What do taxiway lane, taxiway strip and taxiway shoulder mean? I am developing a game which involves an airport simulation. And I am looking into the general rules that traffic control has for busy airports and am also confused on the terminology of a taxiway.

According to ICAO taxiway widths have 3 types of labeling which is as follows:

Taxiway Lane
Taxiway Strip
Taxiway Shoulder

What is the taxiway shoulder? I am fairly sure the lane is the 2 outer yellow lines from the center  taxiway line right? And the strip is the entire taxiway width, but I am unclear on the shoulder label? I could not find an image that showed what this was.

According to the Skybrary from EUROCONTROL and a UK CAA document on taxiways markings (Visual Aids Handbook UK CAA CAP 637 (2007)), the definitions are:

Taxiway Strip

An area which contains the taxiway and gives protection to aircraft from obstacles and other taxiways.

Image Source: Transport Canada

Taxiway Lane

This one is ambiguous and could not be found citation on, except for a document from the BAZL. Taxilanes or Taxiway Lanes are dashed taxiways, which give guidance to stands and aircraft parking positions.

Taxiway Shoulder

The taxiway shoulder is the paved or unpaved area beyond the double taxiway edge line, indicating that the load bearing capabilities beyond these lines can be different from the taxiway weight allowance.


Why did this old Japan Nakajima J1N airplane use a Yagi rather than a parabolic antenna? Picture source.

As per my understanding, a Yagi antenna is a directional antenna with limited gain, which it broadcasts or receives the microwave signal to and from the front side. It can only receive signal if the transmitting antenna is not exactly in front of it, or can receive with limited/very limited quality, depending on the direction. Parabolic, however, has better reception than Yagi.

My question is, why did this old Japan Nakajima J1N airplane use a Yagi rather than a parabolic antenna?

Note that the assertion "It can only receive signal if the transmitting antenna is not exactly in front of it" is wrong. The most sensitive direction for receiving is in fact exactly in front of the antenna, so if the incoming beam is directly in line with the yagi shafts, the maximum signal strength will be received.

A parabolic antenna would be bigger across than the width of the plane's fuselage, causing a huge amount of (unnecessary) drag.


How can a non-IFR rated pilot fly SVFR? Carrying on from "Why does flying IFR require a rating?" How can a non-IFR rated pilot file and fly SVFR without visual contact with the horizon?

For the U.S., Wikipedia says 1 mile visibility is the limit. Isn't that too low even in daylight?

Having only the surface in-sight, be it a calm lake or urban area, without seeing the horizon, must be a huge workload for a VFR pilot.

In order to fly an SVFR clearance, the pilot and planned flight must meet several criteria.  The AIM 4-4-6 as well as 14 CFR 91.157 spell out the basic requirements:

You must have at least a private pilot certificate to obtain an SVFR
clearance during daylight hours as well as an instrument rating to obtain an SVFR clearance at night.  Student pilots are not permitted to request an SVFR clearance.
You must obtain an SVFR clearance to depart from Class E, D, C and B
airspace if visibility is below VFR minimums. SVFR clearance may be prohibited in some Class D, C, and B airspace due to the volume of IFR traffic.  Check the airspace NOTAMs
for these areas prior to departure.
You must have at least 1 statute mile visibility on both the ground and in the
air as well as remain clear of clouds (airplane) or simply remain clear of clouds and have at least 1 statute mile visibility for operations in Class B, C, and D airspace (rotorcraft helicopter).

All an SVFR clearance allows is for a VFR pilot to enter, depart or operate in controlled airspace using day VFR minimums for Class G airspace.  If it is done correctly by a competent private pilot and only in these conditions, it can be done safely as it provides the pilot with enough visual references to safely operate in VFR.  It is also advisable to do a realistic assessment of one's own abilities to control an airplane in marginal conditions and set conservative minimums for things like congested airspace or other weather in the area.  It is not advisable to do this if weather briefings anticipate IMC after departure.  Likewise if you have little experience operating in congested controlled airspace or if you struggle to stay ahead of the airplane under additional stressors, SVFR may not be advisable.


Is it true that as of 2014, flight reviews are waived for current flight instructors under FAA rules? I'm assuming this is false, or I wouldn't be asking...

Just the other day, another flight instructor in my local area, whom I know, told me:

  "... new rule as of 2014: if you keep your CFI current, you don't need
  a flight review!"

This is in regards to the FAA system.

I couldn't find a source for that, and I have never heard this before.

I am aware that a requirement to have one hour of ground instruction as a part of the flight review is waived for current CFIs, but I have never heard that the flight portion is waived as well.

My flight review is coming up, so it has been almost two years since I have personally received a flight review, which was in 2014.  I'm just wanting to verify this information and receive a source if it is true.

It is false.

14 CFR §61.56(f) states:

  A person who holds a flight instructor certificate and who has, within
  the period specified in paragraph (c) of this section, satisfactorily
  completed a renewal of a flight instructor certificate under the
  provisions in §61.197 need not accomplish the one hour of ground
  training specified in paragraph (a) of this section.

Also, AOPA has some great input on this topic:

"Pilot's Guide to the Flight Review"

Bottomline: You are correct, your friend is not.

Maybe there was a misunderstanding in the conversation whereby they were specifically talking about their own certificate (and any ratings they may be seeking that may take place of the flight review) as opposed to a general term?


What kind of antique WWI aircraft model is this? Inventor's prototype? I've discovered an interesting WWI era model of an aircraft and I am trying to find out what could it be. It is 29" long and it looks like not a hobby model, but an inventor's prototype. I love the idea of the extra fuel tank above the cockpit. It connects with a bigger fuel tank near the engine. Any ideas?

Beautiful find..., an original scale model from the 20s.
At first glance, the rudder is a typical "Sturtevant" design..., but the rest of the fuselage appears to be from another aircraft, or a type of Sturtevant that I am not familiar with. It could also be a free work, a personal design by the modeler... It looks like an old rudder concept for a "modern" fuselage design.

Sturtevant S-4
Sturtevant S-2


Why is this 777 zig zagging over the Pacific (and delayed by 2.5 hours in air)? Why is this 777 (CX 806 on June 6 2017) zig zagging over the Pacific (and delayed by 2.5 hours in air)?

It's just a glitch. The most reliable public live flight tracking site is Flightradar24.com (but even it has bugs), and it shows that CX806 has flown in more or less a straight line and will be arriving early.


Why did moving the CG aft on the Wright Brother's plane improve handling? In response to Peter Kämpf's answer to this question, why did moving the CG back on the Wright Flyer improve its stability?

It did not improve stability, but flyability.

The Wright Flyer had the CG located aft of the neutral point and was unstable in pitch. A longitudinally unstable aircraft will deviate from its trim point, and when flown by a human pilot, will have a wavy flight path. The Wrights called this undulation. It is caused by the delay in the pilot's response and his tendency to overcompensate, so the aircraft is oscillating around the trim point (= the angle of attack where all moments around the pitch axis are in balance). This delay is more problematic when the eigenfrequency of the motion is higher. All Zeppelins were unstable in pitch above a certain airspeed and in yaw over the full speed range, but nobody bothered. These things were so big that any motion needed a long time to develop and deviations from the trim condition were easy to correct.

With aircraft, things are different, because they are more maneuverable and much smaller. The characteristic parameter here is the short period mode which characterizes the pitch motion. Its frequency is around 1 Hz for small aircraft and can be approximated like this:
$$\omega_{\alpha} = \frac{v_{\mathrm{trim}}}{i_y} \cdot \sqrt{\left(\frac{c_{m\alpha}}{\mu} + \frac{c_{L\alpha}\cdot c_{mq}}{\mu^2}\right)}$$

Nomenclature:
    $\omega_{\alpha} \:\:\:$ Eigenfrequency of the short period mode
    $v_{\mathrm{trim}}\:$  trimmed airspeed
    $i_y \:\:\:\:\:$  Radius of inertia around the pitch axis
    $c_{m\alpha} \:\:$ pitch moment gradient over angle of attack
    $\mu \:\:\:\:\:\:$  reduced mass. $\mu = \frac{2\cdot m}{\rho \cdot S \cdot l_{\mu}}$
    $c_{L\alpha} \:\:$ lift coefficient gradient over angle of attack
    $c_{mq} \:\:$ pitch damping coefficient
    $m \:\:\:\:\:$  mass
    $\rho \:\:\:\:\:\:$  density of air
    $S \:\:\:\:\:\:$  reference area (normally wing area)
    $l_{\mu} \:\:\:\:\:$  mean aerodynamic chord

To answer the question, all it needs is the first factor of the equation. The frequency increases with airspeed and goes down with the pitch inertia of the plane. By adding a weight at the back of their airplane, the Wrights increased this pitch inertia, thus lowering the eigenfrequency and making it easier to control. Make no mistake: The Flyer became even more unstable, but the instability became easier to correct because the deviations from the trim point built up more slowly.

Modern replicas of the Flyer have their CG ahead of the neutral point and are naturally stable.


How is health monitoring of large aircraft engines and components done? How is online (in-flight) and offline (between flights) health monitoring of large aircraft engines and other essential components done?

As far as I have been told, there are a lot of measured channels (at least for engines), but:

what exactly is measured?
How are the data evaluated during flight?
How are the data evaluated on the ground (from long term point of view or after/before failure)?

EDIT: You can consider Boeing 747 or 787 as a large aircraft (to narrow down the question as requested).

Methods of recording data and what's monitored differ between manufacturers but speaking as a Rolls Royce employee, the engine I'm responsible for, the AE2100D3 on the Hercules, is done via downloads. The flight computer records many different channels during flights and ground runs which are downloaded daily, then trended and analyzed. RR HQ then flag any anomalys and send out data for customers to act on, i.e. vibration problems, reduced performance etc. Big engine such as Trents are monitored in real time whilst they fly which is really impressive.

As regards to what exactly is measured, I could list lots of stuff but primarily it's broken down into vibration (all rotating components vibrate, and have allowable limits for this) and performance (referencing pressures and temperatures through the engine to give a performance margin or figure) Anything that either exceeds or drops below set limits raises a maintenance alert.
Engine control units/FADECs constantly monitor all sensors, as do the crews, again anything that needs attention will trigger some sort of warning or information system
Generally through trending and graphs, or in terms of component lifing, etc there will be a count.


Calculation QNE and QNH, with flight level and QNH set lower (higher) than QNE Hi Student pilot here.

Lets say Mr pilot is flying at FL75 and QNH is set at 995 hpa, however there is a mountain in the way at 7000', will he below or above the mountain?

If you could visually explain that would be even better.

Since you used the term "Flight Level" (FL75), we must assume that the altimeter is set to 1013.25, and that the altimeter reads 7500'.

The math is basically this: each milibar (or hPa) is worth about 27 feet.  We know that his altimeter is set to 1013 hPa, but the actual QNH is 995 hPa, a difference of 18.

18 * 27 = 486.  So, the aircraft is either 486 feet ABOVE 7500, or 486 feet BELOW 7500.

So.... how do you know whether to add or subtract?  We can remember the phrase "High to low, look out below"... but what does that really mean?

Let's say that an aircraft is in an area where the QNH is really 1013, and is at an altitude of 7500'.  The pilot flies along the route for a while without adjusting his altimeter. The QNH has been steadily dropping (unbeknownst to the pilot) and is now 995 hPa. Since the pilot failed to obtain the local QNH as he passed by various stations (or, by asking Air Traffic Control every hour or so), he has also failed to adjust his altimeter to the new QNH reading.

Here is what has happened: As the aircraft continues to fly from the higher pressure area into a lower pressure area ("High to low"), the altimeter will start to go up. The pilot will unknowingly descend in an attempt to keep the aircraft at the desired altitude of 7500'. The aircraft will continue to get lower and lower ("look out below"), but all the while the pilot thinks he is maintaining straight and level.

So, we know that the aircraft is 486 feet BELOW his indicated altitude.  Therefore, the aircraft is actually at an altitude of 7014'.  He will BARELY miss that mountain peak that is at 7000'. If the QNH was one milibar lower, he would be at 6987'and hit the mountain.


What is involved in changing runway/taxiway/approach lighting? When a runway inspection determines that there are bulbs out on any of the runway or taxiway lighting fixtures, what is involved in changing them?

Does the runway/taxiway need to be shut down for all bulb changes? (Obviously for center line markers, but what about edge markers?)
What is involved in changing bulbs for any sort of landing system lighting? (i.e. ALS, PAPI, VASI, etc)

To answer your two questions:

Unless the runway is a very busy one, or the failure is such that it can have an adverse effect on the safety of operations, runways are not closed to replace failed lamps.
Bulbs are not changed in the field, with rare exceptions such as PAPIs. Typically, the maintenance team will have hot spares ready to be installed of every kind of fitting. In the event of a failure, they will replace the whole fitting, which can be done in a few minutes, and replace the bulb at the workshop.

The replacement of a fitting typically involves the isolating of the circuits, untorqueing and disconnection of failed fitting from circuit, connection of new or serviced fitting, torqueing, and powering circuit again.

In the case of PAPIs, the bulbs are replaced on site. The replacement is done by opening the PAPI box, and replacing the halogen bulb.

By the way, bulb changing is becoming obsolete with the wide adoption of LED airfield lighting.


Can you turn a large airliner using only rudder input? Is it possible to turn a large jet like the Boeing 747, Airbus A380 or other airliner using only the rudder, i.e. without using the ailerons on the wings?  Will it take longer to turn to a new heading? I find the tilting when ailerons (wing flaps) are involved is uncomfortable.

Yes you can, and this is the backup mode for turning the A320 when the Fly By Wire has failed. It is not very comfortable though:

Changing direction using only the rudder creates sideways acceleration, not good for passengers with drinks in front of them
Since the rudder is located above the center of gravity, the aircraft leans the wrong way when rudder only is used, amplifying the sideways acceleration. A ship has the rudder below the center of buoyancy and leans into the turn when rudder is deflected.


Is wing sweep needed on supersonic aircraft? Area rule states that bodies with the same crossectional area distribution have the same drag. Does that mean I could use a straight wing on mach 1.2 aircraft with performance as high as sweep winged plane as long as they have the same area distribution?

Sweep is not strictly required, but helpful to increase supersonic L/D. Just witness the length to which aircraft manufacturers went to sweep wings for Mach 2+ flight. However, sweep comes with its own set of problems.


How and when is a VFR flight plan closed when flying from the US to Canada? I recently flew from US to Canada. As required I filed a VFR flight plan online (at 1800wxbrief.com). The flight plan was activated after I took off by contacting Flight Services at 122.2. They confirmed that the flight plan was activated.

When I landed in Canada I called 1800WXBrief to close the flight plan. But they said that the flight was closed by someone a few seconds/minutes after it was opened. As far as they were concerned the flight plan was already closed. After a few minutes the FBO guys notified me that they had received a call from NavCanada about us and upon notification of the safe arrival of the plane, NavCanada had closed the plan.

Does someone know how this process works or is supposed to work? Why do I need to call two different agencies to open/close flight plans?

You should not need to call two different agencies to close your VFR flight plan. Call the nearest ATC unit, FSS (or a FIC) or a CARS is the appropriate action except IFR flights to an aerodrome served by a control tower or FSS where you are not required to file an arrival report unless requested to do so by the appropriate air traffic control unit (CAR 602.77 (3)).

Section 3.12 of the Transport Canada Aeronautical Information Manual (AIM) echoes the regulations from CAR 602.77 (1) and states:

  In order to comply with CAR 602.77, an arrival report for a flight plan shall be submitted to an ATC unit, an FSS (or a FIC) or a CARS as soon as practicable after landing but not later than:

  (a) the SAR time specified in the flight plan; or

  (b) where no SAR time is specified in the flight plan, one hour after the last reported ETA.

This idea of reporting to the closest unit is also supported by ICAO Annex 2 (Rules of the Air), standard 3.3.5.3:

  When no air traffic services unit exists at the arrival aerodrome, the arrival report, when required, shall be made as soon as practicable after landing and by the quickest means available to the nearest air traffic services unit.

Perhaps what is missing from the AIM/CARs is the idea that an arrival report should be filed with the closest ATC unit, FSS/FIC, or CARS. This is because the country receiving the flight (Canada in this case) becomes responsible for alerting services at destination (since it's located within a Canadian Flight Information Region). This concept aligns with the standards in ICAO Annex 11, standard 2.10.1:

  Flight information centres shall be established to provide flight information service and alerting service within flight information regions, unless the responsibility of providing such services within a flight information region is assigned to an air traffic control unit having adequate facilities for the discharge of such responsibility

I can't explain why 1800WXBrief would have seen the flight plan "closed" after a few minutes but responsibility for it would have indeed been delegated to Canada after departure. This might appear as closed to them in their system.

The call your FBO received from NAV CANADA was likely from FSS or the nearest flight planning office at the Area Control Centre asking whether you had arrived since they had an open flight plan for alerting services. Once the FBO notified them you were safe, they likely closed the flight plan.


Why are some Tomahawk missiles' nose duck-nose shaped? Why there is a duck-like shape in this Tomahawk missile's nose?  I see this shape in most Tomahawk images; however, not every Tomahawk's nose is shaped like this.  If it is an aerodynamic feature, what is its common name?

I developed the shape for Convair back in the late 90's.  It was called a chined nose and Carlo is right, there were no aero considerations for this shape.  It was purely RCS.


How far from the runway should a small plane start its descent from 5000ft? I don't fly, don't have a clue. But one of the main characters in my book DOES: it's a Cessna 152, just him at 14 stone and a couple of small bags, all conditions are perfect and he's flown from about 140 NM away. Would 5000ft be about the right altitude?

The question is: how far away is the runway (a grass one on an unlicensed airfield) when he starts his descent? It's a direct approach, no pattern.

For a comfortable decent you generally want to come down at 500 Ft/Min on the Vertical speed indicator. The 152 is doing about 95Kts over the ground (assuming no wind). So you are covering about 1.5 miles a minute to round it off. So you need to drop 5000 ft on your approach to the area. At a comfortable rate that will take about 10 minutes. In that time, covering 1.5 miles a minute, you will need to start your decent about 15 nautical miles out.


Does a RC glider always loop when launched? In the below video, the guy sets "launch mode" for hand launch where he adds a little bit of elevator.
Will a glider always loop up when launched horizontally, even if the tail is set to produce zero lift?
And what determines whether the glider will loop up or loop down (and crash, if possible) during launch?

No, it doesn't loop when launched correctly.
If you launch it so fast that lift is greater than weight, if will pitch up, and may either stall (as happened to me with my foam plane) or may enter a phugoid cycle where it climbs, dives, climbs again, and so on.
But if you launch it at the right speed and right angle (usually slightly down) it will fly smoothly to a gentle touchdown far away. This is the"trim speed" John K was talking about.
By angle I mean direction of flight, not pitch angle, or angle of attack. A stable glider will correct these as a rule.
But if your launch leaves too little lift, it will pitch down. This usually results in an immediate crash, due to the small altitude budget available.
The more lift your elevator is trimmed to create, the higher the optimum speed will be
But it must always have lower angle of attack than the wing, or the plane will be unstable or will nosedive and crash
I often threw my plane at the ground as hard as I could, just to watch it nearly crash, and then zoom up to twice my height.


What are FARs & where can I find them? What is FAR 23, 25, 135, etc? The FARs (or Federal Aviation Regulations) are the regulations imposed by the FAA on aviation within the United States.

Many questions make reference to FAR 23, or FAR 91 etc. What are each of these? Where can one lookup the text?

In the US the "Federal Aviation Regulations" (FARs) is shorthand for referring to Title 14 of the Code of Federal Regulations.

You can browse all sections of FARs at ECFR.Gov.

FAR 23, for example, covers airworthiness standards. § 23.25 regulates weight limits.


What is the stability of a 777-like plane if the engines flameout and the autopilot disconnects and the pilots don't make any inputs? According to Wikipedia:

  If no control inputs were made following flameout and the disengagement of autopilot, the aircraft would likely have entered a spiral dive and entered the ocean within 20 nmi (37 km; 23 mi) of the flameout and disengagement of autopilot.

Does this mean the autopilot automatically disengages when both engines experience flameouts? If so, how likely is it it would enter a spiral dive within 37km of the flameout?

Are there any other control inputs the pilot could have made before flameout that would cause the plane to glide until it impacted the water?

Assuming CG is within limits, the plane is straight, level, and both engines flame out simultaneously, lacking any control inputs, the plane will dive until it reaches its elevator trim speed, then glide at that speed until it impacts.  As the directional and roll stability would be fairly good with the 777, without variable cross wind effects or any other yawing tendencies, it would probably be a straight in crash.

This scenario could be tested under controlled conditions.


Do special procedures exist for commercial pilots flying over Russia? Since Russia, and in particular the Asian part of it, is huge, I was wondering if there are special procedures for commercial pilots to follow over Russia (in particular and specifically Siberia and other sparsely populated parts)? (Except that they use the metric system.)

Does Russia provide radar coverage and flight following services over its entire territory? As an example, do the use procedures like the North Atlantic Tracks, or do pilots implement their "own ATC" by stating position reports regularly, just like over some parts of Africa?

Or is flying over Russia comparable to flying over any other European / U.S. / ... country with continued ATC service?

Does Russia provide radar coverage and flight following services over its entire territory?

Not all countries publish the exact radar coverage, as it is sensitive information. But, if the flight over Russia is IFR (controlled), then the answer is yes, regardless of the remoteness of the area.
The services and limitations can be found in any country's AIP, and the Russian AIP is publicly available. By checking GEN 3.3:

1.3 Radar service is provided at all phases of control service indicated in para 1.2.

and 1.2 basically covers all phases of controlled flight:

1.2 The air traffic control service is divided into:
a) area control service - the provision of control service for flights of all aircraft in CTA (FIR/СТА), except those indicated below in items b) and c);
b) approach control service - the provision of control service connected with arrival and departure of all aircraft;
c) aerodrome control service - the provision of control service to aerodrome traffic, except that indicated in item b).


What would the pros and cons be of this 'zig-zagged' high-sweep wing planform? What would be the advantages / disadvantages of the following wing planform for supersonic aircraft?

The suggested planform is in red; a more conventional, delta planform is illustrated for comparison in white. I was wondering if a zig-zagging leading edge would increase efficiency at high speed due to the increased leading edge sweep without a decreased aspect ratio. I was also wondering if improved control at high angles of attack would be an added bonus, like the "dogtooth" on the F-4 Phantom. I suspect that reduced structural strength could be a disadvantage.

That's called sweep variation along span. What you've done is combine an inner W wing with an outer M wing.

Both of which were never used.

  W-wing: A reversed M-wing. Proposed for the Blohm & Voss P.188 but studied even less than the M-wing and in the end never used.
  M-wing: the inner wing section sweeps forward, and the outer section sweeps backwards. Allows the wing to be highly swept while minimising the undesirable effects of aeroelastic bending. Periodically studied, but never used on an aircraft.

The chordwise flow would be something like this:

The blue area marks an area of very low-pressure and flow detachment. The outboard wing will experience high pressure due to converging flows1. The wing will want to bend up from the middle, and bend down from the tips, structurally that's a nightmare.

The M wing on the right does resemble birds, but birds had to retain their 'arm' joints from their ancestors, and they don't fly at Mach 0.8 speeds.

1 Answer is a wiki for a reason, this is a guess.


How should you coordinate with traffic at non-towered airports? I am a fairly new pilot. I recently flew to a non-towered airport in Quebec, Canada (Lachute, CSE4). There is a significant displaced threshold on each end of the runway. The airport has one taxiway which goes up to about half the length of the runway. Because the taxiway doesn't extend all the way, back taxi is required on one of the runways.

When I attempted to depart I noticed that all CTAF announcements were being made in French. Before I got to my holding point I had to cross the runway and I spoke in English before I did so. I do not speak or understand French. Once I got to the holding point I noticed two aircrafts which were performing touch and goes. There was really no time for an aircraft to takeoff before one of them would be on the base leg or the final. I waited for several minutes. I noticed another plane also waiting at another holding point. A third aircraft was taxiing and about to queue up behind me.

My question is:

What is the correct procedure in this situation? Do we continue to
wait until the other aircraft finish their touch and goes?
If there is no procedure defined (I'm not aware of any), what is
the correct etiquette in this situation?

After waiting for a while I waited for one of the aircrafts to take off. Then I immediately stated my intentions to back taxi on the active runway and started the back taxi. I saw the second aircraft turning from base to final and I accelerated towards the end of the runway and positioned myself towards the beginning of the runway/displacement threshold. There was no way I could have attempted a takeoff.

However, what I did made a number of people very unhappy and they berated me and told me that I should brush up my procedures (in English this time). I haven't come across this situation in my training. Can someone please help clarify the correct/accepted process?

The problem with uncontrolled airports is that sometimes the procedures and "etiquette" can be informal.  The pilots based at the airport have established their own informal procedures which are not published anywhere or are part of any rule book.  In cases like this I would consult the FBO for the local procedures (which you did do) but that doesn't mean that all the pilots at the airport abide by them.  In your situation this is what I would have done:

I would have announced on the CTAF that I cannot speak French and would request that all pilots announce their intentions in English.  By international convention pilots are required to communicate to ATC via English unless there is an emergency.  However CTAF communications tend to be more informal and the pilots at the local airport may prefer to speak in the language they are the most comfortable.  Still the intent of CTAF is to communicate with everyone at the airport to announce their intentions.  It would have been entirely proper to request the pilots to speak in English.
I would have requested the pilots performing the touch and goes to give you a window in which to back taxi and takeoff.  I find it rather rude for pilots to monopolize the pattern and runway performing touch and goes.  If they see that there is a line of planes wanting to takeoff they should leave the pattern for a while and let folks takeoff before resuming their touch and goes.  Asking politely on the radio for these pilots to do this for you is reasonable.
If they were giving you grief for not using the grass to taxi to the runway they had no right to do that.  Taxing on grass can be dangerous especially in tricycle gear aircraft where the potential for a prop hit with the ground is a real possibility.  In my case I am bound by the club rules not to taxi on any surface that is not paved.  Back taxing would be the appropriate thing to do.


Why aren't cell phones allowed to be used in aircraft? What problems do cell phones cause? How is using a cell phone in the air different than using it from the ground?

Why aren't cell phones allowed?/ What problems to cell phones cause?

Most of these cases apparently originate from a series of unexplained events in the 90s which were believe to be caused by electronic gadgets, hence the ban. This was when cell phones appeared, and there was an aggressive ban as a result. NASA has a list which includes some of these and makes for an interesting read.

Now however an increasing list of airlines is allowing them again, depending on jurisdiction. FAA is working on allowing it from a regulatory standpoint. Bear in mind that phones were probably much more powerful back when these rules were introduced.

Mythbuster (episode 6, 2006) did a test on this by sticking in a powerful transmitter into a business jet. Their website gives a slightly different version: It was the FCC, not the FAA, who led the way for this regulation:

  Explanation: Never mind what the chatterbox in the seat next to you
  says about cell phones messing with plane navigation — those metallic
  birds are built airtight against foreign signals and operate on
  entirely different frequencies than cell phones.

  So why all the fuss about phones? When you make a call at 10,000 feet,
  the signal bounces off multiple available cell towers, rather than one
  at a time. That means too many phone-happy jetsetters might clog up
  the networks on the ground, which is why the Federal Communications
  Commission (FCC) — not the Federal Aviation Administration (FAA) — banned
  cell use on planes.

How is using a cell phone in the air different than using it from the ground?

Is it sensible to allow them on aircraft? To quote one of the above sources:

  although the FAA recommends that you still switch to airplane mode
  because you’re not going to get a signal 30,000 feet in the air — the
  only hit you’ll take is a dead battery when you land.

So it's probably not a huge loss if you're flying commercial aircraft at 10,000 meters. In any case, you can't expect a service like you do on the ground, unless like Lnafziger says that the aircraft is equipped with a cellular basestation called a Picocell, illustrated below:

(source: wordpress.com)


Why can't the flex temperature be lower than Tref? Also why can't we perform a flex takeoff on a contaminated runway? This is a huge grey area and my quest to find answers for them is never ending. I have referred to many performance books but to no avail. I hope this question can be clarified. Thanks

The engine is flat rated below Tref, and the thrust decreases above this temperature. The point of using a flex takeoff is to run the engine at a lower power setting, where its limit would be at a higher temperature. Using a temperature below Tref would result in the same thrust as Tref. The graph from Airbus below helps to illustrate the relationship between the variables.

Source


Why aren't any jet fuels heavier than Jet A/A-1/JP-8 in common use? The commonly-used jet fuels fall into two main categories:

Straight kerosenes (Jet A, Jet A-1, JP-8, JP-5, plus, historically, JP-1), which are used in most situations because their high flashpoints make them safer to handle.
Gasoline-kerosene blends (Jet B, plus, historically, JP-3 and JP-4), which are used in very cold climates due to their lower freezing points, but are much more dangerous to handle due to their very low flashpoints.

However, even the straight kerosenes have flashpoints below 40C, which can easily be exceeded in hot-weather operations, potentially with lethal results.  Using a fuel with a somewhat heavier composition (and, thus, a higher flashpoint) would greatly alleviate this danger; for instance, the lighter diesels have flashpoints in the 50C-60C range, and would, thus, seem to be a safer choice than kerosene-based fuels for hot-weather operations (especially in tropical and subtropical climates where very hot weather is more common than elsewhere), where their higher freezing points would not be an issue.

So why aren't there any "heavy" jet fuels for hot-weather use?

As @john K said, fuel needs to be liquid at cruising altitude. The less volatile a hydrocarbon is at a temperature, the quicker it will stop flowing as the temperature drops.

Additionally, the plane is not necessarily landing in the same hot climate it is taking off from. You need a fuel that is stable across the range of temperatures experienced while operating.

This post addresses the specific behavior of different fuels in great depth.


Who closes an airline's IFR flight plan and when? ATA (Air Transport Association of America) defines the various flight phases (ATA Spec 2300, flight phases). The last phase is called Flight Close and is described as "The Flight Close phase begins when the crew initiates a message to the flight-following authorities that the aircraft is secure [...]".

In commercial airline operations, who closes the IFR flight plan? The flight plan is usually filed by the dispatchers, I guess. I have never heard a pilot actually close the flight plan before leaving the aircraft...

When landing at a controlled aerodrome, air traffic control will automatically close the flightplan once the flight has safely arrived. The pilot does not have to do anything in this case. The majority of commercial flights take place at controlled aerodromes, which is probably what makes you think that pilots never close their flightplans.

If landing at an uncontrolled field (that is, one without a control tower), however, the pilot will either close the flightplan by contacting a nearby ATC station on the radio before landing, or via telephone after landing.

This applies equally to IFR and VFR flightplans, to big passenger jets and small one-person GA aircraft. If the destination airport — any airport of any size — has an operating control tower at the time of arrival, they will close your flight plan. If the airport does not have a control tower, or the tower is closed at the time, you have to contact another ATS unit to have it closed.

This is actually very logical when you think of it. When you are on a flightplan, you are automatically provided with alerting service. Meaning that if you do not arrive on time, people will start looking for you. If you are landing at an aerodrome with a control tower, the tower is responsible for your alerting service. They have your ETA (based on your FPL EET and ATD) and will initiate a search and rescue operation if you are late. If flying to an uncontrolled aerodrome, some other ATS unit (for example an area-wide flight information service) is responsible for your alerting service, so they are the ones who need to initiate search and rescue if you do not arrive on time.

Now think of this: if landing somewhere with a tower, the tower obviously knows when you land (they clear you to land, after all, and their job is to look at the runway). Thus, the tower knows that you have landed safely and that alerting service can be cancelled.

However, if landing somewhere without a tower, where another unit (not on-site) is responsible for making sure you land safely, how would they know that you have landed? The only way to be sure is for you to call them up on the radio or telephone to let them know that you have safely arrived. They will then file the arrival time to note that you have arrived safely and no search and rescue needs to be initiated.

And this is essentially what "closing a flightplan" is - it actually just means that your arrival time is sent to whichever unit is responsible for your alerting service. It's not that your flightplan is actually "closed" or "deleted" from some system, it just means that your arrival time is filed so that everyone knows the flight has landed.


Does Active Thermal Imaging (NDI method) detect all types of structural faults in modern civil aircraft? What are the weaknesses of Active thermal imaging in NDI of different composite materials used in aircraft structure ?

How much time and effort does it take to complete a full structure inspection with the latest portable equipment like (C-CheckIR)

No. There is no single NDT method that can identify all types of structural faults in the aircraft.

Active thermography refers to the use of (thermal) exciters like ultrasound, (halogen and xenon) lamps, eddy current transducers and detecting the defects using that fact that the heat produced is different in those areas, usually using infrared cameras.

Though this is a very effective method for detecting defects, especially in composites, there are some disadvantages as well.

The test specimen has to be 'hooked up' to some form of (thermal) loading device. This limits the size of the tested part.
This is an excellent method for detecting subsurface defects; however, as the depth of the defect increases, the defect size has to be larger for detection.
The method requires that the temperature of the region (containing the defect) be uniform. This is a problem especially for materials with high thermal diffusivity like metals, which may require high speed IR cameras.
Though automated algorithms are available for defect detection, most of the (older) methods of thermography depend on the operator for interpretation of results.
The type of excitation technique used can be limited in some cases to prevent damage to the tested part.


Is it possible to start another engine of Mil Mi 8 with one engine started and APU off? In the 737NG, it is possible to start the other engine without APU if one engine is already started, by routing air from the started engine to the other one.

Is this possible in the Mil Mi 8 helicopter?

From that I see in the quite detailed description of the helicopter systems in Russian Wikipedia, looks like both engines have independent electric starters (starters-generators) so could be started independently.

There is no mentioning of APU in the description of all systems. They say power plant consists of the two engines. However as mentioned in comments, the helicopter does have the control panel for starting the "Турбоагрегат". It is generally a name for the device that combines turbine engine and electricity generator. APU is called "Вспомогательная силовая установка (ВСУ)" in Russian.


What aircraft has this pattern of white strobe lights? Just two nights ago, my brother and I noticed a weird flashing light in the night sky out in the countryside.
We regularly observe by naked eye aircraft flying by,  as well as satellites,  and this was not like anything we'd seen before.

It was only white light (no red, no green) , with the following sequence:

 *            _______          _______

Flash   <-1sec->  strong light  <-1sec->   dim light

The lines above the second and third lights attempt to show the fact that they faded gradually, while the first flash was like a camera flash, sudden and strong.

Every 3 seconds the cycle repeated.
The source of the lights seemed to be the same, i.e the same strobe light. Besides, the aircraft was pretty far away or small: with binoculars, it wasn't possible to discern any other strobe lights or a structure of any kind.

We first noticed the light above Ursa Major, it moved towards Cassiopeia and gradually faded away either because it moved away from us or because of the strong moonlight of that night.

Twenty cycles per minute means it wasn't an FAA-approved aircraft, so it probably wasn't manned, or even a weather balloon.

Satellites need no anticollision lights.

The bright strobe combined with the longer fading lights suggests something homebuilt.  The light may have been adapted from consumer bicycle lights, which have quite a variety of patterns.  Professional lights such as Whelen's models prefer flickering to fading, for both efficiency and visibility.


Can I rent a Cessna for a week with my GF with a PPL? I want to do a 45 hour course to obtain a PPL. The course only includes 10 solo hours but states that it is enough to hire light aircraft.

So could I rent a Cessna after this and take a passenger?

Most people do not take 45 hours to get a PPL, the national average is closer to 70. Do not fall for the "get your license in 45 hours" gimicks. They will give you 45 hours of instruction (and you will probably need more), you also then need to book the examiner and pay for that. 45 hours is difficult to do in short periods of time as well, for example I got my license in 47 hours, way below national average, and it took me 7 months (weather/work/instructor availability/aircraft availability/etc).

So theoretically yes, you can, if you are renting from the same place that you took your training. If not, then you will probably have to pass a check-out which will include about half an hour of ground and an hour or so of air with the company renting the aircraft. You may also not be allowed to rent overnight unless you have X number of hours, again this is up to the rental company.

You also need to have insurance which meets the rental company's requirements. Some rental companies won't rent aircraft overnight, so you need to check that, and if they rent for longer periods of time you will end up paying extra even while the aircraft sits on the ground.

For example, a local company will rent one of the 172's for up to 4 days. The regular rental rate is \$125/hr and overnights are charged $375 for each day.


What are the effects of adding winglets to an aircraft not designed with winglets originally? Are there any positive advantages or catastrophic effects on adding winglets to an aircraft not designed with winglets originally?

Aircraft wings are designed for specific weight and cruise speed. When later the manufacturer wants to create a new variant with higher maximum weight, it should get longer wings for optimal efficiency. However, redesigning the wing is a lot of work, because extending the wing means the root bending moment increases, which requires stronger spar, which means heavier and all the calculations have to be redone.

Here is where winglets get useful. They increase the effective wingspan, but while they are somewhat less efficient than extending the wing, they also cause lower increase of the root bending moment. Often, this smaller increase fits in the original extra margin, so winglets can be simply bolted on without having to redesign the wing, making the process much cheaper.

That's why we often see winglets on next generation of anything and rarely on the first generation. On first generation, they are designing the wing from scratch anyway, so they just make it appropriate length for minimum drag.

The main reason to use winglets from the start is if the emerging design just slightly exceeds some size category for airport gates. Then it makes sense to reduce the span to fit and add winglets so the aircraft can be used at smaller—and therefore cheaper and more common—gates.

You can read how winglets work in Is a winglet better than an equal span extension?.


Would TCAS ever issue a "climb, climb!" RA that would stall a jet with a low airspeed? As a for instance, let's say there are 2 jets going at low airspeeds (close to $V_S$) that get too close to eachother and a TCAS Resolution Advisory callout is announced.

Would TCAS issue an RA to order one of the jets to climb, resulting in loss of airspeed and a stall?

The FAA publishes Advisory Circular 20-151A, which says in section 2-17(a):

  Because TCAS II can only accept a limited number of inputs related to
  airplane performance, it’s not possible to automatically inhibit CLIMB
  and INCREASE CLIMB RAs in all cases where it may be appropriate to
  inhibit such RAs. In these cases, TCAS II may command maneuvers that
  may significantly reduce stall margins or result in stall warning


Does 14 CFR 91.146 (Charitable Events) apply if the pilot does not seek compensation or hire? I'm at a loss between regulations §91.146 (Passenger-carrying flights for the benefit of a charitable, nonprofit, or community event.) and §61.113 (Private pilot privileges and limitations: Pilot in command.)

§91.146 contains language that allows a private pilot (who meets 500 hour requirement, among other items) to operate as PIC for a charitable event. The language emphasizes that if the event doesn't meet the charity requirement, it is to be considered commercial.

Do these restrictions under §91.146 / §61.113(d) apply if a pilot is willing to PIC under the criteria of §61.113(a) and cover all expenses of the flight?

  §61.113   Private pilot privileges and limitations: Pilot in command.

  (a) Except as provided in paragraphs (b) through (h) of this section,
  no person who holds a private pilot certificate may act as pilot in
  command of an aircraft that is carrying passengers or property for
  compensation or hire; nor may that person, for compensation or hire,
  act as pilot in command of an aircraft.

  ....

  (d) A private pilot may act as pilot in command of a charitable,
  nonprofit, or community event flight described in §91.146, if the
  sponsor and pilot comply with the requirements of §91.146.

Let's look at this from two angles -- first, what's OK under 61.113 (basically "no compensation except the pro-rata sharing of expenses" when acting as a private pilot).
The FAA has an incredibly broad interpretation of "compensation" - The foundational counsel opinion is an interpretation to Joseph A. Kirwan, and if you search counsel opinions for Kirwan you find a bunch of additional opinions referencing it.
Basically Kirwan and the other opinions state that the receipt of anything of value is compensation.
That could include:

Money, obviously.
Free or discount fuel/oil
Free meal
Lodging
Logging of flight time (if you're not responsible for the operating expenses of the aircraft)
The receipt of a benefit (usually money) by the organizer (charity)
(Weybrecht, 2010 - if they get the ride in exchange for a donation or attendance fee it's 91.146)
"Valuable Good Will"
(Again in Weybrecht from above - so yeah, If you fly your buddy somewhere and they "owe you one" that might be a violation.)

There's really almost nothing you can do under 61.113 except fly somewhere for a hundred-dollar hamburger and split the cost of gas (under the FARs you even have to pay your pro rata share of the burger) - it's very restrictive.

Now let's look at 91.146 - like DJClayworth pointed out what this  basically does is carve out a small set of exceptions that allow community groups and charitable organizations which have friendly pilots to offer "airplane rides" in exchange for a donation without being in violation of the FARs (risking the friendly pilot's certificate, and the possible wrath of the FAA on the organizer).
There are lots of restrictions (Like the 500 hour requirement, the requirement that flights be "Nonstop, beginning and ending at the same airport, and within 25 miles of the airport of origin", the limit of reimbursement for the pilot being "pro rata share of expenses", and notification of the local FSDO).
The FAA wants to basically make sure pilots are not flying tons of these charity flights every year to basically build time, and that charities aren't operating de facto air tour companies under the exemptions of 91.146.

So what's the answer to your question?
Basically If the organization is getting donations/admission fees/raffle proceeds, etc. in exchange for these flights the operation falls under 91.146 (because the charity is receiving compensation -- the donation).


Do jet fighters have air conditioning systems? In most jet fighters, the cockpit is a glass dome and the pilots are exposed directly to the sun.

In addition, they are wearing flight suits and full face helmets (most of the time).

I can only imagine that with no respite from the sun, the cockpit must heat up very quickly.

What measures are there for climate control or pilot comfort?

Yes. Fighter aircraft have air conditioning systems. In general, they are called as Environmental Conditioning Systems (ECS). Their primary functions (as far as cockpit goes) include,

Cockpit Pressurization

Heating/Cooling/air-conditioning

Windshield anti-fog/anti-ice

The systems usually use conditioned engine bleed air or this purpose. The cockpit air conditioning is usually managed by the pilot. For example, in case of F-15, the following system is available:

Image from f-15e.info
with the available controls listed as,

TEMP switch: A three-way switch to manage cockpit temperature. When AUTO, cockpit temperature is automatically maintained at the temperature selected on the TEMP knob. When MANUAL, cockpit temperature may be changed with the knob, but not maitained automatically. When OFF, it shuts down off ECS air.
TEMP knob: A rotary knob to set the cockpit temperature.
FLOW switch: A three-way switch to select air flow. MIN, MAX and NORM settings are available for minimum/maximum/normal air flow, respectively.
FLOW knob: A four-position knob to set the air source. When BOTH, bleed air is supplied from both engines. When L ENG or R ENG, bleed air is supplied from the left/right engine only. When OFF, no bleed air is supplied.

The following image shows the other controls associated with ECS.

Image from f-15e.info


How to determine aircraft altitude and speed, as a passenger? Is it possible for a passenger to determine the aircraft's altitude and or speed or location using any mobile apps.

Not all airlines have displays with constant info about this. I had tried using Google maps, but it did not work, maybe because there was no internet/wifi on the aircraft.

Any simple method?

I always track my flights, so here is my experience:

App using offline maps

As it has been said, you will need an app which can download maps prior to the flight. I never had a flight with onboard wifi, but I guess, there's usually a data volume constraint, which could make it expensive.

I use Mapfactor Navigator (Android), which is an offline navigation system for cars etc.
The maps can be obtained from within the app, the user has the choice between free maps from the OpenStreetMaps project and TomTom maps, which you have to pay.
The maps can be downloaded per country, and big maps are subdivided into smaller pieces. For example, the very detailed map for Germany is divided into four parts, together about 0.8GB of data. The entire USA can be downloaded per state, all together 1.7GB.

It's possible to configure several fields at the bottom of the screen to display speed, altitude, GPS coordinates, distance to destination and so on.

I mainly use this app to explore a country (e.g. by car) on vacation, but it's also fun to use it on board to see what's that location below us.

You may switch off speed camera warning. I once got a warning over Switzerland. The 840km/h were well above the max speed limit of 120km/h, and the fine should have been in the order of seizing all property of the airline. For some reason, the pilot didn't care...

OK, lots of advantages, but there's also a drawback: The app can not just record your flight, though a menu for tracking exists. Nor can it display your currently covered track. It can only record a track when it's navigating you, but you don't want to hear "turn around! turn around!" all the time...

Tracking app

Again, there should be thousands of apps out there. I'm using Open GPS Tracker, which can also display your position / track on an online map. So, you just see a point moving on a gray screen while flying.

However, this app allows to record your track, with up to one point per second, and at the end, you can export it as GPX file, which is the standard. It can be opened by many map tools, also by googles MyMaps or what it's called. The file contains coordinates, precision, time, altitude, speed, number of satellites and course.

One hint: This app makes a sanity check between speed reported by the GPS module and speed calculated from recorded points. If this fails, it doesn't display/record any speed. This often happens onboard, so switch this check off.

Here is a flight from Düsseldorf (DUS) to Las Palmas, Gran Canaria (LPA), including altitude profile, drawn with Marble (Linux KDE program):

Precision

An airliner is usually made of aluminum, which makes it a huge faraday's cage. The reception of any radio waves is very limited (through the windows), and so is GPS.
And as GPS needs a line of sight to several satellites spread as much as possible over the entire sky, the only chance is to have a window seat. There, I usually get a very good GPS signal, while it's already very bad to unusable on the next seat, and don't even think about it on the aisle seat.

Having a window seat, I usually get a good signal. While taxiing, the precision is quite good, as on this flight from Frankfurt (FRA):

Of course, the strength and accuracy of the GPS signal relies on the quality of the GPS module of your phone. My last phone wasn't so good, I often had jumps of several 100m sidewards, or from 7000m to 10000m altitude. This is just because accuracy comes with the number of satellites, which usually increases with altitude. And: The first aim of GPS is to locate your position, the altitude usually is less important. With my current phone, I don't see such problems. No sudden steps aside, and altitude and speed were quite the same as displayed on the entertainment system.

Well, not entirely. I noticed my phone showing an altitude about 50m too high when landing on my last flight. The 20m shown by the entertainment system were plausible, as the airport was nearly on sea level / in the sea. But the too high altitude was still there, even at the beach. Keep in mind the earth isn't a sphere, it's an ellipsoid, though even that's not correct, it's more like a potato. So, sea level isn't the same everywhere. High quality/price GPS receivers know this and contain data to compensate it, but cheap ones just use the ellipsoid model. (However, 50m is nothing during flight, and what do you expect from a phone inside the cabin...)

More hints

For a working GPS, the receiver needs a list of all GPS satellites and their precise orbits ("almanach"), current time and its rough position. If it does not have its rough position, it takes much more time to get a fix (first GPS position). And if it doesn't have a recent almanach, it has to listen to the satellites for a while, as they slowly broadcast it.
As reception of radio signals is quite difficult inside the cabin, it may be very hard to get a fix, and even impossible to get the almanach.
So, it's good practice to prepare your phone before the flight, as reception will be better, and assisted-GPS allows to retrieve the almanach and current position via the mobile network.

Finally: The battery.
Running my two apps on a 4.5h flight takes about 80% battery, and I have a laaarge battery. Of course, this also depends on display-on time. But the endurance could by tested before the flight, and if it's too short, a power bank my help.


Do Grumman F-14s, Panavia Tornados, and other swing-wing airplanes count as "fixed-wing aircraft?" I'm just wondering because the wing isn't fixed, but they aren't rotary-wings either.

Yes - they are still considered fixed wing aircraft. Just because they have variable-sweep sections doesn't change what type of aircraft they are; their aerodynamics, behavior, and performance characteristics are still squarely in the 'fixed wing' category.


How hot is supersonic intake air? How hot is the air at the compressor inlet at supersonic speed? For instance the Concorde at mach 2.2 or other jet engines at even higher speeds.

The air entering the first compressor stage of the SR-71's engines could be as hot as 450C while at maximum cruise conditions. If that air got any hotter, it would begin to soften the compressor blades, and this put an upper limit on the speed of that plane.


What is the minimum distance allowed between two parallel runways? Is there an international regulation for this matter or does it differ from one country to another?

In the United States, the FAA has published Advisory Circular 150/5300-13A, Airport Design , which includes standards and recommendations for airport design, including parallel runway separation.

In summary,

"For simultaneous landings and takeoffs using VFR, the minimum
separation between centerlines of parallel runways is 700 feet (213
m)."
For simultaneous IFR operations, "Dual simultaneous precision
instrument approaches are normally approved on parallel runway
centerline separation of 4,300 feet (1311 m). On a case-by-case
basis, the FAA will consider proposals utilizing separations down to
a minimum of 3,000 feet (914 m) where a 4,300 foot (1311 m)
separation is impractical. This reduction of separation requires
special high update radar, monitoring equipment, etc." Note:
Simultaneous Offset Instrument Approaches allow as little as 750 ft
between runway centerlines.

International regulations do differ. ICAO have their own standards. Here is an example of a document which prescribes airport standards compliant to ICAO Annex 14.


At what age does a regularly maintained airframe most commonly start needing frequent repairs? I am looking to buy a Cessna 182.  I am trying to work out the sweet spot between age and price.  I am looking for a plane that will be really reliable.  I am looking to spend several months flying around the USA with my wife and prefer not to spend my whole time dealing with mechanics.  Some questions:

At what age does a regularly maintained airframe most commonly start needing frequent  repairs?
At what age does the depreciation slow down (so I can buy and sell the plane after three years with minimal loss)?

Not an aircraft owner here, but based on the AOPA article Tips on Buying Used Aircraft, the one thing that stands out is to negotiate a much lower price if the aircraft is close to its time between overhaul (TBO).

  [Let's say] you are purchasing a 1977 C-172N for \$40,000. The TBO for this aircraft is typically 2000 hours, and costs roughly \$20,000; or half the value of the aircraft. If the aircraft you are considering buying has 1800 hours on the engine, you need to expect to spend an additional \$20,000 on the aircraft in your first 200 hours of ownership. Knowing this, it would be in your best interest to negotiate a lower price for the aircraft.

Depending on you where you will be flying, you may be required to install ADS-B by Jan 2020. If the aircraft you are buying is not equipped, then that's something to add to the list of things to buy. (What is ADS-B and who needs it?)

There are also these related posts:

What are the typical facets of ownership costs, for a single engine aircraft?
Is there any limit by FAA on the age of aircraft to be operational?


What are the meanings of various reference lines and sections in a take-off distance graph? I am trying to solve a numerical problem related to determining take-off roll using a take-off distance graph. The parameters are Temp: 90F, Press. alt: 2000ft, wt: 2500lbs, headwind: 20 Knots. I got the following graph (solid red lines):

My questions/clarifications are as follows:

It looks like the first reference line is the "density altitude", correct?
Looks like the second section of the graph is a relationship between aircraft weight and take-off roll (where take-off roll distances are represented vertically on the second reference) at various density altitudes. This seems to make sense because for a certain weight, if I go up, meaning I intercept higher density altitudes, the take-off roll increases.
It is not very clear to me the plotting of the diagonal lines. The way I understood it is that they go from the point of interception of the reference line to a point on the vertical weight line which is midway between the inclined curves intercepting that vertical weight line.

You need to read such graphs strictly from left to right. Each new panel adds the influence of another parameter, and when you are done, the result is corrected for altitude, take-off weight, wind and obstacle height. Except for the leftmost panel, the groups of lines only help you to find the correct slope and do not represent a certain altitude.

You start with the outside air temperature. Pick what the instrument in your cockpit indicates, and go from the temperature axis straight up until you intercept the line which is closest to your given pressure altitude. This can be read directly from the altimeter if it is set correctly. You can try to interpolate between lines, but to be safe pick the next higher value.

Next, move horizontally to the first reference line. From there, follow the slope of the lines until you intercept the x-position which corresponds to your aircraft's mass. If you start between two lines, you should move such that the relative vertical distance to the neighboring lines does not change. Note that the take-off mass is also a value you should know already if your preflight was done properly.

From that point, jump off horizontally until you intercept the next reference line. Depending on wind direction, follow either the dashed or the solid lines until you arrive at the x-position which corresponds to the wind component in runway direction. You will note that for headwind you will move slightly down, so headwind shortens the take-off distance. Makes sense, right?

The last panel helps you to find both the take-off roll (obstacle height zero) and the take-off distance over a 50 ft obstacle. Here you can only extract the values at the x-positions 0 and 50 and interpolation will not work. The y-axis all the way on the right now will tell you the distances in feet.

The reference lines show the values for the standard take-off at MTOW and calm wind. The examples given by the red lines are for two different situations:

Solid red line: OAT is 90°F, pressure altitude is 2000ft MSL, take-off mass is 2500lbs and with a headwind of 20kts the take-off roll is 500ft. At this point your speed should be 62kts (see table).  This is the result for your first question.
Dashed red line: OAT is 15°C, pressure altitude is 6000ft MSL (rounded up from 5650ft), take-off mass is 2950lbs and with a headwind of 9kts your take-off roll is 1400ft and the distance needed to clear the 50ft obstacle at 1.3*stall speed is 2300ft.


Is it very rare to be a senior pilot with no emergency occurrence in history? I was reading a Civil Aviation Safety Inspector from Transport Canada:

  I have met a few pilots who have flown all their lives without
  declaring an emergency. Pilots such as these are very rare.

Source

Emergency landing for this Boeing 727 flying into a serious hailstorm over Switzerland (source: ASN)

Is your experience in line with this TC inspector statement? Is it very rare to be a senior pilot with no emergency occurrence in history?

Let's define emergency as a mayday or pan-pan radio call or transponder code.

In the airlines, the number of flights where an emergency has been declared is about 1 in 600. In general aviation, it could be as low as 1 in 40 or as high as 1 in 6,000, but it's not "most".
In the airlines:
Poking around Google gives this USA Today story: Medical emergencies occur on 1 of every 604 flights, which references an article in the New England Journal of Medicine.
An answer on a different question on this site provides the following anecdote:

had occasion about a year ago to ask our airline safety department
what the most common cause was for declared emergencies in our
operation, and was told that far & away, sick passengers (medical
emergencies) were #1 by a huge margin, and everything else (which
includes all the aircraft-related events) was far down in the weeds in
comparison.

(emphasis added)
We'll assume that Ralph J's answer is correct and that medical emergencies are the lion's share of total emergencies. That being the case, the 1 in 600 number is probably accurate within an order of magnitude.
In general aviation:
Since 2001, the NTSB aviation accident database has been remarkably consistent in terms of the number of reports they get:

About 4,000 reports per two-year span (until 2013, when it dropped to a little under 3,500)
Between 60-90 reports containing the phrase "declared an emergency" within that span

As airline travel continues to be outrageously, shockingly safe, let's run with the assumption that most accidents in the database are non-airline accidents. That being the case, one in 30-40 of accident airplanes (not all airplanes) declared an emergency in a way that managed to make it into the accident report.
That doesn't fit with a fact I found in an AOPA handout though, which says that air traffic controllers provide more than one flight assist per day.  "More than" one could be anything, but let's be super generous and say there are 1,000 flight assists per year. Another FAA source says that there were 24 million GA flight hours in 2015. Figure a GA aircraft holds about 4 hours of fuel, then there were around 6 million GA flights in 2015, or one flight assist per 6,000 flights. That throws a wrench into our other estimate, but it also goes against the "very rare" statement of the inspector in the original question.
From personal experience
Anecdotally, I've flown a few thousand hours and I would say that I've heard aircraft on the radio requesting emergency services less than a dozen times. If I had to guess, I would put the number closer to the 6,000 side than the 40 side, but even if 1 in 40 was correct, 39 pilots out of 40 not having declared an emergency seems to contradict the statement of the inspector.
Conclusions
The TC inspector could be suffering from selection bias. If she or he deals with emergencies all day, it seems less likely that she would come into contact with the (seeming) majority of pilots that haven't declared.


Where is Ronda's airstrip, or why does Ronda have an airport code (RRA) if it has none? I'm puzzled by Ronda, Spain having an airport code.  Ronda has no airport.  I've never seen an airstrip anywhere near either,

Wikipedia notes that some railway stations have IATA codes, but notes that The IATA codes for railway stations normally begin with Q, X or Z, except when the station shares the code with an airport.  So according to the IATA codes it does not refer to the railway station.  ITA Matrix does not know RRA.

The tourist website andalucia.com includes Ronda in a list of unsurfaced airstrips, but uniquely without coordinates.  Other websites place the airstrip in or near the city centre of Ronda, which is untrue, as a topographic map confirms.

Does Ronda have an airstrip?  If yes, where?  If no, why does it have an IATA code?

Apparently, there is an airstrip a roughly 4 km east of the town, as confirmed by an IGN map, IGN aerial photography, and Openstreetmap (Thanks Muzer).  It does not give the impression of active use; a Panoramio photo shows a field of sunflowers.  Its full name on the topographic may is Pista de aterrizaje de CMA, which means Runway of the CMA, where CMA may be Consejería de Medio Ambiente, ar the Andalucian government's Ministry of the Environment (thanks Henning Mankolm).


Which international routes might save fuel and time by using a potential newly "deemed safe" North Korean air space? The Reuters News item Exclusive: U.S. blocks North Korean air traffic revival ahead of Trump-Kim summit - sources says:

  If the space was deemed safe, international airlines could save fuel and time on some routes between Asia and Europe and North America, and North Korea could begin reviving its own commercial aviation industry.

Question: Which international routes in particular, flown by international airlines could save fuel and time on some routes between Asia and Europe and North America by using newly "deemed safe" North Korean air space?

I think the biggest one would be Tokyo - Beijing, and more broadly, anything in Japan north of Osaka to Beijing.

The current airway turns does a dogleg up to right above Incheon airport, (you can literally see the airport and Seoul).

You can play with http://www.gcmap.com to see great circle maps, which are a good approximation of the most efficient route.


Please identify this unusual jump plane Can anyone identify this aircraft:
This plane was used in a horrible skydiving attempt where the person in the back attempted to climb out but was unable. As a skydiver, this made me very uncomfortable. I am guessing there is a large tail on this aircraft that would have made exiting fatal. The full video is here:

That is an Aero L-29 Delfin

Source: onespotter, photographer/copyright: Evgeniy Lebedev


Do you need to put your wings at the center of gravity when building an airplane? I have been wondering about this for quite a while and can't find an answer.

For supersonic speed, putting the wings near the center of gravity would be a good start. Even better, place the wing's center slightly aft of the center of gravity in a conventional configuration.

Lockheed F-104 in flight (picture source)

If you use rotating wings, placing their roots right above the center of gravity has worked well, too, especially if there is only one attachment point for them.

AS 355 Ecureuil helicopter (picture source)

If there is more than one attachment point, however, the rotating wings should be at opposite ends of the fuselage, quite a bit away from the center of gravity.

Boeing-Vertol CH-46 helicopter (picture source)

At subsonic speed it is advantageous to stretch the wings out sideways, so at least their tips are again quite a bit away from the center of gravity.

Nimeta single-seat glider (picture source)

And then there are some odd designs which try to separate the wings from the center of gravity as much as possible, and they still fly.

Rutan Proteus tandem wing (picture source)

So there is no general rule. Maybe these answers help to answer your questions about wing placement relative to the center of gravity.


What does a sport pilot have to do to get a private pilot certificate in the US? What are the minimum requirements for obtaining a privates pilot certificate if a pilot  already has a sport pilot certificate?

The requirements for a private pilot certificate don't changes because you already have a sport pilot license. However by successfully obtaining a Sport Pilot certificate, you should have already completed some of the private pilot requirements.

How much of your sport pilot training counts towards your private
pilot license?
How much of the training will have to be re-done?
Does it depend on
the type of your flight instructor's certificate?

If you hold a Sport Pilot certificate and are looking to upgrade it to a Private Pilot certificate, your best bet is to use the requirements of Part 61 Subpart E. All of the flight time you logged earning a Sport Pilot certificate applies towards Private, but additional hours and types of flight time need to be logged.

The requirements for each are paraphrased below. You'd have to log the difference, which is a minimum of 20 hours, including another 5 hours of dual and 5 hours of solo. There's a lot more to it than what I reference below, but this is the basics.

How much of the training will have to be re-done? This should vary wildly from pilot to pilot. You'll need to redo training as required to meet standards. If you're transitioning right away, theoretically none, but it's likely that some retraining will be required.

Does it depend on the type of your flight instructor's certificate? Yes.  If the instructor has only a sport pilot instructor certificate, none of the dual instruction hours are able to be counted for the private pilot dual hours criteria.  They are not an "authorized instructor" for private pilot privileges.  If the CFI had a CFI-airplane certificate then those dual hours working towards the sport pilot certificate will count toward the dual hour requirements of the private pilot.

See the Kern INK Interpretation

Required for Sport (citation)

20 hours of flight time, including at least:
15 hours of flight training from an authorized instructor and at least:
5 hours of solo flight training in the areas of operation listed in §61.311

Required for Private (citation)

40 hours of flight time that includes at least:
20 hours of flight training from an authorized instructor and:
10 hours of solo flight training in the areas of operation listed in §61.107(b)(1)

If you've chosen a flight school that operates a Part 141 program, you get to do it all over. Hooray!


Any idea what this Ampaire plane is? (Source)
This is certainly not the Ampaire 337 or Electric EEL, which is a converted Cessna 337. It looks like a boundary layer ingestor. Being from Ampaire, it probably is electric or hybrid.
I've tried to find more information about this craft, but failed so far, even from their own website (including the linked page). Google seems to think it's a Learjet. I don't think I've been able to find much, if any other photos of this plane.
The foreground seems to indicate this was a real photo taken from another plane, as you can see window sills, details generally absent in renderings (and many show-off photos). I must admit though, that's not the safest flying around.
Even if it's a rendering, it would probably be a concept. I can't even name the plane yet.
It's beautiful.

It's called the Ampaire Tailwind, and as this article explains, it only exists in scale models and renderings at the moment.


Why doesn’t the minimum drag point meet the point at the best Cl/CD polar? On the first picture, it shows that the minimum drag point is exactly the same as the maximum L/D ratio where it also supposes to be at The point as it shows on the second picture. However, according to the third picture, it doesn’t look like the minimum drag point is at the maximum L/D on the second picture. Why does this happen?

"Minimum drag" at 2deg in image 4.3 is just minimum Cd (coefficient not force). It is the most streamlined position and you will generate the least amount of drag here, for a given speed. You won't generate much lift though, if any. In fact, if you want to fly level (ie. at 1g) you will have to fly so fast that the drag will still become expensively large. Larger that if you were to fly at a more optimum angle of 5deg.
If Cl was constant over aoa, the best Cl/Cd would indeed occur at minimum Cd. ( a fixed quantity divided by the smallest ammount), alas Cl and Cd both increase with increasing aoa, reaching a best Cl/Cd ratio (in your example) at 5deg in image 4.7.
After that point, the Cd will increase a lot more than Cl, thus making the ratio worse.


Should "Thrust Reduction" and "Acceleration" heights be the same for the Boeing 737 NG? Should the Thrust Reduction height be the same, lower or higher than the Acceleration Height?
In other words, what is their "correct" sequence.
I am referring specifically to the B737NG, if it makes a difference.
And I am assuming no Noise Abatement procedures are in place, nor any obstacle clearance requirements.
Just assume one takes off towards the open sea.
I have already read the thread What determines the "acceleration" and "thrust reduction" heights? but it did not answer my above "simpler" question.
I always thought one does not reduce thrust before cleaning up but reading some posts I am in doubt now.

In absence of any other constraints, both thrust reduction and acceleration should be initiated at 1000 feet above aerodrome elevation:

Flap Retraction Schedule
During training flights, 1,000 feet AFE is normally used as the acceleration height
to initiate thrust reduction and flap retraction. For noise abatement considerations
during line operations, thrust reduction typically occurs at approximately 1,500
feet AFE and acceleration typically occurs between 1,500 and 3,000 feet AFE, or
as specified by individual airport noise abatement procedures.

(Boeing 737 NG FCTM 3.32 - Takeoff and Initial Climb)
Regarding your thought of

I always thought one does not reduce thrust before cleaning up but reading some posts I am in doubt now.

It is actually quite normal to reduce thrust before accelerating and retracting flaps. During NADP 1 (Noise Abatement Departure Procedure), which is most common around the world, thrust is reduced first (typically between 800 and 1500 feet) and acceleration is initiated later (typically at 3000 feet). For NADP 2 both occur at the same time. I don't know any procedure where thrust reduction occurs after acceleration.

Both heights can be set independently on the TAKEOFF REF page 2:

Thrust Reduction (THR REDUCTION)
Altitude above origin airport elevation at which the autothrottle reduces from
takeoff N1 to climb N1.
The default value is determined by the airline and is stored in the model/engine
database. The default is displayed in small font.
Manual entries allowed on the ground. Entries must be between 800 to 9,999 feet
and are displayed in large font.
Acceleration Height (ACCEL HT)
Displays acceleration hight for flap retraction.
Default value is from the airline.
Entry is optional. Value is a height from 400 to 9999 feet.

(Boeing 737 NG FCOMv2 11.40 - Flight Management, Navigation - FMC Preflight)


Why haven't helicopter CAT III procedures ever been developed? Why is there no helicopter equivalent to air transport CAT III ILS?  This PPrUNe thread discusses that some helicopter manufacturers have tested coupled approaches down to very low visibility minima (perhaps even zero-zero), but it seems that even with the current capability levels of autopilot technology and ILS ground station sophistication, there's no way for a helicopter to land in minima below RVR 1200'/DA 100' (i.e. the "half minima" rule applied to a standard ILS, or a COPTER ILS procedure).

Because many copter autopilots are capable of flying a Cat I ILS to 200AGL, and then descending on autopilot into a hover at a pre-determined altitude above the runway. The pilot can then descend down to the runway surface without any forward visibility. The radar altimeter is used to judge distance to the ground. Because of the unique capabilities of helicopters and their autopilots, Cat II and Cat III are superfluous.


What is that A340 cockpit panel on the glareshield? I want to know the panel's name and how it works. This picture is an Iberia Airbus A340-600

That display is part of the AFS (Auto Flight System) Control Panel on the FCU (Flight Control Unit):

(Airbus A340 FCOM - Auto Flight - General)

The general idea of the FCU is that you can push in the knobs, which will put the respective autoflight mode in an automatic setting (called managed mode) and show dashes in the display, and you can pull the knobs out and then rotate them to manually overwrite values (called selected mode).

In your example, the display currently shows:

SPD 250: The autothrust system is maintaining a manually selected speed of 250 knots.
HDG ---⚫: The lateral autopilot mode is in managed mode, meaning the aircraft will follow the flight plan programmed into the FMGS. See also this answer.
ALT 08000: The current target altitude for the autopilot is 8000 feet.
V/S -1000: The vertical autopilot mode is to maintain a manually selected descent of 1000 feet per minute.

The FCU allows you to switch between selecting a heading (HDG) vs. a track (TRK) and a vertical speed (V/S) vs. a flight path angle (FPA) with the button at the center. The HDG and V/S in the center of the display mean that the current mode is in heading and vertical speed.


What is a high speed stall? I'm told that planes can actually stall when the airflow over the wing goes past Mach 1?  Why does this happen and how do you design an aircraft to avoid it?

When the velocity of the airflow locally exceeds speed of sound above the wing a shock wave forms and the flow detaches beyond this shock wave.

Similarly to stall, the supersonic separation of flow removes the component of lift produced by decrease of pressure on the upper surface of the wing and so the effects are similar.

I causes reduction of lift and because centre of pressure is about quarter chord on the upper surface, but midchord on the lower, it causes a significant pitch-down moment, which might be impossible to recover even if the post-stall lift is otherwise sufficient to keep the aircraft flying straight. This effect is often called Mach tuck. Supersonic planes often have all-moving elevators to have sufficient control authority to compensate for it.

A difference from normal stall is that after supersonic flow separation the lift remains proportional to angle of attack and so the aircraft continues to behave more or less normally except for the change in trim.

Mach tuck may occur as low as Mach 0.7 depending on aircraft design, because the air moves faster over the wing. It can be delayed by using swept wings, because the shock waves only form when the air velocity component perpendicular to the wing exceeds speed of sound.

Supersonic aircraft eventually encounter supersonic flow separation, but the lower surface lift is sufficient to balance the aircraft weight at that speed and altitude and the aircraft can continue flying with the upper surface flow separated.

That's not the case with most subsonic aircraft, which for efficiency reasons tend to cruise at altitudes where they have very small margin to stall. As the stall speed increases with altitude while speed of sound slightly decreases with the lower temperature there, the stall speed will eventually equal critical mach number, which creates the coffin corner and absolute ceiling for the aircraft. For most civilian transport aircraft the range between stall speed and critical mach number (where drag increases and supersonic flow separation would begin) reduces considerably at cruise altitude, but they usually don't have enough engine power to reach the actual coffin corner.


Is the maximum power the Merlin 61 reciprocating engine occuring at its maximum RPM? Looking at the stats breakdown on Wikipedia here for the Merlin 61 series reciprocating engines used in Spitfire planes, I noticed that maximum horsepower is given at approximately 3000 RPM. But AirPages has what looks like a manual here that lists the maximum RPM as 3000.

Are they simply stating that the same thing: that torque starts to fall off at 3000 RPM? Or are they saying that the engine is just physically incapably of spinning faster than 3000 RPM (seems unlikely)?

In the case of the first one, what is the (approximate) redline for one of these engines?

Power output of a reciprocating engine goes up with speed, and yes, maximum power is reached at maximum RPM. Considering the size and age of the Merlin 61 (27 liters displacement) it had a rather high maximum speed. Some contemporary engines ran even slower:

Daimler-Benz 601E: 2700 RPM for take-off, 2326 RPM continuous power
Daimler-Benz 605A: 2800 RPM for take-off, 2300 RPM continuous power
Allison V-1710-A: 2800 RPM
Klimov VK-107: 3200 RPM for take-off, 2800 RPM continuous power
Jumo 213A: 3250 RPM for take-off, 2900 RPM continuous power

Note that the considerably smaller GA engines still only allow a maximum speed of 2700 RPM. The smaller the engine becomes, the higher the maximum RPM will be. Model engines for RC racing easily top 50.000 RPM.

Age is also a factor. Modern engines run much faster, and the early rotary engines of WW I would run 1350 RPM, max. The radial engine of the Boeing Stearman which I once flew was limited at 1700 RPM, requiring me to throttle back when accelerating for a loop-the-loop so I would not overspeed the engine in the dive.


Do windows on the side of the fuselage increase drag? I wonder this because I'm not too sure glass is easier for air to travel over than metal.

The long length of an airliner fuselage ensures turbulent flow at the station of the cabin windows, so their only contribution to friction drag are the gaps between metal and polycarbonate. The transition from a laminar to a turbulent boundary layer happens before the windows start. In Sighard Hoerner's classic Fluid Dynamic Drag we find in Chapter V these figures on the drag of surface imperfections:

The size of the gaps and the dynamic pressure at their location drives their drag contribution. Let's assume the windows are 0.4 m high, the grooves 2.5 mm (0.1") wide and shallow enough to have a drag coefficient of 0.008. Let's further assume we talk of a Boeing 747-200 with 100 such windows per side and restrict the drag calculation to the crossflow over the vertical part of the gaps. The full opening area of all gaps is $2\cdot100\cdot2\cdot0.4\cdot0.0025$ = 0.4 m² or 0.078% of the reference area of the 747. Wikipedia gives the parasitic drag coefficient of the Boeing 747 as 0.022, so the windows contribute one threethousandfivehundreth of that drag. Negligible, in other words.

But there is another source of drag: The windows are heavier than the metal which they replace, and to carry them around will increase induced drag. If we again assume 200 windows for a Boeing 747-200 at 7 kg each (these are from pre-polycarbonate times!), they weigh a total of 1.4 tons. This is 0.8% of its empty mass and equivalent to 12-14 passengers. To find the impact of this mass on a long-range flight over 6000 NM, we can use the Breguet equation; once with and once without the 1.4 tons of additional mass. The empty mass of the Boeing 747-200 plus 50 tons of payload is 228,100 kg, its L/D is 16, the specific fuel burn of its JT-9D-7 engines is $b_f$ = 0.0000184 kg/Ns and the cruise speed is Mach 0.84, which equates to $v$ = 250 m/s in FL 350:

$$m_1 = m_2\cdot e^{\frac{R\cdot g\cdot b_f}{v\cdot L/D}}$$

When we use $R$ = 11,112 km and run this once with landing masses $m_2$ = 228,100 kg and again with $m_2$ = 226,700 kg, the difference in $m_1$ is bigger by a factor of 1.65 (the take-off masses $m_1$ are 376,584 kg with and 374,237 kg without windows), so carrying the windows around costs the Boeing 747-200 911 kg of fuel or 0.61% of the total fuel mass per flight. This is one onehundredsixtythird of the total drag - still not much, but fourty times as much as the absolute contribution of the windows to friction drag (if we assume that the 747 flies at the polar point for optimum range).

This explains why conversions of airliners to freighters almost always replace the windows by metal plates but don't care that much about the gaps they leave. In the case of the 747 pictured below they are certainly big enough to be visible from afar.

A Japan Airlines Boeing 747 passenger-to-freighter conversion featuring aluminum window plugs. (Photo credit: Flickr)


Maintaining straight and level altitude just a completely random question that I suddenly thought - doesn't straight and level flight prove that the earth's surface is not a globe? Once cruising altitude is reached, the plane remains at the same altitude for the entire flight until it starts to descend for landing. If earth was a globe, we would need to drop the nose of the plane every couple of minutes to compensate for the curve of the earth. Is this correct? Because on my most recent flight, we reached 2000ft altitude and my instructor told me to maintain this altitude for 30 minutes (which I managed to do). I asked why we don't need to compensate for the curve of the earth and he couldn't answer me. Sorry for the random question but it's been bothering me.

Set aside the barometric stuff.  The simple answer is that what we think of as altitude, on a sphere, is really distance from the gravitational source, the center of the sphere.  Therefore, a "constant altitude" is not maintaining the same plane in 3 dimensional space, but the same distance from the center of the earth.


How do high-wing and low-wing aircraft compare in terms of structural damage in a crash? Which type of aircraft is more likely to avoid damage to the aircraft structure: high-winged aircraft or low-winged aircraft?

What factors influence the type of damage usually sustained during a crash?

Regardless of wing position, a crash will damage most or all of the aircraft structure. Since low wings have dihedral, mild cases like a wheels-up landing will mainly affect the center fuselage rsp. the wing box. But most crashes occur in an odd orientation of the aircraft towards the ground, so at least one wing and the fuselage will suffer damage.

There are a few designs which will tolerate foreseeable abuse. On the Su-27, two long iron bars run along the lower fuselage and are the first to contact the ground in absence of wheels. After such a landing, the aircraft is simply jacked up and put into service again.

Su-27 on the ground after belly landing (picture source). Just look at the paint job – the abuse this aircraft suffered is not restricted to this unorthodox landing style.

The main gear of the A-10 only partially retracts, so the bottoms of the wheels stick out of the gear bays and will contact the ground first. A belly landing with an A-10 will require a bit of repair but normally the aircraft is back in the air within a week.

A-10 on the ground after belly landing (picture source). The landing gear design is on purpose: It limits damage in a belly landing. Few aircraft have been designed with such foresight.

Similarly, for tail strike testing a bumper structure is added at the lower rear fuselage. In absence of such precautions, lengthy workshop stays are unavoidable.

But most crashes are less benign. The main factor in a crash is the relative velocity between the aircraft and the structure it crashes against. In most cases, this is a sizeable portion of flight speed, so the energies involved are immense (mass times velocity squared, divided by two).

Boeing 737 Crash site (picture source). As can be seen, both wings and fuselage are heavily damaged. The wing location was not a factor in the extent of the damage. That is how a real crash looks like. Unfortunately.