What was the range of a low-frequency radio range station? The low-frequency radio range is a historic navigation aid that was in use from the 20's to the 70's.

I find it quite interesting. Using AM frequencies, what was the range of a high power LFR station?

A video on YouTube suggests it was even used to cross the Atlantic with stations in Greenland.

Source, LFR across the U.S., 1933.

Secondary question, based on the approach plate below, the red rectangle area shows what I believe is the AM frequency. What about the other four VHF(?) frequencies?

The frequencies seem to correspond to the ranges used by today's FSS/CTAF and military UHF. Searching CAA historic regulations wasn't helpful.

Image source

[Ex-avionics engineer, but not old enough to have worked on this ;)]

It's not so much the power of the station that determines the range, although it does of course impact the range.  The more important factors derive from the wavelength (which is a factor of the frequency).

The wavelengths of low frequency radio are in the order of metres to kilometres.  Signals at wavelengths of this order are subject to a lot less attenuation in the atmosphere since the stuff in air (dust, moisture, air movement due to thermals and wind etc) impact much less on a signal whose wavelength (the distance from peak to peak in the signal) is so large.

They are also subject to the effects of ground wave which means that the signal can follow the Earths' curvature and therefore travel way beyond the normal line of sight, up to a thousand miles or more.

They are also subject to ionospheric refraction or "sky wave".

The effects of the latter two depend a lot on night or day, sunspot activity, weather and so on but safe to say that sufficiently powerful signals ( a couple of kilowatts or so which is relatively small) in these ranges will be receivable over hundreds of miles and sometimes over a thousand miles.

The other frequencies look like 4 VHF and one UHF.  I'm sorry.  I have no idea what these are. My guess is that they are for tower, area etc in some order dictated by the plate legend.


Why do RNAV airways exist? I assume there's some stupidly obvious reason that I'm missing, but why bother creating RNAV airways when I thought the entire point of RNAV was not needing to fly along a suboptimal preset path?

I can see the need for waypoints, especially around the corners of restricted airspace that you'd need to dodge rather than just flying direct everywhere, but I'd think an RNAV flight plan would just be a handful of such critical waypoints--no "airways" needed.

RNAV freed aircraft from the airways that were already in place that may have zig zagged from VOR to VOR, but with the limitations of the ATC system based on human controllers, it is still desirable to keep most aircraft on a "road network" so to speak to make it easy to manage separation, so RNAV airways were created between major centers that provide straighter roads between cities you might say.

Try to imagine thousands of flights going hither and yon all on their own random tracks, instead of being fed along specific airways, without a bank of supercomputers to manage the separation, and you can see the problem that the RNAV airways solved.


How many aircraft does an ATC controller usually handle at the same time? My question relates to the question What is the maximum number of planes a controller can control?, which asks about the maximum limit. One comment indicated 35 aircraft per hour for en-route segment. I, however, are not interested in the maximum number of aircraft per sector, but in the typical number of aircraft.

I am now interested in the typical amount of aircraft per enroute Air Traffic Controller at any given time during the day (how many aircraft are handled at the same time by an en-route controller).

While I am sure that there is no universal ground truth, can anyone report experience? To limit the scope, let's assume continental U.S. or Europe during the day, upper airspace.

Depends entirely on complexity, rather than sheer numbers. In ATL I can comfortably handle somewhere around 60-70 departures per hour from a ground control position. More than double that when you factor in arrivals. That’s a VERY low complexity situation, with everyone moving one direction.

On the flip side, I’ve worked TRACON radar positions with five aircraft dodging severe weather and worked my ass off. High complexity.

ARTCC sectors are different in that they have known numbers, and will go from green to yellow to red depending on saturation. These are based on routings, in trail restrictions and so on. Again, all complexity.


What is the airplane with the best flying characteristics? I'm reading Stick and Rudder by Wolfgang Langewiesche, and in Chapter 7 titled, "What the Airplane Wants to Do" he discusses stability. In discussing it, he says that no plane yet built is completely "well-behaved" and that the plane closest to perfection is Fred E. Weick's Ercoupe.

It's been over 50 years since this book was written. Have aircraft flying characteristics improved? How much have they improved? And what airplanes have we built that have the best flying characteristics (which are the "best-behaved")?

First, let's get a little perspective
Stick and Rudder was written in the early days of aviation. To a modern reader, things were really weird back in the early days of aviation.

For a while, air traffic control was a guy sitting in lawn chair next to the runway waving a big flag that said "GO".
Parts on the plane just failed.  Planes would crash on their way back from bombing Hitler, a truck full of mechanics would come out to bolt on some (hopefully) new parts, and then they'd take back off in the crashed airplane to go bomb Hitler some more.
One time, the Allies bombed Switzerland by mistake. This was a world where more than one airplane could miss not only a target, but the entire country.

The kinds of things that went on in those days as a matter of routine would send any modern-day NTSB investigator into full-blown panic attacks.
What I'm getting at here is that it's a mistake to judge Stick and Rudder by modern standards.  This is not the equivalent of brain surgery.  You have to think of this as a surgeon just trying to get other surgeons to wash their hands with soap before they operate.
Now on to your questions

Have aircraft flying characteristics improved?

Yes. One example out of many:  Cuffed wings.

How much have they improved?

Enough that Wolfgang didn't need to write a second book.

And what airplanes have we built that have the best flying characteristics (which are the "best-behaved")?

An Airbus flying in Normal Law.
There's a section in Stick and Rudder (page 160 in some editions) where Wolfgang says that a "foolproof" airplane is one in which the controls have been restricted so that the pilot is mechanically incapable of pulling the airplane to an angle of attack which will result in a stall.  Guess what?  A pilot flying in normal law can yank on elevator all day long and not stall that Airbus.
An Airbus in normal law automatically trims itself.
An Airbus in normal law automatically increases power on the engines if a pilot pulls the airplane into a high angle of attack.
Some people might hesitate to put words in a dead man's mouth, but he's not here, so I'll go for it:  The best behaved airplane according to Wolfgang would be a modern-day Airbus airliner.


Is there an official method to do pre-departure briefings? We're using our simulator more at university, and while I might try to do a departure briefing (weather, route, etc.), it ends up fairly unstructured. None of us students have any formal qualifications and we are doing this for enjoyment, although we are keen to do it as authentically as possible.

FAA has an example online, that I gather is maybe be a bit overdone:

I've searched around for a recommended (check)list to go through for pre-departure briefings, but come out empty handed.

Is there such a document endorsed by either the EASA or the FAA?

The article linked below may be highly relevant, although it isn’t endorsed (directly) by any regulatory body. It describes how one company dissected their briefing concept and proposed improvements following a critical review of the adequacy, effectiveness and safety impact of their briefings in the operational context: Briefing Better


How are VFR / GAAP approach points selected? This is kind of an Australia based question.

How are VFR approach points selected and why they are where they are? Also what challenges will pilots face from the GAAP (General Aviation Airport Procedures) approach points to the VFR approach points transition?

The reason for VFR approach points is to provide an orderly arrival procedure into busy or complicated airfields.

I’ll use the example of Bankstown airport, which is the primary GA airfield for Sydney. I have (very crudely) circled the two VFR approach points in green:

Two RN is the approach point when arriving from the south or west. This is identifiable from the air as a large radio tower next to the intersection of two major highways. To the north, prospect reservoir is even easier to see as a dam just south of another large highway. Easy identification from the air is a key requirement for a VFR point, so you don’t get lost.

Why funnel inbound traffic through these points though? Well firstly, much of the airspace over Sydney is Class C and reserved for the heavies in and out of YSSY to the east. You can ask to enter this airspace but chances are you’ll be denied. To the south you also have restricted military airspace over Holsworthy, and to the north-west (mostly out of this map) you have Richmond airbase, two no-go zones. As a VFR pilot you’re not allowed to use GPS as a primary means of navigating, so tracking via these visible approach points greatly helps in not avoiding these areas.

Using approach points also helps the Bankstown ATC. Firstly though I need to clarify that in 2010 all GAAP airports were converted to Class D airspace, which is more in line with international setups. The main change for pilots was that entering via VFR approach points isn’t actually mandatory anymore (unless otherwise stated in the ERSA, which is the case for Bankstown).

Anyway, Class D airspace has ATC but no radar. Therefore ATC relies on procedural separation – that is, pilots broadcast where they are now and where they are going, and ATC makes sure it will be X minutes before someone else says they are on the same path.  So, if two aircraft report passing Prospect within 30 seconds of each other, ATC would probably tell the trailing aircraft to slow down or fly an orbit.

You ask about the challenges of 'transition' but I'm not sure what you mean - these are the entry points for Bankstown, from which it is quick and easy to visually track to the circuit. For other Class D airfields, as I said before, now that they are no longer GAAP you don't have to enter via approach points unless otherwise stated. And if a procedure is stated, AFAIK it will always involve a VFR approach point.


Why are these spec and serial numbers blank on a part's plate of a WWII US military plane? These pictures are of a plate from WWII US military plane that crashed in the high mountains of central Japan.

People living there say that after the war officials recovered the crash sites and some parts were put on display in a museum nearby.  This plate is attached to a small metal box which is part of the museum collection.

It says "gear box type JH-1045" manufactured by "Jack & Heintz, Cleveland Ohio".

But SPEC. and SER. are blank.  I assume these are where the spec number and serial number should go?

It looks like somebody carefully cut those parts off the plate.  People there say that was not done after the recovery, so the plane was flying with this plate as it is.  Nobody remembers the type of aircraft nor where the rest of the wreckage went.  I do not know whether the numbers were scraped off before flight or were just originally not there.

Why are these spec and serial numbers blank on the parts plate of a WWII US military plane?

Regards,
Naoya

I suspect the reason for this has nothing do with aviation and better fits at our history or statistics stackexchange counterparts.

Information about the production capacity of the enemy is of major strategic importance. Using the serial numbers of a relative few aircraft one can make a quite accurate estimate of the total number of aircraft produced. This was found out during world war II and is known as the German tank problem.

What I suspect is that after this methodology was developed, producers were asked to withheld the serial numbers from their products and/or replace them by a cryptographic equivalent.


What methodology did ICAO use to create the overall code nomenclature for airports? If an airport is from North America, then it starts with K and so on.

How did ICAO get the letters from?
Why does the Philippines region starts with A?
Why do airports in Izmir have
LTBx prefix?
Did they do some random letter ballot box?
Also why they decided to make 27 regions?
Why Does The Arctic have so many codes and why multi letter codes?
Honoring the countries that operates the adjacent runways to the science facilities perhaps?

I wanted to ask multiple questions but how they got names questions are about the exact same stuff and probably has the same answer and Arctic is almost exactly about the same topic too but I don't think it really needs a seperate question.

There is no one, easy answer for where each region (or country) got their one- or two-letter designation.  Many of them evolved over time.  When the ICAO (as an organizational body) was formed out of the international conference in Chicago in November 1944, dozens (or hundreds?) of things needed to be standardized between nations.  One of these things was a standard way to identify airports.  (another was aircraft registrations... a minor, but related, blurb about that at the end)

Many of these attending countries already had a "standardized letter prefix" from the 1912 convention in London regarding telecommunication call signs. For example, Canada was C (easy to understand why), and the United States was either W or K (less easy to see why, but there is history there, too -- see below). Other countries who were members to the 1912 convention had various call signs, some of which started with numbers.  These countries, obviously, did not easily convert over to a letter prefix system that ICAO was adopting.  At the end of the day, there were numerous ICAO committee meetings (and I can only imagine some heated arguments between delegates) that eventually resulted in the various regions and sub-regions we know today and that are depicted on the map below.

A small bit of history on how the USA evolved to the letter K:  In the late 1800s, when telegraph was getting under way and Morse Code was in heavy use, there were two very easy to use Morse Code letters: A (dot dash) and N (dash dot).  The US Government reserved these two letters for its military telegraph station call signs, and assigned A to the Army and N to the Navy. Makes some logical sense so far.  Of course, the civilians were wanting to get in on the revolutionary break through of wired (and eventually wireless) telegraphic communications, so the US Government created a civilian set of call signs in addition to the military. To do this, they simply added a single dash to each Morse Code letter, and the dot-dash (A) became dot-dash-dash (W) and the dash-dot (N) became dash-dot-dash (K).

The USA now essentially had four different letter-prefix designations for its radio station call signs: A and N (military use), and W and K (civilian use). The W and K call signs were also geographically separated with K being assigned to all stations in the west, and W for all stations to the east. The "border" between K and W changed over time, eventually landing on the Mississippi river, but that's another topic.  You still see this today in your AM/FM music broadcasting and TV stations, with most stations "out west" being a Kxxx identifier.

Eventually, voice radios became very popular and all new stations were only issued the letter K. W-stations were grandfathered in. Additionally, radio stations began to be carried onboard aircraft, and the previous military-only letter of N was eventually assigned to all airborne radios, including civilian. Aircraft began marking their exteriors with their N-xxx radio call sign.

Anyway, to make a long story short (too late?), the US was able to exert is muscle at the 1912 conference in London and all 4 of those letter prefixes (A,N,W, and K) were retained for sole use to the US.  But 35 years later, during the formation of the ICAO and the resulting subcommittees, the US agreed to be "Letter K" for its airport designations and "Letter N" for its aircraft registrations, losing the letters W and A (at least in the ICAO books).  Also, remember that Alaska and Hawaii were not yet states, so they were both lumped into the Pacific Region [P] with sub-regional designations of PH and PA, along with all the other Pacific Region subs (PG for Guam, PM for Midawy, PB for Baker, etc.).


Why the gradient of $C_L$-$\alpha$ graph increases with the Mach number? From the JAA ATPL Book 13 (Principles of flight) the gradient $\frac{dC_L}{d\alpha}$ of the $C_L$-$\alpha$ graph increases for higher Mach numbers. Can someone explain why this is the case?

This increase in lift curve slope with Mach is commonly predicted via the Prandtl-Glauert correction for 2D airfoil:

$$C_{l_\alpha}=\frac{C_{l_{\alpha_0}}}{\sqrt{1-M_\infty^2}}$$

where $C_{l_\alpha}$ is the 2D lift-curve slope, $C_{l_{\alpha_0}}$ is the 2D lift-curve slope in incompressible flow, and $M_\infty$ is the free-stream Mach number (Ref. Anderson, Fundamentals of Aerodynamics), and is accurate before local shock appears.

The physical reason is the magnification of pressure change due to density change (compressibility), as understood from the isentropic relation:

$$\frac{\rho}{\rho_\infty}=\left(\frac{p}{p_\infty}\right)^{1/\gamma}$$

where $\rho$ is density and $p$ is pressure (Ref. Drela, Flight Vehicle Aerodynamics).


How can planes with the same stall speed and power-to-weight ratio have such different takeoff field length, climb rate, glide ratio, etc? I am interested in better understanding the performance differences between different planes that seem to be similar in many important ways but that differ greatly in performance.

For example, take single engine turboprops A, B, and C that all have a regulation stall speed minimum of 61 knots, and that all have similar power to weight ratios at takeoff. Turboprop A has a takeoff field length of 1,200', B is 1,600', C is 2,400'. If they all have the same stall speed (and a similar lift-to-weight ratio, I would think) and similar power to weight ratios, shouldn't they have similar takeoff field length requirements?

Lancair Evolution

550hp at takeoff (750hp in flight)
4,550 lbs MTOW
max speed ~295 knots
1,200' field length
~10:1 glide ratio

Epic E1000

960hp at takeoff (1200hp in flight)
7,500 lbs MTOW
~330 knots max speed
1,600' field length
~17:1 glide ratio

Daher TBM 900*

850hp
7,400 lbs MTOW
~330 knots max speed
2,400' field length
*65 kts stall speed http://www.flyingmag.com/pilot-reports/turboprops/tbm-850-even-faster

If these planes have the same stall speed (and therefore, my intuition would think, similar ratios of lift to weight and drag), and have similar ratios of power-to-weight, how can they have such different field length requirements and glide ratios?

EDIT: UPDATED INFO

Stall speed is as defined by the FAA for Part 23 aircraft certification. Here's a link to how the FAA requires the stall speed to be validated.

Wikipedia defines this Vs0 speed as:

  Stall speed or minimum flight speed in landing configuration.

Are we comparing apples to oranges again? The differences in take-off length are far too big with such similar performance numbers, and I agree that they should be closer together - if we are really comparing the same thing.

Take-off means that the aircraft has to gain an energy difference with a potential and a kinetic component. FAR 23.53 demands a height of 50ft, and FAR 23.51 a speed of 1.2$\cdot\text v_{S}$, but adds more conditions that could be significant here. If the speed for continued safe flight is found to be higher, that speed must be used as the basis of the take-off performance.

The 61 kts stall speed limit only applies to aircraft below 6000 lbs MTOW, so two of the three are not constrained by this limit. Interestingly, the heavier aircraft have longer take-off lengths.

If the airplane weighs more than 6000 lbs and is certified in the commuter category, FAR 23.59 comes into force. It relaxes the height requirement (35 ft instead of 50) but adds a factor of 1.15 to the demonstrated length.

If all take-off distances would had been determined with the same rules and if the stall speed in take-off configuration would be equal between all three types, the take-off distance would be very similar. But I am sure both conditions are not met.


Can I fly in Europe using an FAA Statement of Demonstrated Ability (SODA)? I want to become a airline pilot but I have Monocular vision. I have no vision in my left eye but I have good vision in my right eye. I have read that I cannot become a pilot in Europe because of this condition.

So I just want to know if I can get a Statement of Demonstrated Ability (SODA) equivalent in Europe and then become a airline pilot?

If that is not possible, then can I take an FAA medical class 1 with a SODA, and then move back to Europe and fly in European airspace and fly internationally?

If that is not possible, then can I take an FAA medical class 1 with a
  SODA, and then move back to Europe and fly in European airspace and
  fly internationally?

Potentially, the FAA vision requirements, require you to have 20/20 in both eyes individually (corrected or uncorrected). You can find a summary of the regulations here to pass a standard medical. However the FAA does have a special issuance for people with monocular vision which you can find more info on here

  An applicant will be considered monocular when there is only one eye
  or when the best corrected distant visual acuity in the poorer eye is
  no better than 20/200. An individual with one eye, or effective visual
  acuity equivalent to monocular, may be considered for medical
  certification, any class, through the special issuance section of part
  67 (14 CFR 67.401)

This would make you eligible for a class 1 medical which would allow you to train here in the US as well as get a full FAA commercial/ATP ticket which is valid in most of the world. Bottom line is that you can become an airline pilot (at least under FAA rules) and fly international, moving back to your home country may be an issue if they don't recognize an FAA license or the airline has its own medical regulations.


Has there been an aircraft with multiple type of engines? Has there ever been an aircraft that can fly using at least two different type of engines? For example, a piston engine and a turbine engine, or a piston engine and a electric motor.

To clarify the question:

It is not necessary to operate both engines at the same time. However the pilot must have the ability to switch from one engine to another engine while in the air.
The engines must generate power using completely different mechanisms.
VTOL/STOL aircraft (e.g. V-22, F-35) does not quality because the aircraft is simply directing thrust from the same engine elsewhere.
The question is not asking about variants of an aircraft model where each variant is fitted with a different kind of engine. Both engines has to be fitted on the same airframe and operable at the same time.

The Convair B-36 Peacemaker had six Pratt and Whitney radial piston engine propellers and four GE turbojets. The turbojets were used during takeoff and shut down during flight.

 image source Wikimedia Commons


How do I know when to use flaps in glide approach or force landing? During glide approach or practice force landing, I can see the aim point moving down. It means the aircraft will overshoot the field. But I am not sure when should flaps be used or which stage of flaps should be used. I concern that deploying flaps too early, the aircraft will not make it to the field.

This is not so much for normal power-on approaches, but the proper way to manage a forced landing approach is to use some way other than flaps to vary your sink rate as required.  Gliders do it with spoilers, which allows the glider's descent angle to be varied between maximum glide and nearly straight down at any time, which is why the one-shot landing aspect of gliders is really not such a big deal; it's easy to place it anywhere you want.

With power planes you use a forward slip as your variable drag tool.  As you are getting in close, a few hundred feet, you drop just takeoff flap to lower the stall speed and apply some forward slip, ideally roughly half of the maximum you can apply, to be about what seems to give you the correct descent path.

It's as if you had some power.  If you are overshooting, increase the slip angle to descend steeper like you were reducing power, if undershooting, decrease the slip to descend less steep like you were increasing power (a little bit).

Don't drop landing flap until you are down to the last hundred feet or so when making the field is assured.  Just about all aircraft can be slipped, but some may be restricted from slipping with full flap.

If you use and practice this method you will get good at placing the airplane precisely into a forced landing spot without power, and a forced approach will lose its terror as long as there is an open place to land.  I'd be disappointed with an instructor who wasn't teaching slipping to control descent rate in a power off emergency.


Why is rain above freezing level (altitude) not always "freezing rain"? How is rain that is encountered ABOVE the freezing level (altitude) not always "freezing rain"?  And how commonly does this occur?

Situation: Light rime ice in forecast (approximately 10-15K MSL(?)), so freezing level about 10K.  Climbout through forecast light rime and did not get any ice at all.  None.  Kept climbing, initially VMC but then encountered IMC somewhere around FL180(?) and then encountered rain.  (Been in snow once and this didn't look like snow.....BTW, no snow in forecast at all.  No freezing rain in forecast, either).  Smooth ride/no turbulence.  Kept climbing to get above rain due to altitude being above freezing level.  NO ice formation/accumulation at all.  Climbed all the way to FL280 before broke out of IMC/rain.  NO/ZERO ice accumulation.  How is this possible?

The freezing altitude or $0\,^{\circ}\mathrm{C}$ isotherm is the altitude at which the temperature is $0\,^{\circ}\mathrm{C}$ in free atmosphere. This altitude varies and is usually only temporary as it depends on a number of factors.

"Iso0". Licensed under CC BY-SA 2.0 via Commons.

Freezing rain is a condition in which the water droplets become super-cooled (i.e. in liquid condition while below the freezing point of water) and freeze on coming to contact with cold surfaces. This condition happens when snow formed at altitude completely melts and supercools into large droplets.

Source: www.srh.noaa.gov

It can be seen that, to form freezing rain, both warm and cold layers are required. One reason for not encountering freezing rain above the freezing line is that the temperature does not rise above the freezing point of water. In this case, we get snow or sleet.

"Ice Storm Chart" by RicHard-59 based on image by J.R. Carmichael - Own work. Licensed under CC BY-SA 3.0 via Commons.

Thought the above figure is for ground level, it applies for other altitudes also. The phenomenon of freezing rain is dangerous for airliners as the water droplets freeze on coming into contact with aircraft surfaces and can cause loss of lift among other problems.

Post-flight image shows ice contamination as a result of encountering Supercooled Large Droplet (SLD) conditions near Parkersburg, WV. Source: icebox.grc.nasa.gov


What are the requirements for an aircraft to be allowed to perform fast taxi runs? In the UK, are any certifications or particular checks legally required for a retired aircraft to perform fast taxi runs (only)?

Would it still be possible to do them if the main wing spars have been cut and shut, for transportation purposes (no ferry flight)?

Regulation wise, no, there are no regulations which have to be met to conduct a high speed taxi test.  All that's needed is an aircraft with the capability to accelerate to speed and stop as well as a runway long enough to do it on.  If at a towered field, you'll have to get a clearance to do this.

It used to be mechanics would take aircraft freshly out of maintenance out for high speed taxi tests to verify the work was done right.  One such high speed taxi test went ary for a USAF mechanic named George Johnson in 1956 and earned him his first - and successful - solo at night in an F-86!


(Why) Do airliners travel together sometimes? While browsing through the planes in FlightRadar (once again), I've noticed that sometimes some airliners from the same airline company seem to travel "together" on long distance flights to destinations located relatively close to each other (Like Finnair from Helsinki to Hong Kong and to Singapore or to different Japanese cities). The planes were separated vertically by about 2000ft but otherwise quite close to each other. Is there any advantage to this or a good reason? Or is this a pure coincidence?

I do not have inside knowledge of Finnair operations, but I would expect that they have a limited number of staff who speak Japanese, and so logistically running the check in desks for several flights to Japan at the same time allows the airline to schedule checkin staff with appropriate language skills to cover the appropriate flights.

There are also restrictions at both Helsinki and in many Japanese airports that restrict night operations and aircraft on the ground overnight do not earn the airline money.  As a result, there is a limited range of flight times that ensure that the aircraft are operating continually.


Why is the combustor volume of a jet engine decided by altitude? I have read that the combustor volume of a jet engine is decided by the maximum altitude up to which that aircraft will fly. I'm getting confused by that, because the maximum mass flow rate will occur at sea level so the combustor volume should be decided based on sea level. Can anyone explain how the volume is decided?

Short Answer

It is less the volume than the length which limits the maximum altitude. The cross section of the combustor is determined by the volume flow coming from the compressor and the desired flow speed in the combustor, so this dimension is given. To enable operation at lower pressure, the length of the combustor must be sufficient, so a longer combustor will have a higher volume. That is why you have read that volume determines maximum operating altitude.

Background

The factors which make ignition easier are

pressure
temperature, and
spark energy of the ignition system

Ignition is made harder by

mean fuel droplet size (bigger droplets take longer to evaporate)
flow speed in the combustor, and
higher turbulence intensity.

For combustion to take place, first the fuel droplets injected into the air stream need to evaporate. This is made easier by higher temperature and pressure, and the lower both are, the more residence time of the fuel-air mixture in the combustor is required for good combustion. Longer combustors have higher pressure losses and weigh more, so engine designers try to limit their length.

With increasing altitude, the pressure in the combustor drops because the compressor will simply lift the pressure at it's inlet by a given multiple. Therefore, combustor pressure drops in sync with ambient pressure, and the required length for sufficient combustion goes up.


How is an ILS approach conducted when following a heavy aircraft? I'm following a much heavier aircraft on an ILS approach to a large airport.

Ideally I'd like to stay a bit above the glide path and land late, both to avoid the turbulence and also get off the runway quicker.

Is that actually a good idea, and how would I do that in IMC?

Other bodies may advise differently but I will answer for the FAA.

The FAA covers this in their wake turbulence handbook as well as many other scenarios you can look over.

Basically you can fly above the glide slope as you have assumed but you should always take precaution as it cant be known if the leading aircraft is at or above slope.

As in similar situations, separation services may be provided, load permitting.

  2.10.5.1 Air Traffic Control Assist

  Air traffic controllers are able to provide sepa- ration  distance
  information to  pilots  when workload  permits  and  they  have  radar
  dis- plays in the control tower.  They can provide airspeed
  differential between aircraft and may advise pilots following another
  aircraft when they are overtaking the preceding aircraft.

The document outlines some other methods and is worth a read.


Why are airliner cockpits not shielded from lasers? With the recent increase in laser incidents reported by pilots, why don't airliner manufacturers shield airliner cockpit glass from lasers?

The Abrams tank is shielded, protecting the crew from lasers. Why could a similar process not be employed in airliners?

Money aside there is a bit of a practical reason as well. One of the simplest ways to protect against lasers is by filtering it using glass of a particular color, depending on the laser we are talking about red or green glass (and some other colors here and there as well). Generally they look something like this

Coating an airplane windshield in glass of this tint, or a green tint would potentially impair the pilots ability to properly view PAPI or VASI lights which require red/white or red/green differentiation.

It would also cause the pilot to perceive all lights (during a night landing) differently.


What is the name or part number of the Bose 'Lemo' aviation headset connector? In a similar direction to this question, I was wondering if anyone knows the name or part number of the connector commonly featured on Bose aviation headsets such as the A20. It is commonly know as the 'Bose connector', 'lemo connector' or the '6-pin connector'.

The A20 manual merely calls it the 6 pin plug (page 13) and gives the connector dimensions (page 35).
The name 'lemo' suggests it's one of the connectors developed by the LEMO company (perhaps something from the B or K series?).

The connector on the end of the headset's cable is a P-Series. Specifically it is PN PAG.M0.6NL.AC65NZ. You will need to purchase the strain relief separately. If you are looking for the socket Then you need PN PRG.M0.6NL.LC65N for inline connections or PTG.M0.6NL.LC65N for Panel connections.

Unless you own or want to buy the crimp tool, you will need buy solder contacts (and buy extras if you've never soldered these before.) In my experience, universal crimpers don't work well enough with LEMO parts. If you are doing panel mount consider how important FAA compliance is in your situation and consider paying an avionics guy or consulting a DAR (or whichever governing body and official is salient to you.)

UPDATE: On closer reading of the P series catalog, the first letter of the last sequence determines whether the connectors are crimp or solder. A and L indicate male and female solder, respectively. C and M represent male and female crimp. The part numbers provided above are, therefore all for solder connection.

Note that it is possible Bose had a special variant made for them. In most cases this means special keying to make the connector proprietary. It is possible file keys off of generic connectors but that is not really recommended. I disclaim any responsibility if you waste $23 or have an uncomfortable conversation with your FSDO or DAR. Note also that these parts can be a bit hard to research because they are actually made by Redel, a subsidiary of LEMO. Calling these things LEMO connectors is a bit like calling a Porsche 911 a Volkswagen 911.

I've included links to digikey and mouser in my references. Either site is a great source for parts in the US and should stock all the parts I've referenced.

Additionally, here is the P-series catalog.


Why does directional stability decrease at supersonic speeds? As an aircraft accelerates through the transonic region from full subsonic to to full supersonic flow its directional or yaw stability decreases. What causes this reduction?

It is a combination of several effects:

Aeroelasticity: With the higher forces at high speed, the structure deforms such that the effective flow angle at the tail surface is reduced.
The supersonic lift curve slope of the tail surface decreases with Mach while that of the fuselage stays roughly constant, so with higher Mach the tail contribution to stability shrinks while the destabilizing contribution of the fuselage stays the same.
Tail location: At supersonic speed the density of air on the upper fuselage is reduced while that on the bottom is increased. Since the vertical sits on top of the fuselage, it flies in rarefied air. Ventral fins, on the other hand, become more effective.

The supersonic lift curve slope is approximately $$c_{L\alpha}=\frac{4}{\sqrt{Ma^2-1}}\cdot\left(1-\frac{\lambda}{2\cdot AR\cdot\sqrt{Ma^2-1}}\right)$$
Note that the second term is for the influence of the triangular surface on the tip where the pressure difference is reduced. Nevertheless, it shows that lift curve slope of the vertical decreases with increasing Mach number.

For the fuselage, the lift curve slope is that of a slender body:$$c_{L\alpha}=\pi\cdot\frac{AR}{2}$$
Note that this equation is independent of Mach, so the destabilizing fuselage contribution stays constant over Mach.

For the beneficial influence of ventral fins see the diagram below which has been published by Lockheed in The F-104 Strafighter Test Pilot's Notebook by Glenn L. Reaves (source):


Can TCAS be used to confirm "traffic in sight"? If a pilot is asked to confirm traffic in sight, but they have hard time locating the traffic visually, however, they can see it on the TCAS display.

Can they confirm they have the traffic in sight and are able to maintain visual separation based solely on TCAS?

No, "in sight" or "visual contact" means seeing the actual traffic visually, with your eyes. When you report "traffic in sight," then the controllers are allowed to issue a clearance such as "maintain visual separation" or "follow that traffic, cleared visual approach...". They can't issue those clearances when you only see the traffic on TCAS. In fact, having the traffic on your TCAS display doesn't really help them.

The only time that I'll even mention that I have the called traffic on TCAS is in a situation where it may save the controller extra transmissions pointing out the traffic "now at 2 oclock moving to 1 oclock" etc. If he knows that I'm getting bearing from TCAS & will call it when I see it, that may save some radio congestion, but until I see the traffic and report it in sight, he can't clear me for anything based on visual contact.

TCAS is a great tool for collision avoidance & for awareness, but it isn't designed as a "follow that traffic" tool.


What are the regulations for crossing the Atlantic in a twin engine prop plane Are there ETOPS like regulations for private planes?

If the plane has the range (4000km+), can it do it in one go?

Aircraft operating under Part 91 have no ETOPS requirements. ETOPS is only applicable to Part 121 and Part 135 operations. FAR 121.161 only applies to operators of twin-engine turbine aircraft in scheduled airline service. The rules for Part 135 are in 14 CFR Appendix G to Part 135, Extended Operations (ETOPS) and excludes multiengine transport-category turbine-powered aircraft.


Is it practical to descend in a lost communication scenario? This is a follow-up to my previous question here -
  Lost radio communication after take-off in IMC - what are my options?.
  Please refer to that to understand the scenario of this question.

If, for e.g, at one point during the flight, I see a minimum en-route of 9000' and so I climb up to 9000' from 8000'. Now, if the next segment has a minimum en-route altitude of 3000', shall I go back to my previously held altitude of 8000' (which became my assigned altitude before and is now the maximum amongst all the other available altitudes) or shall I maintain 9000' and consider it to be my "new" assigned altitude?

Apart from a regulatory perspective, I'd also like if someone could weigh-in on practical perspective - would it be better in terms of traffic separation for ATC, etc.

So the question really is - is it practical to descend, or do the regulations want you to descend and hence ATC does not expect you to descend?

I've had different answers to this particular question from different Flight Instructors, and hence looking for a definite answer.

The rules on this are well-established and clear. They are laid out in FAR §91.185(c)(2). In particular, you should fly at an altitude which is (emphasis mine):

At the highest of the following altitudes or flight levels for the route segment being flown:
(i) The altitude or flight level assigned in the last ATC clearance received;
(ii) The minimum altitude (converted, if appropriate, to minimum flight level as prescribed in §91.121(c)) for IFR operations; or
(iii) The altitude or flight level ATC has advised may be expected in a further clearance.

For each segment of your route, you evaluate the minimum, assigned, and expected altitudes, and fly the highest. In this case, you'd fly at 9,000 feet on the leg where the MEA is 9000, and then descend back to 8,000 when the MEA drops to that altitude or lower.
If you lose your radios and squawk 7600 (or stop squawking altogether), ATC will expect you to fly those altitudes. They will provide separation between you and all other IFR traffic at 9,000 feet on the first leg, and 8,000 on the second leg. The only exception to this is if you encounter VFR conditions, in which case you should maintain VFR, land, and call ATC so they stop holding the airspace open for you.
In this situation, you should not worry about inconveniencing ATC or other traffic. We have these rules specifically set up so that nobody trades paint if a radio fails. ATC will manage IFR traffic separation for you. "Better in terms of traffic separation" happens when everybody follows the same plan.


What is the purpose of a Traffic Pattern? I always see images with a runway and a rectangular flight path over it and ask myself why do the pilots take off, fly around the runway and get back and land, what is the purpose of doing that: take off, fly parallel to the runway and land? Am I missing something?

Source

I think there are two parts to your question: why do traffic patterns exist, and why do people fly around them in circles?

First, a huge amount of aviation effort goes into avoiding collisions, for obvious reasons. One part of that is making everyone behave as predictably as possible, so that you know what to expect from other pilots and where to look for aircraft near you. That's why there are regulations on airspace, altitudes, speeds and all sorts of other things that affect how and where aircraft fly: if everyone is following the same rules then life is much easier. For example, if you're driving down a one-way street in your car, you can be (reasonably) confident that you won't meet someone coming the other way, and drive accordingly.

Because aircraft operate very closely together around airports, there's a higher risk of collisions and it's especially important to have very clear rules for how and where pilots take off, approach the runway and land. The traffic pattern is the aviation equivalent of road markings: it 'shows' where you should fly in order to fit in with everyone else, fly in the same direction, be visible to others, and generally be as obvious and predictable as possible.

Second, why do pilots take off, fly around the pattern and land again? Usually, because it's a great training exercise. In the process of going around the pattern you have to perform multiple important maneuvers and tasks, including:

Taking off
Climbing out in a controlled, precise way
Making coordinated turns
Managing airspeed
Operating key aircraft systems like the landing gear, flaps, lights etc.
Using checklists
Working with ATC (if it's a controlled airport)
Descending in a controlled, stable approach to land
Landing

Since taking off and landing are often considered the riskiest parts of a flight, doing pattern work is a great way to get as much practice as quickly and easily as possible. For example, I just got back from doing some night pattern work: I did 10 takeoffs and landings in about 35 minutes. That packs a lot of practice into a short amount of time, which is useful for everyone but especially for student pilots.


Where can I find complete aircraft blueprints for the purpose of study? Where can I find aircraft blueprints for the purpose of study? I find that I learn a lot more when I am able to get the big picture of a machine that is used in real life (for example, to understand how computers work, I pored over complete circuit diagrams of older computers and studied the complete source code of older operating systems, assemblers, and compilers). I am hoping to apply this method of learning for understanding aircraft, but it seems that there is a lack of publicly available designs.

Questions:

Are there publicly avalable aircraft plans (for example, of older, but relevant, commercial/military jet aircraft) that are good for study?
Is my proposed method for understanding aircraft viable in this field?

You might buy some kit builder plans, as they have generally more detail than I have seen in commercially available aircraft.

With commercially available aircraft, I have bought several aircraft new, and despite pre-purchase attempts, have been unable to shake loose a complete set of prints.  Even the limited prints I was able to receive were essentially licensed, and NDA agreements were executed, copies had to be accounted for, etc.

You might be able to find prints from one of the better plan developer, which might meet your needs.  Some might be rather inexpensive.  I have plans for the Varieze and LongEz and have seem plans for other aircraft. Some are more detailed than others.

However, I would like to set an expectation that you will learn little about aircraft design, and perhaps a tiny bit about aircraft manufacturer.  There are better materials, including textbooks.


How does the Airbus flight computer's voting system work? From what I've read about Airbus planes is that their fly-by-wire system works by having three different flight control computers calculate what the plane should be doing and then vote on all the three outcomes about which to take. I would hope that they all give the same result all of the time, but as I understand it this is used to make sure that decisions based on faulty data doesn't scatter the plane across the ground. How does this actually work? How does the computer vote which result is the correct one, is it just a majority vote? What happens when all three outcomes disagree?

Also, is this system only in place when operating in normal law? And are they actually different software implementations or is the only difference that they are fed input from different redundant sensors?

As far as I read in various documents about A320 and remember them correctly:

There are three systems handling different parts of the primary flight control:

ELAC (elevator & aileron computer) controls pitch with elevators+trim and roll with ailerons.
SEC (spoiler & elevator computer) controls roll with spoilers and if ELACs fail, pitch with elevators+trim.
FAC (flight augmentation computer) implements yaw damper. Its command is added to the rudder command. In A320 rudder pedals have direct mechanical (hydraulic) link.

The ELAC and FAC are composed of two identical units each, the SEC of three identical units (but only two of the units are used as backup for ELAC).

Each unit is composed of two dissimilar computer boards. One used i386 CPU, the other m86k CPU and each has independently developed software (to minimize risk of the same software bug in both).

One of the boards in each pair calculates the output and the other one verifies it. If the verification fails, that unit declares fault and disconnects. This is the primary way of detecting faults.

I found no reference to comparing outputs of the identical units. Except for spoiler control there are only two output and the check board is more reliable way of detecting faults anyway.

If the FAC fails, the aircraft won't maintain coordinated flight well and will tend to dutch roll, but pilots can compensate it with rudder input.

If the SEC fails, the ELAC can handle control alone. Just spoilers won't be available.

If the ELAC fails, the SEC can take over too. Turning with spoilers may cause some more drag, but not a big problem.

If both ELAC and SEC fail, the pitch trim wheels have direct mechanical (hydraulic) link and roll can be controlled by rudder by taking advantage of the yaw stability. I don't think it was ever needed in practice. Note, that is for A320 family; which controls are available in case of failure of all flight computers is different in each Airbus type.

As for data input, there are three ADIRUs (air data and inertial reference unit) and each flight computer takes input from all three and compares them. It needs two matching (similar within some limit) values to consider it trustworthy. If either more than one unit fails or no two agree, the flight computers degrade to alternate law or direct law.

In alternate law, the system stops providing alpha protection (stall), overspeed protection and, depending on what failed, other flight envelope protection (there are two kinds, with different protections lost).

In direct law it reverts to directly mapping the stick position to control surface position similar to mechanical controls. But most faults only result in alternate law except if all inertial references were lost (that would be very difficult to handle as it would mean unreliable attitude indicators too, but I don't think that ever happened either; the inertial systems are very reliable).

Alternate or direct law can also be entered if some control surface (or its actuator) fails and somewhere in the computer failure sequence, but I don't remember the exact condition (FACs calculate the limits, so if FACs fail, it will certainly degrade).


What is the range of an air traffic control tower's radio transmission? What is the maximum distance the voice messages sent by the tower on a radio channel can be received by an aircraft?

VHF transmissions are limited by line of sight. So, assuming the transmitter is at the tower location, and assuming the aircraft is at cruise altitude (say F300, or 30,000 feet or more), the maximum range is perhaps 200 to 300 km before the curvature of the earth eliminates the line of sight. This also depends on weather conditions and the transmitter power.

In practice, VHF coverage may be extended using additional transceiver sites on the same (or different) frequency. This is particularly important in mountainous terrain.

For oceanic flights where there is no place to put additional transceiver sites, HF (shortwave) radio can be used which has a much greater range (thousands of km), especially at night. Some aircraft are also equipped with satellite phones so controllers can simply call them. However, this wouldn't be the tower controllers talking to the pilots over the ocean, as tower controllers aren't responsible for en route control.


Locked out of private jet - how do you get in? Ok I'm not a jet owner, I'm a novel writer. I wanted to get my airplane facts right for the story.
Say my character has a mid-size (can go overseas) private jet. Has a door lock on the outside door and cargo bay. The bad guys stole his keys, so now he's locked out. My character is a pilot and is with a friend who is a jet mechanic. If the mechanic has tools, and 24 hrs, would they be able to get in to their jet and fly it?

If so, how would the mechanic go about getting in (while leaving the aircraft in flyable condition)?

Or would the characters need to call a locksmith?

I was thinking pretty high in the sky (I was going to have the mechanic literally unscrew the door and then put it back on) but then I thought I'm probably being unrealistic and I should ask someone who's actually worked with jets.

It depends on the exact model. Bobby pins or any key that physically fits will get you into some, you'll need real picks for others, and some custom jobs may require a police snap gun or a locksmith's services. This doesn't correlate with aircraft price: the larger and more advanced, the less likely it is to have any locks at all. At the high end, jumbo jets have no locks and have a (not so) convenient hatch in the gear well, so you can climb inside even without a ladder.

Mechanical locks, with the exception of the more robust types used on burglary-resistant safes and vaults, offer only very superficial security. Airplanes are protected against professional threats by external access restrictions (fences, hangars, guards). When parked at a small local airport, opportunistic theft is deterred by "security through obscurity": very few people are able to operate one, with model-specific skills are involved, and even fewer could make use of a stolen jet. Unlike car parts, aircraft parts come with paperwork.

The locks used on most aircraft doors are small pin and tumbler cylinder types that can only protect against passers-by. The stock locks on the most popular light planes even use wafer tumblers, which offer no resistance to picking - some light bumping with a key from another lock of the same type will get it open. Quite a few owners have opened plane doors with a wrong key by accident.

If you're not concerned about property damage, as in an emergency situation, no picking skill is required to open the kind of locks you'd find on a private aircraft. A non-matching key or a flat-head screwdriver, jammed into the keyhole and forcefully rotated with a pair of pliers, can break small cylinder locks' pins and allow the lock to open. Larger locks require a bit more effort, but it's all fairly intuitive work of destroying what's in the way of opening the latch.

In non-pressurized aircraft, you can also bypass many locking mechanisms by applying well-directed force, which slightly deforms the door to allow the latch can exit the door frame. In some cases this can be done non-destructively, just by elastic deformation. Pressurized doors fit too tightly for this, but the lock is still a standalone device, not tied into the door's operating and sealing mechanism, so damaging it won't leave the plane inoperable.

24 hours is far more time than would ever be needed. 1 hour is enough time to get a professional locksmith, which, with proof of ownership, can get you into any stock aircraft/boat/car/other vehicle with usually no damage to the lock. Another hour will get you a new set of keys, or a change of locks with new working keys.

The time it takes to get into a locked aircraft, in an emergency situation, should be between 20 seconds and 20 minutes, depending on the plane, the characters' skills and equipment, and their willingness to damage the lock. For a larger jet you'll definitely be going after the lock, not the door.

The only entry-resistant doors in aviation are those separating airliner cockpits from the passenger cabin, with electronic locks and solid locking mechanisms. They're rated against different threat models than UL vault doors, but my best estimate based on their construction and weight would place these doors at around TL-15 level, with about 15 minutes of power tools resistance.

For reference, the highest ratings for safes and vaults are TRTL-120 and TXTL-60, indicating 120 minutes contact time resistance against power tools and torches, or 60 minutes against explosives and small thermal lances. In absence of a security response, 24 hours and a good hardware store can get you into Fort Knox.


Could the S.H.I.E.L.D. C-17 actually have a sensible center of gravity? In a question about whether tail surfaces add to lift, I thought of a fictional example where the tail surface very much adds to lift: The Agents of S.H.I.E.L.D C-17, highly modified and super-engined.  Presumably the T-tail vertical stabilizer (still present) provides downforce for trim, and the aft wing provides lift; though that wouldn't necessarily have to be so.

And my first reaction was "The center of gravity on this would be totally unworkable." But is that really true?

I mean, it looks like the rear wing would account for about 20% of lift, maybe a tick more because it is being blown by the forward engines.  So if you marked the main-wing center of lift and the aft-wing center of lift, the aircraft CG would need to be inside that range, about 20% aft of main-wing.

Would that put the CG aft of the rearmost landing gear wheel?  Wouldn't it "pop a wheelie" the moment they lost elevator authority?

But then, if their Stark/Asgard/Tesseract tech can get 150,000 lbf out of a PW2000, maybe they can move the landing gear aft.

If you haven't seen Agents of Shield, spoiler alert...

    One hat-trick that aircraft can do is "tip the engines up" and go into full VTOL.

 The cattywumpus angle of some of the engines are dynamic adjustments for station keeping; this is obvious in the video.

 That seems to place some very particular demands on Center of Gravity,  noting that the engine lift is significantly forward of wing lift.  Especially when you fail an engine - worst case being a tail engine.  Presumably, everything is specced so a single engine rollback in VTOL/hover mode could be easily compensated for. Clearly, that would factor into CG also, as the loss of a tail engine would be the worst case, necessitating the CG stay fairly forward.

 Would the CG for forward flight be compatible with the CG for vertical hover?

Might have been better as a canard design.  Yes, you can have two wings bearing weight with the CG in between.  But the fore wing must stall first.  This C17 would have problems unless there was a lot of weight up front, or if the rear wing(s) stalled first.  But note that the extra engines could go on the main wing, or the second wing could be mounted above or below the first, or even in front, making it an Avanti Piaggio from hell.  This design actually might have a chance if the T tail was removed as the transport version of the B-58 Hustler.

But for the movies, this design will certainly do.


What's P-Factor and why does it occur? Whenever I hear anyone talking about P-Factor, (whether it be single-engine left turning tendencies or multi-engine loss of directional control scenarios), someone always brings up the fact that the descending blade of a propeller generates more thrust than the ascending blade.  I'm wondering why that's the case.

What is P-Factor and why does it occur?

For simplicity, assume a single-engine plane with a two-blade propeller. Just imagine an aircraft is perfectly level and moving forward through the air. The angle of attack on both blades of the propeller would be the same. Now imagine the plane pitches up a bit. One blade's angle of attack will increase and other will decrease.

(source: AOPA.org)

Within reason, the greater the angle of attack, the greater the thrust generated. So one blade (or, to be more precise, a blade on one side of the aircraft) will generate more thrust than the other.


Can a drone hitting a plane be mistaken for a birdstrike? Could a bird-sized consumer drone be digested by a jet engine, and not be recognized as a drone, mistaking it as a bird strike?

I'm thinking of the situation during the flight - like an engine making a short unusual noise, but works OK; not sure that can even happen eating a small bird?

As was pointed out, the debris of the object will look different in obvious ways when checking the engine after flight

I would assume a major factor is how the engine handles the drone, in terms of defects or running anomalies.

The battery comes to mind, hitting a turbine blade might be a problem - depending on the battery size.

There are certainly drones with very small batteries, that I assume will do no obvious harm, and certainly ones with batteries big enough to do harm for sure.

Would one be able to tell the difference before landing?  Not likely in many scenarios.

Case 1: Bird hits windshield: blood & guts are immediately visible.  Drone hits windshield, cracks are visible but not much else.  The crew CAN immediately figure out, if they've ever see a birdstrike on the windshield, that this was something else.  (Of course, it could just be a shattered outer pane -- those do fail sometimes, not necessarily due to any collision.  Never had one go in flight, so I don't know if the sound of the pane shattering might be mistaken for a collision {or vice-versa}, or not.)

Case 2: Bird hits near the cockpit but NOT on a windshield.  Sounds like a sharp crack, like a piece of gravel hitting your automobile windshield at highway speeds.  If a drone did the same, it would probably sound pretty similar, and without the blood/guts to see (or not see), the ability to notice what's missing may not be there.

Case 3: Bird hits the engine, and it starts running poorly. Sometimes you will smell the guts cooking in the core of the engine (i.e. they get into the bleed air system & thus into the air conditioning), and that's a clear sign that your engine ate a bird.  But the bird CAN miss the core and still cause problems with the fan blades.  Most birds that miss the core are chopped up by the fan blades & the crew had no idea until after landing that anything happened, but a big enough bird can cause damage that way.  So if the engine starts running rough, hot, and with some vibration, the absence of "cooked goose" odor isn't necessarily going to drive the conclusion that the collision had to be with something other-than-a-bird.  One might suspect that a lot of damage with no smell seems unlikely to be a birdstrike, but there are cases where some engine component has failed & caused engine damage (ranging from barely noticeable up to catastrophic), and you can't really know much about causality for the engine doing what it's doing until you're on the ground.

Now, all of this assumes that the crew doesn't see the object that they hit.  Which they very well might.  Everything in that case is obviously an entirely different discussion.


Why would a pilot's armrest be a no-go item? From the end of issue #216 (June 1997) of Callback:

  Another First Officer also learned too late the importance of consulting the MEL before take-off.

    Inbound equipment arrived late. About 5 minutes before pushback time, I discovered that my right armrest was stuck in the UP position. I attempted to free it, but no luck. I contacted maintenance and asked them to bring something to lubricate the mechanism. A mechanic did so, but to no avail. We figured we could just go with it in the UP position. It did not occur to us to look it up in the MEL, as it did not seem to be a safety-of-flight item.

    Upon our arrival, we were told that the armrest is a no-go item. The continuing flight was cancelled due to this fact, since no spare seat or replacement part was immediately available. The Captain and I were both amazed that something as simple and innocuous as an armrest would be considered a no-go item. In the future, I will check the MEL for any item, no matter how seemingly insignificant.

Why would a pilot's armrest stuck in the up position be a danger serious enough to require grounding the aircraft?  One would think, like the aforequoted pilot did, that it would be, at worst, a minor inconvenience, and certainly not a safety-of-flight issue...

Perhaps it was just an oversight on the part of the creators of the minimum equipment list.

As I understand it, minimum equipment lists generally provide a list of those items which are permitted be inoperable. So if any piece of equipment is inoperable, and it's not on the list, that automatically means you're not allowed to fly.

(Going by the name, you'd probably expect a minimum equipment list to be, you know, a list of the minimum required equipment. But for one reason or another, it's not.)

So, in all likelihood, nobody thought to add armrests to the minimum equipment list. As a result, flying with an inoperable armrest was automatically prohibited.

However, things have since been adjusted: the FAA has added the armrest to the master minimum equipment list for the Boeing 757. So, it is now legal to fly your 757 with a stuck armrest, as long as it is stuck in the "up" position.


Why are some US STAR fixes/waypoints included in FAA's legacy files but not in FAA's published STAR procedures? I have noticed that some US STAR procedures include (slightly) different number of waypoints, depending on which source material is consulted. Take for example the CAMRN4 STAR and its corresponding description from the legacy files provided by FAA. In the legacy files, the reporting point GAMBY is mentioned between KARRS and CAMRN, whereas in the published information it is omitted.

S0095  NW N3905438W07448012SIE     SIE.CAMRN4   CAMRN FOUR
S0095  R  N3924521W07427171BOTON K6   S0095  R  N3934583W07416141HOGGS
K6
S0095  R  N3940336W07410055PANZE K6
S0095  R  N3950271W07359096KARRS K6
S0095  R  N4000222W07352083GAMBY K6
S0095  R  N4001023W07351398CAMRN K6
S0095  AA N4043436W07324483FRG
S0095  AA N4038237W07346433JFK

Is there a reason for this or have I misunderstood something?

Revisions are made to improve traffic flow, adjust for infrastructure(eg local airport change in number of flights or nav beacon decommissioned), simplify procedures for pilots and ATC, or address some other routing conflict or safety issue.
This is why IFR charts and terminal procedures are only valid for two months.

For example there is a victor airway near here that had its MEA raised from 3000 to 5000 because it was discovered that at the lower altitudes something was causing the VOR signal to bend significantly and planes were getting dangerously close to a mountain, I think they may have even had a couple of crashes.


Can FMC be programmed to do fast maneuvering in fighter jets? As we know we set the flight path etc in FMC but can it be pre programmed to do high speed maneuvering and shoot the ammo as per the preset conditions?

It could be kind of self moving UAV with the pre stated path, waypoints, targets to hit and the return path along with the type of ammo to hit depending upon the kind of target.

Pre-programmed high speed maneuvering is already being done in the case of target drones derived from fighter aircraft like the QF-16 (which is derived from F-16). According to multiple reports,

  The QF-16 ... is capable of pre-programmed maneuvers such as high-G turns, barrel rolls, split-S, etc.

While some research has been carried out on fully autonomous weapons systems, at present there is always a human being in the loop (at-least) for pressing the 'kill switch'. A few of the problems in a fully autonomous system operating in enemy airspace are:

Operating the UAV in hostile area and responding to threats. Though the QF-16 drones can fire chaff and flares to escape from incoming missiles, drones that can operate in hostile environment are still in their infancy. This requires significant improvements in ability of the UAVs to detect, differentiate and prioritize the threats and respond to them.
The UAVs should have the ability to search/track, acquire and engage the target while not ignoring friendlies or neutrals. Though some tests have been carried involving automated target tracking and some missile do have the ability to discriminate between the target and surrounding buildings (based on prior information),the technology is still some way off.
There are significant political, legal and ethical issues in using automated killing machines.

Some missiles like the Tomahawk has the ability to navigate along a predetermined path and hit targets, though they cannot do high speed maneuvers (or return, obviously).


Can an F-16 fly with conventional hydraulic powered controls without a computer controlled Fly By Wire System? Radio Controlled models of F-16s fly fine without computer controlled flight systems. Apparently these model aircraft are not unstable in pitch but probably positive in pitch stability. There may be trade offs in high AoA capability but it would seem that an F-16 with sufficiently forward CG would be able to fly using conventional or hydraulic controls like for example the F-4 or F-5.

I did some searching and got an extremely interesting answer here:
By the way, I should have worded my question differently :  the F-16 does have hydraulically powered controls, but the pilot inputs are sent through a computer first.

  They designed the plane so it could be fitted with conventional
  hydro-mechanical controls if the fly-by-wire system couldn’t be made
  to work acceptably. “We spaced the bulkheads so that we could move the
  wing back and have a statically-stable airplane,” says Hillaker. “We
  were just giving ourselves some insurance. The wing would have had to
  have been moved back eighteen inches. All we had to do was make the
  two bulkheads have the same load capacity. One of them that we
  would’ve moved the wing to was higher than it needed to be, unless you
  moved the wing back.”  The structural differences carried over to the
  production F-16 design, but fortunately were never needed. The
  fly-by-wire system’s control problems were quickly ironed out and the
  plane, even with all its advanced features, steadily gained support
  both in the U.S. and abroad

So model makers note: get the CG for the F-16 and move it back 18 inches or whatever the equivalent is on your model for a stable airplane.

http://www.f-16.net/articles_article13.html


What is meant by "fuel flow: on " in checklists? What is mean by "fuel flow: on " in checklists? For example:

http://www.projectlear45.nl/docs/Checklist_LEAR45.pdf

In the real aircraft that checklist item would mean bringing the thrust lever of the engine to be started up out of cutoff and to the idle position. This would be accomplished by physically moving the thrust lever forward slightly out of the cutoff detent.

However, in the computer flight sim for which the linked checklist provides guidance, the cutoff position of the thrust levers is not simulated. Instead, thrust lever positions below idle command reverse thrust. For this reason, the checklist calls for using the computer keystroke ctrl-shift-F4 to command fuel flow on. This keystroke combination commands mixture full rich in simulated piston aircraft.

In the real Lear 45, fuel flow and scheduling during start is controlled by the Digital Electronic Engine Control (DEEC). For this reason, the start checklist calls for setting the appropriate thrust lever to idle prior to commanding engine spool up in preparation for the DEEC to automatically start actual fuel flow once the appropriate compressor speed is achieved.

It is worth noting that after initially setting the thrust lever to idle—or hitting ctrl-shift-F4 on your computer—the fuel flow indication should read zero. The check for appropriate positive fuel flow comes later in the start sequence.

Compared to setting the thrust lever to idle in the Lear 45, the analogous control command for starting most piston engines would be mixture to full rich and for most turboprop aircraft would be fuel condition lever to low idle or similar.


Do modern aircraft still have mechanical sensors as backup to GPS? A comment here Why does "no aircraft cross directly over the pole"? indicates that modern aircraft use GPS for navigational purposes, which makes perfect sense.  However, do these aircraft also have backup mechanical sensors (altimiter, magnetic compass, etc.) in case GPS signals go haywire or are not available?

In light aircraft they typically do: Glass-Panel aircraft will also have traditional "steam gauge" backup instruments of some kind.

Note the airspeed indicator, attitude indicator, and altimeter to the left of the pilot's PFD.

This is however no longer guaranteed: A completely independent electronic backup system with its own power source may be used in place of the traditional "steam gauges".
This can be seen on new Cirrus aircraft, which have digital standby instruments (in the green box):

Similarly transport category jets may have traditional backup instruments:

Or they may have an electronic backup system:

Note that the electronic instruments in these cases aren't GPS-referenced: They are gyroscopic instruments with pitot and static input for airspeed and altitude/vertical speed calculation.


Would a propeller extracting air from a cylinder with holes in it be an ideal lift apparatus for a VTOL aircraft? I am wondering if enough lift can be created for a VTOL aircraft using a propeller that is extracting air from a cylinder which is closed at one end and has holes in the top half of the cylinder.

Please reference the conceptual drawing below.

I believe that when the propeller is turned on and air is flowing in through the holes and out of the cylinder, there will be low static pressure inside the cylinder and the cylinder will be lifted up by the ambient air pressure outside the cylinder pushing against the bottom half of the cylinder. Lift should occur because the bottom half of the cylinder has a larger surface area compared to surface area of the top half of the cylinder which has holes in it.

So, would a propeller extracting air from a cylinder with holes in it be an ideal lift apparatus for a VTOL aircraft?

Already invented by an Italian priest in the 17th century. His version was simpler, having no engines or propellers...

https://en.wikipedia.org/wiki/Francesco_Lana_de_Terzi


Is there an aircrew bunk in the 747 cockpit? Reading this article, I came across the quote :

  Pilots also enjoy its creature comforts: at BA the 747s are known as
  the ensuite fleet. “Our little bedroom is within the cockpit: you can
  stick your pyjamas on and clean your teeth without anyone seeing you.
  And coming out the bunk when you wake up, it’s a different light and
  you’re in a plane cockpit in the sky,” he says.

I know there are crew sleep areas on large aircraft but I've never heard of there being a bunk.

Does anyone have a floor plan for the cockpit which would illustrate how do they fit those cabins there?

Yes, there is a crew rest with two beds (bunk) connected to the cockpit on the 747. As MainMa notes, this can be found on 747-400 or 747-8 models, but not the older models. It can be seen on the seating charts here:

The crew rest is directly across from the two lavatories. While the lavatories open into the aisle of the cabin (grey area), the crew rest opens into the cockpit. There is a layout here that shows a how the upper deck is arranged. It's a freighter, but is was converted from a passenger plane, so it has the same crew rest location.

With the introduction of the 747-400, the position for the flight engineer was removed (seen below), with those functions being replaced by computers. This opened up a bit of room behind the pilot seats.

Source


What is the VOR reference signal? What is the VOR (VHF Omnidirectional Range) reference signal?
I have to calculate the spectrum of this signal.

VOR Ground Station is aligned with magnetic North. It emits two signals:

a 360° sweeping variable signal
an omni-directional reference signal

When an aircraft receives those signals, its receiver compares those and a measures the phase difference. This gives a precise radial position of the aircraft which is displayed on its Omni-Bearing Indicator (OBI), Horizontal Situation Indicator (HSI) or a Radio Magnetic Indicator (RMI), or a combination of two different kinds.

This picture shows the two signals:

Blue is 360° sweeping signal
Green is omni-directional reference signal


How does a fighter jet perform good and quick maneuvers with such small wings? Fighter jets like the F-16, F-15, etc. have wings smaller than the length of the fuselage and can perform great maneuvers very quickly while an airliner with a long wingspan takes a lot of time to perform these kind of maneuvers. How does a short wingspan on a fighter jet perform such great maneuvers?

Fighter (combat) aircraft are designed to perform quick maneuvers in order to get into a position quickly to engage and shoot down an enemy aircraft or evade incoming threats (like missiles, etc.). Civil aircraft like airliners are designed with other things in mind like comfort, safety, reduced fuel consumption, etc.

The wings are only a part of the story in performing maneuvers like those performed in air combat maneuvering, which depends on a number of aircraft characteristics like,

Power - For carrying out most of the maneuvers (like wingover), the excess power available matters. Fighter aircraft have more excess power, which translates into more acceleration. That allows it it enter into maneuvers quickly compared to the civil aircraft. In case of emergencies, the combat aircraft can use their afterburners to gain significant extra power.
Thrust-to-Weight Ratio - Most of the modern fighters have high thrust-to-weight ratios, usually more than 1 (which allows them to accelerate in vertical climb). This allows the fighters to accelerate far faster compared to the civil aircraft. For example, F-15 (>1) had a thrust-to-weight ratio more the three times that of the Concorde (~0.33).

Source: strategypage.com

Stability Most of the fighter aircraft today are designed to be unstable. This makes the aircraft respond to control inputs much more quickly compared to the airliners (which are usually not unstable in the roll axis). This means that the combat aircraft are capable of maneuvering much more quickly.
Inertia In case of large wings, the roll inertia is very high. This prevents them from performing quick maneuvers. Also, the damping of the large wings is also to be considered. In case of fighters, however, the short wings, having smaller inertia helps in achieving high roll rates.
Wing Loading The smaller the wing loading, the better the turn performance. Most of the combat aircraft employ a blended wing-fuselage design, that reduces the load on the wings. For example, the Eurofighter Typhoon (~300 kg/$m^{2}$) has about half the wing loading of A380 (>600 kg/$m^{2}$). In fact, an F-15 produced enough lift with half a wing gone to perform a successful landing.

Source:www.armchairgeneral.com

Control Surfaces- In general, the combat aircraft have more number of control surfaces like canards (in addition to primary control surfaces) compared to the civil aircraft. This enables the pilot to maneuver the aircraft much more quickly compared to airliners.

Source: www.blokeish.com

Due to these reasons, the fighter aircraft are able to perform maneuvers much better and faster compared to airliners.


Is it recommended to have an ADS-B transponder in ALT mode on the ground? Early on in training I was told that unless the airport specifically noted it on the chart, that the transponder was turned to ALT (altitude) mode just prior to taking the runway for take-off (lights, camera, action), and was changed back to SBY (standby) immediately after exiting the runway.

Recently we had a Garmin GTX-345 ADS-B transponder installed in our aircraft and as part of the ADS-B rebate program you need to do a check-out in "rule airspace". When I got the test report from the FAA I noticed that I passed the air portion but failed the ground portion due to an insufficient number of reports (messages) while on the ground. I retook the test making sure to put the transponder in ALT mode at the hangar and subsequently passed.

This leads me to believe that the transponder should be in ALT mode pretty much all the time. Is there any recommendations from the FAA that say that ADS-B transponders should be active while on the ground?

The GTX-345 Manual (2-1) has this to say:

  The transponder system no longer supports a pilot selectable GND mode. The
  transponder should always be in ALT mode prior to moving on the airport surface.
  It must be in ALT mode when operating in certain controlled airspace, in
  accordance with 14 CFR 91.215. For guidance on transponder operation, refer to
  the FAA Aeronautical Information Manual (AIM), 4-1-20(a)(3)

(Emphasis mine)
Is this backed up by the FAA?

Yes, it's in the the AIM 4-1-20:

  3. Transponder and ADS-B operations on the
  ground. Civil and military aircraft should operate with the transponder in
  the altitude reporting mode (consult the aircraft’s flight manual to
  determine the specific transponder position to enable altitude
  reporting) and ADS-B Out transmissions enabled (if equipped) at all
  airports, any time the aircraft is positioned on any portion of an
  airport movement area. This includes all defined taxiways and runways.


Is skydiving in IMC (through clouds) legal and safe? (1) What are the legal considerations for skydiving into clouds? I see many skydivers did fall into and out clouds in online videos. However, the clouds are mostly scattered or thin-layered. How about in widespread hard-IMC, say OVC 008?

(2) What about maintaining the actual safety? How does a skydiver maintain attitude and stable position in IMC and not disoriented? and separation from other traffic?

EDIT: The legal consideration of my context is within US, but open to legal regulations worldwide.

It is not legal to conduct skydiving into clouds, atleast in US. From 14 CFR §105.17   Flight visibility and clearance from cloud requirements:

No person may conduct a parachute operation, and no pilot in command of an aircraft may allow a parachute operation to be conducted from that aircraft—
(a) Into or through a cloud, or
(b) When the flight visibility or the distance from any cloud is less than that prescribed in the following table:

Is it safe? Probably. The chances of mid-air collision are pretty small, but they can happen as is does with aircraft. Midair collisions between skydivers and between aircraft and skydivers are rare, but not unheard of. There has also been reports of near misses between aircraft and skydivers through clouds. So, its better to be safe.


What license is needed to fly the electric "Volocopter" helicopter? Here is a video of the aircraft in flight.

The Volocopter Looks like it would fly quite differently than a helicopter. Is that true? Does that matter? Is it still a helicopter license that's needed?

The German transportation ministry has decided to create a new aircraft category for this machine.

From Aviation Week:

  Karlsruhe-based E-volo says the Ministry has commissioned a two- to three-year trial program to create a new category of ultralight aviation to cover the two-seat VC200 rotorcraft now in development. [...] Under the trial program, the German Ultralight Aircraft Association, Sport Aircraft Association and Federal Aviation Office will work with E-volo to create a manufacturing specification, legal regulations and training requirements for the new "Volocopter" ultralight rotorcraft category.

So according to this, the exact licence, and training requirements will be deteremined by the currently running trial program. It seems the manufacturer tries to position the craft as some sort of rotational-wing ultralight.


Is there any particular reason for the cockpit of the 747 being on the upper deck? The cockpit of the 747 is on the upper deck, but the cockpit of the A380 is situated on the lower deck. Is there any reason (be it engineering or anything else) for the location of the cockpit?

Boeing actually never expected the 747 to be so successful. They thought supersonic aircraft were the future. But Boeing knew that an aircraft the size of a 747 would be great for the cargo market. So they designed one aircraft that could be easiy converted into a cargo version.

The cargo 747s can literally open their nose. It is quite impressive. To accomodate this, the cockpit needed to be on the upper deck. Hence the passenger version had the same requirement.


What creates most drag during flight: fuselage or wings? From pic 1, I know the drag line is below the thrust line, but I am puzzled about where the drag line is in pic 2?

Secondly, what creates most of the drag in flight, is it the fuselage or the wings?

It's the wings. Most of the time.

Best L/D is reached when the induced drag is equal to the non-lift-related drag. Induced drag is a byproduct of lift creation, and that is predominantly done by the wings. Therefore, induced drag (physically a backward tilt of the lift vector away from the direction in which lift is defined) is produced by the wing.

For the remaining drag you can do a very rough estimation based on wetted surface and friction drag. Here the wing again produces a substantial fraction which must be added to its induced drag.

For racing aircraft like the Supermarine S.6A (which won the Schneider Cup back in 1931), the fuselage, struts and the floats did produce almost all drag at high speed. This would be a clear exception to the answer given above. However, even with this aircraft, at low speed (during take-off and landing) the wing would most likely create at least half of the drag force.

On the Dornier Seastar (your first example) the thrust line is chosen so high in order to move the propellers and turbine intakes away from possible splashes of water. The resulting pitch moment is trimmed away with proper elevator deflection. In your second example a lot of drag is created by the many bracing wires. At low speed the wing will produce most of the drag while at high speed the drag line will move down when the unfaired pilot (and wheels, engine and tank) and the many wires will create most of the drag.


What is the difference between a propeller and a turbo propeller? I have found the differences rather interesting between the Beechcraft Bonanza engine and a turboprop, I have heard there the same and they're different. But I need a straight answer.

I think you are trying to ask

  What is the difference between a propeller and a turbo propeller?

A traditional propeller plane is powered by an reciprocating (piston) engine. These can be in the form of radial, flat, or V style engines with a few other configurations used here and there.

On the other hand a turbo prop is a propeller plane that is powered by a turbine engine. In this instance the shaft of the turbine is used to drive a propellor. One could think of this as putting a propellor on the front of a jet engine.


How does a failed turn and slip indicator behave if the gyro isn't spinning at all? I have my own theories, but I have never experienced a turn coordinator or turn and slip indicator's gyro failing first-hand.

If the gyro isn't spinning, would the instrument behave like a weak accelerometer but on a different plane of movement, or would it just do nothing at all?

For example, would the weight of the motionless gyro of a turn and slip indicator resist movement laterally when the plane is rolled and cause a momentary turn indication from roll or are the centering-springs strong enough to overcome virtually any inertial resistance offered by the weight of the gyro?

Another way of asking this is if you held a turn and slip indicator unit in your hand with the display window facing your palm and you rotated (rolled) the unit side-to-side rapidly in sort of a door knob turning motion, would the turn rate indicator needle tilt at from the center position on the display at all?

It depends on how it fails, there are lots of possibilities on what caused it to stop spinning and they can all lead to different outcomes. In this instance it just kind of bobbed around as if it were free floating. But if something is jamming the mechanics it may simply stop moving altogether so it really just depends on how it fails.


Why does one announce "Thrust Set"? I have watched many aircraft takeoffs now where the flight deck announce 'Thrust Set', just after the engines are set to full.

Forgive the dumb question, but why does one announce that the thrust is set, perhaps more importantly, why is it necessary in the takeoff procedure?

I did attempt some research before posting, but the closest article I got did not make much sense to me I am afraid.

  For the GE CF6 engines, N1  should be stable at 70% before the TO/GA switch is pushed to set the armed thrust limit. If TO/GA is not pushed by 50 knots, thrust must be set manually and when VNAV goes active at 400', the A/T will automatically go active in THR REF, so you don't need to select anything if the A/T is armed.

There was at least one incident where a Boeing 737 attempted to takeoff with the throttle levers not set to takeoff power.

The procedure is designed to ensure

the thrust lever is where it is supposed to be
the engine indications show the correct amount of power is produced

In some airlines, the procedure calls for both pilots to put their hands on the levers and advance them together. Either way, the purpose is to have both the pilot flying and pilot monitoring to ensure takeoff power is properly applied.


Is an AFSP registration required for rotorcraft rating? I hold an FAA private license with ASEL and AMEL class ratings and with an instrument add-on rating. [I'm trying to be precise but, basically, I've an FAA multi/IFR PPL.]

I'd like to add a Rotorcraft-Helicopter class rating to my PPL. [I.e., get rated in an R44.]

I did my fixed-wing training with AFSP approval. (I'm a permanent resident.)

Do I need to obtain AFSP approval for my helicopter training?

According to the AFSP FAQ,

  Category 3 Clarification - For flight training in the operation of aircraft with a maximum certificated takeoff weight of 12,500 lbs. or less, Candidates must obtain AFSP approval for the following three training events:

  Single Engine Land (SEL)

  -- Includes initial Airman's Certificate, including a private, recreational, or sport pilot certificate. If a private and/or commercial license is the candidate's initial FAA license, it is considered an initial airman's certificate and is not exempt.

  Instrument Rating (IR)

  Multi Engine Land (MEL)

  Each of these three events requires a separate training request.

  All other training events on aircraft with MTOW of 12,500 lbs. or less are exempt from AFSP regulations, including Commercial Pilot License (CPL), Airline Transport Pilot License (ATPL), and Certified Flight Instructor (CFI). These events are exempt only if the candidate holds an FAA stand-alone pilot certificate.

But, when asked, the AFSP said that I do need to get AFSP approval. (Citing no rule.) I've asked for clarification but does anyone know for sure?

The problem is that person writing the FAQ seems to not understand the category and class system for pilot certification. The interim final rule (the actual regulation) does not make the distinctions you have discussed from the FAQ. See https://www.flightschoolcandidates.gov/IFR_Alien_Pilot.pdf as Category 3 does not specify an FAA pilot certificate category or class, just MTOW of 12,500 pounds or less, which means a R-22, R-44, Sikorski/Schweizer 300, seaplanes, gyrocopters, gliders, lighter than air, etc. unless specifically exempt elsewhere.

According to https://www.flightschoolcandidates.gov/TSA-2004-19147-0337.pdf the measure that they use with regards to whether or not you are subject to the "threat assessment" is whether you are taking training that will "substantially enhance piloting skills" but then it further states that the requirements are for the "initial pilot certificate, including a private, recreational, or sport pilot certificate."

It would be very hard to argue that training towards a certificate in RH is not going to "substantially enhance piloting skills". However, when they came up with the FAQ it appears that they have ignored that there is any category of aircraft outside of that of airplane (and any class outside of land airplanes).

Adding on RH (or Instrument-Helicopter) to ASEL/ AMEL/ Instrument-Airplane would be your "initial pilot certificate" in the rotorcraft category, helicopter class, or your "instrument rating" for that category.

For the sake of not getting yourself or your flight school in potential serious trouble, you should probably apply under the Category 3. If I were in your position I would omit the "probably" of the last sentence, but I am not a government regulator and I am not an attorney, so there is always a degree of uncertainty with regards to my personal interpretation of this material.


Why are there different number of propeller blades on the inboard and outboard engines? The Junkers G 38 has four propeller blades on the inboard but only two on the outboard engines.

What's the reason for this special arrangement and is there any benefit?

The inboard engines were of a different type, and more powerful than the outboard engines. Hence, the props had to absorb different power, so they were four-bladed for the inboard and two-bladed for the outboard engines.

Yo can see the specs of the airplane here
https://en.wikipedia.org/wiki/Junkers_G.38#Specifications_(G.38_1929)


What is the "one-in one-out" FAA rule for IFR traffic landing or departing at an airport without a tower or at an airport with a closed tower? Does the rule say that only one IFR aircraft may land or depart at an airport at one time? I'm having trouble finding the official rule in an FAA document.

What about other VFR traffic that may be flying in the traffic pattern doing practice touch-n-goes? Would that activity be affected by the rule?

Several sections of the AIM give guidance on this. It is explicitly stated that only one aircraft at a time is given a departure clearance. It is implied that there would be no approach clearances until the departing aircraft’s position is known by ATC.

  4−4−1. Clearance

  a. A clearance issued by ATC is predicated on known
  traffic and known physical airport conditions. An ATC clearance means
  an authorization by ATC, for the purpose of preventing collision
  between known aircraft, for an aircraft to proceed under specified
  conditions within controlled airspace.

  5−2−6. Departure Restrictions, Clearance Void Times, Hold for Release,
  and Release Times a. ATC may assign departure restrictions, clearance
  void times, hold for release, and release times, when necessary, to
  separate departures from other traffic or to restrict or regulate the
  departure flow.
  1. Clearance Void Times. A pilot may receive a clearance, when operating from an airport without a control tower, which contains a
  provision for the clearance to be void if not airborne by a specific
  time. A pilot who does not depart prior to the clearance void time
  must advise ATC as soon as possible of their intentions. ATC will
  normally advise the pilot of the time allotted to notify ATC that the
  aircraft did not depart prior to the clearance void time. This time
  cannot exceed 30 minutes. Failure of an aircraft to contact ATC within
  30 minutes after the clearance void time will result in the aircraft
  being considered overdue and search and rescue procedures initiated.

  NOTE−
  1. Other IFR traffic for the airport where the clearance is issued is suspended until the aircraft has contacted ATC or until 30 minutes
  after the clearance void time or 30 minutes after the clearance
  release time if no clearance void time is issued.

  5−5−4. Instrument Approach

  b. Controller.
  1. Issues an approach clearance based on known traffic.

  5−5−4. Instrument Approach a. Pilot.
  1. Be aware that the controller issues clearance for approach based only on known traffic.


Is it possible to do a Live-stream web cam on an airplane over the oceans? Just wondering if this technology exists or has been attempted. For positioning purposes.

No, there is no mid-ocean real-time streaming video useful for positioning purposes.


What does "reserve take off" mean in engine parameter documentation? In ATR 72-500 FCOM document I found engine parameters including power settings as "Reserve Take off". What does that mean?

I've seen this mentioned in story (unfortunately in Czech) about flying in Bhutan on ATR-42 (a smaller version of the same aircraft). Basically in most situation it is recommended to use less then maximum rated power to reduce wear of the engine and that setting is marked as “take off” and the maximum rated power is only used in high density altitude (hot and high) conditions or very short runways and is labelled “reserve take off”.

Most other aircraft don't have setting labelled like this, but taking off at less than maximum rated power is common. It is called “derated” or “flex” take-off.