What are the financial implications for Lufthansa (and other airlines) of keeping the back row of their A320neo free of passengers?

Not being able to sell seats on the last row would (in Lufthansa's case) theoretically mean a 3.3% loss of revenue: LH setup for A320neo is 180 seats, 6 seats in last row.

But, only theoretically, because seat occupancy rate for Lufthansa Group was  81.4% (2018). It is very unlikely that all of the flights operated with A320neo would fly 100% fully booked. In a non fully booked flight, the last row would obviously be the first one to be left empty. The actual loss of revenue would be way less than 3.3%, but how much, it is impossible to say.

Anecdotally I'd say that it is a blessing the last row is out of service for now, this Business Traveller article will give you an idea  why: no window, seats do not recline, legroom is smaller...

World Airline News: Lufthansa Group becomes the largest airline group in Europe with 142 million passengers in 2018


Can hood time in a glider be logged as simulated instrument time for FAA IR purposes?

In the US, yes. According to the FARs you only need to have three hours in an airplane in preparation for the flight test and you must fly the cross country in an airplane so that’s probably another 3 hours.

It looks like you can log hours under the hood in a glider, but it would have to be with an airplane CFII. However, I don’t know that you would be able to train in any of the areas of operation except for (4) Flight by reference to instruments; so it probably wouldn’t be worth your time. I don’t know how you would fly an approach or fly a course by reference to navigation systems.

So as a practical matter, the answer is no.

  §61.65   Instrument rating requirements.

  (c) Flight proficiency. A person who applies for an instrument rating
  must receive and log training from an authorized instructor in an
  aircraft, or in a full flight simulator or flight training device, in accordance with paragraph (g) of this section, that includes the
  following areas of operation:

  (1) Preflight preparation;

  (2) Preflight procedures;

  (3) Air traffic control clearances and procedures;

  (4) Flight by reference to instruments;

  (5) Navigation systems;

  (6) Instrument approach procedures;

  (7) Emergency operations; and

  (8) Postflight procedures.

As an aside, I used to rent out my Cherokee to helicopter commercial students who needed instrument training

  (i) Five hours on the control and maneuvering of a helicopter solely
  by reference to instruments using a view-limiting device including
  attitude instrument flying, partial panel skills, recovery from
  unusual flight attitudes, and intercepting and tracking navigational
  systems. This aeronautical experience may be performed in an aircraft,
  full flight simulator, flight training device, or an aviation training
  device;


Where is the modification of an aircraft from floats to wheels and vice versa logged?

If the aircraft was type certified in either configuration, then no STC is necessary. Technically there should be an entry in the logbook for a landing gear configuration change, because it's considered maintenance and all maintenance is supposed to be recorded. Unless the aircraft is registered as "experimental" then the pilot is not allowed to perform anything more than Elementary Maintenance as defined by the regulations.

In Canada you don't need to reference the section of the AMM you performed the work to, they just make it mandatory to make reference to any work performed in accordance with another standard, such as an STC or a component maintenance manual. I've worked in four other countries and they had the same rule regarding the entry of maintenance, but I couldn't say for sure if it was the same way everywhere.


Why is this Instrument Approach NA for certain radials, yet it depicts a feeder route for those radials?

Your confusion may stem from the way you are viewing the instruction not to use it for arrival on the radials 356 to 157. If you were arriving on the 356 Radial of the PIE VORTAC, your course/track (and/or heading in calm winds) would be 176°. If you were arriving on the 157 Radial of the PIE VORTAC, your course/track (and/or heading in calm winds) would be 337°. If you were arriving on the 85 Radial of the PIE VORTAC, your course/track (and/or heading in calm winds) would be 265°. All of these arrivals would necessitate a hard, sharp turn at a potentially steep bank angle. This will need to be avoided.
You are able to use other routes to the Initial Approach Fix other than flying first to the PIE VORTAC. Like flying directly to the RUYKI waypoint as your first point on the IAP. This is especially valid since arriving on any of the above mentioned courses/tracks will place RUYKI in easy access of the pilot. This would be much simpler than trying to make that hard, sharp turn at a steep bank angle. Only minor adjustments from the arrival course/track at an appropriate distance from RUYKI would need to be made. This has the added benefit of reducing confusion and freeing up airspace from conflicting traffic.
If you are concerned with using the STARs as feeder routes, you would use the PIE VORTAC as your transition to the IAP from all STARs with endpoints West of KTAP. You would fly directly to RUYKI from all STARs with endpoints East of the IAP. If you have to lose altitude from your descent from the STARs, you would use the Hold en lieu of a course reversal to do so.


What are the advantages or disadvantages of a mid wing design?

The mid wing is mostly used in combat aircraft and rarely in passenger jets. The reasons are mostly structural.

Aerodynamically, the mid wing is the best option as it is much more streamlined and has less interference drag compared to the high and low wings.

The mid-wing also has neutral roll stability, which is good from the prespective of combat and aerobatic aircraft as it allows for the performance of rapid roll maneuvers with minimum yaw coupling.

The mid wing has certain disadvantages when it comes to structural design as far as passenger and cargo aircraft are concerned- the wing will have to either pass through the fuselage, eating into usable volume or the structure has to be strengthened around the fuselage to carry the loads. This is the main reason this type of wing is rarely found in commercial airliners.
There are some aircraft which do have mid mountedwings, like the Piaggio Avanti, which has the wings passing behind the cabin and canards and the Hansa jat, which solved the problem by sweeping the wings forward and thus passing it through the rear fuselage. These types are rare, however.

Image from hansajet.de
This type of wings are used by a number of combat aircraft, however, for example, the Dassault Rafale.

Image from http://indiandefence.com
For combat aircraft, the adoption of mid wings means that the landing gear have to retract into the fuselage for keeping the length under check. The mid wing allows for the carriage of weapons and fuel tanks in underwing pylons however. Also, the pilot's visibility is not affected during turns as in the case of high wing.


What is the Space Shuttle's command law?

The Space Shuttle's manual stick mode is called Control Stick Steering (CSS).

It commands load factor in pitch (yaw is similar). In pitch it of course accounts for the existing load from vertical deceleration. And rate in roll. When released it holds the attitude.

A second submode is indicated airspeed hold (the stick controls speed via the speed brakes), else S/B operation is manual.

(NASA Space Shuttle Digital Flight Control System)


How was the "frozen wing flap grease" problem solved? (Antarctica, 2001 emergency evac)

Flying with the flaps extended is perfectly possible, just inefficient. At that point they were probably just trying to get in the air, not worrying about their fuel efficiency or airborne speed. Otters normally land and take off with flaps somewhat extended. The main problem is that with flaps fully extended, acceleration will be low, so it will be a long, slow takeoff. One issue is that if the plane has any icing, being in a full-flap condition can lead to a stall.

Once things get down to -50F or below, stuff really starts to freeze. For conditions like that you need to start replacing grease with graphite lubricants. Even fuel freezes so the planes have to use special heaters.

Here is a more technical description of the event by an electrician:

  We then refilled the smudge pots and brought out tanks containing
  about 1,000 gallons of fuel to refuel the plane. They also brought out
  3 Herman-nelsons, portable diesel heaters used to warm up planes and
  other big equipment. At about 2:15AM, the plane was started but some
  of the hydraulics in the tail controlling the flaps were frozen. We
  called to get the Herman-nelsons back to heat up the flaps. They ran
  their engines the whole time, and we had to bring out another 100 or
  200 gallons of fuel.

  Finally, at about 5:00 AM, the plane was working right and was ready
  to go. But then it appeared the plane was stuck in the snow. So a
  couple of guys stood on a car-like vehicle with tank treads, and shook
  the plane's wing. This caused the whole plane to rock back and forth.
  But finally the plane broke free and taxied to the skyway. The plane
  turned around and took off and flew in the -64F air.

  Brother Aaron Coy, Local 48 Portland, OR Amundsen-Scott South Pole
  Station, South Pole, Antarctica

There are no hydraulics in the tail, obviously, so the electrician is confused about something. The hydraulic system in an ski-equipped Otter is used for the flaperons (in the wing) and for the ski controls.

Twin Otter at Casey Station


Navier-Stoke vs Prandtl lift calculation

The Navier-Stokes equations represent a highly non-linear set of equations. Actually, although the have almost 2 centuries, they are one of the Millennium Prize Problems. Most of the interesting phenomenas represented by these equations include turbulence.
In specific conditions and hypothesis, analytical solutions have been demonstrated which is allowing us to understand the problem and physicis by reducing the complexity of the equations.
The law of Poiseuille appeared also after Navier-Stokes, and event the Darcy equation is empirical, not derived from Navier Stokes.
The interest of aerodynamics started to increase at the end of sXIX (first wind tunnel was constructed on 1871), so, in front of the complexity of this phenomena and the challenge the Navier-Stokes equations are some simplified equations appeared with some specific conditions. One of them was the the Prandtl lifting line theory.
One of the advantages of this theory is that relates the aerdoynamic properties of a wing to its geometry, without the need to calculate the complete flow field... think about that in CFD you have to calculate the complete flow field during hours (days?) in order to understand the properties and behaviour of a surface, this theory gives an analytical answer...
Still this theory is useful today, as helps to understand the behaviour of the wing.


What is the exception applicable to basic VFR weather minimums in FAR 91.155?

CFR 91.155(b)(2) has the exception:

  (2)Airplane, powered parachute, or weight-shift-control aircraft. If the visibility is less than 3 statute miles but not less than 1 statute mile during night hours and you are operating in an airport traffic pattern within 1/2 mile of the runway, you may operate an airplane, powered parachute, or weight-shift-control aircraft clear of clouds.

So if the visibility is less than 3 statute miles (not less than one statute mile at night), you can operate in Class G as long as you are clear of the clouds and within 1/2 mile of the runway. It does not mean that the entire exception applies at night, only that at night, you need to have at least 1 mile of visibility, otherwise during the day you can operate down to nothing as long as you are clear of the clouds.


How do pilots cope with pressurization changes?

There is a chance you suffer from aerosinusitis but you should consult a physician to obtain a proper diagnosis (Disclaimer: I am NOT a doctor). For what its worth commercial planes are pressurized generally to about the pressure you would see at 8000 ft. this equates to about .75 Atm. In the reverse case 33ft underwater already has you at 2 Atm.

When I fly (generally unpressurized) I usually chew gum which i find helps.


Are there any airports that require arriving/departing flights to fly under an obstruction?

It would not surprise me if someone, somewhere had done it, maybe even for good reasons (for example, possibly during the barnstorming era, one of the world wars, or perhaps on an Air America / POW rescue mission or similar) but thinking about an airport doing it as standard procedure brings to my mind phrases like "outrageously dangerous", "criminally irresponsible", and "out of your mind".

So I'm going to go with no, there aren't.


How does the performance of an aircrafts propeller change with respect to distance from obstructions?

A propeller accelerates air, and the stream tube going through the propeller disc can be idealized as something which is initially wider than the propeller disc and contracts while being accelerated (Froude's propeller hypothesis). Now two types of obstruction are possible:

Obstructions to the flow near the propeller axis, and
Obstructions to the flow near the stream tube.

It is quite obvious that something which blocks the flow will reduce the propeller's efficiency, and since flow speed is higher behind the propeller, the same obstruction will reduce performance more if placed behind the propeller disc. This is why pusher designs show better performance with the same engine power.

But also objects near the outer edge of the propeller can reduce efficiency. When a wall on one side ahead of the propeller prevents air from flowing towards the disc, the flow though the propeller disc is disturbed and efficiency will suffer. Similarly, a wall past the propeller will prevent a symmetric outflow, and the stream tube will attach to the wall (Coanda effect). This can be used to the advantage of high lift devices on wings, but will generally reduce efficiency.

For experimental data, I recommend to read NACA reports like the one for engine cowling development or this one on fuselage-propeller interference.


If I have a float plane, can I land on any body of water?

It really depends on the state, though you can't land in National Parks (the National Park Service regulates that, not the FAA).  The FAA doesn't care where you land it, though if you ball it up due to poor choice of landing area then they'll have something to say.

Some states don't really care where you land (like Oregon), others don't let you land anywhere (like New Jersey).  You should contact your state and get the regulations from them.


Carburetor Heat Required on Carburetor equipped GA aircraft?

Carb heat is not specifically required by regulation. What is required by the following rule is a means to prevent ice accretion:

  14 CFR 33.35 Fuel and induction system.

  (b) The intake passages of the engine through which air or fuel in
  combination with air passes for combustion purposes must be designed
  and constructed to minimize the danger of ice accretion in those
  passages. The engine must be designed and constructed to permit the
  use of a means for ice prevention.

Carb heat is the most common solution, but alternate solutions may be acceptable.


What's the mechanical 'whoosh, whoosh' sound in this video?

It's the sound of the trim wheel rotating on the center console of the Boeing 737.

The trim wheel controls elevator trim. It can either be moved automatically by the autopilot, or manually by the pilot. The pilot can push the trim button on the yoke with their thumb (left for the captain, right for the copilot).

This is a photo of a B737 classic series, but this feature is unchanged on the NG series.

In this specific instance, it sounds like there were two small manual push on the trim button.


Why is the centre of pressure for a real wing with low aspect ratio more forward than that in two-dimensional flow?

The center of pressure is defined as the point on the wing/airfoil where there is a zero net moment. This definition means that it is a function of the lift and subsequently of the lift coefficient. Airfoil theory overestimates the slope of the lift curve due to the absence of wing tip effects. With regards to the second question - I think the answer is rather subjective. Mathematically the limit of a very low aspect ratio is a 2D airfoil moving through unconstrained medium. How high an AR can go is mainly dictated by structural soundness of the wing. For real aircraft, have a look at the classic example of a low aspect ratio wing - F-104. Typical high aspect ratio aircraft are most gliders. I would point you to the exceptionally interesting read that is Theory of wing Sections by Abbott and Doenhoff and also any book on aerodynamics, e.g. Anderson


Placement of positioning lights on A320 winglets

Position lights are only visible in certain sectors (see image). The red and green lights on the wings are not supposed to be visible from behind.

Image source: Learn to fly


When is an aircraft handed over from Center to Approach?

In general, aircraft are handed over on frequency to the next controller via a simple instruction to change the frequency:

  R: "Lufthansa One Two Tree, contact Langen Radar 128.550"
  A: "Contact 128.550, Lufthansa One Two Tree"

The simplified order of contacted stations for a commercial flight, depending on availability and airspace structure is:

  Delivery (if available)
  Apron/Ground (if available)
  Tower
  Departure (if available, sometimes handled by Approach)
  Enroute ACC/Center (multiple stations along the route)
  Arrival/Approach
  Director (if available / in use)
  Tower
  Ground (if available)

The point and altitude or flightlevel where the handoff is initiated is agreed upon in Letters of Agreement between the different sectors or ACC/ARTCC stations.

(Source: SentryRaven - Own Work)

The above picture shows the airspace around Köln/Bonn (EDDK) Airport, with the Köln Arrival East (KAE) sector being actively displayed in black. The STAR entry / clearance limit fixes are GULKO and KOPAG, in the east. Most traffic not arriving via NOR VOR in the west will terminate at these two fixes, which also serve as the handoff fix between the center controller (Paderborn High, Taunus and/or Rhein Radar Upper Control) and the arrival controller responsible for Köln East Sector. The Letter of Agreement between those sectors states that traffic arriving to Köln/Bonn via GULKO and KOPAG is to be cleared to FL100 and cleared for the respective STAR out of GULKO or KOPAG. The handoff is initiated approaching FL100 and approaching the entry fix, before the sector boundary.

The handoff is therefore based on airspace structure and sector boundaries, not on a preset distance from the airport. While arrivals from the east are handed off at FL100 over GULKO and KOPAG, arrivals from the west at NOR VOR are handed off at FL140-FL170.

Landing and Take-Off clearances are issued by the Tower controller, as the approach controller is not necessarily based at the same airport but in most cases in a remote facility together with other approach and center controllers. They have no visibility of the airport and can thus not issue these clearances.

The handoff to Tower usually happens when the aircraft is established on the final approach segment of the published approach (usually after passing the Final Approach Fix (FAF)) or a visual approach to the runway.

The phraseology is the same as above:

  R: "Germanwings Two Six Alpha, contact Tower 124.975"
  A: "124.975, Germanwings Two Six Alpha"


Which commercial aircraft can stay in the air the longest?

A commercial airship, like the 'Zeppelin NT' can stay airborne for 24 hours.

The record (for a military US-Navy blimp in the 1950s) is 264 hours, 12 min. It covered more than 13,000 km.

  Record flight of 8,216 miles in 264 hours. Lakehurst NJ to west Africa to Key West FL non-stop. (Source)


None, his combat unit was ground attack, not air to air, so it is unlikely he ever was involved in air to air combat.


What is the guy in green showing to the F/A-18E pilot before catapult launch?

That's a weight check. The sign has the weight of the aircraft in pounds. The catapult crew guy first shows the presumed weight to the PIC who must give a thumbs up, agreeing, "Yes, that is the weight I believe my aircraft to have."

The crew guy must then show the same exact set of numbers to the catapult chief operator, who must also approve it: "Yes, the catapult is set to launch that weight.

You can actually see both verifications happening in the two photographs above, the first one is to the PIC, the second to the catapult operator. Only when both verifications have occurred will a launch be permitted.


What is the exhaust from the end of jet wing prior to landing?

The only places where any fluid leaves a flying jet aircraft are the engine tail pipes, outflow valves and air cycle machine exhausts, and the auxiliary power unit exhaust, but that is usually only used on the ground.

None of these exhausts usually leaves any visible trail at low altitudes. The engine (and apu, if running; it is a small engine) exhausts contain a lot of water, but are very hot, so it remains a vapour; it only condenses at high altitudes where there is very cold. And the air from outflow valve—excess air leaving cabin—and from air cycle machine—air used for cooling—do not have any more water in them than the ambient air.

What on the other hand might leave visible trail is condensation is vortices behind wing-tips and sometimes end of flaps. This is just fog forming in very humid air due to decrease in temperature, like it might in the coldest hours around dawn, except here the cooling is local, caused by decrease of pressure that accompanies generation of lift by wings (this is called adiabatic cooling).

Regarding fuel, when the engine power is reduced, less fuel is simply pumped to the engines, so more of it stays in the tank. There is absolutely no reason to waste it by venting it anywhere—except for very, very rare case where the aircraft needs to return due to some malfunction, and needs to get lighter to avoid more damage on landing; but this intentional fuel dumping is always done at high altitude so the fuel evaporates before it could get to the ground and contaminate it.


Why is a control surface that allows two sides of airflow better than those that allow one?

For low drag, you want to minimize the surface changes presented to the air flow. Large changes in the surface will create turbulence and pressure changes that contribute to drag. Small changes will minimize these sources of drag.

When you move a control surface like an aileron or elevator, air is flowing past both sides of the airfoil. Although this changes the direction of the flow, which gives the control force as well as some drag, the air can still flow past both sides.

In the case of a spoiler, the air cannot flow past both sides. This increases the frontal area presented to the flow, and creates a low pressure area behind the deployed surface. Creating a low-pressure area behind an object is a big contributor to drag, which is why aerodynamic bodies tend to have a teardrop shape.

Spoilers on the wing also have the effect of reducing lift. By disrupting the smooth low-pressure flow over the upper surface of the wing, they reduce the effectiveness of the wing, effectively stalling the affected portion.

For an illustration of both principles in action, see this video of a speed brake on a Mooney. This shows how even a relatively small object, when disrupting the air flow, can add a significant amount of drag.


What was the commercial speed of Concorde?

The Concorde cruised at 1350mph (~Mach 2.05 at 55,000Ft.)

Concorde’s fastest transatlantic crossing was on 7 February 1996 when it completed the New York to London flight in 2 hours 52 minutes and 59 seconds.

When it flew the average flight time (was) around 3 hours 30 minutes, but can be slightly longer if the aircraft (needed) to hold before landing at the local airports.

Wind is a huge factor in flying. A headwind or tail wind can mean a big difference in flight time. The Concorde cruised at a significantly higher altitude than most airplanes ~55,000Ft. which means it was subject to very different wind than its sub sonic lower flying counterparts. At that altitude winds in excess of 100Kt are common place. So you could see a 200Kt difference in speed depending on direction.

Also of note the speed was often called out using Mach's Number (the Concorde flew a bit over Mach 2). However since Mach's number accounts for air density,  Mach 1 at 55,000Ft. is 660MPH which is significantly lower than the often quoted Mach 1 = 760MPH (which is the speed of sound at sea level).

One of the best sources of info on flying the Concorde is this podcast interviewing one of the pilots.


Can passenger movement in an airliner make it stall?

I used to teach sport parachuting, and we occasionally pranked the pilots by shifting the weight around.

A Cessna 206 set up for parachuting will have all but the pilot's seat removed, the jumpers sit on the floor. Everyone moves forward for takeoff and then sits back for the ride up. The instructor (me) sits on the floor where the co-pilot would normally be, facing aft, everyone else faces forward. I would wait until the plane was trimmed for climb (and well above 1000 feet) and then motion the passengers to come forward a bit (the pilot cannot see this happen). He adjusts trim as usual, thinking nothing of it. Passengers come forward some more. Trim adjusted again. Eventually we have 5 people wearing 20kg packs all jammed up into the first 2 "rows" and the trim almost fully nose up.

One signal, and 1/3 of the airplane's gross weight quickly moves almost 2 meters aft (in a 4 meter cabin), followed by a sharp pitch up in both the nose and the pilot's blood pressure. The stall alarm usually goes off too.

Mid-size tailgate aircraft used for jumping are regularly stalled by too many people on the tailgate for too long. The rule there is stay forward until it's your turn, then go aft and get out (if the buzzer goes, you get out NOW).

So it's possible to stall a small aircraft by moving the passengers around.

Scaling this up to airline sizes, we find that the passengers are a rather smaller percentage of the airplane's gross weight, and the presence of things like seats, bulkheads and galleys at the rear prevent 300 people from gathering rapidly at the back. The rather large hydraulically powered elevator also has substantial authority over the aircraft's attitude.

So no, a small group of passengers won't be stalling an airliner out of the sky no matter where they stand. Noticed by the pilots: possibly.


How does a flux gate compass system work?

Fluxgates are a way to determine a magnetic field, in this case for navigational purposes. The basic principal is based on the lines of flux that the magnetic field of the planet gives off, a nice overview can be found here:

  The flux gate compass that drives slaved gyros uses the characteristic
  of current induction. The flux valve is a small, segmented ring, made
  of soft iron that readily accepts lines of magnetic flux. An
  electrical coil is wound around each of the three legs to accept the
  current induced in this ring by the Earth’s magnetic field. A coil
  wound around the iron spacer in the center of the frame has 400 Hz
  alternating current (AC) flowing through it. During the times when
  this current reaches its peak, twice during each cycle, there is so
  much magnetism produced by this coil that the frame cannot accept the
  lines of flux from the Earth’s field.

There is a good video here as well.

Older, pre-glass HSI's are often slaved directly to them, like this one. On newer systems the flux-gate is a component of the AHARS.

Lots of aircraft use them, they can be installed on everything from a small GA plane all the up though an A380. These days they are fairly small units.


What makes flight recorders harder to find than tagged sharks?

They're different usage cases, and have to be engineered differently. Three major points:

A shark tag doesn't have to survive a 500mph impact (#7 on the list) with the ground, and a flight recorder has to be able to do so. It adds a lot of padding and weight, and limits the kind of battery that can be used.

Sharks also don't dive to a depth much greater than 3000 feet on most occasions. A planes flight recorder is designed to survive to a much lower depth, under much larger amounts of pressure. Not to mention being designed to survive all sorts of other things.
Another point regarding depth, it is much harder to search for a signal at a depth of 15,000 ft, than it is even at a depth of 5000 ft. This article shows how big of a difference you get between even 20 meters and hundreds of meters (not thousands), it gives a good idea of what I mean.

If a shark tag fails, nobody cares. If you tag 100 sharks and 30 of the tags survive, you still have some pretty good data. But if one airplane crashes and its black box fails, it's considered unacceptable. They are required to survive 100% of the time.

All of these differences combined mean that black boxes are manufactured to much higher standards, and as a result they are bulkier, have different sorts of radios and require much more battery life (to support the larger systems) than a shark tag. All this conspires with the difficulty of getting a receiver deep into the ocean to make finding FDRs/CVRs really difficult.
That's not to say they couldn't design one that is much better, it just becomes extremely expensive (as all things are on airplanes). And you have to determine if these edge cases (like flight MH370) are worth making an airplane a few million dollars more expensive (between R&D and certification, the later being quite expensive).
I think the theory was they should be able to find any one of these within a month, and that may take some rethinking (maybe 3 months, or a year perhaps?) But they'll never be as successful as shark tags just because the requirements to be able to find one at that depth 100% of the time are quite different from the needs of a shark tag.


That's the ILS heading to the runway.

Based on how runways are numbered, runway 11's heading will be somewhere between 105° and 114°, 114 nails it down.


How can I calculate the maximum range of an aircraft descending with power (not gliding)?

You can use the lift to drag ratio (L/D) to calculate for just about any stage of flight if you compensate it properly. Assuming your descent is steady-state, lift is equal to weight, using the L/D you can then determine drag. Next take drag and subtract the thrust produced by the engine to get the amount of excess drag need to be covered by gravity. You glide ratio will be lift divided by excess drag. This makes for a simple calculation of your variables remain constant, however you will need to use an integral if you want to compensate for changes such as differences in engine power at different altitudes, and reduction in weight as fuel is burned.


Is the 737-800 circular PFD for AOA or RA?

It’s a customer option (i.e. the operator can choose and specify) to switch between the two; presumably by pin programming the computer responsible for generating the display symbols.


Why does the Dassault Falcon 7X's cockpit have ashtrays?

In the United States, the smoking ban only applies universally to air carriers on scheduled flights. The regulation states

  §252.4   Smoking ban: air carriers. Air carriers shall prohibit smoking on the following flights:

  (a) Scheduled passenger flights.

  (b) Nonscheduled passenger flights, except for the following flights
  where a flight attendant is not a required crewmember on the aircraft
  as determined by the Administrator of the Federal Aviation
  Administration:

    (1) Single entity charters.

    (2) On-demand services of air taxi operators.

  (c) Nothing in this section shall be deemed to require air carriers to
  permit smoking aboard aircraft.

So for essentially all of the Falcon's missions, such as Part 91 corporate flights, and private charters under 10 passengers, smoking is permitted, as long as an "adequate number of self-contained, removable ashtrays" are provided (14 CFR 23.853(c)(1) or 25.853(f)).

Said ashtrays from a factory photo:

Closeup found here:


What is a localiser back-course approach and how does it work?

A localizer back course is simply flying on the back side of the localizer to the runway.  How a localizer works is it sends out two signal lobes:  one at 90Hz and the other at 150Hz.  The localizer needle in the airplane compares the relative strength it receives from both lobes and then shows a deflection.

See this figure from the Instrument Flying Handbook (2015) published by the FAA.

Notice the top left of the picture shows the same lobes on the same side of the runway.  Now imagine flying the front-course, the blue lobe is on the right.  If you are flying the back-course, the blue lobe would be on the left.

The localizer needle doesn't know if you are on the front-course or the back-course and will show the same deflection for both situations.  The problem comes in for the back-course is that the needle deflection is deflected the wrong way.

To answer your questions.

What does back-course mean?  It simply means you are flying on the opposite of the localizer signal.  If there is a back-course published, the signal strength will be strong enough to fly the approach as required.
How common is a back-course approach?  There are currently 69 back-course approaches in the United States.  There are approximately 1,893 ILS approaches.  This is around 3.5% of back-course approaches as compared to ILS approaches.
The same flight and navigation instruments required to fly a front-course ILS is required to fly a back-course ILS.

From a technique standpoint.  Whenever I fly a back-course approach, irrespective of whether I am using an HSI or VOR receiver, I will always set in the front course.  For pilots that use an HSI this will provide for "positive sensing" meaning the needle will deflect correctly.  For pilots using a VOR, the needle will shade bottom numbers that correspond to heading that need to be flown to get back onto the back-course approach.

If this was a back-course approach, notice that the needle is deflected to the right.  Conventional wisdom says you need to turn away from the needle to re-intercept.  I say to select a heading under the needle to fly.  That heading will be approximately 120°.  Take a look at the heading indicator and determine that you most likely need to turn left to re-intercept the back-course.  Try it and you will see it works.  Conversely, I also teach the same concept for an ILS except the heading to fly is on top of the VOR indicator instead of on the bottom.


Cessna 172/182: Should I set the tank selector to the R.H. tank after parking the airplane?

The C172S manual I have says to set the selector to left or right as part of the "securing airplane" checklist:

  Fuel Selector Valve -- LEFT or RIGHT to prevent cross feeding

I was also taught to set it to right during my initial training. The idea is to prevent cross-contamination or leaks if one tank is compromised. Another reason is that if you park the aircraft on a slope, you could end up with an imbalance between the tanks, as you said.

So the POH confirms that it prevents cross feeding, at least in that model: you should always check the POH for your specific aircraft.


Reference Map of EUROCONTROL charging zones

That is the map of the European airspace, however you have mirrored it such that north is now south and vice versa.

source: Eurocontrol

GC    Spain Canarias
AZ    Portugal (Azores)
LP    Portugal Lisbo
LE    Spain Continent.
LF    France
LS    Switzerland
LI    Italy
LM    Malta
LG    Greece
LC    Cyprus
LT    Turkey
UD    Armenia
UG    Georgia
LB    Bulgaria
LA    Albania
LW    Republic of North Macedonia
LY    Serb.-Montenegro
LD    Croatia
LQ    Bosnia Herzeg.
LJ    Slovenia
LO    Austria
LH    Hungary
LR    Romania
LU    Moldova
EP    Poland
EG    United Kingdom
ED    Germany
EH    Netherlands
EB    Belg.-Luxembourg
ES    Sweden
EK    Denmark
EF    Finland
LZ    Slovak Republic
LK    Czech Republic
EY    Lithuania
EN    Norway
EI    Ireland
EV    Latvia


Three major reasons:

1) Advanced aerodynamics using CFD analysis and wind tunnel testing as well as construction with lightweight and largely seamless composite materials provide a very 'slippery' airframe that doesn't create a whole lot of induced or parasite drag for a given speed.  Very thin, high aspect ratio wings are used.  Access panels are kept to a minimum.  All joints are smoothly blended together.  Landing gear is retractable and fully enclosed.  Fasteners are flush and heads taped over.   Gaps and edges are puttied or taped sealed prior to flight.  The airframe exterior has been waxed and highly polished for as smooth of skin as possible.  The entire aerodynamic envelope has been very carefully studied and optimized to minimize areas producing turbulence and as a consequence parasite drag.

2) Minimized flat plate area.  The cross section of the aircraft has been kept to the bare minimum needed for structures and systems and virtually nothing for crew comfort.  The cockpit is really tight and built around the shape of the pilot's body - even to the point of requiring the pilot wear an oxygen mask connected to a fresh air vent to facilitate breathing.

3) Sacrificing docile handling characteristics.  The wings and flight controls are maximized for high speed flight as opposed to easy and forgiving flight characteristics.  If you look at a Beech Bonanza or a Piper Archer, you'll note that they have very thick wings which handle well at low speeds and give an inexperienced pilot a lot of forgiveness in sloppy handling before departing from controlled flight at the expense of producing a lot more induced drag.  This isn't the case of the Nemesis and it demands a very good pilot at the controls to fly it at the correct speeds and numbers with little margin of error.


Why does pitot tube freeze at an altitude whose temperature is way below the freezing point?

First, AF 447 was flying into the top of a tropical storm. The air was much more humid and warmer than that of the standard atmosphere.

Next, in the absence of seed crystals or nuclei, water vapour or liquid droplets stay in the air down to temperatures of -48.3°C at sea level pressure without freezing. From the linked article:

  Droplets of supercooled water often exist in stratiform and cumulus
  clouds. An aircraft flying through such a cloud sees an abrupt
  crystallization of these droplets, which can result in the formation
  of ice on the aircraft's wings or blockage of its instruments and
  probes, unless the aircraft is equipped with an appropriate de-icing
  system. Freezing rain is also caused by supercooled droplets.

So it was the impact with the probe which caused the supercooled droplets to freeze.


But nowhere either there or elsewhere online can I find how to calculate the profile drag.

Seems like you were searching for the incorrect terms. Try searching "boundary layer integral momentum equation", "von Karman boundary layer integral", "momentum deficit", "boundary layer Kinetic energy dissipation integral" or something similar. You should get plenty of resources/lecture notes on the subject.

  So does anybody know how to calculate the form drag for a given aerofoil (eg NACA4412)?

In essence, this is done via integrating the "Integral Momentum Equation" or its non-dimensionalized version "von Karman Equation" over a coordinate system defined over the airfoil contour.

  I can get the skin friction drag from boundary layer calculations but have no idea where to go from there.

If you study the "Momentum integral equation" stated above you can see there are two contributors to the momentum deficit or its rate of change. one is skin friction and the other is the profile drag which is equal to - mass defect * rate of change of edge velocity.

Put it in another way, the skin friction term usually is dominated by the front portion of an airfoil where due/ds mostly favorable and the profile drag is dominated by the pressure recovery region aft of the airfoil because of the negative velocity gradient and higher mass defect.

But the story does not end there, because you will have to add the viscous dissipation happening in the wake up to the far-field as well. This is usually done using the "Squire-Young" equation by applying the previously obtained momentum deficit at the trailing edge.

PS :
All above being said, you can easily use XFOIL for such calculations. But understanding what's going on under the hood in such an application, might provide one with great insight and appreciation for what they have got for free.


How does a pilot report a person (on the surface) in distress?

I would treat an active SOS signal from the ground the same way I would treat an ELT signal on 121.5: Contact ATC (or Flight Service if you're not sure what ATC frequency to use) and inform them of the event.

As with reporting an ELT you should be prepared to tell ATC:

What kind of signal you've observed
(ELT, signal light, signal mirror, "SOS" or "HELP" spelled out with rocks…)
The time you observed the signal
(Ideally you'll report it while overhead & actively monitoring it)
Your location and altitude

Ideally you'll be able to give your location as a GPS fix as SHAF described.
If that's not possible there are other options, in roughly-descending order of accuracy:

A DME fix (radial & DME distance)
A VOR fix (the intersection of two radials from separate stations)
A VOR radial & visual landmark (ideally something on the sectional chart)
While just a radial is not very useful it can be helpful in conjunction with a landmark: "South side of Mt. Greylock, on the 350 radial off Chester VOR" helps narrow down the search area considerably.
A visual landmark based on the sectional chart.

ATC may also ask you to circle the distress signal and ident in order to get a radar fix to supplement any of the above.


What effect would there be if the brakes were locked at touchdown?

I've seen it happen many times (ask any rental place about this). You get a big bald spot cut into the tread. Sometimes it goes all the way through the tire.

If it happened on one side, you'd likely get a ground loop.


Why offload bags for missing passengers when flights are allowed to carry unaccompanied non-PAX air-cargo in holds?

Partial answer:

The rule about offloading passenger bags is known as Positive Passenger/Bag Matching. It was introduced after the Pan Am 103 bombing in 1988 where a bomb was placed in a suitcase that was checked through to New York without belonging to any passenger on the plane.

By the practices of the time, all bags tagged with the right flight number would be loaded onto the plane, without pausing to cross-reference them to passenger manifests. The investigation never found out for certain how the suitcase with the bomb had entered the baggage system (an inside job at Luqa airport was suspected but not proved), but the outcome was to require matching of all the bags to actual boarded passengers before departure.

So this is not necessarily a case where explosives were placed in the checked bag of a passenger who should have boarded but didn't -- but it is close enough to see that the risk is not pure fantasy.

The rule applies to all international passenger flights, but not to US domestic flights; the US authorities apparently have better trust in their ability to screen checked bags for explosives before loading them onto a plane.

I would assume that air cargo also undergoes similar screening and that is why it is not subject to PPBM rules -- even outside the US there is better time to screen cargo thoroughly than there is for bags that are only checked an hour or two before departure.

This Travel.SE question and its answers have more information about PPBM.


When using the Source Panel method and dealing only with sources and sinks, why do lift and drag equal zero?

A single source, or a source sheet comprised of infinitesimal sources (sinks are just sources with negative strength), produces a velocity field that contains no circulation. Without circulation, it can't possibly generate any lift. The Source Panel Method is just a discretized computational method for source sheet. It, therefore, only produces non-lifting flow.
Drag, in the context of incompressible potential flow, only arises through induced drag. Without lift, induced drag would also be nil.
To predict lifting flow, vortex sheet modeling is typically used that, by construction, produces non-zero circulation (unless the integral of sheet strength is zero by prescription). An additional prescription of the Kutta condition is required to guarantee a unique physically correct lifting flow.

Image collated from: http://web.mit.edu/16.unified/www/SPRING/fluids/Lecture_Notes/f18.pdf
A mathematically equivalent methodology is to use doublet sheet modeling, using the following tranform:
$$\vec{\gamma}=\hat{n} \times \tilde{\nabla}\mu$$
where $\vec{\gamma}$ is the vortex sheet strength, $\hat{n}$ is the sheet normal, $\mu$ is the doublet strength, and $\tilde{\nabla}$ is the surface-gradient operator.
Somewhat confusingly, a doublet is a combination of a source and sink that are separated by an infinitely small distance. A single doublet is non-lifting. However, a lifting flow can be generated if the doublet sheet varies in strength. This video based on Drela, Flight Vehicle Aerodynamics provides an extremely good intuitive explanation.


Do Flight Simulation Instructors stop the simulator before a simulated crash?

I would say that crashes happen fairly frequently on initial type courses where new pilots are moving up to jets, and mainly on what are called "V1 cuts", where an engine is failed right at rotation or just after.
Many are not ready for the hard roll you get with a swept wing airplane when it yaws hard and you are slow to counteract it with rudder.  Before you know it, the wing tip is on the ground.  The instructor has to let the pilot try to recover and usually has to let it go all the way.
Otherwise, instructors will normally try to freeze the sim just before a crash because of time wasted waiting for the machine to reboot and having to reconfigure all the settings the instructor has set up for the session. This wastes very valuable and expensive sim time (I was also told it was hard on the equipment, but I'm not sure why).
It's not done to avoid traumatizing the students though.  One basic tenet of training is to make things memorable, so overall, a crash-in-the-box is a plus.
You can get a bit lost in the moment and forget you are in a simulator if the pressure is dialed up high enough (after 4 hours of abnormals and emergencies, you get wound up pretty tight; I used to tell people it was like spending hours in a cement mixer filled with bowling balls), but that effect is pretty superficial and when a crash happens, you know you are on an amusement park ride in the end, and you're not going to wet your pants in your last simulated moment of life.
In fact, aside from the visuals, which on the latest ones are pretty good but still not like a real view, after you get used to it, you start to become more and more aware of the physical differences from a real flight, like the motion sensations that don't quite fit what you are seeing (they really only simulate accelerations and decelerations and short term jerky up/down and rolling/yawing movements with any realism, which is good enough most of the time), and the sound of the hydraulic gear working below you, and that tends to kill the "lost in it" effect even more, and it becomes more and more like an amusement park ride as you go back for recurrent training.


Does in-flight Wi-Fi require regulatory approval?

The FAA touches upon it in this letter

  Current FAA regulations require an aircraft operator to determine that
  radio frequency interference from PEDs is not a flight safety risk
  before the operator authorizes them for use during certain phases of
  flight. Even PEDs that do not intentionally transmit signals can emit
  unintentional radio energy. This energy may affect aircraft safety
  because the signals can occur at the same frequencies used by the
  plane’s highly sensitive communications, navigation, flight control
  and electronic equipment. An airline must show it can prevent
  potential interference that could pose a safety hazard. The PED ARC
  report helps the FAA to guide airlines through determining that they
  can safely allow widespread use of PEDs.

The operator is responsible for determining that the unit does not create any interference they link off to this document which is pretty verbose and outlines a lot of the info you may be looking for on this front.

This document elaborates a bit more on the regulations

  Aircraft with an FAA-approved system— such as an Onboard Mobile
  Telecommunications System (OMTS), Wireless Fidelity (WiFi), airborne
  access systems (AASs), or Network Control Units (NCUs)—are considered
  PED-tolerant for PEDs used with the installed system. If an aircraft
  model has demonstrated tolerance for both transmitting and
  non-transmitting PEDs, the operator may allow PED use during all
  phases of flight on this aircraft model.

Aircraft need to be shown to be PED tolerant for Wifi units. You can find an AC covering whats involved in that here.


Do motor glider pilots ever "cheat" and use their motors to thermal?

Do yachtsmen turn on the motor when under sail to increase their speed a little bit just for fun?  Not unless they have to get somewhere in a hurry, or to get somewhere when the wind dies. Kind of defeats the point of sailing.  Soaring is simply sailing turned from a 2 dimensional art to a 3 dimensional art, by rotating the lift vector created by moving air to a vertical axis from a horizontal one.

You have to understand that the whole point of soaring is the "game" you play with the atmosphere.  You're either into the game or you aren't and a motor pollutes the game if you use it while playing, except in specific circumstances.

Most motor gliders use the motor to launch and hunt for initial lift, then once lift is found, the motor goes off and the game starts (if you're are being towed and your tow pilot is any good, he/she is also hunting for lift for you while on tow and will try to get you near or in a thermal when you get to release altitude).

In general, you will use the motor mainly to launch and find lift, then only to rescue yourself if you get caught low.  So the motor is mostly to eliminate the tug, and the need for retrieve crews if you land out, or retrieve tows if you land out on a usable airstrip.  High performance motor gliders with retractable motors have to go through a retraction/extension procedure as well, so that is another factor in discouraging motor use until you really need it.  Of course, the other problem is you're more likely to need it, because the ballast of the launch motor hurts your sink rate, like having water ballast you can't get rid of, and it's more of a struggle to stay aloft in weak lift.  But again, this is normally a late in the day gotta-get-back situation.

On the other hand, there are "touring" motorgliders, with medium gliding performance and that are meant to be usable as long-range cross country aircraft in the travelling sense, with engines and props that facilitate starts and stops quickly at any time, as well as pure soaring, and landing gears that make normal power plane airport operations feasible.  You could really call these "hybrid" aircraft.

In these cases you may well indeed use the motor to supplement weak lift if it's to help you get from A to B.  But even there, you're making a lot of noise, and it's so much more pleasant with it off, so you'll avoid running the motor when you can.  This is probably more akin to "motorsailing" yachts that are a hybrid of power boat/sail boat.

With the newest electric motorgliders, you may use the motor more to help with thermaling, but they still make a bit of a racket compared to motor off (fast turning prop) and have limited endurance, so you still would tend to avoid using it unless necessary.


How significant is the lift induced drag contribution to total drag of aircraft at cruise speed?

According to an article on leehamnews.com, the drag breakdown for an A320 at FL 370 and Mach 0.78 is:

  The 7,900 lbf of drag is composed of 4,700 lbf of Parasitic drag or drag independent of lift and 3,200 lbf of Induced drag or drag caused by lift.

With the induced drag being ~40% of the total drag.

Related:

Why would maximum fly-time (endurance) not coincide with max L/D operating point?
Why is the thrust/drag increase much lower at a lower FL with weight the only variable?


Why is the B737 altitude display unneccessarily ambiguous?

Because thats how old school "steam" altimeters work/look and glass cockpits were designed to work similarly such to reduce unfamiliarity when transitioning. Prior to the screen age a drum altimeter would have read out and increased in much the same way the glass cockpit does now.

(source)

You will also notice the 10's and 1's place's are joined and rounded off by 20's. This has to do with the common arrangement of tick marks on any old altimeter as well as the fact that in a fast climb the one's digit would be unreadable.

On any note, its not ambiguous to a pilot, its actually quite accurate if you know what you are looking at.


Do horizontal stabiliser force direction change with CG variation for a given aircraft?

The ideal cruise condition, which minimises induced drag, is for the tail to exert zero lift. This avoids any wasteful tip vortices from the tail.

However for most planes the CG shifts during flight, if only because fuel is being used up. Also, trim conditions change with speed, rate of climb, altitude and a host of other variables during flight. The tail spends most of its time a little away from the ideal zero-lift condition, and it can go either way.

The "lifting tail" was much discussed in the early years of aviation. It has a destabilising effect which limits the stable CG range and every plane has a maximum safe level of lift from the tail while remaining stable. Nevertheless, away from that limit it contributes lift which helps to offload the wing and allows it to be that bit smaller.
According to Berriman; Aviation, Methuen, 1913.

"On some machines the tail planes are cambered like the wings and help to support the weight in flight. The angle of incidence of the tail is less than that of the wings, however, and the principle [of weathercock stability] apples equally to such cases." -- Page 69.

Berriman gives some supporting analysis in terms of CG and CP to explain what he summarises as weathercock stability. The subtleties of the lifting tail would be further elaborated in subsequent years.

The bigger the tail, the greater the CG range can be accommodated, and also the greater the temptation to offload the wing a little. The limit is the tandem-wing aircraft, where for stability the fore wing is loaded more heavily than the aft, but the aft still contributes substantially to the lift under all flight conditions. A tandem-wing modification of the Westland Lysander flew experimentally during WWII and test pilot Harald Penrose confirmed that its handling was more stable than the conventional version and had a greater CG range.

So ultimately, every plane has its own practical tail loading, which may be normally up, normally down, or variable around the zero point.

There is a myth that for a plane to be stable the tail must always exert a downforce. This seems to arise among students for two reasons. One is that, when the AoA increases, dynamically it must exert a larger relative change in downward moment about the aerodynamic center than the wing's upward moment. Diagrams showing this effect always have a large down-arrow at the tail and it is easy for the student to forget that this is a relative change not an absolute value. The other is that the wing works hardest at takeoff, when fully laden and at its slowest flying speed; when the tail pushes sharply down to rotate the nose up, the wing has to compensate for that as well, so this is the design condition for sizing the wing and everybody has to learn it. Put that first diagram alongside and you have a myth in the making. If you failed to understand any of this paragraph, then you too may fall for it!


In the ARINC specification, does "sig bits" include the sign bit?

In A429 BNR words bit 29 is the sign bit.  Individual label descriptions are not entirely consistent in that many will identify bit 29 as part of the sig bits field.
In any case it's important to look at the details of a specific label, especially the range, MSB, and LSB values.  Some are always positive (such as airspeed) and so the sign bit is assumed to be positive and bit 29 can be the MSB.
One common factor is that the majority of BNR labels are coded in 2's-complement binary.  In this case, the MSB is half the range and each of the following bits is half the value of the previous. Example: For a "heading" range of 0 to 359, the MSB (bit 29) is 180, the next is 90, followed by 45, 22.5, 11.25, etc. Alternately, you can declare bit 29 the sign bit and the range becomes -180 to +179.
So you'll note that in 2's-complement encoding, it doesn't matter if you consider bit 29 as an MSB or a sign bit.  The difference is that if you call it MSB, the range is 0 to 359.  If you call it a sign bit, the range is -180 to +179.
You can prove this to yourself by declaring bit 29 as a sign bit and code -135 degrees.  Then declare bit 29 a MSB value of 180 and code 225 degrees. The coding should be the same.


What is the difference between RVR and visibility?

The definitions are somewhat different:

Visibility for aeronautical purposes is the greater of:

the greatest safe distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognised when observed against a bright background;

the greatest distance at which lights in the vicinity of 1000 candelas can be seen and identified against an unlit black background.

Runway Visual Range (RVR) is the range over which the pilot of an aircraft on the centre line of a runway can see the runway surface markings or the light delineating the runway or identifying its centre line. (ICAO Annex 3)

(Visibility on SKYbrary)
The RVR is specific to the runway and its actual lighting system (i.e. can be different for different runways of the same airport at the same time), where visibility only refers to the general range an object or light can be seen in the current conditions.

RVR can be measured along the runway, e.g. using a transmissometer:

RVR equipment is typically found at larger airports, and RVR visibilities can be reported for up to four designated runways at an airport. It's calculated using sensors like this:

The sensors are located along the runway, and they're approximately 14 feet higher than the centerline of the runway.
On most runways equipped with RVR, there are three sensors: a touchdown sensor, a mid-point sensor, and a rollout sensor.

(boldmethod.com)
On the other hand, visibility is typically measured by detecting scattered light from a strobe (scatterometer):

The most common method of measuring the extinction coefficient is the forward scatter system. A high intensity xenon strobe transmitter directs a beam of light in the visible spectrum at the air close to the sensor and a photo diode at the adjacent receiver is used to detect the amount of light received. The extent of scattering is increased by the presence of particles of water, dust, sand or smoke. The use of transmitted light within the visible spectrum allows this type of instrument to most accurately simulate human perception of visibility. The range of visibility for which a measurement can be derived is typically between 15/20 m and 20/30 km with an accuracy up to 10 km of +/- 10%. A typical instrument is illustrated below:

(Automated Cloud Base and Visibility Measurement on SKYbrary)
For more details on measurements, see:

How is the visibility at airports measured?

How do visibility and RVR compare?
The ICAO Aerodrome Meteorological Observation and Forecast Study Group published A Comparison of RVR and Visibility Reports:

Previous studies have shown that the reported value of RVR is typically higher than the associated visibility value. [...] These findings are consistent with the fact that the assessment of RVR takes advantage of high intensity runway lights while the visibility assessment is based upon lights of moderate intensity.
[...]
A comparative review of the 5,662 METAR / SPECI from three aerodromes over a five year period that contained both prevailing visibility and RVR information revealed that, in equivalent terms for 2825, or 50 per cent, the RVR report was less than the visibility.
[...]
meaningful predictions of RVR from prevailing visibility reports can only be  accomplished if the assessment of both RVR and visibility is by reference to common sensor(s).

It seems, RVR is typically higher than visibility, but only if the runway lighting system is using high intensity lights.


What effect does driving convictions have on a PPL?

In the US, driving while under the effects of alcohol and drugs may have a adverse effect on your medical certificate.  Additionally, I have heard (from an FAA inspector) second hand that in one instance, someone who had a driver's license revoked for a large number of speeding and reckless driving circumstances, eventually had a medical certificate revoked.

Arrests, and administrative actions require reporting to the FAA Aeromedical branch within 60 days and failure to do so can not only affect a medical certificate, but also pilot certificates, instructor certificates, A&P certificates, controller certificates, etc.  The penalties for non-reporting are significant.

Addendum:  US pilots are required to make TWO reports relative to substance and alcohol issues.  Part 67 requires reporting notifications, arrest, etc. to the Aeromedical Branch. Part 61 requires a notifying Security at FAA upon conviction  or disposition.

Reference item 8 in the below FAQ which is provided for AME guidance:

  https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/media/SubstancesAbuseDependenceFAQ.pdf

Also, according to FAA documentation, the normal look back on substance abuse is 2 years.


If my parachute fails to open, why should I aim for land rather than water?

If your parachute fails to open entirely you are almost certainly extremely dead no matter where you land, however occasionally people do survive. A partial failure of a chute is much more survivable. You will be coming down much faster than you would with a good chute, and you are going to get injured, probably badly. Think broken legs and arms with neck or back trauma. You may sustain a concussion as well, and you will certainly go into shock.

If you come down in the water you will be injured and unable to keep yourself afloat, and it will be much harder to rescue you. On land help will be much closer and, and as @RonBeyer says in comments, you can't drown on land.

Land has features which may help you survive: trees, vegetation, hay bales, crops, snow, and many other things may cushion your impact enough to make the difference between life and death. Water is the same wherever you go, and doesn't have nearly enough give to cushion an impact.


What are the physical/aerodynamic implications of designing a prop guard for multirotors?

Aerodynamically, one can say that those prop guards create some kind of Fenestron (Like some tail rotors in helicopters), which will reduce the tip losses of the propeller.

On the other hand, they will increase drag in forward flight, reducing the UAV top horizontal speed. If you take a look at the Aibotix X6 you see a one piece prop guard designed aerodynamically to reduce drag in forward flight.
In the particular case of your image, the black web also decreases the area of air flow into the propeller, certainly reducing its efficiency.

Another prop guards disadvantage is the weight they add. Even though they might be made of lightweight material, they have to have some strength to resist any impact.

To sum up, with a prop guards like those, you should loose top speed and around 2 minutes of flight time.

One last tip: if you want to fly your UAV close to trees, forests or power lines, be careful with the prop guards because you might end with your UAV hanging on a tree branch 10m high... (happened to me :/)


Autotrack means the FLIR (Forward Looking InfraRed) sensor attempts to track whatever object falls inside the tracking area. It means whatever the pilot was trying to keep up with was producing emissions in the infrared (heat) and the system was automatically tracking it.

Boxing a moving target is having the tracking system detect and track a target you have selected. In this case, the other pilot was asking if he had selected the target manually (boxing) or if the system detected and autotracked the target on its own.


Why does only the right outboard aileron on the A320/340 float up when the aircraft is in the emergency electrical configuration?

EDIT: This answer is specific to the A340; the A320 is somewhat different.

TL;DR

In the emergency electrical configuration, neither of the two remaining flight-control computers can control the right outboard aileron, and it floats up under aerodynamic forces.

Long version

Some background: all Airbus aircraft from the A320 onwards have five flight-control computers, which translate the pilots' control inputs into control-surface movements.

These are divided into two categories:

Three flight-control primary computers (FCPCs, also known as PRIMs, for "primary"):

FCPC 1 (also called PRIM 1, or P1 for short)
FCPC 2 (aka PRIM 2 or P2)
FCPC 3 (aka PRIM 3 or P3)

Two flight-control secondary computers (FCSCs, also known as SECs, for "secondary"):

FCSC 1 (also called SEC 1, or S1 for short)
FCSC 2 (aka SEC 2 or S2)

Not every flight-control computer can control every control surface; the most critical controls (such as the elevators) are connected to four, or even all five, computers, while less critical surfaces only get two, and the least-critical (the individual spoileron panels) are connected to just one computer apiece (as there are six spoileron panels per wing, with each of the five computers controlling at least one panel on each wing, providing a great deal of redundancy).

On the A340, each of the inboard ailerons is connected to four of the five computers (FCPC 1, FCPC 2, FCSC 1, and FCSC 2); by default, the left inboard aileron receives input from FCPC1, falling back on FCPC 2, FCSC 1, and FCSC 2 (in that order), while the right inboard aileron defaults to FCPC 2, with FCPC 1, FCSC 2, and FCSC 1 to fall back on.

However, each of the A340's outboard ailerons is connected to just two computers.  Both outboard ailerons default to FCPC 3; the left outboard aileron has FCSC 1 as a backup, while the right aileron falls back on FCSC 2.

The A340's RAT can only generate a limited amount of electrical power, especially since a considerable amount of its output has to go into maintaining pressure in at least one of the aircraft's hydraulic systems, in order to allow the aircraft to remain controllable; normally, the hydraulic systems are pressurised by engine-or-APU-driven pumps, but, if the aircraft runs out of fuel (one of the very few circumstances that can simultaneously render all engines and the APU inoperative, and the main reason why the RAT exists), only the RAT is left, and it has to provide both electrical and hydraulic power.  As a result, a lot of electrical load-shedding has to take place to reduce the aircraft's electrical demand to something the RAT can handle; as part of this, three (for the A340) of the five flight-control computers are powered off, leaving only FCPC 1 and FCSC 1.  Additionally, due to the limited hydraulic pressure available from the RAT, the A340's outboard ailerons are deactivated to reduce the demands on the aircraft's RAT-pressurised hydraulics.

The overall effects on the A340's four ailerons are:

Left outboard: Not used; however, as FCSC 1 is still available, the aileron does still receive flight-control commands (although all they do is tell it to stay put), which helps to keep it from drifting away from the neutral position.
Left inboard: Operates as normal.
Right inboard: As FCPC 2 is unpowered, falls back to FCPC 1, and continues to operate.
Right outboard: Not used, and, as both of the two computers able to control it (FCPC 3 and FCSC 2) are offline, receives no flight-control input at all; as a result, its position is now solely dependent on the aerodynamic forces on the aileron, which tend to cause it to float upwards from the neutral point.

As explained in @ymb1's answer to an earlier question of mine:

  The manual does not give a direct reason (not unheard of), but in fact there's more than one reason.

  ► As a quick summary, you lose 2/3 of the spoilers and the outer ailerons, and if more unlucky, you lose 5/6 of the spoilers.

  [...]

  In emer elec config, the plane loses 3 of the 5 flight control computers; what remains are P1 and S1 (refer to diagram above).
  The outer ailerons go into an unpowered state to conserve hydraulic fluid/pressure – the right aileron upfloats* like on the A320 (no P3 and S2).

  [...]

  The references (click to view):

  All images are from the A340 FCOM, and color highlights are mine. Do not use for flight.

  A330 vs A340

  Thanks to @JZYL, note that there are some differences between the A330 and A340, while the A340 would announce MOST SPOILERS being INOP, the A330 would announce HALF SPOILERS (an extra computer remains powered). The same rationale given should apply though.

  * This is also confirmed from [this FCTM][6] (smartcockpit.com) of an airline with both the A330 and A340 in its fleet (see PDF page 207):

    (...) The AP will disengage when the failure occurs but AP 1 can be reengaged on the A333 if the EMER GEN is powered by an EDP. As there is no AP available in this configuration in the A340, the Captain must take control and fly the aircraft manually. The A340 aircraft is out of trim in roll due to right outboard aileron upfloat, caused by no power being available to Prim 3 or Sec 2, and neither pitch trim or rudder trim is available. (...)

  Note: I haven't found a reason for the different architecture, but ETOPS is a possibility.

(All bolding, italicisation, etc., original to source.  Kudos to @ymb1 for digging up all this information and explaining it to me.)


Who has the higher authority, the pilot in command or ATC?

It isn't a black and white issue of who has higher authority.  A pilot in command (PIC) is the ultimate authority for the safe operation of his airplane.  An air traffic controller is the authority for the block of airspace or pavement he controls.

When you are operating under ATC, it is your responsibility to comply with their instructions as long as they fall within the regulations, they are safe and you are able to comply,  If ATC issues an instruction contrary to regulation or something that would compromise safety, that is when you exercise your PIC authority to deviate from their instruction.  If you are unable to comply, you exercise your authority to deviate and explain why you are deviating.  When you cannot comply with an ATC instruction, for whatever reason, it is the job of ATC to accommodate your and move other airplanes out of your way.

The regulatory basis for the PIC authority and ability to deviate from ATC instructions is in 14 CFR 91.3

  §91.3   Responsibility and authority of the pilot in command.

  (a) The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.

  (b) In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule of this part to the extent required to meet that emergency.

  (c) Each pilot in command who deviates from a rule under paragraph (b) of this section shall, upon the request of the Administrator, send a written report of that deviation to the Administrator.

The basis for ATC's authority is 14 CFR 91.123

  §91.123   Compliance with ATC clearances and instructions.

  (a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. However, except in Class A airspace, a pilot may cancel an IFR flight plan if the operation is being conducted in VFR weather conditions. When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC.

  (b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.

  (c) Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory, deviates from an ATC clearance or instruction shall notify ATC of that deviation as soon as possible.

  (d) Each pilot in command who (though not deviating from a rule of this subpart) is given priority by ATC in an emergency, shall submit a detailed report of that emergency within 48 hours to the manager of that ATC facility, if requested by ATC.

  (e) Unless otherwise authorized by ATC, no person operating an aircraft may operate that aircraft according to any clearance or instruction that has been issued to the pilot of another aircraft for radar air traffic control purposes.

Absent an emergency, an urgent need* or an inability to comply with ATC, a pilot is required to obey an ATC clearance.  Given this relationship and its exceptions, its is hard to quantify who has a "higher" authority.  Both are the ultimate authorities of their domains, but who overrules who is dependent on the situation.  In general however, ATC will be issuing proper clearances that a pilot is bound by regulation to follow, though the pilot must exercise his authority to execute that instruction in a safe manner.

*Urgent needs include things like TCAS RA events and things like weather deviations.  In most cases ATC will help you out with a deviation, but if a controller refuses to allow a deviation, I would happily exercise my PIC authority to safely operate my airplane and turn left/right a few degrees rather than penetrate a thunderstorm updraft.

In the particular case above, the audio exchange between DL2422 and Atlanta ground is

  DL2422: Good morning Atlanta ground, delta 2422 approaching 3 South taxi Quebec

DL2422 is at the southern exit of ramp 3 and requesting taxi with ATIS information Q.

  Ground: Delta 2422, behind the MD88 from your right, runway 27R, taxi via Mike and hold short of Dixie.

ATC has instructed DL2422 to let an MD88 pass from right to left, to taxi on taxiway M to runway 27R but to hold short for taxiway D (in ATL D is "Dixie" due to the larger number of "Delta" airplanes).  To follow this instruction, an airplane should taxi south from spot 3S on taxiway L5, cross L and then turn left on M, then taxi on M, stopping short of D and awaiting further instruction.

  DL2422: OK behind the 88 from the right, 27R Mike short of Dixie, DL2422

Here, DL2422 acknowledges this correctly.

  Ground: DL2422 they won't let you go to Charlotte until 57 minutes after the hour, time now 29 after

  DL2422: OK copy 57, DL2422

DL2422 has been issued a wheels-up time, but their taxi clearance has not been amended.  They are still cleared to taxi via M short of D.  Sequencing to meet this time will happen east of D in further clearances.

  Ground: DL2422, you are supposed to be on M

  DL2422: Yes sir, we're going out there right now.

  Ground: Looks like you joined L

  DL2422: You know what, we'll taxi out there any way we want unless you tell us to, I don't like your attitude.

  Ground: I don't have an attitude sir, I'm just saying it looks like you joined L instead of M and I'm just trying to correct you before you stay on L.

  DL2422: Ok, cause my god, there's another plane out there, its like 6 miles away.  Your attitude is really something sir, we're out here on M. Good morning.

  Ground: Good morning.  There was no attitude, I was just trying to correct you, that's my job to correct you if you mess up.  I'm just trying to make sure everyone is doing what I ask them for certain reasons.

  DL2422: You make a mistake every 2-3 minutes, but my attitude is not like yours, we're out on M and you didn't tell us how to get there so next time you can try doing that.

The DL captain is making a scene and a very roundabout argument that the taxi route did not specify how he was supposed to transition from spot 3S to taxiway M.  I agree that this is the case, but do not understand why any assumption would be made other than to taxi straight out and turn left on M.

This is a good example of a minor deviation that had DL2422 just turned right and then left and said "oops, fixing that, joining M, thanks!", then that would have been the end of it.  This captain's unprofessional display will instead net him disciplinary action and classify his deviation as "willful" rather than "accidental".

For a clearer visualization of the event, see this image:

In this image, the green circle is the starting point of DL2422 and the blue line is the cleared taxi route with the assumed transition to M via L5.  The short red line is the initial taxi route DL2422 took.  It is not clear where they transitioned to M, so I did not extend the red route past the first possible transition.

There appears to be some controversy over the verbiage of "behind" used in the ATC taxi clearance.  The only reference I can find to this word in a cursory search is in FAA order 7110.65 (ATC procedures) in section 3-7-2 that gives example taxi clearances.  This does not define "behind" but does give distinct examples that clearly differentiate "behind" from "follow".  Given that I cannot find a better reference, all I can offer instead is years of experience in a 121 cockpit based at busy airports like IAH and EWR and plenty of visits to others like ORD, ATL, LAX, DTW, IAD, etc where clearances involving the words "behind" and "follow" are quite common.

Behind Use of this word means that you are waiting for an aircraft to pass.  You are giving right of way or yielding to the traffic in question.  This clearance is often given when holding short of an intersection and waiting for perpendicular traffic to cross the intersection before you continue through it.  Much like waiting at a stop sign in a car.  You are not expected to follow the airplane in question and even if you are assigned a turn to taxi along the same route as the airplane, you have your own clearance and are not following that aircraft.

Examples:

"Continental 1234 taxi to runway 22R at W via K hold short of S", followed by "Continental 1234 you'll see a B767 passing right to left on S, behind him continue to runway 22R at W via K R hold short of W"

In this case it is quite explicit that an airplane will be passing across your route of taxi and after it passes you are to continue taxiing straight ahead -- not to follow that airplane.  Consider an alternate setup:

"Continental 1234 taxi to runway 22R at W via K hold short of S", followed by "Continental 1234 you'll see a Citation from the right at S, behind him taxi via S W hold short of R.

In this case, you are waiting for traffic from the right again, but this time you are turning left after it passes.  You will be taxiing behind it, but you are not following it.  The Citation has a clearance to taxi S, cross runway 29, to parking.  Your clearance is S turn right on W -- to follow the Citation would be wrong.
Follow Use of this word means you are going to fall in behind this airplane and follow it wherever it goes.  You clearance is no longer a specific taxi route, but simply to follow the airplane.

Examples:

"Jetlink 1234, your sequence is the third airbus to your right, the one painted purple.  Follow that airplane to runway 22R at W.  Once behind him, monitor tower, you are number 28 for departure.", which will be followed by
"United 3412, hold short of J, let the EMB-145 get in line then follow him to runway 22R at W.  Monitor tower passing L, you are number 29 for departure"

These clearances are used to get airplanes in line in a specific sequence and simplify giving repeated complex taxi instructions when you can just follow to conga line to the runway.


What are the consequences of hail damage to a small GA plane?

Like anything in aviation, it depends...

There are a lot of discussions on the internet about it you can find

Here (mooney)

Here (cessna)

And Here

It is a case by case situation and depends on the extent of the hail damage and what/where the damage occurred. In many cases the issue crops up that you can not simply bang the dents out you would need to reskin the panel. This can, depending on the aircraft be a costly process.

There are planes out there flying with light hail damage and it causes no problems, in many cases its purely cosmetic. A lot of planes flying out there have other similar damage (tool drops, bird strikes, impacts from rocks etc) and fly just fine.

An good A&P would most likely be able to tell you if the particular Cessna in question is still airworthy.


When a hold is distance based, do you still used a timed entry?

I haven't found any specific guidance for hand flying entries to RNAV (RNP) holding patterns. But part of the concept of RNAV is that the navigation system can provide the complete desired path including hold entries.

Referring to RTCA DO-236C RNP MASPS and the requirements for holding operations, I find the following: The dimensions of the hold pattern are defined based on altitude, airspeed, bank angle, and an allowance for wind. The length of the inbound/outbound leg is defined by the database or entry. In your case this is 4 NM, and is defined as d1. The width of the pattern (d2) is computed based on the above variables.

Without the details, we can still make an approximation. If you're flying at 120 kts and performing a 2 min turn (1 min for 180 deg), your pattern width (d2) would be about 1.3 NM.

The rules include the following statement:

  When performing an entry into the holding pattern, the navigation
  system is permitted to use an inbound leg length (d1) that is equal to
  the holding pattern width (d2) instead of the length defined in the
  database or from pilot entry.

So the end result is that your entry cannot exceed the 4 NM leg length, and could have an inbound leg length as short as 1.3 NM.


The key is in the part of the procedure description I've highlighted:

When local altimeter setting not received use Northeast Philadelphia altimeter setting -- you're using the altimeter setting for an airport 15 miles away.

15 miles may not seem like a lot of distance, but it's enough for there to be a notceable variation in altimeter settings. The FAA assumes this error will be in the least favorable direction (i.e. your altimeter will indicate you're higher than you really are), and accordingly they take some precautions when you're using another field's altimeter setting.
In this particular case:

The decision altitudes (DAs) are higher.
Baro-VNAV (vertical guidance for your descent based on your altimeter) is not authorized.
The use of the charted Visual Descent Point (VDP) is not authorized.

The VDP is telling you "If you are on the approach path and remain at the MDA until over this point on the ground you'll be on the glide path to the runway" (or alternatively "You can plan a constant-rate descent that intersects the MDA over this point and you'll be on the glide path to the runway").

Using the charted VDP is specifically not authorized in this case because the nominal descent angle you will have passing through it counts on your altimeter being accurate and your aircraft being at the MDA. Since the MDA has changed and we're using a remote altimeter setting the location of the VDP isn't going to be what's shown on the chart. (For example, if you're 60 feet higher than you "should" be & everything else is perfect the VDP moves further away from the airport to provide the same glide path at a higher altitude).

Rather than charting several visual descent points (which would be futile anyway as you can't know the altimeter error portion of the equation) the FAA just says "Don't use it: Fly the approach until you have the runway environment in sight and then figure out your own glide path intercept based on the visual references you have."


Why does JBU1825 from Ft. Lauderdale to Lima show a large zig-zag in the route?

It isn't, as a screenshot taken later in the flight will show:

The dashed line is FlightAware's attempt to plot the planned route of flight. It's not always accurate, and FlightAware sometimes includes strange zig-zags. If you go to skyvector.com, choose "Flight Plan," and paste in the route shown by FlightAware (BEECH5 BAHMA URSUS UL780 TBG UL780 VAKUD UL780 TRU UV1 ATATU ATATU2), you'll get the more logical route that appears to match the actual flown route:


Easiest thing is to imagine you're in a motorboat on a river, with a current, driving in circles at a constant water speed, indicated by a water speedometer that measures the dynamic pressure of the water more or less the same way as an airspeed.

Your path relative to the bottom of the river will be a spiral and your speed over the bottom will be faster or slower as you move with or against the current, as you make a perfect circle in the water, but your indicated speed through the water will be constant.

Airplanes are exactly the same.  The air is a big river.  You're just in it instead of floating on top.


What is a navigational fix? Where can I get navigational fixes for a local airport?

A navigational fix is a waypoint that can be used to navigate to, from or between airports or other navigational fixes. Navigational fixes can be GPS-based coordinates, radio-based navigational aids like VORs or NDBs or airport themselves, which have a defined airport reference point with set coordinates.

Navigational fixes or aids are usually not placed around runways, but those that are used for approaches or departures (mostly VOR or NDBs) are placed at or in the vicinity of the airport. See below for the placement of the Barmen (BAM) VOR, which is one of the approaches fixes used for the ILS approach to runway 23L and 23R and the, nowadays no longer used, NDBs DX and LI as the outer markers for the instrument approach.

(Image Source: www.skyvector.com)

Navigational fixes required for approaches or departures to a specific airport will be available in the countries' AIP, in the publications for the specific approach or departure routing, e.g. navigational fixes along a STAR or Transition from the Initial Approach Fix (which is a navigational fix as well) to the Final Approach Fix.

(Image Source: VATUSA)

The above displays the navigational fixes for the transitions/arrivals into Memphis International Airport.

For a list of available radio navigational aids around an airport, you can try sources like SkyVector.


Does FAR 91.155c apply to class E surface extensions?

FAR 91.155(c) uses the phrase “within the lateral boundaries of controlled airspace designated to the surface for an airport” to describe the airspace where a Special VFR clearance is required to operate under Visual Flight Rules below a ceiling of less than 1000’ AGL.
The FAA often uses the phrase "surface area" to refer to the controlled airspace that actually surrounds the airport for which it is designated, specifically excluding any surface-level Class E "extensions".  An argument can be made that in the context of interpreting the meaning of the FARs, this is the most correct understanding of the phrase "surface area".  This interpretation is based on the difference between the language used to describe surface-level Class E "extensions", and the language used to describe other surface-level Class E airspace, in the "Airspace Designations and Reporting Points" document, current edition FAA Order JO 7400.11E.  For more on this, see the related ASE question What indication has the FAA given that phrases like "surface area of Class E airspace designated for an airport" do or don't include E4 "extensions"?.
But the phrase "surface area" does not appear in FAR 91.155(c).
However, the phrase "designated for an airport" does appear in FAR 91.155(c).  An argument can be made -- again, based on  based on the difference between the language used to describe surface-level Class E "extensions", and the language used to describe other surface-level Class E airspace, in the "Airspace Designations and Reporting Points" document, current edition FAA Order JO 7400.11E -- that this phrase excludes surface-level Class E "extensions".  Again, for more on this, see the related ASE question What indication has the FAA given that phrases like "surface area of Class E airspace designated for an airport" do or don't include E4 "extensions"?.  According to this interpretation, FAR 91.155(c), which contains the requirement that the ceiling be at least 1000' AGL, would not apply in the surface-level Class E "extensions".
However, one problem with this argument is that FAR 71.71(b) seems to either 1) use the phrase "designated for an airport" in its description of all surface-level Class E airspace, or 2) omit any reference to surface-level Class E "extensions" at all, in which case it seems the "extensions" might be construed not to legally exist at all. Obviously, the latter interpretation is somewhat problematic.  This seems to imply that the phrase "designated for an airport" should not be construed to exclude surface-level Class E "extensions".
It's also unclear as to whether or not SVFR should ever be authorized in surface-level Class E "extensions".  FAR 91.157(a) uses the phrase “within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport” to indicate where a SVFR clearance may be authorized.  Again, just as with 91.155(c), the phrase "surface area" is not used in the regulation, but the phrase "designated for an airport" is.  So the language for the two regulations is quite parallel.
Therefore it seems that if the 1000' ceiling requirement is construed to apply in the surface-level Class E "extensions", then it should be permissible to authorize SVFR flight in the surface-level Class E "extensions", and if it is construed not to be permissible to authorize SVR flight in the "extensions" by virtue of FAR 91.157(a), then the 1000' ceiling requirement ought not apply there either.
(Note that there are sometimes other operational reasons unrelated to FAR 91.157(a) why SVFR flight is not authorized in some specific surface-level Class E "extensions"-- one such case is noted in the second-to-last paragraph of this 2010 response from the FAA ATO Western Service Center.)
The last paragraph of this 2010 response from the FAA ATO Western Service Center (same link as immediately above) concludes that due to the wording of FAR 91.157(a), SVFR should not be authorized in surface-level Class E "extensions".  This implies that the 1000' ceiling requirement ought not apply in surface-level Class E "extensions" either, due to the parallel construction of the language of FAR 91.157(a) and FAR 91.155(c).
One problem with this 2010 response from the FAA ATO Western Service Center is that is contains the passage "The language in FAR 91.157 exactly matches the language in FAAO 7400.9T par 6002.".  This is not actually quite true, because FAAO 7400.9T par 6002. contains the phrase "The Class E airspace areas listed below are designated as a surface area for an airport."  As we've already noted above, neither FAR 91.157(a) nor FAR 91.155(c) actually contain the phrase "surface area".
FAA Order 7110.65Y, entitled "Air Traffic Control", states in section 7-5-1 that Special VFR flight will only be authorized "within the lateral boundaries of Class B, Class C, Class D, or Class E surface areas, below 10,000 feet MSL."  As noted above, there are many instances where the FAA has used the phrase "surface area" to refer only to the controlled airspace that actually surrounds the airport for which it is designated, specifically excluding any surface-level Class E "extensions".  So this passage could be construed as guidance that Special VFR flight should not be authorized in surface-level Class E "extensions".  If this guidance is just based on FAA policy but doesn't accurately reflect the meaning of FAR 91.157(a), then it perhaps it should not be construed as "releasing" the surface-level Class E "extensions" from the 1000' rule, even though, as argued above, the wording of FAR 91.155(c) is very parallel to the language of FAR 91.157(a).
In actual practice, controllers will often authorize SVFR flight in surface-level Class E "extensions".  For more on this, see this related ASE answer.  (And controllers generally use the word "surface area" in its most logical sense-- meaning the entire column of controlled airspace that is in contact with the earth's surface, including any surface-level Class E "extensions".)
The truth is that the FAA is deeply divided as to whether phrases in the FARs like "surface area", "designated for an airport", and "surface area of controlled airspace designated for an airport" should or should not be construed to include surface-level Class E "extensions".1  Ambiguity around this issue has existed ever since the 1993 "alphabet" airspace re-designation.2  There's some consideration of a future rule-making effort to address this issue.3  It's possible that the language in AIM 3-2-6, as well as in the legend of the Chart Supplements, that reads "Surface area arrival extensions become part of the surface area and are in effect during the same times as the surface area" will be changed in the future to avoid implying that all regulations that apply to the core "surface area" should automatically be construed to apply to the surface-level Class E "extensions" as well.4
Due the confusion around this issue, whenever a pilot is issued a SVFR clearance for a given controlled airspace, he or she should verify whether or not it includes any adjoining "extensions", in any case where that might be a factor.  It would also be wise to ask the controlling agency for any given airspace whether they construe that the limitation against operating below a ceiling that is less than 1000' AGL applies in the "extensions".  The "safe" course of action, naturally, would be to assume that it does.
Footnotes:
1,2,3,4) Source-- comments made by high-level FAA staffers during April 2021 airspace charting meeting.
Related ASE questions and answers
A: Does an SVFR clearance extend to Echo surface extensions?
A: Does an SVFR clearance extend to Echo surface extensions?
A: In the US, in actual practice, workload permitting, will ARTC facilities grant SVFR clearance for surface-level Class E “extensions” (E4 airspace)?
Q: What indication has the FAA given that phrases like "surface area of Class E airspace designated for an airport" do or don't include E4 "extensions"?
A: What indication has the FAA given that phrases like “surface area of Class E airspace designated for an airport” do or don't include E4 “extensions”?
A: Is the official weather report for an airport in Class D airspace controlling for its Class E surface extension?
Q: Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?


Why there is a 'MACH' in this Compressibility Correction Chart?

As I read it, the upper arch pointed to by Mach 1.0 represents the correction necessary at the different pressure altitudes when flying at Mach 1.0, while the lower arch pointed to by Mach 0.8 represent the correction necessary at those pressure altitudes when flying at Mach 0.8.

i.e. the correction necessary at 30,000 feet at Mach 1.0 is roughly -30, while the correction at that same altitude but Mach 0.8 is only roughly -15.


How is the speed of a helicopter controlled?

There are many fine articles existing that discuss how the throttle is used to input power into the rotor disc system to lift the helicopter, and how the rotor disc system is tilted to change the direction the helicopter flies. Putting more tilt into the forward direction makes the helicopter fly faster in that direction.

Optimum cruise speed is discussed in this paper, where knots of airspeed vs fuel needed is derived/plotted.  I wouldn't consider fuel wasted if one wanted to go faster, any more than driving 75 mph vs 55 mph on the highway is wasting fuel.  You just get to your destination faster. "Time is Money", yes? So what is worth more - an extra gallon or two of fuel/hour, maybe outrunning a storm in the process, or climbing above turbulent air, vs your time being spent travelling and doing productive work (or vacationing) at your destination?
http://www.eaa1000.av.org/technicl/perfspds/perfspds.htm


Can I measure induced drag with a simple wind tunnel test?

Yes, by the textbook definition $C_D=C_{D_0}+KC_L^2$.
Your measurement at AoA=0° gives $C_{D_0}$, 500 N.
Your measurement at another AoA=15°, by subtraction, gives $KC_L^2$, the induced drag at that AoA, 200 N.
If measurements at many AoA's yield a consistent $K$ and $C_L$,
then you gain confidence in those values.
If the airfoil is strongly cambered, a better fit to the equation is made if you add another term proportional to $C_L$ (not squared).


How long did the SR-71 take to get to cruising altitude?

According to the performance data in the manual it takes 19.9 minutes to get to 70,600 feet.

Refueling time will depend on how much fuel is needed for the mission as well as how long it takes to hook up to the tanker. The manual covers the operations for that but  I dont see a flow rate of fuel in there. A lot of that stuff is covered in this podcast.