Are the size and location of the registration number regulated? On modern airliners, how large are the registration numbers?

I know they are on the tail, but are they also under a wing?

Do the regulations vary by country? If so, what is the US regulation?

Under FAA jurisdiction, these items are regulated under 14 CFR 45.

The size of the registration markings must generally be at least 12 inches high:

  §45.29

  (a) Except as provided in paragraph (f) of this section, each operator of an aircraft must display marks on the aircraft meeting the size requirements of this section.

  (b) Height. Except as provided in paragraph (h) of this part, the nationality and registration marks must be of equal height and on—

  (1) Fixed-wing aircraft, must be at least 12 inches high

The markings must be displayed on either the vertical tail surfaces or the sides of the fuselage.

  §45.25

  (a) The operator of a fixed-wing aircraft must display the required marks on either the vertical tail surfaces or the sides of the fuselage, except as provided in §45.29(f).

  (b) The marks required by paragraph (a) of this section must be displayed as follows:

  (1) If displayed on the vertical tail surfaces, horizontally on both surfaces, horizontally on both surfaces of a single vertical tail or on the outer surfaces of a multivertical tail.

  (2) If displayed on the fuselage surfaces, horizontally on both sides of the fuselage between the trailing edge of the wing and the leading edge of the horizontal stabilizer. However, if engine pods or other appurtenances are located in this area and are an integral part of the fuselage side surfaces, the operator may place the marks on those pods or appurtenances.

There are exceptions to these requirements, but these exceptions will not generally apply to the modern airliners referenced in your question.

While the regulations do not prohibit it, I think it would be unusual for the registration to be displayed in more than one location on a given side of the aircraft—for example, on both the tail and the fuselage.

Under ICAO requirements, these items are described under Annex 7.

Annex 7, paragraph 3.3.1 includes the additional requirement for heavier-than-air aircraft that the registration markings should be displayed on the lower surface of the wing structure.

  3.3.1 Wings. On heavier-than-air aircraft the marks shall
  appear once on the lower surface of the wing structure. They
  shall be located on the left half of the lower surface of the
  wing structure unless they extend across the whole of the
  lower surface of the wing structure. So far as is possible the
  marks shall be located equidistant from the leading and trailing
  edges of the wings. The tops of the letters and numbers shall
  be toward the leading edge of the wing.

The FAA has no such requirement, but other jurisdictions do, such as the UK's CAA, which is effectively identical to the ICAO guidance.

The ICAO size requirements for heavier-than-air aircraft are similar to FAA requirements, with the obvious exception of the wing markings. These requirements are found in Annex 7, paragraph 4.2:

  4.2.1 Wings. The height of the marks on the wings of
  heavier-than-air aircraft shall be at least 50 centimetres.

  4.2.2 Fuselage (or equivalent structure) and vertical tail
  surfaces. The height of the marks on the fuselage (or
  equivalent structure) and on the vertical tail surfaces of
  heavier-than-air aircraft shall be at least 30 centimetres.

Note that 30 centimetres is approximately equivelant to 12 inches, and 50 centimetres is approximately equivelant to 20 inches.


Is this the first single-engine helicopter clean-sheet design since 1976? An upstart in the helicopter business, Marenco Swisshelicopter, claim their SKYe SH09 is:

  “the first single-engine helicopter designed with
  a clean sheet of paper” since 1976.

  If you compare this market with the
  automotive market, it’s like we’re competing with cars from
  1976 whose only upgrades have been airbags and a GPS
  scrolling map. The market has not seen real innovation in
  years.

What 1976-design are they referencing and how accurate is their claim?

Most modern helicopters use two engines for added safety. This reduces the field of competing designs. Also, a good engineer will always leave proven details unchanged and focus on improving flawed designs. So it is hard to prove that a new design from an established helicopter company will truly be a clean-sheet design.

The possible new designs from 1976 could be:

Aerospatiale AS-350 Écureuil: First flight 1974, introduced 1975. Note that the AS-355 is a two-turbine variant of the single-turbine AS-350.
Robinson R-22: First flight 1975, introduced 1979. It has a single reciprocating engine and was indeed a clean-sheet design by Frank Robinson who started the company in 1973. He had worked previously at Bell Helicopter and Hughes Helicopters.


How does gross weight affect the Minimum Controllable Airspeed (Vmc)? I am about to get my MEL added to my CFI, and I cannot get my head around the multiple explanations for how gross weight affects Vmc.
The accepted answer is that The higher the gross weight, the lower is the Vmc.
I have been proffered two contradictory explanations, from both internet articles, manufacturer documents, and other CFIs, both of which seem to me (I have an MSME masters degree in Aero) to be flawed.

That because the aircraft is slightly banked into the direction of the good engine, the horizontal component of Lift (HCL) opposes the yaw from the rudder, thus allowing the aircraft to slow to a lower airspeed before full rudder authority is required to counteract the yaw from the operating engine.
This is wrong, because if you're in a bank, the HCL (by definition, it is HORIZONTAL!), is no longer lined up with the lateral axis of the aircraft. It is misaligned by exactly the bank angle, so, although there is a component of the HCL opposing the yaw force from the rudder, there is an exactly equal and compensating component of the Vertical Component of Lift (VCL) that will be augmenting the Yaw force.  This argument is bogus.

I mean if you think about it simpler, the Lift vector is always, ALWAYS, perpendicular to the wings, so that any effect of Lift along the lateral axis (parallel with yaw forces), must necessarily be zero.
The fact that is not aligned with the earth horizon is irrelevant.

The other rationale I have been presented with is that as the gross weight increases, the resistance to motion (Engineers would call this rotational inertia) increases, and makes the aircraft more stable. This is true, but it is an argument about dynamic stability, not about static stability. In other words, this affects the aircrafts resistance to changes in yaw/sideslip angle. Vmc is about static stability, i.e., at what airspeed does the aircraft, in a static, (unchanging) zero sideslip angle, require full rudder defection to hold the aircraft (STATICALLY) at that zero sideslip angle against all the yaw forces being produced by all the factors resulting from Asymmetric thrust?
So this argument or rationale also seems to be incorrect to me.

Where is the flaw in this reasoning?
By the way, the only effect of Gross weight on Vmc that I can think of is the obvious one, The higher the gross weight, the greater the Angle of Attack required to hold 1 G (Level flight), and obviously, both P-Factor and adverse yaw increases with AOA. So the higher the Gross weight, the greater the P-Factor, and the greater the yaw-induced aerodynamic effects of the asymmetric thrust. So, if this logic is correct, Higher Gross weight means Higher Vmc, not Lower.

I think your objection to #2 is exactly correct, and your #1 is where the misunderstanding may lie.

The point of VMCA is essentially to maintain a constant heading, and when you have no more rudder authority to make that happen, you're there -- and any slower, with slightly less rudder authority, your heading starts to change in the direction of the dead engine.  With no bank, it's all rudder; the lift from the wings doesn't tend to move the nose in any direction.  With bank, there is now a component of the lift from the wings that does tend to affect heading (which is the dynamic of banking when you turn -- the heading change comes from the lift created by the wings, not from the lift generated by the rudder).

If you are banking into the good engine, that component of lift tends to change your heading toward the good engine and away from the failed engine.  Since the asymmetric thrust is working to change your heading toward the failed engine while you hold rudder to oppose that change, you now have the component of lift from the wings that is assisting your rudder.

If you consider a case of symmetric thrust, you can hold a heading with right wing down and left rudder or vice versa; the lift from the wings is working to change your heading to the right, and your rudder is counteracting that drift. At some point, with enough bank, you run out of rudder authority & the airplane will turn, although pretty badly uncoordinated.  With an engine out, you CAN fly straight ahead holding bank into the dead engine, you just need a lot of rudder authority (i.e. lots of speed above VMCA) to hold your heading -- the rudder is fighting both the asymmetric thrust and the component of the wings' lift. And doing that, you'll run out of rudder authority a lot sooner (i.e. at a higher airspeed).  If you switch to bank into the good engine, the component of lift from the wings is now working with you, and that's the usual case for computing and demonstrating VMCA.

I suspect that the confusion on your point #1 comes by conflating horizontal (earth reference) with horizontal (aircraft reference). Hopefully the explanation above separates things out?

And, to bring things back to gross weight, the higher the weight, the greater the lift from the wings, so a Sin(5 degrees) (I think that's right -- LONG time since I took Trig!) component of "more lift" is a greater force to resist heading change than that same component of "less lift" with a lighter aircraft.  The other forces involved in the balance, the asymmetric thrust and the rudder force, are independent of aircraft weight.

Best wishes for your MEL checkride!


How can I find out if a close encounter in flight would be classed as an airprox? I was on a Jet2 flight LS257 which left Leeds Bradford (LBA) at 06.30 on Sunday the 11th of September 2016.

Approximately one hour and ten minutes into the flight we passed very close to a Ryanair jet going in the opposite direction. I know that distances can be deceptive but this was much nearer than any time I have ever seen in the past. I often watch for other planes and have seen them countless times at varying heights and going in all directions but this was extremely close in my opinion.

Is there a way to check how close the two aircraft were?

I've finally identified the flight you most likely saw out of the window. There was an oddity with Fligtradar24 where the data was missing for the flight, but I've straightened out that mystery.

First for the Flightradar24 oddity:
You were on B757 registration G-LSAE on from LBA to PMI. The previous flight that aircraft had taken was LS444/EXS4CX from HER to LBA. For some reason when your flight left LBA it was still showing on FR24 as LS444/EXS4CX. After it crossed into France over Le Havre it changed to showing as LS831/EXS81WF which is usually a flight from MAN to PMI. I can't explain this, but the registration, time and route matches exactly with the routing shown for LS257 on FlightAware, so this is your aircraft.

Now for the flight you saw:
There were only two RyanAir flights that you crossed paths with that might have been close enough to see. FR6462/RYR88FJ passed about 15-20 miles from you. But at 6:39 UTC over Lunay, a RyanAir B737, flight FR9052/RYR43EZ passed very close. I'm sure this is the aircraft you saw. According to the data, your aircraft was at 35,000 feet on a heading of 164° feet and the RyanAir was at 36,000 feet on a 12° heading. So, although the lateral separation was very close, the standard vertical separation of 1,000 feet was maintained.


How common are diversions to high-latitude airports for intercontinental flights? Comments to this question point out that diversions and emergency landings are not the same.

Many flights between Europe and North-America pass over (very) high latitudes and cold climates such as Greenland and northern Canada.  How common are diversions such as this one?  Or, more specifically, out of all scheduled passenger flights between Europe and North America, how many are diverted to high latitude airports?  For the purpose of this question, I am considering incidents where passengers were forced to leave the plane and change to one or more other planes, rather than a flight that lands and takes off again continuing to its final destination without passengers deplaning.

Very very uncommon. Goose Bay, Canada, is a diversion airport for US-Europe flights. If you search Aviation Herald for "goose", you will find about 2 to 3 flights divert there each year.

3 flights diverted in 2017:

Delta A330 Oct 20, engine problem
SAS A340 April 16, low cabin pressure
Air France A380 Sep 30, engine structural failure

2 flights diverted in 2016:

Virgin B787 Nov 22, engine oil leak  United B767 Sep 15, generator/APU failure

3 flights diverted in 2015:

American B757 Sep 30, electrical problem
Delta B767 July 31, generator failure
United B767 June 12, flight controls

2 flights diverted in 2014:

Delta B767 Aug 9, engine problem
Delta B767 May 1, engine shut down

In all these incidents except for 2, the report in Aviation Herald states a replacement aircraft was required. Sometimes the delay was 6 hours, sometimes the next day. In the 2 other incidents, it's unclear if a replacement aircraft was required or not, but in both cases maintenance was required, so at least a delay occurred.

This compares with a bird strike, or fumes/smoke in the cabin, almost daily somewhere. It's much rare than even lightning strikes, of which 25 were reported in 2017.


Is it necessary to have my full name (including middle name) on my student pilot license? So my student pilot license is missing a middle name, but my drivers license, written exam, and passport all have it printed.

I've spoken with the DPE, and he says it may be an issue, or it may not, and that he is going to look into it.

I've called FSDO, airmen certification branch, and other DMVesque organizations, and they all seem to say the same thing:

  Oh, you need to talk to (insert amorphous bureaucracy here)

Does anyone know who I actually need to talk to, or if this is even an issue? Do I just need to call FSDO and insist that they fix the issue, or what?

The DPE said that with the written exam being OK it may be a non-issue. Would love to hear from a DPE on here if possible.

Alright so here is the outcome:

I called FSDO, spoke with a real nice guy who told me to give him a call if I couldn't handle this online.

Called a zillion bureaucracies, all telling me to call someone else.

Called the nice guy at FSDO, set up an appointment for a name correction not a name change. Went to the appointment and was in and out in under an hour.

If you're having the same issue, I would recommend bringing every official identification you've got: passport, birth certificate, drivers license, etc.

Tl;DR call FSDO and tell them you need a name correction. NOT a name change. Can't stress that enough.


How does centre of pressure change with angle of attack? I've been given the distance of centre of pressure from the leading edge with a certain angle of attack and was wondering if it's possible to calculate the new position when the angle of attack changes.

This Wikipedia article explains that the movement of the center of pressure with changes in angle of attack depends on the airfoil shape.
In summary:

For a symmetric airfoil, as angle of attack and lift coefficient
change, the center of pressure does not move. It remains around the
quarter-chord point for angles of attack below the stalling angle of
attack.
For a conventionally cambered airfoil, the center of    pressure lies
a little behind the quarter-chord point at maximum lift coefficient (large angle of attack), but as lift coefficient reduces (angle of attack reduces) the center of pressure moves toward the rear.
For a reflex-cambered airfoil, the center of pressure lies a little ahead of the quarter-chord point at maximum lift coefficient (large angle of attack), but as lift coefficient reduces (angle of attack reduces) the center of pressure moves forward.

I do not have a simple expression that can be used to predict this movement of the center of pressure, but I suppose a computational fluid dynamics package can be used to model this for the specific airfoils used on the aircraft.


What's the difference between SLG strut used in B777 and truck position actuator used in any other aircraft like B747? Do they serve the same purpose ? If not what's different ?

The SLG strut (found on B773ER) is a truck position actuator on steroids.

The truck position actuator is used to bring the landing gear truck into a position suitable for stowing in the wheel well. This is true for all Boeing aircraft.

The SLG (Semi Levered Gear) strut on the B777-300ER is additionally used to increase T/O performance. During T/O the wheel truck is locked perpendicular to the strut, shifting the point of rotation from the middle of the truck to the aft wheel. Thereby the rotation pitch can be higher and the tail clearance during rotation is increased by about 30cm / 12in.

After selecting gear up it behaves like a normal truck position actuator, moving the landing gear truck into stow position before the gear is retracted. During landing it is disconnected and serves only as a shock damper.

Source:

FCOM B777-300ER
http://boeing.mediaroom.com/2003-06-18-Semi-Levered-Gear-Performs-During-Boeing-777-300ER-Flight-Tests


Is any readback required when ATC uses the phrase "RADAR CONTACT"? As the title says, is a readback required? I've heard some people say that it's not required, while some others say we should readback our call sign only. Some even say just push the transmission knob twice to inform the controller that we are acknowledging.

Which one is the correct action and what are the references or publications?

No. It is an information by the controller to let you know that you have been heard & identified. As he doesn't pass any relevant or critical information, there is no need to readback.
The same goes with e.g. wind information given by ATC.


What type of aircraft is this Airplane in Riga (junkyard)? My relationship with the Mil Mi-6 led me to this Wikimedia photo of a time-worn Mi-6 in Riga airport.

In the photo there are the Mi-6, a Skoda Fabia, some picnic equipment, other stuff and a supersonic jet fighter (is it really a jet fighter?) with a large, red "43" on the nose. Here it is a detail from the wikimedia photo

What airplane is the "43" red?

Bonus points for the white "27" on the left (but it's difficult because you have just a detail of the nose) and the jet bomber (?) on the right, partly hidden by the red metal ladder.

An Su-7U. I initially confused it with a Mig-21 and later with an Su-17 due to the similar nose cone, but you can see the exact airframe on the Museum's website:

The wing fences are a giveaway, as is the tail shape and slightly less prominent intake cone.
From the museum website:

At the beginning of 1960's Sukhoi Design Bureau finished to develop its new fighter-bomber Su-7B («Fitter») and another important task arised — to make two-seat training variant of this type. This objective was urgent because Su-7B was hard to control, especially on landing and critical flight stages. Two-seater, designated Su-7U («Moujik»), destined to make training process easier and quicker for pilots.
Nevertheless Sukhoi team managed to release first Su-7U prototype only in October, 1965 due to its high workload connected with evaluation of Su-7B and another projects. Trainer was a bit longer than Su-7B, also was unmounted one of the two cannons in order to reduce weight. The rest of the armament remained mostly the same. Crew seats were located behind each other under the separate canopies. Rear canopy was equipped with large retractable mirror to improve instructor's field of view on take-off or landing. Also instructor had full set of instruments and controls and was able to interfere in flight whenever he decided. Emergency ejection system allowed crew to leave aircraft in dangerous situations separately and safely.
Su-7U production commenced at Komsomolsk-na-Amure Aviation Factory in 1966 and continued till 1971, together with Su-7BKL and Su-7BMK manufacturing. Two-seater' export modification Su-7UMK was bought by Algeria, Afghanistan, Egypt, India, Iraq, Syria, North Korea, Poland, Czechoslovakia and took part in 1970-80's wars and conflicts. Soviet Air Force used Su-7U for very long time — till beginning of 1990's, because of its similar performance with Su-7B's successor Su-17.
Museum's Su-7U serialled 43-red and has production number 2318.


Are cargo aircraft ever ferried empty? If the amount of cargo is not evenly distributed across a network a freighter will sometimes have to fly a route not loaded to capacity. Do cargo freighters ever have to be ferried empty to alleviate this "back-haul problem"? The link uses the example of trucking, but my question is to what extent this issue manifests itself in scheduled air cargo (e.g. FedEx, UPS, etc.).

(Note: My assumption is that this affects scheduled air cargo operators more severely than specialty cargo operators doing "one-off" hauling of special goods)

Cargo airplanes are ferried empty in some situations, sure. Maintenance is a common reason, or one leg of charter cargo flights. It's pretty rare in scheduled cargo flights as it would mean there's not a single package going that direction, there's almost always something to take.


What are the statistical probabilities of commercial aircraft accidents? Is there any study showing how probabilities of various kinds of aviation (e.g. crash-landings, fatal crashes, mid-air collisions) accidents have increased or reduced over time?

Short answer

The International Air Transport Association (IATA) publishes each year a report about aircraft accidents in the world. The latest one indicates these average figures:

There are 3.3 billion passengers per year.
There are 100,000 flights per day.

Over the last four years the accident rate decreased from 94 to 73 accidents per year.

In 2014, among these 36,500,000 flights:

There has been a total of 73 accidents
12 accidents had fatalities (641 fatalities).

Extracts from IATA 2015 report

(Source: IATA report)

Period 2010-2014

(Source: IATA report)

Type and fatalities:

(Source: IATA report)

Geographical distribution:

(Source: IATA report)


What is the helicopter in the background of this image of the V-22 Osprey? I found a photo of a V-22 Osprey alongside an unknown helicopter on the left corner:

It's an MH-53 Pave Low.  In the Air Force Special Operations Command (AFSOC), the CV-22 replaced the MH-53, although there were several years when both were in the inventory.
From the look of the beach, this photo was taken near Hurlburt Field, Florida, which is where they were both based as the first CV-22's came on-line.  Hurlburt Field is also the headquarters of AFSOC.


Wind shear questions I had a discussion and I'm curious on an experienced pilots knowledge.  When taking off, let's say from telluride. You have a tailwind, but when you get off the ground you experience and windshear that turns into a headwind dramatically. What are the hurdles you'll face? At telluride it says to only land and take off on certain runways, so I know this could possibly happen. Also would the lift generated from the sudden increase in headwind cause the AOA to start increasing without you pulling back on the yoke???

A headwind gust for a given elevator trim condition will result in an increase in airspeed,
which will pitch the nose up.  The aircraft will also "balloon" upwards from increased lift.
Vertical rise will contribute to lower relative wind, but will also put additional downward pressure on tail, again raising the nose.  The effect will be temporary as AIRSPEED will rebalance to the air mass.

As always, the trim will only allow the AOA to increase a to a point before the tail goes from lift negative (downforce) to lift positive (upforce), preventing further increase in AOA.
An excessively forward CG with greater trim will make these effects more noticable.

The real danger under these conditions would be turbulence from the wind shear and
mountainous terrain.  In light recreational aircraft, one may wish to be very cautious about
air travel until weather improves.  In the mountains, wind speed and direction can be extremely localized and variable, and should be carefully monitored.


Will the Boeing 737 be built with a geared turbofan engine? I've been excited about the potential impact the new Pratt & Whitney PW1000G geared turbofan is going to have on aviation in the form of improved fuel efficiency. There are apparently already plans to retrofit the Airbus A320 with this new geared turbofan engine on the A320neo. The Boeing 737 is a close competitor with the Airbus A320, and could likely also benefit from a retrofit to a geared turbofan. During some hangar chat, I heard it said that there isn't room on the 737 to fit the wider geared engine.

Are there any plans to release a 737 with a geared engine?

If not, could this put the 737 behind its competitors, especially the A320?

The current 737 NG has only one engine choice, the CFM-56. Although this means less choice for the customer, it allows the manufacturer to focus on supporting only one type of engine. The comparable A320 has options for the CFM-56 and the V2500.

The A320neo effectively replaced the CFM-56 with the LEAP-1 and the V2500 with the PW1000G. The 737 MAX will replace the CFM-56 with the LEAP-1, and continue to provide only one engine choice. Note that on the A320neo both engines offer comparable performance overall, and orders are basically split between the two.

Although the 737 MAX is behind the A320neo in sales, it's unlikely that adding another engine choice would make much difference for the considerable expense it would require. The cheapest option is to use the PW1000G, and that still requires a lot of work for the manufacturer to integrate it into the airplane, and then test and certify the 737 with that engine. As with the LEAP-1 and CFM-56, Boeing would prefer to have their own minor version of the engine certified, which adds more expense. There's just no incentive to add another engine option at this point.

A future version of the 737 could possibly use a geared turbofan, but it's too early to tell if such a version will even be built. It certainly remains an option for future designs as engine manufacturers develop the technology further.


Does transport-type certification account for engine separation and its possible effect on hydraulic lines? This question is inspired by the United Airlines Flight 328 where the No. 2 engine is damaged.
Some multi-engine aircraft are design to withstand the detachment of an engine while some are not. Boeing 747 is designed to operate after an engine detaches from the pylon. In 1993, Japan Airlines 46E successfully landed after the No. 2 engine detached from the aircraft (1) In El Al 1862 and China Airlines 358, the detached engine struck another engine. Those are outside of the design scope. On the other hand, the detachment of an engine on a DC-10 would sever hydraulic lines to the control surface as in the case of American Airlines Flight 191.
Many twin engine aircraft are certified with ETOPS so that in the event that one engine failed, the aircraft can return to an alternate airport within the certified time span. However, the ETOPS scenario listed by FAA only includes engine shutdown but not engine separation. (2)
Are there any twin-engine aircraft that are controllable after an engine separation?

Unsure whether it is designed to withstand an engine separation, but Boeing 737 seems to have an engine separation memory items:
https://www.johanpercherin.info/airline-pilot-training/boeing-737-memory-items-engine-fire-severe-damage-or-separation/
And 777 has one as well:
https://www.theairlinepilots.com/forumarchive/b777/b777memoryitemsandlimitations.php


Why are there no commercial supersonic flights at present? I'd think that on certain heavily trafficked routes, especially ones with lots of business travelers, there would be a market for high-speed (supersonic) flights?

Why are there currently no supersonic commercial flights? (Or are there?)

There a several reasons for the demise of commercial supersonic aircraft.  And there is a strong possibility we may be able to take a ride on a supersonic aircraft by 2021.
Supersonic commercial aircraft have a lot of constraints on them which are not present on subsonic commercial aircraft and which military aircraft are not subject to.

Prohibitive Development Costs
Supersonic aircraft - and in particular high supersonic and hypersonic aircraft - are considerably more expensive to design and manufacture as they require the use of novel materials and manufacturing techniques in their design.  As you pass about Mach 2, heat starts to become a major problem, weakening traditional aerospace aluminum alloys to the point that they are no longer a viable material to construct an aircraft from.  The airframes also expand and contract considerably in the heat and this must be accounted for in the design.  Designers are forced to seek out more exotic materials like Titanium alloys, high temperature composites, etc.  and it is not just structure that requires novel materials to address this - fuel systems, electrical wiring, mission systems, even sealants and paint all must be chosen so as to combat heat but still satisfy traditional design metrics like safety, durability, and economics.
The result of this are very high development costs:  Adjusted for inflation, Concorde costs the governments of England and France some $28 billion or roughly 5 1/2 times the cost that Boeing spent to develop the 747.  Similar figures were consumed on the design and development of the ill fated Boeing 2707, which never progressed past the mockup stage, even after re-design.
Limited Cabin Capacities
Super Sonic Transport (or SST) design favors a slender, needle-like fuselage which limits the number of people which the jet can carry.  The Concorde was limited to approximately 100 passenger in very narrow seats; the 2707 could carry 260 people but had a length of over 300 feet making it very awkward and unruly in existing terminal aprons or taxiways.  This also makes the SST very unprofitable for its operators, as Concorde proved.  Over the last 50 years no more than 20 SSTs have ever been operational and all with only three airlines - British Airways, Air France, and the Soviet Aeroflot - all of which were heavily subsidized by their respective governments.
Propulsion Inefficiencies Restrict Range
Design of SSTs have in the past been hampered by the high fuel consumption rates of turbojet engine imposing a design range limit of approximately 4,500 NM.  This effectively curbs sales to airlines looking for SSTs to fly the pacific rim routes where the times savings offered by a supersonic aircraft would be the most pronounced.
Supersonic Flight Over Land Still Prohibited
Supersonic aircraft generate noxious sonic booms which can cause damage to fragile structures on the ground and generally are a nuisance to the inhabitants below.  While advancements in quiet supersonic transports are happening, global aeronautical regulation bodies still prohibit supersonic flight over land, restricting an SST to subsonic flight over these regions, making its operation exponentially more expensive than a traditional subsonic aircraft.
Concerns Over Safety Operating in Rarefied Atmosphere
A high speed SST would be required to operate in the higher parts of the stratosphere in excess of 60,000 feet.  While this is achievable for military pilots in full pressure suits, there are considerable risks to civilians in street clothes at these altitudes should a rapid decompression occur.  At these heights a rapid decompression will boil your blood inside your veins (very painful way to die).  It also cannot be combated with traditional supplemental oxygen systems, making such a scenario very dangerous for passengers.
Environmental Concerns
The 'dirty burning' turbojet previously discussed create a lot of NOX emissions, far more that today's high bypass turbofans, which poses risk of increased depletion of stratospheric ozone.
Cost Savings
A conventional high bypass turbofan subsonic airliner is between 16-20 times more efficient on a cost per passenger per NM basis. A typical transatlantic ticket on a 747-8 is approximately 1500 USD.  A ticket on the Concorde was about 11,000 in today's dollars.

Taken all together and faced with the reality of designing such a craft with 3 million parts, 6 million lines of software code, all tested and validated, which is restricted only to transatlantic routes, aircraft designers quickly see the handwriting on the wall and the aircraft is doomed from the drafting paper upward.
But that's not to say the supersonic dream is dead.  Aerion in Reno, NV and Airbus are in the process of developing a 16 passenger supersonic business jet, capable of Mach 1.6, with a tentative rollout and flight in 2021.  Areion claims the jet will have a 'boomless' cruise up to Mach 1.2 at or above FL350 and hopes this will coax regulating bodies into permitting supersonic flight over land.  Whether this attracts enough customers willing to pay the estimated $100 million price tag per aircraft remains to be seen.


Can I include my point of departure in the three landings for my commercial solo cross-country? I flew a cross-country with one stop on the way down: A -> B -> C
From A to C is over 250nm in a straight line and over 300nm total.
The next day I flew back: C -> A
That covers the 3 landings at intermediate (B), destination (C) and back at departure (A). But does the landing back at the departure location count as one of the three?

It depends on how you classify the flight. More importantly, it depends on how the DPE classifies the flight. Most people consider any flight with a stop longer than a fuel break as the end of the flight at the fuel stop, and the beginning of a new flight at the subsequent start up. Some sticklers would consider anytime you shut down the engine on the ground, the end of that flight.
You can log it any way you want. I doubt any DPE will count a flight with an overnight stopover between legs as one flight.
Here is an alternative. Takeoff at Airport A. Fly a closed traffic pattern to a full-stop, taxi-back landing. Fly to Airport B where you perform a full-stop, taxi-back landing. Fly to Airport C where you perform a full-stop landing. As long as the straight line distance between A and C is more than 250 Nautical Miles, your total distance is over 300 Nautical Miles, and you are either solo or performing the duties of PIC with an instructor, you should be good for the FAA Title 14 CFR Part 61.129(a)(4)(i) requirements for a commercial pilot.
Note that the regs don’t stipulate a full stop, taxi-backs. If you are flying solo, it gives you time to set up for the next leg. Although it is hard to believe that there is not another suitable airport in 300 Nautical Miles. In what area are you flying?


Do helicopters have trim? How does it work? I recall having read somewhere that “helicopter in forward flight behaves just like a badly trimmed airplane”. So I'd like to ask:

Do helicopters have trim?
If so, how does it work?
And is the helicopter stable when properly trimmed?

It depends on what you mean by trim.

If you mean a a mechanism that allows the pilot to reduce the control forces in order to allow the helicopter to be flown hands off, then the answer is a qualified yes.

If you mean a trim tab attached to a control surface, then the answer is no. Many airplanes which have a trim control do not use a trim tab. For example, Pipers have an anti-servo tab on the elevator, which the pilot uses to reduce control forces.

Since helicopters are unstable -- meaning if you take your hand off the cyclic the aircraft will be in an unusual attitude within a second -- nothing short of electronics and actuators will allow a heli to be flown hands off.

But every heli except the smallest ones, have considerable stick forces, which make them difficult to impossible to handle without some kind of assistance.

The simplest setup is what you find on the original 4-seat R-44 Astro, which lacked hydraulic assist. On top of the cyclic you will find a 4-way "hat" switch which uses electrical actuators on the cyclic to reduce the control forces necessary to fly it.

Larger helicopters have hydraulic assist, which allows the copter to be controlled with just two fingers. Inop hydraulics is considered an emergency.

Big helicopters have a stability augmentation system, which allows the helicopter to be flown hands off. An SAS is required for IFR flight.


Why is a class 2 medical not valid in Canada? Upon reviewing the requirements for the Recreational Pilot Permit and Private Pilot License in Canada, I see that only class 1, 3 and 4 medicals are approved.

Are EASA class 2 medicals not valid in Canada at all?

The Cat 2 medical in Canada is only for Flight Engineers, Navigators (once upon a time) and Air Traffic Controllers.  https://www.tc.gc.ca/eng/civilaviation/publications/tp13312-2-menu-2331.htm


How is RVSM approval obtained for a properly equipped airplane? If an airplane is already equipped for RVSM flight, how do we obtain a Letter of Authorization (LOA) for RVSM in order to actually fly in RVSM airspace?

You can find lots of information on RVSM at this FAA website.

From This MSWord document found on that site:

  Operational Approval or Authorization.   The FSDO or CMO will grant operational approval or authorize the operator to conduct RVSM operations by issuing Operations Specifications paragraphs B046 and D092 to air carriers or issuing a Letter of Authorization (LOA) to general aviation operators, as appropriate.  Individual operator RVSM-compliant airframes are listed in D092 or on the LOA, as appropriate.  The FSDO or CMO will take this action after it has determined that the operator’s aircraft are RVSM compliant; it has approved the operator’s RVSM maintenance program; a CMO has approved or a FSDO has accepted the operations programs and the office has accepted the operator’s plan for participation in the monitoring program.

This Excel spreadsheet lists points of contact at various FSDOs.


Why are some aircraft built in a single country, whereas others are a collaboration of many countries? The USA has developed numerous aircraft; Sweden developed the JAS Gripen and France developed the Rafale, by themselves.

But most of the modern aircraft developed by the UK and Germany needed collaborations. Yet both of them have the technology and enough money to build aircraft on their own. Why did the Eurofighter need collaboration among four countries?

On the other hand being a collaborative effort, the F-35 became one of the most problematic projects in aircraft history. So why collaborate?

Why did Eurofighter need collaboration among four countries?

For production volume.

We are still in an era of relatively low-volume high-value combat aircraft compared to the early years (say pre 1950).

Cost per unit is less if the development costs are spread over a greater number of manufactured units.

Individual European nations each have requirements for relatively small numbers of aircraft. If they each develop and manufacture their own aircraft, costs to each are likely to be higher.

Politically, it is easier to sell a military aircraft to politicians whose countries benefit from the manufacturing.

There are also benefits in sharing development costs.

Given the close economic, political and military ties between European countries, collaboration makes sense.


What is this small black rubber strip protruding out of the flap track fairing of the A320? On the Airbus A320 wing there in whilst in flight a small black rubber strip protruding out of the flap track fairing. What is it please?

It appears to be one of the rubber seals that are on the moveable flap track fairing.

source

Since the fairing moves away from the wing it has probably come loose and is caught between the fairing and the flap.

I can't find a good photo of a fairing from an A320, but here is a photo of the fixed fairing from an A350. It's hard to tell if they are exactly the same, but you can see that they look similar.

source


How do I simplify explanations for the drag formula? With reference to aircraft aerodynamics:

As the aircraft speed increases the aerodynamic load increases in a
mathematical relationship proportional to the air density and the square of
velocity.

What does the above statement mean in layman's terms? Consider explaining it to a high school student.
Also, what's the simplest explanation for the drag formula too?

Fd=1/2 *Density *Velocity^2 *Coeff. drag *Area

Part 1:
As an aircraft travels faster, drag increases more in thicker air (usually lower to the ground) more than it does in thinner air (usually higher in the atmosphere).
Also, doubling speed quadruples drag.
Part 2:
Force of Drag (self-explanatory) =
Density (the thickness of air or how many molecules there are in a cubic meter) * Velocity^2 (the aircraft’s speed multiplied by its own value)
divide this value by 2
then multiply by Coefficient of Drag (basically, a value that shows how easily an object will slide through the air)
finally, multiply by Area (how much surface is actually in contact with the air. Obviously, a bigger object will interact with more air, increasing drag).
Hope this helps!


Can a US pilot fly a German D-xxxx aircraft in Germany? Can a pilot with a US FAA certificate and a proper rating legally fly a D-xxx German-registered aircraft within Germany? How about the rest of the EU? Does it matter which type of aircraft? I'm most interested in gliders, but the question is more general.

No. A US licenced pilot can not fly a German registered aircraft in Germany.

Generally you must always have a pilot licence issued by the state that the aircraft is registered in.

Obtaining a licence for that country can be relatively easy based on the fact you already have a licence from another country, but you will need a new licence or some kind of documentation issued by the governing country.

There is an FAA rule that allows a US licenced pilot to fly a foreign registered aircraft the USA, but I think this is rather unique as I believe no other country allows this.


How can an airplane keep going forward if it has no thrust? Every pilot is familiar with the basic model of aircraft forces:

If lift is greater than weight, the plane climbs, if less, descends.  If thrust is greater than drag, the plane accelerates, if less, decelerates.  In unaccelerated flight, all must be equal.

In an engine-out situation, there is no thrust, so if a constant glide ratio is to be maintained, I thought the plane must be pitched forward so the forward component of lift does the job thrust would normally do in cancelling drag.

However, in the Airplane Flying Handbook, 4-3, figure 4-2, it shows an example lift-drag diagram that shows $L/D_{max}$ ($= V_{BG}$) to be about $6°$ AoA.  Wouldn't that result in lift having a backwards component and slowing down the aircraft to the point of stall?

What am I missing here?

Angle of attack is not equal to pitch angle. Yes you can decompose weight into a forward and a perpendicular component - to airstream! Or you can draw lift relative to airstream.

In this drawing, pitch angle is zero and AoA = 6 deg. Lift now has a forward component relative to gravity.


Do mechanical attitude indicators have rotation limits? Do mechanical attitude indicators have limits to the rotations they can display?
Wondering since gyros suffer from gimbal lock when two axes become aligned (e.g., at 90 deg pitch, if you were doing aerobatics?)
Digital gyros suffer from gimbal lock as well, though the cause is now the mathematics which loses one degree of freedom when two axes become aligned.

They do. When an attitude gyro is rolled or pitched beyond its limits, the gyro gimbals hit their stops and the instrument is said to "tumble".
Tumble resistance is more important in military craft, which traditionally use a gimbaling mechanism that can withstand any amount of roll without tumbling- which differs from those used in GA aircraft.
These two types of attitude indicators have names, and I invite the experts on this site to furnish them.


Why do flight schools refuse to tell me the price of a course? I have searched many flight schools' sites in my area and none mentions prices, I tried to contact by email and later by calling them, but they still won't tell me the price, why is that?
Shouldn't I know they price before I decide to do it?
Especially during a pandemic, they should definitely discourage you to pay meaningless visits to the academy for information on the cost and tell you right away?
Why do flight schools do that?

Mostly because what takes one individual 50 hours, will take another 75, and someone else 100.
For that reason, most if not all flight schools will only tell you 2 things

The minimum number of hours required to get the certification you're after (PPL, Night Rating, Instrument Rating etc).
The cost per hour of instruction, and the cost per hour of the various aircraft they use.

While we're on the subject, I should add that you should be wary of putting down a large upfront cost to any school. I have heard too many stories of flight schools going insolvent and students losing their money. Often you will see a discount for "block bookings" - if you can afford it pay just as you go, and if you do decide to upfront a block booking only spend what you could stomach losing.


What plane cost less per mile to operate for one person? The 98 Toyota Corolla has a strong history for being a low maintenance, fuel efficient and cheap car. 400k mile reliability if driven with respect and preventative maintenance.
What plane has these qualities with at least a 450 mile range? So I can fly back and forth to flight school instead of driving.
I am sure there are many that will fit the bill but I am looking something for beginners and the cheapest way to fly myself.
Second Scenario: Suppose only using the basic maintenance, without anything more than an oil/filter etc., which plane would last the longest. Obviously simpler plans require less money per nautical mile; of those which would last the longest?

No plane has these qualities, planes require a lot more servicing than cars both legally and practically. Similarly aircraft parts have service limits and heavily suggested rebuild times. Most if not all light aircraft require major servicing (or receive major servicing) at the 2000-2500ish hour mark.
There are comparatively little regulations on car maintenance. Most states require only a yearly inspection that boils down to a visual check of brakes, lights and a few other things as well as an emissions test mostly to keep the DEP happy.
Aircraft on the other hand require a verbose yearly "annual" inspection that can take days for a mechanic to complete. On top of that aircraft equipment needs to be routinely tested and checked for it to be legal for certain types of operation. On the contrary no one ever checks your cars speedometer or tach for proper operation.
Broadly speaking aircraft are also grounded if just about anything is not working where as most people often operate their car with small (or even large) issues. If you ever had an engine knocking issue in an aircraft you would be on the ground as fast as practically possible where as I know people that have driven cars thousands of miles with an "engine knock".
Airplanes also change substantially less than cars so small iterative fixes become difficult. If Toyota finds an issue in the 98 Corolla they can easily fix it in the 99 version. Fixing an airplane can require a lot of paper work, or if its a large issue an mandatory AD may be issued and everyone will be forced to fix it while 98 Corollas may still be out with their issues to this day.

If you just want a straight answer... A Piper Archer or a Cessna 172 (let the internet debates begin...)


What is the minimum weight aircraft in which someone can build logged flight time? What is the minimum weight aircraft in which someone can build logged flight time? Is logging flight hours in an ultralight possible?

There is no weight limit, requirement, nor restriction for logging time in a logbook. However, there is a requirement to only fly aircraft that are properly certificated, registered, and airworthy regardless of if you log the time or not. Part 103.7 allows ultralights to fly without certification or registration. If you are flying an aircraft not meeting certification, registration, inspection, and airworthiness standards, you are flying illegally unless it meets the weight, horsepower and other criteria of Part 103.1.

  §103.7 Certification and registration.
  (a) Notwithstanding any other section pertaining to certification of aircraft or their parts or equipment, ultralight vehicles and their component parts and equipment are not required to meet the airworthiness certification standards specified for aircraft or to have certificates of airworthiness.

  (b) Notwithstanding any other section pertaining to airman certification, operators of ultralight vehicles are not required to meet any aeronautical knowledge, age, or experience requirements to operate those vehicles or to have airman or medical certificates.

  (c) Notwithstanding any other section pertaining to registration and marking of aircraft, ultralight vehicles are not required to be registered or to bear markings of any type.

Combining this with Part 61.51(j) would prohibit the logging of ultralight experience gained today for the purpose of initial certification or currency.

  (j) Aircraft requirements for logging flight time.
  For a person to log flight time, the time must be acquired in an
  aircraft that is identified as an aircraft under §61.5(b), and is—

  (1) An aircraft of U.S. registry with either a standard or special airworthiness certificate;

  (2) An aircraft of foreign registry with an airworthiness certificate that is approved by the aviation authority of a foreign country that is a Member State to the Convention on International Civil Aviation Organization;

  (3) A military aircraft under the direct operational control of the U.S. Armed Forces; or

  (4) A public aircraft under the direct operational control of a Federal, State, county, or municipal law enforcement agency, if the flight time was acquired by the pilot while engaged on an official law enforcement flight for a Federal, State, County, or Municipal law enforcement agency.

Furthermore, Part 61.52 does not allow for the logging of ultralight experience gained today for the purpose of initial certification or currency.

  §61.52 Use of aeronautical experience obtained in ultralight vehicles.
  (a) Before January 31, 2012, a person may use aeronautical experience obtained in an ultralight vehicle to meet the requirements for the following certificates and ratings issued under this part:

  (1) A sport pilot certificate.

  (2) A flight instructor certificate with a sport pilot rating;

  (3) A private pilot certificate with a weight-shift-control or powered parachute category rating.

  (b) Before January 31, 2012, a person may use aeronautical experience obtained in an ultralight vehicle to meet the provisions of §61.69.

  (c) A person using aeronautical experience obtained in an ultralight vehicle to meet the requirements for a certificate or rating specified in paragraph (a) of this section or the requirements of paragraph (b) of this section must—

  (1) Have been a registered ultralight pilot with an FAA-recognized ultralight organization when that aeronautical experience was obtained;

  (2) Document and log that aeronautical experience in accordance with the provisions for logging aeronautical experience specified by an FAA-recognized ultralight organization and in accordance with provisions for logging pilot time in aircraft as specified in §61.51;

  (3) Obtain the aeronautical experience in a category and class of vehicle corresponding to the rating or privileges sought; and

  (4) Provide the FAA with a certified copy of his or her ultralight pilot records from an FAA-recognized ultralight organization, that—

  (i) Document that he or she is a registered ultralight pilot with that FAA-recognized ultralight organization; and

  (ii) Indicate that he or she is recognized to operate the category and class of aircraft for which sport pilot privileges are sought.

Weight is not a factor in logging time. And, there is no prohibition against putting things in your logbook that can not be counted for the purposes of initial certification or currency. Although, care should be taken with this. Your logbook is your property. However, your certification gives the FAA the right to inspect your logbook however it chooses. I have co-pilot time logged in a turbine-powered helicopter that I can never count towards anything.

There is also no prohibition against getting an ultralight registered and certificated as airworthy. It might be a lengthy and expensive (and probably improbable) endeavor. But, as soon as you do, it becomes an ultralight no longer according to Part 103.1

  §103.1 Applicability.
  This part prescribes rules governing the operation of ultralight vehicles in the United States. For the purposes of this part, an ultralight vehicle is a vehicle that:

  (a) Is used or intended to be used for manned operation in the air by a single occupant;

  (b) Is used or intended to be used for recreation or sport purposes only;

  (c) Does not have any U.S. or foreign airworthiness certificate; and

  (d) If unpowered, weighs less than 155 pounds; or

  (e) If powered:

  (1) Weighs less than 254 pounds empty weight, excluding floats and safety devices which are intended for deployment in a potentially catastrophic situation;

  (2) Has a fuel capacity not exceeding 5 U.S. gallons;

  (3) Is not capable of more than 55 knots calibrated airspeed at full power in level flight; and

  (4) Has a power-off stall speed which does not exceed 24 knots calibrated airspeed.


Can anyone Identify this FLY FAIR seaplane? This photograph, from my family's collection, of a high-winged, dual rotary engine, amphibious airplane, probably in the 1930's, appears to be an excursion plane at a fair since it has "FLY FAIR" written on the wing.  It appears to have the ID number of NC-155, or NC-156, or NC-158. It is difficult to recognize the last number.  I have searched and searched and not only cannot find other photos of this particular plane, but I can't find any photos of an identical plane.  I'm looking for Make, Model, and any additional information you may have. Your help is greatly appreciated.

That is a Sikorsky S-38B
I am not sure about the registration. My guess is NC196H, but it is one out of this list:

NC158H,
NC159H,
NC195H,
NC196H,
NC197H,
NC198H,
NC199H,

See aircrafthistory.org.uk
The FLY FAIR marking may be a reference to the 1933/1934 Chicago World Fair / "A Century of Progress International Exposition". Jamiec found this photo album by George Buivid on auction that documents a trip to the Chicago World Fair in Sikorsky's own S-38 aircraft:

Picture source: Flyingclippers.com Artist: Mike Machat

source: Wikipedia original source: NACA Aircraft Circular No.79


Did the Mig 21 have differential stabilators to help the ailerons? The MiG 21 had all-moving tailplanes or stabilators. When rolling, did one stabilator pitch up and the other down to act as secondary ailerons and help the main ones on the wing?

No.
MiG-21 (any modification) didn't need it and didn't have it. With its low-aspect-ratio delta wing and most mass concentrated in the centre, it was agile enough with standard ailerons.
The elevator had a single hydraulic booster driving both halves of the stabiliser.
Differential stabiliser was used on MiG-21's successor, MiG-23. That one had no ailerons at all; it had full-span flaps on its swing wing instead. Roll was controlled by the spoilers and the differential stabiliser.


(See Included ILS Chart) What to Do After SMT RDL 084? Below is a screen grab from the ILS RWY 25R approach chart for HKG/VHHH. What should the plane do after passing SMT radial 084 (or TD D8 NM)?

It doesn't look like immediately turn heading 253 degrees; from an algorithmic point of view does the plane do an RNAV from PLOVE to RIVER, then track SMT radial 253 after RIVER? Or does it start to track SMT 253 right after SMT radial 084?

Also, what does "ITFR" stand for in this graph? The ITFR distance measures from the east and west side of the runway are based on two different ILS localizers, is that correct? Thanks!

(Source: AD 2-94A, Aeronautical Information Publication, Hong Kong Aeronautical Information Services)

SMT RDL 084 is simply a lead radial, so it is there to let you know when to start your turn so that you can intercept the SIU 253 course without overshooting it during the turn.

Just below and to the left of the airport is the box which shows the ILS frequency.  It tells us that the DME identifier for this ILS is ITFR, so the distances are provided based on the distance from the DME transmitter associated with the ILS.


Why is the sound quality of onboard public address so bad? While not a frequent flyer, I did fly common airliners quite a lot, and each time the (very) low sound quality of onboard public adress system has always struck me.

We all know technology makes it possible to have a "HiFi" sound quality almost everywhere, so why don't major manufacturers (Boeing and Airbus) provide better sound quality systems?

While this is of course not mandatory to make an airplane fly, it is related to passenger safety. Better sound quality would allow crew instructions to be better understood during the pre-takeoff briefing and in the event of an emergency.

I have flown with several airlines, and there are already enough other factors that make it difficult to understand what's being said on PA:

On board noise: air conditioning, running engines, neighbors talking, kids crying, ...
Strong or difficult english accent when either the crew or the passenger are not english-native speakers.
Crew speaking really fast.

The airplane companies can't do much on the above items, but they can improve the technical aspects. Of course, I do understand that this would require increasing weight (loudspeakers are heavy...) thus reducing commercial load.

Side question: How do US/EU regulations handle this point? Do they have any specs on sound quality requirements?

Note: I haven't tried recent planes such as A380, so maybe it has been improved.

For the regulatory portion of this question.

  14 CFR 121.318

  No person may operate an airplane with a seating capacity of more than 19 passengers unless it is equipped with a public address system which—

  (a) Is capable of operation independent of the crewmember interphone system required by§ 121.319, except for handsets, headsets, microphones, selector switches, and signaling devices;

  (b) Is approved in accordance with§ 21.305 of this chapter;

  (c) Is accessible for immediate use from each of two flight crewmember stations in the pilot compartment;

  (d) For each required floor-level passenger emergency exit which has an adjacent flight attendant seat, has a microphone which is readily accessible to the seated flight attendant, except that one microphone may serve more than one exit, provided the proximity of the exits allows unassisted verbal communication between seated flight attendants;

  (e) Is capable of operation within 10 seconds by a flight attendant at each of those stations in the passenger compartment from which its use is accessible;

  (f) Is audible at all passenger seats, lavatories, and flight attendant seats and work stations; and

  (g) For transport category airplanes manufactured on or after November 27, 1990, meets the requirements of§ 25.1423 of this chapter.

  [Doc. No. 24995, 54 FR 43926, Oct. 27, 1989]

  14 CFR 25.1423

  A public address system required by this chapter must—

  (a) Be powerable when the aircraft is in flight or stopped on the ground, after the shutdown or failure of all engines and auxiliary power units, or the disconnection or failure of all power sources dependent on their continued operation, for—

  (1) A time duration of at least 10 minutes, including an aggregate time duration of at least 5 minutes of announcements made by flight and cabin crewmembers, considering all other loads which may remain powered by the same source when all other power sources are inoperative; and

  (2) An additional time duration in its standby state appropriate or required for any other loads that are powered by the same source and that are essential to safety of flight or required during emergency conditions.

  (b) Be capable of operation within 3 seconds from the time a microphone is removed from its stowage.

  (c) Be intelligible at all passenger seats, lavatories, and flight attendant seats and work stations.

  (d) Be designed so that no unused, unstowed microphone will render the system inoperative.

  (e) Be capable of functioning independently of any required crewmember interphone system.

  (f) Be accessible for immediate use from each of two flight crewmember stations in the pilot compartment.

  (g) For each required floor-level passenger emergency exit which has an adjacent flight attendant seat, have a microphone which is readily accessible to the seated flight attendant, except that one microphone may serve more than one exit, provided the proximity of the exits allows unassisted verbal communication between seated flight attendants.

  [Doc. No. 26003, 58 FR 45229, Aug. 26, 1993, as amended by Amdt.
  25-115, 69 FR 40527, July 2, 2004]

There are systems in place to increase volume in certain instances, eg, on the 767 both engines running gives a 6 dB increase and O2 masks dropped gives an additional 3 dB gain in volume.


Is there a symbols chart or legend for common aerospace equations? I've read a lot of answers on this site that make references to various aerospace equations.

So many of these are awesome responses, but I have trouble understanding the math because I don't know what all the symbols in the equation mean, or what units they are referring to.

For example, this question uses the equation below and even has a really cool picture to go along with it:

However when trying to understand the "mass flow" function I didn't see any explanation of what the lowercase "t" variable was.

I am sure this is common knowledge for many people, but are there are any charts out there for amateurs like myself to understand the different symbols commonly used in fluid functions and their implied units?

Or is this really a matter of needing to learn aerospace in general as the equations are too diverse to understand by a symbols cheat sheet?

Unfortunately, the nomenclature used can vary from source to source, and the same variables can even be used for completely different things depending on the context. It is generally good practice for the author to describe the variables they use, but we've all been guilty of skipping that step.

In any case, there are many helpful sites such as See How It Flies or the Aerodynamics Index from NASA that tend to use pretty 'standard' notation. BUT, there is no single cheat sheet that has every variable for every analysis and one should always be careful to double check.


What is this device they bring on board from the jet bridge when we park? Every time I deplane a Virgin America A320, I notice that they grab something from the jet bridge, and stuff it between the jump seats. I haven't seen any other commercial airlines with things like this.

It is a temperature probe for the preconditioned air (PC air) unit.

Bleed air is required in order to operate the air conditioning packs on an aircraft*. Thus, either an engine or the auxiliary power unit (APU) must remain running, burning jet fuel.  PC air pumps heated or cooled air into the aircraft and allows the pilot to shut down the engines and APU to conserve fuel.

This is what the system looks like from the outside:

A probe (located in the passenger loading bridge) is inserted into the cabin to regulate the air temperature while PC air is hooked up and running.

Upon parking, ground crews will typically hook up both ground electrical power and PC air, especially if the aircraft will be parked for any length of time. Since the air hose takes some time to unroll and roll, PC air may not be used if the flight is a "quick turn" and the APU will be left running.

* Except for the Boeing 787, which has a no-bleed system.


How many US airman's certificates are revoked, roughly, per year? There is a lot of literature devoted to FAA enforcement (see https://www.aopa.org/training-and-safety/pic-archive/faa-enforcement/faa-enforcement)

What is the threshold for revocation? The thing that specifically got me interested was a near collision runway video - assuming it wasn't an ATC/taxing instructions error, would this type of thing be sufficient? I'm also interested in what the appropriate penalty would be for that

FAA Order 2150.3B, Appendix B lists violations and the civil penalties (fines) and certificate actions which are to be imposed by the FAA. The rest of the document also discusses how investigations of certain violations are undertaken and thresholds. That order gives much more detail than you'd ever want to know.

A common theme is revocation is called for when the action is intentional.

These are what are the FAA initially charges you with, so they are higher than what actually happens. A certificate action is either negotiated as a settlement, or if it can't, it goes before an administrative law judge, then appealed to the NTSB, then appealed to the Federal court system.


Why do entertainment system headphones on aircraft have two pins? In most commercial flights where headphones are provided for inflight entertainment they have two pins, unlike single pin connections which we use on the ground (e.g. for mobile phones).
Is there a particular reason why it is done that way?

One reason could be that people can steal a single pin headphone. But still it is not compelling enough reason.

The three main reasons are:

Prevent theft of headphones due to incompatibility with home systems
Redundancy, if one connector breaks, the other will still provide audio
Before the 3.5mm jack was used, a pneumatic system was in use, which required two connectors.

This question has been asked on different websites already, but here is a detailed explanation that sums it up nicely:

There are a couple main reasons:
First, the airlines were trying to prevent theft of headphones. The two-pronged plugs have been around on airplanes since way before the airlines started charging for headsets. Back then, headphones were not usually easily carried around as the portable earbud style had not become popular yet. By using a two-pronged setup that is not used in most other audio systems, the motivation for passengers to steal the headsets went down immensely.
The second reason is redundancy. When a standard stereo headphone jack with three internal connections (right, left, and ground) breaks, you will often lose audio in both the left and right channels. However, with the two-pronged design, if one of the jacks breaks then there will still be audio going through the other channel. While this is annoying for the user, it is an easy way for the airline to defer maintenance on that individual seat's audio system until both the left and right channel are non-functional.
The two-prong design is a relic of the past, before headphones were bundled with so many of the mobile devices we now buy. Planes with updated inflight entertainment (IFE) systems usually have the standard stereo jack as most passengers prefer using their own headsets now. Slowly these old connectors will be completely phased out.
Another less obvious (and probably less likely, but interesting nonetheless) reason, though, is based on airline complacency. Airlines, especially US based airlines, are notoriously slow in changing their tactics. Back before the 3.5mm jack became the standard for headphone audio connections for IFEs, airplanes used a pneumatic headphone design. These headphones were similar to stethoscopes where hollow tubes would be plugged into the armrest which had actual soundwaves coming out (instead of analog electrical signals). These systems were much more reliable than the standard electrical system and the headsets themselves were very cheap to replace. Since the pneumatic system required two separate plugs for the left and right channel (since you cannot mix physical sound waves into a single hole), all armrests were designed with two holes for audio. Airlines were likely so used to having two jacks for audio that they continued with the same design when they switched to electrical audio signals.
(Source: www.quora.com - Author: Raj Misra)


Which map projection is typically used on ATC radar screens? Displaying a (roughly) spherical surface on a flat map turns out to be pretty difficult. There are many different map projections, each with their advantages and disadvantages. Some of the most common ones are cylindrical (Miller), conical (Lambert) and azimuthal.

On aviation maps and charts, I often see the Lambert conical projection used. This made me wonder: on an ATC radar screen, which projection is typically used? It is important that the controller can easily estimate both headings and distance by looking at the screen. For large sectors especially, an inaccurate projection might make this difficult.

Clarification: The discussion of whether the choice of projection will have an operational impact at all is an interesting one. My question, however, is not about how important the choice of projection is, but rather what projections are commonly used. I have a professional interest in this, even if the choice of projections is not operationally important.

Maybe different standards are used in different companies or different regions of the world. If that is the case, a brief summary of the most commonly used standards would be appreciated.

I can only speak by experience, and this is relevant to PALLAS installed in Greek ACC and LGAV approach. What I concluded while discussing with ATCOs is that the projection used is gnomonic. Unfortunately I haven't read any document to prove it (this is pure observation) and even if I had I couldn't cite it (for obvious confidentiality-related reasons).

Anyway, gnomonic is the projection I've used while developing the PALLAS simulator for HCAA and the results were identical. So what characteristics has the gnomonic projection:

Every straight line you draw on it, is part of great circle. This is of great importance since great circle arc between 2 points is the smallest distance between those 2 points. And when flying you want to avoid extra miles
It heavily distorts areas of the map away of the projection center, but gives a very good approximation close to the center. That makes it suitable for relatively small geographical ares.
You can never see a whole hemisphere. If you have a look at the article in Wikipedia, you will see why.

You might want to take a look at this picture which is not from the real system but the simulation. Unfortunately I don't have photo of the system that shows the concept, but I hope this does. Note the 19th and the 30th meridians that are straight lines (every meridian is a great circle arc) and how they converge to the north. Also note the blue-ish line measuring a random distance. This is guaranteed to be a great circle distance. So every straight line on the map, either from a tool like the one pictured or an airway, is a potential trajectory for an aircraft to follow. That way you see the "truth" each time you see a straight line.

Copyright: own work, tool DARSSY

PS: Now regarding your actual question of what projections are commonly used: others have mentioned stereographic while I mention gnomonic (and I'm pretty sure it is this one) for PALLAS. So there is no such thing as commonly. Projection is a tool. And as such you have to pick the right one for each situation. Now I don't know what your professional interest is, either a pilot, ATCO or a fellow developer wanting to write his/her own simulator (or even CWP???) in any case I would suggest you contact someone that knows the internals of the specific system you are interested in.

Regarding accuracy, you first need to address radar accuracy which is affected by coverage, track distance from the radar, atmospheric conditions and other factors that fall beyond the scope of the answer. Then you can wonder if it's worth the pain to analyze if the projection might trick the controller into errors.


Do F-22's use cartridge start to start engines? What method does the F-22 use to start its engines?

In the video below, you can see a flap open and flame and steam shoot out as the engine starts to spin up.  Is this an example of cartridge start?  If so, could anyone explain how this works in greater detail?

Video of F-22 engine start:

It's a Jet Fuel Starter (JFS) system, used by the F-16 and other jet fighters. On-board compressed air (called Stored Energy System) is released onto a turbine, which starts a small gas turbine engine, which then mechanically engages with the engine's gearbox to spin it.

F-22 calls it Auxiliary Power Generation System.

On the F-16 the JFS allows two bursts/attempts, before needing to recharge (re-compress the air). And if I'm not mistaken, it can be charged after two failed attempts using hydraulic pressure from the brake accumulator, as the engine would not be able provide hydraulic pressure to charge the system yet.

Following the release of the high-pressure gas, the sudden expansion and subsequent cooling causes condensation, which is the smoke we see in the video. The two flaps that open prior to the compressed air release are the intake and exhaust doors for the small gas turbine engine.

The F-22 certainly doesn't use a cartridge start (Coffman engine starter). That's mainly for WWII-era reciprocating engines, and some old jet engines.

On an airliner, the equivalent system is an APU. It's started using the battery and then it drives the engine's gearbox using bleed-air. It's a slow process compared to releasing compressed air, especially when you are to scramble as quickly as possible. Technically, both systems are APU's.

This longer video gives us better clues: you can see the JFS's smoke, then see its heat haze, followed by each engine's heat haze. Each step accompanied by sweet music.

(YouTube) Smoke and heat haze from the JFS.


What is automatic control connections and how does it work? The Rolladen-Schneider LS4B control connections are automatic. This feature, also called automatic control hookup seems to be common. The last time I assemble a glider was more than a decade ago, and controls had to be mechanically (re)connected one by one.

What is automatic control connection? (I imagine it is some mechanism connecting controls when assembling wings). How does it work?

The automatic hookup uses a catchment area to mechanically force the pushrod into a receptacle to ensure a proper mechanical connection when the parts of the plane are connected.

As an example, I have sketched below how the ailerons would be connected. The blue structure is the fuselage-side part, and the green structure is the wing-side part of the control linkage. The pushrod coming from the stick is connected to a trapezoidal cone which is hinged at the same point as the wing-mounted pivot lever which is moving the pushrod connected to the aileron.

The opening of the trapezoidal cone is sized such that the end of the pivot lever will always be caught by it, regardless of the stick position and the aileron deflection. At the base where the end of the pivot lever rests when both parts are connected, the exact position and play between both can be adjusted, so the automatic connection will not have an adverse effect on handling.

I once witnessed an aborted winch launch of the SB-8 in which the linkages to the ailerons were interchanged. The pilot noticed the wrong operation of his ailerons before becoming airborne and released the rope quickly, but could not avoid a ground-loop, because he had pushed the low wing into the ground when trying to correct the plane's attitude. I was glad not to have been in his position, because I am not sure I had reacted as quickly. Automatic connections would have made this mishap impossible.


How is the glide ratio affected when converting a wheeled plane to floats? I'm looking for published data that describe the effect on glide ratio when an aircraft is converted from wheeled to float configuration.  I suspect that the glide ratio goes down considerably due to all the drag from the floats and attachments, but an internet search turned up nothing.

I'm particularly interested in DeHaviland Beavers and Otters (which commonly have their gear switched between wheels and floats), but any source would be appreciated.

As glide ratio is the same as the L/D ratio, the increase in drag due to the addition of floats will reduce it. The Beaver's POH gives the effect of addition of floats in the glide ratio:

DHC-2 Beaver's Glide ratio; image from DHC-2- Beaver POH

Note that at their configuration for best glide ratio, there is a drop in about 10% in glide ratio for the configuration for floats. This will differ for different configurations and operating conditions, but the basic effect of addition of floats will be a reduction in glide ratio.


Is it sensible to harness wind energy on an airplane? Is it sensible to harness wind energy on an airplane?

Actually the idea is to build an electric aircraft whose power comes from solar and from wind while the plane is landing. instead of using spoilers as airbrakes, these wind turbines separately mounted could add drag and harness energy at the same time . In other words, regenerative braking.

Normally not: Extracting energy from the airflow produces drag, which must be overcome by added thrust. Since every form of energy conversion produces losses, more thrust energy must be added than can be gained from the airflow.

Only when the engines fail and the generators stop running does it make sense to extract energy from the airflow. In airplanes there are two applications which are driven by "wind energy":

Older airplanes use gyros for the artificial horizon which are powered by ram air. This way the gyros work even after an engine failure.
Jets use Ram Air Turbines (RAT), propeller-driven generators which are moved into the airflow when all other means of generating electricity and hydraulic power have failed. Note that this is done in unpowered flight and increases the sink rate.

Deployed RAT (picture source)

Rocket-powered airplanes have no easy way to generate electricity, so the Me-163 B used a small windmill at the tip of the fuselage to drive a generator.

Me-163 B (picture source)

EDIT:
With your question's new focus on electric propulsion the answer will become different. Now you most likely will have propellers which are powered by electric motors. During landing, those could run inverted and charge a battery, which will most likely be empty by the time the aircraft lands. This can be done during final approach until the end of the runout after touchdown. It can be expected that any electric airplane will have a high L/D, so deploying speed brakes to allow for a steeper approach makes sense.

I would be surprised if an additional device would be economical, however. This recharging must be done by the regular propulsion system, or it would add dead weight during most of the flight.

You asked for formulas, but all I can provide here are some back-of-the-envelope calculations. First, it must be said that variable-pitch propellers will be lousy as windmills, because their camber and twist are wrong for windmilling mode. I would expect that their efficiency is around 30%, which means that only 30% of the energy extracted by drag will be converted into mechanical energy which drives the electric motor.

Next, running an electric motor as a generator will again require compromises. Good motors make poor generators, and re-wiring the motor for better generator performance will degrade its efficiency in normal use. You will quickly lose more than you gain from the short flight phase when running the motor inverted makes sense.

Now let's assume that you keep your propulsion system at top efficiency (say, 90%) and accept that it will only convert 10% of the drag energy into electric energy. Let's also assume that your prospective solar airplane has an L/D of 30 which needs to be reduced to 10 for a practical approach. You do this from 1000 ft downwards and use the windmilling propeller also during the runout. Approach speed is $v$, mass is $m$ and the initial energy of the airplane is $305\cdot m\cdot 9.81 + \frac{m}{2} \cdot v^2$. Two thirds of the potential energy go into propeller drag, and to be generous we assume that 100% of the kinetic energy will also go into propeller drag, even though the braking force of the propellers at low speed is really lousy and needs support from wheel brakes.

Now it is important how fast your airplane flies, because this will shift the ratio between potential and kinetic energy. To keep things simple, I will relate both to the energy required for the next flight. 10% of the full kinetic energy will accelerate the aircraft to less than one third of its flight speed - after this, the remaining 91% of the energy to reach $v$ must be added by charging the batteries between flights.

The electric energy taken from the potential energy will help you climb to 60ft or sustain level flight at $v$ for a distance of 1800ft. At an L/D of 30 the airplane will fly a distance of 30,000ft without thrust, and by braking you will extract the energy to cover 20,000ft, which at 10% conversion efficiency (and 90% propulsion efficiency!) will carry you over just 1800 ft.


Who decides when landing gear requires an overhaul? "If the landing gear on your aircraft is required to be overhauled periodically..."

So is there a case where its been decided that landing gear does not require to be overhauled?

The aircraft manufacturer in consultation with the regulatory authority will publish a maintenance schedule that details what maintenance is required and at what interval.

For simple types the maintenance my be no more that a visual inspection and a tyre pressure check.


Could an airliner with only one functioning engine recover from a stall? If a modern commercial airplane such as a Boeing 787 would stall with only one functioning engine, is it possible for the pilots to right it or would it require two functioning engines?

Yes, but the challenge is managing the asymmetric thrust effects when applying power during the stall recovery.
Pilots are trained in the sim for two stall (actually, just stick shaker onset) situations: high altitude and low altitude.  Low altitude stall recovery training is normally done by slowing until the stick shaker starts, then adding max thrust while lowering the pitch attitude moderately, only enough to keep the speed just above stick shaker onset.
The objective is to minimize altitude loss while accelerating.  The training doesn't actually get the airplane to a full aerodynamic stall; pilots are trained to start the recovery as soon as the shaker goes, which is still a few degrees below the actual stall AOA (as a rule, only production or experimental test pilots will take airplanes past stick shaker right into the natural stall, or stick pusher activation if equipped with one).
I don't believe anybody actually trains for stall recovery while single engine (I never did when training on the CRJs).  In any case, if you had to deal with that, you just have the added complication of managing the yawing motions caused by the asymmetric thrust, and the much more sluggish acceleration, so in addition to managing pitch, you are pretty busy with your feet to keep the airplane straight, and you would have more altitude loss.
At high altitude, it's similar, except that the recovery maneuver is much more aggressive in the thin air. With little to no reserve power, you pretty much have to dive to gain speed, and you cover a lot more distance through space to get the same indicated airspeed rise than at low altitude, so the indicated speed increase is slower.
So you pitch over a lot more, with no effort to minimize altitude loss and you let the airplane dive and wait for the speed to come up. If you were single engine (you would be descending anyway to single engine ceiling if you were) you would be doing the same sort of fancy footwork to allow for the asymmetric thrust and keep the plane straight, to the extent that you have thrust to work with to help accelerate.
So you could say a single engine stall is perfectly recoverable, but the extra workload increases the chance of secondary problems from mishandling (like secondary stall).


How should I deal with a cable break at low level during a glider winch launch? What should I do when rope breaks at 220-360 ft [75-120m] when there is not sufficient runway to land ahead and not sufficient altitude to make a return manuover and land with the wind direction?

Depends on the wind and the surrounding area. If there is enough headwind, you will be surprised how short your approach will be in a proper sideslip. Practise sideslipping at altitude, so you know what to do in an emergency! Otherwise, look around for an open field where to land; gliders are easily disassembled and carried back to the airport.

When the cable breaks, push the stick forward. Be prepared for dirt flying up and into your eyes if you push hard enough! Then stabilise at the minimum sink speed, release the remaining cable and look around for your options. There should be some:

Land straight away if headwind plus sideslip allow for a steep descent.
Fly straight a bit, then turn around 180° and land opposite to your direction at take-off. Do this only when there is no or almost no wind! 100m of altitude is plenty enough for this trick.
Keep flying straight and land on an open field near the airport.
Fly a triangular, shortened pattern and land in the regular direction.

If the airport is surrounded by forest or houses on all sides, try to land on the glider port - normally, the altitude bands required for the landing straight on, the 180° return landing and a landing from a proper pattern overlap enough so that there is never an altitude that would not allow to land on the airfield.


How does the canard plan of the Dassault Rafale work? I'm quite puzzled after seeing some videos of the Dassault Rafale. When pulling the stick, the canard plan should move as in this video (low speed, high angle of attack, stick pulled backward on average). But, this a high load and high speed maneuver, the canard plan's position should be similar but it is not.

How is that possible? Does the canard plan act as a canard plan only at low speed, the elevon doing most of the job at high speed?

I'm double puzzled as this canard behaviour seems to be the same for the SU-30.

The answer is in two parts. First, at higher speeds, control surfaces have more air moving over them and so they don't have to angle as much to provide the same force necessary to move the jet as they do at slower speeds. In fact, a thin control surface like this canard will stall at lower angles of attack than a thicker profile would (the thinner profile reduces drag which is why it's used here), and a stalled surface can't do its job.

Second, modern jets like the Rafale have fly-by-wire systems with flight limiters, to avoid the pilot overstressing the airframe at high speeds. The first video shows the Rafale in landing configuration, approaching a carrier at maybe 150kts. The second video shows high-G maneuvers at probably between 300 and 400kts. The forces at play on the canard are, in general, related to the square of the speed of the air moving past them, so if the system allowed the canards to present the same angle to a 300-knot flow as a 150-knot flow, all other things being equal the canard would be under 4 times the stress. At 450 knots that canard would be under 9 times the stress. Very quickly you would exceed the mechanical strength of that canard surface entirely, and then you wouldn't have a canard surface at all. So instead, the canards are moved at a shallower angle, with the difference in pitch rate, up to what the flight limiter will allow the entire aircraft to do, is made up using the elevons on the wings.


Why does Qatar Airways fly over Syria and Iraq? I saw on Flightradar that Qatar Airways still fly over Syria and Iraq. Why do they think that airspace is safe? I dont want to have to worry about my plane being shot out of the sky on my trip.

They are trying to save themselves money, and their customers time.

First of all, why do the planes follow that route?  From your comments, you are going from Philly to Doha.

You might want to take a look at great circle routes to see why the planes are coming into Doha from that direction.  The Great Circle route depicted goes right through Syria and Iraq: it's the most efficient way to get there. Beyond that, Qatar has a few limitations that other airliners don't have, in that region, due to some diplomatic problems with their neighbors, who won't let them overfly their airspace: Saudi, Egyptian, and UAE airspace for the time being is closed to them.  (thanks @reirab)

Diversions cost money

Some typical diversions in that region are well spelled out in this article in the Economist.

What you may be seeing is that, for some flights that pass over the region, rather than landing within the region, they are accepting the risk that their airliners at 30,000+ feet might, maybe, get targeted on a really bad day (see the Malaysian Airlines flight shot down over the Ukraine a few years ago (MH 17)). But the odds of that are very low.  They most likely will not be disturbed.  (Or so a risk management case can be made).  A more conservative view of risk is offered here, in an Ops Group posting from September of 2018.  (Thanks to @ZachLipton for the link).

Route diversions have very real fuel costs, and costs in time.

Image from the Economist, Oct 20, 2018 edition.

The article mostly addressed flight into Lebanon by Middle Eastern carriers.  Flying into Beirut is of higher risk since the aircraft have to come down through the risky / war zone airspace for final landing, but it's instructive to illustrate how costs go up when more direct routing can't be taken due to safety precautions around conflict zones.

  But for years the airspace over Syria has been crowded with warplanes. The Gulf airlines no longer use it. Instead Emirates, the flag carrier of Dubai, detours across Saudi Arabia and Egypt, adding 700 km to the trip.  The journey takes even longer on Qatar Airways, which was barred from Saudi airspace after a dispute between the Gulf countries erupted last year. Its route from Doha to Beirut resembles a crook: north over Iran, west across Turkey and south down the coast. What should be a 1,825km flight drags on for 2,865km. {snip}
  For travellers this is a nuisance, adding an extra hour or two to journeys. But for airlines it imposes real costs.  Qatar Airways posted a 766 million dollar  profit in the 2017 financial year.  In the 2018 financial year, it lost 69 Million dollars. Operating costs were up by 15%; passenger numbers were down 9%. “We didn’t raise the ticket price,” says Akbar al-Baker, the CEO. “We had to absorb the additional cost.”

  Emirates and Etihad, the flag carrier of Abu Dhabi, run five daily flights to Beirut. With the detour around Syria, they log an extra 2.7m km every year. Depending on the aircraft, that means up to 19 million litres of additional jet fuel, about $11.4 million at current prices. {formatting changes by me to make this fit}

@DavidRicherby points out, fairly, that this local problem is a bit different from the great circle route's need to make an adjustment, in terms of how much extra time and effort a given regional route costs, but it's useful as an illustration of how costs go up when these problems have to be dealt with.

I don't want to have to worry about ...

Then don't.  What you worry about is under your control.

How many airplanes has Qatar airways lost in the last seven years (the length of the Syria civil war) to being shot down? Zero.
What does that say for your odds of this being a low probability
risk?

If you still worry, have you investigated one-flight life insurance?  I used to always buy that whenever I flew, through American Express, back in the 80's and 90's since I was just married and I had young kids.  I'd buy a million dollars worth for about 14 dollars each way.  If you are that worried, buy the life insurance.  It's about the same odds a winning the Lotto for your family.

Full disclosure: I do not now work, nor have I ever worked, for Qatar Airways.


How does a Boeing 737 look like at night from 2000 meters away? I am asking about the current crash of a Boeing 737-800. Due to the unfortunate crash of Ukrainian 752, I am trying to figure out what can be seen from the launch pad when they decided to shoot the plane. I determined the plane was at 4620 ft AGL and climbing. According to my calculations, the line of sight distance from the operator to the plane was 2058 meters = 6729 ft away.

So I want to know how a 737-800 looks like from the ground 6729 ft away at night.

I would like to know if it is possible to mistake a 737-800 for anything else from that distance at the night time with full visibility. Can anyone provide a picture of that?

At night, at that range, it will look about like a dot of light, probably with a red flashing beacon and white flashing strobe lights.

That's what you'll see from essentially every aircraft at that range at night, unless the pilot chooses to turn off some or all lights.

But you're seeing the LIGHTS, not the AIRCRAFT, at that distance, and the ability to visually identify what aircraft it is, is essentially nil.


Why is a 3 degree descent angle used? Following on from this question on the descent rate formula.

It appears from the answers and comments that a 3 degree slope is pretty standard across the board.

I would like to know why a 3 degree descent rate is used? I thought it would vary based upon the scenario.

Basically, it's a combination of historical significance, passenger comfort, and ease of mental calculation.

Historically, before aircraft were pressurized a rapid descent would be uncomfortable for passengers. At the speeds typically flown, a 300ft/min descent was deemed to be comfortable enough for the typical passenger.

  Many aircraft had a cruising speed between 100–120 miles per hour (160–190 km/h). Three miles would be traveled in about 1.5–1.8 minutes, resulting in a rate of descent of about 550–660 feet per minute. That was about as fast as passengers could comfortably adapt to the changing pressure on their eardrums. However, many pilots used a 300-feet-per-minute descent rate because doing so is almost unnoticed by passengers. A pilot cruising at 10,500 feet would calculate that in order to be at 1,000 feet at his destination, he would have to descend 9,500 feet. Dividing 9,500 feet by 300 feet per minute, that descent would require about 32 minutes. If his ground speed was 120 miles per hour (190 km/h), he would begin his descent about 64 miles (103 km) from his destination (traffic permitting).

As you can see, there is a reasonably simple mental calculation that can be done there. This is commonly referred to as the rule of three which is in part quoted above.

That covers descent from cruising altitude, however you are right that flight in IFR will depend on procedures, and scenario. An example is London City Airport which uses a much steeper descent profile of 5.5 degrees on approach to land.


Why does the V-22 Osprey have twin stabilizers? I've noticed that the Bell Boeing V-22 Osprey has a twin vertical stabilizer, while the AugustaWestland AW609 has a T-Tail.

Bell Boeing V-22 Osprey with twin stabilizers. Credit: Boeing

AW 609 (T-Tail) Credit: Airliners.net

I understand why it was used for fast jet fighters, but why was it used for the V-22? What are the advantages?

The V-22 was designed to be operated by the US Marine Corps on-board US aircraft carriers. Any airplane that operates off of a carrier has to be relatively compact in order to be able to fit onto the carrier's elevators and short enough to fit into the hangar deck. A twin tail spreads the elevator authority over 2 smaller control surfaces instead of 1 big surface, making the aircraft shorter, and the placement at the ends of the elevator reduces its overall size footprint.

The other benefits of a twin tail are a reduced radar cross section (the V-22 needs all the help it can get there) and increased redundancy as if one tail is damaged there is another one available. The wide placement of the stabilizers reduces the chance that enemy fire will take out both at once.