Why is the battery turned off for checking the voltage on the A320? Preliminary cockpit preparation section requires BAT check for 25.5V with BAT off (The beginning step). Since BAT indicator always show respective voltage, why they must be switched off?

The voltage varies with what is connected to the bus.

Adding load will, for every electric source, reduce the voltage. And you wouldn't know how much is still OK without also knowing what is powered.
When the battery is charging (e.g. from ground power), you'll see the charging voltage even if the battery is empty.

With battery off you remove this variability, so they can give you exact number that signifies the battery is sufficiently charged.
(IIRC there are few things on the hot bus that are always connected, but their power consumption is known, so you check the battery under well defined conditions)


Is there an aviation career where I would help design an entire aircraft and its systems? If I want to design and build planes, what career would that be? Would it be a mechanical engineer, systems engineer, or what else. (I feel like saying aerospace engineer is too vague and most companies like Lockheed Martin don't have that as a job but mostly as a business unit other jobs fall under.)
Also, is there a job in which you design and build planes and pilot planes? I really want to become an engineer that designs planes but still want to pilot them as a fighter pilot or test pilot, I just want to know if there is possibility of doing both.

You were born 100 years too late.
In order to be an improvement over existing designs, airplanes become ever more complex and every detail is optimised over years and years. The days when someone like Robert Hall or Kurt Tank would design and test fly their designs are long gone.
The best you can do is to design an experimental aircraft and maybe market it as a homebuilt or a kit plane. But forget about designing front-line fighters all by yourself: This by now involves thousands of engineers and the test pilots have very different careers from those of the lead engineers.


How is the correct air speed for fuel combustion obtained at the inlet of the combustor? Many jet aircraft travel at speed of about Mach .8 which at an altitude of 11 km represents an airspeed of about 300 kt or 150 m/s.

If fuel was injected into air at this speed, the mix would just leave the engine before being burnt, combustion would occur behind the aircraft. From different readings, I believe the correct airspeed in the combustor must be around 10 or 20 m/s to maintain the combustion within the combustor.
In the compressor section, air from the intake is forced to rush into a convergent annular tunnel to compress it. Intuitively, this design won't slow air, or not slow it enough.

General Electric J85-GE-17A, source: Wikipedia

How engineers are able to slow air without decompressing it?

Combustors usually feature recirculation zones in which the combustion takes place either completely or which at least anchor the flame. This can be done by several designs

Sudden jump in cross-section in combination with vorticity
Flame-holder bodies
Central displacers
Vorticity brake-down

The blade channel of a compressor is actually divergent. Deceleration of a flow goes along with an increase of the static pressure (see diffusors). Additionally, a compressor transfers work into the fluid, thus further increasing the fluid density. The divergent cross-section of the annular channel between hub and casing is designed to keep the axial velocity somehow level. High axial (or more correctly meridional) velocity levels cause higher friction losses. Low velocities reduce the transferable power of a compressor stage, thus requiring more stages.


Can I get pop-up IFR clearance to waypoint (intersection)? Let's say I departed from the airport to fly to the practice area (VFR).
However, there is a thick cloud layer between where I am at right now and practice area. I already got a report that practice area is clear and VFR.

To go through the cloud, I need to request IFR to go through the cloud.
At this point, can I request pop-up IFR to any waypoint (as a destination) that is in practice area?

Will I be able to cancel that IFR flight right after I go through the cloud and when I am not in IMC?

Yes, you can file to a waypoint or navaid and can cancel IFR anytime you want. Whether or not ATC will grant a popup clearance depends on the facility and their workload. In places with a lot of flight training (Florida, Southern California), ATC, in particular the TRACONs, usually grants popups.


Why are brake temperature limitations lower when the brake fans are running? In the A320 FCOM it is stated that if the brake fans are running prior to takeoff then the brake temperature must be below 150 degrees Celsius. But if the brake fans are off then our limitation is 300 degrees Celsius. Any reason behind such different limits?

The fans cool not only the brakes, but also the temperature sensors, at different rates. The temperature difference is a measure to correct this anomaly. From the document  Proper Operation of Carbon Brakes by Airbus Flight Operations Support:

  ... the  temperature  indicated in the cockpit when the brake fans are running is significantly lower than the temperature indicated when the brake fans are OFF. This is because the brake fans are ventilating the brake temperature sensor that is not located inside the material itself. Therefore,
  as soon as the brake fans are running, the indicated brake temperature  decreases almost instantaneously.

  ... For all brake types, when  the  fans  are  running, the difference ranges typically  from  approximately  50°C  at  100°C actual brake  temperature up to about 150°C  at  300°C  actual  brake temperature.

  ... When fans are selected, the warning will disappear instantaneously,  but the takeoff must be delayed until the indicated temperature  consistently decreases below 150°C (for a warning set at 300°C)


Is there a European equivalent of VFR Flight Following? In the US, Flight Following is a radar service provided to VFR aircraft on a best-effort basis. Controllers provide traffic advisories but they don't issue clearances or instructions and the pilot is responsible for maintaining separation from other aircraft, observing altitude, airspace and other flight rules etc. Flight following is only provided when the controllers' workload permits and it may be terminated at any time.

Is there an equivalent service in Europe? I've heard of something in the UK called "basic service" but I don't know if it's the same thing and if it's UK only or a Europe-wide service.

Yes, it is called Flight Information Service (FIS). FIS is defined by ICAO, and the term is used in most of the world. "Flight following" is a local term used only in certain countries.

A flight information service (FIS) is a form of air traffic service which is available to any aircraft within a flight information region (FIR), as agreed internationally by ICAO.
It is defined as information pertinent to the safe and efficient conduct of flight, and includes information on other potentially conflicting traffic, possibly derived from radar, but stopping short of providing positive separation from that traffic.
Flight Information also includes:

Meteorological information
Information on aerodromes
Information on possible hazards to flight

FIS shall be provided to all aircraft which are provided with any air traffic controller (ATC) service or are otherwise known to air traffic service units. All air traffic service units will provide an FIS to any aircraft, in addition to their other tasks.


How much pollution is created by an airplane taking off? I read on a site that a 747 taking off emits the same amount of air pollution in the first 5 miles or so as 3000 cars. This seems extreme (accepting that the cars will be average).

Are there any more precise comparisons for 2 or 4 engine aircraft?

To provide more detail, let's look at some actual numbers. Without knowing where you got this information, the term "air pollution" is especially vague. But let's see what we can do. I'll compare CO (carbon monoxide) emissions since I could find that for both cars and jet engines.

The new 747-8 uses the GEnx-2B67 engine. The older 747-400 has a few engine options, one of which is the CF6-80C2B5F. Emissions information about these engines is available from EASA tests, and available for the GEnx and CF6. More info about the tests is here.

Based on that information the two engines have the following CO emissions at takeoff, reported as grams per kg of fuel burned:

CF6: .05 g/kg CO
GEnx: .17 g/kg CO

The fuel burn rates at takeoff for the engines are reported as:

CF6: 2.685 kg/s fuel
GEnx: 2.451 kg/s fuel

To find a value of comparison for cars, the EPA standards are here, in units of g/mi. Let's assume that we are using a recent model year, certified to the ULEV (Ultra-Low Emission Vehicles) standard.

ULEV: 1.7 g/mi CO

Now we need a way to compare these values. Let's use your initial value of 5 miles as the comparison distance. The jet engines will remain at takeoff thrust over these 5 miles, and the cars will meet the ULEV standard.

So how long will it take the 747 to cover those 5 miles? Let's look at the whole takeoff run, from a complete stop. This means that it will take about 40 seconds to cover the first mile down the runway. After that, lets assume it averages 160 knots, or 185 mph, over the next 4 miles. This means it will take 78 seconds to cover the rest of the distance, for a total of 118 seconds.

Computing the emissions for the takeoff:

CF6:

$$\begin{align*}
2.685\,\mathrm{kg/s} \times 0.05\,\mathrm{g/kg} &= 0.13\,\mathrm{g/s}\text{ CO}\\
0.13\,\mathrm{g/s}\times 118\,\mathrm{s} &= 15.84\,\mathrm{g} \text{ CO per engine}\\
15.84\,\mathrm{g}\times 4\text{ engines} &= 63.4\,\mathrm{g}\text{  CO per takeoff.}\end{align*}$$

GEnx:

$$\begin{align*}
2.451\,\mathrm{kg/s} \times 0.17\,\mathrm{g/kg} &= 0.42\,\mathrm{g/s}\text{ CO}\\
0.42\,\mathrm{g/s}\times 118\,\mathrm{s} &= 49.17\,\mathrm{g}\text{ CO per engine}\\
49.17\,\mathrm{g}\times 4\text{ engines} &= 196.7\,\mathrm{g}\text{ CO per takeoff.}\end{align*}$$

The car will be easier to compute:

$$5\,\mathrm{mi}\times 1.7\,\mathrm{g/mi} = 8.5\,\mathrm{g}\text{ CO per car.}$$

The 747-400 holds 416 people, and the 747-8 holds 467 (3-class configuration). Let's assume each car will carry 4 people.

$$\begin{align*}
416/4 &= 104\text{ cars}\\
467/4 &= 116.75\text{ cars.}
\end{align*}$$

We'll split the difference between cramming the three extra people into other cars and adding another car, and just leave it as 116.75 cars. Totaling the emissions from all cars:

$$\begin{align*}
104\text{ cars}\times 8.5\,\mathrm{g/car} &= 884\,\mathrm{g}\text{ CO}\\
116.75\text{ cars}\times 8.5\,\mathrm{g/car} &= 992\,\mathrm{g}\text{ CO.}\end{align*}$$

So comparing the 747 and the cars:

747-400: 63.4 g CO
104 cars: 884 g CO
747-8: 197 g CO
116.75 cars: 992 g CO

So a 747-400 is equivalent to about 7.5 cars, and a 747-8 is equivalent to 23.2 cars, comparing the takeoff run with average vehicle emissions.

I found this pretty surprising. It would be more fair to compare a takeoff with a drag race or a 0-60 test on the cars, which is probably not what the emissions test requires.

If anyone has more info or sees an issue with this please let me know.


Do multi engines face the torque effect? Do multi engines face the torque effect? What about jets?

Maybe you mean the p-factor. If both engines are rotating clockwise, the plane yaws to the right. If one rotates clockwise, the other counter-clockwise, the effect cancelles out and the plane flys straight.


What happens with RNAV procedures on the way from AIP publication to FMS database? I'm particularly interested in Approach procedures, but I guess it applies for RNAV procedures in general.

On one side, the national Air Navigation Service Provider (ANSP) is responsible for the design of the procedure. The procedure charts are usually available as PDF files through AIP website (e.g. the terminal procedures available at FAA).

On the other side, the RNAV procedure is coded in binary format inside aircraft's FMS. The airborne databases that can be directly loaded to the FMS are provided by external companies (Jeppesen, Lufthansa, Navigraph).

What happens between those two points is kind of puzzling for me.

I know of ARINC-424 standard for aircraft navigation data that is used for "preparation and transmission of data". Then there is AIRAC cycle which as I understand provides fixed dates for any changes to become effective.

The questions are:

Who takes responsibility that the database being sold to airline or any user reflects the original procedure published by ANSP?
How does the coding process look like. Is it based on PDF charts or there is another exchange format available (e.g. AIXM)?

The navigation database is technically a component of the GPS or FMS navigation system.  As such the manufacturer of the GPS or FMS is responsible for ensuring the database works with the equipment.

The database itself is usually prepared by a database provider such as Jeppesen. They have to work with the manufacturer to format and structure the database to work with the GPS or FMS.  After Jeppesen builds a database for a given cycle the GPS/FMS manufacturer will test the database before it's released.

Depending on their business agreement, the database subscription may be purchased from the manufacturer or direct from Jeppesen.

Jeppesen obtains the data from the ANSP and must process the data in accordance with RTCA DO-200B, Standards for Processing Aeronautical Data.  (Available for purchase from RTCA Inc.)

In the case of the FAA, the data is available in numerous formats, most commonly in ARINC 424 format.

There's a great deal of info available on the FAA Aeronautical Information Services website.


Why is the take off speed and distance reduced by head winds? A headwind of 20 knots and a true airspeed for the take-off safety
speed being 120 knots, the ground speed is only 100 knots.  Getting to a true ground speed of
only 100 knots will require less distance.

Anyone can explain to me is that mean that the distance for take off will be less and also the take off speed will be less?
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You're correct that a headwind will reduce the takeoff roll (takeoff distance). As far as takeoff speed, the airspeed will remain same, but the ground speed will be reduced.

In the simplest sense, an aircraft rotates for takeoff when it generates enough lift (leaving aside other considerations). This is dependent on the airspeed as the lift generated is propotional to the square of airspeed (provided the other factors like wing area and lift coeffecient are kept constant) at a density altitude. As a result, it is the airspeed, not the groundspeed that matters.

If you have some headwind, the effective groundspeed is reduced by the same amount- resulting in reduced takeoff distance. The effect of the wind on landing distance is similar to the takeoff distance. You can see this in the following figure.

Image from avstop.com

As it can be seen, the presence of winds can have a significant effect on the takeoff disantances required (note that the airspeed remains the same in all cases). Due to this, the direction of prevailing winds can have a significant effect on determining the runway headings. From Influences on Airport Layout:

  The weather patterns of an area, especially the prevailing winds, are a major factor in determining runway headings. Prevailing winds are defined as the direction from which the winds blow most frequently. Remember that airplanes take off and land into the wind. Let's say that at a given airport the prevailing winds blow in from the west 65% of the year, while 30% of the year the wind blows in from the east, and the remaining 5% coming from the northwest. It would be best then to orient the runway W (27) and E (9). That would mean that approximately 95% of the year airplanes would be landing and taking off into the wind.


What is the purpose of squawking 7777? Aircraft use transponders to communicate to ATC their position and status. Some squawk codes are reserved, such as 7700 (emergency), 7600 (communication failure), 7500 (hijacking), 1202 (glider), 1200 (VFR), etc. One of these, 7777, is apparently used for "military interception." What does this mean in the United States? Under what circumstances would it be used on a civilian / military aircraft?

In countries outside of the US, 7777 may be used by test transponders (RABMs) to check correctness of radar stations (BITE). e.g. on top of a mountain.

In the US, it seems that it is used as well on active air defense missions without ATC clearance. This would mean that the interceptor aircraft would change it's squawk to 7777 for the military/civilian air traffic controller to see it properly (if not filtered out on civil radars).

A link to the US intercept procedures is here.


Why are US Regional Airline starting wages so low? With 2,000hrs of flight time, a commercial ticket for ASEL and AMEL, CFI, CFII, MEI, and a Master's in Aeronautical Science I could easily qualify to fly right seat for a regional airline, but I just can't compete with pilots willing to work for \$17k/yr. For comparison, federal minimum wage is currently just over $15K/yr.

Why are the starting salaries at US Regional Airlines so low?
It seems odd that pilots go through extensive training which takes a great deal of time and expense, but they have to be prepared to work for what is a very low salary compared to other jobs that require a high level of skill and education.

Supply and demand is one explanation, but I really don't understand how there is so much competition for flying jobs but at the same time there is a supposed "pilot shortage".
Are there really so many pilots out there that the competition for jobs drives down starting salaries so low?

I am hoping to understand why it is that well-qualified pilots appear to have so little earning power in the marketplace.

Well, the short version is: The airlines pay what they have to pay in a free market.  They can get away with it because pilots are willing to accept it.  Like any other business they are in it to make money and keeping costs down is just as good as making extra money, so they aren't going to volunteer anything extra.

Now, why do pilots do it?  Because of the promise of better things down the road.  It isn't as good as it used to be, but after being at the airlines for a few years, you can make a livable wage and as you get further into your career at a major airline, you still get paid pretty well for a "part time" job.  As I've heard other pilots say before:  It's better than a "real" job!

Other pilots do it just because they love it and can't imagine doing anything else!


"All exterior lights" when crossing a runway? Landing light, too? AIM 4-3-23 (f) says "all exterior lights should be illuminated when taxiing on or across any runway".  AC 120-74B 7.h.2.c has similar words, except that it's limited to "crossing a runway".  Both conflict with other guidance, which would imply that turning on the landing light is a signal of your intent to take off.  Seems that it should be "all exterior lights except landing lights".  How do the pros interpret this?

This is discussed in this question: Should landing light be off during line up and wait position?
When crossing a runway, you do use landing lights along with everything else, and since you're on a taxiway, the presence of the landing lights in this case isn't understood as intent to takeoff since you aren't lined up on a runway.
For an aircraft that is at the end of the runway, lined up & in a position to take off, that's when the idea of "landing lights on = intent to take off" applies. When on-to-hold, everything else is on, mainly to make the aircraft visible in a "please don't land on me" sort of way, but the landing lights off provides an assurance to Tower controllers & anybody who is crossing the runway down-field that you really are planning to remain stationary right now. Then, with takeoff clearance, the landing lights come on. And if I thought that I'd been cleared to cross the runway but the other aircraft (lined up) has landing lights on, I have an earlier cue that he is powering up, so I'll hold short & ask the controller what's up. Matters not if he was wrong, I was wrong, or controllers were wrong; we're all better off if the taxiing aircraft doesn't enter the runway ahead of somebody accelerating toward takeoff speed, and the concept of "landing lights on = intent to takeoff" helps there.
And, conversely, if I'm starting to advance power for takeoff & somebody with all lights on seems to be rolling toward "my" runway, all those lights (A) helps me see him all the better, and (B) gives me a cue as to his intentions.  So I might reconsider continuing the takeoff until things get resolved.
Conflicts like that are (thankfully) quite rare, but because the consequences are so grave, keeping everybody aware of everybody else's intentions is a really good thing.


Combating flutter with mass distribution? Considering aeroelastic flutter, when an eigenfrequency of the wing meets with an aerodynamic frequency, the commonly mentioned solutions make sense: avoid the convergence zone by limiting speed, or by increasing the wing's eigenfrequency trough stiffness, reduced weight, or reduced span.
Makes sense, especially if I use the spring and mass model for the wing:

I'll use the analogy with the conventional spring as it makes things easier to understand for me.
So Wikipedia says: "Prediction involves making a mathematical model of the aircraft as a series of masses connected by springs and dampers which are tuned to represent the dynamic characteristics of the aircraft structure. [...] Small carefully chosen changes to mass distribution and local structural stiffness can be very effective in solving aeroelastic problems."
My 3 questions are:
1: Do I understand correctly that with this approach, the wing will act similarly to the following model, where the motion is rather chaotic?

2: This should have no certain frequency. Does this mean flutter is avoided?
3: Does this mean flutter can be avoided by redistributing mass around the wing, without increasing stiffness or reducing mass?

Do I understand correctly that with this approach, the wing will act similarly to the following model, where the motion is rather chaotic?

No, your combination of masses and springs will have several eigenfrequencies. For aeroelastic analysis only the lowest eigenfrequency counts because this will couple with aerodynamic frequencies at the lowest flight speed. Once you fly faster, the next eigenfrequnecy in line will resonate, but that is only hypothetical because flutter caused by the lowest frequency has already destroyed the airframe.
In very rare cases the lowest eigenfrequency will already couple with aerodynamic oscillations at speeds below stall speed. Then the aircraft can be operated in the gap between the lowest and the second-lowest eigenfrequency.

This should have no certain frequency. Does this mean flutter is avoided?

No, since it has several eigenfrequencies, flutter is as certain as before.

Does this mean flutter can be avoided by redistributing mass around the wing, without increasing stiffness or reducing mass?

Flutter cannot be avoided, only its speed shifted up by damping. The rule always is to place the center of gravity ahead of the axis of rotation (that would be the elastic axis in case of wing torsion), so any movement causes an inertial damping force. This is the reason for the forward location of wing mounted engines.


What are the performance adjustments for a Beechcraft B1900D on a wet runway? I am doing runway analysis for B1900D and AFM Section 5, does not provide correction to V1 or the takeoff weight for takeoff on a wet runway.

Appreciate if someone can provide information regarding such correction or the method.

According to the Transportation Safety Board of Canada when they conducted an investigation into a Beechcraft 1900D overrunning a runway in 1997, they found out that the AFM does not include that information you request, nor was it available to the pilots.

  The snow-covered, slippery condition of the occurrence runway differed from the bare,
  dry surfaces on which the AFM data is based.

and

  There were no performance data available to the pilots to determine the aircraft's
  accelerate-stop distance under snowy and slippery runway conditions.

and

  The James Brake Index (JBI) published in the Canada Flight Supplement contains a table which may be used to
  adjust calculated landing distances to compensate for slippery braking conditions. JBI correction factors for
  compacted snow or snow-covered runways range from 80% to 250% higher than hard dry surfaces. Transport
  Canada did not require the manufacturer to provide data on the effects of soft or wet runways, slippery
  runways, or runways containing loose snow on the aircraft's accelerate-stop distances or take-off distances.

How can the aircraft be approved? They say:

  The manufacturer was, as a condition of the aircraft type approval,
  required to determine and supply certain aircraft performance data including the balanced field lengths at
  various take-off weights, temperatures, and altitudes.

I.e., V1 corrections for non-dry runways were (are) not a requirement for the 1900D.

If the AFM you have is current, then it hasn't changed since. If not, then it may be present in the latest AFM. (But I wouldn't count on it, so verify before placing a purchase order.)

You may also look into the aforementioned James Brake Index.


Why does the B777-200 freighter not use the letters I, N, O and Q for deck positions? The B777-200 Freighter has positions on the main deck to describe how the cargo will be loaded in a left to right sequence. They are identified as A, B, C, D, E, F, G, H, J, K, L, M, P and R.

What is the reason that the letters I, N, O, and Q are omitted?

Those letters are commonly unused in aviation in markings, registrations etc. They might be easily confused with similar letters (I with J, N with M) and are therefore left out.


Visualising downwash over a finite wing The downwash is caused due to higher pressure below the wing than above it (for a positive lift generating wing that is). What I am not able to understand is how would the flow be in a gross sense? Will the flow move bottom to up around the wing tips and move top to bottom along leading and trailing edge? I thought of this because it is the only way I am able to justify that downwash induces a negative velocity component which decreases the angle of attack that the wing sees at the leading edge.

But can’t the air also move bottom to up along leading or trailing edge? To me, at leading edge it seems unlikely based on intuition because of the air upstream constantly trying to direct the air ahead but at trailing edge it seems more likely.

So what is the correct visualisation of downwash over a finite wing?

Downwash is a misleading concept when discussing airfoil lift. Instead, just focus on the pressure distribution around the airfoil.

If I understand your confusion correctly, you are picturing, correctly, that there is an overall low pressure on top and an overall high pressure on the bottom, then why isn't air flowing from high pressure to low pressure?

This will indeed be the case, if there is no airflow. What you are missing is that, the static pressure distribution is caused directly by the airflow around the airfoil. The distribution is steady-state, because the combination of dynamic pressure and static pressure resists further changes; it's at an equilibrium.


Starting on the left magneto only - why? I had been flying a PA-28 Archer III for quite a few months before I sat down to properly read through the POH. Something stood out to me about the starting procedure (emphasis mine)

Open the throttle lever approximately 1/4 inch. Turn ON the
battery master switch, alternator switch, left magneto switch and the
electric fuel pump.
Move the mixture control to full RICH, verify the propeller
area is clear and engage the starter. When the engine fires, release
the starter switch, and move the throttle to the desired setting. Turn
ON the right magneto switch. Check the oil pressure for a positive
indication.

Having previously flown aircraft where a key operates the starter, and that key has to travel past left, then right magneto to the start position I was starting with both Mags in the ON position (For those unaware, the Archer III varies in that the left & right magneto are operated by a rocker switch).
The obvious answer to the question of "Why start the engine with only 1 magneto live?" is "Because that is what the POH says to do!" - I am nonetheless interested in the electrical or mechanical reason why? Or perhaps there is some safety aspect at work?
Does anyone know the details?

The reasons seems to be that only the left magneto is equipped with an impulse coupling which delays and intensifies the spark during engine starting:

Many opposed reciprocating engines are equipped with an impulse coupling as the auxiliary starting system. An impulse coupling gives one of the magnetos attached to the engine, generally the left, a brief acceleration, that produces an intense spark for starting. This device consists of a cam and flyweight assembly, spring, and a body assembly.
[...]
The impulse coupling has performed two functions: rotating the magneto fast enough to produce a good spark and retarding the timing of the spark during the start cycle. After the engine is started and the magneto reaches a speed at which it furnishes sufficient current, the flyweights in the impulse coupling fly outward due to centrifugal force or rapid rotation. This action prevents the two flyweight coupling members from contact with the stop pin. That makes it a solid unit, returning the magneto to a normal timing position relative to the engine.

(flight-mechanic.com on Impulse Coupling, emphasis mine)
On an aircraft with key operated ignition (where the start position comes after both), the right magneto is grounded while you hold the key in start:

Most airplanes have an impulse coupling on the left mag only. During engine start, the ignition key grounds out the right mag, so only the left mag provides spark. The timing of the spark from the left mag is retarded (later than usual) during engine start so the engine will start easier. Once the ignition key is released from the start position, the timing of the spark is restored to normal, and the right mag starts firing.

(askacfi.com)


What does Elon Musk mean by "electric jet"? Elon Musk has said that he has a design for a vertical take off and landing super sonic electric jet. I was under the impression that jet engines work by burning fuel, expanding volume and thus creating force. How can this be done electrically?

Jet noun

a rapid stream of liquid or gas forced out of a small opening

A Jet Engine is an Engine which uses a Jet for propulsion. Typically, a "rapid stream of gas", in which the gas is air. Really, we could count pretty much any aircraft engine as a jet, but it depends on how "rapid" you require the air to be before it's a jet.

In a typical jet engine as we define it now, the jet is created by burning fuel and air... but there's no requirement for that to be the case. An electric jet would simply use an electric motor to create a rapid stream of air.

Would it really be a "jet" engine? That depends how fast the air is - but most people see "jet" as being a fast, powerful, reliable type of aircraft, so it's as much about marketing as anything else. An Electric Prop or Electric Plane doesn't sound as cool as Electric Jet... (Although I'd argue that ElectroJet/ElectroProp/ElectroPlane are awesome names and Elon Musk has let himself down by not using one of those names)


What, exactly, is a "co-pilot"? When I speak of a co-worker, or a co-driver, I'm speaking of a mutual relationship and status (that's simply how the prefix co works in normal English) and I'm pretty sure it's what most people mean too.

When people speak about co-pilots on the other hand, it seems they might mean one of several things:

They are speaking of two pilots who happen to be working as part of the same crew, who are therefore co-pilots (which seems the most correct usage).
They mean a pilot who isn't the captain.
They mean the pilot monitoring rather than the pilot flying.
They think the aircraft has a pilot, and a kind of assistant pilot of lesser abilities known as a co-pilot.

(This last seems to be strangely prevalent, as if people imagine an airliner might be crewed by a fully-qualified professional and by some sort of assistant whose job is the aviation equivalent of holding the ladder, who looks forward to the day they'll be allowed to climb up it themselves.)

Weirdly, I have actually heard air crews use co-pilot in ambiguous ways, as though even they have given up trying to use the word with care; once I heard an announcement in one language that referred to the captain and the first officer, and then immediately afterwards in another to pilot and co-pilot.

Questions about co-pilot

It seems reasonable to say "my co-pilot" when speaking of a fellow crew member. However:

Does "the co-pilot" have any meaning (note the use of the definite article)?
Is co-pilot ever a rank?
Does the term appear in aviation regulations?
Is it used in crew management policies?
Is there indeed any standardised or formal use of it within the industry?

Does "the co-pilot" have any meaning?

Yes, Merriam-Webster says:

  co- prefix

  :having a usually lesser share in duty or responsibility: alternate: deputy • copilot

and

  copilot

  :a qualified pilot who assists or relieves the pilot but is not in command

while dictionary.com says:

  variant of com- before a vowel, h, and gn: coadjutor; cohabit; cognate. The prefix co-, now productively forms new words from bases beginning with any sound ( co-conspirator; co-manage; coseismic), sometimes with the derived sense “auxiliary, subsidiary” ( coenzyme; copilot), and, in mathematics and astronomy, with the sense “complement” ( codeclination).

Both sources mention / hint at the co-pilot not being the highest in the command hierarchy.

Is co-pilot ever a rank?

Yes, the co-pilot is the second-in-command (SIC), right after the captain (even if the co-pilot has more hours than the captain—it does happen). If the captain ate the fish, the co-pilot becomes pilot-in-command (PIC).

Does the term appear in aviation regulations?

It's very rare (nowadays at least), usually second-in-command will be used. Here's a mention of co-pilot in an FAA advisory circular (not a regulation per se).

  The Mentor Pilot. A mentor pilot is a professional aviator acting as a coach, co-pilot,
  teacher, and role model, sharing experience and expertise in the complex environments in which
  the EA500 will operate.

Is it used in crew management policies?

Not really. The terms used are pilot-not-flying (PNF) or pilot monitoring (PM), and pilot flying (PF). Because the captain and co-pilot can be either, they usually swap roles. The captain can be the PF on the out-bound leg, and PM on the return flight, for example. But the captain remains the PIC even when the co-pilot is the PF.

Is there indeed any standardised or formal use of it within the industry?

Popularity varies by location / culture / era. First officer (F/O) is also a valid alternative. Searching for jobs on Google, copilot returns ~9 million results, while F/O returns 30 million.

Using Google's Ngram Viewer could be skewed due to the F/O's usage in maritime environments.

What does ICAO say? (My addition.)

It's not bothered really:

  What is a multi-crew aeroplane?

  It is an aeroplane that requires a flight crew of at least two pilots. One of them is the pilot-in-command (the captain) and the other is the co-pilot (or first officer).

Related:

What are common airline crew titles and positions?
When does a flight require a copilot?
What are the roles of the co-pilot in commercial aviation?
Can two captains fly an airliner?
What is a Second Officer?


Does an instrument exist to measure the different types of drag? Does a 'drag meter' exist that separately shows total, induced and parasite drag?
If it doesn't, and in theory, would it be possible to build one?

Yes, partially.  A wind tunnel's wake rake (an array of pitot tubes) can be adapted to measure in-flight profile drag (form drag plus skin friction).
Measuring Wing Profile Drag using an Integrating Wake Rake, by Pifer and Bramesfeld, in Technical Soaring 36(3):74-82, 2012.
The article doesn't have any in-flight photos, so it may not have actually been flown at time of publication.

@quietflyer mentioned Richard Johnson, who indeed has flown an airplane with a drag rake.

The wing drag rake was installed on N3176T’s left wing trailing edge, 1.0 meters outboard from the wing root joint. ...

R. Johnson, "A flight test evaluation of the SZD-55-1," Soaring, March 1992.
The drag rake itself is described and shown in another article:
R. Johnson, "At last: an instrument that reads drag!," Soaring, October 1983.


How do I calculate propeller effects on pitching moment? I have read somewhere that propellers have an effect on the pitching moment of the aircraft. Having said that, I have a couple of questions.

Is this a significant effect in model aircraft? If so, are there major differences between pusher and tractor configurations?
Finally, how would one calculate this effect?

The propeller causes pitching (and yawing) moments. There are two main reasons for that:

1) flow change around the fuselage (and central wing and tail)
2) thrust change.

Thrust change is simpler to grasp and estimate. The thrust vector will cause a moment, because (90% of the time) it's a bit tilted and does not pass through the CG of the aircraft.

Several model aircraft have intentionally tilted propeller / motors. The perfect amount of tilt is found through flight tests, because its simpler and more accurate to try and feel the effect.

A pusher configuration has quite similar concerns related to thrust vector, however the flow change effect is much less than a tractor configuration. This is because for the pusher configuration the accelerated flow does not effect the air vehicle any more.

Calculation of these effects range from hand calculations (spreadsheets) to CFD and finally to flight tests (where you'd do controlled tests to derive the model parameters).

For RC aircraft I'd suggest following the rule of thumbs that have been established in the RC communities.

Finally, tractor / pusher configuration selection should be based on several other factors and thrust moment is probably not the most important one.


Delta fleet plans - all Airbus? (and Bombardier) With Delta ordering A321neos and C-Series not 737 Max 10s, A339s, A359s instead of 789's, might Delta be on their way to an all-Airbus fleet? Or going away from Boeing?
Was the 737 Max vs A321neo deal really a "P&W over CFM" deal? Or was it just "Airbus > Boeing" etc. in disguise?
Would Delta ever actually order (and take delivery of) any 787's in the future? (Maybe in like 10, 20 years or so)

It does not seem that Delta is on the way to an all-Airbus fleet. As a starting point, they plan to take delivery this year of the first of at least 75 of the Bombardier CS100. That points to many years to come of non-Airbus aircraft for them. They also continue to receive new Boeing 737-900ER aircraft.


Is there a light civilian helicopter capable of a 250 NM trip without refueling? Is there any light civilian (GA) helicopter that's capable of making a 250 NM trip with required fuel reserves? I'm thinking of something smaller and lighter that a private individual might buy. (I'm thinking about something that costs less than USD 150K, if that helps to explain the type/size of helicopter I'm asking about.)

The Robinson R22 and RotorWay A600 look like they wouldn't make it without a refueling stop, and I haven't found any extended range STCs for these either.

Does anyone know if such a helicopter exists?

I would need a definition of the word 'light' as it is a little relative.  Most light turbine helicopters eg a Bell 206 JetRanger or a Hughes 500 will do this job just fine.

It is a little difficult to locate a reciprocating engine powered helo that meets those criteria.  The Guimbal Cabri G2 and the Robinson R44 would be my choices for that but cost over $300,000 a piece.

The Schweizer (now Sikorsky) S333 would be another good choice.  It is a light turbine helicopter and can be obtained for just shy of 200,000 USD, though you may be required to put another 100,000 USD or so into it.


In current missile, what is the guidance law used at terminal phase in homing missile guidance? In current missile, what is the guidance law used at terminal phase in homing missile guidance?

eg: Proportional navigation, Augumented PN, Optimal Guidance Law, etc

At what distance the terminal phase guidance engage for Air Interceptor Missile(AIM) { eg: sidewinder, Derby, etc }. This is for active seeker(radar). And what is the terminal phase guidance used for active (radar) seeker.

what are information get from seeker to guidance system at terminal phase using active seeker(radar), other than Line_of_Sight(LOS) and Relative range(R) between missile and target.

According to this easy to read brief introduction:

Optimal Homing Guidance Laws

  Other Optimal Homing Guidance Laws, many modern guidance laws require
  an estimate of time-to-go (tgo), which is the time it will take the
  missile to intercept the target or to arrive at the closest point of
  approach (CPA). The tgo estimate also is a critical quantity for
  missiles that carry a warhead that must detonate when the missile is
  close to the target.


When do pilots have to submit position reports? While over non-radar controlled airspace (e.g. the North Atlantic, the Pacific, or over vast parts of Africa), pilots will submit position reports. Is there a regular time interval in between position reports, or is that only dependent on reaching a waypoint in the flight plan? What happens then, if waypoints are hundreds of miles apart (which would be the case for example over northern Canada)?

Can the position reports be also submitted via CPDLC (Controller-Pilot Data Link Communication)?

It's not fixed. I checked ICAO Annex 10 Vol II that lists the SARPs for communication. It will be down to the FIR the flight is being conducted in. For the NATS (UK) side of the Atlantic, I found this document (may not be current).

The basic intervals are whichever comes first:

Waypoint on the flight plan
One hour had passed
ETA has changed for the next waypoint by +3 minutes
Interval based on whether north or south of 70°N.

CPDLC is used, and can be automated too (ADS-C). If the FIR does not support CPDLC, then it will be via voice. According to Boeing, FANS 1—which handles reporting via datalink—saves a lot of time and improves accuracy:

  The uncertainties of traditional voice position reporting and the delay associated with high-frequency relayed voice communications [result in 20 to 45 min to make a position report].

And depending on the ADS-C (C for Contract) agreement, the reports can be as frequent as every 5 minutes.

For the US side of things, check section 5-3-2 of the AIM and the section titled additional reports. It's similar to the above. They also note:

  For aircraft providing automatic position reporting via an Automatic Dependent Surveillance-Contract (ADS-C) logon, pilots should discontinue voice position reports.


What is the flight trajectory of a commercial airplane in regards to altitude v/s distance? So, my friend and I got into an argument regarding the flight trajectory of a plane. He said that for half the journey the plane is ascending and for the rest, it is descending and hence making a parabolic curve. I argued that it ascends and then stays at the same altitude for the journey before descending to make a trapezoidal curve. After some contemplation, I think that both of us are right just that the baseline reference is different where he took it as a straight line between the two places without the curvature of the earth and hence it would make it parabolic while I took the trapezoidal curve by accounting the curvature of the earth.

We can also say it is from a different of view with him being in space while I am running on the ground to measure the altitude.

So, can someone clarify and tell who is right and whether what I think is correct or not?

It would be helpful if someone can actually plot the two graphs.
Thank you.

Your friend is not correct and you are somewhat correct. For now I will consider long-haul flights as the effect is more visible. As the aircraft takes off it climbs towards it cruising altitude, say 33,000ft. Then during the cruise the airplane uses fuel meaning that the aircraft is effectively losing weight. Since during a steady cruise, lift = weight the aircraft will have an excess lift if nothing but the weight changes. This will make the aircraft climb to higher altitudes were the air is thinner and thus more lift is required.

Thus on some long-haul flights you can see that the flight ends at 38,000ft. Then the pilot initiates the decent for landing. Depending on ATC the aircraft is allowed to gradually climb during cruise to higher altitudes. If that is not allowed the aircraft will climb once every hour or so to a higher flight level.


What is a Cruise Captain? I wonder what is a Cruise Captain, albeit I assume they are here to fly the cruise phase.

Differences in responsibility / authority with a Captain?
From training / certificate standpoint, what is required?
When are they seen on board?
Is the Cruise Captain the pilot-in-command when they officiate?

According to the discussion here it seems a "cruise captain" is the captain who flies only during the cruise stage of flight. You can find a job listing for a "cruise captain" here but it does not elaborate much on the duties. To act as the pilot in command (at least by FAA regs) they would have to be current, and type certified in the aircraft in question. It seems the term is more a turn of phrase and the regulations are not any different for a cruise captain. On very long haul flights that may require 3 full crews, there will be a crew in the middle section of the flight that never sees takeoff or landing from the cockpit.

The report you have linked in the comments defines cruise captain in the foot note on page 3.

  Cruise Captain in this report refers to a pilot certificated as cruise
  captain by the Malaysian Aviation Authority, and is qualified by the
  company to act as PIC during cruise only and who was engaged in the
  operation of the aircraft.

It sounds like "Cruise Captain" in this case is a Malaysian Aviation Authority term (although it may apply elsewhere as well). I am looking for the actual regulation that defines it but have not yet come across them.


Does ground speed represent the horizontal speed measured at sea level? Which of the following vectors is refered to as the Ground Speed?

The green one I expect is TAS, the blue one would be Vertical Rate

Note that for simplicity I did not draw them as geodetic curves, but the black one should be shorter than the gray one because of the earth's curvature.

Does the Ground Speed represent the horizontal speed relative to surface at the sea level?

Ex: Helicopter climbing verticaly will have GS=0?

Does the Earth's curvature affect the GS? As the length of the gray vector will be longer the higher the altitude is. Does that mean a plane flying at 1km will have higher GS than a plane flying the same total speed at 10km?

edit:

I'm simulating aircraft movement along a straight trajectory by constant speed. To simplify, the input is start coordinates & altitude and finish coords & alt.

That means the plane can ascend or descent during simulation. I know the total distance between A & B and distance at sea level. So first thing I tought of was:

GS = distanceAtSL / (totalDistance / speed)

In relation to image:

I know the length of Green line and I can calculate how long it will take the plane to reach the end. The time to finish is constant for each line & I know the length of the black line so using formula speed = distance / time I should be able to get the "Ground Speed".

Correct me if I'm wrong.

(Source)
Ground speed
Ground speed equipment on-board aircraft measure the speed against the ground. Except in the case shown above where distance information is derived from a ground station (DME station).
Curvature
Ground speed is not derived from true airspeed. When using GPS, or an inertial navigation system to measure the ground speed, it will be the speed across the ground. It is the rate of change of the latitude and longitude, so you don't need to include the curvature.
Once an aircraft (or crew) know the ground speed and TAS, the wind information is then known (how fast the mass of air the aircraft is in is moving).
True airspeed
True airspeed is the speed inside a mass of air. In a zoom climb in an F-15, TAS will be pointing almost the same direction as the [upward] nose of the F-15.
If the mass of air is moving due to head- or tail-wind, then this wind speed is subtracted from (or added to) the horizontal TAS to get the ground speed. (But again, this is not how ground speed is calculated, because there is no direct measurement for the horizontal TAS.)
Vertical speed is how fast the plane is climbing/descending. It's measured by sensing the rate of change of the static air pressure.
RE: edit

I'm simulating aircraft movement along a straight trajectory by constant speed.

This is not how airplanes fly in real life. But for the sake of your model, and if you don't have wind simulation, then the known green distance and the time it takes to move from A to B will do just fine to compute the ground speed.


Is a certificated pilot considered to be a student pilot when training in a new category or class? Inspired by this question, is a pilot certificated in one category or class considered to be a student pilot when training in a new category or class?

To take a specific example, if a pilot holds a Private Pilot - Glider certificate and then decides to add ASEL, is he considered a Student Pilot while he's training for his ASEL? By "considered" I mean, do regulations that refer to "student pilot" apply to the pilot?

Or, to put it as simply as possible: what is the FAA's regulatory definition of "student pilot"?

No.  The regulations that apply to a student pilot do not apply to the private pilot working on a new category or class rating.

§61.81   Applicability.
This subpart prescribes the requirements for the issuance of student pilot certificates, the conditions under which those certificates are necessary, and the general operating rules and limitations for the holders of those certificates.

The required endorsements for a private pilot working on a new category or class rating are also different.  Student pilots are required to have endorsements for pre-solo flight training, a solo endorsement each 90 days and an endorsement for each cross country.  The student pilot must also abide by all the limitations placed on those endorsements by the recommending instructor.
A private / commercial / ATP pilot working on a new category or class rating is required to have one endorsement.  Again, any limitations placed on the endorsement by the recommending instructor must be followed.

To act as pilot in command of an aircraft in solo operations when the pilot does not hold an appropriate category/class rating.
I certify that (First name, MI, Last name) has received the training as required by § 61.31(d)(2) to serve as a PIC in a (specific category and class of aircraft). I have determined that he/she is prepared to serve as PIC in that (make and model) aircraft. Limitations: (optional). /s/ [date] J. J. Jones 987654321CFI Exp. 12-31-19

Required endorsements for FAA certificated pilots are found in AC 61-65.


Means of protection against hunter-killer UAVs I would like to know all existing technological means of defending an area against the MQ-9 Reaper or other hunter-killer unmanned aerial vehicles (UAVs) used by the United States in countries like Afghanistan, Syria, etc. Such means should either force the UAVs to leave the area or crash.

By far the cheapest method for protecting a limited area would be to use an aerostat to carry aloft a jammer. Vehicles like the Reaper rely on a satellite uplink to maintain their command and control. As long as the aerostat is well above the altitude of the Reaper it can easily jam it. The cost of this option might be around \$1 million with an annual operating cost of \$200,000 and an effective diameter of about 10-20 miles.

A more expensive, but more flexible response would be to just shoot it down. To do this you would need an air surveillance radar, a high performance turboprop with machine guns like a Texan or Super Tucano, a pilot and a crew to operate the radar. With this method you could deny a pretty large area, maybe 100 miles in diameter easily, possibly more. The cost of this would be about \$3 to \$5 million plus annual operating costs of about $500,000. If you want to spend a bit a more a Yak-130 would be an excellent light attack jet to consider for anti-drone work. You might be able to find a used Yak for under \$10 million and it is a bitchin aircraft that can go double the speed of a Predator plus it has its own radar.

Missile systems would not really work because the types you would need to reach the altitude a Reaper operates at, are very expensive and complex (which is exactly why the Reaper flies at those altitudes). However if you could catch the Reaper while it was taking off or landing, a small missile like an RBS 70 would be even cheaper, assuming you could obtain that weapon.


Why does only the right outboard aileron on the A320/340 float up when the aircraft is in the emergency electrical configuration? When the A320/340's RAT is powering the aircraft's systems, the aircraft goes into its emergency electrical configuration; one of the effects of this is that the right outboard aileron becomes unpowered, and floats up.  Why does only the right outboard aileron go into the upfloat position?

EDIT: This answer is specific to the A340; the A320 is somewhat different.

TL;DR

In the emergency electrical configuration, neither of the two remaining flight-control computers can control the right outboard aileron, and it floats up under aerodynamic forces.

Long version

Some background: all Airbus aircraft from the A320 onwards have five flight-control computers, which translate the pilots' control inputs into control-surface movements.

These are divided into two categories:

Three flight-control primary computers (FCPCs, also known as PRIMs, for "primary"):

FCPC 1 (also called PRIM 1, or P1 for short)
FCPC 2 (aka PRIM 2 or P2)
FCPC 3 (aka PRIM 3 or P3)

Two flight-control secondary computers (FCSCs, also known as SECs, for "secondary"):

FCSC 1 (also called SEC 1, or S1 for short)
FCSC 2 (aka SEC 2 or S2)

Not every flight-control computer can control every control surface; the most critical controls (such as the elevators) are connected to four, or even all five, computers, while less critical surfaces only get two, and the least-critical (the individual spoileron panels) are connected to just one computer apiece (as there are six spoileron panels per wing, with each of the five computers controlling at least one panel on each wing, providing a great deal of redundancy).

On the A340, each of the inboard ailerons is connected to four of the five computers (FCPC 1, FCPC 2, FCSC 1, and FCSC 2); by default, the left inboard aileron receives input from FCPC1, falling back on FCPC 2, FCSC 1, and FCSC 2 (in that order), while the right inboard aileron defaults to FCPC 2, with FCPC 1, FCSC 2, and FCSC 1 to fall back on.

However, each of the A340's outboard ailerons is connected to just two computers.  Both outboard ailerons default to FCPC 3; the left outboard aileron has FCSC 1 as a backup, while the right aileron falls back on FCSC 2.

The A340's RAT can only generate a limited amount of electrical power, especially since a considerable amount of its output has to go into maintaining pressure in at least one of the aircraft's hydraulic systems, in order to allow the aircraft to remain controllable; normally, the hydraulic systems are pressurised by engine-or-APU-driven pumps, but, if the aircraft runs out of fuel (one of the very few circumstances that can simultaneously render all engines and the APU inoperative, and the main reason why the RAT exists), only the RAT is left, and it has to provide both electrical and hydraulic power.  As a result, a lot of electrical load-shedding has to take place to reduce the aircraft's electrical demand to something the RAT can handle; as part of this, three (for the A340) of the five flight-control computers are powered off, leaving only FCPC 1 and FCSC 1.  Additionally, due to the limited hydraulic pressure available from the RAT, the A340's outboard ailerons are deactivated to reduce the demands on the aircraft's RAT-pressurised hydraulics.

The overall effects on the A340's four ailerons are:

Left outboard: Not used; however, as FCSC 1 is still available, the aileron does still receive flight-control commands (although all they do is tell it to stay put), which helps to keep it from drifting away from the neutral position.
Left inboard: Operates as normal.
Right inboard: As FCPC 2 is unpowered, falls back to FCPC 1, and continues to operate.
Right outboard: Not used, and, as both of the two computers able to control it (FCPC 3 and FCSC 2) are offline, receives no flight-control input at all; as a result, its position is now solely dependent on the aerodynamic forces on the aileron, which tend to cause it to float upwards from the neutral point.

As explained in @ymb1's answer to an earlier question of mine:

  The manual does not give a direct reason (not unheard of), but in fact there's more than one reason.

  ► As a quick summary, you lose 2/3 of the spoilers and the outer ailerons, and if more unlucky, you lose 5/6 of the spoilers.

  [...]

  In emer elec config, the plane loses 3 of the 5 flight control computers; what remains are P1 and S1 (refer to diagram above).
  The outer ailerons go into an unpowered state to conserve hydraulic fluid/pressure – the right aileron upfloats* like on the A320 (no P3 and S2).

  [...]

  The references (click to view):

  All images are from the A340 FCOM, and color highlights are mine. Do not use for flight.

  A330 vs A340

  Thanks to @JZYL, note that there are some differences between the A330 and A340, while the A340 would announce MOST SPOILERS being INOP, the A330 would announce HALF SPOILERS (an extra computer remains powered). The same rationale given should apply though.

  * This is also confirmed from [this FCTM][6] (smartcockpit.com) of an airline with both the A330 and A340 in its fleet (see PDF page 207):

    (...) The AP will disengage when the failure occurs but AP 1 can be reengaged on the A333 if the EMER GEN is powered by an EDP. As there is no AP available in this configuration in the A340, the Captain must take control and fly the aircraft manually. The A340 aircraft is out of trim in roll due to right outboard aileron upfloat, caused by no power being available to Prim 3 or Sec 2, and neither pitch trim or rudder trim is available. (...)

  Note: I haven't found a reason for the different architecture, but ETOPS is a possibility.

(All bolding, italicisation, etc., original to source.  Kudos to @ymb1 for digging up all this information and explaining it to me.)


How common are emergency landings for airliners? Is there really more than one per day at Heathrow? I've just found an article on one of Italy's most popular newspapers, the "Corriere della Sera", which states that emergency landings are far more common than is normally believed: according to it, at Heathrow there's at least one emergency landing per day. I find this number incredibly high. Is that true?

The article (which is more a collection of "quick facts") doesn't specify the source. I've turned to Google for further info, and the only result I've found is an article by The Telegrpah, which states that the average at Heathrow is slightly above one per week. Even assuming the Corriere journalist wanted to report that figure but got confused and accidentally wrote one per day instead of one per week, it still sounds very high.

An article on abc7ny.com (no idea how reputable that site is) mentions 66 emergency landings at JFK, 50 at Newark and 34 at LaGuardia over a 20-weeks span, from February to June of 2011.

On the other hand, the answers to these two questions on Quora indicate that emergency landings are very rare.

So, if we only consider airliners, how common are emergency landings really?

As pointed out by UnrecognizedFallingObject in a comment, it depends on what is meant by "emergency landing". Is there a commonly accepted definition? If not, since we have to draw a line, I'd say a Mayday counts for sure, and I'd also include a Pan-Pan. Below that, I think we can ignore it.

No, there isn't more than one emergency landing at Heathrow per day

The UK Air Accident Investigation Board (AAIB) defines serious (reportable) incidents in Appendix A of this document.  If we assume that an 'emergency' landing is one caused by one of the incidents in the list, then we can examine the AAIB reports to determine the number of emergency landings at Heathrow (the site supports filters).

I could only find three incidents reported at Heathrow in 2015:

27 July 2015 Airbus A320-232, G-EUYE - In flight fumes
5 February 2015 Airbus A330-323, N273AY - Collided with airbridge
6 March 2015 Boeing 777-236, G-RAES - Air turnback due to flight crew feeling unwell

Only two of these involved an 'emergency' landing.  2015 may not be a typical year, but a cursory check of the reports for 2014 and 2016 to-date suggests that there are very few incidents.

If you want to get a feel for the number of airline incidents and accidents each day, take a look at AVHerald (you might want to make a contribution to Simon's running costs).  That site reports 29 landings at Heathrow after accidents or incidents, of varying seriousness.  You'll see that, of the thousands of flights each day, there aren't that many problems reported.


Why does British Airways fly a short haul flight in a B767? British Airways operate a flight from Edinburgh airport to Heathrow airport every morning in a 767. Aren't these wide-bodies meant for long haul flights?

Aircraft selection for a particular route is quite complex, especially for a large airline that operates many different types of aircraft.  You're correct: generally speaking widebody aircraft are used for longer flights, but there are a number of other factors at play.  Some of these could be that a route has a very high peak demand, where a lot of people want to go from A->B at a given time.  LHR to Edinburgh seems particularly likely to be one of these city pairs.  Sydney to Melbourne is another one, and is only about 400 miles if my memory serves.  In both of these cases there is a dominant national airline in the mix (BA, Qantas) whereas in the USA there are almost always 3 or more large airlines operating any heavy route (New York to Boston, or Washington DC to Chicago, etc).

Aircraft scheduling also plays a role.  For example, the 767 in question might be scheduled to fly from Heathrow to Edinburgh and back in the morning, before picking up a long-haul flight to the USA in the afternoon.  If there's a 4 hour "gap" in the schedule for that particular aircraft, it might make more sense for the airline to run it as a short out-and-back rather than have it sit on the ground at LHR.

Also, Heathrow is notoriously busy, and getting a takeoff/landing slot there is extremely expensive.  The high landing fees are charged at least partially regardless of the size of the aircraft, so there is some economic motivation here to divide those fixed costs by a larger number of passengers.

As another data point, I checked the daily schedule between Haneda (the main domestic airport in Tokyo) and Hiroshima (~400 miles away) and found the following list of flights:  9x 737, 4x 787, 2x 767, 2x 777 - so in this case you have almost half the flights on widebody aircraft, and probably closer to 75% of the total seats.

It's also entirely possible (I haven't checked the schedules) that this 767 run is temporary, due to a period of peak demand or at a point in the year where the demands on that aircraft type are lower elsewhere in the route structure.

So in summary: it's very hard to know all the reasons that a flight might be operated with a specific type.  You need to know a fair bit about the economics of the city pair, the fleet makeup of the airlines, the likely competition for the route, how the route timing interacts with other flights, the congestion level of the airport, and a lot of other things.


Who defines the callsign for radio communication? I started flying with VATSIM and but I couldn’t find a proper answer to this question online. Who defines a callsign for a plane in a given flight? Is a callsign set to a airplane? Is it related to the letters on the fuselage?

The proper procedures for use of aircraft call signs with ATC in the U.S. are spelled out in the FAA Aeronautical Information Manual (AIM).

For Commercial flights the call sign is usually preceded by the company name (e.g., "United two-seventy five").  The last digits (e.g., "two seventy five" [275]) are associated with the city pairs/route that the aircraft is flying.  Flight numbers are internally derived by the carrier based on its needs for publishing/tracking/scheduling.  So, for example, a particular company's flight from SFO to DFW that operates 7 days a week at the same time normally would always carry the same flight number (such as UAL 527 [ I just made up this number for illustration purposes]).

With respect to proper radio communication techniques:

Under normal circumstances (for non-commerical civil aircraft in USA), on initial contact with ATC pilots should state the aircraft's full call sign.  For example - "November 12345" or "Cessna 12345." After initially establishing communication with that ATC facility, during subsequent transmissions, the pilot may abbreviate the call sign by using the "prefix" (i.e., "Cessna") and the last 3 digits or letters (i.e., "345") such as "Cessna 345."

It is never appropriate to not include the "prefix" (i.e., "Cessna" or "November") and only use the last 3 digits/letters (i.e., "345").

From the AIM:


Why did the CAA not use Monarch aircraft to repatriate stranded Monarch passengers? This week Monarch airlines went bust, leaving hundreds of thousands of passengers stranded abroad.

The CAA has been secretly planning for some weeks a repatriation 'airlift' in case the airline folded. Apparently they are chartering 30 or so planes from airlines including Qatar Airways for this.

Since Monarch is now bust, all the Monarch aircraft are sitting idle on the tarmac. Why not use those planes to repatriate people? Surely, it would be a lot cheaper and easier than chartering a whole bunch of other aircraft. They could even use the Monarch crews, who are all now unemployed, after all.

Pondlife pretty much hit the nail on the head.

When a business goes bankrupt or bust, depending on jurisdiction, the assets of the company may not belong to the company anymore, they may belong to creditors. Monarch may not have even owned them in the first place, since some airlines use leases from other airlines or banks to get aircraft.

Even if Monarch did own the aircraft, and they went belly-up meaning the aircraft were basically nobody's, now you have to worry about insurance and liability. The aircraft need to be insured to fly, and there is an assumption of liability if something (like a crash) were to happen. There are logistics like maintenance, repairs, etc. Somebody will have to go through all the aircraft and make sure that they are legal to fly (review logs, maintenance records, etc).

Then you have the crews: they are not employed, and the CAA isn't going to employ a bunch of pilots for a couple of weeks just to run ferry flights. The pilots may demand benefits, etc. It would be difficult or impossible to contract them as private parties (since most insurance companies would not let you do that).

So the easiest option is to let somebody else take care of all that by using charter flights. They have the infrastructure (pilots, planes, fuel contracts, insurance, etc) to get these people out. The CAA just has to call them up and say "we need X number of people picked up from ABC on some-date", and the charter company takes care of it. Of course it is a little more expensive than doing it yourself, but you aren't trying to basically build a short-term airline and then shut it down again.


What is the name of Control equipment? I wanted to know the name of equipment that controls the control surfaces of an aircraft by taking commands from the pilot through it's hotas stick. The aircraft could be a combat 50's or 60's a/c, so possibly there would be a specific name of such control equipment.
Will this equipment be the most safety critical equipment in such an aircraft compared to other equipment such as NAU (Navigation and Attack unit) or will there be any other more safety critical equipment in an a/c?
Edit: Let the a/c be a Mirage.

Most aircraft of that era used hydraulic systems to actuate the flight control surfaces.  And yes, controlling the aircraft is critical to flight safety.


Was the 1992 Gimli DHC-4 Caribou accident ever investigated? On August 27, 1992, 3 people were killed when a de Havilland Canada DHC-4 Caribou crashed immediately after takeoff at Gimli Industrial Park Airport.

Wikipedia describes the accident as follows:

  Three people were killed on August 27, 1992 when a NewCal Aviation turbine-modified de Havilland Canada DHC-4 Caribou they were aboard crashed on the airfield during climb-out after a short take-off from the airport. The aircraft nosed sharply up, arced right and nosed into the ground. […] The cause was listed as failure to deactivate the plane's gust-lock control in the cockpit, […] [T]he Transportation Safety Board of Canada has no record of this incident.

The entire flight was captured on a video which has circulated on the Internet.

Was this accident ever officially investigated? If not, why not?

It was, but from what I can tell the report has not been digitized yet.

The gust locks were left installed. The aircraft was being operated in the restricted category as they were retrofitting with the PT-6’s.

Here’s an analysis from James Donnelly, Bombardier Aerospace. Starts on page 7.

http://www.asasi.org/papers/2001/Four%20Unrelated%20Accidents.pdf

Essentially the rigging was done incorrectly. The gust locks did reduce engine thrust, but didn’t kill it completely. Takeoff roll was 20% longer than calculated.


How to calculate the number of blades? Inspired by building a new drone, I got lost in curiosity.
What if I have a fixed length of rotor blades and a target amount of lift I want to, well, lift. How do you calculate the number of blades?

I have read a lot about disk loading and was intrigued by this answer (https://aviation.stackexchange.com/a/32252/44213) which found a correlation between diskloading and amount of blades (or lift per blade). It made me wonder; is it actually possible to calculate the number of blades? If it matters (and I guess it does) I want to use a naca0012 airfoil.

Searching around I did find the relation between the number of blades and decreasing efficiency/lift per blade when you add a blade. Also the fact that is would be easier to lengthen the blades is something I found. But if lengthening is not an option, how can you actually calculate this? And, to complete the question disturbing me, what effect does a second disk (like the chinook) have on these calculations?

Any help is much appreciated. Any links will be read thoroughly.

Determining the number of blades is one of the steps in designing the main rotor of a helicopter, but not the first one. The main rotor design process is an iterative process with quite a few input parameters, which depend on the mission type:

Max. TO weight
Max. speed
Installed engine power
Autorotation performance
Noise
Manoeuvring g
Blade profile
Blade area
Vibratory loads

Using these inputs, the design process determines:

Rotor diameter. This determines the disk loading: lower disk loading results in better hover performance and auto-rotational performance, higher disk loading in better cruising flight performance.
Tip speed. As close as possible to the drag divergence speed in cruise, also a limiting factor in selecting rotor diameter.
Rotor solidity. How much disk area is actually occupied by blade area, determined by blade stall limits in manoeuvres. Increasing the rotor solidity requires more engine power, but increases the blade stall margin.
Number of blades. Mostly based on dynamic criteria, less on aerodynamic ones. The Bell 212 shows that rotor solidity can be increased by using wider blades, but using more blades minimises vibratory loads and the noise per blade passing.

The rotor design process is quite broad, and can best be found in the theory books which also contain statistical data to aid the initial stages. The plot below is from Leishman and shows that light helicopters have a blade length of about 4 meters, apparently a good length for this weight and mission type.

The overlapping twin rotor disks of the Chinook result in one rotor operating in the wake of the other, reducing efficiency and requiring more disk area. So total disk loading will reduce.

Two good books on helicopter stuff: Helicopter Aerodynamics, Stability and Control by Ray Prouty, and Principles of Helicopter Aerodynamics by J. Gordon Leishman.


Are overwing exits still useable if the flaps can’t be lowered? Essentially all narrowbody airliners (except for the very smallest propliners), and many widebodies as well,1 are equipped with one or more overwing exits for use in an emergency evacuation; these hatches, located at the window ends of rows of passenger seats, open (as the name suggests) onto the wing, from where, during a land evacuation,2 occupants escape off the trailing edge (almost never the leading edge, for some reason) in one of two ways:

On aircraft where the flaps reach within 6 feet of the ground when fully extended (the 737 is an example, as are most regional jets - DC-9, CRJ, etc.), the occupants simply slide down the extended flaps to the ground.
If the flaps don’t reach low enough on their own, as with widebodies, big narrowbodies, and the A320, one or more evacuation slides inflate from the exits over the trailing edge of the wing, providing a safe path down to the ground.

Either case presupposes that the aircraft’s flaps can be lowered completely; even if an aircraft has inflatable overwing slides, these are still designed to deploy over the lowered flaps (a slide designed to deploy over retracted flaps would trail on the ground with the flaps down, impeding egress from the bottom of the slide), while, with low-slung aircraft, the flaps are the slide.  However, many types of malfunctions can prevent an aircraft’s flaps from deploying fully, or at all:

A flap jam at a position other than fully-down will, obviously, prevent the flaps from deployed to the full-down position.
As flaps on essentially-all-but-the-smallest airliners are hydraulically-driven, a total hydraulic failure will render the flaps inoperable; on many-to-most airliners, even a loss of just one or two hydraulic systems will disable the flaps, as the flaps are less critical than the primary flight controls (the aircraft can still be safely landed with flaps retracted without much difficulty, while a safe landing with the primary flight controls inoperative is a crapshoot at best) and require a great deal of hydraulic force to deploy against the aerodynamic loads opposing their downward movement, making them a top candidate to be sacrificed if hydraulic-pressure-generating capability is limited (for instance, if all engines have flamed out and the hydraulics are running on RAT or battery power).

Do aircraft with overwing exits have special procedures for safely using the overwing exits in a land evacuation if the flaps can’t be lowered (or can only be lowered partway), or are the overwing exits simply unuseable on land if the flaps don’t deploy fully?

1: In some widebodies, the role of overwing exits is instead filled by full-size conventional exit doors a short distance forward and/or aft of the wing; these full-size exits allow for faster evacuation compared to the same number of overwing exits (which are limited in size by wing-root structural considerations), but create gaps in passenger seating, and, thus, are only used on aircraft large enough that the extra space required isn’t a problem.  Some widebodies, such as the 767, have both overwing exits and full-size near-wing exit doors.
2: In the event of a ditching, the water level typically comes all the way up to the wings, eliminating that particular problem (although creating several others).

The 737 doesn't have any special procedure for such a case. It would be the Captain's decision to use or not use the overwing exits. Factors such as the usability of other exits, the nature of the emergency, and the number of people on the aircraft would enter into the decision.


How do I determine the VFR pattern altitude at an airport? How do I determine the VFR pattern altitude at an airport? Can I find it on a sectional?

In April 2013, the FAA's Charting Group met to discuss this question.  The standard pattern used to be 800 ft AGL, and the Chart Supplement (formerly called Airport/Facility Directory or A/FD) was inconsistent in listing them.  Ultimately they decided:

  Chris Criswell, AJV-22, reported that, per ACF recommendation, all traffic pattern altitudes, standard and non-standard, will be added into NASR (the AFD) for all airports. This will be a day forward implementation beginning in July 2014.

Some other places the TPA is recommended to be 1000 feet AGL:

Advisory_Circular AC90-66A

  c. It is recommended that airplanes observe a 1000 foot above ground
  level (AGL) traffic pattern altitude. Large and turbine powered
  airplanes should enter the traffic pattern at an altitude of 1,500
  feet AGL or 500 feet above the established pattern altitude. A pilot
  may vary the size of the traffic pattern depending on the aircraft's
  performance characteristics.

The Chart Supplement (A/FD) will typically list the Traffic Pattern Altitude (TPA) if it is non-standard (not 1000 ft/1500 ft AGL)

The FAA's Airplane Flying Handbook says

  The traffic pattern altitude is usually 1,000 feet above the elevation of the airport.

Now the Chart Supplement (A/FD) will be the definitive guide!


In missiles, what actuators are used for the control surfaces? In a normal airplane, hydraulics or even cable-pulled systems are used to power the control surfaces. In a missile, that seems infeasible. What device is used to move the control surfaces, and where does it get its power?

Battery powered servo actuators.
From www.acc.af.mil, for the AIM-120 Scorpion:

The control section consists of control electronics, actuator batteries, and four independently controlled servo-actuators.

Further on the actual AIM-120 control mechanism:
(Courtesy of the Turkish AF http://web.deu.edu.tr/atiksu/ana44/air3.html)

The Weapons Control Unit (WCU)-11/B consists of four independently controlled electro-mechanical servo actuators, four lithium-aluminum batteries connected in parallel, and a steel fuselage section that is bolted to the propulsion section aft skirt. Each actuator consists of a brushless DC motor ballscrew, an infinite resolution potentiometer directly coupled to the output shaft, and pulse width modulated control electronics. The output shaft is engaged directly to a squib actuated lock so that it does not interfere with the fin (control surface) installation and removal.


PIC Emergency Authority Under 14 CFR 91.3 ---> "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."

Under which circumstances will that imply that the PIC deviate from Part 91?

Could it imply that Wx minimums won't apply?

Could it imply that Minimum Altitudes no longer are required?

Could it imply that Wx minimums won't apply?

Yes

  Could it imply that Minimum Altitudes no longer are required?

Yes

Since both of those things are rules under part 91 ("this part") specifically 91.155
and 91.119 you can indeed deviate from them as per 91.3.

The answer to "which circumstances" is far to broad to be defined in an all encompassing way which is why the FAA writes it the way they do.


What mechanism did the turbine reversers of early high-bypass turbofans use? Nearly all jetliners nowadays use fat, efficient high-bypass turbofans (turbofans with a bypass ratio greater than or equal to 5:1).  As the vast majority of a high-bypass turbofan’s thrust comes from the air blown past the engine core by the fan, rather than from the superheated air and exhaust gasses coming out the core’s tailpipe, thrust reversers on these engines generally only redirect the bypass air (saving on maintenance costs and reliability, as the reverser never has to come in contact with the hot, corrosive core exhaust); as such, these types of reversers (usually cascade-type reversers, where the entire rear portion of the fan cowling slides rearwards, although some smaller aircraft use clamshell-type reversers, where several discrete petals open up in the fan cowling to redirect air forwards) are often known as fan reversers (as the air they redirect has passed through only the engine’s fan, and no other rotating parts of the engine).

However, very early high-bypass turbofans (GE TF39/CF6, P&W JT9D, RR RB211), used primarily on the first generation of widebodies (747 Classic, DC-10, L-1011, A300B1/2/4), also included separate turbine reversers, which redirected the engine’s core exhaust.  Apparently, they were unreliable and required frequent maintenance (due to their frequent exposure to the core’s superheated, corrosive exhaust gasses), they were yet another complicated mechanical system on an already-very-complicated airplane, and they provided little additional stopping power on top of that provided by the fan reversers (due to the core of a high-bypass turbofan providing only a small fraction of the engine’s total thrust); as such, most airlines deactivated the turbine reversers on their fleets after a few years.1

The only reference I have handy at the moment that actually points out the turbine reversers is this diagram of the DC-10-30’s wing-mounted (#1 and #3) engines and pylons.  Unfortunately, I do not have access to a copy of the DC-10 Structural Repair Manual, so this is all I have to go on regarding its turbine reversers:

(Image by McDonnell Douglas, via the BEA [page 102, discussing a part which came loose from a different part of the CF6-50 engine, later resulting in damage to another aircraft]; modified by me.)

Other than clearing up the location of the turbine reversers (which wasn’t that much of a mystery to begin with), the diagram provides essentially nothing else in the way of information.  What sorts of mechanisms were used for the turbine reversers on these early high-bypass turbofans?  Did they use a target-type mechanism (the kind that one immediately thinks of when one hears the term “thrust reverser”, with the two big bucket doors swinging out into the airstream behind the engine), like those nearly ubiquitous on the older airliners equipped with turbojets or low-bypass turbofans?  Clamshell doors?  Something else?

1: I can think of one other potential problem; the core exhaust of a high-bypass turbofan is considerably hotter, less dense, and oxygen-poorer than the bypass air, and, thus, would tend to be more prone to causing engine surges were it to travel far enough forward to be reingested into the engine intake.  Even redirected bypass air (heated solely by the compression imparted by the engine’s fan) can easily cause an engine to surge (this is one of the reasons why the use of reverse thrust is not recommended at low speeds, the other biggie being the danger of the engine ingesting loose debris kicked up by the reverser airflow), and the much-hotter and somewhat-less-oxygenated core exhaust would presumably be even more surge-promoting were it to enter the intake; however, I do not, as of yet, have any solid evidence that this was a problem in practice, so this is pure speculation on my part (which is why it’s in a footnote, rather than the question itself).

You're asking about turbine (hot) reversers of early high-bypass turbofans.
747

flickr.com and twitter.com

It had the same mechanism as the cold bypass (blocking doors), similar to what the C-17 (right image) uses nowadays.
L-1011

Lockheed L-1011 TriStar - Airliner Tech Vol. 8

It had target-type, but only during development.
DC-10

Design Features of the CF6 Engine Thrust Reverser and Spoiler (sae.org) and airliners.net

It had– "something else."


How was this airline (statistically) never had a fatal incident? Ryanair make around 725,044 flights per year. This They have been operating for 35 years, so have accrued around 25,376,540 flights.

They have also never had any fatal incidents or even major injuries related to a flight. Statistically, they should have had around 2 or 3 by now at least.

How and why is this airline so much safer, statistically (based on average commercial aviation fatality statistics) than almost any other airline in the world? (Easyjet being the closest with a similar perfect safety record).

First of all, Ryanair has more than 700,000 flights per year now, but not during their entire 35 year existence. The total number of flights you give is therefore too high.

Assuming aircraft accidents are purely statistical (which is not true, of course), one can estimate the number of accidents you expect using a Poisson distribution: the probability of having $ k $ incidents with $ \lambda $ expected incidents is given by

$$ P(k) = e^{-\lambda} \frac{\lambda^k}{k!} $$

To get the expected number of incidents, we take the overall accident rate of 1 in 2.5 million flights (aviation-safety.net, for 2018, has been higher during the last 35 years) and multiply it with the total number of flights. For 25 million flights this would be $ \lambda = 10 $. This results in in a probability for 0 accidents of only $ P(0) \approx 0.004 \% $. Even when assuming 12.5 million flights in total (as suggested by David Richerby in the comments assuming a linear increase from 0 to 700,000 flights per year), one still obtains $ P(0) \approx 0.67 \% $ with $ \lambda = 5 $.

This means Ryanair is indeed safer than the average airline flight world wide, but so are many other EU or US airlines. Safety is not just a statistical coincidence, regulations are very strict in Europe and training is good resulting in higher than average safety records.


Is it technically possible to have nuclear-powered hot-air balloons? Could a balloon use non-fissile isotope, like Pu-238, to heat air in the envelope to stay afloat for years?

let's put political and health related problems aside, and consider if it's technically possible at all. Say, as an unmanned, high-altitude scientific/weather station.

I know that:

Pu-238 has power output of 0.54 watts per gram
Its half-life is 87.7 years (power output halves after that time).
great most of the energy can be radiated out as heat, and transferred to surrounding air.

I don't know what buoyancy can the hot air balloons provide, and what kind of energy input they require to stay afloat. So - would it fly?

Most likely no.

RTG does not have enough power. The burner of the hot air balloon requires 2 to 4 MW of power (here) so you need at least 4 tonnes of Pu to produce that (2000,0000 / 500 = 4000 Kg), assuming 500 W per kg (0.5 W/mg). From the source, a moderate size balloon can lift few hundred kilograms at most.

The true nuclear reactors provide much more power, but they are heavy. Hyperion, for instance, provides 25 MW and weighs 50 tons, so performance per kg is even lower. It could power a cluster of say five balloons, but they would not be able to lift 10 tonnes each.

From the other side, nuclear reactors are probably not optimised for the minimal weight, assuming that just a heat output is required. They are built to match different requirements, so some specially built device may be capable of lifting the balloon.

Lockheed Martin is developing a very promising device.


What is the highest operational ceiling for an air-breathing jet engine? An air-breathing jet engine can only operate at relatively low altitude, where the atmosphere is dense enough. However, some jet-powered aircraft can operate at an altitude higher than 20 Km (e.g., the SR-71). For really high altitude, aircraft are equipped with rocket engines (e.g., the X-15)

What is the highest operational altitude for any air-breathing jet-powered aircraft?

Below[1] shows the hypersonic breathing corridor. Without LOX or rocket assistance, the limit is around 140,000 feet (40 km) at around Mach 15.
In 2004 NASA's X-43 achieved a record Mach 9.6 at 109,000 feet (nasa.gov), which if you compare below, is a good match for the aforementioned corridor.

1: Smart, Michael. "Scramjets." The Aeronautical Journal 111.1124 (2007): 605-619. (PDF)


What is the air temperature inside of a tire right after landing? What is the maximum design air temperature inside of a tyre of an Airbus A380's and a Boeing 747-800's main gear fitted with brakes, before landing after a 10 hour flight and right after landing?  Are there instruments to measure this? Do pilots take readings before and after landing?

Are there instruments to warn pilots about tire irregularities prior to landing? If so, what is the procedure then?

I'm not sure that there is a maximum design temperature and even if there was it wouldn't be that high, probably no more than 120C.

The problem is not the temperature inside the tyre but actually the temperature internal to the carcass. The hot spots are around the bead area and around the cords on the shoulder of the tyre due to the loading. The rubber compounds will start degrading above 160C. This will be considered in the design of the tyre.

The design will have been tested under representative speeds and loads on a rig and the temperatures checked to make sure that the temperatures are within the required limits. At the Goodyear Technical Centre they have a large steel flywheel which they rotate to represent landing speeds and then use a hydraulic ram to simulate the landing gear and push the tyre onto the flywheel. They cycle this several times and then measure the temperatures throughout the carcass.

An under inflated tyre will suffer increased deflection of the carcass and be prone to over heating. Hence the main concern is then to maintain the correct operating pressure. The tyre will have charts specifying the correct pressure to use for the loading and landing speed.


What is a flight leg and why it is so important for an aircraft? A flight leg is basically flight from one point to another point, (I'm not sure if flight leg number increase with touch and go around). I would like to know more about flight leg under what all conditions usually it increases and when it is reset.

Also, most important why is it so important for an aircraft/airlines because usually it is 1 or 2 flight leg per travel. From what I know, flight leg is most important parameter in case of recording or storing data in NVM but I believe flight phase should be sufficient enough.

I don't think flight leg is important for either aircraft no airline.

The reasons why most flights have one or two legs is purely economic. Aircraft have to be operated with rather high load factor to be profitable. If you have a line with less passengers, you really want to use smaller plane or run it less often. Because different links have different demand, it's rather rare to have many consecutive links with similar demand so it would make sense to fly them with one plane as multi-leg flight. And few people would want to fly the whole trip as the stop-overs take rather long.

For aircraft what matters is not legs, but cycles, meaning pressurization cycles. For pressurized aircraft the material fatigue is most closely related to the cycles and since each cycle also involves one period of running the engines at high thrust, the engine wear is also somewhat related. It does not matter whether the aircraft accumulates 4 cycles in 4-leg journey or 4 separate journeys.


Is it normal for visibility to be missing from the METAR? I have noticed at a local airport the AWOS METAR oftentimes is missing visibility measurements. In talking with other more experienced pilots, they tell me this isn't an isolated thing. They indicated that they read between the lines of the other data on the report (or other reports) to get an idea of what weather to expect.

Example:
KTPF 132055Z AUTO 29004KT SCT080 30/22 A2991 RMK AO2 PWINO

The recording always states "VISIBILITY MISSING" meaning it has a sensor and is just... not working?

My questions are:

Is it really normal to see reports without viz?
Why does this happen so often for AWOS when ATIS doesn't have problems with it?
Should this be reported to some entity (NOAA/FAA) to get these systems repaired or exchanged?
The fact that it is missing visibility information does not mean that visibility is unobstructed, right? I have heard people assume this.
If the recording says "VISIBILITY MISSING", is it indicated in the METAR somewhere?

My questions are:

  Is it really normal to see reports without viz?

Yes!  Well, maybe not "normal", but it does happen.  Automated weather stations are like another piece of equipment and components fail from time to time, including the components which measure the visibility.  The other components also fail from time to time (I've see ASOS/AWOS reports without temperature, barometric pressure, etc.)

  Why does this happen so often for AWOS when ATIS doesn't have problems
  with it?

You shouldn't see this at all with ATIS, because a human is involved, and if the equipment which measures visibility is inoperative, a trained observer (often the same person that is manually recording the ATIS) can look out the window and record the visibility themselves.

  Should this be reported to some entity (NOAA/FAA) to get these systems
  repaired or exchanged?

I would let the airport manager know just in case they weren't aware.  They are responsible for notifying the FAA.

  The fact that it is missing visibility information does not mean that
  visibility is unobstructed, right? I have heard people assume this.

If the visibility is missing, it means just that.  It is missing.  It might be 1/4 SM or it might be 20 SM. Some people may make assumptions that if there is no precipitation, that the temperature / dew point spread is high, etc. that the visibility is good, but that is a potentially dangerous assumption because visibility can be influenced by many different things.  There could even be a dust storm coming through when everything else looks good!

  If the recording says "VISIBILITY MISSING", is it indicated in the metar
  somewhere?

Sort of.  It's just "missing" (i.e. the entire wind block from the METAR will not be there), so if you don't see it then, well, it's missing.


What is the format of the airport codes used in an ACARS OOOI message? How are the departure and arrival airport codes in the OUT, OFF, ON and IN (OOOI) fields identified by ACARS and transmitted to ground systems?

For example, if my aircraft is diverted unexpectedly to Bangkok because of some emergency, will ACARS send the arrival airport code as BKK in the IN message? If so, how will it be identified?

ACARS messages, unsurprisingly, use IATA airport codes.

See ARINC 618, 619, 620 etc.

- ACARS, Dr. Maarten Uijt de Haag, Ohio University


Would adding a fairing to landing gear to spin the tires before landing yield enough benefits? I was reading answers to this question: How long do airliner tires last? Can this be improved? and it seems to be reasonable to keep things simple and rethread tires instead of designing motors to spin them up.

However, what if one was to implement a simple aluminum housing like the one in the drawing below which will provide the following benefit.

When gear is deployed, due to friction of air only on the exposed part of tire thread, tire will spin up on it's own.

Has this ever been considered? Why would this kind of design work/not work for large airliners?

NOTE: the inside of the wheels are open for cooling purposes as well as various ducts can be incorporated for efficient cooling of the brakes.

Check out this answer to a similar question. What it boils down to is that pre spinning gear has been looked into but there are implications of spinning up that kind of mass. The rotational inertia created created by doing so effects the handling of the aircraft. On a similar note its often easier to have a simple part that wears out and needs to be replaced often (like a tire) than a complex part that needs maintenance and is more likely to be problematic.

The part you describe is pretty common on small aircraft to reduce drag over the wheels. As far as I know it does not aid in spinning the tires. Since the tires are more or less flush the air simply flows over them.

For what its worth these boots also can get in the way. If the plane lands hard the tires will balloon out and rub up agains the sides of the boot (depending on the tolerances) this may break the boot the tire or both.