Was differential thrust used in the P-38 to improve turn performance? In the P-38 Lightning could differential thrust be used to improve turn performance ? If so what was the procedure ?

According to WW2 pilots, no. Aside from the dangers in adjusting 1600hp on one side of the aircraft on the fly in the midst of a dogfight... With the P38, they didn't need to. The P38 had an inherent advantage over single engine prop fighters of its era. Its engines (and propellers) rotated in opposite directions, canceling out any torque effect. The counter rotating engines and props were considered a big secret on the P38 when it was first designed. (as if anyone couldn't look at the angle of the props on each side and tell that.)

The pronounced torque of the 1600hp-2000hp single seat fighters played a major role in aircraft handling: both in takeoff and power on maneuvers, something WW2 flight simulators never seem to reproduce. Single engine fighters would roll left far quicker than they could roll right, due to the immense torque of the engine/prop combination, aiding in the left roll but inhibiting a roll to the right. This was most evident at lower altitudes, where the air is thicker and the torque effect more pronounced.

Not so with the P38 - contra rotating engines and props canceled the torque, and the P38 could roll right far quicker than any single engine fighter. While the P38 did have several issues at high altitude, WW2/Vietnam ace Robin Olds held that nothing could beat a P38... down low. (revisit the Dogfights/Air Ambush episode for that)

So, no, they didn't use asymmetrical engine power for maneuvering with the P38 - they didn't need to. Just roll right and turn - no single engine fighter of that day could stay with you.


Is it OK practice to use one altimeter on QFE and one on QNH (local flight, dual altimeters)? PPL student, wondering on how this practice is viewed. The aircraft I'm learning to fly in has a small Dynon EFIS which displays horizon, airspeed, heading & altitude. It also has a regular altimeter.

Assuming I'm going for a local flight, returning to land where I departed, is it OK practice to leave the Dynon on QFE and the Altimeter on QNH? This way I don't have to change any settings.

I would turn it the other way around. Assuming the Dynon EFIS is your main flight instrument I would dial in QNH or QNE (depending on your altitude). Common practise is to always have the second altimeter set to QNE (1013.25hPa; 29.92inHg) but if you do not need an altitude reading in Flight Levels it's fine if you set up one altimeter to QFE.

But remember: Even using this practise you HAVE to change the settings. QFE and QNH are both depending on the local pressure and therefore change pretty often. If you are on a cross country flight you then have to change both altimeters to different settings in order to have a correct altitude and a correct height readout.

Also make sure that you always use the same altimeter for altitude and the other one for height so you won't use faulty values from the wrong altimeter!


How do pilots get enough sleep in preparation for a long night flight? Are pilots authorised to use sleeping pills to rest before long haul flight that departs at night hours? This question comes in mind as I have flown Turkish Airlines flights that depart at 2.30 at night arriving in the morning with the duration of the flight of about 8 hours. Since the pilot or the co-pilot have to be awake (I suppose, at least one of the 2..) during the flight they will have to get good rest during the day. Sleeping during the day is quite difficult and not natural and this is where my question comes from. If not, what remedies do they use?

Short answer: Sleep aids cannot be used this way in the US. FAA regulates the use of such medications with a delay:

Pharmaceuticals (Therapeutic Medications) Sleep Aids:

More on medication advice to medical examiners: Pharmaceuticals (Therapeutic Medications) - Do Not Issue - Do Not Fly.

Only the zaleplon molecule (a Z-drug ⁞ hypnotic) could be used in a practical manner (not publicly available in France nor likely in many other countries).

Circadian rhythm

What you are referring to has got the scientific name of circadian rhythm (circa = around, diēs = day), which is the subject of an article at SkyBrary: Circadian Rhythms. About the night flights:

  Night operations create a host of problems for flight crews. The
  primary problem is having to work efficiently and safely at a point in
  time when the work requirements are not in synchrony with circadian
  rhythms. Under worst-case conditions, crew members must perform
  demanding tasks during the early morning hours (2 am to 6 am) when
  their biological functions and performance efficiency are at their
  lowest level. This problem cannot be quickly solved by adaptation of
  the biological clock. Complete adjustment to night work requires at
  least 21 night shifts in a row with no days off. Adjustment of the
  biological clock does not even commence until about 10 days after a
  shift change.

Fatigue

Long article about Fatigue Countermeasures in Aviation, about zaleplon:

  This misalignment of the sleep/wake cycle and endogenous circadian
  rhythms could be the result of shift lag, jet lag, or attempting
  sleep at other than the habitual bedtime or at the second circadian
  dip in the afternoon. For such circumstances, the U.S. Air Force and
  Army have approved the limited use of temazepam, zolpidem, and
  zaleplon. These hypnotics can optimize the quality of crew
  rest in circumstances where sleep is possible, but difficult to
  obtain.

Inflight rest

As additional information about sleep management inflight: On a 8-hour flight, usually there will be 3 pilots, and each one will be able to sleep (outside the flight deck).

Air France Inflight rest for crews.
Air Canada When do pilots get to rest during long haul flights?
What Do Cabin Crews' Chillaxation Spots Look Like?


Why would landing the space shuttle on water have been unsurvivable? For an aircraft unable to reach a runway on land, ditching in water is a common and, generally, highly-survivable option; however, for the space shuttle, according to Wikipedia, "...an ocean ditching was not survivable" (although it lists no source for this claim).  What was it about the space shuttle that made it incapable of ditching into water in a survivable manner?

The shuttle lands at 220 mph and would break up. This is 40% faster than airliners with twice the energy to dissipate and the shuttle structure is a great deal lighter. The orbiters were designed to go to space, ending each mission of their 100 mission lives by landing on a smooth runway. Airliners are designed for forty to a hundred thousand landings or more and they don't always fare that well in water either.

(Youtube - Ethiopian 961)


Why the dynamic pressure is not mentioned in the explanation of lift by Bernoulli's principle? Usual "explanation" of lift using Bernoulli principle

This theory is:

Air over the wing is accelerated, its dynamic pressure increases with velocity.
The static pressure over the wing decreases (due to Bernoulli principle, see below).
The opposite occurs below the wing, static pressure increases.
This results in an imbalance in static pressure between sides, and explains lift origin.

Source

Bernoulli's principle

Bernoulli's principle explains "an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy":

$$p + \frac{1}{2}\rho V^2 + \rho gh = k$$

where $k$ is a constant. In the case of a wing, $\rho gh$ is so small it can be omitted, the principle can be stated:

$$p_0 = p + \frac{1}{2}\rho V^2$$

where $p_0$ is a constant known as total pressure, the first term is the static pressure, and the second one the dynamic pressure.

The explanation of lift ignores the imbalance of dynamic pressure

The previous theory ignores a similar, but opposite, imbalance of the dynamic pressure (as the total pressure is constant, the arithmetic sum of the two imbalances is also constant):

Why is the force created by static pressure put ahead in the explanation of lift, and the force created by dynamic pressure is not mentioned? If this force is ignored because not significant, why and how much is this force smaller?

In short, "dynamic pressure is not pressure at all" (A Princeton paper on dynamic pressure and Bernoulli's theorem).  "Dynamic pressure" is a term that designates the decrease in pressure, as a consequence of the fluid's / medium's flow velocity.

I recommend that you also examine what NASA has to say:

  Integrating this differential equation:

  ps + .5 * r * u^2 = constant = pt

  This equation looks exactly like the incompressible form of Bernoulli's equation. Each term in this equation has the dimensions of a pressure (force/area); ps is the static pressure, the constant pt is called the total pressure, and

  .5 * r * u^2

  is called the dynamic pressure because it is a pressure term
  associated with the velocity u of the flow. Dynamic pressure is often
  assigned the letter q in aerodynamics:

  q = .5 * r * u^2


How does one determine if an airplane meets airworthiness directives? There seems to be no way to determine if airworthiness directives for your airplane have been complied with. Does anyone know? I found this FAA website but you can type in a type of aircraft and nothing comes up. Also does anyone know where I can find safety bulletins for an aircraft?

Compliance with Airworthiness Directives (ADs) involves an appropriate logbook entry. Examine the aircraft logbooks, or have someone competent in the subject matter—an aircraft mechanic, for example—to determine if applicable ADs have been complied with.

Each AD requires different compliance measures, ranging from a one-time inspection or parts replacement to recurring inspections. In each case, a logbook entry should be made to document compliance. Apart from the logbook entry, the aircraft or components concerned can often be inspected to confirm compliance, such as checking for a marked part ot that a placard installed. The details of what such an inspection could confirm would vary depending on what the AD requires.

In some cases, such as AD 68-17-04, which deals with Cessna stall warning systems, the AD calls for a one-time inspection followed by installation of a placard. The placard calls for the pilot to test the stall-warning system as part of pre-flight. In such a case, compliance with the AD extends beyond the actions of maintenance personnel, and will include pilot compliance with aircraft limitations—the placard.

Now, you seem to be asking three questions, beyond the title question of How does one determine if an airplane meets airworthiness directives? Let me paraphrase these questions:

How does one determine if ADs have been complied with?
How does one find ADs that apply to an aircraft?
How does one find "safety bulletins" for an aircraft?

The first question I have answered above.

The second question is primarily the purview of aircraft mechanics, especially IAs where applicable. The site you linked is a good way to find applicable ADs. It sounds like you may have run into some difficulty in getting the site to work correctly. A search for "Cessna 172" returns 21 ADs. Since ADs list aircraft or component applicability by make, model, and serial number range, among other criteria, each AD will need to be examined to determine if it is applicable to any given aircraft.

The third question is more difficult. Airframe, powerplant, and parts manufacturers may issue Service Bulletins and disseminate them at their choosing. Some manufacturers are easier to deal with in this regard than others. An exhaustive answer on this topic is beyond what is appropriate here, in part because it is constantly changing. If in doubt, contact the manufacturer for what you need.


How do I calculate the aircraft's deviation from track in this exam question? I’ll have my PPL exam soon. I asked my instructor at the school about this question and even he doesn’t know the answer. I’ll appreciate your help.

  Question 22

  Flight from point A to point B. NDB is point B.

  magnetic track (MKK)=245°
  magnetic variation (“delta” m)=5° W
  magnetic compass swing ( “delta” k)=3° E

  When 30 km inbound to point B, your QDM-225° What is aircraft
  deviation from track?

  Right of track 10km(5.4 nm) (Nk=+10km)
  Left of track 10 km (5.4 nm) (Nk=-10km)
  Right of track 6km(3.2 nm) (Nk=+6km)
  Right of track 12,55km(6.7nm) (Nk=-12.5km)

Pretty easy... You are 225° QDM, the track was 245°. Neither QDM nor MKK is nothing about variation or deviation, because both of them are magnetic (i. e. variation already applied) courses (i. e. not heading, therefore deviation is also not an issue).

20° deviation from track at 30 km to the station gives us 30 * sin(20°) = 10.26 km, i. e. approximately 10 km. Our QDM is less than desired track, and we are moving to the South-West, so we are to the North-West of our desired track, i. e. we are on the right side of the desired track. Therefore, the answer is 1, right of track 10km (5.4 nm) (Nk=+10km).


How does the control-board on small drones govern their flight? I saw this YouTube clip for a light weight drone, under a few ounces, with very impressive maneuverability. They used styrofoam for frame and taped the rotors and battery and the control chip to it. It maintains the balance, controls the four motors, pitch and yaw, lift and thrust, basically pilots the drone.  And can do automatic stall recovery or aerobatics?

It seems like the most complex part of these drones, gyro, accelerometer, balance, aviation and navigation (all packed on a tiny board), is the most easy to make and cheapest part!

Can somebody explain to me how the this small flight command center feeds the controls of rotors? Does it have any sense of right side up, gravity? Can it sense the wind by measuring the drift?

Maneuverability with this kind of drone comes with their small size and high thrust-to-weight ratio. When you scale such a dynamic system, the time scales with the square root of size, so the smaller the drone, the higher its agility.

Can it do automatic stall recovery? No, because it never stalls.

Can it do aerobatics? Only figures which are possible with quadcopters if the right control sequence has been pre-programmed. Regular model airplanes can fly pre-programmed aerobatic figures on the press of a button for at least a quarter of a century now.

Does it sense gravity? Yes, by filtering the signals from the accelerometers through a low-pass filter. The dominant vector of the filtered acceleration points down.

Can it sense the wind? Only sudden wind changes, but not constant wind. If you add an absolute reference like a GPS receiver, then yes.

A gyro is a sensor for rotary movements, so it will only sense rotations. It does this with three tiny oscillating structures, orthogonally mounted to each other. A rotation will cause the resulting Coriolis force to move them, affecting their capacitive characteristics, which can be used to measure the turn rate in all three axes.

Accelerometers are needed to measure acceleration, and they also measure gravity. Here again, you will find three tiny, orthogonal structures which are deflected by an acceleration, much like a horizontal beam bends down in Earth's gravity field. Again, capacitive changes are measured and converted to acceleration values in the three axes.

Modern sensors combine both acceleration and turn rate in so-called six-axis sensors (PDF!). They can be run at several Kilohertz, so they take measurements a couple of thousand times per second. This fast rate is needed for the almost instantaneous reaction of virtual reality glasses; the sensors in drones should be happy with a few hundred measurements per second.

A big problem of such miniaturized sensors is their drift: If you only rely on a gyro, you will never be able to tell if the system is truly at rest. If the system is standing still, you can use a 6-axis sensor and take the direction of gravity to remove this drift. But you will still not be able to avoid drift in the rotation around an axis parallel to the gravity vector, plus in a moving system you cannot measure the true direction of gravity, so another sensor is needed which is not affected by movements: A compass. It measures the magnetic field, again in three axes, and can be combined with the first two in 9-axis sensors.

The latest generation of sensors can include an ASIC to run sensor fusion software, so the output is not only digital, but already corrected for drift and presented as quaternions, which are superior for calculating rotations. Also, they include only the two inertial sensors and can act as a sensor hub, so the compass can be placed freely where it is least affected by soft iron effects (PDF!) and is connected via a databus (I²C or SPI).


Where can I find runway usage statistics of USA airports? Ok I’m looking for stats and data of planes arriving at various airports and what runways they use most. I need to know the most used runways for arrivals in airports here in the States. Can anyone point me in a direction where I can easily find this info?

Like @CrossRoads said in his answer, there is no data available on which runways are used most. You will need to listen to LiveATC on several days and keep track of the winds to get a rough estimate. For example, from listening to the tower at KSFO I gather that they usually land on 1L and 1R and take off on 10L and 10R. However, when the winds are too strong out of the east they use 10L and 10R for landing.

Likewise, if you listen to the tower at KJFK you can tell which runways are in use on any given day. There appears to be more variability there because the winds are much less consistent.

And then there are airports like KOAK and KSJC that have one runway or set of runways that GA aircraft use and one for the big guys.

The airports might keep that kind of information so a call to a few of them might give you some answers, but I am not aware of it being published anywhere.


Could older airplanes be retrofitted with engines with chevrons? The 787 uses a variety of sound reducing mechanism including engines with characteristic chevrons:

(Source wikimedia commons)

Would it be possible for older airplanes to also have this type of quieter engine retrofitted? I'm assuming the engines would have to be recertified of course. But do the chevrons implicate a particular type of wing or airframe that requires them to be designed in from the beginning?

The chevrons do not implicate a particular type of wing or airframe. However, the engine does need to be designed around having the chevrons, since they affect the performance as well as noise. And the engine design certainly can affect the design of the wing.

In reality, chevrons are more likely to be incorporated in an engine design from the start rather than retrofitted later. And a new engine design will probably be for a new airplane design. This could be a totally new plane like the 787. But it could also be a new derivative, like the 747-8 or the 737 MAX.

So while chevrons can be added to the engines on an existing aircraft model, it's much more likely that the aircraft model will be upgraded in other ways as well to accommodate the new engines. Adding chevrons is likely to be part of a design change large enough to justify changes to the aircraft as well.

However, these changes are not really specific to the engine having chevrons. Changes to the wing and airframe will be due to the inclusion of a new engine, not just the addition of chevrons.


How would the Airbus A320 PFD respond to failure of all pitot and AOA sensors? In theory, if all 3 pitot tubes and all 3 AOA-sensors would fail simultaneously for a period of time, could the PFD still deliver correct roll angle and horizontal displays? How would the plane calculate the actual airspeed?

The primary flight display¹:

is a single display, but it shows five separate instruments:

On the left, the speed tape. This shows the value from the pitot probe.
In the middle the attitude indicator. This shows attitude from gyroscopes. All gyroscopes are grouped in the “inertial reference unit”.
On the right the big tape is altitude. This shows the value from the static port.
The smaller tape at very right is vertical speed. It is normally taken from the inertial navigation system, which is part of the inertial reference unit, but can fall back to the static port.
On the bottom is compass. This shows the value from the inertial reference unit, which has drift automatically compensated by reference to magnetometer.

The angle of attack is not displayed anywhere. It is only used for stall warning, as part of the alpha-protection logic and for checking the weight set in FMGC.

For all the instruments, each instrument shows value from one input. The three pitot probes, static ports and inertial reference units each feed one of the three displays in the cockpit: captain's PFD, copilot's PFD and the standby instrument (which in the modern version looks like smaller PFD and is placed between captain's (left) displays and the centre display.

When any of the input fails, the computer will generate a warning (accompanied with the annoying cricket sound) stating that the values do not match, but it leaves it up to the pilots to determine which one is wrong. The pilots can then switch the displays to show the one they determined as trustworthy.

So:

If all pitot probes failed, the speed would show nonsensical values, but the attitude, altitude and heading would remain operational. The system would fall back to alternate law. There is an unreliable airspeed procedure where the aircraft is kept in safe speed range by reference to attitude and vertical speed. Failure to execute that procedure properly was an important part in the accident sequence of Air France flight 447.
If the angle-of-attack vanes fail, the stall warning and alpha floor protection will not work, but all displays would work. However, the system may actually not notice that they failed as evidenced by the accident of XL Airways Germany flight 888T. This was a test flight where they intentionally tried to activate the alpha-floor and it did not activate without any prior indication because the AoA-vanes froze due to improper wash.

¹ The image shown clearly is supposed to be Airbus PFD, but some elements like the protection indicators and the Mach number are missing. I just didn't quickly find better as this one is very readable.


On the F15-E, can the WSO take over if the pilot is incapacitated? The F15-E Strike Eagle features a two-man cockpit. The pilot in the front seat and the WSO (Weapons System Officer) in the back seat.

If the jet is cruising straight and level is mechanically sound but the pilot becomes completely incapacitated (from a heart attack for example) can the WSO take over and land the aircraft? I could imagine that the correct procedure may be to just eject both the pilot and themselves. Do WSO's learn to fly the F15?

The following image is the backseat cockpit area of a F-15 E where the WSO sits. Note the control stick and the throttle control I've highlighted with red arrows. Surely this means the WSO has the ability to take over control?

source(http://i61.tinypic.com/dbqp2q.jpg)

Short answer, yes.  However, it is important to note that the WSO is not a pilot.  The WSO is trained to operate the weapons systems, not fly the aircraft, but does have basic flight controls including throttle, stick, rudder pedals, compass, HSI, etc.  He does not have good forward visibility and would likely have to be talked in on final approach by the tower, as his view is obstructed by the pilot's seat.

Although the F-15E was developed from the D-model used for pilot training, the airframe was significantly redesigned for it's new purpose, and the back seat of an E-model bears only a passing resemblance to the back seat of a D-model.  The WSO has a very specific and complex set of tasks which does not include flying the airplane, and his controls are designed around that purpose.  He has more screens than the pilot to look at, and two side-stick controllers (not part of the flight control system) that are used for controlling / selecting / guiding / programming / etc. a large variety of weapons. He also has primary control over the FLIR and laser pods used for target designation and tracking.

On a final note, it is not uncommon (although less common in these days of sequestration) for non-aircrew personnel to be given 'incentive rides' in the back seat of aircraft like the F-15D/E or F-16D, and during these rides control of the aircraft is invariably passed to the passenger.  I was privileged enough during my Air Force career to get a ride in the back seat of an F-15E (tail number 88-1671 at Seymour Johnson AFB, NC) and can say from personal experience that it is possible to fly an F-15E from the back seat.  It was the most exhilarating 5 minutes of my life.  Fortunately for both of us, the pilot didn't experience any problems during the flight...


What will the pilot do if all the airspeed indicators fail? Are there any alternate instruments to indicate the airspeed in case of pitot tube failures?

Some aircraft have angle of attack indicator, but most don't even though they have the sensor and use it for stall warning.

What you normally have is an unreliable airspeed procedure. This generally says that you should, depending on phase of flight, maintain specific pitch, set specified thrust and then adjust for rate of climb/descent while keeping the pitch.

Since aircraft is trimmed for speed, generally the procedure calls for being light on controls and correct mainly with engines. Exception is Airbus which keeps auto-trimming even with speed disagree warning on, so there side-stick controls climb and power controls pitch almost independently.

See also unreliable airspeed procedure for A330.


Would there be any further restrictions on the Zapata Flyboard Air than current FAA regulations for ultralight aircraft? We are seriously considering investing in Zapata Flyboard Air personal hovercraft.  We will use it on the east coast of USA Delaware, Maryland, New Jersey.  The Flyboard Air was designed to fit FAA guidelines for ultralight aircraft.

However this article covers how this vehicle has been banned from flight in France where Zapata is based.  While aviation regulations have always been more stringent in Europe, we don't want to risk our investment.  Would there be any additional regulations for this type of personal hovercraft over and above those already applicable to ultralight aircraft?

Would federal regulations override state and local laws that are bound to come?  How about Homeland security and privacy concerns?

If the Flyboard Air meets the definition of an ultralight from 14 CFR 103.1 then only part 103 regulations would apply. 103.7 says that ultralights are exempt from airworthiness, registration and pilot certification requirements, and 91.1(e) says that general flight regulations don't apply to ultralights.

Based on the specifications on Zapata's website, there are two models: the Flyboard Air EXP and the Flyboard Air UL. The EXP doesn't meet the part 103 requirements (its fuel load and top speed are too high) but Zapata says the UL was designed to comply with part 103 and the quoted specifications do seem to be OK.

Assuming that you're fine with the UL model there are still two points in part 103 that might be an issue for you. First, the stall speed requirement in (e)(4):

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

I don't know how the FAA would define a "stall" for a Flyboard and their detailed guidance on part 103 (dated, but seems to be still current) doesn't clarify it. It does say that a "recognized technical standards committee" can confirm that the requirement has been met, but I don't know who that means. You might want to ask Zapata how the UL complies with this requirement (and how they documented it).

Second, you can't use an ultralight in some commercial activities. The FAA document lists activities that are allowed (e.g. airshow participation) and others that aren't (e.g. aerial advertising). If you plan to use it only for private recreation then that doesn't matter, of course.

Finally, note that the FAA's document says that if you "encounter" an FAA field inspector for any reason it's up to you to prove that the ultralight meets the definition in 103.1. If you can't, they'll consider it as an aircraft for compliance/enforcement purposes. Before making your investment, I'd make sure that you're confident you can prove it really is a part 103 ultralight. If you aren't sure that you have the right information to do that, you could contact your local FSDO and ask them to review whatever you have and tell you if they would be satisfied.

(This answer is only about federal aviation regulations. If the Flyboard causes a lot of noise as mins mentioned, or disturbs people or the environment in some other way then there could be non-aviation, state or local laws that would apply.)


Is this an external cannon on an F-16? What is the black pod starboard of the front landing gear on this F-16-I? At first I thought that it was a laser finder, but upon closer inspection it seems to resemble some type of short cannon. What might it be?

What you seem to have found is the Litening Targeting Pod.

  Northrop Grumman's widely fielded LITENING system is a combat proven,
  self-contained, multi-sensor targeting and surveillance system.
  LITENING enables aircrews to detect, acquire, auto-track and identify
  targets at extremely long ranges for weapon delivery or nontraditional
  intelligence, surveillance and reconnaissance missions. Source

pod http://media.defenceindustrydaily.com/images/ELEC_LITENING-AT_on_F-16C_lg.jpg

The F16 does have a cannon as well, but it's located on the port side under and aft of the canopy:


Why does a pilot want to hold a Squawk Code when leaving Class B airspace? I was listening to liveATC today... Controller clears this guy into the class B for a transition and throws him a code. Some time passes and the pilot has now transitioned the bravo and is leaving the airspace. The conversation goes roughly like this:

ATC: N12345 are you going to want a handoff?

N12345: No sir but we'd like to hold our code

ATC: Okay, N12345 you are leaving my airspace, radar services terminated, squawk VFR, frequency change approved, see ya!

Now, I guess this boils down to two questions:
1) Why would he want to keep his code if he's not being handed off to another controller? What difference does that make?
2) Why did the controller still say to squawk vfr, even if the pilot wanted to keep his code and the controller said that's fine? Didn't the pilot go against an atc order by keeping his code and not squawking 1200?

I'm a sport pilot and have yet to use flight following (nor do I have my class B endorsement), so maybe I'm just missing something due to lack of exposure!

The pilot means: I'll be back again, so please don't assign this code to someone else.

Less workload for a pilot going in and out of class-B airspaces, and less hassle for the controllers, so they don't keep assigning a different code to the same plane.

The pilot will switch to the VFR code (1200 in the USA), and then use the one he's written down and used earlier for future passes.


Why is the thrust/drag increase much lower at a lower FL with weight the only variable? From and related to: What is the relation between drag and weight?

  Friction drag is not affected by the angle of attack change.
  The [induced] drag will increase with the square of the mass increase.

I have no doubt about that, in fact I was going to post the same answer, the reason I waited is because I could not explain the A320 performance figures using this method.

The drag breakdown for an A320 at FL 370 and M0.78 is:

  7,900 lbf of drag is composed of 4,700 lbf of parasitic drag (...) and 3,200 lbf of induced drag.

Let's consider a 32% weight increase -- from 50 to 66 tonnes. Applying 1.32^2 to the induced drag raises the total drag by 30%.

If we used the FF (fuel flow) as a thrust (also drag) measure -- since at a given FL / IAS / TAS the TSFC shouldn't vary that much when the N1 is ± a few percent --

... we find the ΔFF is 7% at FL 290 and 20% at FL 370. 20% is closer to the 30% thrust/drag estimate. Why is the thrust/drag increase much lower at a lower FL with weight the only variable?

At a lower flight level the air density is higher, so a lower lift coefficient can be trimmed and the induced drag is a smaller fraction of total drag. Hence, the mass increase causes a much lower increase in overall drag.

At higher altitude the friction and pressure drag is lower but the induced drag is higher, so increasing the mass will cause a much higher jump in drag.

Now for the numbers: In FL 290 the indicated speed is 155.362 m/s, so the dynamic pressure $q$ is 14,784 N/m². I use surface area $S$ (124 m²) and aspect ratio $AR$ (b²/S = 10.33) from Wikipedia and guess that the Oswald factor $\epsilon$ is 0.8. Now the lift coefficient $c_L$ at FL 290 and 50 tons mass is
$$c_L = \frac{m\cdot g}{q\cdot S} = 0.2675$$
This allows us to calculate the induced drag:
$$D_i = q\cdot S\cdot\frac{c_L^2}{\pi\cdot AR\cdot\epsilon} = 5052\:\text{N}$$
which is just 1136 pound-force; about a third of what you give for FL370. This fits well with the given thrust increase at FL290 which is about ⅓ of the increase at FL370.


What equipment does an A320 need in order to operate under RNP 2? What are the aircraft equipment/systems eligibility requirements for Airbus A320 airplanes to operate in RNP 2 airspace?

According to ICAO/EASA till 12/2015 Version.
And from Airbus getting to grips with modern navigation.

  Regulatory Authorities have published standards for specific
  airspaces. Provide certification and operational requirements for
  Basic RNAV (RNP-5 Type) and for Precision RNAV (RNP1 Type) within
  European airspace (refer to Annexes 5.1 and 5.2 at the end). FAA Order
  8400.12A addresses RNP-10 operations in oceanic and remote areas (refer to Annex 5.3 at the end). Also RNP AR required equipment is
  specified in several sources and the FCOM manual of airbus. In
  addition for RNP 2 specific terminal and approach operations the
  requirements are specified on the approach charts of airports that implementing it.

Most of the operators/airlines are using the standard required equipment for RNP 1.

  According to FCOM A319/A320/A321 FLEET / PRO-SPO-51 P 8/10 The minimum navigation equipment required to enter RNP 1 airspace is:

  ‐ One FMGC

  ‐ One MCDU

  ‐ One GPS

  ‐ Two IRS

  ‐ One FD in NAV mode

  > ‐ Two NDs (the temporary display of ND information via the PFD/ND
  switch is permitted on one side).

Some helpful information also about RNP 2 you can find also here: http://www2010.icao.int/NACC/documents/meetings/2013/pbn2013/ops7-en.pdf

Moreover Airbus company under PRO-SPO-51 P 5/10 in FCOM refers as RNAV1(2)
so it takes exactly the same equipment for RNP 1.

Let me know if something is different, or if you have different information from another specific-related documentation.


Why does flight duration differ for the same flight? I was checking the flight duration between two places over a 2-3 month period. The flight duration for the same flight is different for different months. For example, some days the flight takes 13 hrs 10 minutes and some other days it's 12 hrs over the same distance. How does this happen? Moreover, this data is available long before the departure of the flight; I am curious to know the reason. What are the factors that decide this?

Several possible reasons:

different equipment (not every aircraft flies at the same speed)
different routing
known seasonal changes in high altitude winds (which can prompt routing changes)
extra time built in in some periods for historically experienced frequent delays during those periods (e.g. in summer when a lot of inexperienced travelers with small children are expected, boarding and deplaning tends to take longer than in spring and autumn when there's more business travel).

I'm sure there are other reasons as well.


Why aren't tilting propellers used as an alternative for ailerons or elevators? I was wondering what are the reasons for not using tilted propellers fixed to ailerons/elevators/elevons? Or even on wings with no control surfaces at all? Wouldn't the 2nd way of thrust vectoring greatly simplify aircraft design?

There is a huge variety of VTOL aircrafts, but all seem to have puller propellers in frontal wing area with ailerons/elevators separate.

It isn't done because a moving control surfaces is easier to design and build than an engine mount that rotates.

Plus the associated structure needed to accommodate the thrust, p-factor, and gyroscopic loads is going to be a lot heavier than ailerons, spoilers, moving tail plane, etc.

Another issue is if one loses one or both engines, your roll and pitch control disappear as well.


Why is Bombardier selling off all of its airliner series? Bombardier’s product lineup formerly had three separate families of airliners (in addition to its side business with the Challenger, Learjet, and Global business-jet series):

The DHC-8 (Dash 8, Q-Series1) line of 39-to-90-seat regional turboprops, acquired with Bombardier’s 1992 assimilation of de Havilland Canada (hence the “DHC” in the name); the DHC-8 itself had originally entered service back in 1984.
The CRJ (Canadair Regional Jet) line of (surprise!) regional jets, which entered service later in 1992 as a stretched airliner version of the Challenger 600 business jet (which was originally produced by Canadair, and was acquired, along with its parent company, by Bombardier in 1987, thus explaining the “Canadair” in the CRJs’ long-form name); the original version was the 40-to-50-seat CRJ100/200 series, produced until 2006, but this was later superseded by the 50-to-104-seat CRJ700 series, which entered service in 2001.
The CSeries line of 108-to-160-seat midrange jets, a homegrown Bombardier design which entered service in late 2016.

Recently, however, Bombardier has been selling off their airliner lines seemingly as quickly as they can find buyers to take them off their hands:

In mid-2018, Bombardier sold a majority stake in the CSeries to Airbus (who renamed it the Airbus A220), and sold off its remaining stake in the project in February 20202 (although Bombardier does continue to build them at its Montréal factory, albeit merely as an Airbus contractor).
In mid-2019, the DHC-8 was sold to Longview Aviation Capital, which resurrected the De Havilland Canada name for a company it established to build the aircraft.
Finally, Bombardier is currently (as of mid-2020) finalising a deal to sell the CRJ series to Mitsubishi Heavy Industries, which would drive Bombardier out of the airliner market completely.

These sales are allegedly to improve the company’s profit margin; however, divesting oneself of one’s flagship products seems completely self-defeating (in a boiling-the-seed-potatoes kind of way) as a strategy for making more money, as it eliminates their ability to sell more of these aircraft in the future.  (Moving out of the airliner business to focus solely on business jets is looking especially stupid right now, given that business aviation, unlike commercial aviation, is unlikely to recover more than partially from the current state of affairs.)

What is Bombardier trying to get at here?

1: Technically, the Q-Series moniker only refers to the later DHC-8s equipped with active-noise-suppression equipment; however, with the exception of the DHC-8-100 (which was never equipped with the system, and which left production in 2005), all DHC-8s delivered since mid-1996 are so equipped, including all DHC-8-400s.

2: Thanx to @JZYL for pointing this out.

It's important to understand that Bombardier Transportation/Aerospace, while ostensibly a company separate from the original Bombardier family (which only retained a minority stake when it was split off from Consumer Products - snowmobiles, watercraft, etc), is still actually controlled by the family due to a bizarre dual class share structure where the family retains its minority stake in the form of class A shares that have many more votes per share (I think it's 9 or 10 votes or something like that) than the single-vote class B common stock.  This gives the family control of the company, and makes it takeover proof (also making it very difficult to raise private capital), even though its equity stake is a small minority one.

But the basic problem is the C series and to a lesser extent the Global 7000, just about broke the company.  So broke they were forced to give the program to Airbus more or less for free.  The CRJ line was neglected due to the commitments for the C with little in the way of proper design updates.  This handed over dominance on the Regional side to Embraer (who's newest Ejet is basically a baby C-series technology wise) and CRJ production is winding down (it is now a Mitubishi product - M's interest wasn't in the Regional Aircraft program, but its support and spares organization, where M was hopelessly lacking).

On the corporate side, the Lear 85 disaster and the Global 7000/7500 development was another money hole, almost as bad as the C.

So in nutshell, since the traditional government money tap the company has traditionally relied on has largely dried up, the family has decided to dump everything (including rail) and just retain the consumer products operation, the separate family controlled company, upon which the whole business was founded, that was spun off some years ago.


Is skydiving not NOTAMed in the US? Recently there was a mishap at South Lakeland Airport in Mulberry, Florida where a Cessna 170 collided with a skydiver. Luckily all involved suffered only minor injuries. As far as I know, skydiving in Germany must be NOTAMed, is this not the case in the US?

The incident was caught on a series of stills:

14 CFR 105 covers parachute operations in the USA.

There is not a requirement for a NOTAM, but since this happened at an uncontrolled airport the nearest ATC facility must be notified at least 1 hour in advance but not more than 24 hours in advance and, they must have approval from airport management.

Then for the actual jump, ATC must be notified at least 5 minutes prior to jump via radio from the aircraft.

  §105.23   Parachute operations over or onto airports.

  No person may conduct a parachute operation, and no pilot in command
  of an aircraft may allow a parachute operation to be conducted from
  that aircraft, over or onto any airport unless—

  (a) For airports with an operating control tower:

  (1) Prior approval has been obtained from the management of the
  airport to conduct parachute operations over or on that airport.

  (2) Approval has been obtained from the control tower to conduct
  parachute operations over or onto that airport.

  (3) Two-way radio communications are maintained between the pilot of
  the aircraft involved in the parachute operation and the control tower
  of the airport over or onto which the parachute operation is being
  conducted.

  (b) For airports without an operating control tower, prior approval
  has been obtained from the management of the airport to conduct
  parachute operations over or on that airport.

  (c) A parachutist may drift over that airport with a fully deployed
  and properly functioning parachute if the parachutist is at least
  2,000 feet above that airport's traffic pattern, and avoids creating a
  hazard to air traffic or to persons and property on the ground.

  §105.25   Parachute operations in designated airspace.

  (a) No person may conduct a parachute operation, and no pilot in
  command of an aircraft may allow a parachute operation to be conducted
  from that aircraft—

  (1) Over or within a restricted area or prohibited area unless the
  controlling agency of the area concerned has authorized that parachute
  operation;

  (2) Within or into a Class A, B, C, D airspace area without, or in
  violation of the requirements of, an air traffic control authorization
  issued under this section;

  (3) Except as provided in paragraph (c) and (d) of this section,
  within or into Class E or G airspace area unless the air traffic
  control facility having jurisdiction over the airspace at the first
  intended exit altitude is notified of the parachute operation no
  earlier than 24 hours before or no later than 1 hour before the
  parachute operation begins.

  (b) Each request for a parachute operation authorization or
  notification required under this section must be submitted to the air
  traffic control facility having jurisdiction over the airspace at the
  first intended exit altitude and must include the information
  prescribed by §105.15(a) of this part.

  (c) For the purposes of paragraph (a)(3) of this section, air traffic
  control facilities may accept a written notification from an
  organization that conducts parachute operations and lists the
  scheduled series of parachute operations to be conducted over a stated
  period of time not longer than 12 calendar months. The notification
  must contain the information prescribed by §105.15(a) of this part,
  identify the responsible persons associated with that parachute
  operation, and be submitted at least 15 days, but not more than 30
  days, before the parachute operation begins. The FAA may revoke the
  acceptance of the notification for any failure of the organization
  conducting the parachute operations to comply with its requirements.

  (d) Paragraph (a)(3) of this section does not apply to a parachute
  operation conducted by a member of an Armed Force within a restricted
  area that extends upward from the surface when that area is under the
  control of an Armed Force.

Even more information is available in AC 105-2E.


How works the system of frequency for aircraft commercial Airline Hello  I have to present a weather radar technology but i m block on  Air convention of communication.

I need to know how they exactly attribute licence to an aircraft and how all this aircraft can communicate without create collision between their communication .

Question one : Who attribute frequency for an Aicraft and how ?
- How are they attribute telecommunication frequency for commercial Aircraft .Each time they do a new fly someone give them a new frequency band ? They have a frequency band  for a specif numbers of fly ( E.g after 10 fly ) ?

Which authority give frequency band each countries ? but that mean if it's not a international authority you can use the frequency band only in this countries
Which authority decide into international zone what frequency band do you use ?

Question two : To much aircraft for number of channel
You have more than 20 000 aircraft use in the world however  I read you have 118–136.975 MHz Airband and only  potentially permitting 2,280 channels
so that mean a channel is use by more than one aircraft so what happen if two commercial aircraft have to use the same range of frequencies how their is not interference ?

My source :
 (https://en.wikipedia.org/wiki/Airband )
http://www.caa.co.uk/Commercial-industry/Airspace/Communication-navigation-and-surveillance/Radio-licensing/Radio-licence-categories/

Thanks you in advance for your supports.
Best regards,
CANAL Bastien

I think you have a misunderstanding on how individual radio frequencies are used.

Individual radio frequencies are not assigned to aircraft.  They are assigned to Air Traffic Control facilities like Control Towers or Area Control centers.

Each aircraft will have it's own "radio licence" but they can tune in any frequency that is needed for both transmitting and receiving. All aircraft in a specific area will use the same frequency as assigned by ATC. You may have 20 or 30 aircraft on the same frequency, but only one aircraft should be transmitting at any time.

There is a lot of congestion on the radios in a busy sector and "CPDLC" (Controller–pilot data link communications) is gradually being introduced in many areas. This allows ATC and the pilot to communicate directly via data-link text messages.

In some areas where there is no ATC control, aircraft can monitor or communicate on a common "air to air" frequency.  123.45 is used in some areas.


Can a missile be fired when a fighter jet is inverted? Is there an attitude limit for firing a missile from a fighter jet? Can the pilots fire them when they're pulling Gs, or inverted?

The combat advantage of fighters (as opposed to heavier-payload bombers) is their maneuverability, therefore a missile delivery restriction such as g-limit (think Sidewinder heat-seeker in a dogfight) or attitude would unnecessarily restrict their efficacy.

As a Vietnam-era fighter and attack pilot I fired both unguided (aim and shoot rockets) and guided (target lock-on and shoot) missiles, and neither had associated attitude limits. Missiles that fall clear of the weapon station before rocket-motor ignition (such as the TV-guided Walleye or the optically-pilot-guided Bullpup) are obviously restricted from negative g to ensure safe separation from the airplane, i.e., negative g release from an under-wing weapon station would all but guarantee impact with the airplane.


Why don't modern fighter aircraft hide their engine exhaust? In many photographs, the F-4's unique geometry hides one or both engines. I've been told that this is one of the terrific accidental features of the F-4, as it would help shield the hot exhaust from sensors used on heat-seeking missiles.
Is it true that the F-4 was harder to target with heat-seeking missiles due to the shape of the empennage? If so, then why don't modern aircraft use a similar design?
Example images:

There are a few which do (none of them in production, though) and the reason is the added weight and restrictions in varying nozzle geometry for best efficiency.
The tail arrangement of the F-4 is the result of its heritage. Early McDonnell jets all had the fuselage extended past the engine exhaust in order to shift the engine mass forward, near the wings, so the internal ducting could be as short as possible while the long fuselage held the large amount of fuel required for their initial design as long-range escort fighters. Originally the engines were placed in the wing roots (F2H Banshee) and moved into the fuselage as wings became smaller and thinner while engines grew in size.
Compare the XF-88, the F3H of the Navy, the F-101 Voodoo and the F-110, later to be renamed F-4, and the similarity should be obvious. Other manufacturers like Northrop with their the F-89 Scorpion used the same layout. Like all earlier models, the initial designs of the F4H (the F-4 in the old Navy designation system) used a straight tail. To be fair, at this time IR guided missiles were in their infancy and a low IR signature was not part of the requirements.

XF4H-1 wooden model (picture source)
The later addition of dihedral to the outer wings and anhedral to the tail was for aerodynamic reasons, not to improve IR signature.
NASA's history pages report that

the […] high position of the horizontal tail in combination with the wing-shape parameters led to undesirable nonlinear pitching-moment characteristics at high angles of attack. The large anhedral angle, or droop, of the horizontal-tail surfaces greatly improved the pitching-moment characteristics, as well as increasing directional stability. To achieve the proper balance in dihedral effect for the integrated aircraft configuration, however, a large positive dihedral angle was incorporated in the outer panels of the wing. In addition, the wing dihedral elevated the wingtip vortexes relative to the horizontal tail and further improved the pitching-moment characteristics of the aircraft.

The biggest threat using IR targeting are small, shoulder-launched missiles which target the airplane from below. The F-4 engine and tail arrangement will do nothing to hide its IR signature from them. There are modern fighter designs which hide their IR exhaust, and they place the exhaust on the upper rear fuselage for the reason outlined above.

Top view of the Northrop XF-23 (picture source). However, using a rectangular duct for high-pressure flow requires much more mass than a round duct. Also, optimizing this duct for afterburner operation and thrust vectoring is much harder than with a round duct right at the end of the fuselage.


Would a flight consisting of solely first-class passengers be cancelled due to center-of-gravity issues? Consider any modern jetliner (narrow-body and widebody separately) in a standard 2 or 3 class configuration. If somehow only first-class or business-class passengers bought seats, would that plane be impossible to fly because all the weight is focused up front? And since they are premium-class they can't be moved aft for load-balancing.

If this is (practically) impossible, then doesn't that suggest there is a minimum number of economy passengers required as "ballast" for every premium passenger?

I suspect one answer might be that the flight wouldn't be profitable anyway with few-to-none economy seats sold, so it would be cancelled. But let's suppose in that case the aircraft needed to be flown anyway because it was required to be at the destination airport, profitably or not. Doesn't that suggest there is a maximum "premium-only" passenger count that would actually be less than the number of premium seats? I.e they would have to tell some premium passengers "sorry you're bumped, or you can go to economy" despite the plane being 80% empty?

It is much more difficult to load a plane so that the center of gravity ends up being too far forward than too far aft.
Excessive weight forward can almost always be counteracted by increased trim on the stabilizer.

When small GA planes crash due to Balance, its almost always too much rear-weight, not too much forward-weight.

Especially in the case you describe, the pax probably have luggage, and the luggage can be loaded in the rear of the plane for balance.


Why does wake turbulence sink? There has been a remarkable story this week of a Challenger 604 business jet being rolled after encountering the wake turbulence of an A380.

A Challenger 604 at FL340 operating from Male-Abu Dhabi passed an A380 opposite direction at FL350, one thousand feet above, about 630nm southeast of Muscat, Oman, over the Arabian Sea.
A short time later (1-2 minutes) the aircraft encountered wake turbulence sending the aircraft into an uncontrolled roll, turning the aircraft around at least 3 times (possibly even 5 times), both engines flamed out, the aircraft lost about 10,000 feet until the crew was able to recover the aircraft, restart the engines and divert to Muscat. The aircraft received damage beyond repair due to the G-forces, and was written off.

I subsequently discovered that wake turbulence sinks; according to Wikipedia:

At altitude, vortices sink at a rate of 90 to 150 metres per minute and stabilize about 150 to 270 metres below the flight level of the generating aircraft.

Well, now I know where not to fly my business jet...
Incorrect assumption
(See accepted answer below)
Presumably the vortices sink because they are denser than the air they were whipped up out of, but it's not clear to me why they are denser.

Lift is created by accelerating air downwards. The same goes for wake turbulence: The vortices form at the boundary between the downward-moving strip of air (wake) from surrounding air that tries to fill the void left by the wake.

Friction will eventually dissipate the kinetic energy of the wake, but in case of heavy aircraft the motion will continue for several minutes. By that time it will sink down hundreds of feet or hit the ground. This is driven by inertia; density differences do not exist unless the atmospheric lapse rate is above the adiabatic rate and the wake warms less quickly from increasing atmospheric pressure than the surrounding air.

In the end, the weight of any heavier-than-air vehicle is supported by an area of higher pressure on the ground. Some mechanism has to transfer the weight force from the flying aircraft to the ground, and that is the downward-moving wake. When it slowly dissipates, it will leave a slightly higher air pressure below it. When that happens at supersonic speed, the more focussed pressure change is high enough to be audible on the ground.


What are these wheel-chocks made of and what color do they most probably have? I found a new hobby of mine: Colorizing black and white photos. My first project was a B-17 and now I'm working on a He 162 Volksjäger. The plane is on ground and fixed with wheel-chocks.

Now the question is what they are made of and what color they could have. Maybe there is a specialist for german aviation in WWII out there.

Those chocks were made out of wood; I am guessing that they were unpainted or painted a bright color, for visibility. Today, they are made out of rubber or a synthetic. Rubber grips better than wood, but the wood chocks were most likely made out of wood, to preserve the rubber for the war effort.


What is the difference between a nacelle and a cowling? I see these terms used almost interchangeably. To my understanding they both refer to the covering of an engine. Is there a technical difference between the two?

The definition of a nacelle refers to the housing of anything on the outside of an aircraft. Engines are the most common thing in these housings.

  a streamlined housing or tank for something on the outside of an aircraft or motor vehicle.

The definition of a cowling is specifically a removable cover of the engine.

  the removable cover of a vehicle or aircraft engine.

So a nacelle refers to the whole covering of an engine that is outside the plane, typically on the wing. The cowling would just be the removable part of this cover. As Jan Hudec commented, engines mounted in the nose, as is typical in smaller aircraft, would have a cowling to allow access and cooling to the engine, but technically not a nacelle, since the covering would be part of the fuselage.


Was the Coanda effect known in 1868 to Matthew Piers Watt Boulton (the one who described the first ailerons)? Matthew Piers Watt Boulton is known as the inventor whose 1868 British patent No. 392 nullified any claim of the Wright brothers that they discovered the ailerons (see FIG. 5-7).
It seems now that another invention in the same patent (see FIG. 1) shows an engine similar to one that uses the Coanda effect (see the picture: "Diagram of a generic engine that harnesses the Coandă Effect to generate lift (or forward motion if tilted 90° on its side)" for comparison).

The question is: Did Boulton have really in mind the Coanda effect when he proposed the engine in FIG. 1?

This is the explanation Boulton gave to FIG. 1:

"A body is provided having the form of a solid of revolution tapered at the stern and prow on front. An annular jet of aeriform fluid is caused to issue at its fore part in front of its convexity so as to mix with air and create a mixed stream which flows or sweeps over the convex surface, finally quitting it backwards. In this case the action of the jet causes reduction of pressure on the front and thus produces propulsive effect."

"Figure 1 is a longitudinal section of a body or vessel constructed according to my Invention, propelled by an annular jet issuing at its front. a is the body or vessel containing fluid under pressure and shaped so as to offer little resistance to longitudinal movement in the direction of the arrow e; b is a tapering front or prow connected to a by thin ribs; and c is a cavity so formed with an opening round its periphery that an annular jet of fluid can issue by it perpendicularly to the longitudinal axis of a or nearly so. When the jet so issues it tends to reduce pressure on all sides. By virtue of this reduction of pressure the air (or other medium in which the body is placed) in front being free to move flows backwards towards the jet and mingles with it, while the body a being also free to move, moves forwards in the direction of the arrow e. The jet instead of issuing from c perpendicularly to the longitudinal axis of a may be made to issue at any desired angle by suitably forming the passage round the periphery of c."

FIG. 1 shows an engine that seems to use the Coanda effect and FIG. 5-7 a wing with ailerons (driven by a pendulum but the patent specifies they can also be controlled by hand).
The entire patent of Boulton can be consulted HERE

A diagram of a generic engine that harnesses the Coandă Effect to generate lift (or forward motion if tilted 90° on its side).

The accompanying text clearly describes an application of the Bernoulli effect. However the resultant backwards airflow shown in the drawing is given no explanation, other than that implied by the fact that the device is drawn forwards. So there is no evidence of the Coanda effect, in which the airstream clings to the device skin, being understood.
Would it have worked? Probably, but it would have been pretty inefficient.


Can an unserviceable component be fitted on a serviceable aircraft for a maintenance check? I was doing some reading on aviation regulations and I wanted to understand from an expert whether the following situation is allowable or not. I have reviewed EASA continuing-airworthiness guidelines but am still unclear as this is a bit of a unique scenario.
Appreciate if you can shed some light on whether this situation is permissible or not.

A component fails and is removed from Aircraft A and declared unserviceable (with an "unserviceable" tag).
A similar component is removed, via robbery/cannibalisation, from another aircraft (Aircraft B) undergoing maintenance activity (A or C check), and provided to Aircraft C, which has a similar failure.
There is now a "hole" in Aircraft B, since the component has been robbed/cannibalised to support Aircraft C for the latter's maintenance requirement.
The original failed component (from Aircraft A) which was declared unserviceable (with an "unserviceable" tag) will be used to support the maintenance check inspections/tests for Aircraft B.
These tests are to inspect/test aircraft systems, and the "hole" needs to be plugged to carry those out.
The unserviceable component will eventually be removed from Aircraft B as unserviceable (with the "unserviceable" tag).

EASA Regulations do not specifically preclude you from doing what you are planning to. They leave an awful lot of room for interpretation. How you do your maintenance is up to you, as long as you meet the core requirements and that your processes can be audited.
Additional rules for this type of activity would normally covered by a local procedure (such as Robbery). If you do not have a covering procedure internally then you should absolutely be checking with your Quality Assurance department to validate your actions before undertaking the procedure.


In a full-rudder sideslip in a Schweizer 2-22 or 2-33 glider, is the descent rate higher at 50 mph airspeed than at 60 mph airspeed? Is it really true that in a full-rudder sideslip in a Schweizer 2-22 or 2-33 glider, the descent rate is higher at 50 mph airspeed than at 60 mph airspeed?
Likewise, is it really true that in a full-rudder sideslip in a Schweizer 2-22 or 2-33 glider, the no-wind glide path is steeper at 50 mph airspeed than at 60 mph airspeed?
I've heard several instructors in my glider club assert these things.  Some allege that at higher airspeeds the fin overpowers the rudder and reduces the obtainable slip angle (as measured by the yaw string).
I've logged plenty of time in these types of gliders but never have attempted to explore this issue experimentally.  But my intuition is that the slip angle (as measured at the yaw string) is not significantly larger at a lower airspeed than a higher airspeed, and that a given slip angle (as measured at the yaw string) produces much more drag (and also much more sideforce, requiring a larger bank angle to compensate) at a higher airspeed than at a lower airspeed.  Therefore I would expect the descent rate to be higher at a higher airspeed, and I would also expect the glide path to be steeper at a higher airspeed.
The minimum sink rate airspeed and the best L/D airspeed in these gliders are both in the neighborhood of 40 mph.
Bear in mind that the no-wind glide path is determined by the ratio of Lift to Drag, which is very nearly equal to the ratio of Weight to Drag.  So the question about the glide path is simply a question about which configuration creates more Drag.  Also, it is clear that if the glide path in the full-rudder sideslip is in fact steeper at 60 mph than at 50 mph, then the sink rate cannot be higher at 50 mph than at 60 mph.
Since the purpose of the full-rudder slip is to steepen the glide path and get the glider on the ground closer to the beginning of the runway, the glide angle is actually the parameter of greatest interest, but for whatever reason, in discussions between instructors and students I've heard the assertion phrased in terms of sink rate just as often as in terms of the actual glide path or glide angle.

Full disclosure: I have exactly 3 hours logged in a glider and have never specifically flown the 2-22 or 2-33.
That said, I do have some experience and understanding of slips, and the principles should be the same.To answer your question, I will draw from quotes taken from this article on Boldmethod.com.

In a forward slip, the amount of slip, and therefore the sink rate, is determined by the bank angle. The steeper the bank is, the steeper the descent.

However, there will be a limit to how much bank angle you can introduce before you can no longer hold a constant ground track.

In light airplanes, the steepness of forward slips and sideslips is limited by the amount of available rudder, or the rudder-limit. You may reach a point where full rudder is required to maintain heading.

If you are already at this point, with full rudder deflection, maximum allowable bank, and a constant ground track, there’s only one variable left - Pitch. Pitching down increases speed and increases descent rate.

As you lower the nose, airspeed and descent rate will both increase. The additional airspeed will give your rudder more effectiveness, allowing you to increase the slip. The opposite is true of raising the nose.

This means that you are absolutely correct. Properly configured, a higher airspeed should give you a higher descent rate.


How to visualize compass deviation? What will the magnetic compass which has an Easterly deviation of 10 read when the true heading is North
Will it read 350W or 10E?
I understand that the 10E East variation means that the underlying magnet is swung 10 deg clockwise instead of pointing to true North. So it is now pointing to 10E. But I guess since the readings are done from opposite side of the compass for the end user, the reading shown will be 350W.
Help!
edit : The question is different from what is answered at How do I convert true heading to magnetic heading or the other way around? --  My question is mainly regarding how to visualize the same. - John's answer below is perfect.

I assume your question is about Declination/Variation, not Deviation that is addressed with the compass correction card.  It's confusing because you are reading the compass card from behind so to speak and you are rotating around the magnet, which is always aligned with Magnetic North, when you turn.
So forget about the magnet alignment and just consider the compass card indication that is telling your where the nose of the airplane is pointing, and think it through this way:
If you are flying straight toward the Magnetic Pole on the 10 Deg E Variation line, your compass heading will be 360/0 Magnetic, and your True Heading will be 10 Deg, because the nose is pointed 10 Deg to the right of the True North Pole with your compass showing 360/0 Magnetic.
If you are flying straight toward the True North Pole, your true heading is 360/0 True, and your Magnetic heading will reflect the fact that you are pointing 10 degrees to the left of the Magnetic Pole in order to point straight at the North Pole.  This will show as 350 on your compass.
Hence the "East is Least" rule for Easterly Deviation (West of the Agonic Line). To fly a specific True Heading, point so that the Compass indicates 10 Deg LESS (least=less=subtract from True for a Magnetic heading to fly) than your target True Heading; to fly 360 True, Point at 350 Magnetic.
So, per your question, if you are flying 360/0 True, that is, pointing straight at the North Pole, your compass will show 350 Magnetic if you are on the line of 10 Deg Easterly Declination/Variation.


Can an airline order a 777 with 787 flight deck avionics? So an airline orders a 777, but instead of the cockpit in that, they request the 787 cockpit installed in their 777, is this even doable?

I'll answer based on the one precedent I'm aware of. Yes. But whether the manufacturer agrees is up to them.
In 1996 Saudia ordered 29 MD-90s with MD-11-style cockpits from Honeywell, including the overhead panel.
Which Honeywell then supplied for the MD-95 (later renamed Boeing 717) as well.
From Honeywell's press release:

Saudi Arabian Airlines (Saudia) has specified Honeywell's 8-by-8-inch flat panel liquid crystal displays for its new McDonnell Douglas MD-90 airliners.
(...)
In a separate development, Douglas has also decided to provide Honeywell's flat panel displays for the recently launched MD-95 aircraft program.

Regarding the specific 777/787 example, the 787 shares a lot already with the 777, which reduces the cost of training a 787 flight crew if they're already type-rated on the 777. Therefore, there's little incentive for both the airline and manufacturer to go that specific way.

For different reasons (not one airline's order) the 767-400ER comes with a 777-style cockpit, including the big displays.

The 767-400ER incorporates a new flight deck similar to that on the 777 (...) The overhead panels are largely unchanged (Boeing).


What is a Pressurization Safety Valve? Here you can see two of them on the B747. What are they and what's their function?

Source: FAA's Pilot's Handbook of Aeronautical knowledge

The pressurization relief valves are on the left side of the fuselage and are used to provide protection (for the aircraft) against excessive differential pressures. In this case, they are set to open at a differential pressure of 63.8 KPa (with 66.9 KPa) as a backup. From ATSB Investigation Report on the depressurization of Boeing 747 VH-OJK:

  The relief valves provided protection to the aircraft against excessive differential pressures, with the external latching doors providing a positive indication of valve operation. Aircraft systems documentation
  specified that the valves open at a differential pressure of 63.8 kPa (9.25 psi) to vent the fuselage interior to the ambient atmosphere. An additional relief setting of 66.9 kPa (9.7 psi) acts as a backup.

The same report shows the external blowout doors of the (both) relief valves open, as shown below.

In a related note, there is a negative pressure relief valve to prevent vacuum damage to aircraft during a rapid descent. Usually, this is a spring loaded valve that opens inwards at negative pressure differential.


Are the holes inside the engine nacelle used for uniform intake of air? I read the post here: What is the function of the holes in splitter plates?

My question is, what are those hole looking things inside the engine nacelle?

It seems reasonable to me that as air enters the intake slower air would accumulate towards the outboard portion of the engine nacelle due to the shape of the leading edges. You want the air to enter the blades uniformly so you could add these pinholes which would remove the slower moving air. This would lead to more even distribution of faster moving air and subsequently better engine performance.

Am I tracking correctly?

Edit: here’s another picture

They are for reducing noise emissions. According to Wikipedia,

  Liners are applied on the internal walls of the engine nacelle, both in the intake and by-pass ducts, and use Helmholtz resonance principle for the dissipation of incident acoustic energy.

The Helmholtz principle (Wikipedia again) can be watched (or rather heard) when blowing over a bottle which produces a sound.

  Helmholtz resonators are also used to build acoustic liners for reducing the noise of aircraft engines, for example. These acoustic liners are made of two components:
  a simple sheet of metal (or other material) perforated with little holes spaced out in a regular or irregular pattern; this is called a resistive sheet;
  a series of so-called honeycomb cavities (holes with a honeycomb shape, but in fact only their volume matters).

  Such acoustic liners are used in most of today's aircraft engines. The
  perforated sheet is usually visible from inside or outside the
  airplane; the honeycomb is just under it. The thickness of the
  perforated sheet is of importance, as shown above. Sometimes there are
  two layers of liners; they are then called "2-DOF liners" (DOF meaning
  Degrees Of Freedom), as opposed to "single DOF liners".
  (Wikipedia)


Engine Oil Consumption limits part of certification? Does anyone knows if Engine Oil Consumption limits are part of the engine certification requirements?

Indirectly yes, the FAA engine certification guidelines can be found here. The FAA does not really care how much oil you burn so long as you specify it in the documentation and the installation can provide enough to safely run the engine with some margin on top of that.

  Paragraph 23.1011(b)

  The engine requirements for oil quantities and temperatures are
  established by the engine manufacturer and may be found on the Type
  Certification Data Sheet or in the engine installation manual. The
  airplane installation must not cause the engine limits to be exceeded
  under normal operations.

  Paragraph 23.1011(c)

  Paragraph 23.1011(c) requires that, “The usable oil tank capacity may
  not be less than the product of the endurance of the airplane under
  critical operating conditions and the maximum oil consumption of the
  engine under the same conditions, plus a suitable margin to ensure
  adequate circulation and cooling.” In other words, there needs to be
  enough oil (usable supply) to allow the engine to consume the usable
  fuel. This should be substantiated by a quantitative analysis. In
  addition, a suitable oil quantity margin for system circulation is
  necessary for all engine installations. The oil system should be
  capable of maintaining the engine within its operating limitations
  (i.e., oil temperature with the minimum oil quantity provided for
  circulation). Cooling tests do not need to be performed with a low
  usable oil supply provided the oil is properly cooled at all oil
  levels.

(To avoid copying all the text here) The document explains how to calculate these numbers as well under Specific Oil Consumption (SOC) and further under Single-engine Installations/Multiengine Installations. The content of Paragraph 23.1011(d) as well as Paragraph 23.1011(e) discuss feeding and pumping the oil around as needed.


Why is a Cessna C560 circling Washington DC during the protests? Right now according to FlightRadar24 there is a Cessna C560 circling Washington DC.

It took off from Manassas Regional Airport and has been circling ever since. No other identification is listed.

Is there any other way to find out what this plane is doing and why it would be flying now?

According to the Washington Post, an unidentified C560 was also seen circling protests in Baltimore in 2015. The FBI stated the aircraft were theirs and "specifically used to assist in providing high-altitude observation of potential criminal activity to enable rapid response by police officers on the ground."

FlightAware shows the callsign of the flight over DC tonight as JENA120, consistent with the callsigns used by FBI flights during the Baltimore flights.


Are low pressure (LP) compressors and booster compressors the same thing? Based on the above picture, are "LP compressor" and "Booster compressor" different names for the same thing or are they actually different things?

The same. LP (low pressure) compressors in turbines are sometimes referred to as booster compressors.


What happens if full collective pitch is suddenly commanded on most modern helicopters? Related, but not the same: What happens when you apply full cyclic + collective?

If the pilot suddenly applies full collective pitch on a turbine powered helicopter, will the engine stall? It seems from the other question, that this is not typically mechanically limited, so it is possible to force this onto the helicopter. However, does it cause the engine to stall? Any other problems?

I'll assume you're talking about typical turbine helicopters.  The fuel controller on a helicopter's turboshaft is used to regulate rotor RPM via its gas generator's (the compressor/burner/turbine section) speed and torque.  The RPM governor setting is coarsely set with throttle, then fine tuned with a trimming function controlled by a toggle (blip) switch on the collective to set the precise rotor RPM the governor will maintain.

The fuel controller will now govern rotor RPM automatically at that setting as you load the rotor with collective, by increasing fuel flow to increase the torque output of the gas generator.  So torque, fuel flow and Turbine Outlet Temperature (TOT) will all rise as you pull collective.  Both torque and TOT have operating maximum limits, so how much collective you can pull is therefore limited by a torque and/or TOT red line.

Trying to take off in marginal conditions due to load, temperature or altitude, you will find yourself pulling pitch until you are at a TOT or torque limit before you can even hover, and if you really really had to get airborne (like say you were an overloaded medivac Huey in Vietnam), you'd have to get the machine sliding along the ground first to get some translational lift in order to take off (one big advantage of wheeled landing gear).

Anyway, it's a hydromechanical fuel controller/speed governor that just does what it is told, so if you just haul the collective all the way up just sitting there, it'll depend on how much fuel the controller has to dump in to maintain RPM as you shoot off the ground straight into the sky.  You will probably exceed the TOT or torque limit or both, making it a very expensive takeoff.


Cessna 172: at which RPM should the oil pressure reach the green arc? I am part of a team developing a Cessna 172 P model for FlightGear, an open source free flight simulator. We are now trying to improve the oil pressure and temperature simulation, and we have a question concerning the behaviour of the oil pressure at startup. The oil pressure gauge in the model P ranges from 0 PSI until 115 PSI, with a green arc region between 50 PSI and 85-90 PSI. What we are trying to figure out is in which circunstances the needle should be in the green arc region.

I have checked many different checklists for the 172 and many state that the throttle should be at 1000 RPM for the oil check, so that the oil pressure should be at least 50 PSI. On the other hand, the 1982's POH does not state that the oil check should happen at a particular RPM; it only says that the throttle should be OPEN 1/8 INCH on p. 4-7. But the POH is quite confusing concerning this issue, since it simply says Oil Pressure -- CHECK but not that the oil should be on the green arc. To add more confusion to it, on p. 4-12 it says:

  After starting, if the oil gauge does not begin to show pressure
  within 30 seconds in the summertime and about twice that long in very
  cold weather, stop the engine and investigate.

So nothing again about the green arc or 50 PSI, just about the gauge being alive. This is perhaps the reason those checklists include the 1000 RPM figure, perhaps the engine is not able to give 50 PSI or more of oil pressure when at idle (aprox. 750 RPM in the case of our model).

TL;DR

in the Cessna 172P, at which RPM should the oil pressure be equal to or above 50 PSI?
what is the procedure for oil pressure check, should it be done at 1000 RPM or at idle throttle?

Your answer will be elusive.  The problem is that oil pressure is a function of the oil, oil temperature, time, engine pressurized oil draw (the "wear" of the engine), and RPM.

I am confident a model could be created using the above parameters, and possibly one or two more.  However, you are probably not interested.

I have about 8000 hours of instruction given in C172M, which is a different engine.  With 100 weight oil, at 20C or higher, I teach that oil must be moving up within 5 seconds, and with 1000 RPM it must be approaching or in the green within 10 seconds or there is an engine shutdown.

In contrast, with 80W oil, at 32F (we require preheat if engine temp is below 32F and the aircraft is at home base), I teach that the oil pressure must be moving within 5 seconds and in the green within 15 seconds.

These times are on our customized checklist, and do not address cold weather ops although they are quite common for us.

We will not start taxi until the oil is in the green arc. We always look for movement of the oil gauge within seconds after the engine start. We bring the engine above 500 RPM, but not necessarily to 1000 RPM waiting for the oil to rise up.  A factor in not going to 1000 RPM immediately is that the engine wear without full flow on a journal bearing is the square of the surface velocity. On the other hand, the pump volume is nearly linear with respect to the rotational velocity.

Also, note that we use straight weight oil 90% of the time.  Multivis oil will behave differently.

To address your two questions, I propose you use the following:
-1000 RPM for oil check all the time

500 RPM idle typically yields 30 to 35 PSI


What turbine blade alloy did the Jendrassik Cs-1 use? Wikipedia says that the first turboprop aircraft engine was the Jendrassik Cs-1 invented in Hungary by György Jendrassik.

It says it was supposed to run at 1000 hp but "combustion problems" limited it to 400 hp.

I would like to know what turbine blade alloy it used. Could not find this info online. I have a feeling the blade alloy limits were what limited the engine power, since that is the main limiting factors on gas turbines in general.

Note: The Hungarian version of the wikipedia article says the turbine ran at 550 C, and...

  A turbinalapátokat 50% reakciófokú csavart, szárnyprofil keresztmetszetű hőálló acélból gyártották precíziós öntéssel, és speciális beerősítéssel szerelték a rotorba.

Google translate:

  The turbine blades are made of 50% reactive twisted, heat-resistant steel with wing section cross-sections, and are specially mounted in the rotor.

Don't know what that means. 50% steel? Then what is the other 50%? Also, there is no citation for it.

Jendrassik's own patent from 1939 does not go in-depth into the alloys. However, for the turbine blade legs he mentions "austenitic [stainless] steel" as preferable (see PDF page 3).

From that era, a Swiss patent from 1937 on the materials of gas turbine parts also discusses austenitic steel, in particular (translated from German):

  Alloy of an austenitic steel containing 25 to 35% of chromium, 25 to 35% of at least one of austenite-forming metal [e.g. nickel], 1 to 4% of titanium and 0.3 to 0.8 (preferably 0.4 to 0.6%) containing carbon, optionally up to 3% silicon and up to 10% molybdenum.

It is close to the composition of the 316 stainless steel (source), which has a mechanical maximum temperature of 590°C (source).


What is the difference between 'warning area' and 'ADIZ'? Are they overlapped with each other? On FAR AIM, definition of warning area is

  Airspace of defined dimensions,
  extending from three nautical miles outward from the
  coast of the U.S, that contains activity that may be
  hazardous to nonparticipating aircraft

And on Wikipedia, definition of ADIZ is

  Airspace over land or water in which the identification, location, and control of civil aircraft is performed in the interest of national security.

I was confused because the definition of these two airspace is similar with each other. And I thought that those area could be overlapped with each other. Could anyone explain the difference, or at least an example chart that contains this two areas?

And if an aircraft tried to fly to the U.S territory from the sea, which area does the aircraft encounter first : 'warning area' or 'ADIZ'?

You can find a good explanation of Warning areas (and lots of other areas) in the answer to this question.

ADIZ is effectively the controlled area that surrounds the US/CANADA border. The picture from the wiki article shows it quite well

The ADIZ was created to have an area to identify inbound, out of country, aircraft. As per the FAA

  All aircraft entering U.S. domestic airspace from points outside must
  provide for identification prior to entry or exit. ADIZs have been
  established to assist in early identification of aircraft in the
  vicinity of international U.S. airspace boundaries (AIM Section 6,
  5-6-1)

As far as I know there are no ADIZ areas internal to the country, although warning areas may be anywhere within the nations jurisdiction. I see no reason they could not overlap each other either.


Can a passenger drone perform auto-rotation? (Source)

The Dubai Drone is an Ehang passenger drone planned to start commercial services in July 2017.

If there is a failure, can such an electric multi-copter auto-rotate a landing?

I'm wondering, if an electric motor would even allow auto-rotation, and if the autopilot could handle it? Are there regulations for devices like that?

That drone has fixed-pitch rotors, and that pitch is optimized for thrust, not for autorotation. In the absence of power, those rotors won't autorotate. They will stop rotating 'in the right way' and then start windmilling in the opposite sense. That windmilling will cause drag and some deceleration of the fall, but not of the same magnitude as an autorotation, that is a different condition.


How feasible is BAE Smart Skin? I just came across this article on LinkedIn, and I have a few questions about it.
Some of BAe's claims are things such as:

Aircraft set to become more human as engineers develop smart skins which can detect injury
The revolutionary ‘smart skin’ concept will enable aircraft to continually monitor their health, reporting back on potential problems before they become significant. This would reduce the need for regular check-ups on the ground and parts could be replaced in a timely manner, increasing the efficiency of aircraft maintenance, the availability of the plane and improving safety.

In the past I have seen some claims of a similar nature (such as skin that adapts its shape to be more aerodynamic based on phase of flight).  What I am wondering is:

Is this really technically feasible?
Can such a skin really do what BAE claims?
Will this have any adverse effects on the aviation industry? (Usually people are so enamored with new technology and the good it can do, I am more curious if anyone has thought of the downside.)

Smart skins are at least 20 years old and, like fusion energy, just around the corner since then. The usual concept is to embed optical fibers in the structure and shine laser pulses through them. If the fiber is damaged, it will transmit less light, and by measuring the return time of a very short laser pulse, even the location of the damage can be detected. This concept requires fibers with the same break elongation as the load-carrying material, so they break just when a crack in the structure starts. To detect even small cracks, a lot of fibers must be evenly placed, which is only possible with fiber reinforced plastics. The effort to place a light source and a detector at each end of every fiber has so far prevented a practical application, at least to my knowledge.

Other techniques send clearly defined "pings" through the material and detect the propagation of the sound wave with a number of microphones. By comparing the measured signal with a reference signal, damage can be detected in metal structures as well. This technique needs some processing power, but is easily within the scope of modern microcontrollers. However, outside noise will interfere with the measurement, so it needs well defined conditions to be effective.

The downside would be more mass, investment and operator training. Generally, more advanced techniques for structural health checks have been steadily introduced in the last 80 years. Given the high cost of maintenance today, I expect that deployed damage detection technology will continue to advance, with a healthy time gap to what is possible in the laboratory. So there is some truth to those BAe claims, but I would hardly call it revolutionary.

Even more advanced are concepts of self-healing structures which contain capsules of a two-component resin. When the structure breaks, the capsules break as well and the freed resin helps to mend the crack.

If you ask me, the mass of those microcapsules would be better invested if it carries load right from the start, so the structure will tolerate higher loads and more load cycles. But I guess those research grants need to be spent somehow, and marketing departments need to write about revolutionary discoveries on a regular basis.


Where does the final approach segment begin on an ILS approach? Where does the final approach segment begin on an ILS approach? It may not be as simple as it sounds to answer. The reason I ask is because I've found some support for at least two answers.

One is that final begins when passing the glide slope intercept point a the last no lower than altitude for the approach. This is the point denoted by the lightning bolt arrow on government charts.

Another answer I've heard is that it begins when glide slope has be intercepted within the limitations of the glide slope and on an approach segment. For the example plate above, this would mean that if the glide slope were intercepted between SILKY and JAKOR the pilot would be considered to be past the final approach fix for all intents and purposes and might even configure the airplane for landing at that point rather than passing JAKOR at the published glide slope intercept.

I think there are valid arguments for both, but I'd apprecate more insight and references on the topic.

No arguments needed, it's very specifically defined. According to the FAA's Pilot/Controller Glossary under SEGMENTS OF AN INSTRUMENT APPROACH PROCEDURE:

  c. Final Approach− The segment between the final approach fix or point
  and the runway, airport, or missed approach point. (See ICAO term
  FINAL APPROACH SEGMENT.)

So it starts at the FAF, which is defined in the same document as:

  FINAL APPROACH FIX− The fix from which the final approach (IFR) to an
  airport is executed and which identifies the beginning of the final
  approach segment. It is designated on Government charts by the Maltese
  Cross symbol for nonprecision approaches and the lightning bolt
  symbol, designating the PFAF, for precision approaches; or when ATC directs a
  lower-than-published glideslope/path or vertical path intercept
  altitude, it is the resultant actual point of the glideslope/path or
  vertical path intercept.

In your example, that means the final approach segment starts at JAKOR. I may be wrong here, but your original thought might have been that the final approach starts when you're established on the glideslope, which could be outside JAKOR. That makes sense in a general way, but it isn't how the term is defined.


Can the thrust reversers still be activated if the landing gear won't extend? In the case of Boeings, I understand that the thrust reversers cannot be activated unless the landing gear is extended.

However, would it still be possible to activate the thrust reversers if the landing gear cannot be extended due to a technical malfunction, and the aircraft has to belly land? Would it be helpful to activate thrust reversal in this scenario?

(Source) LOT Polish Airlines Flight 16
All Boeings, minus the 717 and 727, have wing-mounted engines. A belly landing will already damage the engines and potentially rupture fuel or hydraulic lines, so no. Some reverser types employ target doors, which require clearance to the ground.
In case of tail-mounted engines, the answer will depend on the flight manual and the extent of the gear extension failure (partial, all, main, nose).
An MD-80 manual notes:

IF Nose Gear Unsafe, Both Main Gear Extended:
Idle reverse thrust may be used with caution for deceleration.


How (or where) do I find an airfoil optimized for low reynolds numbers (100,000~150,000)? Looking to build a RC plane. Because the span is going to be small and the speed relatively low, I estimate the R-number to be around 100,000. Is there an airfoil optimized for that range of Reynold's Number?

Try the HQ series from the UIUC Airfoil Data Site. That is HQ as in Helmut Quabeck (model airfoils), not Horstmann-Quast (those would be glider airfoils).

Another possible source is the website of Martin Hepperle.

Unfortunately, there is not one, but hundreds of airfoils optimized for the model aircraft range of Reynolds numbers. To be any more specific, I would need to know more about how you plan to use that model:

Will it be a glider with a low wing loading, trying to stay aloft as long as possible?
Will it be a fast glider for ridge racing?
Will it be a powered model for aerobatics?

Each case will need different airfoils.


Who can carry out airworthiness inspections? My understanding is that aircraft regularly have inspections for defects just like cars in the U.K. have an annual MOT test to check their condition and safety.

My question is, who can do these inspections and what qualifications/certifications do they need?

I'm primarily interested in CAA requirements but FAA requirements would also be interesting to know.

I can speak to the FAA requirements.  The basic requirement for the annual inspection (commercial aircraft have additional requirements) comes from 14 CFR Part 91.409

  §91.409   Inspections.

  (a) Except as provided in paragraph (c) of this section, no person may
  operate an aircraft unless, within the preceding 12 calendar months,
  it has had—

  (1) An annual inspection in accordance with part 43 of this chapter
  and has been approved for return to service by a person authorized by
  §43.7 of this chapter; or...

And the related requirement regarding who can perform this is covered in Part 43 and is in two parts; who can perform the work and who can approve the return to service.

The work must be performed by someone specified in 14 CFR Part 43.3 in which the general case is:

  §43.3   Persons authorized to perform maintenance, preventive
  maintenance, rebuilding, and alterations.

  (a) Except as provided in this section and §43.17, no person may
  maintain, rebuild, alter, or perform preventive maintenance on an
  aircraft, airframe, aircraft engine, propeller, appliance, or
  component part to which this part applies. Those items, the
  performance of which is a major alteration, a major repair, or
  preventive maintenance, are listed in appendix A.

  (b) The holder of a mechanic certificate may perform maintenance,
  preventive maintenance, and alterations as provided in Part 65 of this
  chapter.

  (c) The holder of a repairman certificate may perform maintenance,
  preventive maintenance, and alterations as provided in part 65 of this
  chapter.

And the approval for return to service must be per 14 CFR Part 43.7

  §43.7   Persons authorized to approve aircraft, airframes, aircraft
  engines, propellers, appliances, or component parts for return to
  service after maintenance, preventive maintenance, rebuilding, or
  alteration.

  (a) Except as provided in this section and §43.17, no person, other
  than the Administrator, may approve an aircraft, airframe, aircraft
  engine, propeller, appliance, or component part for return to service
  after it has undergone maintenance, preventive maintenance,
  rebuilding, or alteration.

  (b) The holder of a mechanic certificate or an inspection
  authorization may approve an aircraft, airframe, aircraft engine,
  propeller, appliance, or component part for return to service as
  provided in Part 65 of this chapter.

Requirements for mechanics and inspection authorizations are spelled out in 14 CFR Part 65, Subpart D.

The regulations also allow manufacturers and repair stations among a limited number of others to perform the work as well.  (see links)


How do you calculate the true bearing from a station (QTE)? Assuming that :

You are flying on a compass heading of 141°,
The compass deviation is given as +3°,
The variation read on the chart is 3° East,
The wind correction angle is +10° and
The relative bearing to the airport is 307°

what would the radial from the station be to the true north?

I thought QTE was a standard term. I did not know that American pilots did not know it.

*QTE: True Eminent from station — What is my true bearing from you? QTE = Reciprocal of true bearing to station.

To derive the true bearing I did the following.

I assume that since compass heading is 141° and deviation is +3°

Magnetic heading should be 141-3 = 139°
True heading (would be without the variation given as 3°E) = 139 +3 = 141°
True bearing to station = True heading + relative bearing = 141+307 =  448°
True bearing = 448-360 = 88°
True eminent from station = 268°

However the answer given is 274°.

I want someone with more aviation knowledge to tell me if I am wrong and if so, where is the "break" in my logic?

Reason for question: Navigation problem with an answer given, however I believe the answer to be wrong - Needed an expert opinion.

You are quite close to the answer, you just made a mistake with the sign of east compass deviation, hence underestimated the true heading by 6°. The actual angles are like this:

The compass deviation is given as +3° while it should be given as 3° east, like the variation. It could be misleading.

Exactly as you then developed, the unknown yellow angle is equal to:

True heading + (relative bearing - 180)
147 + (307 - 180) = 147 + 127 = 274°