Can I get an EASA Class 1 medical with high astigmatism? I have high astigmatism (5 dioptres) and myopia which is under the limit. Is it possible to acquire a class 1 medical? If I recall correctly it's up to the ophthalmologist if he will judge me able to get the certificate?
If not is there something equivalent to the FAA SODA? I know about a medical flight test but I have no idea how it works and if it's possible to do it in order to acquire a class 1 medical.

There isn't an equivalent of FAA SODA under EASA regulations.
The final decision is up to the ophtalmologist (in agreement with the AME). You should bring to the medical examinations all supporting material to help him take an informed decision.
In case you won't pass the medical examination, you will be given right to appleal. For the appealing procedure you will have to prepare a dossier to persuade that you are fit for the EASA Class 1 medical.
Good luck!


How does skydiving flight cause shock cooling? While answering this question (How can reducing power too quickly on a piston engine damage it?), barit1 said that:

  Skydiving planes see a LOT of shock cooling, and they pay for it at overhaul time

What exactly happens during a skydiving flight which causes a lot of shock cooling?

Skydiving flights are abusive on engines for a number of reasons, but it's all tied to the fact that these flights are all about getting up to altitude, kicking the jumpers out, and putting the plane back on the ground as fast as possible so you can pick up the next group and do it all again, as many times as possible in a day.

While all skydiving descents aren't as dramatic as the video I linked to its not uncommon for skydiving pilots to make a very rapid descent at or near idle power. This causes a more drastic temperature change in the engine (particularly the cylinders, which are not producing as much heat but still have lots of air blowing through the fins).

In addition to the potential damage from rapid temperature changes the engine is also spending relatively little time at cruise power (it's either at full throttle climbing or near idle descending), and depending on the operation may be shut down between jumps. This is far from the ideal situation where the engine would run at 60-75% power as long as possible.


Is it allowed to scatter human cremains (ashes) from an aircraft? A serious question, here: There's gotta be a pilot out there somewhere who has done a memorial request to spray someone's ashes over a city street. I'm gonna do it out of spite for a lousy little mill town in Central Pa. There seems to be no laws against it on the books. 500' fly-overs are okay, spreading ashes falls under no FAA rule that I can find. When I go (soon, I'm an AO affected Vietnam Vet), I plan to have a contract with a crop-duster or acrobatic pilot for a decent show. Aside from (moral) advice, can someone comment, please? I wish to know of any known regulations governing this, especially any against.

AOPA has an entire article on it that's worth reading and while it's generally fine with the FAA (assuming the pilot isn't being careless or reckless), there may be other regulations or laws that apply. The article mentions:

Permission needed for scattering over federal land
Permission needed for scattering over water (federal and local regulations)
State burial requirements

But there are two specific aviation regulations that might apply to the flight. First, 14 CFR 91.15:

  §91.15   Dropping objects.

  No pilot in command of a civil aircraft may allow any object to be
  dropped from that aircraft in flight that creates a hazard to persons
  or property. However, this section does not prohibit the dropping of
  any object if reasonable precautions are taken to avoid injury or
  damage to persons or property.

Second, you said that you plan to have a "contract" with someone to scatter the ashes, which implies that you're going to pay the pilot. If that's the case, then the pilot may not use an experimental aircraft for the flight. That's because the FAA considers carrying human ashes to be carrying property (Harris interpretation, 2009) and 91.319(a) doesn't allow carrying property for compensation in experimental aircraft:

  (a) No person may operate an aircraft that has an experimental
  certificate—

  (1) For other than the purpose for which the certificate was issued;
  or

  (2) Carrying persons or property for compensation or hire.

Finally, note that accidents can and do happen and in at least one case two people died while spreading ashes (although to be fair, the toxicology data was fairly 'interesting' in that one).


What's the purpose of the cable connected on the top of the fin? A321neo has on the top of the fin, backwards, a long tube, which looks like the pitot tube on the Boeing 707, but on the opposite way, and connected on it, a cable (I think because it is a test flight).
What is the purpose of each one?
Picture's credits: www.airbus.com/presscentre

It is a Trailing Static or Trailing Cone used in test aircraft to measure free stream values. From Airdata Measurement and Calibration:

  By trailing a long tube behind the airplane, a nearly free-stream static pressure measurement can be taken. A perforated cone at the end of the tube acts as a drag device to keep the tube stable.

Image from NASA Airdata measurement and calibration

It is used in test aircraft. The image below shows the trailing cone attached to the 787 dreamliner (pictured at Paris airshow).

Image from flyingsquadron.com

This image shows the trailing cone assembly used in 787 dreamliner.

Image from airpigz.com

The device is specified by FAA and JAA as one of several methods that can be used to perform flight calibrations. According to FAA Advisory Circular 91-85:

  Where precision flight calibrations are used to quantify or verify altimetry system performance they may be accomplished by any of the ollowing methods. ...

  • Precision tracking radar in conjunction with pressure calibration of
  atmosphere at test altitude.

  • Trailing cone.

  • Pacer aircraft.

  • Any other method acceptable to the FAA or approving authority.


What means of navigation did commercial Soviet airplanes use in the 50s-90s? Nowadays, practically all Western commercial airplanes use some kind of GNSS/GPS as primary means of navigation, sometimes paired with inertial navigation systems and user-friendly computer interfaces (FMCs). This allows planes to follow very precise routes in long flights, also shortening flight times by flying more "direct" routes. Before the 1980s and the use of GPS in civilian aircraft, instrument navigation was pretty much all about VOR/DME/NDB.

How about the Soviet aircraft built between the 1950s and the 1990s? How close were the Soviet navigation systems to the Western ones, and what were the major differences?
It's common to see a "navigator" position in Soviet aircraft cockpit videos. Was it so complex that it required an extra crew member?
Did the Soviets ever get to use GPS navigation or at least FMCs in their planes?

The Soviet Union had GLONASS for aviation civilian use in the latter part of the requested 50s-90s period.

  From 1982 to April 1991, the Soviet Union successfully launched a total of 43 GLONASS-related satellites plus five test satellites.

  (...) For a long time, the USA could not find out the nature of those "objects". The Telegraph Agency of the Soviet Union (TASS) covered the launch, describing GLONASS as a system "created to determine positioning of civil aviation aircraft, navy transport and fishing-boats of the Soviet Union".

and

  (...) the Ilyushin Design Bureau learned much from the Il-86 program and in 1988 developed the Il-96, with the 80-400-type computer integrating triple INS, Omega and GLONASS displays in the navigation HUD for Cat IIIA performance (aviationtoday.com).

VOR/DME, ADF, inertial, and Doppler navigation were all present on Soviet airliners in varying combinations based on the mission/plane. They also had computerized astro-navigation (not sure if a Western equivalent existed for the civil aviation -- the computerized part):

  [C]ommercial transports (...) were able to hold the large central TsNV navigation computer complex (multiple boxes with different sub-functions), although the TsNV was too large for smaller aircraft. The complex’s main unit was the BTs-63A astro-orienter, which included an auto sextant, course indicator and computer. Inputs by the navigator to the digital navigation computer (TsNV) were through a PUISH keyboard, part of the control-indicator unit (aviationtoday.com).

Navigators were part of the crew (primarily for long-haul), but it took longer for the navigator position to become redundant compared to the West. Longer not because of a technological deficit, but because of stronger unions and job creation.

Let's look at an example, the Ilyushin Il-62 (1967—), it's long range and it matches the period.

(wikipedia.org) Part of the navigator's panel showing 1) ADF and 2) DME.

Above you see ADF and DME instruments. And much like the attitude indicators, they're the same but with a different look. A typical Soviet VOR (CDI) instrument is shown below (they also used kilometers for the DME):

(wikimedia.org) CDI instrument for VOR on the Ilyushin Il-62.

  Its avionics include a

  Polyot-1 automatic flight control system -- a "super autopilot," able to be programmed with a set route which it can fly without human intervention but under constant flight crew monitoring
  ICAO Cat. 1 approaches standard, Cat. 2 optional
  Doppler navigational radar...
  replaced by triplex INSS (Inertial Navigation System Sets) on Il-62M after 1978
  and by GPS (Global Positioning System) navigation sets on many aircraft after 1991
  triple VHF and HF flightdeck radios
  automatic direction finders
  Soviet and Western instrument landing system receivers
  [VHF] omnidirectional radio range and radio beacon receivers.

(Edited to be a list for easier reading.)

I also found en route charts for the Soviet Union showing NDB and VOR stations (but I couldn't confirm the date).

The first plane to have an FMC as it is known today as default equipment, was the Boeing 767 (1981), a few years later (1988) the Ilyushin Il-96 followed in the glass cockpit trend:

  It features (...) a glass cockpit, and a fly-by-wire control system.

(airliners.net)

Addendum:

I tried to look for specific dates, the best I got to was an American 1974 report, 'CIVIL AVIATION OF THE USSR', by the Foreign Technology Division, Wright-Patterson Air Force Base, Ohio, which noted:

  More than 90 airports were reconstructed or newly built, lines were equipped with modern means of air navigation and radio equipment.

Also since the USSR joined ICAO in 1970 (nytimes.com), it's safe to assume at least since then any radio-based navigation technology that's been in use eventually met the standards of international civil aviation.


Why are the 737 trim wheels located so close to the seats? I recently had the opportunity to try a 737 simulator and one thing that struck me was the placement of the trim wheels. They are located dangerously close to the seats and, man, do they spin fast. I can only imagine the pain if you accidentally leave the manual trimming handle retracted or if you get some hair stuck in there.

Why are they placed this way? I would assume that a less prominent placement would still allow easy access for manual trimming.

My guess is that the manual trim wheel handle (when not motor driven) to adjust it manually needs to be:

easily accessible from the seat.
generate a sufficient amount of torque by moment arm.

Which leaves this as one of the few spots where it could be conveniently placed. You can find the same thing in older aircraft cockpits including the L1011, B727 and B747-100/200. The 737 design remains very unchanged from when it first flew.


What is the best method to time your round out or flare in Cessna 172? I am a student pilot and I usually round out too high and I am not sure why. Can somebody  guide me how to make decision whether I am too high or not.

The usual cause for flaring too high is that the pilot is looking at the runway in front of the propeller instead of down at the far end of the runway.

Next time you're up with your instructor, have him do the landing, and look at the far end of the runway while using your peripheral vision to judge your height above the surface.

On the next lap, you fly the airplane, and try to get the same sight picture, both in front of you, and in your peripheral vision.


What is the relationship between Angle of Attack and Angle of Incidence? The Angle of Incidence (AoI) of most GA planes is 6°. Assuming a plane with an Angle of Incidence of 6 degrees--

How do we calculate pitch attitude if we know the direction of the flight path and the Angle of Attack?  This is essentially a question about whether Angle of Attack is measured in relation to the chord line of the wing, or in relation to the longitudinal axis of the fuselage.

During takeoff, the Angle of Attack (AoA) is often 11° or more.  Is the 11° AoA measured in relation to the chord line of the wing, so that the pitch attitude at takeoff is 11 - 6 = 5 degrees?

Not really.

The angle of incidence is the angle between the chord of the wing and the longitudinal axis of the airplane.  But the plane is mostly free to pitch as necessary.  So if the best thing is for the wing to have an AOA of 11°, then it can pitch to that point.

Now if the angle of incidence were too different, it could increase drag on the climb-out, or the thrust angle might be less than optimal.  But there's no direct relationship.

The angle of incidence is a figure about the geometry of the plane.  The angle of attack is how the wing is oriented to the wind.  They don't "add" together.

If you did the math the other way (AOA - AOI), you'd find the angle the wind is making with respect to the airplane axis, not a figure that you tend to need.


Does Buoyant Lift Force scale with Load Factor? Let's say I am flying an airplane that has a weight of 100,000 kg with a 1G load factor at normal steady flight. I have helium lift assist that is providing 50,000 kg (50%) worth of buoyant lift force upwards. Therefore, my aerodynamic lift has to provide 50,000 kg (50%) of upwards lift to remain in flight.

If I go into, let's say, a 60 degree bank maneuver and induce a 2G load factor to the airplane (so now the perceived weight goes up to 200,000 kg), does the buoyant lift force scale in some manner with the load factor, or is the lift force completely static and continue to provide 50,000 kg worth of positive lift regardless of the induced load factor? In other words, does the aerodynamic lift have to provide 150,000 kg of positive lifting force during a 2G maneuver to keep the plane airborne?

It would probably be easier to think of it as a 50,000kg aircraft with a "normal" wing.  This untruth will make calculating accelerations and turn rate incorrect (because the actual mass will make it more sluggish).  But the wing at all times has to provide 50,000kg of vertical lift for the craft to not accelerate downward.

Then just like a regular plane, the wing has to double the (aerodynamic) lift at 60 degrees.  This allows it to have 50,000kg vertically and the craft doesn't descend.

  If I go into, lets say, a 60 degree bank maneuver and induce a 2G load factor to the airplane

I don't prefer this language.  The load factor is the result of the lift.  If you had a wing that couldn't provide increased lift (it was already at the point of stalling), then banking wouldn't increase the load factor.  It would either stall the wing or the plane would start accelerating downward.  Saying the load factor has increased suggests to me that the lift has already been accomplished.

  does the buoyant lift force scale in some manner with the load factor, or is the lift force completely static and continue to provide 50,000 kg worth of positive lift regardless of the induced load factor?

The buoyant force is constant and always vertical.  Instead of coming from the relative wind, it comes from the vertical pressure gradient in the atmosphere.  So in the simple analysis, it isn't affected by banking.  But since the gravitational pull on the airplane is also constant and always vertical, you can just combine them to understand what the aerodynamic wing is required to do.


What is METAR and how is it read? I was reading an article about TAM Airlines Flight 3054 crash and I saw the following:

METAR

  SBSP 172200z 35008kt 7000 -ra Bkn008 Ovc070 15/14 Q1018
  SBSP 172200z 35008kt 7000 -ra Bkn008 Ovc070 15/14 Q1018
  SBSP 172100z 34008kt 6000 -ra Bkn009 Ovc070 16/14 Q1018
  SBSP 172030z 32009kt 7000 -ra Bkn013 Ovc080 16/14 Q1018
  SBSP 172000z 31012kt 8000 -ra Bkn016 Ovc080 17/14 Q1018
  SBSP 171900z 34009kt 9999 -ra Bkn016 Bkn080 18/15 Q1017

Questions:

What is METAR?
How is it read?
What is the difference between the International METAR codes and the
North American METAR codes?

METAR is a Meteorological Aerodrome Report which is for a specific place, at a specific time.

The first line is a report from Sao Paulo at 22:00 on the 17th.

You can use a service such as this one to decode METAR reports.

The rest of the lines are more reports for different time and days.

The groups are:

 SBSP       Reporting station ICAO code
 172220Z    Day of the month (17) and current time in UTC (2220) (Z for Zulu time)
 35008KT    Wind from 350 degrees true at 8 knots
 7000       Horizontal visibility on the ground in metres
 -RA        Current weather (RA = rain), the minus indicates light, plus indicates heavy
 BKN008     Broken clouds at 800 feet
 OVC070     Overcast clouds at 7000 feet
 15/14      Temperature 15C, dew-point 14C
 Q1018      regional atmospheric pressure 1018hPa / US systems use inHG / others use millibars


How can wingtip vortices affect the direction of the relative wind in front of the leading edge? I have a question on aeroalia's answer on this post (Why does the vortex created by wing affects its own angle of attack?).

If I'm not mistaken, wingtip vortices are generated behind the trailing edges of the wings and, even if we assume wingtip vortices somehow can reach the front area of the wings, it would only be able to affect the relative wind in front of the leading edge on the far outboard of the wings close to the wingtips, because after all it's wingtip vortices. Then, how could it be said that the upwash from the wingtip vortices changes the direction of the entire relative wind?

Please don't believe everything you read. You healthy scepticism is your best defense against the nonsense you might read about wingtip vortices.

What causes the flow to increase its angle when approaching the leading edge is the low pressure region above the wing. This is not only the main contributor to the wing's lift, but also the reason for the flow pattern ahead of the wing, in combination with the overpressure region around the stagnation point.

Please read this answer and let me know if something is left unclear.


How can I fix the stalling of an RC plane after the addition of floats? I'm modifying a RC plane into a bi-plane with floats and it keeps stalling. I don't have a bigger battery or better motor to add so how do I fix this? This is the biggest challenge I've ever faced.

Your model is based on the FX-803 Piper Cub model shown in this video. It's made from expanded polystyrene wings and fuselage, with a two channel radio that controls thrust from two motors mounted below the wing, with overall thrust controlling pitch and differential thrust controlling yaw. There are no moving control surfaces, and the propeller on the nose is a cosmetic windmilling attachment.

Your extra wing, lashed on with elastic bands, may or may not produce lift, but adds additional weight and drag below the thrust line, inducing a significant nose down moment. Your carved foam floats add additional drag even further from the thrust line exacerbating the nose-down problem, and further increasing the weight.

The original model was built and trimmed to give flying characteristics that could be controlled by simple thrust adjustments. There is no moving surface with which to counter the added drag, and even if there were, it is unlikely it would have sufficient authority to overcome the problem.

The modifications may also have moved the centre of gravity significantly, possibly beyond the point where it is fixable.

The model shown in the video has sprightly performance on limited power. The additional weight and drag you have added could easily overwhelm the available power.

You could try adding a fixed elevator to provide significant down force at the tail, but this will further compound the drag issue, and could also affect centre of gravity.

Realistically, I doubt you will be able to get this to fly. If you do, please come back and post a video!


How to approach flying a new aircraft? What's a few of the first things you look at before flying an aircraft you're unfamiliar with. Do you look at emergency procedures, V speeds, or weight and balance. I'm just curious on what other experienced pilots have done in the past when approaching a new aircraft. Do you have your own system on what you look at first? I'm sure some guys and gals have made mistakes and have learned from it, so I'm just wondering if there was something you do particularly when in a new frame.

How to approach flying a new aircraft?

Find an instructor. Period.

Your instructor will, based on your past experience, guide you through the transition. For example are you going from Cessna 152 to 172? Or Cherokee to Cessna? Do you have experience with manual trim? Glass cockpit experience? These are just some examples. The process is so dynamic & variable that one cannot give a concrete answer here.

Say you have a PPL, and you want to exercise your privileges on this new aircraft. Your task is simple: demonstrate that you can perform what a PPL is supposed to perform if you were to do the checkride in that aircraft. You can expect to go through the entire PPL syllabus, only at a much faster pace because (hopefully) you understand every concept, it is just the matter of applying them to a new aircraft. Your instructor will not have to explain theories to you; it will be a lot more flying and a lot less ground school.


Do airliners have horns for use on the ground? When an airliner is on the ground, does it have a way of making a noise that can be heard by other people on the ground? Something like a car horn?

(Source) Ground call horn.

There's a horn the pilots can sound to attract the attention of the ground engineer, so they can talk on the intercom (by wearing a headset). It's not loud enough to have any effect in the air—or when the engines are running loudly.

It's more of an annoying alarm really.

Taxi lights can be flashed on/off to attract the attention of ground crew, also opening a window and waving would work.

(Source)

(Source) Ground crew member wearing a headset connected to the plane.


Aerodynamics of a Propeller I'm having troubling understanding where the relative wind is coming from for a propeller. The relative wind that I do know is the one that comes right in front of the aircraft which flows over the wings which is an airfoil. The propeller is also an airfoil, which leads me to believe the relative wind would come from the opposite direction of the propeller, but where?

The NOAA National Weather Service Glossary defines relative wind in a way that might help you make sense of this:

  Relative Wind: The wind with reference to a moving point. Sometimes called APPARENT WIND.

From the diagram in the linked question, you can see that the relative wind is a vector opposite the propeller's 0 degree angle of attack. Simplified, this relative wind is the speed the wind would appear to flow if the air was moving, instead of the propeller. But since the propeller is moving and not the air, we call it relative wind: relative to the propeller, the air is flowing over it because the propeller is moving.

However, I'm sensing from your question that you might think there is only one relative wind vector, and that is the one parallel and opposite direction to the 0 degree angle attack of the main wings.  However, the as you can see from the definition, any moving point is going to have relative wind!

Remember that relative wind is just the wind in reference to a moving point. So once the airplane is in forward motion, even though the air in the propeller's plane of rotation is no longer still, the relative wind that the propeller "feels" is still coming from the same direction as before, but the magnitude may be modified by the change in the actual speed of the air in the propeller's plane of rotation. Then to get the strength of the relative wind on the propeller, you'd need to add the wind vector caused by the forward motion.

At the risk of over-explaining, remember it's relative wind. Rather than the air blowing (creating wind), the object is moving, so the wind is relative to the moving object.


Qualification Requirement of Aircraft taxi and landing lights? Can anyone provide any standard through which taxi and landing lights are certified for use on aircraft?

And which certification is required for military aircraft lighting systems?

There is no mention of any lighting regulations in the DGCA schedules however you should take a look at PART VI - AIRWORTHINESS as it will depend a bit on if the aircraft is Indian made or foreign built. From my reading of it if the aircraft is Indian built there is no regulation covering it but if the aircraft is foreign built, in order to receive and airworthy certificate you will need to cary over the foreign airworthy info. This may in turn mean that the light must adhere to the regulations of the certifying body of the aircraft such that the airworthiness can be carried over.  The actual usage of the light does not seem to be regulated under DGCA regulations.


Why does the Boeing 787 have fewer cockpit windows? Why does the Boeing 787 have fewer cockpit windows? The 787 has only 4 cockpit windows, whereas other airplanes have 6. Here is a comparison between the 787 and 777:

^ 787
V.S.
777 v

It is because of the carbon fibre. This is the same reason that the 787 has bigger passenger windows. Here you can find a link explaining the polarized windows on the 787. Because of its higher tensile strength, you can have bigger windows. Windows are considered weak points in the fuselage where there is no structural reinforcement. This means that the windows have to be supported by the fuselage and structural components around the window. Boeing Pilots do not fly with their elbow out the window during flight, so Boeing removes that feature. They added bigger windows because they could. There is there separation for the six windows because there is support needed.

Hope this helps, Charlie


What factors influence the maximum speed of an airship? I'm interested in learning about the physics of airships; in particular, how you determine an airships maximum speed.

For example, the Hindenburg topped out at about 80 mph. The ship itself weighed about 130 tons, not including cargo, passengers, etc.

If it weighed less could it have achieved a higher top speed, or would 80 mph have been about the fast it could have gone regardless, for other reasons such as drag/air resistance?

If it had twice as many engines, could it have gone twice as fast?

These are oddly specific, noodly questions, and I'm not looking for the answers themselves, but rather I'd like to be pointed in the direction of the math/physics fundamentals for getting the answers. I'm working on designing some fantasy airships for an RPG, and of course while they're not real and very fantastical, I do want them to have some semblance of verisimilitude, and imposing real world physics (with some wiggle-room for the fantasy part) I think helps a lot.

Thanks so much for your time and answers!

I'll do this without most of the math since your target audience won't want to read equations in your story.

In the simplest terms, the maximum speed of an airship occurs when the maximum thrust generated by its engines is equal to the drag it experiences while being pushed through the air at that speed. That drag depends on the diameter and length of the airship (more specifically, the projected frontal area and the total "wetted area" of the entire vehicle's outer skin).

This is a complicated business because the relationships between all of those variables are strongly nonlinear- for example, the drag varies with the speed squared and the power required at a given speed varies with the cube of the speed.

So in your story: doubling the power of the engines will increase the airship speed only slightly, at the cost of doubling the fuel burn rate and therefore the fuel tank capacity- and thereby reducing the useful payload.

Similarly, doubling the length of the airship will roughly double the wetted-area drag, which means you have to double the horsepower of the engines or their number in order to achieve the same maximum airspeed as the shorter airship.


Why don't small props have a gear? Small GA-Aircraft like a Cessna 172 or a Piper PA-28 have an engine similar (I think) to the one of a car.

But why don't planes have a gear and a lever to change the gear?

Would'nt they achieve a faster prop speed by doing that?
Would it be possible?
Would it be useful?

Because there is no link between the wheels and the engine.

When the car is moving slowly, wheels turn slowly so the engine must turn slowly as well. However piston engines do not work below certain RPM, so the gear switching must be implemented even for small cars.

Propeller can always turn at the speed sufficient to sustain the engine running. If the plane moves too fast (or must stand in place), wheel brakes can be applied.


How is flight envelope protection implemented in Dassault Falcons? In normal laws, envelope protection is implemented differently on Boeing and Airbus fly-by-wire systems, as highlighted in this question. I don't want to reopen a debate about which one is better (both have been proven to be good), I'm looking for information about another manufacturer's implementation.
If I understand correctly, Airbus won't allow the pilot to exceed limitations (such as load factor) while Boeing will make them really hard to exceed them.
Dassault Falcon jets (after the 7X) are fitted with fly-by-wire implementing flight envelope protections (as mentioned in this article.
I would like to know what happen if the pilot's input tend to exceed flight envelope limits (high-G maneuver -both negative and positive G-, high angle of attack, over-speed, high bank angle).
On a fully functional Dassault Falcon 7X (or newer) in normal laws, can the pilot put the aircraft outside its flight envelope? Can the pilot make the aircraft stall (excessive AoA), perform high-G maneuver (excessive load factor), put the aircraft in inverted flight (bank angle > 90°)? Will the aircraft refuse pilot's input or just make them hard ? In short, how is flight envelope protection implemented on Dassault falcon jets?

My information on the Falcon 7x and 8x comes from Aviation Week and Flying Magazine pilot-reports.
It would appear that the Dassault FBW philosophy is very closely aligned with that of Airbus. Namely,

It employs a C* control law without speed stability;
It uses passive sidestick instead of control column;
It employs 3-axis envelope protection, complete with bank angle protection (via positive spiral stability beyond 35 deg), load factor protection, AOA protection and high speed protection;
It even has a control-by-wire backup system similar to the mechanical backup available in the A320 and A330.

The fact that it has a C* control law, which provides flight path stability and not speed stability, and that it has a passive sidestick without force feedback, the envelope protection would appear to be a must-have for certification, rather than nice-to-have. By all indications, the limitations are hard constraints that cannot be overridden by pilot inputs in Normal Law.


What is 'level' to a G1000? I used to fly a Cessna 550 with 'steam gage' mechanical gyros. The Attitude Indicator always had its flight director solidly on the horizon in level flight -- to the extent a mechanical instrument could be seen accurately.
I recently started flying a Phenom 300 with a G1000 panel. It is curious to me that level flight in the Phenom is always about 2.0º nose up pitch:

And a detailed pic of the command bars in level flight at FL430:

My question: Why would level flight be indicated by nose up pitch? What does 'level' actually refer to?

Level flight just means not climbing or descending.  Where the nose is actually pointing is another matter.
The pitch you are seeing is the "deck angle".  Pitch attitude is normally referenced to the longitudinal axis of the fuselage (and normally, the cabin floor or deck) relative to the horizon for the loading and speed you are at.
The deck angle will be the overall AOA of the wing for a given flight condition plus or minus the wing incidence relative to the fuselage. If the incidence is zero, meaning the wing mean chord line is parallel to the fuselage's long axis, and the wing is operating at a 2 degree overall AOA at that altitude and speed, there's your pitch attitude; +2.  I would expect to see at least a deck angle of a couple degrees when flying at 210 kt indicated in a jet, unless the wing had an incidence of several degrees.
Say the Phenom has a wing incidence of about 1 degree, and that the wing is actually working at an overall AOA of 3 degrees at 210kt; the resulting deck angle would also be +2.
In the Citation with the mechanical spherical attitude indicator with Flight Director, you have to allow for the parallax error due to the gap between the indicator and sphere if your sight line is off a bit, and perhaps the Citation II has a higher wing incidence, and along with a lower wing loading cruises with a lower deck angle of 1 degree or less. With a mechanical indicator it'd probably look close enough to 0 degrees to make that conclusion.


How do Class B transitions work in the US? I'm just wondering about VFR requests relating to class bravo airspace in the US:

Is requesting VFR flight following in a class bravo the same thing as requesting a class bravo clearance?
Does requesting a class bravo airspace transition automatically include VFR flight following (radar traffic information service)?
If I am cleared into the bravo airspace and the controller gives me a heading and altitude to fly that clips the airspace of an underlying class C / D airspace, have I satisfied the requirements to enter said airspace (class C - 2-way communication and squawking mode C, class D - 2-way communication)?
Why does ATC provide traffic advisories for VFR aircraft in class bravo airspace at all if they are on the hook for providing separation?

Is requesting VFR flight following in a class bravo the same thing as requesting a class bravo clearance?

No. Flight following just means that the aircraft is receiving traffic advisories. A VFR aircraft needs explicit clearance to enter the Class B. The pilot should net ATC know that they intend to enter the Class B.

Does requesting a class bravo airspace transition automatically include VFR flight following (radar traffic information service)?

Yes, ATC must separate VFR aircraft from VFR/IFR aircraft while in the Class B. (7110.65X Section 7-9-4)

If I am cleared into the bravo airspace and the controller gives me a heading and altitude to fly that clips the airspace of an underlying class C / D airspace, have I satisfied the requirements to enter said airspace (class C - 2-way communication and squawking mode C, class D - 2-way communication)?

If ATC has given specific instructions that take a pilot through other airspace, then ATC should coordinate this with the appropriate controllers. Per 7110.65X Section 7-9-2 the controller should also either vector aircraft to stay in class B or to inform them if they are leaving it. Pilots should not change frequencies on their own unless asked, and the pilot should ask the controller if they are unsure.

Also, note that:

  Assignment of radar headings, routes, or altitudes is based on the provision that a pilot operating in accordance with VFR is expected to advise ATC if compliance will cause violation of any part of the CFR.

Why does ATC provide traffic advisories for VFR aircraft in class bravo airspace at all if they are on the hook for providing separation?

As described above, ATC is required to separate VFR aircraft from other aircraft in the Class B. ATC is instructed by 7110.65X Section 2-1-21 to:

  ...issue traffic advisories to all aircraft (IFR or VFR) on your frequency when, in your judgment, their proximity may diminish to less than the applicable separation minima.

Unless a VFR aircraft has explicit instructions, ATC does not know for sure what they will do. And IFR aircraft may still need to perform unexpected maneuvers like a missed approach. Traffic callouts make it easier to apply visual separation if needed.


Why did the Boeing 787 switch back to separate IRS systems? The Boeing 737 uses two independent IRS systems (see also Why are there two IRS switches on the 737NG?):

(source: 737 NG FCOMv2 (11.10.21 - Flight Management, Navigation - Controls and Indicators))

and the Boeing 747 uses three independent IRS systems:

(source: 747-400 FCOMv2 (11.10.9 - Flight Management, Navigation - Controls and Indicators))

For the Boeing 777, they switched to a single ADIRU:

(source: 777 FCOMv2 (11.10.10 - Flight Management, Navigation - Controls and Indicators))

The reasons are explained in this answer to the question How many Inertial Reference Systems are on a commercial aircraft?:

  Fast forward to the Boeing 777, the pilots only have one such unit: the ADIRU, or Air Data Inertial Reference Unit. The ADIRU by itself is a fault tolerance unit - within this unit, there are multiple gyroscopes and accelerometers. In the past, when multiple redundant units are provided to the pilots, there were instances where the pilots had trouble identifying the malfunctioning unit or switched to the wrong unit, and the plane crashed. Now there is only one unit, and the redundancy mechanism is auto-managed.

This makes perfect sense to me and should have improved safety. But I was surprised to find that the Boeing 787, which is in part based on the 777, switched back to two separate systems:

(cropped from source)

Question: Why did they change back? Was there something wrong with the 777 ADIRU?

There were also other practical end use issues as well. Having worked in the manufacturing and repair of theses fault tolerant units, one of the benefits was supposed to be the ability to plan maintenance. You could have a gyro or acceleromter voted out and still be able to take off and fly, since the F-T ADIRU had six gyros/accels and the SAARU four gyros/accels. Problem was the airlines weren't really taking advantage of this. They'd wait until you'd have two gyros or accelerometers voted out before and then be unable to take off due to restrictions. Some of the sensors sat voted out for years, with no replacement occurring.
Of course the airlines pointed the blame back the design. The F-T ADIRU was the third most expensive part of the 777 behind each engine. Most of them also did not carry spares for their repair inventory due to the costs of spares. Spare F-T ADIRU a couple years ago were running north of 2 million a piece. They found that the aircraft had less down time with a split system then using the fault tolerant system. Largely because they had ample spares for the split systems due the spare parts costing 1/10th the cost of the fault tolerants.


Is there a KPI to measure average hours flown? I am working on a report for a small charter airline and I want to set a key performance indicator (KPI) to measure average hours flown.

Is there a practice in aviation field to consider optimum flight hours for an airplane? An arbitrary example: Let's say I have a Boeing 767 and I want to consider if that particular model is profitable (I know it depends on payload, routes, and many other things), does it have to make an average 300 hours per month?

Is there such thing in aviation?

I want to set a KPI to measure average hours flown.

You might want to check block hour:

  (aviation) The time from the moment the aircraft door closes at departure of a revenue flight until the moment the aircraft door opens at the arrival gate following its landing. Block hours are the industry-standard measure of aircraft utilization.

(Emphasis mine.)

The Wikipedia article airline cost glossary lists very common terms and KPI's.

One of those terms that could also be applicable to your case (revenue passenger miles) was asked about here: Which aircraft type flies the most annual passenger-miles?


Why do airplanes use an axial flow jet engine instead of a more compact centrifugal jet engine? Axial flow jet engines take up a lot of space. Centrifugal jet engines create high pressure. Can you create a centrifugal air pump that pushes as much air as a axial jet engine. Centrifugal air engines reach higher speeds from my research. What are the main disadvantages of centrifugal air engines from the standard axial engines.

Centrifugal compressors only produce a more compact engine at low mass flow, which means low thrust.

The amount of thrust an engine can produce is proportional to its intake area times exhaust velocity. Increasing the latter is undesirable, as energy and thus fuel consumption is proportional to velocity squared. So engine designers target mass flow to gain more thrust, not more velocity.

Since they are 3D structures, in a basic solid design (that you'd find in early jets and small modern turbines), the volume of a centrifugal compressor grows in cubic proportion to its diameter, while frontal area, which limits its mass flow and thus its thrust, increases only as diameter squared. This creates a cube-square law.

Large real-life parts are filled with lightening and cooling channels, so the mass-to-area law is more complex. Still, it cannot eliminate the volume effect entirely. The end result is that the mass of centrifugal compressors grows considerably faster than their mass flow.

At the highest power levels, centrifugal compressors become prohibitively heavy even for fixed powerplant machinery, where durability otherwise trumps weight, so the largest base load powerplants run all-axial. With axial compressors, the flat design with a short air flow path allows mass to only grow in direct proportion to mass flow, and very powerful engines can be built within reasonable dimensions.

It's not pure cube-square law in either case, but it's something like k1*massflow^[2.5, 2.8] for centrifugal versus k2*massflow^[2.2, 2.4] for axial, where k2>k1, giving centrifugal compressors some advantage in small sizes. Centrifugals are also much cheaper to produce (at least small ones).

High-performance engines, such as those in commercial aircraft, also need to pack more thrust into the smallest cross-section they can, while maintaining efficiency, so as to reduce drag and also fit under the wings, enabling heavier jets. Axial compressors offer a lot more intake area for any given cross-section - thus more thrust.

The smallest jets, where thrust requirements are small and the engine's cross-section is very small compared to the fuselage, can afford the extra diameter of a centrifugal or diagonal flow compressor. Yes, it's the same cube-square law (also reduced somewhat in practice) that keeps the engine cross-section to total cross-section ratio increasing as aircraft go up in size. Small centrifugal compressors are simpler, easier to build, and more robust than small axial ones.

So in every industry, as power grows, there is a crossover point from centrifugal to axial. For aircraft where drag is critical, it's just above small bizjets, mobile ground and helicopter turbines stay centrifugal or mixed up to a few MW, and in the tens of megawatts even fixed powerplants switch from axial/centrifugal to all-axial.

Engines close to that crossover point typically combine axial and centrifugal stages. Newer diagonal compressors are in-between and quite good, offering an even more tailored compromise.


Robinson R22/44/66 Headset Plug For Bose A20 Headset What type of headset connector plug is used on R22/44/66 Helicopters?
Is Bose A20 Headset a good one to be used on helicopter?

Helicopters use a U-174/U or U-93A/U single-plug headset connector. Most aviation headsets come with PJ-068 & PJ-055B or equivalent. You will need an adapter. The second part of your question calls for an opinion, which is out of scope for this service.


777 small wing panel moving all the time during landing What is the small wing panel called that moves up and down all the time during landing?

See the following video:

What purpose does it serve?

That control surface is called a flaperon.

The flaperon functions as both a flap and an aileron to provide roll control, as with an aileron, and increased lift and drag, as with flaps. The flaperons on either wing move down together as flaps, and move up and down opposite each other as ailerons.

In the video, steady movement following that of the surrounding flaps from one position to another is an indication of operation in the role of a flap. If we could see the other wing we would see that flaperon moving in sequence. However, the short up and down movements, as opposed to the stationary flaps, is an indication of operation in the role of an aileron. If we could see the other wing we would see that flaperon moving opposite the flaperon in the video.


Where is this VFR reporting point ("Water Tank" near Thousand Oaks, CA) in real life? I was looking at the VFR sectional near Thousand Oaks, California. The chart has a "WATER TANK" labeled, but I see many water tanks in Thousand Oaks on the Google Maps satellite view.

Does anyone know which water tank they are referring to on the sectional? And why would they choose something so easily confused with other "water tanks"?

(skyvector.com)

The tank is west of Oak Park (Oak Park Canyon), but there is some conflicting information about the exact coordinates of VPLWT.

From FAA JO 7350.8P:

  34-10-49.0000N 118-46-16.0000W.

Converted into decimal degrees: 34.18028°N 118.7711°W

Google Maps

Obviously no tank here!

As @ymb pointed out, this document has been cancelled, and in the current version (JO 7350.9N), the coordinates have changed:

  34-11-01.0000N 118-46-41.0000W.

Converted into decimal degrees: 34.18361°N 118.7781°W

Google Maps

An underground tank, well visible from the sky. The tank itself is likely similar to this (it may be it, but not sure):

"Local officials recently toured and inspected the new Oak Canyon water tank under construction in Oak Park", source

Other tanks

There are also two external tanks in the neighborhood, but none corresponds to FAA coordinates, e.g. this one:

Google Maps

which is a bit north of the underground tank. Overall picture:

Google Maps

It seems FAA has not done a good job about this waypoint identification. While the current source identifies a tank, it should be mentioned this tank is underground, as this makes a difference.


Does rolling or yawing affect the angle of attack? If I'm on final in windy conditions and I need excessive rolling and yawing movements to stay on centerline and say, my pitch stays constant - does rolling or yawing change my AOA such that I could stall?

No that's not how it works.  You shouldn't need "yawing" movements on final before the landing flare.  That implies that you are using rudder to push the nose left or right to keep the runway sight picture where you want it, a very bad practice.

Never use rudder to stay aligned with the runway, except in the landing flare.  Other than that, only use rudder to keep the ball centered, or to side slip to lose altitude.  At all times, unless you are side slipping on purpose, use coordinated banked turns to stay aligned with the runway prior to the flare.

The rolling movements should be just those movements required to make coordinated banked turns to adjust heading to stay on centerline, or to get back on centerline.  Maybe 20 degrees of bank. Ball centered as much as you can keep it centered in bumps.

Moderate banked turns in a descent with ball centered create zero risk of stalling if speed is attended to.  Stall/spin accidents happen when pilots try to shove the nose with rudder to point it at the runway, causing uncoordinated flight, on top of sloppy speed control, so that if they get too slow, with the airplane slipping or skidding, when it stalls it flicks over the inside wing and down you go on your ride to oblivion.

If you are keeping bank angles within reason, ball centered, and speed on the proper approach speed, you won't stall the plane and normal control inputs will not get you close to stalling the plane. And with any modern plane, if you do stall it but the ball is centered, you won't depart in a spin and you can recover instantly.  Coordinated ball centered flight is the most critical item after speed control.


What is the difference between the Flight Control Systems of different F16 models? it is mentioned that the F16 A/B variants had an analog FCS, while the C/D version introduced a digital FCS starting from block 40.

Can somebody elaborate on the differences between them and point me to some reference?

The  main difference  is  processing speed, with the digital FCC's being faster than the analog models ( the analog-equiped aircraft it takes their FCC longer to detect the over-G, determine a correction, and send the correction to the actuators)and that's why first blocks until the 40 blocks will show +9G in the HUD .


How can I tell if an aircraft is equipped with fly-by-wire or with a FADEC? Can anyone help me with a link or advice on how I can identify whether an aircraft is fly-by-wire (FBW)?

I understood the function of FBW, however if I want to know if a SA227 or smaller type of aircraft has FBW, I am not sure how to identify it? Is there a link or a way to exactly say which type of aircraft have FWB and which don't?

The same applies for FADEC as well.

Only an aircraft model can be fly-by-wire or not, not an individual airframe of the same model.

Designing FAA/EASA certifiable fly-by-wire systems is extremely expensive, so only expensive aircraft, produced in large numbers, are going to have it. All Airbus since the A320 and Boeing 777 and 787 airliners are fly-by-wire, so are high-end Dassault bizjets. Recently the club has been joined by Bombardier, Embraer, Sukhoi, Irkut (Yakovlev) and Mitsubishi.

This doesn't include military aircraft, though you'll largely see the same players there with the addition of Lockheed, Northrop, MiG, BAE and a few other all-military contractors. Air forces have more need for fly-by-wire and are more risk-tolerant than airlines.

The SA227 is not fly-by wire. For the most part, if you have to ask, or if it's affordable below corporate level, it's probably not fly-by-wire.

EEC (of which FADEC is the most advanced subtype) versus hydromechanical engine control choice is specific to the engine and the airframe. It's not readily visible. An airframe will either have cables and hydraulic lines or sensors and wires. The majority of jet airliners currently flying use EEC or FADEC engines.


Flex temperature isn't actually "fooling" the FADEC, right? I'll be using Airbus terminology here because that's what I know, but I guess the concepts are universally applicable.
The way I understand flex temperature is: It's a user interface for pilots to request a derating of engine power to reduce wear on the engine. Simple enough, makes sense.
But in understanding why this is being input as a temperature, I have often encountered confusing explanations. Many videos and forum posts will say something like this:

Flex temp will fool the FADEC to think the outside air is hotter than it actually is.

That cannot be correct, right? If the FADEC actually thought the air was less dense, then if anything it would increase engine power, not derate it.
What makes more sense to me is this:

By entering flex temp, you're intructing the FADEC to produce only as much thrust as TOGA would produce at that increased temperature.

Simple. We're not fooling the FADEC, it knows full well how much thrust it is producing and that's good.
Using a temperature value as the input (instead of some percentage of engine power) also makes sense because pilots need to be aware of this parameter anyway when considering altitude, runway length, and aircraft weigth to verify a takeoff is possible.
If I'm correct, why is this "myth" of fooling the FADEC so prevalent? I find this notion very confusing and counter-productive when learning about this.
Does the FADEC even actually deal with outside air temperature in its logic? Why and how? Or does flex temp really just translate to a thrust value (possibly together with altitude)?

There are at least two misconceptions in your question:

The way I understand flex temperature is: It's a user interface for pilots to request a derating of engine power to reduce wear on the engine.

This is not quite correct. A derating would imply that the engine thrust needs to remain at the derated level after an engine failure. A FLEX or assumed temperature method takeoff allows setting higher thrust in case of an engine failure, so it's not a derating. See also What is the difference between Assumed Temperature and Derate takeoff thrust?

If the FADEC actually thought the air was less dense, then if anything it would increase engine power, not derate it.

This is not correct when the engine is temperature limited. The hotter the air, the hotter the EGT at the same fuel flow. Therefore, the FADEC has to reduce fuel flow to the engine for higher air temperatures, which reduces thrust.

Consider the following slide from this Airbus presentation:

You can see that the engine is flat rated (see What is a flat rated engine?) below a temperature Tref, which means the engine is not limited by EGT and can provide the same thrust regardless of temperature (see e.g. this answer for other limitations). If the temperature is higher than Tref, the FADEC has to reduce fuel flow to keep the EGT below the limit. This results in less maximum available thrust.
By entering a FLEX temperature, the FADEC will reduce fuel flow to the engine as if the actual temperature would be that high. We can argue about the semantics of whether or not this is actually fooling the FADEC, but the fact is that the FADEC will reduce the fuel flow accordingly. This will then actually give you a lower EGT than the maximum because the actual air temperature is colder and therefore reduces engine wear and tear.
The FCOM contains some additional information about what the FADEC does:

The FADEC system performs the following functions:
Control of gas generator

control of fuel flow
acceleration and deceleration schedules
variable bleed valve and variable stator vane schedules
control of turbine clearance
idle setting

[...]
Power management

automatic control of engine thrust rating
computation of thrust parameter limits
[...]

(Airbus A320 FCOM - Power Plant - FADEC)

When the thrust lever is in the FLX/MCT detent:

On the ground
The engine runs at the flex takeoff thrust rating if the crew has selected a flex takeoff temperature on the MCDU that is higher than the current Total Air Temperature (TAT). Otherwise the engine produces Maximum Continuous Thrust (MCT).

(Airbus A320 FCOM - Power Plant - Thrust Control System)


What is the necessity of Obstacle Departure Procedure(ODP)? What is the necessity of Obstacle Departure Procedure(ODP)?

Standard Instrument Departure(SID) is enough, isn't it?

Departure procedures are way to get IFR traffic from the airport to the en route system. There are four different procedures.

If an aircraft may turn in any direction from a runway within the limits of the assessment area and remain clear of obstacles that runway passes what is called a diverse departure assessment and no ODP is published.
There are a few in Kansas and Nebraska but  Florida, which is also pretty flat, only has a couple at military bases.

Obstacle Departure Procedures (ODP) are only used for obstruction clearance and do not include ATC related climb requirements. They often have higher visibility minimums and climb rates greater than 200 fpnm. Most are given as text, though occasionally there are graphical representations of them. They frequently have other restrictions, e.g. the tower must be open and monitoring a VOR, not available if local altimeter setting is not available. All but a few airports have an obstacle departure procedure.

A Standard Instrument Departure (SID) is an ATC-requested and developed departure route. Pilots must have at least the textual description of the procedure. SIDs always have a graphical depiction. Unlike Obstacle Departure Procedures, SIDs usually have portions where the altitude is restricted—either minimum or maximum. Most SIDs have multiple transitions to get you into the en route system. Small airports generally do not have SIDs and most airports that have scheduled air carrier service have at least one SID. While the primary purpose of a SID is to ease pilot and controller workload while getting the aircraft into the system, they also provide obstacle clearance.

A visual climb over airport (VCOA) is a departure option for an IFR aircraft, operating in VMC equal to or greater than the specified visibility and ceiling.

A radar departure is another option. They are established when ATC has a need to vector aircraft on departure to a particular ATS Route, NAVAID, or fix.

All departures (except VCOA) assume that the aircraft will cross the departure end of the runway at 35' or more, continue on the runway heading until reaching 400', and climb at a rate of 200 feet per nautical mile. Standard minimum visibility applies, 1 mile for 1 and 2 engines and ½ mile for 3+ engines.

You can read more about departure procedures in FAA-H-8083-16 Instrument Procedures Handbook, Chapter 1 Departures


What are the failure mode(s) for flying cars in case of power loss? There seem to be lots of plans (and even some working prototypes) for various autonomous flying cars and flying taxis.

Most of these seem to be based on vertical take-off using some variety of an electric quad-copter (or something very similar).

Conventional planes can glide in the event of engine failure, and traditional single rotor helicopters can auto-rotate. Both techniques should get the aircraft safely (more or less) down assuming the controls remain effective.

What is supposed to happen with a quad-copter based flying car/taxi if the power fails? I don't think the fixed props on a quad copter can auto-rotate, so how are they supposed to land? Ballistic parachutes? or something I've missed?

UPDATE for clarity (I hope). The media seem to use phrases like flying cars/flying taxis and autonomous aircraft or drones almost interchangeably. I'm talking about aircraft that have no (or minimal) wings (and therefore can't glide) and no capacity for auto-rotation. Here are a few examples...

Now have a look at this final photo, it shows an electric aircraft (a glider) with a battery fire. Being a glider the survival options were relatively simple, the pilot landed ASAP and got out of the aircraft. This doesn't seem to be an option for any of the designs I've pictured above.

As I am closely working on some of these projects, I think I can answer.

Let me start from:

  if the power fails

this is a rather extreme situation, since everyone is including emergency functionality in case the batteries get below a charge guard level, triggering an emergency landing (still powered).

So to have the "power fails" scenario that your phrasing suggests, you would need a sudden fire or failure of all the battery packs installed on the craft.

What's more likely is that one of the engines will fail, but that's less critical, since all these crafts will have 8 engines as a minimum exactly for this scenario. And once again, this will trigger a powered emergency landing.

Nevertheless, you are right in assuming that these crafts can't autorotate, and some projects are evaluating/have evaluated the inclusion of emergency parachutes similar to the ones seen on some general aviation fixed wing aircraft.


What is the difference between directs and shortcuts in the Route Availability Document? I am studying about directs and shortcuts in aviation. While flying, an airplane can move from an airway to another by using directs or shortcuts.

What I want understand is the difference between directs and shortcuts.

I know some of the information is contained in the RAD (Route Availability Document) but I don't understand if contains infos about direct or shortcuts or both.

A shortcut is a deviation from the filed flightplan given to an aircraft by ATC during the flight, if traffic and other factors permit. A flight crew cannot expect to get any shortcuts, so they cannot plan for it.

Routes in the RAD are flightplannable routes. If a direct route is available in the RAD, it can be used when filing the flightplan, prior to the flight. This allows airlines to plan for the shorter route, thus allowing them to bring less fuel and advertise a shorter flight time.


How loud is a private corporate jet? It's a movie/TV trope that people can talk to each other and even whisper on commercial airliners in flight.  In a story, it’s pracical to confront the reality of the experience and have characters have to deal with the noise when flying.  But, how does a private jet compare?  Will an intern flying with the big boss for the first time find it refreshingly better, or even worse, or what?

It's certainly reasonable to think a business jet cabin is quiet. Several business jet makers pride themselves on having models with quiet cabins. It varies a lot depending on the business jet, and exact numbers for the cabin sound level aren't usually listed.  It varies for airliners too with the A380 being an example of a very quiet jet and the 777 being noticeably louder.

If you're on a luxurious G280 or G650, the sound level would be relatively very quiet at less than 50 db (unofficially).  Even other private jets from my limited knowledge allow you to have conversations at even a few feet of distance without much struggle.  If you were operating an old loud engine like a Learjet 24 (which actually had turbojet engines) or a GII, the sound would probably somewhat limit conversation.

Exact sound levels are hard to find, in part because measuring a consistent sound level depends on so many factors, including cabin configuration, airspeed, engine thrust, air conditioning status, and position inside the aircraft.  Engine loudness, which is only part of the picture, is well studied and published (example).

Loud jet engines are rarer these days thanks to variety of factors, including the fact that operating loud jets is just plain illegal nowadays in many countries.  They actually make hush kits for older engines to get them down to legal levels.


How can the wind speed and direction be calculated from on-board measurements? I am currently learning C++ on my own in my spare time. I am writing a little application that will help me while at work.  I have come across a situation where I have some given values, but im not sure of the formula to use in order to render the end answer I am looking for.

Basically, I have the following parameters available to me:

Desired Track
Current Heading
Ground Speed
True Airspeed

I am interested in finding the wind speed and wind direction.

I have googled and googled for hours. Obviously most people use the old aviation E6B. However, that obviously doesn't work for programming. I was wondering if anyone happened to know, or know how I can find that formula.

With the set of parameters available to you, you cannot do this.

If you have the actual track instead of the desired track, you will be able to calculate the wind.

The simplest way to do this is using vector math.

There are three vectors to consider:

ground speed vector $\vec{V_{gs}}$
air speed vector $\vec{V_{as}}  $
wind speed vector $\vec{V_{ws}}  $

$\vec{V_{gs}} =\vec{V_{as}} +  \vec{V_{ws}}  $

$\vec{V_{ws}} = \vec{V_{gs}}  - \vec{V_{as}}  $

I assume the actual track angle ($\phi$) and heading ($\psi$) are with respect to the true North.

The north component of your air speed is then: $V_{as} \cdot \cos(\psi)$ and the east component of your air speed is: $V_{as} \cdot \sin(\psi)$

For ground speed the decomposition is: north: $V_{gs} \cdot \cos(\phi)$ and the east component of your ground speed is: $V_{gs} \cdot \sin(\phi)$

$$\begin{bmatrix}
       V_{ws,north}\\
       V_{ws,east}
        \end{bmatrix} = \begin{bmatrix}
      V_{gs} \cdot \cos(\phi) -
      V_{as} \cdot \cos(\psi) \\
      V_{gs} \cdot \sin(\phi) -
      V_{as} \cdot \sin(\psi)        \end{bmatrix}$$

You now have the north and east component of the wind vector. This you can change to a speed and direction, but I leave that last part up to you. Don't forget that wind direction is usually reported as the direction from which the wind is coming.

To find the wind speed from the North and East components use the root of the sum of the squares:

$V_{ws}=\sqrt{V_{ws,north}^2 +
       V_{ws,east}
^2}$

The wind direction can be found by

$\tan^{-1} (\frac {V_{ws,north}}{V_{ws,east} }) $

Note that this will give a division by 0 for winds exactly from north or south.

To implement it in a computer language the atan2 function can be used. This prevents division by zero and also returns the direction of the full range of the circle instead of semi-circular

wind_dir = atan2(-wind_north, -wind_east)

This should give the direction from which the wind is coming in radians.


What does QBD stand for? I recently heard the term QBD which the Aviation Dictionary explains is the fuel endurance in terms of hours. If it is an acronym, what is its expansion? If not, what is it derived from?

It comes from Q codes for morse communication. They where set up without a clear rhyme or reason that I can see besides being ordered alphabetically.


What happens when the logbook of an aircraft is lost? If the logbook for an aircraft is lost, how does one replace it? Is the airplane still airworthy?

In order to state the plane is airworthy you must be able to show that all AD's have been complied with and that the aircraft is within annual (or 100 hour) inspection; these proofs are typically found in the logbook so no, without the logbook your aircraft is probably not airworthy. It may be possible to fly the plane legally in the US anyway if you receive authorization from your FSDO (which, I believe, would be a "ferry permit").

It's not legally required that your logbook be complete to the beginning of time, just that it shows the current requirements are met (along with the signatures/cert numbers of the AI's that are stating them to be met). However, an incomplete logbook is very important from a resale point of view. Not having complete logs will make a plane very difficult to sell and will certainly affect the price most purchasers would be willing to pay.


What is the Relation between Critical AoA with Chordline? I read here an explanation about angle of attack (AoA) as below:
Overly long (forward-back wise) wings will generally have a smaller critical Angle of Attack while smaller ones will have more tolerance before stalling since Airflow starts to become turbulent in form of eddy currents.

I never heard that claim before neither I ever read. I have searched in this forum if someone asked that question previously, but seem is not. I could not find. Is anyone have reference to this claim?

It is a bit unclear, but I think what he is trying to say is if you have longer chord, then separation of the flow will happen at lower AOA than with a shorter chord, which is plausible as the boundary layer grows thicker and thicker with longer distance. And stall=flow separation basically.


Determining the total drag of a propeller driven aircraft while turning with a load factor of n = 2? I understand that the total drag includes the parasitic and induced component, with the parasitic component being the same as with straight and level flight.
How do I calculate the induced component?
The end goal is to produce a graph of drag versus airspeed.

Induced drag $D_i$ is proportional to the square of lift $L$:
$$D_i = \frac{2\cdot L^2}{\rho\cdot v^2\cdot\pi\cdot b^2\cdot\epsilon}$$
where $b$ is wingspan, $v$ is flight speed and $\rho$ is air density. $\epsilon$ is an efficiency factor which tends to be between 0.8 and 1. Compared to straight and level flight, induced drag will quadruple when turning at 2g and the same flight speed.
In order to know how much total drag goes up you need to know how much of your total drag is due to induced drag. Only then can the question be answered.
If your straight and level polar point is that for best range (when zero-lift and induced drag are equal), 2g flight at the same speed will increase total drag by a factor of 2.5.


Has an unauthorized civilian ever tried to land on an aircraft carrier? Has there ever been an attempt by a civilian 'daredevil' to land a plane on a US aircraft carrier?

I came across the Red Square Landing and coupled with this video it made me wonder if there was ever a civilian who attempted - illegally, of course - to land a plane on a carrier?

I'm not exactly sure whether this counts, but I think the landing of South Vietnamese Air Force Major Buang-Ly on USS midway using a Cessna O-1 Bird_Dog comes pretty close.

Though Major Buang-Ly was not a civilian, he has never seen a carrier before and the landing wasn't exactly illegal. It was permitted by Captain Larry Chambers during Operation Frequent Wind, who even scuttled helicopters on the deck to ensure safe landing.

The image below shows the aircraft as it comes to a stop.

Image from forum.worldofwarships.com


Are there regulations that limit the airports an air carrier can visit based on rescue equipment? ICAO Annex 14 (which deals primarily with SARPS for international airports) outlines requirements for rescue and firefighting that the airports shall have based on the fuselage lengths of the planes that visit said airports. Each category would define the equipment, amount of foam, discharge rate, etc.

Here the international airports comply with the users' requirements. It made me think of the other way around.

Suppose a pilot flies a tiny GA plane to a remote uncontrolled airport on a scenic tour. I don't expect that airport to have any means of rescue and firefighting apart from perhaps a call made to the local police.

But now suppose an air carrier decides to carry passengers to that airport.

Are there regulations that limit the airports an air carrier can visit based on rescue equipment? If not, how is the minimum level/category of rescue and firefighting guaranteed when not dealing with international airports?

For at least part 121 operations supported by part 139 certified airports or 139 airports that have unscheduled passenger traffic in aircraft capable of carrying more than 31 passengers; yes

  Operators of Part 139 airports must provide aircraft rescue and
  firefighting (ARFF) services during air carrier operations that
  require a Part 139 certificate. The guidance and resources below
  address ARFF training, ARFF vehicles, and other aviation fire and
  rescue requirements.


Does the Lilium VTOL wings produces lift during takeoff? I just had a look on some of the recent development in the personal VTOL electrical aircrafts.
I am wondering if the Lilium VTOL wings produces lift during takeoff?
I would expect a quit high wind speed moving over the wing generating negative pressure, hence, beside the thrust force generated by the fans additional lift is generated over the wings? Is this correct?

The take off is aided purely from the mini fans which is pointed vertically at the aft of the wing to generate pure vertical thrust. The wings will generate only drag and zero lift because the airflow(aerodynamic force) is attacking perpendicular to the chord line. Hence the wings are used only to aid the flight in cruise.


What's on the upper deck in the picture (circled) of Cathay Pacific Cargo Boeing 747-8F? Cathay Pacific Cargo Boeing 747-8F

Image Source

Is that a resting area for pilots or passengers seats?

What's behind those windows is the crew seating and rest area.

There are no passenger seats on those planes, the seats are specifically for the pilots and the people handling the cargo.


When is a sailplane a sailplane? A simple question that I could not find an answer to:
When is a sailplane a sailplane (from a regulatory point of view), especially a powered one of the TMG (touring motor glider) variety?
EASA has some quite simple definitions, presumably modelled over the similar ones from ICAO, according to which:

‘Sailplane’ means a heavier-than-air aircraft that is supported in
flight by the dynamic reaction of the air against its fixed lifting
surfaces, the free flight of which does not depend on an engine.
‘Powered sailplane’ means an aircraft, equipped with one or more
engines having, with engine(s) inoperative, the characteristics of a
sailplane.
‘Touring motor glider’ means a specific class of powered sailplane
having an integrally mounted, non-retractable engine and a
non-retractable propeller. It shall be capable of taking off and
climbing under its own power according to its flight manual.

From this simple chain of definitions, it would seem that, for instance, a Cessna 152 could be classified as a TMG: It can take off and climb under its own power, and with the (non-retractable) engine inoperative it will do free flight sustained by its "fixed lifting surfaces", otherwise known as wings.
Since a Cessna 152 is not normally seen as a glider, I presume that there are more rules that need to be respected before a plane can be called a glider (or sailplane in EASA's classification).
I know that CS-22 contains the specifics, but is there a simple set of rules to determine if an aircraft belongs to the class of (powered) sailplanes as opposed to normal aeroplanes?

There are indeed several steps between a pure glider and a powered aircraft. The criteria were historically quite simple:

Gliders with an auxiliary engine, which is just for getting them home in adverse weather, but not powerful enough for take-off. The propeller is in almost all cases retractable, so their aerodynamics is identical to their pure glider version, apart from a slightly higher minimum wing loading.
Motorgliders with an engine powerful enough for autonomous take-off, but with aerodynamics which gives them less than 1 m/s minimum sink with the engine switched off. This minimum sink decides if they are still powered gliders. This would be the TMG category.
Powered aircraft with an unpowered minimum sink speed in excess of 1 m/s. The Cessna 152 belongs into this category.

With the introduction of glassfiber motorgliders with their higher wing loading, the minimum sink rule could not be maintained, and manufacturers lobbied for a change in regulations. As it currently stands, CS-22 defines sailplanes to be within its scope if the maximum weight is below 750 kg. Powered sailplanes must not have more than two occupants, weigh 850 kg or less and have a span loading of 3 kg/m² (mass per span squared) or less.

CS 22.71 restricts minimum sink in unpowered flight to 1.0 m/s for single seaters and 1.2 m/s for two seaters.

Please note that suitable instrumentation should also be added for a motor glider to be counted as a sailplane, such as a variometer.


Why did the Ju-87 Stuka have a siren? Why did the Ju-87 Stuka have a siren? Was this for purely psychological reasons or did it help the pilot in some way?

Wikipedia:

  The B-1 [variant] was also fitted with "Jericho trumpets", essentially propeller-driven sirens with a diameter of 0.7 m (2.3 ft) mounted on the wing's leading edge directly forward of the landing gear, or on the front edge of the fixed main gear fairing. This was used to weaken enemy morale and enhance the intimidation of dive-bombing. After the enemy became used to it, however, they were withdrawn. The devices caused a loss of some 20–25 km/h (10-20 mph) through drag. Instead, some bombs were fitted with whistles on the fin to produce the noise after release.

So, yes, it was purely psychological and actually hindered the pilot by reducing air speed in ordinary flight and they were removed when they stopped having the psychological effect.


Aerodynamics of lift How can lift on a canvas covered airplane wing in level cruising flight be explained without introducing Bernoulli ? Both upper and lower surfaces are bulged out,which indicates lower than ambient static pressure on both surfaces.

I am not sure if I got your question completely.
As I am not entirely sure what you mean by leaving out Bernoulli.

Let's start with the lift issue:
Lift is created when the pressure (-forces) on the upper wing surface (suction side) and the pressure (-forces) on the lower surface do not cancel each other out. Usually this means that there is a net-force pointing upward (in level flight). Lift is therefore not directly connected to the ambient pressure. Does this answer the lift part of your question?
Image taken from wikipedia

Now let's focus on the bulged out surfaces:
I would guess there are at least two effects:

As you can see from the picture above the pressure is lower (than ambience) on
pressure and suction side (but since the pressure on the suction
side is lower than on on the pressure side, there is a net-force
(lift)).
Depending on the aircraft, it could be that the high-pressure in the stagnation point of the wing or aircraft pressurises the wing and cabin which would increase the effect from above. A bit like the canopy of a paraglider.


Why don't 747s use unreliable, but cheap, jet engines instead? I'm a neophyte who was reading a little bit about jet engines, and the economics behind them. In particular, I was curious about what makes jet engines so expensive compared to piston engines.

A recurring theme that came up, again and again, was the cost of quality control, and related factors like product liability. Jet engines are designed to be ultra-reliable under conditions of high stress, and understandably that drastically adds to the cost of manufacture and design.

However, what doesn't make sense is why these standards are so universally high, even in the case of jets on multi-engine craft with redundancy. It would seem that you definitely want reliability on a single-engine craft, a multi-engine that can't fly when it loses an engine, or even a two engine craft.

But for a four-engine aircraft like a 747, why pay so much for ultra-reliability? A 747 can stay at cruising altitude with only 2 engines. Modern jet engines have a failure rate of about 0.01 per 1000 hours. A 747 could use engines with a failure rate of 1 per 1000 hours, and still achieve the same safety profile as an aircraft with only 1 engine of redundancy. (Assuming engine failure rates are independent)

I'd assume that relaxing the jet manufacturing process to allowing 100X less reliability would drastically reduce costs. It seems like we could be manufacturing very cheap four-engine aircraft by allowing for high-failure rate engines. What am I missing here?

The cost of a jet engine is mainly dictated by the operating conditions: high temperatures (sometimes above the melting point of the metals used) and high rotation speeds. This means you need high-performance materials even for a low-reliability engine: if you compromise material performance too much, it'll fail on the first start.

Failures are risky. Having to shut down an engine mid-flight is one thing, but we've had some recent failures where chunks of metal were launched at high speed into the wing and fuselage.

The industry has gone the other way: by making the engines more reliable, it's now possible to build a long-range airliner that uses only 2 engines instead of four, reducing the purchase, maintenance and fuel cost. It makes little sense to set up a special B-quality production line for a single aircraft type that's being phased out anyway.

Failures are costly. An in-flight failure means taking the aircraft out of service to repair the failure, which means having extra aircraft on standby to replace it.


Under what circumstances can a flight attendant unbuckle and get up during landing? Lately I've been on several flights where the flight attendants had to talk sternly to passengers that were getting up either just before landing or just after (which is quite obvious to everyone since the talking to is done over the PA system).

Now this made me wonder what FAs can do if the passenger just refuses to comply? Can FAs get up and forcefully seat passengers (would they have to talk to the pilot first to abort the landing)? If not, are there any circumstances where the FAs can/should/must unbuckle during a landing?

An FA is a member of the crew and can get up or sit down as they wish during any phase of the flight. As to what they can do, they can have the pax arrested the moment the aircraft door opens. If that is not a good reason to obey instructions, I don't know what is! If the pax becomes a threat to the safety of the flight, yes, they can certainly get physical to put an end to the situation and secure the cabin.


Is « Shepherd One » really used internationally by air traffic control for Pope's flight? CNN:

  The President flies on Air Force One. The Pope flies on "Shepherd
  One." That's the Federal Aviation-approved call sign for the Boeing
  777 in which he'll be traveling around the United States, according to
  an official from American Airlines, which will be operating the plane.

Wikimedia:

  Shepherd One is the international call sign of any aircraft carrying
  the pope onboard. The airline which is used for such transportation is
  usually Alitalia

Source

Perdue site ('Cradle of Astronauts'):

  Flying Pope Francis – Purdue alum honored to fly 'Shepherd One'

From Crux Now catholic press:

  The plane isn’t really called “Shepherd One.” People in the United States
  call it that, but the phrase is a media conceit rather than an
  actual call sign.

Ghafla.com:

  Did you know it’s Americans who baptized the plane carrying the Pope
  ‘Shepherd One’? Well, their very own presidential jet is called ‘Air
  Force One’ so they thought since the Pope is a shepherd leading the
  Catholic Church, his plane should be called ‘Shepherd One’.

Question: Does ATC around the world, starting with Italy and the US, uses the specific call sign Shepherd One?

The FAA declared that as an official call sign for 2015-09-21 to 2015-10-15.

The order it cancels (.pdf here) had the bottom row filled out wrong (SHEPRD1 and "SHEPHERD ONE" were transposed, and "SHEPHERD" was typoed).

A document released on 2016-05-26 lists it in the "deleted special assignment" table (here).

So it's not a permanent reserved identifier in the US; but it might be recurring.

Wikipedia claims here (and here) that in Italy the Papal flights are named "Volo Papale ###", where the ### is a serial number (seemingly the number of times this Pope has flown).  I'll admit that I haven't been able to find anything akin to faa.gov for Italy, France, Australia, or the UK which would corroborate either "Volo Papale" or "Shepherd One".

  Typically, the Pope flies on a chartered Alitalia Jet. The Pope's flight is often nicknamed "Shepherd One" by the press, while the actual callsign is "Volo Papale" (papal flight, in Italian) followed by a serial number.


Do elevators have cambered airfoils inverted or symmetrical airfoils Do horizontal stabilizer of ga planes e.g cessna 172(or ultralights e.g lazair) have cambered airfoils inverted to provide the tail downward force or do they have symmetrical airfoils at negative aoi to provide the downward tailforce during flight.

Generally they are either symmetrical airfoils (like NACA 0012) or flat plates (especially on fabric airplanes).  The horizontal tail doesn't have to work as hard, or operate over as wide an AOA range, as the main wing in generating downforce, so you can get away with what amounts to, on most fabric airplanes, a slightly streamlined sheet of plywood.

There are some specialty exceptions. The Zenith 701 family of homebuilt STOL aircraft are unusual in having a heavily cambered flat bottom airfoil for the tail (actually, flat topped, since it lifts downward and is installed "upside down").  They did this to get as much down force as possible at very low speed and since the airplane is a bit of a slug anyway, the draggy tail airfoil wasn't so much of a penalty.

A homebuilt I had started on but never got anywhere with, called the Pegazair, had something similar, having ripped off a few of the 701's design elements.

Also, it was a practice at DeHavilland Canada to use tail airfoils with a bit of negative camber to improve down force at low speed on their STOL designs.  I'm sure there are others.


What are the basics of flying non-revenue? I've never worked for an airline, but I know that one of the benefits of working in the industry is that you can fly for free or almost free on a space-available basis.  I realize that every airline is slightly different, but what's the general procedure for this?  To provide a concrete example, let's say I live in New York and want to non-rev to Miami tomorrow.

How would I know if a space is available?  How far ahead will I know that I have a seat?  Can more senior employees beat me out or is it first come, first served?  Do I need a boarding pass?  If not, how do I get past the TSA checkpoint?

In general, how does flying non-rev work?

There are a few classes of Non-rev travel.

Jumpseating
Online pass travel
Interline pass travel

Jumpseating
This is open to pilots and flight attendants, air-traffic controllers (not sure if this is currently true, but it used to be), certain company and government officials (e.g. the FAA and others).
In general pilots can only occupy pilot jumpseats and flight attendants can only occupy flight attendant jumpseats.  I know of cases where pilots can sit in the FA jumpseats but this is largely a topic of the Pilots and FA Union contracts.  In general pilots can jumpseat on any other 121 carrier and some 135 carriers.  Note that jumpseating does not necessarily mean you'll be in the cockpit, as current regulations stipulate you should not sit in the cockpit unless there are not seats in the cabin available.
If you list for a jumpseat you will generally be the lowest priority for a cabin seat, boarding after all other non-rev travelers and then in a specified priority order jumpseaters will fill up the cabin and then the cockpit jumpseats until space is exhausted.
Jumpseating is the most versatile of the options, but the most limited in who can use it.  It is good to keep in mind your jumpseat agreements probably allow jumpseating on cargo 121 carriers in addition to passenger 121 carriers, so keep Fedex, UPS, Atlas, etc in mind when travelling.  Your spouse/kids won't be able to join you though.
Online Pass Travel
The specifics of this travel depends on your airline, but I will speak in general terms.  Pass travel is usually available to the employee, the employeers domestic partner or spouse, the employees minor children and the employees parents.  There is usually also a program for a limited number of passes for friends (buddy passes).
Pass travel is usually limited to your airline those you have a business relationship with.  For example a regional carrier can usually pass travel on the legacy carrier they contract with.  A legacy carrier can usually pass travel on its regional contracts.  If a regional contracts with multiple legacies, you sometimes only pass travel on the legacy system of the legacy you perform flights for.  It can be complicated.
There is always a defined priority for pass travel.  In general employees ride before spouses/parents/children who ride before buddy passes (except when travelling together, you may all share the priority of the highest priority pass on the itinerary).  When multiple companies are involved, the priority levels may reflect a higher priority for the company operating the flight employees than the legacy/regional contract carriers.
Again, this will vary greatly from company to company and you will learn the specific rules that apply to you when you are hired somewhere.
Interline travel
These passes are known as ID75, ID90, etc where the number is the percent discount from a full fare ticket.  You can generally buy passes for yourself, your spouse/domestic partner and your children.  No buddy passes.
To get an ID90, you visit your travel office and request an interline ticket for a specific city pair.  For example you can buy an ID90 for Rome - NYC.  You get an old school paper ticket for that route and no specific airline.  When you want to use the ID90, you present it to the ticketing agents for the airline you want to ride that flies the route you want to fly.  They will in turn issue you a non-revue standby boarding pass.  These are generally lower priority than online pass travel when it comes time to board.  These tickets are fully refundable, so they are often purchased as backups to get home when travelling in case you cannot get back with online passes.
How it all works
If you are the employee, you have a company ID and use this to get through security.  If you are the spouse/partner/child/buddy, then you will print out a standby boarding pass and use that to get through security.  You can check bags, which will get tagged standby and should board if you do.  It can be good to remind the gate you have bags checked when you get a seat.
If you are flying on your own carrier or under your legacy brand, you generally have computer access to the passenger boarding totals.  These can often be hard numbers of people booked, checked in and standbys listed.  You can use this to gauge the likelihood of getting on a plane.  If you are travelling offline then a carrier might have a phone number available but they may only tell you "it looks good!" or "it looks bad" and will not divulge numbers.
Once you are at the gate, you play the waiting game.  You will have a boarding priority which may look something like this for a legacy carrier flight:

Legacy pilots
Legacy flight attendants
Legacy retired pilots/FA
The legacies regional contract pilots / FA
Legacy spouse/parents/domestic partner/kids
The regional contract spouse/parents/domestic partner/kids
Codeshare pass agreements
Buddy passes
Interline passes
Cabin jumpseats
Cockpit jumpseats

This will assuredly vary based on who you work for and who they contract with, and is just to illustrate the complexity of the priority structure.  Within each category listed above there is an internal priority that for many is based on date of hire, others based on time of listing.  Again, this varies.
After all the confirmed revenue passengers board, the gate will board the revenue standby passengers, and once they are on and the number of empty seats is known (misconnects, people not in the boarding area 15 minutes prior to departure, etc), they will board according to the non-rev priority.  When the cabin is completely full, no more non-revs may board except for the jumpseaters, who may then fill the available jumpseats.
Putting it together
If you wanted to non-rev from NYC to Miami tomorrow and your company flies that route, then you just wake up in the morning, list yourself, take a look at the boarding totals and head to the airport.  If you don't even want to do that and you are a pilot, you just go down to the airport, find a gate with a plane headed to Miami and list for the jumpseat on that plane.  If the many rules of priority work out, you get on and you go to Miami.
Some considerations
Pass travel often has a dress code.  Don't show up in a tshirt and shorts unless you know you are allowed, you can be denied boarding.  Make sure all of your pass riders are behaving themselves.  This is especially important to impress on anyone you give a buddy pass, as when they screw up as a pass rider, you can have your pass travel suspended as punishment.


Do (or can) pilots observe religious fasts when flying? This question is about religious fasts like the Muslim Ramadan and others.

Is there a civil aviation regulation about this? Must a pilot eat and drink by the regulations (or abstain from flying), or is this an issue left to the pilot's personal decision?

Obviously if a flight takes long hours and the pilot can't eat and drink, or abstained from eat and drink for long hours before the flight, this can affect the pilot's performance. I don't know enough to say if it can actually impact safety but it is obvious that the claim would not be far fetched.

How is this issue addressed in airlines? For example in Muslim countries where I would expect a significant number of pilots to be Muslims, if a religious fast is widely observed this could be an issue.

There is no general answer for this question. Do pilots observe religious fasts during flying? Some do, as this article notes:

... although Islam gave permission or leeway to break fast if one found it tiring during the flight, most pilots and cabin crew still chose to fast.
“So, I fasted for 10 hours 50 minutes, compared to 13 hours 42 minutes in Kuala Lumpur and 11 hours 11 minutes in Melbourne. Much shorter time than fasting in Melbourne, isn’t that interesting?
“However, on June 29, 2016, I will be flying to Jeddah. Jeddah residents will be fasting for 14 hours, 54 minutes while KL residents will fast for 13 hours 43 minutes. I will probably have to fast for 17 hours! This is when I have to be really patient. I may break my fast once I have landed.
For the safety of passengers and to ensure a smooth flight, if both pilots are Muslims, they take turns to eat, he said.

However, there is no way to tell for certain how many aircrew observe religious fasting, as this pilot may be talking about that particular airline, for example.
As for Can they observe religious fasting, it depends on the regulation and company policies. Most of the civil aviation authorities don't have anything specifically related to religious fasting, preferring to cover them under fitness for duty, though there is atleast one case where the regulatory authority explicitly forbid fasting.

Indonesia’s Directorate General of Civil Aviation ruled that all safety-sensitive aviation personnel must eat while on duty during Ramadan, the Islamic month of fasting


What's the correct ATC phraseology to enter a nonpublished hold? Before entering on a hold (stack), the ATC should instruct the turns and headings to be accomplished by the crew.  If it is not printed on the charts, as on STARs, what is the correct phraseology to be used by ATC?

You didn't mention any particular country or jurisdiction, but for the US the FAA's ATC orders say in section 4-6-4:

  PHRASEOLOGY−
   HOLD (direction) OF (fix/waypoint) ON (specified radial, course, bearing, track, airway, azimuth(s), or route.)

  If leg length is specified,
  (number of minutes/miles) MINUTE/MILE LEG.

  If
  direction of turn is specified,
  LEFT/RIGHT TURNS.


How do the various DUATS differ? In terms of technical capability, what are the comparative advantages and disadvantages between the following?

CSC DUATS from Computer Sciences Corporation
DTC DUAT from Data Transformation Corporation
www.1800wxbrief.com from Lockheed-Martin

Both DUAT (DTC) and DUATS (CSC) provide the same information. They are functionally equivalent.
You also left one out: Lockheed-Martin operates a web-based briefing service at
https://www.1800wxbrief.com/ .

Which you prefer to use for interactive access is largely an aesthetic consideration - as a pilot you can sign up for an account on each of these services, so the usual advice is to sign up for all of them and use the one you like better (personally I used to prefer DTC's DUAT interface, but the direct (1800wxbrief.com) system is a now my preference for web-based briefings when I'm not using ForeFlight).

From a non-interactive standpoint, CSC DUATS has an API that can be used by other programs (like ForeFlight) to receive weather/NOTAMs/etc. and to file flight plans. This can be advantageous, however Lockheed-Martin has recently (2013) implemented an XML-based API that lets application developers directly communicate with the automated flight service system, and it is likely that this will be the preferred way to handle this sort of thing as time goes on.


Are NPRMs published in the Federal Register? Are FAA NPRMs (Notices of Proposed Rulemaking) published in the Federal Register?
I am currently researching the history of some airspace rule changes from the early 1990's, and am trying to figure out whether searching the Federal Register will turn up NPRMs, or only the resulting Final Rules.
For instance a "Terminal Airspace Reconfiguration NPRM", which is referenced on page 38963 of the Federal Register Volume 57 # 167 (Thursday August 27 1992).

Since posting my question, I've learned that the answer is "yes".  For example, the following URL opens to a FAA NPRM published in the Federal Register: https://www.federalregister.gov/citation/57-FR-18954


What is an autopilot washout filter? In the context of aircraft autopilot design, I do not understand what is washout filter is [Heading Hold - Lateral Dynamics] and what is it used for.
May anyone explain to me?

A washout filter is used in a yaw damper autopilot to remove the steady state component from the yaw rate sensor. Feedback from the rate sensor is used to damp dutch roll mode, but during turns coupling between yaw and roll results in the aforementioned undesirable steady state yaw rate component. Detail is on pg103 of: this document