What is the difference between the words "airlines" and "airways" semantically?

This answer assumes that you are asking about the business name chosen by various air transport companies, such as "American Airlines" vs "British Airways".

Short answer:

There is no difference semantically. It's purely a marketing decision. The company decides which "sounds better", and uses that as their official business name. There are several other similar nouns used in business names as well:

"Air" (either before or after): Air France. Korean Air. Or even as part of the name: Ryanair.
"Aviation": Grant Aviation.
And then don't forget that Delta uses a space:  Delta Air Lines.
And then there are even some companies using several different nouns throughout their sub-divisions:  "Trans Executive Airlines of Hawaii" is the name of a single airline company, but their cargo services are performed under the name "Transair", and their passenger services are performed under the name "Interisland Airways"

Long answer:

There is some historical context, going back to the days when ocean travel was the only form of international travel between continents separated by oceans. A "line" was a route between two points. A "liner", then, was a ship that sailed that line. Since it was on the ocean, it was commonly called an Ocean Liner, and companies that popped up to provide a scheduled service on those lines used the term "line" or "liner" in their name: Black Ball Line, or American President Lines.

When Trains came into being, they took up the same vernacular from their ocean transport heritage. The system of rails between two points was usually built by a company for its own use, and was sometimes called a "railroad", or a "railway", with no discernible reason why some chose one term over the other. The term "line" was still used, interwoven into the industry: a "main line" was a company's main route between two cities, and a "spur line" would branch off to a smaller town.  Some companies named themselves with either the "roads" or the "ways" part: The Kansas Pacific Railway, or the Western Pacific Railroad.

The next major transformation in the transportation industry was air travel, which again borrowed terminology from both its ocean and rail heritage. An "air line" was a route between two points, and an aircraft providing service on that line was an "air liner", and company names went one of two directions: Air Lines (such as "Eastern Air Lines"), or Airways (such as "Western Canadian Airways")

The terms "air liner" (for an aircraft) and "air line" (for a company) eventually worked their way into the single-word terms as we know them, and they are officially defined, today.

But even in the early days, there were still many different nouns working their way into the company names: National Air Transport, Western Air Express, or Ford Air Transport Service. Following the Air Mail Scandal, (in which existing companies had to give up their air mail routes), many companies either merged or simply changed their names to re-gain air mail contracts. Several companies with names of XXX Air Lines (with the space) simply changed to XXX Airlines (without the space), and this is now why we see this term (Airlines) in company names today.  (with Delta Air Lines being a notable difference)


Why are civilians not allowed to fly demilitarized US fighter jets?

That's because US military is particularly concerned about chopping up its assets before civilians can lay their hands on them. The procedures are covered in US DoD Manual 4160.28 Defense Demilitarization: Procedural Guidance.
The procedures for 'demilitarizing' military aircraft are particularly brutal:

Military Aircraft
(a)  Aircraft (Figure 29 and Figure 30) that are specifically designed for military purposes shall be demilitarized as follows:  at a minimum, cut or break completely through at least one lobe of the fuselage trifurcated horizontal and vertical stabilizer spar attachment fittings, on both the right and the left hand sides of the stabilizer carry-through spar assemblies.  This demarcation of the prescribed DEMIL procedures is to ensure the aircraft is rendered unfit for flight.

(emphasis mine).

Demilitarization Procedure; image from Popular Mechanics

(b)  Helicopters (Figure 31) specifically designed for military purposes shall be demilitarized by crushing, shredding, or smelting the entire airframe and fuselage, ensuring that the transmission mounts and supporting structural beams, engine deck in area of mounts, wing attaching mounts and support beam structure, and fuselage to tail boom attaching mounts and tail rotor gear ox mounts have been destroyed.

So basically, it boils down to the fact that the US military makes sure that the airframes won't fly again. Of course, there are ways around this- you can assemble the aircraft from parts or some aircraft will simply escape the procedure and is avialble:

In a letter to the chair of the House Armed Services Committee, AOPA President Phil Boyer ... stressed that certain aircraft (possibly aircraft not demilitarized) had been carefully maintained over the years and were now serving useful purposes.

but these are quite rare.


From ARINC 429, Attachment 6:

  Label 025, Selected Altitude (BCD)
  Five binary coded decimals.  Range is up to 50000.  Resolution is 1
  foot.

  Bit 29 (MSC) ------------------------------ Bit 11 (LSC)
  4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1

  1 0 0 | 0 0 0 1 | 0 0 0 0 | 0 0 0 0 | 0 0 0 0
  The above line codes to 41000 ft.
  Note: Negative sign is annunciated in the sign/status matrix.

  Label 102, Selected Altitude (BNR)
  16 bits of data. Range of 65536. Resolution (value of LSB) is 1 foot.

  Bit 28 (MSB)------------------- Bit 13 (LSB) (Bits 12-11 are set to 0)
     1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 0

  The above line codes to 41000 ft.

  Note: Negative values are encoded as the two’s complements of positive
  values and the negative sign is annunciated in the sign/status matrix.


What emergencies or failures should I report to ATC?

You don't specify a country, so I'll answer for the US and hope that other countries are similar.

14 CFR 91.183(c) is the closest I can find to a "requirement" to report an emergency.  It only directly applies to IFR flights, but I can see no reason why VFR flights shouldn't do the same.

My rule of thumb is that if I wouldn't have taken off had I known about the problem then, it needs to be reported now.  Common examples might be low fuel, rough engine, weather approaching VFR limits or required instrument failure.

Note that while the FAA earned a bad rap for excessive enforcement actions in the 1980s, in the 1990s they adopted the stance that declaring an emergency is a sign of good decision making and risk management, and the stats since then show virtually no enforcement actions after emergencies, so when in doubt, I'd err on the side of declaring.  At worst, there may be a "counseling session" if they later decide that the situation didn't warrant it.


Can variable incidence wings replace ailerons?

So did the Wrights in their 'Flyer'. It had no ailerons, but the wings could be slightly deformed to roll the plane.

Possibly for constructive reasons, ailerons are almost always used today for roll control (spoilers are sometimes used in very light planes) but the Wrights' method was more elegant...


Is there a difference between MEA and MOCA within 22 nm of a VOR?

You are right. Within 22 nautical miles of the VOR, there is no practical difference between an MEA and a MOCA.

However, it should be noted that the 22 nmi is only a limitation if navigating via VOR's.

14 CFR - CHAPTER I § 91.177  Minimum altitudes for IFR operations

  (a) Operation of aircraft at minimum altitudes.
  Except when necessary for
  takeoff or landing, or unless otherwise
  authorized by the FAA, no person may
  operate an aircraft under IFR below—

  (1) The applicable minimum altitudes
  prescribed in parts 95 and 97 of this
  chapter. However, if both a MEA and a
  MOCA are prescribed for a particular
  route or route segment, a person may
  operate an aircraft below the MEA
  down to, but not below, the MOCA, provided
  the applicable navigation signals
  are available. For aircraft using VOR
  for navigation, this applies only when
  the aircraft is within 22 nautical miles
  of that VOR (based on the reasonable
  estimate by the pilot operating the aircraft
  of that distance)

The MOCA provides "obstacle clearance requirements for the entire route segment," so if the applicable navigation signal is GPS, and you're receiving it, then you've met the requirements. This is why sometimes you see a MOCA on segments which aren't within 22 nmi of any VOR.

One other practical difference to keep in mind is that, especially in mountainous areas, you're much more likely to get radar coverage, and have better communcations clarity, at the MEA than the MOCA (I saw this a lot in Idaho). In those cases, ATC is probably going to prefer the MEA.


Are pilots legally required to verbally declare an emergency to invoke §91.3(b)'s deviation authorization?

The short answer is no, there is no specific requirement for VFR flights to state an emergency, however you may be expected to explain yourself and your actions once you reach the ground.

  My assumption is no because a 2-way radio is not even required in all
  locations.

To expand on this you don't need a radio on board for VFR flight (FAA FAR 91.205) so they would have a legally contradicting issue if they required you to announce when you don't have a radio. As mentioned by Ron in the question you linked the rule is "Aviate, Navigate, Communicate" If you are too busy with the first two that is far more important.

Im not sure where they are pulling the quotes but this NASA presentation on emergencies sums it up well.

  “…an intent of 91.3 is to ensure the PIC will handle the emergency in
  a manner necessary to save lives and not be worried about regulatory
  compliance.”

  “I’ve never seen a pilot violated for deviating from a
  regulation when that pilot has either declared an emergency OR has
  stipulated in ANY written response to the FAA that an emergency
  existed at the time of the deviation.”

This article has some interesting points from a lawyers perspective on the situation,

  Madsen defended a case for a pilot who deviated from an assigned
  altitude due to extreme turbulence while flying a Cessna 150. The
  pilot had dropped his handheld mic, so he couldn't initially
  communicate his situation. He stabilized the airplane and was about
  600 feet off his altitude when ATC called him. At that point he was
  able to find the mic and he told the controller what had happened.
  "It's unrealistic in some situations to communicate your emergency
  before you secure the aircraft," Madsen said. "You want to control the
  aircraft first." Madsen said the case was ultimately dismissed, but he
  felt it would have been much easier to defend had the pilot declared
  his emergency.

Here we can see that ultimately the pilot was in the right and while he should have declared, there was no legal grounds that required it.

On some level you are at the mercy of the FAA with this one and its clearly a case by case basis (as is everything in aviation) and the lawyer in the above article goes on to say

  Some FAA field offices take the wording very seriously. Such was the
  case with the Cessna 150 pilot who deviated from his altitude. "They
  questioned why he didn't state an emergency and call out mayday, and
  they took great issue with the fact that he didn't use the accepted
  terms," Madsen said.

Again the case was ultimately dismissed whether or not they were happy about that.


Does mid-air refueling have very hard constraints on weather?

The receiver has to have visual contact with the tanker to complete the rejoin, so finding a clear block of airspace (i.e. not IMC) is necessary. Beyond that, none of the factors mentioned really matter much.  Turbulence can make refueling more difficult, although it's often possible to find an altitude with a decent ride.

Mostly, AR can be done; the times when it can't are much more the exception.


Why is the end of the F-35's jet nozzle 'spiky'?

Stealth. The F-35's nozzle is designed in that manner to reduce the IR and radar emissions from the aircraft (sometimes called Low Observable Axisymmetric Nozzle (LOAN)). From the press release which announced the test results:

GE Aircraft Engines' new LO Axi (Low Observable Axisymmetric) Exhaust System was successfully tested recently ... testing being conducted under the Joint Strike Fighter (JSF) Technology Maturation Program ...

According to GE,

... LO Axi Nozzle was installed by the South Dakota Air National Guard in an F-16C and ground-tested to verify installation compatibility with an operational aircraft system. Both infrared (IR) and radio frequency (RF) measurements were made by GE Aircraft Engines (GEAE) with the F110-GE-100 engine operating at power settings ranging from idle to maximum afterburner. The resulting test data verified that the LO Axi Nozzle achieves its installed signature goals during operation.
In addition to geometrical shaping and special materials for signature control, the LO Axi Nozzle also incorporates an ejector that enhances nozzle cooling.

The system was originally tested on a F-16. The following image shows the nozzle while it was under testing

Detailled rear view of a standard P&W F-100-200 still installed in the LOAN aircraft and the LOAN nozzle in the foreground (LMTAS photo); image from f-16.net


Why are all-moving horizontal stabilizers common but all-moving rudders rare on fighters?

Basically, in fighter aircraft you need a lot more of elevator than rudder.

For most aircraft, the required size of the elevator is determined by one of the two corner cases:

Sufficient control and balance at low speed, particularly on landing;
Sufficient control for high-G manoeuvres.

For fighters and aerobatic aircraft, the latter is usually the main factor; for others, the former.

In contrast, rudder is usually sized for crosswind landing and, if applicable, for the asymmetric thrust (one engine out) case. It's easy to see that due to closely packed engines on most fighters and higher speeds, both these factors are relatively smaller compared to other aircraft (e.g. airliners).(1) Whereas the elevator demand gets worse. This is why.

There are two main problems that arise at supersonic speeds.

The centre of pressure of the wing (and the neutral point) moves back significantly. This obviously creates a strong nose-down moment (and makes the aircraft statically very stable in pitch for the same CG), requiring a lot of control to re-trim the aircraft and execute any manoeuvre. This is the reason for 'Mach tuck' (in fact, this is the Mach tuck), and not the rubbish from the quoted Wikipedia passage.
Efficiency of the elevator fades. At lower subsonic speeds, the elevator effects the air not only above/below it, but also ahead of it. The approximate efficiency of the conventional elevator at such speeds can be expressed as

$$k_{\mathrm{elev}} = \sqrt{\frac{ S_{\mathrm{elev}}}{S_{\mathrm{stab}}}}$$

Therefore if the elevator $S_{\mathrm{elev}}$ occupies half of the stabiliser area $S_{\mathrm{stab}}$, its effect will be not $0.5$ but rather $\sqrt{0.5} \approx 0.7$ (compared to the all-moving surface). But at supersonic speeds such propagation upstream cannot happen, and the efficiency falls to the area ratio, i.e. $0.5$ in this example. This favous all-moving surfaces.

The second point affects the rudder just the same, of course. But the static directional stability (point 1) doesn't increase like it happens with pitch (in fact, it can fall), and the overall demand is lower, so conventional rudder is still acceptable. Nevertheless, there are a few aircraft with all-moving vertical tail, for example, Tu-160.

In other circumstances, conventional control surfaces are better (i.e. lighter), so they are used whenever possible.

(1) This should not be confused with the whole vertical tail sizing. This one is often determined by the stability dynamics, and directional stability of supersonic aircraft can be rather bad, demanding big tail - but not necessarily big rudder.


What is a fuel tank float valve and how does it work?

I don't know about the fuel float valve of the F35A. A float valve is basically the principle used in toilet flush: A device that:

senses liquid level in a tank, and
open/close a valve according to this level.

The device may rely on a float acting on a horizontal lever, or it may be a float sliding vertically along a rod.

There are several float valves on this schematics of the Boeing 737 fuel system:

Source

If this doesn't work, the tank may be reported as always full, as for the F35A of your report.


What is the definition of "geometric height" referred in the ISA Model?

In the ICAO Standard Atmosphere model, as described in ICAO Doc. 7488, the geometric height is equivalent to the orthometric height.
The ISA model uses a hydrostatic equation to calculate the pressure differential over a geopotential height difference.
The reference height (0 meters) of the model is the mean sea level. It furthermore assumes a standard acceleration due to gravity, conforming to a latitude of 45.32'33". This $g_0 = 9.80665$ m/s2 is used to convert between geopotential height $H$ to geometric height $h$.
For this purpose the ISA model assumes a non-rotating earth with uniform mass distribution, so that only Newton's gravitation law can be used to obtain the relation between $H$ and $h$:
$H=\frac{rh}{r+h}$.
with $r = 6356766m$ the radius of the nominal (spherical) earth.
Now to orthometric height.
The orthometric height of a point is the distance H along a plumb line from the point to a reference height (typically the mean sea level).

Image source: ScienceDirect: Evaluation of the various orthometric height systems and the Nigerian scenario – A case study of Lagos State
The plumb line however, is not a straight line. Due to rotation of the earth and gravitational anomalies due to an irregular mass distribution in the earth, the plumb line curves.
Within the ISA model, orthometric height and geometric height are the same, because the model assumes the earth is uniform, spherical and non-rotating. Therefore the plumb line in the ISA model is straight.
In the real world however, the orthometric height (measured along the curve of the plumb line) is thus not equal to the geometric height (which measures along a straight line).
The difference are extremely small; for practical purposes this can be ignored in most fields and orthometric height is usually said to be the same as geometric height.


What is the difference between Angle of Incidence (AoI) and Angle of Attack (AoA)?

Angle of Incidence is fixed by the designer of the aircraft. It does not change in flight.

Angle of Attack is the angle between the chordline of the wing and relative airflow during flight.

That is definitely something that changes during operation of the aircraft in flight. Consider slow flight, for example. You reduce power and raise the nose to reduce airspeed. The direction of the airflow remains the same, but the angle between the airflow and the wing chordline, the Angle of Attack, increases. Raise the nose too much (and hence increase the AoA), and the airflow will separate from the top of the wing and you will stall.

On aircraft like Cessna trainers, the stall warning is a very basic indicator of Angle of Attack, to warn you when you are about to stall.

More advanced Angle of Attack indicator systems use a vane to measure the angle of the relative airflow, and give you more information about AoA.


Why do landing gear tires smoke upon touchdown?

Because the tires are momentarily skidding on the pavement as they rapidly spin up from standstill to the jet’s touchdown speed.  It’s just a puff of burnt rubber but the tire tread itself becomes quite warm, reaching 600-700°F for an instant.  It’s also the reason a pilot does not ride the brakes upon touchdown as this could cause a blowout as the tire is ground up rapidly.


What is the speed above which painting an aircraft black (or dark) results in lower skin temperature?

This might be more of a question of altitude and the ability to remove heat as a function of air density. The SR-71 has a cruising altitude of ~26km and the Concorde has a crusing altitude of ~18km. Of course a black coating makes it absorb more solar irradiance, but the designers would have taken this into account and ensured that energy balance favors a desirable temperature. The SR-71 had at most two passengers, so comfort cooling can be focused on the cockpit compared to a passenger plane. The Concorde on the other hand had a much larger passenger cabin which would lead to much higher parasitic cooling losses with a black skin.

This chart shows the decrease in density, but whether it's enough to justify a different approach to passive thermal control is hard to say:

The implication is that at high altitudes, heat generated inside the vehicle needs to be removed by a combination of convection and radiation. This is especially important for the Space Shuttle as it needs to maintain temperatures in the lack of atmosphere although the black tiles did not serve as the orbiter's primary radiators. They only needed to insulate the orbiter from aerodynamic forces and the high temperatures. While reentering the atmosphere, the heat comes from air compression in the atmosphere and the black tiles would have helped to re-radiate some of the heat away from the orbiter.


Why do the ratio of proppeler plane over jet engine seems to have change in Bucarest airport during the covid19 crisis?

I have no idea about Bucharest specifically, but at least in the US, many GA pilots are taking advantage of the significant reduction in airline traffic to fly into big airports they're normally not welcome at. And, for the most part, ATC is welcoming these GA flights because they're bored too.


How to calculate aerodrome elevation given QNH and QFE

QNH is the pressure setting that will show the aerodrome's true altitude at field level, QFE is the pressure setting where the altimeter will show zero feet at field level. The rule of thumb is that pressure changes 1 hpa per 30 feet, so the formula you would use is (QNH - QFE) * 30feet/hpa = field height. In this case that is (1031hpa - 985hpa) * 30feet/hpa = 46hpa * 30feet/hpa = 1380ft.

If the QFE is greater than QNH you would get a negative number, which would mean the airfield is below sea level. This is pretty rare, but they do exist, so don't mess with the QNH - QFE order.


What is this "stick" on top of Cessna 152's wing, and how does it work?

Short answer: They're antenna(s) for the onboard VHF radio(s).

Airplanes aren't actually required to have radios. But, if you want to fly into certain classes of airspace, you must have at least one VHF radio on board, to communicate with air traffic control. A lot of planes (in fact, I would say the majority of them) actually have two radios installed. Thus, you see planes with zero, one, or two antennas.

Having two radios has several advantages, beyond just the obvious "backup in case one fails" advantage. Most often, one will be used to listen to the ATIS/AWOS/ASOS or other automated information broadcast while the other is used to keep in touch with ATC. You could also use the second one to contact Flight Services, or (if you're charter/commercial) keep in touch with your company (although that last one is getting more and more likely to be done with a cell phone or the internet).


How much thrust and fuel are required to get a B767 moving from a complete stop?

This research paper may be of interest for you. According to their data the 777 burns about 250Kg of fuel on taxi on average with a few data points showing burns well over 700Kg of fuel. This paper which quotes the previously linked paper talks a bit about different fuel saving methods and their impacts, like single engine taxi and what not. In short taxi distance will always burn a bit more fuel, the primary concern is taxing for takeoff (since you don't want to cut into your estimates). Once the plane is back on the ground it becomes less of a safety concern as running out of fuel becomes an inconvenience (that a tug can solve) and less of flight risk.

Here is an interesting paper on fuel burn rates if you were to extend a runway by 500Ft. They provide data/estimates for many air frames.


Does a private pilot certificate require a certain number of ground school hours?

For training conducted under 14 CFR 61 there is no requirement for groundschool.  The only requirements are that you take and pass written tests, but how you prepare for them (formal groundschool, self-study, etc) is completely up to you.  You will need a recommendation from a flight instructor to take a written test, so your preparation method and readiness for the test will be evaluated before you are allowed to take it.

The only exception to the above statement is knowledge tests for airline transport pilot certificates with airplane multi-engine class ratings taken after 31 July 2014.  These written tests do require specific groundschool training minimums, which are specified in 14 CFR 61.156

If you are instead training under 14 CFR 141, your school has a specific curriculum and examination authority approved by the FAA.  The specifics of your program will dictate what groundschool is required to take the relevant written exams.  The groundschool aeronautical knowledge baseline requirements are specified in 14 CFR 141 Subpart F.  For a private pilot certificate with an airplane category rating, these requirements are:

  35 hours groundschool training in

  Applicable Federal Aviation Regulations for private pilot privileges, limitations, and flight operations;
  Accident reporting requirements of the National Transportation Safety Board;
  Applicable subjects of the “Aeronautical Information Manual” and the appropriate FAA advisory circulars;
  Aeronautical charts for VFR navigation using pilotage, dead reckoning, and navigation systems;
  Radio communication procedures;
  Recognition of critical weather situations from the ground and in flight, windshear avoidance, and the procurement and use of aeronautical weather reports and forecasts;
  Safe and efficient operation of aircraft, including collision avoidance, and recognition and avoidance of wake turbulence;
  Effects of density altitude on takeoff and climb performance;
  Weight and balance computations;
  Principles of aerodynamics, powerplants, and aircraft systems;
  If the course of training is for an airplane category or glider category rating, stall awareness, spin entry, spins, and spin recovery techniques;
  Aeronautical decision making and judgment; and
  Preflight action that includes—

  How to obtain information on runway lengths at airports of intended use, data on takeoff and landing distances, weather reports and forecasts, and fuel requirements; and
  How to plan for alternatives if the planned flight cannot be completed or delays are encountered.


How do airliners prevent raising the gear on the ground?

Most airliners have a protection system for this which is based on Weight-on-Wheels (WoW): sensors which detect load on the wheels (which implies that the aircraft is in contact with ground). For safety reasons this can be bypassed and there's usually a small lever in connection to the gear lever to do this. This image illustrates the 737 gear lever where you can clearly see a "lock override" which fills this functionality (red part)


Who makes the call to start in terrible weather conditions?

Who else might make that call? The airline?

Yes, if the airline thinks the weather is too bad at a particular airport for safe operations, it can just cancel all flights from that airport without asking the pilots.

  The airport?

If the airport closes completely, then it is closed. No flights can depart any more, even if the pilots consider it safe.

  Is it really only up to the pilot to make this decision?

If neither the airline cancelled the flight nor the airport has closed, it is indeed up to the pilots, or more specifically to the PIC (Pilot In Command, the Captain on an airline flight). They are ultimately responsible for the safe operation of the aircraft and have to make the decision:

  4.5.1 The pilot-in-command shall be responsible for the safety of all crew members, passengers and cargo on board when
  the doors are closed. The pilot-in-command shall also be responsible for the operation and safety of the aeroplane from the
  moment the aeroplane is ready to move for the purpose of taking off until the moment it finally comes to rest at the end of the
  flight and the engine(s) used as primary propulsion units are shut down.

(ICAO Annex 6 Part 1 - 4.5 Duties of pilot-in-command)

The SIC (Second In Command) also gets a say in this because of crew resource management, meaning if they think it is unsafe to depart, they can and should speak up.

  Are there official rules about departing in such conditions?

The respective national aviation authority may have rules on when a departure is permitted, but this will depend on the exact location. The pilots will however have received rules and training from their airline, which should indicate when a departure is allowed. The most important aspect to consider are the aircraft limitations. There is no legal crosswind limit for a takeoff, but e.g. the Boeing 737 FCOM lists a demonstrated value:

  The maximum demonstrated takeoff and landing crosswind is 33 knots.

(Boeing 737 NG FCOMv1 1.10.2 Limitations - Operating Limitations)

It would be considered unsafe to depart with a stronger crosswind.

Note that limitations for landing are typically stricter than for departure and the pilots are legally required to check the expected weather at the destination airport before departing.

In Europe, Eurocontrol can also delay a departure due to expected weather en-route or at the destination airport. See What is the difference between en-route delays and airport delays?.


What is the maximum crosswind component for large airliners?

From this site:

  During the type certification process, the FAA requires the manufacturer to demonstrate that its airplane can be controlled in 90° crosswinds up to 20% of VS0.


Is there a specific procedure for grounding a pilot?

It depends on how/why you are grounded and who does the grounding.

The FAA can legally ground you if your license gets suspended (or in rare cases completely revoked) there are formal proceedings the FAA has in place. You can find the AC that covers it here.

AME's can can deny you a medical certificate which can prevent you from flying. In this case you are also legally grounded as you may no longer comply with FAA regulations.

AME's may also make grounding recommendations. Say you start taking a new medication that is legal on the FAA's list. The general advisory is to "see how the medication effects you" prior to getting back to flying. Often this is subjective and there is not really any hard guidance on time limits for every medication. These groundings should be self imposed by the pilot.

You can be practically grounded by say a flight school or insurance company. This falls more into the "not fit to fly" category. Technically you are legal to fly but other practical limitations may prevent you from flying. Lets say you show up to rent a plane and you are clearly sick. You say you "feel fine" but the flight school is under no obligation to rent to you and may chose not to if they feel you are not fit to fly.

Every pilot is responsible for a self assessment prior to making any flight to ensure they are fit to fly. Ultimately an infraction could fall under 91.13 Careless or Reckless Operation. In this case you may or may not be legal to fly but its up to you to make that self assessment and not fly.


Are we on the "wrong boat" with eliptical spanload all these years?

The elliptical and bell curves give optimal solutions to different problems. Obtaining the most efficient wing for a given span leads to the elliptical distribution, whereas the most efficient wing for a given load is given by the bell distribution. For a given central load, the bell or Prandtl wing will have longer span but a lighter structure and reduced tip losses.

For a swept wing the Prandtl type is inherently stable, so there is no immediate need for a tail stabilizer. However practical considerations include CG range, and this is the tailless type's big weakness: unless it is sharply swept, as in a typical supersonic delta, it will need a separate elevator, fore or aft, to apply the large trim changes necessary. For a straight wing an airfoil with reflex camber to give a static center of pressure will also  make it stable. But such airfoils are relatively inefficient and wing area must be increased. All this reduces the practical advantage of the Prandtl wing well below its theoretical value.

Roll inertia will also be affected by the increased span, which can impact highly manoeuvrable or very large aircraft.

One way of looking at the Prandtl wing is to see the tip section as a vortex-reducing winglet, which just happens to be blended in. I recall the Airbus A380 chief designer saying that it makes little difference in practice whether the winglet section is horizontal or vertical.

Having said all that, I am a fan of the Prandtl wing (which is really the Dunne-Prandtl wing, as J W Dunne discovered it empirically and flew it as the D.7 twenty years before Prandtl did the maths). Now that NASA have rediscovered it, I would expect it and its design principles to find some modest wider application in the future, with or without a tail. For example in long-endurance electric drones with fixed CG and minimal maneuvring needs.


What are ways to reduce drag and noise generated by the landing gear?

The biggest noise reduction is achieved by closing most of the landing gear doors again after extension is complete.

Of the factors that influence drag and noise, one is the distance between wheel and fuselage. The picture below is taken from S. Hoerner's book "Fluid Dynamic Drag", chapter XIII.5 of which deals with the drag of landing gears.

Another influence is the shape of the landing gear strut. Since most airliner landing gear legs are oleo struts, they are round for practical reasons. Fairing them would already help, as can be seen from the lower line in the plot above. Another improvement can be achieved by covering the wheel hubs. However, the reduction of the drag and noise caused by extended, retractable landing gears has been studied but few of the results have yet found their way into actual aircraft. According to this DLR report, a fully faired A320 landing gear would reduce noise by 10 dB while partially fairing the most noisy parts of an A340 landing gear would reduce noise by 5 dB. The picture below is taken from this report.

For fixed landing gears, I recommend NACA Technical Report 485 which contains results of full-scale tests on several gears. NACA Technical Report 518 contains results for partially retractable gears.


Why would FlightAware show this meandering flight path?

It looks as if the GPS location was only updated at intervals, and the software extrapolated the missing path information using bezier curves.


Airplane generations - how does it work?

While airliners don't have "model years" like cars do, they are certainly changed over time.

There are major "generations" of some aircraft types, like the 737. The "original" (-100,-200) was replaced by the "Classic" (-300,-400,-500) which was replaced by the "Next Generation" (-600,-700,-800,-900) and most recently replaced by the "MAX" (-7,-8,-9,-10). While technically still the same aircraft type, there can be major differences between them, especially from the pilot's perspective.

The 767 hasn't had any major "generations," but it has had multiple models, as is common with airliners. These are mostly just adjustments to fuselage length, fuel tanks, and structures. Other than small changes to systems, or different guidance to prevent a longer fuselage from stiking the ground on takeoff or landing, there is minimal training required. The 767 cockpit was even designed to be common with the 757 to minimize required training.

The FAA requires pilots to get a specific "type rating" to fly any aircraft over 12,500 lb max takeoff weight. The scope of this rating is negotiated between the manufacturer and regulator like the FAA. This could change with new versions, as with the 747-400, or even be common, as with the 757 and 767. There may also be training for each minor model, though not as in-depth as a new type certificate.

There are also changes made within the minor models over time. The biggest changes would probably be things such as modifying the winglets or adjusting the engine installation to get better performance, or a new cabin interior design. There are also many smaller changes that occur throughout the airplane. There isn't really a regular schedule for these like in the car industry, as there's less turnover in the aircraft market and major changes can be very expensive to certify. There would have to be a significant benefit to make a change requiring new pilot training, which is why those changes tend to happen in the more major "generations."


Is this scheme for a single-fan electric airship with a rocket-like geometry workable?

The best propeller driven vertical take-off and landing craft would be a helicopter, actually. Yes a duct around a propeller increases thrust, but upsizing a propeller creates way more thrust from the available power.

Propeller thrust has scaling effects with size due to different Reynold numbers, data does not scale up well. Best way forward from where you are now would be to look at the weight, rotor dimensions and installed power of existing designs for small helicopters such as the R-22. Or better yet, design an electrical version of the Hiller Flying Platform Platform.


What is this intake bottom the wing of C-5 and why is it placed there?

This C-5 cutaway indicates it's a "Heat Exchanger Inlet (76)" or "Ground Cooling Fan (78)"
EDIT: Upon closer inspection of this higher-res image, it may be the intake for the Ground Cooling Fan.


Sailing vessels work by exploiting the motion difference between the air and the water.  The sail holds the air and the keel holds the water.

Unless you have some severe wind shear (which comes with its own problems), or you have truly massive sails, there's no gradient for you to exploit because it's all air.


How are you supposed to get the East/West variation on this question in the FAA PPL written exam?

Real answer: The FAA screwed up in preparation of that exam question (this sometimes happens; they aren't perfect) and cropped the sectional to where the isogonal lines and or isogonal values are not visible.  As it happens I know that area of the country pretty well.

It works out that Claxton has about a 6.5 deg W magnetic variation (get the full VFR sectionals for that area) and Varnville is just shy of 7deg  W variation; I'd use 6.75 deg W as your number for mag variation over the duration of the flight.  That works out to a course of 051 deg magnetic, 56.5 NM along the route.  With winds at 290 at 18 kts cruising at a true airspeed of 85 kts, this gives an aircraft heading of 041 magnetic in cruise with a ground speed of 93 kts.

Now here's the thing: what is your groundspeed during climb out?  That's going to also be necessary to calculate how much ground you cover during your 2 min climb to cruise. And critical to answering the question correctly.

Now, IF WE ASSUME a constant groundspeed of 93 kts, from point to point, that gives a flight time of 36.5 minutes.  If we further assume the two minutes of climb are not enroute and just maneuvering from takeoff to on course right over the Claxton airport and we descent into Varnville at 93 kts as well, we get a figure of 38.5 minutes total flight time.  Therefore, I'd select 'B' as my answer.

As a side note, I landed an LSA out at Varnville only once and that place is virtually abandoned; it was difficult to identify as an airport from the air, the runway is anemic and derelict, there are virtually no buildings there and all I could find for traffic there was a decrepit C-150 rusting in the sun.  I took off again - and very glad my engine didn't quit, leaving me stranded there.


Why would a pilot's armrest be a no-go item?

Perhaps it was just an oversight on the part of the creators of the minimum equipment list.

As I understand it, minimum equipment lists generally provide a list of those items which are permitted be inoperable. So if any piece of equipment is inoperable, and it's not on the list, that automatically means you're not allowed to fly.

(Going by the name, you'd probably expect a minimum equipment list to be, you know, a list of the minimum required equipment. But for one reason or another, it's not.)

So, in all likelihood, nobody thought to add armrests to the minimum equipment list. As a result, flying with an inoperable armrest was automatically prohibited.

However, things have since been adjusted: the FAA has added the armrest to the master minimum equipment list for the Boeing 757. So, it is now legal to fly your 757 with a stuck armrest, as long as it is stuck in the "up" position.


Why is the fuel pump in the startup procedure for a Cessna 172?

Many 172s are fuel injected.

I've flown both carbureted and injected 172s.

On a carbureted model, you prime by pumping the primer between 2 and 5 times.

On a fuel injected model, you prime by running the fuel pump for about 3 to 5 seconds with the mixture open.

As for why you do that, the short answer is because the POH says so.
The more precise answer is that gravity feed alone is not enough to push fuel through the fuel injectors (which are very tiny little holes in the cylinders)


Can pilots choose runway and landing direction?

Pilots can request a particular runway approach course and landing but in a controlled environment they are at the mercy of ATC. At high traffic (read busy) commercial airports they are unlikely to get their request. As far as I know, shy of an emergency declaration you cannot insist on a non standard runway and expect to get it.

At a quiet class C or D airport they may very well get what they ask for. I did this a lot during my training at a quiet class D airport. If the winds were favorable to one runway but my instructor wanted to practice cross wind approaches we would request the non standard runway and if no one was around they would often grant it.

Generally you don't want to fly the non preferred runway if there are windy conditions as landing with a tail wind can be dangerous.


Are there any manoeuvres that would be considered unrecoverable in a General Aviation / Training Aircraft?

Yes, easily. Just fly fast enough.

If you deflect a control surface fully at a speed above $v_A$, the risk of a structural failure is very real. After all, at $v_D$ only a third of the mechanically possible deflection is allowed (see §23.441 for the rudder and §23.455 for the ailerons). Even combining full deflections of more than one control surface at $v_A$ is not covered, as is a repeated deflection in sync with rigid body oscillations which can create excessive loads. For a definition of the design speeds, see §23.335.

The regulations require minimum control forces so the pilot feels when he/she overstresses the airframe, but they are still within the strength of a normal adult.

Also, if you fly too fast in gusty weather, you can overload the structure. This is rare because the 25ft/s gusts which must be tolerated up to $v_D$ are quite uncomfortable to fly through.


Is turboshaft fuel efficiency affected by N2 loading?

The free turbine shaft can be called $N_2$, but $N_f$ is more common.
Your fuel control for a turboshaft is not so simple. It requires a Fuel Control Unit and an engine control that needs to know how much torque is being produced at the $N_f$.

A fuel control unit [acts] as an intermediary between the operator's controls and the fuel valve. The operator has a power lever which only controls the engine's potential, not the actual fuel flow. The fuel control unit acts as a computer to determine the amount of fuel flow needed to deliver the power requested by the operator.

and

[A] turboprop or turboshaft engine control system has an additional job to do that is not shared by its turbojet and turbofan counterparts. It must control the speed of the propeller or the free turbine, and it usually governs the pitch angle of the propeller blades. (Source)

If you are not bypassing the FCU and other engine control systems, you do need a varying load to have control over the fuel flow (indirectly).
Running an unloaded turboshaft at high power is very dangerous, as the free turbine will be rotating at RPM's way above its design limits. Unloaded free turbines may also cause an auto shutdown.

By Emoscopes (Own work: drawn using XaraXtreme) [GFDL, CC-BY-SA-3.0 or CC BY 2.5], via Wikimedia Commons

Free turbine engines are now commonly fitted with a device to shut off the fuel supply at the HP cock if torque in the turbine output shaft suddenly falls to zero.
A drawback to the simple free turbine turboprop is its behaviour if the load suddenly falls to zero. In such a case, the unconstrained free turbine overspeeds and will be destroyed by centrifugal forces.

In other words, you do need a load of varying degrees, you cannot test an unloaded fully assembled free turbine engine.
As for efficiency, efficiency is a measure of fuel flow per unit thrust/torque, so a load is needed to get that measurement.


Which one is more effective produce power of this two turbine's location?

The power will be the same. But the aircraft with wing mounted engines will have less drag. Contributing factors are:

Engines are heavy. Putting them aft means there is a big difference in centre of gravity between empty and loaded aircraft, so larger horizontal stabilizer is needed to keep it in trim over the range of centres of gravity. It is also needed for rotation on take-off with forward CoG, since the main gear must be behind the aft-most CoG position. That means more trim drag.
Putting something heavy, like engines, on the wing ahead of it reduces flutter, so the wing can be less stiff, and thus lighter. This means more payload, or less induced drag at the same payload.
Engines ahead of the wing fit nicely with the Whitcomb area rule. At the tail they add a lot of cross-section where it should be tapering off already, slightly worsening the transsonic performance.

So engines tend to be wing-mounted on all but small low-wing aircraft where they would have too little ground clearance.


Why is tailwind during final approach and landing so dangerous?

It's not so much a matter of "pilots typically get very uncomfortable" as it is "pilots recognize that it is an inherently less safe situation", and pilots (at least the ones you want to fly with) tend to be somewhat safety obsessed.

So Why are tailwinds during landing "bad"?
The same reason tailwinds in cruise flight are good: you're moving over the ground at a higher speed.
The amount of energy the aircraft has (and thus its landing distance) is roughly proportional to the square of the groundspeed.

Let's consider the plane I fly as an example (a Piper Cherokee) because I know the numbers:
if I'm flying by the book then when the wheels of my plane hit the ground my indicated airspeed should be around 45 knots.

No Wind
If there's no wind my ground speed and my indicated airspeed will be about the same - my brakes will have to slow me from 45 knots to a stop before I run out of runway.
The brakes on the Cherokee aren't Porsche brakes (they're tiny little things), but they're up to the task and a book-perfect landing would have me stopped in 600 feet.
15-Knot Headwind
A 15 knot headwind reduces my groundspeed to 30 knots - at 2/3 the speed I can stop much sooner with the same braking force, which means less wear on the brakes and a greater safety margin of runway remaining.
A book-perfect landing in these conditions would have me stopped in about 270 feet.
15-knot Tailwind
A 15 knot tailwind increases my groundspeed to 60 knots. The tiny little brakes on the Cherokee CAN stop me, but they're going to take much longer to do so: A book-perfect landing would take over 1000 feet to stop (nearly twice the "normal" no-wind landing roll).

The big consideration above is landing distance -- as you noted in your question you can solve that with a longer runway (more pavement means more room to stop), but there are other dangers with tailwind landings, mainly in the fact that Landings don't always go according to plan.
The slower your groundspeed at landing the less energy you have to get rid of if something goes wrong

Consider the three landings I outlined above, but let's add a problem to the mix: One of my tires blows right at touchdown, and the plane veers off the runway into a ditch.
There is much less energy to dissipate with a 15-knot headwind (30kt groundspeed) than there is with a 15-knot tailwind (60kt groundspeed) - it's roughly the difference between crashing your car driving through a school zone versus speeding on a highway.

Fortunately it's really easy to avoid landing with a tailwind -- most runways are bidirectional (Aspen, which you mentioned in your question, is a notable exception due to geography).

ATC (or at uncontrolled fields, the pilots themselves) will "turn the airport around" once a certain tailwind limit is reached.  Precisely when that happens depends on the airport and the traffic mix (at my home field, with mostly small piston aircraft, ATC will typically switch the runway when the tailwind component exceeds 5 knots - at JFK they might land a jet with a 10-knot tailwind rather than messing up the arrivals).
Of course there's nothing that says a pilot has to accept a landing with a tailwind: If the pilot is not comfortable with the conditions they can request a runway aligned so the winds are more favorable. (There is a somewhat famous case of an airline pilot at JFK who ultimately decided to declare an emergency to ensure a landing on a favorable runway).


Why can't this blended wing body trijet airliner fly?

As the comments point out, the main landing gear is too forward. Delta wings (and blended) typically land (and takeoff) with a high nose-up, should be an easy fix.
Left wing is longer, again easy fix.
Outboard control surfaces (normally would be elevons) are both pointing down on approach (or is it climbing?), tail heavy?
For a blended wing body, the airline still chose a tail-fin logo (backwards mind you)!
Natural pitch stability is required for certification, but the way it looks this design is unstable in pitch. Note that all trailing flaps are deflected down, something which will generate strong pitch instability. There is no obvious means by which a counteracting pitch response could be generated.
It looks as if payload is held mostly in the forward part. While it could be balanced when empty, with any sensible amount of payload it will be hopelessly nose-heavy.

Related: Why is there really only one basic design for passenger airplanes?


What is the time derivative of the angle of attack?

Assuming that there isn't an error in the books you've read:

Both formulas are true. It's true that

$$\frac{d\alpha}{dt} = \frac{w'u - wu'}{u^2 + w^2},$$

and it's also true that

$$\frac{d\alpha}{dt}= q + \frac{Z}{mu}.$$

From this, we can conclude that

$$\frac{w'u - wu'}{u^2 + w^2} = q + \frac{Z}{mu}.$$

Both of these two formulas describe the way that the angle of attack changes, but they describe it in different ways.

I'm not sure exactly how the $q + Z/mu$ formula was derived, but it seems to be related to the fact that angle of attack is related to pitch and the flight path. Specifically, for flight with zero bank angle, the angle of attack is the pitch angle minus the climb angle. It looks like the $q$ term comes from the rate of change of pitch, and the $Z/mu$ term comes from the rate of change of climb angle.


Would there be a restriction on my Sport Pilot license if I do my checkride in an aircraft without rudder pedals like the Ercoupe?

The restriction you're talking about does exist, but there's no explicit wording for it. It's described in FAR 61.45(b)(2):

  An applicant for a certificate or rating may use an aircraft with operating characteristics that preclude the applicant from performing all of the tasks required for the practical test. However, the applicant's certificate or rating, as appropriate, will be issued with an appropriate limitation.

One of the most fundamental tasks in the Sport Pilot PTS is maintaining coordinated flight (you won't find it as a discrete task, but if you look at the PTS the phrase "while maintaining coordinated flight" occurs multiple times), and an Ercoupe without rudder pedals relieves the applicant of that responsibility because the aileron/rudder interconnect basically does it for you.

I'm not sure exactly how this works for Sport Pilots, but as you cannot demonstrate to the examiner that you can "maintain coordinated flight" they could reasonably apply the same restriction to your Sport Pilot certificate as they would to a Private Pilot certificate ("Limited to aircraft without rudder pedals").  You would need to demonstrate to a DPE or Examiner that you can operate an aircraft with rudder pedals at some later date to remove the restriction (it is a restriction on the certificate so the only way to remove it is to have the certificate amended/reissued/replaced).

The easiest way to avoid the entire issue is to prepare for and take your practical test in an aircraft with rudder pedals. You can do everything in the Ercoupe and then switch to the Cub for a week to brush up on systems and polish your maneuvers in that plane and get used to using your feet.


How did the 9/11 hijackers find their way to New York City?

Several of the hijackers, including Mohamed Atta, held at least private pilot certificates and had undergone ATP level jet training in DC9 and 737 full motion simulators in December of 2000. Atta himself held a commercial license with instrument and multi engine ratings. They were well versed in aerial navigation techniques and more than capable of navigating the aircraft in question back to New York City and Washington DC after it was hijacked and secured.

A basic scenario that any private or commercial pilot could have done:  the hijackers knew the flights they were booked on and the rough routes they would take to their destinations. A little basic planning amongst themselves would have produced the approximate position the aircraft would be at at the time it was hijacked.

Once seized and the flight crew liquidated, they could quickly determine their positions either from their headings and next waypoints or with a simple VOR fix (any competent private pilot can do this). The autopilots could quickly be disengaged and the airplanes hand flown using basic pilotage (good weather prevailed over the east coast that morning) or radio navaids to return to their targets. The navigation and flying they did that day was relatively simple.

As an update, I know these kinds of questions float around with “9/11 truthers” and other conspiracy fanatics as some sort of proof that the official explanation is incorrect. Quite often they cherry pick quotes and ignore any other evidence that won’t fit their narrative. Combine that with the public that’s largely ignorant about aviation, it allows these kinds of ideas to fester very well without challenge.


Why weren’t the Comet’s overhead ADF windows roundified along with its passenger windows?

It wasn't the square-ish windows (they still had round corners, just not as rounded as modern square windows).  They knew square windows were less than ideal stress wise and built the frame structure to take the expected loads.  They just screwed up the calcs and didn't quite make them heavy enough.

The problem was stress concentrations at the rivet holes in the areas of the corners were higher than calculated.  They could have just beefed up the structure with more rivets and doublers.  The switch to round was to alleviate the stress problems without the weight penalty of reinforcing the structure.

The holes in the roof were already sufficiently beefy, or perhaps they added a reinforcement.  You will see square holes in pressure hulls on various airplanes for component pass-through all the time, where a square hole is desirable for some reason.  If you make the frame heavy enough, it's not an issue.  It's just that a round hole is a bit lighter than a square one so most of the time a round hole is preferred.


What's the minimum timeline for fixing the issues/finding from NTSB/FAR?

That is up to the civil aviation authority, which in most countries is distinct agency from the investigation board (in USA this is FAA), to decide.

They will take into consideration how likely the problem is to repeat, how big risk it would be if it does¹ and as secondary criteria how much work the fix is and how much it will cost. What must be done will be published in an airworthiness directive.

If the problem is serious, they will prohibit any further flights except for testing purposes until fix is installed. And remember the fix may not be known yet. For example after the 787 battery fires, FAA published airworthiness directive that prohibited operations until “approved fix is installed” couple of days after the third incident when they just started to discuss what the fix should be with Boeing and whole fleet remained grounded for almost half a year until the modified batteries were ready.

On the other end of the scale a problem may not necessarily result in mandatory change at all. Many issues simply result in mandating additional inspections, shortening intervals between inspections or shortening maximum service life of some component, which may be relaxed again if the manufacturer develops an improved version of the component and the operator installs it, neither of which is mandatory. Even quite severe problems may just be solved with inspections, because most components have inherently limited life and the problem just indicated higher wear then originally anticipated.

¹ It is important to remember that the investigators don't only investigate crashes, but they get reports of all incidents, which means any failure where there was elevated risk. They then investigate those where they consider the risk significant or that are more common then expected. So often things are investigated where the probability of fatal outcome is low. In such cases the investigators will only consider safety and will publish a safety recommendation, but the aviation authority has to also consider other practical aspects and may choose not to enforce it.


Here's a good pilot write up of the A380's fuel systems:

https://captaindave.aero/2017/09/07/the-a380-fuel-system/

Of particular note is this paragraph:

  Towards the end of the flight there are two additional fuel transfers. Any fuel remaining in the trim tank when the time remaining to destination drops below 80 minutes is pumped forward. Similarly, when the time remaining to destination drops below 30 minutes any fuel left in the outer tanks is moved.

So, clearly, on the A380 not only is the fuel usable but it's also a standard operational procedure to utilise it.

I would expect that any fuel trimming is either

Contingent on having more fuel outside of the trim trank. As that fuel depletes, the trim will change, necessitating (or at least allowing) the movement of fuel back away from the trim tank

or

The change in trim is about optimisation, rather than keeping the aircraft within safety tolerances. On a long trip in a large airliner, small changes in trim could have real impacts on efficiency and fuel usage without necessarily impacting control and safety.


Which pilot (pilot flying, pilot monitoring) handles CPDLC (operates CPDLC interface)?

With most airlines, the PM(pilot monitoring) handles datalink communication, with confirmation from the PF(pilot flying) before executing any  instructions, clearances, or changes.

As with everything, there might be some exceptions at some airlines.


Why is a downwind wind speed given in wind checks for aircraft on final?

'Downwind' speed does indeed mean that the aircraft will be landing with a slight tailwind. Each aircraft/airline has a maximum downwind component which is acceptable to land with - generally about 5-10 knots. From my experiences as a private pilot in Australia, I have observed that ATC will tell the flight crew the current downwind component without being requested to do so. I find that they will also advise if the crosswind component is more than about 5-10 knots. It has been a few months since I last heard it but I believe the wording is along the lines of "Qantas 32 heavy, wind 210 at 7, maximum downwind 7 knots, runway 01 cleared to land". This information is also available on the ATIS.


Can I count simulator hours towards a commercial flight certificate training?

According to the FAA, yes you can count those hours, but they can only count for only

Under FAR part 141:
7 hours(35%) of 35 hours of flight training towards a private pilot certificate
17 hours(50%) of 35 hours of flight training towards an instrument rating
36 hours(30%) of 120 hours of flight training towards a commercial pilot certificate
10.5 hours(30%) of 25 hours of flight training towards a multi-engine rating
12.5 hours(50%) of 25 hours of flight training towards an ATP cerfificate
2.5 hours(10%) of 25 hours of flight training towards a flight instructor certificate
1.5 hours(10%) of 15 hours of flight training towards an instrument flight instructor rating.

From http://www.dctaviation.com/#!sim-faq/ccj4
From what I see, you can probably fill up your remaining hours with sim time because you only have a little over 20 hours left and you can have 28 more hours of sim time towards your certification.


Why not leave an electric fuel pump on all the time?

The electric fuel pump is used to provide an extra safeguard against fuel starvation during critical operations in siphon fed fuel systems where either there is an increased risk of this happening or where sufficient altitude does not exist to resolve a problem such has switching fuel tanks or during takeoff and landing operations.  While one could in theory continue to operate the electric fuel pump continuously throughout flight operations, it it not necessary and just adds additional wear and tear on the unit.


If the landing gear is stuck in an airliner, can the crew go down and manually open it?

On older (WWII-era) large planes, the crew had access to a manual crank to lower the gear if the automatic extension/retraction system (usually a linear actuator powered electrically) failed. I don't know of any that had a gravity-based manual system; I'm sure a few bomber crews would have appreciated something like that after having to crank the handle to get a disabled main gear locked. Here are the manual crank ports for the B-17, on the forward bomb bay bulkhead with red arrows indicating the direction to crank:

The B-17 had a retractable tail gear as well, so there was a third manual crank in the tunnel to the rear gunner's position (but if there were multiple gear failures, the main gear would be the priority).

On more modern airliners with hydraulic extension/retraction, manually cranking the gear into place isn't as much of an option (especially since any access to a crank linkage would be in either the passenger cabin or the cargo hold). For these aircraft, the gear are designed with a "manual extension" or "gravity release". This basically disconnects the gear strut from its uplocks and the hydraulic cylinder, allowing gravity to pull the gear down and then momentum (or a spring mechanism) will engage the downlocks. Here is a diagram of the 737's manual gear panel on the right-hand wall of the flight deck:

The 747 has a manual nose gear extension system in the avionics compartment below the first-class cabin. The 747's main gear are much more complex, but it is still possible to let gravity pull them into place, by using a set of "alternate gear extension" switches on the overhead panel to release each gear from the hydraulics and uplocks:

It doesn't always work; a Virgin Atlantic 747 pilot was forced to make an emergency landing with the outboard right main gear stuck in a half-extended position:


How much does it cost if someone falls ill before take-off?

It's hard to get an exact figure, there are fuel prices, the time to taxi, gate charges, medical charges for the removal of the person on the plane, staff costs, and more. I can't guess at most, however from a fuel cost perspective I know for the 747-400 at LHR many airlines use a figure of 1000kg in planning for APU and taxi to takeoff. An A380 would be more, I'd ball park a figure of 1380kg for the airbus based on the MTOW difference (a rough approximation). 1380kg is about 1750 liters, at about .50 GBP per liter that's about 875GBP, or about 1150USD at today's conversions. So the fuel alone would cost somewhere around a grand, I'd imagine you could comfortably double that by the time all is said and done.

As for passing the cost on to the customer I've never heard of that being done for a genuine illness, or even a suspected illness. I don't know if they could if they wanted to, however I cannot imagine them trying it, the reputational fallout would be enormous.


What is the reason for the fence aft of the static ports on some airplanes and helicopters?

In yet another example of unique helicopter design complexity, issues can arise when it comes to mounting static ports on the side of the fuselage where they may fall within the rotor wash. Ideally, static ports should be mounted in an area of undisturbed air, but other design considerations sometimes make this impossible. Additionally, helicopters can fly in directions other than forward, including in the direction of the static port itself. To counter pressure differences from sideslip, many helicopters use a second port on the opposite side. To adjust for rotor wash interference and ensure that the instruments read correctly in climbs and descents, small structures may be placed around static ports to speed up air flow with convex surfaces or slow them down with dams (what you refer to as fences or steps).
Although there is no picture provided, I think this may be what you are asking about:

For more information, you may look here:
https://books.google.com/books?id=rxryAgAAQBAJ&pg=PA409&lpg=PA409&dq=helicopter+static+port&source=bl&ots=p-H9klAkUl&sig=ACfU3U2Yda5qCljafTMg97TSlRH_EpC13g&hl=en&sa=X&ved=2ahUKEwj7paLgkLzqAhUIWa0KHZseD2cQ6AEwG3oECAgQAQ#v=onepage&q=helicopter%20static%20port&f=false


There is not one stall speed, instead there are several, depending on aircraft configuration and flight conditions. They are used to determine speeds for the safe operation of the aircraft or for limit speeds.

For example: The stall speed in landing configuration and level flight with the actual weight is used for determining the approach speed. By multiplying with a safety factor of 1.3, you arrive at the recommended approach speed. Or: The stall speed in take-off configuration is used for determining the rotation speed. And so on.

Another example: The speed range in which it must be safe to deploy flaps is limited by 1.4 times stall speed of the clean aircraft, or 1.8 times the stall speed in landing configuration, whichever is greater. Or: The maneuvering speed v$_A$ is calculated by multiplying the stall speed of the clean aircraft with the square root of the maximum allowable load factor. And so on.

If you wonder what a stall is, maybe it helps to read the answers to this question. It is not flow separation or exceeding a specific angle on the control surfaces that determines the stall condition, but the reversal of the lift curve slope over angle of attack: Stall is when more angle of attack will no longer increase lift, so it is the angle of attack of the whole aircraft that counts. Physically, this means that large-scale flow separation appears over part of the wing. A good design will still have fully working control surfaces at this point.


How long does it take for a regular size airliner jet engine to be warm?

A320 with IAE engines has one of the longest shafts in business, and thus is most sensitive to temperature variations/deformations.

Don’t know what the producer requires, but operator procedure is 5 minutes from start to take-off power if the engine was shut down for more than 2 hours before.

Interestlingly enough, this is on top of other temperature limitations (eg min oil temp) and is the same time, regardless of outside temperature ( eg oil on cold day may take longer to warm up)


How should a private pilot renew their part 107 certificate?

As a holder of an FAA private pilot certificate, you can take a free course to “renew” a Part 107 certificate. You will first have to create and register an account on the FAA Safety Team website. You should do this anyway to earn WINGS credit toward your next flight review.

The site states..

  The Part 107 Small Unmanned Aircraft Systems (UAS) Recurrent course describes the operational requirements to continue to operate small UAS in the National Airspace System (NAS) under Title 14 of the Code of Federal Regulations (14 CFR) part 107, small Unmanned Aircraft Systems. ***Note: This course may be taken by remote pilots who qualify for relief under Special Federal Aviation Regulation (SFAR) No. 118 to satisfy the aeronautical knowledge recency requirements of 14 CFR 107.65(a) or (b) for a period of six calendar months. FOR PART 61 PILOT CERTIFICATE HOLDERS WITH A CURRENT FLIGHT REVIEW (IN ACCORDANCE WITH 14 CFR PART 61.56), SUCCESSFUL COMPLETION OF THIS ONLINE COURSE SATISFIES THE RECURRENT TRAINING REQUIREMENT TO REMAIN CURRENT AS A PART 107 REMOTE PILOT WITH A SMALL UAS RATING. All other interested individuals may complete this online course as a self-study resource.

A Part 107 certificate does not have an expiration date. You lose the privileges associated with it if you do not renew your currency by taking a refresher course.

The FAR/AIM states...

  §107.65 Aeronautical knowledge recency.
  A person may not operate a small unmanned aircraft system unless that person has completed one of the following, within the previous 24 calendar months:

  (a) Passed an initial aeronautical knowledge test covering the areas of knowledge specified in §107.73(a);

  (b) Passed a recurrent aeronautical knowledge test covering the areas of knowledge specified in §107.73(b); or

  (c) If a person holds a pilot certificate (other than a student pilot certificate) issued under part 61 of this chapter and meets the flight review requirements specified in §§61.56, passed either an initial or recurrent training course covering the areas of knowledge specified in §107.74(a) or (b) in a manner acceptable to the Administrator.


Which computer controls auto thrust on an Airbus A320?

More specifically on your question:

See diagram below:

In the autothrust mode (A/THR function active), the FMGC computes the thrust, which is limited to the value corresponding to the thrust lever position (unless the alpha-floor mode is activated).

  So as you can see computers/controllers that control the A/THR are:

  FCU
  FMGC/S
  EIU or EEC
  FADEC
  ADR

The **speed or Mach target may be:

  ‐ Selected on the FCU by the flight crew

  ‐ Managed by the FMGC.

EPR mode is the normal mode to control the thrust. The required EPR is set by controlling the fuel flow.

DSC-70-35-20 P 1/2

The FADEC has two mode of power setting, EPR and N1 modes.
The FADEC computes the command EPR as a function of :

‐ Thrust Lever Angle (TLA)

‐ Altitude

‐ Mach number

‐ Ambient temperature

‐ Air inlet total temperature (T2) ‐ Service bleed.

Arming conditions of the A/THR are numerous. The following is a list of the most important ones:

‐ One FMGC operative

‐ One FAC operative

‐ Two ADIRS operative

‐ Two FADECs operative

‐ One channel of the FCU operative

‐ One LGCIU operative

‐ A/THR is not manually disabled (instinctive disconnect pb has not been pressed for more than 15 s).

  So to summarise:
  FMGS computes the THR and the FADEC computes EPR and through EIU/EEC and ECU commands the fuel flow to the engines in order
  to give the desired EPR.


The altitude you fly at should be determined by the following:

Where you are safest.  Crossing 5500 foot mountains at 6500 simply is not a good safe practice.  Your altitude should be higher at night, if for nothing else, to give you more time to diagnose a problem or pick a suitable landing spot.  When my primary students fly the hills around here, I insist that their final cruise be above 3000 AGL.  That keeps them out of 2000 foot towers (most are just 1500 feet), and gives them time to pick a landing spot, and gives them altitude for getting radio assistance from FSS or ATC.  Higher is better, but I tend to not encourage 10,000 foot level flights for student pilots because there are other risks.  You should consider all the risks associated with altitude.  Lumbering along at 11,000 feet may not be the least risk option.
Your altitude selection should help you in navigating.  Being up higher lets you pick landmarks, see more VORs, reach more ATC and FSS facilities.  Generally, my students do not use GPS (as student pilots), so if they get lost, they have to descend and read water towers and things like that to find themselves.  That doesn't happen often.
Your altitude should keep you in good weather.  If you are a VFR pilot, you will probably not want to make your trip on top, with a 1000 foot ceiling below you. Again one needs to balance risk.  Being at an altitude which keeps you below the scattered layer, keeps visibility good, and can make a trip more enjoyable.  But if Nervous Nancy is taking her first plane trip, and is predisposed to motion sickness or is simply nervous about bumps, then you want to pick an altitude that will be a bit smoother.

The whole exercise of picking the right altitude, the right route and even the right day is part of a big optimization problem, where you are looking at safety, enjoyment, economics and other factors.  There is no magic altitude, no perfect route.  What is good 80% of the time may be not so good 20% of the time, which is why ADM (Aeronautical Decision Making) is emphasized in training and recurrent training.  Having good visibility, nice tailwinds, a smooth ride and plenty of altitude over the terrain are always nice.

Oh, one exercise you might try...I tend to do this with flight review students...we do airwork at altitude over the hills or low mountains about 25 to 30 miles from the airport.  I pull power and they dive for the nearest pasture, which has down slopes which exceed the descent profile of the aircraft with power off, the gear and flaps down, and heavy slipping.  Or select a field which has an up slope which is extreme enough so that a landing is impossible.  Then I suggest that they try the home airport.  "But it's 20 miles away."  or maybe 25, and they might have a good tailwind at 5000 feet above the airport.  And they start the glide.  On the way we pick alternates, including flat grass strips, along the way.  Almost 100% of the time, the lightly loaded aircraft makes the airport, and they are amazed that they were able to travel so far without power.  And the take-aways are many, which include that having a couple of thousand feet below you really opens up your options.  And to not pick the first field you see.  With altitude, there may be others as you get to more favorable terrain.

I have managed to fly many decades, many hours and never so much as scratched paint on an airplane.  However, before every flight and during every decision, I ask myself what an objective, after the fact, review board would say.


Is there any order of loading containers into aircraft instead of weight balance?

Yes, there is.

Premium luggage (business and first class) is loaded such that it is the first to be retrieved.
HAZMAT (HAZardous MATerials and items, if applicable) is loaded differently; and placed in different parts of the cargo hold.

There are some areas of the cargo hold (in passenger airplanes) that cannot be used to store ULD, only loose cargo or other special items (such as the transportation of pets).

Some airlines offer temperature controlled ULDs, which require their own special handling.

Of course, transportation of human remains is handled differently.

Strictly for cargo operations; as these are normally multi-stop trips - the ULDs are loaded in the order in which they are to be unloaded.

However, keep in mind that it is very rare to have perfectly uniformly loaded ULDs or crates. So often the loadmaster has to make sure the CG of the aircraft is taken into account when loading and unloading.


Is there a Non Directional Beacon(NDB) morse code sound database?

Here’s a website that has some NDB sounds that can give you examples of what an NDB sounds like.

Basically each NDB transmits a one, two, or three letter identification.

On the chart, you can tell what to listen to by looking at the dots and dashes next to the identifier. In the example below, Chualar is UAD

..-
.-
-..


Why will reducing the boarding time reduce the costs?

It's not as much boarding as much as standing around does not generate any revenue.

Use Your Capital Assets: 25 minutes a day is a lot, and in some cases is equivalent to a domestic leg. Rather than arriving at 23:00, you could arrive at 22:30 and still squeeze in an additional short flight before midnight. If you're flying 10 flights a day and you can now fly 11, you're doing 10% more work with the same amount of assets. Estimates for a flight hour of a B737 are ≅ \$3000-\$3500 in the US, for an aircraft worth perhaps $60 million.
Fixed Costs: You're looking at a bit of fixed costs, such as insurance. The more flying time you can squeeze out of the plane, the cheaper each hour will become on average.
Less Staff, More Product: You need a certain number of ground staff. If you can cut the time required for an aircraft to be handled by ground staff by 20% (50 → 40 minutes), that potentially means that they could handle an additional aircraft in their shift. This principle applies for airline flight crew, as well. It's a lot cheaper to let the your pilot fly a few hours more than needing to hire another one.
Standing around is not always cheap either: Depending on airport cost/fee structure, you may be charged less for the ground time. This is not only standing around; for instance, Munich airport charges you €44 for every 30 minutes of using a ground power unit.


Will the new Part 23 changes reduce the cost of avionics for existing aircraft?

Unfortunately not: the purpose of the part 23 rewrite is to make it easier to certify a new aircraft type (not individual avionics or other systems) and it doesn't apply to existing aircraft. AOPA has a good overview, including this (emphasis in the original):

  10. Are the performance-based standards applicable to all aircraft?

  No.  The new process of using performance-based standards is limited
  to new airplanes certified under Part 23, which would include
  airplanes with a maximum passenger-seating configuration of 19 or
  less, and a maximum certificated takeoff weight of 19,000 pounds or
  less.

To address the cost point directly, in theory if the part 23 rewrite creates additional demand for new aircraft, and if those aircraft use avionics that can also be retrofitted to existing aircraft, then the increased demand might reduce prices. But that's highly speculative.


Why is the ICAO prefix for Alaskan airports "P"?

Definition from wikipedia:

The ICAO (/ˌaɪˌkeɪˈoʊ/, eye-KAY-oh) airport code or location indicator is a four-letter code designating aerodromes around the world. These codes are defined by the International Civil Aviation Organization, and published in ICAO Document 7910: Location Indicators are used by air traffic control and airline operations such as flight planning.

https://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/ICAO_FirstLetter.svg/1200px-ICAO_FirstLetter.svg.png

This is a map of every ICAO airport code wordwide.

Alaska has PA, PF, PO and PP as airport codes. P = Eastern North Pacific.
PA=USA (Alaska) (also PF, PO and PP)

There is no special meaning behind the letter P and these codes, it's just a classification!!


What is the approximate range of the Pelegrin Tarragon?

According to the manufacturer, it has a range of 1,300km.


Did factors specifically related to the concorde design influence the Air france flight 4590 crash?

In short: No, the crash of 4590 could happen to other aircraft in the same situation: i.e. a blown out tire, a tank fire, subsequent structural issues, and at least two engines (of 4) not running properly.

The official accident report summarizes the causes pretty well (and is worth a read)

  The accident was due to the following causes:

  • High-speed passage of
  a tyre over a part lost by an aircraft that had taken off five minutes
  earlier and the destruction of the tyre.

  • The ripping out of a large
  piece of tank in a complex process of transmission of the energy
  produced by the impact of a piece of tyre at another point on the
  tank, this transmission associating deformation of the tank skin and
  the movement of the fuel, with perhaps the contributory effect of
  other more minor shocks and /or a hydrodynamic pressure surge.

  • Ignition of the leaking fuel by an electric arc in the landing gear
  bay or through contact with the hot parts of the engine with forward
  propagation of the flame causing a very large fire under the
  aircraft’s wing and severe loss of thrust on engine 2 then engine 1.

None of these are related to the design or construction of the airframe itself. This podcast with one of the pilots also touches upon the accident and is perhaps one of the best primary sources of Concorde info.


Aerobatics in "firm" IMC -- how would one do it?

No - you don't do it.

First and obvious reason, there's no body to see it.

Perhaps much more important is safety though. When pulling a loop, it's not like flight simulator where you just yank the stick aft and watch the attitude indicator (AI). An aerobatic pilot is constantly checking his attitude by looking at his wing tips, quickly glancing the left and right sides back and forth.

In fact, the AI is usually caged (meaning it is locked to prevent rotation) in such violent maneuver. The proper procedure is cage the AI, perform the maneuver, check straight and level (visually), then uncage the AI. If you don't, the gyroscope will tumble quite some time before it settles again, rendering it useless. Meaning, if you perform in IMC, you won't have accurate AI information for recovery.

For nearly vertical maneuvers (e.g. stall turn, rolling while vertical), even a functioning AI wouldn't help, since horizontal direction is undefined in this state. The AI and compass will just flip, yet you have no way to determine which way you go.

Violent G-forces also mean it is much more difficult to read instruments during such maneuver.


How does the efficiency of a fixed wing compare to a rotary wing?

Helicopters use more fuel than airplanes (considering everything else being equal).

When helicopters are traveling slow, they need more energy to hold their weight. When traveling fast (according to their standards), the rotor drag is very high. This is the primary reason they need more power. More Power = More Fuel.

Conventional aircraft have much less drag at a given weight and speed than a helicopter.

Helicopters travel slow. When they burn more fuel per hour and travel slowly, fuel consumption per mile is much worse. They also stay low. Most have turbine engines, turbines burn lots of fuel at low altitudes.

Wikipedia has a good article about energy efficiency in different vehicles.

  Two-seater and four-seater flying at 250 km/h with old generation engines can burn 25 to 40 liters per flight hour, 3 to 5 liters per
  100 passenger km.
  The Sikorsky S-76C++ twin turbine helicopter gets about 1.65 mpg-US (143 L/100 km; 1.98 mpg-imp) at 140 knots (260 km/h; 160 mph) and
  carries 12 for about 19.8 passenger-miles per gallon (11.9 litres per
  100 passenger km).


What is the origin for "squawk" having two different meanings in aviation?

According to Wikipedia (which has cited sources), the transponder usage comes from...

  The use of the word "squawk" comes from the system's origin in the
  World War II identification, friend or foe (IFF) system, which was
  code-named "Parrot".

As for the maintenance reference, one of the accepted definitions is

  To inform

or

  To report an infraction

It may just be coincidence that they are used as they are.


What are some differences that make the new 737 MAX winglets more efficient than a conventional winglet?

The 737 MAX winglet is the latest develpment in the 'winglet war' going in between the Boeing and Airbus.

As it has been described how winglets work and its advantages, I will not go into those. Most of the wingtip devices in use today are there simply to reduce the effect of wingtip vortices i.e. they are more or less vertical to the wing.

For example, the 737-200 winglets produce little lift.

Source: .b737.org.uk

The same goes for 737-800 variants, which use blended winglets which do produce a little lift (redistributing the spanwwise loading).

"A Garuda Indonesia Winglets Boeing 737-800 NG" by FathirLeone - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

And also the 737 NG 'Split Scimitar' wingtips (where do they get these names?).

This adds some weight to the aircraft. For example, the 737 winglet weighs arounf 180 lbs and the total structutal weight increase due to it is around 480 lbs. Obviously, the winglets more than compensate for this increase, that's why we see them used.

With modificaitons, the wintip devices can be used to produce lift and this is the path being taken today with new wingtip device designs, especially with the blended winglet. Boeing took this to the extreme in 787 raked wingtips, which is basically in the horizontal plane, which increased the actual aspect ratio of the wing.

Source: malaysianwings.com

Another idea is to use them to generate lift by changing their angle of installation. This makes the 737 MAX winglet somewhere in between the legacy 737 and 787 winglets. The 737 MAX Advanced Technilogt (AT) winglet has two parts:

An upper part which is at an angle, resulting in some lift being produced.
A lower strake.

The idea is that the winglets also produce some lift in addition to drag reduction. According to Boeing,

  The AT winglet further redistributes the spanwise loading, increasing the effective span of the wing. The AT winglet balances the effective span increase uniquely between the upper and lower parts and therefore generates more lift and reduces drag. This makes the system more efficient without adding more weight.

The AT winglets distribute spanwise loading like this:

Source: b737.org.uk

Note: the first one is the baseline aircraft with no winglet. The second one has the 'blended' winglet, while the third one gives the AT winglet. As can be seen above, some of the lift is generated by the winglets itself.


What constitutes a flight review for the purposes of eligibility for a remote pilot certificate under 14 CFR 107.61(d)(2)?

You have to take into account the intent of the regulation.  I think the regulations intent is to ensure the pilot has been evaluated on his knowledge within the previous two years by either a CFI or examiner.

With that in mind, a flight review by a CFI or passing a practical test by an examiner satisfies the requirement for the remote operator to take the full initial knowledge test.

From the preamble to the Part 107 final rule.

  The FAA proposed that a certificated remote pilot must also pass a recurrent aeronautical knowledge test every 24 months. Like the flight review requirement specified in §61.56, the recurrent knowledge test provides the opportunity for a remote pilot’s aeronautical knowledge to be reevaluated on a periodic basis. The FAA adopts this provision as proposed, with one change. As discussed in III.F.2.i, the FAA exempts part 61 pilot certificate holders from the requirement to complete recurrent knowledge tests as long as they satisfy the flight review requirements of §61.56 and complete an online training course every 24 months

Page 6 paragragh g.

  The FAA agrees with commenters who suggested that requiring part-61- certificated pilots who satisfy the flight- review requirements of §61.56 to take an initial or recurrent knowledge test is unduly burdensome. Through initial certification and subsequent flight reviews, a part-61-certificated airman is required to demonstrate knowledge of many of the topic areas tested on the UAS knowledge test. These areas include: Airspace classification and operating requirements, aviation weather sources, radio communication procedures, physiological effects of drugs and alcohol, aeronautical decision-making and judgment, and airport operations. Because a part 61 pilot certificate holder is evaluated on these areas of knowledge in the course of the part 61 certification and flight review process, reevaluating these areas of knowledge on the initial and recurrent knowledge tests conducted under part 107 would be needlessly duplicative.

Page 13 paragraph I


How to compare turboprop engines and with which values?

This database covers turboshaft and turboprop engines. Typically, the key factors one would use to compare such engines are:

SFC: Specific fuel consumption. This is how many kg/s (or lb/s) of fuel the engine consumes to produce 1 kW (or 1 hp). To calculate the SFC, divide the fuel flow at a throttle position by the amount of shaft power produced at that throttle setting. SFC decreases as overall pressure ratio increases. A low SFC means a more fuel efficient engine.
Specific power. This is, how much shaft power (kW) is produced per kg of air ingested by the engine. To calculate this, divide the shaft power by the air mass flow. A high specific power means you can get the power you need from a smaller, and hence lighter engine. A higher figure occurs when the engine has a high turbine temperature, and aerodynamically efficient compressors and turbines.
Power to weight ratio. To calculate this, divide the shaft power produced by the engine weight. As above, a higher figure occurs when the engine has a high turbine temperature, and aerodynamically efficient compressors and turbines.


The means of starting most turbine engines is high pressure bleed air.  This bleed source typically comes from an APU but may also come from an already running engine (crossbleed start) or an external huffer cart.

In some airplanes the start is completely FADEC controlled and need only be initiated and monitored by the flight crew, and in other airplanes certain steps must be manually initiated.

The process below best describes a turbofan engine.  Read @Falk s answer for information on differences with turboprop engines.

Turbofan basics

Refer to the image below (Credit: K. Aainsqatsi, Wikipedia):

The portions of the engine I will be referring to below are:

The N1 fan, N1 shaft and N1 turbine which are displayed in green and labelled "Fan/Low-pressure compressor", "Low pressure shaft" and "Low pressure turbine".  These units are connected and move as one piece.
The N2 compressor, N2 shaft and N2 turbine, displayed in purple and labelled "High pressure compressor", "High Pressure shaft" and "High pressure turbine".  These are connected and move as one, but independently of the N1 shaft.  Un-pictured is an accessory drive that is geared to the N2 shaft to drive engine accessories.
The hot section, pictured yellow and labelled "Combustion chamber".  This is home to a constantly burning fire in a jet engine.

Engine Start

The process of the engine starting follows this basic formula

Through the opening of bleed air valves, bleed air is sent to an air turbine starter.  These devices typically use the high pressure bleed air to spin and engage a centrifugal clutch connected to the engines accessory drive.  This in turn causes the N2 shaft within the engine to spin.
With the N2 shaft spinning, the N2 compressor and the N2 turbines are spinning.  This begins to force air through the engine from front to back.
With the accessory shaft and N2 shafts spinning, accessories should start working and this can be verified by oil pressure indications on the EICAS.
With increased N2 rotation, ignition will be turned on.  These igniters are located in the hot section of the engine and produce small sparks.  There should be an indication on the EICAS that the ignition is active.
With further increase in N2 rotation, fuel flow will be introduced.  This will be verified on the EICAS.  Once fuel flow is noted, it is important that the next stop happen fairly soon.
Light off!  The fuel is lit by the ignition and now the fire burning in the hot section supplied by air from the compressor is producing thrust across the N2 and N1 turbines.
As the engine is producing thrust across on the N1 turbine, the N1 shaft is spinning the N1 fan and the EICAS will note this increase in N1 rotation.  N1 and N2 rotation speeds increase.
Above a N2 threshold, bleed air valves supplying the the air turbine starter will close and the starter disengage. The igniters will turn off at some N2 threshold.
The engine will settle into a stable idle thrust setting.

What can go wrong?

Hung start

N2 fails to spin up sufficiently for fuel flow to be introduced.
Each start has a time limit and the start will be aborted.

No ignitors

Abort the start and switch igniters.
Give MX a call.

Failure to ignite

Fuel flow is introduced but light off has not occurred in a proper timeframe
Fuel is building up in the engine and if light off does occur, it can be damaging.
The start is aborted and dry motoring is performed to clear the engine.

ITT exceedence

There is usually a limitation in the inter-turbine temperature during engine start.
If this is exceeded the start must be aborted
This may require coordination with MX before another start is attempted.

The air turbine starter fails to disengage

This must be corrected before departing
In some engines, MX can correct this with the engine running.

The bleed air shutoff valve supplying the air turbine starter fails to close

This may require an engine shutdown to remedy
However, in some airplanes, this valve can be manually shut by MX with the engine running
Coordination with MX required.

Runaway N1 or N2

If the FADEC isn't managing fuel flow properly, the engine may not settle but continue to spin up.
Abort the start.
Coordinate with MX before attempting a restart.

What about starting the engine in the air?

If the engine suffers a flameout, an airborne restart may be attempted.  These starts typically happen one of a few ways:

Crossbleed start
APU start
Windmilling start

The APU start is essentially the same process as above.  The crossbleed start, which can also be done on the ground, merely substitutes a running engine at a high power setting to provide the bleed air for starting and is otherwise the same as above.

The interesting start is the windmilling start.  The necessity for this means something bad has happened.  To need a windmilling start, this means that there are no bleed air sources to supply the air turbine starter.  This can mean that all engines are out and the APU is unavailable (BAD!), or merely that bleed valves to a shutdown engine have failed closed and are unable to be opened.

For the EMB-145 that I am familiar with, a windmilling start required descending at an airspeed between 260 KIAS and 320 KIAS and could not be attempted above FL250.  In short, you hope that the mass flow through the engine is enough to spin the N2 compressor as the ATS would.  With an N2 indication within the engines airstart envelope, you introduce spark and fuel and hope that the engine lights.  In the worst case, if you too slow and unable to provide enough airflow prior to light off, the engine can quickly overtemp and be damaged.  For this reason it is especially important to abort this kind of start as soon as an abnormality is detected.


Does taking a long time to solo mean that I'll take a long time for training in general?

Yes, that much time pre-solo is a huge red flag.

If you have 80 flight hours logged and no solo, unless there is some unusual extenuating factor (e.g. those 80 hours were spread over many years), something is seriously wrong. Either:

You do not have the right aptitude for flying
Your instructor is incompetent, or
Your instructor is deliberately milking you.

If the instructor hasn't already had a frank discussion with you about your progress and prospects by this point, that would indicate #2 or #3.


When should I request clearance to return to altitude, after leaving cruise altitude?

The “cruise” terminology you are questioning is really not used anymore. It still appears in manuals, but it was very confusing and fallen out of use. The intention of a “cruise” clearance was to allow the pilot to climb or descend as required with the specific cruise altitude window. In your question that was 4000’-6000’. However, today people the same request would be made as “request an altitude block 4000-6000”. ATC would respond “(callsign) is cleared the block 4000 to 6000.” No further calls are required from you while maneuvering in that altitude block.
Sometimes a “cruise climb” clearance will be issued to heavy aircraft to allow them to climb slowly and level off for a while when they are too heavy to climb all the way to their final altitude. In that case they can climb as they are able but are not allowed to descend out of an altitude they have already climbed to.


What is the function of this fixed protrusion on the tail?

That is almost certainly a navigation antenna.

From the E190 AOM (Airplane Operations Manual):

You can see the VOR2/LOC2 antenna rather more clearly in this photo:

(The VOR1/LOC1 and VOR3 antennae are embedded within the tailfin.)

Similar nav antennae are used on many smaller aircraft such as (more modern) light aircraft, utility aircraft, business jets and some regional jets.