What makes the swooping noise when a jet flies overhead? I've lived near several airports and have grown accustomed to a certain noise a jet plane makes when passing overhead: a swooping sound, very bass-heavy, that dives rapidly in pitch, maybe 1.5 seconds in duration. It happens toward the very beginning of the plane's audibility and is followed by the normal sound of the jet passing above.

Is it simply the Doppler effect as the plane passes overhead and its noise rapidly changes?

Or is there a mechanism on the airframe whose actuation on an approach might make this sound? Sometimes the same plane makes this sound more than once, which makes me think it isn't simply the Doppler effect.

The effect you noticed is the result of the combination of Doppler effect and sound absorption.

Sound absorption in a fluid is proportional to

$exp(- \alpha \nu^2 x)$

where $\alpha$ is a dimensional constant, $x$ is the traveled path, and $\nu$ is the sound frequency.

In its own reference frame, the airplane emits always the same sound, irrespective of whether it is approaching or receding from the observer. But for the observer, the frequency of a wave (which is $\nu_0$ in the plane frame) seems $\nu_a = \frac{\nu_0}{(1-v_j/c_s)}$ when the airplane is approaching, and $\nu_r = \frac{\nu_0}{(1+v_j/c_s)}$ when the plane is receding (here $c_s$ is the sound speed and $v_j$ the airplane's speed). Thus the perceived frequency jumps by a factor

$F = \left(\frac{1+v_j/c_s}{1-v_j/c_s} \right)$

This means that the absorption coefficient, at the time when the airplane is passing overhead (thus $x \approx H$, the plane's height over the ground), jumps from

$D_a = \exp \left(\frac{-\alpha H \nu_0^2 }{(1-v_j/c_s)^2}\right)$

to

$D_r = \exp\left(\frac{-\alpha H \nu_0^2 }{(1+v_j/c_s)^2}\right)$

For typical values for the atmosphere, and the propagation of sound waves in it, this means that $D_a \ll 1$, while $D_r \approx 1$.

Hence, what is happening is that, as the airplane passes roughly overhead, the sound goes from being deeply absorbed, especially at high frequencies, to not being absorbed at all (its normal sound, as you call it). The strange sound you noticed is what you perceive as the lower frequencies are becoming less and less absorbed, and thus the sound spectrum changes.

EDIT 1:

after I wrote my reply, DClayton (in a comment above) gave a very important hint that this is exactly what is happening when he noticed that the same effect appears with gliders, hence it is unrelated to engine sounds (I ignored this, thanks).

EDIT 2:

it is also worthwhile remarking what happens for high-altitude planes, when observed from the ground: in that case, the traveled distance $x$ is sufficiently large that all frequencies audible to human ears are absorbed, so that the plane goes from being nearly silent when it is approaching to being very clearly noticeable as it is receding.

You may try this on a clear day with high humidity at high altitudes, when over-flying jets leave white wakes: you will be unable to hear them as they approach (even though you can see them thanks to the presence of the white wake), but you can easily hear them as they go away, but just keep in mind that all of this is delayed by the (substantial) time it takes for sound to reach the ground, which, for 33,0000 feet or more, is of order 30 seconds. In other words, you will hear the noise level grow perceptibly about 30 seconds after the jet has passed the point closest to the observer, i.e. 30 seconds after flying directly overhead.


How does a runway inspection radar work? In AC 150/5220-24 FAA mentions radar equipment to detect foreign object debris (FOD) on runways, based on stationary and mobile radars with an astronomical precision, e.g. able to detect an object as small as 3 cm at a distance of 1 km.

Xsight Systems

How do these systems work?
Do they completely replace visual inspections?
Are they common on international airports?

Looking at their patent it appears it uses a multi spectrum system (radar & electro optical) to track all object: birds, aircraft, and FOD.

It uses a radar to detect objects

  The potential foreign object source identifier subsystem preferably includes potential foreign object source detectors such as a tower-mounted millimeter wave sensor (MWS) detector

And a specialized light sensor to determine the makeup of the object

  FOD identification functionality may be added to the FOD detectors, such as functionality which identifies the material which constitutes the FOD. Remote spectrometry functionality, such as that used in mineral prospecting satellites, may be employed for this purpose.

A neat function too is the ability to determine the where the FOD came from and send pictures of the FOD and the offending source to airport officials

  The ascription output may be presented to an airport official in an airport control center on a display console which may show on a first portion  of a screen, an image of the detected FOD and its location, both preferably in a zoomable format, along with a time stamp, and on a second portion of the screen, an image or other representation of a most probable source of the detected FOD, preferably in a zoomable format, along with its time stamp.

It appears it also fuses sensor data with aviation data to augment it's determination

  flight database data indicating recent aircraft movements and optical identification data indicating vehicle movements is supplied to data fusion functionality which also receives ASMGCS data and weather data and interfaces

If it works as advertised it not only replaces visual inspection but also provides realtime feedback for bird control and communicating with aircraft falling apart.


Do helicopters try to take off and land into the wind? When helicopters take off and land is it preferable to point the nose into the wind? Since a helicopter is providing its own lift does it matter which direction wind is coming from?

In general, helicopters require less power while flying forward (or backwards) compared to hover as translational lift (of Effective Translational Lift, ETL) is produced. Even though the blades are providing lift by rotation, the airspeed experienced by the blades is different if wind is present. For example, if there is headwind $v$, the advancing blades will have an airspeed of $r \omega + v$, while the retreating blade will have an airspeed of $r \omega - v$. As lift is proportional to square of airspeed, the implications are obvious.

For this reason, it is preferable to take off into the wind, rather than take off vertically.

Note that the power required is same for headwind or tailwind. However, tailwind landing (or takeoff) has some disadvantages from stability and power management point of view that is it generally discouraged, like:

In case of landing in tail wind, it is very difficult to abort landing and re-gain forward airspeed. Moving from negative speed to forward speed initially decreases the air speed the main rotor experiences, and the Power Curve shows an initial increase in Power Required. As the helicopter accelerates from negative (ground) speed, the main rotor system loses translational lift before it goes through zero airspeed. As a result, the power required increases, which requires increased pedal application and tail rotor power, precisely when the power requirement is high.
If there is a power failure, the chances of safe landing is reduced.
There is more risk of running out of directional control. In case there is a tailwind, the helicopter vertical tail (and fuselage) may align try to align with the wind, resulting in uncommanded yaw. If not corrected with proper pedal input, this may lead to loss of control.
In case of landing, the possibility of brownout or whiteout conditions is more in case of tailwind.


Can I leave my smartphone turned on in the checked-in luggage? For obvious reasons, that's the best way of tracking the whereabouts of my luggage. Once the plane lands, it would establish a 3G connection, and I would be able to access its GPS position.

Your phone must be in airplane mode whether it is in the passenger cabin or cargo hold.  In this case the phone will never establish a 3G connection and won't meet your desired use case.

Leaving the phone with cell service on will likely also not solve your problem.  Cell phones tend to use a lot of battery trying to connect to a tower when there are none in range.  By the time you land your phone may have already shut down from losing power.  If the bag is lost it may be deep in the bag handling areas of the airport or some other corner with no cell service and certainly no GPS signal.  In all likelihood unless someone mistakenly takes your bag home and decides to charge your phone and turn it back on this plan of yours will not work.


Why are callouts of changes in the Flight Mode Annunciator not automated? With many airlines it seems to be standard that the Pilot Monitoring observes the Flight Mode Annunciator (FMA) and calls out any changes in the autopilot mode displayed on the FMA (I guess to raise awareness to the new or armed flight mode). Why are these announcements not automated (i.e. computer generated voice like the altitude announcements during final approach)?

The responsibility of checking the FMA after a mode-change is not the PM's alone. If the PF calls for VNAV, the PM will select VNAV, now both of them need to check VNAV is active.

Regarding aural alerts, there are already alerts to when the flight deviates from the norm, for example an altitude warning (which doubles as approaching target altitude), stick shaker, low-speed / over-speed, etc.

But, your question is about changing the flight-mode, say from VNAV PTH to VNAV SPD, or VNAV to FLCH. As mode changes are a direct consequence of crew commands, I don't see a benefit.

One downside I can think of is that the ATC will hear a lot more aural warnings as the crew changes the modes while reading back an instruction.

As for the effectiveness of such system, say in case the crew pressed the wrong button and they were too tired to double-check the FMA, they shouldn't be flying in the first place.

  The analysis of accidents and numerous scientific publications have demonstrated that operational stress and fatigue can result in pilots neglecting crucial information, such as visual and aural warnings. This phenomenon, called channelized attention is defined as being “the allocation of attention to a particular channel of information, diagnostic hypothesis or task goal, for a duration that is longer than optimal, given the expected cost of neglecting events on other channels, failing to consider other hypotheses, or failing to perform other tasks” (Wickens, 2005). It seems possible that this phenomenon might occur during the go-around phase which is often unexpected, uncertain and of sudden onset, and may take place after many hours of flight.

(Emphasis mine.)

That's from a BEA study on Aeroplane State Awareness During Go-Around.

Too many alerts and any human will become used to the regular sound with mode changes regardless of what the aural warning says. Eventually it'll become background noise.

The ideal level of warnings is not to overload all the senses, and let the aural warning be when something is crucial, so the training can kick in with speedy recovery actions versus a relatively slow diagnosis of the situation.


How is the pitot/static system of a helicopter affected by rotor downwash? Since the fuselage of a helicopter is affected by downwash from the rotors, how is the pitot static system affected?

The pitot tube is not much of a problem - it's your typical pitot tube, pointing forward (toward the nose of the helicopter) to measure forward airspeed. Airspeed is somewhat less important to a helicopter pilot than it is to a fixed wing pilot since lift is generated by swinging the rotor around instead of moving the whole vehicle through the air.

The static port requires a little more thought, because it should be located in an area of "undisturbed air", and being in rotor wash is certainly not "undisturbed".
On the R22 the static port is actually located inside the shell per the maintenance manual and is thus shielded from rotor wash:

You could locate the static source in a similar unpressurized-but-shielded compartment in a pressurized helicopter.

On other helicopters the static port is on the fuselage as on most aircraft, for example this one is on an HH-2D Seasprite:

Note that the static port is slightly recessed on the seasprite to keep it out of direct rotor wash.  Multiple static ports may also be used (again, as you'll find on other aircraft) to give an average static pressure and reduce the effects of rotor wash on the static pressure reading.

As with all static systems there will still be some degree of error - no system is measuring truly static air. As long as it's within a reasonable tolerance all the instruments should be able to be calibrated to read correctly though.


How can I find places to store/land a private airplane? Say I'm the proud new owner of a Cessna 172.

To celebrate, I want to fly my family from Texas to Orlando Florida for a weekend visit.

Local takeoff is easy enough. I live close by, and I know the locals so I can "borrow" a runway.

However, how do I coordinate the landing in Orlando? I know commercial options are available like the Orlando International Airport, but that seems... expensive.

Even if I paid to land the Cessna (which I have no idea of the red tape involved with this), I'd still have to find somewhere to "park" to plane for my weekend trip.

However, looking at other options in the area I see several flight schools, and even some "private owned" airports with operational runways.

Which brings me to my question: if the pilot of a small aircraft wants to land in place far yonder, what's the best way to plan for this?

Is it common practice to call all the "small guys" in the area first and see if they're willing to work with your flight schedule?

If they gave you the go-ahead to land and store your aircraft in their facilities, is there any paperwork you should sign to protect your aircraft in the case of theft/vandalism?

What if the commercial airport is the only viable "runway" you see close to your target destination? What red tape is involved with landing/storing a small aircraft on commercial landing strips?

The first thing you usually do as a pilot is to look at a sectional chart, which shows all the airports and airspace in the area you want to fly (and transit). They look like this:

You can see that the Orlando area offers a number of airports. I would avoid anything with the word "International" or "INTL" in the name. Mostly these airports cater to commercial traffic; GA traffic is allowed but usually requires a lot more work to get you in, especially if you are only VFR (not instrument rated or on an instrument flight plan).

You can see Orlando Apopka (X04) in the upper left corner, but also available are Executive (ORL) just above Orlando International or Kissimmee Gateway (ISM) in the lower center/left. If you want to make sure the airport has fuel, these are denoted by the "ticks" around the airport symbol:

If you want to look at more sectional charts, they are offered for free on sites such as Skyvector which also has flight planning tools.

To answer your other questions:

  Which brings me to my question, if the pilot of a small aircraft wants to land in place far yonder what's the best way to plan for this?

Flight planning is part of your initial pilot training. By the time you earn your PPL you will have planned a number of cross-country flights (albeit not that far as Texas->Florida). It starts out by picking an airport and looking up the information in the chart supplement along with one or two alternates. You then call the Fixed Base Operator (FBO) and ask about fuel rates and overnight parking, and then continue on with your flight planning tasks (like checking weather, routing, etc).

  Is it common practice to call all the "small guys" in the area first and see if they're willing to work with your flight schedule.

Calling the FBO you intend to visit is advisable, especially if you need to use services like parking or crew cars. This lets them know to expect you and they can tell you what they charge. Some smaller airports won't charge for ramp tie-downs if you buy a certain amount of fuel, etc. Some airports don't have an FBO so they are "self-serve", meaning you pull up to a gas pump just like in your car and fuel yourself.

  If they gave you the go-ahead to land and store your aircraft in their facilitates is there any paperwork you should sign to protect your aircraft in the case of theft/vandalism?

Leaving your airplane at the airport isn't like parking it in the parking structure. Airport access is tightly controlled, especially at airports that have FBO's or operating control towers. Some smaller airports don't have that and if you know how to find the codes you can pretty easily get through. Either way though, vandalism/theft is usually a non-issue. The biggest worry you have is weather. If you are really concerned about your aircraft, you can ask the FBO if they have a hangar and if there is space available. Storing your aircraft in the hangar can be very expensive. Typically you just tie down on the ramp and put in some sun-shades.

  What if the commercial airport is the only viable "runway" you see close to your target destination? What red tape is involved with landing/storing a small aircraft on commercial landing strips?

I assume you mean a major commercial airport like Orlando International. The only "viable" option to me denotes an emergency, as you should have planned to fly somewhere else and only in an emergency would you want to land at a major commercial airport. If you need to declare an emergency and land, ATC will clear the airspace and make you the only user of that airport. As for storage when you get there, many airports even the size of Orlando International have a GA area where you can tie-down, but getting fuel and even the ramp space will be very expensive.

  Say I'm the proud new owner of a Cessna 172.

  To celebrate I want to fly my family from Texas to Orland Florida for a weekend visit.

Just FYI, a Cessna 172 is not a "family trip" aircraft. Two adults, one kid, and baggage will pretty much max out the aircraft. You can remove fuel to add more weight, but then you are puddle-jumping.

  Local takeoff is easy enough. I live close by, and I know the locals so I can "borrow" a runway.

Unless the airport is marked private (PVT) you are free to use it and don't have to "borrow" anything. Only airports marked as such in the chart supplement will require prior authorization to land there, so the majority of airports are "public use" and you can just jump in your plane and fly there without warning (as long as the weather is above minimums).


What are the amber triangles on the ECAM bleed page on an A320? In FCOM they say that triangle becomes amber when RAM AIR flap is not fully open, and both pack flow control valves are closed.
Here the RAM air flap is emergency ram air or RAM Air flap for the Packs?

It refers to the valve controlled by the guarded RAM AIR pushbutton referred to as "emergency RAM air" in the system diagram.
When the triangles (think of them as arrows indicating flow) are white the triangles indicate sufficient flow of air for conditioning/pressurisation.
The normal position of the guarded Ram Air pushbutton is 'off', ie no light illuminated.
In case both packs fail/shutdown, i.e. both the pack valves are closed, the remaining source for getting airflow through this system is the RAM air. If that is not fully open, while the pack valves are both closed there is insufficient airflow and the triangles therefore turn amber.


Could the principle of owls' silent flight be used for stealth aircraft? I was wondering about the ability of owls to fly so silently. Is it because they flap gently, they flap less often or do is their structure responsible? I was thinking their principle of stalking can be applied to stealth aircraft. Is it possible?

Their primary wing feathers have an unusual structure incorporating a fringed, comblike leading-edge, which reduces wind noise.  The wing feathers also have an overall softness or flexibility.  The trailing-edge of the wing is also dominated by soft, fringed edges.  Even the underwing lining (covert) feathers have an unusual softness that plays a role in sound suppression.

See for example --
https://www.owlpages.com/owls/articles.php?a=7n ,
https://animals.howstuffworks.com/birds/owl-fly-silently1.htm .
Google "owl feather structure" for more.

I'll leave it mostly unsaid, as to whether any of these features are worth incorporating into a jet-powered aircraft.  Maybe some of these features might be applied to the intake or exhaust areas, in a more rigid metallic form?


What are the effects of the tilted lift vector in a banked plane? I want to clarify the effects of the change in direction of the lift vector caused by banking in a plane.

Banking rotates the lift vector creating a horizontal component. I have read that some effects of this horizontal component are as follows:
1) It acts as a centripetal forcing inducing circular motion in the plane.
2) It generates sideslip such that in dihedral planes there is an increased angle of attack in the lowered wing, and a decreased angle of attack in the raised wing. This generates a restoring moment facilitating roll stability.

So my questions are as follows: How does the horizontal component of the lift have both a centripetal effect and a slide slip effect? (A more general question) In a banked turn under cetripetal force, what causes the change in the heading of the plane such that its longitudinal axis remains facing the relative wind?

Perhaps I have somewhat answered the first question with the second: initially under the centripetal force the plane does not yaw to have its longitudinal axis aligned with the new air velocity vector and therefore sideslip occurs? I am not sure, please let me know.

Thanks

In a banked turn under cetripetal force, what causes the change in the heading of the plane such that its longitudinal axis remains facing the relative wind?

The simplest case of a flat wing will create lift orthogonal to its direction of motion and the direction of wingspan, and some drag parallel to its direction of motion. Both lift and drag will act in the plane of symmetry. Let's assume that drag is compensated by a constant thrust, so the level wing is in equilibrium. A tilt will contribute a sideways lift component that is not compensated by weight and will accelerate the wing sideways.

This will move the wing into the direction of lift and reduce its angle of attack. Lift will drop which reduces sideways acceleration. Unfortunately, this also means that gravity will not be fully compensated. The wing will be accelerated downwards which increases its angle of attack. Both effects will settle at a point where the wing moves side- and downwards, the sink speed depending on the drag increase since more lift in total must be generated.

But the picture is incomplete without the contribution of the tail surfaces. The sideways motion will cause a side force on the vertical tail which will weathervane the aircraft into the direction of sideslip. Only that lateral stability contribution will start the turning motion. Now you get a continuous process in which the wing accelerates the whole airplane sideways and the tail will yaw it into the wind, resulting in a not well coordinated turn. The yawing motion will add a centripetal acceleration which will eventually balance the sideways acceleration from the tilted lift force.

Since we decided to leave thrust constant, the added lift requirement will cause more drag and the aircraft will sink in order to compensate for the energy loss from turning. If we now add the freedom to change the elevator deflection, we can trim the aircraft for the higher lift and a lower speed so that (depending on the position of the initial state on the power curve) the aircraft could fly a level turn at a lower flight speed.

I also neglected pitch stability so far. At higher bank angles it becomes important and contributes to the turn in proportion to the sine of the roll angle. With a constant elevator deflection, pitch stability will try to keep speed constant and pitch damping will reduce the turn rate. Once we allow to adjust the elevator, pulling will reduce pitch damping and trim a higher angle of attack, so the turning rate will pick up.


Airfoils designed for reverse flow This question might seem strange as almost all aircraft have the air flowing over the wing in only one direction. However if you wanted to design an airfoil would have a good L/D in the forward flow direction, but would also generate lift, or at least not have excessive drag under reverse flow conditions, how would you go a about finding such an airfoil?

The Aerobie flying disc uses an airfoil that looks like a fish. The fish tail creates stability in a spinning disc, but also quite a bit of drag I believe. If stability is not a concern, I think another airfoil shape may provide less drag.

https://en.wikipedia.org/wiki/Aerobie

http://www.aerobie.narod.ru/aerobie.htm

You would copy the cross-setional shape of the frisbee plastic disc toy, which generates lift as it spins and travels through the air by using a shape which looks like the leading edge of a wing no matter which way it is pointing. a wing with two "leading edges" like this is not as efficient as a wing with a tapered trailing edge, but it works well enough to fly significant distances and provide fun for its users.


Is there an in-flight built-in-test in an airplane? Is there any in-flight built-in-test in the airplanes separate from the in-flight monitoring?

The thing that separates a BIT/BITE (E=Equipment) from continuous fault monitoring is that the continuous fault monitoring simply responds to exceedances of various paramters or values outside of specified limits in real time as they happen (say where an analog voltage signal of a device drops below a minimum of X or exceeds a maximum of Y), whereas a BIT/BITE test is a specific routine where simulated fault signals are injected into a circuit to see if a fault monitor is doing its job.

BIT or BITE tests of electronic controllers can be categorized into three types:

Start Up BIT: Most common.  A test routine automatically run on power up of the controller.
Initiated BIT: Controllers may have a manually initiated BIT/BITE that can be run any time, but this is usually triggered by a button on the controller itself in the avionics compartment, or through a maintenance access portal in the aircraft maintenance diagnostic system, and usually doesn't have a flight crew initiated facility (but may in some cases).  These are normally intended for troubleshooting.
Continuous BIT: A controller may run an internal self test routine on a continuous cycle while powered up, where a controller has fault detection circuits that can't be allowed to have dormant failures, even for the duration of the flight.


How to request to fly on a flight level, different from the direction, according to the charts? According to the direction, there are correct FL to fly, but due to weather, or traffic, the pilot would request a different FL, from the chart (according to the direction). Is there any correct phraseology to request it?

Say you are flying on a route that requires an even level, but you would like an odd level such as FL350. The phraseology to use would be

  Request FL350

The rest is up to ATC. Depending on local agreements and the current situation, we may be able to grant you the level right away, maybe we need to pick up the phone and talk to downstream sectors or maybe we can't offer the level at all. In any case, there is no harm in asking.

Regarding the part of your question that mentions weather, if you are requesting a level change because of extreme weather (such as moderate/severe turbulence or icing), state so in your request. We will then handle your request with higher priority, and you are more likely to get the different level.

  Request FL350 due to moderate icing


What made the below flight path to have very low speed during the middle of its course This is an ongoing flight details of my in-laws travelling from Frankfurt to India. I observe the speed of the craft is drastically reduced to 100mph and then picked up normal.
Could someone please explain this?

Thanks,
Raj

What you are seeing is merely a glitch in the publicly available telemetry sites like FlightAware use.

They aggregate flight data from the FAA (ASDI), EUROCONTROL and others to feed their sites, but this data is not always accurate, and doesn't need to be.

For that interval, the speed was either malformed or reported as 0/unavailable (don't remember exactly) due to bad data.

The aircraft did not slow to 100mph or lower unless it landed :)


Is there a use scenario for the Detote value? Im currently working on the fuel calculation of an airplane, when i stumbled upon a value called "Detote". When asking around, no one knew what the use case of this value is or why it even exists.

In the handbook it is described as follows:

  A DET (detotalizer) fuel amount is a digital value from which the
  fuel used, as measured by the fuel flow meter, is deducted, allowing a
  comparison to be made with the measured fuel contents.

This value can be set via the UFCP and will show up on the MFD.

What are the application scenarios for the Detote value?
Did you see this value implemented on an aircraft?

On 747-100/200 aircraft, the "detotalizer" was on the flight engineer's panel. The image below is, I believe, from a 747-400 because those on the -100/200 aircraft were mechanical digits rather than electronic, but I couldn't find an image of the earlier version.

Before engine start, the f.e. set the aircraft gross weight and the total amount of fuel. From that point, the instrument kept track of of your decreasing gross weight and fuel quantity.

The amount of fuel showing on the detotalizer was considered to be more accurate than that shown by the fuel quantity gauges, and thus was controlling for en route flight decisions.

Besides quickly and accurately giving the amount of fuel remaining in general, it was critical to redispatch operations (sometimes called reclear). See the "Reserve reduction" section of the Wikipedia article on flight planning for a detailed redispatch explanation.

Basically, though, redispatch allows you to legally get to a destination for which you can't (or don't want to) carry enough fuel to to reach that destination with the required reserve fuel. What happens is that you're dispatched to a destination short of your desired destination. Then, nearing the destination to which you were dispatched, you are then redispatched to the desired destination.

An example. I used to fly JFK to Tel Aviv, a flight that always required a redispatch in a -100 and sometimes in a -200. The flight was usually between 10 and 12 hours, depending on winds, how you hit the North Atlantic track system, and routing through Europe. Let's say the expected fuel burn was 275,000 lbs. The dispatch fuel requirement would be that plus 5% reserve (from memory, might have been a higher percentage). So, to be legally dispatched to Tel Aviv, you had to have 288,750 lbs of fuel at takeoff. But let's say the most fuel you could load (or wanted to) was 280,000 lbs.

No problem. You dispatched to Athens, well short of Tel Aviv, and for which the fuel requirement was considerably less than the 280,000 lbs you had on board. You used a route that took you over the Mediterranean on the way to Tel Aviv through an intersection abeam Athens. You had two flight plans aboard: one from JFK to Athens and one from that intersection to Tel Aviv. The fuel requirement for the second one was the burn from the intersection plus 5%. Thus the reserve fuel requirement for redispatch was 5% of something like 30,000 lbs (burn from the intersection to Tel Aviv) versus 5% of 275,000 lbs (burn from JFK to Tel Aviv).

Coming up on the intersection, you looked at the detotalizer. If it showed at least the required legal fuel on the second flight plan, you called the company and were redispatched. If it showed less, you would turn left at the intersection and refuel at Athens. As I remember, I never had to do that, although, truth be told, there was the occasional fudging of a hundred pounds or two, maybe three, but never more than that.


Why would banking be a problem for passengers on the Flying-V aircraft? In this article, the author raises doubts about the viability of this aircraft:

  Sadly for the Flying-V, it will probably fail like the blended wing
  body designs we've seen down the years. It's for the same reason, too:
  airplanes bank as they turn. That's not much of a problem in a
  conventional airliner design, where passengers are never that far from
  the plane's central axis. But as you move further out from that
  central axis the effect becomes a lot more pronounced.

credit: Edwin Wallet, Studio OSO

I don't really understand how banking is a problem. The angle for the passenger remains the same, the only difference being an increased of vertical acceleration when the airplane is initiating / retracting the bank.

An apparent simple solution would be to... bank more slowly...

Is there something I'm missing?
Would the vertical acceleration really be a concern for passengers?

There are two possible sources of discomfort for passengers sitting farther away from the aircraft's longitudinal axis during a roll manoeuvre:

At the start and end of the roll manoeuvre, the angular acceleration will be felt as a stronger vertical acceleration, as you pointed out (vertical as in perpendicular to the cabin's floor).
Between the start and the end, the aircraft will be rolling at constant angular speed (or roll rate), so the angular acceleration will be zero, but the passengers will still be moving along a circular trajectory (around the aircraft's longitudinal axis) and therefore will also be subject to a centrifugal force (parallel to the cabin's floor) that grows proportionally with the distance from the longitudinal axis.

The roll manoeuvre itself may only last a few seconds, but if the above effects are strong enough, it could be enough to make some passengers feel properly queasy, especially if it's repeated a few times as during departure and arrival procedures.

As you suggest, rolling more gently and more slowly would limit these effects. However, instrument flight procedures always involve standard rate turns, with turn radii expected to remain within certain limits, depending on the aircraft's speed. Rolling more slowly would increase the aircraft's overall turn radius and could make it harder or impossible to comply with currently published procedures.


What kind of WWII aircaft is this? I saw this plane at a warbird fly in and would appreciate some assistance identifying it.

I can only tell you what I'm rather sure it's not..

Grumman TBF Avenger

Other US-operated Torpedo Bomber types

Grumman F4F-3 Wildcat

Republic P-47 Thunderbolt

Any ideas?

[EDIT]

Also, is this yellow aircraft the same model, only with a different paint scheme? The nose looks different, but perhaps the cap/cone has been removed, perhaps for maintenance. Otherwise the canopy, wheels, and gear covers look identical.

A North American T-6 Texan Trainer, probably the NJ/SNJ Texan variant.

"SNJ-1 at NAS Pensacola c1940" by U.S. Navy - U.S. Navy National Museum of Naval Aviation photo No. 1996.488.166.090. Licensed under Public Domain via Commons.

The North American Aviation T-6 Texan is a single-engined advanced trainer aircraft used to train pilots of various air forces including (but not limited to) USAAF, USN, RAF from (before) WWII well into the 1970s.


E-2/C-2 left thumb control? For some reason I ended up binge watching E-2s and C-2s doing shots and traps on YT. One thing caught my eye; especially during the approach, the pilot’s left thumb is in constant motion pressing a control on the yolk.
One imagines the radio PTT, but there seems to be no relationship between the clicks and talking during the times where both are visible, and it’s not like they are push-n-holding, it’s click click click!
So then one starts thinking about trim, but what madman designs a plane that requires so many trim adjustments during landing, and then requires a separate push for each adjustment?
Anyone know what’s going on? Here’s an example:

UPDATE: here's another example:

Look around 0:55 and again at 1:25 - his thumb is positively dancing. I can see in this video it is a hat, so I guess it is trim.
Never having flown anything larger than a s-twotter, what is going on here? I'm used to adjusting trim maybe one or two times in the circuit, this is nuts.
P.s. why the heck is there a privacy screen on the door?

Most likely the pilot is trimming the airplane to alleviate control pressures after he adjusts his airspeed in the pattern.  Ideally you want to trim out any kind of control pressure that you have to place on the yoke, or rudder pedals, first adjusting your speed as desired using the power levers, then trimming using elevator-rudder-aileron trimming procedure. The “coolie hat” switch on the left grip on the yoke provides both elevator and aileron trim.


Does Jeppesen display runway declared distances on their charts? I noticed that Jeppesen includes additional runway information on their 10-9 or 10-9A charts.  Are these listed values consistent with FAA runway declared distances?

No.

What does the runway distance mean under "Additional Runway Information" on Jeppesen plates?
What are Runway Declared Distances?
How do pilots use stopway, EMAS, clearway and displaced threshold?
How do runway declared distances affect my takeoff distance?

Jeppesen uses its own method to calculate additional runway information.  They have been providing additional runway information long before the FAA started providing declared distances and are fairly accurate but there is some discrepancies pilots using Jeppesen products need to be aware of.
Analysis of the two runway distance providers show Jeppesen's takeoff value is very close to the FAA's TORA value.  Jeppesen's landing beyond threshold value is the same value as the FAA's LDA value.
The two values that Jeppesen does not provide information for is TODA and ASDA.

TORA: Takeoff runway available
TODA: Takeoff distance available
ASDA: Accelerate-stop distance available
LDA: Landing distance available

It is the ASDA value that will get multi-engine pilots in trouble.  From the previous Q&As we learned that multi-engine pilots are required to ensure the airplane's accelerate-go distance is not greater than the TORA or TODA value (depending on whether or not their airplane can use a clearway for takeoff considerations) and their accelerate-stop distance must be lower than the ASDA value.
If these multi-engine pilots fail to reference applicable declared distance information they could potentially takeoff at a weight greater than allowed by their AFM and FAA regulations.
The FAA has developed a presentation talking about runway declared distances:
http://www.faa.gov/tv/?mediaId=1132

How about examples:
Lake Tahoe, CA (KTVL)

Analyze the data and you will see that if multi-engine pilots only go by the takeoff distance on Jeppesen charts they could takeoff overweight.  Jeppesen does not include ASDA values on their charts.
These pilots may conclude they can use the whole length of the runway for takeoff performance.  If their takeoff distance is the runway length they will lose the runway safety area protections designed to keep them safe.
There are many other examples.  KPIT, KSUN, KGYY, KPBI, KMIA.  Airports big and small have this issue and multi-engine pilots need to be aware of the lack of information presented to them by Jeppesen.
Stay safe!

An email from Jeppesen concerning this oversight:  After reading the email response below, it may not be a good idea to trust the runway information presented by Jeppesen.

Our Airport Diagram Charts are designed to be used for air navigation, flight procedures, and airport operations. They are not designed for aircraft performance planning. The distances contained in the Usable Lengths section of the Jeppesen Airport charts are informational and are not intended to be used for take-off and landing performance planning. These distances are provided on the charts to assist with the operational use of the runway. In order to comply with published declared distances, pilots need to reference take-off and landing performance planning data that is provided by either their own performance group, or another provider, such as Jeppesen’s OpsData service. OpsData provides on-demand runway take-off and landing performance analysis for airports worldwide, in part by analyzing, using, applying and presenting Airport Declared Distance data.
Another reason that the usable lengths are informational is that we do not revise our charts for all state source that we receive, we instead analyze that source and then revise charts based on our process criteria. What this means for the usable lengths is that we only process charts for changes in usable lengths when the change is greater than 200’. If the only change on a chart is the usable lengths and they are less than 200’, then we will make a note of the change and apply it to the chart when it is next revised sometime in a future revision. On the other hand, OpsData will update declared distances and re-run performance calculations whenever any of the lengths change by 25’ or more.
We don’t identify what the Usable Lengths should and shouldn’t be used for in the Airway Manual. Since the lengths are not intended to be used as declared distances, we have refrained from labeling them as such. That is why only some lengths are supplied and they are located under the heading ‘Usable Lengths’. The Introduction section defines the lengths we do supply and mentions that they are in regards to the physical runway length only (i.e. they don’t take into account any stopways, clearways, etc.).
AIM 4-3-6 provides the definitions of declared distances and where pilots can find them, which is the Chart Supplement (formerly the A/FD). For pilots that don’t have the availability of performance planning services, this would be where they could go to find that information.


What is a (rough) rule of thumb for calculating fuel consumption in a modern jet airliner like Boeing 737 - 300? I'm wondering what would be a rough rule of thumb for calculating the fuel consumption of a modern airliner like a Boeing 737 - 300.

I am not asking for anything from the plane's manual or even a rule of thumb to be used by pilots, but rather a "general idea", to be able to compare the fuel consumption of different modes of transportation.I am citing the Boeing 737 - 300 as an example as it is a pretty common type of airplane, but feel free to answer for another type of passenger aircraft.

Here are some very rough values for the 737-300, that a certain airline uses to compute manual flight plans in case the computer system fails.
Climb - 2950lbs / 15mins
Cruise - 5500lbs/hr
Descent - 600lbs / 20mins
Hold - 2650 / 30mins
Alternate - 1950 / 20mins
Min arrival fuel - 6300lbs
Recomended arrival fuel - 8300lbs
These numbers were based on a 27000lbs payload (approx 130pax plus bags)

source: http://www.airliners.net/forum/viewtopic.php?t=722273

[EDIT: I've edited the answer to remove any mention of the 737-300 being one of the most common 737 variants, thanks for the constructive comments!]


In the US, are inside loops permitted while flying a US- registered DG-1000S sailplane in the "utility" category? Are inside loops are permitted while flying a US-registered DG-1000S sailplane in the US in the utility category?

FAR 91.1 seems highly relevant:

  §91.9   Civil aircraft flight manual, marking, and placard
  requirements.

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

More information: the English version of the factory-produced flight manual for the German-made DG-1000S glider (may be downloaded here) states the following--

  2.6 Approved manoeuvres Category „Utility“: The glider is certified for normal gliding in the "Utility" category. Simple aerobatics are
  approved but only without waterballast and with the weight of the rear
  pilot compensated by ballast in the ballast box in the fin see section
  6.8.7.

  The following aerobatic manoeuvres are approved with all spans:

  Spins

  Chandelle

  Inside loop

  Turn

  Lazy Eight

  Recommended entry speeds see section 4.5.8.1.

The manual then goes on to describe additional maneuvers allowed when flown at a lower weight limit, in the "aerobatic" category:

  In addition to the manoeuvres in category „Utility“ the following manoeuvres are approved:

  Inverted flight

  half flick roll from normal to inverted flight with half loop

  half loop and half roll

  half flick roll from inverted to normal flight

  half roll and half loop

  slow roll

Before answering, you may wish to  consider the significance of the last quoted phrase in FAR 91.9, "or as otherwise prescribed by the certificating authority of the country of registry".  A "yes" answer to the basic question implies that this phrase in FAR 91.9 does not somehow prohibit looping a US-registered example of this glider in the US.

Stuff you quoted in your question seems to provide the answer you're after:

2.6 Approved manoeuvres Category „Utility“: The glider is certified for normal gliding in the "Utility" category. Simple aerobatics are approved but only without waterballast and with the weight of the rear pilot compensated by ballast in the ballast box in the fin see section 6.8.7.
The following aerobatic manoeuvres are approved with all spans:
...
Inside loop


What does LNAV engagement exactly mean? I notice the term LNAV engagement being frequently mentioned in aviation related discussions or in several FAA's relevant material. Take, for example, this quote from Order 8260.58A (PBN Instrument Procedure Design) which states:

  Order 8260.58A [5-1]: The ICA must be long enough to allow LNAV engagement (500 feet above airport elevation).

I am aware that LNAV means "Lateral NAVigation" but I have some trouble understanding what does "engagement" exactly mean and why an aircraft have to climb at 500 feet above airport's elevation before the initial turn for this engagement to happen. Could someone point me in the right direction?

Some old aircraft (737 Classic comes to mind) don't allow arming LNAV/NAV AFDS mode on the ground, as you normally have to be at least 400ft above ground (ICAO PANS OPS says 396ft) before making turns more than 15 degrees, at which point you would engage LNAV. I guess the regulation takes old aircraft into account.

On the newer aircraft, you can arm LNAV/NAV mode on the ground already and it normally becomes active at 50ft.


Are there any known maintenance issues with older Mooney wooden wings? Are there any maintenance issues or ADs for the older Mooneys with wooden wings? I'm looking at a 1958 M20A (always hangared) and I'd like to know if there are specific points to check.

You may want to look around here or here or even here but the short answer is they are a wooden wing airplane that comes with all the issues a wooden wing airplane does. One of the major things to look out for is the M20A's that had a wooden tail, those should generally be passed up on. The later planes should require some inspection of the joints where the tail meets the rest of the airframe as it is a stress point (if memory serves). For what its worth you are better off with a metal mooney. With a wood plane you need to inspect for rot the way you would for corosion on a metal plane.

Like any wood aircarft the M20A's can suffer from delamination which would need to be checked for. unfortunatly the list of people that still work on wooden planes is dwindling with time so it may be hard to repair this. It would be well worth the effort to seek out a mechanic that has experience with the A model and can work on a PPI for you.

You can find all the AD's for the M20A here.


Where is the best centre of gravity for planes like the Berkut 360? I am making an RC plane similar to the Berkut 360. Can anyone please suggest where is the best location for the centre of gravity for such a plane? (With explanation please)

I cannot tell you the exact location or the locus of the CoG for the current aircraft but I can provide you a method that you can use to find the appropriate location for the aircraft to be statically and dynamically stable in flight that you can use for any future aircraft.

I'll put it simple, CoG alone means nothing, you need to know the Neutral Point (NP) of your aicraft, that is the point that if you place CoG there you'll have neutral stability (i.e. the airplane will not tend to increase or decrease a pitch up input you give with your RC). The NP is considered in practice the aft limit of your CoG.

What matters in terms of stability and control is the distance of CoG from NP that is given by what we call Static Margin (SM). An empirical rule for SM is given as

$ SM \equiv \dfrac{x_{NP}-x_{CoG}}{\bar{c}} = +0.05\ \ \ ...\ +0.15 $

where $c$ is the mean aerodynamic chord (MAC) and $x=0$ is at the leading edge of the wing's MAC.

Now, a general method to compute the NP is to use an open-source Vortex-Lattice Code like AVL of MIT (Mark Drela) (http://web.mit.edu/drela/Public/web/avl/). If you know the geometry of your airplane, and of-course you know it since you're building it, you can make the model of the airplane and with AVL you can obtain the NP from an analysis.

If you are lazy, and need an empirical and fast way to compute your NP x location then you ca.. Whoops! winglets as Vstabs... I am not sure about the validity of empirical formulas for this aircraft and you should do the algebra of flight mechanics to deduce them. It's cool but a VLM code is more general.

If you find the $x_{NP}$ you can find the $x_{CoG}$ values that satisfy longitudinal static stability criteria and then with trial and error decide what value in this range gives you the best flying experience as there is no "best" value in engineering if you don't specify the optimization constraints.

Good luck!


What does rudder input control in normal law in an A320? I understand form documentation that in normal law, pedal input is not necessary to keep coordinated flight. It is merely said that using the pedals is not necessary. Later in the documentation it is said that the law for the yaw axis is either normal, alternate or direct (depending on the condition). For the normal law, automatic functions are implemented (yaw damping, coordinated flight). What happens when the pilot provides a non-neutral command on the pedals? Such information is well documented for pitch an roll control (command of load factor and roll rate), but not for yaw.

On the A380, the documentation states that, "A pedal deflection results in a proportional sideslip and bank angle". I found no such precision for the A320, but it seems reasonable to assume the pedals command a sideslip angle.

In normal and alternate law on a A320, do the pedals command a sideslip? If not, what do they command?

You are correct. On all Airbus FBW aircraft, the rudder pedals normally control the sideslip angle, beta. See this presentation for a source, slides 3, 5-6.

As a note, on pre-A345/A346 models, the rudder pedals are mechanically connected to the rudder. However, the FBW system adds in an additional input, via the yaw damper servos, to drive the rudder to the position the FBW control loops want.

Additional details can be found in Advances In Aircraft Flight Control, M. B. Tischer, page 90:

  Finally, it was decided that the rudder pedals would command a combination of sideslip and roll angle to restore some of the conventional aircraft behavior.

Figure 5 shows that the rudder command is a gain-scheduled proportional control based on sideslip, yaw rate, roll rate, and roll angle. The gain scheduling is based on airspeed and high-lift configuration.


Are there common standards for aviation graphical user interfaces? I'm searching for graphical user interface in aviation guidelines.
Yet I miss the correct terms and I don't really know where to start.

Let's take an example:

what's the meaning of the green color?
what's the meaning of the pink color?
is the color code regulated?
is this look (color, fonts, layout) regulated globally or does this vary by airplane type?
…

I guess that's a bit of a naive question but I gotta start somewhere.

A bit more Background: I'm a graphic designer. I have to create a web-interface for a national air rescue service. They want the look and feel to be as aviation specific as possible. The web app won't be used in the airplane itself so it is not regulated and it provides non-critical services.

One thing is that the interface should look cool and "techy". But on the other hand I don't want to use colors or layouts which are either very regulated or have a highly specific meaning.

I think your best bet might be going through the Instrument Flying Handbook [PDF, Large!] by the Federal Aviation Administration. It has plenty of nice graphics, if you're fine with a lot of other irrelevant stuff in the document. There's also the Chapter 8, Instruments, of the FAA Pilot Flying Handbook [PDF], which is a bit more compact.

I'm not sure there are any exact specifications how these things have to look. I suspect the minimum requirements are given in the certification specifications, and how they are then presented may be up to the manufacturer.

For instance, in EASA CS-23.2600B:

  The  applicant  must  install  flight,  navigation,  surveillance,
  and powerplant installation controls  and displays  so  that  a
  qualified  flight  crew  can  monitor  and  perform  defined  tasks
  associated  with  the intended functions of systems and equipment. The
  system and equipment design must   minimise  flight crew errors, which
  could result in additional hazards

I'd interpret "minimise  flight crew errors" to not do anything overly ambitious with the instruments that deviate from the norm, i.e. what everybody else is doing.

In EASA CS-23.2610A:

  Each aeroplane must display in a conspicuous manner any placard and
  instrument marking necessary for operation.

It does happen that this stuff can be different- while the military is generally more flexible, the U-2 reconnaissance aircraft has a speed indicator that goes the opposite direction.


Why couldn't Air Moorea Flight 1121 use pitch trim to land safely? On August 9th, 2007 an Air Moorea Twin Otter crashed into the ocean. The cause of the crash was determined to be loss of pitch control after an elevator cable snapped.

In my world (Cessna 152), if an elevator control broke I would be pretty sad, but the pitch trim tabs would probably allow me to put the plane down safely somewhere.

As far as I could tell based on my research, the Twin Otter is equipped with a pitch trim tab (aircraft are required to have them, but they can come in a variety of forms). Why couldn't the pilot use pitch trim to descend safely?

--EDIT--

In my checklists, I am required to "set trim for takeoff" in the engine run up. What is the point of this step if that trim setting doesn't hold the proper attitude for not falling out of the sky?

--EDIT #2--

In a highly hypothetical follow up question, would it have been possible, with 400' of altitude, for the pilot to go so hard nose down that he could pull out in an inverted configuration and fly the plane safely that way (the only cable that snapped was the elevator-down cable)?

All quotes in this answer are from the English translation of the BEA accident report.

The elevator cable broke at "an altitude estimated at between three and four hundred feet",(p. 7) and there were eleven seconds between that time and the point of impact. If it had happened higher, the pilot would potentially have had time to figure out what happened and pull out of the dive with trim. Taken by surprise and not knowing what happened, the pilot simply did not have time to recover.

The Twin Otter would have been demonstrated to be recoverable from an elevator cable break as part of its certification (p. 17):

  The CAR 3 regulation, basis of certification for the DHC6, requires a flight test demonstrating the aeroplane’s capacity to land using only the elevator trim in the case of failure of the primary longitudinal control of the aeroplane.

However, there's a big difference between "can be landed using just trim" and "can be recovered by a pilot who is surprised by the emergency". Flight tests performed during the investigation showed (p. 63, emphasis mine):

  At [the height the incident aircraft was at], only immediate action on the trim located on the centre pedestal would make it possible to recover the airplane. The test also showed that from level flight it takes about three seconds for a pilot trained for and prepared for this exercise to recover the airplane.

Unfortunately, on this flight there simply was not enough time to discover the problem, figure out what went wrong, and recover (p. 63):

  The highly dynamic nature of the events following the failure must be emphasized here. Eleven seconds passed between the pilot’s exclamation and the impact. This only left a short time for the pilot to analyse the situation and apply a solution that he had to improvise. In addition, the stress associated with the airplane’s attitude and the difficulty in estimating his height, in the conditions on the day, in relation to the surface of the water, certainly affected his powers of analysis. The pilot was not trained or prepared, either during his training or during type rating, as indeed most pilots aren’t, to react to a loss of pitch control. Only a reflex action could thus have
  allowed him to recover the airplane before the impact.

To answer the edits to the question, note that the airplane was not trimmed to "fall out of the sky". The pilot called out the trim checklist item before flight(p. 17), and so should have set it to the takeoff setting. Presumably this would require gentle back-pressure for rotation and climb. The event that initiated the failure process was retracting the flaps(p. 39). This changed the flight dynamics, and therefore the elevator control loads. The flight testing discovered that this created a "pitch-down moment"(p. 39):

  To counter this effect and maintain the aeroplane on its initial trajectory, it was necessary to exert considerable pitch-up effort on the elevator control.

This is not a cause for concern. The procedure is to hold pressure on the controls and adjust trim to relieve the pressure. However, it was at this point that the elevator cable snapped, so the pilot was interrupted and didn't complete the process. If the incident had happened at a higher altitude, the airplane would have recovered itself from the upset (p. 42):

  [S]tick free, the flap retraction led to a pitch-down moment varying the aeroplane
  trim between 20° and 30°, the rate-of-climb indicator going to stop at less than
  3,000 ft/min and speed reaching 140 kt in twenty seconds, then the aeroplane
  recovered on its own in level flight in five seconds, the total loss in height being
  seven hundred feet[.]

To the last question, flying inverted would not be necessary for recovery. I do not know the maneuvering characteristics of the DH-6, but I am unsure that an outside loop could successfully be completed starting at 300-400 AGL.


Why does NASA's B-52 008 have a smoking engine in this photograph? This is a photograph from the launch of an X-43 from the NASA owned and operated B-52 '008'. It appears that one engine is producing a plume of smoke in the photograph. Why is this?

Source

@Adam is right. The aircraft, NB-52B has smoke generator installed to assist in tracking.

A smoke generator has been installed on the left wing of the Boeing NB-52B Stratofortress mothership to assist in tracking the airplane.

Its use during the test of X-38 is detailed here:

Outside I could see the white trail from the smoke generator in the number-2 engine nacelle of the NB-52B approaching from the east
... I aimed my telephoto nearly directly up at the tip of the smoke trail.

As the same aircraft was used during the X-43 tests, it certainly served the same purpose.


Why is it called "base" leg? When flying a circuit, the leg after downwind and before final is called base. Where does this name come from?

Traffic pattern (circuit) phases are named so that they do not cause confusion1. I think of it as the leg which is taking me towards my landing/home base. (It is just a memory aid.)

However, the following reason is the best one which I found:

  This leg represents the foundation for the final approach, that is,
  the base from which the final approach is initiated.

Another reason is as follows, although it is similar to a memory aid:

  ... base leg is called “base” because it is really the foundation of
  your landing (the “base” of a house is its foundation – and if it
  isn’t right, the whole house will never be right) – if the base leg
  isn’t right, your whole landing will suffer for it.

1: Although, upwind leg, crosswind leg and downwind leg relates with the wind direction too. But if wind is perpendicular to the runway, downwind leg is not actually downwind, but it is still called the downwind leg.


A321 Two unsuccessful strong crosswind landing attempts. What was actually going on? As a passenger on A321 I have recently experienced the following:

The plane took off in strong winds (25-30 knots) and then proceeded to the destination, which it reached in 45 minutes. At first attempt the plane touched the ground with its rear landing gear and then it immediately went full throttle and took off again. After making a circle, the situation repeated after which we flew back to the original port.

The pilot said: "I made the decision to go back because the wind is over 100 km/h, which is above this aircraft limits".

100 km/h is over 53 knots which is way above the limitations of A321.

Crosswind - Takeoff 29 kts
Crosswind - Landing 33 kts
Crosswind with Gusts 38 kts
Tailwind - Takeoff and Landing 10kts

My questions are:

Should the pilot have even attempted to land? Wasn't it too risky?
Should he have even taken off knowing about the weather conditions at the destination airport? How is this kind of decision normally made?
Since takeoff limits are lower than landing, was it safe take back off upon unsuccessful landing attempt? In other words if the winds are bad enough for landing do you want to take off rather than force the plane down and see what happens?

Based on the provide date, I looked up weather history and the METAR (weather report for pilots) was:

CYUL 110700Z 24033G49KT 15SM -SHSN OVC033 M02/M08 A2937 RMK SC8 SLP948

Which translates, in English, to:
CYUL weather report at 11th day of the month, 0700 UTC time: Winds at 240 degrees at 33 knots gusting to 49 knots, visibility 15 statue miles, little snow, overcast clouds at 3300 feet, temperature -2C, dew point -8C, altimeter 29.37 inches of mercury; Remarks: scattered clouds at 800 feet, sea level pressure 948 milibars
49 knots would be equivalent to 90 km/h, but it is possible that the wind report by the ATC tower was higher at the time of landing.
How much crosswind was there?
Assuming the pilots attempt to land at 24L / 24R, there would be little or no crosswind. However the high wind speed + high variation of wind speed would be a problem: the fluctuation is 16 knots. For a small airliner like a A321, 16 knots of airspeed gain / loss is a lot. The pilot did not feel comfortable putting it down, so he chose to divert. The decision was a wise one: he tried enough (2 attempts) and concluded he'd better get back while there is still fuel left.
(Side story: I once heard a GA pilot who go-around 9 times on the same runway because of high wind. On his 10th approach he crashed)
Was it wise to takeoff?
Yes. Scrolling back the clock a few hours to the time when the pilots would prepare their flight, the weather forecast was:

(...) FM110400 24030G40KT P6SM BKN025 OVC050 (...)

Which translates to: from 0400 UTC time onwards, wind would be 240 degrees at 30 knots gusting to 40. Well, not good, but this was 9 knots below the reported gust when they actually arrived. Moreover, an alternate airport which was within reach and with better winds was chosen. This flight was short, and it is not surprising that on such short flights the alternate is return to the departure airport.
Was it wise to abort the landing and apply full power?
Absolutely! Forcing the plane onto the runway is the exact opposite of what a pilot should do. I will tell you, most (I don't have a number, but a fair guess would be >80%) of the landing accidents occur because the pilots failed to recognize that the aircraft was not fully prepared for landing (gusting winds, too high on approach, flaps not configured etc.). If those pilots chose to apply full power, go around and give it another shot, many lives would have been saved. Many people perceive aborting a landing as "dangerous"; in fact, it's the best thing to do in those situations.


Does maximum altitude increase when pilot is acclimatised? Normally 10,000 ft is considered safe altitude for emergency descents and 12,000 ft a maximum that can be flown in unpressurised aircraft without using supplementary oxygen.

But when flying in the mountains with a crew that normally lives at say 5,000 ft or more, can they afford higher altitude? And by how much?

Note: The 12,000 ft I've seen somewhere, but I don't know whether it is actually a regulation or just recommendation.

Yes, maximum possible altitude at which a pilot can fly an Unpressurized Airplane without the need for supplementary oxygen does increase with acclimatisation. But the international aviation laws do not take this into account and hence they have a general altitude limit for unpressurized flying without supplementary oxygen.


Why did the Boeing Max operated by Lion Air disintegrate upon crashing in the sea from a low altitude? The Lion Air Max crashed in the Java sea from a low altitude. What is the structural integrity strength of the fuselage?

I am curious to know the structural strength and integrity of commercial airliners like Boeing. The Lion Air doomed flight did not achieve cruising altitude of the standard 35,000 ft. I don’t know the exact altitude achieved but due to the MCAS triggering, I believe the jet didn’t reach cruising altitude. Why did the jet disintegrate upon impact from a mid-level altitude? I know it plummeted at 400 MPH but is there no structural strength to absorb the impact? Are jetliners not constructed to withstand high volume impact?

Because of a high speed impact

The official accident report published by the Komite Nasional Keselamatan Transportasi (KNKT) shows the data from the FDR (flight data recorder) for the accident flight. This is the altitude and airspeed it recorded:

As you can see, the aircraft reached an airspeed of around 450 kt before the FDR stopped recording (the Vmo of the 737 MAX is 340 kt according to b737.org). The altitude was around 6000 ft, which I would not really call "low altitude". Also note how fast the altitude dropped towards the end: the aircraft went from about 5000 ft to impact in only around 22 seconds resulting in descent rates in excess of 10,000 ft/min.

The report further says:

  The recovered wreckage identified consisted of, but was not limited to, parts from
  the left and right engines, both main landing gears, parts of the empennage, parts of
  the forward and aft left passenger doors, parts of the wings, a flight crew oxygen
  bottle, and parts of a circuit breaker panel. The damage to the aircraft suggested a
  high energy impact.

So the primary reason for the disintegration was the high speed at the time of the impact. No commercial airliner could possibly survive this. Have a look at this car crash test at only 200 km/h:

(HIGHSPEED CRASH TEST - 200 KM/H Ford Focus vs. Concrete Block on YouTube)

The car is completely destroyed by the impact on a concrete block. As Zeiss Ikon pointed out in the comments, "at even 100 kt, water is harder than concrete". And 450 kt is over 800 km/h, meaning 4 times faster (i.e. $ 4^2 = 16 $ times higher kinetic energy). Nothing that can still fly could possibly be built to survive this.


What does "spark plugs appear yellow at the ignition point" mean? I was reading the DLE-120 engine User Manual and saw this paragraph:

Caution: Running the engine with a lean fuel mixture will cause the engine to overheat and burn the electrode of the spark plugs. Pay close attention to the High-speed Needle adjustment. Running the engine with the proper fuel mixture will make the spark plugs appear yellow at the ignition point.

What does "yellow" mean in "Running the engine with the proper fuel mixture will make the spark plugs appear yellow at the ignition point"?
Does anybody have any experience or images of this phenomenon?

Use the tip residue to evaluate the combustion process
The yellow the manual is describing is the normal condition found in the top left corner:

If the plug is not the yellow/tan shown in the top left, then it will almost certainly look like one of the other pictures. This is a strong hint that what is going on inside the cylinder is not optimal, and points in the direction of the problem.


For airliners, what prevents wing strikes on landing in bad weather? For any low-wing aircraft, particularly the MD-80 or some of the private jets, CRJ's, the wings appear about 5ft or less above the ground. It seems that just few degrees of roll before touchdown would cause a wing strike on the runway and a disaster.

How do pilots and aircraft manufacturers avoid this ? It seems like with the thousands of daily flights - in all sorts of inclement weather conditions - this (fortunately) isn't a problem. (I'm not saying it's never happened, just that it seems exceptionally rare.)

So my question is, why isn't this a serious problem? I would expect turburlence and wind gusts to do all sorts of unpleasant things to aircraft, one of which might be disrupting the roll a couple degrees and planting the wingtip into the runway. What steps do pilots and aircraft designers take to mitigate this?

It's not how high the wing is off the ground, but the angle between the main landing gear when compressed and the tip of the wing, which with the wing dihedral makes it even higher off the ground – on the MD-80 that's 2.6 m (8'7"). This will be the roll angle limit.

It's for that reason, unlike smaller high-wing general aviation planes, big jet-liners don't decrab as much in a crosswind landing, whereas decrabbing (going one-wing-low) would be a problem. From an MD-80 flight manual:

Crosswind Landing
On final approach, establish a crab angle into the wind to hold the aircraft on the extended centerline of the runway. Maintain the crab angle until just before touchdown, then use the rudder to align the aircraft with the runway. The touchdown is made with cross-controls as necessary to track straight down the runway. Keep wings as level as possible as the wingtip will touch at an 8° bank angle. Do not hold off downwind wheels; prompt and firm runway contact will greatly assist in rollout stabilization.

So the prevention is respecting the limits, good training, and knowing when the weather is too gusty to just abort the landing.
It does remain a concern though. Wikipedia has an article on it, and the issue would also affect the engine when wing mounted, but with the engine typically forward of the wing, it's given better clearance when the nose is still higher for flaring. The A320 accident mentioned on Wikipedia seems to have been the result of both pilots controlling the plane during landing.
In 1997 a 747 hit the runway with the outer engine when landing in Kai Tak:

(flickr.com)
A more recent one is a Bombardier Global 6000 in 2014.


What kind of airspeed does a (3D) GPS measure? Assuming a GPS receiver is advanced enough to compute 3D position/velocity with reasonable accuracy, it can indicate not only the aircraft's ground speed (which ignores altitude changes), but something akin to airspeed as well. If there was no wind, this would be equivalent to true airspeed. In reality there would be wind so it is "TAS minus wind". Since this completely ignores the actual air (the value would have been the same if there were no atmosphere), however, calling it anything related to "airspeed" seems like a misnomer to me.
Is there a standard terminology for this kind of velocity measurement?
EDIT:
It seems my question was quite vague and providing more detail about what I'm trying to do would help. I'm writing the documentation for a GPS-based tracking device, which would be used in fixed-wing aircraft. The GPS is exceptionally good, with very high precision and quick sampling rate. It even provides very accurate speed, which is Doppler-shift based AFAIK. This data will be sent through telemetry. I'm trying to label the data channels in a way that would be useful for aviators down on the surface, so I'm trying to familiarize myself with the proper terminology. Therefore if I label this ("3D") velocity as "airspeed" (indicated/true airspeed), it will be misleading. If I label it "ground speed" (which is 2D), it will be misleading as well. My question is only whether a standardized name for this type of velocity exists; if there's nothing widely used, I'll just coin a name of my own (e.g. "3D velocity") and explain it well enough in a tooltip.

Q: "What kind of airspeed does a GPS measure?"
A: "None whatsoever."


Was the Boeing 747 designed to be supersonic? I heard a rumour that the Boeing 747 was originally designed for supersonic cruising.

Is this correct? Are the airframe and wings able to cross the sound barrier without damage?

No. The Boeing 747 was not designed for supersonic flight, though during testing, it was pushed quite close to the sonic speed:

Tom Cole, a spokesman at Boeing Commercial Airplane Co., said original flight tests of 747s conducted in 1969 and 1970 took 747-100 models to speeds of Mach 0.99.

However, the aircraft is not built for sustained supersonic speeds:

... Boeing and the FAA said the 747 is not built for sustained flight at the speed of sound. Its engines aren't powerful enough nor is it designed to deal with a destabilizing shock wave that develops around the speed of sound.

However, it is just possible that the airframe and wings can cope up with the supersonic flight, at least for a little while, though any sustained flight is not possible. There have been cases where the 747 has gone quite near the speed of sound and lived to tell the tale.
China Airlines Flight 006 went into a dive and went near supersonic speeds before the captain could recover it. As a result, large portions of the horizontal stabilizers were ripped off, and the wing was bent permanently upwards.

Damage to China Airlines Flight 006 empennage. By NTSB - China Airlines Boeing 747-SP Accident Report by NTSB, http://www.rvs.uni-bielefeld.de/publications/Incidents/DOCS/ComAndRep/ChinaAir/AAR8603.html, Public Domain, Link
In 1991, a Boeing 747 of Evergreen airlines entered a steep right wing bank and approached sonic speed before recovery was completed. NTSB notes:

... the airplane was in a steep right-wing-down bank. The flight  lost  approximately 10,000 feet of altitude, and the airplane approached supersonic speeds (0.98 Mach) before the recovery could  be  completed.

Later, the Israelis took it close to sonic speed. In these cases, parts of the aircraft certainly experienced local supersonic flow; however, the airframe and wings are not designed for supersonic flow nor are the engines powerful enough. In one case, the aircraft suffered extensive damage (though it was repaired and returned to service).


What is that term to describe the wing motion range? What is that term naming the range of motion of the wings when on the ground (hanging/drooping) then bends upwards during flight?

The term that you are looking for is Wing Flex. The extent of flex is a product of the material.The wing needs a stated definitive strength. With metal, that transforms into a given amount of flex. IOW, the flex, is basically just a by-product of the materials and high aspect ratio design and is not a design goal in itself. The benefit is, smooth ride during a turbulence.

Aerodynamically you do pay a penalty. However, to a certain extent this will be offset by lighter weight and the much superior strength, facilitates the high aspect ratio which more than make up for the loss due to the flex.


Can the MH-60 helicopter fly without one or all of the stabilators? The MH-60R helicopter has a horizontal Stabilator that consists of three subassemblies, RH Stabilator, LH Stabilator, and Center Stabilator.

Can the aircraft fly without the RH Stabilator?

Can the aircraft fly without the entire Stabilator?

Assuming there is no STC ("Supplemental Type Certificate") that addresses this as an existing modification, the answer, in terms of acceptable aircraft airworthiness, is a hard no.

"Can the aircraft fly" is a tricky question in some ways, but dead-easy in others.  And remember: a helicopter is a thousand moving parts spinning wildly around an oil leak.

If you're looking at it from a flight physics and dynamics perspective, as a result of a mishap/damage in flight, (assuming no other problems like a damaged rotor or loss of hydraulic fluid,) and whether you can control the aircraft safely to the ground, a skilled pilot rated for this aircraft "type" would probably be able to wrestle the aircraft to a safe landing.  The main rotor does the work of holding the helo aloft, and the tail rotor holds the attitude steady against the torque of the main rotor.  The stabilator (stabilizer-elevator combined surface) does not contribute to total lift in hover, although it may affect lift in forward flight.

However, any mission the helo had been in the midst of should be immediately abandoned for the sake of making the landing.  Even if you were rescuing someone from drowning in the ocean, you're more likely to just add the flight crew to the tally of the dead if you persist in trying to make the bird work while in an adverse configuration.

This does not answer what an actual pilot of that type - which I am not - would experience in flight.  But the stabilator is considered a flight control surface, and you never take to the air without your flight controls 100% operational.

But ending up missing part of your flight control surfaces during flight would be considered an emergency condition.  If instead the aircraft is already on the ground, in need of maintenance, and one is considering a "ferry flight" to somewhere else to better service it, there are many things that an inspector could let slide for just a ferry flight, but this is not one of them.

Such a stabilator contributes to the control, stability, and balance of the aircraft, and without the entire stabilator, the aircraft is not in flight configuration, and therefore, it's not "airworthy".

Definition of Airworthiness:

  The aircraft conforms to its type design and is in a condition for safe operation.

Source: 14 CFR Part 3.5(a)

Even if a cogent argument is somehow made that the helicopter is "in a condition for safe operation" while lacking all or part of its stabilator, it still utterly fails the first half, being: "conforms to its type design".

A note regarding balance:
Many mid-sized helicopters have an acceptable CG (Center of Gravity) range that's about the size and shape of a large mobile phone (as I write this in early 2016).  This is a larger craft, flown by the military, so its CG envelope may be the size of a small to medium tablet device.  Loading various people near the CG location doesn't shift the CG very much, which is why the main passenger/cargo area is always under the main rotor.  But that stabilator flight control surface could weigh 20, 50, 100 pounds or more, and removing that from the end of a long lever arm at the end of the tail boom will cause a noticeable shift in CG location, possibly putting it out of range for the aircraft.  This is also a situation that a skilled pilot in an emergency may be able to compensate for if action is taken immediately, but is a condition you never enter into knowingly. That way lies only heartache and doom.

I am an FAA certified A&P (Airframe and Powerplant) mechanic, and during my training school, the third-ranking member in the entire FAA (in 2007) came and gave a talk on a few different topics, but primarily on the concept of airworthiness.  It comes down to this:  Are you SURE it will fly safely?  How sure?  Would you put your kids in that aircraft and let it fly?  As aircraft mechanics, we need to be that sure that the aircraft is safe to fly, or, it simply isn't.

  An aircraft is fully airworthy, or it's not airworthy.

The Sikorsky SH-60 Seahawk, without a complete stabilator, is not airworthy.


Would this be a dangerous impeller to use for a drone? I am considering using a 3D printer to make unconventional impellers for a custom-made drone that I am planning to build. I am concerned that these plastic impellers may explode if their motors' RPMs get too high.

Please see the drawing below.

This drawing is showing two views of an enclosed centrifugal blower impeller with forward curved blades and the bottom plate of the impeller has holes in it. I am thinking that the high static air pressure that will be created within the impeller will generate a good amount of lift for the drone.

This design was inspired after I watched a Youtube video about a drone that uses cross-flow fans for lift:

My concern is that if the motor's RPM gets too high, the static air pressure inside the enclosed impeller will get too high and the impeller will explode, sending plastic shrapnel in all directions.

Because of this explosion risk, would it be advisable that I not use this potentially dangerous impeller?

EDIT

I just want to point out that the blades will be embedded within the enclosed impeller and that the whole impeller is rotated by a motor. The blades will not be part of a separate squirrel cage that will spin within a stationary enclosure that has holes in the bottom of it.

I know those things as squirrel cage blowers. As the video says, they are a good choice if you want to move a moderate amount of air without exposing rotating blades.

Impeller, by the way, was initially the word for a sort of airscrew that is moved by the flow. The small thingy in the nose of the Me-163 rocket interceptor was an impeller and needed for driving the plane's electric generator. Unfortunately, this word has recently been abused to mean shrouded propellers.

The proper name for those blowers is "centrifugal fan", and I will continue to use this word for the remainder of this answer.

As @pericynthion says in the comment, air pressure is less of a concern than centrifugal loads. Basically, the blades spin air around and hurl it to the inner housing of the blower, increasing pressure when the kinetic energy of the swirling air is converted to pressure as the air slows down. If we assume that air comes to a total standstill at the housing (which it doesn't, otherwise the blower would choke), the maximum attainable pressure is determined by the radius of the cage $r$ (in meters) and the rotational speed $\omega$ (in rad/sec) of the blades.
$$∆p = \rho\cdot r\cdot\frac{\omega^2}{2}$$
For a 20 cm blower spinning at 3000 RPM this would be 5.9 bar. The centrifugal acceleration $a$ on the blade would be
$$a = r\cdot\omega^2$$
which produces 1000 g with the same parameters.

To give you an idea about the efficiency: It is generally desirable to accelerate a large volume of air a bit rather than to accelerate a small amount of air by a lot. Therefore, helicopters use the largest practical rotor diameter, so they can capture as much air as possible for lift creation. Centrifugal fans cannot enjoy the same luxury and can only use the air which enters them from the side. As you can see from the two formulas above, your ideal centrifugal fan runs at a low speed but has a large diameter for the best ratio of pressure over centrifugal loads.

If you build them without regards to the loads, yes, those centrifugal fans can indeed be dangerous.


How do you properly enter the NDB34 published approach at Friday Harbor (KFHR)? I'm having trouble figuring out the correct procedure to enter an approach such as:

Let's say you are cleared from ISLND for the NDB approach.  How do you maneuver safely and legally to the the outbound leg once you reach the IAF?

My guess is the correct way would be a turn to the outbound course from the NDB.  Then a right turn direct to the NDB and a direct entry to the outbound course, then proceed as charted.

First of all, do not let the depicted holding pattern confuse you.  It is only there because the missed approach procedure happens to have the hold at the same place, and for the purposes of the course reversal may be ignored.
In this case, you have options because the course reversal is simply a "barbed arrow".
AIM 5-4-9. Procedure Turn and Hold-in-lieu of Procedure Turn(a)(1) says:

On U.S. Government charts, a barbed arrow indicates the maneuvering
side of the outbound course on which the procedure turn is made.
Headings are provided for course reversal using the 45 degree type
procedure turn. However, the point at which the turn may be commenced
and the type and rate of turn is left to the discretion of the pilot
(limited by the charted remain within xx NM distance). Some of the
options are the 45 degree procedure turn, the racetrack pattern, the
teardrop procedure turn, or the 80 degree 260 degree course
reversal. Racetrack entries should be conducted on the maneuvering
side where the majority of protected airspace resides. If an entry
places the pilot on the non-maneuvering side of the PT, correction to
intercept the outbound course ensures remaining within protected
airspace. Some procedure turns are specified by procedural track.
These turns must be flown exactly as depicted.

In other words, do what you want as long as you either stay on the protected side or correct to intercept the outbound course if you find yourself on the non-maneuvering side and you stay within 10 miles of the NDB.
Personally, I would:

Cross the NDB and then simultaneously:

Turn left to a heading of about 129 degrees (depending on the wind)
Descend to 2,300 feet

Start the outbound timing as I cross the 69 degree bearing TO the NDB (90 degrees)
Intercept the outbound course of the procedure turn and then fly the rest of the course reversal as depicted (the 45 degree procedure turn).

However, as I said in the beginning, you can do it however you like within the constraints that the AIM gives.
I did find a rather interesting article which states that ICAO rules are a little different, but I won't go into the specifics since this is an FAA chart.  For those who are curious though, take a look at it here:  Course Reversals.


Can planes take off from a treadmill? Note that this is more of a Physics question than an Aviation one.
  This topic has been extensively covered on the Physics Stack Exchange site, and the answers there are recommended reading for anyone curious about the forces and physics involved.

If you had a giant treadmill that was an infinite plane, had an infinitely adjustable speed, and could tread along any of its dimensions, could an airplane take off from it?

Everyone collectively went "Oh god, not this one" because this same question has sparked some intense debates in the past. Aircraft rely on airflow over the airfoil (wings/tail etc) to produce lift - which is independent of the movement of the tires. This means that with enough air going over the wing, the aircraft will fly even if it isn't moving forward at all relative to the ground.

This is why aircraft on ramps at airports need to be tethered to the ground. This isn't only to prevent them from rolling around, but from taking off should the air flow get fast enough over the wing.

If you are interested in an entertaining segment, the MythBusters did a fairly scientific experiment of this.

             Although it isn't perfect, I think it does a good job of explaining the concepts.


How do RC airplanes create thrust without using propellers or rockets? I haven't wondered how RC planes create thrust until now. I know some literally use rockets, but what about the small ones, that don't use propellers? How in the world do they manage to create thrust in the air without propellers, or rockets?

Also, how do they control aileron? Does an RC plane have a rudder? Do RCs have to be registered with local aviation authorities (if in Canada)?

They create thrust the same way that the full size ones do.

In the case of a piston engine type aircraft they have either have a miniature version of a piston engine, or an electric motor which turns the propeller.
In the case of jet engine, like your picture, they have miniature versions of a jet engine.
Sometimes, the jet engine in an RC aircraft is actually a propeller made to look like a jet engine.

  Also, how do they control aileron

Usually by using servos to pull cables and pullies - essentially like aircraft used to before fly-by-wire systems were introduced.

  Does an RC plane have rudder?

Some do, some don't. Its the difference between 2 and 3 axis controls. Anything like the one in your picture almost certainly do.

  Do RCs have to be registered with local aviation authorities

Sometimes, It depends on jurisdiction and and often weight.


Can I log flight training outside the US in a US-registered aircraft? I work outside the USA. I have access to fly an airplane with work. I'm working on my instrument rating. Can the time I'm flying be used towards my instrument rating requirements? We always fly on an IFR flight plan and I can fly "under the hood." The guys that I'm working with are all CFII and willing to sign my log book and the a/c have N tail numbers.

Yes. The FAA doesn't care where you fly, and you can even log training time with a foreign instructor. Logging time in a US aircraft overseas is completely fine.


When did the FAA begin offering added-rating tests for flight instructors? I don't recall there being abridged versions of the knowledge test for added CFI ratings when I earned my initial CFI certification such as AIF(flight instructor instrument added rating), and back then I would have had to have taken the full FII(flight instructor instrument initial CFI certification) test.

I could have simply forgotten since 2009.

When did the FAA begin offering added-rating flight instructor knowledge tests?

Could you decode your abbreviations for us. I just took all of the tests and I am not familiar with those abbreviations.

Just to clarify for those who are not familiar with the knowledge tests. You need to take the Fundamentals of Instruction knowledge test (FOI) for all of the instructor certificates. You can take the Basic Ground Instructor (BGI) test, Advanced Ground Instructor (AGI), and Instrument Ground Instructor (IGI) if you want to get a Ground instructor certificate. To get your CFI certificate you need to take the Flight Instructor Airplane (FIA) test. CFII requires the AIF. There are separate tests for Sport Pilot Instructors.

If you are adding a rating to an existing certificate, you can take an abbreviated version of the test, e.g. if you already have your CFI Airplane, then you can take the add-on test for gliders and only have to answer 25 questions rather than 100, and the questions will focus on glider operations assuming you already know the rest of the stuff.

Once you have any instructor certificate, you never have to take the Fundamentals of Instruction test again.

I don’t know when the short tests started, but if you look at Order 8080.6D which was published in 2003, you can see that short tests were available then. Since you had your CFI in 2009, you had the option of taking an abbreviated test for your CFII.


How does gross weight affect helicopter autorotation? The factors which affect helicopter autorotational aerodynamics include airspeed, gross weight, rotor RPM, and density altitude. The effects of these factors can be examined during a few phases of the autorotation, including entry, steady state descent, flare, and touchdown. The effects of gross weight seem very unintuitive to me, so I would like clarification on how gross weight affects the steady state descent and the flare, in particular.
Steady State Descent
My helicopter aerodynamics book says the following:

Gross weight determines RPM at a given collective pitch. At high gross weight, more blade pitch is required to maintain a desired RPM, so higher gross weight results in a slower rate of descent, assuming all other variables remain the same.

So high gross weight decreases descent rate. That's unintuitive to me, so I'm trying to build a logical path. I know from experience that making tight turns during an auto causes RPM to increase. Tight turns increase positive Gs on the aircraft, which is equivalent to increasing weight. So higher gross weight will tend to increase RPM, requiring the pilot to raise the collective (blade pitch) to maintain RPM. There's question 1: why does increasing weight (or G loading) tend to increase rotor RPM?
The second logical step is how this required increase in blade pitch will decrease the rate of descent. I understand that increased blade pitch increases AOA, thus increasing the lift produced by the rotors. However, this increased lift is opposed by the increased weight that started this whole discussion. Here's question 2: for a given increase in weight, is the resulting increase in lift larger? This seems to be the only way to achieve a lower rate of descent.
Flare and Touchdown
My helicopter's flight manual includes the following diagram, titled "Minimum Height for Safe Landing after Engine Failure"

This chart indicates that at a given density altitude, it is unsafe to be too heavy during an auto. I assume that the danger is related to the flare and touchdown, since during the descent it seems safer to have a lower rate of descent. My intuition tells me something about how the rotors store energy as RPM during the descent, and the flare and touchdown dissipate that energy in order to slow the helicopter's forward and vertical speed. It seems intuitive that a heavier helicopter will require more energy to slow, which means at and above some threshold weight, the helicopter will not be able to flare enough to touch down gently. But, is there a more rigorous explanation for high gross weight being dangerous at the "bottom" of the autorotation, i.e. how energy is stored and dissipated in the rotors?

If you look at the situation in terms of power, an increase in weight (or any increase in loading) requires more power. As you don't have this power, the helicopter will descend faster, more air will go through the rotor leading to an increase in RPM. Hopefully this increase in RPM will provide enough lift to stabilize the vertical speed. Increasing the pitch to maintain the RPM within limits provides lift in a slightly more efficient manner so the vertical speed will be slightly reduced (compared to the situation of descending with the collective flat down and RPM screaming over the limit)
That said, I find the affirmation in your book very confusing. Maybe I'm missing something, but a heavier helicopter will descend faster than a lighter one under the same conditions. It needs more power to fly and the only way to get it is to descend faster. That makes landing more dangerous, because you have more vertical speed to offset during the flare and more weight to cushion before touchdown. If increased weight and increased rotor loading would provide lower descent speed I guess everybody would autorotate in fully loaded helicopter and doing tight turns all the way to the ground :)


Has any airliner ever collided with a glider? I've read about many near-collisions between gliders and airliners, but did such a collision ever happen in mid-air, actually?

Yes.  (I found this by Aaron Holmes's hint that he searched only English sources.)
On 1999 Feb 12 at 3:40 pm, a Grob G103 sailplane F-CGXB (possibly "in wave flight") collided with an Airbus A 320 F-GJVG at 8600 feet, near Montpellier, France.  Both landed safely with minor damage.  There were no casualties.
Summary: https://aviation-safety.net/wikibase/24140
Accident report, excerpted below:  http://www.bea.aero/docspa/1999/f-xb990212/pdf/f-xb990212.pdf

L'Airbus A 320 à destination de l'aérodrome de Montpellier Méditerranée est
autorisé à descendre vers le niveau de vol 80. Dans le même temps, en vol local
autour de l'aérodrome de Saint Martin de Londres, le planeur G 103 évolue vers
8 600 pieds dans une ascendance au-dessus de la montagne de la Seranne.
Pendant la descente, l'équipage de l'A 320 aperçoit le G 103 et effectue une
manœuvre d'évitement par la droite. Le bord d'attaque de l'aile gauche de l'A 320
et l'extrémité supérieure gauche de l'empennage du G 103 se heurtent. Les deux
appareils se posent sur leur aérodrome de destination.

L'extrémité arrière gauche de l'empennage du G 103 est arrachée.
Le bord d'attaque du bec n°4 de l'aile gauche de l'A 320 est enfoncé et déchiré.

English translation:

The Airbus A320, with destination of Montpellier-Méditerranée Airport, was authorised to descend to flight level 80.  At the same time, in local flight around Saint-Martin-de-Londres airport, the G103 glider rose to 8600 feet in a climb above the Séranne massif.  During the A320's descent, its crew spotted the G103 and executed an evasive maneuver to the right.  The leading edge of the left wing of the A320 and the upper left extremity of the empennage of the G103 collided.  Both craft landed at their destinations.

The rear left end of the G103's empennage was torn off.
The leading edge of slat #4 of the A320's left wing was dented and torn.