and IIA FDRs shall record the parameters required to determine accurately the aeroplane flight path, speed, attitude, engine power and configuration of lift and drag devices.

Therefore the listing word by word is not defined by the authorities

So

As a start, but not only, it depends on the age of the aircraft, for instance early 737 had 64 words of 12 bits, most of these words have the first 2 bits for binary states(open, closed, selected on or selected off, etc) the remaining bits are for an analog value expressed binary, such as pressure, speed, vario, etc. Some other words are fully for states conditions, that is every bit of the 12 bits of the word indicates a state.

To the opposite of early 737 late 737s have 256 words,
So it doesn’t depend on the type of FDR, but on the specific model of aircraft, the type of FDR is just a consequence; 2 FDRs recording the same number of words won’t have the same words definitions

But more than that:

The FDR will record what it receives from a computer that centralizes all the data and that manages the data into 12 bits words. The recorded data depends on the chronology of received words. This chronology doesn’t depend on the FDR but on the emitting computer that sends the data to the FDR

But also

It depends on the specific options of the aircraft, that’s why every aircraft has its own listing, the investigation center will get this data either from the aircraft manufacturer or from the operator, because the data is also available in the specific maintenance manual of the aircraft.

So unhappily  you have to refer to the maintenance manual of what, of the specific aircraft

Now a hint: if you find in the nature an FDR, how to decode it if you don’t know ahead to what aircraft it belongs?

Externally it has a serial number that will normally allow the required traceability
While reading the data frames the identification of the aircraft is recorded on the first words

Is this a general answer, may be yes. Am I giving the parameters of every recorded word, the answer is no; Am I giving the corresponding units? The answer is no; However I am telling where to find these, that is the specific maintenance  manual of that specific aircraft. Had I to refrain from answering? May be no. Since 1 year, not to give a general answer nobody has answered.  Nevertheless hope this has been helpful.


What happens aerodynamically when we trim an aircraft? I'm trying to understand stability & control. Please correct me if I'm mistaken.
An aircraft will have longitudinal stability if the aerodynamic center (AC) is behind the center of gravity (CG). The AC is a point, where all the changes in the magnitude of the lift effectively take place.
The aircraft will be trimmed if the sum of the moments equals zero.

Question: is the center of pressure (CP) of the total aircraft (wing's lift and tailplane's aerodynamic force) or the AC, that must be positioned to coincide with the CG in order to trim the aircraft?
Do we change the location of the AC when we deflect the elevator?

It depends on the aircraft in question, the arrangement of the lifting surfaces, and how they are designed to ensure both static and dynamic stability.

For a simple case, well consider a traditionally designed airplane with a wing set placed approx midway along a fuselage with a horizontal tailplane at the empennage.

The design provides both good static stability and good dynamic stability.

It does so by placing the center of gravity (CG) ahead of the center of lift (CP) for the main wing and causing the tailplane to produce a downwards lifting force to counterbalance the moment caused by the distance between the CG and the CP.  While this is not as efficient a lifting arrangement as other designs like a canard foreplane, it forms a naturally stable platform in terms of longitudinal stability.  The airplane will remain stable only if these two moments cancel each other out causing the Net moment about the CG to be zero AND if the design naturally returns to a zero moment about the CG when dynamically changing speeds and attitudes.

For trimming, here we will only consider pitch trim for longitudinal stability.  An airplane trimmed for cruising at a specific airspeed and a particular altitude will have a net longitudinal moment about the CG of zero.  If the airplane increases its airspeed, the tailplane arrangement is designed to increase its downward force, creating a nose up pitch moment.  This in turn decreases the airspeed causing the the downward tailplane lift to decrease again, resulting in the nose pitching forward again until an equilibrium of forces and moments is again attained, which will be at the original airspeed for which the plane was trimmed for.  To maintain straight and level flight at a higher airspeed the trimming action will decrease the amount of lift that tailplane produces at the new selected airspeed, again resulting in a net longitudinal moment about the CG to zero.

Longitudinal trimming can be accomplished several different ways the first of which is a design feature which can alter the angle of attack of the tailplane in flight to change the lifting force it creates.  This is common on jetliners and other large aircraft but not common on light aircraft due to the excess weight of the structure.  Another option for smaller aircraft is the installation of a movable servo or antiservo tab on the elevator surfaces.  These tabs force the elevators to a new neutral position, again altering the lifting force from the tailplane and creating a trimmed condition.

In regards to the original question the net CP, that is the combined location of both the center of pressure of the wings and the center of pressure of the tailplane will coincide with the CG on the longitudinal axis of a trimmed airplane.  If the airplane accelerates, the NET CP will move fwd of the CG, causing the airplane to nose up, without additional trimming to bring it back.  Similarly, when the airplane decelerates, the NET CP will move aft of CG, causing the aircraft to nose down without additional trimming.


Are air traffic controllers required to obtain a pilot license? Here in my home country (Hong Kong), all air traffic controllers are required  to obtain a PPL as part of their training. The reason being, if the controllers can better imagine a pilot's perspective, they can better accommodate and provide assistance to pilots. I don't think they are required to keep the license current, but sure they need to pass all PPL exams.

Is this requirement common around the world? (Note that I intentionally do not specify which country or jurisdiction. I'm looking for an answer which lists the countries which have this requirement.)

No, there is no such requirement here in Germany.


What are the differences in door types in a commercial airliner? I was looking on YouTube at crew training videos. One door caught my attention for a Qantas 767. This door was completely electric and slid up and into the fuselage above, instead of out and to the side like most ones I've seen.

My question is how many different door mechanisms are there on commercial airliners and what are the benefits/disadvantages of each?

The only formal classification of door types that I could find is in 14 CFR 25.807, which specifies the emergency exit requirements for transport category aircraft. It defines Type I-IV, Type A-C, ventral and tailcone exits. The doors you usually enter and leave the aircraft through are probably type I or A:

Type I. This type is a floor-level exit with a rectangular opening of
not less than 24 inches wide by 48 inches high, with corner radii not
greater than eight inches.
Type A. This type is a floor-level exit with a rectangular opening of
not less than 42 inches wide by 72 inches high, with corner radii not
greater than seven inches.

These definitions are quite generic, but Transport Canada has a handy list of Aircraft Exit Profiles that gives specific details (often including the type) for many common aircraft. It says this for the 767 main doors:

B-767-200/300ER (Doors 1L/R FWD, 2L/R AFT)
Note: Some models equipped with 2 additional type 1 exits L/R just forward of wing.

H - 1.88 m (6 ft 2 in) W - 1.07 m (3 ft 6 in); Type A
Equivalent force required to move door control handle from closed/locked position to open position (Normal and Emergency): 12 kg
(26 lbs).
Approximate force required to open a door (lift upward) from unlocked to open: 18 kg (40lbs).
"Counterbalance" opening design.
Inward/upward opening doors.
Manually operated except some models equipped with electrical (normal operation) opening/closing option (FWD Entry Door).
Unique arming/disarming mechanism (lever, indicators).

Release button must be depressed and held to move arming lever to "Slide Armed" mode.
Yellow plastic "Emergency Use Only" (bendable) flag moves upward in front of Door Control Handle when slide is in armed mode.
Double channel slides.

Upward rotating Door Control Handle.
"Uplatch" mechanism holds door in open position. Button must be depressed while door is lowered initial few inches, to release.

You can see from that list that the details can vary a lot, even if the basic designs are very similar.
Coming up with pros and cons for every variant would be tough (especially for me, since I know nothing about it!), but obviously some aircraft are larger than others and that will limit how much space is available for the door mechanism. There are also operational considerations: aircraft that frequently operate out of smaller airports without jet bridges may need to have airstairs, which are usually built into the doors.


What is this hole above the intake of engines of Mil helicopters? Almost all the helicopters designed and manufactured by Mil have a hole above the intake. e.g.

What is it for? APU? Other helicopters made by this company:

This link claims it's the central oil cooler intake for the Mi-26.


How much water is produced in jet exhaust? If a jet has typical combustion efficiency, what equivilent amount of liquid water will be created per gallon of jet or kerosene fuel. An acceptable answer can be a ratio in weight or volume to the original unburned fuel. For example an answer might be 1 part in 50 by volume or 1/4oz per pound is converted to water.

An answer in "water vapor" volume should be avoided because gas volume changes dramatically with altitude (pressure) and temperature.

If you are also able to show a comparison for gasoline, that would be even better.

According to Wikipedia Kerosene consists of molecules containing 10..16 C-atoms.
Assuming that the molecules are mainly Alkanes with formula $C_nH_{2n+2}$:

$C_{10}H_{22}$: 10 * 12g + 22g = 142g Alkane contains 22g H which burns to 22g + 11 * 16g = 198g $H_2O$
Ratio Water/Kerosene = 198/142 = ca. 1.39

$C_{16}H_{34}$: 16 * 12g + 34g = 226g Alkane contains 34g H which burns to 34g + 17 * 16g = 306g $H_2O$
Ratio Water/Kerosene = 306/226 = ca. 1.35

I.e. you get something between 1.35g and 1.39g Water per 1g Kerosene.

Comparison to Gasoline:
Main difference of Gasoline is that molecule chains are shorter (4-12 C-atoms).
I.e. H/C-ratio will be higher, i.e. Gasoline will yield more water per fuel than Kerosene.


Why does an aircraft use less fuel while landing as opposed to takeoff and climb? I read that the weight ratio of an aircraft after and before landing, was larger than the ratio after and before takeoff. The weight is lost only due to fuel burn, so why does an aircraft appear to consume more fuel during takeoff than during landing? How does the 'ground effect' play a role here?

Ground effect plays very little here.

When taking off and climbing you need to add kinetic energy and potential energy to the plane in terms of speed and height. Getting that energy requires burning fuel.

When landing you want to get rid of that energy. Easiest way is to turn down the engine (or off when something breaks) and let drag slow you down and trade height for speed.

When taking off the plane will also be heavier because it will have more fuel on board. So it takes more energy to speed it up and get it up high.

It's very similar to climbing a hill and descending a hill, going up takes energy and going down means you can coast.


Can a free-falling aircraft with no horizontal (or minimal horizontal velocity) start up and fly to safety? Inspired by this Grand Theft Auto gif, an aircraft with its engines initially idling is dropped from a high altitude (such as from the top of a building) with no or minimal horizontal velocity. Can it successfully throttle up and fly to safety? How about for

A fixed-wing aircraft, and
A helicopter

Rather obviously, both of these situations are far from likely to occur. As a result, the following is just idle (but hopefully informed!) speculation — I don't recommend experiments!

I'm going to be a little bit cheeky in answering this question -- you've asked if it's possible for “a fixed wing aircraft to [...] get the engines up to speed and fly off.” I'll answer “Yes, but it depends on the aircraft.” For the fixed wing aircraft I usually fly, a K-21 glider, getting the engines up to speed is a doddle — it’s powered by gravity (and essentially stays aloft by the sun). What matters here is the stall speed of the aircraft in question, and how quickly the pilot could recover from the ‘upset’ of being kicked off the top of a tall building, and land somewhere sensible (which can only realistically happen once the aircraft is not stalled). If the relative airflow over the K21’s wings is about 35 knots (40 mph, 65 kph) or greater, they generate enough lift to keep it airborne (and going about 30 m forward for every meter down).

If we assume that you’re a free-falling body, Newton (in the form of $v=u+at$) says that it’ll take about 1.8 seconds to reach that speed, and you’ll fall ($v^2=u^2+2as$) about 16 meters during that time.

Of course, you’ll be pointing nose down at the ground, accelerating, and needing to do something about it — which will take time, and, more importantly distance. But, in the grand scheme of sky-scrapers, mountains and cliffs, 16.2 m isn’t that high. Incidentally, for this reason, bungee launching is a traditional method of getting gliders airborne in parts of the world with big hills — a team of runners using glorified elastic bands shoot brave pilots into the blue yonder, as illustrated by the picture below (at the Long Mynd).

So, given that a hill is enough height for a sailplane to take off, possibly for a few hours on a good day, I’m reasonably sure that something like the John Hancock Centre would provide more than enough time for a pilot to recover from an odd attitude, loop forward to a nose-down dive, recover smoothly from it, and fly away (from the big building behind him).

The gif you linked to featured what looked a lot like a small private jet. I defer to the others on this site with a lot more turbofan experience than I, but I’ll just say this: given an hour that I spent in a 777 simulator, twenty minutes were spent going from “cold and dark” to pushback, I suspect you’d have a much harder time doing it. Of course, rapid engine starts are possible in some aircraft. It depends a lot on the exact circumstances you're asking (and passenger jets tend not to be designed for inverted flight, for example).

By all accounts, this situation isn’t probably going to be very recoverable. If the blades are stationary when the aircraft starts falling, they’ll be fully stalled, resulting in a low-rotor RPM stall, which, depending on the brand of helicopter may not “be recoverable” (e.g., even with a working engine, Robinson helicopters are generally not recoverable from a very low rotor RPM stall). Autorotation is the driven motion of the rotor by the air falling through it, but, as pointed out, fully-stalled blades at any angle will not generate much torque (or lift), and therefore be unable to arrest the rate of descent of the falling aircraft. I presume that the only exception would be a fuselage that could provide lift through another means, such as the V-22 Osprey.


How do engines cope with various intake airflow speeds? On a recent trip out of Washington Dulles to San Francisco, our B777 met with 200+ mph headwinds (as per the passenger entertainment system) at 35,000 ft for the first half of the route, before enjoying 50 mph tailwinds at 38,000 ft over Utah, Nevada and finally California.

The ground speed was displayed at 400 mph for the first half of the trip, then closer to 550 mph. Does that mean that air was rammed into the engines first at 400+200 = 600 mph, then in the second half of the trip at only 550 - 50 = 500 mph?

How do the engines cope with various intake airflow speeds?

The airplane isn't aware of the winds. It just moves through the air mass at a certain speed, and if the air mass is moving it adds or subtracts from the aircraft's speed over the earth.

Drive your boat along a river with a 10 mph current upstream, then downstream, both at 25 mph on the boat's speedo.  The whole time your boat's showing 25 and the hydrodynamic forces acting on the hull are 25 mph forces. What's your speed relative to the shoreline going upstream compared to going downstream?  15 going upstream and 35 going downstream right?

Exact same thing with airplanes.  Navigating ships allowing for ocean currents is exactly the same as navigating airplanes in "air currents", they have "tailwind" currents and "headwind" currents and cross currents where you have to aim for point X to actually proceed to point Y, except things are happening in slow motion in the ship.


What are these circles around the propeller? (Source: www.airliners.net)

These circles I believe are the wing tip vortex formed by the propeller tips or is it just due to the rotation of the propeller. How does this occur?

They are tip vortices formed by the propeller, just like the wing tip vortices.

The propeller produces thrust, just like the normal wing produces lift. As any wing of finite length produces vortices, the propeller also produces them and that is what you see in the picture.

This is not only limited to propellers. The helicopter rotors also do the same thing.


Does the Fokker 70/100 Flight Management Computer really contain the ability to play Pong? This clip now circulating on Facebook (YouTube link) shows two pilots playing a game of Pong on the Fokker 70/100 Flight Management System (FMS). The manufacturer is presumably Honeywell.

Does this feature really exist?

Thoughts:

I would have hoped they had better code review to catch this, but then again I'm not sure how these work. A few veteran old employees who know ADA or whatever sitting in a dark room down the corridor when the new intern shows up?
The hardware is fairly old with corresponding limitations. As much as the flight displays (EICAS) can do decent graphics, the FMC seems pretty 'paginated' and slow to react to button presses.

Update: Thanks for the input. I was fairly certain it was fake but couldn't find the error. It also provoked some interesting software debate :)

The 'clip' is obviously a fake. Standards for avionics software development and testing are rigorous, with development of flight critical software being done by separate (independent) groups and legally required to be reviewed by another (independent) group.
After that testing is done by another group/person who's certified by the regulatory authority. It is very very difficult and downright dangerous to have this kind of codes in flight critical system software.
Also, as BowlOfRed says, there is a point in the video where the finger (of copilot?) goes behind the screen.

Also, from the clip, it appears that the two 'players' predict each other's moves pretty accurately. I'm not very sure if that's the way it is played, but I doubt it.
Of course, to prove that something is impossible is not possible, but I'm quite certain that the clip is a fake.


Why does the Boeing 747 have a nickname but other aircraft do not? Boeing 747 is commonly called Jumbo Jet.

How did it get this nickname and why other airplanes do not have nicknames?

Please note that I am not talking about official names, e.g, Boeing 787 Dreamliner.

How Boeing 747 is called Jumbo Jet?

The Boeing 747 is the world's first wide-body aircraft. For a long time, it was the world's largest passenger aircraft1. When Boeing was designing the 747 in mid-1960s, it expected that in the near future supersonic travel would become the norm. Hence, there would not be a need for the passenger version of 747. Because of this, 747s were designed in a way that they can be easily converted into freighters.

Pan Am, being one of the first customers of 747, wanted to fit two rows of cargo containers2, instead of one. This meant that the fuselage had to be at least 16 feet wide, wider than any airliner at that time. This would have worked fine for cargo, but it would make loading and unloading passengers very time-consuming. To accommodate this, Boeing engineers designed two aisles, which ran parallel through the length of the aircraft, hence the term wide-body was coined.

When the press noticed the huge size, they described it with the catchy term Jumbo Jet. It is also known as Queen of the Skies but that is not common.

  Do other airplanes have nicknames?

Airbus A380 dubbed as superjumbo by media. The only A380 sold as a business jet is called Flying Palace.

Although there aren't official nicknames of airplanes, almost all airplanes earned some nick names. This list contains nicknames for mostly military aircraft.

1 Airbus 380 took over as world's largest passenger airplane in 2007.
2 At that time, cargo containers were cubes that measured 8 feet (2.44 m) per side.


What is the rationale for single engine military aircraft? In aeronautics, redundancy is of primary concern. Having at least two engines is common for civilian aircraft. I expect the military to have at least the same level of redundancy. Moreover military aircrafts are prone to other failure modes such as bullet in the airframe over a territory in which they cannot easily land (e.g. mountains or desert in which pilots can be captured).

I will restrict this question to jet fighters but I think it can be extended to any military aircraft.

I expect modern fighters to have at least two jet engines for redundancy. This is the case for many of them (such as the F-22 Raptor, the Dassault Rafale, the Eurofighter Typhoon, the Su-27 family, the F/A-18 Hornet, and others).

Yet, some modern fighters have only one jet engine (for instance the F-16 Fighting Falcon, the Saab JAS 39 Gripen, the F-35 Lightning II, and the Dassault Mirage 2000). Thus I imagine there are good reasons to abandon engine redundancy, but I fail to see what reasons can outweigh such a feature, especially for military aircraft.

What are the reasons behind the design of a modern jet fighter with only one jet engine?

Because single engine fighters are substantially cheaper to purchase and operate.  Exact figures are hard to obtain, but as an example, an F-15 squadron will spend about 25,000 USD per flight hour whereas an F-16 Squadron spends about 15,000 USD per flight hour.   Effectively, you can purchase and operate twice the fighter force with single engine fighters than with multi-engine fighters.   This becomes very attractive for land based air forces belonging to countries with small defense budgets to operate the maximum number of combat aircraft per unit of currency spent.

Another major advantage to single engine fighters is maximized performance in a minimal size and weight package.  Adding a second engine will produce more thrust but at the cost of greater weight and fuel consumption.  This in turn requires more fuel be carried with a heavier airframe, creating a vicious circle for the design of these airplanes.  Typically in fighter design you want a specific weight ratio $W_a = W_{af}/(W_{af} + W_f)$ as low as possible.  This translates into an airplane which is a nimble, high capacity gas can with as low an empty weight as possible for a given range profile.  This is extraordinary difficult to do with a multi engine airframe.

The major advantage to a multi engine fighter is the same advantage that any other multi engine airplane has: they can carry larger payloads with greater system redundancy.   The large airframes accommodate big powerful fire control radars for detecting and tracking targets at very great distances, etc.  Certain units, particularly the United States Navy, prefer multi engine airplanes for overwater operations for the redundancy of having an additional engine to get you back home.   So too is this a design feature of the A-10 attack jet which anticipates enduring battle damage and the additional engine offers a better chance of limping it home if it gets shot up.

While the redundancy of two engines may seem ideal for combat ops, keep in mind an engine failure combined with the compressor and boat tail drag from the dead engine results in an airplane which has lost 50% of its total available engine thrust and 80% of its combat effectiveness.  All you could do after an engine failure would be to limp the airplane home to a friendly base - provided the enemy is gracious enough to let you do so without jumping your six and blowing you out of the sky!


Are evacuation slides meant to be used as safety boats? What are design considerations and usage procedures for these slides in case of some successful water landing?

For instance, are they meant to be detached from the fuselage at some point?

Or instead are they supposed to keep the whole or remaining airframe floating?

Are there any braces or ropes to grab them?

The inflatable slides are indeed also life rafts and they are meant to be detached. Consider United 1549 (landed on the Hudson). Here you can see the slides inflated and floating

Here you can see people in the slide, which has been detached from the airplane

The Wikipedia article mentions it specifically

  Sullenberger advised the ferry crews to rescue those on the wings first, as they were in more jeopardy than those on the slides, which detached to become life rafts.

It's impractical to keep an airplane afloat in the water. Assuming you successfully land intact, the plane is still a metal tube on the water. It may be airtight, but water will eventually begin to invade. Airbus has a water ditch button to help slow (but not prevent) flooding

  Some aircraft are designed with the possibility of a water landing in mind. Airbus aircraft, for example, feature a "ditching button" which, if pressed, closes valves and openings underneath the aircraft, including the outflow valve, the air inlet for the emergency RAT, the avionics inlet, the extract valve, and the flow control valve. It is meant to slow flooding in a water landing.

You want to evacuate as soon as possible. Remember, the slides help keep some water away from the door, but the plane will eventually flood and sink.


Does the tailplane have a positive/negative camber? I've read that the tailplane produces negative lift, so does that mean it would function like an inverted wing (has negative camber)? The image below is the best illustration I could come up with.

Also, is negative lift and tail down force the same thing?

The tailplane should produce less lift than the main wing, for pitch stability. That is to say, its lift is negative relative to the wing lift. Its lift need not be wholly negative (pointing down), although it usually is during takeoff and landing.

But yes, as a first approximation, the direction of camber matches the direction of lift.

Also yes, negative lift (at the tail or anywhere else) can be called downforce (at the tail or anywhere else).

Here is Peter's explanation.


How challenging is it to land a plane on a tabletop runway? Yesterday(August 7 2020), an Air India Express plane skidded of the runway(Dubai - Kozhikode, IN) and fell almost 30 feet below from the tabletop runway and broke into two pieces. It was also heavily raining and the visibility was low. Unfortunately, 17 people died including the pilot and co-pilot. The pilot was well experienced and had worked in the Indian Air Force. For more info: https://www.msn.com/en-in/news/other/air-india-flight-from-dubai-crashlands-in-kozhikode-both-pilots-among-17-killed/ar-BB17I15z
The runway as I said earlier is a tabletop runway, I heard that these runways create some sort of optical illusion, thus it is challenging to land a plane.

There are a couple of optical illusions that can come into play on tabletop runways:

Because the runway sits higher than the surrounding terrain, depth perception can be thrown off and the runway may seem like it should be lower than it actually is.

Due to the steep drop off just past the end of the runway, it can be difficult to judge the remaining length as it seems to stretch on into the landscape beyond, almost like an infinity pool.

Beyond this, tabletop runways in general tend to punish overruns more than traditional runways because there can be very limited space before the large verticle drop. Precise, well-configured approaches are vital, and proper care must be taken to ensure that the runway provides plenty of length for the landing roll of the aircraft (considering speed, flaps setting, weight, runway condition, etc.)
To simplify: There are plenty of runways that are trickier to shoot, but might not have such a severe penalty for getting it wrong.


Can a PPL be a safety pilot? I got a question from PPL oral checker, but I was not able to answer. The question:

  One pilot is practicing an instrument approach in VMC, can you be a safety pilot?

As long as the "Safety Pilot" possesses the qualifications and under the conditions listed below (from FAR 91.109):

  (c) No person may operate a civil aircraft in simulated instrument flight unless—

    (1) The other control seat is occupied by a safety pilot who possesses at least a private pilot certificate with category and class ratings appropriate to the aircraft being flown.

    (2) The safety pilot has adequate vision forward and to each side of the aircraft, or a competent observer in the aircraft adequately supplements the vision of the safety pilot; and

    (3) Except in the case of lighter-than-air aircraft, that aircraft is equipped with fully functioning dual controls. However, simulated instrument flight may be conducted in a single-engine airplane, equipped with a single, functioning, throwover control wheel, in place of fixed, dual controls of the elevator and ailerons, when—

      (i) The safety pilot has determined that the flight can be conducted safely; and

      (ii) The person manipulating the controls has at least a private pilot certificate with appropriate category and class ratings.


Why doesn't Stratolaunch have connected tailplanes like it has connected wings? As a complete layman, the design of the Stratolaunch airplane, especially when reminding myself of its size, seems too flimsy, in that the only connection between the two fuselages is the center wing. Apart from apparently trusting their materials and connections, what might the reasons have been for  Dynetics engineers to not also connect the tailplanes? Also, are there no aerodynamic disadvantages to having that many more trailing edges (if that's the terminology used)?

There is indeed an Eigenmode possible on the Stratolaunch which does not exist on regular airplanes: If the two fuselages pitch in opposite direction, thereby twisting the center wing. If that happens at the torsional eigenfrequency of the center wing, flutter might be possible.

Stratolaunch in flight (picture source)

Given the pitch damping of the horizontal tails, however, this scenario is rather unlikely. I bet the elevators have plenty of mass balance to avoid this flutter case. Underbalanced, their dynamic response would support flutter, but overbalancing would dampen this flutter mode. Connecting the tails would not make much of a difference and would even reduce pitch damping somewhat in the above mentioned case.

Similar configurations used both, a connection horizontal tail (F-82 Twin Mustang) or individual tails (He-111 Zwilling).

North American F-82 Twin Mustang (image source)

Heinkel 111 Z (image source)


Why Helicopter compulsory need helipad to land? Our Country ministers helicopter didn't land because there is no helipad exist in my location, helicopter needs small place to land, then why Helicopter compulsory need helipad to land?

Helicopters don't need a helipad to land. It is simply safer landing in a helipad. I think the decision was taken in view of safety not to land because of the presence of the minister on board.

See this picture.

That said, why did they come in helicopter if there was no helipad?


USA: Why don't airports raise landing fees to make up for low passenger fees? A question from travel.stackexchange.com about luggage carts prompted a discussion on the economics of airports. The gist was:

American airports have much lower passenger service fees which
 are capped at USD4.50 per FAA rules than foreign airports, which can easily be USD20-50 per person. This results in much
 lower number of amenities at American airports compared to other international airports.

You’d think they’d try to make it back with landing fees.  But Tokyo Narita airport’s landing fee is JPY1550-2000 yen per tonne. A 787-8 has a weight of 172 t so the fee would be ¥258,000 - ¥344,000 or so or roughly USD2300 - USD3100. San Francisco SFO’s landing fee is USD5.54 per thousand pounds. A 787-8 landing weight is 379,200 pounds so the landing fee is around USD2100. There doesn’t appear to be a significant delta here to account for the difference in passenger fees.

My question is: Why don't airports simply increase the landing fees to compensate for the lower per-passenger fees?

This depends on where you are in the country and more specifically who controls the airport. A lot of airports in the US are owned by cities (or local governments) in some capacity. As such changing the landing fees often requires a legislative change which is not always easy. For example here is the legislation that covers the landing fees at both major airports Philadelphia Controls

Changing these requires a policy change at the government level and it takes a long time to get just about anything through the Philadelphia government. In many cases these fees are paid to the municipality anyway and the airport never sees any of the money so the fees don't (directly) help the airport. In a lot of cases the fees do (or at least are presumed) to go back to the maintenance and upkeep of the airport.

Private airports (generally smaller GA ones) can levy fees as they see fit and sometimes do to help with the upkeep of the field.

What airports or more specifically FBO's and other on field operators do is raise operational costs to use their facilities. Rising FBO fees have been of concern lately and sometimes there is no way to escape them if someone has what amounts to all the parking space on the field. It may only cost $5 to land somewhere but keeping your plane there for a while, getting a pre-heat, maybe even using a terminal is by no means cheap.


Some wing parts designation Under the trailing edge, there are 3 features, as seen in the picture. What's the name and the purpose of them?
The chord line is the distance between the leading and trailing edge.
What's the name of the upper and the lower surface of a wing?

The sharp pods are called anti-shock bodies or flap track fairings. See this question for further information. Simply put, htey are there to reduce drag- transonic drag by smoothly varying the cross sectional area (Whitcomb Area rule) and by covering the flap actuators.

The straight line connecting the wing leading and trailing edges is called chord line; the distance between them is called chord length (both are usually called chord).

The upper and lower wing sufraces are called, well, upper surface and lower surface of wing.


What happens to an airborne plane when its type is grounded by an authority? Many countries have (temporarily I think) banned 737 Max 8s from taking off or landing. What happened to the ones in the air? Do they get special permissions or are they forced to divert to a different country that is allowing them to land?

You can find the full wording of the EASA grounding order here which does not specify a course of action for planes mid air but does call for the immediate grounding at the time the order goes into effect (March 12th 2019 @ 19:00Z)

  For the reasons described above, pending the availability of more
  information, EASA has decided to suspend all flight operations of the
  two affected models.

  This AD is considered an interim action and
  further AD action is expected to follow.

The AD points to sections 301 and 303 of the EASA regulations which does not seem to shed much more light on the situation other than;

  Any applicable airworthiness directive must be carried out within the
  requirements of that airworthiness directive, unless otherwise
  specified by the Agency.

Which points us back to the AD, which again offers no specific instructions on immediate grounding.

However according to FlightRadar24's Twitter they are seeing some diversions or at least possible course changes. As people point out in the comments its possible the airlines are diverting the aircraft to airports they can better provide support/maintenance at.


Why do some turboprop engines require motoring after shut down? A retired pilot I know told me about his time flying a Cessna 441 Conquest II. He said that after shut down he'd have to go out and motor the props. What engines require this procedure and what is the purpose?

Rotating the propeller of the Cessna 441 Conquest II is to cool the Garrett TPE331 engine in the aircraft. From airliners.net

  On the Garrett TPE331's we were trained to spin the props after shutdown to get cooling air flowing through the engine, this was done right after shutdown. Half an hour after we did the prop spins we had go back out to the aircraft and rotate the propellers one blade width. Moving the prop one blade width rotated the engine one half turn, this was to prevent the shaft from sagging as the engine cooled causing turbine blades to rub.

The reason is given as:

  Direct drive turbo prop engines sometimes require this to remove residual heat from the engine because once the prop stops turning, so does the engine. When the pilot turns the prop, depending on the gear ratio, he is actually spinning the engine very fast. This helps move some of the heat out of the engine.


Why do fighter jets pilots use an oxygen mask? I always wondered why fighter pilots need to fly with a facemask.
Since the cabin in pressurised wouldn't the oxygen level be the same as in any commercial jet so sufficient for the pilot to remain conscious and aware?
Thank you

the pressurization system in a fighter plane might be able to furnish 10,000 ft cabin altitude at 30,000 feet, but the pilot would need supplemental oxygen when flying higher than that. In addition, if the cabin is breached above 30,000 ft the pilot would have very little time to get his or her mask on before blacking out, so the mask is worn at all times.


Could a flight ever be considered to be operating under Visual Flight Rules and Instrument Flight Rules at the same time? In the US, could a flight ever be considered to be operating under Visual Flight Rules and Instrument Flight Rules at the same time?

If not, where in the FARs is this spelled out?

Consider the specific case of an IFR-rated pilot flying an IFR-equipped aircraft, but with no IFR or VFR flight plan filed and no IFR clearance requested or delivered, staying in Class G airspace and observing the VFR cloud clearance and visibility requirements spelled out in FAR 91.155.  How can we determine whether this flight is operating under VFR or IFR?  Why could it not be considered to be operating under both?

Bonus question-- is there any specific case, falling within the general conditions described above, where it would matter whether the flight were operating under VFR or IFR?  Assuming that the pilot intends to, and is able to, remain in Class G airspace and observe the VFR cloud clearance and visibility requirements spelled out in FAR 91.155, would it be practical for the pilot to decide in advance that he will simply flip a coin to determine the answer if ATC, or anyone else, enquires whether he is operating under VFR or IFR?  With the added proviso that if no one makes such an enquiry, he will leave the coin unflipped until after landing, at which point he will flip the coin to see whether the flight was conducted under VFR or IFR?  Would such a plan present any practical difficulties?

Related, but not the same--

Can an IFR clearance be issued and flown through IMC in class G airspace? -- note that several of the answers, as well as many comments, to this question also address a different question (which probably ought to be asked as a separate ASE question), which is "May an IFR-rated pilot flying an IFR-rated aircraft in Class G airspace violate the VFR cloud clearance requirements without an IFR clearance?"

No, you can't be both VFR and IFR at the same time. It would be like saying that a ball is both red and blue at the same time. You are either one or the other, never both.

If the pilot hasn't received an IFR clearance from flight services, then they are operating under visual flight rules, regardless of their intentions, capabilities, or flight plan. The sole exception is in class G airspace, specifically when they're flying a pre-set departure or arrival procedure from an airport. If a VFR pilot enters a cloud (and there's no emergency in progress), then they are breaking the law, and they can't just decide later that "oh, I was actually IFR at that time".

ATC is never going to inquire about which rule set you're operating under unless there's some kind of administrative foul-up. They're the ones that either did or did not issue you the clearance, so they already know which rule set you're operating under.


When should I use the global Reynolds number and when the local Reynolds number? I know that for the wing, the Reynolds number is based on the MAC. This makes sense to me, as the boundary layer develops along the length of the wing.

However, what kind of Reynolds number needs to be used if there is a flap behind the main wing and there is flow pattern like this:

Source

Some of the air particles  will have streamed along the wing before hitting the flap, so I would say then you should use the wing Reynolds number.

But, on the flap, also a new boundary layer will start. Particles coming through the gap will only see the flap, and will thus experience a flow with a lower Reynolds number (based on the flap length).

If I'm talking about flow phenomena on the flap, should I be using the global Reynolds number (based on the wing chord), or the local Reynolds number?

Definitely use the local Reynolds number on each of the flaps! The flap will only work properly if it is allowed to produce its own, fresh boundary layer. If instead it inherits the slow, thick boundary layer of the wing or flap ahead of it, the flow would soon separate and the flap would loose most of its effectiveness.

Note that a Reynolds number is always a local phenomenon. At 2 m from the leading edge, the Reynolds number is twice as large as at 1 m. Only when you compare total coefficients for the whole airfoil would the Reynolds number at the trailing edge be used.

If the distance between your bodies is more than a few centimeters, the boundary layers will not interact, so again the local length should be used for the Reynolds number reference length.


Does the Boeing 737 MAX use electro-hydraulic actuators? I know the B747-8 uses electro-hydraulic actuators as does the 787, but what about the 737 MAX?

The Max will have hydraulic systems very similar to the NG airplanes, except for the spoilers; those will be "fly-by-wire" and electrically controlled, but still hydraulically actuated. (Edited to correct what I had wrong in the original post. The comments are correct.)

Discussion of the FBW spoilers' capabilities


Why don’t large aircraft (larger than ~737-size) have even partial manual-reversion capability? Essentially all large aircraft1 have flight control surfaces powered, either directly or indirectly, by hydraulic actuators, as do most medium-sized and some small aircraft.  Small- to medium-sized aircraft with hydraulically-actuated flight controls essentially always have some form of manual reversion capability, where the primary flight control surfaces (always the elevator and ailerons, and sometimes the rudder as well) are operated manually by the pilots, usually by control cables attached to the pilots’ yokes and pulling (depending on the aircraft) either on the control surfaces directly or on servo tabs which then generate aerodynamic forces which move the control surfaces.  This allows the flight control surfaces to remain operational in the event of a total failure of the aircraft’s hydraulic systems, albeit requiring the pilots to exert a (sometimes considerably) greater force on the controls to operate them.

Large aircraft, on the other hand, generally have no manual-reversion capability at all.  This is ostensibly due to the greater aerodynamic forces acting on their flight control surfaces at cruising speeds, which would require superhuman strength to completely overcome (despite the fact that, before hydraulic flight control boosting came into wide use, many, many large and fast aircraft were successfully flown with purely manual controls through the use of a number of force-reducing tricks).  However, in a no-hydraulics situation, having any manual control capability at all, even with a significantly- to considerably-reduced control authority and range of movement compared with hydraulically-boosted operation, would be an extremely-useful adjunct to throttle pitch control and steering (which – especially throttle steering – are difficult, sluggish, clunky, and only really usable for coarse altitude and flightpath adjustments).  So why don’t large aircraft have at least partial manual-reversion capability, despite even a little flight control authority being far, far better than nothing at all?

1 I'm using "large" here to mean "larger than a 737 MAX 10".

Adding in manual control mechanics for a large aircraft has serious drawbacks:

Weight: For a large aircraft, the weight of pulleys, cables, etc., will add up quickly. This costs money in fuel and by reducing the useful load of the aircraft.
Complexity: The manual system would have to be routed through the entire aircraft, including passing through pressure bulkheads and other structure. This takes a lot of time to design, install, and maintain. While there are certainly ways to deal with the high forces involved, that just adds more complexity.
Vulnerability: There have been multiple accidents in which manual control systems were improperly set up or jammed. The manual system would have to be designed so that fly-by-wire system would still work even if the manual system develops an issue. If an event is catastrophic enough to cripple all of the hydraulic/electrical systems, there's a good chance a manual system would be disabled as well.

The alternative is to design a hydraulic system that can match or exceed the reliability of a manual system. Of course this is not without its own complexities and issues, but virtually all modern airliners have gone this route. The weight and complexity of a manual system are not worth the remote probability that such a system would be both necessary and useful.


Gyro Erection System I have a hard time understanding the physics behind the pneumatic erecting system in an attitude indicator. According to my book and the linked image, the applied force is “precessed 90 degrees” (anti-clockwise seen from above) and thus re-aligns the gyro. I understand how the pendulous vanes change the exhaust of the air, but since this part is stationary, i.e. not rotating, how can the net force be precessed?

https://savageplane.files.wordpress.com/2017/06/pendulous-vanes-figure-10-101-screenshot-from-2017-06-06-171632.png

Gyroscopes have two types of motion.

The gyroscope spins within its housing (usually at a pretty high speed).
The housing can change attitude within some limits.

The vanes aren't part of spinning gyroscope, but they are part of the housing (which can shift/rotate with respect to the airframe).  The vanes create a torque to change the attitude of the housing.

There is a youtube video with some animations that try to show this effect.


Propeller Characteristics at Different Altitudes Assuming I have a propeller with a given diameter (D), pitch, blade twist, and number of blades, I can theoretically analyze discrete airfoil sections in XFOIL and come up with lift and drag polars for the airfoil sections, for a given Reynolds number. Using the new information along with the pitch and twist (to give angle of attack for each section), the overall thrust and torque for the propeller blade can be solved for given operating conditions (RPM and airspeed). Even more accurately, the induction airflow factors can be accounted for to adjust the velocity vectors and angles of attack experienced by the airfoil sections on the blade, and an iterative solution can yield more accurate thrust and torque data for the propeller. Doing this at different operating conditions (RPM and airspeed) can give many data points, allowing for a generation of a thrust, torque, and efficiency curve vs advance ratio. I have done all of the above for a certain propeller.

However, if I wanted to change my flight altitude (and thus air density would be different), my Reynolds number could be vastly different for the same operating conditions. Does the thrust, torque, and efficiency curves for the propeller still hold up? Or does the different Reynolds number mean that if I solved the airfoil sections thrust and torque data again, they would yield different dimensionless data as a function of advance ratio?

I'm happy to provide more details. Looking forward to figuring this out!

Your lift and drag polar is Reynolds number dependent. You need to check if you are happy with what XFoil generates for you. Airfoil characteristics are fairly constant over a wide range of Re, so it might not effect you at all.

Also, if you are running high tip speeds, there is another pote increasing altitude drops the temperature as well, so you are increasing the tip Mach number, which you need to make sure stays within the validity limits of your calculation method.


Why do cargo airplanes fly fewer cycles then airliners? Reading Why do cargo airlines frequently choose passenger aircraft rather than aircraft designed specifically for cargo?, some answers say that cargo aircraft fly less than passengers aircraft.  Why?

It's due to the overnight parcel distribution model which limits the available operating time.  A parcel picked up by 5pm needs time to get a terminal, and then has to get to the destination distribution terminal in time to be distributed and dropped off by mid afternoon the next day.

This means the heavies in the freight business do their flying overnight running between their distribution hubs (being a "Freight Dog" pilot is considered a night shift sort of career with fewer hours flown per year than pax flying, maybe 300-500 hours vs 700-1000 flying pax) so that freight can arrive at distribution points in the morning where it goes out to sub terminals on smaller aircraft during the day, or sent out by truck.

For example, Fedex runs aircraft in and out of Atlanta only between 10pm and 6am.  For many years I worked at an airport with a Fedex Terminal and you would wonder how anything got done because all you ever saw during the day was parked MD-11s lined up in front of the terminal, apparently just sitting there, with no freight movements to speak of after about 7 am, except for smaller a/c flying sub-distribution runs through the morning.  Well they are actually just waiting for their outgoing freight to arrive and if you happened by at midnight, it was pretty busy and there was a fair number of a/c coming and going.

So a freighter has maybe an 8 hour operating day, whereas a passenger a/c gets flogged like a mule and starts flying at 6 am and runs until 9 pm.  Plus the loading and unloading process for pallets is somewhat slower than with self-propelled human cattle getting on and off for you.  So you can't really do more than a couple of legs per day.

To provide context, this UPS fact sheet shows a fleet of 255 UPS jets doing 318 daily trips on average

It says "In-Out" trips for that 318 number, so lets assume that's actually 2 legs, 1 in and 1 out, for 636 actual flight cycles.  That's only 2.4 cycles per day overall, almost as easy a life for the airplane as corporate.


Would installing 6 engines on an Airbus A380 and or Boeing 747-800 achieve a shorter take off distance? Would installing 6 engines on an Airbus A380 and or Boeing 747-800 achieve a shorter take off distance?  Would that result in excessive acceleration and harmful or uncomfortable G-forces? Would the extra thrust and leverage exert excessive force on the wings?  How about braking,would the braking be shorter if all engines were fitted with thrust reversers

Would installing 6 engines on an Airbus A380 and or Boeing 747-800
  achieve a shorter take off distance?

Yes in theory, more thrust is faster acceleration.

No, because engine/wing interaction is not simple:

For the 747: the flaps will need an additional thrust gate, which will reduce the flaps capability.
For the A380: since it doesn't have a thrust gate, the additional thrust will create extra drag and pitch down moment, making it harder to lift the nose.
Bolting on engines is unrealistic, as it will require a new wing to take into account the extra forces on the wing.
The extra weight of the engines and their associated systems will increase the weight, which in turn will reduce the acceleration due to the increased normal force on the tires.
The extra engines will intake some of the air meant for the wings, so alongside the reduced capability of the flaps, there goes the full potential of the wing.
After a successful higher-speed takeoff, the extra engines will draw more fuel than needed (jet engines run less efficiently at lower-power). Which will result in a diminished range capability.

  Would that result in excessive acceleration and harmful or uncomfortable G-forces?

No, you can use the engines at low thrust if needed.

  Would the extra thrust and leverage exert excessive force on the wings?

Idem.

  How about braking, would the braking be shorter if all engines were
  fitted with thrust reversers.

Yes, in theory, this could be shorter.

No, with the decreased lift, the airplane will land at a faster speed, so no, not necessarily.


What is the lowest RNP approach requirement without being RNP AR? I was recently told by a friend that as soon as RNP for an approach is below the 1.0/0.3nm standard that it is required to be RNP AR.

At least here in Australia, a curved segment anywhere on the approach will qualify it as RNP AR, even if the RNP is 1.0/0.3nm.

Is there a hard and fast rule for RNP AR?

In ICAO DOC 9905 (Required Navigation Performance Authorization Required Procedure Design Manual) you can find the following definition in Chapter 2.1

  RNP APCH versus RNP AR APCH

  2.1.1 RNP APCH is defined as an RNP approach procedure that requires a lateral TSE of +/-1 NM in the initial,
  intermediate and missed approach segments (MAS) and a lateral TSE of ±0.3 NM in the FAS. Guidance on
  implementing RNP APCH operations can be found in the PBN Manual, Volume II, Chapter 5, Implementing RNP APCH.

  2.1.2 RNP AR APCH is defined as an RNP approach procedure that requires a lateral TSE as low as ±0.1 NM
  on any segment of the approach procedure. RNP AR APCH procedures also require that a specific vertical accuracy be
  maintained as detailed in the PBN Manual, Volume II, Part B, Chapter 6. The datum crossing point (DCP) for RNP AR
  procedures is the point located above the landing threshold point (LTP) or the fictitious threshold point (FTP). The RNP
  AR APCH criteria apply only to those aircraft and operators complying with specified additional certification, approval
  and training requirements. RNP AR APCH procedures are only published where significant operational advantages can
  be achieved while preserving or improving safety of operation. The RNP AR certification and approval requirements are
  contained in the PBN Manual. For the purposes of applying the criteria contained in this manual, RNP AR procedure
  obstacle protection is associated with RNP navigation accuracy requirements. The RNP navigation accuracy
  requirement is used to determine the area semi-width value (in NM) of a protection area associated with a segment of an
  instrument procedure.

So, yes, any procedure below the 1.0/0.3 NM standard is defined as RNP AR.

You will not normally find curved segments (RF turns) on an RNP APCH chart, as these segments require a recent FMS as noted in ICAO DOC 8168 Vol. II Part III Appendix to Chapter 5.

  Note 5.— RF may only be used for RNP procedures flown by aircraft equipped with systems that are compatible with ARINC 424-17, or later.

In those cases the chart will be promulgated with RF required.


Turboprop vs turbofan (in regional aircraft) I'm trying to figure out WHY turboprops are more efficient at lower altitudes and airspeed, while turbofans are better at faster speeds and higher altitude.

Simplistically, my explanation is the following:

Gas turbine part of both turboprop and turbofan engines is basically the same, so BOTH must benefit from increasing altitude.
However, as TAS also increases with the altitude, turboprops start experiencing supersonic effects (shock waves) at propeller tips, which limits their ceiling.

Is this explanation correct? What formulas can support it? Why turbofan is less efficient than turboprop at lower altitudes?

Thanks.

Turboprops are more efficient, because they accelerate more air by less to create the thrust, and therefore the air carries away less energy , since kinetic energy is proportional to square of velocity. This is true at all altitudes.

Neither engine benefits from altitude. They do benefit somewhat from the colder temperatures up high as heat engine efficiency is proportional to the ratio of high and low absolute temperature. But the main benefit from flying high is that drag is proportional to density, so in the less dense air up high the aircraft flies faster with the same thrust. This is true for both engine types.

The key difference is that turboprops are limited by true airspeed as when the propeller tips get close enough to speed of sound, shockwaves start to form that create massive drag (and a lot of noise) and the efficiency declines fast. In contrast the inlet of a turbofan modifies the pressure field around it so that the air always hits the fan the same speed independent of the speed of the aircraft, converting the extra velocity to pressure instead. Therefore turbofans maintain their efficiency to higher true airspeeds.

Since the low density at high altitudes also increases true stall speed, the true airspeed restriction of turboprops creates an altitude restriction too.

So for short routes where there is not enough distance to climb up as high, the higher efficiency of turboprops is better and turboprops are used. But for longer routes where you can climb up above about 30,000 ft and fly most of the route there, the increase in efficiency due to lower density and resulting higher true airspeed offsets the lower efficiency of the turbofan engines and they become better.

Plus flying faster reduces other costs. For short routes the aircraft spends larger fraction of time on the ground loading and unloading and refuelling, so flying faster has less effect and you want to minimise the fuel burn. But for longer routes flying faster means the aircraft can make more trips in a given time and the crews can make more trips and therefore the fixed costs spread over more passenger miles, which makes it worth flying faster even if it means using a bit more fuel. That again requires using turbofan engines.


How to calculate normal takeoff ground roll when the POH only has Short Field Takeoff tables? The Cessna 172S POH only has Short Field Takeoff Distance tables.  How do pilots determine ground roll for a normal takeoff on a long field with hard surface?

The examples in the POH only deal with short field takeoff.  Similar thing with chapter 10 in the Pilot's Handbook of Aeronautical Knowledge.  It's either short field takeoff or referring to charts that don't exist in the Cessna 172S POH.

Do pilots look up the short field ground roll, apply the adjustment factor for headwind and apply another adjustment factor?

The POH says, on page 5-4 "...keeping in mind that the distances shown are based on the short field takeoff technique.  Conservative distances can be established by reading the chart at the next higher value for weight, altitude and temperature."

Does that mean to use the chart, but use the row for the next highest PA and the column for the next next highest temp when determining normal takeoff ground roll?

I've searched this forum and haven't found anything applicable.

In the C172S POH I have, it's on p. ii (Performance - Specifications): 960ft ground roll and 1630ft total over a 50ft obstacle. The note on p. iii says:

  The above performance figures are based on airplane weights at 2550
  pounds, standard atmospheric conditions, level, hard-surfaced dry
  runways and no wind. They are calculated values derived from flight
  tests conducted by Cessna Aircraft Company under carefully documented
  conditions and will vary with individual airplanes and numerous
  factors affecting flight performance.

In other words, it's a useful number to know but you're unlikely to get exactly that performance unless you're a Cessna test pilot in a brand new aircraft. If you own the aircraft (or rent it often) you might want to spend some time actually measuring takeoff distances yourself, to see what performance you're really getting.


How A330-200 or 243 would be much safer under the ETOPS terms? I am flying this week to France in an Airbus A330-200. I have a phobia of flying I have several questions here on the aviation forum. The plane is A330-200 is the one we're going with and I am reading about it. It works under the term ETOPS.

I read this part and now I am scared more than ever and I didn't understand it correctly:

  In aviation vernacular, the colloquial backronym is "Engines Turn Or
  Passengers Swim", referring to the inevitable emergency water landing
  of a twin engine aircraft after a double engine failure over water
  outside gliding range of land. But ETOPS operation has no direct
  correlation to water or distance over water. It refers to flight times
  between diversion airports, regardless as to whether such fields are
  separated by water or land.

The company I am flying with, its fleet has an average age of 5.6 years in 2016, making MEA one of the youngest fleets in the world.

ETOPS (Extended Twin Operations - at least that’s what it used to be called) is a set of rules comprising of flight planning, flight operations, aircraft maintenance, flight training and administrative procedures which are geared towards making aircraft operations safe in those regions where diversion airfields are not easily found, e.g. when crossing large oceans.

When these rules are obeyed (i.e. when operating under ETOPS), that should make flying very safe.


How do I find out the fuel consumption of the PT6A for a lightly loaded aircraft? The Fuel consumption of PT6 engines provided by manufacturers are as follows.

Cessna Caravan - Consumption ~47? GPH. At full load at ~160? Kn.
Quest Kodiak - Around 49 GPH at full load at ~170 Kn
Pilatus PC12 - Around 69 GPH at full load and cruise speed of ~250Kn

I was analyzing the fuel consumption levels, distance travelled and the impact of the engine, when only one or two passengers are travelling. I couldn't find any information on the internet about fuel consumption when the aircraft is just loaded with 400-600 pounds.
Any information or sources where i could find this information?

You need to obtain the specific fuel consumption (SFC) for the particular dash number of PT6 (scroll down to the bottom for the chart with the data). For example, the -67A turboshaft is down around .47 lb/hp/hr, close to piston engine territory, but most are between .5 and .6 lb/hp/hr.
So pick the dash number of engine applicable to the airplane you want to compare, note its SFC, and now all you have to do is calculate the HP required of a given aircraft at a given weight to cruise at a given speed, and that you should be able to interpolate from the airplane AFM/Operating Manual's cruise performance and power required chart data, working out the HP required to cruise at Speed X, and Weight Y.
Once you work out the required HP, and you know that engine's SFC, you're there.


Why does the DHC-6 pitch down when the flaps are retracted, rather than up? Air Moorea Flight 1121 crashed because one of its elevator cables broke immediately after the pilot retracted the flaps, but before he could trim out the resulting pitch-down moment - to quote the English translation of the BEA report,

The operator called for the reduction in engine RPM before retraction in order to mitigate the pitchdown moment caused by the flap retraction and so that the right hand, after having positioned the flap control lever on 0°, could be placed be placed on the elevator trim in order to reduce the effort on the control column. [report page 17/PDF page 19]
...stick free, the flap retraction led to a pitch-down moment varying the aeroplane trim between 20° and 30°, the rate-of-climb indicator going to stop at less than 3,000 ft/min and speed reaching 140 kt in twenty seconds… [page 42/44]
In flight, the loads on the cable are at their greatest when it is necessary to counter the pitch moment induced by the retraction of the flaps. [page 61/63]
The malfunction occurred at the top of the initial climb, passing through 350 feet, when the pilot retracted the flaps then adjusted the engine parameters. While he was adjusting the parameters with his right hand, he was holding the wheel with his left hand while pulling back to counter the pitch-down moment and stabilise the airplane on its flight path. It was only at the end of this process, which lasted nine seconds, that he would adjust the trim.
[...]
The flight tests showed that during flap retraction, when pitch control is free, the airplane dives with a high pitch angle. [page 63/65]

and, finally,

The DHC6 Twin Otter has significant pitch-down moment when the flaps are retracted. [page 67/69]

How can this be?  Flaps extend downwards from the trailing edge of a wing, and, thus, should always produce a pitch-down moment when extended (like applying nose-down elevator, except with a much shorter moment arm), and a pitch-up moment when retracted.  Why is the DHC-6 different in this regard?

The Twin Otter isn't unique.  Flaps have varying effects on different airplanes.  Some pitch up with flaps extended, some pitch down.   The pitching moment from flaps isn't just from the nose down moment from the increase in airfoil camber; it includes effects of increased downwash on the tail, which creates a pitch up moment, and to some degree, changes in the vertical aerodynamic center resulting from adding drag up high or down low (like the mild pitch down moment caused by gear extension).

In the Twin Otter the double-slotted flaps are extremely powerful and create a very strong downwash increase at high angles as opposed to just mostly turbulence you get with simpler flap setups. The result is the net effect of flap extension, with the high wing and the location of the horizontal stabilizer, is pitch up because those forces are stronger than the nose down moment created at the wing itself by the camber change.


Can I find out why an aircraft squawked an emergency code (7x00)? I have recently been using a mobile app to track flights, which is really cool.  I live in the rural heartland of America, so it's an event for me to see an A380 actually flying.

Every once in a while, a squawk 7700 alert will come up, which I understand is the emergency transponder code. There are more, such as 7600 and 7500, which I find are less common.

My question is, is there a way to do some post-mortem followup as to why the aircraft squawked the code?  Is this public information that can be found by some agency such as the NTSB?

This FAA webpage has a list of the various transponder codes and what they are used for, which will give you an idea of what the problem is.  Unless there is an actual aircraft incident or accident which requires the FAA to investigate though, you won't be able to find a record of it.  In fact, pilots aren't even required to file a report unless requested, and those don't go into a public database.

For actual incidents or accidents, you can look at the NTSB Accident Database & Synopses.

For pilot reports to the NASA ASRS self-reporting safety system, you can search their database.  If the pilot filed a report then you will see it show up there.

Commonly used emergency codes are:

7500 - Hijack Code
7600 - Loss of Radio Communications Code
7700 - Emergency Code

Also, some countries use the code 7000 for VFR traffic (which is not an emergency code), but the US uses 1200 instead.


How strong someone should be in order to fly without "power steering"? Planes these days use fly by wire systems while older ones had a mix of hydraulics with electronic assistance like the MD-11 (And maybe 737-800?).

But what would happen if you lost the electronic systems and you had to fly manually? I remember an incident of this happening in a MD-11 and pilots using raw muscle power to operate the flying surfaces (And using something like 10 kilos of force only to keep the yoke in place) or putting 10 kilos of force to the yoke constantly (My memory isnt exactly bad. It was a months ago)

So How much raw muscle power is needed to fly an MD-11 or an 737-800 without assistance for 10 minutes and then land? Through two pilots or as a single person.

You can't.  Most of these airplanes are flown with hydraulically powered control surfaces with no mechanical input possible from the cockpit flight controls.  The flight controls just operate servo control valves in the hydraulic actuators, like the bucket on a front end loader but a little fancier.  If it's FBW, the FBW system does the same thing at the actuators using torque motors operated by the FBW computers to drive the servo control valves.

There will be two, or three, hydraulic actuators driving each control surface.  The flight controls in the cockpit just control the extension/retraction of the actuators. Control feel in these airplane comes from spring devices in the control circuit to simulate "air loads".  There is no direct connection between the pilot and the dynamic forces acting on the control surface.  If you lose all of the hydraulic actuators, you lose the control surface.


What’s this vortex generator like thing below the wing? In Barcelona’s El Prat Airport I saw some ceiling fans and noticed that they have on the lower part of the wings something that looks like a wingtip device or vortex generator.

As far as I understand vortex generators, they prevent the boundary later to detach / move the separation point. But that’s no issue below an airfoil, is it?

The manufacturer, Big Ass Fans, calls those devices “air fences.” Based on this naming I assume they are most likely there to redirect spanwise flow on the longer airfoils, not to prevent separation. Such a narrow airfoil built to move at a steady speed and loading would probably not suffer from separation issues. They are basically the same as wing fences.

source:Big Ass Fans website

Wing fences are usually found on swept wings, because that’s what’s responsible for the spanwise flow, and the fan blades don’t appear to be swept. But in the case of a fan there will probably be a certain amount of radial flow due to the spinning motion. After a significant distance this could build up to be significant enough that the fence might help to redirect it.


Which countries permit pilots to carry a firearm? In the US, the FFDO programme trains and permits pilots to carry a firearm in the cockpit.

Do any other countries have a similar programme?

I spent a bit of time Googling this and I couldn't find any other country that systematically arms pilots using a public, open program like the FFDO. What countries might do in secret is anyone's guess, though.

The most obvious candidate is Israel, since El Al is famous for its tough and often very visible security. There are many reports that El Al uses sky marshals (one article says "on all flights"), but I couldn't find any mention of the pilots themselves being armed. That doesn't mean they aren't armed, but it at least suggests that there is no public program in Israel comparable to the FFDO.

For the same reason, the lack of information about similar publicly recognized programs in other countries strongly suggests that they don't exist.