If I'm instrument current in an ASEL, am I also considered current in an AMEL? FAR §61.57(c)(1):

Within the 6 calendar months preceding . . . logged at least the
following tasks and iterations in an airplane, powered-lift,
helicopter, or airship, as appropriate . . .

I would infer from this that 1) instrument currency does NOT carry over from one category to another but 2) that it does carry over from one class to another within a category. Is that accurate?

Yes, you maintain instrument currency by category, not class. 61.57(c) only mentions class in the glider-specific requirements in (c)(3). The FAA doesn't mention it at all in related legal interpretations.
Note this wording from 61.57(c)(2) (emphasis mine):

A pilot may accomplish the requirements in paragraph (c)(1) of this
section in a full flight simulator, flight training device, or
aviation training device provided the device represents the category
of aircraft for the instrument rating privileges to be maintained and
the pilot performs the tasks and iterations in simulated instrument
conditions. A person may complete the instrument experience in any
combination of an aircraft, full flight simulator, flight training
device, or aviation training device.

See also this legal interpretation, Griffith (2008) (emphasis mine):

Generally, all appropriate endorsements for passing the instrument
proficiency check, which would be otherwise given if the check were
passed in an aircraft, can also be given when one passes the check by
using an FTD, as long as the FTD represents the appropriate aircraft
category for the instrument privileges sought.

It's true that you have to pass an instrument checkride (or at least some specific tasks) in a class before you can exercise those privileges in that class, but that's a one-time thing that doesn't affect how you maintain currency. See this question for more details.


Part 65.61.d.2 IFR Requirements I have a question regarding this requirement as I work on my IFR SEL rating:

  Forty hours of actual or simulated instrument time in the areas of
  operation listed in paragraph (c) of this section, of which 15 hours
  must have been received from an authorized instructor who holds an
  instrument-airplane rating, and the instrument time includes [...]

The question is, if 15 hours of the 40 hours is required to be with an authorized instrument rated instructor, then how do you gain the other 25 hours of the required 40 hours?  Wouldn’t all 40 hours have to be with an instrument rated certified instructor?

If you're under the hood in VMC + VFR, you could have an appropriately rated pilot (i.e. PPL) in the other seat as the safety pilot. If the other pilot is instrument rated (but not a CFII) + is the PIC for the flight, you could even be the sole manipulator of the controls in IMC + IFR, although that gets into the questions about logging PIC vs acting as PIC, which is its own set of issues. The "safety pilot" option is probably more typical.


How does blade solidity ratio relate to thrust/power/torque of a propeller? for quite some time I was using ABBOTT formula for static thrust estimation on a two-bladed propellers:

$$
T=6.8\times10^{-5}\times D^{3}\times p\times RPM^{2}
$$

$T$ is Static Thrust (N); $D$ is propeller diameter (m), $p$ is propeller pitch (m); RPM (1/s)

I was, however, unable to find any formula which would include number of propeller blades.

Standard thrust estimation methods all seem to rely upon the "propeller disk area" which is always assumed for a two-bladed propellers.

The closest I was able to get is something called "blade solidity ratio", or "rotor solidity":

$$
\sigma = (B c)/2\pi R
$$

where $B$ is number of propeller blades, $c$ is chord of each blade, $R$ is radius of the rotor.

The question is - how does blade solidity relate to thrust/power/torque?

Each propeller blade is a wing in itself, and like a wing carries the weight of the plane, the propeller blade carries its fraction of the total thrust of the propeller. The more blades, the lower the fraction of each blade.

Low disc loadings are associated with two- or three-bladed propellers. Those can be found on GA aircraft and older, slow designs like pre-WW II aircraft. With turboprops and near-transsonic designs, more blades are needed to distribute the aerodynamic loads and to reduce the lift coefficient especially at the tips.

There is no strict formula, but in general a higher disk loading is associated with a higher solidity ratio.


Do commercial passenger airplanes have cambered airfoils? It seems to me that they logically would, since they have no need to fly upside down like an aerobatic plane would (so they would not need a symmetric airfoil for any conceivable reason). That being said, is that correct, and does anyone have a link to a reliable source where that is stated?

I think it's safe to say that all passenger planes use cambered airfoils, although I wouldn't be surprised if someone finds a case of an aerobatic plane being used to carry a paying passenger, just to prove me wrong.

There's a fairly comprehensive list here. You'd have to look them up to be sure, but many of them use codes that indicate thickness and camber. For example, the first digit of a NACA airfoil is the camber.


What is the material of this tow bar? What are the materials used in a tow bar of the pictured design? I am interested in the materials use for the tube (which aluminium alloy?) and the materials of the lunette mount flat and inside structure.

Aircraft towbars are almost exclusively aircraft-grade aluminum or
  steel in construction  to meet or exceed the working load. Not only
  must the towbar be able to safely pull/push the vehicle, it must also
  be able to withstand the towed vehicle's inertia.

Source

Although there are several components that make up the tow bar they all must be strong enough to withstand the forces exerted on them. That's what the label on your picture is for, it dictates what aircraft you can use the tow bar on. Larger aircraft = Larger more robust tow bar.


Did Clement Ader make the first flight even before the Wright brothers? Clement Ader invented in the late 1890s, a plane that looked like a bat. It had a steam engine. Witnesses said it went airborne at least once and recorded a distance just over 50 meters. The Wright brothers made their first controlled flight in 1903.

Lots of people flew before the Wright Brothers.  Some of them even survived!
The Wright Brothers are credited as inventors of the airplane not because they flew, but because they were the first to take flight in a vehicle which:

Lifted itself using its own power (which gliders and kites did not)
Was aerodynamically controllable by the pilot (which Ader's aircraft was not)
Remained in sustained flight, rather than taking momentary flight before returning to Earth


How are the 737’s elevator and aileron cables attached to their control tabs without impeding the control surfaces’ motion under hydraulic power? The 737 (all versions thereof) is one of the few jetliners still in production to have any manual-reversion capability for its flight controls in the event of the loss of all hydraulic systems.  If hydraulic pressure is lost in both the A and B hydraulic systems, control tabs on the elevators and ailerons unlock, and the elevator and aileron control cables, which are directly attached to these tabs, deflect them to produce aerodynamic forces that move the elevators and ailerons in the desired direction.1  When hydraulic pressure is available in either of the two primary systems, the control tabs are locked to their respective control surfaces and move with them.
Thus, the control tabs - which are still attached to the control cables even when locked to the elevators and ailerons under hydraulic power - deflect in the opposite direction when the flight controls are being moved hydraulically compared to when in manual-reversion flight.  For instance, when a pilot commands up elevator in hydraulic flight, the elevator actuators move the trailing edge of the elevators, and of their control tabs, upwards, even as the control cables themselves are trying to pull the trailing edges of the elevator control tabs downwards (as would be necessary when commanding up elevator in manual-reversion flight).  How does the 737’s flight-control system prevent the forces generated by the hydraulic flight-control actuators from feeding back through the control cables (via their attachments to the elevator and aileron control tabs) and forcing the pilots’ yokes in the direction opposite their control inputs, or, alternatively, the forces exerted directly by the control cables from impeding the control surfaces’ motion when under hydraulic power?

1: Not all of the 737’s control surfaces have provisions for manual control; the spoilerons (which deflect asymmetrically to assist the ailerons in rolling the aircraft) are inoperative if the A and B hydraulic systems both fail, while the rudder (which provides yaw control independent of roll) can be powered by the third, standby hydraulic system2 if both the A and B systems fail, but does not have manual-reversion capability in the event of a failure of all three hydraulic systems.
2: The standby hydraulic system (which can provide hydraulic power to move the rudder, actuate the thrust reversers, and - if the ALTERNATE FLAPS switch is engaged - extend the leading-edge high-lift devices) is normally unpressurised, but can be manually activated by the pilots (and activates automatically in the event of a hydraulic failure during critical phases of takeoff and landing); this is generally done in the event of a failure of one or both main hydraulic systems, but the standby system can be engaged even if both the A and B systems are fully operational (useful for clearing some types of rudder jams, although less so nowadays than was the case with the 737’s pre-2008 rudder-control system).

The tabs themselves are not locked -- that lock you mention is upstream: an input lock. Next time you sit next to the wing, watch the aileron as the pilots check the controls and notice how the tab moves opposite (alternatively, and rewindable, you can watch it here).
With the input locked, the tabs are free to move without directly feeding back into the actuators/rods/cables (indirectly though, the elevator tabs serve two different functions depending on the flight regime).

Source: b737.org.uk

Above is a photo for the elevator/tab deflection as seen on ground with the elevator up and tab down. And when unpowered, the elevators droop, and the tabs would be trailing edge up as expected, as seen in the following photo:

Source: wikimedia.org

The mechanism
For the elevators, the cables (from the control column) move the aft control quadrant. From there, no more cables -- a rod moves a differential (floating) lever, which is the input to 1) the hydraulic actuator 2) the manual reversion lever (either/or).
With hydraulic power available, locking pistons lock the manual reversion lever (not the tabs). With loss of hydraulic power, the now unlocked manual reversion lever changes the differential lever's pivot point -- switching the input to the aero tabs.
Here's a drawing from Boeing's manual reversion patent. I colored the differential lever yellow and the manual reversion lever red (locking pistons are shown in another figure), and drew the two pivoting axes:

Source: patents.google.com

This is how with the manual reversion lever locked (hydraulics working), elevator movement would move the tabs in the correct non-impeding opposite direction (rod 34 need not translate), e.g. pull back - elevators up - tabs down. This is also illustrated in Fig. 5 in the patent.

Source: gov.uk/aaib-reports

Above are the rods that move one of the tabs on a 737-700. The ailerons are covered by the same patent (same principle).
But that is not all
At low-speed, triggered by the extension of the TE flaps, a hydraulic/spring mechanism shifts the pivot point of the tabs, which in turn reverses the tabs behavior, making the tabs follow the elevators, e.g. pull back - elevators up - tabs up. This increases the camber giving more control.
The relevant Boeing patent is here; it's an earlier design where each elevator had two tabs, as seen on the 707:

Source: publicdomainpictures.net

On the 707 (and KC-135, etc.), the inboard tabs are the convertible type -- their anti-balance mode is to make the pitch control heavier in cruise; the balance mode is used at low-speed (activated by stabilizer position) to counter the increased air loads on the elevators' top surface when the stabilizer is more nose down. (The 707 pitch/roll is not hydraulically powered.)
When the elevators are pushed down by air loads, the inboard tabs would already be down, keeping the elevators at neutral (no input required), otherwise the stabilizer effectiveness would decrease. And with any input, they would assist -- that's opposite the 737 at low-speed as noted earlier. The mechanism for the convertible function on the 737NG is seen in the following drawing:

Source: slideshare.net

At low-speed and with no hydraulics available for that mechanism, the tabs remain in the balance (assist) function -- move opposite the input, in order to the move the elevators as intended in manual reversion.
Finally, here are the different tab deflections during maintenance testing (elevators are up):

Source: b737.org.uk

To summarize: the lock is for the input (therefore no impeding action), and the tabs on the 737 do a lot behind the scenes.


What are the correct names for the two faces of an airfoil? When representing a wing airfoil, often the low pressure is on the top side and the lift is positive:

In this case upper and lower sides are enough to understand the role of the surfaces, But this is meaningless for a rudder or for a compressor blade.
Are there names to identify the faces in relation with the direction of the lift. (In French specific names, extrados and intrados, are used in relation with camber.)

You can call the two opposite sides suction side (for face on the convex side of the camber curve) and pressure side (for face on the concave side of the camber curve).

This has been used in a number of cases- for example in NASA Report CR-1767 Section Data for Thin, Highly Cambered Airfoils in Incompressible Flow:

  .. flow separation on the pressure side at negative incidence angles and on the suction side at positive incidence angles.

for airfoils and in National Energy Technology Laboratory Handbook:

  The airfoils are curved, convex on one side and concave on the other, with the rotor rotating toward the concave side. The concave side is called the pressure side of the blade, and the convex side is called the suction side of the blade.

for compressor blades.


Why would aircraft engines be mounted with "toe out"? According to Wikipedia, on the Douglas DC-4E...

  [...] the four 1,450 hp (1,080 kW) Pratt & Whitney R-2180-A Twin Hornet 14-cylinder radials were all mounted with noticeable toe-out, particularly the outer pair.

(Emphasis added)

Why would the engines be mounted toe-out, instead of straight in line with the direction of flight? Is this practice common today?

According to this source

  The engines were toed out slightly to improve engine-out handling;
  three tailfins were used to ensure that the aircraft could keep flying
  more or less straight if both engines on one wing went down.

I belive it was done to keep the thrust more equal in the event of an outboard engine loss, i.e. they are inline with the direction of flight when an engine loss occurs. Keep in mind that at the time these planes were designed engine failure was a [very]common thing and the mentality was a bit different than it is now. If a little bit of toe out mounting took a speed toll but made the aircraft far more controlable in the event of an engine loss it was considered worth while.

In modern multi-engine propellor aircraft counter rotating propellors (left side and right side props spin oposite directions) are generally employed to fix this problem and avoid the critical engine issue. I do belive that some single engine aircraft still do employ a slightly canted engine position for this reason.


What happens when the velocity of the lower surface of the airfoil is lower than the velocity of the free stream? At a certain AOA I noticed that the speed of air in the lower surface of the airfoil is lower than the free stream's speed. What is the consequence of that?

Local pressure will rise above the freestream pressure. Speed and pressure are linked, as expressed in Bernouilli's principle. Also the local temperature will rise, as expressed in the ideal gas law.

Note that at all angles of attack there is one point where the local flow speed will decrease to zero in 2D flow: This is the stagnation point. On wings in three dimensional flow this becomes a stagnation line, and swept stagnation lines still have some residual flow speed, but in all cases the local speed is below the free flow speed at and around the stagnation line.

Since lift is proportional to the pressure difference between the upper and lower side of the wing, this slowing down is welcome. Another beneficial effect is the lower wall friction of the slower flow. However, the thicker an airfoil is, the higher will be the flow speed on both sides, due to the displacement effect of the thicker airfoil. Thinner airfoils are structurally less efficient, so a compromise needs to be found which allows enough internal structure while keeping thickness reasonably low.


Why is the TPA listed on the Chart Supplement (AF/D) sometimes lower than 1,000 AGL? I'm looking at B19 in Maine, and it recommends a Traffic Pattern Altitude (TPA) of 995 MSL (800 AGL). Wouldn't 1,000 AGL be safer?

B19 is close to the Portland class C airspace, which starts at 1500 MSL, so a TPA of 995 MSL provides 500ft of vertical separation.


How can a pilot involved in serious accident remain unknown? Somewhat similar to this question. A short part from Wikipedia article about Emirates Flight 521 (emphasis mine):

The captain was an unnamed 34-year-old UAE national who had been with Emirates since March 2001 and had logged 7,457 flight hours, including 5,123 hours on the Boeing 777.

In which situations or under which circumstances a name of pilot involved in serious crash may remain unknown or hidden?

In this case, it's most likely that the source for the story (the airline?) simply chose not to name the pilot and the editor of the Wikipedia article didn't seek another source that might have done so.
It's virtually certain that the pilot's name appears in the official reports of the incident.  The airline likely chose not to give the name for PR or legal reasons.


What is "Bird Strike Speed"? I read through the reference speeds of the Hawker 850XP and I stumbled upon the "Bird Strike Speed". It is specified as "280 KIAS up to 8000 ft".

What does that speed mean?

Aircraft structures are required to withstand the structural damage caused by birdstrike. According to 14 CFR 25.571 - Damage - tolerance and fatigue evaluation of structure:

(e)Damage-tolerance (discrete source) evaluation. The airplane must be capable of successfully completing a flight during which likely structural damage occurs as a result of -
(1) Impact with a 4-pound bird when the velocity of the airplane relative to the bird along the airplane's flight path is equal to Vc at sea level or 0.85Vc at 8,000 feet, whichever is more critical;

In case of aircraft with high cruise speed, the speed may be limited below 8000 ft to comply with this regulation. As Bird Strike Requirements for Transport Category Airplanes notes,

... to meet current bird strike criteria, some manufacturers specify relatively low $V_{MO}$ and $V_{C}$ airspeeds up to 8000 feet, that increase above that altitude.

The 'bird strike speed' is likely this.


Does asking for deviation due to weather give ATC any leeway for reducing separation between aircraft? When needing to deviate due to weather, does asking for deviation "due to weather" give ATC any leeway in terms of aircraft separation?

No, it does not. ATC can specify a restriction to the deviation, especially in a non-radar environment where they can't keep an eye on you.

The only thing that frees ATC of separation responsibilities between two IFR (or IFR/VFR depending on airspace) aircraft is if one them reports the other in sight, and is issued an "maintain visual separation". After that the responsibility of not hitting the other aircraft, or its wake, rests solely with the pilot in command.


What would be the general steps for making a flight in a biplane? I'm a writer, the story I'm writing is set in 1942. It's an alternate history of sorts, so there's no pesky WW2 to worry about, but technology has developed in roughly the same way. As part of an action sequence, my character, Scarlet, is going to steal a biplane to escape pursuit. She has a pilot's license and knows how to fly, but until this point, she hasn't needed to actually show her stuff.

What I do need to know, in layman's terms, are the general procedures of how the flight would go, any preparation that might be needed, and approximate speeds.

First follow @Jim's advice for getting the plane set up and the engine running.

A biplane is most likely a taildragger, which means that it has two main wheels and a third all the way in the back. This will give the plane a nose-high ground attitude, and taxiing to the runway will involve Scarlet to wiggle the plane left and right because the forward fuselage is obstructing her forward vision. This is not made easier by the fact that tandem two-place biplanes, the most common type, are flown from the back seat in order to get the center of gravity right.

Next, she should wait until engine temperature is high enough to run the engine at full load. I would expect that in a pursuit she skips that step but will worry that oil temperature has not reached the required temperature. The next step would be the magneto check which she will also skip.

In the takeoff run she will first orient the aircraft into the wind and then gently apply throttle so the aircraft doesn't end up in a headstand (meaning the propeller pulls the nose into the ground without the wheels moving). This also requires her to pull the stick all the way aft so the empennage (horizontal tail) keeps the tail low. A headstand is shown in the second picture of the second linked answer (this one).

Airfields back then were mostly round grassy patches, so the take-off direction could be freely selected in order to take off directly into the wind. However, you might want to add some suspense when Scarlet finds her biplane at the wrong end of the field and has no time to taxi across it, but takes off with a tailwind. This will make the takeoff run longer and the climb after takeoff more shallow, so she might just barely escape collision with an obstacle there.

When the aircraft picks up speed she should reduce back pressure on the stick and move the stick to a roughly central position in order to reduce downforce on the tail so the tail can lift off the ground. Bonus points for mentioning the gyroscopic effect from the propeller as the aircraft lifts its tail which requires the brief application of rudder to keep the nose pointed into the desired direction.

Liftoff is rather unspectacular and happens when the aircraft is fast enough. However, if elevator trim is set the wrong way, the aircraft will stay on the ground for too long (too much nose-down trim) or lift off too early at a too slow speed (too much nose-up trim). Trim means that either a spring in the elevator linkage or a small auxiliary flap is set such that it pulls the elevator to a certain deflection angle. This is helpful for adjusting control forces according to the desired flight speed and center of gravity location, but if it is set the wrong way on takeoff, Scarlet might be surprised by unusual stick forces.

While the takeoff is flown at full rich mixture, once in the air Scarlet should adjust the fuel to air mixture in the engine according to flight height. You might want to add a dramatic moment where the engine runs rough or even stutters due to too lean mixture.

After that, the escape should be easy.


Is a vertical stabiliser needed for straight line flight in a glider? My team is designing a glider and I am unsure about whether or not to include a vertical stabiliser. The task the glider must complete is to achieve the largest possible displacement in a straight line.

Our glider will not be able to automatically adjust the vertical stabiliser's position so it would stay upright and inline with the glider's fuselage for the duration of the flight. Since our glider does not require any changes in it's yaw angle (because it is flying in a straight line), I don't think there is a need for it.

Should we include a vertical stabiliser or not?

The stabilizer is meant to keep the nose pointing into the wind.

Any asymmetry in he wings/fuselage will create a tendency to yaw, you will need to compensate for that. The easiest is a fixed vertical stabilizer at the rear.


Why does the DC 4 airplane not tip backwards? The wheelbase of the DC-4 is very short relative to the fuselage

The 4 engines weigh a combined 7,000 pounds. It would seem like even with the weight of the engines, it's not enough to prevent the plane from tipping backwards. If a really fat passenger sat in the back of the pane, it would tip.

Although the landing gear are pretty far forward on the DC-4 the weight of the engines places the center of gravity in front of the main landing gear. It's unlikely that a passenger would be heavy enough to tip it, but freight certainly can. When loading freight tipping is prevented with the use of a tail stand, as can be seen in the photos below.

Image source

Image source


How does an Airbus aircraft connect to the Internet? I would like to understand better where (physically in the aircraft) and how the Internet connection is received on an Airbus aircraft, in particular in an Airbus A380, and then how this system is linked to the access points that serve the passengers. What path(s) bring(s) the connection from the antenna to the access points that make it available to the passengers?

There are three different ways that aircraft can give internet access to its passengers, which will most likely be on at around 38,000 feet. First off, to have Inflight wifi, there needs to be a ground-based internet server, a transmitting dish, or a satellite dish. There must also be a receiving and transmitting antenna on the aircraft and an onboard server and a Wi-Fi router.

The first system is the ATG system, which stands for Air-To-Ground transmission. It requires two antennas that are installed on the belly of an aircraft so that it can pick up signals from the ground-based cell towers. With this system, a passenger can receive at least 3 Mbps and one of the highest currently is 9.8 Mbps by gogo wifi.

The next system is the "Ku-Band" Service, which was formerly used by the military. K, short for Kurz (meaning short in German) and u for under the original NATO/K-band frequency range. This system works by a ground station sending signals to a satellite first, and then reflect off the satellite and send the signals to the aircraft. The signal is then decoded and then transferred to the router. This can deliver about 50 Mbps with this system, but you still have to consider that there will be more than a hundred passengers on the aircraft. Since this system has to send signals to a satellite first, there could also be delays on signals and could get slower as more aircrafts use this service. If you've seen aircraft with a pod on the top of its fuselage, you may not know that under it sits a satellite antenna, which rotates and can adjust itself to the nearest satellite.

The last system is the "Ka-Band" Service. K still stands for Kurz, and a stands for above since this is in the upper region of the native frequency band which is at 20–36 GHz. This service can deliver about 70 Mbps. Presently, there are two ViaSat (a satellite wireless service provider) Ka-Band satellites, one covering the US, and one covering Canada and parts of Europe.

Some aircraft even have a hybrid system, so they can use Ku-Band and Ka-Band service depending on which has a better signal at the time, so it would depend on the internet speed on which the A380 you are referring to is.

An onboard server will be required on the aircraft for an Inflight Entertainment system, which will run three services: a media server, a DRM (Digital Rights Management) license server, and a device provisioning server. The media server is for storing your content keys (but doesn't necessarily have to be on the media server, it can be on a separate onboard server). The device provisioning server will need to store a reserve of device personalities (unique device credentials) for distribution to onboard mobile devices (via your mobile app) upon request. The signals from the satellite (in a Ku/Ka-Band service) will be transmitted into the pod/antenna, then into the onboard server, which will be transmitted to several routers distributed throughout the aircraft. For example, an A320 or a B737 usually have two routers. The signal is sent to your phone, then signals will be sent back to the antenna, then to the satellite, which is passed back to the ground.

More about in-flight wifi at HOW does WIFI WORK on AIRPLANES? Explained by CAPTAIN JOE


Calculations for altimeter settings for variations in barometric pressure Pls help me with these 2 questions

An aircraft is standing on an airfield 220ft above sea level on a day when the barometric pressure at ground level is 1004 mb. If the pilot sets the altimeter to read 220ft on this day, what will it read if the barometric pressure drops to 992 mb.

An aircraft sets off from airfield A (126 ft above sea level) where the ground pressure is 1010 mb and flies to B (762 ft above sea level) where the ground pressure is 985 mb. If the pilot sets his altimeter (incorrectly) at 26ft at A, what will it read when it lands B?

Question 1: 550 ft.

Question 2: 660 ft.

(rounded to the next multiple of 10).

Atmospheric pressure drops by 1 mbar for every 8.5 m or 27.7 ft of altitude between 0 and 1000 ft, and the differences of your cases from the standard atmosphere are small, so I did not use corrections.


How do you start a jet engine if the start valve is stuck closed? I was recently on a flight aboard an Airbus A380 where the flight was delayed 2 hours. The reason was claimed to be a start valve fault on engine #4, where it was stuck closed. According to the captain, they were able to get the engine started after manually starting the engine at the gate. How does this work?

Perusing the A380 Training Guide, Edition 01, 01 Sep 2008, Section 5 - Engine Starts, Subsections 5.8.6 (Engine Start Valve Stuck Closed),

  5.8.6 Engine Start Valve Stuck Closed

  ECAM actions – ENGINE MASTER OFF.
  Check MEL, and in conjunction with, advise LAE of situation in preparation for Start Valve Manual Operation.
  For Start Valve Manual Operation on Engines #2 and #4, the adjacent engine (if already running) will require shutdown, to enable LAE’s
  access to the manual start override procedure on the port side of the
  affected engine.
  As the CAB Pb on the RMP is common to the Cockpit, Ground and Cabin Crew, advise the Cabin Crew to refrain from using the Cabin Interphone
  during the procedure.
  When ready, accomplish normal engine start sequence:
  a)    Engine Start Selector to IGN/START.
  b)    Engine Master Lever to ON.
  c)    Command LAE to OPEN START VALVE AND KEEP OPEN.
  d)    At 50%N3, command LAE, START VALVE CLOSE.
  e)    Monitor engine parameters closely until stabilized.
  Advise Cabin Crew upon completion of procedure.
  In flight, only windmilling start will be available.

Glossary (correct if needed, please):
ECAM = Electronic Centralised Aircraft Monitor
LAE = Licensed Aircraft Engineer
CAB = Cabin
Pb = Pushbutton
RMP = Radio Management Panel
IGN = Ignition
N1/N2/N3 = N1 is LP (Low Pressure stage), N2 is IP (Intermediate Pressure stage), N3 is HP (High Pressure stage)
MEL = Minimum Equipment List

ECAM will display "ENG MASTER X ........ OFF" (X will be the engine with stuck valve)
(A320 display, only shows two engines, instead of four) (The message will appear in the lower left quadrant.)
Check the Minimum Equipment List (MEL) to determine if loss of engine is GO, GO IF, or NO GO, if failure is not in the MEL, it is classified by default as NO GO. Advise the on-site Licensed Aircraft Engineer (LAE) of the warning message in preparation for completing the Start Valve Manual Operation procedure.
If the engine with the stuck valve is #2 (left side inboard) or #4 (right side outboard), the adjacent engine will be required to be shutdown before commencing the manual start procedure. (This is because the engineer has to access the left side of the engine and for safety's sake the other engine, which would be gehind him must be shut down. If the fault is on the left outboard (#1) then the engineer would be on the far side of the engine from the #2 so #2 does not need to be shutdown.)
Since the Cabin Pushbutton (CAB Pb) on the Radio Management Panel (RMP) is common to the Cockpit, the Cabin Crew area AND the Ground circuit, the pilot should advise the Cabin Crew to not use the Cabin Interphone during the procedure. (If the pilot and the engineer are discussing starting the engine (or not) they don't want a flight attendant to be talking about starting pre-flight stuff at the same time, if the engineer heard the word start, he might wrongly assume it was the pilot.)
When pilot and engineer are ready, begin the normal engine start sequence with changes:

a) Turn the Engine Start Selector to IGN/START. (This is a panel from an A320, so only two engines are shown.)

b) Flip the Engine Master Lever (For the faulted engine) to ON. (This is a panel from an A320, so only two engines are shown.)

c) Over the interphone, command the engineer to manually open the start valve and keep it open. (I haven't yet looked for and found a schematic for an example engine, sorry. As shown in other diagrams/answers, it might be a socket wrench, etc.)

d) Watch the Engine Warning Display. (Again, A320, only two engines.) (This is an A380, showing N3) Once N3 is spun up to 50%, over the interphone, command the engineer to manually close the start valve.

e) Monitor the engine parameters closely until all are properly stable.

f) After the engineer has closed up the engine and vacated the area, start the other engines, if one was shut down per step 3.
Over the cabin interphone, notify the cabin crew that the procedure is complete. ( so they can resume using the interphone if needed. )
If the engine failed in-flight and upon restart a stuck valve warning was shown, all of the above would not be possible. At that time, the only way to restart the engine would be to attempt a windmill start (using the flow of air through the engine to turn the engine), there are other procedures for that.

Also, I do not yet have the engine schematics to show what the LAE actually does.


Why are Inline Engines more commonly used than Radial Engines? Back in the early days of aviation radial engines were very popular, it seemed like all of the big planes of the 20s, 30s and early 40s used them.  But some time during WWII (or so it seems to me) aircraft manufacturers switched from radial engines over to inline engines.

Why was there a switch?  Why do modern manufacturers rarely, if ever, use radial engines?

Example of a Radial Engine for those who are unfamiliar:

The big advantage of radials at the beginning was their large frontal area, which meant they could be air cooled. An inline air cooled engine can run pretty hot on the rear cylinder. The bigger the engine, the more of an issue cooling becomes. There are some huge air cooled radials, in sizes that would be unthinkable for an air cooled inline engine.

As technology advanced, more complex water cooled engines became more popular. However air cooling was still a big advantage in military planes, due to the absence of a delicate cooling system that could be damaged, enabling radials to persist in this arena. Of course these days no-one would dream of putting a piston engine in a fighter.

Nowadays liquid cooling is almost universal for piston engines in general applications, with small aircraft being one of the few areas where air cooling has managed to hold out to some extent (see below.) In the absence of a military application that prefers air cooling, the large frontal area has become the radial engine's downfall, due to the large aerodynamic drag it produces. The other problem is that the valve gear is quite complicated, which means overhead camshafts and multiple inlet/exhaust valves per cylinder are impractical. This makes efficiency vs power to weight ratio a big issue as follows:

For an engine to have good power to weight ratio it must run at high RPM. To run at high RPM it must breathe effectively. To do this with just two valves they have to open wide. To stop them colliding with the piston, the compression ratio must be low, which limits efficiency. Hence most modern engines have more than two valves per cylinder to get around this problem.

Further reading

Pratt & Whitney R-2800: 46L displacement, over 2000hp from an air cooled engine, by no means the biggest!

Excellent animation of the valve gear, which also tends to illustrate the difficulty of putting more than 2 valves on a cylinder. Also, lots of history (obviously.)

In World War II both Double Wasps (46L air cooled radial) and Merlins (27L water cooled V, licensed from Rolls Royce in Britain and built locally by Packard) were used by the American military. I once read a very good authentic World War II discussion about the tactics of when to use air cooled radial fighters and when to use water cooled ones. Unfortunately I can't find it. Here's one of the many discussions on the subject. Note that the Merlin had overhead camshafts and 4 valves per cylinder, like modern engines, whereas the Double Wasp obviously did not.

Modern air cooled engines

I am more of an engine guy than a plane guy, but I've just been looking at modern air cooled aviation engines. They are only available in much smaller sizes than typical WWII fighter engines. Typically they have 4-6 cylinders, too few for a radial, but enough to cause cooling problems on the rear cylinder in an inline.

The compromise is a flat (boxer) engine with 2 or 3 cylinders on each side. This also overcomes two other problems with radials: upper cylinders obstructing pilot view and oil collecting in the lower cylinder when stopped. You also have at least one of these problems with an inline, depending if you mount it upright or inverted.

Small aero engines can be either water cooled or air cooled. The designer has to ask: given the issue of reliability in aviation, does the weekend pilot really want an engine as complicated as the one in his car, with water cooling, cambelts and engine management, all of which could go wrong?

The air cooled engines I've seen (Lycoming) do only have two valves per cylinder, all driven from a common camshaft. (A simpler choice than the cam ring on a radial) I haven't seen an air cooled flat engine with overhead cams and multiple valves per cylinder, but it would be easier achieve than doing the same thing on a radial.


Does a left spin differ from a right spin for a single-engine propeller aircraft, in terms of spin characteristics & ease of recovery? Given a single-engine propeller aircraft with its nose-mounted propeller rotating on the right-hand side when viewed from the cockpit, and given the typical effects like P-factor, prop-wash and gyroscopic forces associated with the propeller -

Would there be any differences between left-hand and right-hand spin modes? (Differences both from the physics perspective as well as perceptional difference from the pilot's point of view. For example, the differences could be there from a theoretical perspective but minor enough that the pilots can ignore them in real life).
If the answer is yes for Q1, which side, in this particular case, would have a more severe spin in terms of spin rate, loss of altitude and so on?
If the answer is yes for Q1, which side, in this particular case, would have a harder recovery compared to the other side?

To reduce variables, let's assume there are no asymmetries in the aerodynamic configuration which may make the aircraft favor one direction over the other for  spin and we are only considering the effect of propeller-rotation-direction-related effects on the spin.

Chipmunk, left-handed engine: Spinning to the left, recovery takes 3/4 turn, spinning to the right, recovery takes 1/4 turn. In either case, descent rate is 6000ft/min, so not affected by the airflow direction.


When is Minimum Safe Altitude Warning triggered? I know that Minimum safe altitude warning (MSAW) alerts ATC and pilots if an airplane is under the risk of controlled flight into terrain.

But when is this alarm triggered? What is the minimum altitude for it to trigger? If a plane is landing, should it be triggered just before landing?

It will confuse ATC if every plane that is landing triggers that alarm.

There must be some limitations. So, what are they?

The system projects the altitude that an aircraft will be at based on recent track and a calibrated "look ahead time" and an expected controller response time.  That value is then compared to a calibrated altitude floor.  If the aircraft is projected to be below the floor, then the controller will be alerted.

The specific values for all those things are calculated to minimize false alarms, accommodate the type of operation and local operational needs.  The values are specific to that facility and that area and so a straight answer isn't exactly possible.

Here are a few interesting resources in case they help.
Minimum Safe Altitude Warning
EUROCONTROL MSAW Guide


What is the function of the scissors link in helicopter flight controls? What is the function of the scissors link on the rotor of a helicopter?
I assume it has something to do with the flight controls, but I'm not quite sure what.

the scissor link ensures the upper swashplate rotates with the rotor blades (and the lower with the body) while ensuring enough movement for the plate to control the craft (tilting and up and down).

(http://en.wikipedia.org/wiki/File:Robinson-Rotorhead.jpg)

  To keep the stationary swashplate from rotating with the rotor, a scissor mechanism is added. The scissor connects the swashplate to the fuselage. The scissor consists of 2 parts which are connected by a hinge. One end is connected to the helicopter using a hinge, while the other is connected using a ball joint. This means that the swashplate can move freely up and down, and can freely tilt in any direction, but can't rotate around the mast.[source]

this is needed because the control linkage is typically attached with balljoints which would otherwise allow for too much relative movement.


What is the work routine of a boomer operator in a refueling aircraft? This is a boomer operator:

(source by John E. Lasky - United States Air Force)

If he is not refueling an aircraft, or the plane is not on a refueling mission, what is he doing? Is he sitting in that small cabin all the time, or is he free to move on the aircraft? Can his role be taken by anybody from the crew, or is he the only person on board who can handle the refueling boom?

The boom operator (or boomer) can freely move around the aircraft. The boom operator position is usually accessible from the cargo hold and the operator can use the opening to move from his/her position. This is especially important for the KC-135 Stratotanker, which has the boom operator working in a prone position.

Image from sobchak.files.wordpress.com

While the operator is not fueling other aircraft, he/she has other responsibilities to carry out. According to the US military job description of a boom operator, the boomer,

  Prepares and verifies load plans, directs cargo loading, and unloading operations, and inspects aircraft load to ensure hazardous cargo compliance and weight and balance status of aircraft. Ensures adequate safety equipment and passenger comfort items are on aboard aircraft. Instructs passengers in use of emergency equipment and emergency procedures.

among other things.

The boom operator is a specialist and his/her job cannot be done by anyone else on board. The operator also has to be qualified for the type of aircraft he/she is refueling. From interview of a USAF boom operator in foxtrotalpha:

  Every receiver is a little different, so we have specific qualifications for heavy aircraft and fighter aircraft, called gulf and Charlie.


What are these things on the A350's instrument panel? https://imgur.com/a/BF2Ghpv
.
.
On the FCU Panel, there are some buttons or switches that are not on a320s and some older Airbuses except the A380. what's that and what the function?

These are the EFIS CP (EFIS Control Panels) for the captain's and First Officer ND's (respectively). For example, clicking on the ARPT button will display airports on the relevant ND (Navigation Display, the right part of the left screen, or the left part of the right screen in the image you provided).

It's pretty clear in this close-up photo.

You can see the mentioned controls in the top left corner and the ND display in the PLAN mode (which shows the entire flight plan).

The barometric pressure setting can also be changed using the EFIS CP.

Opposing your comment regarding the A320, The EFIS CP in the A32X (A318-A321)  is also in a very similar location.


Is anyone able to identify this vintage aircraft please? I have this plane on an art glass print in my home.  A lot of people ask what the plane is and I have been unable to identify it.  Any ideas?

It appears to be a Spartan 7W Executive.


Why are the largest civilian aircraft not adapted for military use? Frequently, civilian aircraft models are militarized, e.g. into the role of tankers, AWACS and others.
In this militarization, we see a lot of "medium-large" aircraft, such as B707, A330.
The super-large models, B747 and A380, however, do not see militarization. The current 747-based Air Force One, comes to mind, but that's more or less a one-off.

What are the reasons for not seeing more B747s and A380s being put into a military role?

A huge B747 or A380 would make a quite extensive flying gas-station.

There are several angles to this question, so I'll try to address what I think is important. My so-far short career has so far involved working almost exclusively with 747 derivatives, so I don't have as much to say about the A380, but I'll touch on it as I can.
In summary, the decision to modify a commercial aircraft for military use comes down to cost, schedule, performance, and politics. The platform needs to be the right one for the mission, be available in time to execute the mission, be worth the money for its capabilities, and be politically appealing. These four factors are best addressed on a case-by-case basis. The 747 has a much longer and more storied history than the A380, and I am not aware of any thoughts to militarize the latter; however, the 747 has been adapted for military use in several circumstances and there have been even more preliminary studies about doing so that never made it to production. So here is a brief summary of those programs. Hopefully looking at each will satisfy your curiosity and give a picture that answers the question.
Civil Reserve Air Fleet
Adapting an aircraft for military use does not necessarily involve modifying it in any way. The United States has the Civil Reserve Air Fleet (CRAF), a program through which domestic airlines pledge the availability of some of their aircraft to the Department of Defense "to augment the Air Mobility Command's long-range intertheater C-5s and C-17s during periods of increased airlift needs." Currently, none of these aircraft is permanently modified. Perhaps the interior of a passenger model gets reconfigured for a CRAF flight, but they are the same airplanes that members of the public fly on regularly. Back when Delta and United flew 747s, nearly all of them were available to the CRAF; now it is only 747 freighters that are available. The cost-schedule-performance analysis of this setup is favorable. The DOD only pays for the airplanes when it needs them, and is legally allowed to use them any time it needs them. Airlines get compensated at above-market rates when their aircraft are used. And unless you need to land on an austere runway, fly through contested airspace, perform an airdrop, or load/unload extremely quickly on the ground, a 747 can do almost anything that a C-5 or C-17 can, and usually more efficiently.
However, in the late 1980s and early 1990s, about two dozen early-model 747s were structurally modified specifically to support the CRAF, including N739PA:

The fuselage structure of N739PA differed from the majority of Boeing 747 aircraft in that it had been modified to carry special purpose freight containers on the main deck, in place of seats...The effect of this modification on the structure of the fuselage was mainly to replace the existing main deck floor beams with beams of more substantial cross-section than those generally found in passenger carrying Boeing 747 aircraft. A large side loading door, generally known as the CRAF door, was also incorporated on the left side of the main deck aft of the wing.

The CRAF door can be clearly seen in this photo:

Again, the analysis is favorable. The modifications were relatively simple structural ones and the DOD paid an ongoing subsidy to operators of these aircraft to offset the cost of the extra weight, which was much less expensive than maintaining a fleet of military-only aircraft of comparable capability.
I do not know what capabilities there are for NATO or other European countries to press civilian aircraft into service, but they do not seem extensive. This is where I think you'd most likely see an A380 used in a defense role.
Airborne Aircraft Carrier
Here's a fun one that didn't make it very far. The idea was to use a 747 as a flying platform for the launch, recovery, and refueling of small fighter aircraft:

Boeing's report sung the praises of this idea, of course, but my feeling is that it was something of a solution in need of a problem. The USAF had experimented with the idea before and found it to be technically feasible but operationally difficult, which was likely again the case here. Although the proposed schedule was favorable, the performance would not have matched a mission, and the cost of putting the system together and deploying it would likely have been huge.
Advanced Tanker Cargo Aircraft
The 747 was indeed converted for use as a refueling tanker, albeit in small numbers. The KC-10 won over a 747 variant mainly due to lower costs and better overall performance. The KC-10 could operate out of smaller airfields and had an all-new boom, as opposed to the 747 contender's barely-modified KC-135 boom with poorer handling qualities and less clearance away from the aircraft. There were a few other technical aspects favorable to the KC-10 as well, not to mention the inherent ongoing cost savings of flying a trijet over a quad.  Additionally, McDonnell Douglas at the time was in need of a lifeline for the DC-10 program and thus applied more political pressure. It should also be noted that the 747-based tanker design was better suited operationally for refueling long-range bombers and transports than fighters. As the other answers and some comments point out, an enormous tanker has some inherent deficiencies when directly supporting combat operations. My opinion is that Boeing focused too much on the long-range mission when trying to sell their solution, but this might be the best example of the 747's size as a direct and insurmountable detriment, whereas in most of its other military roles its size is its greatest benefit.
Despite the US not adopting the 747 solution, Iran purchased a couple of them, and at least  one still flies:

For Iran, the cost-schedule-performance triangle was beneficial. My guess is that Boeing offered a discount to Iran to get some tankers operationally deployed to help boost their case with the USAF, they were available almost immediately, and Iran's military operations were more concentrated and less reliant on situations that would put such enormous links in peril.
And just because it's interesting, it was the very first 747, RA001, that was modified to test this refueling concept, as seen here:

RA001 still boasts most of that equipment (the boom is long gone, though), but it should be noted that there were no modifications to the fuel system to allow it to pass fuel—the hardware was for testing tanker-receiver contacts and boom dynamics only. You can see RA001 up close for yourself at The Museum of Flight. And if you do stop by, say hi—I'm one of the volunteers on the restoration crew for this airplane.
Cruise Missile Carrier Aircraft
Another interesting one that never made it past the drawing board, although it got farther along than it usually gets credit for. The idea was patented by Boeing during the B-1 program as a way to supplement that aircraft and ease the B-52 into retirement.

It was eventually canceled in favor of the B-2 and upgrades to the B-52. History has questioned that decision, but at the time costs were deemed too high given commitments to the aforementioned platforms, and the considerable performance was still not found to fit well into the contemporary operational concept.
E-4
The E-4 was the first 747 derivative to enter military service. There is not much to say about it technically that Wikipedia doesn't, but it is worthwhile to note that, in the view of the Air Force, having four engines is a must on this type of platform. In the early 1970s, there wasn't much by way of twins, so that was taken care of at the time of aquisition. Redundancy and survivability are primary design drivers, so although its systems could probably have been transferred to a smaller, cheaper airframe, there is no way to match the mission assurance of four engines. Along with that, it would be tough to find a way to generate enough electricity on the airplane to power all its systems without four engines. Additionally, the first two airframes were offered to the government at a discount due to their being built for a canceled order.
Non-Developmental Airlift Aircraft
More a case study than anything, this might actually be the best example for how cost, schedule, and performance are balanced. I highly encourage you to read this retrospective:

...[the NDAA] was originally developed in the early nineties due to poor cost and schedule performance during phase two...of the C-17 acquisition. Forty C-17s were being built for phase two; and due to problems, alternatives were sought with respect to the remaining 80 aircraft. Attempting to leverage commercial industry, the NDAA promised a low-cost alternative to the DOD acquisition process. However, since this was an alternative for the C-17, DOD stipulated that the NDAA would have to be a jumbo cargo aircraft capable of carrying outsize cargo. The NDAA study focused on a minimally modified Boeing 747 cargo aircraft. These “minimal” modifications included hardened decks and a flipup nose and ramp system for ease of straight-in loading versus the sidemounted-cargo-door style loading of the commercial industry. Consequently, the price for the NDAA alternative increased from under \$150 to about \$200 million per aircraft. Nevertheless, after examining several options, the most cost-effective solution was an 86/30 mix of C-17 and NDAA aircraft. This mix, however, did not allow for a full strategic brigade airdrop nor was it optimized for tactical airlift requirements and lesser regional contingencies in support of peace enforcement scenarios. These requirements were better met by the military-specific C-17. Ultimately, the Defense Acquisition Board decided to procure the fleet of 120 C-17s and no NDAA.

Airborne Laser
The YAL-1 ultimately suffered from cost, schedule, and performance problems. The idea was to fly around a huge laser that could heat up and destroy ballistic missiles from afar. The 747 platform was chosen because it was the only airframe large enough to contain the huge tanks of chemicals needed to generate a laser strong enough to have any effect. But after almost two decades and more than five billion dollars, it still needed a laser many times more powerful to be operationally viable, so it was canceled. One prototype flew for over 10 years, but was unfortunately scrapped.

VC-25A
The VC-25A is generally what people think of as Air Force One, although technically that designation applies to any USAF aircraft with the president onboard. Again, the number of engines was a major design driver, and in this case the size and iconography of the 747 helped it tremendously. The DC-10 was competed as an alternative, although it never was a serious contender and was reportedly only included to get Boeing to lower its price. As with the E-4, survivability, redundancy, and power requirements support a four-engine airplane; the floor space of a 747 also supports a lot of functions that couldn't otherwise coexist. Even by the time the VC-25A was introduced, the 747 had an enduring and recognizable preeminence in the history of aviation and Unites States prestige that the government found attractive to its branding as the president travels the world. Commonality with the E-4 airframe was also a consideration. In this case, politics and performance played an outsized role in selection of the aiframe, with cost and schedule secondary. Obviously there was much willingness to spend the big money and wait some extra time to fulfill all the requirements.
VC-25B
Once again, we have power and redundancy requirements driving the selection of the airframe for the next presidential aircraft. There was some early talk about perhaps pursuing an A380 option, but politics quickly put that idea to bed in favor of the 747-8. The VC-25B will have modifications similar to those of the VC-25A, and will probably look similar:

The program has been much in the news due to cost, schedule, performance, and politics, but is overall proceeding with similar priorities as the VC-25A program did.
Conclusions
I count about 30 747 airframes that have been modified and flown for military purposes. Obviously that's not a huge number, but it is actually fairly respectable for an aircraft of its era, although 707 variants are clearly more ubiquitous (it's important to note, however, that the C-135 family is not a derivative of the 707). Nowadays, with the KC-46 and P-8 leading the way, commercial derivatives are becoming more attractive to the armed forces. But with production of the 747 winding down, we are unlikely to see any more variants beyond the VC-25B: parts will become more difficult to obtain and the labor force skilled with the airframe will dry up. The 747's size and capabilities have both helped and hindered it along the way, and it warrants a case-by-case look at each program to see how cost, schedule, performance, and politics have played a role. The A380 is a somewhat different case, being more recent and less revolutionary in its era than the 747. It has not found a military mission that cannot be accomplished with smaller, cheaper airplanes, and it has no history of modification to help it win over the decision-makers. I am doubtful that we'll ever see it take on a military role.  A lot more could be said about any of my examples and the overall picture, but I hope I've dispelled the idea that the 747 is not used militarily, and I hope I've provided some insight as to why it is not used more.


What distinct challenges are faced in taxi operations that aren't found in other phases of flight? The Federal Aviation Administration (FAA) made Runway Incursion Avoidance a special emphasis area and added it as a required task in several of the Practical Test Standards (PTS) documents. All the PTS documents have a bullet item that reads something like this:

  Distinct challenges and requirements during taxi operations not found in other phases of flight operations.

I have reviewed the applicable sections of the Pilot's Handbook of Aeronautical Knowledge and AC 91-73B, but I haven't found a concrete answer on what exactly these challenges are. If an examiner asked me to explain these challenges I'd do my best, and I'm sure I could come up with some good arguments for my thoughts, but I like to know what the FAA is looking for when they ask a question and this one doesn't seem to have an exact reference.

Well in air you don't have to worry about kangaroos in your path or a wheel falling off unnoticed, or people beside a taxiway mistakenly indicating you won't hit a golf cart.  Heaven forbid you accidentally retract the landing gear.

Jokes aisde, taxiing can be a major challenge even for experienced pilots. First off, your traditional warning systems don't work.  You can't check your route using a low or mid-range GPS because they don't have airport taxiway information.  You won't get a "terrain!" warning when you're about to head off the end of a taxiway.

Steering is difficult because the control surfaces are used differently on the ground, especially in a crosswind.  You don't use your ailerons or elevator to control your path; you use them to keep the wings from lifting and to keep you on the ground.  You use the rudder and steerable nose wheel/tail-wheel (if present) to keep you on the right path, with help from the brakes only when necessary.   Those brakes definitely will be necessary in a tail-wheel aircraft with a strong enough crosswind.  If you fail to control the ground path in a tail-wheel aircraft, an unstable and difficult ground loop can develop.

Did wbeard52 mention low visibility? You can technically land a plane in zero visibility if your plane and the airport are properly equipped, but good luck naviagting the taxiways afterwards. A pilot once remarked that "Taxiing at ORD the first time in low visibility conditions is impossible," and another remarked that he was so confused by low visibility he had to have a follow-me truck guide him. [source]

Taxiing can also be confusing in good weather, especially at night.  Sometimes the taxiway letters jump randomly around the alphabet, sometimes markings are obstructed, sometimes there's construction (you don't see construction much in the air!).   The FAA has an entire handbook appendix devoted to avoiding runway incursions that explains these navigational issues.

You also have to be vigilant for obstacles around you (like those kangaroos I mentioned earlier).  In a tail-wheel aircraft with a high nose, for example, it's recommended to zig-zag a little so you can see what's right in front of you.   In aircraft like the B777-300 they actually have camera systems to augment visibility.  (see this question and the FAA's Airplane Flying Handbook ).

You can also look up a list of recent taxiing incidents here


Since when did European regulations require the ability to suppress alerts? Thanks to @Gerry's comment on a recent answer of mine, the 2011 ruling on the FAA's amended 14 CFR § 25.1322 mentions:

Adopting this rule also harmonizes flightcrew alerting standards between the FAA and the European Aviation Safety Agency (EASA).

That's related to suppressing alerts, which Airbus aircraft have had since at least the mid-80s – the EMER CANC button for example on the A320 for suppressing spurious alerts.
This made me wonder since when EASA (or its predecessor) have had the similar rule that was adopted? (I couldn't find my way around the historic regs of EASA.)

Since June 2011.
EASA first proposed a change to CS 25.1322 in NPA 2009-12 (Notice of Proposed Amendment) in November 2009:

CS-25 contains a certification specification (CS 25.1322) that dictates the colour of
warning, caution, advisory, and other message lights that are installed as annunciation
displays in the flight deck. As presently written, CS 25.1322 addresses visual alerts only in
the form of coloured lights installed in the flight deck. No specifications are stipulated to
cover new technologies or the use of alternate media, such as aural tones/voice that can
be more effective. CS 25.1322 is therefore considered outdated and does not address the
safety concerns associated with today’s display systems.

EASA then included these changes to CS-25 (the Certification Specifications for Large Aeroplanes) in Amendment 11 on 27 June 2011. The version of CS 25.1322 before (last amendment of 16 December 2010) shows this text:

CS 25.1322 Warning, caution, and
advisory lights
If warning, caution, or advisory lights are installed in
the cockpit, they must, unless otherwise approved by
the Agency, be –
(a) Red, for warning lights (lights indicating a
hazard, which may require immediate corrective
action);
(b) Amber, for caution lights (lights indicating
the possible need for future corrective action);
(c) Green, for safe operation lights; and
(d) Any other colour, including white, for lights
not described in sub-paragraphs (a) to (c) of this
paragraph, provided the colour differs sufficiently
from the colours prescribed in sub-paragraphs (a) to
(c) of this paragraph to avoid possible confusion.

(EASA CS-25 Amendment 10)
Afterwards, the text is very similar to the one in 14 CFR:

CS 25.1322 Flight Crew Alerting
(a) Flight crew alerts must:

provide the flight crew with the
information needed to:
(i) identify non-normal operation or
aeroplane system conditions, and
(ii) determine the appropriate actions,
if any;
be readily and easily detectable and
intelligible by the flight crew under all
foreseeable operating conditions, including
conditions where multiple alerts are provided;
(3) be removed when the alerting
condition no longer exists.

(b) Alerts must conform to the following
prioritisation hierarchy based on the urgency of flight
crew awareness and response:

Warning: For conditions that require
immediate flight crew awareness and immediate
flight crew response.
Caution: For conditions that require
immediate flight crew awareness and subsequent
flight crew response.
Advisory: For conditions that require
flight crew awareness and may require subsequent
flight crew response.

(c) Warning and Caution alerts must:

be prioritised within each category,
when necessary;
provide timely attention-getting cues
through at least two different senses by a
combination of aural, visual, or tactile indications;
permit each occurrence of the
attention-getting cues required by sub-paragraph
(c)(2) to be acknowledged and suppressed, unless
they are required to be continuous.

(d) The alert function must be designed to
minimise the effects of false and nuisance alerts. In
particular, it must be designed to:

prevent the presentation of an alert
when it is inappropriate or unnecessary;
provide a means to suppress an
attention-getting component of an alert caused by
a failure of the alerting function that interferes
with the flight crew’s ability to safely operate the
aeroplane. This means must not be readily
available to the flight crew so that it could be
operated inadvertently or by habitual reflexive
action. When an alert is suppressed, there must be
a clear and unmistakable annunciation to the flight
crew that the alert has been suppressed.

(e) Visual alert indications must:

conform to the following colour
convention:
(i) Red for Warning alert
indications.
(ii) Amber or yellow for Caution
alert indications.
(iii) Any colour except red or green
for Advisory alert indications.
use visual coding techniques, together
with other alerting function elements on the flight
deck, to distinguish between Warning, Caution
and Advisory alert indications, if they are
presented on monochromatic displays that are
incapable of conforming to the colour convention
in paragraph (e)(1).

(f) Use of the colours red, amber and yellow on
the flight deck for functions other than flight crew
alerting must be limited and must not adversely
affect flight crew alerting.

(EASA CS-25 Amendment 11)


Case Study: Did I need to declare an emergency? I am a fairly newly minted private pilot licensee (PPL). I had just taken off from a small private, (but open to the public) airfield. We are under the shelf of Class B, but are G up to 700 and then E to the B above at 4000.

My instructor noticed our oil Pressure gauge was very close to the red line, and so of course we  headed back. I was about to make a call to inform CTAF we would be crossing midfield and joining the left down wind. Instructor takes control and makes a call asking if any others are in the pattern. Then declare that we will be entering a right down wind (we are a left hand field).

A voice pipes up: Are you declaring an emergency?. I reply no, this is an urgency. (By now the wisdom of my instructor's decision to not cross midfield was clear: It would take much less time to land; it kept us out over paddocks should the situation get worse; It would not take us over houses as the left down wind would.)

Said voice pipes up again: This is the airfield manager, you must declare an emergency if you are using a right hand pattern. My Instructor told me to ignore him and make another call to CTAF asking for any traffic to report position. There was no traffic. We landed without incident.

Who was correct? The manager or us- and does anyone have a FAR/REF to support the conclusion. The old adage Aviate, Navigate, Communicate seems to apply here - but what might the manager be basing his claim on and why?

Before we delve into this one.  Let's be clear that it is much easier for us to sit at a computer with books in hand and review decisions made under urgent circumstances.

Technically, the airport manager was correct here because per 14 CFR §91.126(b)(1):

  "Each pilot of an airplane must make all turns of that airplane to the
  left unless the airport displays approved light signals or visual
  markings indicating that turns should be made to the right..."

There do not appear to be any caveats to that rule.

To un-bind a flight from this rule, one would need to take advantage of §91.3(b)

  "In an in-flight emergency requiring immediate action, the pilot in
  command may deviate from any rule of this part to the extent required
  to meet that emergency."

In my personal experience, I have seen plenty of pilots fly around the pattern in whichever manner is convenient to them; entering on right or left bases for final, approaching for VFR straight-in landings from 15 miles out, etc.  So far, I haven't seen any repercussions for these actions, which is probably why your instructor did not agree with the airport manager.

Another thing that shouldn't go without being said is that this situation was none of the airport manager's darn business.

By verbally acknowledging that there was not an emergency, your instructor placed a liability on himself.  §91.3(b) allows the pilot to deviate from a part 91 rule, but to my knowledge, there is no statute that actually requires recognition of an emergency to be verbally declared or announced under non-ATC-controlled VFR flight.

By leaving the question, "is there an emergency?", unanswered, there is a chance to retrospectively say, "yes, we had an emergency and that's why we deviated from the rule."  However, since he told the airport manager that it was only an urgency he kind of shot himself in the foot if someone were to decide to raise the right turn as a legal issue, but I would be very surprised if anyone does.

To summarize and give you a more direct answer.

You had a valid emergency
You had no responsibility to verbally declare it
You did deviate from a legal regulation to meet the needs of that emergency

Sounds to me like you've got a very competent instructor.

Edit: I came across this Letter of Interpretation, which is sort of related to your situation.


Why do suborbital planes feature H-tail and/or large wingtips? Spaceplanes that are suborbital are mostly supersonic and feature H-tail or rather large wingtips. This looks to be similar to a H-tail configuration but I'm unsure abut how it works, which is why I say large wing tips. They focus on a delta wing and elevon for the pitch and roll and yaw seems to be controlled using this.
For example look at the following spaceplanes.

References:
1. https://www.virgingalactic.com/articles/VSS-Unity-First-Powered-Flight/
2. https://www.sncorp.com/what-we-do/dream-chaser-space-vehicle/
3. https://www.flyfighterjet.com/xcor-lynx-space-flight

Dreamchaser isn't intended to be suborbital. Don't know about your 3rd picture, but the Spaceship 1 & 2 were designed by the same person/company, so it's not surprising they use the same design elements.

The designs of Dreamchaser vs Spaceship N address two different problems.  An orbital vehicle has to decelerate from ~17,000 mph, while a suborbital vehicle on a ballistic trajectory (simplistically straight up and straight down) starts from zero speed at its high point, and needs to keep from gaining too much speed.  So if I'm not mistaken, a main function of the H-tail is to allow the entire vehicle to act as a drag device.  That wouldn't be practical for an orbital reentry vehicle due to heating & aerodynamic forces.


Could the autopilot have rectified the flight path without any crew input on the Aeroflot Flight 593? In the case of the Aeroflot Flight 593 air crash, could the autopilot have rectified the flight path of the Airbus at any point if the crew had not attempted to correct the spin, even while partially disengaged as it was after the son applied to much force to the control column?

  Despite the struggles of both pilots to save the aircraft, it was later concluded that if they had just let go of the control column, the autopilot would have automatically taken action to prevent stalling, thus avoiding the accident.

The PIC had given his seat and controls to his son (a visitor in the cockpit without any flight qualifications). The autopilot was in perfect control of the A310 until the son of the PIC had disengaged the automatic aileron control by applying sufficient control force. Up to a certain banking angle, fully engaging the AP would have resolved the problem. Without control over the ailerons, the AP could not recover the plane's attitude. The banking angle was out of the operating range, and the plane was not able to maintain its altitude.

Unfortunately, both pilots had trouble to become aware of the situation, and they also had a lack of understanding of the A310 controls. After fully disengaging the AP, the AP could not help with the lateral control any more.

This is very simplified, of course. A lot of elements contributed to this "accident". I recommend to read the Investigation report.


Is the NTSB hostile to pilots, as depicted in the movie 'Sully'? This is based upon events portrayed in the movie Sully.  If the film is taken at face value, what we basically see is a (fairly brazen) stitch-up attempt by the NTSB (National Transportation Safety Board), where they try to steer an investigation towards a predetermined conclusion of 'pilot error' (and very nearly succeed) using:

Naively unrealistic computer simulations that assume a pilot would divert towards the nearest landing strip immediately after a birdstrike without needing any time to evaluate the damage to their aircraft, attempt to diagnose and troubleshoot the problem, or coordinate with air-traffic-control.
Similarly unrealistic simulations using real pilots who have been trained/conditioned to divert immediately after the simulated birdstrike.
The deliberate omission of the fact that the pilots only succeeded in their simulation attempts after multiple failed training attempts, up until the pilot involved in the actual incident calls BS on the whole charade.

The only motivation posited in the film for the NTSB's attitude was that the insurance company would have preferred a conclusion of 'pilot error'.  Thus, my questions are:

Is the film's portrayal of the NTSB accurate, either in terms of having a general anti-pilot bias or in terms of the particular investigation depicted having had an anti-pilot bias?
Why would the NTSB care about acting in the interest of insurance companies (particularly to the extent that they'd be willing to throw pilots under the bus to do so)?
Does an insurance company avoid a payout in the case where an aircraft is lost due to pilot error (as opposed to mechanical failure, birdstrike, or other unavoidable scenario)?

I think it is quite unfair to paint the NTSB investigators as villains just for the dramatic effect when nothing of the sort happened in real life.

It is the job of the NTSB to investigate all possible reasons for the accident. It includes pilot error among other things. They were doing precisely that in the actual investigation. Among other things, the NTSB concluded that:

The captain’s decision to ditch on the Hudson River rather than attempting to land at an airport provided the highest probability that the accident would be survivable.

The simulations carried out by the NTSB were part of the investigation and were much more elaborate:

The pilots were fully briefed on the maneuver before they attempted to perform it in the simulator. The following three flight scenarios were flown:
(1) normal landings on runway 4 at LGA, starting from an altitude of 1,000 or 1,500 feet on approach;
(2) attempted landings at LGA or TEB after the bird strike, starting both from zero groundspeed on takeoff from runway 4 at LGA and from a preprogrammed point shortly before the bird strike and loss of engine thrust; and
(3) ditching on the Hudson River starting from 1,500 feet above the river at an airspeed of 200 kts.

Note that the NTSB clearly mentions that the pilots were briefed before the simulation. NTSB noted clearly in its report that immediate turning of the aircraft after the bird ingestion did not reflect what could've been done in real world:

The immediate turn made by the pilots during the simulations did not reflect or account for real-world considerations, such as the time delay required to recognize the bird strike and decide on a course of action.

The simulations (along with the case where there was a 35 second delay to account for pilot response) was done entirely by the NTSB with no input whatsoever from the flight crew. As The Guardian notes:

And then the investigators – not Sullenberger – asked a pilot to wait 35 seconds before attempting an airport return. That flight didn’t make it. Consequently, the NTSB was unequivocal in its declaration that the Hudson was the right call.

Actually, the movie was so inaccurate in the portrayal of the NTSB that the real people involved asked the names of the investigators in the movie to be changed:

... a draft script included the names of real-life NTSB officials, but Sullenberger - who is an adviser on the film - requested they be taken out.
He said, ‘These are people who are not prosecutors. They are doing a very important job, and if, for editorial purposes, we want to make it more of a prosecutorial process, it ain’t fair to them,”’ said Hanks.

There is no evidence to determine that the NTSB acted in the interest of insurance companies (or anyone else) in this investigation. The situations in which an insurance company is liable depends on the particular policy (as far as I know, liability is usually for negligence).
While the investigation may not be perfect, there was no kangaroo court anytime during the investigation. There was no attempt at public lynching, as The Guardian notes:

In fact, in his memoir, Sullenberger reflects that he was “buoyed by the fact that investigators determined that Jeff and I made appropriate choices at every step”

There was no cover-up by the NTSB and there was no Kangaroo court (you can easily look up the public hearings in this case) to pin everything on the flight crew on behalf of somebody else. Though not perfect, there is nothing to suggest that the investigation was not conducted professionally.
It is sad that the movie portrayed officials performing their duty as villains just because it was decided that the people would rather have the ancient good Vs evil show in the movie rather than the truth (while I'd have to agree that the movie would've looked more like documentary otherwise, that is no excuse).
The problem though, is that more people will be seeing the movie than reading the report or looking up the actual investigation that people will have a entirely uncalled for negative opinion of the NTSB, which may affect the future investigations. As Robert Benson who carried out investigation on the Flight 1549 noted in an article:

"I do not know why the writer and director chose to twist the role of the NTSB into such an inaccurate depiction. .... The movie may actually be detrimental to aviation safety. Pilots involved in accidents will now expect harsh, unfair treatment by investigators. They and others who see the movie will now believe that the NTSB enters into any investigation with preconceived notions, and that we are intent on destroying reputations. Simply untrue. The NTSB is the best friend an airline passenger never gets to meet."


What are the requirements to convert a license from Iran to USA? What is required for someone who has CPL, IR and CFI licenses from Iran to fly in USA? What is the requirement to convert license?

You cannot convert the CPL to FAA-CPL. What is possible is to obtain a FAA-PPL certificate by verification of the your current foreign license. This certificate will be valid as long as your foreign license is (plus medical conditions, and 24-months PPL flight review required for any PPL in the US).

With the PPL certificate, you will be able to obtain IR and CPL:

Pass IR and CPL written tests.
Attend training for IR and CPL practical checks.
Accumulate at least 250 flight hours. Time in the foreign country with the foreign license will count as well, but at least 3 hours are required with the FAA instructor. The instructor will vouch for the candidate is ready for the check-ride.
Pass CPL and IR practical checks.

A valid residence permit will be necessary to use the FAA-CPL.

The CFI roadmap is similar, written tests and checkrides are mandatory, there no minimum hours to be flown in the US. As a large part of the knowledge required is similar to many ICAO-member countries (teaching, meteorology, navigation, aerodynamics, etc) this shouldn't be a problem to be certified FAA CFI.

Related:

Do I need a PPL license for a CPL license?
I have a European EASA license - what do I need to do to be allowed to fly in the US?
Can a pilot with an ICAO Multi-Crew Pilot License fly an airliner into the U.S.?

References:

Required knowledge FAR 61.123 et seqq.
Required flight experience FAR 61.129.
Pilot certification in the US on Wikipedia.
Process for foreign CPL to FAA-PPL conversion (FAR 61.75).
Flight Instructors FAR 62.181


What are some common aileron failures? There are a few parts to the control system for an aileron in a light aircraft, such as the rods, bellcrank, cables, chains etc. What are the main reasons for aileron failures and what parts wear the most during their time?

When talking about that sort of thing, you're really looking for single-point-of-failure weak links that are difficult to detect during a walkaround or inspection.  Hinges don't normally just let go with no warning.  They get loose and sloppy first.  Same with bellcrank bearings, rod ends, and pulley bearings.  Things in general on airplanes can get really loose and sloppy and still work because there are large fudge factor margins built into the design (like, a crack on a piano hinge might have to progress to 80% across it before normal loads would make it break).

If you're talking about "aileron failure" as in "spontaneous complete loss of aileron control", this is an extremely rare event.  If you had to pick something, you'd generally look for items that can just degrade with no obvious signs and then suddenly let go.  On the typical single-loop cable run control system you'll find in a Cessna or similar, that weak link is the control cable itself, at swages and where the cable bends to go around pulleys, or from corrosion.  The check for cable degradation, besides visual inspection, is to wrap a rag around the cable and pull it along feeling for wire snags (or you can use your bare hands if you enjoy the potential for surprise searing pain).

For cable corrosion, it can seem attractive to go with stainless cable, but stainless cable is weaker and SS doesn't like to rub against itself and the cable tends to fret and break down at pulley bends (why aircraft SS cable has a lubricant in it - the identical-looking SS cable you get at the hardware store doesn't).  In the transport world and in GA I think, you will find mostly galvanized carbon steel cable, which is stronger and doesn't break down as readily (the zinc is a very effective inter-strand lubricant, as well as corrosion preventative).

In terms of overall wear and tear, generally it's parts with moving bearing surfaces that see concentrated loads.  The aileron hinge closest to the control rod will always get loose and sloppy first.  The bearings in the bellcrank in front of the aileron where the bearings are under a constant radial pre-load from cable tension, on top of flight loads.  Pulley bearings at 90 degree bends where radial loads are high.  Pulleys and bearings oriented horizontally go bad sooner than vertical ones because the oil component of the grease in the bearing leaks out over time and the bearing rots out.

In the end though, most of the degradation isn't wear and tear, it's degradation from lack of use.  Like cars, airplanes do not do well sitting stationary for long periods, especially outside.


Why don't modern aircraft have landing gear that can swivel to compensate for crosswinds? When landing, crosswinds can be very expensive. They cause go-arounds, diversions to other airfields and even crashes.

Currently pilots crab in the air to counteract crosswinds and, at the last moment, throw the aircraft around to face directly along the runway. This is a challenging and risky manoeuvre - it can cause asymmetrical stalls and worse.

The nose wheel can already be rotated. If the main gear could also rotate, the plane could land in a crabbed attitude and continue that way along the runway until speed had dropped to taxiing speed.

How come aircraft don't have this feature?

EDIT

It has been flagged that this question is similar to a previous one, Is the main landing gear of a large airplane designed for sideways (crabbed) touchdowns?

My question is different. In those cases the landing gear does not actively turn to face in the direction of travel relative to the ground, it is merely designed to cope with the extra stress of hitting the runway obliquely. The allowed angle may be quite small. A swivelling undercarriage would allow for a large angle of crab with no attendant stress to the gear because the wheels would be aligned with the runway.

As pointed out on that other question, this design feature was adopted for the B-52. I am asking what factors persuaded designers to abandon this idea.

Videos (2) of B-52 landing in this manner
http://www.skilledpilots.com/video-this-is-how-a-b-52h-lands-in-a-crosswind-and-stays-completely-sideways-while-deploying-a-parachute-and-slowing-down-on-the-runway/

There is one aircraft I know of that can do exactly what you state, the B-52:

This plane has steerable dual-bicycle gear which allows the crew to point the gear along the runway while the fuselage is "crabbed" up to 20* off the runway centerline. AFAIK the gear are slaved to the ILS; you dial in the OBI to a course and the gear will point that way even if the aircraft points differently.

The reason this was done is primarily due to the design of the rest of the aircraft. It's a very "dense" design, cramming a lot of weight into a very small package, requiring massive wings and tail just to keep the thing under control at altitude. These surfaces then become huge sails at lower altitudes, and with the high, anhedraled wing arrangement on a relatively low fueselage, there's not much room for error. B-52 pilots often say you have to fly 2 seconds ahead of the plane, it's that slow to react to pilot input. So, classic "de-crabbing" techniques involving a hard rudder with counter-aileron just aren't going to work with a BUFF. You have to land crabbed and correct after touchdown, and on a dry runway that isn't a good idea either with an aircraft of this size.

Modern airliners, for their size, are much easier to maneuver on the whole than the BUFF. Really big ones, like the 747, actually have steerable main gear as well, but AFAIK the 747's mains can only be actively steered on the ground, and because they counter-steer to the nose gear (helps bring the tail around corners; imagine driving something about 4 times longer than an 18-wheeler) they would actually be pointed further off the runway line when de-crabbing.

Four- and six-wheel main gear systems used on larger airliners (777, 787, A380) actually have a small amount of castering built in; if you watch YouTubes of crosswind landings (there are several) you'll see that the rear two wheels of each gear touch first and actually twist the entire "truck" into line with the aircraft's actual direction of travel. Then as the plane settles on the gear and the fuselage lines back up with the runway, they'll straighten. Planes with one- and two-wheel main gear don't need this as much (and such a system isn't as effective as the first point of contact of a tire is directly level with the gear strut instead of behind it).


Can the Landing gear be lowered when system A hydraulic pressure is lost in Boeing 737? In the FCOM OF BOEING 737 HYDRAULIC SECTION I went through the part Landing gear transfer unit that it is used to raise the landing gear at a normal rate when system A EDP volume is lost.
My query is if only the hydraulic system A is lost with landing gear up position can it lowered using system B hydraulic or do we need to use manual gravity gear extension?

Normal gear extension is by the A system; alternate gear extension is by manually releasing the up-locks, allowing the gear to free-fall into place. There is no provision for any other alternate gear extension beyond that, such as via the B or Standby hydraulic systems, electrics, pneumatics, or otherwise.


How much time does it takes to buy a landing slot? According to Wikipedia, landing slots are sold for several million dollars at busy airports such as London Heathrow. Given this high value, such transactions may take weeks to conclude. Moreover, some slots can be free quickly and unexpectedly (e.g. when a company cease activity).

My question is: for the busiest European airports (Heathrow, Schiphol, Charles de Gaulle,...), how much time does it take to complete these steps (and the steps I cannot imagine):

The airline decides to open a new route
The airline identifies the slot they'll buy
The airline begins negotiations to buy the slot
The airline acquires the slot
The airline can operate this slot
The airline begins to use this slot

I know that in the Netherlands this procedure is open and not obscured behind a login portal.

In the Netherlands the commercial airports are operated by the Schiphol Group, the number of flight movements or slots per airport is determined in collaboration with the government. For Schiphol this is now 500,000 per year. The allocation of the slots is governed by a second body which is set up to be non discriminating in the allocation of slots. Most of the answers to your questions can be found there: https://slotcoordination.nl (English website)

Who allocates slots?

  Under the European Union rules – (EC) Regulation 95/93, as amended -,
  a Member State of the EU needs to appoint an airport coordinator for
  each coordinated airport. The same coordinator can be appointed for
  more than one airport. SACN has been appointed for coordinating AMS,
  EIN and RTM. Coordinators are independent bodies to maximise
  transparency.

How often are slots allocated?

  Slots are allocated for each season, and slot coordination recognises
  two different ones. There is a Winter season and a Summer season. The
  mark of the change of season coincides in the EU with the change of
  summer/winter time. The difference is recognised to make sure we use
  daylight optimally.

How are slots allocated?

  The allocation planning process starts around six months before the
  start of each season. Slots are allocated free of charge from a pool
  of available slots. Allocation takes place according to certain
  priority rules in a neutral, non-discriminatory and in a transparent
  manner. The leading principle of distribution is based on historical
  precedence, the so-called grandfather rights. When an airline operates
  a series of slots in a season for 80% or more, it can hold on to the
  same series in the next same season. When it operates less than 80% it
  loses its historic rights (the so called ‘use-it-or-loose-it’ rule).
  Slots can be re-allocated until the day of operation.

What happens when the requested slot is not available?

  An airline can keep its request on the list of ‘outstanding requests’
  to see if during the allocation process slots become available over
  time. Airlines can freely exchange slots. Prior to each season a
  worldwide Scheduling Conference takes place enabling face to face
  meetings between airlines, airports and coordinators to improve the
  allocation process.

Apart from being assigned a slot, an airline also needs to file a request with the airport to request for the required services to handle the aircraft. Schiphol has a very informative website with a lot of publicly available information:

For passenger handling (gates, check-in, etc.)

https://www.schiphol.nl/en/operations/page/passenger-process/

For aircraft handling (gate assignment procedure etc.)

https://www.schiphol.nl/en/operations/page/aircraft-process/

If you want to know more about the trade in landing slots then I would suggest opening a new question since there is a lot to tell about that subject as there is a lively trade going on there.


What is the location of AC for typical modern airplanes? Some sources state that AC must be located behind CG, so that AC is stable.
There is a source, which throughout the study of stability and control consider AC located ahead of CG and positive cambered tailplane, stating that such airplane will be stable.
I understand that there is not only one right decision and it's possible to design aircraft with AC located both behind CG and in front of.
The question is, what is typical arrangement of CG and AC for most modern large jet transport aircraft? (especially interested in b737 and a320)

AC of the whole aircraft must be located behind CG, so that AC was naturally statically stable [in pitch, or more accurately, by angle of attack]. This pretty much follows from the definition of AC, and there is no way around it.

However, this is not the whole story.

First, it is possible to design an airplane with 'positive cambered tailplane'. As such, there is no requirement that the tailplane produced negative lift (for a classic design); there is merely a requirement that the tailplane had a lower lift coefficient than the wing.

Second, a statically unstable airframe can still be made stable by using computer control. From the point of view of the pilot, F-16 or Su-27 are stable, even though their airframes are not. In some marginal cases, when the aircraft has a lot of pitch damping, even average pilot can cope with mild instability.

As for airliners, all of them have AC behind CG, but I don't have specific numbers.


Should people flying UAVs be called "Operators" or "Pilots"? I'm wondering if there is any formal/official definition* pertaining to the title given to people controlling Unmanned Aerial Vehicles? Are they "more" correctly titled Operators or Pilots?

*As set by ICAO, EASA or FAA for instance.

Examples:

The Guardian: "Life as a drone operator"
Air Force Times: "Enlisted drone pilots? Decision expected early next year"

I've had a look through EASA Directive 2009/48/EC where it states:

  Operator shall mean any legal or natural person, operating
  or proposing to operate one or more aircraft;

That does not provide a distinction between the entity organizing (e.g. airline) and the actual person doing the flying. A commercial pilot will not title himself an "aircraft operator" but will call themselves a pilot. This is less well defined with UAVs.

The oxford dictionary defines pilot as:

  A person who operates the flying controls of an aircraft

So, technically, the drone operator should be called a pilot.

FAA National Policy Order 8130.34C Airworthiness Certification of Unmanned Aircraft Systems and Optionally Piloted Aircraft Section 6 specifically calls the person operating the UAS (only if it has been issued with an airworthiness certificate ) Pilot.:

  UA Pilots and Observers.

  a. PIC Roles and Responsibilities.

  (1) The PIC must perform crew duties for only one UA at a time.

  (2) All UA flight operations must have a designated PIC. The PIC has responsibility over each flight conducted and is accountable for the UA flight operation.

  (3) The PIC is responsible for the safety of the UA as well as persons and property along the UA flight path. This includes, but is not limited to, collision avoidance and the safety of persons and property in the air and on the ground.

  (4) The PIC must avoid densely populated areas and congested airways in accordance with § 91.319.

The order requires the PIC to have a minimum of FAA PPL:

  b. UA PIC Certification and Ratings Requirements.

  (1) The PIC must hold and be in possession of, at a minimum, an FAA private pilot certificate, with either an airplane, rotorcraft, or powered-lift category; with single- or multiengine class ratings, appropriate to the type of UA being operated.

  (2) The PIC must have and be in possession of a valid second-class (or higher) airman medical certificate issued under 14 CFR part 67, Medical Standards and Certification.

UK CAA also talks about 'Pilot Qualifications required to operate Unmanned Aircraft'. ICAO also uses the term 'pilot' for people controlling an UAV.

Both USAF and RAF call the UAV operators pilots- RAF calls them Remotely Piloted Aircraft System Pilots and USAF, Remotely Piloted Aircraft Pilots and they do get the 'wings'

"United States Air Force Unmanned Aircraft Operator Badge" by SSgt Austin May of the USAF - http://www.af.mil/news/story.asp?id=123170151http://www.mildenhall.af.mil/news/story.asp?id=123170577. Licensed under Public Domain via Commons.

However, there has been no UAV pilot license issued as far as I know.