Why is the A320neo considerably ahead of B737Max? The A320neo has a 16% higher market share, 1022 more orders, 316 more MoU's and $122.1 bn greater estimated value than the B737Max.

Though both were released at almost the same time (231 days gap) with identical features and price (rather B737Max is  $15 mn cheaper), why is the A320 flying past the B737?

Data source : PDXLight

I certainly would not say that the 737 MAX is "losing heavily" to the A320neo. The A320neo is entering service in the next couple of months (October 2015.) The 737 MAX isn't entering service for another 2 years (2017.) I don't think many aircraft manufacturers would be upset with having 2,727 orders for an aircraft that is still 2 years from even entering service. It should further be noted that the A320neo was right around the same total when it was 2 years from entering service.

Some additional factors that come into play:

The A320 line tends to be more popular in the low-budget Asian market, which is growing significantly right now.
The U.S. Dollar is currently relatively strong compared to the Euro, due to lots of economic problems in the Eurozone. This means that products exported by European manufacturers are relatively cheaper than products exported by American manufacturers compared to their usual price difference. Obviously, that's an advantage for Airbus, as it means that it's cheaper than normal right now for customers to buy Airbus vs. buying Boeing. This is, again, especially important to the cost-sensitive low-budget markets.
Airbus' Chinese assembly line allows them to make A320s for the Asian market quite a bit cheaper than Boeing can make 737s for that market, due to the major differences in labor costs.


What are the rules in the UK about overflying built-up areas for fun? I live in North London.  It's not like we don't have a fair amount of noise pollution from the sky, with helicopters, and jets landing at LHR with a stupidly shallow glide path angle.

But in addition, quite often on a Sunday afternoon I hear this buzzing of a small propeller plane.  It often seems to circle the area quite a few times before eventually going away.  We had one today: I looked at it, and (this time) it was a small plane with two props, one on each wing.  I have no idea what type of aircraft it might have been.  It was flying low enough for the buzzing to be distinctly intrusive, and therefore affecting potentially tens of thousands of people.

It may not have been a flight simply for fun. I presume there's no way of finding out... but does anyone know what the rules are for just randomly deciding to fly over a built-up area like this for the fun of it?

PS I have friends in Cambridge and you often see small light planes overflying that town. They have a friend who owns a light aircraft, and once or twice my friends have said "oh, yes, that's Jim's plane", and have confirmed he does it for recreation.

Does anyone know what the rules are for just randomly deciding to fly
  over a built-up area like this for the fun of it?

In UK, the master document for air regulations is The Rules of the Air Regulations (ROTAR). UK being still part of the EU, they refer to a common set of rules at the EU level, the Standardised European Rules of the Air aka SERA (qui sera sera...)

UK ROTAR state a minimum flyover height, one for VFR, one for IFR:

  The minimum heights for VFR flights shall be those specified in
  SERA.5005(f) and minimum levels for IFR flights shall be those
  specified in SERA.5015(b)

and SERA says:

  SERA.5005:

  (f) Except  when  necessary  for  take-off  or  landing,  or  except
  by  permission  from  the  competent  authority,  a  VFR  flight shall
  not  be  flown:

  (1) over  the  congested  areas  of  cities,  towns  or  settlements
  or  over  an  open-air  assembly  of  persons  at  a height  less
  than  300  m  (1  000  ft)  above  the  highest obstacle  within  a
  radius  of  600  m  from  the  aircraft;
  (2) elsewhere  than  as  specified  in  (1),  at  a  height  less
  than 150  m  (500  ft)  above  the  ground  or  water,  or  150  m
  (500  ft)  above  the  highest  obstacle  within  a  radius of 150 m
  (500  ft)  from  the  aircraft.

So for VFR: 150 m, but 300 m in populated areas.

  SERA.5015:

  (2) elsewhere  than  as  specified  in  (1),  at  a  level  which
  is  at  least  300  m  (1  000  ft)  above  the  highest  obstacle
  located within  8  km  of  the  estimated  position  of  the  aircraft.

And for IFR: 300 m above obstacles.

As you see this is not very high. In addition, as you mentioned, aircraft landing or taking off will indeed fly below these minimums.

  Jets landing at LHR with a stupidly shallow glide path angle

Landing cannot be done at high angle, the proper slope is the result of two elements:

Aircraft cannot afford a high descent speed, since the vertical rate determines how hard the landing gears will touch the runway and whether they will be damaged.
Aircraft cannot slow down under a given speed without losing their capability to create lift. This minimum speed and the previous maximum vertical speed determine a maximum slope.

This glide slope has been chosen so that it is compatible with all sorts of aircraft approach speeds and vertical rates.

A standardized value of 3° is common. But when the approach area is limited, or when this is desirable to maintain a higher altitude a longer time to reduce noise on the ground, then this angle can be increased to 3.5 or 4.5°, or even 5.5°, this is the case for some approaches at Heathrow as @TomMcW told us.

Source

Alternatively, some airports have lower angles, down to 2.5°.


What are the effects of dihedral on net lift of a wing? I read somewhere on the internet that dihedral decreases wing lift,so my question is will dihedral decrease the lift of an airplane wing since the wings are attached to the fuselage  at an angle ? If yes,will anhedral also decrease the lift produced by the wings?
If dihedral/anhedral decrease wing lift,is the decrease in lift negligible im comparison to thesame wing(with thesame area,aspect ratio) but without dihedral?

The effect of dihedral on lift can be obtained applying high school trigonometry:

$$
L=L_0 \, cos \,\theta
$$

where $L_0$ is the lift of the original flat wing and $\theta$ is the dihedral angle. This holds true for negative values of $\theta$ as well.

Since the cosine can be approximated by unity for small angles, the net effect is negligible in most practical cases, e.g. $ cos(5^o)= 0.996$


In theory which causes more parasitic drag? A large smooth wing or a small, rough exhaust port? I'm new to aviation and I have a basic, mechanical question.  Wings produce a lot of lift-induced drag, especially at lower speeds.  But according to this chart that drops off as velocity increases.

However despite the fact that lift drag declines as speed increases the wings still represent roughly 70%(+/-) of the surface area of an aircraft and they do produce parasitic drag.

So my question is despite the enormous surface area that the wings represent do small, irregular shaped items such as exhaust ports produce more parasitic drag as a plane nears its top speed?

The pictures below are from a P-51 which has a top speed of over 400mph.  At that speed is the wing or the exhaust port the biggest drag producer?  Or is this maybe a close call?

Thanks so much for any input!

The wing creates more drag due to the much larger area.

The wing is beautifully streamlined and the flow stays attached to the wing if the angle of attack remains below stall values. So friction drag is the only drag that acts upon the wing, while stubby shapes like exhaust ports have friction drag and pressure drag. This means that area for area, short stubby shapes have way more drag, as illustrated in the figure below from Prouty. But multiply with the length of the wing & stub, and the picture changes.

But the exhaust ports don't have pressure drag, because the exhaust gases are ejected backwards, in the spot where normally the separated airflow would extra drag.


What is the wear limit for tires? I have 2500hrs and have flown over 30 types of aircraft. I am also a A&P. I have never seen a POH, manufacture or FAA suggestion for wear limits of a tire. The flight school I got my pilots license (1980), would wear the tires of Cessna training aircraft bald on the outside of the tire and flip them on the rims, then run then bald on the opposite side. On airliners and transport aircraft I have seen chunks of rubber missing, cord and belts exposed, etc more so on freight than passenger aircraft. Surely there must be some standard or legal requirement.

( I have seen FAA, mfg, and other info prohibiting flight if tire pressure exceeds +-5%)

Yes, there is, but it is not by regulation. It is in Advisory Circular 20-97B.

For example, section 7 would apply to most of your pictures:

  (7) In-Service Inspections (Operator).

  (a) Tread Damage Removal Recommendations. Tires that exhibit any of the following characteristics symptomatic of damage should be removed from service:

    (1) Cracking and/or cutting in a tread groove that is undercutting material adjacent to the crack or cutting that has lifted or can be lifted.

      NOTE: Do not probe cuts or embedded FOD when the tire is inflated.

    (2) Undercutting in a tread rib.
    (3) Transverse cracking in the tread that is visible at the surface and shows progression along an angular path down into the rubber.

  (b) General Tire Removal Recommendations. Tires with any of the following conditions should be removed from service:

    (1) Sidewall cuts that penetrate the outermost structural ply.
    (2) Internal separations characterized by bulges or distortions in the tread casing or sidewalls.
    (3) Heat or slippage evidenced by reverted or charred rubber above the wheel flange.
    (4) Tires worn or flat-spotted to the outermost casing ply (bias) or outermost belt (radial).


What is the fastest possible transatlantic flight today? I'm working on a novel that, as part of the backstory, requires samples of a biological agent to be flown from Incirlik Air Base to labs across Europe, and then finally from the UK to the US.

In the context of the story, time is critical. Using any currently available aircraft (large or small, civil or military, US or allied etc.), what is the shortest flight time that could realistically be achieved?

If you prefer something more realistic and readily available, go with the fastest business jet, the Cessna Citation X, or if you need a little more range, the Gulfstream 650. The Cessna can cruise at Mach 0.935 over maybe 3000 miles (officially 3460 nm, but certainly a little less when flown at top speed), and the G650 has a range of 6000 nm at Mach 0.925. Thanks to @Lnafziger for helping with the facts. Bonus: Both are useable from a lot more airstrips than any airliner.

The flying time from London to New York will be less than 5 hours - still quite a bit faster than flying with an airline. By the way, the airliner record on this route is still held by the Vickers VC-10 with a tad above 5 hours. If you go from London to Boston, the Cessna will have just enough range, for all other routes I recommend the Gulfstream.

The bureaucratic procedure for making an F-22 available will give your protagonist ample time to cross the Atlantic dozens of times in a business jet. Add to this the stationing of a refueling tanker in the middle of the Atlantic (hint: That alone takes more time than what the F-22 needs to fly the full distance, so its realistic mission time will easily double).


What is the meaning of "transition area" as used by the FAA? Has the meaning changed over time since the term was introduced? What is the meaning of "transition area" as used by the FAA?  Does it currently have a specific meaning?  Does the FAA still use the term at all?  Has the meaning changed over time since the term was introduced?  Is it a term that ceased to have a specific official meaning after the September 1993 "alphabet" airspace reclassification?

Additional context:

FAR 71.71 reads--

  § 71.71 Class E airspace. Class E Airspace consists of:

  (c) The airspace areas listed as domestic airspace areas in subpart E
  of FAA Order 7400.11D (incorporated by reference, see § 71.1) which
  extend upward from 700 feet or more above the surface of the earth
  when designated in conjunction with an airport for which an approved
  instrument approach procedure has been prescribed, or from 1,200 feet
  or more above the surface of the earth for the purpose of
  transitioning to or from the terminal or en route environment.

Does this suggest that the term "transition area" is best reserved for areas of Class E airspace with a floor at 1200' AGL?

The term "transition area" does not appear in the FAA's "Airspace Designations and Reporting Points" document, current edition Order JO 7400.11D.

As airspace with a 1200' Class E floor has proliferated to cover most of the US, it seems to have become a common practice to use the term "transition area" specifically to refer to areas with a 700' Class E floor that are protecting instrument approaches. Is this really a correct practice?

As per the FAA Procedures for Handling Airspace Matters:

Transitional areas, Class E, are designated to serve terminal and en route aircraft to include helicopter operations such as:
a. Transitioning to/from terminal and en route.
b. Transiting between airways and routes.
c. En route climbs or descents.
d. Holding.
e. Radar vectors.
f. Providing for course changes.
g. When the route under consideration is almost all within existing Class E airspace and small additions would complete the coverage.
NOTE-
The only areas that are normally excluded in the Class E description should be limited to Mexico, Canada, SUA and international airspace. Exclude SUA only when active. Do not exclude Federal Airways or other airspace areas.
h. En route training operations.

Link here.
I don't know that this definition has necessarily "changed", but they apparently thought it needed clarification in 2011.


Where can find Service Ceiling of an aircraft? I would like to figure out the service ceiling for Cessna 172N and I couldn't find it anywhere in the POH.

Where can I find it? In POH or somewhere else? If in POH, please post a snapshot of it.

It is in the pilot handbook, before the title page [PDF], under "performance-specifications"


Why don't aircraft use nuclear propulsion? Nuclear propulsion research for aircraft was abandoned during the 50's.

Why wasn't it revived ever?

TL;dr - too heavy :-)

It's just not a good energy source for something like an aircraft.

Nuclear energy is superb for instances where you need continuous output over a long period of time, for example a satellite, which is going to be there for years without maintenance or refuelling. A very small amount of nuclear material in an RTG such as those on Voyager 1 and 2 can provide heat energy that can be used to power the satellite. This model works in this use case because the only real alternative (solar power) hasn't anywhere near the output required as the Voyager craft fly ever further away from the Sun.

Also, submarines are a good use case - if you remain under the sea for months or even years at a time, diesel or anything that uses oxygen is not suitable, so a nuclear power plant is ideal.

But while for a satellite the power unit can be very small as the actual output power required is small, to power an aeroplane or a submarine you require a large power plant, and that will also require a lot of shielding (as a side effect of nuclear reaction is radiation...)

On a submarine, that's okay - weight can be dealt with, but on an aeroplane weight is key. You just can't do it efficiently and safely. You need shielding that can cope with a crash - which is going to be massively heavy, so you won't have any passenger or cargo payload left.


What are the aerodynamic differences between the different types of slotted flaps? How do the different types of slotted flaps (Single, double, and triple as well as a non-slotted one just for comparison) differ aerodynamically? I read in Joe Sutter's book 747 that a double-slotted flap design for the 747 had 8 knots higher speed than a triple-slotted one. How does that work?

The high energy air that passes through the slots prevents boundary layer separation over the top surface of the flap. Though, this increases drag but it improves the stall characteristics of the airfoil. In other words, we can have higher maximum lift coefficient (Cl_max) by having higher maximum angle of attack (alpha_max). So, higher the number of slots higher Cl_max one could reach, there should be a limit. In case of a fixed weight of an aircraft,a higher lift coefficient implies that one can fly at lower speed before it stalls. A comparison between different types of flaps (up to double slotted)can be found in the book Aircraft Design and Performance by Anderson.

Source:
The same book.


Is lashing equipment considered part of a ULD? How should a load controller state additional lashing equipment on a load sheet in the context of ULDs? Should the additional weight equipment be added to the ULD's contents, or added to the ULD tare weight? Listing the additional equipment as Equipment In Compartment (EIC) does not seem to be a possibility.

Normally I would put this as a comment since I retired in 1999, and I don't know what current practice is. However, this is a bit too long for a comment. Also, this is from memory and it's been a long time now, as it's from my experience with load sheet preparation in the late 1980s and the 1990s. If a more recent useful answer appears, I'll simply delete this.

Further, this answer only directly addresses the question's last sentence:

  Listing the additional equipment as Equipment In Compartment (EIC) does not seem to be a possibility.

The airplane does not, of course, care whether the extra lashing weight is tare weight or content weight. What it cares about is the total weight at the ULD position, and that's what the weight & balance calculations (probably done by computer) will use, whether given as one value or two values (tare & content) that have to be added.

Just adding the extra weight to a compartment without specifying where in the compartment it is would effectively put it wherever the compartment centroid was. That would be correct only if the ULD happened to be at that position.

In actual practice it could be argued that just adding to a compartment rather than a position in that compartment would be acceptable in some instances. For example, let's say you're very close to max takeoff weight before the addition, but the c.g. is well within limits. The ULD locations would have been decided by the software (or manually by the loadmaster) to put the c.g. nowhere near the limits. Adding a few pounds of extra lashing might put you over max takeoff, but it's going to make little difference to the c.g.

All of the three cargo carriers I was involved with insofar as weight & balance were concerned simply listed the total weight at a position. No differentiation was made between tare and cargo. Thus the addition of extra lashing was simply added to that positions weight, usually by rerunning the software to get a new solution.

The most common reason I observed for adding extra lashing was that when loading the ULD to a position, they found that one or more of the floor locks to hold the ULD in position were broken. For such cases, the loading manuals specified how many locks could be inoperative and how much extra lashing there had to be. Frankly, that extra weight was often ignored, but it was sometimes accounted for.

I don't have a definitive answer as to whether extra lashing should be added to tare or content. That is irrelevant to the airplane, though I can well imagine that there might be a form somewhere that required such a split. If someone had asked me back when I working which it should be, I would have said that it should be added to the tare for the simple reason that the ULD is there to safely contain the content. If for some reason extra containment weight had to be added to make the ULD safe, that would seem to be tare weight to me.

And I imagine that a customer, who had paid money for a certain amount of weight to be shipped, found out that because of broken parts on the airplane he had to pay more, he would not be happy.

A thorough search of the weight & balance manuals for aircraft might yield additional relevant information. Some such manuals for 747s and 767s can be found at http://terryliittschwager.com/wbmanuals.php


Should you blow through the final approach course if the ATC forgot about you? So you were being vectored for the final approach course (ILS/RNAV/whatever) and the controller forgot about you for some reason (busy). Assume you called them and they were not replying. Also assume you were not yet cleared for the approach but they told you to assume the x approach. Would you blow through the final approach course and wait for them, even though you might conflict with traffic, or turn inbound even though you had not been cleared and potentially take a beating later?

Yes, blow right through it.  You should never deviate from a clearance to "take a beating" later simply because you think you know better than the controller.  If the controller is busy it is for a reason, and it is very possible they are extending you on purpose for spacing.  You could very well conflict with traffic even more by taking your own turn.  It is far better to let them fix the overshoot they caused than to battle the FAA over a flight violation.

If you genuinely think the controller may have forgotten about you, you should continue to attempt contact, while pressing IDENT with each transmission.  If it is so busy that you can't get a word in edgewise, press IDENT anyway.  I have done this and received an immediate turn without even having to transmit on the radio.  It is designed to get their attention, just don't overuse it.

The only exceptions where you should deviate from an assigned vector are if you are lost comm or have an emergency.  In either case make sure you are squawking appropriately.

I would consider a vector towards terrain a pending emergency if not turned within some appropriate period of time.  When I was instructing in the Navy, during simulator rides I would force a missed approach at McChord AFB, give a climb to 5000' and a left turn towards Mt Rainier.  I would then fail the crew's radios.  It was always a good lesson in terrain awareness, especially for young aviators from flat states.


How does the ADF null positions find where the NDB is? I understand how it operates for the most part, although I don't understand how the null positioning works. This image below doesn't include the sense antenna that limits it to one null position, however how is the null position created? Wouldn't the signal still be received at that position, how does it become null?

Also does the null positioning tell you where the NDB is? If it's null wouldn't that mean no signal is being received so the beacon wouldn't be in that direction? Or do you find the null position, the assume it's 90 degrees from the beacon?

Short answer

Do you find the null position, then assume it's 90 degrees from the
beacon?

That's correct. For the antenna pattern shown in the question, the angle between direction of nulls and peaks is 90°. When sensing a null (or a peak) there are two possible and opposite directions for the beacon. This ambiguity has to be removed. This could be done by triangulation, with a second reading of the angle of arrival after the receiver has moved a bit, but in the modern ADF antenna this is not required, a sense antenna is added to the loop antenna to change the radiation pattern (i.e. the sensitivity vs. the azimuth):

Radiation pattern of the loop antenna, and loop + sense antenna system (measured in a horizontal plane)
With the sense antenna, the null is at 180° of the peak, and there is no ambiguity. However the performance of the system is degraded by the sense antenna, thus usually two measures are done, without the sense antenna (for maximum accuracy) and with the sense antenna (for ambiguity removal only). See further down for the details.
The reason we prefer to sense the null direction is the signal received is fading at the larger rate near the null than it is increasing in intensity near the peak. The change being more pronounced near the null, sensing the null is easier and gives a better accuracy.
Electromagnetic waves simply
Contrary to what is often thought, the classical high-level principles behind EM waves, which explain how the loop antenna can work, are quite easy to summarize.
The very common representation of an EM wave:

Electric and magnetic components of an EM wave. Source
A wave propagates in 3D space and its electric and magnetic fields are not dissociable, they are a single electromagnetic field which energy is carried by photons (though according to Richard Feynman, EM sources produce not physical particles or waves, but wave-like “probability amplitudes” that propagate at c in space. QED! Well... let's stick to good ol' photons!).
A NDB transmitter is an electric generator, generating an alternating current in a basic vertical conductor which length is tweaked to make it resonant at the frequency used (it's a dipole antenna). Three laws are then governing what happens:

Ampère-Maxwell's law says 1/ the vertical current creates a circular magnetic field around the antenna (Ampère's initial idea). The field intensity follows the variation of the current, 2/ the same happens with an electric field instead of a current (Maxwell addition).

Faraday's law of induction says a varying magnetic field creates an electric field. This field opposes the magnetic flux which created it according to Lenz's law. Lenz's law is a kind of reaction principle.

So AC current creates a variable magnetic field. The energy of the magnetic field comes from the current in the antenna.
As the magnetic field is variable, using the two laws above alternately, we see when a magnetic field varies a variable electric field is generated. When an electric field varies a variable magnetic field is generated.
The energy of the electric field comes from the magnetic field, as postulated in Lenz's law: The electric field opposes the magnetic field changes, therefore it is a force, aka the back electromotive force (back-emf).
What's great is an actual current (electrons) is required only to generate the initial magnetic field, the subsequent magnetic fields are due to electric fields, not depending on a conductor and/or electrons to expand:

Electric and magnetic fields generated from a point of a vertical antenna in a given direction
From left to right: A current is created in the transmitter antenna. If we focus on any point of the antenna, the local current creates a magnetic field around the point. This field induces now vertical loops of electric field, each loop in turn creates a new magnetic field, and so on.
The two fields, normal to each other, are the two inseparable aspects of the electromagnetic field. They exist at the same time, and the repeating process leads to their propagation as wave. As fields have no mass, they can travel at the speed of light.
This process occurs in 3D space, we see concentric shells of electric field radiating from the whole length of the antenna, and between these shells the magnetic field linking the shells:

Still image of electric and magnetic fields. Source (animation).
The electric field at the top and bottom of the antenna is missing, we can predict a "cone of silence" at the vertical of some radio aids using vertical antennas.
The wave crosses conductors while expanding. A conductor acts as a reception antenna. Depending on the conductor ability to couple more or less strongly with the electric and/or magnetic fields, a given portion of the energy from the fields is converted back into current, by virtue of the same reversible laws.
ADF principle
The ADF receiver uses a small-loop antenna (the circumference is small compared to the wavelength), which principle is to sense the magnetic field of the wave, the antenna is actually a coil.
This loop antenna is unusual in the sense receiving antennas generally couple with the electric field of the wave. However sensing the magnetic field is efficient at lowest frequencies and for direction finding applications.

How is the null position created?   Wouldn't the signal still be
received at that position, how does it become null?

Correct, the signal reaches the antenna with the same mean intensity, regardless of the orientation.
Let's look at an everyday life example: Hearing a sound without seeing the source doesn't prevent us to determine its direction. Unless the sound is coming from straight ahead or straight behind, one ear receives the sound first, the same for any reflection, our brain does the rest. Moreover our ear pinna is not symmetrical, this also allows to separate a front sound from a back sound at the same distance, or one low from one high. This localization is irrespective of the mean intensity of the sounds.
Likewise the loop antenna reacts to the combined result of instantaneous amplitudes at all points of the antenna. According to the law of induction, two points of the loop receiving the signal with a phase difference due to the difference of distance from the transmitter (left side below) will be at a different potential, creating a current in the conductor between these points:

ADF antenna sensing NDB magnetic field (not to scale)
On the other hand (right side), when the loop plane is normal to the direction of the wave, each point of the loop receives the magnetic field with the same intensity, no back-emf is created, no difference of potential is measured, no current circulates, this is a null.

Note the antenna is actually much smaller than the wavelength and the phase difference is very small. But the loop antenna is a coil, it is easy to have multiple turns of wire, each turn "collecting" an additional amount of the magnetic field. However as the increasing impedance cancels partly this gain, a reasonable compromise has to be found.

"LW/SW receiver" with a ferrite coil antenna (a coil which inductance is reinforced by a ferrite rod) must be oriented in the direction of the station to maximize reception.
Rate of variation of gain
We mentioned earlier the radiation pattern of an antenna, which is a representation of its relative gain according to the direction. For the loop antenna:

Radiation pattern of the loop antenna (dotted line for the vertical plane). Source
The gain is provided in decibels, which is the logarithm of the ratio between the intensity in the direction considered, and the intensity in the direction of the maximum. By principle the maximum is 0dB (100%) and other values are negative (less than 100%).
When looking at the indications in green, The dip in received energy (the null) near +/- 90° is narrower than the peak near 0°/180°. This tells us about the rate of variation of the sensitivity:

Signal is maximum at 0°, but varies only by less than 2 dB (1.2x) on a range of 60° around the maximum.

Signal varies by more than 30 dB (31x) for only 30° around the minimum/null.

It means it will be more accurate to determine the direction of the null rather than the direction of the peak (which is the direction of the transmitter). This is the case of many types of antenna: Nulls are more pronounced than maximums.
Loop antenna with sense antenna
There is a problem with the loop antenna: It has a symmetrical radiation pattern, when a null is found, there are still two possible opposite directions for the transmitter. The solution is to use an additional element, the sense antenna, which is an antenna with the same sensitivity regardless of the azimuth. It is said to be omnidirectional and is usually usually coupling with the electric field. The two antennas can be combined in such a way the resulting pattern has a heart shape (cardioid):

Radiation pattern of the loop antenna combined with sense antenna
One lobe of the loop antenna (here in blue) adds with the sense antenna, the other is subtracted from the sense antenna, creating a gain dissymmetry.
The ambiguity isn't possible anymore. The null is now opposite to the maximum, while they where at 90° before adding the sense element. When the null direction has been determined, the NDB direction is the exact opposite.
Back to the audio field, this antenna system is very similar to the sound engineering technique called MS stereo using one mono (mid) and one stereo (sides) microphones, though this technique is valid for only a 180° azimuth range.
The usual procedure to determine the direction is:

First find a null with the sense antenna off, because the sense antenna smooths out the null dip in the radiation pattern. This give the direction with 180° ambiguity.

Do a second but rough measure with the sense antenna on to remove the ambiguity.

Modern ADF antenna
On modern ADF, the antenna doesn't rotate to determine the direction of the NDB. Instead the antenna system is a combination of multiple fixed antennas electronically commutated. By selecting different associations, an appropriate radiation pattern is formed and rotated.
A practical realization:

Source


What is the difference between point-to-point and low-cost airlines? In describing major airlines, are "point-to-point" and "low-cost" synonymous? Or is this an over-generalization?

What is the difference between point-to-point and low-cost airlines?

Point to point describes an airline that focuses on delivering services without a connecting hub. This cannot be said to imply low cost.

A independent airline flying between some islands and not offering connections would fall into this category as much as Ryanair, Easyjet or Spirit Airlines.

Low Cost generally implies a point-to-point operation. They structure their business model around filling aircraft on high-demand routes.

Reasons for this: The cost and complexity of handling and organising hubs and connecting flights violates their carefully controlled profit margins and structure.

Hence IMHO you can normally assume a low-cost operation will be a point-to-point operation, but not the other way around.


Is the IOSA useful even if not all airliners are IATA members? Given the two facts:

According to wikipedia, the IATA represent a little more than 80% of available seat kilometers. It makes sense as some airlines are not IATA members.
Under each region over the world, an organisation is dedicated to make sure civilian aviation is safe, following ICAO's standards (EASA in Europe, FAA in US, ...)

As I understand, the IATA has its own certification program (IOSA). It seems to me that it doesn't make sense: it doesn't cover all commercial aviation (some low cost carrier are not part of the IATA and still represent a significant part of the traffic), and its purpose is the same as other civilian organisation (FAA, EASA,...) acting under the ICAO's rules.

I'm quite sure I'm missing something, but is the IOSA useful as it does not cover significant airlines and its purpose seems to be covered by other organisations?

IOSA is basically an audit program under IATA. It is not a regulatory regime and as such is different from the FAA, EASA etc, which have force of law. In fact, IOSA is only one of the various audits offered by IATA, which include:

IATA Operational Safety Audit (IOSA)
IATA Safety Audit for Ground Operations (ISAGO)
IATA Standard Safety Assessment (ISSA)
IATA Fuel Quality Pool (IFQP)
IATA Drinking-Water Quality Pool (IDQP)
IATA De-Icing/Anti-Icing Quality Control Pool (DAQCP)

IOSA deals with the operational management and control systems of an airline. The IOSA standards and recommended practices are derived from the ICAO recommendations. From the IOSA  Standards Manual

Sources for IOSA Standards and Recommended Practices (ISARPs)
The safety and security requirements published in the Annexes to the Convention on International Civil Aviation (ICAO Annexes) are the primary source for specifications contained in the ISARPs. Safety and security requirements in the ICAO Annexes used as the basis for ISARPs are those that
are applicable either directly or indirectly to the air operator.

However, these standards are not regulations (as are those defined by FAA etc.):

ISARPs contained in this manual have been developed solely for use under the IOSA program and contain the operational criteria upon which the audits are based. ISARPs are not regulations. (emphasis original).

The usefulness of the IOSA to airlines if from the fact that it is a standard recognized by most other airlines- instead of going to different auditors to ensure compliance of standards, they can agree on a common standard (also IOSA is required for IATA membership).


After an emergency landing, what procedures should the pilot follow? In case of an emergency landing (non-fatal) on a road/highway or in a large field, what happens next?

Should police be contacted?
Should aircraft owner and/or insurance be contacted?
In case landing is on a road or highway, what should the pilot do?
In case of landing on someone's personal property, what should one do?

There seem to be two parts to your question. First, what practical steps can I take on the ground immediately after landing? Second, which authorities must be notified?

For the first point, there are just too many scenarios to have a single answer but basically you should immediately check for injuries or damage to property and activate the emergency services if required. After that, secure the aircraft to prevent any further damage, call your insurance company and inform the aircraft owner and local property owner (as applicable). I'd also suggest giving your family a call rather than have them hear on TV news that you were "in a crash landing".

There are more dramatic possibilities, of course: if you ditched or landed in a remote area or in extreme weather then actual survival could be your highest priority. But that's a topic for another site.

For the second point, at least in the US it's possible that you don't have to notify anyone. If no one is hurt, nothing is damaged, and none of the incidents requiring immediate notification occurred (see 49 CFR 830.5 and the AIM 7-6-2) then there's no legal requirement to inform anyone. The authorities in this case would be the NTSB, not the FAA, by the way. There's a more detailed discussion of these requirements here.

An additional concern that I know nothing about is liability and other legal issues. Getting legal advice - e.g. from your insurance company or AOPA - would probably be a good idea whatever the circumstances.


Why might DTK on GPS not match depicted course on approach plate? I hope this isn't a dumb question, but I haven't flown a whole lot of GPS approaches and today I observed something that I cannot explain:  There was a 2 degree split between the Desired Track (DTK) displayed on the GPS, and the inbound course shown on the approach plate.
If it matters, the approach was the RNAV 16 Y approach at KRNT, and I was using my club airplane's Garmin GTN 650.  The database in the GPS was up to date, and my approach plate in Foreflight was current.  DTK showed 159, and the plate showed 157.
Not a big difference, but they ought to be the same, right?
At first I thought it might be displaying track direct from my present position, but I had early turned the fix a little coming from the west, and was lined up a bit right which would have made the course needed to correct a few degrees less than 157.
And as I made minor course corrections back and forth across the final approach course the DTK never wavered.
Is there a good explanation for this difference that I'm just not aware of?

Here is the final answer handed down directly from the Garmin technical support department. After a conversation with one of their aviation technicians, he told me that the error seems to be in their database. The same discrepancy (a track of 159 instead of 157) appeared whenever he reviewed the KRNT 16 RNAV Y approach from his end. He even rolled back the database to check previous versions and it has been this way for quite awhile. When asked about a possible magdev discrepancy, he said they they acquire all of their deviation data from the same governmental source that the chart makers do. He said that they are releasing a magdev update in the near future that MIGHT fix the problem, but said that it was most likely just entered wrong in their database. He opened a case file to make sure  it is addressed and said that he will notify when it has been taken care of.


When resetting the heading indicator to match the magnetic compass, do I need to use the compass deviation card? At least every 15 minutes we set the Heading Indicator's number to match the number of the magnetic compass.

In this situation, should I consider the deviation card below the compass card or not?

Yes the DG is supposed to be set to the corrected magnetic indication whenever you set it, so you should mentally add or subtract the degree or two or three based on the closest segment on the card as a standard practice.

I agree with Michael however that it's not really that big a deal for VFR flying in the real world, especially in the age of GPS where you can just adjust heading based on GPS ground track on your phone or a tablet to go from A to B and you don't even really need to look at your compass (although, you might suddenly find you need it, so don't neglect it).

If you were doing old fashioned dead reckoning navigation, precision in holding a heading is important.  Or in the IFR world where you have to fly headings in a clearance.  Even there though, the allowable calibration error on a compensated (that is, WITH the deviation accounted for) compass is +/- 10 deg (!), so the little 2 or 3 degree calibration card can be quite a bit off anyway and still be legal.


Was this a successful deployment of an MD-88 tail cone evacuation slide? In this video, the tail cone is popped off as part of the evacuation.

It stays attached on a lanyard which seems to be more of a hazard than letting it fall free.  Additionally, the slide doesn't deploy.

It's clear that the rear and front port exits are the safe ones, but did something go wrong here?

(P.S.  I'm not talking about the actions of the pax, just about the tail slide).

Considering that the slide was not deployed, it is definitely unsuccessful. The MD-80 series (also the DC-9 and boeing 717) had tail cone assemblies which could be jettisioned in case of an emergency.

When operated, the tailcone is expected to swing to the left of the fuselage due to to its own weight because of the way it was rigged.

The jettison cone is attached to the slide through a lanyard, which passes through two eyelets in the tail cone and is attached to a spring in the middle of the cone.
As the jettison mechanism is activated, the tail cone is released and because of the way it is rigged, turns 90$^\circ$ and moves to the left of the aircraft to keep it from interfering with the slide deployment.
As it falls, it pulls on the slide container via the slide lanyard, moving it so that it can inflate and delpoy, while the tail cone remains to one side of the aircraft.

You can see it in the images below:

All images taken from Accident Report IN-045/2004

The following image shows the undeployed slide (in an MD-81) from the inside along with the lanyard.

Image from aircrewbuzz.blogspot.in

The release can be made by three ways- there is an emergency handle on the aft bulkhead door, one at the end of the catwalk and another one in the exterior of the handle.

In this case, the tail cone has pulled the lanyard, but the slide has failed to delpoy. While I'm not sure why the cone is hanging, it appears that the lanyard has snagged somwhere, probably in the cam rotator.

Note: This would not be the first time the slide has failed to deploy/deployed unsuccesfully or has deployed inadvertently. Also, see this discussion on the MD-88 tailcone jettison and slide deployment mechanism here.


Is it required to contact approach when flying VFR into a Class D airfield? Is it required when under VFR to contact an airfield's approach when approaching to land at a class D?

KDLH is my example airfield. They possess independent radar approach and departure (same frequency) with a separate tower frequency. What would be the process of approaching this airfield under VFR?

No it is not required to contact approach. Unless you have to go through a larger D, C or B airspace to get there. I don't know of any larger Ds in the US, but there are plenty of D-airfields underneath C and B airspace.

In Germany (and I think around Europe, not sure though), there's a distinction between the tower-D and the approach-D (the former being called D-CTR, and the other just D), to enter the approach-D you'd have to talk to approach, but if you can sneak under/around it, go ahead and call the tower directly, let them know where you are, and they'll tell you how to enter their airspace. In the US, they'll probably just tell you to enter the pattern (like "N12345, enter and report the right base for runway 5").

In Europe you need an explicit clearance and they'll usually tell you how to enter (like "DEFGH, enter control zone via Echo, report Echo", Echo being a reporting point on the chart, Echo usually being to the east, with November, Whiskey and Sierra being north, west and south respectively (usually, that is, there may be more, and they may be placed differently, but they're always on the sectional or the terminal area chart)


Why are some parked aircraft angled away from the taxiway center line? With all the aircraft parking going on these days images like this one have made me wonder why the aircraft aren't just parked nose-to-tail:

I realize that rotating the longitudinal axis can help in cases where you move the nose of one aircraft past the tail of the next aircraft. But most of the time the aircraft in the image above are far enough apart for that to be a benefit.

Here's what seems to be a more efficient example:

One thought is that it might be due to prevailing winds on the airfield? Or is this just specific to the A380 or the location?

If the pavement is wide enough and strong enough (both of which will vary depending on the model of plane) for staggered parking, then that is the most space-efficient option.

If not, then you have to park them single-file. Simple geometry tells us that turning planes roughly 45 degrees (◼◼◼) will be more space-efficient than nose to tail (). For the same reason, some very congested airports have tighter angled parking at gates, whereas those with plenty of room use faster straight-in parking.


Is it possible for an SU-25 to fly high enough to shoot down a Boeing 777? A common theory from pro-Russian netizens surrounding the MH-17 tragedy is that it was a Ukrainian SU-25 ground attack fighter plane which shot down the civilian airliner. However, MH-17 was flying at 10,500m when the service ceiling of an SU-25 is 7,000m. They say that this discrepancy is made by the fact that the Ukrainian pilot used afterburners to get to the height MH-17 was flying at. Is this actually technically possible?

There is an excellent answer at http://scottlocklin.wordpress.com/2014/07/21/can-the-su-25-intercept-and-shoot-down-a-777/

The SU-25 is a ground attack fighter unsuited to intercepting and/or shooting down 777s. If the Ukrainian air force wanted to do so, they have better aircraft available.
The SU-25 max speed is slower than a cruising 777.
The SU-25 has an operational ceiling of 16000 ft with max weapons to 23000 ft clean, MH17 was at 33000 ft.
It is an unpressurised aircraft.
As a ground attack aircraft it probably only rarely carries air to air missiles. It can carry the R-60 infra-red air-to-air missile which has a 6 lb warhead effective against small aircraft.

An R-60 once hit and destroyed one engine of a small BAE 125 business jet at 35000 ft but failed to bring it down, apparently the missile failed to explode.
KAL902, a Boeing 707, was hit by an R-60 and made an emergency landing 40 minutes later.

The R-60 is a short-range missile (5 miles). The Russians claim the SU-25 came within two or three miles of MH17.

On the whole this makes the SU-25 a poor choice for shooting down a cruising 777.

It seems unlikely that a 777 would be shot down in this way. Not impossible, but far less likely than other proposed scenarios such as those involving BUK (SA-11) ground to air missiles.

Results of an R-60 hitting a jet engine on a small business jet.

Results of an R-60 hitting a Boeing 707 ... two R-60s were launched, one missed.

These R-60s were fired by supersonic interceptors, not by SU-25 ground-attack aircraft.


What difference does the choice of paved runway surface make to aircraft? What difference to the pilot does it make it say a runway is Concrete or Asphalt?
Does it require different information in the flight management system or other calculations?

Concrete is better for certain large airports. Asphalt never completely hardens, and will always behave like an extremely viscous liquid. So when you heat it up (on a hot summer's day), it becomes less viscous. When you put a heavy weight on it (like an airliner), it will tend to flow away from and surround that airliner. Planes pull up to a gate, sit for an hour or so, and suddenly their wheels have sank into the ramp six inches and they can't move. Same with runways, the constant shock of landing aircraft cause the asphalt to buckle and warp eventually.

Concrete has issues in the cold, however, especially if it is not laid well. It can buckle and crumble when it expands and contracts. However, it only gets stronger as it ages and it can easily be made to withstand the hardest of landing impacts.

The type of material does not make any noticeable difference to takeoff/landing performance.


What help do you have to provide if you are seated in the emergency row and there is a situation? Follow up from What if there are no volunteers to sit in the emergency exit row? and @mins 's comment:

  I'm curious... What prevents someone to say they will assist and then just rush out of the plane when the need to assist is here? Tons of people are ready to promise anything to get what they want, and then just say they didn't understand what they were asked for (or more likely swear that they were not asked anything... show me the evidence...)

..What are actually your responsibilities in case an actual emergency occurs and you have to do the assisting tasks?

When sitting at the exit you need to be the first one out of the plane. Basically when the emergency is declared and the captain says, Evacuate, Evacuate, you go to your door, check the outside for fires. Then you open the door en be the first one out of the door. You then put as much distant between you and the plane as fast as possible. Or you assist on the outside of the plane by making sure people create enough distance between themselves and the plane.

What could with hold them from sitting there is the responsibility to get the door open. Or the fact that they enter a shock and will be unable to move during an emergency.


In high-altitude piston aircraft, what type of forced induction (boost) is used? In high-altitude piston aircraft, what type of forced induction (boost) is used? Turbocharger or supercharger?

You can have either (turbo- or super-) or both (superturbo-), there is also the turbo-compound engine.

Most WWII aircraft engines had mechanically driven superchargers, and the turbosuperchargers (with intercoolers) were added to achieve desired altitude performance.
Modern aviation piston engines designed to run at high altitudes typically include a turbocharger rather than a supercharger. The change in thinking is largely due to economics. Aviation gasoline was once plentiful and cheap, favoring the simple, but fuel-hungry supercharger. As the cost of fuel has increased, the supercharger has fallen out of favor.
— Wikipedia [edited for context; citations missing from main article]

During WWII, two-speed two-stage intercooled superturbocharged engines were common.
(Frames from YouTube)
Compressed air via the exhaust-driven-turbine is channeled to a geared mechanically-driven supercharger. (The jet-engine must have had a laugh.)

You get the super part, which is a mechanically-driven compressor boost.

The turbo part, which is a turbine-driven compressor boost.

Intercooler for cooling the air.

The two speeds and stages are for low- and high-altitude operations. Otherwise the engine could blow at low-altitude.

A good example is the Wright R-3350 Duplex-Cyclone used on the Boeing B-29 Superfortress and other aircraft. Delivering up to 3,800 shp (2,830 kW).

Above is an example of having both, however as noted in the comments, superturbocharger as a term is nowadays used to describe a turbocharger.

Here's a declassified training film—from which the above frames were taken: Turbosupercharger: Master of the Skies (1943)


Is is possible to have an aircraft launched from a submarine or directly from under the water? There are actually small UAV launched by submerged submarines and projects around submersible aircraft, I'm interested in a view of the current state of launching aircraft from submarines.

Does anything prevent aircraft to be launched and recovered using submarines platform today?

What is the current state of deployment of such technology around the world?

The Japanese navy did that in WW2. https://en.wikipedia.org/wiki/I-400-class_submarine


How do aircraft differentiate between missile locks? I have explored many similar questions such as:

How does a Missile Lock Work?
How is a missile lock detected?

In reading there respective answers, I have learnt about the multitude of detection mechanisms employed, but one question lingers and remains unanswered:

How would an aircraft differentiate between the multiple missile lock signals it would likely be receiving?

In a dogfight scenario (although they can occur over a large distance) a single aircraft may well detect the signals emitted by either the missile as part of an "Active Radar Homing" mechanism, or from the launcher itself as part of "Passive Radar Homing", regardless of whether the aircraft is the intended target, presumably causing every aircraft in the area to be notified to the single missile lock.

I don't pretend to be well versed on the subject of aerial warfare, yet I consider it nonsensical that every aircraft in the engagement be notified to the missile lock of a single aircraft as it would distract the pilots, all of whom would be required to ensure that they are not the targets.

Non-holographic radar systems such as those used in fighter aircraft and active guided missiles only point in one direction at a time. Normally, when the radar is in search mode, a mechanism inside the radar makes the beam move from side to side (possibly up and down as well), so it has a wider field of view and can pinpoint the direction of any aircraft it finds.

The aircraft with the radar warning receiver (RWR) sees a brief pulse of radiation every second or so: only when the beam is pointing in its direction. This way, it knows the radar emitter is in search mode, and the direction of the emitter. Every aircraft in the radar's field of view will see the beam at different times, and they will all see the radar on their RWR screens. In a combat zone this is potentially a lot of emitters, but the RWR can analyse the radar signal to identify the radar: what type of aircraft, SAM, or ground radar it is, and whether it's friendly or enemy.

Getting the position of the target only every second isn't good enough to guide a missile towards it. When the radar is in track or launch mode, it stops scanning the beam, and keeps it pointed at the target aircraft.

The RWR on the target aircraft now sees much faster pulses of radiation, so it knows that it is the sole target of the radar. At this time, it can warn the pilot of a missile lock. But because the radar is now only pointing in this one direction, other aircraft in the area don't get illuminated by radar at all. Their RWR systems won't pick anything up. Only the aircraft that's actually threatened gets the missile lock warning.

In addition, the same analysis that can identify what type of radar is illuminating the aircraft can also identify fully active radar-guided missiles. Like when the aircraft's radar is in track or launch mode, the missile's radar emitter only points in one direction, and doesn't scan, so only the target aircraft will see it.

Obviously it's a little bit more complicated than this. There are a lot of details about how frequent the radar pulses are, and how the RWR knows the range of the source, but I hope I've captured all the important information in an understandable way.


Have objective and verified tests been done of the effects of personal electronic devices on a commercial airliner's operation? Have any governmental agencies done comprehensive tests on the effects of personal electronic devices used in the cabins (and cockpits) of commercial airliners?

With the ubiquitousness of cell phones, laptops, kindles, ipads, etc, it strikes me that everyone seems to just know that using a cell phone in the cabin of an airliner has no appreciable/measurable affect on the electronics of the aircraft.

Yes, they have done a lot of testing, hence why they now finally realize that most electronics are of no harm, and you can use them.

The FAA announcement page has a link to a fact sheet of their report, as well as a link to the PDF of the report.

In addition to the FAA report, other agencies have weighed in (such as Boeing).  Basically, the rules were instituted in the 1960s, and remained virtually unchanged since then, so it was time to make a change.


Does an SVFR clearance extend to Echo surface extensions? Sec. 91.157
Special VFR weather minimums.
(a) Except as provided in appendix D, section 3, of this part, special VFR operations may be conducted under the weather minimums and requirements of this section, instead of those contained in Sec. 91.155, below 10,000 feet MSL within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport.

Suppose I'm granted an SVFR clearance to land at KSTS (a typical towered airport with a Delta airspace and Echo surface extensions). Can I fly through the echo extensions with only SVFR minima? (e.g. for helicopter just clear of clouds) Or do the 91.155 minima apply. This really boils down the definition of "designated to the surface for an airport".

This is an answer to the question provided by my checkride examiner Barry Lloyd

On 01-26-2010, a query asking whether SVFR is available in Class E extensions was routed to FAA ATC Headquarters. Below is a response to that query from the FAA ATO Western Service Center:

"Our opinion is:

FAR 91.157 (a) ..."special VFR operations may be conducted"..."within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport." This permits SVFR clearances within the vertical extension, not the lateral/horizontal extension of an airport designated surface area.

FAAO 7400.9T par 6002. Definition of Class E2 airspace: "The Class E airspace areas listed below are designated as a surface area for an airport."

FAAO 7400.9T par 6004. Definition of Class E4 airspace: "...airspace extending upward from the surface designated as an extension to a Class D or Class E surface area."

The language in FAR 91.157 exactly matches the language in FAAO 7400.9T par 6002. Par. 6004 does not match and the FAR does not permit SVFR operations in the lateral extension of a surface area designated for an airport; only within the vertical extension.

Presumably this could be corrected if we indeed want to provide for SVFR within lateral extensions, but it is currently not permitted.

There are other operational issues involved: eg. an extension to a Class D surface area where the tower provides SVFR services within the Class D airspace as is permitted via LOA. They cannot issue a SVFR clearance in the E4 extension. If permitted, the controlling agency, presumably the ARTCC would have to do this.

Our opinion is that E4 airspace is not part of the airspace designated as the surface area for an airport. The surface area for an airport is D, C, or E2. Extensions are treated differently from surface areas designated for an airport, ie there is no communication requirement. In addition extensions, by definition in 7400.9, are not airspace designated as the "surface area for an airport"."


Are checklists always written in English? Are checklists normally written in English? If pilots are native speakers in another language, is it possible/legal for them to use the translated version of the checklist?

This may be different for the small private aircraft and commercial airliner. Please cover multiple cases when possible.

Soviet Union pilots probably used Russian for checklist. However I ask about open, developed countries (Germany, France, etc) and planes that are used all over the world.

It is definitely common here in Germany to use German checklists (German is not an ICAO language).
see http://www.motorflugschule-egelsbach.de/Downloads/Diverses/C172_R04.pdf for example.

However since many systems and acronyms used have English terms anyways it boils down to a combination with English.


How do you report reckless pilots? I have never reported reckless behavior by other pilots to the FAA, but I have thought about it several times. The only problem is that usually I will only know the tail number, not the name of the pilot. Since the owner of the aircraft may be different than the one flying it, how does one go about making sure the complaint is filed against the right person?

The FAA provides an online reporting tool here I would say it falls under "aviation concern". In your description if you include tail number and time they should be able to figure out who was flying (or in the cockpit if its a 2 man situation). You can also contact your local FSDO and report the tail number and time of incident. Aircraft owners/renters (the people the tail number will trace back to) will more than likely know who was flying a given tail number at a certain time so as long as you know when it happened you should be ok its not necessarily on you to know who was flying but the tail number and incident time is key.


If cabin lights are dimmed during night landing so that your eyes will get used to the darkness, why do they let you use the reading lights? Everytime the question of "why do they dim the lights during night landings" pops up, people say that it's to make passengers' eyes used to the darkness if an evacuation is needed (see: Why are the lights inside commercial airplanes turned off during take off and landing?)

However, on every commercial flight I've taken, the flight personnel always makes sure to mention that you can use the reading lights above you if you want, which are powerful enough to compromise your night vision (and that of people sitting next to you).

If the motivation is safety, why don't they disable these too? If anything, they should not be encouraging their use.

That is a good question. It is most likely a compromise. Turning down the cabin lights allows for night vision adaptation for most. Its better to have at least some of the passengers adapted, than none at all. Its a compromise between optimal safety (night vision adaptation) vs customer service (being able to finish reading your Harry Potter book).


Why does the IL-76 have a lump at the bottom of its nose? Why does the IL-76 have this lump at the bottom of its nose?
Why can't it be gotten rid of?

The 'lump' holds a ground surveillance (mapping) radar.
IL-76 has two radars: the usual meteo radar in the nose and the ground surveillance radar (primarily for navigation). In addition to that, like all contemporary Soviet long(er)-range transports (esp. military ones), it has a dedicated navigator position with the glassed 'verandah' for better view of the ground.
Most commonly, this navigator position took up the nose cone space that is (nowadays) usually reserved for the radar. If you look at most modifications of Tu-134 or Tu-114, you'll see they have a similar (but smaller) 'hump' underneath to house the meteo radar. But the widebody IL-76 could afford both the nose radar and the navigator station under it, plus a dedicated mapping radar.
The navigator's seat and equpment don't extend much below the lowest window, so most of the space is used for the radar rather than the navigator.


How does Chicago O'Hare's tower sequence aircraft at peak capacity? This older question asks at what interval planes take off and land from ORD. The accepted answer (one takeoff or landing every 30-40 seconds) jives with my math: 2416 operations a day on average, with winds in a non-cardinal direction all those flights must use just two runways, so worst-case each runway would have a plane rolling along it every 75 seconds round the clock (so a plane takes off or lands from somewhere in the airport every 37.5 seconds).

My question is, how? At that rate, approaching planes would be spaced a scant two and a half minutes apart, and as soon as a landing plane passed over the numbers, a departing plane would be told to line up, then to take off as soon as the landing plane had cleared the runway, and if they hesitate even a few seconds the plane behind them would have to go around. How is this traffic density maintained long-term, especially since, like any airport, it has peak periods of activity exceeding the average?

Follow-up question; is ORD as bad as it gets, or are there "denser" airports with lower total aircraft movements but fewer runways? I heard Heathrow is so bad its airspace is ICAO Class A, prohibiting VFR flights entirely, in part due to the fact the airport handles practically every international flight into London on just two runways.

Chicago runs simultaneous triple parallel approaches. And as soon as an aircraft clears the runway, another one is allowed to cross the threshold.

Chicago Tower actually does not do the bulk of the sequencing of aircraft. Chicago TRACON actually sequences the aircraft before they are handed to the Tower. Even before that, Chicago ARTCC begins to sequence inbound aircraft. Similarly, aircraft are handed to departure (TRACON) almost immediately after taking off. Departure procedures are optimized for safety and efficiency.

This figure breaks down runway usage percentage for arrivals and departures in April 2015 (7am - 10pm traffic)(source paper). It highlights the common westbound landing flow with triple parallel runways. You can also see two diverging runways used for the bulk of departures, with sporadic usage of others.

Note that this is all after an airport runway overhaul. Consider that 2014 saw almost a 10% decrease in operations from the year 2005. Having talked to controllers that have put in time at Chicago Tower, it is as crazy to handle as humanly possible.


If the Captain's screens are out, does he switch seats with the co-pilot? If captain's screens are out, and let's say that the airplane is about to land and the captain is supposed to land it, will he/she switch the seats with the co-pilot? or does he/she depend on the small little analog gauges on his side?

If the plane is on final approach and the pilot flying loses his displays the co-pilot (who is also rated to fly the aircraft) may take over. Perhaps more importantly the system is built to avoid this. The "screens" you mention are independent and both (2 screens per side) are capable of displaying the primary instrumentation/information, a situation where both fail simultaneously and completely is rare.

All screens in the cockpit are generally visible from both seats, any pilot who was a former flight instructor (and many likely were) has plenty of experience viewing instrumentation from the opposing seat. Flying and landing like this should be of little issue.

In good weather to land an airplane the most important instrument is the airspeed indicator (and perhaps angle of attack indicator if you have one). With that in mind the pilot flying may continue the approach if the backup instruments are still working and in view, that is after all why they are there.

Some airline operational specs may have specific procedures for this as well but as far as I know the FAA does not really have anything to say on the matter.


What is the derivation of 15 and 11.3 used for estimating pivotal altitude? Pivotal Altitude Explained: Teaching eights on pylons the easy way at AOPA repeats a common formula for pivotal altitude.

  To estimate pivotal altitude, square the groundspeed and then divide by 15 if you use mph, or 11.3 if you prefer knots.

Where do the 15 and 11.3 magic numbers come from?

A possibly surprising result is even airplanes as different as a humble Cessna 152 and a Boeing 747, if able to fly the same speed in the same conditions, would use the same pivotal altitude. The airplane’s velocity and acceleration due to gravity are the only factors in determining pivotal altitude. Detailed derivations by John S. Denker and by ERAUSpecialVFR (13:57 YouTube) are included below.
The exact formula for height above the pylon is
$$h = \frac{v_{air}\cdot v_{gnd}}{g}$$
where $v_{air}$ and $v_{gnd}$ are velocities relative to the air and ground, and $g$ is acceleration due to Earth’s gravity. This shows that the common approximation of squaring groundspeed is the calm-day special case.
Assuming we want to know $h$ in feet, we need to connect the building blocks, namely the units of measure, appropriately. Given that $g$ is 32.17405 ft/s² (that is speeding up by 32-ish feet per second every second), compatible velocity will also be denominated in ft/s. To see why, you can think of the units as canceling out, as in
$$\frac{\frac{\textrm{ft}^2}{\textrm{s}^2}\equiv v^2}{\frac{\textrm{ft}}{\textrm{s}^2}\equiv g} \Rightarrow \frac{\textrm{ft}^2}{\textrm{s}^2} \cdot \frac{\textrm{s}^2}{\textrm{ft}} \Rightarrow \textrm{ft}$$
At least in the airplanes I fly, the airspeed indicator displays knots or miles per hour. The conversion factor from knots to feet per second is $\frac{6{,}076}{3{,}600}$ because there are 6,076 feet in a nautical mile and 3,600 seconds per hour. For statue miles to feet per second, the factor is $\frac{5{,}280}{3{,}600}$. Remember that the formula for pivotal altitude has two velocity factors, so we must square the conversion factor.
$$d_{mph} = 32.17405\ \textrm{ft}/\textrm{s}^2 \cdot \Biggl(\frac{3{,}600\ \textrm{s/hr}}{5{,}280\ \textrm{ft/SM}}\Biggr)^2 \approx 14.9569\ \textrm{mph}^2/\textrm{ft}$$
and
$$d_{kts} = 32.17405\ \textrm{ft}/\textrm{s}^2 \cdot \Biggl(\frac{3{,}600\ \textrm{s/hr}}{6{,}076\ \textrm{ft/NM}}\Biggr)^2 \approx 11.2947\ \textrm{knots}^2/\textrm{ft}$$
Then performing the dimensional analysis to see that the units of measure fit in the knots case, for example:
$$\frac{\textrm{NM}^2}{\textrm{hr}^2} \cdot \frac{\frac{\textrm{ft}^2}{\textrm{NM}^2}}{\frac{\textrm{s}^2}{\textrm{hr}^2}} \cdot \frac{\textrm{s}^2}{\textrm{ft}} \Rightarrow \textrm{ft}$$
That is, the squared airspeed converted to $\frac{\textrm{ft}^2}{\textrm{s}^2}$ divided by the acceleration due to gravity yields a quantity in feet.
Thinking of the magic numbers in the denominator may show more clearly what’s happening. In the case of knots, $\frac{1}{11.3}$ is around 0.0885 feet per knots squared. This means approximately the same as 9 feet per knots gained or lost, per 100 knots (because 9 ≈ 0.0885 × 100). Likewise for statute miles, the pivotal altitude changes by about 7 feet per mph airspeed change, per 100 mph the airplane is traveling. In either case, given two airplanes where one is flying twice as fast as another, a unit of airspeed gained for the faster will have twice the impact on its pivotal altitude as compared with its slower counterpart.

5. Derivation of the Nifty Formula

We wish to derive the nifty formula for the altitude required during a turn on pylon in the presence of wind. We will be using the following quantities:

$R$, horizontal position vector, from pylon to aircraft
$h$, height above the base of the pylon
$V_{Gnd}$, velocity relative to the ground
$V_{Air}$, velocity relative to the air
$W$, wind vector = constant, independent of time
$a$, acceleration vector = derivative of $V_{Gnd}$

or (equivalently) = derivative of $V_{Air}$

$g$, acceleration of gravity

Assumption: We assume constant $\lvert V_{Air}\rvert$ i.e. constant airspeed.

The velocity relative to the air, $V_{Air}$, is perpendicular to $R$. That is, $$V_{Air} \cdot R = 0 \tag{4}\label{eq4}$$ This is required by the rules of the game. The heading is perpendicular to $R$ because the wing is pointing at the pylon, and the airspeed vector is parallel with the heading because we require coordinated flight (zero slip).

The acceleration $a$ is antiparallel to $R$. This is required by the rules of the game, since the wing is pointing at the pylon. That means the horizontal component of lift is pointing at the pylon. Meanwhile, all other forces add up to zero in accordance with the constant-airspeed assumption. Because $a$ is antiparallel to $R$, we have:

$$a \cdot R = −\lvert a\rvert \lvert R\rvert \tag{5}\label{eq5}$$

We will be interested in what happens to all these quantities after some time $\Delta t$ has passed. Time-stepping the equations of motion gives us: $$
\begin{align}
\textrm{new}\ V_{Air} & = \textrm{old}\ V_{Air} + a\Delta t \\
\textrm{new}\ R & = \textrm{old}\ R + V_{Gnd} \Delta t
\end{align} \tag{6}\label{eq6}
$$

Combining equation $\eqref{eq6}$ with equation $\eqref{eq4}$ gives us the time-delayed version of equation $\eqref{eq4}$:$$(V_{Air} + a \Delta t) \cdot (R + V_{Gnd} \Delta t) = 0 \tag{7}\label{eq7}$$

Multiplying out equation $\eqref{eq7}$ gives us: $$0 = V_{Air}\cdot R + a\cdot R\Delta t + V_{Gnd}\cdot V_{Air}\Delta t + a \cdot V_{Gnd}(\Delta t)^2 \tag{8}\label{eq8}$$ The first term vanishes in accordance with equation $\eqref{eq4}$. The second term reduces to $\lvert a\rvert \lvert R\rvert \Delta t$ because of equation $\eqref{eq5}$. The fourth term is negligible in the limit of small $\Delta t$.

Rearranging the remaining parts of equation $\eqref{eq8}$ gives $$\lvert a\rvert = \frac{V_{Air} \cdot V_{Gnd}}{\lvert R\rvert} \tag{9}\label{eq9}$$ This tells us the magnitude of the acceleration. The direction is antiparallel to $R$ as mentioned [elsewhere]. So now $a$ is fully determined, since we know its direction and magnitude.

As usual, when the aircraft is properly banked toward the pylon, the geometry of the situation is shown in figure 3 [shown below]. In this geometry, the law of similar triangles tells us $$\lvert a\rvert = \frac{h}{\lvert R\rvert} g \tag{10}\label{eq10}$$

Combining equation $\eqref{eq9}$ and equation $\eqref{eq10}$ gives us the nifty expression for the required height at any point during a turn on a pylon:$$h = \frac{V_{Air} \cdot V_{Gnd}}{g}\tag{11}\label{eq11}$$ You can readily verify that this reduces to the conventional expression for the pivotal altitude in the no-wind case.

Physics of Flight - Pivotal Altitude - Lesson 6 by ERAUSpecialVFR

Figure created with Khan Academy

$\sum F_y = 0 \Rightarrow L \cos\theta = mg$

$\sum F_x = ma_c \Rightarrow L \sin\theta = \frac{mv^2}{R}$ (centripetal force)

$\frac{L\sin\theta}{L\cos\theta} = \frac{\frac{mv^2}{R}}{mg} \Rightarrow \tan\theta = \frac{v^2}{Rg}$

$\tan\theta = \frac{h}{R} = \frac{v^2}{Rg} \Rightarrow h = \frac{v^2}{g}$

$\therefore PA = \frac{GS^2}{g}$

$\begin{aligned}
  PA = \frac{GS^2}{g} &\approx GS^2\cdot\frac{\left[\left(1\frac{\textrm{nm}}{\textrm{hr}}\right)\left(\frac{1.15\ \textrm{sm}}{1\ \textrm{nm}}\right)\left(\frac{5{,}280\ \textrm{ft}}{1\ \textrm{sm}}\right)\left(\frac{1\ \textrm{hr}}{3{,}600\ \textrm{s}}\right)\right]^2}{32.17\ \textrm{ft}/\textrm{s}^2}{} \\
                      &\approx GS^2\cdot\frac{(1.687)^2}{32.17} \approx GS^2\cdot\frac{2.845}{32.17} \approx \frac{GS^2}{11.3}
  \end{aligned}$


Are there specific names for airport vehicles used for de-icing? Do de-icing vehicles used at airports for de-/anti-icing procedures have special names? I-ve searched the internet but have not found the exact names of these vehicles.

As far as I can tell they don't have their own name specifically they are part of the airports Ground Support Equipment. They have non-powered and powered support equipment, De/anti-icing vehicles fall under the powered category. Trying to find a better link than the one I found on Wikipedia In case you want to see that link
In case you want to buy one Heres a manufacturers website of GSE


Is a trimmed flight not always an unstable system? As soon as I am flying in trimmed flight condition, my pitching moment around the center of gravity becomes zero. So my center of pressure has to be located in the center of gravity, so that there is no resulting turning moment.
But assume, there comes a wind gust, and the angle of attack will increase. This causes the center of pressure to move forward in front of my gravity location. So the aircraft will become instable because the angle of attack will further increase (nose up). The only thing the pilot could do is to use the elevator to trim in pitch.
So in the end, as long as I want to use the principle of "trimmed flight" , I will always have to use control surfaces to counteract the unstable flight condition. So why to care about stability, in trimmed flight it will always come to an unstable flight condition as long as I do not use the elevators?
Can you follow me? Is this true?

But assume, there comes a wind gust, and the angle of attack will
increase. This causes the center of pressure to move forward in front
of my gravity location. So the aircraft will become instable because
the angle of attack will further increase (nose up). The only thing
the pilot could do is to use the elevator to trim in pitch.

This is not accurate.  Are you familiar with "free-flight" model airplanes?  Some of them are stable enough to be flown in the middle of the afternoon when the atmosphere is full of thermal updrafts and downdrafts, with no input from a pilot whatsoever, and no automatic control system (autopilot etc).
You are correct that if some disturbance increases the angle-of-attack of the wing, with a conventional airfoil with no "reflex", the center of lift and center of pressure of the wing will move forward, which is destabilizing.
But the tail is also seeing an increase in angle-of-attack, or if the tail is set to fly at a negative angle-of-attack in normal flight, then the angle-of-attack of the tail becomes either less negative or somewhat positive due to the disturbance.  Regardless of which of these is the case in any given instance, the change in angle-of-attack of the tail, which is far from the CG and therefore exerts lots of leverage, causes the center of lift and center of pressure of the whole aircraft to move aft of the CG.  So the aircraft noses down to a lower angle-of-attack, where the center of lift and center of pressure are again co-located with the CG.  That's how pitch stability works.
For more, see this section of John Denker's "See How It Flies" website.
Note-- for simplicity, I'm assuming that the only forces we need to consider are the "upward" or "downward" ones.  I.e., that the "center of lift" and the "center of pressure" are one and the same.  This is not exactly true.  For example, if the thrust line were way above the CG, then it would still be true that the center of pressure (including the effect of the thrust vector) was co-located with the CG when the aircraft was at equilibrium, but the center of lift would have to be a bit ahead of the CG.  If you find this simplification to be objectionable, then just (mentally) strike out "center of lift" from my answer and just leave "center of pressure".
In my answer here, I'm assuming that some sort of disturbance, such as a sudden updraft, has increased the angle-of-attack of the aircraft.  However, there's actually an additional question embedded in your question, which is "will a purely horizontal gust of wind cause a change in the angle-of-attack of an aircraft that is flying horizontally?"  That's a whole other "can of worms" that we may not really need to get into right now, but let's at least "lift the lid" and take a peek.  The answer to that appears to be that the sequence of events is as follows:  gust of wind from front -> increased lift -> upward curvature of flight path (which may temporarily decrease the angle-of-attack slightly) -> nose-up change in pitch attitude to conform to new direction of flight path -> continued upward curvature of flight path and continued nose-up pitch rotation.  All assuming that the aircraft has not yet come to equilibrium with the new velocity of the surrounding airmass at any given point in the chain of events.  It's not obvious that the angle-of-attack is ever increased above the original angle-of-attack.


Has anyone built an aircraft with a flat ring wing? When I try to search for circular wing aircraft, everything I find has the wing loop up over the top of the craft.
What I want to see, however, is basically an Aerobie Flying Ring, but with a motorized propeller, etc.
I'd be equally happy to see a "real" plane, or an RC one.
Also, while I would expect the wing to be attached to the fuselage via cables, I'd be equally interested in learning about alternatives (e.g. blended wing).

George Kitchen patented a design and half-built a biplane. It was completed by Cedric Lee and Tilghman Richards in 1911 but failed to fly. Richards went on to develop a series of increasingly successful Lee-Richards annular monoplanes before the outbreak of WWI.
This was a serious and promising design, having been wind-tunnel tested by the National Physics Laboratory in the UK during development. Kitchen and Richards understood that the strange shape would create vortices which trailed back over the rear part of the wing, and they used these to help impart stability. The monoplanes were indeed all safe and stable in flight (although the first was tail-heavy), a rare characteristic in those days. Pilots included Gordon England, Gordon Bell and NS Percival.


In the US, is it legal to cover up some of the required gyro instruments during flight under IFR in actual IMC? In the US, is it legal to cover up some of the required gyro instruments during flight under IFR in actual IMC?

The purpose being for "partial panel" practice.

To my knowledge there's nothing illegal about practicing partial panel in real IMC, however it's a spectacularly bad idea to do so. A failure of vacuum instruments in IMC is an emergency because you can easily lose orientation and dig a big hole in the ground. A safety pilot won't be able to help unless they have a separate set of instruments to rely on, and even then upset recovery in IMC is inherently less safe.

If you want to practice partial panel pleeeeease do so in VMC, with a safety pilot.


How does an airplane do a Kulbit manoeuvre? Some time ago, I came across a GIF of a Russian military airplane doing a Kulbit manoeuvre (Probably for showoff). How, in terms of control surface movement, does an airplane to the Kulbit?

Source: Reddit

The Kulbit maneuver is a variation on the Cobra maneuver (Pugachev's Cobra) with a higher pitch rate and continuous positive pitch rate throughout the maneuver. It requires two things:

A docile pitch behavior of the airframe over the full angle of attack range of 360°. Docile means that the pitch moments stay low and do not change abruptly with the angle of attack.
Thrust vectoring nozzles to keep the pitch rate up.

An electronic flight system is helpful to make execution easier, but is not strictly required. Also helpful is an engine-intake-combination which does not stall the compressor if the outer flow is reversed briefly. As you can see, the control surfaces only play a minor role - they are only important initially to start the pitch-up motion. This is done by negative elevator and/or positive canard deflection.


How can a single misplaced screw so massively increase a stealth aircraft's radar cross-section? In this comment on one of the answers to an earlier question of mine, @CarloFelicione points out how even the tiniest of imperfections can make a stealth aircraft much more visible to radar:

  A screw not properly seated on a maintenance panel can make the plane show up like a barn door on a radar. Not the size, it’s the reflectivity that matters

How is it possible for a single loose screw to increase a stealth aircraft's radar cross-section that dramatically?  Why does it show up like a barn door, rather than like, well, a screw?

In RCS, size does not matter once you move beyond the scale of the wavelength of the radar. Therefore, the RCS of a panel with an edge length of 10 cm is (theoretically at least) the same as one of a panel with 1 m edges. The screw must be so poorly placed that it will cause a larger panel to stick out so it has no electrical contact, with the edge pointing in the right direction, then this massive increase in RCS is indeed possible.


Do the FAA's InFO publications carry any regulatory or legal weight? The FAA publishes Information for Operators documents giving:

  valuable information for operators that should help them meet certain
  administrative, regulatory, or operational requirements with
  relatively low urgency or impact on safety.

Some of these documents seem to offer interpretations on regulatory matters, and are sometimes cited as such. In some cases, these interpretations may provide permission to operate more freely. However, I could imagine that in the case of others, the interpretations may prove to be more restrictive and burdensome than a plain reading of the regulations.

What regulatory or legal weight do do these InFO publications carry, if any?
Since these notices are directed at certified operators, does the answer vary depending on the audience?

An InFO (Information For Operators) document is an informational document containing recommendations. Quoting directly from FAA Order 8000.91:

  Much like a Safety Alert for Operators (SAFO), which contains critical safety information, an Information for Operators (INFO) message contains valuable information for operators that should help them meet administrative requirements or certain regulatory requirements with relatively low urgency or impact in safety. INFOs contain information or a combination of information and recommended action to be taken by the respective operators identified in each individual INFO.

They are not regulatory changes/obligations (like ADs) or formal notices of violation (administrative actions) - they're just a "friendly hint" that the FAA is concerned about something and would like operators to be aware of it and take action if the operator's analysis determines it to be necessary.
If the situation addressed in an InFO or SAFO document doesn't improve it may wind up prompting a regulatory change.

The InFO and SAFO programs are very similar, so FAA Order 8000.87A covering the SAFO program may also be of interest.


What is the purpose of classifying fighters? Fighters are classified by generation, as explained in this answer. Given this Wikipedia sum up, some fighters are not clearly in a defined generation, especially for 4th generation subclasses. Thus people may not agree on a list of fighters that belongs to a generation.

Some of the previous generation (generation 4, 4+, 4.5, 4++) are still actively produced (e.g. Rafale, F/A-18E/F)  while the F-22 (definitely 5th generation) is no longer in production.

Airframe designed a long time ago (e.g. the F-15, F/A-18) still receive updates that make it competitive on international market (the section about potential operator of the F/A-18 on Wikipedia give an overview for the F/A-18), even in front of 5th generation fighters (at least in Canada for the F/A-18 and the F-35)

Another capability we cannot rely on to define generation is stealth. The A-12 and more precisely its variant YF-12 was stealth supersonic aircraft with weapons (AIM-47) inside internal bays, but was not a 5th generation fighter.
Moreover, since ECM can be fitted on a fighter, this fighter expose some stealth feature.

Given those facts, it seems that since the 4th generation, knowing a fighter is classified as a specific generation does not provide information about its production year, its capabilities nor its competitivity in front of other nation's fighters.

In short, since the 4th generation, generation does not provide reliable information about capabilities, features nor designed or production year.

What information does the generation of a fighter give? How useful it is to know a fighter belongs to a specific generation?

People like to classify things, to divide them into categories.  Categorizing allows people to get an initial broad understanding of a complicated subject more quickly.  It is therefore very useful for purposes such as marketing and articles aimed for people who aren't necessarily subject matter experts.  However, classification is necessarily a crude tool that often isn't exact, leading to confusion and arguments about where the category boundaries lie.

People who are subject matter experts, such as designers of a new fighter plane, or military analysts trying to determine the capabilities of a new secret aircraft produced by other countries, presumably don't spend much time wondering into which category to put a given aircraft.  Instead they focus their time on the details of the subject, the same details that are too much information for the person trying to get the quick grasp of the complicated subject.

To answer your questions specifically, knowing the generation of a fighter gives someone a rough idea of its capabilities, and allows the person to quickly compare a given fighter aircraft to other fighter aircraft.  Knowing the generation of a fighter is useful for people who aren't experts on the subject who need a quick broad understanding of the capabilities of historic and modern fighter aircraft, and who need to know roughly where a given aircraft fits into the large picture.


Where do flaps and elevators get input from? How are flaps and elevators controlled in both a fly-by-wire or manual airliners? Is it from the yoke or the joystick as in Airbus or military aircraft?

For how long and in what stage of the flight are flaps kept down? E.g. at takeoff, are flaps down until the aircraft reaches the required altitude or do aircraft rely on just elevators-down-nose up position to change altitude or raise the nose?

Let's take the two most prolific airliners as examples, the A320 and the B737.

A320

For aircraft pitch control, the A320 has a horizontal stabiliser which can be trimmed, and an elevator.

The elevator can deflect very rapidly, and is actuated via hydraulic actuators. They receive their inputs from the digital flight computers, which compute appropriate inputs depending on pilot side stick input and aircraft flight state.
The horizontal tail can be trimmed: moved relatively slowly via a screw jack driven by two hydraulic motors. The hydraulic motors receive their inputs from the flight computers, which provide commands for auto-trim of the stabiliser. Direct mechanical control can also be used: the trim wheels have a mechanical cable connection with the hydraulic motors, rotating the trim wheels directly commands the hydraulic motors to run. The trim wheels are situated on either side of the thrust levers.

Flaps get their input from the flap lever. The A320 simply has settings 0,1,2,3,Full, and the pilot selects the proper number in the appropriate flight phase. From A320_Briefing_For_Pilots:

B737

The B737 has the same arrangement as the A320: a moveable horizontal stabiliser, and an elevator.

Again, the elevator makes the rapid deflections, actuated by hydraulic actuators. They receive their inputs from mechanical cables, connected directly to the columns in the cockpit. A feel spring provides artificial entering forces, proportional to the airspeed (q-feel).
The stabiliser is actuated via a screw jack, which can be rotated via electrical motors (by flipping the trim switch on the control wheel) or directly via the trim wheels, which are connected to the stabiliser via mechanical cables. From this link:

  Trim can be applied by electric trim switches, autopilot or a manual trim wheel. Electric and autopilot trim may be disengaged by cutout switches on the control stand in the event of a runaway or other malfunction.

  Moving the control column in the opposite direction to electric trim will stop the trim, unless the STAB TRIM switch is set to OVERRIDE. This function could be used to control the pitch of the aircraft with trim say in the event of a jammed elevator.

  The trim authority varies according to aircraft series and method of trim. The full range is only available with the manual trim wheel, but if at an extreme setting, electric trim can be used to return to the normal range. There are two electric trim switches on each control column, the right is for the direction and the left is an earth return for protection against spurious electrical signals.

Flaps again get their inputs from the flap lever, next to the thrust levers. There are slots for the lever to be situated at the appropriate flap setting, noted in degrees deflection.

Image source


What training is required for a class B endorsement? 14 CFR 61.95 requires solo student pilots to have an endorsement to (a) fly through class B airspace or (b) takeoff/land at a class B airport.  However, the requirements to get it are pretty vague:

(1) The student pilot has received both ground and flight training from an authorized instructor on that Class B airspace area, and the flight training was received in the specific Class B airspace area for which solo flight is authorized;

There are similarly vague training requirements for Recreational pilots in 14 CFR 61.101(d) and Sport pilots in 14 CFR 61.325.
Is any particular content or amount of time expected, or is it at the CFI's sole discretion to decide when a given pilot is competent enough to endorse? Does the training itself need to be logged as such, separate from the endorsement?

I can not find any guidance other than what you have already noted for Class B airspace endorsements. The ground and flight training requirements seems to be left up to the discretion of the CFI. Though, it seems to be very similar to a solo endorsement as having criteria that is subjective to student and instructor.
Similar to a solo endorsement, a conservative CFI would only endorse the student for a specific airport, in a specific Class B airspace (and not the actual Class B airport), for a specific timeframe, and specific conditions. Even though the endorsement must be given within the preceding 90 days of the flight, the conservative CFI would specify a specific date and time instead of a blanket authority.
That being said, your entire logbook would then serve as a record of adequate training. Previous corresponding flights with the CFI would be logged in the logbook as evidence of training.


Do small aircraft have sockets for passenger headsets? I am currently training for my PPL. in the Cessna 182s we use I've only ever noticed two sets of ports for the headsets. If there were additional passengers in the back seats, how would they communicate?

The rear seats of a Cessna 172 has headset jacks, I imagine the 182 has the same.

You can see them in this picture:

Image source

You might also find them over the shoulder of rear passengers - as can be seen in this image (copyright attached)

That links the rear-seat passengers to the same intercom you're used to from a front seat passenger.


Does a CFI need an Instrument Rating https://www.ecfr.gov/cgi-bin/retrieveECFR?gp&n=14y2.0.1.1.2&r=PART#se14.2.61_1183

The or below is very confusing.  Doesn't it mean I need an Instrument rating or one of the things that follows it in the list?  Or means one or the other, not both.
Furthermore, when would one of the things that follows in the list NOT apply?

(2) An instrument rating, or privileges on that person's pilot certificate that are appropriate to the flight instructor rating sought, if applying for—

(i) A flight instructor certificate with an airplane category and single-engine class rating;

(ii) A flight instructor certificate with an airplane category and multiengine class rating;

(iii) A flight instructor certificate with a powered-lift rating; or

(iv) A flight instructor certificate with an instrument rating.

For most people, the answer is yes—you need an instrument rating to be a CFI or CFII for the categories that are listed.

It is possible to become an ATP by using military experience. In that specific case a person has instrument privileges but may not have an instrument rating.