Can anyone explain the reflex wings used in powered paragliding?

I'm haven't flown them but am very familiar with them and the reflex wing controversy because I was interested in getting into the sport (I normally fly power and gliders).

A reflex wing when in "reflex mode" offloads the aft part of the wing and shifts the pressure distribution forward.  Effectively, the rear part of the wing is being allowed to "trail", or partly trail, up and not do any (or much less) work.  It's a bit similar to gliders with flaps that have a reflex setting, where the flap is angled trailing edge up a few degrees for high speed penetration flying, which off loads the trailing edge and moves the wing's pressure distribution forward and makes it behave as if it had a narrower chord.

It's not related to reflexing flying wing aircraft trailing edges for pitch stability, where the trailing edge provides downforce in place of the absent tail; that simply can't work and isn't necessary in a paraglider.

The effect of reflex is to somewhat reduce the effective wing area, increase the effective aspect ratio, and reduce induced drag in the process.  A 26 sqm wing becomes effectively a 20 sqm wing (I'm just picking numbers here) with a narrower chord and what amounts to some loose fabric (the unloaded trailing edge) trailing behind it.  Because the TE is unloaded, you can't use the normal trailing edge drag brake steering and have to use "tip steering" controls.

The different pressure distribution increases the inflation pressure at the front of the wing and makes it more collapse resistant, and this is one of the reflex wing's selling features besides slightly higher cruising speed.  The downside is that when they do collapse, they do so violently with way more altitude loss and if you are close to the ground your wing will pretty much fling you into the dirt like a rag doll if you get a collapse.  I don't believe there are any current wings that can meet EN cert requirements while in reflex mode.  This means if you value your life you don't use reflex below a recoverable altitude, say 500 ft.

Having researched it a lot myself and noted the same thing you did, only a 5 kmph benefit, I'm not keen on reflex myself, especially after watching videos of how they behave when they collapse.


What might the business model be for a hypersonic jet?

Well it’s cool but it’s nothing new.  Hypersonic transports and runway to orbit vehicles have been proposed since the late 1970s but never materialized into flyable hardware for a number of reasons, mainly engineers have not been able to solve the technical challenges associated with structures, propulsion, mission profiles, heat transfer and protection, operating costs for skittish airline operators, etc.

The new Boeing hypersonic transport may be the quantum leap forward for air and space travel but it could easily join the heap of fantastic ‘paper airplanes’ that never flew or possibly flew as clandestine prototypes such as:

Rockwell National Aerospace Plane - “Orient Express” from Reagan’s
1986 State of the Union Address.
Lockheed SR-91 “Aurora” reconnaissance aircraft.
High Speed Civil Transport concept from the
1990s
Lockheed Martin X-33 / VentureStar SSTO concept
German Sänger concept aircraft
Lockheed SR-72 Spy plane of the 2010s

As far as the passenger world is concerned, the big market are the transpacific routes, where the high-speed would make a major difference in travel times for both the public as well as business travel. If you could design a hypersonic aircraft that has a 6000 - 7000 mile range with operating costs in the neighborhood of 30 to 40% higher than existing subsonic airframes, you would have a game changer. But that’s always been the challenge.

Who knows, maybe the technology now exists to attempt a successful hypersonic manned aircraft.  I for one would welcome it as I find current aircraft are becoming insufferably boring.  OEMs churn out one bland subsonic twin jet after another, just wringing a few more knots out of a few less gallons of gas with new avionics etc.  I was supposed to be living on one of those cool Gerry O’Neill space colonies at this point!


Can a GA headset be used for listening to normal audio or with a cell phone?

I actually know a guy that does this. He bought a nice noise canceling headset but then stopped flying and now he uses it on long flights and quite enjoys it. For what its worth noise canceling headphones have come down in price over the years and you may simply be able to sell the headset and buy a less bulky set of headphones for the money you make. But if you dont want to go through the hassle then there is nothing stopping you from using aside from having a boom mic dangling off it.

For what its worth a lot of noise canceling headphones now have mic inputs as well so you can answer calls from them as well.


How will the Rolls Royce UltraFan provide reverse thrust?

The flow direction reverses only through the bypass duct pulling by blades with negative pitch. A portion of it will still be sucked by low pressure compressor making 180° turn into the core. Having to counteract the losses in turn will obviously reduce the performance.
As stated in research paper by the team funded by Rolls-Royce plc: "the core mass flow rate was 57% of that at take-off conditions, for bypass duct flow rates of 74% of total take-off mass flow."

Another design by Pratt & Whitney features reversed position of the whole core requiring two turns of the flow for incoming and outgoing air. So, these turns are not a big problem as we see them traded for other pros.


Would "Mad" Mike Hughes' steam-powered rocket have been certified airworthy by the FAA?

Interesting topic.  Rockets and spacecraft are still highly experimental vehicles and are recognized as such under 14 CFR §1200.  The laws, liabilities, and regulations for private spaceflight are largely uncharted territory at this point, though §1266.102 requires all participants aboard the ISS and NASA launch vehicles to sign a liability waiver prior to flight.  Essentially, in the eyes of the law, you’re on your own in doing this and if your injured or killed, neither you nor your estate can hold any participants in your cosmic ordeal liable.  Given that many flat earthers view NASA as the enemy of their efforts, any laws in regards to spacecraft certification would probably be viewed in a negative light and disregarded.

Using §91.7 here is pretty nebulous as there is no definition or standard here for airworthiness of such a craft.  These guys were testing an experimental vehicle at a remote site far away from other persons or property and flying only a single flight crewmember.  There’s really no law saying you can’t take a risk like that under those conditions.


Why do full service airlines prefer to run a separate low-cost carrier?

They still want to get into the low cost segment but want to market themselves differently for better penetration. You can only present so many images of a brand to customers: You can't show both the super-cheap prices with happy youth on them and posh first class at the same time.
They do not want to tarnish a nice brand by mixing it with a low cost carrier and what that is perceived to entail. For instance, Germanwings got a somewhat infamous reputation recently, and Lufthansa is probably happy their name was not more frequently used in media. Low cost is also associated with less good customer service and hidden fees.
Crew are often less well paid, and they are sometimes put under a separate working agreement and company to try to prevent conflicts. Some legacy carriers have very good pay which is difficult to reduce. Management does not want to be bound by these when expanding or adjusting their business.

Each case is pretty specific depending on exactly they are trying to do and achieve. For many American Carriers and Lufthansa, the last one is probably the principle reason.


Does pumping fuel to each wingtip affect roll trim in a stabilized turn?

Not if the fuel pumped to the wing tips in equal amounts so that the lateral CG is unchanged.  But... there are effects related to the inertia of the fuel mass (the wings become spokes in a flywheel, you could say).

I have some flying time a plane that has all of its fuel in the wing tips, in tuna fish shaped tanks, 25 usg per side.

The difference in handling qualities with the tips nearly full and the tips nearly empty is all related to inertial effects of the fuel mass; roll rate, roll inertia, yaw inertia, and roll response to yaw.  The roll rate you can generate by skidding the plane is much lower with the tips full.  The influence of dihedral in damping and restoring roll deviations is reduced.  Disturbances are amplified because of the flywheel effect of the tip mass and this is especially noticeable in yaw; there is more of a tendency for the tail to wag in bumps.

But in a stabilized bank in smooth air, the amount of fuel in the tips made no difference in increasing or decreasing overbanking/underbanking, except to the extent that the interia of the fuel dampens or inhibits the usual restorative forces.  So if you had an airplane that can be banked and holds the bank angle with no input, there is no major effect of fuel in the tips in changing that characteristic, until you hit a bump and the inertial effects start to work.  However, where the airplane has an overbanking or underbanking tendency, the flywheel effect will inhibit it starting and tend to keep it going once started.

So to answer the basic question, if you had a plane that naturally wants to roll out of a turn when inputs are removed, the effect of fuel in the tips will be to reduce that effect somewhat, so it will still roll level but take longer, and once level it will tend to overshoot more.  It it wants to overbank into a spiral dive, same thing that way.


I found this forum discussion from a few years ago, which stated:

LH Express was their brand name for domestic services for some years in the mid 90s. I'm not sure when the LH Express name disappeared, but they definitely were not promoting the Express name in 1997 any more. So the aircraft you saw was probably just not repainted yet. LH used to operate B737 of various series and several Airbuses.

One of the guys went on to say it was a low-cost domestic route, set up in competition to Deutsche BA. Unfortunately, it did not succeed enough in competition and was eventually shut down. They did fly some small Boeings like the 737, and the Airbus 300 and 310.
Additionally, a NY Times article from 1992 gives a small blurb about the startup of the line:

Under the new strategy, eight key domestic German routes are to be served by a special spin-off division, Lufthansa Express, that promises passengers a better on-time record, faster check-in and a chance at bargain prices.
...
Another innovation of Lufthansa Express will be bargain prices on late-night and short-notice flights. Passengers get a 55 percent discount savings on flights after 7:30 P.M., even without advance reservation, for example.
...
The most controversial aspect of Lufthansa Express is something passengers are unlikely to hear much about: The starting pay for a crew on Express flights will be about 25 percent less than on traditional Lufthansa flights.

Another thread here has a few minor other details. Interestingly enough, Amazon still has a listing for a model LH Express 737 (out of stock).


Why do older planes not have a middle hand luggage compartment?

Since the L-1011 was born prior to airlines charging for checked baggage, and passengers didn’t feel the need to bring massive carry-on items with them, the L-1011 featured compact overhead bins that were (to quote advertising of the day) “sized for a lady’s wig box.”

Source: airlinereporter.com

The link provides really good information on the L-1011.


How can I triangulate a position using two DMEs?

We can find the exact method to use online, after all this is a common 3D trigonometry problem. I'll use Michael Geyer
US DoT report: Earth-Referenced Aircraft Navigation and Surveillance Analysis. The principle is:

The two DME distances determine two spheres which intersection is a circle. The aircraft is on this circle.
The aircraft altitude determines a surface (depending on how altitude is measured, it can be a quasi-plane or a surface of constant pressure) which intersects the circle at two points. The coordinates of the points can be computed from the two DME distances and the altitude.
As a matter of fact DME signals at the two points are identical, therefore one must be eliminated by some method.

Intersect two spheres to get a circle

The slant distance determined with DME tells us the aircraft is on the surface of a sphere centered at the DME station, with radius equal to the slant distance. By interrogating two DMEs, two intersecting spheres are determined. The intersection is a circle (pink circle in the figure below). The closer the aircraft is to the line joining the two DME stations (the baseline), the smaller the circle, down to a single point when the aircraft is exactly on the baseline.

Intersect the circle with a surface to get two points

The aircraft is flying in a quasi horizontal plane. This plane intersects the circle at two locations (green points in the figure above) which are symmetrical to the baseline and where the aircraft must be located. By using the direct information we have (altitude and slant ranges), we can compute the coordinates of the two points.

Eliminate the ghost location

At a given time, the aircraft could be located at either points and still receives the same DME signals. In the mathematical solution, this will appear when using a function like $\arcsin(x)$, which gives two angles for the same x value, e.g. 40° (90°-50°) and 140° (90°+50°).

There are several methods to eliminate the virtual position:

Monitor the progress of the aircraft: If the aircraft flies north, the top point moves north while the bottom point moves south. We can detect such illogical trajectory (e.g. using a predictive Kalman filter).
Use a third DME: The third range sphere will intersect the other two at only one point.
Determine aircraft bearing using a VOR, preferably collocated with one of the DME.

In large aircraft, position is determined using multiple means including inertial and GNSS, so it's not difficult to know where the aircraft is approximately.

Determination of the points coordinates

The DME/DME/Elevation case boils down to:

  Two DME stations $\small U$ and $\small S$ with known latitudes, longitudes and altitudes ($\small L_U$, $\small \lambda_U$, $\small h_U$ and $\small L_S$, $\small \lambda_S$, $\small h_S$).
  An aircraft A with known altitude ($\small h_A$).
  Two measured slant distances ($\small d_{UA}$ and $\small d_{SA}$)

$\small C$ is earth center (earth radius is $\small R_e$. Following the method mentioned previously, we execute these steps:

  Step 0: Convert slant-ranges to angular distance
  Step 1: Solve the spherical triangle for each station
  Step 2: Confirm inputs are consistent and a solution exists
  Step 3: Solve the spherical triangle USA
  Step 4: Compute aircraft latitude and longitude

Step 0: Convert slant-ranges to angular distance

With altitudes and slant ranges known, it is possible to calculate angles $\small \theta_{SA}$ ($\small \widehat{SCA}$) and $\theta_{UA}$ ($\small \widehat{UCA}$) between DME and aircraft. For each DME $\small x$ ($\small x$ being either $\small U$ or $\small S$):

$$\theta_{xA} = 2\space \arcsin \left( \frac{1}{2} \sqrt{\frac{(d_{xA}-h_A+h_x)(d_{xA}+h_A-h_x)}{(R_e+h_x)(R_e+h_A)}} \right)$$

By convention we need to name $\small U$ the station which is westward. This allows us to refer at the aircraft position like "the one south of the baseline".

Step 1: Solve the spherical triangle for each station

The first actual step is to get the angle $\small \theta_{US}$ formed by the two DME stations and earth center:

$$\sin \left( \frac{1}{2}\theta_{US} \right) = \sqrt {\sin^2 \left( \frac{1}{2}(L_S-L_U) \right) + \cos(L_S) \cos(L_U) \sin^2 \left( \frac{1}{2}(\lambda_S-\lambda_U) \right)}$$

where $\small L_U$ and $\small L_S$ are latitudes of $\small U$ and $\small S$ and $\small \lambda_U$ and $\small \lambda_S$ are longitudes of $\small U$ and $\small S$.

We will need to know one of the azimuth at the extremities of the baseline between $\small U$ and $\small S$:

$$ \tan(\psi_{S/U}) = \frac {\cos(L_S) \sin(\lambda_S - \lambda_U)} {\sin(L_S) \cos(L_U) - \cos(L_S) \sin(L_U) \cos(\lambda_S - \lambda_U)} $$

Step 2: Confirm inputs are consistent and a solution exists

If the slant ranges are 10 NM and 15 NM, and the known distance between stations is 30 NM, then there is no actual solution, something must be wrong. This step checks whether the two DME range spheres intersect. We have already computed angles $\small \theta_{UA}$ and $\small \theta_{SA}$ and the one between stations $\small \theta_{US}$:

If $\small \theta_{UA} + \theta_{SA} < \theta_{US}$, then the spheres don't intersect (centers too remote)
If $\small \left| \theta_{UA} - \theta_{SA} \right| > \theta_{US}$, then spheres are concentric, they don't intersect.

Step 3: Solve the spherical triangle USA

Now we know the three sides of the triangle $\small \widehat{USA}$, we can determine any of its angles. We need only the angle with its apex at one station:

$$\cos(\beta_U) = \frac {\cos(\theta_{SA}) - \cos(\theta_{US}) cos(\theta_{UA})} {\sin(\theta_{US}) \sin(\theta_{UA})}$$

Step 4: With all data now available, compute aircraft latitude and longitude

It's time to decide which of the two aircraft positions we want by selecting the corresponding azimuth angle at station $\small U$ (it could be at $\small S$, but we did the previous step for $\small U$):

If $\small A$ is south of $\small US$ baseline (assuming $\small U$ is west of $\small S$): $\small \psi_{A/U} = \psi_{S/U} + \beta_U$
If $\small A$ is north of $\small US$ baseline: $\small \psi_{A/U} = \psi_{S/U} - \beta_U$

Aircraft latitude $\small L_A$:

$$\sin(L_A) = \sin(L_U) \cos(\theta_{UA}) + \cos(L_U) \sin(\theta_{UA}) \cos(\psi_{A/U})$$

Aircraft longitude $\small \lambda_A$:

$$\tan(\lambda_A - \lambda_U) = \frac {\sin(\psi_{A/U}) \sin(\theta_{UA})} {\cos(L_U) \cos(\theta_{UA}) - \sin(L_U) \sin(\theta_{UA}) \cos(\psi_{A/U})}$$

I posted a Python implementation on Stack Overflow.


Does autopilot disconnect when a danger alarm like GPWS triggers?

This is the Quick Reference Handbook procedure from an old A320 training manual.

(The EGPWS procedure is a memory item, pilot's are not expected to look this page up when they encounter a EGPWS warning)

The first two sub items answer your questions. The autopilot needs to be switched off manually and the instruction is to pull up to full back stick and maintain. The Alpha protection will prevent the aircraft from stalling, that is why the stick can be maintained at full back deflection.

Airbus' safety magazine FAST #23(PDF) giving guidance on flying protected aircraft, specifically advices pilots to apply full backward stick deflection in GPWS situations since the alpha protection will prevent the aircraft from stalling and the resulting flight path is the most effective way away from danger.

To illustrate a possible the effects of Alpha protection in an (E)GPWS situations, let's go to Bilbao again, but now in March 2001(PDF). An A320 on final approach encountered a wind shear causing the aircraft to descent fast. This caused the GPWS to trigger a warning. The pilot applied TOGA power and back stick deflection, but the Alpha protection predicted the aircraft to stall and prevented a higher nose attitude. As a result the aircraft didn't stall but crash landed on runway threshold. This accident demonstrates that the GPWS does not affect the flight envelope protection system.


What is the working principle of trim tabs on the elevators?

The trim tab is like a control surface for the control surface. By changing camber at the rear end of the control surface, it creates a local force which changes the balance of forces such that the force-free deflection angle (sometimes called auswehwinkel after the German word for this angle) is shifted in a direction opposite to the deflection of the tab.

You could do the same with springs along the control rods, or a mass somewhere which pulls the control surface to the same force-free angle. But when speed changes, so do the aerodynamic forces, and your force-free angle will change. The forces caused by the tab change with airspeed, so the force-free angle set by a tab is unaffected by speed.

Don't confuse a trim tab with a Flettner tab: The trim tab stays at the same angle with varying control deflection, while the Flettner tab will move in opposite direction to reduce the stick forces caused by the deflection of the control surface. By setting the zero-deflection position of a Flettner tab, it can in parallel work like a trim tab and shift the zero-force deflection angle to the desired point.

Small aircraft like the Diamond Katana even have an anti-Flettner, where the tab is moving in the same direction as the control surface in order to increase stick forces. This is needed to fulfill certification requirements.

In practice, a combination of both springs and tabs is used to set the desired control forces and their gradient over speed.


As a commercial pilot, can I fly my spouse for her work?

The prohibition you're worried about as a CPL is "holding out" flight services to the general public, which can be summarized as providing both plane and pilot as a package to strangers.

In this case, you would be providing both plane and pilot, so your concern is understandable.  However, there is a clear personal link from you to your wife and via your wife to her employer, i.e. they're not the "general public", so you're okay.  It would even be okay if your customer were a bona fide friend, rather than your wife or her employer.

If the company could rent (or otherwise provide) the plane and separately pay you to fly it, you wouldn't need that personal link.  Given you're renting from a flying club, that's not possible, but it's something to keep in mind for future scenarios.  Do check with the flying club to make sure it's okay with them and their insurer.  I assume you have the appropriate insurance for yourself.

The pro-rata stuff only applies to a PPL, and given the FAA's policy that flight time and even employer goodwill can count as "compensation" even if no money changes hands, a PPL could still get busted even if they "eat the costs" as you propose.  As a CPL, though, you don't have to worry about that, just the "holding out" rule.


What are the differences between Bearing vs Course vs Direction vs Heading vs Track?

This is how I explain it, hopefully it helps more than hinders!

Heading:
This is where my nose points - and seeing as my nose is attached to my head, this is where my head (and thus my machine) is pointing relative to North.

Course:
This is my INTENDED path of travel that I have calculated taking into consideration winds, variation and declination.

Track:
This is my ACTUAL path traveled over ground - just like a set of tracks I would leave behind in the snow or sand, relative to North

Bearing:
This is the angle between the location of an object, machine or destination and either:
- my heading. This is called 'Relative Bearing'.
- or magnetic  north (direction toward the magnetic north pole). This is called 'Magnetic Bearing'.

So from the picture, if I take off from Springfield enroute to Shelbyville. My course (the intended path) is due East, or 090 degrees. I notice my winds are Southerly (from 183 degrees / to 003 degrees), so I make my heading 095 degrees to compensate for wind drift (or 5 degrees crab into the wind).

If my calculations are bang on, my track should be the same as my course, however I misjudged the winds, finding out my resulting track over the ground is 081 degrees - I must correct (by increasing) my heading to get back on course.

Now with some airports, the navaids (NDB or VOR) are not directly at the airfield but some distance away, so if I wanted to either fly directly to the NDB or figure out my position in space during enroute nav checks, I would take the bearing to the NDB/VOR either relative to my heading or relative to magnetic north to find its position.

Hope this helps.


Can a pilot with an ICAO Multi-Crew Pilot License fly an airliner into the U.S.?

The MPL doesn't allow the holder to fly as Pilot-in-Command, although in a pinch he probably could do it.  It's a basic ticket to allow a non-ATPL pilot to fly as a fully qualified crew-member of an aircraft that otherwise requires the full ATPL ticket.  Elsewhere the pilot would likely be accumulating only solo experience, and he won't be much use when transitioning to a multi-crew airplane.  The MPL only allows the holder to act as copilot, 2nd officer (flight engineer) or cruise pilot, not as PIC, on any flight including to the USA. Where it's used, the MPL holder will be granted his ATPL when he completes any additional regulatory requirements and has accumulated the required hours. The MPL pilot is entitled to fly in his aircraft as co-pilot from anywhere outside the USA into the USA, although not in a USA-registered aircraft. Some pilots start their MPL training after completing A PPL or CPL beforehand.


Is there any data repository of discontinued commercial routes?

departedflights.com has a list of historical routes both by airlines and (a few) hubs. Though it is not complete, it has a lot of data.


How to navigate an aircraft without GPS?

The question you should be asking is rather, how did airliners navigate before the widespread adoption of satellite-based navigation systems such as civilian GPS?

One can navigate by way of landmarks (as is typical in low-altitude VFR general aviation), but more typical in commercial aviation in the absence of GPS would probably be to navigate by either inertial navigation, or by radio beacons. There are or have recently been several systems that can be lumped together as "radio beacons", such as for example NDB, VOR/DME and ILS, which are used for different purposes, and have different strengths and weaknesses. Until recently, another such system was LORAN.

Major airports typically offer a number of radio beacons that can be used for locating the airport, and there are normally waypoints, sometimes associated with radio beacons of their own, along which a route can be flown even without external references (such as in instrument meteorological conditions, IMC). 757toga's answer to this question shows what such a navigation system for long-distance flight can look like.

GPS does make it easier to fly the most efficient route possible under current conditions, but it is hardly required in order to fly some route from one airport to another. Being prepared to fly without GPS might, in the simplest of cases, simply mean that you plan for a slightly less direct route and treat your non-GPS navigational aid equipment as required, possibly even primary, rather than secondary or nice to have, since you know there's a clear risk of losing GPS through no fault of your own or of the onboard equipment.


Jessica Cox explains it herself in this video:

https://www.youtube.com/watch?v=b2IqpPSF9-U

She's using her legs in place of hands (I.e, using her feet to manipulate the controls, throttle etc) and she specifically flies an Ercoupe which has no rudder pedals.


How does thrust reversal work on a jet engine, and when should it be used?

The engine does not move, the air flow is only redirected. The method of redirecting the flow varies with the size, configuration, and manufacturer of the engine. The flow does not need to be directed completely forward; the flow is generally mostly outwards and partially forward. This is still enough to create significant drag and slow the aircraft down.

In smaller and older engines, the entire flow is redirected. This corresponds to the first two configurations below. Buckets or clamshell doors close over the jet flow to redirect the air.

In larger engines, particularly high-bypass turbofans, only part of the air is redirected. This corresponds to the last configuration below. The core air from the engine still exits normally, but the bypass air from the fan is redirected. Since the bypass air on these engines is a much greater flow than the engine core air, this results in a net reverse thrust. There are multiple mechanisms, but the general idea is to deploy doors that block the bypass air and send it through the sides of the engine cowl.

Turboprop aircraft just change the pitch of the propeller blades such that the propeller pushes air forward instead of backward. The pitch in which the blades provide reverse thrust is called the "beta range."

In civil aircraft, reverse thrust is only used when on the ground. There are typically interlocks in the system that prevent the thrust reversers from deploying if the aircraft does not sense that it is on the ground. Once the aircraft touches down, the pilot will deploy the reverse thrust. Some military aircraft like the C-17 can use reverse thrust in the air. This enables them to perform very steep descents.

Reverse thrust is more of an "optional" method of braking (see this related question), only to provide extra stopping power when needed. This particularly helps when braking force is less effective, such as in rain or snow. Before landing, pilots will take into account the wind, aircraft weight, runway length, and any contamination of the runway (rain or snow). Based on this they will know what kind of braking force is needed and whether they should use thrust reversers.

The thrust reversers don't always have to be operational for an aircraft to fly. Some operators choose to disable them, which decreases maintenance costs. The thrust reversers can also break, in which case they will be mechanically locked to prevent them from deploying until they can be fixed. Pilots will consider this when they are computing their landing distance.


Is there a standard that defines all Special Service Requests?

... however, I can't find a reference to where IATA would publish these codes.

You can find it here.

Before committing to the purchase of the document, check the free Table of Contents to make sure it has what you want.


What are the typical lift, lift coefficient and drag coefficient for a A320 in cruise?

In s/l flight, weight and lift are practically equal, so  –if those are metric tons– the lift will be 72000 x 9,8 = 705600 N. Now, concerning the CL, we may solve for CL the expression for lift:

$C_L = \frac{2 · L}{\rho V^2  S } $

$C_L = \frac{2\cdot9.8\cdot72000} { 0.366 · 230^2 · 122.6 }$

$C_L = 0.595$

Now, assuming a L/D of 15, the CD = 0,594/15 = 0,039


What are the pros and cons of having canard control surfaces versus a horizontal tail control surface?

For statically stable aircraft, the canard is a spoiler in disguise. It will create a strong downwash right behind itself, coupled with an upwash outward of $\pi$/4 of its semispan. With changing angle of attack and lift coefficient, the vertical position and the strength of both up- and downwash will change, so the wing incidence variation over wingspan can be made right for just one angle of attack.

Pros

The force to effect flight path changes works the right way, so pitch response times of canards are slightly better than those of a conventional configuration.
The wing can be further aft, so in short business jets the cabin might not interfere with the wing spar.

Cons

The induced drag at off-design points is higher than that of a comparable conventional configuration.
The bigger lifting surface must keep some stall margin, so the total lift coefficient will be smaller than that of a comparable conventional configuration. In the end, a canard will need more wing area.
Control surface deflections will add to the already high lift coefficient of the canard plane, increasing lift demands on the surface with the smallest margins.
The highest lift coefficient is needed at the surface with the smaller Reynolds number. Normally, the reverse would be better.
If the engines are mounted below and ahead of the wing, they will be hit by the wake of the canard, reducing intake efficiency and compressor stall margins.
To make sure that the control surface will be the last thing on the plane to run into compressibility problems, it should have less lift coefficient and more sweep than the wing. In the end, a statically stable canard will have a lower cruise Mach number than a comparable conventional configuration.
The landing gear must be made to retract into the fuselage, because the wing is too far behind the center of gravity to allow the gear to retract into the wing.

I could go on, but I guess you see by now where this is heading …


How common are 400Hz supplies in aircraft?

In modern military and commercial aviation, aircraft power is 3-phase 115V at 400Hz (AC), and 28V DC.  This is standard just about everywhere.

AC power is 3-phase 115V AC at 400Hz (alternating current).  When the engines are spinning, this power is produced by onboard generators (alternators) feeding redundant power buses.  On the ground, this is typically sourced from a ground power unit (GPU).  During emergencies, AC power may be produced by an auxiliary power unit (APU).

DC power is provided by converting a portion of the 115V AC power to 28 volts DC for powering many of the avionics systems and charging the aircraft battery.

EDIT: My apologies, contrary to my original answer (I was thinking powering the cockpit displays/indicators mostly), a lot of navigation and pitch/attitude sensors take 26vac/400Hz input power.  Rate gyros, compass, flux valve, etc.  See, e.g. this section from a Cessna Citation.


How does hydraulic actuator servo valve feedback work?

The actuator in the first picture is a position follower system and only works as intended if the servo valve is closed as a consequence of the resulting piston displacement. The system in the picture works if the cylinder end is connected to the flight control surface (the left eyelet with the cross in it) and the piston end is connected to the structure frame. The key for understanding is the shift in the centre of rotation:

The servo valve is closed when the summing bar is vertical.
At first, the cylinder is stationary and the pilot deflects the stick, rotating the summing bar about the lower hinge and opening the servo valve. (Black dotted line).
While the pilot keeps the stick stationary, the cylinder moves in response of the servo valve opening. If the initial deflection was to the right, the piston moves to the right. The centre of rotation is now the top hinge (mechanical input).
When the summing bar becomes vertical again at the point where the pilot now holds the stick, the servo valve closes. (Red dotted line).

The second diagram does not show how the cylinder is attached and where the mechanical input is connceted to at the botttom. It could be a position follower system or a simple velocity output where input deflects the servo valve, oil starts to flow as long as the input is open, and the output end moves with a speed proportional to the input deflection. If the lower "First Mechanical Connection" is attached to the moving surface and the cylinder is free to move, we get a mechanical position follower again.

The mechanical feedback provided by the summing link was how the first generations of hydraulically operated systems worked. Nowadays controllers are electronic, not mechanical: a position transducer measures cylinder output, and adjusts servo valve input in response to the control laws programmed in the controller.


Smooth descent at 1500 feet per minute from 30,000 to 11,000.  Nothing unusual.
Or was there a blip somewhere in the data that I scrolled past?  (Where?)

Edit: The blip at 13:16 is from 36,000 to 29,600 and back, in less than a minute.  A 12,000 fpm dive followed by a 12,000 fpm climb (and vicious G force at the pull-up) is probably impossible for an A320-232.


When filing a VFR Flight Plan, where/how do you include intent to use a Class B transition?

Since VFR flight plans are only used for SAR, and your route would only matter if you aren’t talking to ATC, I would file the route you intend to take if ATC denies you the B transition—or refuses to talk to you entirely.
If they do talk to you and grant the transition, then there will be a clear record of your actual path, and nobody will bother to look at (that part of) the route in your VFR flight plan. Or any other portion of your route where you have Flight Following, for that matter.
Note that, for calculating ETE and required fuel, Murphy’s Law says you should use whichever route is longest.
If you’ll be getting a WX briefing, mention the possible diversion to ensure your briefer checks that area too, but realistically, you won’t get in if there’s anything there serious enough to matter.


What is the difference between static and dynamic stall?

Static stall is what we typically think of, when we think of stall. Slowly increasing AOA and then loss of lift as the flow separates.

But pitch rate (rate of increase of AOA) has an impact too. At high pitch rates, the wing can go beyond normal stall AOA and still provide significant lift, but for just a short period of time. After that, the bottom falls out. This is dynamic stall.


How far back from the final approach fix can you intercept the glideslope?

From the navaid limitations section of the FAA Order 7110.65 (below), it's 10 miles from the transmitter. For the minimum altitude, it's shown on some charts as a lightning bolt.


Is it possible for an airliner to safely fly with doors open?

The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a modified 747 that has an 5.5 m x 4.1 m door that is opened during flight for the installed in infrared telescope. But the door is usually closed during takeoff and landing.

But according to this story there are emergency procedures to land with an open door and it had to do so once, when it became stuck half open.

Images courtesy Wikipedia


Is there a downside to trying multiple flight instructors?

No. Definitely try more than one CFI and ideally, more than one school. This is the smart choice and one I recommended regularly when I was an active flight school CFI.

You're about to spend a ton of money - do the due diligence and spend more up front to make sure you don't waste time and money with someone whose teaching style or personality clashes with you as a student.


How are "preferred routes" assigned if there is more demand than capacity on a route?

Air traffic services (at least in the US) are handled on a first come first serve basis. That's the overarching protocol. Beyond that, it's situation dependent.

In the air, controllers give pilots what they want if possible. In practice the situation is quite fluid. Maybe all three can't go on the same path now, but in a minute there will be enough clear airspace to make it happen. Or maybe they go on a route very close to but not exactly what they requested.

If (for some reason like a prominent jet stream) many airplanes are filing the same (or very similar) flight plans so that certain airspace will be overwhelmed, there is an entire division of the FAA dedicated to deciding where and when aircraft need to be rerouted. Here's some info @mins linked to in a comment.

Also, your question seems to assume competing airlines. For all ATC cares, A, B, and C could all be flights of the same airline.


What equipment do you have to have for ADS-B? Mode A/C transponder
  only or do you also need Mode S too? Is ADS-B tied into Mode S or are
  they completely 2 different components?

Either a mode S transponder with Extended Squitter (the ES broadcasts the ADS-s data) which broadcasts on 1090 mhz or a UAT (universal access transceiver) broadcasting only ADS-B data on 978 mhz. Both transmissions are received by FAA ground stations and the aircraft is placed in the ATC computer system where you see the ADS-B info.

  Do you need a Mode S transponder to fly? (I think from what I read
  Part 121 ..commercial you do, but not required for GA if inside the
  US)

yes, the advent of ADS-B does not change any requirements for transponders. Someday maybe but not now.

  What is an Example of an ADS-B "code" ? ....to clarify...If it is
  registered to the tail number, I would assume you have to register a
  specific "code" to tie the 2 together.

All ADS-B transmissions must output the same transponder code value that the pilot has dialed into the transponder. All ADS-B equipment has some sort of interface the determine Transponder code and that code goes along with the ADS-B transmission.

  Is the ICAO hex number the same as the ADS-B number/code?

ADS-B equipment broadcasts transponder code, ICAO hex, and the pilot's choice of flight ID or N number. There is something called anonymous mode and I'm not sure what's sent while in that mode.

  I ask about ICAO hex because I see some ADS-B equipped GA with hex
  numbers in the system and some do not have hex numbers but still
  verified ADS-B equipped. I want to know if they are both needed!!!

I've installed approx. 25 ADS-B units in small GA aircraft and every configuration I've seen has a entry for ICAO address. It's possible that you've seen improperly configured units or maybe there's something about it I don't know.

  @jScarry> I’m confused about your premise. Why would a pilot call ATC
  to verify

    that their ADSB is working?

The A in ADS-B stands for automatic so it works without any control input from the pilot whatsoever. Its just always on without having to actually turn it on. Consequently, he has no real idea whether or not it is working other than the possible absence of a fail message... so he calls ATC to ask him if his ADS-B is showing up or not. Most likely this is his first flight after the install and he just wants to know that he's showing up and that his $7k is actually doing what it's supposed to.


Why does the F16 HUD give you one number for your speed and the analogue gauge another?

The primary airspeed indication is in the HUD. You can select CAS (calibrated airspeed), TAS (true airspeed) and GND SPD (ground speed) on the HUD panel on the right console.

The backup airspeed indicator (the analogue gauge you are referring to) is located below the ICP (integrated control panel) on the center console. It can indicate from 80 kt to 800kt with a scale in 10 kt increments up to 400 kt and then 50 kt increments up to 800 kt. It is a rather basic analogue instrument providing IAS (indicated airspeed) only.

As the scale is very coarse (higher precision is not needed) you won't be able to see a noticeable difference when the HUD is switched to CAS. Most probably the HUD was switched to TAS or GND SPD. But without further information or an example photo from your side it is hard to tell.


What is the difference between deice and anti-ice?

De-ice is a system that removes ice that has formed on a part.

Anti-ice is a system that prevents ice from forming on a part.

A heated leading edge(bleed air) is an example of an anti-ice system.

A inflatable boot on a leading edge is an example of a de-ice system.


How are foam cores shaped for tapered and swept back wings?

I'll assume you're already researched the methods for hot wire cutting foam blocks in the Rutan moldless method and are familiar the hot wire tool and airfoil templates you make and the template cutting process.
You can do it two ways; make hotwire templates with the longitudinal axis airfoil contour (the stretched airfoil shape resulting from the sweep) to stick on the end of the foam blocks that you have already truncated with the 10 degree sweep, or make the templates to the airfoil profile perpendicular to the mean chord line, stick them on to the blocks with square ends, and truncate them to the 10 degrees sweep angle after you've cut them out.


Why are some ATC call signs different than the flight number?

It's a solution to the Call-sign Confusion.

  Many large airlines operate call sign de-confliction programmes. These involve reviewing company call signs to ensure that aircraft with similar call signs are not likely to be routinely in the same airspace at the same time, and a process to systematically resolve ongoing issues arising from reports of similar call signs from their flight crew, ANSPs or other operators.

In busy airports, it's very common to have many flights with similar [sounding] call-signs (ATC perspective). You'd often hear the ATC stress the intended target.

Potential effects are:

  Loss of communication, loss of separation, level bust, AIRPROX, or midair collision.

However, passengers expect their bookings to be numbers, hence the split between ICAO call-sign (air traffic control) and IATA flight code (booking). From a marketing perspective, a changing IATA flight number isn't good for the customers and booking systems.

Taking TK656 (THY3YE) as an example, we also find TK65 and TK56. If one of those three were to return (emergency) or be delayed, it will add unnecessary confusion if it meets one of the others. There could very well be other operators with similar numbers in and out of Istanbul as well.

  Solution:

  Large operators should routinely consider using a combination of numeric and alphanumeric call sign formats.

  Guidelines:

  Avoid the use of similar call signs within the company
  Where practicable, proactively co-ordinate with other operators to minimize similar numeric and alphanumeric elements of call signs
  Avoid call signs with a four-number sequence; all-numeric call signs should be limited to a maximum of three digits
  Do not use the same digit repeated more than once (e.g. RUSHAIR 555)
  If letter suffixes are to be used with a preceding number sequence, limit the full string to a maximum of four alphanumeric components and, to the extent possible, coordinate letter combinations with other airspace and airport users
  Do not use alphanumeric call signs which have their last two letters as the destination’s ICAO location indicator (e.g. RUSHAIR 25LL for a flight inbound to London Heathrow)
  Where the total number of flights operated is large, it is likely to be best to use a combination of wholly some numeric and some alphanumeric call signs rather than all numeric or all alphanumeric
  If similarly-numbered call signs are unavoidable within a company, allow a significant time (at least 3 hours at any shared-use vicinity) and/or geographical split between aircraft using them
  If it is considered that useful capacity in the allocation of call signs has been reached, then consider applying for and using a second company call sign designator
  Do not use similar/reversed digits/letters in alphanumeric call-signs (e.g. RUSHAIR 87MB and RUSHAIR 78BM)
  For short haul flights, avoid using number sequences for particular routes which begin the day with ..01 and then continue sequentially through the day.

  —skybrary.aero [edited for proofreading]

Note: unlike the US, in Europe and elsewhere pronouncing numbers in a call sign requires saying each number individually, e.g. four-three-one-one, and not forty-three-eleven.


Difference between constant speed and variable pitch propellers?

Your understanding is essentially correct.  A constant speed prop is governed.  A variable pitch prop is not.

Constant speed props are also variable pitch.

A constant speed prop will only maintain speed if there is sufficient power from the powerplant.

Most constant speed props will require slight tweaking to maintain the rotational speed during a flight.

Constant speed props require a governor, and the flyweights are a component of a governor.


What are the implications of no longer requiring a complex aircraft for the commercial/CFI checkride?

First, as Ron pointed out (and as the FAA Notice you quoted says), you still need 10 hours complex (or turbine) training time for a commercial single-engine certificate. The only change is that you no longer need to do the checkride in a complex aircraft.

Your main question seems to be if it will eventually be possible to instruct in a complex aircraft without having any complex experience. That could indeed happen if the FAA ever implements a proposal to allow Technically Advanced Aircraft (TAA) time as an alternative to complex time for commercial single-engine. Then you could fly a Cirrus (or another fixed-gear TAA) instead of something complex and become a CFI with no complex experience. That proposal requires a change to the regulations so it's a bigger deal than just changing the ACS and it hasn't happened yet.

But, it's already the case today that instructors don't need to be endorsed in the aircraft they instruct in: if they aren't acting as PIC then they don't need to be qualified as PIC. (Whether doing that is a good idea or not is another issue.) So instructors without endorsements wouldn't be a new issue at all, although it might become a more important and common one.

However in reality, insurance often determines what an instructor can do, not the FAA. I fly a C182RG, which is a complex aircraft, and the insurance policy specifies the experience requirements for instructors who use it. In a hypothetical future where you can become a CFI with zero complex time, you simply wouldn't meet the insurance requirements to provide instruction in that aircraft. I know insurance isn't mandatory anyway, but for CFIs and other professionals it's often the deciding factor in what they can and can't do.

As for unintended consequences of this change, I have no idea and we can only speculate. For example, complex single-engine aircraft prices may fall as flight schools sell them off.


What is turbulence, and how does it happen?

Air turbulence is very much the same as the currents of a river.

When a parcel or stream of air moves differently than the area around it, you get turbulence as you transition between them.

An example would be if you are outside on a windy day but stand behind a tree to "get out of the wind".  If you step out from behind the tree, you will feel a sudden "jolt" as the wind hits you.  If it's a particularly strong wind, it could even cause you to lose your balance for a second until you compensate for it.  Well, these invisible air currents affect an aircraft in much the same way.

It isn't normally dangerous, and I think of it like driving down a bumpy road.  Of course, it's usually even safer in an airplane because even if you hit a big "pothole" you don't have to worry about it throwing you off the road into a tree.

The actual movement of the air can be caused by several things:

Wind hitting something (like a building or a mountain) and displacing it (just like rocks in a river).
Air being heated by the ground which then causes it to rise.
Weather activity like fronts, thunderstorms, or jetstreams.
An aircraft moving through the air will cause turbulence of its own (known as wake turbulence).


Why are Vertical tails generally tapered?

The vertical tail and the horizontal tail are wings, and follow the same construction rules. The span-wise lift distribution is much better if the wing is tapered: more lift at the root, less at the tip.

The wing can be built lighter, root area is larger, torsion stiffness is higher.
Vortex induced drag is lower.

As a reference, from Torenbeek: pages 232 & 233

  It is observed that nowadays there are basically three forms of straight wings: the tapered wing, the untapered (rectangular) wing and the wing with a prismatic inner portion and a tapered outboard portion.

About taper for wings (and for tail surfaces):

  Tapered wings have been adopted for the majority of aircraft since they offer an efficient solution on account of their low induced drag, high maximum lift, low structural weight...(and) acceptable stalling characteristics can be obtained, provided the wing is not too sharply tapered.

Untapered wings are inferior and cheap:

  The untapered wing is attractive from the point of view of manufacture, since only one airfoil contour is involved; this simplifies jigging as there are no compound curvatures. It is aerodynamically inferior to the tapered wing, but may nevertheless be the logical choice for inexpensive private aircraft, where the utilization factor is low and initial cost and cheapness of components are important.


What are the differences between type B message format and EDIFACT message format?

There are many types of messages which are used very specifically within the aviation Industry and TypeA and Type B are the most notorious ones.

Its not the message format that differentiates them , its the characteristic message delivery and response that does.

Type A - Expect immediate application response, have timeout handling in place at the application level, delivery is not guaranteed and could expect loss of messages. EDIFACT is one of the well known industry accepted and following TYPE A message formats..

Type B - Guaranteed delivery and will make anything and everything possible to deliver the message . Does not expect an immediate response back.

Regarding the format of the messages, the type A message formats are governed by PADIS ( PASSENGER AND AIRPORT DATA INTERCHANGE STANDARDS MESSAGE STANDARDS DOCUMENT). It does differ for each applicaiton( reservation, ticketing, DCS etc). Here is a sample one for PNRGOV standards.

https://www.iata.org/iata/passenger-data-toolkit/assets/doc_library/04-pnr/PNRGOV%20EDIFACT%20Implementation%20Guide%2013_1.pdf

For TYPE B , always refer to the AIRIMP documents which governs the TYPE B mesasge formatting..

Here is a sample of the same..
ftp://ns.tais.ru/pub/doc/AIRIMP34.pdf

Thanks,
Jothi


The canard is a design which stabilizes in front but also adds lift, whereas elevators at the back actually subtract lift.  As the Voyager needed to take energy efficiency to the extreme, this would be a prime design choice.  His motivation may be in the book written about the Voyager, but a significant number of his designs were canards.


Why did my instructor recommend that I fly a Piper Seminole down to the runway rather than trying to flare it like a Cessna?

I'm guessing that is a landing technique that your CFI has developed for handling a Piper Seminole on landing.  Don't worry; everything is fine.

Most likely this is because the PA-44, like it's single engine cousin, the PA-32 and late model Cherokee Arrows rapidly loses energy and sinks quickly once the power is pulled out.  These tend to be the landing characteristics of larger, heavier aircraft.  Cutting the power too early in the approach to roundout could cause this aircraft to slow and drop rapidly leaving a neophyte student with little energy left to flare to a smooth touchdown.  The CFI is trying to make you cognizant of that fact; I'm sure he's endured plenty of firm landings by students with high time in C152s or C172s flying final at 65 KIAS, then chop power over the threshold markings (piano keys) to arrive at a good flare and touchdown; that technique won't work in larger twins and the best way to fly a shallow glide slope is to do so with power, then pull it out just as you begin the flare about 7-10 feet off the runway.  The airplane should then settle into a nice flare 1-2 feet off the runway, quickly exhaust all of its energy and touch down on the mains just as you hear the stall warning tone.

Another factor is the aerodynamic slipstream from the propellers. As wing mounted tractor engines push air over the wings behind the propeller disks, this, in turn is generating additional lift.  During a stabilized approach, this airflow become part of the lift the wing must generate in order to remain on speed at the selected rate of descent.  When the pilot pulls throttles to idle as part of the roundout process, this additional lift is terminated.  Combined with the high drag from the idling low pitch propellers, this causes the airplane to slow down and sink very rapidly; you will feel this in the seat of your pants if you pull the throttles out too early.  If a student pilot remains ignorant of this effect and does not compensate for it, you may be in for a very hard landing or worse.

The Piper aircraft, as you have found out, are designed to put up with a lot of sloppy handling from a new pilot and still shine.  The controls have all the finesse of a Mack truck and they really have to be manhandled to fly them.  IMO it's an attempt by the manufacturer to 'idiot proof' the airplane and make it safe and marketable to a wide range of pilot skill.

All tricycle gear aircraft should be flown to the roundout such that once the flare is established, the airplane should run out of energy and quit flying rapidly.  Strict adherence to a controlled approach speed of 1.3 Vso on final should be used (on small aircraft), but the rate at which the airplane slows and descends when the power is reduced to idle varies between airframes.  Some airplanes do this faster than others; each one has it's own unique handling characteristics and you will have to become familiar with them as you progress through different aircraft.

One note on you flying: for a VFR traffic pattern, aim for the numbers or use an optical glideslope (eg VASI, PAPI, etc), if available, on final until you have become proficient with flying the PA-34.  The 'chevrons' are a blastpad and frangible arrestment for stopping an overrun and are not designed to support an airplane during normal flight operations.  Touchdown too early and end up on the blastpad, it is possible the aircraft could break through and cause damage to the airframe, props or landing gear.  You're also likely to clip other objects like runway threshold lights with that kind of a landing.


What are the "parts" of a SID procedure?

FAA Order 8260.46F - Departure Procedure (DP) Program describes "... the policy, guidance, and standardization for initiating, developing,
processing, and managing the Departure Procedure (DP) Program."

Your questions are broad-based, but Order 8260.46F should provide the answers you are looking for.

Here are two figures from Order 8260.46F.  These figures are accompanied by descriptive text and illustrate the type of information in the Order which should be responsive to your questions:


How is device control software checked for quality?

I've worked on some certified software in a different domain (and slightly less strict); the principle would be similar here.

Basically the certifying authority will want to make sure that proper risk analysis was done on the system—both software and hardware—and risks were mitigated to get to certain level of reliability.

The authority does not have programmers to actually review the code. They will be checking the requirements, the test coverage, records that all procedures were followed. All code must be traceable to requirements that caused it to be written, tests that cover it, there must be records it was reviewed, that all the tests passed.  All requirements must have their tests, then there have to be various stress tests, exploratory tests, the test plans have to be reviewed. There will be various static checks too and guidelines to follow. It is a massive amount of paperwork to make sure risks were not missed.

And then the required estimated mean time between failures for critical systems is so insanely low—IIRC for critical systems the mean time between critical failures must be (estimated) at least 10⁹ hours—that there is simply no way to demonstrate it by tests alone. Even the hardware won't have that reliability—it is hundred thousand years. So the system has to be designed so that it can fail safe and fail over to a backup and then the mean time between failure of all the systems during single flight is what gets above the target.

So there is procedure, but the maker does it and the certification authority only verifies that it was followed.

The safety critical code is indeed usually written in C, or sometimes C++ or Ada. However, safety critical, and any other hard real-time, code must be written with use of static memory only. This eliminates large class of problems that C code is normally known for, and the simplicity of C makes it easier to statically check—and the makers of critical software have powerful advanced tools for doing it—, so it is actually quite good fit.

The code still actually tends to be pretty ugly. It is hammered heavily with the tests, but when fixing issues found, preference is to do smaller changes to avoid breaking other parts that already passed the tests, which adds to its ugliness. Nobody thinks its perfect either, but that's not the point. The hardware is not perfect either, so the backups, fail-safes and fail-overs are designed to handle both kinds of failures.

And note that the current Boeing issue is actually a problem with the requirements. The trim system may run away for example if the switch gets stuck, which is always a risk with mechanical switch, so there must be a cut-off switch to disconnect it. And, judging from the public information only, it seems whoever designed this system argued that that cut-off switch is sufficient to handle failure of the new addition too, so the system was not considered critical and fault detection was not included in the requirements for it. But in doing so they apparently underestimated the human factors involved—specific details will be subject to analysis in the investigation and it is what usually takes so long.

Update: The article about the recent B38M crash (ET-302) links to an FAA document FAA and Industry Guide to Product Certification that gives overview of the whole process. It is not particularly about software, but the general process still applies to that.


Why does the FAA SPL require different endorsements depending on cruise speed?

When looking at the rules on ecfr.gov you will find references at the bottom of the paragraph indicating the Amendment, Federal Register notices, and other documents related to the rule.

In this case it leads to the following FAA doc.  That document includes the following explanation for the rule;

  II.B.5. REQUIRE 1 HOUR OF FLIGHT TRAINING ON THE CONTROL AND
  MANEUVERING OF AN AIRPLANE SOLELY BY REFERENCE TO INSTRUMENTS FOR
  STUDENT PILOTS SEEKING A SPORT PILOT CERTIFICATE TO OPERATE AN
  AIRPLANE WITH A V Current regulations require student pilots seeking a
  sport pilot certificate to receive and log flight training in the
  control and maneuvering of an aircraft solely by reference to flight
  instruments. This training must be received before conducting a solo
  cross-country flight or any flight greater than 25 nautical miles from
  the airport from where the flight originated. It also must be received
  prior to making a solo flight and landing at any location other than
  the airport of origination. These requirements are detailed in § 61.93
  and are applicable to persons seeking a student pilot certificate to
  operate any category and class of aircraft. That section, however,
  does not specify any minimum flight training time to meet these
  requirements. In addition, current regulations for the issuance of a
  sport pilot certificate do not require an applicant to receive flight
  training on the control and maneuvering of any aircraft solely by
  reference to instruments. The FAA is concerned that persons exercising
  student or sport pilot privileges in airplanes with a maximum airspeed
  in level flight with maximum continuous power (VH) greater than 87
  knots calibrated airspeed (CAS) may inadvertently encounter conditions
  less than those specified for VFR operations due to their greater
  speed and range. Operators of these aircraft are more likely to
  encounter instrument meteorological conditions than operators of other
  categories of aircraft. In order to enhance the ability of these
  pilots to appropriately react to the possibility of encountering
  instrument meteorological conditions and the potential consequences of
  attempting continued visual flight rule (VFR) flight in instrument
  meteorological conditions, the FAA is proposing to require persons
  operating an airplane with a VH greater than 87 knots CAS to receive
  and log 1 hour of flight training on the control and maneuvering of an
  aircraft solely by reference to instruments. The FAA recognizes that
  persons may currently be authorized to operate aircraft with a VH
  greater than 87 knots CAS. To provide those persons with a reasonable
  period of time to obtain this training, the agency is proposing that
  the training be completed by 1 year after the effective date of the
  final rule. This training would include straight and level flight,
  climbs and descents, turns to a heading, and recovery from unusual
  flight attitudes. Due to the slower speeds and limited capabilities of
  categories and classes of aircraft other than airplanes, the FAA is
  not proposing that this requirement be extended to operators of those
  categories and classes of aircraft and airplanes with a VH less than
  or equal to 87 knots CAS. The FAA notes that for training to be
  conducted solely by reference to instruments in visual meteorological
  conditions, it must be conducted with a view-limiting device.

My take is that earlier rules covered the conditions with VH less than 87 KCAS.  The FAA felt it was necessary to add rules to cover flight at the higher airspeeds.


Why is the Mooney's signature tail profile different from most planes?

The best explanation I've heard is that at high angles of attack the rudder is nearly vertical providing the pilot better yaw authority.  I don't know whether this is true or not but it makes for a good story, doesn't it?

The story goes something like this:As the plane pitches up, the rudder, being slanted "forward," moves closer to a vertical position and provides better directional control at low speeds.  Conversely, at high angles of attack a swept tail (and rudder) moves further away from a vertical position and is, in theory, less effective.

Some go on to speculate that the leading edge of the vertical stab, being un-swept, protrudes further into undisturbed airflow at high AOA/low airspeeds which may slightly enhance the pilot's ability to control yaw at the edge of a stall.

I've never spun a Mooney (I did complete my CFI in an M20F/201) nor do I have a burning desire to do so.  I imagine that it's not a friendly spinner.  Catching the spin early would be critical in a slippery air frame like a Mooney.

A brief online search of Mooney tail lore yields everything from pure marketing to discussion of wetted area to better directional control during landing to spin recovery/prevention to "those swept tails provide no speed benefit and are simply designed to look good."

Here is one discussion (of many) on a Mooney forum regarding the tail design: http://mooneyspace.com/topic/9905-mooney-tail-aerodynamics-not-backwards/

I doubt very much that it's simply a marketing gimmick (although, it could be as simple as that!).

I believe that the explanation I've relayed here is merely "somewhat plausible" as it was gleaned from hours of beer-fueled hangar talk and some Google searching...not exactly a scientifically rigorous method of research.  I have no credible references and, as far as I know, no data exists to back any of it up.


What are the lettered and numbered signs next to airport runways and taxiways?

From left to right in your image

  16 CAT II / III

Refers to the runway number, and also the ILS Category that particular runway supports. However that is just secondary information. The primary purpose and position of this sign is actually to indicate the hold-short position for the numbered runway.

  E6 34/16

Refers to the taxiway designation (E6) and the runway(s) it leads to (34/16 being the same runway 34 one way and 16 the other)

  {Unreadable} and E6 L→ 10→

Both of these signs are the same, one is pretty much unreadable the other is again on taxiway E6 and points that Taxiway Lima (L) is to the right as is runway 10.

Pilots are unable to see these signs on landing, signs like this on taxiways are almost exclusively for ground operations - not just the aircraft but the variety of vehicles that operate on the apron of an airfield.

These signs are equally not useful at the point of takeoff, none of the information presented on them is relevant for that phase of operation.

Pilots will have a "map" of an airfield with them which will indicate the same information as presented on these signs. Ground controllers will typically mention which taxiways to use when guiding aircraft (and other vehicles) using the apron and taxiways. For example, at the airfield pictured the ground controllers may have instructed the pilot that they were cleared to "hold short of Runway 10 via Taxiway Echo 6" or may have told a landing aircraft that they should "clear the active runway at Taxiway Lima".

Here is a graphic that many websites use a variation of:

Source: americanflyers.net


Why isn't the Transition Altitude depicted on SID charts?

FAA

Because it is a fixed value at 18,000 feet.

ICAO-style and Jeppesen

They show the TA (and sometimes the TL) on SID charts.

ICAO Annex 4 confirms the depiction on SID charts (chapter 9):

  9.9.4.1 The components of the established relevant air
  traffic services system shall be shown.

  (...)

  5) transition altitude/height to the nearest higher 300 m or
  1 000 ft;


What is the correct name of this aircraft subsystem in English?

From the product page and Google translate:

  Newton is designed for use in unmanned aerial vehicles (UAVs), civil and special purpose. Designed to determine the parameters of flight and navigation and automatic flight control UAV, payload control and to ensure information exchange with the ground control station (NPU).

  Support RTK technology for high-precision positioning according to the satellite radio navigation systems (SRNS)
  The high accuracy of the orientation angle according to the SRNS
  Possibility of interconnecting with foreign strapdown inertial navigation system (SINS) on the fiber-optic gyro (FOG)
  Possibility of controlling any types of payloads including mode gyrostabilization
  Available in a block of flight and navigation built-in radio for transmission of telemetry and control commands
  The presence in the radio unit built ground goniometric RTK-receiver of the SRNS signals

It's an FMS (Flight Management System) with a capability to connect to an INS.

As for diagrams for the F-35, the general public doesn't know what the F-35 cockpit looks like, let alone schematics for avionics.


Who is the pilot in command when the pilot in command is resting?

The PIC is ultimately responsible for operation and safety, for everybody and everything on board, from pre-flight preparation till post-flight activities.

On long-haul flights there must be a sufficient number of relief crew members to substitute the nominal flight crew. This is regulated in national legislation and implemented in airline standard operation procedures (SOP). Details are apparently different from airline to airline.

The Captain is the highest ranking member of the flight crew, and will be designated as PIC. When the PIC takes a rest, there must be a qualified substitute available. That will be a Senior First Officer (SFO) in some airlines. In any case, the substitute will have gone through a dedicated training.

During the rest of the PIC, the substitute will act as PIC. The sleeping Captain remains PIC, and remains ultimately responsible. If there is an incident during his rest, it would have to be investigated if that incident was (partially) due to earlier decisions, actions or omissions, or if the problem was caused entirely by the relief crew.


Are there any precision approaches that use only GNSS/LAAS?

The FAA has an FAQ on GBAS (ground-based augmentation of GPS/GNSS). It says they no longer use the term LAAS, instead they now use GBAS to be consistent with ICAO terminology. A GBAS approach is called GLS on the approach charts.

The FAQ has information about where GBAS is used:

  Where are operational GBAS systems located?

  Currently, two U.S. locations have obtained operational approval for
  public GBAS use and support revenue airline traffic. These stations
  are located at Newark Liberty International Airport (EWR) and Houston
  George Bush Intercontinental Airport (IAH). Internationally, several
  airports have GBAS and support revenue operations (Bremen and
  Frankfurt, Germany; Sydney, Australia; Malaga, Spain; Zurich,
  Switzerland; and 15 Russian locations).

Newark (KEWR) has 5 GLS approaches, Houston (KIAH) has 6. I looked at a couple of the approach plates and they didn't require any additional equipment apart from the GBAS equipment itself. Note that GBAS is not the same as the 'typical' GPS/WAAS combination used for RNAV GPS approaches, and it requires different equipment:

  Can the same avionics be used for GBAS and WAAS?

  The GBAS and WAAS standards are different and initial avionics and
  integrations only supported one of the two capabilities. Emerging
  aircraft integrations can support both services (e.g. A350).


Your options, as you pointed out, are either to climb over this area, To go around it, to go under it, or wait until the segment expires or is expected to subside.

Another option available would be taken by this information with PIREPS.  What are pilots reporting happened to them in this air space at this time?   The SIGMET noted that there was occasional severe turbulence expected in that area which is pretty vague.  If there are a very large number of PIREPS widespread throughout that block of airspace, it’s a good bet that it is very turbulent throughout and may not be a good idea to penetrate it.  If the PIREPS are few and don’t repeat much turbulence in that airspace, then it may be advisable to fly through.  Just keep the speed at that recommend by the manufacturer for penetrating turbulence and keep the fasten seat belt signs on.


How does a single engine tail wheel landing gear airplane turn when it is on the ground?

The rudder cable circuit is also connected to the steerable tailwheel through springs that provide a compliant connection.  When you push a pedal it also creates a turn in that direction on the ground.

However the arrangement is unstable in the rolling plane.  The main traction elements, the two front wheels, are ahead of the center of mass so the thing wants to switch ends, like pushing a shopping cart backwards.  So there is no rolling self-aligning tendency like with a tri-gear and you have to actively provide "artificial stability" with your feet.

That, plus the kind of laggy response when the little wheel in the back is turned, with a springy connection, means there is usually a little foot dance going on while you are rolling.  When necessary, you use differential braking to help things along if a steering input (a stab on the rudder) isn't having the effect you want.

Once you are rolling above about 30 mph, the rudder itself starts to provide most of your steering control.

Taildraggers take quite a bit more attention and skill to control while rolling, which gives them a bit of cachet that trigears don't, among pilots that are into that sort of thing (like me).

How it all works:  In the exploded image below, Item 6, the steering horn, is connected to the rudder itself and it turns Item 26, the steering fork (or half fork in this case), which has the wheel on it (the springs are to provide some give to the connection to avoid over stressing things when the wheel touches down unaligned with the surface).

The interconnection between 6 and 26 has various parts that make it work a bit like a breakout clutch; 6 can turn 26, but if 26 is turned by an outside force above a certain point, its connection to 6 releases and it can caster or swivel freely until they line up again and re-engage.

So when you are rolling and work the pedals, the pedals/rudder turn the steering horn (Item 6) and it turns the fork (Item 26) with the tire as if they were a single unit and the airplane turns.  If you are nearly stopped and want to spin around to park, you lock one of the brakes and this puts so much side load on the tailwheel it breaks the fork out of its connection to the steering horn and it's free to swivel.

Later when you are rolling straight and the steering horn and tailwheel are lined up, they lock together again and you have steering control back. The internal breakout mechanism has to be set up so the breakout force required isn't too high (hard to make swivel) or too low (starts swiveling freely when you don't want it to).  You don't want it to start swiveling while you are still rolling at speed and using it for steering, or, like shoving a shopping cart backwards, around you go! (It's called a ground loop)

This is a "steerable/free castering" tailwheel and variations of this type of system are used on probably 95% of GA tailwheel airplanes out there.  When steering with this system, brake can be used as required to assist with steering because the steering authority is limited compared to a nosewheel but you generally only  apply brakes if you really have to, to avoid wearing the brakes out (the springy nosewheel connection in a Cessna 150 is similar).


What is ILS CLASS in this airport NOTAM?

This is a change in the ILS Facility Classification code. In your example the code is I/C/2 for ILS with GP, which means:

The ILS category is CAT I
Quality of Course C, which means localizer performance follows performance requirements until 100ft
Integrity level 2 (see ICAO Annex 10, Volume I for details)

The changes can also be found in the Kazakhstan eAIP UAII AD 2.19.
Here is a detailed description of the three codes in the classification by ICAO:

ILS FACILITY CLASSIFICATION AND DOWNGRADING
The  ILS  facility  classification  system  provides  a  more  comprehensive  method  of  describing  ILS  performance  than  the  simple  CAT  I/II/III  classification.  An  example  of  an  ILS  facility  classification  is  “III/E/4”.  ILS  facility  classification  is  described in Annex 10, Volume 1. A facility’s “class” of performance is defined by using three characters as follows:
a)    The first group of characters (I or II or III) indicates conformance to the facility performance category standards contained in Annex 10, Volume I. This character indicates if the ground equipment meets a facility performance Category I, II or III.
b)    The  second  group  of  a  single  character  defines  the  ILS  point  (Figure  C-1)  to  which  the  localizer  conforms  to  the  facility  performance  Category  II/III  course  structure  tolerances.  These  classifications  indicate ILS conformance to a physical location on the approach or runway as follows:

A:    7.5 km (4 NM) before the threshold;
B:    1 050 m (3 500 ft) before the threshold (CAT I decision point);
C:    Glide path altitude of 100 ft HATh (CAT II decision point);
T:    Threshold;
D:    900 m (3 000 ft) beyond the threshold (facility performance category III requirement only);
E:    600 m (2 000 ft) before the runway end (facility performance category III requirement only).

c)     The  third  group  of  a  single  character  indicates  the  level  of  integrity  and  continuity  of  service.  It  is  generally  accepted,  irrespective  of  the  operational  objective,  that  the  average  rate  of  a  fatal  accident  during landing due to failures or shortcomings in the whole system, comprising the ground equipment, the  aircraft  and  the  pilot,  should  not  exceed  $1 \times 10^{–7}$.  This  criterion  is  frequently  referred  to  as  the  global risk factor. In Category III operations, this objective should be inherent in the whole system. In this  context  it  is  of  the  utmost  importance  to  endeavour  to  achieve  the  highest  level  of  integrity  and  continuity  of  service  of  the  ground  equipment.  Integrity  is  needed  to  ensure  that  an  aircraft  on  approach  will  have  a  low  probability  of  receiving  false  guidance;  continuity  of  service  is  needed  to  ensure that an aircraft in the final stages of approach will have a low probability of being deprived of a guidance  signal.  Integrity  and  continuity  of  service  requirements  are  defined  in  Annex  10,  Volume  I,  Chapter 3, 3.1.3.12, for the localizer and Chapter 3, 3.1.5.8, for the glide path.

(ICAO Manual of All-Weather Operations)


How should night time be determined and logged in a fast westbound plane?

I don't think many airline crew actually bother to log the day/night breakdown.

At my airline we have different pay rates for day and night flying, so we do care, but the company "Electronic Logbook" tracks the day/night breakdown for us. The system is not 100% accurate and we sometimes get paid more or less day or night then we actually fly in, but it tends to average out over the year.

In the summer, polar routes can be as much as 15 hour flights of daylight, while the same route in the winter can be 15 hours of night flying.

On some flights we will see the sun set, and then rise, and set again, as we chase the sun and our route changes from northwest bound to southwest bound.

Here are some samples of summer/winter, day/night Toronto to Hong Kong flying in my eLog:


How to maintain straight and level flight after a climb?

Attitude + Power = Performance
Performance is your airspeed, climb/descend rate, and rate of turn.
Attitude is pitch, bank, and yaw.
Power is RPM, if you have fixed pitch prop.

So how do you transition from climb to level flight? When you reach 2000ft, or maybe 1950, push forward on the yoke or control stick to about level pitch, check the altimeter to make sure you're at 2000ft, not climbing or descending.  Your airspeed will start going up. Maintain forward pressure, it is going to increase as the speed increases (you can put some trim in to help).  Once you reach the desired airspeed, reduce throttle to keep the airspeed constant.  Then use trim to take out the pressure on the yoke.

Now this will give you a workout, because if you don't know exact RPM that you need to maintain desired speed, you will be chasing it and working the yoke to keep constant altitude.  So I would lower the nose after the climb, let it accelerate, then lower RPM to 2200 and keep the plane in level flight with the yoke and trim.  After a few minutes when everything is stabilized, I would note the airspeed.  Then I would reduce RPM to 2100, retrim nose up to keep level, wait a few more minutes and note the airspeed for 2100 RPM.  And so forth.  You can build a table of RPM and airspeed.  Then, next time you fly, you will just set the correct RPM for desired airspeed.


You seem to assume the maps are being transmitted from the UAV.
They are almost certainly not (and if they are that's a poorly engineered system and I would be embarrassed that my government wasted my tax dollars on such a lousy design).

Maps are relatively static data, so it would be logical to store them on the computers at the ground control station (where you could have the entire world's terrain and likely aeronautical charts/airspace boundaries on your hard drive, along with current weather data and other useful information).

Moving the map to keep up with the position being relayed from the UAV is computationally trivial: iPads do it for real aircraft (ForeFlight & similar products) and your car's GPS system does it when you drive - neither system is as powerful as the typical desktop computer.

All the UAV would relay to the ground station is its position (and any other pertinent data dictated by its mission, such as photos/video). This arrangement minimizes the bandwidth required to control the vehicle, as well as its RF signature (less stuff to transmit back to base).

For autonomous UAVs, particularly ones which have to avoid airspace incursions, some subset of airspace data appropriate to the route of flight may be loaded on the vehicle, but I wouldn't call these "maps" - it's a much more compact representation of coordinates marking boundaries in 3D space (similar to the Jeppesen NavData products - possibly even using those products) . Such vehicles may also have terrain data loaded before flight if they lack other means to avoid collisions with terrain while operating autonomously.

  Disclaimer: I have no experience with the RQ4 or any other military UAVs - this is just a common-sense engineering assessment.


Is there a cockpit indication if the B737 flap load relief is not working properly?

The cockpit indication would be that the flaps don't retract as expected. The subsequent flap overspeed would then be captured by the Flight Data Recorder, the same as any other exceedance. But I'm unaware of any specific indication on a cockpit display that indicates directly "the Flap Load Relief isn't working".


Is it allowed to wear polarized sunglasses in cockpit?

This FAA document describes considerations for choosing sunglasses for pilots.

Since the document concludes, that

  Polarized sunglasses are not recommended

I presume there is no rule that would explicitly forbid it. However there is always the “operate aircraft careless and reckless manner” paragraph and if you badly screwed up while wearing such sunglasses and there was grounded belief that some of the disadvantages of such sunglasses contributed to the incident, you could be charged with that.

The document quotes following reasons why they are not recommended:

may reduce or eliminate visibility of instruments with polarization-based anti-glare filters,
may reduce or eliminate visibility of LCD instruments (LCDs emit polarized light by design),
may interfere with visibility through an aircraft windscreen by enhancing striations in laminated materials,
may mask the sparkle of light that reflects off shiny surfaces such as another aircraft’s wing or windscreen, which can reduce the time a pilot has to react in a “see-and-avoid” traffic situation.

Even if your plane does not have any instruments with polarization filters and no issues with striations in laminated windshield, filtering reflections from other aircraft is definitely not what you want.

Note that in most other situations, filtering reflections (from water, cars, metal roofs etc.) is desirable and is why polarized glasses exist, because reflections from close objects can be blinding. But in aircraft you are far from the sources of reflection, so the risk of blinding reflection is low, while the reflections can alert you to presence of other aircraft that might otherwise be hard to spot when looking towards the sun.


What parts of the 787 are produced with 3-D printing (besides air ducts and hinges)?

Another example of printed parts is electronics covers.

It wasn't necessarily "essential" to use 3D printing, but economical or beneficial versus other choices. For aircraft parts, 3D printing has a few advantages over more traditional methods of manufacturing:

Much less delay for manufacturing. A new part can be designed and
then 3D printed very quickly. Traditional methods need much more time
to create tooling for each new part. If you are delaying a product
worth millions, time is important, and the faster method will have a
big advantage.
There can also be less cost in manufacturing. The cost of initial
tooling for a part only pays off in the long run if many parts are
produced. A 3D printer can potentially make many different parts,
with minimal added expense to make a new design.
The design can also be made more efficient. 3D printing can create
shapes and designs that are not practical with traditional methods.
This can reduce the weight and complexity of parts.


Are winds that are not from the prevailing wind direction more often gusty, and why?

A little more info about where your airfield is would be helpful.

The generic answer would be that a significant weather event would be required to over come the prevailing winds.  Also, as winds changed from prevailing to cross, gusts and shears would be more likely.  Local low level factors such as terrain, buildings, and trees may also taken into account. The airspace along the runway is generally more clear of these effects as compared with across it for a single runway.  Larger airports with multiple runways provide more options.


What are the difficulties in building transonic airliners?

That is because as you approach the transonic regime, the drag on the airframe begins to rise and can reach up to ten times the subsonic drag. after you go supersonic, the drag falls down again- and this makes the transonic regime the worst place to operate a plane from a fuel burn standpoint. So you either stay subsonic, operating below the drag rise point, or supersonic, comfortably beyond that point.
Another consideration is this: Even if you are subsonic but nearly supersonic, there will be points on the airframe where the airflow is locally supersonic. You can actually see this in Boeing's long-distance planes, where a cabin seat at roughly mid-chord affords you a view out the window of the normal shock sticking up from the wing at high-speed cruise. If the flow goes supersonic at one of the control surfaces, it may upset the controllability of the plane, which would be undesirable- so better to stay comfortably out of the transonic regime for cruise.


Why are planes using rivets & not welded construction?

Short answer: High-strength aluminium alloys are tricky to weld correctly. Aluminium is such a fine material for aircraft structures that the need to rivet it is gladly accepted.
Two things are important:

While steel has a temperature range in which it gets more and more runny, aluminium alloys change from solid to liquid within a few degrees. Also, heat conductivity in iron-based alloys is lower than in aluminium, so heating steel locally will keep the surrounding material cooler and more solid compared to aluminium. While welding thin sheets of steel is trivial, it needs lots of experience in aluminium. For very thin sheets, special equipment like a water-cooled copper backing on which the aluminium sheets rest, so their back is cooled, are needed. Also, the melting temperature of steel and titanium is high enough for it to glow long before it melts, while aluminium will melt without giving you any optical hint of its temperature.

High-strength aluminium is produced by progressively aging and precipitation hardening the material. The usual alloys use copper atoms dispersed through the aluminium matrix which locally distort the atomic lattice and strengthen it. If they are heated and rapidly cooled by welding, the copper distribution would be changed and the material would be weakened around the welding area. To harden the finished structure again is rather impractical in most cases, so riveting is the better alternative.

A third speciality is the oxide layer on aluminium, which has a higher melting temperature than the base material. You need an AC TIG welder to disrupt the aluminium oxide layer, so your choice of welding techniques is rather limited.
Also, riveted structures are easier to inspect and to repair. Most repairs need to remove aircraft structure for access, and a riveted structure is easier to disassemble and to put together again after the repair using slightly thicker rivets.
My experience with aluminium welding stopped at 4mm thick sheets; while thicker ones were easy to weld, I never managed to weld thinner ones. You sit in front of your structure and heat the spot where you want to start welding. Watching it through the darkened head screen you wait until the spot under the arc becomes glossy, which signals that the surface has started to melt. Now you need to add your welding wire like crazy to keep the spot from heating more, and get the spot moving. If you fail to do so, a second later you will have a hole under your arc, because the aluminium has molten completely and has fallen away. Doing this with 2mm sheets was a pure exercise in futility for me - the moment the surface became glossy it fell away already.

Edit:
Thanks to @voretaq7 for sharing the link about friction stir welding in the comments! This is made possible by precise positioning of the parts and a computer-controlled welding head and will see wider application in the future. Eclipse Aerospace claims it helps them to avoid 60% of rivets in their jet aircraft.


What happend to the airframe of the Aloha Airlines Flight 243?

According to Planespotters, it appears that the airframe in question was destroyed in August 1988.


Is it ATC's responsibility to ensure read backs are correct?

A controller, should be on the lookout for all incorrect readbacks. But controllers are human, and can easily miss them, or say things in correctly. Incorrect squawk codes are often more of an annoyance versus an actual separation issue. It'd become an issue if they didn't take action when it was noticed that there was an incorrect code airborne, and let you truck on your way and not perform appropriate handoffs or inform others of any issues with your flightplan/target.

Most of the time, an incorrect beacon code will be flashing on the scope, if it's not assigned to someone else, and the controller will look through their list to find the correct code. If you tag up under someone else's code, then it becomes more of an issue, as they have to realize it's incorrect, suspend the datablock, and flightplan(or most likely drop it out of the system and reenter it) (flightplan issue is often delegated to others in the operation), and hunt for your correct code.


How are duplicate call signs dealt with?

The scenario you're asking about is common.  Let's say that your Delta 158 from South Korea to Detroit is running several hours late, and the decision is made to operate the A320 DTW-BOS on time.  ATC doesn't accept having two aircraft flying with the same callsign at once due to exactly the sort of confusion you suggest, so something has to change.

What will happen is that the second flight -- i.e. the one that isn't already airborne, will get a new ATC callsign.  Sometimes you'll hear something like "Delta 158A" as the callsign of the flight, or they may use something entirely different like "Delta 9158" as the ATC callsign for that flight.  Each company will have their own method of resolving the conflict; some use letters, others don't.  Some can go to "9000 + original flight number," and others will simply use something like 9001 for the first "stubbed out" flight that day, 9002 for the next, and so on.

But, the basic answer is that the ATC callsign of the flight changes.

Which does NOT mean, incidentally, that the flight number as far as the passengers are concerned has changed.  It's possible to be "Delta 9158" or "Delta 9001" or "Delta 158A" or whatever for ATC and still be "Flight 158" when talking on the PA to the passengers.  The fact that the ATC callsign changed is transparent to the rest of the operation, since reservations, ticket counter, baggage handling, and so forth isn't upset when 158 ICN-DTW happens to overlap (in time) 158 DTW-BOS.  Only ATC worries about that, so the fix is only visible to them (and the pilots & dispatchers).


Why at some airports/airfields you need to fly a non-standard circuit/pattern?

The specific reasons will likely vary with each individual airport, but the most common reason I've seen is noise abatement.

If the north/south runway is on the west side of town, using right traffic when landing on 18 will keep the planes from flying over the houses.

From the pilot's point of view you fly the circuit making right turns instead of left turns.  It's easy to do and is covered in initial training.


What makes a jet single pilot certified?

According to this blog:

Up until 1977, the FAA required all jets to be operated by two pilots. In ‘77, Cessna was given approval on a single-pilot variant of the Citation I, the Citation I-SP. The aircraft met the 12,500-pound maximum takeoff weight threshold for small aircraft, but that wasn’t the only single-pilot qualification. Cessna also had to convince the FAA that its pilot workload was low enough for one pilot to handle safely.
According to J. Mac McClellan with Flying Mag, in order for an aircraft to qualify for single-pilot certification in the 70s, “you had to have a boom microphone for hands-free communications-somewhat uncommon 30 years ago-and a fully functioning autopilot. There was also the quaint requirement for a transponder ident button to be mounted on the control wheel. In those days, we would ident on almost every controller handoff.”
One of the most important (and obvious) requirements for single-pilot certification of an aircraft is the fact that all gears and controls must be accessible from the left seat. The autopilot must be seamlessly integrated into the airplane’s navigation systems, and it must be functional for every flight operated by one pilot. The aircraft must have hands-free communication, as well. Aside from those concrete requirements, the rest is subjective.
After a series of test flights, the FAA’s test pilots must come to the conclusion that the aircraft is safe for a single pilot to fly. The design of the aircraft’s controls is one of the most important factors, as one pilot must be able to operate the throttle, the yoke, control wheel, and other flight controls easily from the left seat.

So, all of the aircraft's controls must be operable from the left seat, there must be hands-free communication, and an integrated autopilot.
Now, of course, there is also a single-pilot type pilot's certification, which a pilot can obtain to legally fly aircraft which meet all of the requirements above, yet are larger than the 12,500-pound maximum takeoff weight threshold.


What is the difference between nautical air miles and nautical ground miles?

A nautical ground mile is one nautical mile over the ground.  A nautical air mile is one nautical mile through the air mass.  This distance can be different because of wind.
For example:
If you are flying at 100 knots true airspeed in a zero wind condition, nautical ground miles will equal nautical air miles.
However, if you are flying at 100 knots true airspeed into a 100 knot headwind, your nautical ground miles will alway be zero, regardless of how many nautical air miles you fly for (at 100 knots).
Anything in between will result in some variance affecting the “net displacement of the aircraft”.  This variance can be calculated using the basic wind triangle.


What does "Crew: Top of your mind!" mean in commercial aircrafts?

Could it rather be « crew: top of climb » which some airlines use, but 2 things contradict this: a TOC mid flight is unlikely and although used by some airlines it is more the top of descend we indicate to the flight attendants for them to start preparing for landing.