Does the yaw damper require manual activation on modern airliners?

787
On the 787 there is no activate/deactivate button for it. Yaw damping and turn coordination are always active as long as the flight controls law is in primary mode. In secondary or direct modes, yaw damping becomes degraded.
Primary being the fly-by-wire's fully functional mode. Source: 787 FCOM.

MD-11
On an older generation plane, for example the MD-11, there are buttons for the yaw damper, 4 in fact for the 4 channels, they are rarely used (always on) unless there's a fault and after troubleshooting you want to take a channel out.
(airliners.net) Four yaw damper buttons on the MD-11's overhead panel.

737 Next Generation
On a 737, after a flight is completed and the IRS knobs are moved to the off position, the yaw damper switch automatically goes to the off position.
I suspect the rationale back then (carried over from earlier 737 variants) was you can't have the switch on the "on position" and the fault light illuminated when there was no fault. (The yaw damper needs a functioning ADIRU, which needs input from the IRS.)

(airliners.net) Yaw damper and IRS controls on the 737 overhead panel.

Autopilot and yaw damper
In most (if not all) planes that come with a yaw damper (YD), engaging the autopilot (A/P) is not needed to enable the YD, i.e., you can hand fly and still have the YD on, whether there's a switch for it (737) or not (787).
In the MD-11 if all four channels failed, the A/P can only be used in cruise. So as you can see, you need the YD for the A/P in the MD-11, not the other way around. Source: MD-11 QRH.


Are there regulations that limit the airports an air carrier can visit based on rescue equipment?

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

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


Does shrouding a propeller minimize induced drag by equalizing the downwash velocity along its blades?

Basically, yes. The difference between shrouded and unshrouded propeller is that the shrouded one can produce uniform thrust across the diameter, while for the unshrouded one the thrust decreases near the tips.

That way a shrouded propeller accelerates more air than an unshrouded one of the same diameter. This air therefore needs to be accelerated to lower speed, and therefore carries away less kinetic energy, requiring less induced power¹.

However, diameter can be varied, so the efficiency comparison is not that straightforward. When the propeller spins relatively slowly, making it larger is better, similarly to how increasing wing span is better, aerodynamically, than adding winglets.

However increasing the speed of the tips increases parasite drag, especially if it becomes supersonic. And since increasing size while maintaining angular speed increases the orbital speed of the tips, increasing size only helps to a certain point. That's when shrouds become useful.

¹ In propellers and rotors it is called induced power rather than induced drag, because it counts directly against the engine power. It also describes the physics better, since in both cases it is the work that is done on the air by the reaction to the generated lift/thrust.


How reliable are Lycoming and Continental general aviation piston engines?

Short (pilot's) Answer

"Reliable enough for you to fly behind one, flaky enough that you should always expect them to fail at the least convenient moment."

Short (Mechanic's) Answer

"More reliable than the pilot!"

Longer Answer

You can't really know the failure rate, but you can know the accident rate attributable to engine failures.

The NTSB looked at this back in 1972 and Embry-Riddle still has the report available. It's very interesting reading, and goes into great detail on the specific causes of engine failure.
Totaling up everything they classified as "engine failure" gave a failure-related-accident rate of just under 18 per 100,000 hours (i.e. "Assuming proper maintenance you could theoretically fly 5,000 hours in piston GA aircraft before you'd have an engine-failure-related accident.")
There may be a more current NTSB study on this, I honestly didn't look too hard as I expect the numbers to be broadly similar today.

The 24th Nall report shows 61 "powerplant" accidents (all engine types, and including the propeller and associated systems) - the number is not broken down per 100,000 hours but doing a little extrapolation from their other figures it works out to about 0.4 accidents per 100,000 flight hours (or "Assuming proper maintenance you could theoretically fly 200,000 hours in piston GA aircraft before you'd have an engine-failure-related accident.")

The mechanic's answer of "More reliable than the pilot!" comes into play when you look at the pilot-related accident numbers: In the 1972 NTSB report I cited engine failures made up 13% of the total accident figure. In the 24th Nall report all mechanical accidents were 14% of non-commercial fixed-wing accidents (17% of commercial accidents) - that includes a number of other systems (e.g. landing gear) which are unrelated to the engine.


How does latitude affect the air temperature at 8 km altitude where planes fly?

In the troposphere, air at altitude is colder than air at ground level. But surprisingly, air at altitude at the poles can be warmer than air at altitude at the equator. From the wiki article on troposphere (I added the bullet points):

  The troposphere is heated from below by latent heat, longwave radiation, and sensible heat. Surplus heating and vertical expansion of the troposphere occurs in the tropics.

  At middle latitudes, tropospheric temperatures decrease from an average of 15 °C (59-degree Fahrenheit) at sea level to about −55 °C (-67-degree Fahrenheit) at the tropopause.
  At the poles, tropospheric temperature only decreases from an average of 0 °C (32-degree Fahrenheit) at sea level to about −45 °C (-49-degree Fahrenheit) at the tropopause.
  At the equator, tropospheric temperatures decrease from an average of 20 °C (68-degree Fahrenheit) at sea level to about −70 to −75 °C (-94 to -103-degree Fahrenheit) at the tropopause.

  The troposphere is thinner at the poles and thicker at the equator. The average thickness of the tropical troposphere is roughly 7 kilometers greater than the average tropospheric thickness at the poles.

There is quite a bit of variation in the troposphere as a function of place on earth, and much effort has been put into creating a standardised atmosphere that can be used for practical purposes around the world. The ICAO standard atmosphere serves that purpose. It cannot account for local wind conditions and humidity.

I found a graph in an old paper format uni book on the atmosphere, depicting average conditions in two separate places on earth, Berlin and 40° latitude in North America. The graph shows that although the temperature lapse rate is very similar in both cases, there is a difference in temperature at a given height. The arrow gives the temperature difference at 8 km height, also transported to 0 m (less average difference) and to 10 km (more average difference).

Above is for average temperature at two different places on earth, at similar latitudes. I could not find any direct comparison between average temperature at altitude of the poles and the equator - the wiki article seems to indicate that average temperature at the poles is higher at high altitude, a surprising indicat


Why are in-flight entertainment systems not very evolved?

It's expensive. If you wanted to build something like an XBox or Playstation into each seat,  you're talking about an absolute minimum of \$300 per seat (\$60,000 for a small-ish aircraft like a 737, \$160,000 for a typical A380, and probably much more). While that doesn't sound like a lot on the price of an airliner, it certainly adds up over a fleet of hundreds of aircraft... all of which means you have to add to the ticket price and become less competitive. And that's just talking about gaming.
Safety/security. Allowing the passengers to connect to the system, no matter how well designed, is a potential security hole. This can be avoided to some extent if you completely separate the systems, but there's always potential for someone to find a loophole you didn't think of (overloading the in-flight entertainment and messing up the electrical power, for example). Dealing with this would add significantly to the cost above.
There isn't much need to. Most people who fly are either happy with the in-flight movie choices, or bring their own iPad/Kindle etc.
While using Airplay to send movies from your iPad to your TV works pretty well for one or two devices at home... it quickly falls apart when you're trying to make a wireless network capable of handling 200-800 streams at once!
General safety concerns: despite the fact that we're now fairly confident that having electrical devices on with their WiFi/Bluetooth/4G off is safe, to send the movies they'd need to turn WiFi or similar on, which is a potential risk

In short it's a lot of risk and cost, for not much reward. If you have an iPad with you, why do you need to send the movie to the TV screen in front of you? You can just watch it on the iPad.

Note also that some airlines do have some basic multiplayer gaming built into the IFE: although it's more "Connect 4" than "Battlefield 4"


How can I find places to store/land a private airplane?

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

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

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

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

To answer your other questions:

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

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

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

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

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

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

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

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

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

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

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

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

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


How can investigators tell the difference between impact damage and explosion damage when investigating debris from a crash?

The short answer (to the question in your subject line) is that in an explosion the skin is blown outward, and in impact damage it's (usually) blown inward: In other words you can tell the direction of the force applied by which way the skin around a break/penetration is bent, if you recover the right bits of the aircraft.

The labs start with "Boom = Outie, Crash = Innie", and they can also look at burn patterns (on the paint or as changes in the heat treatment of the metal), chemical residue (if it hasn't all washed away or been contaminated), etc.

In addition to leaving chemical traces or heat-related damage explosions also tend to be physically "messy", so there's usually some physical evidence. Shrapnel punctures through control surfaces are a distinct possibility in an explosion (those punctures generally have a different characteristic than denting and tearing from impact with rocky ground, and again if you get lucky you might even find bits of shrapnel inside the punctured control surface).

The longer answer (to the rest of the question) is that sometimes you can't conclusively tell what happened, particularly from just a single piece of wreckage like a control surface.
In fact quoting from the story you linked there are three different (and valid) theories about what could have caused the damage seen on the particular piece of debris in question:

  The rear damage could have been caused if the airliner had its flaperon down as it went into the ocean, some members of Exner's group wrote in a preliminary assessment after looking at photos and videos of the component.

Entirely plausible: Impacting water at speed could tear chunks out of the trailing edge of a flaperon. It could also break the control surface free of the rest of the wing.

  But the lack of damage to the front makes it more likely the plane was in a high-speed, steep, spiral descent and the part fluttered until it broke off, the group said.

Also plausible: Aerodynamic flutter could break pieces of the flaperon off, or tear the entire control surface from the aircraft (in which case damage may be evident at the points where the flaperon attached to the rest of the wing)

  The lack of damage to the front section "tells me that the component could still have likely been back in its original position inside the wing itself,"

Still plausible but a bit more exotic: The flaperon could have broken off post-impact (and the damage to the trailing edge could have occurred on impact, post-impact, or even pre-impact while the aircraft was still flying).

Note that a lot of what's being put forth in that article (and others) is speculation based on a few photos showing only part of the debris (so far I haven't seen any showing the "bottom" of the debris). A conclusive determination can only be made when the debris is recovered and examined in its entirety.
Attempting to draw conclusions without the full picture can lead to interesting results: The apple is perfect until you see the other side.


How frequently are airline pilots switching between aircraft types (e.g. Airbus, Boeing, etc)?

Airline pilots are typically only certified and current on one type. It is rare for a pilot to be certified and current on multiple types because they must do re-current training and check rides for each type in order to remain current and legal. The extra cost for training and check rides would not make financial sense to an airline trying to be competitive with other airlines.


What happens to cabin pressurisation when the engines fail?

Closing the outflow valve would seal up the plane, so it wouldn't depressurize immediately. Once the pressure falls below a safe threshold the oxygen masks would drop. The masks are good for about 15 minutes.

Air Transat flight 236 which ran out of fuel over the Atlantic holds the record for the longest unpowered glide in an airliner. It lasted about 19 minutes.

The APU can provide pressurization, but if you're out of fuel that won't work either. Air Transat was running off the RAT and I doubt that can provide pressurization. BUT if you factor in the outflow valves being closed and the last part of the glide being below 10,000 feet the oxygen masks will provide ample time for the passengers to stay safe.


Does the downwash created by induced drag increase or decrease lift?

It is not "this causes that" - all is happening together. Let me explain:

For me to understand aerodynamics, it helped to disregard all that talk of vortices and induction, but focus on the pressure field around a wing. When the theory of flight was developed, electricity was new and exciting, and it just happened that electric induction could be transferred to lift. Now every author still copies the explanations from a century ago, but they are totally unintuitive.

Every air molecule is in a dynamic equilibrium between inertial, pressure and viscous effects. Inertial means that the mass of the particle wants to travel on as before and needs force to be convinced otherwise. Pressure means that air particles oscillate all the time and bounce into other air particles. The more bouncing, the more force they experience. Viscosity means that air molecules, because of this oscillation, tend to assume the speed and direction of their neighbors.

Now to the airflow: When a wing approaches at subsonic speed, the low pressure area over its upper surface will suck in air ahead of it. See it this way: Above and downstream of a packet of air we have less bouncing of molecules (= less pressure), and now the undiminished bouncing of the air below and upstream of that packet will push its air molecules upwards and towards that wing. The packet of air will rise and accelerate towards the wing and be sucked into that low pressure area. Once there, it will "see" that the wing below it curves away from its path of travel, and if that path would remain unchanged, a vacuum between the wing and our packet of air would form. Reluctantly, the packet will change course and follow the wing's contour, but not without spreading out (= pressure loss). Spreading happens in flow direction - the packet is distorted and stretched lengthwise, but contracts in the direction orthogonally to the flow. This fast-flowing, low-pressure air will in turn suck in new air ahead and below of it, will go on to decelerate and regain its old pressure over the rear half of the wing, and will flow off with its new flow direction.

A packet of air which ends up below the wing will experience less uplift and acceleration, and in the convex part of highly cambered airfoils it will experience a compression. It also has to change its flow path, because the cambered and/or inclined wing will push the air below it downwards, creating more pressure and more bouncing from above for our packet below the wing. When both packets arrive at the trailing edge, they will have picked up some downward speed.

Behind the wing, both packets will continue along their downward path for a while due to inertia and push other air below them down and sideways. Above them, this air, having been pushed sideways before, will now fill the space above our two packets. Macroscopically, this looks like two big vortices. But the air in these vortices cannot act on the wing anymore, so it will not affect drag or lift. See here for more on that effect, including pretty pictures.

What is lift?

Following the picture of a pressure field outlined above, lift is the difference of pressure between upper and lower surface of the wing. The molecules will bounce against the wing skin more at the lower side than at the upper side, and the difference is lift.

Or you look at the macroscopic picture: A certain mass of air has been accelerated downwards by the wing, and this required a force to act on that air. This force is what keeps the aircraft up in the air: Lift.

Either way, you will arrive at the same result. By the way: Most of the directional change happens in the forward part of the airfoil, not at the trailing edge!

Induced drag

The misconception about those "wingtip vortices" and induced drag is hard to eradicate. Most authors copy what has been written before without clearly understanding the issue. Therefore I repeat it here again: Induced drag is the backward-pointing part of the pressure force vector. The vortices are only a consequence of downwash, which in turn is a consequence of lift creation. At the same speed, more induced drag is indeed linked to more lift, but the causality is different: Lift and induced drag are both part of the pressures acting on the wing. If you add up all the pressure forces acting on a wing, their resulting vector will point slightly backwards. The streamwise component is drag, and the component orthogonal to the direction of movement is lift. This is just a defininion, made for simplicity.


Do all single-engined aircraft experience torque that cause a turning tendency during the takeoff roll?

There are four reasons why a propeller aircraft will exhibit a left-turning tendency: torque, spiraling slipstream, P-factor, and gyroscopic precession.

Torque is due to Newton's third law of motion. As the engine spins the propeller, the propeller spins the airplane in the opposite reaction. Since most propellers spin clockwise as viewed from the cockpit, this results in a tendency to roll (and therefore turn) to the left. For jet engines, the rotation of the blades is cancelled by the stator blades redirecting the airflow the other way.

The spiraling slipstream is caused by the fact that the propeller is rotating, causing the air moving through it to also rotate. This spiral flows around the plane, eventually hitting the rudder. Because, again, the engine is rotating clockwise, it will tend to push the rudder to the right, forcing the nose left. Jets don't suffer from this, because, again, the internal stators make sure the exhaust gasses are (mostly) linear.

The P-factor is caused by the fact that the airplane isn't perfectly level. It will usually have a slight nose-up angle. This means that the descending blade has a higher angle of attack, and thus produces more "lift" (a.k.a. "thrust") than the rising blade. Since most engines rotate clockwise as seen from the cockpit, this means that the blade on the right will be the one producing more thrust. Jet engines don't have this because the airflow in the engine is redirected to be parallel to the engine centerline, regardless of the plane's actual angle of attack.

Gyroscopic precession is kind of complicated, so I can't really explain why this happens without a digression into a bunch of complicated physics. Just know that, if you push on the edge of a rotating disk, it will create a force 90 degrees ahead of the point you're pushing on. For a tail-dragger aircraft, lifting the tail is the same as pushing on the top of the propeller disk, thus, precession creates a left-turning force. But then, when either kind of airplane pulls up to take off, this actually causes a right-turning force. Jet engines are no different from propellers in this regard, and will produce these forces in exactly the same way. It's just that the gyroscopic precession in a typical airplane is much, much smaller than the other forces, so the creators of X-plane probably didn't think it was worth programming such a tiny force into the game.


What is a jet (unit) shown in Windows 10 calculator?

It is not a unit. It is just Microsoft trying to be funny. Or to convey an idea of the magnitude.

Thanks @Jackie for pointing out that around March 2019, Microsoft has released this calculator as open source under MIT license. It is available in this Github repository. The source code sheds light on the definition of these pseudo units:

Description in ./src/Calculator/Resources/en-GB/Resources.resw:

<data name="UnitName_JumboJet" xml:space="preserve">
   <value>jumbo jets</value>
   <comment>A jumbo jet (eg. Boeing 747), used as a
            comparison measurement unit for length.
            (...)
    </comment>
 </data>
...
<data name="UnitName_Jet" xml:space="preserve">
   <value>jets</value>
   <comment>A jet plane, used as a
            comparison measurement unit for speed.
            (...)
    </comment>
 </data>

Conversion coefficients in ./src/CalcViewModel/DataLoaders/UnitConverterDataLoader.cpp

/*categoryId, UnitId, factor*/
static const vector<UnitData> unitDataList = {
        ...
        { ViewMode::Speed, UnitConverterUnits::Speed_Turtle, 8.94 },
        { ViewMode::Speed, UnitConverterUnits::Speed_Horse, 2011.5 },
        { ViewMode::Speed, UnitConverterUnits::Speed_Jet, 24585 },
        ...
        { ViewMode::Length, UnitConverterUnits::Length_Paperclip, 0.035052 },
        { ViewMode::Length, UnitConverterUnits::Length_Hand, 0.18669 },
        { ViewMode::Length, UnitConverterUnits::Length_JumboJet, 76 },
        ...
};

Apparently these definitions assume length in meter, and speed in cm/s. Thus, in Redmond the typical cruising speed of a typical jet is 478 knots. We also learn that Clippy is 3.5 cm tall.

888.88 km/h are very, very lucky speed digits for Chinese people. Any aircraft manufacturer or airline would benefit from promoting this cruising speed...


Why do No Tail Rotor (NOTAR) helicopters use an enclosed variable pitch fan?

They use a shrouded fan because these use less power than a jet for generating the same thrust. I could find a reference in Principles of Helicopter Aerodynamics by J. Gordon Leishman: he states that using jet exhaust for anti-torque required high power and that directional sensitivity was poor.

Hiller Aircraft made a tailless prototype.
The Nord Norelfe was constructed in 1954 and was used for the Aerotecnica AC-14 mentioned in the OP.
The design was tested in the Cierva-Weir W-9

The reference to high power would refer to the generic issue with jets providing thrust: it costs less power to accelerate a higher volume of air to a lowish velocity (like a propeller does) than to accelerate a lowish volume of air to a higher velocity (like a jet exhaust does).


According to the pattern and altitude, this aircraft is probably doing aerial photography or 3D mapping (or both !) for services like Google Maps or Apple Plans.
The Partenavia P-68 Observer is actually made for this kind of missions. According to this link, the Italian State Police uses it too.

Since it's happening over Rome, it could be on an archeological mission too, but that is speculation.


Is it possible (not practical) to create a liquid nitrogen jet?

At best, the mechanical energy you can release by evaporating liquid nitrogen would be about its heat of vaporization, which is 5.56 kJ/mol or roughly 200 kJ/kg. (Converting this energy to useful thrust probably requires you to use the expanding nitrogen to drive a turbine that drives a fan or propeller, but that's a Simple Matter of Engineering, at least comparatively).

The chemical energy density of jet fuel is about 46 MJ/kg.

Even if we suppose the efficiency of your nitrogen engine could be a bit better than that of hydrocarbon-burning engines, this still mean that you would need to carry about a hundred times more nitrogen (by weight) than jet fuel for the same result.


How is a glider recovered and returned to an airport after landing in a field?

All gliders can be disassembled to take off wings and elevator.

For each glider type there is a car trailer into which the glider fits after disassembling.

Here you see the “reverse” process (assembly):


Can someone actually "fly under the radar"?

In many cases, yes you can fly under the radar because typical civilian radar is line of sight, meaning that it has to have a straight unobstructed path to an object in order to "see" it.

This is because it works by sending a radar signal out and waiting for it to reflect off of something.  If it reflects off of another object, like the ground, a mountain, a building, a thunderstorm, etc. then it won't see what is behind it.

Since the earth is round, flying "under" the radar is flying beneath the coverage area that the radar can "see" directly from where it is, and the height of radar coverage depends on the distance from the site as well as the terrain.

An example is here:

The top half shows how the curvature of the earth affects it and the bottom half shows how other objects can shadow radar (even though is is using aircraft radar, the same principle applies).

That being said, there are other types of radar and other ways of utilizing radar that minimize this problem and make it nearly impossible to fly under it.

One common type in use is the Tethered Aerostat Radar System:

This is downward looking radar attached to a 25,000 ft. tether.  From 15,000 ft. it can detect aircraft and even vessels all of the way down to the surface of the ocean out to 200 miles.

Another type is Over-The-Horizon Radar which can see further by reflecting radar off of the ionisphere like this:


How do I calculate the landing weight in this situation?

First calculate your weight on the ramp:

$$
\mathrm{Empty~Weight} + \mathrm{Crew} + \mathrm{Fuel} = \mathrm{Ramp~Weight}\\
538\, \mathrm{kg} + 150\, \mathrm{kg} + 93\, \mathrm{L} \cdot \Bigg[\frac{0.72\, \mathrm{kg}}{\mathrm{L}}\Bigg] = 754.96\, \mathrm{kg}
$$

During Taxi, you said 2 gallons of fuel will be used:
$$
\mathrm{Ramp~Weight} - \mathrm{Taxi~Fuel} = \mathrm{Takeoff~Weight}\\
754.96\, \mathrm{kg} - 2\, \mathrm{gal} \cdot \Bigg[\frac{2.72\, \mathrm{kg}}{\mathrm{gal}}\Bigg] = 749.52\, \mathrm{kg}
$$

Then subtract the weight of the fuel that will be used on the trip:
$$
\mathrm{Takeoff~Weight} - \mathrm{Trip~Fuel} = \mathrm{Landing~Weight}\\
749.52\, \mathrm{kg} - 10\, \mathrm{gal} \cdot \Bigg[\frac{2.72\, \mathrm{kg}}{\mathrm{gal}}\Bigg]= 722.32\, \mathrm{kg}$$

(Source of conversions)


Is medical certification required for flight attendents?

One of the first flight attendants anywhere, Ellen Church was also a registered nurse and certified pilot. She was unable to find work as a commercial pilot but she did have another influence on the nascent flight attendant industry: she convinced a major airline to hire only nurses.

She approached BAT (the forerunner of United Airlines) looking for a pilot's job, a futile hope for women in those days. But the BAT exec did like Church's other suggestion: that commercial airliners carry nurses on board.
Smelling a publicity coup, and figuring that on-board nurses would help quell the public's fear – very real at the time – of flying, he sold her proposal to the boys at the top. BAT hired eight nurses, including Church, for what it thought would be a three-month experiment.

These early flights attendants bore little resemblance to their modern counterparts, however

They were expected to haul luggage, screw down loose seats, help with fueling the plane and finally, at day's end, help the pilots push the plane into the hangar.

In modern aviation, trying to hire a registered nurse as a flight attendant doesn't seem to be a requirement. Here's Delta's page on hiring and it says

While specific positions will have unique requirements (example: Flight Attendant minimum age requirement is 21 years of age; see individual job descriptions), you must possess at least a H.S. diploma/GED equivalent, be at least 18 years of age, and possess current authorization to work in the U.S. to work at Delta.

The individual job descriptions are for language knowledge. None list a nursing degree as a requirement.
What changed? Well, mainly the medical profession. Nurses today have a LOT more educational requirements. Additionally, a lot more places use nurses. So nurses are in high demand now. Adding that requirement onto a flight attendant job would make the position more expensive and harder to fill.
Additionally, there might be legal liability. While simple medical devices (like AED devices to restart a heart) supplement and can prove of some limited use, imagine a flight attendant having a nursing degree and someone has a medical emergency or dies on their aircraft. Suing the airline would be a tempting. Legal liability is a very real problem here

A colleague of mine, however, was not as fortunate and encountered a much more serious condition -- urosepsis -- on a flight to London. [snip] My colleague missed her connecting flight, as did many passengers, and the other physician had to accompany the patient to the local ER because the emergency medical service worker did not want to be held liable for the IV line the ICU physician had inserted before the plane landed.

And

Unfortunately, liability is a very real concern, particularly in scenarios when you're not practicing in your regular clinical setting. Generally, physicians are covered by the Aviation Medical Assistance Act of 1998, which protects physicians who provide in-flight emergency medical assistance in the same way that state Good Samaritan laws do. It goes without saying that you do not have to volunteer if you do not feel comfortable with the situation or are concerned for your own safety. If you have had a few drinks or have taken sedating medications, you need to use your judgment about whether to respond.
Since you are volunteering and not technically on duty, under the 1998 law, you are covered as long as you don't engage in any willful misconduct or commit gross negligence. You should make yourself aware of the law's limitations. Many physicians feel a moral obligation to help in a medical emergency, and, thus, we can find ourselves in these situations.

If passengers leap into action to help a distressed patent, the airline avoids liability.


Does having a halo effect after LASIK disqualify you from being a pilot for the Air Force or commercial pilot?

FAA doesn't allow airmen with complications like halos. etc. From FAA Guide for Aviation Medical Examiners:

  The FAA expects that airmen will not resume airman duties until their treating health care professional determines that their post-operative vision has stabilized, there are no significant adverse effects or complications (such as halos, rings, haze, impaired night vision and glare)...

A medical examiner should certify that the applicant (for pilot) is not suffering from any such complications:

  An applicant treated with a refractive procedure may be issued  a medical
  certificate by the Examiner if the applicant meets the visual acuity standards and the Report of Eye Evaluation (FAA Form 8500-7) indicates that healing is complete; visual acuity remains stable; and the applicant does not suffer sequela such as; glare intolerance, halos, rings, impaired night vision, or any other complications.

USAF doesn't allow individuals with cases where the surgical outcome affects one's performance of duties; having a halo effect would be a disqualifier.


Is ATC clearance or permission required to fly helicopter routes and transitions in the Los Angeles area?

According to the FAA's JO7210.3AA Facility Operation and Administration (chapter 11, section 5):

  Pilot adherence to charted helicopter routes and the recommended
  altitudes or flight ceilings associated with them will normally be
  voluntary. However, controllers may assign charted routes and
  altitudes and expect or request pilot compliance with them, provided
  such procedures are called for in specific FAA−operator Letters of
  Agreement, or are necessitated by traffic density and/or safety
  considerations; controllers also may restrict operations within
  designated operating zones when requested by local law enforcement
  officials and the restriction would not adversely affect other
  aircraft operations.

In other words, it's mostly a voluntary thing but pilots should still be aware of them and prepared to follow them if instructed.

And you have to consider the airspace as well: large parts of some routes are in uncontrolled class G airspace, e.g. the PALISADES coastal route, west of Santa Monica. ATC doesn't control traffic in class G, so asking for permission wouldn't make sense.


How did the term 'Buttered the bread' originate?

Back when actual butter was the main spread to put on bread, it took a very gentle touch to spread butter straight from the refrigerator (icebox) without tearing up the bread.  Thus, a very smooth landing might be said to have "buttered the bread" because it went on smoothly enough to keep from tearing anything up.

This probably also evolved into "greased it on" or "greaser" to refer to a similarly smooth landing.


Source: dailymail.co.uk

It's a crashed Super DC-3 (C-117D) in Iceland.

  On Nov 24 1973, the US Navy airplane - a Douglas Super DC-3 - was forced to crash land on Sólheimasandur beach
  The crew all survived the impact, but the plane was abandoned rather than recovered - and lies there still
  All that's left is the plane's fuselage amid rumours a local farmer stole the tail to mysteriously sell it on

It started its life as a C-47A with construction number (CN) 12554, the 2,554th in sequence. It was for the USAF (tail-number 42-92722). It was then converted to become an R4D-5 (Super DC-3 / C-117D) for the US Navy, and was given the new CN 43309 (tail-number 17171).*

First flight was 1944. It crash landed after encountering icing conditions en route on a supply mission to a radar station (aviation-safety.net).

* rzjets.net and abcdlist.nl


What if all passengers pay to check in extra baggage?

To answer the questions as asked,

We won't depart over the maximum takeoff weight. We'll do something to bring the takeoff weight down to not exceed the limit.
Generally, people fly as scheduled if at all possible, and as much as possible their bags go on the same plane that they do, and other cargo is a lower priority. There are exceptions; passengers might be denied boarding when the plane is simply too heavy with every one and every thing on board, but this is a last resort and not particularly common.
Total weight is total weight, and the more of it there is, the more limited your options become.  This is explained in more detail below.
If the people are overweight, it's probably not a factor in the numbers, because for scheduled commercial flights, most airlines use average numbers for passengers and their carry-on bags.  So it doesn't matter if they're all skinny or all heavy, they all count for the same "200 lbs".  For military charters and sports charters, actual weights are used, and some non-US carriers may use actual weights as well.

Okay, that's the what; let's discuss the "why":

There are a lot of "it depends" elements here, but in most cases, what happens is that the amount of other freight that can be carried gets reduced, and in the worst case some of the bags stay behind.  But that's probably fairly uncommon.  It's a very worst-case scenario when you can't even take all the passengers -- pretty rare, in my experience.

Your maximum takeoff weight is limited by one of three limits:

a takeoff limit (how much the airplane can weigh to take off & climb out while meeting all of the various requirements),
an enroute limit (essentially, if you lose an engine at some/any point enroute, can you clear all of the terrain along the way to get to a suitable landing site), and
a landing limit (your expected landing weight is no greater than the maximum allowed landing weight).

In practice, the enroute limit is pretty rare, and if the departure runway is long enough, the landing limit is usually the most restrictive.  So, most of the time, your limit boils down to: basic weight of the aircraft, plus cargo, plus passengers, plus landing fuel, can't exceed the maximum certified landing weight.  The aircraft weighs what it weighs, and a full load of passengers is essentially a given weight (most flights use an "average" weight value rather than actual passenger weights).  So the interesting variables are the landing fuel, and the cargo weight (bags plus freight).

If it's a good weather day and no alternate is required, then the required fuel for landing is one number -- let's say 5,000 lbs in a 737, assuming a fairly "best case" sort of day.  (Various operators may have slightly different numbers, but this is a high-level explanation, not way down in the details.)  But if the weather is bad, that number can go up: allowing fuel for holding, as well as for a possible diversion to an alternate.  Depending on how bad the weather is and how far away the alternate, minimum landing fuel might be 8,000-10,000 lbs for a 737, or more.

Thus... my maximum landing weight is 144,000 lbs for a 737-800.  If the airplane and the people weigh 125,000 lbs, I have 19,000 lbs left over.  If my landing gas is 5,000, then I can take 14,000 lbs of bags/cargo/whatever -- which is a lot.  If the weather is crummy at the destination and instead my min landing gas is 12,000 lbs, then I'm limited to 7,000 lbs of bags.  If today's flight had 6,000# of bags and 3,000# of cargo, it all goes in the first case, but not in the second, and it's usually easier to let the freight take the next flight than the bags -- it gets expensive to deliver bags that the airline didn't get on the same plane as the passenger!

There can also be instances where the max takeoff weight is more limiting... a high & hot airport and/or short runways can limit how much weight you can take off with.  So perhaps "today" where I'm departing, the best that I can do (after considering current winds & temperature and the various runways available) is a max takeoff weight of 165,000#.  If I'm burning 25,000# of gas getting where I'm going, then I'll land at 140,000# -- max landing weight (144k) is no longer the limit, max takeoff weight is.  And the computation now looks at the various weights plus min TAKEOFF fuel compared to the max takeoff weight, rather than weights plus min landing fuel compared to the max landing weight.  But the basic process is essentially the same.

Okay, disclaimer, there are various other things than can come into play that I've glossed over for the sake of simplicity -- max ZFW and improved climb and wet landing runways and plenty of other stuff.  If you're studying for your dispatcher license, this is NOT the answer to address all your what-if's.  It's just an overview.


Why is it harder to maintain laminar flow on larger aircraft?

Sort of interesting that very slow, lower Reynolds number airfoils, such as models, actually have to trip the airflow to form a boundary layer.

Surface friction causes the air near the wing surface to move at the wings speed.  In a wind tunnel this is slower than the free stream, in the air, the moving wing speeds up the air around it.  In relative terms, the effect is the same.

Boundary layers are draggier than laminar flow, but much less draggier than turbulent flow.  The boundary layer is like "grease", helping reduce drag and create lift.

At higher subsonic Mach numbers, early efforts at a "laminar flow wing"  for long range escort fighters  resulted in something resembling an airfoil flown backwards, with a sharp leading edge, a very gently increasing thickness (to keep laminar flow), maximum thickness further back towards the trailing edge, and a much shorter taper to the trailing edge.
This is reminiscent of the blunt "boat tail" approach being tried these days, also found in bullets.

Though successful, low speed handling and stall characteristics led to some needed modifications.

But chord length, and airspeed, as well as airfoil type and surface smoothness, are very important parameters in predicting airflow around a wing.  Airfoil Tools, on the web, is a great place to begin to explore airfoil types for various applications.  Particularly of interest are Coefficient of Lift vs AOA, and Lift/Drag ratio.


Does the center of mass for an airplane have to be over the wings?

No.

One relatively trivial example is a tandem wing (or a canard with a very large forward surface, if you will); the center of mass will be between the lifting surfaces, positioned so that the forward surface flies at a higher coefficient of lift than the rear (to give static longitudinal stability).

If you build your model with the motors on short arms, so that they're a bit above the wings when in quadcopter mode, you may be able to manage the CoM shift so that you automatically get the balance right for forward flight in wing lift.


Won't sonic booms prevent Space X's BFR intercity transport plan from being acceptable?

The only way to get anything that far that quickly is to send it into space, and that's exactly what Musk is suggesting. The BFR will launch a passenger carrying spacecraft out of the atmosphere and into a sub-orbital path, it will re-enter the atmosphere close to its destination. Rockets launch pretty much straight up and a sonic boom would have to compete with the rocket itself on noise. Once above the atmosphere there is no sonic boom because there is no air.

On re-entry all spacecraft create a sonic boom, for most of the re-entry this is  inaudible from the ground because the air is extremely thin, once in the lower atmosphere it gets louder. By the time the spacecraft gets low enough to create a really big sonic boom it's usually at a subsonic speed and would not make any boom at all. The shuttle and Apollo spacecraft both created sonic booms on re-entry, that's covered in this Space SE Question.

So, are sonic booms a problem in this idea? It depends, the space shuttle re-entered over the continental US many times and it never bothered anyone, but if it was happening a few times a day it might be a problem. You could get around that for the most part by re-entering over sparsely populated areas or the ocean.

More likely it's not the sonic booms that people won't want from a noise perspective, but the launches.


How heavy are turbofan and turboprop propeller blades?

According to this ATSB Australia Report, the Original Blade Weight of the Trent 800 Blade that failed was 11.6KG. The weight of the blade in grammes is etched into the blade root.
https://www.atsb.gov.au/media/33974/tr200100445_001.pdf Page 9/10.
Fan Blades of the same type all differ (slightly) in weight and are chosen specially to balance the engine when it rotates, or balance weights are added to the blade much like your wheel on your car. This is to avoid vibration.


Why don't turboprop planes have push engines that use thrust more effectively?

Pusher engines do not generate more thrust; they are basically the same engines, but mounted in a different configuration. As pointed out by @JanHudec in the comments, this configuration can be more efficient since in a traditional puller configuration the air displaced by the propeller washes over the wings and fuselage, thus increasing drag.

There are several considerations, such as those set out in the reference already given by Greg Hewgill in comments.

However, the main reason why propeller pushers are not as used on commercial aircraft is safety. Consider an aircraft taking off. If the pusher engines are placed, as usual, at the rear of the A/C, then the propeller tips are rather close to the ground. Even if the propeller does not actually make contact, any debris present on the runway and lifted by the A/C can conceivably end up within the propeller disk. This would be, naturally, at about the worst phase of flight to lose power.

This is perhaps less of a concern on drones and small aircraft used in GA. The pilot (and owner) may choose to forego a bit of safety to obtain a more compact aircraft and where the pilot's field of view is not interfered with by the presence of a spinner disk.

Another point that can be considered is the fact that turboprop engines are generally used in commercial aircraft that require shorter take-off and landing distances, to connect to smaller airports that handle jets with difficulty or not at all. In this case, a pusher configuration that requires higher speeds and longer runways would not be appropriate. On the other hand, in a puller configuration some of the prop-wash can be used to generate further lift through the Coandă effect and decrease take-off distance.


What is the axis of rotation in a high alpha roll?

That depends on the control system of the aircraft, in case of fighter jets with fly by wire technology and modern fly by wire airliners the yaw control law usually tries to rotate around the velocity vector, which in calm air is the same as the incoming air-stream vector. (according to my university lectures)

The difference in the target yaw rate (r) is just the body roll rate around the x-axis (p) times the tangent of the angle of attack (with the sign flipped, depending on which coordinate system you use).


What pilot certificates were needed to fly the Space Shuttle?

FAA considers space shuttle either a military aircraft or spacecraft and hence its rules don't apply on space shuttle.

However, requirements to be a pilot for a space shuttle are:

  ... at least 1,000 hours pilot-in-command time on jet aircraft

It means that you need type rating to operate a heavy jet aircraft (not light jet). Weight of an empty space shuttle is 172,000 lb (78,000 kg)1. In addition, you need the additional requirements mentioned by NASA (link above), which include education and health standards to meet.

Operating empty weight of Airbus A380 is 610,000 lbs.


Too soon to pass the IATRA exam? (Canada)

If you have the time on your hands might as well get started with the study part.  IATRA is the ATPLs condensed into a single smaller 50 question exam.  You will expand your knowledge base and it never hurts to acquire knowledge sooner rather than later.
Don't take the exam right away though, as it is only good for 2 years and it might be a lot longer than that before you'll land a job that needs a multi-crew qualification.  There's a lot of pilots on furlough and it's going to be several years for the industry to reabsorb them all.  Most of the opportunities are going to be in the North.


Why do heavy bombers not carry air-to-air missiles?

Well, actually, they do.

Or at least it has been proposed on several occasions.

The ill-fated A-12 stealth attack aircraft was going to carry 2 x AIM-120 AMRAAMs as part of its defensive package when it went into combat.

Larger fighter-bombers like the FB-111 did in fact carry the AIM-9 Sidewinder AAM for defensive use.  And the Sukhoi SU-34 advanced theater bomber derivative of the SU-27 Flanker air superiority fighter can carry all modern Russian made AAMs, both IR and radar guided in addition to air to ground ordnance.

The EA-18G Growler electronic warfare derivative of the F/A-18F Super Hornet also carries AIM-120s for defensive use.

There is rumored to be an 'Arsenal Plane' in development by the Pentagon, which is very similar to a Cold War proposal for a VC-25 Cruise Missile Carrier Aircraft, a flying cruise missile launch platform based on the commercial 747-200 airplane.  The DoD's new 'Arsenal Plane' is rumored to be capable of carrying virtually every conventional - and possibly air-launched nuclear - weapon in the DoD's inventory, including AAMs.  Exactly what form this aircraft will take is unknown, but is supposed to be adapted from existing large cargo aircraft or commercial aircraft.

Depending on the types of AAMs desired to carry, mounting and launching them from an existing aircraft would not be a terribly difficult task.  Structural modifications would be necessary on primary components to install pylon hardpoints.  Additional infrastructure for power and datalink lines between mission systems and the missile would be necessary, and additional mission systems such as air-to-air fire control radars, IRST systems all would have to be installed.

Now a while a large aircraft could carry such weapons, their use against a fighter would be limited to stand-off launch and use in defensive retreat; the launch aircraft is just not designed to maneuver with a modern fighter in ACM, which limits the application of these systems in war.

So could it be done? Sure.  Is it a wise idea?  Well, that's debatable.

Historically, defensive armamaent for large, high value aerial assets eg bombers, tankers, transports, etc has been very ineffective.  In World War II, heavy bombers were equipped with multiple gun turrets to protect against enemy fighters.  So convinced were Allied planners that this strategy would give the bombers adequate protection, they sent waves of bombers over Germany with horrible results; the slaughter of heavy bombers over German airspace by Luftwaffe fighters nearly cost us control of the skies during the war.  This massacre only ended with the introduction of long range escort fighters to protect the bombers against enemy interceptors.  The terrible record for 'flying fortresses' protecting themselves with guns combined with the introduction of guided missiles convinced planners to eliminate defensive guns from bomber designs.  In the '50s they were limited to a single tail mounted and remotely controlled turret.  By the '60s, they were totally eliminated from new designs.  High losses to bombers from SAMs over North Vietnam convinced planners that the best defense for the manned bomber was to avoid detection in the first place.  Low altitude terrain masking, electronic warfare, passive low observable design features and stand off launched weapons like cruise missiles were the preferred protection for manned bombers in the '70s and into the '80.

Just what the future defensive systems for manned bombers remains a bit of a mystery.  Both the USAF and Northrop Grumman aren't making many public comments about the new B-21 bomber under development, but it appears likely that stealth combined with a the latest net-centric warfare capabilities will be the cornerstones of its design.  Whether this bomber will carry AAMs is unknown.


How much radiation is an airline pilot exposed to in a year?

The average additional annual dose for flight crew is 2.19 mSv (milli sieverts).  http://www.hps.org/publicinformation/ate/faqs/commercialflights.html

The typical annual dose from background sources is 4 mSv (this varies enormously on the Earth's surface). However, as a rough order of thumb, the annual radiation dose of a flight crew member increases by about 50% compared to sitting on the ground.

For comparison with other sources, having a chest CT scan provides you with a 7 mSv dose over the period of a few minutes.

The maximum permitted dose in one year for a radiation worker under US Federal Law is 50 mSv.

For more comparisons of radiation dose, see https://xkcd.com/radiation/

On a technical point, the premise of your question is incorrect.

Flying exposes us to additional cosmic background radiation because we are at a greater height above the Earth's surface, not because we are closer to the sun. We are protected from cosmic radiation by the presence of the Earth's magnetic field, which extends far into space and is not an issue here except very close to the poles; and more importantly, by the layer of atmosphere above our heads that tends to absorb cosmic rays before they reach the surface. At 40,000 feet, the bulk of the atmosphere by mass is below you.

It is not presently believed that a substantial fraction of these rays are emitted by the sun. For one, you will continue to be irradiated by them at night.

(For interest, if you could see the cosmic background radiation, it would be approximately as bright on the night sky as star light is; for complex reasons the two energies are in rough equipartition.)


Has there ever been an commercial airplane with rear-facing seats?

Some airlines do offer rear facing seats in business/first class. However, this is more to save space than for increasing safety. For example, British Airways offers a mix of forward and backward facing seats in its business class.

Source: Forbes.com

BAC Hawker Siddeley Trident offered rear-facing seats while it was in service. (Note the visible cockpit).

Source: airliners.net

Armed forces of a number of countries use rear facing seats, like the RAF and USN in their C-2 Greyhounds.

"C-2A interior DN-SD-03-16988" by Camera Operator: PH1(AW) Shawn P. Eklund, USN - US Defense Visual Information Center photo DN-SD-03-16988. Licensed under Public Domain via Commons.


What process do flight attendants and pilots follow to bid for routes?

It totally depends on the airline and is different from one airline to another. There is no standard way of distributing schedules. Some of the ways that I have personally experienced or have seen it:

Bids by seniority: The crew will bid for flights/rosters based on their seniority. Juniors will cry rivers.
Fair share: The crew will get turns, if you take a specific flight this month, next month you will not get it until everyone else gets it, and so on. Seniors hate this, they will feel unjust and keep complaining that how come a junior took their righteous flights and off.
A combination of fair share and seniority: Crew will get points, the amount of points they get depends on their seniority and other factors, then they use these points to bid for flights or days-off. For example, you can bid 100 points on getting days-off during Christmas and another 100 on getting a Paris flight during new year's eve, while someone else will throw his/her 200 points on the days-off only, and so on.

Almost all systems have some sort of giving the crew the option to at least bid for their desired off. Some other airlines just distribute the rosters randomly and then the crew will trade duties to get their desired flights and days-off, some have a system depends on the crew performance, there isn't really a standard way.

The ultimate target for airlines is to distribute flying hours among the crew equally, to avoid unnecessarily over-time costs and crew legality issues.


Why are propeller driven aircraft commonly built with a higher wing aspect ratio and a straighter wing angle?

Speed is the reigning factor here, and aerodynamics as well of course.

Speed.
Propeller driven aeroplanes operate at lower speeds than jet engines - propellers are more efficient until compressibility effects start to appear, and it is these same compressibility effects that influence the wing shape as well. Compressibility as in: give air enough time to move out of the way and follow the wing contour. Usually, propeller aeroplanes operate in this aerodynamically docile speed regime.
Aerodynamics.
A wing creates lift by deflecting air downwards, and is most efficient if there is a large amount of air deflected a bit: the least induced drag is created. So the wingspan is the most important parameter here. Lower speed aeroplanes will stick their wings straight out, as much as possible without creating large structural issues due to wing root bending loads becoming unmanageable.
Aerodynamics at higher speed.
Once shock waves start to appear, drag rises rapidly. But only the air flowing perpendicular to span concerns us for the lift creation, and therefore we can present the wing at an angle and use the lower perpendicular speed component for lift creation. But swept wings create many more structural problems than straight wings, and also since we're going faster already the argument of more air at less deflection speed is of less relevance. We have many more problems to tackle here than only minimise induced drag.


Does the Ground Proximity Warning System (GPWS) see through clouds?

Modern airliners typically use a Terrain Awareness and Warning System (TAWS) with two sources of information for triggering warnings: the radio altimeter and a global terrain database. See e.g. the Boeing 737 NG, which uses EGPWS (Enhanced Ground Proximity Warning System):

  Ground Proximity Alerts

  The GPWS provides alerts for potentially hazardous flight conditions involving
  imminent impact with the ground.

  The GPWS monitors terrain proximity using an internal world wide terrain data
  base. Proximate terrain data shows on the navigation display. If there is a potential
  terrain conflict, alerts are provided based on estimated time to impact. These alerts
  are “look-ahead terrain alerts.”

  The GPWS provides alerts based on radio altitude and combinations of barometric
  altitude, airspeed, glide slope deviation, and airplane configuration. The alerts are
  for:

  excessive descent rate
  excessive terrain closure rate
  altitude loss after takeoff or go-around
  unsafe terrain clearance when not in the landing configuration
  excessive deviation below an ILS glide slope
  excessive deviation below glidepath

  These alerts are “radio altitude based alerts.”

(Boeing 737 NG FCOM 15.20.11 Warning Systems - System Description, emphasis mine)

For the terrain database to work, the aircraft needs to know its position from a GNSS source (like GPS), but can also use another source (like inertial position) as backup:

  5.3 Primary Horizontal Position Sources. Horizontal position for TAWS must come from a GNSS source
  meeting ETSO-C129a or any revision of ETSO-C145, ETSO-C146, or ETSO-C196 (or subsequent). As an exception, TAWS equipment limited to installation in aircraft where the EU Regulation on Air Operations
  does not require such equipment may be configurable to operate solely on a non-GNSS position source.

  5.4 Alternate Horizontal Position Sources. Retaining TAWS functionality during GNSS outage or
  unavailability provides a safety benefit. It is acceptable and recommended to incorporate a secondary, non
  GNSS position source, to provide horizontal position when the GNSS is not available or reliable.

(ETSO-C151c, thanks to DeltaLima for pointing this out)

So there are two signals that need to work in clouds for full TAWS capabilities.

Radio Altimeter:

For the radio altimeter to work in a cloud, the radar signal needs to be able to penetrate the cloud and reflect off the ground. Only the part of the cloud below the aircraft is relevant here. Airbus published a nice overview of factors that could result in erroneous RA values:

  The external causes may be linked
  to aircraft flying over:

  Other aircraft, hail clouds or
  bright spots, i.e. terrain presenting
  reflectivity variations.
  Runways contaminated with water or snow.

  In these cases, the RA condition
  may not be detected by the systems,
  which continue to use the erroneous
  RA values.

(Airbus Safety First Magazine - Radio Altimeter erroneous values, emphasis mine)

So normal clouds should not affect the radio altimeter, but clouds with dense precipitation (like hail) can have such an affect. Note however, that if the radio signal reflects off the cloud itself, it could result in a false positive alert, but not a false negative.
GPS signal:

Here, the clouds above the aircraft are relevant, since they could block the signal to the satellite. The GPS signal is however largely unaffected by weather:

  Does RAIN or SNOW or CLOUDS affect the reception of my GPS receiver?

  Answer:  No.  Not so as the user can tell without instrumentation.

  [...]

  The GPS signal frequency of about 1575mhz was chosen expressly because it is a "window" in the weather as far as signal propagation is concerned.

(gpsinformation.net)

Even if the GPS signal is temporarily lost, the Alternate Horizontal Position Source can take over. The inertial position accuracy from the ADIRU would slowly degrade over time, but provide a good position estimate just after the GPS signal is lost.


Is "General Aviation" a well-defined term in the US, in the EU and/or elsewhere?

The FAA does not include a definition of General Aviation in CFR 14 (aka Federal Aviation Regulations) Part 1 (General Definitions and Abbreviations), but, from a functional perspective, in the US, GA is generally used to refer to any civilian operations falling outside of Part 121 and some Part 135 operations (Commuter and Charter Operations - regional feeders have and may still operate under this section if they can meet the requirements, as it is more relaxed and easy to comply with than part 121).

With respect to the FARs, it's important to remember that Part 91 covers ALL types of flight operations UNLESS its provisions are EXPLICITLY overriden by another paragraph (as would be the case with an air carrier's Operating Specifications, part 121, 135, and other sections dealing with more specialized aerial applications). Part 119 also deals, in a very general sense with conducting flight operations for compensation.

IMO, you're not likely to go wrong using the term to refer to everything civilian outside of scheduled carrier and medium/large cargo operations (e.g. Atlas, Evergreen, FedEx, UPS). The caveat is, of course, that GA operations are so diverse that this is more of an "everything else" category rather than the much clearer images conjured up by a flag/commutter/regional carrier or a large cargo operator. If you're unclear about whether a specific application or air operator falls under GA, go ahead and ask.

The FAA division of airports is more likely meant to reflect that certain airports have certain primary intended purposes (e.g. many of the nation's largest airports do not allow Part 91 operations, only air carriers) and may require certain types of infrastructure in order to allow them to perform those roles.

And yes, using a 737 as a personal plane under Part 91 would fall under GA - Boeing even makes a specialized version just for that, see the BBJ.


Should spoilers and reverse thrust be deployed before nose gear touches down?

It depends on the aircraft (and conditions). In some aircraft like the MD-11, the deployment of ground spoilers causes a nose up pitching moment- in such a case, the spoilers should be deployed after nose landing gear touches down.
An example is the incident in Hawaii where the aircraft, a MD-11 exhibited a pitch up tendency during landing and the pilot had to initiate a go around. The factual report noted:

The MD-11 Flight Crew Operating Manual, Volume II, Landing Roll Procedure, contains the following note:
Ground spoiler deployment causes nose up pitching moment. This effect is most noticeable at aft centers of gravity. It is important to check the nose up pitching tendency with forward pressure on the control column and smoothly lower the nose wheel to the runway.

In some cases the deployment of thrust reversers could also have similar effect. In such cases, the thrust reversers and spoilers should be deployed after the nose wheel touches the ground, while in other cases, it is done after the main landing gear touches down and before the nose gear touches down. From FAA Airplane Flying Handbook:

... some airplanes tend to pitch noseup when reverse is selected on landing and this effect, particularly when combined with the noseup pitch effect from the spoilers, can cause the airplane to leave the ground again momentarily. On these types, the airplane must be firmly on the ground with the nosewheel down, before reverse is selected.
Other types of airplanes have no change in pitch, and reverse idle may be selected after the main gear is down and before the nosewheel is down.

There are other issues as well- deployment of thrust reversers before the nose wheel touches the ground means the pilot may not have sufficient authority for steering the aircraft in case one of them doesn't deploy. To prevent this some aircraft restrict the use of full reverse thrust till the nose landing gear is on ground (though idle reverse is permitted once the main gear touches down).
Also, for aircraft having engines in rear, the deployment of clamshell type thrust reversers can have clearance and debris ingestion issues which can limit their deployment. Also, the effect of spoiler deployment on the aircraft aerodynamics has also to be considered. For example, Boeing states:

The MD-80 and MD-90 in-flight spoiler lockout mechanism prevents the undesirable flight control configuration of deployed spoilers in either the speed brake or ground spoiler mode when flaps are extended.

There are also other aircraft (like Tu-154) where the thrust reversers were deployed before touchdown. So, all in all, it is better to consult the particular aircraft manual to decide when the spoilers/thrust reversers are to be engaged.


What if you refuse to fasten your seatbelt?

In the US it is an offence under federal law.
A loose 180lb/80kg projectile inside an aircraft is a threat to other passengers during turbulence, in the worst cases of passenger misbehaviour cabin staff can and have forcibly restrained passengers and/or diverted to a nearby airport to have the passenger deplaned and sometimes arrested.
Seven Ways to Get Kicked Off a Plane
Family kicked off plane

A 3-year-old, who refused to use his safety belt, caused a flight to be delayed after his father could not get him locked in his seat belt on board an Alaska Airlines plane.
The pilot returned to the gate on Saturday and asked the father and child to get off the plane.

Why you need to wear a seatbelt

For passengers who refuse to wear seatbelts when the sign is illuminated and who are disruptive to the crew, the FAA can impose a maximum fine of $25,000.


The yaw damper is, in simplest terms, an "autopilot" for yaw. When engaged, it operates the rudder (or whatever yaw control method is available in exotic aircraft, like the B-2 flying wing).

Its primary goal is to counteract the typical Dutch roll aerodynamic mode of many aircraft. It also helps keep turns coordinated by automatically providing the necessary rudder inputs to avoid slipping/skidding in a  turn.

In normal aircraft the yaw damper is part of the automatic flight control system (AFCS) or "autopilot." It can usually be engaged on its own without the rest of the autopilot. On the other hand, most autopilots require the yaw damper to be engaged when the rest of the autopilot is engaged (you can have yaw damper without autopilot, but not autopilot without yaw damper).

For large / transport aircraft, the yaw damper is usually engaged throughout the entire flight profile except for takeoff and landing.

It is required equipment (link is to FAA certification regs but similar regs apply elsewhere) in many (most?) transport aircraft, which tend to suffer Dutch roll instability, but flights can sometimes still be made if the yaw damper is inoperable per the minimum equipment list (MEL), with restrictions. This depends on the exact aircraft type and any extra operator policies (company rules). Note that usually an inoperable yaw damper also precludes the use of the rest of the autopilot.

Modern digital yaw dampers are part of an integrated digital autopilot system. They use accelerometers and rate sensors to determine the aircraft's motion. It then runs the numbers through special algorithms to determine what rudder inputs need to be made in order to damp any Dutch roll and to coordinate a turn. It then provides those rudder commands to a servo or hydraulic system which operates the rudder.


What prevents jet engine designs with larger bypass ratios?

For ungeared two-spool designs, bypass ratios cannot be increased further. Since the fan is coupled to the low-speed turbine, increasing it would overload the turbine. Only if the engine is run at a higher core temperature can the power provided by the low-speed turbine be increased. This would require either better materials (which are not available) or lower times between overhauls (which are costly).

Note that the engines of the Rolls-Royce Trent family have the biggest bypass ratios. Rolls-Royce went with three-spool designs which allow for a finer adjustment of the speed of the different engine components.

When a reduction gearbox is placed between fan and turbine, even a two-spool design can support a larger fan, and this solution will be used in the next generation of P&W engines. Smaller engines like the ALF 502 which is used in the BAe 146 rsp. Avro RJ, used this already years ago to fit a fan to a single-spool engine. For bigger engines, transmitting the enormous power in a compact gearbox was too challenging until now. Just the heat generated by the gearbox of a 200 kN thrust class engine running at 98% efficiency would be almost 400 kW - this needs to be shed somehow!

Another problem remains, however. Bigger fans need bigger nacelles, and their drag increases with the square of the fan diameter increase. Increasing the bypass ratio of a high-bypass engine even further yields diminishing returns, which tend to be compensated by the increased nacelle drag once the bypass ratio grows beyond 12 to 15. To make bigger bypass ratios economical, active laminarisation on the nacelle will be needed.


The principle in 'Trompe' is applied to airplanes?

You are basically describing an ejector pump. This would not be very efficient, I'm afraid (I'll try to dig up some comparative figures).

The arrangement in this case would be a jet engine used to accelerate an amount of air inside a duct. With a long enough duct, the end result would be a single airmass exiting at (somewhat) uniform speed. Unfortunately, because energy must be conserved, the kinetic energy of the air exiting the apparatus would not even match the kinetic energy of the air exiting the jet engine, because of turbulence, skin friction of the duct etc.


Is it feasible to recuperate energy from landing aircraft by using a runway sled with regenerative braking?

What you propose might be technically possible, but that doesn't make it a good idea.

However, any benefits would by tiny compared to the immense cost, the extraordinary engineering efforts required, and the horrendous risk of something going wrong.

Airports have long, wide runways for good reasons. Airliners don't touch down on a single spot. Your "sled" would need to be a very wide and extremely long platform.

The sled would need to be able to bear the weight of a large airliner as it touches down. A large plane can damage a concrete runway. The sled is going to need to be extraordinarily strong.

Your platform will need to accelerate from zero to the speed of a landing airliner in very short order; if it causes the plane to decelerate too rapidly instead, it will tear bits off the plane, or limbs and heads off the passengers.

Good luck designing and manufacturing this huge, strong and and extremely lightweight sled.

(Maybe you can design the sled to match the speed of the incoming plane. That would solve some problems, but only at the expense of introducing some even more exciting new ones, like having just constructed the world's largest and most lethal railgun.)

What's going to happen when something goes wrong? You now have a wheel-less airliner, in difficulties, at landing speed, plus a huge sled also possibly travelling at 300+ km/h. I don't even want to be in the same town as that, never mind at the same airport.

What will you gain? Not much in the way of saved energy from regenerative braking; the energy cost of maintaining the machinery that can cope with such savage braking effects will greatly outweigh it anyway.

And actually, taxiing is good for aircraft engines, because it allows them to warm up before being used at full power (it may even be good for them after landing, to allow them to cool down more slowly).

So, nice idea, but in this case, the wheel, all of 5000+ years old, is an invention better-suited to airliner landings.


The transponder usually uses its own pressure reading, not what is set in the pilot's altimeter. So to prevent cheating as you describe, it is inspected and calibrated every 24 months. Tampering with it would be difficult to do on the fly because you'd have to adjust it based on the current atmospheric conditions and what altitude you want to seem to fly at. But yes, you could, in theory, adjust its readings to broadcast something different.

As far as I'm aware, only major violations are really pursued, or if ATC knows who you are when you commit the violation.


How far along was JFK Jr. in his instrument training?

From the NTSB accident report:

Pilot Training
On October 4, 1982, the pilot started receiving flight instruction. Over the next 6 years, he flew with six different CFIs. During this period, the pilot logged 47 hours, consisting of 46 hours of dual instruction and 1 hour without a CFI on board. The pilot made no entries in his logbook from September 1988 to December 1997.
In December 1997, the pilot enrolled in a training program at Flight Safety International (FSI), Vero Beach, Florida, to obtain his private pilot certificate. Between December 1997 and April 1998, the pilot flew about 53 hours, of which 43 were flown with a CFI on board. The CFI who prepared the pilot for his private pilot checkride stated that the pilot had "very good" flying skills for his level of experience.
On April 22, 1998, the pilot passed his private pilot flight test. The designated pilot examiner who administered the checkride stated that as part of the flight test, the pilot conducted two unusual attitude recoveries. The pilot examiner stated that in both cases, the pilot recovered the airplane while wearing a hood and referencing the airplane's flight instruments. After receiving his private pilot certificate, the pilot flew solo in his Cessna 182 and received instruction in it by CFIs local to New Jersey. He also received instruction at Million Air, a flight school in New Jersey, and flew their airplanes. During calendar year 1998, the pilot flew approximately 179 hours, including about 65 hours without a CFI on board. On March 12, 1999, the pilot completed the FAA's written airplane instrument examination and received a score of 78 percent.
On April 5, 1999, the pilot returned to FSI to begin an airplane instrument rating course. During the instrument training, the pilot satisfactorily completed the first 12 of 25 lesson plans. The pilot's primary CFI during the instrument training stated that the pilot's progression was normal and that he grasped all of the basic skills needed to complete the course; however, the CFI did recall the pilot having difficulty completing lesson 11, which was designed to develop a student's knowledge of very high frequency omnidirectional radio range (VOR) and nondirectional beacon operations while working with ATC. It took the pilot four attempts to complete lesson 11 satisfactorily. After two of the attempts, the pilot took a 1-week break. After this break, the pilot repeated lesson 11 two more times. The CFI stated that the pilot's basic instrument flying skills and simulator work were excellent. However, the CFI stated that the pilot had trouble managing multiple tasks while flying, which he felt was normal for the pilot's level of experience.
The pilot attended this training primarily on weekends. During this training, the pilot accumulated 13.3 hours of flight time with a CFI on board. In addition, the pilot logged 16.9 hours of simulator time. The pilot departed from FSI for the last time on April 24, 1999.
The pilot continued to receive flight instruction from CFIs in New Jersey in his newly purchased Piper Saratoga, the accident airplane. One CFI flew with the pilot on three occasions. One of the flights was on June 25, 1999, from CDW to MVY. The CFI stated that the departure, en route, and descent portions of the flight were executed in VMC, but an instrument approach was required into MVY because of a 300-foot overcast ceiling. The CFI requested an instrument flight rules (IFR) clearance and demonstrated a coupled instrument landing system (ILS) approach to runway 24. The CFI stated that the pilot performed the landing, but he had to assist with the rudders because of the pilot's injured ankle. (For additional information about the pilot's ankle injury, see Section, "Medical and Pathological Information.") The CFI stated that the pilot's aeronautical abilities and his ability to handle multiple tasks while flying were average for his level of experience.
A second CFI flew with the pilot between May 1998 and July 1999. This CFI accumulated 39 hours of flight time with the pilot, including 21 hours of night flight and 0.9 hour flown in instrument meteorological conditions (IMC). The pilot used this CFI for instruction on cross-country flights and as a safety pilot. On July 1, 1999, the CFI flew with the pilot in the accident airplane to MVY. The flight was conducted at night, and IMC prevailed at the airport. The CFI stated that, during the flight, the pilot used and seemed competent with the autopilot. The instructor added that during the flight the pilot was wearing a nonplaster cast on his leg, which required the CFI to taxi the airplane and assist the pilot with the landing.
The CFI stated that the pilot had the ability to fly the airplane without a visible horizon but may have had difficulty performing additional tasks under such conditions. He also stated that the pilot was not ready for an instrument evaluation as of July 1, 1999, and needed additional training. The CFI was not aware of the pilot conducting any flight in the accident airplane without an instructor on board. He also stated that he would not have felt comfortable with the accident pilot conducting night flight operations on a route similar to the one flown on, and in weather conditions similar to those that existed on, the night of the accident. The CFI further stated that he had talked to the pilot on the day of the accident and offered to fly with him on the accident flight. He stated that the accident pilot replied that "he wanted to do it alone."
A third CFI flew with the pilot between May 1998 and July 1999. This CFI accumulated 57 hours of flight time with the pilot, including 17 hours of night flight and 8 hours flown in IMC. The pilot also used this instructor for instruction on cross-country flights and as a safety pilot. This CFI had conducted a "complex airplane" evaluation on the pilot and signed him off in the accident airplane in May 1999. According to the CFI, on one or two occasions, the airplane's autopilot turned to a heading other than the one selected, which required the autopilot to be disengaged and then reengaged. He stated that it seemed as if the autopilot had independently changed from one navigation mode to another. He also stated that he did not feel that the problem was significant because it only happened once or twice.
The CFI had made six or seven flights to MVY with the pilot in the accident airplane. The CFI stated that most of the flights were conducted at night and that, during the flights, the pilot did not have any trouble flying the airplane. The instructor stated that the pilot was methodical about his flight planning and that he was very cautious about his aviation decision-making. The CFI stated that the pilot had the capability to conduct a night flight to MVY as long as a visible horizon existed.

So he had enrolled in a school to earn an IR training, and he had completed 12 of the 25 lesson plans, meaning he was about half way through training. His total experience, as of the log book that was available, was 310 hours, 55 hours at night. He had 36 hours in the accident aircraft (9.4 at night). About 47 of his hours took place between 1982 and 1988, he did not fly between 1988 and 1997. The NTSB report does not contain his total IFR hours.


Why does the Airbus A320 series seem to rock left and right in level flight?

As nobody has answered this in 4 days I'll add this "layman's" input.

I am not a pilot or aeronautically trained, but I understand that essentially all airliners have a dynamic yaw instability aka Dutch Roll and have stabilisers designed to address this. ANY feedback error correction system requires SOME error signal to derive the feedback from and how much error and how it manifests changes with system.

@mins I'm no expert in this area BUT all aircraft are different and you'd be surprised (or should be) if they all behaved the same. The overall combination of a wide range of dynamic forces leads to the end result.

As I recall (probably from Peter R March's very interesting 'The 747 story'  Dutch roll was not a major factor in large aircraft until the larger jets and they lost a prototype with an experienced pilot inexplicably. Subsequent investigations and close calls showed the cause was a dynamic yaw-roll coupling. AFAIR this is caused by the high yaw-induced rolling moment of swept wings and as these are standard fare as speeds rise all large/fast modern airliners have this issue and have a yaw damper to make it unnecessary for the pilot to deal with it.
Without a yaw damper, the vertical tail would need to be much larger to provide enough damping. This costs weight and drag and creates problems of its own due to the location of the tail upwards of the line of symmetry. When the aircraft yaws, the wing creates a rolling moment. This rolling motion causes a drag difference which, together with the directional stability of the tail, swings the aircraft's tail around to the other side, and the process repeats in the opposite direction.

It may be, and I'm 'mentating' this with no proof at all, that they are up against a regulatory barrier and that correcting the problem may lead to them having to do something else expensive. eg early British cars were long stroke not for any technical reason but due to taxation advantages as taxing was based on bore AREA. For a given cc size bore area was reduced by increasing stroke. This limited achievable RPM. Japanese engines had no such limits and I remember our amazement in the early days of Japanese motorcycles at the under-square high revving Japanese motorcycles - which gave them a power per cc rating advantage.

Similarly some America's cup yachts at one stage had their ratings improved by tacking light metal sheeting on their decks. This made NO difference whatsoever.

As an example of stabiliser interaction in another field - many modern cameras have inbuilt motion stabilisers. These need to be turned off when the camera is used on a tripod - or else the compensation system causes the camera to "hunt" about the essentially perfectly stable tripod. I've read of people who had major blur issues through failing to realise this.


Does weight and balance of an airplane matter more on takeoff?

By regulation, a "weight & balance" must be computed before departure to ensure that the weight is within the weight limits for a number of different conditions and that the weight is distributed such that the c.g. (center of gravity) of the airplane is also within the longitudinal c.g. limits for those conditions. That c.g. is typically computed assuming the the passengers are in the seats they have been assigned. If the passengers are seated elsewhere, the computed c.g. is not accurate. In other words, the pilots wouldn't know where the c.g. is or whether it is even within limits.

The takeoff trim setting is affected by the c.g. If the pilots set the trim according to the computed value, and the c.g. is considerably aft of that, on liftoff the nose is going to want to pitch up more than the pilots expect. If the c.g. is so far aft that it is well beyond the aft limits, serious control problems can occur. If the c.g. is far forward of what the pilots are expecting, they're going to have to pull harder on the elevator control than expected to get the aircraft to rotate, and that is going to extend the takeoff roll.

Different makes of aircraft vary widely in c.g. limitations and how tolerant they are limit wise of passenger placement in aircraft that are not full. For example, when I was flying Metroliners, if you had few passengers, you had to ask them to sit toward the rear. I once got a strange look from Rosey Grier (Google him if you don't know who he is) when I had to ask him to sit in the back of the aircraft.

Once you're in the air, the movement of passengers is of lesser concern balance wise. You're at speed, the elevator is fully effective, and the pilots or the autopilot keep the airplane in trim. In other words, the trim is what it is rather than a computed value that might not reflect reality.

Also, on large aircraft, once you're in the air in level flight and if you're so inclined, you can work out your weight by using your fuel flow, pressure altitude, and airspeed. Then with the weight and your trim setting you can come up with your c.g. I would guess that most of the glass cockpit aircraft probably do that for you automatically if you request it. My experience stopped with the 747-200, which is now a near relic.

The c.g. limits are defined conservatively, and usually in terms of the percent of the mean aerodynamic chord. It's not a case of that if the aft c.g. limit is 33% mac (a common value for 747s) and you're at 33.1% you're going to crash. It's just a case that you're beginning to move into an area that gives you a lesser degree of controllability than is deemed necessary for some situations. Continued movement to an extreme value would eventually make the aircraft uncontrollable.

Insofar as the bags-left-behind part of the question, I don't think their absence would cause a problem. If the computed c.g. including the bags was right right up against the aft c.g. limit, their absence could conceivably put the c.g. beyond the aft limit. The pilots might notice it, but handling it would not be difficult. However, aircraft are typically not loaded such that their c.g. is close to a limit. A preferred aiming point for 747-100s, -200s, and -400s is 26.6% mac.

Just for the heck of it, I did a weight & balance for a 747-400, loading it so that the takeoff c.g. was 26.6% mac. I then took 5000 lbs (100 bags x 50 lbs each) out of the most forward baggage area. This changed the the c.g. to 28.0% mac, still within limits. On the 747, a given weight of baggage misplacement has less potential to affect the c.g. than the same weight of passenger misplacement because the passenger seating extends over 20 feet forward of the most forward baggage compartment and over 17 feet aft of the most aft baggage compartment.


What does it mean when a runway's safety area is not standard?

Here is a view of 05/23 at CRW:

Source: Google Maps

At either end of the runway there is a large drop off, here is another view:

Source: WVGazetteMail.com

(In March of 2015, the EMAS at the approach end of 05 was destroyed in a land slide as shown in the picture above, I cannot find a picture if it has been repaired, the NOTAM date indicates that it has not been.)

The FAA defines a Runway Safety Area (RSA):

  What is a runway safety area (RSA)?
  An RSA is a defined surface surrounding the runway prepared or suitable for reducing the risk of damage to airplanes in the event of an undershoot, overshoot, or excursion from the runway.

And has standard dimensions:

  The RSA is a rectangular box surrounding the runway and is based on the runway
  design code. The dimensions range from 120 feet to 500 feet in width and 240 feet to 1000 feet in length beyond the departure end of the runway. (see FAA Advisory Circular 150/5300-13, Airport Design)
  Generally, on airports that serve air carrier aircraft, the RSA extends 250 feet either side of the runway centerline and 1000 feet beyond each end of the runway.

So it doesn't look like there is a suitable area for an RSA given the size and expected traffic that the runway handles.


Does the Prandtl flying wing have a lower maximum speed than other designs?

Short answer: Yes.
Maximum speed is correlated with wing loading. A high wing loading shifts all speeds up. A flying wing will always have a lower wing loading in comparison to a conventional design when payload, range and landing speed of both are identical. So you will start at a disadvantage.
Due to the high lever arm of the conventional tail, the conventional configuration can use high-lift devices (or highly cambered airfoils) for a much higher maximum lift coefficient than what is possible in regular low-pitching-moment airfoils. This allows to keep the wing small for the same landing speed. Unfortunately, the flying wing is restricted to those low camber or even reflex airfoils because its surfaces for creating a pitch balance have a small lever arm and, consequently, a poor moment-to-lift ratio.
The design of the Prandtl wing leads to a bit of downforce at the tips when in normal flight in order to lower the wing's root bending moment. But only a bit. Sweep places this downforce in the aft region of the wing so the inner, more forward region has to create all the lift for carrying its own weight, the payload and, of course, compensate for that downforce, too. Since the low wing bending moment will allow for a light wing, the total lift requirement is rather low, too, but still encumbered by the aforementioned loads.
Now to the maximum speed: A flying wing will allow for very low drag coefficients. There are no intersections between parts and no tailboom which adds friction drag, so for a given wing loading a flying wing will allow to reach high speeds with limited power. However, the lower wing area of the conventional design with the same landing speed has less wetted area and so can easily accommodate that tailboom drag. Once the details like part intersections are well designed, the conventional design should come out ahead.
What you need to watch out at high speed is flutter: That wide, light, swept wing will start to flutter much earlier (at lower speeds) than the rigid, strong, small, straight conventional wing. With sweepback you will encounter a speciality of flying wings, a coupling between the short period mode and the wing bending eigenfrequency. Since the short period mode frequency goes up with speed and the bending eigenfrequency is constant over speed, flying fast will bring both together and require a stiff wing in order to shift that point up. Don't forget that pitch damping of flying wings is an order of magnitude lower than that of conventional designs, so the short period mode will show up in a Prandtl wing if you go fast enough.


Is it possible to access the baggage compartment in flight?

There are 4 classes of cargo compartments listed in 14 CFR 25.857 for transport category airplanes. The main concern with in-flight access is in regards to fire safety.

Class A: Crew will easily discover fire from their station (and therefore be able to suppress it as well)
Class B: There is a fire/smoke detection system, and access for crewmember to use a hand fire extinguisher
Class C: There is a fire/smoke detection system to alert the crew, and a fire extinguishing/suppressing system installed
Class E: For cargo-only aircraft (no passengers): There is a fire/smoke detector, and a way to shut off air flow to the compartment

So basically, there has to be some way to both detect and address a cargo fire. Class A compartments are those such as in the cockpit where a detection system is not necessary. It sounds like the ATR example would be Class B, since they had a fire indication, and the crew had access to extinguish the fire themselves.

In larger planes with cargo in the lower hold, the compartments are usually Class C, so they have a detection system and a suppression system, and in-flight access is not required. As David Richerby's answer notes, the compartment may be accessible, but that doesn't mean that crew could effectively locate or fight a fire in those areas. Especially for large cargo holds, a fire suppression system installed througout the hold is much more effective than crew members gaining access at certain locations. This also provides the benefit of isolating the main cabin from the fire extinguishing agents.

Besides fires, there are even rarer instances where cargo compartment access could be helpful. But even in that case, it was better for the plane to just come back and land to access the cargo compartment.


What is the purpose of the glazed round area atop the Ju 87 Stuka G?

(Source) Ju 88 model.

Not just the 87, some Ju 88 models also had it, with no access to it in-flight. As mentioned, it's an antenna. The antenna is part of the EZ6 direction-finding unit.

The glass is not for viewing. It's the construction method to keep the installation as thin as possible. The sense antenna is painted on the glass.

  The PRE/6 ferrite antenna for the EZ/6 was extremely flat so that it could be mounted in a 10 cm deep "tub". The lid of the tub was a plexiglass cover with a star shaped sense antenna sprayed on. The plexiglass cover would sit flush with the aircraft skin so that there would be no air resistance from the antenna (unlike the earlier loops used with the EZ 2). (Source)

(Source)

(Source) The EZ6 unit with its different components put together by a serious hobbyist. In the glass box you can see the rotating antenna, and the thin sense antenna on top.