What rules allow a student pilot to add oil to an airplane? A private pilot oral exam guide I'm reading asks a basic question about an issue I had taken for granted:

You have just completed the first leg of a long cross-country and notice that the oil level is approaching the one quart low mark. As a private pilot, can you add the quart of oil yourself or is a mechanic required? (See 14 CFR Part 43)

Clearly this must be preventative maintenance? No. 14 CFR Part 43 Appendix A does not explicitly list adding oil as preventative maintenance.
Searching online I found a lot of forum posts discussing this issue, some suggesting it is "obviously" preventative maintenance per the definition, but 14 CFR Part 1 does not define preventative maintenance, and others suggesting it isn't maintenance, it's servicing, but this isn't defined either.
How does this work if you're a student pilot on a solo cross country? If you shut the engine off and check the oil, are you stuck if the oil is low?
The best answer I can find is adding oil is not "maintenance" or "servicing," it is Normal Procedure per the Pilot Operating Handbook / Information Manual. The Cessna 172S POH as part of the preflight check on page 4-10 states:

Engine Oil Dipstick/Filler Cap -- CHECK oil level, the check dipstick/filler cap SECURE. Do not operate with less than five quarts. Fill to eight quarts for extended flight.

The POH is a little ambiguous how much oil to add, but it clearly states the pilot executing this procedure should add oil.
I believe this how a student pilot can add oil to a plane, or at least a Cessna 172S. Is this correct or is there a better explanation?

The FAA doesn't consider adding oil to be maintenance. The Hochberg (2016) interpretation says:

The subject of adding oil is often debated; however, we note that it
is not an item included in part 43, appendix A, paragraph (c), which
lists items the FAA considers to be preventive maintenance.

Also see the FAA's Flight Standards Information Management System, under Elements of Maintenance (emphasis mine):

In broad terms, it has been generally upheld that basic servicing
tasks, such as fueling and adding oil, are neither maintenance nor
preventive maintenance. But even that has some caveats. When adding
oil requires a precise sequence of steps or partial disassembly to
gain access, then that would be considered a maintenance activity.
Adding oil to an oleo strut for example, would be a maintenance
activity, whereas adding a quart of oil to a GA aircraft would not.

Since adding oil isn't maintenance - at least not in a simple GA aircraft - part 43 is irrelevant and there's no requirement to have any type of certificate to be allowed to add it.


What is the sweep angle of the Boeing 787's horizontal stabilizers? What is the sweep angle of the horizontal stabilizers on a Boeing 787 Dreamliner? Does it have to be equal to that of the wings, and how is it determined?

(Source: Boeing)
Simple image analysis shows it has higher sweep.
The general rules of empennage design can be found here (Hamburg University of Applied Sciences).

The sweep of the horizontal tailplane should be approximately 5° larger than the sweep of the wing. Thus a higher critical Mach number of the horizontal tailplane can be achieved and a loss of efficiency due to shock waves is avoided.
In addition, the lift gradient of the horizontal tailplane can be less than the lift gradient of the wing due to the increased sweep, so that the horizontal tailplane only reaches the stall state at larger angles of attack than the wing.

The main wing sweep is easily found on Wikipedia, it's 32.2°. In comparison, the stabilizer angle is 36.00° (source).

Related: How are the dimensions of the empennage determined for jetliners?


How does setting takeoff flaps improve aircraft performance? A study guide I recently found indicates that Vmc and aircraft performance improve with takeoff flaps set. The Vmc improvement makes sense but the performance improvement does not. At a basic level, drag = bad and flaps add drag...a lot of drag.

The question is, "how does aircraft performance improve with takeoff flaps set?"

The Airplane Flying Handbook (FAA-H-8083-3B) page 12-17 indicates that takeoff flaps will degrade aircraft performance:

  If flaps were used for takeoff, the engine failure situation becomes
  even more critical due to the additional drag incurred.

See also FAR 23.149.

I think the term "takeoff performance" in that context means takeoff distance and departure gradient for obstacle clearance.  Obviously, takeoff distance is shorter with takeoff flap than without.  And a departure with takeoff flap will generally, depending on the airplane, have a steeper gradient than without, even though the total climb rate is degraded with takeoff flap out.  On an IFR departure, or a regular airplane clearing trees at the end of the runway for that matter where you fly at best angle instead of best rate, gradient is the key performance factor, not so much rate of climb.

Transport aircraft generally don't start to accelerate to retract flaps at least until reaching 1000 ft agl, to keep the initial climb segment as steep as possible. Some noise abatement procedures for airliners require keeping takeoff flap deployed beyond the normal retraction schedule, typically to 3000 feet instead of 1000 feet.  This is to keep the climb as steep as possible to a higher altitude so as not to upset unusually sensitive neighbours farther away from the airport.

That sort of thing is a luxury that jets enjoy because of the massive power reserves. Not so much in a piston twin, which has very little performance reserve when single engine and loaded.  Where an AFM says to do so, you would want to avoid climbing with takeoff flap any more than you have to for obstacle clearance, since if an engine quits, the airplane's climb gradient becomes more of a descent gradient until flaps and gear are retracted, and even then what climb you get is pretty stately - and only if your speed and technique is spot on.

So I don't think the seemingly contradictory conditions you gave are inconsistent in that context.


How to compare two SFCs, one in thrust, the other in power (both turbofans)? I want to compare some recent turbofan engines in terms of fuel efficiency, particularly the PW535A and FJ44-4.

I found the SFC for the PW535A to be 0.44 lb/h/lbf. I couldn't find anything on the FJ44-4, except for an earlier model. The FJ44-3A has a SFC of 0.456 measured in kg/kW*h.

Firstly, how can I effectively compare these? I tried rearranging the units so they could immediately be compared but kept ending up with laughably different values.

Furthermore, where might I be able to find data on the FJ44-4?

For comparing turboprops vs turbofans, you would normally divide the turboprop's SFC by the prop's thrust coefficient at comparison airspeed.

For two turbofans, always compare TSFC. It's a function of airspeed and altitude too, but the curves can be found in the paperwork, and for common engines online.

Jet engine SFC is rarely mentioned and has few practical applications outside of engine design and engineering. All the customer (pilot, etc) will see is thrust.

The FJ-44's TSFC is right there on the wiki page you've linked. The entry for 44-4 is n/a, but you can generally assume it about the same among the variants. The actual vatiance is within a couple percent.


How "over-engineered" were old planes and how "over-engineered" are they now that we have more advanced testing and research options? I've seen several times on shows on television, and even talking to older pilots, where they will tell me that old planes were "over-engineered" to add some margin for errors on the designed engineering calculations. Of course, no specifics are given, and so I was thinking in this current age of super-fast computers, better wind tunnels, new software tools, and decades of actual experience, when people design new planes, how much of a margin to they design into them now?

It seems like confidence in computer modeling seems to be pretty high, and "over-engineering" seems to have typically meant making things stronger than they "need" to be, more reinforced elements, all things which add to cost and weight of an airplane which are factors that are at odds of profitability and performance.

You are right that older designs used (and needed!) higher safety margins. I would, however, not call this over engineering. But that is besides the point.

The biggest advances have been made in materials! Not just new alloys, but much better quality control in manufacturing. The aluminium sheets and slabs you would get from a factory 50 or 80 years ago had much greater variations in local strength, and in strength between different production batches. The same goes for fasteners, forgings, whatever. Computer-controlled manufacturing and the relentless effort to improve quality and consistency have made this possible. Only wood is still the same as it was then, but Basil Bourque is right: Processing the wood has also improved by leaps and bounds.

But now consider what we do when we stress a wing: We use the maximum static lift coefficient, add aileron deflection and use that bending moment at v$_A$ to size our wing spar. We do this by applying a safety factor of 1.5 (§25.303). For parts with a more error-prone production process additional factors need to be added (see §25.619).

And now consider what happens in the real world: The dynamic maximum lift coefficient, which does not obey the rules and regulations imposed by the FAA, will easily be 1.3 times bigger than the static lift coefficient used for stressing the wing spar. In tests up to 150% have been achieved. Makes you think how sensible that safety factor really is. While we understand the static loads very well (because they are easy to study), dynamic and fatigue loads still happen to surprise the engineers from time to time. A little extra margin sometimes can be quite useful.

On the Eurofighter the structural safety factor was indeed reduced to 1.4 with the reasoning that more precise modeling and simulation would allow to use a smaller margin.


Mathematical function in performance diagrams I have taken upon myself to digitise some scanned old performance diagrams, e.g. roll distance as function of mass and OAT, TAS as function of power setting, etc. The obvious goal is to allow the computations to be performed in a computer instead of on paper (that is: almost never). I have written some tools to do measurements of the line intersections in the documents, so consider that problem solved.
However, what are the best functions to fit to the measured
coordinates? In selected cases, a straight line would be valid, but most often not. After all, the functions are typically solution to differential equations…
What functions are reasonable to adapt to the measured data?
Simple polynomial have the advantage that all measurements are used to fit one set of parameters. However, they are also well-known to produce oscillations between measured points. On the other hand, interpolating cubic polynomials have less oscillation problems but are… interpolating, so the measurement errors are not smoothed out. Furthermore, I have estimates of the measurement uncertainty of each point, so I would like to use that for fitting a global function.
Ideally, I would like a closed-formula for each type of curve, but I know that might be a tall order. My goal is to automate the computations, so the required precision is in the order of what you would produce with a pen and a ruler.
So, what do you suggest I do? My background is in computing science, but the physics behind these curves is beyond me. Any suggestions will be appreciated.
As an example I attach the "roll distance as a function of OAT, mass, and wind" for our PA-28-161. The image shows the actual document from our POH. I apologise for the Swedish labels, but this is in fact our legal document. The left panel shows OAT and pressure altitude, middle panel is take off mass, and rightmost panel shows wind.
Thanks

If you have a good set of well-spaced points, a best-fit polynomial in $x^2$ or $x^3$ is usually good enough. It's true that high-degree polynomials oscillate, and are therefore unreliable, but you're safe with squares and cubes...
This site is free and quite good: MyCurveFit.


Does the 2020 ADS-B -Out requirement apply to aircraft with only a wind-driven generator (electrical system)? Since my J3 Cub was was not originally certificated with an engine-driven electrical system it's clear the 2020 ADS-B-Out mandate (U.S.) does not apply (except where specifically noted in FAR part 91).

If I install a wind-driven generator providing a limited electrical system for my J3, will I now be required to comply with the ADS-B Out 2020 regulations?

Part 91 is mostly clear on the subject:

  §91.225   Automatic Dependent Surveillance-Broadcast (ADS-B) Out
  equipment and use.

  (a) After January 1, 2020, and unless otherwise authorized by ATC, no
  person may operate an aircraft in Class A airspace unless the aircraft
  has equipment installed that—

More detail, that describes 1090 MHz ADS-B out equipment...

  (b) After January 1, 2020, and unless otherwise authorized by ATC, no
  person may operate an aircraft below 18,000 feet MSL and in airspace
  described in paragraph (d) of this section unless the aircraft has
  equipment installed that—

More detail describing 1090 MHz or UAT ADS-B out...

  (c) Operators with equipment installed with an approved deviation
  under §21.618 of this chapter also are in compliance with this
  section.

If you have this deviation, you're good.

  (d) After January 1, 2020, and unless otherwise authorized by ATC, no
  person may operate an aircraft in the following airspace unless the
  aircraft has equipment installed that meets the requirements in
  paragraph (b) of this section:

  (1) Class B and Class C airspace areas;

  (2) Except as provided for in paragraph (e) of this section, within 30
  nautical miles of an airport listed in appendix D, section 1 to this
  part from the surface upward to 10,000 feet MSL;

  (3) Above the ceiling and within the lateral boundaries of a Class B
  or Class C airspace area designated for an airport upward to 10,000
  feet MSL;

  (4) Except as provided in paragraph (e) of this section, Class E
  airspace within the 48 contiguous states and the District of Columbia
  at and above 10,000 feet MSL, excluding the airspace at and below
  2,500 feet above the surface; and

  (5) Class E airspace at and above 3,000 feet MSL over the Gulf of
  Mexico from the coastline of the United States out to 12 nautical
  miles.

That's all airspace where ADS-B is required. A summary is shown in the following graphic:

Source: FAA

  (e) The requirements of paragraph (b) of this section do not apply to
  any aircraft that was not originally certificated with an electrical
  system, or that has not subsequently been certified with such a system
  installed, including balloons and gliders. These aircraft may conduct
  operations without ADS-B Out in the airspace specified in paragraphs
  (d)(2) and (d)(4) of this section. Operations authorized by this
  section must be conducted—

That specifies which aircraft have an exception (with following detail on specifically what airspace they can operate in.) It has, however caused confusion as the wording is very similar to Part 91.215(b)(3) which specifies "an engine-driven electrical system" as opposed to "an electrical system".

Subsequently the FAA has published a Legal interpretation that clarifies the intent was not to create a more stringent requirement for ADS-B Out than for transponders; specifically from the interpretation:

  As such, we have concluded that the same aircraft excluded from the
  transponder requirement are excluded from the ADS-B Out equipage.
  Accordingly, an aircraft that subsequently has been installed with
  batteries or an electric starter would not be required to equip for
  ADS-B Out.

So it appears that your J3 is exempt and would remain so unless you installed an engine-driven electrical system.


Why doesn't civil navigation equipment support TACAN? Now even handheld aviation radios have GPS, VOR and ILS! I wonder why modern LCD screens with radios and navigation doesn't have TACAN? Is it coded, not useful, not certified or not used anymore? I don't think there is a problem to implement the electronics nowadays.

Civilian aircraft can use part of TACAN, the Distance Measuring Equipment (DME) signal is the same as civilian DME. As for the directional component one big reason is that the military don't want you to.

Even if the military didn't mind there would likely be no demand as the costs of using TACANs outweigh the benefits. TACAN is essentially a more accurate version of VOR, and although the complexity and weight of the system has reduced the antenna is still apparently 100 pounds (45kg). For light aircraft that's a fair chunk of useful weight taken off. Cost-wise a VOR setup will set you back somewhere around \$6000 just for the equipment, call it closer to $8000 installed (roughly). A TACAN is a more sophisticated system which would cost a great deal more, say finger in the air of \$20,000, maybe more. TACAN antennas would need to be certified for every single airplane model, and that's going to add to the costs.

So for a light aircraft I'm going to lose usable weight to an antenna that is also going to throw off my weight and balance, and that's going to cost me at least \$20k when all the equipment, installation and recertification costs are factored in. That's big cash when I already have VOR, ILS, DME, NDB and 3+ satellite navigation systems already available. Oh, and I can also call up ATC most places and say 'help!' if it all goes wrong. There's just no benefit. My phone can tell me where I am if every system on the airplane fails as it has a built in GPS!

For commercial large airplanes it's the same situation. In addition to all the above most will have redundant inertial navigation systems, so even less need for it.


Where do the names "First", "Business" and "Economy" class originate from? As said in the title: where do the names "First", "Business" and "Economy" class originate from? Why they didn't use the names "First", "Second" and "Third". After all it can be hard for someone not that familiar with English to find out that "Business" is ranked higher than "Economy".

They used to use those ordinal class names (first, second, third), borrowed originally from train and ocean liner class designations. British railway classes were first, second and third classes, while ocean liners typically had first, second and steerage (which itself became a derogatory term that was changed to "third class", especially as steerage evolved from a converted section of cargo space to purpose-built passenger accomodations).

The change to the modern airline classes is an example of the euphemism cycle, and occurred through the 1960s and 1970s as travel in general increased dramatically while the average income of the travelers nose-dived. In the U.S., the primary driver was the stigma of people in those sections being called "second class" or "third class" as "political correctness" started becoming a big thing with the civil rights disputes. This led to a rebranding of lower numbered classes by airlines; second class, being a popular choice for frequent flyers on corporate business seeking a compromise between the low cost of the economy section and the amenities of first class, was renamed "business class", while the main passenger cabin holding the bulk of passengers with the lowest-cost tickets (average Joes going on vacation, visiting family or just needing to get somewhere on a short travel schedule) was called "coach", "economy" or simply "standard". All of these terms have survived at least informally, but "economy" is the one most often used by the airlines to denote this service level.


Can an APU exhaust make a contrail in flight? I saw this picture in a local newspaper.

My thoughts were, silly artists, that's the APU exhaust, it won't ever produce a trail like that during takeoff (or ever).
Of course, the picture is clearly photoshopped, as can be seen by the planes' outlines. But somebody didn't do the research :)

Just to be sure, were my thoughts correct?

APU may be used in flight as second source of power or bleed air if one of the engine systems is inoperative. If it is so used, it might leave a contrail the same way engines will, though as DeltaLima notes, it's exhaust is hotter and the air behind the fuselage is more turbulent, so the range of conditions where it will leave a contrail is narrower than for the engines.

And it is an exceptional situation, so it is extremely rare. Most of the time the APU is switched off once the engines are running and only switched on again after landing, because when engines are running, they provide everything the aircraft needs.

In B737NG (the lower aircraft in the picture), the APU can be used as bleed air source up to 17,000 ft. This is too low for normal cruise, but if bleed system fails, pilots will descend to this altitude and start APU to provide air-conditioning for the remainder of flight to a suitable nearby airport. It can also be used up to 41,000 ft as power source, so the aircraft may cruise with one generator inoperative and running APU.

In A320 (the upper aircraft in the picture), the APU can be used together with one bleed air system up to 20,000 ft and for power generation up to 41,000 ft. So again, the aircraft may cruise with one generator inoperative and running APU.

However:

Normally there would never be contrail behind APU and none behind engines unless both engines failed and APU was started as backup power source (US1549 did start APU when the engines failed, though it is unlikely there was contrail at that altitude).
Contrail does not start right behind the engines. The water in the exhaust needs some time to cool down and freeze before the contrail becomes visible.


What are the advantages of single vertical stabilizer over a twin set? Why did the PB4Y patrol aircraft use a single fin while the B-24 it was derived from used twin fins?  I have read that the twin fins were thought to be superior but this was realized to be false.  Why did engineers believe the twin fins to be superior and what caused them to reconsider?

Why did engineers believe the twin fins to be superior?
There doesn't seem to be any single definitive reason for selecting the number of vertical fins on an aircraft design (except, obviously, for the twin-boom designs such as the Lockheed P-38 or Fairchild C-119).  I've seen all of the following cited by one authority or another as advantages of multiple vertical fins.  (Sorry, I didn't save or remember the sources.)

Reduced hangar overhead requirement.  This is the most common reason for including total aircraft height in a purchase specification, and it is a sine qua non requirement for carrier deployment.
Also I remember reading a magazine article that supplied this reason for the triple tail on the Lockheed Constellation.

Reduced cantilever stress at the root.  This may actually save weight over the single-fin design.  It may also help keep a tactical aircraft from disintegrating under the enormous stress of combat manoeuvres.

Reduced parasite drag.  The lower half of a vertical fin can be twice as thick as the upper half.  A twin tail design effectively omits the lower half and uses the upper half twice.

For multi-engine designs, operating the rudders in the engine slipstream affords improved rudder authority at low speed.  Pilots who taxi loaded bombers into takeoff position between other loaded bombers like lots and lots of rudder authority.
Also I notice that practically all the big flying boats of the 1940's Flying Clipper era had multiple vertical fins.  Those craft had some tricky low-speed steering requirements — they not only had to make their way through a busy harbor, but usually docked and undocked without a tugboat.  I'm only guessing at the connection though.

A single vertical fin can be masked by the fuselage wake at high angles of attack.  You can see how this could be a problem for modern fighter aircraft, which look like flying tennis courts.  Traditional bomber designs with their broad wings and heavy aerodynamic loading can also generate quite a troublesome fuselage wake.

Improved position and field of fire for a tail gunner.  I don't see it myself but I've heard the claim so I'm including it here.
I concede that the tail gunner slot in the Avro appears to benefit from the absence of bracing structure.

Reduced rudder-induced roll due to a shorter rudder offset moment.  Fast tactical military aircraft have short wings, and you don't want the rudder to extend further from the roll axis than the ailerons do.  On the other hand, the rudder doesn't need to go all the way to the top of the fin, does it.

Twin fins can be canted to reduce radar return.  They usually are, although I don't understand how the designers know where the hostile radar will be.

On the A10, the vertical fins actually mask the hot engine exhaust over a large angular area.  Thus in order to aim a ground-to-air heat-seeker up the tailpipes of an A10 you have to be directly behind it.  Which means that a few seconds ago you were directly in front of it, so good luck with that.


Does the 787 gust alleviation system make a more comfortable ride or for a more stable aircraft? The 787 active gust alleviation system, similar to the system used on the B-2 bomber, improves ride quality during turbulence.

Ride quality in a B2 bomber means a more stable weapons platform.

Ride quality in a 787 means passenger comfort.

(I must add that I have never flown in a 787.)

Is the 787 more comfortable than a normal plane of similar size?

Both, but the improved comfort and stability are only side effects.

A gust alleviation system uses trailing edge flaps (ailerons, elevators and sometimes spoilers) to counteract local lift changes caused by flying through up- or downdrafts. The flap is deflected to change the local incidence and camber of the wing in order to reduce the change in lift due to gusts. This helps to lower the collective cyclic loads the structure has to endure over time and allows to use a lighter, less strong structure, or it allows to stretch out the inspection intervals for the same structure.

Since the structure will experience smaller deviations from the average load factor, you, the passenger, will experience a smoother ride in gusty air. In calm air the system will not make any difference.

Also pitch changes are smaller since the flight will be less bouncy and the tail surface lift can be smoothed out over time in the same way. Therefore, a gust alleviation system works similar to artificially enhanced stability.

A major problem is the unavoidable lag in reaction. If the bending moment in the wing spar is measured, a computer has to calculate the appropriate response, has to command changes in hydraulic pressure and flight control surfaces need be moved. By the time the flow around the wing is affected by the flaps, the gust has long passed. Therefore, it needs instruments like laser anemometers to measure the wind ahead of the airplane so the reaction can be timed correctly.

The answer to your last question would primarily be based on opinion, so I leave answering it to you.


What are Electro Hydraulic Servo Valves and Solenoid Operated Valves? What is Electro Hydraulic Servo Valve (EHSV) and Solenoid Operated Valve (SOV)? Also what is the difference between these two valves?

Basically, these two are used to control the hydraulic fluid in actuators. I am working on a aircraft program where SOV are used in Aileron, Elevator & Rudder actuators while EHSV are used in Multi-Function Spoilers [or just spoiler]. I think someone explains these two valve basics would provide me the reason for the selection of these valve to control the hydraulic actuators.

A solenoid is an induction-based actuator. In its simplest form it is a magnetic rod inside a coil of wire. Run a current through the wire and you create a magnetic field that creates a force on the rod, moving it one direction or the other. The force with which this occurs is proportional to the current through the inductor (audio speakers use this exact same principle to make the cone vibrate).

A solenoid-operated valve usually functions as a simple gate; the solenoid mechanism pulls or pushes a simple flat valve allowing the fluid to pass through or not. It's technically possible, but not usually feasible, to use a solenoid as a variable valve; for it to be accurate would require very low friction so the current applied to the solenoid (and thus the force on the valve) could be varied to produce smooth variations in valve position.

Solenoid-operated valves are typically used as triggers for larger mechanisms, including the electrohydraulic servo valve.

An electrohydraulic servovalve uses electrical current to move a "flapper", similar to a solenoid. The flapper controls the flow of hydraulic fluid to one side or the other of a spool valve. That moves the spool valve, allowing the supply pressure to feed an actuator cylinder, moving it one way or the other. However, that same movement also allows hydraulic pressure to return up to the flapper, providing a countering hydraulic force to the electrical force that moved it, called "negative feedback". Eventually these forces balance, and the flapper re-centers, closing the spool valve. The net result is that the actuator cylinder has moved a certain set distance, proportional to the strength of the input current.

These valves are used to provide smooth, high-strength motion in a hydraulic system. This type of valve, for instance, can be used to move the control surfaces of a large airliner, without requiring high-pressure hydraulic lines or tensioned cables to link the hydraulic system to the yoke in the cockpit. Instead, the yoke (or sidestick) controls the current through electrical wires leading to the EHSVs. That link is much easier to maintain (and cheaper to build in the first place) than older systems on previous generations of aircraft.


How do they fill fuel in big aircraft? Being a passenger, I usually will have view from only one side of these planes and hence don't know if same thing is happening on other side of the plane. I have observed hoses connected to wings, but there are always many connections to plane when its on ground and never sure which one is for fueling.

Looking at the answers for fuel tank description here or here, when they are filling fuel, do they connect hoses to each tank individually or just connect to one tank? Or is it per side - fill up each side individually.

Also suge/vent tank at the tail end of a380 seems to too high. Do they fill in those tanks too?

After fuel calculations are done, is there a standard fuel distribution that has to be done to every tank for weight/balance reasons?

My answer is limited to commercial type aircraft (e.g., B737/757/767, etc.).  There is variance between aircraft types.

  Question: when they are filling fuel, do they connect hoses to each tank individually or just connect to one tank? Or is it per side - fill up each side individually.

For most large commercial aircraft (e.g., B757, B767 etc.) single-point fueling is done from one location underneath one of the wings.  This single-point fueling system allows fuel to be
loaded to all tanks, e.g., Left/Right Main wing tanks and the Center tank (if necessary) from a single location.  The switches on the single-point refueling panel operate pumps
and cross-feed valves to allow all tanks to be fueled from this single location.

  Question: Also suge/vent tank at the tail end of a380 seems to too high. Do they fill in those tanks too?

A "surge" tank (or similar notation) is normally dry but is designed to hold fuel that passes through the main fuel vents (due to expansion or overfilling) in the normal tanks so that the fuel does not spill out (on the ground) and cause a fuel spill.  This fuel ultimately works its way back to the normal tanks through gravity.

  Question: After fuel calculations are done, is there a standard fuel distribution that has to be done to every tank for weight/balance reasons?

Generally speaking Yes.  The location of the fuel tanks in an aircraft is designed (again, generally speaking) to be near the center of gravity (CG) for the aircraft.  So, as fuel is burned during the flight the aircraft does not find itself outside of the appropriate weight/balance envelope. However, calculations are done to ensure this and verify that the fuel loading at the beginning of the flight results in the CG being within limits and that the CG is within limits at the end of the flight after the anticipated amount of fuel is burned.  Generally speaking (again), the aircraft is designed to stay within limits for most types of operations considering possible fuel, cargo, and passenger loads that may be encountered during normal operations.

FYI - If the single-point fueling system is inoperative for some reason over-wing fuel points allow for manual filling of the main tanks.  Also, should the Fuel Quantity Indicating System (FQIS) system fail and
the total amount of fuel in the tanks cannot be determined, fuel quantity can be measured using measuring sticks (with a reference chart available to determine (manually) how much
fuel is in each tank.

Below from ABXtranet.com is a picture of the fueling procedures for a B767 and a picture of the Fuel Control Panel (B767 Single Point Refueling):

Here is the link to ABXAir's B767 Fueling Procedures Manual:
refuel procedures ABXAir


What is this board given to world war II pilot? What is this board given to world war II pilot?

The photo in the question is a screenshot from the movie "Midway"(2019).

The board is a Mark 3A Plotting Board used for navigation by pilots flying from U.S. Navy aircraft carriers during World War II.  It can be seen carried by various SBD Dauntless pilots in this scene from the movie "Midway" (2019) from 0:24 to 1:07.

Photo credit: National Air and Space Museum, Smithsonian Institution

Plotting Board Instructions

Photo credit: National Air and Space Museum, Smithsonian Institution


What is pressurization influence (if any) on maximum G load an airliner can withstand? Reading here about skin thickness of airliners I was wondering if, considering  some pressurized airliner at cruise altitude, there are differences in maximum operational acceleration loading the fuselage can withstand.

For instance, could an "inflated" cylinder better withstand compression stress during a 2.5g turn, compared to a similar unpressurized airframe?

Are there different limitations related to pressurization level?

For skins in the upper half of the fuselage in bending tension, the pressure acting on the skin is just adding to the tension stress on the skin from fuselage bending, so it doesn't help there.  For skins and stringers in areas of the fuselage where loads are in compression, the pressure if anything will displace the structure (bulge it out) in effect "bending the column" and making it less able to take compression loads (maybe only a few thousandths of an inch, but still something).  On the other hand, the pressure will tend to help keep the tube circular, so it will probably tend to reduce stress on circular frames that are resisting the tube from collapsing in bending.

The most stressed area in the fuselage is compression stress at the bottom just behind the wing, (next to the pivot of the seesaw you might say) and there is usually a heavy compression beam structure down that that is not helped or hindered much by how much pressure is acting on the pressure hull.

Overall, none of this is taken into account in the structural design and there normally aren't any specific structural restrictions between pressurized and unpressurized flight as far as G loads go.  For example, you won't see different published G limits, or Turbulent Air Penetration Speeds, or Maneuvering Speeds, for pressurized and unpressurized conditions.


Is there a source of deicing holdover time tables? Depending on the types of de-ice and anti-ice fluids used, the HOT changes.
Is it possible to post some HOT table here?

Here are some holdover charts I have access to.


How was the high-bypass concept invented? (Source)

Wikipedia says:

  After [the Ryan XV-5 Vertifan demonstrated] that large amounts of air could be moved through a lift fan, an 80 in (2.0 m) tip drive fan turned through 90 degrees, driven by a more powerful J79 engine, was built to demonstrate an efficient cruise fan. The concept of a large diameter cruise fan was incorporated in the General Electric TF39 engine, used on the Lockheed C-5 Galaxy.

Was the XV-5 responsible for ushering in the high-bypass concept?

The economic drive is discussed here:

What drives and/or allows the move to higher-bypass turbofans on jetliners?

I'm more after the evolution of the engineering concept I think, i.e., the different iterations and studies—a brief history lesson.

The need for a turbofan was realized as early as the mid-30s.

The first jet aircraft were subsonic and the poor suitability of the propelling nozzle for these speeds due to high fuel consumption was understood, and bypass proposed, as early as 1936 (U.K. Patent 471,368). The underlying principle behind bypass is trading exhaust velocity for extra mass flow which still gives the required thrust but uses less fuel. Whittle called it "gearing down the flow".

In the mid-60s, the USAF A-X and CX-XX programs accelerated the development of the high-bypass jet engines. The winners of the programs were the Fairchild Republic A-10 Thunderbolt II and the Lockheed C-5 Galaxy, respectively.

To meet the [CX-XX] power and range specifications with only four engines required a new engine with dramatically improved fuel efficiency.

The TF39 on the C-5 Galaxy was the first production high-power, high-bypass jet engine. It first ran in 1964. The XV-5's lift-fan-inspired-demonstrator helped confirm to GE the feasibility of high-bypass jet engines.
The demonstrator was the GE1/6 (cruise fan variant), it featured a GE1 core engine energizing remote tip-turbine-driven cruise fan of high-bypass. (Sadly, I can't find photos/illustrations.)
Around the same time the Convair 990 Coronado was powered by the CJ805-23, which featured one of the first aft-mounted fans.
(Source) CJ805-23 with the aft-fan.

Transatlantic service needed a higher thrust version of the existing turbojet and a demonstrator engine with a single-stage front fan attached to the compressor was run. It was difficult to start and operate. This experience led to the aft-fan which didn't compromise the operation of the gas generator.

For its time, the TF39 had unique features—namely the 1½ fan-stage—which resulted in an impressive 8:1 bypass ratio, higher figures were seen only decades later on the Boeing 777's GE90.
(Wikimedia) TF39.
The front of the engine features a mini-fan that rotates inside stationary vanes. Behind this first ½ stage is a full-sized fan. A fair proportion of the air entering the ½ stage is also ducted to the bypass stream.
(FLIGHT International, 13 March 1969)

The two-spool high bypass General Electric CF6 (top half section) is based on the same gas generator and turbine as the TF39 (bottom section) which powers the Lockheed C-5A Galaxy.

The mostly civilian and much simpler CF6 was based on the T39, it is found on the Airbus A300/310/330, Boeing 747/767, DC-10/MD-11, and others.
Honorable mentions
Two years before the A-X program, Avco Lycoming was working on the earliest experimental turbofans, but not necessarily high-bypass. With development and various derivatives contributing to the Lycoming ALF 502 which powered the Northrop YA-9 entry for the A-X program.

(FLIGHT International, 10 February 1972)

The only production fan engine to use an aft-mounted fan is the CF-700, power unit of the Fanjet/Mystere 20.

(Source)

Sources: Various issues of FLIGHT, Wikipedia, and The Power to Fly: An Engineer's Life.


Why didn't Boeing produce its own regional jet? Boeing, although it produced many larger narrowbodies, never designed its own regional jet; the only regional jet it ever produced was the DC-9 (from 1997 through 2006, in the DC-9-80 and DC-9-90 series), a (McDonnell) Douglas aircraft which Boeing inherited from Long Beach through a corporate merger.

Why didn't Boeing design and build its own regional jet earlier, to compete with the DC-9?

Boeing did have a small regional jet called the Boeing 727. This plane was designed to operate at smaller airports, with independence from ground facilities as a selling feature. The best example is that the 727 had built-in stairs in the rear underbelly of the aircraft. This could be opened in flight until some hijacker known as DB Cooper jumped out to make his escape.

The 727-100C could have a combination of 54 passengers and  four cargo pallets of freight or up to 94 passengers in a mixed class with no freight.

Until it ended production at 1,832 aircraft, the 727 was the most popular passenger jet ever sold. Since that time, the most popular plane ever sold was the Boeing 737, which could have as few as 85 passengers with the 737-100.

Boeing met a definite need for airlines since it sold so many aircraft. A better question might be what could McDonnell-Douglas have done to meet airline needs and still be a viable competitor.

Two Class Seating Arrangement:

https://frequentlyflying.boardingarea.com/vintage-airline-seat-map-american-airlines-boeing-727-100-from-1977/


What does the actual path of air within a turbojet engine look like? While Wikipedia describes the flow path as axial, I wonder if the path could be helical instead. Wikipedia explanation is described first in section 1, section 4 is for what could be the actual flow path, and sections 2 and 3 list the reasons for that. Section 5 is my question.

1. Usual high-level explanation

Wikipedia explains air flow in a jet engine this simplified way:

Flow path, Wikipedia, author: Jeff Dahl

Not obvious on the picture, there is a stator with vanes after each rotor, to create the pressure increase on vanes pressure side, and to straighten the flow for the next stage of the cascade, else there would be no compression and the engine would be an expensive fan. See this question for a picture showing the stators.

2. Taking into account blade and vanes

Usual depiction of the path, taking into account blades and vanes, is zigzagging, similar to:

The path above seems valid for motionless blades and vanes, ignoring blades are in rotational motion. If we dive into a bit more detailed explanation, the path would be refined like this:

Vanes pressure side is upward while blades pressure side is downward.

3. Taking into account blade rotation

With blades rotation, blades of the second stage do move while air is traveling across the first stage. While rotating, second stage blades deflect older air,  which now exits the second stage using a vane which is lower than the vane it exited the first stage (during this time air of the first stage has reached the second stage, but is deflected by an upper blade, etc):

Air path is therefore spiraled a bit, the exact amount of the helical displacement depending of the ratio between air axial speed and blades angular speed. This is not necessarily the exact vane angular spacing (or a multiple of it).

4. Seemingly more consistent depiction of air path

If this was the correct way it works, then the overall flow would rather be helical than axial, something more like this:

5. Question: How blades and vanes impact overall air path? How the air path can be better explained, taking into account blades are not fixed?

I'm looking for some details, perhaps blade/vanes geometry and airspeed, not an over-simplified view.

(Source) Image shows CFD simulation for a jet engine carried out by Northern Arizona University.

Pretty much as your illustration, but more turbulent and not as many complete turns.

Let's take one rotor disk at a time.

Each blade on each disk is like a wing. Air is rushing in at it. And it, is moving down on the air (or up from the other side). Giving the blade an angle of attack.

In a wing, air is pushed down.

So, one disk will push down on the air on one side, up the other, left and right top and bottom—the stator disk will straighten it out for the following rotor. And so on, i.e., a stepping swirl.

If the stator reversed the flow, it will be an immense angle of attack for the receiving rotor, i.e., the rotor will stall. So, a stepping swirl makes more sense.

While a propeller, an axial compressor, and a turbine are different in what they do, I don't see why the shape of the corkscrew of the propeller I asked about here—would change for any rotating disk carrying airfoil blades—

(Source)

—except in magnitude and thermodynamic properties.

To complement the earlier CFD image, here are two more:

(Original image) Three stage transonic compressor.

(Source) Analysis of Rotor-Stator-Interaction and Blade-to-Blade Measurements in a Two Stage Axial Flow Compressor


Is this explanation of adverse yaw correct? It is explained here that adverse yaw is caused by the difference in induced drag due to the difference in lift being generated by each wing.

I've also seen a couple of websites (including Wikipedia) that argue that this explanation is wrong. They explain the cause of adverse yaw as being the change in the direction of the lift vector during a roll, or what some refer to as the "twisted lift" concept. They usually have a diagram like the following:

source

The twisted lift explanation discounts a difference in induced drag due to a change in the amount of lift. They contend that lift and drag remain the same but they twist in different directions. The descending wing has a slightly higher local AoA and the rising wing slightly lower. Since lift is perpendicular to the local airflow the lift vector rocks forward on one wing and aftward on the other.

This explanation seems flawed to me.

First of all, in the diagram they show the force on each wing being the same. If that were the case the aircraft wouldn't roll at all, it would ONLY yaw.
Second, the vector of lift being perpendicular to the airflow is correct, but that is really just an arbitrary division of the total aerodynamic force. The yaw axis of the plane is not dependent on airflow. It would be dependent on the portion of the force vector parallel to the wing chord, aka the axial force. As shown in another question, depending on a number of factors the force vector in relationship to the wing does not necessarily move forward with an increase in AoA.
I can't come up with solid numbers, but trying to figure this out for normal flight speeds it would require a very fast roll to even make a 1° difference in local AoA. I ran numbers for a 3° per sec roll at 120 KTAS on a 36ft wingspan (C172) and came up with a change in AoA of about .27°, and that Is only at the wingtip. It would decrease the closer it got to the fuselage. It doesn't seem like it would be enough to cause a significant change in vector and a resulting yaw moment. Or at least it would be secondary in magnitude to the difference in the drag due to reduction of lift.

Since the changes in lift are being created either by changing the effective camber of the wings (ailerons) or by altering the trailing edge flow (spoilerons) rather than a change in AoA I don't think it's quite so simple to predict that the direction of the aerodynamic vectors will necessarily move in opposite directions as this theory assumes.

If this explanation is correct can someone show me what I'm missing?

First of all, in the diagram they show the force on each wing being the same.

In a steady roll, i.e. when the roll rate is constant, the forces are the same. A non-zero moment causes angular acceleration, so when the aircraft is rolling with constant rate of roll, the moment must be zero, which means the lift on both wings have to be equal.

That rules out difference in magnitude of lift as the source of the difference and leaves the difference in angle as the only plausible explanation. The explanation is correct.

When you first deflect ailerons, the wing with aileron down does indeed start to produce more lift and the wing with aileron up less lift. This difference causes rolling moment, which causes the roll rate to increase. It already starts causing adverse yaw due to the difference in magnitude of lift too.

However as the roll rate builds up, the angle of attack increases lift on the wing going down and decreases it on the wing going up until the lift equalizes and the roll rate stabilizes. At that point the lift is the same and the adverse yaw is caused by different direction of lift due to different angle of attack.

The fact that ailerons are deflected throughout the roll might lead you to think that there is still difference in lift. But there isn't. The aileron deflection just changes the roll rate in which the forces are in equilibrium.

Also while the angle between realtive wing and the total aerodynamic force (which corresponds to the relation between lift and induced drag) is in general not constant, in this case all the factors it depends on — wing span, air speed and density — are (almost) the same for both wings, so the difference in angle of attack is the main factor for the direction of the resulting force.

And last, but not least: How It Flies is very reliable regarding the physics (and most other things too). I would be very surprised to find an incorrect explanation there.


When do I have to contact Centre when departing/arriving at an airport with an ATF? I'm looking at St-Frédéric airport in Quebec, Canada (CSZ4) and specifically at the "COMM" section. It says that there is an Aerodrome Traffic Frequency (ATF) on 122.8 but it also seems to say that you need to contact Montreal Centre (135.025) on arrival and departure:

Does this mean that Montreal Centre is to be contacted only when the ATF (UNICOM) is not operating, or do I have to contact it at all times?

The Aerodrome Traffic Frequency is a frequency for aircraft to use to aid self-sequencing at airports where a control tower is not operational. Another name for it is the Common Traffic Advisory Frequency. 122.8 MHz was the original frequency designated for UNICOM use and remains one of the more common ones.
The APP/DEP frequencies listed tell pilots that, if they desire to talk with ATC (as IFR flights probably would!), they need to contact Montreal Centre on 135.025 once airborne. Montreal Centre is also the arrival frequency that would help IFR arrivals get established on an instrument approach procedure, if one existed. Centre most probably does not have radio coverage to the ground on this frequency, and even if they did they would not provide towered-airport control services.


What are the limits to lateral Centre of Gravity imbalances? I've never seen lateral CG limits prescribed for aircraft (though I have very imited experience in this realm).  Presumably, aircraft are designed to keep the center of balance as close as possible to center of lift, with any imbalances are far more likely to occur fore to aft than side to side.

But, for instance, what if fuel only drained from one wing during flight?  How much of an imbalance would this create?

Are there on-board systems in general aviation to prevent this?

What are the effects of a lateral imbalance on handling, and how could pilots compensate, if possible?

Edit 1: Please do not restrict your answers to fuel loads.  Is there a percentage-based (e.g. greater than X % aircraft total wingspan) or positional-based (e.g. lateral CG moved outside of the fuselage) DNE from an engineering standpoint?

Edit 2:

Also seeking design input, considering experimental and purpose-built aircraft such as White Knight Two exist.

I also note that despite the larger cargo volume of the Airbus Beluga, it cannot carry near as much weight as the smaller-volume C-5 Galaxy.  Is this a benefit of the C-5's design in placing the wings above the fuselage or is there such a thing as vertical CG limits?

Lateral c.g. limits are prescribed for large aircraft both for max fuel imbalance and for what is being carried in the fuselage. It's basically impossible to exceed the max lateral imbalance in a passenger aircraft. Exceeding the max in wide body cargo aircraft can be done and is checked for, but it takes an unusual load to exceed the max.

The 747-400, for example, has a max lateral imbalance of 10,000,000 inch-pounds. If you load 207,205 lbs on one side only of the main deck of a 747-400 freighter using size code M pallets, you will exceed the maximum. To see this happen (if you're using Firefox or Chrome--IE won't work) go to 747.terryliittschwager.com, dismiss the flash screen, and then click on test load #6 near the bottom of the page. That will trigger exceeding the lateral imbalance limit. Scroll down to the Lateral Load Imbalance graphic to see the max lateral loading envelope and the point that shows the load exceeding it.

Here are some approximate weights for a 747-400 freighter:

basic operating weight 365,000 lbs

max fuel 360,000 lbs

max cargo 245,000 lbs given the 610,000 max zero fuel limitation and a 365,000 bow

Note that you cannot carry max fuel and max cargo. A common 747-400 max takeoff weight is 875,000 lbs.


Did WW2 airplanes ever jettison their empty external fuel tanks to act as weapons? Jettisoning an external fuel tank over a populated area is prohibited by the FAA as it will almost certainly cause injury and damage to the people in that area.
But did war airplanes during World War 2 ever use that fact to their advantage?
As an example, say a P-51 Mustang dropped its bombs onto a city/town as a part of its mission, and then they realize that their external fuel tanks are empty, and are ready to be jettisoned. Well, couldn't the P-51 just jettison the external fuel tanks over the city/town to cause some additional damage?
So, did war airplanes during World War 2 ever actually jettison their empty external fuel tanks over bombing targets to cause additional damage?

Yes, and not even empty tanks. It didn’t always work, but it’s happened:
     This is how American pilots used drop tanks as bombs during WWII.
Fun fact, cellulose drop tanks were developed to save metal during the war! The article references P-47s, but I would not be surprised if P-51s did the same.


How is a stalling speed not affected by airspeed? A question from the aerodynamics section of the FIA written:

Which action will result in a stall?

Incorrect answer: Flying at too low an airspeed

Correct answer: Exceeding the critical angle of attack

I could be flying in straight and level flight and if I slow down below stall speed the airplane will stall. So how can it be said that flying at too low an airspeed will not result in a stall?

Flying at too low an airspeed will result in a stall, but what "too low" is entirely depends on the situation. For example, if you try a very steep climbing turn, you can stall at an airspeed where you would be fine in level flight.

The answer is an incorrect answer, not because it's factually wrong, but just because it's not general enough. Exceeding the critical angle of attack always causes a stall, and it is the cause of every stall, so it's the best answer to the question. The examiner wants you to understand that the angle of attack is the mechanism that causes stalling, and that it can happen at different speeds.

It's quite common for these (and other multiple choice) exams to have an "incorrect" answer that isn't completely wrong, but isn't as good as the correct answer because it only applies in some conditions or is less general in some other way. In this case, another "incorrect" answer would be "pulling the stick back too far". That's an action that might result in a stall, if you're already at a high angle of attack, but it's not really the cause and isn't always true.


How does the turbulent boundary layer thickness affect separation? I read that for a turbulent boundary layer, a thicker boundary layer separates earlier than a thinner boundary layer? Why is that? Or is it the other way around?

On a flat plate the thickness of the boundary layer grows along the flow path without a tendency to separate. Therefore, thickness alone is not the culprit.
However, when the pressure gradient in flow direction becomes positive (increasing pressure), the flow will slow down and thickness grows much faster than in non-decelerating flow. Now separation happens when the speed at the surface drops to zero. Right before separation you will see an exponential growth of the boundary layer, but it is only an indication for the decelerating flow which really is to blame for the separation.


What is the weather term for snow and dust mixture? An old pilot friend of mine told me today a story that I thought was interesting.

He said that he was flying into Wichita, KS a couple decades ago and was listening to the ATIS when the weather report indicated snerd.  He called up the approach controller and asked what snerd was and the controller stated it was a mixture of the blowing snow and dust coalescing making a big mess.  The pilot stated he broke out of the clouds and all he saw was a brown mess all over the place.

Does anyone know if this is actually called snerd? If not, what is the correct term?

I lived and flew in North Dakota for about three years. While I was there, people talked about (and I experienced) the delightful mixture of snow and dirt called snirt. It can be the result of plowing sanded roads, and also can be caused by the high winds that come out of Canada blowing dirt from fields onto areas still covered in snow. Google image search has some good examples.

I have a feeling that's what was described by your friend. It appears in Wikipedia's list of types of snow, but as far as I am aware it is not an FAA or NOAA term.


What is the true top speed of the SR-71? By "true" top speed I mean the absolute fastest horizontal airspeed the aircraft can achieve if damage to the engines is disregarded (similar to how the MiG-25 apparently can reach mach 3.2 but may damage its engines beyond repair). Catastrophic structural failure (of anything beyond the engines) is not permissible in this scenario.

In "The Untouchables" Brian Shul claims that he reached mach 3.5 while evading a missile. This is also stated in the Wikipedia article on the SR-71 with a citation to the same book.

Are there any other sources than his own book that can confirm or reject this claim? Can it be argued for or against this top speed claim on technical merit or physical limitations?

On Wikipedia it is also stated "Maximum flight speed was limited by the temperature of the air entering the engine compressor, which was not certified for temperatures above 800 °F (430 °C).[57]"

However, it is not clear how much abuse beyond this the compressor could take. It is possible to give some estimate or educated guess based on the materials used?

Based on the SR-71A operational envelope, the top Mach number was Mach 3.3 when authorized by the commander and Mach 3.2 otherwise. The top airspeed was 400 kts equivalent airspeed when supersonic and 450 kts equivalent airspeed when subsonic.


Why is the XB-70's Top speed only about 60mph higher than its cruise speed? The maximum and cruise speeds listed for North American XB-70 Valkyrie are:

  Maximum speed: Mach 3.1 (2,056 mph, 3,309 km/h)
  Cruise speed: Mach 3.0 (2,000 mph, 3,200 km/h)

Why is there such a small difference?

From the excellent point in the comments, the XB-70 was designed for one thing; speed. It was, until the Blackbird, the fastest manned air-breathing aircraft. It was intended to outrun Soviet interceptors like the MiG-25 and fly higher than ground-based anti-aircraft weapons of the day, making it a possible first-strike weapon. As such, it wasn't going to loiter around at 80% throttle.

A second point is that since the B-70 project was cancelled for several reasons (cost projections, development of ICBMs and of high-altitude fast-tracking SAMs), the two prototypes were used primarily as testbeds to push the envelope of air-breathing craft. As such, data regarding their fuel efficiency curve was secondary to more basic problems of aircraft design for hypersonic aerodynamic flight.


Is there a set of laws which govern international flights? A few years ago, my brother and I were aboard an Emirates flight from Australia to New Zealand. At the time, I was 16 and he was 14.

At one point in the flight we were both offered alcoholic drinks. Considering the drinking age where I am from is 18, and ID is required if you look under 25, this came as quite a surprise to the both of us.

Considering different countries have different laws and aircraft often have multinational crew and passengers, what laws govern international flights?

International Airline is bound to follow the law of country of registration. Hence your flight limits you to dringking law in Abu Dhabi which is 18

Note some airline, Turkish here, have some policy not to serve alcohol on certain flights. On my experience with Hong Kong airline, the flight in-bound to Hong Kong only serve juices where out-bound had Tsing Tao :)

A not a really related topic but something more to read on travel.SE : Is it legal to drink your own alcohol onboard a plane over international waters?


Is a VOR usable on the ground when it's located at a higher elevation than the receiver? According to the AIM 1-1-8, a VOR can be usable at an altitude below the altitude where the VOR is. But the figure only shows the VOR service volume down to zero feet AGL:

Where I fly, the VOR is at a higher elevation than the airport. Can I consider that the VOR is reliable to use in this situation? I would appreciate any references.

In order to receive a VOR station there must be a line of sight from the airplane to the VOR.  This is basically what your chart is referencing, you can maintain line of sight at longer distances at higher altitudes.  It could be possible that the VOR is higher than the airplane and you could receive the VOR while flying below the VOR as long as you have line of sight.  However it would probably be best to make sure you have enough altitude before you try to intercept the VOR to make sure you don't have a controlled flight into terrain incident.


In the U.S., Is it ever legal for an aircraft to occupy the runway turnaround area while another is taking off or landing? In voretaq7's answer to the question Is there a name for the area for aircraft to back track near the runway threshold?, it is mentioned that runway turnaround areas are considered part of the runway to which they are attached and that any aircraft in the turnaround zone are considered to occupy the runway.

I noticed that in the picture provided in his answer showing a runway turnaround area, the runway edge stripes actually included the runway turnaround area:

However, I've also noted that at the small, uncontrolled GA airport I've most often flown from, the runway edge stripes do not include the turnaround area:

Of course, in either case, a departing aircraft must cross the runway hold line and enter the runway to back-taxi to the turnaround area in the first place. However, I'm curious under what, if any, circumstances is it legal under the U.S. FARs for an aircraft to land or take off on a runway while another aircraft occupies the turn-around zone on that runway? And, of course, I'm talking about normal operations here, not emergencies.

Does the runway edge stripe configuration matter, for example?
How does this differ between controlled and uncontrolled fields?

For the sake of simplicity, let's assume that both aircraft in question are light GA aircraft, not aircraft whose wings might stick off the sides of the runway, and that all parts of the aircraft in the turnaround zone are on the turnaround side of where the runway edge line would be were it a straight line (like it is in the second picture.)

I have seen both landings and takeoffs with another aircraft in the turnaround area at the bottom field pictured above, including a couple of aircraft back-taxiing out there (under mutual agreement and while in radio communication with each other) and the second of them wait in the turnaround while the first takes off.

Jim's answer is accurate. Unless there is a proper boundary between the turnaround and the runway, an aircraft should not be there while other aircraft are landing or taking off.

In the FAA's AC about airport design:

  Obstacle Free Zone (OFZ). The OFZ is the three-dimensional airspace along the runway and extended runway centerline that is required to be clear of obstacles for protection for aircraft landing or taking off from the runway and for missed approaches.

The dimensions of the zone are different depending on the aircraft size and approach minimums. Specifically the runway OFZ has widths from 120 to 400 feet. This is the zone typically protected by the hold lines (pictured in Jim's answer), which are typically placed to provide adequate separation for the worst anticipated case at that airport.

Regarding the edge markings, they should be parallel to each other and not follow the edge of a turnaround pad. From the AC on airport markings:

  When a taxiway connects to a runway or the runway has turn pads or turnarounds, the runway edge marking remains continuous between the runway and these adjoining infrastructures.

If the turnaround pad is designed to be occupied while the runway is in use, this is referred to as a holding bay. A proper holding bay would look like this:

This illustration comes from the airport design AC. Notice that the FAA considers this poor, because it provides no guidance such as taxiway center lines for pilots to follow.


Why aren't airports built with future expansion in mind? There are currently numerous controversies around the world in regards to airport expansion, where local residents are opposed to new runways or changes in the hours of operation. The most famous example is probably Heathrow airport, where it took decades to finally approve a plan to add a third runway.

But why aren't airports built in a way where future expansion is possible? E.g. why wasn't an area 5 kilometers around Heathrow reserved for new terminals and runways, even if it wasn't clear if they're ever going to be required?

Many European airports are built relatively close to the cities they serve. Airports in the US are (in general) further away, where an expansion is easier to do, e.g. Denver International Airport:

  The distant location was chosen to avoid aircraft noise affecting developed areas, to accommodate a generous runway layout that would not be compromised by blizzards, and to allow for future expansion.

Heathrow on the other hand is old. It has such a long history that it has its own Wikipedia article (which ironically starts in 1410!). It started as a small airfield in the 1930s and it was in a very rural area at the time:

  The land was at the time used for market gardening and wheat growing.

It was then greatly expanded as a military airport during World War II. After the war, the airport was turned into a civilian airport. The original runway layout way quite different compared to today, as the following image from the 1950s shows:

(image source: Wikimedia)

This image still shows the rural surroundings. But London expanded further and further and eventually the airport was fully surrounded:

(Google Maps)

Why was the land not reserved?

Because land in London is extremely valuable. The time after World War II saw the greatest expansion of London (size wise, not population wise):

  The population peaked in 1940 at around 8.5 million, before declining and then rising recently to just over 8 million. Despite the decline and the devastation caused by the second world war, the 20th century saw the largest urban expansion in London’s history.

(The Guardian)

At the same time, other airports were expanded to serve the Greater London area: Gatwick was expanded during the 1950s, Luton in the 1960s and Stansted was converted to a civilian airport in 1966. With all of these airports available, there was no need to anticipate a large expansion of Heathrow. The land was much more valuable as an urban area.


How many bird strikes are there per year? Any world-wide statistics? Does anyone know where I could find where the highest rates of bird strikes are?

Along the same lines, other wildlife, such as moose or bears on runways?

Bird Strikes Worldwide

From Hedayati, R., Sadighi, M., Bird Strike, 2016:

  According to currently available data, it is estimated that a bird-strike event occurs once every 2000 flights (Khan, Kapania & Johnson, 2010). Further analyses of bird-strike statistics have shown that only 20% of bird strikes are actually reported by aviation staff. This means that the extent of economic and human losses resulting from bird strike could be much higher than what is currently presumed (Chuan, 2006). Consequently, this suggests that conducting further indepth studies on how to better capture reliable bird-strike event statistics and formulating strategies and solutions
  would be beneficial.

From EASA, Bird Strike Damage & Windshield Bird Strike - Final Report, 2009:

  It had been intended to use the International Civil Aviation Organization (ICAO) database of bird strike statistics as a prime source of bird strike information, giving details of worldwide bird strike incidents and accidents. However, despite the best endeavours of fera, Atkins and EASA, it was not possible to gain access to this source of information. Therefore the literature search does not include data from regions such as Asia and Australia. Reporting levels from these regions are low and it is likely that even with access to ICAO data, there would be limited useful information available beyond that already available from UK and USA/Canada sources. It is estimated, based on previous fera Bird Management Unit experience, that the UK and USA/Canadian data obtained represents approximately 50% of all worldwide bird strike reports. Also regions such as Russia, China and South
  America do not routinely contribute data to the ICAO database.

Wildlife Strikes in the United States of America

From FAA, Wildlife Strikes to Civil Aircraft in the United States 1990-2014, 2015:

  The number of strikes annually reported to the FAA has increased 7.4-fold from 1,851 in 1990 to a record 13,668 in 2014. The 2014 total was an increase of 2,267 strikes (20 percent) compared to the 11,401 strikes reported in 2013. For 1990–2014, 156,114 strikes were reported. Birds were involved in 96.9 percent of the reported strikes, terrestrial mammals in 2.2 percent, bats in 0.8 percent and reptiles in 0.1 percent. Although the number of reported strikes has dramatically increased, the number of reported damaging strikes has actually declined since 2000. Whereas the number of reported strikes increased 127 percent from 6,009 in 2000 to 13,668 in 2014, the number of damaging strikes declined 24 percent from 764 to 581. While there was a 20 percent increase in reported strikes from 2013 to 2014, the number of damaging strikes declined 4 percent from 606 to 581. The decline in damaging strikes has been most pronounced for commercial aircraft in the airport environment (at <1,500 feet above ground level [AGL]). Damaging strikes have not declined for general aviation (GA) aircraft.

From Hedayati, R., Sadighi, M., Bird Strike, 2016:
According to the FAA, there were approximately 11'500 bird strikes in the US in the year 2014.

Bird Strikes in Australia

From Hedayati, R., Sadighi, M., Bird Strike, 2016:

  A significant proportion of all occurrences [...] involve aircraft striking wildlife, especially birds (Bureau, 2009). According to a report (Australian aviation wildlife strike statistics: 2004-2013) providing aviation bird strike and animal strike occurrence data, reported bird strikes have increased from 1085 in 2004 to 1751 in 2011. The Australian aviation industry experienced a reduction in reported bird strikes in 2012 relative to 2011.
  Among the 1568 reported bird strikes [...] in the year 2013, [...]

Bird Strikes in Brazil

From Hedayati, R., Sadighi, M., Bird Strike, 2016:

  Brazil is one of the most suffered countries from bird strike because it has the world’s second largest aircraft fleet as well as the world’s second largest number of bird species. [...]
  The annual number of reported bird strikes has increased from 235 in 1993 to 587 in 2004.

Bird Strikes in the Czech Republic

From Hedayati, R., Sadighi, M., Bird Strike, 2016:

  In the period 1993–1999, the data relating to 165 collisions was entered into the Czech Air Force’s database.

Bird Strikes in France

From Hedayati, R., Sadighi, M., Bird Strike, 2016:

  The annual number of recorded bird-strike events in France exceeds 700, [...] (2008) [...]

Bird Strikes in Iran

From Hedayati, R., Sadighi, M., Bird Strike, 2016:

  Within the years 1996–2011, 271 bird collisions in 32 airports were registered by Iran’s Civil Aviation Organization (CAO).

Bird Strikes in Saudi Arabia

From Kutbi, N., Bird Strike, 2014:

  30 in 2011, 19 in 2012, 37 in 2013

Bird Strikes in the United Kingdom

From Hedayati, R., Sadighi, M., Bird Strike, 2016:

  The total number of reported strikes in the UK has increased from 608 in 1991 to 2365 in 2011: [...]


Is the Reynolds number the same for both the airfoil and wing? If not, why/how does it change? This question might be stupid, but I don't understand this one thing: does the Reynolds number change when you go from the airfoil to the wing? Or is it the same for both?

From the equation that defines it, you can see that its value depends on some properties of the fluid (air), the speed that an object moves through the fluid, and the length of the object.  Nothing else.

For an airplane wing, the length, aka "characteristic linear dimension," is conventionally chosen to be the chord of the wing.  The wingspan doesn't affect the Reynolds number.  Neither does the choice of airfoil.

In other words, given an airfoil (say, a segment in a wind tunnel at a particular chord, airspeed, and air density), and given a wing on an airplane built from the same airfoil with a different chord, airspeed, and air density, the Reynolds numbers for these two situations are likely to be different.


How to control torque effects on the ground? I'm building a Lippisch ground effect vehicle with it's wingtips almost touching the ground, but because of torque effects the left wing actually does touch the ground, so it can't lift off. It even can't go straight.
Adding ailerons isn't an option because this problem has to be solved on te ground (zero speed) and not in the air (because it doesn't get there).
Does someone know something how I can solve this problem?

The Lockheed U2 had the same problem (bicycle wheel base and they had to prevent one end being dragged on takeoff).

They solved it by adding "pogo wheels" that self detach on take off. (the ones on the orange sticks.)

(source wikipedia)


Why are propeller airplanes still made? Airplanes with propellers were invented a long time ago. After that, jet engines came into existence. My question is: why do we still have propeller engines?

The reasons I can think of are:

They are cheaper;
They cannot achieve very high speed;
They are not very noisy (though not always).

Besides these, are there any other reasons general aviation airplanes built nowadays don't have jet engines?

Jet engines are only efficient at high altitudes and high speed (25,000+ feet or so and 300+ knots or so true airspeed).  The cost of making and operating an airplane capable of flying there is very high, and most general aviation flights have no need of such performance (or expense) hence, propeller airplanes.

Reciprocating engine propeller airplanes are relatively efficient at low altitudes and airspeeds, they are more economical for the average types of general aviation flights.  They are also much cheaper to build and operate than a turbine powered airplane.

Turboprops fill the efficiency gap between reciprocating and pure jet engines, being most efficient at mid altitudes and airspeeds.  Still more expense and performance than most general aviation flights need though.


How does having a bigger engine placed slightly more forward and higher impact the plane in pitch? I'm asking about general aerodynamics for under-wing twin-jets – I'm not after information/speculation on the Max 8 crashes/systems, but I mention the crash below because of what I see as an unclear (to me at least) explanation:

In response to Lion Air Flight 610, leehamnews.com wrote:

  All objects on an aircraft placed ahead of the Center of Gravity will contribute to destabilize the aircraft in pitch.

But as one commentor wittingly pointed out, wouldn't the fwd engine also move the CG fwd.

And then:

  [G]enerating an angle of attack close to the stall angle of around 14°, the previously neutral engine nacelle generates lift. A lift which is felt by the aircraft as a pitch up moment (as its ahead of the CG line), now stronger than on the 737NG. This destabilizes the MAX in pitch at higher Angles Of Attack (AOA).

I read this as insufficient pitch authority, not pitch instability. Going by the text above, I would also imagine the destabilizing force to be a drag from the larger nacelle's bottom, not lift. For example, the relaxed pitch stability of the MD-11 warranted an LSAS system, but not a special anti-stall system.

I tried to look for an official explanation for why MCAS was added to understand the general aerodynamics, but the prelim report doesn't mention it.

I've presented what has me confused, but the question is the one in the title, wrt general aerodynamics, not 737 Max or MCAS.

This is an "I think" rather than "I know" answer so if you disagree please feel free to explain why.

In normal straight and level flight it shouldn't have a significant impact. But at a high AoA, at least a significant portion of the engines are ahead of and crucially, above the CG. The nacelle will be producing both lift and drag the resultant effect of both forces, being above the CG, will be a pitch up moment.

Even if this extra force by itself isn't enough to make the aircraft unstable in pitch, it will require the pilots to make a stronger nose-down command, but when you're so close to a stall you want that to be as easy as possible.


What does the word "boot" mean? I found this word "boot" in one book. The chapter was connected with ICING operations, and I found this word with little explanation:

  A tube bonded to a surface, e.g. wing edge. When pressurized with fluid, it breaks up ice.

Please explain what is it?
What aircraft equipped with it?
Photos would be nice.

Versalog already told the core of the thing. Most prop aircraft which are approved for flights into known icing conditions have such boots to remove the ice from the wings leading edge.
Those boots are either inflated manually whenever you need them (by the press of a button of course), at regular intervals or automatically whenever ice is detected.

Check this picture, the black thing is the boot on a Dash 8's wing:

Link


What are the flight training options for a private pilot's license in the US? In the USA, what training options does a student pilot aiming for their private pilot license have?

There are lots of options. Flight training is the US is usually divided into part 61 and part 141. Part 61 is general flight instruction and any FAA approved instructor can teach you under it: many part 61 instructors are independent or work for or with FBOs at GA airports. Part 141 governs flight schools that have a standard curriculum and are much more structured; they're often associated with training commercial pilots looking for airline careers. The license you get is exactly the same whichever way you learn.

There are pros and cons to both approaches, this article summarizes them well but the most important general point is probably that part 61 is 'one on one' training so it can be tailored for you and fit your schedule, whereas part 141 is 'school' training and if you can't follow their schedule then it usually isn't possible anyway. For that reason, part 61 is often the only practical option for many private pilots who have jobs and families.

Perhaps your real question here is "how do I find an instructor?", in which case you need to search the web, check out local FBOs and flight schools, ask for recommendations from pilots you know and so on. It's definitely worth investing some time to find the right instructor for you, because that can make a huge difference to your progress (and your costs).


What is the life limit due to metal fatigue in large bombers? This article explains how the B-52's will be kept flying for 100 years.

Replacing the engines, electronics, etc. is one thing, but when would metal fatigue become a problem? These planes are huge and, I expect, rather heavy (at least when loaded up) and although they fly fewer cycles than passenger airliners, a hundred years is a long time.

Obviously I expect the military to be aware of this, but I'd love to hear what you folks think.

Metal fatigue and fatigue corrosion are and have been a problem since the type's introduction. They always fatigue and corrode, they always undergo expensive repairs due to corrosion. DIEGME degradation of fuel tanks has been a particular culprit, and it has been reduced with new coatings.
Bombers aren't pressurized, so the whole fuselage doesn't fatigue the way it does for airliners. The hard limit for wing spars fatigue can run into the centuries, considering that these planes don't fly all that much.
100 years is a bit of an exaggeration. The oldest B-52 in service come from the late 50s to 1962, when the production ended. So at retirement time the planes will be just 90 years old. There is a lot of B-52s sitting idle in storage, since they used to be considered strategic and fell under SALT cuts, and they're available both as spare part sources and as restorable airframes.
Why shouldn't a 100 year old plane fly? The USS Constitution is 220 years old and she's still sailing the seas, a considerably more hostile environment. It took a lot of restoration, but not quite to the extent of the Theseus' ship. Not everything is built with planned obsolescence like cars or iphones; ships and planes are built to last, as long as the owner spends the money needed to keep them up.
Keeping the old planes intact may not be cheap, but new bombers are far more expensive. The B-1B is half a billion a piece, so is the Tu-160. At the same time, most of the work the USAF does is milk runs in a threat-free environment. It doesn't call for advanced supersonic or stealth machines, it calls for something that's easy to service and cheap to run. The B-52 fits the bill better than any other bomber the USAF has. The only extant competitor is the Tu-95.
The B-52 can in theory be replaced by something even cheaper to run. Plenty of Boeing manufacturing capacity will sit idle for a long time, and, given a supply of olive drab, they'd fit the job even better. But this can't happen, because every military procurement program since the WW2 begins and ends with feature creep, doubly so in the Air Force. Only existing inventory can be kept as simple as it is.

All of this essentially leaves no choice but to keep up the current planes. Aluminum is cheap, it's silicon that's expensive, and B-52s have very little of that.


How is the jet engine inlet danger area affected when airborne? Boeing published engine hazard areas as shown below:

I am curious as to how the danger area is affected when the aircraft is in flight as the jet engine is still vulnerable to foreign object damage.

Assuming idle power conditions at 10000 ft (or just airborne in general), are the danger zones the same as on the ground? If not, would there be a way to calculate this?
Knowing the danger zone for both idle and full power, would it be possible to calculate the danger zone distance for different power settings? E.g. 50% N1.

Let's assume the A320 is powered by V2500 engines, one of the options for it. This engine has an air mass flow of 355 kg/s. At sea level, air density is 1.225kg per cubic m. Hence, 355 kg/s = 355/1.225 = 290 cubic m/s.

Now, let's assume the aircraft is still at sea level, but now at Mach 0.8 (unrealistic, but we'll correct that next). The fan diameter is 1.6 m, which gives an intake area of 2.0 sq.m. Also, Mn 0.8 at 0ft is 272m/s. Hence, every second, the intake sweeps a volume of 272 x 2.0 = 544 cubic m. But, the engine only needs 290 cubic/m of air, per second assuming air density in the intake is the same as the air surrounding the aircraft. Therefore, the diameter of a streamline tube of the intake air will actually be smaller than the diameter of the engine inlet. It will be the area that sweeps 290 cubic m/s at 272m/s = 290/272 = 1.07 sq. m., or a diameter of 1.17m, not 1.6m.

Basically, the engine takes the airflow it wants, not what the intake area x forward speed provides. If the engine wants more (such as when the aircraft speed is low, or stationary, but the engine rpm is high, such as at the start of the takeoff roll), the engine will draw air from a large area in front of the engine (as per the max takeoff conditions diagram). Conversely, when the aircraft is at high speed, and the engine throttled back, the intake will spill the excess air it is providing (causing spillage drag).

Now, let's correct the fact the aircraft can't do Mn 0.8 at sea level. Let's re do the calculation at 35,000ft (10,700m). Here, air density is 0.38 kg per cubic m, and pressure and temperature are 3.46 psi and  219 Kelvin (-54C), compared with 14.7psi and 288 Kelvin (15C) at sea level. Thus our 355 kg/s, which is actually a corrected airflow, is a physical (real) air flow of 95.8 kg/s at 35,000ft since theta = 219/288 = 0.76 and delta = 3.46/14.7 = 0.235. Now 95.8 kg/s at 0.38 kg/ cubic m = 252 cubic m per second. Also, Mn 0.8 at 35,000ft is now 237m/s, not 272 as it was at seal level. Hence, every seond the intake area of 2 sq.m is sweeping through 2 x 237 = 474 cubic m per second. But we only want it to sweep 252, hence we need to find the diameter of a streamline tube that will cause this, at 237m/s. Therefore, we need an area of 252/237 = 1.06 sq. m., which occurs with a diameter of 1.16m. This compares with the physical inlet diameter of 1.6m.

Thus, at Mn 0.8, 35,000ft, max power, the green area at the engine intake is now a tube, of 1.16m dia, that extends in front of the aircraft. For how far this extends, depends as suggested, on what reaction time is required for the aircraft to manoeuvre away from an obstacle in this region, or for the object (a bird?) to manoeuvre out of the aircraft's way.

The exact figure of 1.16 is questionable, as the assumption of air density in the intake not changing from the surrounding air is not entirely realistic. But the general result, is I believe, reasonable.


When using the phonetic alphabet, for airways, should we say Uniform or Upper? Listening some RTs, I heard ATCos reporting airways, for example: UL65, UPPER LIMA 65. But the phonetic alphabet says UNIFORM. Why do they say like this, please? Is there any manual in which we can study these differences?

ICAO

ICAO Annex 11 and Doc 4444 confirm the usage of Upper.

Airways are four groups per ICAO, the older group is A, B, G, and R. Those stand for Amber, Blue, Green, and Red. There are three other groups.

So an airway named UG1 will be called Upper Green (not Golf) One on the radio.

Example they give in Doc 4444:

  N0450F310 L9 UL9 STU285036/M082F310 UL9 LIMRI

  (...) the flight will proceed on Airways
  Lima 9 and Upper Lima 9 to a point bearing 285 degrees magnetic and 36 NM from the Strumble VOR. From this (...)

Jeppesen Airway Manual also confirms it, check page 251:

FAA (for airways only)

Q is called Q (kyo͞o) on the radio (not Quebec), J is called J, not Juliet or Jet (Jet is what it means). See FAA JO 7110.65X 2−5−1 AIR TRAFFIC SERVICE (ATS) ROUTES.

  VOR/VORTAC/TACAN airways or jet routes.
  State the word “Victor” or the letter “J” followed by
  the number of the airway or route in group form.

  EXAMPLE−
  “Victor Twelve.”
  “J Five Thirty−Three.”

The FAA is similar in using the color code for the aforementioned group:

  Colored/L/MF airways. State the color of the
  airway followed by the number in group form.

  EXAMPLE−
  “Blue Eighty−One.”

Also check the FAA Instrument Procedures Handbook, page 2-24 of Chapter 2, here are two examples they give:

  UR5—Upper Romeo Five

  UW456—Upper Whiskey Four Fifty Six

Yes the FAA handbook does not agree with their ATC Job Order regarding R being Red (this will be for the old airway system such as those still in Alaska).

Note: the question asks about airways, the information here is not for tail numbers, navaids, etc., only airways.

See here for how the FAA decides on the designations: How are Victor airways defined and numbered?


Could a plane take-off at 20,000 feet above sea level if the temperature is above freezing? I’ve read that “humans have survived for two years at 5,950 m (19,520 ft, 475 millibars of atmospheric pressure), which is the highest recorded permanently tolerable altitude” and that “Daulat Beg Oldie...has an airstrip at an altitude of 5065 meters (16,614 feet), which is the world's highest airstrip.”  I can’t seem to find any record of the highest horizontal take-off in history.  I really want to know if there is an altitude at which humans can survive but take-off is impossible.  Or if there are any other conditions at which humans could survive naturally but where take-off or flight is impossible for some reason other than temperature, weather or terrain.

Like most hypothetical questions of this nature, the answer is "it depends".  Given enough runway at a light loading just about any aircraft with a service ceiling above 20K ought to theoretically be able to take off.  One of the issues you might run into would be exceeding max tire speed.


What written tests are required to become a ground instructor? What are the written tests required to become a ground instructor? Do I have to take the FOI, BGI and IGI? Or just the FOI and IGI tests?

I got confused if I should take the whole three tests - FOI, BGI, IGI - or if just the two IGI and FOI tests are enough?

The FAA offers some nice guidance here

You may also want to check out my answer (a very close to dupe) here.


Why is there no alert if shutting down a running engine during flight? In reference to Flight 235, there is a lot of speculation going on today, and since the flight recorders' data indicate that the running engine was shut down manually, everyone is suspecting that probably the pilots made the mistake to shut down the running engine instead of the faulty engine to attempt a restart.

If that was the case, why can't there be an alert to warn the pilots that they are shutting down the working engine?

In the software world, we attempt to create so many fail safe situations to avoid letting users mistakenly take an action which will kill the process, why can't that be done for a multi-million dollar aircraft where so many lives are at stake?

P.S: I know these are all theories and not any official crash investigation reports but I am curious as to how such suggestions can even be made? Even my radios for radio-controlled airplanes provide many fail safe features.

Because in an emergency situation you do not want to stand in the way of the pilot.(*)

Whoever designs the system knows that it could fail and it also knows that there are two pilots in the cabin. These pilots have been trained to deal with the emergency, have spent hours and hours in simulators to be ready when something happens, you do not want to treat them as clueless users, you want to treat them as professionals that are doing their jobs.

The system told them that there was a failure, if it would have been a black/white decision the system could have already shut off the engine, but it did not: it lets trained personnel to asses the situation and act accordingly.

*: as fooot correctly points out, you do not want to annoy the pilots with warnings (remember, you just told them an engine is not working!), they may be tempted to preemptively cancel them, causing them to miss other warnings that are actually important.


Does the F-16's neutral stability also extend to the negative-G flight regime? If an F-16 pilot pushes the stick forward hard enough to send the aircraft into negative-G flight, does the jet tend to accentuate the new flightpath, requiring the pilot to counter that, or not?

The F-16 is unstable at low speeds, and stable at higher Mach numbers. It has a flight control computer though, which stabilizes the aircraft using the feedback from pitch rate (so from the view of the pilot an F-16 acts similarly as a stable aircraft). This applies to both positive and negative attitude disturbances, so for both + and - G loads perceived by the pilot.


What is the process to remove frost off an airliner? My aunt recently was going on a flight home and she boarded the flight, but her flight was delayed due to frost on the aircraft. She noticed this crane like device above the aircraft wing during the removal process. How do they remove frost off an airliner?

Frost is removed through the application of (typically) Type I de-ice fluid (information about de-/anti-ice fluids). Fluid application is generally from a truck with a lift so that the operator can spray the aircraft from above. The fluid is generally hot, diluted with water and under pressure so you'll see lots of steam coming off of the fluid spray. The truck will drive around the airplane spraying the wings, tail and fuselage as necessary to completely remove snow, ice and frost.

Some airports have static mounted de-ice towers that are more like cranes and some operators have automated trucks where there is no operator in the lift and they can do the whole operation from the cab of the truck.


Why do pilots typically start out in piston-engined aircraft, rather than jets or turboprops? Essentially all pilots begin flying with propeller aircraft powered by piston engines, rather than in turboprops or light jets, even though:

Operating a piston engine requires adjusting the mixture ratio, carburetor heating, ignition timing, and other such voodoo, whereas, with a turbine engine, you basically just turn on the ignition, press the START button, and you’re in business.
Jets and turboprops are orders of magnitude more reliable than piston engines, despite the latter’s decades-long head start in development; destructive failures of aircraft piston engines are much less common nowadays than in the 1940s and 1950s, when they were practically a once-a-flight occurrence, but piston engines still come up short compared to jets, most pilots of which go their entire careers without experiencing a single engine failure of any kind whatsoever.
And when a turbine engine does fail, it does so loudly and unmistakeably - none of those deadly invisible engine failures that killed off the market for piston-engined twinmotors, along with many thousands of their pilots.
In all but the coldest climates, jets and turboprops use Jet A (in the United States) or Jet A-1 (the rest of the world), two very similar kerosenes that are far safer to handle than the avgas burned in most piston engines (Jet A and A-1 have much lower vapour pressures, much higher flashpoints, and much slower flame spread rates than avgas, and, unlike avgas, are not full of tetraethyllead), and more widely available to boot; even in those extremely cold climates where the more enthusiastically flammable Jet B (a gasoline-kerosene blend) has to be used instead, it’s still safer than avgas.
Also, a turbine engine will run happily on avgas if the ground crew refuels it from the wrong container (jets are rightly famous for running on anything that flows and burns, as long as it doesn’t produce an exhaust containing refractory oxide particles), whereas accidentally fuelling a piston engine with jet fuel will cause it to blow its insides to bits just long enough after takeoff for you to now be over a residential subdivision or something similarly inconvenient for a forced landing.
Propellers come with their own complications; the propwash coming off the propeller and hitting the wings and tail creates nasty asymmetrical rolling and yawing tendencies, the pitch of most propellers has to be carefully managed (at least during ground operations, and sometimes in flight as well), and an even slightly nose-low landing, a gust from the wrong direction at the wrong moment, or a bump or pothole in the surface can easily cause an engine-destroying propstrike.

Given all this, why do pilots generally make their debut in piston-propeller aircraft, instead of in light jets or turboprops?

In a word, money.  Have you priced time in a turboprop or light jet, vs time in a C152 or other piston trainer?  Or actually buying one?  You can pick up a decent used single for about the cost of a new car, while turboprop or jet is likely to start at half a million, and go up from there.  And add maintenance costs to that.

Then there are a lot of pilots (I'm one) whose flying just doesn't include what a jet or turboprop is likely to be good at.  I like to fly into short strips, often grass or dirt (and sometimes no strip at all e.g. dry lake beds).  Is your jet or turboprop well suited for that?

Even for someone looking towards a career with the airlines, you can build a lot of the necessary time a lot cheaper in a single-engined prop plane.  For instance, one of my flight instructors started doing that, getting paid plus lots of experience dealing with the mistakes of student pilots.  Then he moved to a job flying a small cargo plane doing pickups for FedEx or someone like that, before getting enough hours to look at an airline job.


Can a CAP Form 5 flight evaluation be used as the flight portion of a flight review? I recently completed successfully a Civil Air Patrol Form 5 flight evaluation.  I was told that the Form 5 satisfied the flight portion of the Flight Review.  If true, which additional seminars do I need to complete?

A flight review consists of both a ground portion and a flight portion. You just need a CFI to sign off on the ground training for the flight review.
Alternatively, you could sign up for the FAA Safety Team WINGS program. You get three Flight Activity credits for the above mentioned CAP evaluation. You can earn another three Knowledge Activity credits a number of different ways of your choice. With the three Flight Activity credits and three Knowledge Activity credits, you will complete one phase of the FAASTeam WINGS program. Completing a phase counts as a flight review