As also stated in this answer:

Range is a function of MTOW and empty weight, according to the Breguet Equation for a jet:
$$R=\frac{V}{c_T} \cdot \frac{L}{D} \cdot ln\frac{W_i}{W_i-W_f}$$

with ${c_T}$ = specific fuel consumption, $W_i$ = initial weight, $W_f$ = fuel weight, $L$ = lift, $D$ = drag.

What increases range if other factors remain constant:

Higher speed $V$
Lower specific fuel consumption.
Higher lift/drag ratio.
Higher TakeOff/Landing weight ratio.

The weight ratio can be because of fuel weight used during the flight, but of course chucking ballast overboard helps as well.


What are the different types of take-off minima at the bottom of a Jeppesen airport diagram?

The used acronyms are defined in the Jeppesen charts legend:

CL Centerline Lights
RCLM Runway Center Line Markings
RL Runway (edge) Lights
RVR Runway Visual Range

The first column tells us that a takeoff is authorized with RVR in touchdown zone (TDZ), midfield (MID) and rollout (RO) of at least 150m, if the RL and CL are operational (except during snow, where 400m is required, and for runway 18, where 250m is required).
The second column tells us that takeoff is authorized, if the RVR is at least 200m with RL and CL operational. In this case not all RVR values need to be available (e.g. one of them could be inop).
The third column tells us that takeoff is authorized, if the RVR is at least 300m and RL and RCLM are available (CL is not required, except at night).
The fourth column tells us that takeoff is authorized, if the visibility is at least 400m and either RL or RCLM (day) / RL or CL (night) are available.
The fifth column allows taking off with adequate visual reference during the day with at least 500m visibility. The "adequate vis ref" is defined in the charts legend as:

ADEQUATE VIS REF (Adequate Visual Reference) — Runway markings or runway lighting that provides the pilot with adequate visual reference to continuously identify the take-off surface and maintain directional control throughout the take-off run.


How does a variable-sweep-wing aircraft keep wing-mounted payloads straight?

Mechanically this can be done using the simplest form of pantograph, as a hinged parallelogram with one end fixed to the fuselage and the other to the ordnance pylon. Or, I suppose you could implement a digital one.


How do I use the FAA's WINGS program as a flight review?

The FAA Safety Team's WINGS program allows pilots to bypass the traditional FAR 61.56 flight review by completing a "phase" of the WINGS program.  The program and requirements are detailed in FAA Advisory Circular 61-91 (currently 61-91J).

The short version is that a "phase" of WINGS consists of three credits of "flight activities" and three credits of "knowledge activities", which must be earned with a 12 calendar month period.

Flight credits are earned by flying with an instructor and demonstrating safe & proficient flying skills in specific areas of operation.
For example, one "Basic WINGS" flight activity (worth 1 credit) is demonstrating basic air work - forward slips, steep turns, rectangular course, S-turns, and turns around a point - to Private Pilot practical test standards.
When you have successfully completed a flight activity your instructor can log in to the FAA Safety / WINGS site and give you credit for completing the activity.

Knowledge credits are earned by attending seminars and classes - these can be in-person seminars set up by the FAA Safety Team, or on-line webinars.  Many of the AOPA Air Safety Institute online courses qualify for WINGS credit.

When you complete a phase of wings your flight review clock resets, and your flight review becomes due 24 calendar months from the date you completed that phase.

Ultimately participating in the WINGS program probably means you will be spending more than the "bare minimum" 1 hour of ground time and 1 hour of flight time that FAR 61.56 requires. While you can often complete flight activities in an hour (or much less if you're proficient) the knowledge topics often take longer: the webinars are typically 30-40 minutes each, and in-person seminars can easily last an hour or more.

The major benefit to the WINGS program is increased safety through building your knowledge and proficiency - the seminars are actually informative (and the in-person ones can even be fun, depending on who is running them), and the flight activities are pretty easy (though there are certainly challenging ones available if you want to push yourself and really sharpen your skills). Resetting the flight review is an enticement to encourage all of us to participate.


Why are the F/A-18 rudders deflected in opposing directions during takeoff?

Living Wing

The Super Hornet has a living wing, that is to say, the shape of the wing is constantly in motion throughout every regime of flight. Trailing edge flaps, leading edge flaps, stabs, rudders, and ailerons all move in concert to give the pilot the greatest control during particular phases of flight.

This is evident by the use of the flaps switch. The three flap positions are, Auto (Up), Half, and Full. Up auto means that the flight control system (FCS) will dynamically change the wing based on what it thinks the pilot is trying to do. However, when the flaps switch is placed in the half and full positions the FCS switches to landing mode, and all flight control inputs will be interpreted as such. Even though the flaps switch has been placed to half/full, the pilot has only changed the FCS logic, he has not actually commanded the flaps to a fixed position. There are no fixed gains (flaps positions) like there are in typical commercial aircraft. Instead, the computer adjusts the flaps position to mimic a flaps half/full position, while also giving the pilot the most stable platform it can for landing. The logic has its limits though and if the pilot exceeds 14 AoA in a landing mode (flaps half or full), the FCS may accidently depart the jet. This is obviously bad 200 ft above the ground.  This switch commands the FCS to make flight control decisions and is the toggle between the tactical, and landing modes of flight.

Rudder Toe-In

The particular effect you are referencing is called rudder toe-in. At slower speeds, particularly during high angles of attack, the stabilators may not provide sufficient nose authority to crisply rotate the nose. The massive wing area of the Rhino tends to block the airflow over the stabs. To remedy this problem the Rhino's rudders will automatically bias to the inside and create a downward force, which pitches the nose upwards. While the rudder is toed-in, the pilot can still use the rudders to yaw the aircraft. The FCS selectively moves the rudder position to generate the yawing motion, even while retaining the fared-in position.

Take-off and Landing

During takeoff the rudder will remain in the toe-in position for a fixed 10 seconds after it detects weight off the wheels. This prevents the aircraft from accidentally faring the rudders (and losing nose authority) during one of the most critical phases of flight (AoA probe failures will actually cause the rudders to automatically fare, and this problem is removed by a fixed timing.) During the landing portion of flight, the rudders will also be fared in to give the aircraft more nose authority, and this is handled automatically by the FCS once the pilot commands the aircraft into landing mode by placing the flaps switch out of up auto.

Other Functions

While the Rhino does have small speed brakes that extend during full speedbrake deployment, the primary method of increasing drag to rapidly slow the aircraft is through the use of the control surfaces. The FCS will increase the drag by lowering the flaps, toeing-in the rudders, lowing the ailerons, and deflecting the stabs, all while still giving the pilot a stable platform to fly the aircraft--it's an impressive aircraft.

During high alpha maneuvering, the Rhino will again deflect the rudders to the toed-in position while the flaps switch is in up auto. With the FCS logic in auto, the computers will attempt to retain control of the aircraft during max performance maneuvers, and will automatically schedule the flaps and rudders to compensate for high AoA and slow speed flight. Because the nose is cocked up and the airflow is disrupted over the stabs, the rudders will again create that pitching force that will assist the pilot in maintaining nose authority through any regime of flight.

Emergencies

As stated before, there are times when the rudders may suddenly fare themselves which can have devastating effects during the final portion to land. Rudder failures are serious problems and should be treated as such.  Higher landing speeds and extra caution will be used, and the pilot should understand that wave offs may be impossible due to lack of nose authority in close to the ramp.


If an aircraft decompresses at altitude will everyone start farting?

No, they will not.

In the case of a rapid decompression, an aircraft will make a very rapid descent to a altitude, and while I'm not a physician or an expert on these physiological and biochemical processes, I doubt very much that would be enough time for dissolved gases to be released into the digestive tracts.

Even if it were, a person who experiences a sudden accumulation of gas in the gastrointestinal tract may experience discomfort or even pain, but it takes a while for gas to make its way to an exit - as anyone who has suffered from trapped wind will know.


Was the Space Shuttle landing sequence executed manually or automatically?

Since that's really three questions, I'll address them separately.
1. Did the shuttle have or use autoland?
The space shuttle did have autoland capability, in theory. When the shuttle was being developed, it was imagined that flights could last so long that human pilots might get rusty, or have their ability to function under gravity impaired due to muscle atrophy from extended time in micro gravity.
Unfortunately, testing autoland on the space shuttle was a bit risky. If anything went wrong, the shuttle has no ability to disengage and go-around, and it might be too late for a human pilot to intervene and still make a safe landing.
They did try evaluating an incomplete implementation of the autoland on STS-3, where the lineup, final approach (outer glide slope), and preflare maneuvers would be performed by the autopilot, at which time the commander would take control and complete the landing.
The result was one of the worst landings in the history of the program. The autopilot was unable to maintain a stabilized airspeed, at first closing the speedbrake completely, then opening it again until airspeed was low, then closing again at 4000 feet which caused the orbiter to be too fast by the time commander Jack Lousma took over. He didn't really have enough time to get a feel for the aircraft or make corrections, so it hit hard and fast.
Afterwards, it was decided to discontinue testing of the autoland system, although the implementation was eventually completed.

Development of an automatic approach and landing system was terminated indefinitely due to the inability to implement an FAA [Federal Aviation Administration]-like powered aircraft certification program for an unpowered glider like the Space Shuttle. That is, an automatic system cannot be reasonably certified for an aircraft without a go-around capability in the event of an autoland system failure, because the only recourse in the Shuttle is to land rather than to execute a wave-off maneuver as in a powered aircraft. The practice of having to salvage a good landing out of a poor approach is not professionally accepted airmanship.
Further, the STS-3 experience was classified as a “late-takeover” action in which a failure of the autoland system in even closer proximity to touchdown could result in an upset too late in the landing phase to be reasonably recoverable. "Monitoring" the approach versus actually "controlling" it induces a time lapse in the mental-to-physical control conversion process which increases in criticality for manual takeover as the aircraft approaches touchdown. An automatic failure on the IGS, with no recourse for a wave-off, would be unsafe compared to a totally manual- controlled approach.

The quote is from NASA Johnson Space Center Oral History Project where Jack Lousma gives a great description of the flight and landing a little less than half way down the page.
The Columbia Accident Investigation Board Report did recommend testing the autoland system, but to my knowledge, it never was.
Just to clarify, the autopilot was used for most of reentry on every flight, but I believe your question was specifically about the final stages of flight and landing.
2. What sort of simulator was used for training?
So the shuttle was hand-flown for landing (a fly-by-wire system, so it's arguable that there's no true manual mode), and that means pilots have to be trained.
They were actually trained in several different simulators. There was SAIL (Shuttle Avionics Integration Lab) where they did serious integrated systems and software testing.
There were also fixed and motion-based simulators in Houston. These were collectively referred to as the SMS (Shuttle Mission Simulator). These were used for training for all phases of shuttle flights, not just landing. They were particularly useful for simulating contingencies, like an RTLS abort (return to launch site). It's similar to how simulators are used in the aviation industry to train for scenarios which would be too dangerous to train for in a real aircraft.

The motion-base SMS. Image Source
For nominal conditions, the best simulator for landing the space shuttle was actually another aircraft referred to as the STA (shuttle training aircraft). This was a modified Gulfstream II which would fly with its main landing gear lowered and thrust-reversers engaged to simulate the high drag profile of the orbiter. The left side of the STA cockpit was built to mimic the layout of the shuttle, including the heads up display.

Images from the STA's Wikipedia page
The STA was used for both training shuttle pilots and for evaluating weather conditions at landing sites on launch and landing days.
Lastly, there was also an on-orbit simulator that the pilots would use for practicing in the day or two before landing. It was basically a laptop with special flight-simulator software.
3. Is the simulator available in any flight simulators?
The answer depends on exactly what it is that you're asking. The actual software used on shuttle computers (written in HAL/S) is ITAR restricted, so it is not available to the public. Sadly, even the on-orbit simulator has never been released, to my knowledge.
However, there are several simulators which let you fly some or all of reentry and landing to varying degrees of realism.

SSMS 2007 is a pretty high-fidelity simulator, but has a horrible, not even remotely accurate, reentry and landing.
On phones and tablets, I love fsim Space Shuttle. It's decently realistic, but only lets you fly the subsonic portion of flight.
Orbiter, which isn't a shuttle-specific simulator, but there are shuttle plugins. I've flown several manual reentries in Orbiter, but you really have to know what you're doing or you won't make the runway. That's probably the best option if you're really interested in orbital mechanics, and a terrible option if you're not.
X-Plane has a Space Shuttle scenario, but it's not particularly realistic.
I know some people fly Shuttle missions on Kerbal Space Program, but I've never played with it at all so I can speak to it one way or the other.

Interestingly, the motion-based simulator from the SMS was donated to the Aerospace engineering department of Texas A&M, and it was discussed making the simulator at least partially available to the public. Unfortunately, I think they ran out of money to actually put the thing together and run it, so it's effectively just sitting in boxes in a room somewhere. They have a facebook page, but it's been a long time since I've seen any progress.


Why don't aircraft use nuclear propulsion?

TL;dr - too heavy :-)

It's just not a good energy source for something like an aircraft.

Nuclear energy is superb for instances where you need continuous output over a long period of time, for example a satellite, which is going to be there for years without maintenance or refuelling. A very small amount of nuclear material in an RTG such as those on Voyager 1 and 2 can provide heat energy that can be used to power the satellite. This model works in this use case because the only real alternative (solar power) hasn't anywhere near the output required as the Voyager craft fly ever further away from the Sun.

Also, submarines are a good use case - if you remain under the sea for months or even years at a time, diesel or anything that uses oxygen is not suitable, so a nuclear power plant is ideal.

But while for a satellite the power unit can be very small as the actual output power required is small, to power an aeroplane or a submarine you require a large power plant, and that will also require a lot of shielding (as a side effect of nuclear reaction is radiation...)

On a submarine, that's okay - weight can be dealt with, but on an aeroplane weight is key. You just can't do it efficiently and safely. You need shielding that can cope with a crash - which is going to be massively heavy, so you won't have any passenger or cargo payload left.


In which countries a medically unfit US pilot can fly?

It completely depends on the condition. Just because you're denied a FAA medical it doesn't automatically mean you can't get one to operate in another country.

For example, colour-blind pilots can fly up to First Officer level in Australia, and we have no mandatory retirement age. But we are stricter on things like head injuries.


Is there an increased concern for stall safety in a 1G steep turn?

To fly a 60-degree bank coordinated turn with 1 G on the aircraft, you'll be dropping like a rock.

But your stall speed with 1 G on the aircraft is what it is, regardless of how you obtain that 1 G -- straight & level, or coordinated turn with deceleration down to reduce the G loading, or inverted & pulling 1 G... the angle of attack that stalls your wing will be reached at the same speed in all of those cases.


Why can't planes use only flaps in the tail section instead of stabilizers?

Your question is partly covered here regarding why the vertical stabilizer is important. The empennage (tail surfaces) of conventional planes provides both passive and active stability. Like the feathers on an arrow (which is where the word empennage comes from), they help the airplane to remain pointed in the direction of flight as well as providing active control surfaces. The cost of providing stability is added weight and drag, but if the surfaces are removed, the stability aspect will need to be provided manually, or alternately. This is how unconventional aircraft like the B-2 flying wing, or even modern fighter aircraft, are able to fly.

So, yes, we can fly airplanes without conventional tail surfaces. Some designers like Burt Rutan have created unconventional designs for general aviation. However, design changes will also have drawbacks. At the very least these designs behave differently than conventional planes, which requires special attention. The strange appearance is also reason for some pilots to distrust them.

If the plane is going to be unstable without computer control, that introduces safety problems. In military aircraft the pilots can eject when issues arise. But unlike modern commercial planes, the pilots cannot simply take over control if the computers fail.

There is also an aerodynamic issue with what you propose. Conventional control surfaces deflect the entire surface, so air continues to flow past both sides. However, if you only deflect one side of the surface, air is only flowing past the outer face. This acts like a spoiler and creates extra drag. Though this drag will be the force controlling the plane, it is not as efficient as moving a control surface. As Peter Kämpf pointed out, it is much more feasible to increase the effectiveness of the existing surfaces than to eliminate them.

Modern airliners represent a compromise between efficiency and safety based on currently available technology. Although alternate designs have been proposed, these configurations create their own unique problems.


How is the Cessna 172S G1000 Electrical System powered?

It would appear that there is a standby battery controller PCB.  It's important to note that M BUS VOLTS are read off the crossfeed bus as there is no main bus.  The label is a bit misleading in my opinion.  It's been awhile since I have flown a G1000 C172 but if I remember correctly you should not see 1.5volts on the M BUS VOLTS but zero.

The checklist is verifying the PCB box doesn't have a fault that will allow the standby battery to power more than just the essential bus.  Unfortunately, the POH is silent as to why this check is done.


What causes the vortex on the tip of this vertical stabilizer (CFD Simulation)

The subtitle of the video states:

  This video shows a high-fidelity CFD simulation of flow control applied to realistic wing profiles using PHASTA and ParaView Catalyst. Work done by Michel Rasquin from Argonne and Ken Jansen from UC Boulder.

Realistic wing profiles sounds like: we're actually looking at a wing in a vertical orientation - or in a horizontal orientation from a viewpoint that causes some confusion. Looking at a wing at some Angle of Attack that creates lift, and therefore the visualised flow pattern. And then the two vortices are caused by the end effect of finite wing span.


Does any one know if the PFD or ND or any other screen on an commercial aircraft work like a computer or something else?

All multi-functional displays in modern avionics are just computers. Typically, they are only responsible for presentation of the supplied information, but may do some processing: for example, display certain alerts in the right conditions. Also, they manage some of the user pilot input and mode switching.

G1000 PFD diagnostics page

Nearly all the data comes in on digital bus(es), in aviation most commonly ARINC 429 or even Ethernet with a custom protocol.

Bare sensors either have a dedicated microcontroller that converts the readings to a digital format, or are connected to a dedicated processing unit (also a specialised computer), such as ADC (Air Data Computer) which collects and processes all the air-related data (airspeed, altitude, temperature, etc.)

Even then, typically, this semi-processed data don't go to displays directly. All the sensor data are collected by a sort of integration unit (e.g. GIA for Garmin systems), which does most of the processing and decision making. Then, the necessary information is relayed to the displays.


When do I have to contact Centre when departing/arriving at an airport with an ATF?

The Aerodrome Traffic Frequency is a frequency for aircraft to use to aid self-sequencing at airports where a control tower is not operational. Another name for it is the Common Traffic Advisory Frequency. 122.8 MHz was the original frequency designated for UNICOM use and remains one of the more common ones.
The APP/DEP frequencies listed tell pilots that, if they desire to talk with ATC (as IFR flights probably would!), they need to contact Montreal Centre on 135.025 once airborne. Montreal Centre is also the arrival frequency that would help IFR arrivals get established on an instrument approach procedure, if one existed. Centre most probably does not have radio coverage to the ground on this frequency, and even if they did they would not provide towered-airport control services.


Are there any LSA aircraft that can be flown IFR in IMC?

Sorry to reanimate this rather old question, but I'm surprised none of the previous answers mentioned the Evector SportStar MAX, which has a model that is IFR equipped and which was available several years before this question was asked. From its POH (section 1.2):

  Certification basis

  SportStar MAX complies with the ASTM F2245-07a Standard Specification for Design and Performance of a Light Sport Airplane, issued by ASTM International Committee F37.

  IFR version complies with FAR 91.205 requirements, ...

Here's a Plane & Pilot review of the IFR version, and here's a Press Release from Evector about this model.

Evektor followed the MAX model with the Harmony, and at least one place on their website suggests it too is available in an IFR equipped version.


Why do shockwaves progressively move aft as speed increses?

The answer is deeply rooted in the theory of compressible fluid dynamics, so for a fully satisfactory take on the matter you might want to refer to a textbook on that topic (such as Thompson or Shapiro). I will try to give a qualitative explanation.

For our discussion here, let's consider a shockwave as the way to abruptly slow down a supersonic flow and recover pressure; abruptly, because, since disturbances cannot propagate upstream in a supersonic flow, the flow has no way to "know" that the disturbance is coming and it isn't able to "smoothly" accomodate it (as it happens in subsonic flow). A disturbance here is, for example, the presence of the airfoil and its effect on the velocity and pressure fields.

Let's have a look at your picture. In a) the flow is subsonic everywhere and we have no particular issues with that (although we might want to consider some compressibility corrections).
Now, the flow accelerates over first portion of the upper surface of the airfoil, so the speed of the flow there is greater than the speed of the free stream flow (and greater than the speed on the lower surface, so we can have lift).
We can see that for free stream Mach numbers $M_\infty$ (ie flight speeds) close to 1 the flow over the upper surface can actually reach local Mach number $M$ of 1 and even above, because of that acceleration.
This is exactly what has happened in b): here $M_\infty$ is greater than the critical value (usually given as 0.8) and there is a supersonic bubble right there in the middle of the upper surface.
The flow downstream, however, is still subsonic, therefore it has to slow from the supersonic condition it reached and to do so a shockwave appears. This shockwave usually interacts with the boundary layer, adding a very high adverse pressure gradient to the one already experienced towards the trailing edge, so the boundary layer will most likely separate, leading to stall.

As we increase the flight speed, more and more of the flow over the airfoil becomes supersonic, also on the lower side, therefore the shockwaves "travel" downstream until, close to $M_\infty = 1$, the whole flow on the airfoil is supersonic, as in d).

As you can see from c), the shockwave on the lower side actually overtakes the one on the upper side. This is because the lower side is usually "flatter", so the shockwave appears later (ie at higher $M_\infty$) since it experience less acceleration (which is due to the curvature), but it also experience less deceleration towards the trailing edge and the local flow will be supersonic over a longer distance along the lower surface.

For even higher flight speeds, a detached shockwave appears in front of the airfoil: the purpose of this wave is to "turn" the flow around the airfoil. As the flow is supersonic, this turning of the flow can't happen "smoothly", but like we said it is the shockwave that abruptly accomplishes it.
The flow behind this curved shock is still supersonic (except for a region right around the nose of the airfoil) so later downstream we once again find the shockwaves which help the flow go back to its undisturbed free stream conditions.
The detached wave significantly increases drag; in some application this is optimal (eg in the atmospheric re-entry of a spacecraft), but it is detrimental for supersonic flight. This is why supersonic airfoils are designed to have a sharp trailing edge, so that the turning of the flow can be accomplished by oblique shocks attached to the edge, resulting in less drag.

As to answer your last question: where does the shockwave position itself? The answer lies in the boundary conditions, that is to say the conditions that have to be restored downstream of the airfoil: these will be the free stream speed and pressure.
Without going into much details about the variation of pressure with velocity in compressible flows, let's just say that the shock position is such that afterwards the flow has enough "space" left to recover subsonically. So, say you have to recover to a pressure of 1 to the freestream pressure of 10 (random numbers with no meaning) at a certain distance downstream from the airfoil: if the shockwave increases the pressure to 6, it will be positioned in such a way that after the shock (where the flow is subsonic) there is enough space for the pressure to increase "smoothly" (subsonically) by 4 and restore freestream conditions at that distance.
The increase of pressure across a shockwave is given by the shock strenght and can be seen as proportional to the Mach number, so at higher Mach the shock is stronger, the pressure recovery is higher and the shock will position further downstream, since the flow will have less pressure to recover subsonically and can do so over a "shorter" distance.


How does the reverse thrust work while landing?

During the landing reverse thrust of an aircraft engine is seen that the compressor fan rotates in opposite direction

This is wrong

Reverse thrust does not reverse the rotation of the fan/compressor/turbine.

Reverse thrust "simply" redirect the airflow coming out of the turbine in the reverse direction (well, almost, as we'll see in a moment) w.r.t. the usual one.

In the image you posted, the thrust reversers are deployed, and you can see them circled here:

The airflow is the coming out not from the back of the engine, but from the sides, slightly directed forward. The thrust (i.e. the force that the airflow is imposing on the aircraft) is directed backwards, while normally is directed forwards, it is then reversed.

This is nicely illustrated in this image (source)

NOTE: there are different typologies of thrust reversers, this is only one of them, but none of them require spinning the engine in the opposite direction.


How do mixed-bag-of-hardware military coalitions handle communications, IFF, et. al. interoperability?

You do multinational exercises

This is a good question that was in part answered for some NATO and neighboring countries under a program called the "Partnership for Peace."  That's one of many methods various nations have used to exercise and practice interoperability, which includes figuring out the communications play.  SEATO was another regional interoperability vehicle, as is OAS.

The first exercises I got involved with (mid-to-late 90's) were Non Combatant Evacuation Operations and Peace Keeping exercises with former Warsaw Pact countries.  It was very much a crawl, walk, jog, trot, run, sprint development model.  It doesn't happen overnight, but exercises, practice, training, and extensive military-to-military contacts go a long way toward identifying what is and what isn't interoperable.

As to "swapping IFF boxes" that's rather pointless.  You can develop procedural control for (Return to Force)RTF procedures, and you  have to accept that in a lot of cases you can't use encrypted comms.  What you do as a group is develop a comm plan that uses generically common radio equipment (do we all have VHF? Yes? No?).  Each operation will have its own wrinkles and details.

You build on previous multilateral operations like UN Peacekeeping

Since the UN stood up in 1945, over a hundred nations have some experience in contributing forces and equipment to UN Peace Keeping operations, and to other UN combined operations (like the UN Operations in Bosnia before 1995, or the peace keeping in the Sinai forever).  With this experience, nations have built up some "lessons learned" as a base for working with each other.

There is no easy button; you have to do formal planning

You don't just show up with your five helicopters, say "We are here!" and get to work right away.  Your air force staff will be in contact with the other countries' air force staffs and a communications plan will be established.  A general layout for forces will be agreed, such as "who goes where?" and it takes detailed effort to establish that.  A whole host of other details get ironed out like how to get the fuel to the airfield. (See problems in Rwanda, 1994, for a prime example of the nightmare that can be).

Military Planning, both long term and short term, is an art in and of itself. (It's painful -- been-there-done-that-got-the-t-shirt -- but it must be done).


How does the battery master switch activate the battery contactor in Cessna 152?

I think two of my premises were wrong.

The battery contactor is activated by connecting the left contact to ground (instead of 24 V as I thought). It works different from the starter contactor (which has a permanent ground connection).
The battery master switch toggles between ground [on] and floating [off] (instead of primary bus [on] and ground [off] as I thought).

Like this, the plane will be able to start!


What happens if you take off with a direct tailwind?

Given how few bounding criteria you have in your question, the general result is

For fixed wing aircraft: your ground speed will be significantly
higher than if you'd taken off heading into the same wind, and thus
you'll tend to use up more runway before lifting off.

Example: with a take off speed of 100 kts, going into or downwind is the difference between 90 knots or 110 knots ground speed before reaching take off speed when the wind down the runway is 10 knots.  This difference becomes more pronounced as wind speed increases; it's a differential of 2 x wind speed.

With a long enough runway it won't matter in terms of "taking off before running out of runway."  On a short field it may matter a great deal.
For Rotary Wing aircraft: you may need a bit more power to hover when
lifting off with a tail wind.  The FAA has this guidance:

  Headwinds are the most desirable as they contribute to the greatest
  increase in performance. {snip} When taking off into a headwind,
  effective trans lational lift is achieved earlier, resulting in more
  lift and a steeper climb angle. When taking off with a tailwind, more
  distance is required to accelerate through translational lift.

For a variety of aircraft types, if the tail wind is high enough your manual will recommend against/prohibit down wind takeoffs, but that varies enough between models and types that a general answer can't encompass all of the variations.


Why burn fuel at departure airport instead of flying to destination before emergency landing due to deflated tire?

I have no idea what a deflated tire indication is on a 737, but perhaps the news media got something wrong in their reporting. (Nah... that never happens, does it???)

That said, the cardinal rule of landing gear problems is to leave a good configuration alone, so don't retract a gear with a possible problem, since it might not come back down again.

With the landing gear extended, your fuel burn per mile is far greater than with the gear up, so "enough fuel to get to XYZ" (based on normal gear-up cruise) isn't nearly enough to get there with the wheels down.

Any time an airliner takes off from a field they couldn't return to (most often, this comes up because the weather isn't good enough for a published approach back in), they have a "takeoff alternate" that they could get in to within a prescribed distance -- typically an hour's flying time.


What is Tropopause height, and how is it determined?

According to Wikipedia, the World Meteorological Organization defines tropopause as

  The boundary between the troposphere and the stratosphere, where an abrupt change in lapse rate usually occurs. It is defined as the lowest level at which the lapse rate decreases to 2 ˚C/km or less, provided that the average lapse rate between this level and all higher levels within 2 km does not exceed 2 ˚C/km. Occasionally, a second tropopause may be found if the lapse rate above the first tropopause exceeds 3 ˚C/km.

The tropopause height varies with latitude and season. The variation with latitude, based on annual mean conditions, is shown below:

Image from das.uwyo.edu

Troposphere can be identified only if the lapse rates (the rate at which atmospheric temperature decreases with increase in altitude) in the stratosphere and troposphere are known. Also, weather phenomena like thunderstorms shift the tropopause. As a result, the height of the tropopause is forecast based on localized weather conditions, and is not a fixed boundary.

The International Standard atmosphere, however, defines tropopause as lying between ~11,000 and 20,000 meters (geopotential altitude) above MSL.


Does an SVFR clearance extend to Echo surface extensions?

This is an answer to the question provided by my checkride examiner Barry Lloyd

On 01-26-2010, a query asking whether SVFR is available in Class E extensions was routed to FAA ATC Headquarters. Below is a response to that query from the FAA ATO Western Service Center:

"Our opinion is:

FAR 91.157 (a) ..."special VFR operations may be conducted"..."within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport." This permits SVFR clearances within the vertical extension, not the lateral/horizontal extension of an airport designated surface area.

FAAO 7400.9T par 6002. Definition of Class E2 airspace: "The Class E airspace areas listed below are designated as a surface area for an airport."

FAAO 7400.9T par 6004. Definition of Class E4 airspace: "...airspace extending upward from the surface designated as an extension to a Class D or Class E surface area."

The language in FAR 91.157 exactly matches the language in FAAO 7400.9T par 6002. Par. 6004 does not match and the FAR does not permit SVFR operations in the lateral extension of a surface area designated for an airport; only within the vertical extension.

Presumably this could be corrected if we indeed want to provide for SVFR within lateral extensions, but it is currently not permitted.

There are other operational issues involved: eg. an extension to a Class D surface area where the tower provides SVFR services within the Class D airspace as is permitted via LOA. They cannot issue a SVFR clearance in the E4 extension. If permitted, the controlling agency, presumably the ARTCC would have to do this.

Our opinion is that E4 airspace is not part of the airspace designated as the surface area for an airport. The surface area for an airport is D, C, or E2. Extensions are treated differently from surface areas designated for an airport, ie there is no communication requirement. In addition extensions, by definition in 7400.9, are not airspace designated as the "surface area for an airport"."


Is it possible to survive a free fall from an airliner at cruise altitude?

Chances are you would not survive but lets explore this a bit more in depth for the sake of education.

This article from popular mechanics explores the very issue. There is some research that has gone into the topic of hitting the ground but the research is rarely about cases from the height you are asking about (~30,000ft). Some relevant info

First off at that altitude you really can't breathe that effectively so hypoxia will be your first concern followed closely by extreme cold.

Hitting water:

  Studies of bridge-jump survivors indicate that a feet-first,
  knife-like entry (aka "the pencil") best optimizes your odds of
  resurfacing.

Hitting the ground:

  The question of how to achieve ground contact remains, regrettably,
  given your predicament, a subject of debate. A 1942 study in the
  journal War Medicine noted "distribution and compensation of pressure
  play large parts in the defeat of injury." Recommendation: wide-body
  impact. But a 1963 report by the Federal Aviation Agency argued that
  shifting into the classic sky diver's landing stance—feet together,
  heels up, flexed knees and hips—best increases survivability.

Your best bet for surviving the airplane break up is if you are stuck in a situation similar to that of Vesna Vulović who did survive the situation you describe. Unfortunately there is some debate as to what actually happened so take the info at face value.

  “Speed has never killed anyone. Suddenly becoming stationary, that's
  what gets you.”  ― Jeremy Clarkson


Do manufactures list the maximum speed of an aircraft based on its theoretical maximum speed or dive speed?

The 365 knots listed in that brochure is (as noted in the text) the maximum cruise speed. That is the maximum speed at which the aircraft can be expected to operate under normal circumstances in level flight. It is not related to the Never Exceed speed, which depends on the structural limits of the aircraft (as well as air pressure and atmospheric conditions etc.). The maximum cruise speed is interesting for planning purposes, as it gives you an indication of how far you can expect the aircraft to go in a certain time window. It is not, however, very interesting to pilots, who will operate the aircraft with regards to the actual structural limits.


Do small airfields provide ATIS? If not, what weather reporting service is available?

There is no minimum definition of a "terminal" in and of itself. The "destination terminal" of a flight is simply its planned endpoint. That's usually, but not always, a man-made complex designed to facilitate human flight, which we call an airport. However, you can file a VFR flight plan to fly out to a friend's fallow field in BFE, miles from any airfield listed on a sectional:

It's then your responsibility, as it always is in VFR, to ensure you can operate the plane safely at all times, including getting the plane on the ground and then back up in the air without causing personal injury, property damage, infringing private property rights, violating noise ordinances, etc.

Sectional diagrams use the term "airport" to refer to any place that is registered with the FAA to be used for the purpose of aircraft takeoffs and landings. These places may be more specifically called airstrips, airfields, air parks, aerodromes etc to indicate relative size, construction, ownership or facilities.

The only requirements for an airport to be documented by the FAA and appear on a sectional are:

The location must meet minimum guidelines specified in the Airport Certification Manual, including land grading for smoothness and drainage, obstruction/obstacle clearance in three dimensions, and minimum safety markings and wind/traffic pattern indicators that are necessary to support aircraft takeoffs/landings at the location (really the only thing every airport requires along these lines is a windsock; everything else is provided as needed for the specific location or as desired by the field's users). This usually requires a minimum amount of maintenance/upkeep by its owner for the purpose, even if it's just a grass field (it would have to be regularly mown and weeded to remove certain spiky or wood-stemmed plants, for instance).
The location must be registered with the FAA by its owner/manager for this purpose (they can register it as a reserved/private airfield, and then only limited information will be given on the sectional, primarily as an advisory that the location is available for emergency landings).

That's all there is to it. Besides a windsock which is the absolute minimum, no minimum facilities must exist; even the traffic pattern/landing direction indicators are optional if traffic can always use a left-hand pattern and determine the runway approach from the windsock. Rhome Meadows Airport (T76) between Fort Worth and Decatur, TX is a grass strip, with no lights, no tower, no fuel, no hangars, and the displaced threshold on the south end is marked with two white painted tires (no threshold markings to the north). Nearby Heritage Creek Airstrip is only slightly better, with low-intensity runway edge lights. Despite this, both are fairly active for unimproved strips, with about nine flights a day involving each one in some way (TO/L, T&G).

Here's the airport section of the legend for FAA sectionals:

You can see that there's a wide array of symbology available to indicate at a glance what the facility offers; control tower or no, length and configuration of hard surface runways if any, usage type, presence of FBOs for fuel/maintenance, navigational aids, and radio information including ATIS, AWOS, ASOS, control towers, UNICOM etc. Obviously a control tower needs a radio frequency, but there is no requirement that a towered facility have ATIS. ATIS is usually found at towered airports as its purpose is to reduce controller workload, but nontowered airports can have ASOS/AWOS stations which provide practically the same information regarding weather, without the superfluous runway information (at nontowered airports, the pilots usually determine the approach/departure direction). If an airport has no reporting whatsoever, you would usually tune to the nearest listed AWOS/ASOS.


How can the F-15 and Su-27 achieve a high top speed without variable wing geometry?

They simply have enough thrust to do so with their given wing. There is no rule that high speeds are associated with variable sweep wings or that you need such a wing to go fast. As a matter of fact many of the testbed super sonic aircraft
as well as the really high speed stuff dont have swept wings.

Wing design can effect efficiency (which may or may not be a concern in fighters) and can limit top speeds but that simply means that for a fixed shape wing it must be optimized for a desired speed range.


Going by probability it's likely a KC-130 as there are quite a few of those in the world. The recognition feature would be that it has four teardrop pieces of underwing gear with the external fuel tanks inboard and the drogue refuelling systems on the outboard.  There are no other obvious lumps or bumps in the picture to indicate other mission equipment such as cameras or weapons systems to narrow down which particular variant it could be.


What is the use of saw-teeth present on the nacelle outlets of modern turbofans?

These "saw-teeth" or "chevrons" or even "acoustic liners", are there to help reduce noise generated from the operation of the engine.

As hot air from the inner core of the engine mixes with the other, cooler air, it generates noise. These "saw-teeth" are there to help smooth that mixing, thereby generating less noise which is the result of turbulence. These are seen on the Boeing 747-8 (as seen in your picture) and the Boeing 787.

The reduction of sound generated means that less noise insulation is needed for use in the fuselage of the airplane. Less insulation means less weight. Less-weight equals less fuel burn, which means that chevrons are great for passengers, and economics.

There's only one difference from your picture. As much as we would like them to blow kisses to everyone, that's not what they are there for. :)


Sounds like that plane has (or once had) an STEC autopilot installed - CWS stands for Control Wheel Steering - basically it allows you to set a pitch attitude / turn rate using the yoke, which the autopilot will then maintain until instructed to do otherwise.

If the autopilot is still installed you also normally use the CWS mode as part of the preflight routine to get the autopilot to activate so you can make sure you can overpower it (details on the preflight as well as using the CWS feature can be found in the autopilot manual, which should be with the POH).

If the autopilot is no longer installed the switch technically should have been removed with the rest of the system and a blanking plate installed in its place.


Electromagnetic waves propagate actually using different means at the same time:

Space wave (direct line of sight)
Sky wave.
Ground wave (or surface wave)

Space wave vs sky wave vs ground wave

Note: Electromagnetic waves are not entirely understood. The terminology around ground waves varies with authors. Some authors don't make a difference between space and ground wave, they just consider both as the ground wave. This is not the case here.

The sky wave propagation develops at night and extends the range of LF/MF frequencies. The sky wave is the result of reflection in the ionosphere, the upper layers of the atmosphere, at an altitude between 100 and 300 km.

NDB range is increased, but VOR and DME range are less impacted. While range is increased by the sky wave, perturbations appear, changing the relative bearing of the NBD signal, decreasing accuracy.

HF radio transmission (voice) range is also increased, as the effect exists regardless of the modulation or use.

Frequency spectrum overview

To facilitate the understanding, we need to have an idea of the whole radio spectrum of waves and how aviation uses this spectrum.

Sky wave

The sky wave propagation takes benefit of the possibility for EM waves to be reflected in the atmosphere.

Light is an EM wave, and it can be reflected by a smooth surface: Metal, glass and water are good reflectors. This is the same for other radio EM waves. A good mirror for radio waves is a layer of ionized atoms. Atom ionization consists in losing or capturing one of more electrons, and becoming electrically unbalanced.

Natural ionization occurs in the ionosphere under the bombardment of solar rays. This takes place in the F-layer at about 300 km, and in the E-layer at about 100 km. Waves can be reflected by these layers when they are active.

However the D-layer just below blocks waves during the day because of the ionization of nitrogen monoxide $\small NO$), with a maximum below the frequency of 10 MHz. This effect decreases at night when the source of ionization disappears.

The higher layers are ionized more and more longer than the lower ones, and ionization persists more in the higher layers. The combined effects of D, E and F layers leads to

An absorption of LF/MF/HF frequencies by the D-layer at daytime, preventing them to reach the E and F layers able to reflect them.
A reflection at night and twilight when E-layer and above all the F-layer are still active and the D-layer has ceased blocking waves.

Sky wave propagation

Because the sky wave proceeds by "skips", it is more effective at specific distances from the transmitter and is characterized by minimums and maximums spaced along the direction of propagation, the distance between maximums depending on the frequency.

Remarks:

Because low frequencies are the only ones subject to sky wave propagation, over-the-horizon (OTH) radars use them instead of SHF.

Over-the-horizon radar. Source.
There is some controversy about the role of the US HAARP project in creating artificial ionized mirrors to use "sky wave" during the day (manipulating atmosphere is prohibited by international treaties).

As the propagation of NDB frequencies is augmented at night by the sky wave, a NDB can be detected at a greater range by a receiver. This is also true for other mode of communication in the same range of frequency (e.g. voice communication in HF over the oceans).

The sky wave propagation is associated with a slow variation, the signal can disappear and reappear a few seconds later. This is due to the instability of the reflection, the heterogeneity of the atmosphere layers, and the recombination of waves after a multi-path trip and a rotation of the polarization. This fluctuation is globally known as fading.

While sky wave propagation is in general a good thing but, like any other multi-path phenomena, it also has negative effects: It changes the polarization of the waves and the direction of the wavefront. As ADF works by detecting the direction of the signal wavefront, a reflected NDB signal introduces inaccuracy in the ADF indication.

The beacon seem to move, and the bearing is not reliable. Some cross check is necessary to confirm the validity of a bearing.

The ground wave propagation encompasses reflection on ground and obstacles, diffraction on obstacles and horizon, and refraction thanks to current induced in ground.

Because of the refraction and diffraction, this mode of propagation tends to follow Earth curvature, but it mostly affects LF and MF, higher frequencies (e.g. VHF and UHF) do not really take advantage of this propagation.

The ground wave is due to several factors which slow down the wavefront where it is closed to the ground (the wavefront is a moving spheroidal surface around the transmitter where the wave has the same phase, the wave propagates perpendicularly to its wavefront).

Ground wave: Wavefront slowed down by ground

As the wavefront is vertical at a longer distance, communication distance is increased.

However as the ground wave progresses, its slowed down wavefront is less and less vertical and the effect less and less significant.

Electromagnetic waves are composed of two fields: electric and magnetic, which are perpendicular and normal to the direction of propagation. The wave polarization, that is the plan where the electric field oscillates, considerably influences the ground wave attenuation. Vertically polarized waves (NDB and HF voice communication) propagate better than horizontally polarized waves (VOR variable signal).

The ground wave propagation, like the direct wave propagation, occurs any time, day and night.

Space wave, direct line of sight

A word about space wave propagation: While it's true this is a direct line of sight communication, it's also a simplification. Space waves are usually reflected, diffracted and refracted, exactly like visible light. So the space wave propagation happens without direct line of sight too. This is what allows cell phones to work in cities and/or indoor.

There is a lot of attenuation associated when the wave direction of travel is changed, and usually the wave follow different directions at the same time, some recombining at the receiver location after having traveled a different distance, hence arriving with a different phase (multipath propagation).

Multipath has been difficult to deal with in the era of analog transmission. To prevent significant attenuation limit the power of the transmitter and the size of the aerial, critical transmission channels, like terrestrial high-band radio links have been carefully designed with a Fresnel zone clear of any obstacle, limiting communication towers implementation to specific locations.

With digital modulations (and ease of implementation of fast Fourier transform algorithm in modern electronic circuits) space wave communication is now more easy to manage and these constraints are a bit relaxed.


I can think of a couple of open source UAV projects:

Paparazzi is a complete system of open source hardware and software for Unmanned Aircraft Systems, including autopilots and a ground control and planning station. All of the hardware plans and software source code you need to make a drone from scratch are available on github. But not everyone has the equipment to make a printed circuit board at home.
Open pilot is an autopilot for UAVs. They also sell hardware if I remember properly, which might make it a bit easier if you're just starting.

If you just want a simple introduction to flying drones, DIY drones has a quick guide to the basics.


Navigation Fixes

The words that you are hearing are navigation fixes that are published on the pacific crossing charts.  They are used so that aircraft can report their position to Air Traffic Control using a standard, easy to say name that is located at a specific geographic location.

You can think of them like street intersections.  Instead of saying 29 degrees 44 minutes 18.8 seconds North, 95 degrees 24 minutes 38.5 seconds West (GPS coordinates), you would say the intersection of South Shepherd Drive and West Alabama Street1.  In the case of aviation though, they take it one step further and give it a five letter (usually) pronounceable name like the ones that you are hearing on the radio.

The navigation fixes that you refer to are standard reporting points located on airways going between the SW coast of the US to/from Hawaii:

GALIP and DIALO are on R576 (outbound airway)
GITLE is on R585 (inbound airway)

To see an actual chart and to follow along, the FAA offers IFR Enroute Aeronautical Planning Charts on their website (these would be on the PORC chart).  Here is a low resolution excerpt from the area that we are talking about:

A typical flight will file an airway with only the start and end fixes along with the airway name instead of specifying every fix on the route.  For instance, it might look something like GALIP R576 OGG which tells ATC that they will fly directly between all of the fixes on the airway: GALIP DADIE DIALO DUSAK DRAYK DENNS OOG.  The filled in triangle at each of these fixes means that it is a mandatory reporting point, and they will be required to make a position report every time that they cross one.

Position Reports

Position reports are given in a standard format specified in the AIM 5-3-2:

  d. Position Report Items:

  1. Position reports should include the following items:

  (a) Identification;

  (b) Position;

  (c) Time;

  (d) Altitude or flight level (include actual altitude or flight level
  when operating on a clearance specifying VFR-on-top);

  (e) Type of flight plan (not required in IFR position reports made
  directly to ARTCCs or approach control);

  (f) ETA and name of next reporting point;

  (g) The name only of the next succeeding reporting point along the
  route of flight; and

  (h) Pertinent remarks.

Example (from 5-3-1):

  (Name) CENTER, (aircraft identification), (position), (time),
  (altitude), (type of flight plan), (ETA and name of next reporting
  point), (the name of the next succeeding reporting point), AND
  (remarks).

Or a better example:

Los Angeles Center, N1234, over GALIP at 1645, Flight Level 370, Estimating DADIE at 1730, DIALO next

Then, when they get to DADIE, they do it all over again:

Los Angeles Center, N1234, over DADIE at 1730, Flight Level 370, Estimating DIALO at 1818, DUSAK next

This continues until the aircraft is identified on radar again at which time they can discontinue reporting unless specifically requested by ATC.

1 Mapped here for the curious.


Why does this statement about intrastate aviation in Alaska appear in airworthiness directives?

It's there because the law requires it. 49 USC 40113(f):

  (f)Application of Certain Regulations to Alaska.—
  In amending title 14, Code of Federal Regulations, in a manner affecting intrastate aviation in Alaska, the Administrator of the Federal Aviation Administration shall consider the extent to which Alaska is not served by transportation modes other than aviation, and shall establish such regulatory distinctions as the Administrator considers appropriate.

Alaska relies on aviation to reach certain communities, and so Congress requires the FAA in its rulemaking process to consider whether aviation rules should be different for Alaska based on whatever it considers to be "appropriate." The cost/benefit ratio for a safety regulation could be different for Alaska—grounding certain aircraft may cut off some areas entirely—, so the FAA is required to at least think about the effects of their decisions on the state.

The above assertion is a statement that they've considered Alaska when issuing the airworthiness directive and decided it should apply the same there as everywhere else.


Engine oil in quart plastic bottles is considered to be good for 10 years unopened.

The Exxon document here lists a 10-year shelf life for each of the oil products listed when stored in unopened, undamaged quart containers between 0 and 40 degrees C (32-104 degrees F).


Are there ever temporary flight corridors?

Flight corridors (airways) are just standard routes to simplify communication from controllers to pilots when describing where they should fly and between controllers when handing over flights. But the controllers can assign arbitrary vectors (headings and altitudes) to aircraft whenever they see fit.

So there is no need to formally set up a temporary corridor. If the traffic for whatever reason does not fit the usual corridor, the controller will simply assign any free vector and explain the situation to the next controller. They do that all the time anyway.

However in non-radar environment (e.g. oceanic or in case of radar failure) airways become important tool for the air traffic control, because it would not be feasible to keep track of positions of all the aircraft on ad-hoc routes. With airways the controller knows which airways intersect so planes on them need to be separated vertically and only needs to track the aircraft progress in one dimension (along the airway) instead of two (on map).


What is the best way to align with centerline on final, rudder or slip?

Your method #2 is consistent with current FAA doctrine, and when practiced yields acceptable results.

Rudder for longitudinal axis alignment (parallel) with the centerline.

Aileron for drift.

Have a stable approach, and maintain vigilance of both inputs when on low final.  If you practice the technique for your entire final approach, you get extra practice time, and may master the technique faster.

FAA has a publication, On Landings I  (and also a II and III publication) which are all great at describing the technique.  Every student should have a copy for review.  FAA-8740-48  a copy is here: https://www.flyingd.net/documents/on-landings-part-i.pdf

To answer a comment...if you are left of the centerline, and there is no wind, and your approach is stable, then you need some right aileron to get your longitudinal axis over the centerline, and you will have to adjust your rudder while maneuvering, to keep the longitudinal axis aligned and at least parallel to the centerline.

Drift with aileron, alignment with rudder. Constantly modifying input to get the desired drift and alignment.

Aileron for drift.

Rudder for alignment.

Pitch for airspeed.

Power for altitude.


Why can a plane land in zero visibility conditions but not take off in zero visibility?

Using a HUD, an airliner can take off with visibility as low as 300’, and land with visibility as low as 600’. Without a HUD, you need 500’ (and appropriate runway lights/markings, plus regulatory approval) for takeoff, and whatever your autopilot Cat III autoland system (along with the landing runway) is approved to for landing. (Or 1800’ for cases of no Cat II / Cat III capability.)

As noted, a pure “zero visibility” landing (a Cat IIIc) doesn’t yet exist, because while the autopilot can bring the aircraft to a stop on the runway, some visibility (300’) is still required to taxi clear and get to the parking spot.

Thankfully, visibilities below 500-600’ are pretty rare in most places. Not all airports have the taxiway lighting required for low-visibility (typically, below 1200’ lateral visibility) taxi operations. That is an airport limitation, not an aircraft limit.

Talking about so many feet of lateral visibility, the actual nomenclature is Runway Visual Range, or RVR. That is reported in feet in the U.S., and often in meters elsewhere.


How are composite materials on aircraft joined?

Ideally, fiber composites are bonded and connected by a scarf joint. The scarf ratio is determined by the ratio of fiber tensile strength and the shear strength of the resin. If your fiber takes 3000 N/mm², the resin transmits 20 N/mm² and the fiber content is 60%, the ratio is 1:90, so a 1 mm thick composite layer would need to be joined over a length of 90 mm. In reality, such a ratio is impractical to achieve, so lap joints are used when accepted by the certification authorities. This is the case for for composite gliders, where you will find both scarf and lap joints.

In the early days of powered composite aircraft, fiber composites were seen with the experience of aluminium in mind, and treated with the same methods. Therefore, the Lear Fan and its contemporaries had to use rivet joints throughout the structure. The idea was that by riveting the airframe could be more easily disassembled for inspection and repairs. Riveting carbon fiber composites is quite problematic: You need to use expensive titanium fasteners because aluminium rivets would quickly corrode when in electrical contact to the electrochemically much nobler carbon fibers. Drilling and countersinking holes cuts the very fibers which you try to connect, so you have to double up on wall thickness what is destroyed by the riveting. But the FAA still insisted on rivets - even stringers on panels were riveted, when bonding would had been the most sensible solution.

Aircraft engineers have an expression for composites that are treated like metal: Black Aluminum. The LearFan was pure Black Aluminum. Many of the engineers in this project ended up with Beech when they produced the Starship, so many of the same techniques were transferred as well. At least, the Starship had a fuselage shell which was laid up on a mandrel and then cut just aft of the cockpit section to get the mandrel out. The splicing of the two fuselage sections was then done by a tapered lap joint; if you want, a practical way of making a not-quite scarf joint.

Today we have a new generation of engineers who slowly accept that the nature of composite structures requires their own methods of treatment. But you will still find riveted joints even in modern composites structures. Old habits are hard to break.

A good reason for riveting is to avoid peeling at the edges of a bonded joint. Engineers with no experience rivet their composites, once they gain some experience they switch to bonding and with lots of experience they add rivets again.


How is rotor airfoil analysis different than fixed wing airfoil analysis?

You are correct on many fronts.  Rotor blades see a varied load along their length, resulting in twisting, bending, and lagging (e.g., the blade being bent against its direction of rotation) loads.  It's a mess.  And, yes, all those effects feed back into blade aerodynamics, but that's a much more complicated answer that you might be looking for.

What you are describing is the foundation of blade element theory.

Let's consider a helicopter rotor, independent of the helicopter fuselage, and look at one annular ring of it while the rotor is in hover (so we have an axisymmetric flow field):

If we look at that annular ring, it would "cut" through a section of the rotor, which, in 2D, would look something like an airfoil.  If we drew a bunch of vectors on it to represent the forces acting on the airfoil and the direction of the relative wind, it does look a heck of a lot like our 2D airfoil free body diagram from fixed-wing aerodynamics.  And, truly, blade element theory (BET) considers it as such.

In BET, elements of the blade (such as the 2D airfoil above) operate without impact on the other blade elements.  If you can determine the inflow at a particular blade section, you can determine the sectional lift and drag, and, integrating those properties across the blade, you can determine the thrust production and torque requirements that correspond to a particular operating condition.  That said, while most of the labels on that diagram are familiar from fixed-wing flight, there are a few that should be different, namely: the induced velocity, inflow angle, and tangential velocity.

As you stated, the horizontal speed of the blade is going to change based on where you are on the blade, radially speaking--which is absolutely correct.  If we look at a distribution of elemental velocities around the rotor, it's going to vary as shown here, in a plot from Leishman's Principles of Helicopter Aerodynamics (which has a great description of how to implement all of this, as well as some basic corrections for going into some rudimentary higher-order approximations).  Note the hover case on the left hand side, where the velocities are axisymmetric, versus the forward flight case on the left hand side, where the velocities are asymmetric.  That second case is a whole 'nother can of worms, and we'll get there in a minute.  Stick with the hover case for now.

So knowing your radial location can get you the element's velocity, and knowing your climb rate and help you get how fast flow is moving vertically through the rotor, but flow has to be moving vertically through the rotor even when the aircraft's not climbing -- else our analogy of a rotor being a big fan (which it is) doesn't correspond with reality.  Hence, there's some inflow speed, and it makes sense that that inflow speed is correlated to the amount of thrust being produced by a given element of the rotor...and this is the crux of the problem for us, since it has to capacity to dramatically change the angle of attack of the blade section (and thus our lift and drag predictions).  So: how do we estimate the inflow velocity?

A simple approximation uses momentum theory (i.e., a quasi-1D analysis on fluid moving through the rotor disk, treating the rotor as a device that simply adds momentum to the flow) to determine the inflow on the rotor along that annular section, assuming that the inflow is axisymmetric.  For what it's worth, it's a simple way to capture inflow velocity variation (and thus angle of attack variation as well) across the rotor disk, which is something that momentum theory cannot do alone, and it's decent at what it does.  It has been the de-facto standard of the wind energy industry for awhile as more complex CFD computations have caught up to the industry's analysis needs and desires.

However, when flow is no longer axisymmetric, we get into a big mess of approximations to determine what that inflow does look like, since the wake will start to interact with the inflow as well and that, somehow, needs to be accounted for.  It is here that we start to depart from analytical expressions and look to computational models using free-wake theory or higher-order models.  Where fixed-wing models advance in similarity by modeling the wing's wake, viscous effects, etc, rotary wing models model a rotating wake that is being convected and recirculated by both rotor effects and the freestream.

That said, the expressions for a rotor in hover are relatively easy to code up, depending on how much fidelity you want (e.g., how much you know about the airfoils used on the blade as well as how the blade tapers and twists along its length).  Googling around, I found a MATLAB code that might be useful, again, depending on your problem: https://www.mathworks.com/matlabcentral/fileexchange/21994-analysis-of-a-rotor-blade-system-using-blade-element-momentum-theory


What are the differences between fuel types (comparing with vehicles)?

Broadly speaking, there are three families of motor fuel that you're probably interested in: Diesels, Kerosenes, and Gasolines.
The difference between the families mainly has to do with the molecular weight (and thus boiling point / vapor pressure) of the fuel components - in order above from heaviest to lightest. The differences within each family are related to refining, blending, and additives, as well as process controls imposed on the fuel.

The Diesel Family

In the diesel family we have things like Highway Diesel and the various grades of home heating oil.

For transportation purposes these fuels are used in compression-ignition engines ("diesel engines"), where a high temperature and pressure will cause the fuel to ignite and burn, producing power.
For other purposes (like heating) we basically light the stuff on fire and are happy it burns.

The Kerosene Family

The Kerosene family are close cousins of the Diesels, including K-1 and K-2 Kerosene (obviously) and Jet-A.

Jet-A is a high-purity kerosene based fuel manufactured under a specific ASTM standard (D1655), with specific physical properties, and is used in jet turbine engines.  Fuel not meeting the Jet-A specification is generally recycled in the production chain for other purposes (for example it may be used in blending kerosene for heating, or blended into highway diesel).

Jet-A is suited for turbine engines, but can also be burned in other compression-ignition piston engines like diesel can (there are a wide variety of aerodiesel engines available from several manufacturers).

Other grades of Kerosene are used for motor fuels, cooking fuel ("camp stove fuel" is typically kerosene) heating, lighting, etc. depending on their refining and purity.

The Gasoline Family

In the gasoline family we have Avgas, Autogas, and "Gasohol", all designed for use in spark-ignition engines.

Aviation Gasoline (Avgas)

Avgas actually comes in several grades, all manufactured to an ASTM standard (D910), with specific physical properties and specific permitted and required additives (such as Tetra-Ethyl Lead - TEL).

The grade (octane rating) of aviation gasoline is identified by colored dyes added to the blend.
The colors used in the US are:

Green: AvGas 100 (100/130 Octane)
Blue: AvGas 100LL (100/130 Octane)
(This was formulated as a replacement for AvGas 100, with half the lead - hence 100LL - Low Lead)
Red: AvGas 80 (80/87 Octane)

Generally 100LL is the most widely available aviation fuel because it works in the widest range of engines.

Autogas (automotive gasoline)

Automotive gasoline comes in multiple octane grades, but generally it's all varying blends of "regular" (87 octane) and "premium" (93 octane or higher).
Automotive gasoline is manufactured under a different ASTM standard from Aviation gasoline (there are several applicable standards, D4814 is commonly used), which permits different additives including ethanol (usually up to 10%).

"Gasohol"

Gasohol is a slang term for automotive gasoline with any amount of ethanol blended into it, but these days it's often used to refer to blends like E85 (85% Ethanol, 15% gasoline stock).
Flex-fuel car engines and a few other specialty engines are designed to burn this fuel.

So what's the difference?

Why don't we burn highway diesel or heating kerosene in a 747?
In a word, purity. The additional controls imposed on Jet-A fuel by the associated standard produce a product with well-known properties. When you fuel a plane with Jet-A you can be confident that fuel won't freeze in the tanks at altitude (at least not unless you cold-soak it below -40 degrees). You also know the fuel will be "clean" and won't gunk up fuel filters or leave deposits inside the combustion core of the engine that can cause problems later.

On the other hand we don't burn Jet-A in a Mack Truck because it would be prohibitively expensive: Highway diesel doesn't have to meet the same strict tolerances as jet fuel, and theres no reason to burn a more tightly specified (and thus more expensive) fuel when a less expensive one is readily available.

The difference between Aviation Gasoline and Automotive Gasoline is a bit more subtle: the core blend stocks are extremely similar, but the additive packages are very different.

The biggest concern for aviation users is usually the ethanol commonly blended into automotive gasoline: Rubber components in aircraft fuel systems were not designed to handle alcohols, and can be damaged/degraded by ethanol.

For cars the concern is the lead found in aviation gasoline. Any "modern" car (with a catalytic converter and oxygen sensors in the exhaust system) can't burn leaded fuel as the lead byproducts in the exhaust will foul both the catalyst matrix and the oxygen sensors (though a 1950s Plymouth Belvedere would have no trouble burning the stuff).

Work on an unleaded aviation fuel is ongoing - theoretically the fuel that comes out of that process could be equally suitable as a road fuel and an aviation fuel, however the chances of it making its way to your corner gas station are relatively slim, except possibly as a blend stock from batches that don't meet the final specification for a 100-octane unleaded aviation fuel, but are suitable for recycling into automotive gasoline blends.


For what reasons might a taxiway be mistaken for a runway?

Essentially, some taxiways look very like runways and they might even be more visible to pilots in certain conditions. That leads the pilots to focus on the taxiway rather than the runway.

In 2007 the FAA commissioned a study into ways to avoid pilots landing on taxiways, with special emphasis on KSEA (Seattle-Tacoma). One of their goals was to address exactly the scenario in the article you linked to:

  Find a solution for the Seattle-Tacoma International Airport (SEA-TAC)
  problem by  identifying possible visual aid enhancements to prevent
  pilots from mistakenly  identifying taxiway Tango as the adjacent
  runway 16R as a landing surface.

The study mentions several reasons why pilots mistake taxiways for runways:

A pilot will generally associate an air traffic control (ATC) instruction such as “cleared to land runway 16R,” with their visual presentation of the runway configuration. In other words, pilots see a taxiway where they expect to see a runway: this was a particular problem at KSEA because until the third runway was built, it had 16L and 16R, with taxiway T located to the right of 16R. Therefore a pilot landing on 16R would see three 'strips' with taxiway T as the rightmost one and might assume it was 16R. KSEA now has 3 runways with taxiway T between 16R and 16C.
Some taxiways look physically very like runways, i.e width, surface material, square edges etc.
Some taxiways stand out more clearly in low light conditions because their surface is lighter than the runways
Sun glare can hide runway and taxiway markings so that pilots can't tell the difference visually

There's also an FAA engineering brief that explains how to identify potential problem taxiways, it gives essentially the same information as the study.

Both documents say that the most important point is to alert pilots in advance about the potential problem by giving warnings via ATIS, charts and so on. That's especially true for pilots who aren't familiar with the airport, and GA pilots make more mistakes than airline pilots so presumably training and general currency/professionalism as well as having at least 2 pilots in the cockpit makes a difference too.


Why are piston engines so unreliable in airliners?

This statement is not entirely true. the R2800 engine was considered at the time to be quite reliable in comparison to the R3350 and the R4360. Those engines represented the evolutionary dead-end of big piston power, where pushing to more power began making the engines less reliable than their lower-power predecessors had been.

Part of this was simple statistics, where the probability of failure of a machine scales with the number of parts it contains. In crude terms this means doubling the number of pistons doubles the opportunity for something to go wrong with one of them in the engine. Note also that those extra pistons do not provide redundancy, in the sense that a failed piston will fill the oil system with broken metal, causing the other pistons to fail not long after, or start the engine on fire.

Turbine power plants provide more uptime and longer TBO's than the piston engines they replaced as well as more power for less engine weight. These attributes offset the greater replacement costs and higher fuel consumption in applications where uptime and power were required to enable a viable business model.

Cost-sensitive, low power applications still make use of pistons, with the breakpoint being around ~300HP. This is at least partly due to the fact that as turbines are scaled down in power output, their efficiency usually suffers, and their manufacturing costs do not fall fast enough to compete with pistons in the 250HP arena.


How is the direction chosen when landing a seaplane on water?

Here is a nice little article on it. But in general the small waves on the water will curl with the wind and can even be used as a wind indicator. For calm water you can obviously chose your direction based largely on wind (but if the water is very calm there is likely little wind). Obstructions will play into choosing direction as well and it is advised to overfly the intended landing area before touching down. As for rough water landings the article states

  It is impractical to describe an ideal rough water procedure because of the varying conditions of the surface. In most instances, though, the approach is made the same as for any other water landing. It may be better however, to level off just above the water surface and increase the power sufficiently to maintain a rather flat attitude until conditions appear more acceptable

Your elements are (in no particular order)

Obstacles
Wind
Landing Area (you need enough distance to actually land same as a paved strip)
Possible Rough Conditions

You must also keep in mind where you can actually land a seaplane. Not every body of water is legal to land a sea plane in (emergencies aside). You may want to check out this recently released book on arguable the first guy that flew a seaplane around the world.


How to deal with both a speed and an altitude crossing restriction while in VNAV PTH descent (Boeing 737NG)?

With both restrictions entered on the LEGS page, VNAV will build a deceleration segment immediately prior to the point to reduce speed from 240 to 210 knots in (almost) level flight. There is no need, typically, to come out of VNAV, use the speed brakes, or do anything else like that in order to have VNAV meet both speed & altitude constraints.
Thus, the Top of Descent point will be about 3 miles sooner for a restriction to "cross XYZ at 9,000' & 210 knots" than it would be to "cross XYZ at 9,000' & 240 knots". It takes about 1 NM to slow 10 knots in level flight at idle.
The exception to not needing to come out of VNAV is if you end up with excess energy - perhaps unexpected tailwinds. In that case, you have to lose the energy, which is most easily done with the speedbrake. Switching between modes doesn't bleed energy, although it may affect the tradeoff between kinetic & potential energy. (If you have enough distance, using Speed Intervention to increase speed CAN bleed off excess energy by increasing drag. BUT, you then have a longer decel segment... so to gain from this you either have to spend several minutes at the higher speed, or be descending to a point with only an altitude restriction, but no associated speed.)


Aston Martin do something similar with their 'Aeroblade', which replaces the rear spoiler, so the concept of using air to guide surrounding air is viable. Whether it's more efficient than using a physical object, remains to be seen.


What are the duties of an ATC supervisor?

In the FAA, there are two types of "supervisors" who might be on duty at any given time: a genuine managerial supervisor, who is part of the managerial pay scale and is not part of the bargaining unit (union); or a "controller-in-charge," a "line" controller (a bargaining unit employee) who has been certified to perform most but not all supervisory duties if a supervisor is on break, not scheduled that day, etc. Sometimes the supervisor or CIC will be working a control position, or they might be working at a desk in the back of the operation not talking to any aircraft directly.
In either case, the general duties of the supervisory position are:

Running the shift (determining the break schedule, approving sick leave, etc)
Assigning controllers to combine or decombine control positions as traffic and complexity warrant
Assigning on-the-job training to ensure trainee controllers get sufficient training time
Monitoring the operation and, if they feel it is necessary, instructing a controller to take a specific action to ensure safety (this happens very rarely!)
Coordinating with surrounding facilities—not about individual aircraft (the controller on position does that) but about traffic management initiatives, contingency situations (e.g. telling people "we lost commercial power so we're on generators, be prepared in case we lose those too"), etc
Answering the commercial phone if people call (survey pilots informing where they will be operating, military ops calling to see if a plane can come do practice approaches, someone claiming they saw a UFO, noise complaints, etc, etc)
Keeping the daily log up to date (logging equipment outages, runway closures, etc)
Coordinating with other facilities or airport operations regarding emergency aircraft or crashes

The CIC authorized to carry "on the spot" corrections—telling the controller on position they need to do something else for safety reasons—but is not authorized to perform personnel actions like officially counseling a controller about a loss of separation. That's reserved for the actual supervisors.
Of note, if you hear a controller give an instruction and then another controller comes on the frequency and gives a different instruction, that isn't a supervisor. That's the instructor plugged in alongside their trainee controller. During training the certified trainer controller is responsible for the position, so they will give their trainee latitude to make their own mistakes but will step in to prevent an actual safety event.


On an inverted aircraft, is the ILS glide slope sensing reversed?

Well first off said stunt is illegal under 91.303 aerobatic flight regs and 91.13 careless and reckless operation of an aircraft.  And it's also very dangerous.  But no, it would not result in reverse sensing due to the fact that the ILS system is only capable of sensing whether it is receiving more of the 90 Hz signal as opposed to the 150 Hz signal and interprets this as either above or below glideslope.  It cannot differentiate between erect and inverted flight.


What are the dynamic stability properties of an aircraft with wings exactly at the vertical CoG?

It is a common misconception that the vertical CG position (relative to the wing) plays a major role in roll stability. It doesn't; it's mostly about aerodynamics. (You mention it yourself in "as a result of the differences in localized airflow...")

There are other important factors at play as well: dihedral angle, wing sweep, design of the vertical stabiliser.

Presumably, you are interested in the behaviour of an aircraft with the perfectly neutral roll stability. If so, it needs at least these conditions:

General symmetry about the horizontal plane, which includes:

Zero wing dihedral;
Symmetric (e.g. round) fuselage;
Wing at the centre of fuselage (vertically);
Symmetric vertical stabiliser (e.g. with dorsal fin);
Absolute rigidity so that the symmetry remains under load.

Zero wing sweep (straight wing);
Lack of any artificial stability augmentation.

(Technically speaking, the geometric symmetry is not necessarily required: we can compensate one effect with another, say, wing sweep with anhedral. But in the spirit of the original question, let's assume the full symmetry).

We should also assume a reasonable stability in pure yaw.

So, if you induce a pure roll disturbance and then remove it,

the aircraft will start rolling.

Because it has some inertia about the roll axis, it will not simply stop when you remove the disturbance. The only force that will counteract the roll now is roll damping. It naturally occurs because the descending wing has higher angle of attack (and vice versa). The strength of the effect depends on the square of the wingspan, but in theory the spherical cow will keep turning forever, albeit with ever-diminishing speed.

So far, nothing would induce a yaw, and the airflow would still be symmetric.

However, as roll develops, and the aircraft keeps the same pitch balance, the lift will become insufficient to keep it level. The usual thing happens:

the aircraft enters a spiral dive.

Now, this is not a symmetric situation anymore. There is a side force from gravity; sideslip will develop; the aircraft will yaw due to its yaw stability that we assumed. Things start to get complicated (that is, 'normal'), with many variables involved. Even in the vertical plane, despite postulated symmetry, the shadowing and other cross-flow effects on the top and bottom of the wing will be different (the wing, by definition, cannot be aerodynamically symmetric when it generates lift), and thus some roll effect may be observed.

So it's hard to predict further behaviour in general. At one extreme, with stubby wings and slender body and very strong initial disturbance, the aircraft may barrel roll many times and may even enter a peculiar stable roll motion due to inertia coupling. At the other, the aircraft will just roll a little and will enter a gentle (nearly) coordinated turn with very slight descent.


What are Operations Specifications (OpSpecs)?

Putting aside the legal definition for someone else, they are a set of rules that an operator (an airline for example) agrees to operate by. The FAA has to approve them. The ops specs can be more restrictive than applicable FAA regulations, but never less restrictive (as I remember). They cover many things, some of which (that I can remember) are:

Type of equipment you're going to operate.
Where you're going to operate.
Extent to which VFR operations will be allowed.
Types of navigation equipment permitted.
Who you can offer your services to.
Crew training required.
Duty and flight time limitations.
Disciplinary protocols to follow.
Flight planning, dispatch, flight following requirements.
Lists of who is who: chief pilot, flight standards director, etc.

There are a lot more areas, but basically it's how you're going to operate your airline. The thing to remember is to give yourself as much leeway as possible. Don't do something stupid like saying that if someone fails an alcohol or drug test that you're simply doing to fire them. Provide for as much VFR operation as you can possibly get the FAA to agree to. Don't saddle yourself with impossible maintenance requirements if you have a mechanical problem in, say, Harare.

Ops specs are best written by someone who has been around the block many times. Write them poorly and you're going to cost yourself a lot of money that you would otherwise not have to spend. If you get a recalcitrant FAA inspector, it's worth fighting it out. Appeal as necessary until you get what you need. Don't be afraid to show up the ignorance of FAA newbies that may have been assigned. Also, remember that the FAA regions are not standardized. It may even be worth considering changing the region where you're technically based to get what you want.


What happens to the cabin pressure if all the packs (ACMs) stop working?

If all ACM failed, an alarm would sound in the cockpit. And two messages would appear on the ECAM/EICAS¹. One indicating that the ACMs failed and the other indicating that cabin altitude² is rising above desired level.

Pilots would execute corresponding checklist, and the one for rising cabin altitude calls for rapid descent to 10,000 ft. That is the altitude where humans can breathe safely.

If the problem is a hole in the fuselage, the oxygen masks would drop to allow breathing until the aircraft descends, and emergency descent (with full spoilers) would be done. But if it is just failed pressurization, the outflow valve would close and the pressure would only decrease slowly, so the aircraft would most likely descend before the masks would be needed and they would not release. Even normal rate of descent is usually sufficient in such case.

If you're flying above mountains, there are additional rules where to fly to avoid any terrain rising above 10,000 ft, which will be part of the flight plan. For example flying along the mountains of Peru, you'd need to deviate toward the ocean during such descent.

Now at lower altitude, the aircraft flies slower while burning more fuel, so it probably won't be able to make it to the original destination any more. However when planning flight and calculating the required fuel this is taken into account, so the aircraft has enough fuel that it can make it to one of suitably selected diversion airfields if it needs to descend to 10,000 ft at any point along the route.

¹ Modern aircraft have a display on which information about any problems and abnormal conditions is printed, which is called ECAM by Airbus and EICAS by Boeing. Older aircraft had large panels of warning lights.

² Pressure in the cabin is usually given as altitude at which that pressure occurs in standard atmosphere. Normal cabin altitude is 7,000–8,000 ft, 10,000 ft is maximum safe altitude (with generous safety margin). The oxygen masks fall out if the cabin altitude exceeds 14,000 ft.


What is the third airport near Dubai visible on Google Maps?

The airport is Al Minhad Air Base:

  Al Minhad Air Base is a military installation in the United Arab Emirates. The base is located approximately 15 miles (24 km) south of Dubai and is operated by the United Arab Emirates Air Force. It is currently the headquarters of Joint Task Force 633 and supports Australian operations in the Middle East.

If you turn on Google Earth view, you can see the single road leading into the airbase from the east:


What is the best option when the headwind exceeds the maximum airspeed?

Before even taking off, a pilot is required to get a weather briefing, including winds.
 Wind speeds are usually predictable and well known.  If a pilot was flying against strong headwinds, with no good landing alternate, he screwed up his flight planning before he even started the engine.  A headwind doesn't even have to be strong enough for negative GS, just strong enough to cause concern.

Winds vary by altitude in both strength and direction.  If a pilot does find himself in such a situation, changing altitude by a few thousand feet, higher or lower, can very likely change both the wind direction and speed to something that is manageable.


What is the true meaning of the word "roger" when used on the radio? What is its origin?

In the US, the "textbook" meaning is in the Pilot/Controller Glossary:

  ROGER − I have received all of your last  transmission. It should not be used to answer a  question requiring a yes or a no answer.

The AIM 4-2-3 gives an example of using it to acknowledge instructions:

  Acknowledge  with  your aircraft identification, either at the
  beginning or  at the end of your transmission, and one of the words
  “Wilco,” “Roger,” “Affirmative,” “Negative,” or  other appropriate
  remarks; e.g., “PIPER TWO ONE  FOUR LIMA, ROGER.”

As a counterpoint to that, when I first learned to fly in South Africa I was told never to use Roger in transmissions because it doesn't tell the controller anything useful (obviously the FAA disagrees).

And as for the etymology, that's already been covered in another answer:

  This usage comes from the initial R of received: R was called Roger in
  the radio alphabets or spelling alphabets in use by the military at
  the time of the invention of the radio


Can an online course replace "ground school"?

Here in the states this depends on if you are training at a part 61 school or part 141 school

Strictly speaking there is no ground school requirement for a part 61 school and you are even allowed to study the material on your own. However your instructor must endorse you for the written test so many schools prefer to know that you did at least some ground school usually from them. Online is more than acceptable in this case (especially if they provide you with the endorsement) however its best to talk to your instructor before doing so and make sure they are ok with it.

  §61.103   Eligibility requirements: General.

  (1) Conducted the training or reviewed the person's home study on the
  aeronautical knowledge areas listed in §61.105(b) of this part that
  apply to the aircraft rating sought; and

  (2) Certified that the person is prepared for the required knowledge
  test.

  (e) Pass the required knowledge test on the aeronautical knowledge
  areas listed in §61.105(b) of this part.

For part 141 it depends what they got approved in their curriculum. You can find the full regulation here.

  §141.55   Training course: Contents.

In the 141 case you most likely can not complete the training on line due to the fact it wont fall under their approval.

Also of note from this FAA doc

  Note: If you are enrolled in a part 141 school with test examining
  authority, the school will administer the knowledge test during the
  curriculum.

Its important to note that it does not matter if you are training at a part 61 or part 141 school you end up with the same PPL.

You can find 100% of the information you need to pass the written test for free in the FAA's published handbooks particularly this one.

On a bit of a personal note, I started at a 141 school that shut down about half way through and finished my PPL at a part 61 school (with the same instructor). At the 141 school there was a rigid curriculum and almost always a half hour to hour of ground instruction prior to our flight as dictated by their approved curriculum. At the 61 school I was allowed to work the material at home before hand and come in mainly for my flying but 15 min of discussion usually occurred prior to my flight anyway. I did at least 50% of the ground material on my own and passed the written without any issues but its important to understand what you are undertaking if you go the self study route.


To be perfectly honest, LEGO does have a habit of mashing similar airplane designs into their own models. The twin-tail airplane has most of the features of the F/A-18 with its trapezoidal wings and slanted, trapezoidal vertical stabilisers. The F-14's contribution to that design is mainly in the engine intakes.

The single-tail airplane has most of its design from the Saab JAS 39 Gripen but the vertical stabiliser looks like it comes from the Dassaut Rafale (Knowing LEGO pieces, it could also be that they couldn't find a proper piece to fit).

Of course LEGO also has this unholy mash-up of the F-22 and F-35. So it does not surprise me that they have multiple plane designs in these airplanes.