Can I join the Navy after a corrective eye surgery and still be a Naval Aviator?

I had this explained to me by an OSO a few years back. The answer is a qualified, yes, but the devil is in the details.

At the time, no procedure that involved cutting a corneal flap was approved. This means that LASIK and similar procedures were not approved for aviators. (This may change, but I think its unlikely). So that leaves PRK and similar procedures that only modify the the cornea's surface. This follows recommendations my medical professionals that recommend people that play contact sports to opt for PRK instead of LASIK.

However, here is the detail that was explained to me that I consider to be "the catch", you must already be in the Navy. In other words, you must have already made a commitment, then once inside, you can apply for the waiver and use a Navy approved opthamologist to perform the procedure. The problem with this is that if you are a person that is only interested in being a pilot, you must sign up for some other reasons (it might be aviation related, but not pilot) then once commissioned, then you can ask them to waive the rule and allow you to have vision correction surgery.

Also, at the time it was explained to me, you needed to wait for 1 year after the procedure before being considered for an aviator position. This is logical as they want to see if the procedure was successful and healed properly.

If you're already in the Navy this is great, but if you want to join the Navy for the sole purpose of being an aviator, I would look very closely at the details, and get it in writing before you commit.


Can I count PIC time when regaining night currency with an instructor?

You can log PIC time because you are "the sole manipulator of the controls of an aircraft for which the pilot is rated" (14 CFR 61.51).  That's all that is required in this case for the pilot to log PIC time.

So since a pilot must be night current in order to fly with passengers, (61.57(b)) the question becomes, "is a flight instructor considered a passenger if they are providing instruction"?

AOPA has a flight briefing about this specific scenario where they quote FAA legal interpretations as saying:

  "We agree that, for purposes of section 61.57(b), an authorized
  instructor providing instruction in an aircraft is not considered a
  passenger with respect to the person receiving instruction, even where
  the person receiving the instruction is acting as [pilot in command].
  (The instructor must be current, qualified to instruct, and hold a
  category, class, and type rating in the aircraft, if a class and type
  rating is required.) The instructor is not a passenger because he is
  present specifically to train the person receiving instruction.
  Neither is the person receiving instruction a passenger with respect
  to the instructor. This training may take place, even though neither
  pilot has met the 61.57(b) requirements."

Note that they say in this case, since neither of them is a passenger, that technically neither the pilot or the flight instructor has to be night current.


Why do new jet engines cost billions to design?

Even if we ignore the salaries of everyone involved; engineers, sales people, management, Q/A teams, manufacturing teams, more sales people, and then a few spare engineers...

  I don't understand. If it's just designing a jet engine, then raw
  materials cannot possibly be a major factor even if it's something
  like titanium or composites.

While the raw materials alone are not necessarily costly, the materials, as well as the machining and processing, can be quite costly. This can be further compounded if the engine uses some kind of new material for which there is no effective production method yet. This was the case for the entire production of the SR-71 Blackbird which needed to figure out how to work with titanium before actually building anything. Even once the bespoke parts are produced for a new engine the company will then need to figure out how to produce the parts in sufficient quantity to produce the engines for market.

  How many prototypes could you possibly need? I mean I hope it's not
  all trial and error.

It's not, but the FAA may require various demonstrations where they destroy the engine and you can bet the manufacturer is going to try that out before running any official tests. Once passed initial tests flying prototypes will need to be built and tested on real airframes that cost money, running jet fuel that costs money.

  The other thing is computer software, which I thought would make
  things easier and cheaper to design. Granted you cannot just input the
  desired thrust and press a button, but surely there is decent fluid
  dynamic software out there that can help you design something much
  easier and faster than before.

It makes some things faster, like FEM, and surely makes complex routing easier, but like a good wrench, CAD software is a tool that makes things faster and easier. It does not do the work for you.


What is the one-engine-inoperative maximum range flight configuration?

The optimization problem is unchanged from the all engines operative (AEO) cruise optimization. You should still:

Climb as high as practical (colder, thinner air is better for range)
Set the lift coefficient such that drag is minimized for propeller aircraft ($c_{Di} = c_{D0}$). For turbojets, minimize energy per flight time ($c_{Di} = \frac{1}{3}\cdot c_{D0}$). For turbofans, pick a value between those two extremes.

For the computation of the theoretical optimum polar point please see this answer for a complete derivation including wind, or this answer for a shorter explanation.

Your flight altitude will certainly be lower, because you need to generate more thrust on the remaining engine (requiring higher density), which in turn will result in a lower TAS (true air speed). The CAS (calibrated airspeed) should stay about the same, however. The configuration (flaps, gear) should stay unchanged, only rudder deflection will be added for asymmetric thrust compensation. The resulting sideslip will increase the zero-lift drag of the airplane a little, so a slightly lower speed than in the AEO case would result.

In the unlikely case that the required density will result in an altitude below ground level, you will need to slow down and need to set flaps to stay airborne, and now the new optimum with flaps will result in a markedly higher lift coefficient because deploying flaps will increase the zero-lift drag quite a bit. If you have the flaps-down polar, the optimum is easy to find.


As late as possible to still meet your company's specific stabilized approach guidelines (mine were 500 ft VMC, 1000 ft IMC).  If you need the drag, then use them earlier.

In the EMB-145 in still wind or a headwind you could cross the FAF at 250 kts and clean and be on speed and configured by 1000' if you dropped the gear at the FAF (and opened the speed brakes and the first notch of flaps all at once).  Normally though, I'd drop the gear around 1000'.

Acronyms:

VMC = visual meteorological conditions
IMC = instrument meteorological conditions
FAF = final approach fix
EMB-145 is the type designator for the Embraer 145 regional jet


Does an AD terminate by issuing new one?

That sounds like a typical US AD where as I mentioned in a previous post, they don't issue "revisions", like AD 2019-12, AD 2019-12 Rev A, Rev B, Rev C etc.   If the AD is basically the same but has some internal change, the FAA will not issue a "Rev A".  They will issue a superceding AD with a new number that is the same as the old one except for various changes which will be spelled out.  So AD 2019-23 will be replaced by AD 2019-32, which supercedes 2019-23, instead of 2010-23 Rev A, as would be done in Canada or elsewhere.

That language tells you that the new AD is issued with administrative changes and that the compliance requirements are the same as the superceded AD, including any repetitive instruction.  In fact the new AD should have all the compliance requirements of the old one included in it.


Why are cockpit instruments white on black dials?

Right instrument face colors are inverted.

Black and white are perfect complementary colors, meaning:

  When placed next to each other, they create the strongest contrast for those particular two colors.

But for instruments if they were inverted, strong daylight shadows will make the numbers and hands harder to read, while at night with the white typically being electroluminescent or reflective for the instrument's red or white light will cause the glow to wash over the black as illustrated below:

The red is used for easier adaptation to the outside at night. Too much glow in either case goes against that.

As for digital displays, the same principle applies. Try reading an eBook in bed with the background white and the brightness to full -- it's very tiring -- that's why eBook readers have a night option where the colors are inverted.

History

The earliest mention of it I could find was from 1937 in Flight when instrument panels (the six-pack) were being standardized:

  The panel itself (...) is first anodised and then stove-enamelled a dull black -- though it may be said that the matt-grey anodic finish is very much better looking than the black panel and does not reflect light or in any way trouble the eyes of the pilot.

And here's another article from 1939 about solving the lighting issues for the instruments, not just the panel. But that wasn't always the case:

(Flight - 1913)

Image source: wikimedia.org


The missile works by predicting where the airplane will be. If you maneuver, it has to re-adjust, wasting energy.

When the missile has lost enough energy, it'll eventually fail to re-adjust.

Now you can try to beat the missile by being far away and fast
or
you can try to make the missile lose a lot of his energy by doing turns, at low speed. (You can even nodge the missile into the ground by making some close-range, low altitude dives)

In this instance, the pilot was probably already low. Or needed more energy for maneuvering and traded his altitude for energy by descending.


Why is mid-air refueling worth it? (or is it at all?)

In some contexts, the economics depends on how special the aircraft you're refueling is.

Consider  something like an AWACS mission. You have this very complex specialized aircraft, with a large, highly trained, crew in addition to the flight crew. If you didn't refuel that during the mission, it might need to spend a lot of its active hours being unproductive en route to and from the war. You would need more of them (and more crews) to reach any given level of in-theater coverage.

On the other hand with aerial refueling you need some tankers scuttling back and forth with fuel for your sentries. But they are cheaper and simpler to operate, cheaper and simpler to crew, and so forth. So even though you may use slightly more aircraft hours in total, the total  costs can be lower.

This doesn't hold to just the same extent for fighters and bombers, because they have to return to base from time to time to stock up on munitions anyway. There are still "readyness" types of missions it would be relevant for. The price tag for an F-35 seems to be in about the same ballpark as for a KC-767, but a KC-767 can service many F-35s in a single mission, so having the tankers do the scuttling-back-and-forth can still be an economic win.

Also, it's a good thing for a fighter that gets into combat not to be lugging around enough fuel to get all the way home by itself.


How common is it for military jets to use civilian airports?

Fighter jets may fly into local fields for airshows, to re-fuel or for needed maintenance in route etc.

What your wife may have seen may have been related to the VIP TFR's that usually pop up in the summer due to the president (or first family) heading back to their home on weekends.

I fly out of KDYL which is fairly close (in aviation terms) and my local FBO has been warning everyone that the Secret Service has instructed them the VIP TFR is going to be common on weekends this summer.

You can find a map of current TFR's here.


Why is it forbidden to wear glasses when leaving the plane during an emergency?

This is because they don't want people holding up the evacuation by searching for their glasses.   It does not mean you are not allowed to bring glasses if you are wearing them but passengers blocking the aisle to search for their glasses would slow the evacuation and risk lives.   They do want you to actually take off your high heels and leave your luggage because these can actually slow you down.   This should be portrayed more clearly.


Why are CJ2+ Anti-Ice & De-Ice Systems separately controlled?

Because they do two different things.

To quote FlightSafety's CJ2 Pilot Training Manual:

  Anti-ice protection systems are incorporated into wing, engine
  components, windshield, pitot-static, and angle-of-attack systems, and
  pylon ram-air scoops.  These systems should be activated prior to
  entering icing conditions.

  The tail deice system consists of pneumatic boots on the horizontal
  stabilizers.

Basically, anti-ice is used to prevent ice from forming in the first place on the protected surfaces of the aircraft.  This is done where it would either be "bad" to have it form in the first place (pitot-static, angle-of-attack, etc.), or where it would be "bad" to have the ice come off after it has formed (and then go through an engine, etc.).

Deice is used to remove ice after it has formed.  In this case it is used on the tail which a) isn't critical if it has a little ice, and b) the ice can be broken off after it has formed and it will just fly off the back of the airplane without damaging anything.

Since they serve two different purposes (and protect different parts of the aircraft), there are two different controls/switches.


Would a 90 kg object jettisoned from an aircraft create a detectable movement?

Yes

It's not just weight, it's also aerodynamics. First let's assume that the aircraft was trimmed slightly nose-heavy (no passengers), therefore it's trimmed slightly "tail down" anyway

When the stair was first opened, it would have been held partially closed by the airflow under the fuselage - it's not heavy enough alone to extend fully against a 100 knot wind.

There was then a two-part change from Cooper leaving the aircraft - one of him walking down the stair, pushing it into the airflow and acting much like the elevator.

When he then jumped, the loss of his weight at the very back of the aircraft, along with a presumed "push" against the door, pushing it further into the airstream, would have simultaneously jolted the tail up, then reduced the weight at the very back of the tail "lever".

90kg doesn't sound like very much, but when it's at the very, very back of quite a long lever, and when combined with the airstair, the results seem perfectly reasonable and, indeed, were proven by the FBI.


Is a retreating blade stall a problem that can be overcome on dual-rotor helicopters?

Dual and intermeshing rotors also suffer from retreating blade stall at high forward velocity. But the effect of this is much less dramatic than with a single rotor.

Retreating blade stall causes a loss of lift on one side of the rotor: the single rotor helicopter will start to roll. A helicopter with two rotors that counter-rotate doesn’t experience this rolling moment, only an increase in drag.


How did the gyro gunsights of WW2 get the range and lead of a target?

You are seriously over estimating the technical capabilities of the time.

The gun-sight is not much more than an intricate slide-rule. You had to feed it information about the target size/aircraft type and it used the gyro information from your own aircrafts turn rates to project a reticule circle on the glass.

The position of the projection is offset from the guns aiming point according to the gyro factors, the set range, and the fall rate of the ammo. When the reticule circle lines up with the wingtips of the target you are at the right distance and angle to the target and you push the trigger.

It assumes you are following the same flight pattern as the aircraft in front of you. That is.. chasing it in a dog fight. That makes it fairly limited in use and effectiveness and would be no replacement for a seasoned pilot.

Additional Reference Links:

Aviators Database

Axis History Forum

Video: Gyro Gunsight Mk IID

CORRECTION:

Upon watching the video it is apparent that the implication that the aircraft must be following the same flight pattern as the target is misleading. In reality the target reticule, and in effect the pilot's aircraft, needs to be turning at a rate to track the target's flight pattern. Further, the range can be adjusted while continuing to track the target. That all sounds a bit like rubbing your head while patting your tummy and I am sure took quite a bit of practice and an accommodating target that maintained a constant heading or turn rate in front of you.


How can I find the location and coverage of aviation VHF transmitters?

This is a useful site for the Oakland (ZOA) Air Route Traffic Control Center (ARTCC), and the locations of these match up with the RCO locations on the sectional. It seems Mt Tamalpais RCAG is the one that applies to my area. The list seems a little out of date, however, as the location of "Priest - RCAG" doesn't have anything on the sectional, or in Google Maps.

Further, there is an FAA site depicting RCOs and frequencies for Alaska.


How will aiport operations at KOAK be affected when taxiway W is promoted to a runway?

Oakland airport runway 12/30 is undergoing a "Rehabilitation" and during the rehabilitation taxiway Whiskey (W) will be serving as an alternate runway.

Therefore, your question "How would airport operations be affected if both runways were active" won't be an issue.   Please see the notice below.


Wing vs wall to wall wing,total drag comparation at same AoA?

I agree with your conclusion that the wall-to-wall wing has more drag than a free-flying wing at the same angle of attack.
But what is the point of this comparison?
People build wings to create lift. These wings might be on airplanes, but also on helicopters, propellers, the fin keels of boats or the blades in turbo machinery. Their purpose is in all cases to create lift. Not drag. Drag is an accepted price for that lift creation, but not their purpose.
So it is pointless to ask for a drag comparison when disregarding lift at the same time. This is akin to asking if a wing that is not moving creates no drag.
You don't even let us know the wingspan of those hypothetical wings. Are they in the same windtunnel, so the free-flight one has less aspect ratio, span and surface? Or is it the same wing, with the windtunnel removed?
So please stop repeating the same pointless and insufficiently specified question over and over. You will not get useable insights because the answers can not be helpful.


I'm not directly familiar with the engines Zapata uses on the Flyboard Air, but I'd hope they're using a kerosene derivative like JP-1 or commercial Jet-A.  Alternatives (gasoline, diesel, various alcohols) have no better energy content per volume, and some (alcohols) considerably less.

There is no case (for low altitude atmospheric flight) in which a rocket can beat an air-breathing jet for specific impulse/specific fuel consumption -- because of the need to carry oxidizer, instead of just using the air for that purpose, the amount of fuel/oxidizer available is limited by tankage.  This is why airliners, warplanes, and private business aircraft use jets or turbine driven propeller engines instead of rockets (not to mention the far higher durability of a turbine compared to a rocket engine).


What is the relation between pressure and airflow speed above an airfoil?

Above the wing, decreased pressure causes the air to accelerate. But it is the plane's velocity that causes the decrease in pressure above the wing.

Much like pressure gradients are the cause of wind.

Or when a fast truck on a highway punches a hole in the air, the air behind the truck rushes in to the lower pressure area.

So when a fast truck/airfoil causes low pressure, the air rushes in / speeds up.

  Bernoulli's principle states that within a steady airflow of constant energy, when the air flows through a region of lower pressure it speeds up and vice versa.

Source: Wikipedia

More information here (NASA).

What happens in a stall, is the drag from the airflow separation outweighs the lift. But the pressure is still lower above the wing.

Leading-edge root extension and delta wings can make better use of high angles of attack.

The NASA link above explains the true relation between airflow speed and pressure, but that's not the only cause of lift, is what I mean.


Where can I find official definition of VFR and IFR?

tl;dr The basic differences between IFR and VFR involve weather, required equipment, filing flight plans and getting a clearance, and the altitudes flown.

Your question indicates that you may not know that there is a difference between Visual Meteorological Conditions (VMC) and Visual Flight Rules (VFR). Likewise between Instrument Meteorological Conditions (IMC) and Instrument Flight Rules (IFR). You can be flying under Instrument Flight Rules in VMC—the airlines do this on most flights. It is not wise to fly VFR into IMC—a huge percentage of general aviation accidents happen because of that.

One source of the definitions is the FAA publication Pilot Controller Glossary, although they sort of presume you already know the concept.

INSTRUMENT FLIGHT RULES− Rules governing the procedures for conducting instrument flight. Also a term used by pilots and controllers to indicate type of flight plan.

INSTRUMENT FLIGHT RULES[ICAO]−A set of rules governing the conduct of flight under instrument meteorological conditions.

INSTRUMENT METEOROLOGICAL CONDITIONS− Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling less than the minima specified for visual meteorological conditions.

VISUAL FLIGHT RULES− Rules that govern the procedures for conducting flight under visual conditions. The term “VFR” is also used in the United States to indicate weather conditions that are equal to or greater than minimum VFR requirements. In addition, it is used by pilots and controllers to indicate type of flight plan.

VISUAL METEOROLOGICAL CONDITIONS− Meteorological conditions expressed in terms of visibility, distance from cloud, and ceiling equal to or better than specified minima.

The FARs only indirectly define IFR but you can get the rest of the definitions from the FARs.

  §1.1   General definitions.
  IFR conditions means weather conditions below the minimum for flight under visual flight rules.

  §91.155   Basic VFR weather minimums. (a) Except as provided in paragraph (b) of this section and §91.157, no person may operate an
  aircraft under VFR when the flight visibility is less, or at a
  distance from clouds that is less, than that prescribed for the
  corresponding altitude and class of airspace in the following table:

The table lists the visibility and clearance from clouds in different kinds of airspace that you need in order to fly under visual flight rules. If the weather is less than the minimums, then you need to fly under Instrument Flight Rules.

You can get an idea of the differences by reading CFR PART 91—GENERAL OPERATING AND FLIGHT RULES Subpart B—Flight Rules


Question 1: Can the LOC-D be flown with the tower closed at all? (The Alternate Minimums clearly state Circling is NA with the tower closed and LOC-D is a circling only approach. But aircraft are commonly cleared LOC-D approach with tower closed...)
Ans: The restriction eliminating the option of flying the LOC-D with the tower closed only applies when designating KSEE as a required alternate.
Question 2: Can you land on 27R with some interpretation of IFR rules?
Ans: At least 2 options:
(1)-Tell approach control (ATC) when they clear you for the approach that you intend on cancelling IFR when you get below the clouds (assuming it's still VFR/VMC). When VFR, cancel IFR and land at your discretion VFR/VMC. If, for some reason, the frequency is overwhelmingly busy and you can't get through in order to say "November**** Cancelling IFR" (hard to imagine) fly the published missed or land on another (none restricted) runway. OR
(2)- Request, at an appropriate time, a "Contact Approach." You would then be responsible for terrain avoidance (still under IFR) and land.
Question 3: What are the limitations on when during an approach you can cancel IFR and legally complete the approach VFR?
Ans: You cancel IFR on the approach when you are operating in legal VFR minimums (Class G in your example).


Why are prop blades not shaped like household fan blades?

1) Airspeed, 2) Forward motion, 3) Size constraints. Just to begin with.

Household fan blades are extremely slow, so they need more chord to push a meaningful amount of air. Aircraft propellers approach the speed of sound at their tips, and low drag is critical. All things equal, more span and less chord is more efficient. Reducing the airspeed for props has diminishing returns, because aircraft themselves move forward through the air, so a very large propeller adds drag to the aircraft however slow it is.

In household fans, size constraints are more critical than efficiency. A high-span, low-chord (narrow) blade would be more efficient in a household fan as well - indeed, you can find household fans with such blades. But they have to either spin faster for the same amount of airflow, which adds noise, or be larger in diameter. Ceiling fans, which can be larger, have longer narrower blades than desk or floor-standing fans.

Ship propellers move in an extremely dense and viscous medium, which changes things even more. The drag of moving through water is extremely high and proportional to V³ power-wise. The thrust force they produce is at most proportional to V², and can be lost to cavitation at high velocity. So their velocity has to be kept as low as possible. The drag cost of adding more chord is also relatively small in water.

On large ships, propellers are already as large as they can be made without sticking out of the water at low draft (on merchant vessels) or reducing the number of shafts that can fit (on combatants). This allows them to spin slower and lose less power to drag.


Can a mistake of a single air-traffic controller cause a collision between planes?

I haven't seen the Breaking Bad episode, but in my experience any aviation related scenes in films and series are usually stretching reality beyond the breaking point.

But it is possible that a single mistake can cause an accident. The probability of that happening is extremely remote, though.

Typically there are a number of safety barriers (also called defensive layers) in the system(1) that prevent any single mistake from developing into a collision. However, every barrier has a small probability of not catching the problem (e.g. due to it not being perfect or being in state of maintenance / failure) so eventually a crash could result from a single mistake.

This is often called the Swiss Cheese Model (originally from Reason, J. (1990) Human Error. Cambridge: University Press, Cambridge.)

When an accident happens, sometimes the phrase "all the holes in the Swiss cheese lined up" is heard, and you now know why.

While the first hole might be the mistake of a controller, the other holes may not be mistakes but are certainly rare circumstances and flaws in the system.  Accident investigation focuses on identifying these contributing factors.

In the Überlingen accident mentioned by Portree Kid, two immediate causes have been identified(2):

  The imminent separation infringement was not noticed by ATC in time. The instruction for the TU154M to descend was given at a time when the prescribed separation to the B757-200 could not be ensured any more.
  The TU154M crew followed the ATC instruction to descend and continued to do so even after TCAS advised them to climb. This manoeuvre was performed contrary to the generated TCAS RA.

The first cause can be seen as a mistake by the controller, however that mistake could only happen because of a number of contributing factors (systemic causes):

  Management and quality assurance of the air navigation service company did not ensure that during the night all open workstations
  were continuously staffed by controllers.
  Management and quality assurance of the air navigation service company tolerated for years that during times of low traffic flow at night only one controller worked and the other one retired to rest.

In addition to the above, the Short Term Conflict Alerting (STCA) system did not display conflicts to the air traffic controller because of maintenance (not listed as a cause in the report, but discussed in the text).

The second cause is not a mistake by the crew of the TU154M, but a latent failure in the way ACAS/TCAS II was introduced. Never did anyone give guidance on what to do if the controller and the TCAS gave conflicting instructions.

In the report this is identified as a systemic cause:

  The integration of ACAS/TCAS II into the system aviation was insufficient and did not correspond in all points with the system philosophy. The regulations concerning ACAS/TCAS published by ICAO and as a result the regulations of national aviation authorities, operational and procedural instructions of the TCAS manufacturer and the operators were not standardised, incomplete and partially contradictory.

So while the accident was caused by a single mistake from the controller, there were also many flaws in the system, which all together allowed the mistake to develop into an accident.

(1) By system I mean the aviation system as a whole, not only the air traffic control (computer) systems.

(2) Überlingen accident report


What does "Constant wind condition during flight" mean?

It means constant, or unchanging wind magnitude and direction.  It could be still air or just a constant upper level wind.  That can happen on local flights but is rare on long cross country flights.


Post MH370, are there developments to improve the tracking of airliners?

No, no technology has been developed that utilize the smartphone of passengers because the airplane is at a location where it is outside the connectivity of any smartphone during the entire flight, except for maybe the first and last few minutes.

A smartphone needs a cell tower to establish network connectivity, which typically has a range of a few hundred meters or at most a few kilometers. Once a plane takes off and climbs to around 5000 feet (which takes only a minute or so), it is out of range of all cell towers. There are departure and approach paths which flies over populated areas, but most flies out to rural areas for noise reasons. And if a plane is over a populated city, you don't need smartphones on board to track it anyway.

The only hope of communication in the middle of an ocean is a direct connection to a satellite. Smartphones are not equipped with the necessary hardware to do that, and I doubt they will in the near future. To connect to a satellite, you will need to know where it is in the sky, which in turn means you need to know your location to a reasonable accuracy and an antenna to point the signal at the right direction.

Your idea about inflight Wi-Fi is an interesting one. Theoretically, if someone's cellphone is configured to report its location once in a while (to help in a situation where the phone is stolen or lost), and that cellphone is connected to internet, it can be used to track a plane's location. However, bandwidth onboard is limited to the Mbps to Kbps range, since it is a satellite connection. In fact it is so limited that you have to paid (quite an expensive price) for it.

Moreover, this solution does not solve the connectivity problem, because the phone needs to rely on the plane's satellite connection to establish connectivity. But there needs not be a phone - the mere act of connecting to a satellite is already enough to track a plane's location.

However, there are changes in the aircraft systems that will allow airliners to be tracked more accurately. For example, ICAO recommends that by November 2018, all aircraft over open ocean should report their position every 15 minutes.


What are regulations for pyrotechnics on planes?

I'll answer for the FAA since thats the jurisdiction I know. Like most things some may consider this careless or reckless operation as per 91.13 which is the FAA's catch-all for odd occurrences that are not worth explicitly regulating.

  Sec. 91.13

  Careless or reckless operation.

  (a) Aircraft operations for the purpose of air navigation. No person
  may operate an aircraft in a careless or reckless manner so as to
  endanger the life or property of another.

  (b) Aircraft operations
  other than for the purpose of air navigation. No person may operate an
  aircraft, other than for the purpose of air navigation, on any part of
  the surface of an airport used by aircraft for air commerce (including
  areas used by those aircraft for receiving or discharging persons or
  cargo), in a careless or reckless manner so as to endanger the life or
  property of another.

I cant find anything that says "you cant tie fireworks to your plane and set them off" but that is an unlikely thing to bother regulating.

The TSA does not allow fireworks to be carried on aircraft and this AOPA article would make it seem as though they are not allowed to be transported by air at all. I would think this includes mounting them to the aircraft so you may be out as a result of this. Your local FSDO may be able to provide some more info on this and what you may need to do to make this ok.

The other thing to consider is that the FAA may consider this "dropping" so you would need to make sure you conform to 91.15.

  Sec. 91.15

  Dropping objects.

  No pilot in command of a civil aircraft may allow any object to be
  dropped from that aircraft in flight that creates a hazard to persons
  or property. However, this section does not prohibit the dropping of
  any object if reasonable precautions are taken to avoid injury or
  damage to persons or property.


What are those tiny circles on fan blades of Trent 1000?

These are certainly targets for an optical CMM (coordinate measuring machine) using laser, structured light or stereoscopy. The targets help define common points on the model from one scan to the next.
@mins linked a perfect example of this in his comment below, from which this image is taken. When doing 3D scanning, you want the dots in a random pattern as in the OPs image, rather than the uniform pattern seen below. This helps the identify and match the dots when going from one scan to the next (called "tie-points"). For the vibration analysis process linked by @mins, the requirements are probably different as the camera doesn't move, so it makes sense to place the dots in a grid pattern.


Does the P&W F100 turbofan engine of the F-16 really produce this much power?

https://en.wikipedia.org/wiki/Pratt_%26_Whitney_F100 gives a maximum afterburning thrust for the F100-PW-220 of 105.7 kN, so you were pretty close there.  Power is not listed on wikipedia, but you can get there.  It lists "Specific fuel consumption: Military thrust: (0.73 lb/(lbf·h))", so all you need to know is the lower heating value of jet fuel, and you can calculate the power. Off the top of my head, 46 MW seems a little high for that size engine, but it's certainly on that order of magnitude.


Why do large turbofans generally have many more LP turbine stages than HP turbine stages?

Because the LP turbine extracts power for the fan, which requires the most power. The HP and IP turbine only extract power for their connected compressors - the LP turbine extracts power for the fan and the LP compressor. The fan does work on all airflow through the engine, the compressors only on a fraction (10:1 for a high bypass like the Trent 1000). The fan produces up to 75% of the thrust of the engine.

From this presentation: the cross section of the Trent 1000. It shows that the LP, IP and HP rotors have different rotational speeds, but does not list them. Another (older) presentation lists them as 3600. 6800 and 10200 RPM. Rotational speed goes down as the volume of the mass stream goes up.

An old textbook of mine gives the power P extracted from a turbine stage as:

$$ P = \dot{m} \cdot u \cdot v_{ax} \cdot [tan (\alpha_2) + tan (\alpha_3)]$$

with

$\dot{m}$ = mass flow [kg/s]
u = tangential blade velocity [m/s]
v$_{ax}$ = axial gas velocity [m/s]
$\alpha_2$ and $\alpha_3$ angles according to the figure below.

So the tangential speed of the turbine blade is in the equation for power extraction, which is composed of rotational velocity and blade radius. The faster the turbine turns, the more power can be extracted per stage, and the fewer stages required. Why then does rotational velocity go down with pressure? (HP = 10,200; IP = 6,800).

The reason is the constructional limits of the turbine. As the gas stream expands, the turbine blades become larger and are mounted at a greater axial distance, which results in greater centrifugal forces which are proportional to blade mass, rotational speed and distance from the axis. In order to limit centrifugal forces, the rotational velocity of the rotor is reduced: each subsequent stage turns at a lower RPM. Notice that a lower RPM can be compensated by mounting the blade further away from the rotational axis.

The LP rotor of an un-geared engine runs at the same rotational velocity as the fan. Its optimal RPM for the turbine may be higher, and that can be accommodated by the geared fan. As the bypass ratio gets higher, the LP turbine will be extracting a higher fraction of total power from the airstream - turboprops and turboshafts have a gearbox in between the LP shaft and the propeller/rotor, and the high bypass fan approaches the relative dimensions of a propeller...


Where is an EASA PPL valid outside of Europe?

Yes, the EASA PPL is valid worldwide, but you must check the local laws prior to fly, for example, here in Brazil to fly a Brazilian registrated airplane (PT-***) you shoud have an ANAC PPL license, but if you are flying to Brazil in an UK based Aircraft( reg. G-****), you can fly it with your EASA PPL.

If you intent to Fly a Non-European aircraft for a long period in a same country, you should validate your EASA license within the local Aviation Authority, that ensures that you get the same level of license as you have from EASA.


Does the wing always have an adverse pressure gradient along the chord?

At the trailing edge of the upper surface, you will always have a pressure recovery as low pressure from the upper surface converges toward the high pressure from the bottom surface at its trailing edge. This is the adverse pressure gradient since pressure is increasing along the chord length. The gentler the pressure recovery, the less likely is the airfoil to have an adverse boundary layer velocity profile, which is the source of flow separation and stall.

Source: https://www.researchgate.net/figure/Airfoil-Cp-vs-x-c-curve_fig9_306374523

Since most of the lift is through the suction from the upper surface, I don't think you will encounter a practical airfoil without pressure recovery.


Why do Turkey and UAE limit the age of aircraft flying over their territory?

Sounds like a market protectionist move by the nations. i.e. The airlines of UAE and Turkey are relatively new. At least their current expansion to a scale that is competitive with the major international airlines is relatively recent. Their airports have also undergone fairly recent expansions to capitalize on their geographical location as hubs between N. America / EU to Asia-Pacific nations.

I suppose they give their own airlines a competitive advantage by restricting older aircraft. The US / European carriers can only allocate the fraction of their fleet that is new to flights to Turkey / UAE which constrains their activities.

The average fleet age of some airlines in 2013:

Delta  16 years
United  13 years
American + US 13 years
Lufthansa 13 years

Now compare with

Turkish  8 years
Emirates 6 years

Basically, international trade treaties have made it difficult for nations to overtly engage in protectionist measures. So bureaucrats figure out indirect means under the guise of technology, quality etc. that are ostensibly  not favoring domestic industry but are effectively a discriminatory measure.

Take the numbers with a pinch of salt because airline fleets are continuously upgraded so the average age of a fleet can change pretty rapidly.

Caveat: The average fleet age may not be representative of the equipment flying international sectors.

PS. I don't think the regulation has much to do with real safety because safety is concerned with many other factors outside of aircraft age. The safety aspects are better regulated by adopting the FAA safety watch-list based on national assessments.

At best, this sounds safety theater. Not safety.


What are different types of weights of an aircraft?

The different terms represent different weights or masses1. For each flight, the weights are taken into account for several reasons.

A brief description about these is below:

Manufacturer's empty weight (MEW)
Also called Manufacturer's Weight Empty (MWE) or Licensed Empty Weight

It is the weight of the aircraft "as built" and includes the weight of the structure, power plant, furnishings, installations, systems and other equipment that are considered an integral part of an aircraft.

This excludes any baggage, passengers, or usable fuel2.

Zero-fuel weight (ZFW)

This is the total weight of the airplane and all its contents (including unusable fuel), but excluding the total weight of the usable fuel on board.

As a flight progresses and fuel is consumed, the total weight of the airplane reduces, but the ZFW remains constant.

Maximum zero fuel weight (MZFW) is the maximum weight allowed before usable fuel and other specified usable agents (engine injection fluid, and other consumable propulsion agents) are loaded.

Operating empty weight (OEW) (Roughly equivalent to basic empty weight on light aircraft)

It is the basic weight of an aircraft including the crew, all fluids necessary for operation such as engine oil, engine coolant, water, unusable fuel and all operator items and equipment required for flight but excluding usable fuel and the payload.

Payload

It is the carrying capacity of an aircraft. It includes cargo, people, extra fuel. In the case of a commercial airliner, it may refer only to revenue-generating cargo or paying passengers.

Maximum takeoff weight (MTOW)

This is the maximum weight at which the pilot of the aircraft is allowed to attempt to take off3.

Regulated takeoff weight (RTOW)

Depending on different factors (e.g. flap setting, altitude, air temperature, length of runway), RTOW or maximum permissible takeoff weight varies for each takeoff. It can never be higher than MTOW. More information is on this answer.

Maximum landing weight (MLW)

This maximum weight at which an aircraft is permitted to land3.

The following image depicts takeoff weight components.

Image Source

Maximum ramp weight (MRW)
also called maximum taxi weight (MTW)

It is the maximum weight authorized for maneuvering (taxiing or towing) an aircraft on the ground.

Aircraft gross weight

It is the total aircraft weight at any moment during the flight or ground operation. This decreases during flight due to fuel and oil consumption.

1: As mentioned (below in comments by SentryRaven), several recent references use the term mass instead of weight. Having a Physics background, I tend to agree and know the difference between weight and mass. I did not use mass as most of the references I included referred mass as weight. However, using correct terminology, all the weights mean mass. Thanks SentryRaven for pointing it out.

2: What is the different between usable fuel and unusable fuel?
Usable fuel is the fuel on board an aircraft that can actually be used by its engines. The small amount of fuel that cannot be drained from the tanks is the unusable fuel. For calculation of range, usable fuel is used. For weight and balance total fuel (usable + unusable) is used.

3: This restriction is due to structural, design or operational limitations.


How should wake turbulence from aircraft on the ground be avoided during landing?

Wake turbulnce occurs when an aircraft is creating lift.  Since, the airliner is on the ground, there is no wake turbulence.

If you are worried about jet blast from the airliner holding short between the runways, then I would land past the airliner by about 1000 ft.  With the airliners engines at idle, there will be minimal jet blast but if the increase power that jet blast increases significantly.


Why both ICAO and IATA headquarters are located in Montreal?

ICAO is headquartered in Montreal because that was the result of a vote by the founding members (PICAO is Provisional ICAO):

  Why was Montreal selected? While insisting on the excellent
  hospitality offered since of the beginnings of PICAO by the federal,
  provincial and municipal authorities, the delegates described Montreal
  like a roundabout of the international means of communication and a
  strategic centre with a formidable economic, scientific, technical and
  aeronautical expansion being felt for a few years. One insisted on the
  vast spaces of the Canadian territory, offering unlimited
  possibilities for the scientific and practical experiments in the
  field of aviation. Moreover, PICAO was to be established as close as
  possible to the central head office of the United Nations.

And IATA is in Montreal because its founding statutes said that it must be in the same location as ICAO:

  Article II of the IATA 1945 Statutes states that “The Head Office of
  this Association shall be maintained in the city in which the
  headquarters of the International Civil Aviation Organization is
  located.”; this article was later amended to leave an opening for a
  possible other place as determined by the General Meeting


How to find the flight paths of an airport?

You can find a great deal of approach path information here but that will only give you the path, and perhaps some intercept altitudes for a given approach it will not give you any speed information. Cruising altitudes will also vary heavily by aircraft type.

  Specifically, I need a figure showing the height vs. speed of a plane
  as it's landing starting from the cruising altitude.

This is broadly specific to each airframe as well as the loading of any given aircraft at a given time. But you can find the information if you know the airframe in question, there are also some limits depending on where you are in the world. The FAA (and presumably most legal entities) cant have different rules for everyone so they broadly break down approach speeds into categories. That should give you a fair idea of the approach speeds. Keep in mind these are airspeeds and local wind will alter ground speeds on an individual day basis.

If you start from the cruising altitude there will be a few phases of the decent that will see various speeds. This depends on what ATC clears you for and what the local conditions call for more on that here.


Checkerboard painted on fuselage of Boeing test aircraft

the checkerboard mark allows accurate indication of the position of the plane using cameras as the plane flies by. by tracking the movement of the checkerboards between frames of a series of camera shots, the plane's speed, roll rate, acceleration, etc. can be measured.


Do left and right mic buttons control both headset microphones?

This is the expected behaviour. The other pilot might make some sound or even talk to someone else. You don't want any noise interfering with your own voice during transmission.  Two microphones picking up your voice might also decrease the sound quality because of the small delay between the two locations.


How should flaps be used during an emergency landing (PPL)?

Specifically in your case you may have lost more altitude in the turn than your instructor or your turns were less coordinated etc. A wide variety of other variables that are hard to note with out accurate course data could have led to your outcome. You would have had to enter the maneuver at the same place/altitude to get similar results and the wind would have an effect here as well. Did you have a head wind or tail wind? Its worth covering some general procedures for this maneuver.

When turning under glide its important to watch your airspeed and know how the plane will sink in a turn since you sacrifice some lift for the turn.

Remember flaps allow you to make a steeper approach with out gaining airspeed but what that also means is your ground speed is effected (slowed).

When it comes to the emergency landing procedure you are free to use flaps at your discretion and as mentioned its generally taught to use them once you are sure you have the field made. If the field is long enough you should shoot for a mid point incase you come up a bit short. Likewise if you are high you can go full flaps and slip it to lose altitude fast (if your instructor has not shown you how to slip a plane to lose altitude I would advise asking him to do so).


Are aircraft still guided by ground marshals?

Typically, marshalling is used to guide aircraft to their parking stand.

There are alternatives available (Visual Guidance Docking Systems) that allow pilots to park their aircraft at the right spot without the aid of a marshaller.

In its simplest form, the parking spot has a big identifier to allow the pilot to select the right stand, a centreline for the nose wheel to follow, a marking where the nosewheel should stop and a mirror so the pilot can see where the nose wheel is relative to the marking.

In its more advanced form, there are pressure plates in the stand that determine the position of the aircraft, a laser scanning system that determines the exact position of the aircraft and whether the stand is obstacle free, and a digital display guiding the pilot during parking.

In case the VDGS is not available or cannot handle the specific aircraft type, a marshaller will have to step in.


As quoted from the entry in the Pilot/Controller Glossary:

  CONFIDENCE MANEUVER− A confidence maneuver
  consists of one or more turns, a climb or
  descent, or other maneuver to determine if the pilot
  in command (PIC) is able to receive and comply with
  ATC instructions.

This could be useful if the controller suspects a hijacking, hypoxia, radio failure, or other situations that would compromise reception and execution of ATC instructions.

Perhaps the best example of an implementation of this would be when ATC suspects a partial aircraft radio failure; a confidence maneuver vector might enable ATC to determine that the pilot was still able to receive instructions, though aircraft radio transmission might be compromised.


Is there a standard format for pre-departure clearances?

I know nothing about PDCs, but it does seem that they are now standardized. One aircrew training site said in April 2014:

  For those of you capable of receiving a Predeparture Clearance (PDC),
  have you noticed a change since the first week of April? The FAA
  changed the way it issues PDCs. Gone are the days of trying to decide
  if you got a reroute in the PDC. The FAA recognized there was a
  problem with standardization with regards to reroutes

The article points to JO 7110.113, Procedures for Issuing Automated Clearances, which says:

  5. Explanation of Policy Changes. This order is revised to provide standardization of PDC clearances across the FAA.

I guess you can read the rest of the JO for more information, it means nothing to me :-)


What medications may pilots take while flying?

AOPA has the best database that I know of, but you have to be a member to view it.  They have some free information on their Medications page though.

There they talk about FAA Policy, and it starts with:

  The Federal Aviation Regulations include no specific references to
  medication usage. FAR 61.53 prohibits acting as pilot-in-command or in
  any other capacity as a required pilot flight crewmember, while that
  person:

  Knows or has reason to know of any medical condition that would make the person unable to meet the requirement for the medical certificate
  necessary for the pilot operation, or:
  Is taking medication or receiving other treatment for a medical condition that results in the person being unable to meet the
  requirements for the medical certificate necessary for the pilot
  operation. Further, FAR 91.17 prohibits the use of "any drug that
  affects the persons faculties in any way contrary to safety."

AMAS (Aviation Medicine Advisory Service) also has a list (which is free) but I don't think that it is organized as well.  They are recommended by ALPA and NBAA though.

The most important thing though, of course, is to self evaluate and make sure that you don't fly if you are having any adverse reactions from the medication, or the underlying condition that you are taking the medicine for.

Any list that you consult has to be used only as a guide though, and not a carte-blanche approval.  Individual people can have reactions even to medications that are considered "safe" and "allowed" by the FAA, and this is why they don't list specific medications that they allow.  The FAA has a brochure called Medications and Flying, and one part of it has a few things to consider before taking any medication:

  First, consider the underlying condition  that you are treating. What
  will be the  consequences if the medication doesn’t work  or if it
  wears off before the ﬂight is over?  A good general rule to follow is
  not to ﬂy  if you must depend on the medication to  keep the ﬂight
  safe. In other words, if the  untreated condition is one that would
  prevent  safe ﬂying, then you shouldn’t ﬂy until the  condition
  improves — whether you take the  medication or not.

  Second, you must consider your reaction to  the medication. There
  are two broad categories  of medication reactions. One is a unique
  reaction  based on an individual’s biological make-up.  Most people
  don’t have such reactions but  anyone can, given the right medication.
  Because  of this, you should NEVER ﬂy after taking any  medication
  that you have not taken before. It  is not until after you have taken
  the medication  that you will ﬁnd out whether you have this  uncommon
  and unexpected reaction to the  medication.

  Third, consider the potential for adverse  reactions, or side
  effects — unwanted reactions  to medications. This type of reaction is
  quite common, and the manufacturer of the  medication lists these on
  the label. You MUST  carefully read all labeling. If you don’t have
  access to the label, then don’t ﬂy while using the  medication.

  Look for such key words as lightheadedness,  dizziness, drowsiness, or
  visual disturbance. If  these side effects are listed or if the label
  contains  any warning about operating motor vehicles or  machinery,
  then you should not ﬂy while using  the medication.

  Side effects can occur at any time, so even if  you’ve taken the same
  medication in the past  without experiencing side effects, they could
  still  occur the next time. For this reason, you must  never ﬂy after
  taking a medication with any of  the above-noted side effects.


Cabin pressurization outflow valve.

Cabin pressure in an airliner is maintained by bleeding air from the engine compressors into the cabin, after conditioning (usually cooling and humidifying) it. Current designs are beginning to use separate air compressors for this.

In either case, the cabin pressure is regulated by controlling the difference between inflow, provided by the bleed or compressor, and outflow, which is a simple motor-controlled valve.

Generally the inflow is set to maximum and the outflow is varied, as this provides the maximum fresh air flow for the passengers.

See also:

How does the outflow valve work on a cabin pressurization system?

How does the cabin pressure controller work in a large commercial airliner?

How does the cabin pressure controller work in a large commercial airliner?

https://www.airspacemag.com/flight-today/how-things-work-cabin-pressure-2870604/

Can an aircraft re-pressurize at high altitude?


How does an engine work when an airplane has $v=0$ on the ground?

To start the engine, the fan blades have to be spun up. This is typically handled by either blowing air through them from some outside source, and/or by using an APU to generate power to drive the shaft they're connected to.

Once the engine is running, it sucks in enough air to keep going on its own.


Qualification for being a pilot-in-command in mutli-crew aircraft (i.e. captain) is independent of type rating (i.e. qualification to fly specific aircraft type). And similarly with the multi-crew rating required to fly a multi-crew aircraft at all (i.e. as F/O).

Therefore the airline selects some pilots and sends them to appropriate training to get the type rating. And those who were captains before can be captains on the new type too.

Since much of the experience applies to any aircraft, usually they'll select the more experienced captains from other types to become captains on the new type.

If the type is widely used elsewhere, the airline will also try to hire pilots from elsewhere who already have appropriate ratings, but obviously there is not much opportunity for that in a new type like A220 (formerly known as CSeries).


91 year old father allowed to fly a plane again?

What Carlo Felicione has posted is true. Your father must have a Flight Review given by an instructor, examiner, or administrator designee within the previous 24 months of any flight of an aircraft where he is acting in the role of Pilot-in-Command. If there is not another qualified pilot at the controls of the aircraft, your father is acting in the role of PIC.

The other issue is his medical status. Given the fact that you have said he has not flown in 35 years, I take it that he had either a private (as you stated) or a commercial pilot certificate and not one of the more recently created licenses. There are varying levels of requirements he has to meet and fulfill based on the type of aircraft operations he is conducting.

In order for him to fly as PIC in a powered aircraft without at least a valid unexpired third class medical certificate, he has to have:

Valid unexpired drivers license
Have been in possession of at least a valid third class medical certificate after July 14, 2006.
Document receiving a comprehensive medical exam to the FAA’s standards from any state-licensed physician of his choice within the last 48 months.
He can not have had his most recent medical certificate or application for a medical certificate denied, revoked, or suspended.
Complete an FAA mandated medical education course on Basic Medical requirements.

In addition...

Title 14 of the Code of Federal Regulations, (Federal Aviation Regulations) Part 61.113 states the following:

  (i) A private pilot may act as pilot in command of an aircraft without holding a medical certificate issued under part 67 of this chapter provided the pilot holds a valid U.S. driver’s license, meets the requirements of §61.23(c)(3), and complies with this section and all of the following conditions and limitations:

  (1) The aircraft is authorized to carry not more than 6 occupants, has a maximum takeoff weight of not more than 6,000 pounds, and is operated with no more than five passengers on board; and

  (2) The flight, including each portion of the flight, is not carried out—

  (i) At an altitude that is more than 18,000 feet above mean sea level;

  (ii) Outside the United States unless authorized by the country in which the flight is conducted; or

  (iii) At an indicated airspeed exceeding 250 knots; and

  (3) The pilot has available in his or her logbook—

  (i) The completed medical examination checklist required under §68.7 of this chapter; and

  (ii) The certificate of course completion required under §61.23(c)(3).

He may, however, fly an aircraft officially designated and certificated by the FAA as a Light Sport Aircraft as long as his most recent FAA Medical Certificate or application for a Medical Certificate was not denied, suspended, or revoked. And, he must not know or have reason to know of any medical condition that would make him unable to operate a Light Sport Aircraft in a safe manner. Also, he can not fly at night, in Instrument weather conditions, or above certain altitudes (the higher of 10,000 feet Mean Sea Level or 2000 Above Ground Level).

  Light-sport aircraft means an aircraft, other than a helicopter or powered-lift that, since its original certification, has continued to meet the following:

  (1) A maximum takeoff weight of not more than—

  (i) 1,320 pounds (600 kilograms) for aircraft not intended for operation on water; or

  (ii) 1,430 pounds (650 kilograms) for an aircraft intended for operation on water.

  (2) A maximum airspeed in level flight with maximum continuous power (VH) of not more than 120 knots CAS under standard atmospheric conditions at sea level.

  (3) A maximum never-exceed speed (VNE) of not more than 120 knots CAS for a glider.

  (4) A maximum stalling speed or minimum steady flight speed without the use of lift-enhancing devices (VS1) of not more than 45 knots CAS at the aircraft’s maximum certificated takeoff weight and most critical center of gravity.

  (5) A maximum seating capacity of no more than two persons, including the pilot.

  (6) A single, reciprocating engine, if powered.

  (7) A fixed or ground-adjustable propeller if a powered aircraft other than a powered glider.

  (8) A fixed or feathering propeller system if a powered glider.

  (9) A fixed-pitch, semi-rigid, teetering, two-blade rotor system, if a gyroplane.

  (10) A nonpressurized cabin, if equipped with a cabin.

  (11) Fixed landing gear, except for an aircraft intended for operation on water or a glider.

  (12) Fixed or retractable landing gear, or a hull, for an aircraft intended for operation on water.

  (13) Fixed or retractable landing gear for a glider.

He may also seek out getting his glider or balloon rating to fly either of those aircraft without a Medical Certificate. This option is a good one for him. But, it will require home to legally get the ratings through an instructor and Designated Pilot Examiner.

the FAA states in 61.107...

  (2) If the applicant has logged at least 40 hours of flight time in a heavier-than-air aircraft, the applicant must log at least 3 hours of flight time in a glider in the areas of operation listed in §61.107(b)(6) of this part, and that flight time must include at least—

  (i) 10 solo flights in a glider in the areas of operation listed in §61.107(b)(6) of this part; and

  (ii) 3 training flights with an authorized instructor in a glider in preparation for the practical test that must have been performed within the preceding 2 calendar months from the month of the test.

His last option, as posted by Crossroads, would be to fly an Ultralight aircraft.

The FAA states in Part 103...

  Notwithstanding any other section pertaining to airman certification, operators of ultralight vehicles are not required to meet any aeronautical knowledge, age, or experience requirements to operate those vehicles or to have airman or medical certificates.

  an ultralight vehicle is a vehicle that:

  (a) Is used or intended to be used for manned operation in the air by a single occupant;

  (b) Is used or intended to be used for recreation or sport purposes only;

  (c) Does not have any U.S. or foreign airworthiness certificate; and

  (d) If unpowered, weighs less than 155 pounds; or

  (e) If powered:

  (1) Weighs less than 254 pounds empty weight, excluding floats and safety devices which are intended for deployment in a potentially catastrophic situation;

  (2) Has a fuel capacity not exceeding 5 U.S. gallons;

  (3) Is not capable of more than 55 knots calibrated airspeed at full power in level flight; and

  (4) Has a power-off stall speed which does not exceed 24 knots calibrated airspeed.

Here are some overly-simplified examples in a nutshell of what you can do if you have a pilot certificate, appropriate ratings and currency of flight.

King Air 100 - you need to have a valid FAA medical.
Cessna 172 - you need to have passed an FAA medical in the last 14 years and have a note from your doctor.
SportCruiser - you need to be legally able to drive a car.
Glider or balloon - no medical needed, just a pilot certificate.
Ultralight - not even a pilot certificate needed.


Is it legal to drop/shoot paintballs from an airplane?

Greg covered this very well in his answer.
The "miss by a surprising distance" bit is especially important here in the context of FAR 91.15 -- you would have to have a VERY large-scale paintball match for this to be viable, and some specific rules of engagement for the aircraft (always firing "into" the arena area as you don't want to miss and send a paintball into someone's car or kitchen window as that would get some distinctly unfriendly attention from the FAA, and probably the local constabulary).

Operationally, if we're doing this with an airplane high-wing aircraft would obviously be the order of the day (Cessna 152), with a pilot (whose sole job is to fly the airplane) and a gunner/bombardier (who is responsible for hitting targets on the ground). You really don't want the pilot distracted by the game.
Your weapons guy is going to have to be able to account for the aircraft's speed and altitude in targeting (which is pretty hard with an adjusted scope/bomb sight - doing it without one is going to be tough).

As for shooting back at the plane, if we're talking about a "regular" airplane (something manned, like a Cessna 152) I would advise against allowing players to target the plane. At safe operating altitudes they're unlikely to hit the plane, but if they do aircraft skin is very thin & dent repair is very expensive: If someone is lucky enough to score a hit it could be a costly "death".

Now, as a paintball player myself I will tell you that I find the idea of death from above when I can't shoot back at the aircraft to be rather unsporting!

What I would suggest instead is to deploy quadcopter drones. These can be had pretty cheaply and with some basic electronics skills they can be modified to carry/drop paint grenades (think Squadbusters) on your enemy.
If you want to get really fancy add a GoPro or some other remote camera to help with targeting, or add a paintball gun to the thing like these folks did.

The FAA's rules for "unmanned aerial systems" are still being written, but if you keep to the general rules for model aircraft (below 400 feet, and not charging anyone money for the drone's services) I think you'll be OK (when the final rules come out you'll have to review your drone for compliance).
As a bonus if the drone isn't too large and you have an indoor arena with liberally-minded management you may even be able to use your drone during indoor games.

(Kill rules for the drone and its operator are left as an exercise for the players.)


Why don't transponders have active and stand-by value like radios?

For navigation and communication radios the feature of having a second readout that can be pre-set to the next frequency is useful since the next frequency is usually known in advance. Your next transponder code is a somewhat random number and the moment that you will get it is not as predictable as a frequency change. Therefore there is no need for a pre-set / standby squawk code in a transponder.

Also, in a communication radio, when you pre-set the wrong frequency and cannot establish communication after the switch over, a single button press will bring you back to the original frequency. This prevents prolonged communication loss. This is similar in navigation radios.
For a transponder such a feature has no value, you won't switch back to the previous squawk code.

The problem of inadvertently selecting a special code can be addressed by other means. For example a digital interface that requires confirmation of the selected code before it is activated.


Why don't aeroplanes use propellers with more blades like the intake on a fanjet?

Every blade will create its own boundary layer and its own vortex sheet. It is more efficient to use fewer blades with deeper chord, because the forward part of a boundary layer contributes most to friction drag.

To keep the lift coefficient on the propeller blade sections in a reasonable range (0.6 to 1.0) for efficiency means that blade chord will be reduced, which will make them less stiff. Again, it will be better to reduce blade count to arrive at a more viable design. All the thrust the propeller creates is pulling on those skinny blades, and they must be strong enough to withstand this force.

Only when the propeller disc loading increases do more blades begin to make sense:
 When engine power increases, the propeller disc area should also grow, but this growth is limited by the resulting speed of the blade tips. Once the flow speed there becomes supersonic, the drag at this section of the blade increases without a corresponding increase in thrust. To avoid that the next best option is to increase the solidity ratio of the propeller, called also the activity ratio.

Make no mistake, this is bad for efficiency. But if there is enough power available, adding more blades is the best way out.

You are right, a lower prop speed allows to increase its diameter, but while tip speed will drop by less than the reduction in prop speed (after all, flight speed should not change), the available thrust from this propeller will drop by the square of the speed reduction, since thrust is proportional to the dynamic pressure on the blades. And thrust you get only from the circumferential fraction of the local speed at the blade; flight speed does not count here and does not help to mitigate the reduction.


Can I use audio containing Canadian ATC/broadcast radio transmissions in a YouTube video?

In countries where it is illegal to listen to ATC chatter like the UK, it is also illegal to post it, and you can see this on LiveATC, where you can easily listen to YKZ, YYZ, YVR, YTZ, and YHZ, etc. in Canada, but you can't listen to UK airport feeds or sectors for example LHR, LGW and MAN.

So assuming that liveatc is not an illegal orginization, (we know that for sure because literally the #1 thing that comes up when you search on google atc, liveatc comes up. And if it was illegal, the RCMP would have taken down liveatc at least in canada years ago!) we can say that no, posting atc chatter online is not illegal in Canada.


There was at least one incident where a Boeing 737 attempted to takeoff with the throttle levers not set to takeoff power.

The procedure is designed to ensure

the thrust lever is where it is supposed to be
the engine indications show the correct amount of power is produced

In some airlines, the procedure calls for both pilots to put their hands on the levers and advance them together. Either way, the purpose is to have both the pilot flying and pilot monitoring to ensure takeoff power is properly applied.


Why don't all cylinders have priming lines?

The airplane maker will not normally install any more primer lines than necessary. In warm environments it's not usually necessary to prime more than one cylinder, so you will see airplanes operated in the southern US with single primer lines more often than in the northern US or Canada.  My old '68 Cardinal only had a single primer port because it had been imported from the US that way (I was in Toronto at the time), and it was murder to get it started even in moderately cold weather without preheat. I had primers run to all 4 cylinders by my mechanic.
Also, you will often see one of the threaded holes at the intake port on a cylinder being used as a tap-off for a manifold pressure gauge, another reason for stopping at 3 lines.
When priming, the objective is to get a good coating of raw fuel in the intake pipes close to the port, that will take 5 or 10 seconds to fully evaporate after starting, to provide that temporary extra-rich mixture.  But not too much.
Over-priming can start a fire when so much gas is squirted in it starts to collect in the intake pipes and drain down into the airbox.  A backfire into the intake system during starting, because an intake valve doesn't quite seal, can ignite the fuel in the airbox, and potentially fuel that is dripping into the cowling.
That's why, when cranking and you hear a "fump!" sound under the cowling, keep cranking!  You need to try to draw any ignited raw fuel back into the intake.  Only stop cranking if you start to see smoke gushing out, and then it's time to leave and tell the owner he can have his plane back (or try to fight the fire if you want).
It's when you start to smell gasoline that you know you've over done it.  Best to stop and wait a while for all the gas to evaporate.
A worse habit is throttle pumping to spray fuel from the carb's accelerator pump into the intake.  You might do it when you start a warm engine; it's not necessary to prime with the primer and little shot of throttle while cranking is enough.
But it's critical to only pump the throttle during cranking. If you pump it while things are stopped, gasoline runs straight down into the airbox immediately.  Probably most cowl fires are from people pumping throttle several times, waiting a few seconds, then starting, then it's "Fump!".... "do you smell something?".


Where does the transponder read altitude, or does ATC get it from radar?

does the aircraft have or need an encoding altimeter interfaced to the
  transponder to report altitude, is it built into some transponders

In order to squawk mode C, you need an encoding altimeter connected to your transponder and the transponder needs to be set to transmit mode C. Does that transponder have a build-in encoding altimeter? That requires a check through the logs and/ or manuals. In my aircraft they are separate, in yours I have no idea.

  or was the Approach controller using altitude as reported by the radar
  if it has height finding capabilities?

Maybe. It depends upon the specifics of the airport. If your transponder's altimeter was calibrated incorrectly or otherwise bad (extremely difficult for you as the pilot to verify in a rental aircraft during preflight) then they may have been trusting your transponder for your altitude data, which was incorrect. If they were using radar with vertical capabilities (precision approach radar is, depending upon your viewpoint of part 91 vs part 121, either relatively rare or everywhere you might need it where I live) they may have been comparing that to your transponder's altitude reported.

All of this depends upon if you checked your altimeter using the current local setting on the runway threshold prior to takeoff. Have I always done that? Yes. Does everyone? No. If your panel altimeter checked out, you used the proper setting during the approach, and your transponder is telling them you are at the wrong altitude the transponder's altimeter appears to be the problem.


Can I log PIC time when training for a tailwheel or high performance endorsement?

Yes and Yes; As long as you are rated for the category, class, and type (if required) of the aircraft that you are receiving the training in you could log both PIC and dual received.

14 CFR 61.51(e)(i) covers the logging of PIC time (which is perfectly legal in the scenario that you describe if you are rated in the aircraft):

  §61.51   Pilot logbooks.

  ...

  (e) Logging pilot-in-command flight time. (1) A sport, recreational,
  private, commercial, or airline transport pilot may log pilot in
  command flight time for flights-

  (i) When the pilot is the sole manipulator of the controls of an
  aircraft for which the pilot is rated, or has sport pilot privileges
  for that category and class of aircraft, if the aircraft class rating
  is appropriate;

Training time is logged per 14 CFR 61.51(h) and you can log that too:

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

That being said, you may not act as the actual PIC however:

  §61.31   Type rating requirements, additional training, and
  authorization requirements.

  ...

  (i) Additional training required for operating tailwheel airplanes.
  (1) Except as provided in paragraph (i)(2) of this section, no person
  may act as pilot in command of a tailwheel airplane unless that person
  has received and logged flight training from an authorized instructor
  in a tailwheel airplane and received an endorsement in the person's
  logbook from an authorized instructor who found the person proficient
  in the operation of a tailwheel airplane. The flight training must
  include at least the following maneuvers and procedures:

  ...

Notice that the regulations governing acting as PIC are different than those governing logging of PIC time.  This was done intentionally because there were so many pilots that were hired as SIC's at airlines with little to no PIC time and flew for years. When it was time for them to upgrade they didn't have enough PIC time even though they had lots of experience and could easily upgrade safely.


What would be the power requirements and performance of a Scroggs-type delta-wing aircraft with a 250 cm span?

First, thank you for unearthing this unorthodox design!

However, it shows that paper airplanes don't scale well. Nevertheless, it follows the same laws of physics, so the same equations should apply for a quick performance evaluation. What have we got?

A flat plate airfoil. Maximum lift coefficient will be between 0.7 and 0.8, so minimum speed at a given wing loading will be quite high.
A sweptback delta wing of low aspect ratio, so the lift curve slope will be low. For the same lift coefficient it needs much more angle of attack than a regular airplane. Since upper side flow is separated, airfoil drag will grow with the square of the angle of attack, and the low lift curve slope ensures that drag will be needlessly high.
A big fuselage with a lot of wetted surface area.
A massive separation area at the back which will produce a lot of drag without any benefit, except for improved directional stability.

Let's start with induced drag. The low aspect ratio ensures a nearly elliptic lift distribution, and lifting 300 kg with 2.5 m of wing will create $$D_i = \frac{2\cdot(m\cdot g)^2}{\rho\cdot v^2\cdot\pi\cdot b^2} = \frac{180000\cdot g^2}{1.225\cdot v^2\cdot3.14159\cdot 6.25} = \left(\frac{g}{v}\right)^2\cdot 7483\;N$$
At 20 m/s flight speed this will equal 3,600 N of drag and at 40 m/s flight speed a quarter of that (900 N). Multiply by speed to get the power needed to overcome just induced drag: 36 kW at 20 m/s and 18 kW at 40 m/s.

But what speed is achievable? We need to guess the wing area in order to find the stall speed. I assume 4 m chord and 1 m span at the leading edge, so the wing area is 7 m². Using a maximum lift coefficient of 0.75, this means you cannot fly slower than 30.24 m/s. Whoa! That is 58.8 kts or just below the 61 kts limit for the old FAR 23.

Let's add some safety margin and continue with 40 m/s flight speed, which corresponds to a lift coefficient of 0.43. Now to the angle of attack - this requires to know the lift curve slope. As a slender body it will be slightly below $\pi\cdot\frac{AR}{2}$, and with an aspect ratio $AR$ of below 1 this is maybe 2.2 per radian or 0.04 per degree. At $c_L$ = 0.43 this is 11°. Multiply the weight with the sine of 11° and you get the cost for flying a fully separated top wing: 506 N. Dragging this through the air at 40 m/s needs another 20.2 kW.

Now to the wetted surface: The vertical surfaces add maybe another 4 - 5 m² to the 14 m² of the wing. The Reynolds number is 11$\cdot 10^6$, so the friction drag coefficient is as low as 0.003 if the surface is smooth. Since the upper wing shows separated flow, I will continue with 15 m² surface area. At 40 m/s this equates to 44.1 N of drag, needing 1.76 kw of power.

The fixed and unfaired landing gear will be another source of drag; here I simply double the friction drag in order to account for it, too. I expect that a detailed drag analysis will not change the result substantially.

Your idea of filling the separation area with a ducted fan is probably costing even more performance. Please consider that now you have a high-speed stream of air flowing through a duct running along the length of the fuselage. Better to narrow the fuselage in the rear half so it ends in a vertical rudder.

If we now assume that you avoid any boattail drag this way, flying straight and level at 40 m/s will need a total of 42 kW. Add 50% for manoeuvring and climbing (those extra 21 kW translate to a climb rate of more than 6 m/s - looks OK) and a propeller efficiency of maybe 75% (look at this answer - that could be as low as 60% in reality!), and you end up with an engine requirement of 84 kW or 112.6 HP. It looks like you need a Rotax 914 or similar engine, the mass of which will eat up one third of your budget.


Why does An-225 (Mriya) perform a low-pass on its landings?

As of the time of writing this answer, this only appears to have happened in one out of the last 6 flights of the AN-225 (the same flight into Warsaw you mentioned, https://www.flightradar24.com/data/aircraft/ur-82060#245b19c0) so I can't say that this is an official "rule", a standard of any kind or any procedure regarding the AN-225.

There are 2 other videos of that particular landing on YouTube:

It is clear in both videos that the first approach is done with the landing gears up, most likely on purpose "for the show", of course with coordination with ATC.

If someone is fluent in Ukrainian they can confirm it quite easily since the communication between the pilots can be clearly heard in the video you provided.


What is the fastest accelerating aircraft on takeoff?

Airplane performance really isn't gauged that way, partly because quick acceleration 'drag race' data is not a pertinent aspect of their flight envelope.  That being said, there are a few examples, one being from the TV show Top Gear where a Bugatti Veyron races a Eurofighter Typhoon - and gets smoked by the jet.

I don't have data on jet fighters as far as linear acceleration; a quick calculation could reveal some basic data.

Take the case of an F-22.  Assuming a 55,000 lbf takeoff weight, lineup, 70,000lbf thrust at full power, then brakes off and rolling, we expect to see an acceleration around:

$$(70/55)*32.2 ft/s^2 = 41 ft/s^2$$

This also assumes no friction from the wheels or air resistance during the takeoff roll.

By basic kinematics, the jet would reach 60mph or 88ft/sec in 88/41 = 2.15 seconds.

So could an F-22 or another high performance jet fighter beat an Model S in a drag race?  Well it's theoretically possible and and as the above example shows, it has happened and it didn't end well for the auto.

As for airliners, the car is going to smoke them until the car reaches Vr for the jet or thereabouts.

And there is no way in hell a Model S is going to do 0-1000 mph.


How should I request flight following when I'm not taking a direct route to my destination?

I would make the request as:

(controller) "N12345, Say your request"
(you) "N12345 request VFR Flight Following from Madison via the Joliet VOR to Cox Dayton; Altitude 5,500"

I don't think all the intermediate points matter, and I think the controller will quickly figure out what you intend.

They may ask for some clarifications, such as:

"Say your equipment"(they're asking if you have a Mode C transponder)
"Spell waypoints"(they want the phonetic alphabet of your waypoints because they are unsure)


Do employers prefer to hire younger pilots?

The answer to that has varied throughout airline hiring history.  There was a time when you'd better be young or else your chances of getting hired by the majors was essentially nil.  Now, "age discrimination" is a thing, and at least officially (in the US, at least) it is probably against policy to treat the 30 year-old ATP with 2000 hours differently than the 50 year-old ATP with 2000 hours.  (Or the 30 year-old commercial pilot with 500 hours different from the 50 year-old pilot with the same resume.)

These days, the regional airlines in the US seem to be so desperate for pilots that if you meet the minimums, it's more a matter of scheduling a class than it is scheduling an interview.  So if you're willing to fly for a regional, even the late 40-something pilot can probably get on with an airline.

Interestingly, this dynamic has its roots in the hiring practices of 30-40 years ago, when the airlines hired large numbers of "young" pilots -- meaning that the senior ranks of many majors have lots of pilot who are close in age and who are now reaching the Age 65 mandatory retirement all together.  This creates significant vacancies at the majors, who draw their new-hires from both the military (which is a fairly constant supply) and from the regionals (which has become where the "slack" has been that is now getting picked up).  The massive demand for hiring into the majors translates into regional captains moving up, and thus out of the regional airline far more rapidly than in the past.  This drives upgrade times at the regionals down, and has put pressure on their hiring departments to keep the right seats filled.

Quite literally, I was recently told that the "hiring" process at one regional has become nothing more than a confirmation that the candidate does meet the basic minimum qualifications (commercial license, 2nd class medical), and scheduling a class date.  If they pass the training, they're hired.

That is a snapshot in time in one country; throughout history that sort of a process is anomalous if not unprecedented.


Why do most commercial aircraft have their fuselage over the wing, instead of under?

Large commercial aircraft have low wings to stow away their long landing gears. Long gears make it possible to stretch the fuselage and still be able to rotate during take-off. Stretching makes it possible to tailor one basic design to a wide range of sizes, lowering the price of a single aircraft.

Large high-wing aircraft with their low fuselage position are easier to load and unload, at the price that the fuselage taper has to start shortly aft of the landing gear, so no stretching is possible. The military doesn't mind and prefers the high-wing variety. That Lockheed likes to stretch their transports (C-130, C-141) anyway is the exception that proves the rule.

Only turboprop-powered civilian aircraft may have a high wing, so there is more space for the propellers and the landing gear can be made short and light. Still, both versions exist. And the ones where the engineers did not know how to attach a jet close to the wing.

Aerodynamically a mid-wing position would be best. This is used when the payload is compact and needs little space, or is hung externally. In bombers, in other words.

In terms of stability and control both configurations are equivalent.


Do any aircraft automatically test that the pitot-static system is functioning properly before liftoff?

First of all, ground speed is already determined by the IRU’s. No need for landing gear sensors although most airplanes do have WHEEL SPEED transducers for anti-skid currently installed. Wheel speed is not always equal to groundspeed but can be at times. For example, wheel speed right after takeoff is different than ground speed because the wheel begins slowing the second it leaves the ground.

Second, airspeed changes with altitude. So, the higher you are the faster your airspeed. This means that taking off in Death Valley might show a different airspeed RELATIVE to groundspeed than in La Paz El Alto.

Third, most of the time, airspeed doesn’t register correctly until about 60 knots. You’ll see that most airspeed indicators have 60 knots as the lowest indication mark. This is because if the airplane is pointed into the wind, it could register spurious readings. So, before any checking gets done, the plane needs to be moving above 60 knots.... Like during takeoff.

Fourth, airspeeds are cross checked during takeoff roll. The vast majority of airspeed splits on a new flight leg occur on takeoff roll and result in a rejected takeoff - your premise anyway. Occasionally it’s not noticed until takeoff. This is rare. The other instances (which I work on more frequently) are in flight malfunctions usually related to inadequate pitot heating.

Fifth, the current system works very well. No need to reinvent the wheel.


How will the alpha lock function intervene when performing a takeoff at heavy weights on the A320?

Alpha Lock is a protection that will prevent surfaces retraction after take off if the angle of attack (ALPHA)is high for the next retracted position of the flaps/slats lever. So even if the pilot puts the selector in the retraction direction the order will be postponed till the angle of attack decreases. This is managed by the Fly By Wire logics. The logics takes into account more particularly the angle of attack and the configuration speed limits.


Are there aircraft exemptions for CPDLC in the NAT area?

There will be no exemptions for the CPDLC rule in the North Atlantic Track area.

The Datalink Mandate will be implemented:

starting 5 February 2015: FL350 to FL390 (inclusive) on all tracks within
the NAT Organized Track System (OTS)
starting 7 December 2017: FL350 to FL390 (inclusive) throughout the ICAO
NAT region.
starting 30 January 2020: FL290 and above throughout the ICAO NAT region.

ATS Surveillance Airspace, airspace north of 80°N and the New York FIR are excluded from the mandate.
This means that aircraft equipped with a suitable transponder / ADS-B transmitter will be able to cross using the Canada - Greenland - Iceland ADS-B corridor without having to carry FANS 1/A equipment.


How much responsibility does ATC have to alert a flight about being in a dangerous situation?

This is potentially a very broad topic, but here's some information about the US.

As a general principle, safety is ATC's first priority so obviously they have a basic responsibility to provide whatever information and action are required to keep aircraft safe:

FAA ATC orders 2-1-1:

  The primary purpose of the ATC system is to prevent a collision
  between aircraft operating in the system and to provide a safe,
  orderly and expeditious flow of traffic, and to provide support for
  National Security and Homeland Defense.

The orders explicitly say that ensuring separation and issuing alerts take priority over everything else. Section 2-1-2, DUTY PRIORITY:

  Give first priority to separating aircraft and issuing safety alerts
  as required in this order. Good judgment must be used in prioritizing
  all other provisions of this order based on the requirements of the
  situation at hand.

Section 2-1-6, SAFETY ALERT defines what an alert is and when to issue one (this section is referenced throughout the orders):

  Issue a safety alert to an aircraft if you are aware the aircraft is
  in a position/altitude that, in your judgment, places it in unsafe
  proximity to terrain, obstructions, or other aircraft. Once the pilot
  informs you action is being taken to resolve the situation, you may
  discontinue the issuance of further alerts. Do not assume that because
  someone else has responsibility for the aircraft that the unsafe
  situation has been observed and the safety alert issued; inform the
  appropriate controller

It's difficult to say much more than that because there are so many possible scenarios. But you can search for "safety alert" in the orders and the AIM to get more information and there's some limited content in the orders 5-15 about radar displays and alerts.

If ATC fails to issue a safety alert and that leads to an accident, then it will be mentioned in the NTSB report, e.g. LAX04FA205:

  Contributing to the accident was the failure of both the Center and
  TRACON controllers to properly respond to the aural and visual Minimum
  Safe Altitude Warning System (MSAW) alert.

But actually acting on a safety alert is entirely the pilot's responsibility, of course (this is from the AIM 4-1-16):

  Once the alert is issued, it is solely the pilot’s prerogative to
  determine what course of action, if any, to take


How do pilots align the HUD with their eyeballs?

The other way around - you set up the pilot for eye-to-HUD alignment. When you are in the right position then you can see all the data-fields on the HUD - if you can't see them, you move your seat.


Do people get less airsick if cabin pressure is at 6000 ft.?

Boeing supported a study that directly addresses your question:

  On the basis of our findings, we conclude that maintaining a cabin altitude of 6000 ft or lower on long-duration commercial flights will reduce the occurrence of discomfort among passengers.

Note, though, that the lower cabin altitude of the 787 is one of its selling points, and the study was conducted not too long before that type's introduction. However, its methods seem reasonable (at least to someone like me with no background in health sciences) and it was published in an important peer-reviewed medical journal.

The Aerospace Medical Association took a broad look at existing literature on the subject shortly after Boeing's study. That review

  did not find sufficient scientific data to recommend a change in the cabin altitude of transport category aircraft;

however, the authors did not dismiss the notion that a lower altitude may increase comfort, and they recommended further study. Just this month, some results of that further study were released. The results showed

  no adverse effects from an environment pressurized to the equivalent of 8000 ft compared to 6000 ft,

although they did not account rigorously for the subjective "discomfort" that I think you mean by "airsick."

My reading of the current research (based on the above) is that there is no evidence to suggest that a 6000-foot cabin altitude is medically better than a higher altitude (up to 8000 feet), but it might make some folks subjectively feel better.


What is the procedure to enter, maintain and recover from a flat spin?

If I remember from flying the Pitts S-2B, entry into an inverted flat spin was fairly easy, starting from an entry in the vertical, similar to performing a hammerhead stall, but using a excess of rudder with insufficient aileron pressure.  Another method is the fly a Lomcovak, which inevitably terminates in an inverted flat spin.

Again, it all depends on the edge of the envelop characteristics of the aircraft in question.  And some aircraft may not be recoverable at all once a flat spin is entered.  With aircraft certified to fly this kind of an aerobatic maneuver, recovery is fairly simple with motions being countered with rudder and elevator pressure.


What is the airplane type in this formation seen above Eugene, Oregon?

They are most likely Embraer EMB 312 Tucanos. Military Tech, Inc. has at least 10 registered in Eugene. Here is one in a similar paint scheme:

Source


How have fuel consumption and emissions per passenger/kilometre declined since the first jet airliners?

Don't know where you can find those details (ICAO or some UN organization maybe?) but you could ballpark it by looking at the specific fuel consumption of a 1950s airliner engine and a modern one.

The JT3/J57 turbojet used on the 707 in the late 50s had a specific fuel consumption of .909 lb/(h lbf) at cruise, and the GE90 used on the 777 is .545.  This means the fuel burn per unit of thrust is about 40% lower on the GE 90 than the JT3. Since a jet engine is just a fancy oil furnace, without elaborate systems to reduce specific kinds of emissions like car engines, the SFC itself should be a good  proxy for overall emissions.

Being conservative by assuming the thrust per pax is roughly the same for modern aircraft vs old ones (I'm sure it's lower), you could use that comparison as representative of the industry and say emissions are at least 40% lower per seat mile now than in the 50s.


What is the purpose of the pressure relief door fitted on the PW1127G-JM engines of the A320NEO?

Inside the nacelle cavity of a turbofan engine and in the casing of the engine core, there are different zones or closed compartments used for ventilation/cooling and in the case of the nacelle lip, also for anti-icing (see the first two images below). If a highly-pressurised duct (such as the anti-ice inlet duct shown in the 3rd image) bursts, the pressure builds up to a dangerous level, despite the ventilation exits. To prevent structural damage to these closed compartments, pressure relief doors are installed which are triggered automatically.

Edit: my first answer lacked some details, so I rewrote it.


Where does the difference between calculated and actual groundspeed come from?

I have a little paragliding experience. While only a tiny fraction of yours, I think I can answer your question, which boils down to: data accuracy.

The trim speed of a fixed-wing aircraft would depend on its weight. Without accurately measuring the pilot's weight (FYI the measurement in small aircrafts is precise to pounds / kilograms) and plotting that against a chart, the speed you were told in school is only an approximation.

I (like others in the comments also) question the accuracy of your speed data.

To accurately measure forward airspeed, you'd need a pitot tube pointing in the right direction.
Or you can use a wind measuring device which measures speed and direction
To measure your ground speed accurately you'd need a GPS.
To combine the two (wind speed + ground speed), you'd need some sort of computer to do the computation, either in real time or with recorded data.
The ground station only measure wind speed at ground level. When you're up in the air (albeit relatively low compared to aircraft), the wind can be different.