How do you win a simulated dogfight/Air-to-Air engagement? When simulating/practicing a dogfight/air-to-air engagement obviously real, live weapons aren't used. So therefore, how is it that these missions are "won"?
So my first question is: In a within visual range fight (assuming FOX 2/guns distances) how is the fight won? Is it determined by who can sit on the 6 o'clock of their opponent, or is there a system kind of like laser tag to determine if a gun shot (or missile simulation) lands on target.
And 2: How can you simulate/practice BVR engagements? Is there a way to effectively use a "virtual reality" missile that can simulate if the target is hit, and further to that, do Countermeasures have any relevance in these practice engagements?

Bear in mind that most of my maneuvering was done from a defensive position due to the aircraft I flew, and that my experience spanned a period 15-30 years ago.  But, I have some perspective that may help answer the question.
First, as a comment mentioned, some are decided at the bar later.  (with hands shooting down watches…)  We also had a saying:  “First person to the chalkboard wins”.  This is in reference to the post-flight debrief practice of diagraming each engagement out on the board, and how whoever was doing the debrief may slant their interpretation of the fight to favor them.
The reality though is that despite egos and the competitive nature of practice fighting we never really tallied or recorded "wins" and losses.  The objective was always to learn, practice, and improve.  There is an honor system in place, and truthfulness is expected to prevail in the debrief.  Just like when wrestling or playing other games as a child, you pretty much know when you have been bested.  And if you try to BS or make excuses you will be called out and very quickly discredited.  So the short answer is that your guess that it is determined by who can sit at their opponent's 6 O’Clock isn’t all that far off.
To get more specific regarding the details of your question, it also depends on the equipment on the aircraft, as well as the level of training being conducted.  ACM (air combat maneuvering) can be as informal as a couple of squadron peers with no special gear scheduled for a local 1v1 proficiency flight, (and good naturedly arguing over who won later) or it could be a large scale coordinated exercise like Red Flag, or a Battlegroup at sea.
In the case of the former, BVR or even close in missile shots or guns would be called on the radio.  The target aircraft will usually respond “chaff/flares” and continue to maneuver.  If the shooter assesses a high probability of countermeasure success, they would respond “continue”.  A successful bug-out or assessed simulated kill by the flight lead would result in a “terminate” or “knock-it-off” call, followed by resetting to predetermined positions and altitude blocks for the next engagement.  Brief notes and fight diagrams will be drawn up on the pilot’s kneeboard during each reset to facilitate debriefing later.  Any disputes can likely be settled by reviewing the HUD video.
If the aircraft is equipped with a CATM (captive air training missile) and/or chaff and flares it will make the training that much more realistic.  The CATM will have all the electronics of a live missile, but no propellant or warhead.  This will allow the offensive fighter to obtain a missile lock, triggering the defender’s RWR, (radar warning receiver) and give the defender a chance to break the missile lock by dispensing actual countermeasures.  (and reinforce use of the correct button – because in a real fight you would want to pump out actual chaff/flares, not key the radio mic!)
In training there are often altitude restrictions on the use of flares, or they may be prohibited entirely depending on the fire danger in the training range area.
For large scale multi-aircraft exercises, the aircraft are usually fitted with an ACMI pod as described here:  https://en.wikipedia.org/wiki/Air_combat_maneuvering_instrumentation
Results are live streamed back to the exercise commanders and staff.  (Picture Flightaware combined with LiveATC, displayed on a wall sized screen, with a room full of professional pilots and controllers critiquing every move.)  These exercise monitors will act as referees in real time, and call out kills as they occur.  The “dead” aircraft will acknowledge, change their squawk to a prebriefed code so they can be identified by remaining participants, change altitude to a safe block, and transit to a designated area to hang out (in shame) until the end of the engagement.
The entire exercise is played back later on the big screen in a theater sized debrief room.  It can be sped up or slowed down as needed.  (As cheesy as the first TopGun movie is, you can see an example of the kind of displays that were in use at the time, and that as I remember were very similar to what was still being used in the early 2000s when I did my last Red Flag)
The debrief lead will provide commentary as it goes, and may pause to ask the pilots for their perspective.  For example:
Debriefer – “Hammer15, you were in missile range here when you called the ‘Fox2’, but based on the opening speed of Nail30 we assessed this as a successful bug-out, do you concur?”
Hammer15 – “Yes, I was showing ___ knots, and the CATM broke lock shortly after that…”


What are the risks in landing on a beach vs. shallow waters? I recently read a story where a pilot of a light aircraft died having attempted to land on a beach.

Would it be potentially safer to try an emergency landing on a beach, or go for shallow waters of 6-10 feet depth, or deeper water? (In the absence of anything more suitable).

Having done my primary training essentially over beaches I'm pretty well-versed in the theory (but thankfully not the practice) of landing on beaches.

Given the possible choices offered at your typical beach, the order of preference for landing areas is generally:

Pavement
People like to drive their cars to the beach. There's probably a road or parking lot nearby, and if it's empty enough that's where you want to land.
Dirt (not sand)
Some beaches have "sandy dirt" areas, usually with low grasses and the like on them. If the beach you're contemplating has such an area it's probably your second-best choice as it will be the firmest ground and closest to landing on a grass strip. (Beware of bumps and rocks!)
Wet Sand
The sand between the high-water mark and the low-water mark on the beach tends to be fairly compacted, so it can make a decent landing area. It will probably be softer than dirt/grass, but give it your best soft-field technique and you can probably set the plane down without damaging it.
Properly executed you can put the plane down without doing any substantial damage, and if it's an actual emergency you're unlikely to get in any trouble.

Dry Sand
Fluffy dry sand is a decidedly soft field situation - soft enough that in a nosewheel aircraft there's a very good chance that no matter how careful you are or how good your soft-field technique is you'll lose one or more of your landing gear - but at least you're on dry land.
The recent incident in Florida is an example of this: the aircraft's nose gear was sheared off as you can see below, but the pilot and passenger walked away (sadly some bystanders on the ground were injured, and one was killed).

Water
Unless your plane is on floats water is basically the landing of last resort - particularly for fixed-gear aircraft. The forces involved in putting your wheels into even 6-10 inches of water are pretty substantial, and there is a real chance of tearing off the gear or losing control of the aircraft in the last few seconds.
Even if the actual landing is uneventful you will be left to contend with being in the water while evacuating the aircraft which adds complexity to an already difficult situation (and if you're far enough out that the depth of the water is measured in feet you're going to have to swim back to shore once everyone is out of the aircraft).

  "Ditching" an aircraft in the water is a subject worth looking into on its own. Smarter people than I have written and spoken volumes about it, but as Skip Miller pointed out we don't really have a lot of hard data.


Can you turn off the instrument panel lights? Do general aviation aircraft generally allow the turning off of the instrument panel lights? By lights I am referring to any screens, bulbs or other devices which shine a light within the cockpit.

It depends.

On my Cherokee, when you turn the navigation lights on you can push the switch up or down. Up gives you bright lights on the panel and down gives you dim lights. There is also an overhead red light that has a sliding door that you can open or close for more or less light. There is one rheostat that controls the lighting in the VOR/LOC indicator.

On my Cessna 210 there are lights in some of the instruments, post lights next to the instruments, and overhead lights. The lights are controlled with two switches and several rheostats. The GPS has independent lighting controls.

The Piper Arrow has two rheostats—one for navigation and radios and one for instrument panel lights. If you turn the navigation lights on there is always some lighting on the radios. The GPS has its own lighting controls.

My friends Piper Dakota has lights for the instruments as well as a light strip along the base of the glare shield that illuminates the entire panel. Controlled by a combination of switches and rheostats.

Older general aviation aircraft have widely varying approaches to nighttime lighting so before you fly at night you need to become familiar with the idiosyncrasies of each one.


Does any one know if the PFD or ND or any other screen on an commercial aircraft work like a computer or something else? Does any one know if the PFD or ND or any other screen on an commercial aircraft work like a computer or something else? Like does the screen work like a computer and read 0s and 1s like maybe for sensors for smoke it sends a particular amount of 0s and 1s to show on the screen there is a fire and have hard drives and graphic cards and all that stuff or do they work completely different?

All multi-functional displays in modern avionics are just computers. Typically, they are only responsible for presentation of the supplied information, but may do some processing: for example, display certain alerts in the right conditions. Also, they manage some of the user pilot input and mode switching.

G1000 PFD diagnostics page

Nearly all the data comes in on digital bus(es), in aviation most commonly ARINC 429 or even Ethernet with a custom protocol.

Bare sensors either have a dedicated microcontroller that converts the readings to a digital format, or are connected to a dedicated processing unit (also a specialised computer), such as ADC (Air Data Computer) which collects and processes all the air-related data (airspeed, altitude, temperature, etc.)

Even then, typically, this semi-processed data don't go to displays directly. All the sensor data are collected by a sort of integration unit (e.g. GIA for Garmin systems), which does most of the processing and decision making. Then, the necessary information is relayed to the displays.


What is the regulatory landing distance for turboprops under FAR 121-135? Flying a FAR part 25, N registered turboprop, within couterminous FAA airspace, under FAR parts 121 & 135 operating rules and performance wise, what are the requirements regarding computation of a suitable runway length as a function of airplane weight and runway surface conditions?

Each aircraft manufacturer is going to supply that data as part of its Aircraft Operating Manual. Operators must use these documents to determine required landing length, and this computation must be calculated during the planning phase of the flight by taking into consideration the estimated weight of the aircraft at the arrival time, as well as forecast winds, runway conditions and types of runways.

The regulatory "mandate" for doing these computations is found in the text of Parts 121.195 and 121.197, as well as 135.385 and 135.387. The relevant parts of each are pasted below, but the full text should be consulted for additional requirements and possible exemptions.

  121.195. Detination Airport. no person operating a turbine engine powered airplane may take off that airplane unless its weight on arrival, allowing for
  normal consumption of fuel and oil in flight (in accordance with the
  landing distance set forth in the Airplane Flight Manual for the
  elevation of the destination airport and the wind conditions
  anticipated there at the time of landing), would allow a full stop
  landing at the intended destination airport within 60 percent of the
  effective length of each runway described below from a point 50 feet
  above the intersection of the obstruction clearance plane and the
  runway.

  121.197.   Alternate airports. No person may list an airport as an alternate airport in a dispatch or flight release for a turbine engine
  powered airplane unless (based on the assumptions in §121.195 (b))
  that airplane at the weight anticipated at the time of arrival can be
  brought to a full stop landing within 70 percent of the effective
  length of the runway from a point 50 feet above the intersection of
  the obstruction clearance plane and the runway.

  135.385. Destination Airport. No person operating a turbine engine powered airplane may take off that airplane unless its weight on
  arrival, allowing for normal consumption of fuel and oil in flight (in
  accordance with the landing distance in the Airplane Flight Manual for
  the elevation of the destination airport and the wind conditions
  expected there at the time of landing), would allow a full stop
  landing at the intended destination airport within 60 percent of the
  effective length of each runway described below from a point 50 feet
  above the intersection of the obstruction clearance plane and the
  runway.

  135.387. Alternate Airports. No person may select an airport as an alternate airport for a turbine
  engine powered airplane unless (based on the
  assumptions in §135.385(b)) that airplane, at the weight expected at
  the time of arrival, can be brought to a full stop landing within 70
  percent of the effective length of the runway for
  turbo-propeller-powered airplanes and 60 percent of the effective
  length of the runway for turbojet airplanes, from a point 50 feet
  above the intersection of the obstruction clearance plane and the
  runway.


Why did Avianca have A318s with PW6000 engine? I want to know about the upgraded PW6000 Avianca A318s. Why did those get upgraded? Did they not produce enough thrust already?

The PW6000 was a second option for engines on the A318, not an upgrade. The rest of the A320 series at the time had options of CFM or IAE engines. The thrust was comparable to the CFM option, but the initial design had worse fuel efficiency than expected, leading some customers to switch their orders to CFM. In the end, only LAN bought A318s with the PW6000 engines, taking delivery of 15. These were later sold to Avianca Brasil, who no longer flies them.


Can you please explain aircraft spin in simple non-mathematical terms? Can you please explain aircraft spin in simple non-mathematical terms?

A spin is a kind of aggravated stall in which one wing becomes more stalled than the other one.  This imbalance in lift results in an autorotative motion abound a vertical axis, generally passing through the inboard wing of the aircraft.  Spins can be initiated be stalling the airplane in a uncoordinated turn, which causes the inboard wing to enter a deeper stall than the outboard wing.  An airplane must always 1) be in an aerodynamic stall in 2) uncoordinated flight in order to enter a spin.


Are there dual pilot planes to pilot myself? I understand planes have 2 piloting systems often?

Is there a plane I can demo fly first flight?

I'm interested in saying I have flown and that's it.

Yes, the vast majority of airplanes have dual controls. You can just call up your local flight school and explain what you want. A "Discovery Flight" is typically 30 minutes of flying, just to see if you're interested, but if you want to go for longer than that, just let them know beforehand.


How are thermals found? As far as I understand glider pilots like to look out for thermals. I assume that when you are in one, you can perceive that and you can make roughly sure to stay in it.

But what if you're not in a thermal? How do you look for one? Are these methods (like finding a cumulus?) significantly/statistically more efficient than just randomly browsing? Or is it mostly a question of luck?

There are a few different things that you can look for, and to some degree it is trial and error as well.  Gliders will have an instrument that measures vertical speed so that they can tell "how good" a thermal is as well (a variometer or a Vertical Speed Indicator(VSI)).

Some of the things to look for:

Color variation on the ground because the difference in the amount of heat absorbed by the ground varies based on the color/composition.  The hotter area will cause the air to rise (hot air rises) and will create a thermal.  I.e. A dark colored area surrounded by a light colored area or vice-versa such as a parking lot with fields around it.
Birds circling in an area because they tend to circle in thermals.
Certain types of cloud formations that can indicate lift.
Other gliders!  :-)
If the wind is blowing across a mountain ridge or other large structure, the wind has nowhere to go but up so is also a good place to look for lift as well.

Here is an example showing how some of the thermals form and how the wind affects them.  Notice also how once the air has been lifted to the point where it cools below the dewpoint that a cloud will form:

Here is another showing how terrain can cause lift:


Can you fly an airplane at a 90° roll angle without losing altitude? I've seen this answer to the question about flying upside-down, but tilted by 90°, there should be no surface creating lift (except maybe the vertical stabilizer).

It depends. As always. If thrust is high enough, why not?
Knife edge flight is a regular part of aerobatic performances, and the fuselage is producing almost* all the needed lift. This requires

Enough speed,
A low ratio of aircraft mass to fuselage side area, and
Enough rudder deflection to trim the aircraft in a sufficiently high sidelip angle.

For horizontal flight your installed thrust must be sufficient to compensate for the high drag in this attitude. This should be no problem with powerful propeller aircraft if their fuel system keeps them supplied at this attitude. Jets must make sure that the sideslip angle can be tolerated by the intake.

The smoke from the exhaust indicates that this biplane flies horizontally. Yes, it is a large model airplane (not man-carrying, but almost big enough for that). But the laws of physics don't change with scale. For an example of a full-size aircraft doing a knife edge, see this video. Thanks go to @romkyns for pointing this out to me!
Note the rudder deflection to keep it at this angle of sideslip. Direction is controlled with the elevator. At this rate of sideslip the propeller thrust contributes to overall lift as well, however, the vertical adds a substantial downforce in order to trim the aircraft and the fuselage has to supply the remaining lift.
* Almost means that the propeller will carry some of the weight, but the large downforce on the vertical needs to be compensated, too. In sum, the lift contributed by the fuselage is very close to the weight of the plane.


How or when can the 250 KIAS speed limit below 10,000ft be exceeded? This arose out of a comments discussion in this question.

The only airspace I really know is the UK.  Here, a controller may issue a clearance to exceed the 250kt limit below 10,000ft for reasons other than minimum safe flying speed, e.g. to expedite a transition for spacing.

Is this common, e.g. in the US?  I know it's open ended but I'm interested in whether this is just some "local" thing.

Not a local thing at all!

In Australia, it is extremely common to hear, especially for aircraft on departure. Listening to LiveATC, particularly Sydney International Approach/Departure (YSSY) you will quite often hear ATC give an aircraft permission to exceed 250KIAS below 10,000ft.

Qantas 123:
Approach, QFA123, with you passing 2,300, climbing 5,000..

Sydney Approach:
QFA123, Identified, Climb FL240, cancel speed restrictions below 10,000..

There are a number of reasons this is used. The first, I have already hinted to in the example radio call above.

Departures:
It is extremely common to hear ATC cancel speed restrictions on departing aircraft. This gives better separation for aircraft departing in the same direction. For example, one of the busiest sectors in the world is Sydney - Melbourne Australia. The common SID's out of Sydney for Melbourne are the DEENA4 WOL transition and the WOL1 Departure, depending on operational runway. As a large amount of aircraft use these departures, the further the lead aircraft can get on the SID prior to the trailing aircraft becoming airborne, the better.

Arrivals:
Again, using Sydney, they receive a large amount of Regional Turbo-Prop traffic (Dash 8-Q300/Q400, Saab 340B, BE350). You will commonly hear Approach cancel speed restrictions on these aircraft on decent so they can give them more space on the approach. They land reasonably slower than a B747/A380, so the more room, the better.

Another reason is simple. These guys are operating commercial operations, hence faster is better, especially on descent. So if there is no or low traffic in the TMA, ATC will commonly release the speed restriction on aircraft to accommodate the company operations.


Do aeroplanes have to balance torque like helicopters? Helicopters need a tail rotor to balance the torque reaction that tends to rotate the main body sideways. Doesnt a single-engine plane suffer the same problem? I would imagine that (for example) the left wing would dip lower than the right due to the torque. How is it countered?

A single engine plane can suffer from control problems due to torque.

An early famous example was the Sopwith Camel

As others have pointed out, torque effects have to be countered using the normal aerodynamic controls available to the pilot. Some aircraft had extra-large ailerons because of this issue.


How does the aspect ratio of the vertical stabilizer affect stall speed? The higher aspect ratio of a vertical tail surface (higher at least when compared to the fuselage) will allow to make the tail smaller, but causes an earlier stall.
  -Peter Kämpf said so here

How does the vertical tail, and more specifically, the aspect ratio of the vertical tail, impact stall?

Generating lift creates downwash. Downwash reduces the effective angle of attack:

Source

A high aspect ratio reduces the downwash and thus also its reducing effect on the effective angle of attack.

Therefore a high aspect ratio wing will experience a higher $\alpha_{eff}$ than a low aspect ratio wing at the same angle, and thus stall earlier.

The same happens with the rudder, but then with $\beta$ instead of $\alpha$.

EDIT: clarifying alpha - beta similarity

So, in the case of sideslip, we have the following situation:

Source

See the similarity between the $\alpha$-image above, and the $\beta$-image.
The mass flow changes direction, and leaves the end of the rudder (more or less) parallel to the rudder chord line. This deviation in airflow direction causes the force to the left.

So for a normal wing ($\alpha$-image), flow enters straight, leaves going down (downwash) and as a consequence the wings give a force up.

For the rudder ($\beta$-image), the flow enters straight, leaves going to the right (downwash, but then sideways) and as a consequence the rudder give a force to the left.

About the stalling, stalling is not limited to the wings, also rudders can stall if the maximum effective angle they experience is above stalling angle ,and the force generated suddenly drops.

If we compare two rudders both with the same airfoil and the same $\beta_{eff_{stall}}$, say 10°.
The $\beta_{stall}$ will be given by:

$$ \beta_{stall} - \beta_{downwash} = 10° $$

If the $\beta_{downwash}$ is 4° for the low AR wing, and 2° for the high AR wing, it will mean the low AR wing will stall at a $\beta$ of 14° and the wing with the high AR will have a $\beta_{stall}$ of 12°.


Why don’t airports use jetways as an airlock to avoid having to repressurize the plane for every flight? Seems like it could save money perhaps. Has this been considered in the past?

I believe there are quite a few misconceptions here:

When an aircraft is "pressurised", it means that at higher altitudes, the pressure inside the aircraft is higher than the pressure outside. At lower altitudes, the pressure is exactly the same inside and out.

Originally, aircraft weren't pressurised, and at higher altitudes the low pressure is a problem for the people on board (lack of oxygen, mostly), and for some hardware (due to the pressure differential).

So the pressure is artificially increased inside the aircraft beyond a given altitude (or more precisely, beyond a given outside pressure): when the aircraft takes off, the pressure goes down as the plane reaches higher altitude, until that pressure is reached, and from then on, the pressure outside continues to decrease while the pressure inside is maintained at that safe level.

So there's no reason to pressurise an aircraft on the ground. It has the same pressure inside as outside.
Even if it were useful, when on the ground, there are plenty of openings other than just the passenger door(s). Other doors are opened for catering and technical staff, cargo doors are open, and so on. So it would be impossible to maintain a different pressure in the aircraft and outside without completely breaking down all operations.

Also, having an "air lock" would require doors on each side. One door would be opened, people would enter the air lock, the door would be closed, the pressure would be changed, the other door would be opened, people would exit the airlock. Then the door would be closed again, pressure brought back to the other level, and the first door would be opened again before more people would be able to enter the lock. This would significantly hamper the flow of people embarking or disembarking.

Additionally, people are already annoyed enough by the changes in pressure on board planes which take quite a few minutes. Doing that in a few seconds to ensure relatively quick movement would just be horrible.

Finally, consider that many aircraft do not use jetways but stairs on the tarmac.


Where does ice collect first on a wing in flight and why? I've seen some reports that say ice forms on the back half of the wing and on the outside edge of the wing (the part furthest from the body) before it will form anywhere else.  I'm wondering if this is true?  Where does ice first form on a wing (in flight) in icing conditions?

"Icing conditions" is a pretty vague term that encompasses a lot of various situations that can cause airframe icing (AOPA pdf report, so it's hard to have one definitive answer. That said, you can expect to accumulate some degree of ice when flying through moisture (clouds, rain, etc) when outside air temperatures (OAT) are near or below 36°F / 2°C. Also as a rule, an aircraft's tail will likely accumulate ice faster than the wing in all conditions.

Flying through very cold temperatures (-15°C -> -40°C)

When flying in clouds and rain at the very low end of the icing spectrum, the most likely form of accumulation is rime icing. This primarily forms on the leading edges of wings and tail surfaces, starting (in most cases) with the tail, and looks (initially, at least) a lot like frost. It can create pretty bizarre structures and is pretty easy to spot. Rime ice is (as far as I have seen or read) not going to accumulate anywhere but on leading edges (wings, nose, engine nacelles, tail) as those are the only parts of the structure impacting the relative wind. Either way, it is highly detrimental to your wing's aerodynamic health.

Rime ice can sometimes form 'horns' that start to grow in a V shape forward off the wing, but only in what I imagine are considered severe conditions. The FAA states that rime "typically occurs with temperatures between -15° C. and -20 ° C".

Flying in relatively warm temperatures (2°C -> -15°C)

At warmer temps, the most likely form is clear ice, which is basically like having solid water ice form around the leading edges - again, wings, tail surfaces, nose, engines. It pretty much follows the shape of the leading edge of surface it freezes onto, but it's heavy and still messes with your aerodynamics. Again, like rime, it's freezing more or less on impact (but with larger droplets) wherever the relative wind strikes the airframe.

In some unusual conditions, aircraft can encounter precip known as Supercooled Large Droplets (SLD); these are cold enough to freeze but not on impact, causing a form of icing known as runback ice (FAA pdf). In FAA tests, "ice shape simulations were found to cause substantial penalties to the aerodynamic performance" of multiple NACA airfoils. Runback ice can accumulate pretty far back along a wing, making it difficult or impossible to dislodge using heat or boots (supposedly TKS fluid protection can mitigate this). It's scary stuff.

The FAA states that "Clear ice typically forms when temperatures are around 2° C to -10°C [but] more hazardous clear ice shapes [...] tend to form at temperatures closer to 0°C".

Flying in medium temperatures (-10°C -> -15°C)

When flying in the middle of the temperature range, aircraft wind up accumulating mixed ice, a combination of rime and clear. According to the FAA, "Mixed ice is most likely to form at temperatures between -10° C to -15° C". It is basically as terrible for aerodynamics as rime ice, and pretty much just as heavy as clear ice. No fun.

Resources:

Wikipedia
AOPA Safety Advisor
FAA Safety course on icing types
FAA Safety course on SLD


Instructing your Kids Can anyone cite any regulation that would prevent my child (not infant) from logging time for a private pilots license (i.e. 12 years from now when they are 16 for a solo, 13 years for a license when they are 17)?
Background: I have children that I would like to start instructing and having them log flight training when they fly with me. I am VFR/IFR and medically current, and have a current FAA flight instructors license, therefore my question doesn't involve my own qualifications. Just if there are any known restrictions against the kid logging flight time. To clarify I don't mean both kids logging time on the same flight, just one kid.
I have found none in the CFRs (e.g. 61).

If your child is going to be around airplanes and flying with you for the next 12 years, they're not going to need to log time from back when they are 4 years old. They will have plenty of logged time later in life.

I would suggest that you pick an age, say at least 8 or 10, where your children can start to fill in log books of their own. If they keep an interest in aviation until that time, getting their own log book that they can fill in themselves will be a big step for them to look forward to.


Why is the angle of attack not proportional to the stagnation point? While I was studying my PPL today, I've encountered a question right below and I wasn't really satisfied with the answer.

Which statement about the airflow around an aerofoil is correct if the angle of attack increases?

The stagnation point moves up
The stagnation point moves down (correct answer)
The center of pressure moves down
The center of pressure moves up

Up here, α is the degree between the chord line and the oncoming airflow.

1) Stagnation point

2) Transition point

3) Transition point

4) Separation point

So, knowing all of these facts I just can't understand the question above. Why is the stagnation point moves down instead of going up while increasing the angle of attack?

From this site:

Notice that at low AoA the stagnation point is smack on the nose of the wing profile, while at higher AoA it is situated on the lower wing surface.

Hence: stagnation point location lowers with increasing AoA.


Which situations would cause a company to ground or recall a aircraft series? Which agencies or companies might decide to ground an aircraft series, and in which situations can this occurr?

There are various levels that a grounding can occur at.

Governing Agency: A legal authority can ground an aircraft make/model/serial number range (or one containing a certain part/system) if it deems they are unsafe or there is some question about the airworthiness. The most recent example of this was the recent grounding of the 787's by the FAA after the battery issue was called into question. Governing agencies can also practically ground an aircraft/make/model by issuing a mandatory AD against it; this will practically ground all airframes until proper maintenance occurs. A federal entity may also chose to not certify an aircraft for operations within a country, and/or the manufacturer may chose to not seek certification in that country although some countries allow one off certificates to be issued. In emergency situations the local governing body may shut down and ground all aircrafts in a certain area. The most prominent example of this that I know of is when all aircraft were grounded following the 9/11 attacks; this is generally more of a ground safety issue than an airworthiness issue.
Operator: The owner/operator can ground an aircraft for safety reasons if they belive there may be an issue with the functionality or operation of the aircraft in question. A good example of this is the grounding of the Southwest 737 fleet due to weight and balance issue, this was done by the airline potentially before a governing authority intervened. Another example was ANA's grounding of its 787 fleet due to engine problems.
Pilot In Command: As the pilot in command of a flight and the one responsible for ensuring the safety of the flight you can ground an aircraft for any reason you so chose and be well within your rights. Let's say on your preflight checks something is out of place or looks wrong; in such a case, the pilot can ground the aircraft until the issue is fixed.
Maintenance Persons: Generally when attacked from this angle it's more of a prevention to return to service than a grounding, but if an issue is found during a stage check or annual the aircraft may be pulled until the issue is fixed. There is an interesting article about withholding maintenance signatures here.
Recall: Manufacturers generally provide AD's instead of a full blown recall however some cases may warrant a full blown recall of airframes. When Porsche dropped the TC for the PFM3200 engine Mooney offered a recall of sorts, the owners could either sell the aircraft outright or the engine retrofit would be subsidized.


What vertical separation is required in a holding stack to avoid wake turbulence? Sometimes in my free time I play Endless ATC, a game where one acts as the approach and departure controller. In the game (as in real life) the controller is forced to put planes in a holding stack, separated vertically by 1000 feet.

Is this vertical separation - 1000 feet - enough on its own to prevent one plane's wake turbulence from affecting the plane immediately below? Or is it possible that I've accidentally had planes fly in each other's wake turbulence?

If so/if not, then what's the minimum vertical separation necessary to ensure one plane's wake turbulence doesn't affect the next plane in the holding stack?

The minimum vertical separation in a holding stack is no different from the minimal vertical separation used elsewhere. This is almost universally 1000 feet. In countries where Reduced Vertical Separation Minima (RVSM) has not been implemented, 2000 feet of vertical separation is required above FL290. 2000 feet is also needed if a non-RVSM equipped aircraft (such as certain older military planes) is flying above FL290. However, not many holding stacks grow to above FL290.

A point to consider is the fact that aircraft produce the most wake turbulence when they are flying slowly for landing. So since 1000 feet is enough during approach, it should also be plenty in a holding stack.

There has been some evidence that 1000 feet of vertical separation may not be enough for certain, heavy aircraft types. In 2017, a Challenger jet had an accident after passing 1000 feet below an Airbus A380 during cruise, presumably because the smaller business jet hit the wake turbulence from the A380. See AVHerald for details. However, this has not (yet) resulted in changed separation minima.

1000 feet is not enough to prevent planes from "flying in each other's wake turbulence" as you say, but in most cases it should be enough to ensure that the wake turbulence has weakened enough to not pose any threat to the lower aircraft. Also remember that wind can have a significant effect on the spread and dissipation of wake turbulence, so on days with a certain wind direction and velocity, the wake turbulence may survive longer than other days.

But the answer to your question remains the same: the vertical separation to be applied in a holding stack (below FL290 and during RVSM) is 1000 feet.


Who is responsible for avoiding collisions on the ground; the pilot or the air traffic controller? I may have some false assumptions here, so correct if needed. It is said that while ATC sounds like they are "in charge" of the airspace surrounding a major airport, control and responsibility for any given airliner is (still) in the hands of the Pilot-In-Command (PIC).

What this means is that if an airliner is given instructions to do something by ATC, and they are unable (or unwilling) to follow those instructions, they are able to tell ATC they are unable and ATC has to work it out, with all of the ramifications that implies. If the ATC controller wishes, they require the crew to contact ATC by other means (the dreaded phone call, I suppose) to explain, but the fact of the matter is, the passengers are ultimatley depending on the crew to keep them safe.

Now, let's take an airliner, at the gate, readying itself for a flight. They receive a pushback and are ready to taxi. They contact ATC Ground for instructions. Ground gives them taxi instructions. Who is responsible for the safety of the aircraft at that point?

Why do I ask this, when it should be obvious, the PIC. However, visibility out of the aircraft is limited, especially in some of the larger craft. As far as I know, there is no "check the mirrors" or "objects in the rear view window may be larger than they appear." The PIC simply CANNOT see behind the aircraft, and so any ground vehicles, personnel, or other aircraft (small or large) could cause an accident, which would be out of the control of the PIC.

At all times, whether in the air or on the ground, whether at the gate or taxiing, the pilot-in-command (PIC) has final and ultimate responsibility for the safe operation of the aircraft. Per ICAO Annex 2 (with similar statements/definitions by individual civil authorities):

  The pilot-in-command of an aircraft shall, whether manipulating the controls or not, be responsible for the operation of the aircraft in accordance with the rules of the air, except that the pilot-in-command may depart from these rules in circumstances that render such departure absolutely necessary in the interests of safety.

As you stated, the pilot is allowed to deviate from any ATC instruction or regulation to the extent necessary to ensure the safety of the crew, passengers and property. If necessary, the PIC may enlist additional resources, such as a ground crew, to deal with issues like not being able to see behind the airplane. For airline operations, this is usually spelled out by the airline's operations procedures, which the PIC effectively "approves" (as the ultimate authority for the aircraft's operation) and carries out.

Air traffic controllers have what you might call "jurisdiction" over certain parcels of airspace and airports. The gates and the area immediately surrounding them are usually not under the jurisdiction of the control tower. They are instead managed by the airport authority. At large airports, the airport may operate a "ramp control" system with its own (smaller) control tower and radio frequencies. Arriving and departing aircraft coordinate with ramp control to get into and out of the gates safely. Ground crews will assist the pilot-in-command with parking and pushback operations, getting the aircraft to a point where the PIC can taxi the aircraft to leave the ramp area and enter the taxiway system in accordance with ATC taxi instructions.

Once on the taxiways, and from there to the runway and into the air, the aircraft is under the jurisdiction of the regular air traffic controllers. The controllers can divide up this area between different positions, usually a "ground controller," a "tower" or "local controller," and one or more approach/departure radar controllers.


Why do holds at or below 14,000 feet have different procedures? When holding at or below 14,000 feet, the time for each leg is 1 minute. However, above that altitude, the legs are flown for 2 minutes, and the turns for 1 minute and half.
Are these differences due to airspeed, or any other recommendation?

The reason for a different turn rate at higher altitude is because of the physics of Indicated (IAS) and True (TAS) airspeed. Many aircraft would find it impossible to do a standard rate turn at high altitudes.

A standard rate turn is 3° per second. This is also known as a two-minute turn because it would take 2 minutes to make a full 360, or 1 minute for a  180°, like each end of a holding pattern.

The bank angle required to make a 3°/sec turn is a function of TAS and bank angle. The formula is:

$bank\,angle =\frac{turn\,rate\cdot TAS}{1091}$

So a standard rate turn at 170kn TAS requires a bank angle of 25°. As bank angle increases so do load factor and stall speed. A 25° bank yields a 10% increase in load factor and a 5% increase in stall speed. For this reason FAA and ICAO regulations require holding patterns to be standard rate, but not to exceed a 25° bank angle.

Here's where the altitude enters the equation. The relationship between TAS and IAS is dependent on air pressure and density. At 5000 feet in standard atmosphere an IAS of 160kn yields a TAS of 170kn. A standard turn at 170 KTAS would require the maximum bank angle of 25°. But in the thinner air at 14,000 that same 25° bank at 170 KTAS is only 142 KIAS.

So as altitude increases, a standard rate turn requires a slower IAS and a higher bank angle. At higher altitudes it would become impossible for many aircraft to make a standard rate turn without stalling. So at 14,000 feet the required turn rate is decreased to 2°/sec, which is a three minute turn (thus 90 seconds for a 180°). Where a standard turn at 14,000 IAS is limited to 142 KIAS, a 3 min turn can be performed up to 212 KIAS.

This is the reason turn rate must be lowered at higher altitudes.


Does a LSA or better license count for drone use? I have a FAA private pilot license. Does that allow me the same flight privileges while flying a drone, as a FAA certificated drone pilot?

No, it does not. But because you are an "existing pilot", the application process is a little different:
FAA: Becoming a (Drone) Pilot

Existing Pilots – What to Expect
Eligibility:

Must hold a pilot certificate issued under 14 CFR part 61
Must have completed a flight review within the previous 24 months

Remote Pilot Certificate Requirements

Must be easily accessible by the remote pilot during all UAS operations
Valid for 2 years – certificate holders must pass either a recurrent online training course OR recurrent knowledge test every two years

Application Process:

Complete the online training course "Part 107 small Unmanned Aircraft Systems (sUAS) ALC-451" available on the FAA FAASTeam website – initial training course areas include:
a. Applicable regulations relating to small unmanned aircraft system rating privileges, limitations, and flight operation
b. Effects of weather on small unmanned aircraft performance
c. Small unmanned aircraft loading and performance
d. Emergency procedures
e. Crew resource management
f. Determining the performance of small unmanned aircraft
g. Maintenance and preflight inspection procedures

Complete FAA Form 8710-13 (FAA Airman Certificate and/or Rating Application for a remote pilot certificate)
a. Online or by paper (see instructions in previous section)

Validate applicant identity
a. Contact a FSDO, an FAA-designated pilot examiner (DPE), an airman certification representative (ACR), or an FAA-certificated flight instructor (CFI) to make an appointment.
b. Present the completed FAA Form 8710-13 along with the online course completion certificate or knowledge test report (as applicable) and proof of a current flight review.
c. The completed FAA Form 8710-13 application will be signed by the applicant after the FSDO, DPE, ACR, or CFI examines the applicant's photo identification and verifies the applicant's identity.
   - The identification presented must include a photograph of the applicant, the applicant's signature, and the applicant's actual residential address (if different from the mailing address). This information may be presented in more than one form of identification.
   - Acceptable methods of identification include, but are not limited to U.S. drivers' licenses, government identification cards, passports, and military identification cards (see AC 61-65 Certification: Pilots and Flight and Ground Instructors)
d. The FAA representative will then sign the application.

An appropriate FSDO representative, a DPE, or an ACR will issue the applicant a temporary airman certificate (a CFI is not authorized to issue a temporary certificate; they can process applications for applicants who do not want a temporary certificate).

A permanent remote pilot certificate will be sent via mail once all other FAA-internal processing is complete.


Can I fly under a Military Operations Area (MOA)? If a  a Military Operations Area (MOA) is designated from 10,000 to 18,000 feet, can I fly under the airspace without any permission?

Yes you can. The MOA floor, 10000ft in this case, is the lower limit of any restrictions a MOA imposes. Otherwise there would be no point in assigning a floor to MOA (or any other airspace for that matter)
See FAA AIM Section 4. Special Use Airspace


Does FAR Part 121 require at least 45 minutes of fuel remaining upon landing? Assuming the reported weather does not require an alternate airport, if an aircraft being operated under FAR Part 121 domestic IFR lands at its planned destination airport and does not have at least 45 minutes of fuel remaining, is this a violation of the regulations?

No, the regulation only concerns dispatching and taking off. Fuel burn will usually vary a little bit based on unpredicted wind shifts, performance variations and traffic deviations.

  § 121.639 Fuel supply: All domestic operations.

  No person may dispatch or take off an airplane unless it has enough fuel -

  (a) To fly to the airport to which it is dispatched;

  (b) Thereafter, to fly to and land at the most distant alternate
  airport (where required) for the airport to which dispatched; and

  (c) Thereafter, to fly for 45 minutes at normal cruising fuel
  consumption or, for certificate holders who are authorized to conduct
  day VFR operations in their operations specifications and who are
  operating nontransport category airplanes type certificated after
  December 31, 1964, to fly for 30 minutes at normal cruising fuel
  consumption for day VFR operations.


Will this specially shaped can produce any lift? I am wondering if a specially shaped can will produce any lift as it moves through the air.
Please reference the drawing below:

This drawing is showing a hollow can that has been cut so that it will have one side that is higher than the rest of the can. The top of the can is open while the bottom of it is sealed with a plate. This higher side of the can will be moving into the wind as the can travels forward. The can will not be angled, the bottom of the can will remain parallel to the the air flow. Also, the can will be made of a very stiff material so that the higher side of it will not bend backwards.
I believe what will happen is that the air flowing over and around this higher side will lower the air pressure inside of the can and the higher air pressure located below the can will be pushing up on it thus creating lift. I'm pretty sure that this is what should occur, yet I'm asking this question to get verification on it because I am not an engineer and I have a limited knowledge of aerodynamics.
EDIT
To keep the can held firmly in a vertical position so that it doesn't topple over in the wind and to keep it perpendicular to the ground, it could be attached to a side of a car like how a car's side mirror is attached.

Any body that is asymmetrical w.r.t. the flow field will produce lift, possibly negative, but certainly not zero.  To estimate the sign and magnitude of the lift, this body is simple enough to just build and try from a moving car, instead of theorizing or running a CFD simulation.


If a twin-engine airplane's propellers both rotate in the same direction, do they still produce a left-turning tendency? If an airplane with two propellers has both propellers with the same rotation direction (say, both the propellers rotate counter-clockwise as seen from nose to the tail), will  be the four left-turning tendencies still be generated?

Yes, for the most part.

Definitely P-factor will still exist and provide a yaw torque in the expected direction.  This is why twin-engined aircraft have a "critical engine".
Engine torque will still produce a roll torque in the expected direction.
Gyroscopic precession will still produce a yaw torque in the expected direction when the aircraft pitches.
The yaw torque from the spiralling slipsteam interacting with the vertical fin-- which is normally quite significant in conventional single-engine aircraft-- is the one effect that may be be greatly reduced in a twin-engine airplane of the usual configuration, since the fin is not located in a strong part of the circulation behind either prop.


Why does the EGT gauge in 172s have no numbers on it? So the EGT gauge on the 172 (and other cessna singles?) doesn't have a numerical scale on it, just markings every 25 degrees.  I know that one is supposed to use the EGT for leaning operations (ROP, LOP, what have you), but it's always stymied me that there are no actual numbers on it.  Any reason why this is so?

The simple EGT gauges do not have numerical scales because you never lean to a temperature.  You find the peak temperature, set the movable red needle to that temperature, and then lean to x degrees lean (or enrichen to x degrees) of peak temperature.

Set the peak temperature at full throttle, full rich at a sea level airport.

This system eliminates the concerns of calibration: Is the gauge calibrated, did the mechanic install the probe in exactly the right spot, etc. etc.


Why do fabric skin constructions not show up much in larger single engine piston aircraft? I noticed that many ultra-lights use fabric skin but are not seen much in GA aircraft, especially compared to carbon fiber? Many skin makers advertise that it can handle that sort of weight. Is this due to difficulty manufacturing, weight, smoothness of surface, strength of material or other factors?

This answer assumes that "GA" means "little piston planes."

Aluminum (or non-fabric) aircraft tend to "hold up" better against the elements.  I would not store a Stinson 108 outdoors but would not think twice about storing a 172 (or Cirrus) on an open air tiedown.  The fabric covering requires a great deal of care compared to the metal (or composite) skin of most GA planes.

Fabric planes must be re-covered every few decades, more frequently if neglected.  This is a non-trivial operation with a price tag to match.  This typically involves reconditioning the now-exposed structure which adds significant cost.  Re-covering and painting a Cub (small plane), for example, can cost an owner tens of thousands of dollars. Stripping, treating, and painting a "metalized" Cessna 120 (similar to a Cub) is a much easier, faster, and cheaper task.

Another consideration is the availability of aluminum.  Aluminum was declared a strategic material in WW2 and, as a result, a great deal of energy was allocated to increase production.  With the war over and the infrastructure in place to produce a lot of aluminum cheaply, why adhere to an antiquated manufacturing process requiring a painstaking level of detail when lower skilled labor can use cheap aluminum to mass produce high quality planes?

In short, fabric planes typically require more care and attention than their stressed skin cousins.  They also require somewhat specialized and skilled labor to build and maintain.  This generally translates into higher costs for everyone involved.

I'm sure there are technical reasons for the shift away from fabric but I'll let Peter (or another technical expert) comment on those.


Why do airplanes use MAYDAY when in danger but ships send SOS? I thought SOS means "save our souls",  but apparently it doesn't.

But ships send SOS when in danger and they used Morse code.  Why do airplanes use MAYDAY?

The difference here isn't between ships and aircraft: it's between Morse code and voice.

The SOS signal is only for Morse code. It's short, easy to send, and easy to recognise. But it's not as convenient to say. It doesn't actually mean "save our souls". The letters were chosen just to form the simple Morse pattern, and "save our souls" is a backformation: it was made up by sailors later, partly as a joke, partly as a mnemonic.

"Mayday" is an English-looking spelling of French m'aidez, "help me". Spoken out loud, it's short, easy to send, and easy to recognise. It doesn't have any sounds that some nationalities can't say (such as r, th, or v). It's a good signal to use as voice, but would be much worse as Morse code, because it's too long.

Back in the days when aircraft were equipped with Morse code transmitters, they would have sent SOS as a distress call, just like a ship. And a ship with voice radio would send "Mayday" instead of SOS. Now that Morse code has fallen out of use, SOS is also disused. You only hear it in movie plots where the plucky hero doesn't have a working radio but can somehow improvise a way of signalling Morse code (usually by holding two wires together on a broken radio).


Are carbonated drinks considered dangerous goods for air freight? I understand carbonated drinks in allowed in cabin, but, is it allowed in air cargo transportation, when you ship in bulk?

Each operator is of course entitled to apply stricter regulations, but there's no restriction against carbonated drinks in the IATA-DGR (based on the ICAO TI, which sets out the framework for dangerous goods regulations).

The maximum amount of pure CO2 an operator may transport in approved packaging (iaw. IATA-DGR) is:

In gaseous form (UN1013): 150 kg on cargo only aircraft, and 75 kg in passenger/cargo aircraft.
In liquid form (UN2187): 500 kg on cargo only aircraft, and 50 kg in passenger/cargo aircraft.
In solid form "dry ice" (UN1845): 200 kg for both cargo and passenger/cargo aircraft


If I'm cleared to land without any specific instructions on how to enter the pattern, what should I do? I learned at an uncontrolled airport. I thought I had controlled communications down pretty well, but I upset the tower controller today.
Situation:
I was coming from the southeast, and tower told me “clear to land runway 5”. He didn’t tell me what leg to fly or anything. It wasn’t busy. So I stayed straight for the left crosswind. He said I should have never crossed the field. I continued left downwind, base, and final.
I know I should have asked for clarification on how he wanted me to enter. Maybe he was also expecting me to have maneuvered to the west side of the airport for a right base.
I could use some coaching on this. What do you all experienced pilots think?

Your description sounds like the diagram below, so I'll proceed based on that.
When a controller gives you a landing clearance while you are a ways out with no intermediate instructions, it's usually because there is nobody else around the controller needs to coordinate and you are being given discretion to proceed by the most direct logical routing to get to the threshold of Rwy 5.
Although there is a published "left" traffic pattern, and normally you would follow the usual protocols to get established for the left pattern for Rwy 5, the landing clearance at that stage was granting you discretion to use a right pattern if it was more direct and that's what the controller expected. When you crossed the field to get to the "proper" side (blue line below), this would get the controller wondering what you're up to as you appear to be just flying off to the northwest until you turn downwind, especially if you are in the habit of using wide patterns.
I would have proceeded direct to a right downwind or even a right base leg (red or black line below) if I was already line up for that, and would have mentioned that in the readback for the landing clearance, such as "Cleared to land runway 5, proceeding direct right base", just to let the controller know my intentions, and if there was a misunderstanding, I'd find out about it then.
There is a contributor here who is an air traffic controller, so hopefully he/she will chime in.


Why are emergency-instructions by cabin crew like "heads down!" not given via PA? I just saw a YouTube video of a landing airliner with the gear not fully extended and the cabin crew gave the instructions "Stay down! Heads down!" repeatedly to passengers but without any technical help like PA. Why is that the case? Why don't they use the PA system for commands like that?

Not knowing that specific video, impossible to tell the scenario.

But in general, you want to not have to rely on technology in an emergency situation. What if you were trained to use the PA system but there is no electricity?
So you train to shout and use non-verbal communications to get your point across in an emergency.


What's a "gateway operation"? From an AvWeb post regarding Trump's upcoming vacation to Florida:

  Anyone planning to fly in the area should be aware of the potential
  for Notams that might include gateway operations.

What's a "gateway operation"?

Looking at this FAA notice from the 2012 RNC convention in Florida, there are multiple references to "gateway operations" and "gateway airport(s)". Specifically:

  Aircraft not operating under a TSA-approved standard security program ... when the TFR is in effect must be security screened by TSA at a designated gateway airport or location.
  ...
  TSA security screening and gateway operations will be available on August 26 for those operators wishing to operate into St. Petersburg-Clearwater International Airport.
  ...
  TSA security screening at the gateway locations will consist of ID
  verification of all passengers and crew, watchlist matching, physical screening of persons and baggage, and inspection of the aircraft.
  ...
  Positive pilot identification procedures will be in effect during this TFR. Special ATC procedures and routes to and from this airport may be assigned prior to departure from a gateway airport. Upon departing the gateway airport, all aircraft must be on a VFR or IFR flight plan, maintain radio contact with ATC and continuously squawk an ATC-assigned discrete transponder code. Intermediate stops are not authorized unless there is an emergency. If an intermediate stop occurs, aircraft will be required to return to a gateway airport to be re-screened prior to continuing flight with the TFR

Then referencing this TSA post:

  Dulles International Airport (IAD) will serve as the newest gateway airport, allowing certain pre-cleared general aviation operations, including corporate aircraft, charter flights, and on-demand operations, to fly directly into Ronald Reagan Washington National Airport (DCA).
  ...
  Aircraft must arrive from one of 17 gateway airports after flight crews have been vetted and passengers screened.

So it would appear that "Gateway operations" are specific security protocols for departing and arriving aircraft within a certain restricted area.

EDIT:

It appears that, if "Gateway Airports" and "Gateway Operations" are synonymous, that it is about strict preclearance procedures defined post 9/11. As far as I can tell, these restrictions are permanently in place for flights in Ronald Reagan National Airport (DCA), due to the obvious risk the airport's proximity poses to various Federal government buildings.

These rules are called "DASSP" for DCA Access Standard Security Program. The consist of the following regulations

  TSA inspection of crew and passengers.
      TSA inspection of property (accessible and checked) and aircraft.
      The start and end dates of flight must be indicated on the TSA flight authorization.
      Identification checks of passengers by TSA.
      Submission of passenger and crew manifests 24 hours in advance of flight.
      Enhanced background checks for all passengers and fingerprint based criminal history records check (CHRC) for flight crew.
      Armed Security Officer (ASO) on board each flight.
      All operations are subject to cancellation at any time.
      All unscheduled operations to/from DCA require an FAA Slot Reservation.


Why do we say certain things three times (e.g., "Mayday, Mayday, Mayday"), rather than two or four? Repetition is a key characteristic of communication in the control tower, cockpit, and control room.  Some phrases, like "Mayday" get repeated. The speaker says the same thing three times. We know this is for redundancy.

Why exactly three times?

Why not twice or four times? Is there research suggesting three is the most effective number, or is there a historical reason for the convention?

Yep, the critical commands are repeated 3 times.  This ensures there is ABSOLUTELY zero doubt in anyone's mind (especially on a big crew airplane) of what needs to be done in a critical situation.  It also standardizes these criticalities across different aircraft and aircrew cultures.  "Bail out, bail out, bail out"  "Eject, eject, eject"  "Abort abort abort" "Pan-pan, pan-pan, pan-pan."  I was 27 years a USAF pilot, and this is how the training has worked for over 50 years.  I only saw these terms used 2-3 times, but it certainly gets your attention and amps up the sense of urgency.  A little history:  back in the day of very poor radio communications, it was necessary to repeat to "get someone's attention" or in the event a single "mayday" didn't come across when the transmit button was pressed.


Are Boeing 737 winglets adjustable from the cockpit? As I taxied past some Southwest 737s during a recent trip I saw what appeared to be different angles of the winglets relative to the wing. Are winglets adjustable, are they arranged differently from Port to Starboard, or is it an optical illusion?

Winglets are fixed to the ends of the aircraft. As can be seen below, the winglet has no movable parts and is fixed to the end of the wings.

http://www.sae.org/dlymagazineimages/2861_2313_ACT.jpg

Boeing 737 winglet; image from sae.org

What you'd seen is an optical illusion. The port and starboard side winglets would not be much different, usually (except that they are mirror images externally).

Interestingly though, Boeing has filed a patent for an adjustable winglet. Airbus is also working on a similar project, called the morphlet.Both of these are geared towards reducing drag and saving fuel.


Does wing with bell lift distribution has negative lift at tips? Does wing with bell lift distribution has negative lift at tips during cruising flight?
Looking at this diagram, tips has very small lift but it is not negative.

https://ntrs.nasa.gov/citations/20180004462  open pdf

1. Summary
As your first plot shows, the optimal Bell-Shaped Lift Distribution (BSLD) is positive throughout its span for an untwisted planform. What's different is that the downwash near the wingtip is negative for the BSLD, thereby giving rise to an apparent thrust and decreasing the overall induced drag compared to the Elliptical-Shaped Lift Distribution (ESLD).
However, for a non-optimal BSLD, you may get negative lift near the wingtips. And when there is geometric/aerodynamic twist, then you will almost certainly get negative lift over some portion of the span at AOAs lower than your design point.
2. Reasoning
Inspired by an Aerocrafty blog (be cautious that the derivation in that article contains some minor errors), we can derive an approximate BSLD without resorting to complex analysis. From Lifting-Line Theory, section lift ($L^{'}$) and upwash ($w$) are given as follows:
$$L^{'}(y_0) = \rho_\infty V_\infty \Gamma(y_0)$$
$$w(y_0) = -\frac{1}{4\pi} \int_{-b/2}^{b/2}\frac{(d\Gamma/dy)}{y_0-y}dy$$
where $y_0$ is the lateral span coordinate, $b/2$ is half span, $\Gamma(y_0)$ is the circulation distribution of the bound vortex, $\rho_\infty$ is the free-stream density, and $V_\infty$ is the free-stream airspeed.
Through a transformation of coordinates (from Cartesian to polar):
$$y=-\frac{b}{2}\cos{\theta}$$
We can write any general circulation distribution as a Fourier sine series:
$$\Gamma(y) = \Gamma(\theta) = \sum_{n=1}^{\infty} {A_n\sin{n\theta}}$$

For an ESLD, the circulation distribution is only the first term, with $A_1=\Gamma_{e_0}$, where $\Gamma_{e_0}$ is the circulation at wing root:

$$\Gamma_e(\theta) = \Gamma_{e_0}\sin{\theta}$$

For a BSLD, we will only keep the first two terms and truncate the rest (noting that due to symmetry, only odd terms remain):

$$\Gamma_b(\theta) \approx A_1\sin{\theta} + A_3\sin{3\theta}$$
Now we can solve for the unknown coefficients $A_1$ and $A_3$ in the BSLD distribution by requiring that a comparative ESLD must have the same total lift ($L$) and root bending moment ($B$):
$$L = \int_{-b/2}^{b/2} {L^{'}dy} = L_e = L_b \tag{a}$$
$$B = \int_{-b/2}^{b/2} {yL^{'}(y)dy} = B_e = B_b \tag{b}$$
That's two equations and two unknowns. The solutions are:
$$A_1 = \frac{b_e}{b_b}\Gamma_{e_0}$$
$$A_3 = \frac{5\Gamma_{e_0}}{3} \frac{b_e}{b_b} \left( \frac{b_e}{b_b}-1 \right)$$
where $b_e$ is the wing span in the ESLD case satisfying (a) and (b), while $b_b$ is the wing span in the BSLD case. That is, we are expressing BSLD as a ratio of span ratio compared to an Elliptical case with the same total lift and root bending moment. Notice that when $b_e/b_b = 1$, we retrieve the ESLD exactly.
2.1 Validation
In the beginning, I mentioned that this derivation is an approximation. But it's not a bad one. Calculating the total induced drag with this formulation, we get:
$$D_i = \frac{2L^2}{\rho_\infty \pi b^2 V_\infty^2} \left[\frac{25}{3} \left( \frac{b_e}{b_b} \right)^4 - \frac{50}{3} \left( \frac{b_e}{b_b} \right)^3 + \frac{28}{3} \left( \frac{b_e}{b_b} \right)^2 \right]$$
Compare this with the exact result from NACA TN-2249:
$$D_i = \frac{2L^2}{\rho_\infty \pi b^2 V_\infty^2} \left[8\left( \frac{b_e}{b_b} \right)^4 - 16\left( \frac{b_e}{b_b} \right)^3 + 9\left( \frac{b_e}{b_b} \right)^2 \right]$$
2.2 Results
Time to get back to the question we began with, can the lift (or circulation) distribution be negative on any part of the span? The plot below shows the circulation distribution of our approximate solution for various ratios:

For our approximate formulation, the most optimal BSLD occurs at $b_e/b_b = 0.8$ ($b_b/b_e = 1.25$ in the plot). As you can see, it's all positive up to the wing tip.
However, as we keep increasing the span (while maintaining total lift and root bending moment), at some point the distribution goes negative near the wingtip. Eventually the bending moment at certain points along the span will exceed that at the wing root (Ref NACA TN-2249).


What’s the purpose of the small “hole” in front of wing root on A320-214? Someone knows what’s the purpose of this little “hole”?

It leads to a vent in the cargo compartment that Airbus calls "Outlet-Extraction". It must be an option that isn't installed very often.


How can a pilot fly a distance of 594 NM connecting two VOR's? I was researching worldwide airway designations when I stumbled upon this airway in Brazil: G678 with an MEA of 15,000 feet and a distance of 594 NM (nautical miles) between navaids.

It's drawn between the BSI and ATF VOR's. Mid-airway around S12°50.12' W52°4.38'.

Flying at 15,000' with BSI at elev ~3500', the line-of-sight is 166 NM. And as far as I know a high altitude VOR reaches out to 130 NM, maybe more, but certainly not 300 NM, right?

The "G" designation is for a non-area navigation route per ICAO annex 11. So it's a non-RNAV route. It's even colored black (vs. blue) on skyvector.

  A, B, G, R for routes which form part of the regional networks of ATS routes and are not area navigation routes.

So, how can it be flown?

You are correct that VOR's rarely have a range of more than 200 NM. However, Alta Floresta VOR (ATF) is colocated with an NDB (and DME). In spite of less accuracy, NDB's have a much greater range (partly because their signals can travel as ground waves). This makes it possible to have a very long segment on the G678 airway without other navigation aids. When leaving the coverage of Brasília VOR/DME (BSI), you should be able to pick up ATF NDB.


How do wing tip vortices that interact with the wing surface affect drag? Often people say vortices are behind the wing so they cannot produce drag, I am not interested in those vortices behind the wing....
I am interested how wing tip vortices which interact with the surface of the wing affect drag and does it make sense to reduce the area of wing tip, because of them?

Wide vs narrow wing tip:

MEng Aeronautics and Astronautics student at Southampton uni here. We've been studying this in some detail recently and I've found that MIT has released a set of lecture notes on finite wing theory, including a really useful document focussing on tip vortices and their impact on aerodynamic performance (http://web.mit.edu/16.unified/www/SPRING/fluids/Spring2008/LectureNotes/f05.pdf). This explains the induced drag acting on a wing/other lifting surface which is caused by tip vortices generating downwash, which in turn alters the wing's geometric angle of attack.
Hope this helps, or at least gives you a starting point for further research :)


Could a P-3 Orion fly off a carrier? The C-130 has proven itself eminently capable of landing on a carrier.

When the S-2 Viking was retired, the Navy didn't really have a good replacement for anti-submarine ops - but anti-sub warfare had also fallen in importance.

Suppose there is a resurgence in need.  The Navy has an excellent ASW aircraft in its inventory; the P-3 Orion (modded L-188 Elektra).  It's not made for carrier operations, but then, neither was the C-130.

Suppose we sort out the smaller details, like making sure the P-3 can refuel from carrier-based aircraft like the F-18 (and thus can take off and immediately tank).  This must be a rolling-on-tires operation; cat launch or tailhook recovery is out of the question.

If the captain can guarantee 35 knot headwind, could the Orion do a "rolling on pavement" takeoff and landing off the carrier?  If needed, it can use the whole deck, obviously it would work better operationally if it could use the diagonal strip.

Well, going beyond just judging from the Electra's itty bitty stubby wings, digging around for Electra performance data I found a page that gives a takeoff distance of 1290 meters, or 4200 feet, which would most likely be the distance at sea level, standard day, max gross.  Which is what I would expect with such itty bitty stubby wings.

Even allowing for more power in the military versions, I'd say it's safe to go with no.


Is there any specific reason why Delta Air Lines doesn't have its own callsign? Many airlines have their own callsigns for use over the radio. A British Airways plane is called "Speedbird", US Airways was "Cactus", etc. So why doesn't Delta Air Lines do the same? It would seem to need one a lot more than others, since "Delta" is the NATO Phonetic Alphabet name for "D", so it would seem to present a huge potential for confusion.

Atlanta airport, Delta's headquarters, uses "Dixie" for the letter, specifically to avoid confusion with the airline. It just seems easier and safer to me for the airline to adopt a callsign rather than deviating from the phonetic alphabet.

Delta Air Lines uses the ICAO three-letter designator DAL and the ICAO telephony designator (also known as callsign) DELTA.

In general, callsigns should be similar or equal to the name of the airline according to the following ICAO rules:

  3.2 In the registration of telephony designators the following rules will apply:

  a) the chosen telephony designator should attempt to resemble the name of the aircraft operating agency or its function
  and be distinct and dissimilar from any other telephony designators in Doc 8585. Ideally it should reflect correlation
  between the three-letter designator, the telephony designator and the name of the aircraft operating agency or its
  function (examples: ARO – ARROW – Arrow Aviation; RAJ – RAJI – Raji Airlines);

  b) in order to reduce the length of transmission the telephony designator should be brief, comprising if possible one
  word of two or three syllables. It should not exceed two words;

  c) three-letter designators may not be used in phonetic form as telephony designators. However, telephony designators
  of long standing (such as KLM or TWA) may be retained, provided that an acceptable alphabetic representation is
  used (example: KAY-ELL-EMM); and

  d) the telephony designator should be easily and phonetically pronounceable in at least one of the following languages:
  English, French, Russian, Spanish.

(ICAO Doc 8585 3. Telephony designators, emphasis mine)

Different callsigns can exist for two reasons:

Old callsigns: Several old airlines use callsigns that existed before these rules were made, like e.g. KLM as mentioned in c). British Airways inherited the callsign SPEEDBIRD from BOAC in 1974, which in turn inherited it from Imperial Airways in 1939. It is named after the design of the Speedbird logo.
Conflicting callsigns: When the airline name is too similar (or equal) to an existing callsign, a different one must be chosen, like e.g. Norwegian mentioned in J. Hougaard's answer. US Airways inherited CACTUS from America West in 2008:

  Early in its history, the airline used the call sign “America West” but it often caused confusion with other airlines ending in “west” (Southwest, Northwest, Skywest). The FAA suggested that America West come up with a new call sign. The company held an employee contest to come up with the new name. Cactus was chosen.

(aerosavvy.com)

While Delta Air Lines is quite old ("Passenger operations began on June 17, 1929", Wikipedia), it did not chose a different callsign. I can only speculate on why, but note that the ICAO phonetic alphabet is only officially used for civilian aviation since 1 April 1952. Before than, other alphabets were common, including the Allied military phonetic spelling alphabets, which used DOG instead of DELTA, so there was no conflict at the time.

Using a different word when confusion is likely (like DIXIE in Atlanta), is explicitly allowed in the US:

  ATC facilities may also request pilots to use
  phonetic letter equivalents when aircraft with similar
  sounding identifications are receiving communications on the same frequency.

(AIM 4−2−7. Phonetic Alphabet)


How many turns of a 737 trim wheel equal 2.5 degrees stabilizer deflection? After the well known crashes I looked at the question of stabilizer trimming. In case of trim runaway the pilot is supposed to "grasp and hold" the wheel manually steering the stabilizer. Hence my question: how many turns of the wheel to achieve a 2.5 degrees deflection of the stabilizer?

About 45 Rotations

In this YouTube video you can see Mentour pilot demonstrating manual trimming of a Boeing 737 NG. They start at about 11:30 with:

  we have 4 units nose down now

and at 12:30 they say:

  now we are at about 3 degrees

I counted 18 full rotations of the trim wheel in this time. This would result in

$$ \frac{18}{4^\circ - 3^\circ} \times 2.5^\circ = 45 $$

rotations for 2.5 degrees of trim change.

Note that the trim indicator is not very precise, so the number is only an estimate:

(frame from the video)


How much lift does the wing attach fitting actually carry? How do I calculate the lift force that the the bolt that join the wings to the fuselage of a strutted or braced airplane carry?

I know in a cantilever airplane,the bolts have to carry all of the lift load on a wing but how about a strutted airplane - how do the wing attach bolts share the lift with the wing braces or struts, i.e. is the lift load shared between them, the bolts carrying half and the bracing wires or struts carrying the other half?

The answer depends on the elastic deformation of wing and strut. Extreme example: Make the strut a rubber band and all lift needs to be carried by the wing and its fittings. Other extreme: Make the wing spar (or attachment points - this works either way) from rubber - now the strut needs to take all the loads.

In real life, stiffness attracts tension and compression, and in order to know the load distribution between wing spar and strut you need to look at them with a slight deformation from loading. How much resistance does each show (in isolation) against that deformation? This will tell you in what ratio the forces will split between wing and strut. Make sure to use the stiffness of the real structure - the material property called Young's modulus is not what I mean here.

If you want to be safe, you need to consider any single point failure and still have a flyable airplane. Normally, you design your structure with a safety factor (usually 1.5, but higher for fittings). Now assume that in turn each of the structural members is missing and calculate the loads on the remaining structure with a safety factor of 1.0. Dimension each part at least for those loads and you should be pretty sure that the intact structure will work out fine.


Which items are allowed on passenger flights but not on cargo ones? I've only ever sent items by air in suitcases accompanying me in passenger flights. But - I'm about to send some items on a cargo-only flight in a few days. I've been told:

  Make sure that there are no dangerous goods in the shipment please (batteries, aerosols, perfume etc.)

while on passenger flights, you can definitely have batteries, aerosols and perfume in your hold luggage. You can even have that in the cabin under certain limitations.

So, my question is: What is the specification of which materials are forbidden for air transport in cargo flights as opposed to passenger flights? And is there a globally-accepted standard for this, or is it airline-by-airline?

I don't know of anything that is prohibited on a cargo flight but not on a passenger flight. There are some things that are the other way around.

On a cargo flight you must declare any dangerous goods and usually pay a DG surcharge. Certain types of DG require seperation from other types. Some need to be segregated into a container that is accessible to the crew in an emergency or has a fire-suppression equipment.

Each country has its own laws as to what is acceptible and the proper documentation required. And each company will have their own set of rules. At my employer we use the slightly more stringent IATA guidelines. This ensures compliance with each country.

The passenger airlines are also required to follow these rules. Passenger luggage is contained in class C cargo holds which are required (at least in the US) to have a fire suppression system as well as a smoke detection system. In an all-cargo aircraft much of the plane is a class E hold, which must have smoke detection, but not a fire suppression system. Therefore certain types of DG have to be segregated into a class B or C area.

So, you can carry perfume in your luggage because the holds on a passenger plane are all class C, where there is fire suppression. But if you send a box of perfume in a cargo flight without declaring it, then it will most likely be loaded in a class E hold where it won't be compliant.


How can filling a tube with foam help prevent buckling? How can filling the empennage (aluminium tube) with Styrofoam stiffen it to avoid buckling as seen in Whingding ultralight?

A simplified analysis of column buckling shows that the axial load required for buckling is directly proportional to the second moment of area of the column's cross section: $F=\pi^2EI/(KL)^2`$`, where F is the buckling load, E is the elastic modulus of the material, I is the second moment of area, and KL is an effective column length based on the geometric length of the column (L) and a variable factor K that is based on the boundary conditions.  The critical term for this question, though, is I.

For example, look at the picture below of a beam that someone is trying to bend.  You can do this yourself with a ruler or a paperback book.

In the upper image, you're trying to bend the book/ruler by pressing down on the spine, and it's really hard to do.  Rotate the book 90 degrees and press down on the cover...and it's relatively easy (unless you picked a phone book).  The material of the book didn't change, only how the area of the cross section that you were bending was distributed in the direction that you were trying to bend the book.  In the same way, adding foam to the tube increases the total area that needs to bend in order for the tube to buckle, which, if you'll allow an approximation, increases the strength of the tube by 5% from the baseline case (a hollow, aluminum tube).  Double the radius, and that becomes 10%.  Double it again, and that goes to around 25%.  Don't take those numbers as gospel, but it should give you an idea that adding area -- even with a relatively low stiffness material -- you can increase the strength of a material significantly.

However, buckling is different from strength.  Buckling is a bending instability caused by compressive loads, and failures in buckling often occur well below the failure load for the structure.  Let's run some numbers for this, using the expression I mentioned back up at the top.

For example, if I run an analysis for a 4.5 ft long, hollow, 1 in diameter tube with a wall thickness of 1/16 of an inch made out of 7075-T6 aluminum (E = 10.3 msi) with both ends effectively pinned, I get a buckling load of 714 lbf (note: the axial compressive load that would make this structure yield would be closer to 8,000 lbf).  Naturally, one could fill that in with metal and increase buckling load dramatically to 1,727 lbf, and, while that's not the query, I am adding some bending stiffness to the tube by filling in the center.  Buckling of a composite column (insofar as I know) is tricky, but, here is an approximation (which will undershoot the actual buckling strength).

If I add foam and say that the foam will not buckle (as it is fully constrained by the tube and cannot deform in any direction save axially, let us say), and then assume also that the purely axial load on the column will be divided between the foam and the aluminum according to the proportion of their elastic moduli (polystyrene has a Young's modulus of about 2.5 GPa), then the aluminum will only absorb about 88% of the load placed on the column.  This increases the buckling load by about 100 lbf (without causing the foam to yield).  However, this does not take into account how the foam will add bending stiffness to the structure, which would further increase the benefits of adding the foam.

In short, you're using a low-weight, cohesive filler material to increase the bending stiffness of a structure, dramatically increasing its tolerance for compressive loads.


How are runway conditions measured? Which method is used to measure the runway conditions?
Is it impossible to land on a contaminated runway?

Measurement

Runway conditions are measured using a friction standard: ICAO Circular 329, Runway Surface Condition Assessment, Measurement and Reporting.

Local regulation applies too, e.g. for UK: RA 3272 – Continuous Friction Measuring Equipment.

  Adequate runway friction characteristics are needed for three distinct
  purposes:

  deceleration of the aeroplane after landing or a rejected take-off;
  maintaining directional control during the ground roll on take-off
  or landing, in particular in the presence of cross-wind, asymmetric
  engine power or technical malfunctions;
  wheel spin-up at touchdown.

(Source -- Source also used for most of the technical details in this post)

Continuous Friction Measuring Device / Equipment (CFMD / CFME)

(Source: Team Eagle)

(Source)

Decelerometer, Brakemeter, Dynometer... for snow and ice.

(Source: Sherwin Industries)

Minimum Friction Level (MFL) μ is specified by local air authority. A value less than 0.34 is seen by ICAO as slippery.

Friction is measured for each third of the runway, in a direction parallel to the runway centerline.

(Source)

Reporting

Runway friction coefficient should be measured at least daily and reported via NOTAM if needed. NOTAM codes for friction measurement equipment:

BOW Bowmonk Decelerometer
BRD Brakemeter-Dynometer
ERD Electronic Recording Decelerometer
GRT Griptester
MUM Mark 4 Mu Meter
RFT Runway friction tester
SFH Surface friction tester (high pressure tire)
SFL Surface friction tester (low pressure tire)
SKH Skiddometer (high pressure tire)
SKL Skiddometer (low pressure tire)
TAP Tapley Decelerometer

A contamination terminology is used for a qualitative description of the runway condition. It can be used in complement of the friction coefficient value, or alone when a measure is not possible.

Sample for water on the runway:

DAMP: the surface shows a change of colour due to moisture.
WET: the surface is soaked but there is no standing water.
WATER PATCHES: significant patches of standing water are visible.
FLOODED: extensive standing water is visible.

Other terms exist for snow, ice, etc.

  A runway or portion thereof shall be determined as being slippery when
  wet when the measurements with a CFME + self wetting tyre shows that
  the runway surface friction characteristics are below the minimum
  friction level specified by the State.

NOTAM sample:

NOTAN A1713/11 Chennai Airport ( VOMM ),  India
A1713/11 1111220910/1112231200 EST RWY
RWY 07/25 LIABLE TO BE SLIPPERY WHEN WET.
THE VALUE OF COEFFICIENT OF FRICTION IS BLW
THE NOTIFIED VALUE OF 0.34 FOR RWY 07/25
IN SECTION AS BLW :-
RWY07 BTN 400M AND 650M
RWY25 BTN 300M AND 500M

As commented by @RonBeyer (thanks!), pilots can also provide their own observations about braking conditions to ATC using PIREPS. PIREPS are voluntary reports by pilots to share information with ATC and other pilots. They are valued because they are current and they may be the only information available at small airfields.

ATC and recorded bulletins provide runway conditions to pilots, in addition of NOTAM.

Impact on roll distance

Weather has many impact on operations, but runway contamination particularly impacts landings, due to the loss of braking capacity. Take-off are also impacted, mostly at the beginning of the take-off roll, when the control surfaces are not active. Runway condition is also important to take into account if a take-off has to be rejected.

A degraded runway condition decreases the longitudinal stability and increases the roll distance:

Note: As mentioned by @Yos233, autobrake LOW and MEDIUM have been inverted
(Source)

Thrust reversers are particularly useful when the runway is not dry:

Note: Autobrake LOW and MEDIUM still inverted
(Source)

Pilots will use similar tables to determine if they can land or take-off. A flight management computer can also be fed with the runway condition for roll distance determination..

Aircraft are tested for their ability to cope with different runway conditions:

A340 test on artificially flooded runway (source)

Note that it is possible to land and take-off quite easily on compacted snow -- and, albeit more difficult, on ice -- taking into account the coefficient of friction:

Alton Bay runway (source)

More

Description of Various Friction-Measuring Equipment
Used in Winter Operations (appendix A)


What happens if the gust alleviation system on an A380 fails? In an answer, a user linked to this video of the gust alleviation system (GAS) on an A380. This seems like a complex system with many moving parts—all the ailerons move completely independently. What happens if the GAS fail, if for instance two ailerons get stuck in an extreme position?

Or maybe even worse: imagine a sensor failure that produces two opposite extremes on each wing, such that e.g. the left wing have all its ailerons in the up position, and the right wing ailerons in the down position.

Could this be fatal?
Are there procedures for this in some checklist?

This is a follow-up for my other question, What is a gust alleviation system?.

This is not question Why do some aircraft have multiple ailerons per wing? as far as I can possibly see (though it was marked as such).

You have a few questions here so I will address them independently. But first off in a more general sense you should understand that everything on an airplane is generally designed with a failure mode this helps to ensure that if something fails it fails in a way to create the least adversity to flight. However there are event scenarios where multiple units fail in such a way that an adverse condition can be encountered. Generally (if you read accident reports) these can be avoided if an emergency landing is executed earlier on.

  What happens if the GAS fail, if for instance two ailerons get stuck
  in an extreme position? Or maybe even worse: imagine a sensor failure
  that produces two opposite extremes on each wing, such that e.g. the
  left wing have all its ailerons in the up position, and the right wing
  ailerons in the down position.

In this case the plane still, to an extent controllable. I don't know for the Airbus, but generally speaking all systems like this have a manual override and can be disconnected. So this is implying that the system is somehow stuck on and not responding. It should be noted that in the Airbus this system does not independently actuate the flight control surfaces and most likely is bused as input to the fly by wire system. On that note a sensor failure generally does not cause extreme inputs but instead causes no input. Most things like this are at least triple redundant (so that you can figure out which sensor is bad) and if all are providing inputs that disagree the system usually disconnects and becomes inop. So to create the case you ask about you would need to have 3 independent sensors provide the same erroneous input which is highly unlikely.

  Could this be fatal?

Its hard to say, but generally speaking no, the direct failure of a single system would not be fatal.

  Are there procedures for this in some checklist?

More than likely but I don't have access to the official checklists so I cant say for sure.


How does GPS measure any plane's ground speed? How does GPS measure an equipped airplane's ground speed assuming that the plane in question actually uses GPS as opposed to an inertial navigation system or other method?

(This was originally part of another question)

GPS is primarily made to determine the position of the receiver.
Therefore, GPS uses several satellites with exactly known positions which send very precisely timed signals. From the time difference between the signals when arriving at the receiver, the own position in space can be calculate, typically given in earths coordinate system.

Get the position two times, calculate distance, divide by time difference, and you have speed.

Another way is to measure the frequency of the signals from the satellites, since it slightly varies with speed due to the Doppler effect. This is similar to the shift in pitch of the horn of a police car passing you.
This method gives you a speed value directly with your position.

As side note:
GPS often is not that precise and gives your position with some offset. BUT the offset is mostly constant, so while the position is not correct, the distance traveled and so the speed is.


Why don't we place the engine in the front of the wings? I learnt in class today that fast-moving air over the wing of the plane, which causes a difference in pressure on the airfoil due to something called Bernoulli's principle.
If this is so why cant the engine be placed in front of the wings since the exhaust from the engine can help the plane in take off.
I'm only a beginner at fluid dynamics thus the silly question.

They can be, as on the An-72/74, which has the engines mounted above and forward of the wings in part to increase lift, utilizing the Coanda effect.
One downside is that this makes access for maintenance more difficult, which is a large factor in operation costs.
https://en.wikipedia.org/wiki/Antonov_An-72
https://en.wikipedia.org/wiki/Coand%C4%83_effect


Can an airplane fly with greater weight than lift and how? I just really don't understand how an airplane can fly with greater weight than lift.

There are many situations where the weight is not equal to the lift.

Lift is, per definition, the aerodynamic force perpendicular to the undisturbed incoming airflow.

The weight of the aircraft is due to gravity, hence pointing down.

An example of a steady situation in which the lift is not equal to the weight is the climb phase. During climb the lift is actually less than the weight.

In your comment you mention a weight-to-lift ratio of 5 : 4. If that would be during an unaccelerated climb, the flight path angle would be 37 degrees and the thrust minus drag would have to be 60% of the weight.

The image below shows the weight vector $W$, lift vector $L$, and excess thrust vector $T$ in a ratio 5:4:3.

The combination of the lift and thrust vectors is equal is size and opposite to the weight vector. It is denoted $W'$ in the image.

For simplicity I left drag out of the image and assumed thrust is purely acting in the direction of travel.


With power off, is it possible to maintain constant altitude for some period of time, until the stall speed is reached? With power off, is it possible to maintain constant altitude for some period of time, until the 1-G stall speed is reached, i.e. until the stall angle-of-attack is reached?

Implicit in the question is the assumption that the initial airspeed is above the 1-G stall speed.

Yes, assuming your are flying level with the engine running and then you turn the engine off, the following will happen:

Without power from the engine, the drag will cause the airspeed to decrease.
Lower airspeed at the same angle of attack implies less lift. Since you want to maintain altitude, lift needs to stay the same (your weight has not changed). Thus, you have to increase pitch.
Eventually, you will reach the critical angle of attack and flow separation will occur, i.e. you stall. The airspeed at which this happens is called the 1-G stall speed, although one can stall any speed.


What is the purpose of this item next to the cockpit window on the B737? Hello does anybody know what the purpose of this odd looking shape is

That protrusion makes it so that the pilot can only grasp, and activate, the handle by sliding his hand in to it from behind - which requires a deliberate action, rather than by accidentally resting one's hand on it from above. Since the window opening inadvertently is undesirable, it makes sense to block off the most likely means on unintentionally grabbing the handle.

It also provides a visual reference for the handle being in the locked closed position... if the handle is aligned with the fairing, it's locked; if not then it isn't.


How did the long loop of tape in a magnetic cockpit voice recorder work? How was the continuous looping of tape in an old-school mechanical cockpit voice recorder physically implemented? 30 minutes seems like a lot of tape to loop continuously, did it move more slowly than a normal audio tape?

Most looped tape mechanisms are a variation of this:

(this is an 8-track audio cassette)

The tape is pulled from the center of the spool, and fed back to the outside of the spool.

Some CVRs use two spools and autoreverse instead.

On the right, an example of a flight data recorder. (on the left, the digital storage of a modern FDR).


Why is the normal operating airspeed so much lower than the cruise speed in this table? I need to work with the following table. I'm interested in vMO which I assume I can simply obtain from converting MMO to vMO through $M = v/ \sqrt{1.4 * 287 * T}$. (Is that correct?)

However, I noticed that the vNO is more than 100 kts less than vcr in this table. From my current understanding, vcr should be given as a TAS, which would mean that the the only way in which vNO could be lower than vcr would be that vNO is given in IAS. However, in that case the difference should be much more than 100 kts, right?

You really answered your own question. Vne is based on IAS, the actual aerodynamic pressure at any given altitude and speed.  This is why the Mach number is included too, as approaching transsonic adds additional stresses to the airframe.

TAS, as mentioned in previous threads will be much higher than IAS at 35000 feet.  It is fun to enter speeds and altitudes into the TAS calculator to see how close one gets to Mach 1 at 250 IAS when you climb.

TAS is groundspeed without wind speed and direction factored in.  It is the actual aircraft airspeed relative to the airmass. Notice 480 is Max Cruise.