When does the use of afterburners save fuel?

If such a pair of states does exist it ought to be straddling a Mach boundary (I think)

e.g. A subsonic & B trans-sonic. Or A trans-sonic & B supersonic etc.

Reasoning: To get from any point A to B in parameter space should usually be a state function i.e. path independent.

i.e. You can give many tiny increments or one large increment.

In our context a parameter space means mostly a {velocity(v), altitude(h)} pair.
To go from A{v1,h1} to B{v2,h2} you need a certain thrust profile. The required thrust profile is not unique.

Now the above path independance statement is true in general, except when a dissipative force exists. Now you no longer have a state function.

Since drag, a dissipative force, is indeed a strong function of speed it will help to not linger in the high drag region i.e. transsonic region with wave drag. In this zone the drag coefficient increases rapidly and you will have a total drag much higher than at both sub-sonic and super-sonic speeds.

And that would give a high thrust afterburner the advantage needed over a dry engine: On afterburner you can zoom through the transsonic region  rapidly than trudge through it incrementally on dry thrust. Thereby saving on drag losses. You are still consuming more fuel per unit time but the time spent is reduced so much that it makes the higher specific consumption worthwhile.

Caveat: This is just an qualitative argument. A more mathematical argument is needed to add rigor to the analysis.

Edit: Maybe these schematic plots help clarify my argument.


What is the purpose of the fin at the Boeing 787 APU exhaust?

As mentioned in the comments, this is indeed an "aerodynamic fence."  Fences of this sort serve two purposes:

Direct airflow; or
Energize (or trip) boundary layer airflow.

The latter are normally perpendicular to the surface on which they are mounted, allowing them to protrude directly into the boundary layer of air flowing over the surface.  You can picture the effect of these types of devices by looking a how water flows over and around a boulder in a stream or river.  "Tripping" the flow mixes the boundary layer with the more energetic air outside the boundary layer.

It is most likely the former, a device used to direct the airflow.  By the time air gets to the tail of an airplane, to the aft most part of the empennage, it is quite unsteady flow. (In this case, imagine the water flow behind a large ship.) The turbulence characteristic of this type of flow can wreak havoc for designers who want to vent exhaust gases or airflow out of the aircraft's APU. This turbulent flow can create stagnant zones which would block the air from exiting the way intended, as described here.  By directing the flow of the air around the exhaust duct, this can be minimized or avoided altogether.  There is, however, probably a small amount of the boundary layer that gets energized by this device, which would further help the designers manage the flow.

The article previously cited calls them vortex generators, which are explained in more detail here and correspond to 2 above.  Fuel that was pooling in the APU was a result of the stagnation of the flow.


Why descent below DA/DH or MDA could only be accomplished using natural vision?

The FAA states it pretty explicitly in their definitions:

  Decision Altitude (DA). A specified altitude in the precision approach at which a missed approach must be initiated if the required
  visual reference to continue the approach has not been established...

and similar for MDA

  Minimum Descent Altitude (MDA). The lowest altitude, expressed in feet
  above mean sea level, to which descent is authorized on final approach
  or during circle-to-land maneuvering in execution of a standard
  instrument approach procedure where no electronic glide slope is
  provided.

To over simplify it a bit: As noted in the comments, ignoring the not in use CAT IIIC approaches the whole point of an instrument approach is to get you down to a specified point where you should be able to see the runway. If you can't, then the weather has degraded and you must either try again or go to an alternate. The big idea being that at some point you need to be able to see the runway in order to land on it. Depending on how precise the equipment you are using is (ILS, GPS, RNAV, VOR, (AFD dare we say)) the height you can get down to without being able to see the runway changes.

As for why there are minimums its likely historical, and at least in part practical. Not all approach systems/options take you right down to the threshold like say a circling approach and its possible to fly a poor approach that is within limits and not be directly in line with the runway when you pop out of the clouds. Thus you will need some time and distance to align visually, so minimums exist. On the historical side, early attempts at instrument landings systems we less than optimal to say the least and you would need time to pop out and align.


Why does Boeing 737 use 2 Inertial Reference Systems (IRS) and GPS?

Could somebody explain a little bit why they need 2 separate GPS and 2 separate IRS?

So that if one fails, the other can still be used to complete the flight.

Airbus even have 3.

  What is meant by "alignment"?

Initialization of the system and solving the "heading problem" through a magnetometer. But this is a different question.


Are there known cases of an airline pilot's becoming incapacitated, while in command of the aircraft, during a critical flight phase?

Here are a couple of examples from two studies that have a lot more detail and background information on pilot incapacitation in general.

From an ATSB study:

  After a normal touchdown, the first officer became unconscious at the
  flight controls and the aircraft began to veer to the right of the
  centreline. The captain took control of the aircraft to return to the
  centreline and completed the landing

From an FAA study:

  A 45-year-old B-737 first officer experiencing an alcohol withdrawal
  seizure suddenly screamed, extended his arms up rigidly, pushed full
  right rudder, and slumped over the yoke during an approach. The
  aircraft descended to 1,000 feet above ground level in an
  uncoordinated turn to 25 degrees angle of bank before flight
  attendants could pull the first officer off the controls, allowing the
  captain to recover the airplane


Why does the diffuser section generate thrust in a jet engine?

But why is the diffuser also providing forward thrust?

The diffuser slows down the flow to ease fuel-air mixing and combustion a bit later. If you only focus on entry and exit speeds, there would be no thrust.

However, if you look at the pressures on the diffuser walls, a different result emerges. Slower flow means higher static pressure, and the total pressure right at the compressor exit is already the highest within the whole engine. The pressure on those widening diffusor walls does indeed push the engine forward because of the forward slant of the pressure vector (which acts perpendicularly to the diffusor walls). Your linked pulse jet page explains this quite well.

Of course, no thrust would result if the flow were not heated and thus accelerated further downstream. So the diffuser all by itself will not create thrust; this happens only when it is placed inside a working jet engine.

  And also why the nozzle is providing rearward thrust?

This is not always the case, but here the nozzle has a converging shape which helps to accelerate the subsonic flow and converts the remaining pressure to speed. The walls now have a backward-facing slant, so the pressure vector on them will contribute a backward-facing component. In addition, the high flow speed along the large nozzle walls causes some friction, which needs to be considered, too.

For a comparison, look at the cone behind the turbine wheels. Its thrust contribution only stems from the forward-facing pressure acting on it.


What preparations should I have to fly from the US to Mexico?

AOPA has a guide here. I think it should cover most of your points apart from visa/immigration, because that isn't really an aviation issue (unless perhaps you're commercial air crew using a flight crew visa). Don't forget to plan ahead for re-entering the US, there are a bunch of requirements for that too, including using eAPIS.

Some points from the guide are:

Documentation: you need a radio license for the pilot and the aircraft
Insurance: add Mexico to your insurance policy if it isn't already covered
Flight plan: you must be on an IFR or defense VFR flight plan to cross the ADIZ
Night VFR isn't allowed in Mexico (with a few exceptions for flights to the US)
It looks like the more paperwork you have with you, the better
FBO services are likely to be more limited than in the US, and fees are often higher

Also check out the Caribbean Sky Tours Pilots Association, they publish a pilots' guide to Mexico and Central America.


Why does the EGT gauge in 172s have no numbers on it?

The simple EGT gauges do not have numerical scales because you never lean to a temperature.  You find the peak temperature, set the movable red needle to that temperature, and then lean to x degrees lean (or enrichen to x degrees) of peak temperature.

Set the peak temperature at full throttle, full rich at a sea level airport.

This system eliminates the concerns of calibration: Is the gauge calibrated, did the mechanic install the probe in exactly the right spot, etc. etc.


From the AIM, 4-3-6 (c)(2):

All 14 CFR Part 139 airports report declared distances for each runway. Other airports may also report declared distances for a runway if necessary to meet runway design standards or to indicate the presence of a clearway or stopway. Where reported, declared distances for each runway end are published in the Airport/Facility Directory (A/FD). For runways without published declared distances, the declared distances may be assumed to be equal to the physical length of the runway unless there is a displaced landing threshold, in which case the Landing Distance Available (LDA) is shortened by the amount of the threshold displacement.

Now for definitions. These terms are defined by the FAA/ICAO in the PCG.
TODA - Takeoff Distance Available. The takeoff run available plus the length of any remaining runway or clearway beyond the far end of the takeoff run available.
TORA - Takeoff run available. The runway length declared available and suitable for the ground run of an airplane taking off.
ASDA - Accelerate-Stop Distance Available. The runway plus stopway length declared available and suitable for the acceleration and deceleration of an airplane aborting a takeoff.
LDA - Landing Distance Available. The runway length declared available and suitable for a landing airplane.
(also Declared Distances from wikipedia)
which lead to other definitions...
Stopway - An area beyond the takeoff runway no
less wide than the runway and centered upon the
extended
centerline of the runway, able to support the
airplane during an aborted takeoff, without causing
structural damage to the airplane, and designated by
the airport authorities for use in decelerating the
airplane during an aborted takeoff.
Clearway - An area beyond the takeoff runway
under the control of airport authorities within which
terrain or fixed obstacles may not extend above
specified limits. These areas may be required for
certain turbine-powered operations and the size and
upward
slope of the clearway will
differ depending on
when the aircraft was certificated.
then for those specified limits of the clearway, in 14 CFR Part 1 we find

Clearway means:
(1) For turbine engine powered airplanes certificated after August 29, 1959, an area beyond the runway, not less than 500 feet wide, centrally located about the extended centerline of the runway, and under the control of the airport authorities. The clearway is expressed in terms of a clearway plane, extending from the end of the runway with an upward slope not exceeding 1.25 percent, above which no object nor any terrain protrudes. However, threshold lights may protrude above the plane if their height above the end of the runway is 26 inches or less and if they are located to each side of the runway.
(2) For turbine engine powered airplanes certificated after September 30, 1958, but before August 30, 1959, an area beyond the takeoff runway extending no less than 300 feet on either side of the extended centerline of the runway, at an elevation no higher than the elevation of the end of the runway, clear of all fixed obstacles, and under the control of the airport authorities.


Why was the tip of the B-52's vertical tail chopped off in 1959?

Boeing B-52G Stratofortress

  In the design of the B-52G, considerable attention was paid to reducing the structural weight. Different materials were used in the construction of the airframe, and the wing structure was extensively redesigned. The most visible difference was a vertical tail which was reduced in size. The height was reduced from 48 feet 3 inches to 40 feet 7 inches, and the chord (width) was increased. The new tail was tested on the first B-52A (52-001) and perhaps also on either the XB-52 or YB-52 before being adopted as standard for the B-52G.


Why does the Cessna 172S Skyhawk use only two blade fixed pitched prop?

You're not wrong, but a fixed pitch two-blade prop has a pretty big advantage: it's cheap. Cheap to buy, cheap to install, cheap to maintain, cheap to repair. 172s are predominantly trainers in FBO fleets, and cheap is the winner. The efficiencies of a better prop are lost when you're just doing pattern work and short cross countries.

Also, when you're not climbing, a two-bladed prop is actually going to be more efficient, not less as it's creating less drag. According to the linked Hartzell FAQ:

  Depending on the combination of [engine power, operating RPM for the propeller, diameter limitations, design requirements, etc] a 2-blade propeller may be most efficient, but as power increases additional blades are generally required to efficiently utilize the increased power.

This means that on a 160 horsepower engine like the 172 is rocking, you aren't going to see particularly tangible benefits from increasing the number of blades. Going to a constant speed prop would, on the other hand, give you greater utilization of power across the entire flight envelope.

For example...

An overhauled McCauley fixed pitch 2-blade propeller that fits a Cessna 172 is $2,100 on ebay. It has no moving parts (I mean, aside from itself) and is relatively easy to balance.

A (non-overhauled?) Hartzell 3-blade constant speed prop off a Piper PA-46-350 Malibu Mirage is $15,000 on ebay with no logs, which is usually a bad sign. It's not a direct comparison to, say, the prop on a C182, but it's probably in the ballpark. It's harder to balance, and requires more maintenance to make sure the constant speed mechanism is up to snuff.

I was only able to find prices on ebay, which isn't the most scientific comparison ever, but it's a start.


Do pilots on approach receive automated warnings of sudden windshear or seismic motion?

Windshear, yes. Seismic events, no.

Most major U.S. airports have a LLWAS -- Low-level Windshear Alert System, which is essentially an array of anemometers around the airport which detect wind speed and direction.  The values from each station are processed by a computer that uses algorithms to detect a windshear or microburst event, and it notifies controllers in the tower.  As a simple example, if the anemometers around the perimeter of the airport are all pointing toward the center of the airport, that's a strong indication that there is a microburst over the center of the airport, with air descending into the ground and then spreading out in all directions.  Obviously, the algorithms can detect cases beyond just that.

And, many airports supplement that system with Doppler radar as well.

Regardless of how they're generated (LLWAS with anemometers, Doppler, pilot reports, visual observations of blowing dust, etc), the warnings are broadcast by the tower controllers, rather than by any automatic system.  In the aircraft, aural warnings from the GPWS (reactive windshear -- noting changes in groundspeed and sink) and the EGPWS (predictive windshear -- returns from the aircraft weather radar) are automatic, but they don't block a radio frequency.  Automated alerts over the tower frequency might block an even more important transmission, so it's left to the controller's judgement when to broadcast the alerts.  (They're usually pretty prompt!)

No airport I'm aware of has a system similar to what the OP described for seismic events.  I would assume that the risks to a high-speed train from an imminent earthquake -- i.e. the train may derail at high speed with catastrophic results -- are far greater than the risks to aircraft.  I've never read anything about what happens when you're landing or taking off in an earthquake, but I'd doubt that anything other than the most severe would have much effect.  And if the earth is shifting enough that you can't keep the aircraft on the runway, well, it's a really bad day for pretty much everybody in that state that day!


What does ''NAV ILS OUT OF SERVICE'' mean?

It means exactly what it says. The ILS is out of service, so you can't use it.

An ILS can consist of several different elements, for example localizer, glidepath, DME, inner/middle/outer markers as well as a bunch of technical monitoring equipment, ATC control panels, warning systems and backup power supplies. Should any of these components fail, it may be required to take the entire system out of service. The NOTAM doesn't say exactly which part of the ILS is broken, but that doesn't matter, since the entire ILS is listed as unavailable. So no, you cannot expect to use the localizer.


What does the letter E signify for the E-3 AWACS?

The E isn't exactly the short form of a word as it is a mission designation. In the US military's Tri-Service aircraft designation system, E indicates that the aircraft performs special electronic missions. Similarly, F implies the aircraft is a fighter aircraft and B indicates the aircraft performs bombing missions.

edit: here is the US military aircraft designation system


Is it possible to fly an EASA registered airplane with an ICAO license?

The ICAO doesn't issue licenses, so there's no such thing as an ICAO license. You have a license issues by the Argentine aviation authorities is ICAO compliant, which means it is recognized internationally, and you can fly Argentine registered airplanes anywhere in the world. It does not automatically give you privileges to fly airplanes of any other registration, so no you cannot fly Polish airplanes at this point.
There may be a way to do it, depending on the regulations in both countries. In some cases you can get a temporary license on the basis of your other license, or get some sort of other written permission. You would need to ask the Polish aviation authority what you need to do.


How does an aircraft designer increase dynamic stability?

Damping is produced by drag and by large induced speeds at the tail surfaces from a given disturbance. This can be caused by long lever arms of these surfaces or by high air density.
More on the topic can be found here:

What is aerodynamic damping?
Will control surfaces on a plane be less efficient at a higher altitude?. The lower density at high altitude reduces the vertical or sideways speed component caused by a rotation relative to flight speed, thus reducing dynamic stability.
Another trick is to use a conventional tail instead of a V-tail, as discussed here.
What also helps is to shift the eigenfrequencies of the plane away from the response delay of the pilot in order to avoid PIOs. An unusual example would be the Wright Flyer.

These planes typically pull out of a dive on their own, but then climb excessively and stall …

This is the classic long period mode in longitudinal stability. Since rotation rates are low, pitch damping also is low and the most important damping contribution is from drag. A low L/D reduces the tendency to overshoot, a high trim speed reduces the tendency to stall (and shifts the motion to higher speeds with lower L/D). Reducing static stability will make the period longer such that it becomes easier for the pilot to react. However, lower stability will make the pitch response more sensitive which increases the risk of too large control inputs.


What are the two turning tendencies that occur during a steep turn?

One of the turning tendencies that occurs during a steep turn is the tendency to over-bank.  This is generally due to the outer wing (wing-up) moving faster thru the air and creating a bit more lift that has to be counter-acted.  A second turning tendency is due to adverse yaw (requiring a bit more rudder during a right hand steep turn).

Here is a link that will help you understand:

aerodynamics of a steep turn


What kinds of jobs could a senior in high school get at a small local airport?

Sure! When I was a senior in high school I had a job as a line boy at a local FBO. We refueled aircraft, cleaned aircraft and moved them in and out of hangars. Not the most glamorous job but it was the beginning of the never ending learning process of aviation.


How can I get flying again after FAA medical rejection for anxiety two years ago?

In general, as I do not have the guidance in front of me presently, if you have been diagnosed with an anxiety disorder, and later taken off the medication with no adverse effect, and the symptoms are absent, you have a high probability of obtaining a medical.

First, your primary care physician should document that you have been off the medication for x months.  Usually two years is good enough.

Then you should shop for an AME.  You want someone who is willing to work with you to get the documentation needed and submitted. Your initial application may be initially deferred, and forwarded to FAA Medical Headquarters in OKC for review. OKC has in the past taken calls on medical certification inquiries, but has also not taken them.  I would call them and ask for their guidance documentation.

If you are an AOPA member, their medical support people are excellent, and will give you specific guidance, as to what reports and findings will be most helpful.

It is possible that you might need an evaluation by a specialist, a psychiatrist, to assure that you are not walking around untreated, and do not show any signs of GAD.  GAD is often considered a long term chronic disorder, and it is not uncommon for people with GAD to have the condition for their lifetime.  In your case, you will want it to be that the diagnosis surfaced with situational circumstances, and the condition is no longer an issue, and the medication is not indicated at this time.

As a CFI, I have had quite a few primary students, and one CFI student who had similar or even more significant psychiatric disorders, and as those were addressed and they were able to drop the medications, they were again qualified for a medical.  Also keep in mind that your road to Basic Med will initially require a 3rd class or higher medical.  So it would be nice to get this administrative matter resolved.

In addition to AOPA, there are places which primarily help pro pilots, but will provide excellent services to help guide you through the process and if you are qualifying, will help you get a medical.  They can be several thousand dollars, and in your case a year of AOPA membership would be very cost effective.

As an example, I had a primary student who had a history of suicide attempts.  It turns out that she felt she was trapped in an abusive relationship.  A couple of years later the situation was different, and her PCP and therapist records were all that was needed to have the FAA issue an unrestricted medical.

For air ambulance, if you are not playing a role which requires a FAA medical, then you will not need one.  In air ambulance, the typical roles requiring a medical are pilots.  I don't know of any air ambulance outfit which requires a FAA medical for their EMTs.  You could always ask at a place that you might be interested in employment.

The FAA medical practices are in place to mitigate perceived risk.  People have situational circumstances in their life which may be outside medical issuance, but their situations also change.  To a degree, the FAA generally recognizes that.

Good luck pursuing your interests.


Why is this video of a G36 Bonanza taking off so scary?

Because those trees will kill them

If you look at this document regarding the Bonanza G36 performance you will note that the lowest stall speed written is 61 kts. 61 kts is 112 kph or 71 mph. We can assume they were going a little bit faster than that but let us say 110 kph / 70 mph.

In that clip, they are just barely keeping airborne. This means the aircraft is extremely sensitive to disruptions. Any loss of power — even partial — or getting knocked back by a collision and thus losing a few knots or upsetting the aerodynamics of the aircraft, is very likely to send it crashing into the trees.

Going 110 kph / 70 mph into a tree is rarely survivable even in a car, and then you have to remember that cars these days are built to withstand crashes while at least keeping the occupants alive, but that assumes crashing into something wide, that distributes the forces over a wide area, and that gives way, like another car. Trees fail that on both accounts.

A G36 does not even come close to any such structural integrity in case of a crash. The cabin will crumple like figurative tin foil, sending the occupants smashing into the trunks of the trees, or throwing them clear of the aircraft only to then smack into other trees or the ground from several meters up and at a high speed. And that is going to be fatal.

Hence, this is scary because if they clip a tree they are very likely to die.


How much energy does unretracted landing gear consume?

While it’s not a true air to air fighter, following are some comparison numbers for the EA-6B Prowler that might help provide a useful ratio for a tactical "fighter type" aircraft.  (Information comes from the NATOPS pocket checklist, under the constant altitude “bingo” fuel divert tables.)
Theses figures are for a flaps-up aircraft, fully loaded with 5 external stores, and both engines operating.  (There are multiple configurations and distances covered in the tables).
Fuel required to go 100 Nautical Miles:

Altitude
Gear Up
Gear Down

Sea Level
3970 lbs
5220 lbs

10,000 ft
3580 lbs
4590 lbs

20,000 ft
3270 lbs
4160 lbs

NOTE:  The gear down figures are worst case and presume a hydraulic failure.  In the event of a hydraulic failure the gear will be blown down pneumatically and the forward main landing gear doors, (that normally re-close to cover the empty wheel well) will remain open.  This imposes some additional drag penalty over and above normal flight with the landing gear down.

You should be able to extrapolate this into something useful, but if you would like more data points please let me know.


What is the origin of the waypoint WORUM (neayby Houston)?

It's worm, as in tequila worm:

  Perhaps even more popular than the actual tequila is the worm crawling around the bottom of the bottle. But the worm, or gusano, actually originated with tequila's “lower-quality” cousin, mezcal, largely as a marketing ploy. The gusano is the larvae of a type of moth that lives on the agave plant.—huffingtonpost.com


What information might go in the remarks section of an IFR flight plan?

The remarks field, also called ITEM 18 field on ICAO flightplans can take a lot of information that you as the pilot deem necessary for controllers or authorities to know about your IFR flight.
The list of possible items in an ICAO flightplan ITEM 18 field is available over at the Skybrary, but here are a few examples that are commonly used:

(c) “TYP/” followed by type(s) of aircraft, proceeded if necessary by number(s) of aircraft, if “ZZZZ” is inserted in Item 9
Example: TYP/2 DE HAVILLAND HERON. Up to 60 characters may be used.
(e) “ALTN/” followed by the name of alternate aerodrome(s) or bearing and distance to navaid/navigation point closest to alternate point, if “ZZZZ” is inserted in Item 16. Up to 100 characters may be used.
Example: ALTN/MEDIUM AIRPORT
(k) “OPR/” followed by name of the operator, if not obvious from the aircraft identification in Item 7.
Example: OPR/BIG COMPANY
(o) “RMK/” followed by any other, plain language, remarks when required by the appropriate ATS authority or deemed necessary. There is no limit in number of characters to be used.
Example:RMK/TRAINING ILS APPROACH AT SMALL AIRPORT
RMK/STUDENT SOLO FLIGHT


In F-16 the pilot or FLCS , use the rudder to address the adverse yaw effects in direction of roll during an aileron roll? or opposite way?

Adverse yaw from aileron deflection, at roll initiation, is a function of wing span: a longer wing span creates more adverse yaw. And a long wing span is not what an F-16 possesses.

Image source

Its main problem at lower airspeed is creating a roll rate at all with such short wings. Deflecting the rudder may help increasing the roll rate - for a left roll, it would be deflected Trailing Edge Right, creating adverse yaw. Which might or might be compensated by asymmetric aileron deflection, depending on the priorities posed upon the manoeuvres of a fighter aircraft at low speed. Of course, it makes much more sense to deflect the horizontal tail such that it helps in the roll.

At high roll rates, adverse yaw is created by the difference in local angle of attack at left and right aileron. Plus an aeroplane with low wing span will start to nutate: it wants to spin about its rotation axis with the highest moment of inertia, so tends to want to convert roll into pitch from inertial coupling. So high roll rates are a different kettle of fish in aeroplanes with short wing span, with lots of work to do for the fly-by-wire computers.

  In the F-16, is rudder used to arrest the adverse yaw effects...

Most probably not. Adverse yaw from aileron deflection is not a large issue on fighter aircraft.


Do modern airplane controls provide force feedback of external forces on the control surfaces?

On some. The Fokker 100 is one, where the aeroforces on the elevator are directly fed back to the pilot. There is a hydraulic actuator helping him, but contrary to the usual solution it is a reversible system where the hydraulics merely amplifies the direct force that the pilot exerts.

The F100 has manual reversion for elevators and ailerons, and it can still be flown reasonable comfortably without hydraulics. The 737 also has manual reversion, but the flight controls are quite heavy without hydraulics - it is about the largest high-subsonic aircraft that can still be hand-flown. Larger planes just have triple redundant hydraulic controls, some with q-feel which artificially replicates the higher air stiffness felt at higher airspeeds. No romantic gusty creaking for those aircraft in a museum.


What plane is this, appearing in the movie Rampage?

It's a Boeing C-17 Globemaster III. The tail markings appear to be those of the 437th Airlift Wing, US Air Force (thanks to TomMcW for the unit identification).

To answer the question yourself, note that you can see the US flag on the vertical stabilizer and the word "Force" behind the cockpit window. Wikipedia has a list of planes flown by the US Air Force and, although the list is quite long, it is categorized by mission, which cuts down the options quite a lot – the plane obviously isn't a fighter, for example, and, conveniently, "cargo" is early in the alphabet so close to the top of the list.

The serial number 2300 (or 7300?) painted on the nose doesn't correspond to an actual USAF C-17; it was probably temporarily renumbered while filming.


Most modern aircraft, which includes long range airliners since around 1970, all airliners since not much later, and basically anything with glass cockpit, do have very accurate accelerometers for all three axis, as part of the inertial reference system.

They are important instruments for the autopilot, as they provide faster feedback on the effect of control deflections than the air-data references, and essential for navigation as cross-reference for detecting GPS errors and the inertial navigation serves as a backup for GPS (and served as primary navigation over the oceans before wide GPS availability). Airbus (since A320) even defines the pitch command by vertical acceleration in the normal law. And yes, they are also used for detecting hard landings and their severity.

The pilot never sees the direct accelerometer output except in fighter and aerobatic aircraft though (well, almost never; there are a couple of other cases).


Are all the engines on a multi-engine plane the same?

Generally yes, but not always. If you include the APU as an engine, the answer would need to be different, but I understand your question concerns just the engines used for propulsion.

For jets, the direction of rotation doesn't make much of a difference, so the same engines can be used on all stations. However, with propellers the swirl does influence flying characteristics, especially at low speed, so special left- and right turning versions of turboprop and piston engines are available.

Maintenance and logistics become much simpler if only one type of engine is used. In the past, not so much emphasis was placed on this, so some airplanes used different types of engines. Examples were:

Convair B-36B, which combined piston and jet engines in the same airframe
Junkers G-38, which used a Junkers L88 inboard and a Junkers L8 outboard. Later, the outboard engines were also changed to the L88. This can be seen from the number of propeller blades: If the outer engines drive a two-bladed propeller, it is the earlier version with the L8.
Hawker-Siddeley Trident 3, which was almost a four-engined jet, because it had a small, tail-mounted RB-162 engine in addition to the three tail-mounted RB-163 Spey to provide thrust on takeoff.
Rutan Voyager, which used a bigger front and a smaller rear engine.


At what altitude do vacuum powered gyros become ineffective?

Just like altimeters, it depends on the specifications.

The manual for this random vacuum attitude indicator says up to 40,000 feet.

(Image source)

  In an aircraft, the vacuum source is often used to power gyroscopes in the various flight instruments. To prevent the complete loss of instrumentation in the event of an electrical failure, the instrument panel is deliberately designed with certain instruments powered by electricity and other instruments powered by the vacuum source.— Wikipedia

In a piston engine airplane the vacuum pump is geared to the engine.

Historically electric motors weren't reliable, that has changed now of course.

At 80,000 feet the air density is only 14% compared to 40,000 feet. I highly doubt it would be feasible (size, weight, RPM) to create such a pump. And I'm pretty sure it's of no use to jets.


A frozen ATPL holder is somebody who has passed all the required (14) exams for the issue of an ATPL but does not have the required flying hours. Strictly speaking, there is no such thing as a 'frozen' ATPL, though a number of training schools do use the term:

A Frozen ATPL holder refers to somebody who has passed all the required theoretical exams but does not qualify him to be issued with a full ATPL until he has logged a total of 1500 hours.
A student from a flying school will normally graduate with a CPL (Commercial Pilot Licence) and IR (Instrumental Rating) (CPL+IR). This Licence is known as the Frozen ATPL.

In order to 'unfreeze' the ATPL, the candidate has to complete a flight time of 1500 hours subject to certain conditions:

... ATPL will remain frozen until you have reached 1500 hours of flying time, which is made up of the following criteria:

500 hrs multi-pilot in transport or commuter aircraft
250 hrs PIC (or 100 Pilot in Command and 150 PIC under supervision)*
200 hrs cross country flights (100 as Pilot in Command)
75 hrs instrument time
100 hrs night flight as PIC or co-pilot


How should airline pilots find out about military activity along their route?

Military operations are conducted in certain airspace blocks that should be well marked on your charts.  If you are IFR your route should avoid such areas, if you are VFR, hope you know what you are doing.


Why does the cabin pressurisation switch have a manual mode?

The B737 Next Generation models (737-600, -700, -800, and -900) all use a digital cabin pressure controller, which has AUTO, ALTN, and Manual modes.  Older 737's may use this digital controller or an analog controller with Auto, Standby, Manual AC and Manual DC modes.

From MyAirlineFlight.com, which also has a depiction of the older, analog panel.

In the digital panel, the Auto mode selects between two digital controllers which swap every flight so that if #1 is primary (in control in the Auto mode) this flight, #2 will be primary next flight.  The ALTN mode makes the "other" controller primary, so that if the primary controller fails, the other one can be selected.  With both the digital and the analog controllers, the Manual mode gives the pilots direct control over the outflow valve.

There are several reasons that this control is sometimes desirable; none of them are particularly common.  First, if you need to perform a ground pressurization check, the pilot or mechanic uses the manual mode to close the outflow valve and allow the aircraft to pressurize on the ground.  It isn't common, but there are some checks that require it.  Second, the manual mode is used to verify that the outflow valve DOES open and close.  This used to be a check performed by the pilots, but (in large part due to the Helios accident mentioned), it is now a maintenance-only function for many operators.

Third, if the flight must be conducted unpressurized, the manual mode allows this -- open the outflow valve fully, and there is no pressure differential -- say if you had a damaged window that needs to not be pressurized while the aircraft is ferried to where the window can be replaced.

Fourth, in the case of an emergency evacuation, it may be necessary to quickly depressurize the aircraft, and the manual mode allows the crew to open the outflow valve with only DC (i.e. only battery) power available.  (The automatic modes need AC power to operate.)

Finally, if both digital controllers fail in flight, then the crew needs a way to control the pressurization, and the manual mode is used for this.  Getting to this point is quite rare, but it can happen.  Controlling the pressurization manually takes a lot of time & attention by the First Officer, so it isn't something that's practiced in the aircraft, and because the really big cues that you're doing it well or poorly come from what your ears feel, it isn't something that's done in the simulator either.  But there has to be a way to manually control the pressurization, so the Manual mode is it.  (Loss of all generators in flight could also put you in this position -- with no AC power the Automatic mode is unavailable.  Again, an extremely rare event.)

With the removal of the outflow valve check from the pilots' preflight, the switch is typically left in the AUTO position always, unless maintenance is doing their checks.  More than a few times, crews got distracted in the middle of the outflow valve check, left the switch in manual, and never got back to it.  The usual result was a Cabin Altitude Warning shortly after climbing above 10,000'; if the crew recognized their error, they could simply switch back to Auto and continue.  If they didn't realize that they'd done, they'd shortly get a call from the back asking why the masks had dropped, and that was usually the big clue that things had gone wrong & they needed to go back & land.

One might wonder why the Manual mode is annunciated by a green light rather than an amber one -- the amber light would show up when checking the Master Caution.  That was a design decision by Boeing a few decades ago, and I don't have insight into their thinking there.  (Much like, why did they use the same horn for Takeoff Configuration Warning as for Cabin Altitude Warning... it evidently seemed like a reasonable idea at the time.)


When crossing a mountain ridge at low height above terrain what consideration is given to turbulence?

From an older FAA Publication on mountain flying:

Mountain Wave
When the wind speed is above about 25 knots and flowing perpendicular to the ridge lines, the air flow can form waves, much like water flowing over rocks in a stream bed. The waves form down wind from the ridge line and will be composed of very strong up and down drafts, plus dangerous rotor action under the crests of the waves. If enough moisture is present, lenticular clouds can form to give a visual indication of the wave action. These clouds are reported in the remarks section of hourly sequence reports as ACSL (altocumulus standing lenticular) or CCSL (cirrocumulus standing lenticular)

Pretty much sums up what you're seeing I guess. As for action:

Ridge and Pass Crossing
On most mountain flights, you will need to cross at least one ridge or pass. Experienced pilots recommend crossing a ridge or pass at the ridge elevation plus at least 1,000 feet. If the winds at mountain top level are above 20 knots, increase that to 2,000 feet. Plan to be at that altitude at least three miles before reaching the ridge and stay at that altitude until at least three miles past it. This clearance zone will give you a reasonable safety zone to avoid the most severe turbulence and down drafts in windy conditions.
If conditions or airplane performance dictate, you may need to fly along the windward side of a ridge to find updrafts for gaining altitude before crossing a ridge. You may also need to circle before reaching the ridge if climbing out of a valley airport. When you actually cross a ridge, you should do so at a 45• angle to the ridge. This allows you to turn away from the ridge quicker if you encounter a severe downdraft or turbulence. Once you have crossed the ridge, turn directly away from it at a go• angle to get away from the most likely area of turbulence quickly. Plan your crossing to give yourself the ability to turn toward lower terrain
quickly if necessary.

As for helicopter mountain flying specifically, I'm afraid you are unlikely to find somebody on here with that experience. You might have better chance on searching for it online and phoning up flight schools that offer such courses (I found a few in the states) for information.


As a passenger, can I use my handheld radio in commercial flights?

I don't know if you are "authorized" to... but I can tell you that it likely won't work.

I've tried a handheld aviation radio in a commercial cabin, and was unable to hear the ATC side of transmissions at all.  This was likely due to having a very short antenna inside a large metal cylinder, a long way from the source of the transmission.

It was nearly impossible to follow the communications when I could only hear my flight crew's side of the conversation.


The 1500 hour rule is still in effect.

The rule wasn't set to expire on the 30th of September; technically the entire FAA was going to expire. Congress votes on the authorization for the FAA to regulate air transportation; that authorization was set to expire 30 September, 2015.

The House voted to authorize funding on 28 September while the Senate passed a 6-month extension on 29 September.

Expect to see similar discussions in 6 months.


HUD

The most common form of head-Up Display (HUD) is simply an out-of-sight display screen reflected in a transparent flat sheet of glass in the viewers line of sight out the cockpit front window.

The glass sheet is called a combiner. It combines the HUD information with the view out of the aircraft.

There are coatings for glass (E.g.) which allow for reflecting a monochromatic image while allowing transmission of other colors.

The display is obviously tailored for that specific use. It must avoid obscuring the view. Therefore it mostly consists of minimal light-colored lines and numerals/letters against a dark background. The dark background allows the pilot to see through the reflection to brighter objects outside - it's a bit like the matt black upper surface typically found on many car dashboards which prevents distracting unwanted images of the top of the dash being reflected into the driver's view out of the windscreen.

Here's an example from Boeing

A HUD display is visible on the left in the pilot's line of sight. Above it, mounted on the ceiling is the projector unit.

The Projector contains optics to make the pilot's view of the display appear to be at infinity (rather than the few feet away it is in reality). This allows the pilot to read the data while their eyes are focused on far-away real-world objects outside the aircraft (runways, weather, other aircraft etc).

EFVS

Beyond the projection of basic flight instrument data is the use of HUDs for Enhanced Flight Vision Systems (EFVS) which provide a kind of augmented reality display that typically uses external infra-red camera systems to identify landmarks (e.g. runway outlines) that may be obscured to the pilot due to fog etc.


Why don't all aircraft use/need nacelle chines?

The chines help when the nacelle is very close to the wing. When the engine of Boeing's 737 was changed from the slim JT-8D to the higher bypass ratio CFM-56 on the 737-300 and later, the chines were essential to avoid large flow separation. Generally, aircraft with higher landing gear can afford to have more space between nacelle and wing and do not need fixes like chines. But when a new engine has been fitted to an existing design, chances are that some vortex generators are needed to fix the new flow conditions.

For the nitpickers: The 737-100 and 200 had underslung nacelles which left no space between wing and nacelle, but that is aerodynamically similar to a nacelle at a larger distance, because no narrow flow paths are created which produce steep pressure gradients. Only a closely mounted, but still separate nacelle will have these flow conditions which need to be remedied by energizing the boundary layer.


Is the turn radius at fixed bank angle really independent of aircraft type?

If the turn is fully coordinated, turn radius at a given bank angle will depend on the speed of the aircraft and the local value of gravity.
This is because of simple vector and geometry: the vertical component of lift must still support the weight of the aircraft (whether that's a hang glider or an AN-225, a Helio Courier on the edge of stall or an SR-71), but the horizontal component, generated by the bank, produces a horizontal (=> centripetal) acceleration that is fixed in relation to gravity for a given bank angle.
The problem is that this centripetal acceleration is determined by both turn radius and speed.  So, if your hang glider and your SR-71 want to make the same radius turn (within their usual flight envelope), they'll do it at wildly different bank angles.


Approach when weather condition is below minimum

You haven't told us what country you are referring to.  I am going to talk about the United States regulations.

There are two separate regulations that come into play.  Part 91 and Part 121 or 135.

Under Part 91.  The pilots are allowed to commence any approach (irrespective of weather) and determine if they can continue to land based on the criteria listed in §91.175(c).

Under Part 121 / 135.  The pilots can only commence an approach (proceed past the final approach fix) if the latest weather received is above landing minimums.  Mainly, pilots are concerned with visibility.  They will not be able to use "flight visibility" as the weather visibility is most likely different as the airplane descends towards the ground.  The pilots must use the weather reported from the airport.

To answer the second question, if the pilots are past the final approach fix and new weather arrives indicating the airport is below minimums, the pilots are allowed to continue the approach to minimums to see if they can land per §91.175.


Why are the modulation depths of the localiser and glideslope different?

From the book "Principles of Avionics" By Albert Helfrick:

  The amount of modulation is twice that found in the localizer. Because the glide slope does not have ident or speech audio, the percentage modulation for 90 and 150 Hz tones is increased.


Which cruise altitude is prefered in engine-out operations of Boeing airplanes?

You'd typically drift down to your max single-engine altitude, which means essentially that max continuous power on the operating engine is sufficient for level flight at that altitude.  Higher than that, you have a slow descent going in order for the thrust you have to maintain the recommended driftdown airspeed.

In general, there wouldn't be any advantage to descending lower than this until you need to do so for approach and landing, so you'd probably remain at that max altitude.  As you burn off fuel, your max engine-out altitude would slowly increase so (hypothetically) you could actually step-climb up a little bit if you were going to be at that new Single Engine cruise altitude long enough, but in practice you'd need to lose the engine a LONG way from landing before the idea of step-climbing up to a higher SE cruise altitude would make practical sense.

The "Max" altitude is only reachable with the thrust of 2 engines, and the "OPT" altitude is probably well above what your max SE altitude is anyway -- it's optimum for cruising with both engines operating, after all.  Granted, a sufficiently high Cost Index and/or strange winds can pull the Optimum altitude down, but in 99% of the cases, Optimum is going to be well above Max Single Engine altitude.


Are centrifugal turbojets easier to make than axial ones?

Centrifugal is easier to make.  It's just a big vacuum cleaner with a kerosene burning furnace behind it instead of an electric motor.  You have a one piece impeller, as opposed to numerous little blades and discs, and can be cast or machined from a block of metal.  It's not dependant on the aerodynamic lift of blades to force air from a large space into a small space. It just pulls it in and flings the air out into a small space, so it's more resistant to surge.  To get surge in a centrifugal compressor engine you have to really obstruct the inlet, whereas with an axial engine you just have to disrupt the flow enough to induce blade stall.

So in the 30s it was WAY easier, cheaper, and faster, development wise, to get a nice running engine using Whittle's design with the centrifugal compressor.  The big downside is that it is less efficient than axial. You can't get the compression ratio that you would get  with an axial because it's difficult to incorporate multiple stages, and the engine is quite large because of the need to fling air out to compress it.  The Germans went with legions of expense, grief and operational delicacy for the better efficiency and smaller profile of axial.

The most obvious example today is the fact that nobody uses axial compressors for turbochargers and most in fact use similar impellers as the turbine as well.  You won't see axial compressors on any of the little micro turbojets used in RC.  A lot of smaller turboprops also use centrifugal compressors, sometimes in combination with axial stages.
That should tell you something about how much easier and cheaper it is to make.


Is it possible for an indirect (Russian) attitude indicator to work in 3D without tumbling?

Yes. It's actually easier.
Just consider the fact that an indirect indicator consists of two separate moving parts with one degree of freedom each, rather than one with two (or even three for navball) DoF. Instead of a ball, the pitch indicator can be a ring with continuous rotation, like so:

Note that most modern attitude indicators have a remote (separate) sensor, with the indicator driven mechanically by little servos (like the pictured AGD-1) or, of course, rendered digitally. This makes things even easier: the gimbal lock is a separate problem of the sensor (avoided with a tracking mechanism, pictured on the left here), while indication can be made however we want. You can easily have continuous pitch as well as continuous roll.
However, this is usually not done (on either type of indication), and this is a matter of convention rather than technical limitations. If we allow unrestrained angles, attitude becomes ambiguous: pitch ±180° with zero roll is the same as pitch 0 with ±180° roll. For this reason, the convention is that pitch is limited to ±90°, so only the second of these indications is valid. The necessary consequence is that roll "tumbles" when going past ±90° pitch. At the same time, the pitch indicator just inverts direction (and so mechanically it can be a semi-circle).
As a result, you will consistently see 180° roll, zero pitch no matter how you arrive to it: by a semi-loop or by rolling. This is reasonable given that continuous rolling is much more common.


Are there any reference values for Cl and Cd of a NACA 0012 airfoil to verify CFD simulations?

Four sets of measured data can be seen in this plot, the difference caused by different Reynolds numbers during measurement. The figure is from Helicopter Performance, Stability and Control by Raymond Prouty. The book is still for sale and is a treasure cove of knowledge on all things sub-sonic. From page 426 onwards it has a section on representing airfoil data with equations, using NACA 0012 as example.

This graph is from Theory Of Wing Sections by Abbott & Von Doenhoff. Contains a chapter of compressibility effects.

$C_L$ and $C_M$ are more extensively represented in the reference books than $C_D$, which is more generally lumped into considerations of Mach divergence number. The same two books will help you further.

The NACA technical report server can be of help as well, a starting point there would be NACA TR 832.


May an uncertificated pilot log non-PIC flight time for future certification?

Your friend can't log any time because he isn't licensed and qualified to fly the aircraft and assuming that you aren't a CFI then he isn't receiving training either. He's just a passenger, although if he wants to record the time for his own purposes that's fine, it just doesn't count for anything as far as the FAA's concerned.

First, 14 CFR 1.1 says that flight time is time acting as a pilot, not just time in an aircraft:

  Flight time means:

  (1) Pilot time that commences when an aircraft moves under its own
  power for the purpose of flight and ends when the aircraft comes to
  rest after landing;

So your friend needs to log time as a pilot. Obviously without a certificate there's no way to log PIC or SIC time, so that leaves training time. The regulations for that are in 14 CFR 61.51 (my emphasis).

  (h) Logging training time. (1) A person may log training time when
  that person receives training from an authorized instructor in an
  aircraft, flight simulator, or flight training device.


Can the ILS glideslope be intercepted from above?

Assuming that you're asking about intercepting the glideslope from above rather than the localizer, the answer is that it is definitely NOT recommended.

There are at least two significant problems if you do this. First, is the fact that at high vertical angles there can be false glideslopes. Looking at the diagram below, if you're coming at the glideslope from above and the needle starts to move, are you intercepting the real 3° glideslope or the false 9 ° glideslope?

The diagram above is the best I could find, but it has one error. It shows a "Flag no signal" at 6°. Actually what you'll have there is another false glideslope, but one which has reverse sensing.

You can, of course, do a reasonability check if you know your distance from the runway, or you could compare your vertical speed if following it with what you know your vertical speed should be, or on the 6° line a command to go up when you know you should go down would be a hint, but it's unwise in my opinion to put yourself in a situation that increases your work load that much during an instrument approach.

You asked about GPWS warnings. None of the aircraft I flew that had GPWS would sound a GPWS warning just from receiving a false glide slope. However, all of them would have sounded the GPWS if you followed a false glideslope and were close to the ground because doing so would give you an excessive sink rate.

A second problem with approaching from above is that the vertical angular width of the glideslope as measured from needle full down to needle full up is very small. As I remember only about one degree. Whatever it is, though, the point is that if you descend into the glideslope with a vertical speed of only a few hundred feet per minute greater than the glideslope itself is descending, the needle is going to go from full down to full up very quickly. Without working it out, I'd guess that if you're inside the outer marker you might well miss its movement if your instrument scan had you away from the needle more than a second.

In the late 1970s a friend of mine was flying a charter in a Cessna 310. He unwisely decided to intercept the glideslope at Salem, Oregon from above. The aircraft hit the ground in the vicinity of the outer marker, killing all aboard. During the accident investigation, the NTSB found from radar data that he had a descent rate greater than 1,000 fpm going through the glideslope.


If both pilots are incapacitated, what happens?

How does Airbus prepare for a dual engine failure on the A320?

The short answer is this isn't something that's realistically planned for because the chance of a double-failure of the redundant systems in question (the two pilots) is pretty unlikely, and many of the conditions that could lead to it would result in a catastrophic loss of the aircraft anyway.

(The most notable exception to that would be a loss of pressurization at altitude, in which case hopefully at least one of the pilots can get their oxygen mask on to make the emergency descent.)

The ATC/Airline system as a whole can theoretically deal with this sort of a double failure in a few different ways. The most common is finding an off-duty employee of the airline who is riding non-revenue (dead-head, jumpseat, etc.) to fill the role of an incapacitated crew member.
This is of course predicated on whatever incapacitated the flight crew not affecting this other person.

If no qualified personnel are available it may be possible to get an experienced instructor on the radio to "talk the plane down", but that relies on having someone onboard who can (a) get access to the cockpit, and (b) at least figure out how to operate the radios to ask for help.
"Talk-Down Landings" have happened in small aircraft on several occasions, but as best I can determine this has never happened in a transport-category aircraft (airliner) outside of simulations and similar thought experiments.


Which industry started to develop CFD software?

The foundation for CFD is the Navier-Stokes equations, published in 1822. The first application of CFD was in aviation in the 1930s; this analyzed two-dimensional flow, computations were done by hand. Then meteorology in the 1940s. Most of the early work was done in academic and government research circles, the first large-scale user was the Los Alamos National Laboratory (for work related to nuclear weapons). NASA was also an early user.
By 1967, Douglas Aircraft was using and developing CFD. Boeing published some of their work in 1968.


Does any USAF fighter jet use surfaces near the front for pitch control?

These surfaces are called canards.
To my knowledge no canard equipped fighter ever entered service with the armed forces, though there were a few experimental prototypes such as the CCV/AFTI F-16 or the F-15 ACTIVE which made use of canard foreplanes.

The Grumman X-29, Rockwell X-31, and Boeing X-36 are other examples of US technology demonstrators which made use of canards for extreme maneuvering, none of which were ever pursued further for development into a fighter aircraft.


Did Southwest airlines retire flight 1380 following the accident, and with what number?

According to FlightAware, Southwest has not operated a flight with flight number 1380 since the accident flight on April 17. The flights with that number for several weeks after the accident were all been marked as cancelled in the FlightAware database; other flight numbers were used:

Southwest uses the same flight number for many flight segments in a day, but their flight schedule shows that flights from LGA to DAL leaving at around 10:30am are using the flight numbers 5227 (Sundays, 10:35) and 237 (weekdays, 10:45).


What should be the relative positions of a wing's aerodynamic center and center of gravity?

1) It doesn't matter much. AC is relevant mostly for aircraft stability, so it is its relationship to the CG of the whole aircraft that matters. Only when the wing is the aircraft (flying wing), the distinction disappears.

Mass distribution (and thus CG) of the wing matters for aeroelastic effects, but then AC is not very relevant.

2) There is little sense in trying to determine spanwise location of AC. AC is related to the lift changes over angle of attack (AoA). When AoA changes, lift (CP) moves forwards and backwards but not sideways. Theoretically, if you consider a half-wing, you might be able to determine spanwise lift movement, esp. on a swept wing. But again, for stability analysis (where AC is relevant), you never need to do that, so you consider the whole wing and relate everything to its mean aerodynamic chord (MAC). L/2, by the way, happens to be on the airplane's plane of symmetry (L is normally the whole wingspan).


Can I continue school for the PPL in another country in another flight school, if it is still inside EU?

Laws within the EU can vary, however I would assume it would be possible to carry on training in another country, however I am not sure.

The best way to know, would be to ask your flight school! :)
They may know, and could contact the school you want to move to and work out a deal.

Best of luck

EDIT: In my country (Australia) it is possible to continue training overseas, even though we are not part of an EU style union.

EDIT 2: As I stated, if you currently undertake flight training, your instructor would know better than any online message board.


How does one test a stall warning during pre-flight?

Stall warning systems generally function on the principle of measuring pressure distribution or angle of attack. As each aircraft will have a different type of stall warning system, the necessary test will vary by aircraft as well. Here, I will answer based on aircraft that I have experience with, but these concepts should cover the majority of light aircraft.

Aural stall warning systems can generally be divided into two types, pneumatic and electric.

Pneumatic

Pneumatic stall warning systems are found in many light Cessna aircraft, including the 172 and 177. The following system description is from the Cessna 177 Maintenance Manual:

  The system is composed of an adjustable plate on the left wing leading edge, connected to a reed type horn by means of plastic tubing. The horn is actuated approximately 5 to 10 miles per hour above stalling speed as a negative air pressure area at wing leading edge causes a reverse flow of air through horn.

See this excerpt from Figure 15-6 in the C177 Maintenance Manual depicting the pneumatic stall warning system and it's location in the aircraft:

To test this type of system, air must be drawn out of the system through the leading edge scoop located in the left wing. The maintenance manual and AD 68-17-04 call for a test procedure as follows:

  Prior to flight, test the pneumatic stall warning system and determine if it is functioning properly, [...] by covering the opening in the left wing with a clean cloth, such as a handkerchief, and applying a slight suction by mouth to draw air through the horn. A properly functioning horn will provide a sound that is clearly audible.

The sound is something like that from a kazoo. In actual practice, speaking personally and from my observations, the "clean cloth" is typically dispensed with.

Alternately, a Stall Horn Tester is available for a small price if you would rather not have to put your mouth on a strange airplane.

Failure of these systems will typically be due to a problem either with the horn—such as a loose reed, or with the leading edge scoop—such as a cracked or misaligned scoop.

Electric

Electric systems operate on some of the same principles, but use a movable tab—instead of pneumatic suction—to sense the change pressure distribution. This type of system is found on aircraft such as the Cessna 182, Piper Cherokee, and Beechcraft King Air.

The system operation can be generalized as follows: pressure changes cause the tab to move up thereby sending an electrical signal which will sound a horn in the cockpit. In some cases the tab actuates a microswitch. In more complex systems the tab actuates a transducer which signals a stall warning computer.

The simpler of these types of systems can typically be tested with aircraft electrical power on by manually lifting the tab and listening for the warning horn. With the more complex King Air system, testing is accomplished with a switch in the cockpit which tests the circuitry and horn. In this system, signals from the stall warning transducer are blocked out by a weight on wheels switch when on the ground, with the effect that lifting the tab will not allow for system testing.

Flight Safety (FSI) offers the following system description in their King Air 200/B200 Pilot Training Manual:

  The stall warning system senses angle of attack
  through a lift transducer actuated by a
  vane mounted on the leading edge of the left
  wing (Figure 15-10).

  Angle of attack from the lift transducer and
  flap position signals are processed by the lift
  computer to sound the stall warning horn
  mounted on the copilot’s side of the cockpit.
  The horn sounds when the following conditions
  are present:

  Airspeed is 5 to 13 knots above stall,
  flaps are fully retracted.
  Airspeed is 5 to 12 knots above stall,
  flaps are in the APPROACH (40%)
  position.
  Airspeed is 8 to 14 knots above stall,
  flaps are fully extended.

  The system can be tested prior to flight by
  placing the STALL WARN TEST switch, located
  on the copilot’s left subpanel, in the
  TEST position. This simulates a stall condition
  and sounds the warning horn.

Figure 15-10 from the FSI King Air 200/B200 Pilot Training Manual

Other Systems

Other types of systems exist with which I have no actual experience, either as a pilot or mechanic. I offer the following information without much real knowledge of it, but hopefully with good sources. Others more knowledgeable than I might be able to verify it.

The Boeing 737 has a stick shaker type stall warning system to provide the required warning, rather than an aural warning system. The SmartCockpit.com B737 NG Warning Systems document gives the following system description:

  Stall Warning System

  The stall warning "stick shaker" consists of two eccentric weight motors, one on each control column. They are designed to alert the pilots before a stall develops. The warning is given by vibrating both control columns. The system is armed in flight at all times. The system is deactivated on the ground.

  Two independent, identical stall management yaw damper (SMYD) computers determine when stall warning is required based upon:

  • alpha vane angle of attack outputs

  • ADIRU outputs

  • anti-ice controls

  • wing configurations

  • air/ground sensing

  • thrust

  • FMC outputs

  • mach compensation

  The SMYD computers provide outputs for all stall warning to include stick shaker and signals to the pitch limit indicator and airspeed displays and the GPWS windshear detection and alert.

  Two test switches are installed in the aft overhead panel. Pushing either of these initiates a self-test of the respective stall warning channel. The No.1 activates the Captain stick shaker, and the No.2 activates the F/O stick shaker. Either stick shaker vibrates both columns through column interconnects.

The same document further defines the test procedure:

  STALL WARNING TEST Switches

  Push – on ground with AC power available: each test switch tests its respective stall management yaw damper (SMYD) computer. No.1 SMYD computer shakes Captain's control column, No.2 SMYD computer shakes First Officer's control column. Vibrations can be felt on both columns

  • inhibited while airborne


How does a jet engine handle suddenly entering a lot of rain?

In another question there is an excellent answer for how thermal expansion is handled in a jet engine.  It's an established fact that jet engines can handle fast temperature swings.  Have you watched how fast an ITT gauge goes up when starting an engine? My answer will focus on rain's effect on a jet engine.

The first thing to understand is that jet engines take a lot of air. That's why they can handle bizarrely heavy rainfall or even water on the runway splashing into the engine from the tires (this water jet has the fun name "rooster tails"). The Airbus 320, for example, goes through 27,000 liters of air every second during takeoff. 2 That means even during rigorous FAA certification testing the concentration of water ingested never gets higher than 20 g of water for every cubic meter of air.  See FAA Part 33.78 Appendix B

In order for you to understand why the water has little cooling effect I have to describe what happens when an engine takes in water, assuming you know the basic parts of a jet engine.  The air/water mixture enters the compressor, and the fan blades in this compressor are spinning rapidly enough to catch a lot of the water and like a centrifuge this water is spun towards the walls.  This helps prevent water from entering the combustion path on a bypass engine, but it does not prevent water from following the gas path, especially on an engine with no bypass around the gas path.

The engine must now adjust for the extra water in the air, and engines are very good at adjusting for these kinds of changes in conditions.  If there's more than one independent compressor rotor, for example, the rotor speeds will change to keep the air moving smoothly and ensure a correct pressure drop across the compressor, called "compressor rematching."  The engine will also increase the fuel to air ration to compensate for the water.  These two processes evaporate the extra water through thermodynamic heating, not through heat transfer.  In essence, the first stages of the engine are providing the extra energy to evaporate the water, so little differential cooling occurs, even if the amount of rain is rapid.

One thing to note here is that the engine actually runs hotter than normal instead of cooler than normal during these events, due to the reasons noted above as well as the extra thrust provided from the water injection.

All the parameter changes noted above reduce your margins for engine flame out and compressor stall.  In practice, an engine should flame-out or surge before water can cause a big enough thermal change to cause engine damage.  If you think about it, the amount of temperature change needed to cause a problematic warping of an engine should be a lot more than the amount required to cause the engine to quit running.

So we've established that jet engines are good at expanding and contracting due to thermal changes.  We've also established that relatively speaking we're actually not talking about a ton of water here, just a few grams per cubic meter of air, which would take a small percent of the engine power to evaporate (~1% by my calculations). Most of the extra water is evaporated not by cooling down engine parts, but by making the early stages of the engine work harder.  Finally, the reduced margins caused by water intake mean that you'll surge or flame-out before you get to warping engine parts.  These principles should apply regardless of whether the water ingestion begins in a matter of seconds or ramps up over several minutes.

In conclusion, in "Investigation of Engine Power Loss and Instability in Inclement Weather,"(pdf)  the FAA noted "Engines typically are not damaged during a heavy rain encounter. Usually the most severe situation is to experience multiple engine flameout or surge with a subsequent pilot initiated engine shutdown."  The report then went on to note that the two incidents where engine damage had occurred from rain were over-temperature events, not from differential cooling.  So your biggest worry when flying through even storm-of-the-century rainfall should not be whether your engine will warp from rain cooling things down.


How is a standard holding pattern flown?

Holding procedures are defined by each country for their own airspace. With that said, member countries of the International Civil Avation Organization (ICAO) generally follow the guidance of Part I, Section 6, Chapter 1 in ICAO Doc 8168, Aircraft Operations, Volume I, Flight Procedures:

  Section 1.1.3 - The procedures described in this chapter are related
  to right turn holding patterns. For left turn holding patterns, the
  corresponding entry and holding procedures are symmetrical with
  respect to the inbound holding track.

While the document does not explicitly state that right-hand holding patterns are the default, it is implied.

  Section 1.4.9 - The still air time for flying the outbound entry
  heading should not exceed: a) one minute if at or below 4 250 m (14
  000 ft); or b) one and one-half minutes if above 4 250 m (14 000 ft).
  Where DME is available, the length of the outbound leg may be
  specified in terms of distance instead of time.

Member countries can deviate from these standards, but if they do, they are supposed to notify ICAO and publish these differences in their respective Aeronautical Information Publication.


If I ferry an aircraft to the United States (from say the UK) is it a commercial or private flight?

This question was answered in an earlier (2013) message.

Generally, if you are ferrying an airplane and are compensated as a commercial pilot, are not carrying passengers or cargo for hire, you are operating under Part 91 of the US federal aviation regulations.  That you are a paid ferry pilot is not relevant.

See 19 CFR 122.1(d) A "commercial aircraft" is any aircraft transporting passengers or cargo for money or other consideration.

As you are not transporting passengers or cargo (both of which would be covered under the commercial operator rules) or you have a passenger as a friend or the aircraft owner who does not pay for passage, you are ferrying an aircraft which is covered as a private flight.

Make absolutely certain you understand how the US eAPIS system applies to you as a foreign national bringing the aircraft into the US, and you have appropriate documentation and the owner is prepared to jump through whatever hoops Customs needs to get the aircraft ashore.  The US Customs Guide for Private Flyers is a useful reference.

Simon, I disagree with your understanding.  There are many operations which are not commercial, with paid pilots.  An example of this is a corporation owns an airplane which requires a pilot.  The corporation can hire a pilot to fly its airplane and carry its parts/executives/employees/friends.  While the pilot must carry a commercial certificate and carry at least a Class II medical certificate, the flight is not considered a commercial flight, nor is the the company considered a commercial operator since it does not hold out its aircraft for hire, unless its in the air carriage business.  If on the other hand that same aircraft owner decided to carry the company next door's freight and executives and charge them for it, that changes the story.


Solutions to improve the aerodynamic behavior of a UAV

You want to move a heavy payload at low speeds. This means that induced drag will dominate the aircraft. If we assume a quadratic polar, the least amount of energy for staying airborne is needed when induced drag is three times higher than friction drag. Assuming a quadratic polar, the optimum lift coefficient at that point is $$c_L=\sqrt{3\cdot c_{D0}\cdot\pi\cdot AR\cdot\epsilon}$$
Obviously, you want a small zero-lift drag, but when you combine this with the high aspect ratio for a very efficient configuration, your lift coefficient will also become very high. You need to be careful to pick the right airfoil, and now Reynolds number effects demand to be observed. Once I know the overall size of your UAV, I can become more specific.

Just an example: If the zero lift drag coefficient is 0.02 and the aspect ratio is 12, the ideal lift coefficient is already 1.5. This is beyond most airfoils at Reynolds numbers below 1,000,000 and indicates a too high aspect ratio. Better add some chord in that case.

Also, some design decisions will look counterintuitive at first. I would strongly encourage you to add wing struts, like in a Cessna 172 or the Dedalus human powered aircraft. They help to save wing weight and thus reduce induced drag.

Don't overdo it with an elliptic planform! This will produce too small a chord on the outer wing and give the design undesirable stall characteristics. Better keep some chord and twist the wing so you will achieve the desired elliptical distribution at the design angle of attack. Better yet, save some wing weight by moving to a more triangular lift distribution – however, for small aircraft the optimum looks still quite elliptic.

The model pictured in your question has a lot of dimples on the fuselage - make sure yours will have a smooth surface.

Also look into improving propulsive efficiency. Use low RPM on a large propeller, if possible. You didn't mention your means of propulsion, so again it is hard to be more specific. Judging from the model, you will use electric propulsion. Use a brushless external rotor with a high pole count (low RPM per Volt).

So please provide more details and then you will receive a better answer.


Why do piston engines in aircraft burn fuel at a higher rate than a comparable car engine?

As others have noted, airplane engines and car engines have very different duty cycles.  An airplane engine will typically run at full power for a few minutes during takeoff & climb, then at a large fraction of max during level flight, which may last for hours, and be throttled back only during descent and landing.

An auto engine, by contrast, only operates at full power for a few seconds, as you for instance accelerate up that freeway on-ramp, then it will be throttled back to produce the small fraction of full power that's needed to maintain freeway cruise speeds¹.  Since the power output is proportional to fuel consumed², your car engine uses much less fuel.  Even though it might be rated to produce the same max HP as the airplane engine, in normal operation it produces much lower HP for the vast majority of its operating time.  You can see this in operation if you drive a car with a real-time fuel consumption gauge.  For instance, my Insight hybrid shows ~25 mpg when accelerating or climbing mountains (using near full power), but 75 mpg or better cruising on a level interstate.

Also note that the actual fuel economy of an airplane isn't that much different from say your average SUV.  I don't have the exact figures any more, but I once calculated that my Cherokee 180 got about 18 mpg.  When you figure that it's going twice as fast, and on longer trips can shorten the actual distance travelled by going in a straight line instead of having to follow roads, the comparison isn't that bad.

¹This, incidentially, is why hybrid cars can use electric assist to get much better mpg - the gas engine can be just big enough for efficient cruise, while acceleration is provided by the electric motor.

²To a first approximation.  It's a lot more complicated in the real world.  Look up BSFC maps if you're curious.


How to interpret/use "Fix Minimums" (at KALB)

The 620 is not at WESTS.

It's been discussed in multiple places, e.g.:

https://mooneyspace.com/topic/19113-ifr-fix-minimums-question-kipj/
https://www.pilotsofamerica.com/community/threads/fix-minimums.28308/

The way to read it is [WESTS FIX] MINIMUMS, and not [WESTS] FIX MINIMUMS, i.e., the 620 is not at WESTS, but the 620 is when you can identify WESTS (having DME on board for the L-DME in your case).

But let's check the AIM (5-4-20):

  When a fix is incorporated in a nonprecision final segment, two sets of minimums may be published: one for the pilot that is able to identify the fix, and a second for the pilot that cannot.

Another reason could be:

  Two sets of minimums may also be published when a second altimeter source is used in the procedure.

An example for that would be the KIPJ ILS Y or LOC Y RWY 23.

Of course when in doubt, contact the FSDO.


How dangerous is to take-off and fly with snow on the wings?

Pilots are allowed to commence a takeoff if the snow is not adhering to the wing and will blow off during the takeoff roll.

It is very difficult to just look at a snow covered wing and know for sure if the snow will blow off. A "hands on" tactile inspection should be conducted and even then you can never be sure about the level of contamination for the entire wing surface.   De-Icing is always the safest option.

To attempt a takeoff with snow and/or ice adhering to the wing is NOT SAFE.  You are gambling with your life, and the lives of your passengers and crew.

That being said, it is possible to do a reasonably safe takeoff with snow and/or ice adhering to the wing, but you will need a much longer takeoff roll, and slow rotation, and climb out.  If you were to have an engine failure you would probably not have sufficient performance to climb out over obstacles, or even remain airborne.

You are gambling that you have enough runway for your "seat of the pants" takeoff and that you will not have an engine failure, because you have no way of knowing the actual aircraft performance.

So again, De-Icing is the only safe option.


What is the takeoff decision speed (V1) for a Gulfstream G500?

Your decision speed also called V1 is the speed at which ou have to commit to taking off whatever happens because you won't be able to stop before the end of the runway after that. This speed is related to the airfield runway length, aicraft TOW, temperature and altitude and will change for each take-off. Therefore there is not a fixed value for a given aicraft.
For the G500 I did find this review

Today our take-off weight with three persons on board and 11500 pounds  of jet fuel (one-third of the max fuel) is 60 000 pounds and our computed speeds are V1: 118 kt for a rotation speed (Vr: 123) and a take off safety speed V2: 129 kt.

And this other one

The G500 was relatively light, loaded with 12,000 pounds of fuel for our flight, which was scheduled for 1.5 hours. Takeoff weight was 59,863 pounds, well below the 79,600 mtow. The avionics calculated V1 at 116, Vr 118, V2 132, and Vref in case of immediate return at 136 knots.

As you can see the value changes slightly but V1 seems to stay around 120kts. Your 200kt speed limit and the altitude and range limit related seems more likely to be linked to the 91.117(b) FAA regulation

Unless otherwise authorized or required by ATC, no person may operate an aircraft at or below 2,500 feet above the surface within 4 nautical miles of the primary airport of a Class C or Class D airspace area at an indicated airspeed of more than 200 knots (230 mph.). This paragraph (b) does not apply to any operations within a Class B airspace area. Such operations shall comply with paragraph (a) of this section.


There have been various proposals to use Western engines on new versions of the An-124:

An-124-200: Proposed version with General Electric CF6-80C2 engines, each rated at 59,200 lbf (263 kN)
An-124-210: Joint proposal with Air Foyle to meet UK's Short Term Strategic Airlifter (STSA) requirement, with Rolls-Royce RB211-524H-T engines, each rated 60,600 lbf (264 kN) and Honeywell avionics—STSA competition abandoned in August 1999, reinstated, and won by the Boeing C-17A.

Antonov fell victim to the fall of the Soviet Union: its HQ is in independent Ukraine which doesn't have the best relations with Moscow, so Antonov's sales cratered and left them with no development funds for new versions of the An-124. Western-engined versions were proposed to generate some sales in the West, but potential buyers were scared off by having to buy a paper project (and having to pay for development of the new version).

Along with the modest improvements to the An-124 being considered for new production of the aircraft, the Antonov organization has also investigating a more ambitious cargolifter, an improved hybrid of the An-124 and An-225 called the "An-124-300". It would feature the fuselage of the An-124 and the extended wing of the An-225, kitted up with modern avionics and engines. Since more powerful engines are now available, only four would be needed instead of six. The cargo floor would be extended, and a palletized loading system would be installed. It would have a maximum range of 11,500 kilometers (7,145 miles) with a 100-tonne (110-ton) cargo. Development costs were cited as less than a billion USD.
Given that the relationship between Ukraine and Russia is antagonistic, the Antonov organization is very interested in "Westernizing" the An-124 and any follow-ons -- using Western avionics and systems at the very least, and possibly re-engining the aircraft with Western turbofans.


What is this black symbol on a VFR chart?

An obstacle, an "Outdoor theater".https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/aero_guide/#sectional_radioaids


Do any aircraft out there use negative lift?

A lot of aircraft generate negative lift- not in the wings, but in the tail plane. This is used for stability. Consider a trimmed aircraft as shown below:

Image from grc.nasa.gov
On most aircraft, the center of gravity (through which weight acts) of the airplane is located near the center of pressure (through which lift acts) of the wing. If the center of presure of the wing is aft of the center of gravity, its lift produces a counter-clockwise rotation about the cg. A positive lift force from the tail produces a counter-clockwise rotation about the cg.
To trim the aircraft (i.e. no rotation about c.g), it is necessary to balance the torques produced by the wing and the tail. But since both rotations are counter-clockwise, it is impossible to balance the two rotations to produce no rotation. However, if the tail lift is negative it then produces a clockwise rotation about the cg which can balance the wing rotation. For this reason, the tailplane is designed to produce a negative lift.
Text from Trimmed aircraft- slightly modified.


Does flutter disappear above the flutter speed?

Flutter happens when elastic and aerodynamic frequencies converge. Normally, the elastic one is (almost) fixed and the aerodynamic one increases with flight speed. When speed increases further and the frequencies move apart again, flutter will die down. However, with further increasing speed more elastic modes will be encountered with ever smaller gaps between them.
There are indeed cases of airplanes which have a flutter mode below minimum speed but are safe to operate within their certified speed limits. The linked article doesn't mention this, but if you fly that thing slowly enough, the tail surfaces will wildly swing caused by a torsional elastic mode of the rear fuselage being in frequency neighborhood with oscillating separations on the tail surfaces. Pretty scary but harmless at that low speed.


Other than the 747, are there any other current, recent or planned airliners with a nose door option?

Excluding those aircraft in your question the answer is no. The 747 started really as a cargo aircraft, but given that more and more aircraft are available, the cost of development of another cargo only aircraft doesn’t make sense. Cargo operators can just buy old passenger aircraft, and they will continue to as the cost of development of aircraft is enormous, and most airlines at the moment (and most likely for the foreseeable future) are favoring smaller, thinner routes.
Sadly, the 747 and its nose door will be only a sight for cargo airlines soon.


When was the first rudder on an aircraft used?

Planes as early as the wright glider (1902) had a rudder, it appears from pictures that the 1900 and 1901 variants did not have rudders but its hard to tell from the photos.

Depending on your definition if you are talking about powered flight the Wright Flyer (1903) had 2 rudders much like its earlier glider predecessor.

In the lighter than air category, the Giffard Dirigible (1852) had a sail like rudder in the aft of the ship. So that may take the cake if you have consider it a true rudder.

Side Note: Patented in 1930 the V-Tail design could be argued as the first design that did not (as far as I know) employ a rudder. The earlier Beechcraft Bonanza's are the most common plane of that design in commercial production. There is quite a bit of debate as to the safety of ruddervators and the general theme seems to be that they are not perfect and do require some care to fly properly.


What design features or systems help to prevent a hard nose landing?

The longitudinal stability of the aircraft.

Aircraft are designed so that at any given elevator position they maintain a corresponding angle of attack¹. Any decrease in AoA creates pitch up moment to increase it and vice versa.

At touch down the pitching moments change a bit, but the general tendency remains, so without change in the elevator position, the plane will tend to keep the nose wheel off the ground. The nose only touches down when the pilot eases the back pressure on the control column, or the plane slows down enough that the elevator efficiency decreases below what is needed to keep the attitude.

The pilot just has to ease the back pressure gently and not slam on the brakes until the nose wheel is on the ground, because brakes do generate significant downward pitching moment (this applies to all vehicles; you can feel it in a car quite well).

¹ except modern fighters, but there the control computer emulates that behaviour, otherwise they wouldn't be controllable.


How is the Max Zero Fuel Weight used in calculating weight and balance?

Maximum Zero Fuel Weight is an operating limitation intended to protect the wing spar structure by limiting the concentration of load, relative to all up weight, borne by the wings in the middle of the span.  In other words it limits spar bending loads at the wing roots imposed by the mass in the fuselage because any additional weight must be in the wing tanks where the additional load doesn't add to root bending.

Generically, Zero Fuel Weight can just mean all up weight minus usable fuel.  However, when an instruction says to use "Max Zero Fuel Weight" it's saying to apply a published MZFW value that is an operating limitation.  In your case you would enter the Max ZFW value from the airplane's Operating Limitations in the AFM into the app.


Would there be any advantages to a wing with a concave upper surface?

The idea behind this design seems to be that the principal cause of lift
of a wing is that the top has a larger area than the bottom, so if we
substitute a top surface with a different shape but the same area, we will
still get similar lift.

This is the idea behind the equal-transit-time theory of lift,
which is incorrect, disagreeing in several ways with
with actual observations of air flowing past airfoils and the
lift forces that result.
NASA has produced a basic but thorough refutation of this theory;
among the points they make are

  The lift predicted by the "Equal Transit" theory is much less than the observed lift, because the velocity is too low. The actual velocity over the top of an airfoil is much faster than that predicted by the "Longer Path" theory and particles moving over the top arrive at the trailing edge before particles moving under the airfoil.

and

  There are modern, low-drag airfoils which produce lift on which the bottom surface is actually longer than the top.

What you generally want in an airfoil is for it to establish streamlines
that carry the air at very high speed over the top and shoot it downward
past the trailing edge. The speed is not determined by the surface area
or length along the top surface; the speed is determined by other things,
and two air molecules that start near each other but go on different sides
of the wing (one on top, one on the bottom) get to the trailing edge when their respective speeds carry them there, generally not at the same time as each other.

Putting a big hollow space on top of the wing
where the air can pile up and then forcing it over a second hump to get
to the trailing edge seems counterproductive.
It might just lead to the wing stalling at relatively low angles of attack,
which would limit the amount of lift you can get from it.
But I am not an airfoil designer, and I don't know exactly what the result would be.


You are correct in the assumption that the typical data recorders being used today are too heavy to float.   They are designed to withstand very high forces, extreme temperatures, and to withstand corrosive environments (like sea water) for long periods of time.

For example:

  A DFDR must obviously have a high degree of ‘crashworthiness.’ The
  first units were required to withstand a momentary shock force of
  1,000gs, the latest test standards now call for a test to 3,400gs for
  a duration of 6.5 milliseconds. The units also have to withstand a
  static crushing force at all of its six axis points of an applied load
  force of 5,000lbs for 5 minutes on each axis. Third, it must withstand
  a 500lbs piercing force test conducted by dropping it onto a ¼ inch
  steel pin from 10 feet. Lastly it must withstand a 1,100°C fire test
  for 60 minutes, and a 260°C oven test for 10 hours.

  It is also required that these units are mounted within the tail area
  of an aircraft, away from the potential crushing force of any engines
  mounted nearby. The DFDR must be watertight to a depth of 20,000 feet
  in sea water, and survive at this depth for 30 days - and it must be
  fitted with an underwater locator beacon which will act like a sonar
  transmitter, by ‘pinging’ a signal through the medium of water that it
  might be laying in.

Time has an article showing the Air France 447 flight data recorders resting on the bottom of the ocean (there are others there):

This particular FDR is pretty common, and weighs about 13.5 pounds1.

Without seeing the original interview, I suspect that the author of the article got confused during the interview and was told that radar could detect debris the size of a soccer ball that is floating in the water and at a different time mentioned that they would be looking for the radio signals emitted by the black box (which wouldn't even be detected by radar).

UPDATE:

That being said, there are black boxes that can float and even eject from the airplane when a crash is detected.  They seem to be more common in military aircraft, and there have been a few attempts to require them in the US (and even have the government pay the $60,000/airplane price) but the bills stalled in congress.  The lawmakers here have recently started discussing this again though.

Deployable Black Boxes have been around since the 60's and are a second set of black boxes meant to be a backup to the main ones.  They can be particularly useful when crashing into water or in the event of a major fire because they would not be within the main crash site.

Here are a couple of articles about them:

Lawmaker Calls for 'Black Boxes' that Eject from Planes
Canada’s ‘deployable recorder’ would have located missing airliner within minutes, experts say

1 See specifications on Honeywell's webpage and page 7 of their product description.


When and how do I align with the runway during an offset ILS approach?

Looking at my old approach plates, the ILS for Rwy 22R at KJFK of 24 JUL 1998 had an inbound course of 220°. The runway centerline was 224°, so a 4° difference. Decision height was 250'AGL.

In the 747, if we broke out before the decision height and had a clear look at the runway, we would in a shallow coordinated turn decrease our heading so as to intercept the runway centerline course visually and then we would visually turn onto and track the centerline.

The difficulty was when it was foggy, and all you could see near or at the decision height were the approach lights but not the runway sufficiently to visually acquire its course. You knew you had to correct to the right, but the tendency, at least for me, was to over correct because the approach lights were seemingly considerably off to the right, the more so the lower you were when you first saw them.

In the 747 you can safely use a 5° bank without dragging anything. As I remember the first thing to drag would be an outboard engine pod, but whatever. Thus, even up to the 100' call of the radar altimeter, a coordinated shallow bank would get you lined up, but you needed to be quick about it as your groundspeed would be around 160kn.

The first time I made the approach under those minimal conditions, I did indeed over correct. My choice going into the flare was enough left rudder and aileron to get the nose to the runway heading and then maintaining the 5° bank to slip back to the left. Having made the over correction that first time, I was careful not to repeat the mistake.

It's been nearly 20 years since I last shot that approach. I looked at the approach plate of 08 MAR 2012 on the Internet, and I see that they've straightened things out. The approach course is 222°, the runway centerline course 223°. Decision height is still 250' AGL.