How did KAL 007 get so far off course? Regarding Flight 007 that got shot down in the Soviet Union, this was reported in the New York Times:

Study Says Korean Airliner Was on Its Intended Course When Downed in '83 (nytimes.com)

Excerpt:

  A retired airline navigator has gathered evidence that in his view
  shows that the South Korean airliner shot down over Russia in 1983 was
  on a deliberate flight path and did not stray accidentally into Soviet
  territory.

  A principal part of his analysis is his refutation of what has been
  the prevailing theory, that the plane unintentionally flew off course
  because of a single-digit mistake in keying flight coordinates into
  the navigation system.

  Leading aviation officials accept the refutation as correct, but still
  insist that the incursion was accidental and not deliberate.

We know this was a modern (at the time) Boeing 747 with a complex inertial flight management system.

No, I do not believe the theories about this being intentional.  Nobody would risk a plane full of passengers like this on purpose.

In 1978 the KAL flight 978 went astray and was forced down on a frozen lake inside Russia.

Korean Air Lines jet forced down over Soviet Union - Apr 20, 1978 (history.com)

I would think this would be on their mind as they prepared for the flight.

So my question is:  How did KAL 007 get so far off course?

Follow-up:  Wouldn't they have noticed?

Chapter 4 of Degani's Taming HAL covers some of the details of this disaster, and is on a NASA site The Crash of Korean Air
Lines Flight 007

It details some of the interface deficiencies in the aircraft's navigation selection system.  We don't have definitive evidence about exactly what happened, but it is possible.  It goes over the idea that it was easy to get the system in a mode where the pilots could easily have thought that the inertial navigation system was engaged, but actually wasn't.

The Mayday show covered this one as well.  They noted that after the FDR was returned, it showed that the FMS was set properly.  Even though it wasn't controlling the plane, it would have continued to show the waypoints being passed as the aircraft crossed to the side.  Given that behavior, it would be very easy to believe that the system is working and you're where you should be.


Semi-circular rule for choosing a FL: Risk of head on collision with borderline headings (179, 359)? If it happens that you fly a 179/359 heading in uncontrolled airspace, what's the risk of collision with aircraft flying in opposite direction?

The adoption of semi circular rules is not meant to prevent collisions on its own. Rather, it is one of several safety nets contributing to a safe and orderly flow of air traffic. In uncontrolled airspace, normal rules of the air apply, for example, two aircraft meeting head on must both alter their heading to the right in order to both pass with the other aircraft on the left.

The actual "risk of collision" you are asking about, for someone flying in uncontrolled airspace, is incredibly small. One reason is that the amount of traffic in uncontrolled airspace is typically quite low, since authorities will most likely establish air traffic control for congested areas. Even in uncontrolled airspace, flight information service is provided in order to - among other things - prevent collisions. And collision avoidance systems, such as TCAS, will also help. Crucially, all aircraft have windows, and the pilots are trained to look out in order to see potential conflicting aircraft and react in time.


How many labels are defined in ARINC 429 for calibrated altitude? How many labels are defined in ARINC 429 for calibrated altitude?

There is no defined "calibrated altitude".
The following are all altitude related labels:

102 Selected Altitude,
107 Selected Cruise Altitude,
120 Range to Altitude,
127 Selected Landing Altitude,
131 Intruder Altitude,
144 Altitude Error,
153 Max Altitude,
162 Density Altitude,
164 Min Descent Altitude (MDA),
203 Altitude,
204 Baro Corrected Altitude #1 & Baro Altitude,
206 Altitude (Variable Resolution),
212 Altitude Rate,
220 Baro Corrected Altitude #2,
225 Compensated Altitude Rate,
251 Baro Corrected Altitude #3,
252 Baro Corrected Altitude #4,
254 Altitude Rate,
323 Geometric Altitude,
361 Altitude (Inertial)


Why did the Swiss International Air LX40 (a 777-300ER) emergency land at Iqaluit airport? Swiss International Air LX40 (a brand new 777-300ER) was en route from Zurich to LA on 1 Feb 2017 when one of the GE90 engines shut itself down because of data from its self-monitoring algorithms.

The crew decided to emergency land at Iqaluit airport on the southern tip of Baffin Island in Canada, which is extremely remote. Getting a new engine to Iqaluit and installed was an incredible odyssey in itself.

The photos of the incident are such that it seems that landing at Iqaluit and trying to do maintenance and take off again would be more dangerous than a diversion to somewhere larger like Nuuk in Greenland.

Given that the 777-300ER could have easily flown the remainder to LA with one engine -- which means it could have easily diverted to a nearby larger airport -- why didn't it? Are ETOPS rules so strict that you must land at the nearest airport and such that the nearest reasonable airport would not be permitted?

Given that the 777-300ER could have easily flown the remainder to LA with one engine -- which means it could have easily diverted to a nearby larger airport -- why didn't it?

Standard operating procedure for engine failure on a twin calls for emergency and landing as soon as possible. That was their closest diversion point at the time, so there they landed.

This is an instance of a more general rule that whenever all redundancy on a critical system is lost, it warrants an emergency and requires landing at nearest suitable airport. Continuing the flight on one engine would most likely considered reckless operation.

Regarding your suggested alternate, “somewhere larger like Nuuk” is definitely not true. Nuuk has runway of mere 3,117 ft, far too short for a 777. The 8,605 ft at Iqaluit is adequate, and it is the standard diversion airport for this area.

Plus it was at least 300 nmi further. You are not risking that when your gliding distance from FL360 is ~120 nmi (and there is no way one engine can keep you up in FL360, so it's more like FL300 and ~90 nmi) and you really can't be sure the problem that killed the one engine is not going to affect the other too.

Also, regarding the complicated repairs, there is no better place nearby. It is just as cold in the whole region and there are no heated hangars where a 777 would fit, so they needed the tent to provide reasonable working environment around the engine in the cold weather and would need it in any other airport in the region. That's why they have it.


Which AFDX connections are used in Airbus A380? AFDX is defined by ARINC 664 Part 7 and used in Airbus A380, I would like to know in which connections on the aircraft is used and for which purposes? Does anyone knows the answer or good documentation from which to start a research about?

There are some resources.
This source shows how AFDX is used as the backbone of the IMA (Integrated Modular Avionics) and lists subsystems such as the air data inertial reference units (ADIRU), Engine Electronic Controllers (EEC) and Electrical Load Management (ELM) Systems as 'members' of the network.

This archived article talks about the development of AFDX to solve real time performance issues with the flyby wire controls of the A380.

Other articles of note would be this. The other articles are behind a paywall but for completeness they are here and here


What is the meaing of the circuit breaker marking "Audio/Mkr" in a PA-28-181? On the PA-28-181 that I fly, there's a circuit breaker called Audio/Mkr. What is that? In the aircraft, there's also a dual GNS430 if that makes it any more specific. I was thinking it could be controlling the speaker on the aircraft?

This circuit breaker is responsible for your Audio Control Panel. It's called Audio/Mkr. because the Audio Control Panel in most aircraft includes the Marker receiver and displays (maybe you noticed the three colored lamps on the left side reading O, I and M, colored white, blue and orange).

If the circuit breaker is out you loose your audio on the one hand side, on the other side you also loose your ability to identify Marker Beacons (functionality explained by Carlo).


What kind of damage would low-level supersonic flight inflict? I was watching a video about "The Big Stick" aka Project Pluto, a nuclear powered SLAM. In the video (I couldn't find the exact video) it said that after deploying its weapon payload a SLAM could fly over its target country as a "vengeance weapon", causing destruction with it's sonic boom for weeks and an altitude of just a few hundred feet.

What kind of damage would a mach 3 flyby at 200 feet cause?

I'm interested in both building damage and possible human injury.

The video is highly inaccurate in that area.

The actual damage the missile would have caused would have been largely radiological, from ejected radioactive material in its exhaust plume.

While windows and weak structures may receive damage from extremely low flying Mach 3 bodies, this would probably be limited to say some broken glass.

The plan was also never really considered. What was considered is having the weapon, now without its warheads, fly to a final target area and do a high speed dive into the ground, the kinetic energy alone combined with the spread of radioactive material from the rupturing nuclear reactor causing the damage there.

Mind that the damage (both physical and radiological) of the weapon flying overhead isn't clear. Different sources list different predictions.
Some way the damage would be minor, others that it would be severe.
But rest assured, the noise would shatter eardrums, the supersonic shockwave flatten crops and lightly constructed buildings, and the radioactive exhaust plume wouldn't have been healthy either.

I've always found this to be an excellent article on the project and the people surrounding it.

Edit: a very interesting article by the designer of the reactor about the problems inherent in the reactor design, and how he thought about the radiation hazard for people on the ground working with the missile:
Merkle public paper


Which are typical rpm values for aeronautical turbines? I wonder which of these has higher or lower rotational speed:

turboshaft
turbofan
turbojet
turboprop

Does anybody know the typical speeds for these kind of engines?

First of all: There is not one single speed on many aircraft engines. Big propeller engines have a reduction gearbox so the propeller runs at a lower speed than the core engine, and multi-spool turbines have an inner, high-pressure section with higher rotational speeds than the outer, low-pressure parts of both the compressor and the turbine. Take the Progress D-27 turboprop for example: It has three spools and a reduction gear, so its components run at four different speeds.

Generally: The bigger the diameter, the lower the typical speed. Fan and propeller blades should run at a high dynamic pressure, but still at subsonic speeds to avoid the higher losses involved with supersonic flow. Since the tip will be the part with the highest speed, and propellers have bigger diameters than fans, propellers run at lower speeds. Also, their bigger diameter makes propellers more efficient. The more air mass is involved in thrust creation, the higher the propulsive efficiency will be. Propellers on slow-flying electric or human-powered airplanes run at only hundreds of RPM, well below speeds where their tips would approach Mach 1, in order to convert as much of the limited power to thrust as possible.

If flow speed allows, core engine parts run at the highest RPM possible, because the faster a turbine or a piston engine runs, the more power it will produce for a given size. Therefore, core engines of the same size run at the same speed, regardless of their type, their bypass ratios or their use. Only stationary gas turbines for power generation might run a bit slower than their aircraft-mounted siblings to increase their life.

The high pressure compressor and turbines of an airliner engine will run at above ten thousand RPM, while the propeller of a large turboprop engine wants to run at about 1700 to 2200 RPM, and in case of the NK-12 of the  Tu-95 the propellers run at only 750 RPM. Both the fan and the propeller are powered by separate low pressure turbines. The fan and low-pressure compressor of a big airliner engine run at between 2500 and 4000 RPM, and the turbine of the PT-6, a classical turboprop engine, at 30.000 RPM. Since power is torque times RPM, a faster running shaft will be lighter than one running at low speed, so the speed is only reduced directly at the propeller mount.

A fan's optimum speed is between that of the compressor and the propeller and would ideally also need a gearbox, but here the transmitted power is so high that a compact gearbox will be hard to design. Even if it runs at 98% efficiency, it will produce waste heat in the order of several hundred kilowatts in case of a big airliner engine. Some small engines with just a single turbine use gearboxes already (e.g. the Lycoming ALF507), and now the next generation of efficient fan engines are also introducing gearboxes. But so far, most engine designs have preferred to run the fan faster than what would be ideal. Note that the tip speed of a modern, ungeared fan is already well above Mach 1.


How are runway lights constructed? How are runway lights constructed so that they are not damaged by aircraft wheels, and can continue to function safely, to demanding specifications, under a wide variety of environmental conditions?

I presume you are asking about lights that are on the surface of the runway like centerline lights and touch down zone lights. The FAA has an AC that covers their design and installation which you can find here. Take a look at section 4.5 "In Pavement Light Fixture Testing". This section outlines some of the force requirements the light must be able to withstand. The FAA currently requires the light to be mounted in an L-868 base can which is imbedded in the runway during construction. There are also a bunch of size requirements laid out in section "3.4. Dimensional Requirements." that describe how the lights are to be built.


Do today's aircraft still have INS (inertial navigation system)? Do today's new aircraft like Boeing 787 still have INS (inertial navigation system)?

Short answer
Aircraft still use inertial navigation systems because INS is autonomous, it doesn't need any external support to work, it provides more information, and is more accurate than a GNSS in the short term. There is no plan to stop using it.
On the contrary, INS is required for certain operations. For instance the B787 cannot be flown without at least one IRU operative. See B787 Master Minimum Equipment List MMEL, item 21-01-01 page 182.
The usual solution for air navigation is to use INS, frequently updated by GNSS to contain drift, as long as GNSS signal is available, accurate and reliable (professional GNSS receivers are able to determine their reliability).

GPS/INS sensors fusion, source

Details
While INS has several disadvantages, namely initial alignment time and drift, it has also unique capabilities:

INS is autonomous, position is determined without external cooperative support.

INS position can be updated 1,000 times per second.

INS provides position information like GNSS, but also orientation (attitude), rotation rate and related accelerations. In the short term these data are very accurate. For example, the yaw damper uses instantaneous motion data to counter Dutch roll.

INS provides True North direction.

On the other hand, global navigation satellite systems (GNSS):

Contrary to inertial navigation systems (INS), are dependent on a lot of factors to work, including space vehicles, ground stations, antennas, or solar activity.

GNSS signals can be obstructed, altered or jammed.

GNSS is updated at a slow rate (e.g. once or 10 times per second, that is by increment larger than 20m for an airliner at Mach .85), due to the heavy computation required to extract and process the weak GNSS radio signal.

The best known GNSS, the American Navstar GPS, is a military system funded and managed by US Air Force.

While GPS is in effect always accurate for civil uses, it must be remembered there is no guarantee from the US DoD on that. The Navstar GPS operational specifications for SPS (civil) service allows for 72 minutes per day (2σ / 95th percentile) with a DOP > 3, that is more than 17m horizontally and 37m vertically. During these 72 minutes, the error is unlimited.

In the field of aviation, GNSS and INS are more and more coupled with air data and magnetometers, that's called data/sensor fusion to take the best of each system, cross check results and detect sensor failure.
As a everyday life example: Without an inertial sensor in a car "GPS receiver" (more accurately: a GPS-aided navigation system), the navigation system would be helpless at roundabouts. The GPS receiver instantaneous precision, its low update frequency, and its lack of orientation sensing would prevent it to correctly derives the actual position and the closest roundabout exit.


What is the effect of airfoil thickness on aerodynamic lift? More than once I`ve read that the airfoil thickness contributes little to the lift compared to the angle of attack and airfoil curvature and has more to do with airfoil stall characteristics.

Could anyone explain this, preferably mathematically?

Thank you

In chapter 2 of his book Fluid Dynamic Lift, Sighard Hoerner discusses the influence of thickness by going to the extreme of an airfoil with a circular cross section:

  Assuming that we would manage by means of boundary layer control
  around the rear side, to displace the stagnation points from zero (at
  the forward side) and from 180° (at the rear side) both down toward 90°
  (at the lowest point), without losing any momentum, its lift curve
  slope would be dCL/dα =4π, rather than = 2π, as in thin foil sections.

Since you desire a mathematical expression: This is the linear approximation he gives:
$$c_{L\alpha} \approx 0.11 + 0.09\cdot\frac{t}{c}$$

Note that the lift curve slope is per degree. $\frac{t}{c}$ is the relative thickness of the airfoil.
In figure 21 of that chapter he uses the concept of the lift angle, the angle at which the lift coefficient reaches unity, to show how the lift curve slope varies over airfoil thickness. This plot should demonstrate how limited the applicability of the approximation is in reality.

The lift angle of airfoil sections as a function of their thickness ratio (picture source).

Stall is dominated by flow separation, and the displacement effect of an airfoil adds to the stresses on the boundary layer which determine when the flow separates. On the other hand, thickness is indirectly influenced by the nose radius of the airfoil, and this in turn determines the suction peak at the nose and at higher angles of attack. A higher suction peak also stresses the boundary layer. In consequence, both a too small nose radius (and too small airfoil thickness) and a too high thickness lower the maximum lift coefficient. The sweet spot is at a thickness of around 10%.

In chapter 4, Hoerner looks into that dependency in detail. The plot below does not include highly cambered, thin airfoils, and the straight limit for thin airfoils is misleading.

Maximum lift coefficient of various types of airfoils as a function of their thickness ratio (picture source).


What would happen if thrust reversal is accidentally deployed during a flight? Is it possible to deploy the thrust reversal, in the cruise phase of a flight? And, if they are accidentally deployed, what could be the possible consequences?

As the cruise phase requires a lot of lift, so certainly the impact would not be very desirable..

If the aircraft is at cruise altitude and speed, the wing will see a large loss of lift, and will become uncontrollable.
It used to be possible to deploy thrust reversers in Boeings. It was not feared as a problem, since early tests showed that accidental deployments were survivable and the plane would stay controllable. However, these tests were only performed at low speeds, since low-speed deployments were assumed to be the most critical (source).

But then in 1991 Lauda Air 004 crashed mid-flight in Thailand after an uncommanded thrust reverser deployment. After this crash, additional safety features such as mechanical positive locks were mandated to prevent thrust reverser deployment in flight.
I'm not sure about Airbus, but I guess all current aircraft have some kind of lock.

Because engines on modern aircraft are so closely attached to the wing, the thrust reverser exhaust flow is right in front of the wing. Therefore, the wing will see a lower flow speed which results in a loss of lift.


Is locking the cockpit door from inside is a normal procedure when one pilot leaves? When a pilot leaves the cockpit to go to the toilet should the second pilot lock the door?

For me it's mandatory in case of the other pilot is taking in hostage and is forced to tap the code.

So can the pilot still in the cockpit can have locked the door and then lose consciousness?

Imagine the pilot goes to toilet and a problem occurs, the plane start to stall for example, and he can't reach the cockpit leaving the other alone to manage the situation.

For me the only situation is 3 pilots or never let him goes outside in small trip.

For most modern, large commercial passenger planes, there is an automatic lock, which then requires the PNF (Pilot Not Flying and outside of the cockpit) to enter an unlock code, or more usually, for the PF (Pilot Flying, and hopefully inside the cockpit) to remotely unlock the door.

The emergency access code typically sounds a cockpit warning buzzer and has a delayed operation, allowing the PF to override this in case of an unwanted, erm, "visitor", yet at the same time, allowing access to the PNF in case of PF incapacitation.

Commercially, three pilots (or two pilots and a flight engineer) on each flight are no longer economically viable for almost all airlines.  Indeed, most couldn't host a third person comfortably for the whole flight - jump seats are fine for short bursts, but not for a long-haul flight, for example.

Therefore, most airlines are now adapting their cockpit manning procedures to ensure another member of the flight crew (typically a flight attendant) joins the PF before the PNF leaves the cockpit.


How does pitch relate to glide angle? When flying a glider, you have a polar curve. As your speed increases beyond best glide, your glide angle gets steeper. Say you are flying at best glide, you are looking through a specific point in your canopy to the spot you would land if you maintained this glide angle until you touched down.
Now say you double your speed. Of course your glide angle would get steeper, the spot will have moved down relative to the canopy at best glide. At the new pitch, looking through a specific point in your canopy to where you would land, would this point be higher, lower or the same?
The reason I ask this question is because I’m learning to glide. When you pitch the nose down to gain speed, it feels as though you are pitching down a long way, but your glide angle doesn’t seem to be affected as much as you would expect it to be. I guess a more accurate question title might be: “How does pitch relate to the polar curve?” But I’m trying to gain intuition on how glide angle changes in relation to what you perceive in the cockpit/canopy.

When you pitch the nose down to gain speed, it feels as though you are pitching down a long way

This is because the change of the cockpit angle towards the horizon is the sum of both the angle of attack and the glide path angle change.
This means that at low speed your speed changes should move the target point up when you go faster (the point is only affected by the change in glide angle while your view is affected by the sum of angle of attack and glide angle change) while at high speed, when a speed change means only very small changes in angle of attack) the target point does not move much relative to the canopy any more (but it will still move a bit up when going even faster).

How does pitch relate to the polar curve?

All you need to do is to add the angle of attack at the respective speed to the polar curve and you get the pitch angle. Like this:

The blue line is the arcsin of the ratio of sink speed to flight speed. It should not be a coincidence that it looks like the sink speed polar. To that line I added the angle of attack (red line) which shows in which direction relative to the horizon the longitudinal axis of the plane points. Since the cockpit is a bit angled down, your viewing angle should be reduced by that amount. Now it is easy to see that the angle changes a lot at the low speed end but stays almost parallel to the sink speed line at high speed. Since I assumed a zero-lift angle of attack of -2°, the red line crosses the blue one at 52 m/s.


Is there any limit by FAA on the age of aircraft to be operational? Is there any restriction by FAA that one can not fly a plane older than 'X' years?

If someone is maintaining an older plane (e.g. from 1990s), are there any regulations which prevents or restricts that person to fly that airplane?

I am interested in finding out both for commercial and smaller general aviation airplanes.

It depends on the aircraft, but in general the answer is that there  are no regulatory age limitations, and indeed we have many aircraft flying that are 50+ years old.

A notable exception is the Robinson line of piston helicopters. The airframe on those helis is limited to 2200 hours or 12 years, whichever comes first, at which point the entire airframe must be completely overhauled. Some of the airframes are indeed rebuilt, but some are also scrapped, depending on level of wear and corrosion.

Since the airframe lifetime is in the LIMITATIONS section of the POH, it is governed by:

  § 91.9 Civil aircraft flight manual, marking, and placard
  requirements. (a) Except as provided in paragraph (d) of this section,
  no person may operate a civil aircraft without complying with the
  operating limitations specified in the approved Airplane or Rotorcraft
  Flight Manual, markings, and placards, or as otherwise prescribed by
  the certificating authority of the country of registry.


How many aircraft can airline put in hangar? Another question talks about aircraft movement in and out of hangar.  Most hangar I see at commercial airport I see one aircraft per hangar.

This makes me wonder how many aircraft can be kept in the hangar depth-wise(ie nose-to-tail direction)? Is larger hangar common?

Note: please do not include special hangars such as those at Airbus or Boeing facility in main answer but side note about those are welcomed.

There are no restrictions. You can put as many aircraft into a hangar as you can fit into it.

Some commercial hangars are neatly arranged.

Some are not as neatly arranged but efficiently packed.

And sailplanes can be lifted and hung from the ceiling for more space on the ground.


Is it possible to land a plane only with the Garmin® Synthetic Vision? A synthetic vision system shows the pilot the position of his plane in a 3D-modelled flight environment.

It's like a 3D TAWS. It also shows the position on the runway:

As I have seen, this feature works quite good. It's sometimes a bit off the centerline, but on the runway.

It is clearly stated that this is only to be used as feature to enhance the situational awareness. And I am also quite sure that this is not authorized as primary navigation source.

But imagine: You are flying in zero visibility. You have an emergency and must land. There is no ILS. (You have done no flight planning and the bad weather surprised you)

Would it theoretically be possible to land a plane only with this synthetic vision?
Is it accurate enough?
Would the plane at least come down in one part?

Apparently yes, according to this 2008 review of the system in a Diamond DA40:

  With [a safety pilot], I stayed under
  the hood for the entire flight—takeoff, en route, approach and
  landing—using the system’s visual cues. I managed to land the airplane
  without breaking anything, barely. It wasn’t pretty, but it
  demonstrated what was possible.


Does an aircraft with higher aspect ratio wings produce more wingtip vortices in a turn than one with lower aspect ratio wings? The Ta-152H was well-known for having very high-aspect ratio wings: 8.94, if I'm not mistaken. Now, compare this to the P-51 which had, if I'm not mistaken, an aspect ratio of 5.86. Does this mean that in a turn the P-51 would produce more wingtip vortices than the Ta-152H?

Easy to follow diagramFor two wings with the same area, the higher AR wing will produce LESS wingtip vortices simply because there is not as much area close to the wing tip that can be affected by the vortices.

The Ta-152H has a wing area of 253 ft^2 while the P-51 has a wing area of 235 ft^2

With those area's being so close together (7% apart) while the AR's are very different (35% apart) it would be a safe assumption to say the Ta-152H produces LESS wingtip vortices than the P-51.


Can a large passenger aircraft recover from a stall? In fighter aircraft, we know that they have good enough of maneuverability. But in case of a passenger airplane, if a stall happens is the aircraft maneuverable enough to recover from it?

The main thing that is required for a stall recovery is just the ability to drop the nose to decrease angle-of-attack and regain airspeed (and, of course, adding power helps, too.) Except in the case of deep stall, there is still sufficient air flowing over the horizontal stabilizers (and, thus, the elevators) in an airliner to push the nose down during a stall. Furthermore, most airplanes (including nearly all, if not all, airliners) are designed with a center of gravity forward of the center of lift. In normal flight, the air flow over the horizontal stabilizers actually pushes the back of the plane down, which holds up the nose. During a stall, this airflow is reduced (still present, but to a lesser degree,) which will cause the nose to tend to drop by default during a stall condition, even if the pilot (or autopilot) gives no additional control inputs at all. As such, normal (e.g. not fighters or aerobatic planes) will recover from a stall on their own with no additional control inputs, given enough altitude.

As already mentioned, some altitude is also usually required for successful stall recovery. This is because the recovery procedures involve dropping the nose which will briefly result in some descent. The lack of sufficient altitude to recover was the main problem in Asiana 214, which crashed just short of the runway in San Francisco. The aircraft was already too low and too slow to recover before the pilots acted. If I remember correctly, they started attempting a go-around only about 7 seconds before the aircraft impacted the seawall. At that point, there was nothing they could do. A small, piston-engine aircraft probably still could have recovered from that situation because piston engines spin up much, much faster than jet engines and could provide the power needed to recover much faster. Pushing the nose down alone would still technically have recovered the plane from the stall condition in this case, but that wouldn't have been very helpful, since it would have meant a nose-first impact into either San Francisco Bay or the seawall, which would obviously have been a much worse outcome.

Another problem that can happen (though is very, very unlikely on an actual airline flight, but much more likely on cargo flights in airliners) is for the cargo to shift to the point that the center of gravity is too far from where it's designed to be for stall recovery to be possible. This is what happened on National Airlines Flight 102, a 747 cargo flight departing from Bagram Air Force Base in Afghanistan. Very shortly after takeoff, the cargo shifted to the back of the aircraft, preventing the pilots from being able to lower the nose enough to keep the plane from stalling. It stalled and crashed before ever leaving the property of the airfield.

In general, pitch stability (more precisely known as longitudinal static stability) is what makes an aircraft capable of stall recovery, not maneuverability. While it may seem counter-intuitive to those not familiar with aerodynamics, it's likely actually easier to recover from a stall in an airliner than it is in a fighter (and almost certainly easier to recover in, say, a Piper or Cessna than a jet fighter.) This is because more maneuverable aircraft (such as fighters and aerobatics aircraft) are usually less stable than less maneuverable aircraft like airliners and normal GA aircraft.

The answers to this question give a thorough explanation of stall recovery which I would recommend reading. Its answers apply to how stall recovery is performed in any normal airplane, not just airliners. That question isn't specifically about whether airliners can recover from a stall, though, which is why I didn't mark this one as a duplicate.


Costa Rica landing in the news, concerns to be taken seriously? A landing in Costa Rica has recently caught some attention in media, for example here.

A flight from Madrid to San Jose allegedly experienced difficult winds and the pilots changed the descent pattern accordingly.

They approached the runway at a very low altitude, scaring both passengers and people on the ground. And considering the footage available in the article, I don't blame them.

The authorities however claim that this was a normal and controlled landing, and that there are no limits how low the approach is allowed to be over the area close to the runway. They admitted, though: "Sure it could have been a little higher, but the altitude and angle of the plane was fine."

Are the authorities right about this, or should the media's, the passengers' and the locals' concerns be taken seriously?

Please don't link to media articles in the general press, but especially not the Daily Mail who generally don't worry too much about facts and have no-one on staff who has a clue about aviation ("activate their tyres in time", "With its landing gear ejected, the plane comes perilously close to hitting ground level too early").
Just look at the rhetoric in the wording of the article body.  It ticks all the boxes:

...within a few feet of terrified drivers...
...Shocked passengers on board...
...eye-catching video...

The Daily Mail tries to get at least one of these a month as clickbait and for comments.
Some critical thinking.

...grazed perimeter fence...

No evidence presented.

...why so many photos...

Because the road is right at the end of the runway and spotters gather there to take such photos.

...passengers shocked...

No evidence presented and most passengers are the worst possible judges of a good approach or not. How would they know?

...how low was it at the threshold?...

No evidence presented.

...airport authorities insist it was a normal and 'controlled landing'...

What evidence is there that it was not?
SJO is known for its tricky and low approaches.  Nothing to see here.


What is the process for a TFR based on law enforcement activity? Regarding the recently announced TFR for the Ferguson, MO area, what is the process by which such a TFR is granted?

The official reason given is "TO PROVIDE A SAFE ENVIRONMENT FOR LAW ENFORCEMENT ACTIVITIES", however, there has been significant commentary on social media arguing that this may be a politically-motivated act to prevent the media from scrutinizing the actions of law enforcement (for instance here).

As far as I know, there is no (public) information regarding threats to airborne vehicles, and despite some initial reports most of the protests in the area have been peaceful.  I'd like to assume that this TFR was created for legitimate, non-political reasons.

Is it common for the FAA to grant a TFR like this to local police?  What is the process by which this is done?  What criteria are considered by the FAA in determining whether such a TFR is warranted?

For the sake of posterity, the full text of the TFR NOTAM is:

!FDC 4/0271 ZKC MO..
AIRSPACE FERGUSON, MO..
TEMPORARY FLIGHT RESTRICTIONS. WITHIN AN AREA DEFINED AS 3 NM RADIUS OF
384428N0901812W (ST LOUIS VORTAC STL129011.0) SFC-3000FT TO PROVIDE A SAFE
ENVIRONMENT FOR LAW ENFORCEMENT ACTIVITIES. PURSUANT TO 14 CFR SECTION
91.137(A)(1) TEMPORARY FLIGHT RESTRICTIONS (TFR) ARE IN EFFECT. ONLY AIRCRAFT
PERMITTED UNDER THE PROVISIONS OF 14 CFR 91.137(B) ARE ALLOWED TO OPERATE IN
THIS 91.137(A)(1) TFR. THESE AIRCRAFT MUST BE OPERATING UNDER THE DIRECTION OF
THE UNIFIED COMMAND AT THE ST. LOUIS EMERGENCY OPERATIONS CENTER AND MUST
CONTACT THE MID-AMERICA AIR OPERATIONS BRANCH AT TELEPHONE 636-825-9341 OR
636-825-9342 FOR PERMISSION TO ENTER THE TFR PRIOR TO DEPARTURE. ST.LOUIS
GATEWAY TRACON, TELEPHONE 314-890-1017, IS THE FAA COORDINATION FACILITY.
MEDIA CONCERNS REGARDING THIS TFR SHOULD BE DIRECTED TO FAA PUBLIC AFFAIRS
THROUGH THE WASHINGTON OPERATIONS CENTER AT 202-267-3333. 1411250415-1411251015

TFRs around "volatile situations" on the ground aren't a daily occurrence, but they do happen fairly frequently.

The concerns are usually twofold: Events on the ground posing a hazard to aircraft (people shining lasers at aircraft, firing guns at them, etc.), and aircraft posing hazards to each other (News 2, News 4, News 11, and Police helicopters all wanting to cover the same area at the same time and smacking into each other).

There are procedures in effect for agencies to request TFRs, and for the FAA to review them. These are covered in detail in FAA JO 7210.3Y, Chapter 19. Particularly relevant to this situation is 19-2-5 (e): "TFRs issued for law enforcement activities require approval from the ATO Director of System Operations Security (or designee)." - a relatively high level of approval intended to safeguard against the use of TFRs to, for example, keep the media away.

In the case of Ferguson the regulatory basis for the TFR is cited as FAR 91.137(a)(1) (to protect persons and property on the surface or in the air from a hazard associated with an incident on the surface), so presumably their major concern is laser illumination or weapons fire from the ground, and the potential for such incidents to cause a surprised pilot to crash into a building or crowd of people.


How large are the pilot rest areas of the A380 and B747-8? How large are the pilot rest areas of an Airbus A380 and Boeing 747-8? What entertainment systems are found in them?

The pilot crew rest areas are not as large as flight attendant rest areas as they only provide space for 2 occupants. A380 and B747-800 pilot rest areas will have 2 sleeping berths, and most airlines will also have 2 comfortable seats equipped with the same in-flight entertainment as the passengers. This gives the resting pilot the choice to sleep in a bed, or relax in a comfortable chair. Sometimes, instead of a chair in the crew rest area, a regular Business class seat will be blocked for the pilot's use.
Airbus A380
Airbus A380 Pilot Crew Rest Area Video

Boeing 747
The B747-800 Pilot Rest area is behind the flight deck. This photo shows 2 bunks with blue bedding. Crew rest seats may or may not be available depending on the airlines own specifications or requirements.


How is it safe and legal to land in parallel runways How come it is safe and legal to land in parallel runways (for example, in SFO).

The planes are way too close, at a distance that would not, I assume, be according to flight regulations and safety rules during cruise flight.

At what distance from airport or below what altitude becomes it ok to fly like this?

Can airplanes also take off in parallel, or only land?

Whether Parallel Runway Operations are allowed at an airport is dependent on many factors, such as:

Proximity of runways to each other
Availability of precision approach systems for each runway

There is two modes that are interesting here, which is the full parallel mode, where lateral separation is no longer required once both aircraft are established in the precision approach and staggered mode, where the runways are too close for parallel mode and need to maintain 2.5 NM lateral separation during the approach phase.

The same regulations apply to departures, you can read about it in EUROCONTROL's SkyBrary.

Related questions:
How are go-arounds safe with parallel runways?


What is exemption 17347 in the context of dispatch for FAA domestic carriers? What is exemption 17347 in the context of dispatch for FAA domestic carriers?

The explanation can be rather complicated, so I’m looking for a simple and straight forward break down.

Also, as a bonus, what is the history behind this exemption?

Exemption 17347 was requested by the Regional Airline Association to extend a pre-existing alternate weather regulatory exemption to apply to regional airlines operating under part 121 because the FAA has changed the language referring to other carriers used in grants of exemption.

  As a separate issue, when A4A previously petitioned for this exemption, the FAA granted relief to the petitioner’s member airlines, as well as to all other “similarly situated” certificate holders, which included any air carrier operating under the provisions of part 121 (Exemption No. 3585). However, in an effort to manage exemptions granted by the FAA and to facilitate operator compliance with the conditions and limitations of a grant of exemption, the FAA is no longer including “similarly situated certificate holders” in grants of exemption.

Regulatory Filing Source


Can an automatic gearbox improve engine transmission for an ultralight? I am working on my dream to build and fly an ultralight aircraft so I wouldn't like to know the following:

Does adding a motorcycle automatic gear box to an  engine improve on the strength for an ultralight aircraft?  The engine in question is a 4 stroke, OHV, single cylinder, 440cc gasoline engine with a TCI ignition.  It produces 18hp at 3600 RPM,  torque 3.0 kgm/2500 RPM (21.7 lb ft), ignition TCI, gross weight 37 kg.
What should be the tail, flaps and wing measurement proportions for such engine?

Thank you

A gearbox is not a useful addition. Some aircraft have geared propellers, but that's a single, fixed gear.
The engine has to be able to turn the propeller when it's in the highest gear you'll use, so that determines how much power is required.

In a car or motorcycle, the lower gears are used to match engine speed to wheel speed, allowing the vehicle to drive at lower speeds than 'idle rpm in top gear' without slipping the clutch or the wheels.

In an aircraft, that function is not needed: a propeller can slip freely.


Do black wings have better aerodynamics? This news article links to a 2019 academic study:
Thermal impacts of wing coloration on surface temperature during bird flight.
Most of birds have dark upper wing feathers. Dark colors keep a sunlit surface hotter compared to white colors.
Do black color or hotter surfaces improve the aerodynamics of wings?
A key consideration might be airspeed: fast air over a plane wing doesn't allow time to heat up the boundary layer so much. Birds and sailing boats operate at much slower airspeed so maybe those get some benefits?

For the bird analogy, you're thinking about this wrong.  Birds have dark upper wings for camouflage, not for aerodynamics.  A predator above them is less likely to see a dark top against a darkish background (the ground).  This is the same reason that many birds have lighter colors under their wings - that looks a bit more like the sky.


Is it true an ILS CAT IIIc can automatically taxi-in an aircraft? I've always wondered how would the theoretical (since no airport/plane has it) ILS CAT IIIc guide the plane off the runway? I mean from the perspective of radio signals. What component in the ILS system can help taxi off the runway after landing?

AVweb and other sources mention that:

  CAT IIIc means an actual zero visibility landing because the airplane not only can land and stop itself, but can also automatically taxi in to parking.

There is no provision in the ILS system to provide for an auto-taxi or runway vacate. IIIc is just zero-zero and roll-out control, not auto-vacate as the linked AvWeb article seems to suggest. Its a logical extension of the FAA definition, however auto-taxi is not part of the CAT IIIc definition or system requirements. The only requirement is to get the aircraft on the runway and stopped.

FAA Circular 120.28C provides for the definition of a CAT IIIc approach:

  c. Category IIIc. A precision instrument approach and landing with no DH and no runway visual range limitation.

Right now there is no airport approved for IIIc approaches because the aircraft would just sit on the runway, it has no way of taxiing in. Until an augmentation system like GPS with WAAS or LAAS, or the "Ground-Based Augmentation System" is developed further, automatic taxi is not there.

There is no provision in the existing ILS signals that allow for an aircraft to vacate the runway. GPS is as close as you can get, but that may be unreliable especially with larger aircraft like the Airbus A380 that doesn't have much play on either side, so GPS accuracy will have to be augmented with something. Additionally a system will have to be in place to avoid aircraft from colliding on adjacent taxiways or to manage traffic in and around the gate.

From a technical standpoint, this is a long way off, even with ground based radar systems, GBAS, and LAAS that are currently undergoing evaluation at several major airports world-wide.

Also see this FAA Document 8900.1 and Order 8400.13D


Can GPS be used in lieu of DME for instrument approaches? Instrument approach charts list the equipment required to fly them in their name. For this example let's say we have an ILS or LOC/DME 36R approach. This approach requires an ILS receiver for the ILS portion, or both a LOC and DME receiver for the localizer only portion.

Let's also say we're flying an airplane that has an inoperative glideslope receiver and is otherwise /G equipped with an IFR-certified and up-to-date GPS. Can the GPS be used in lieu of DME in this case?

Yes, the details are in FAA AC 90-108:

  7. Usage of Suitable RNAV Systems. Subject to the operating requirements in this AC,operators may use a suitable RNAV system in
  the following ways.

  (1) Determine aircraft position relative to or distance from a VOR (see first note in subparagraph 7b), TACAN, NDB, compass locator
  (see second note in subparagraph 7b), DME fix; or a named fix defined
  by a VOR radial, TACAN course, NDB bearing, or compass locator bearing
  intersecting a VOR or Localizer (LOC) course

And all fixes, procedures etc. must be loaded from the GPS database, you can't enter any fixes yourself based on lat/long or whatever (section 9(c)(1)).


What is CVG in turbofan engines? I was chatting with an friend about the Embraer 135/145 and he mentioned that the engines have CVG. I assumed it might stand for "continuously variable" something, maybe "gearing," but I'm not totally sure. What is CVG and how does it impact engine performance?

CVG stands for Compressor Variable Geometry. (e.g., this pdf, page 5).

This is a technique to change the pitch angle of the compressor vanes, much like a variable pitch propeller. Wikipedia does not have an article for the use in aircraft (probably because it's not used all that much), but does have an article on a Variable-geometry turbocharger which is closely related (for non-car-enthusiasts: a turbocharger compresses inlet air with help of a turbine at the exhaust). Basically, this system lets you control the pressure ratio independent of the RPM. Advantages include

More efficient settings based on air pressure (altitude / temperature). You basically decouple the turbine stage from the compressor stage (but instead of a gearbox, you use the vane angle). This way, you can optimize your compressor stage to different conditions while keeping the turbine RPM at the most efficient value.
More efficient cruise performance without compromising TO/GA capabilities. Aircraft engines are heavily overdimensioned to account for take-off power and contingencies, which means a bigger engine than strictly necessary and thus less efficiency in cruise. This can now be partially mitigated by varying the compressor vanes pitch for optimal efficiency during cruise and optimal power during TO/GA
Higher engine RPM possible during approach. Normally, to keep your engines spooled up for eventualities, you need to increase their power, and as such need to increase drag with flaps and spoilers to keep the speed down. Now, you can spool up the engine to a high RPM with low compression ratio, and increase power relatively fast without having to overcome engine inertia by increasing the compression ratio by increasing the vane angle.


Can different departure procedures have different transition altitudes at the same aerodrome? Is it possible for operations and ATC to have different departures procedures with different transition altitudes at a single aerodrome? For example:

SID RWY11 with a transition altitude of 2,000 meter
SID RWY29 with a transition altitude of 2,500 meter

No. The transition attitude in a defined area is fixed. For example, in the USA it is 18.000ft and in many European countries it is 5.000ft. It's impossible to have different transition altitudes at one airport, because that would make it impossible to use vertical separation between aircraft close to the transition layer.


Is it currently feasible to glide airliners from cruise level to ILS glideslope (CDO)? Is this possible for some airports to perform full continuous descent operations (CDO), gliding at idle thrust from top of descent to glideslope interception.

(source: Lubo Mitev's Blog)

LAX and UK airports seem to allow some CDO, maybe not from ToD.
What is the current status of such experimentations?
Is this something that could/should be extended to a lot of (or all) commercial planes?

Yes it is feasible, in fact it is no problem at all for an aircraft to perform a Continuous Descent Approach (CDA). The difficulty is that Air Traffic Control (ATC) can not predict accurately how the progress of the aircraft will be during the CDA, so they will need to add extra spacing from other aircraft to ensure safe separation. This reduces the capacity of the airport. Therefore CDA's are only used when there is no need for high runway throughput.

For example, Amsterdam airport uses CDA's from Top of Descent during the night hours and in the early morning. Around 6.30 AM local time they can no longer offer CDA's without risking separation conflicts with other aircraft as traffic start to increase rapidly around that time. They will need to vector and put aircraft on doglegs to ensure separation minima are honoured.


What flights were significantly affected by insects hitting the fuselage? Related
How do insects decrease aircraft performance?
This questions made me think was these effects actually noticeable in an any flights- maybe the pilots had to big changes to their flight management or did they reach emergency conditions?

It is conceivable that an accumulation of bugs on the leading edge of an airfoil would affect its performance.  In fact, the in flight accumulation of bugs occurs at such a low rate, and only at low altitude, that it's not a problem.

Above a few thousand feet AGL, bug density is negligible.  A car, driving at night, or a small plane flying for hours at low altitude may accumulate a mess of bugs.  Even so, such change in airfoil shape and affect on drag is miniscule on powered aircraft that normally spend moments, not hours, at such low altitude, above which there is no bug density.

The common hazard of bugs hitting the fuselage is restriction to visibility through the windscreen.  Bugs on the windscreen can make it difficult to see other aircraft and creates a myopic focus point for the eyes.

Another conceivable problem is blockage of inlets and ports, through most certificated aircraft are designed with alternate systems, e.g. bypass and redundancies to deal with such emergency.  Flight into icing conditions, heavy rain and ash are of concerns here.


Why has the Bombardier CSeries been delayed in starting service with Delta Air Lines? Delta Air Lines placed a large order for the Bombardier CSeries. I don't know the original projected date for the start of CSeries flying, but I think it already passed.

When is DAL planning to start CSeries flying? What is the reason for the delay? Have any problems with the aircraft itself caused the delay?

This delta news brief from February of this year alludes to the fact they are waiting for the Alabama production facility to be completed, presumably where they will build the aircraft.

  Delta still intends to take as many deliveries as possible from the
  new Airbus/Bombardier facility in Mobile, Alabama, as soon as that
  facility is up and running. However, as the ITC notes, the airline has
  contractual commitments to begin taking deliveries later this year and
  the ITC decision clears the way for Delta to accept deliveries in
  Canada as well....

  ....and while pleased that imports from Canada can now be part of the
  near-term solution, Delta looks forward to taking U.S. manufactured
  aircraft from Mobile when that facility opens.

This article notes that during an earnings call they mention early 2019 as the projected start of operations for the aircraft. The article also notes they were slated to take 15 aircraft in 2018 but "program delays" prevented this. The article does not detail what those delays were (presumably the lack of the Mobile facility contributed along with the tariff issues).


How can a two-engine B787 create three contrails? Today I noticed overflying aircraft (over Sydney at FL400) which appeared to have three contrails. When I checked Flightradar24 app, I saw that this overflying aircraft is B787.
What would be the reason for three contrails with only two engines? Could the third be caused by APU, or just by a wake turbulence, or anything else?
I tried to take a photo using binoculars (sorry for the quality, I tried my best). And also a screenshot of the A/C from Flightradar24 app.

Contrails are created due to variances in the pressure of the air, coupled with the amount of moisture in that air.  When the 2 engines of the B787 blast their exhaust out, the high pressure of the exhaust temporarily causes the moisture to condense.  Two contrails are visible.

However, as the pressure waves from the 2 exhaust trails propagate through the open atmosphere, they interfere with each other.  This interference can also affect the pressure of the moist air between the 2 "primary" contrails, sometimes resulting in another, "secondary" contrail.  In fact, because of this, if there were enough moisture in the air, and the engines were powerful enough, there wouldn't actually be just 3 contrails.  Rather, the contrails would present themselves as the crests of a propagating wave much like the crests of water waves as a duck swims by.  In effect, we would see the 3 contrails separating, and between each of the 3 contrails, 2 more "tertiary" contrails would be visible.

Here on Earth though, the pressure variances and the density/moisture content of the air normalize far before any of that exotic pressure wave stuff could occur.  Except we DO get that one in the middle!


How long can an average aerobatic plane sustain 0g? How long can an average aerobatic plane sustain 0g safely?

An aerobatic aircraft (as well as any aircraft) can sustain 0g until the pilot pulls up, the aircraft hits the ground, or reaches terminal velocity.

In order to sustain 0g  the aircraft must be accelerating towards earth at $9.8 m/s^2$ (meters per second squared). That means there isn't much time before the aircraft reaches its maximum speed. Once the aircraft can no longer accelerate at the same rate of gravity, then the occupants will no longer feel 0g. In sky diving (and physics) this is called terminal velocity, which is the velocity at which air friction prevents the object from falling any faster.

Acceleration is change in speed, so naturally you don't have to be going straight down to be accelerating towards the earth (we're talking about vertical speed). If you are going up at 200kts and begin to decelerate at exactly $9.8m/s^2$ you will "feel" like you are in 0g (free fall) even though you are continuing to go up for a few seconds. But this will only last for a few seconds before the aircraft momentarily reaches its apex and you and the aircraft begin moving towards the earth. If the aircraft can match exactly the acceleration of gravity, then you will continue to feel weightless (i.e. 0g).

But you can't continue to accelerate indefinitely towards earth without either reaching terminal velocity or exceeding the aircraft's maximum speed. So the limit of the sustained 0g flight is the pilot pulling back on the yoke and climbing to prevent the destruction of the aircraft and death of all on board.

However, even if the wings broke off of the airplane, and you were plummeting towards the ground in the fuselage of the aircraft, you would only remain weightless so long as the fuselage continued to accelerate towards the earth at $9.8m/s^2$. At some point, if you had enough altitude, the drag (wind friction) on the fuselage would prevent it from continually accelerating towards earth and you would reach an equilibrium speed where the force of gravity equals the force of drag and you would no longer feel 0gs.


How did this plane get into this position and orientation? taken from https://www.google.com/maps/@-33.9418465,151.174248,945m/data=!3m1!1e3

A) Landing from the east, some crosswind and touchdown off center?
B) Taking off from the east, some crosswind "
C) Landed from the south, for some reason turning left onto runway 27R, heading to international terminal "Global Exchange"?

Option A is out of the question. This would have been a VERY late and unlikely touchdown. Option B is possible, but option C is the correct answer, especially when zooming in: https://www.google.com/maps/@-33.9413253,151.1742231,145m/data=!3m1!1e3

Judging by the tire marks on the runway (which appear to go left) this is clearly not the first aircraft (an Air China A330 if you wondered) to perform this maneuver.

The reason is clear: taxiway A2 (the high-speed exit just before the runway intersection) appears to be closed for maintenance: https://www.google.com/maps/@-33.9433411,151.17333,205m/data=!3m1!1e3

This is also evident by the following NOTAM:

  Q) YMMM/QMXLC/IV/M /A /000/999/3357S15111E A) YSSY B) 18/09/21 13:00
  C) 18/09/23 19:00 D) DAILY 1300-1900 EXC SAT E) TWY A BTN TWY G AND
  TWY L NOT AVBL DUE WIP TWY A2, TWY A3, TWY A4, TWY B5, TWY B6, TWY B7
  AND TWY B9 NOT AVBL TWY B3, TWY B4, TWY K AND TWY B8 BTN RWY 16R/34L
  AND TWY B NOT AVBL TWY H BTN TWY Y AND TWY A NOT AVBL TWY J MAX 52M
  WINGSPAN TWY B BTN TWY G AND TWY B10 MAX 36M WINGSPAN REFER METHOD OF
  WORKING PLAN 17/003


Why are the throttle levers for the Comet's outboard engines shaped funny? The throttle levers for the Comet's outboard (#1 and #4) engines are weirdly shaped, with flanges that extend up and partially over the throttle levers for the inboard (#2 and #3) engines:

(Image cropped and annotated by me; original by Geni at Wikimedia Commons)

Why are the Comet's outboard throttle levers shaped like this?

Sean, this will probably surprise you as much as it did me, but the answer is that it is intended to help keep the hand of the pilot operating the throttles on them and not have it slip off. In my opinion, it's a nifty little design detail.


Which is safer? The Piper Tomahawk or the Cessna 152? I have booked my first flying lesson for 2 weeks time, in my first step to obtain a PPL or LAPL. I had done all of my research on the Cessna family, assuming that is what I would learn in. I was satisfied by the safety and glowing reviews by students and instructors alike.
Anyway, my local school has since told me that they don't have the 152 anymore, so I will be learning in a Piper Tomahawk. Some quick reading here states:

The PA38 accident rate ranged from 0.336 to 0.751 fatal stall/spin accidents per 100,000 flight hours, compared to 0.098 to 0.134 for the 150/152.

and

There was always a concern about the stall and spin characteristics of the Tomahawk. The old adage “be careful what you wish for” applies because an overwhelming majority of the PA38 survey respondents requested an aircraft that would stall with more authority than the 152. And they got it.
You’ll hear many people talk about the stall characteristics of the PA38 like they’re referring to a demon, but it should be remembered that this was essentially a design feature to teach better pilots. Unfortunately, this led to a higher than average stall/spin accident rate that earned the PA38 a less than admirable reputation quite quickly (thus the nickname Traumahawk and Terrorhawk).

This isn't as comforting. So taking into account engine reliability, stall issues, etc. - which aircraft really is safer?

From the Wikipedia article on the Tomahawk:

  Safety record:
  According to the Aircraft Owners and Pilots Association Air Safety Foundation, which published a Safety Highlight report on the Piper Tomahawk, the Piper Tomahawk has a one-third lower accident rate per flying hour than the comparable Cessna 150/152 series of two-place benchmark trainers. The Tomahawk has a higher rate of fatal spin accidents per flying hour. The National Transportation Safety Board (NTSB) estimated that the Tomahawk's stall/spin accident rate was three to five times that of the Cessna 150/152.[2]

Earlier in the article it was stated:

  Before designing the aircraft, Piper widely surveyed flight instructors for their input into the design. Instructors requested a more spinnable aircraft for training purposes, since other two-place trainers such as the Cessna 150 and 152 were designed to spontaneously fly out of a spin. The Tomahawk's NASA[1] GA(W)-1 Whitcomb airfoil addresses this requirement by making specific pilot input necessary in recovering from spins, thus allowing pilots to develop proficiency in dealing with spin recovery.

So what this means is that the Tomahawk was intentionally designed to be easy to spin so that instructors could teach students how to recover from a spin.  Other aircraft, like the Piper Cherokee, are almost impossible to spin so instructors cannot really teach spin recovery in those aircraft.

To answer your question on how this relates to safety that depends on how you look at it.  I would argue that a pilot who knows how to recover from a spin is a safer pilot than one who doesn't.  However since the Tomahawk is actually made to spin, there is the potential for increased spin/stall accidents if the pilot messes up.  Aircraft like the Cessna 152 or Piper Cherokee have design features that can "cover up" a pilots mistakes because they are difficult to spin or stall, but if you plan on flying aircraft that are not so hard to stall then not knowing the proper recovery procedures can get you killed.

The main factor in safety is not usually the safety of the plane but the safety of the pilot.  The vast majority of accidents are caused by pilot error.  I would worry more about evaluating yourself as a pilot and understanding if you have the right mindset to be a safe pilot.


When conducting a circling approach, how close do you have to stay to the airport (especially with the new FAA requirements)? I heard that the FAA recently changed how they calculate the protected area for circling approaches, and it looked quite complicated because it changes based on altitude and speed, etc.  Can you please explain how you know when to use the old -vs- new criteria, what distance you can safely use, and how to figure it out quickly when flying?

The protected area for circling approaches is based on distance from the runway(s), and the size of that area (and your approach MDA) depends upon your aircraft's VREF or 1.3×VSO — or, if higher, your actual IAS approach speed. Here's the graphic the FAA uses to demonstrate this, along with the old protected area radii:

New circling minumums

For approaches that use the new criteria, both Aeronav and Jeppesen charts show an inverted "C" in the circling minimums section of the approach plate. This signifies that the approach uses the new, altitude-dependent protected areas. Those areas are defined in the same way as before, but with different radii.

Aeronav (NACO) format:

Jeppesen format:

As far as figuring out how large your protected area is in flight, you'll have to use the inverted "C" as a cue to look up the table that will be included in the appendices of the approach plates:

The NBAA has a more detailed description of the changes, but this basically sums it up.

The update leaves us with what is honestly a less-than-desirable system. Looking up a table to brief your circling radius in flight (or even prior to your flight) is certainly a lot less useful than simply printing the protected area radius on the minimums section. It's worth noting that feature was proposed in 2009 (p. 4) when the change was being discussed.


What are these vehicles with no callsign used for? I keep seeing these land based vehicles whenever I am looking airports on flightradar24, like in the image below:

Why do they come up on the radar? Do they have a transponder? What is the purpose of these vehicles?

They have Mode-S transponders / ADS-B transmitters specifically for vehicles such a the ERA SQUID, Thales MOSQUITO or Saab Sensis VeeLoPDF.

Typically vehicles that operate on taxiways and runways are equipped with such transponders, which ensures the vehicles can be tracked by the Advanced Surface Movement Guidance and Control System (A-SMGCS).
Vehicles that only operate near parked aircraft are usually not equipped.

When using a magnetic mount, these transponders can be easily transferred between cars. This reduces the total number of transponders needed, but makes it necessary to reprogram the call sign after each transfer. For this reason it may have been decided to have no call sign in the transponder at all for these vehicles at Sydney airport.

An example of an airport using fixed installations with call signs is Amsterdam airport. Using FR24 you can see bird control, maintenance, supervisors, tugs, fire trucks etc. driving at the airport and sometimes,  when they forget to turn the system off, on the highway.

After some further investigation, I am fairly sure they use the Saab Sensis VeeLo in Sydney. The units are magnetically mounted to the vehicles. Each unit transmits using a fixed unique 24-bit address (like all Mode-S transponders /  ADS-B tranmitters) and no call sign. In the A-SMGCS software the 24-bit address is mapped to a call sign which is displayed on the Controller Working Position. There is procedure in place to ensure that when a vehicle is entering the manoeuvring area the correct mapping between the 24 bit address and the call sign is in the A-SMGCS system.


Can you get sucked out of a hole in an aircraft? I had always been under the impression that the forces of air rushing out a broken window or hole in an airplane would be pretty limited and nothing near the levels necessary to carry a body through to the outside. The scene in Goldfinger has always been scoffed at by other pilots I have known.

However, recently I discovered that allegedly the pilot of an airliner was sucked out of a cockpit window in 1990 (re-enactment photo below):

Seems fishy to me. Is this for real? Can you really be sucked out of an aircraft window? Remind me to buckle up. Gives a whole new meaning to the word "deplaning".

Yes, it's real. Here's the official accident report on BA5390, which says:

  The commander had been partially sucked out of his windscreen aperture

And:

  The two men tried to pull the commander back within the aircraft [but]
  the effect of the slipstream frustrated their efforts

There's also Aloha 243 where one cabin crew member was ejected, although that was a really extreme case.


Has there ever been a tail-dragger with retractable tail-gear? This comes from a slightly related question about drag from landing gear.

A tail-dragger is the old-school layout of aircraft, particularly WW2-era fighters. It's also known as Conventional Landing Gear.

The first two landing gear is usually retractable, but the tail wheel is not.

At least, I have never seen such a configuration with a retractable tail wheel. Has there ever been one?

Note: question excludes now more common tri-cycles.

Yes, there are. The Boeing B-17 FLying Fortress is one example of an aircraft designed with a retractable tailwheel.

Source: USAAF via Wikimedia, Public Domain (USGOV-PD)

Another example would be the Vought F4U Corsair:

Source: Wikimedia, cc-by-sa-2.0

Doubtless there are also other examples of aircraft similarly equipped with retractable tailwheels.


How can flight attendants respond to an immediate medical emergency? When an airplane is about to takeoff (after leaving the gate), how should the flight attendants respond to an emergency with a passenger which requires medical immediate assistance?

If the pilot knows before committing to take-off and reaching the point of no return then he will abort the takeoff and ask the tower to send an ambulance and stairs.

If he is committed to take off then he will get into the air and then tell the tower of the emergency; circle around (possibly dump fuel depending on the severity) and land again to get the passenger off board on the ambulance waiting near the runway.

Whether the plane can then top up the tanks and take off again will depend on whether the landing was overweight or not. If it was then the plane needs to be inspected before it can be put back into use and the other passengers will need to leave the plane and wait until the next plane can ferry them on.

The cabin crew will apply first aid until the ambulance crew can take the sick passenger.


How is the direction of the hydraulic fluid changed so that the cylinders and pistons can move backwards and forwards? How is the direction of the hydraulic fluid changed, so that components and actuators (cylinders and pistons) can move backwards and forwards?

The direction of travel is controlled by a directional control valve for a double acting cylinder.

The red line is high pressure from hydraulic pump. when the high pressure fluid is entering the right chamber and push the actuator piston to left.
The low pressure fluid in left chamber (blue line) will leave the actuator and return to reservoir.

If we rotated/move the directional control valve clockwise it will look like the figure below :

The high pressure will enter the left chamber and move the actuator piston to right


Does GA flying in your own plane count toward a Airline Transport Pilot license? The video Why the World is Running Out of Pilots discusses a pilot shortage, and notes the tortuous path to an airline transport pilot license (specifically). It claims there are 1500 flight hours needed.

I also know general aviation is in steep decline over the last 50 years, whilst the cost of GA aircraft have gone up dramatically.  I wonder if there is a connection between these two things.

If you own a small plane and fly yourself around in the "Mighty Luscombe" for fun or Youtubing, do those flight hours count toward the aforementioned 1500 hours?

Is there a floor to the minimum quality of airplane which "counts" - do you need a Cessna class, or will a light sport aircraft, experimental, parasail, or a towed glider suffice?

Does these 1500 hours differ in any way from the ~230 hours needed for a "commericial license", or can you do it all in the same Cessna?

In a general sense, would it help the pilot shortage if the government would act to promote general aviation as a hobby, growing it back to where it was?

The video isn't very clear, but most of the numbers it gives are "total time". This is cumulative, so the 1500 hours required for an ATPL includes the 250 hours required to get a CPL, which itself includes the 35-40 hours required to get a PPL plus the 15 hours required to add an instrument rating to your PPL. Also included in there somewhere will be 10 hours to add a multi-engine rating.

All loggable time counts toward the total. It doesn't matter if the aircraft is an airplane, helicopter, gyrocopter,  glider, balloon, powered parachute, etc. However, at least in the US, ultralights cannot be logged because they are legally not "aircraft".

As noted in the video, most aspiring airline pilots get flying jobs as soon as they get their CPL, most commonly as Certificated Flight Instructors. Many schools even guarantee a job as a CFI for students who graduate. Few people can afford tonrent their way to an ATPL, and it just doesn't make sense to use loans to fly when there is a shortage of pilots to take jobs where they can get paid to fly instead.


What is the fatigue life of a fuselage based on? The fatigue life of the fuselage is based on the number of what? Pressurization cycles?

Most (large) aircraft life times are measured in cycles.

  "Aircraft lifespan is established by the manufacturer," explains the
  Federal Aviation Administration's John Petrakis, "and is usually based
  on takeoff and landing cycles. The fuselage is most susceptible to
  fatigue, but the wings are too, especially on short hauls where an
  aircraft goes through pressurization cycles every day." Aircraft used
  on longer flights experience fewer pressurization cycles, and can last
  more than 20 years. "There are 747s out there that are 25 or 30 years
  old," says Petrakis.

But that only applies to pressurized aircraft, there are large planes that are un-pressurized and their life is generally measured in flight hours. However most large aircraft like say the DC-3 don't have any imposed hourly limit on the fuselage but other parts may be hour/life limited.


Is it a violation to list an alternate airport based on an approach your aircraft is not equipped to execute? A pilot has planned a flight to another airport, and the weather indications at the destination require an alternate airport to be included in the flight plan.  An ILS and a VOR approach exist at the selected alternate airport with standard alternate minimums. The airplane to be flown is not equipped with an ILS glide slope indicator, but it has a VOR.

If the weather at the alternate airport at the estimated time of arrival to that  alternate airport is indicated to be a 700 foot ceiling and 3 miles of visibility is this pilot in the above hypothetical situation violating a regulation by filing that alternate airport?

Another way to word this question is, does the approach that the selection of the alternate airport is based on actually have to be an approach the aircraft is equipped to execute?

Based on the regulation wording in §91.169 this is unclear.  Do any relevant letters of interpretation exist?  Otherwise, can you please provide some written evidence to support an answer on this point?

I have emphasized some of the wording pertaining to how this ties in with a flight plan below in the related FAA regulation.  Nowhere in this wording does it say anything about the aircraft having to be able to actually execute any of the approaches mentioned, only that they're "published for that airport".

I am asking this because it seems contrary to common sense ADM, yet it does not appear to be prohibited.

§91.169(c) IFR flight plan: Information required.

  (c) IFR alternate airport weather minima. Unless otherwise authorized
  by the Administrator, no person may include an alternate airport in an
  IFR flight plan unless appropriate weather reports or weather
  forecasts, or a combination of them, indicate that, at the estimated
  time of arrival at the alternate airport, the ceiling and visibility
  at that airport will be at or above the following weather minima:

  (1) If an instrument approach procedure has been published in part 97
  of this chapter, or a special instrument approach procedure has been
  issued by the Administrator to the operator, for that airport, the
  following minima:

  (i) For aircraft other than helicopters: The alternate airport minima
  specified in that procedure, or if none are specified the following
  standard approach minima:

  (A) For a precision approach procedure. Ceiling 600 feet and
  visibility 2 statute miles.

  (B) For a nonprecision approach procedure. Ceiling 800 feet and
  visibility 2 statute miles.

I have not found any LOI's that cover this specifically but a broad interpretation of

  § 91.205 Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment
  requirements.

  ...

  (d)Instrument flight rules. For IFR flight, the following instruments
  and equipment are required:

  ...

  (2) Two-way radio communication and navigation equipment suitable for
  the route to be flown.

Once can broadly say that if you intend to fly an ILS (alternate or not) 91.205 requires suitable equipment i.e. an ILS receiver and CDI capable of displaying as such.


Where are the first two waypoints for runway 4R departures from KBOS? Departure way points for Runway 4R at Logan Airport in Boston Massachusetts. Can anyone send me a map depicting where the first 2 way-points are for 4R Departures?

Checking the IFR departure plates for KBOS, the first two waypoints for all departures from Runway 4R are NHANT and HURBE. You can see where they are on the Google map below.

BLZZR THREE departure plate for reference.


How many parts are in a Boeing 767? I've been Googling how many parts are in what air planes, but I didn't get a result on how many parts are in a Boeing 767.

Anyone got any ideas or know the answer?

According to Boeing (on the "interesting facts" page on the (former) tour website for their Everett facility) their 767 aircraft contain...

...3.1 million parts in a 767 provided by more than 800 international suppliers.
Boeing 767 Facts - Boeing.com


How are Aircraft Noses Designed? Look at the Learjet, Embraer and Boeing noses which are kinda pointy - drag efficiency aside, how do they come to the final design of the nose?

I’m talking from an aesthetic point of view - how do they design them to be aestheticly pleasing as they are?

By hand, CAD software or other? I don’t think it’s random guesswork I produce what looks good and what doesn’t - do my question is: how do they make them noses?

I don’t think in the early days of the 737 they had advance mesh modeling like we do now!

Aesthetics are by far and away the last thing aircraft designers are optimising for. A better question might be, why do aerodynamically-efficient designs look pleasing, but that would likely be an art or psychology question and off-topic here.

Since aircraft could travel at appreciable speeds, designs have focused primarily on drag reduction. Smooth curves and teardrop shapes on the leading parts of shapes help with this. Before 3D fluid modelling software, this kind of design would be achieved using a combination of fluid dynamics computations done by hand, wind tunnel modelling, and likely a bit of intuition.


Telluride (KTEX): Why is the localizer antenna located where the glideslope should be? Telluride (KTEX) in Colorado, USA:

Source

As visible, the localizer antenna for RWY 09 is located where the glideslope antenna is usually found, abeam the touch down zone. The localizer is normally seen at the end of the runway, aligned with the runway center line.

Why was the localizer moved close to the TDZ at Telluride airport?
What is the practical impact for the pilot to have the localizer beam distant from landing path?

The localizer for runway 09 is offset by 3°, almost certainly because of terrain. That would be a typical reason for a non-standard installation.

The approach plate for the LOC RWY 09 approach notes the offset (more than 3° and it would be an LDA approach):

The final approach course for the LOC 09 is 093°, whereas for the two RNAV (GPS) approaches it's 096°, which is also the current magnetic heading of the runway. The Chart Supplement has various notes indicating that terrain is an issue (and RWY 09 has a displaced threshold) so everything indicates that the localizer is offset slightly for that reason, presumably to avoid signal interference.

As for practical issues for pilots, correcting for a 3° offset shouldn't be a problem. A bigger consideration seems to be that the MDA on the LOC 09 approach is more than 2000' AGL so if the pilot breaks out late he'll very likely have to circle to land.


Why do some back course operations use normal sensing? So the LOC/DME-E approach to KASE lists for the missed approach course to use the I-PKN localizer, but then there's a note 'course outbound is normal sensing'.  Does that mean that in effect, this particular LOC is installed 'backwards' so when flying away from it you get normal indications?  How common is this?  Only for LOC-defined missed approaches?

Notice that in the plan view, the shading of the localizers are on the opposite sides. If you are flying south-west, the actual localizer used for the approach has the shading on the right, while the one used for the missed approach has the shading on the left. This can also be used to tell you what sensing to expect.  The note is also there to make it more obvious that the sensing will be backwards from what you might expect when flying outbound on a "normal"  localizer.

So yes, this particular localizer is designed to transmit backwards and you will get indications that would be normal while flying inbound when flying outbound on the missed.

I'm guessing that because of the high terrain/mountains in the area that they wanted to make it as easy as possible to fly without getting confused as to which way you are supposed to turn.  Combined with the fact that it is never used in a situation where you would be flying inbound makes it a perfect candidate to reverse the sensing.  Unfortunately, in my mind it actually makes it harder to understand.  We are taught from the beginning of our instrument training how to handle flying a localizer outbound, and now we have to do it the opposite way.  Rather confusing if you ask me, but you get used to it.

As far as "how common is it", this is the only one that I've seen (but I'm guessing that there are others)....


What are the rules regarding airlines picking up passengers at stops in foreign countries? Suppose Air Canada flies from Vancouver to Santiago with a stop in LAX. I am vaguely of the belief that they are not allowed to pickup Americans who wish to travel from LAX to Santiago, but I'm curious to know more about these rules (if they exist). Also, how they apply (or not) internationally, ie. not just in America.

The short answer to your first question is that an airline can pick up passengers at an intermediate stop as long as it's previously been agreed by all the countries involved (see below). One example is Singapore Airlines SQ12, which flies SIN-NRT-LAX; many passengers leave and board the aircraft in Tokyo.

More generally, these rules are known as the freedoms of the air but they aren't consistently or fully implemented everywhere and a lot depends on agreements between individual countries. Your first question is about the fifth freedom:

  the right to fly between two foreign countries on a flight originating
  or ending in one's own country

As Wikipedia describes, this isn't always straightforward:

  The negotiations for fifth freedom traffic rights can be lengthy
  because in practice the approval of at least three different nations
  is required

If an airline stops in an intermediate country to refuel or for other technical reasons but isn't allowed to board or deplane customers, that would be the second freedom:

  the right to refuel or carry out maintenance in a foreign country
  without embarking or disembarking passengers or cargo

There's an interesting discussion of fifth freedom flights from a passenger perspective here, and you may get better answers on this topic on travel.SE.


Is it required to memorize checklists for better efficiency? Military pilots are instructed throughout training that they must learn all checklists off-by-heart (in the RAF anyway). This way things get done much quicker, primarily in the event of an emergency when the immediate actions must be performed like 2nd nature.

A recently PPL-qualified pilot friend of mine informed me that he refers to his reference cards for every set of checks. The checks for a Cessna-152 were much much more brief than for military trainers.

I was wondering what the standard is for general aviation, and whether there is a requirement to learn at least engine-failure immediate actions?

In the US the closest thing to a standard, and the requirement (per the FAA's practical test standards), is that you make appropriate use of checklists.
As mentioned in that video "appropriate" leaves some room for common sense interpretation (clearly your first course of action if your engine dies in flight should not be to open the operating manual to the Engine Failure In Flight checklist and begin reading: That would NOT be "appropriate").

I expect most other countries have a similar view on the subject.

As far as what gets memorized, the checklists for most simple aircraft (for our purposes let's say that's anything with a single piston engine, unpressurized, with 6 seats or less -- your average Piper/Cessna/Citabria/etc.) can be memorized. They're not that long and there's not that many of them.

Time permitting a good pilot will generally still refer to the printed checklist even if they did the entire thing from memory, if only to read off each item and make sure they didn't miss anything.

More complicated checklists (like what you might find on a 737 or a C-130 for example) will usually have a set of Immediate Action Items (often called "Red Box Items" because many manufacturers put them inside a big red box at the top of Emergency or Abnormal checklists).
It's generally expected that the flight crew have the Red Box Items committed to memory and be able to complete essentially on instinct.

After completing the Red Box Items all the really important stuff is done, and there is hopefully enough time that it's now appropriate to pull out the checklist (or Quick Reference Handbook), verify that the Red Box Items have all been done, and run through the rest of the items.


What is the optimum separation between contra-rotating propellers? What is the optimum separation between contra-rotating propellers?

What factors determine the distance between the two sets of propellers?

Here is a paper that partially addresses your question; however, they discuss a ducted-propeller system.

  The effect of axial gaps showed that at the design speed combination best performance was observed at an axial gap of 50% of the 1st [fan's] chord.

A lot of research on contra-rotating props has been done for ships, it seems. This thesis indicates that, for ships,

  the effects of the spacing between the propellers is almost negligible with respect to the CRP efficiency.

This paper has an extensive review of rotor spacing for helicopters (it's also a good read for answering your second question). The author notes for one configuration that

  the effect of separation distance on the optimal performance of the system is not very noticeable for practical operation,

but for another that

  the separation distance significantly reduced the influence of the mutually induced velocities.

What all this tells me is that the optimum separation distance is likely highly dependent on the specifics of the propeller design and the aircraft's overall design. Various airflows from the aircraft structures (fuselage, wings, etc.) would affect the interference between propellors. The propellors' rotation speed, size, number of blades, and chord would all come into play. Furthermore, "optimum" could be a balance of any number of things, but most likely efficiency, thrust, and noise. Any commercial or military design would need to undergo extensive trade studies and CFD and wind-tunnel testing for the specific model, not rely on a general rule.


How do I have to fold a emergency slide so it can be reused? I have the opportunity to buy a never used emergency slide from an Airbus A320 for cheap. So I need to know how they can be reused and how to deflate and repack them so I can use it for another time.

WARNING

These slides may contain explosive squibs and/or chemicals not safe for ingestion and it is NOT SAFE to mess with them if you do not know what you are doing! If an airbag in a car can kill or cause injury, imagine an enormous version of that. If one became available for sale, I would be very cautious as to whether it had been made safe/inert. Tread carefully.

Only authorised life support fitter type maintainers at the factory or the approved delegated authority will be able to fold slides up again to the correct standard. It is a specialist type job and a jigsaw puzzle. It is similar to trying to get a tent back in it's bag if you don't use the correct technique.

As with all aircraft maintenance tasks, it may sound like a cop out, but the answer to any how do you do that question is "in accordance with the approved procedure". Find the approved procedure and you will know. It will be in the airbus manual or from the manufacturer of the slide.


Should an IFR-certified radio's automated nav aid identification feature be considered positive identification? Should an IFR-certified radio's automated nav aid identification feature be considered positive identification? Should manual identification still be performed? Does anyone know if this is addressed in any FAA regulation or publication?

An example of automated identification is found on the Garmin 430. When a nav aid is tuned automated identification takes place and the result is annunciated visually.

This question has been discussed a couple of times on the AOPA forums (members only) and the conclusion there was that it's completely fine to trust the automated identification. If the system is fully certified for IFR then why wouldn't you trust it? And if you don't trust one specific feature then why should you trust any of them?

Identifying NAVAIDs correctly is in the instrument PTS but the FAA doesn't require any specific method of checking. In my last instrument checkride I used a G1000 and the DPE had no problem with me using the automatic identification; that's what it's there for.

Having said all that, things can and do go wrong, so cross-checking against other sources is still a good idea. For example, when you load a VOR approach from the database, the G1000 will automatically tune NAV1 to the NAVAID frequency and identify it. If either the frequency or the name doesn't match what's on the approach plate - or if the name is missing because it couldn't be identified - then something is wrong and you need to investigate.

Ultimately I think this is a question of comfort level, both personally and with the equipment. Some people will check the morse ID directly every time, out of habit or preference. Others won't, because they're confident that they know the equipment well enough not only to trust it, but also to identify and handle any problems.


Why does a dual-axis autopilot not allow operation in single-axis? Image source: KFC 225 Pilot's Guide (PDF)

In a dual-axis AP, when no lateral mode is selected, a wing leveler (ROL) mode is activated and can't be disengaged unless another lateral mode is selected. Similarly for pitch attitude hold (PIT). (Those two modes are shown above.)

But why, for example, can't the AP hold only the altitude, and the pilot steers laterally. As far as I know any AP with more than one axis doesn't allow single-axis operation. Control wheel steering (CWS / attitude hold) is not what I mean.

Why's that? Regulation? Design limitation?

One benefit of allowing single-axis – I think – is for climbs and descents when there is no speed hold mode. The pilot lets the plane steer left and right, and they control the climb/descent by manipulating the power/trim. Instead of guessing the proper vertical speed – which keeps changing if it's a long climb/descent, unlike trimming for airspeed.

It is neither a design nor regulation limitation. Best explanation I have is that manual control on one axis with the autopilot on another is a bit impractical and goes against normal piloting training techniques. For example banking left/right involves using both ailerons and rudder, but also adding a little bit of pitch up to increase the wing load in the turn.

I used to fly like this a while ago when the pitch axis of one of the autopilots was inop (failed auto-test). It was actually allowed to dispatch (and use the autopilot) but only lateral (HDG/NAV) control was available, with manual pitch. It was uncomfortable to use, counter-intuitive, and we usually just disconnected and flew the thing manually (well, maybe except cruise).


Altimeter shows 100 foot drop when power is added. Is this a leak in the static system or broken altimeter and how long will the fix take? My instructor and I were preparing for my Private Pilot Check ride today when we noticed that the analog altimeter would suddenly lose 100 feet when we added power.  The only way I can think to explain this is that there could be a leak in the static system that caused the altimeter to read the cabin pressure instead of outside static pressure.  We had the cabin vents open so that when the prop blew in more air it probably caused the cabin pressure to rise slightly causing the altimeter to read a lower altitude.  However, we only noticed an error with the altimeter and not with the airspeed or VSI.  At one point I was in a climb and the altimeter was showing my altitude decreasing and the VSI was showing an altitude increase.  If the problem was a leak in the static system you would think that the airspeed and VSI would be affected as well.  I did call the mechanic about this and he decided to take the airplane out of service.

My question is could this problem be isolated to just the altimeter and not the entire static system.  Also, what would the typical downtime be to fix this issue?  I am supposed to take my check ride Sunday but it looks like that may not happen if this would take awhile to fix.

Note:  This airplane does not have the option of using an alternative static source so no it is not due to the alternate static source being selected.

The mechanic will do a static system leak check.  This is done by applying a sealed off suction source to the static port, then applying an inch of suction, causing the altimeter to rise a thousand feet, then holding that for one minute (I do it using a big syringe connected to the blanked off static port on my homebuilt).  The altimeter is supposed to not move more than 100 feet in 1 minute (that's the rather generous Canadian requirement - not sure of the FAA but I assume it's similar)

If there are no obvious static leaks, and the static port itself seems normal, the mech will probably swap out the altimeter and see what happens.  Or, swap out the altimeter first and then try it out.

The leak check will take about 30 minutes, and the altimeter swap-out a couple hours.  Shouldn't take more than a morning to resolve.


What is required for transatlantic flight in a private plane? What equipment is required to fly a small plane across the Atlantic via Canada, Greenland, and Iceland? Is any additional training required beyond an ordinary pilot certificate? Can it be done in VFR flight?

While probably legal to fly over the Atlantic VFR, it appears getting out of Canadas airspace is a different matter. After a bit of googling I found this article on COPA's website, saying:

  Both for flying in the northern parts of Canada as well as in
  Greenland airspace, an ADF is legally required (refer to TC AIM
  3.16.10 and CAR 605.18). I didn’t have one, so one had to be installed. Other than that, FDOW didn’t need any modifications. IFR
  approved GPS is an absolute must; we had three GPS receivers on board.

  Speaking of IFR: As per CAR 602.19, pilots attempting trans-oceanic
  flight must hold an instrument rating. Even though an IFR flight plan
  is only required above 5,500 feet across the Atlantic, NavCanada will
  not issue an oceanic VFR clearance when leaving Canada. In addition,
  it is extremely unlikely for any airplane to stay in VMC during the
  whole trans-Atlantic flight. Therefore, it’s mandatory that both,
  pilot and airplane are certified and current IFR.

That being said, weather over the Atlantic can be very treacherous, especially if you're unable to climb on top.

There are quite a few stories around about crossing the Atlantic in smaller airplanes, there's also an Ice Pilots NWT episode (season 1 episode 9) where they ferry two water-bombers to Turkey, although not very technical, it's a nice watch.


How does increasing the RPM result in a higher AOA for the blades? I know that an increase in velocity (TAS) reduces the AOA and that makes sense. But how just simply increasing the blade rotation (RPM) results in higher AOA?

Prop blades from side view at two RPMs

Vector diagrams help with visualizing prop blades. Above the vertical vector lines are two RPMs, the horizontal vector lines are the forward velocity (the same for both), and the connecting orange vector lines are the resultant airflows. Note the AOA for the same blade pitch and how it is affected by the airflow at the two RPMs.

Note: that's also why slow/windmilling RPMs result in high drag (negative AOA; airflow hitting top side), and why dead engines are feathered if that's an option.