What procedures are followed for a planned landing in a field? If an aircraft was making a planned landing in a field/sports ground/other large flat area what landing procedures would be followed?

My thoughts are that it would be very similar to a non-towered airport, with self announcing and flying a bit of a pattern to check the landing area is clear.

Obviously this is more likely to apply to helicopter but it could potentially be a plane.

Not just helicopters. It happens all the time in my neck of the woods (Alaska) in small planes with big bouncy tires. We probably have more "field landings" (called bush landings, or "off airport operations") than landings at actual airports. OK, well maybe not quite that many - but enough that my local aviation college has an entire semester course dedicated to it for it's professional piloting program.

The first act is usually a low pass to inspect the conditions and determine the best landing direction (if there is more than one option), assuming that the winds will allow it. If there are other aircraft in the area, which sometimes happens at popular hunting/fishing/floating drop-off locations or glacier tours, then self-announcing on frequency is done like at a non-towered airport.  But, it's usually remote enough that it's not done.

Quite frequently, it's two planes for one party's charter - one to carry the people, and one to carry their gear. In that case, they're usually talking to each other the whole way, and know each other's intentions anyway.


What is turbulence, and how does it happen? I'm not a pilot, so I always wonder when I'm flying why does it happen... Is it because of bad weather, or something else?

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

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

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

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

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

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


Does the Antonov An-225 have an Auxiliary Power Unit (APU)? Most APUs are installed in the rear, see the above image of an Airbus A380 as an example. On the An-225, no APU exhaust is visible at the rear of the aircraft.

So does the An-225 have an APU, and if yes, where is it located?

No. It doesn't have an APU — it has two of them.

They are located close to the main landing gears. From An-225 Mriya is the world’s largest aircraft (English version):

  Auxiliary power plant consisting of two TA-12 turbofans installed in the left and right chassis fairings provides independent power to all systems and starts the engines.

I think "turbofans" is not the proper term here. Actually the TA-12 is (just) a gas turbine (Wiki (Russian), Google translation).

The location of the APUs being much closer to the tarmac might be a reason why Copenhagen airport has (or had) special regulations for its operation on an An-225 (source):

  Special regulations for AN124 and AN225.
  Aeroplane type AN124 and AN225 must not operate their APU unless the pavement
  underneath is protected against heat and blast effects from the exhaust.

I couldn't find a better picture but the exhaust pipe is quite visible here (red circle):

(Source)

I'm not perfectly sure whether the green circle marks the intake, but I guess so.


Why would a propeller have blades of different lengths? The Schempp-Hirth Duo Discus T powered glider has a five-bladed propeller, with blades of different lengths.

What is the purpose of such an arrangement?

You are right.  They are unequal length blades.  Schempp refers to the propeller as being "noise optimized" and you can see that the blades are free to flap (forward) like helicopter blades (which flap up) so that the asymmetric thrust axis from having the propeller disc offset from the rotational axis doesn't place bending loads on the hub.  And obviously, the blades will be mass balanced to place the center of gravity at the hub axis.

I'll go out on a limb here and say that some genius figured out a way to reduce the horrific noise level caused by such a small propeller by having the blade tips each run in a slightly different path of rotation.  Brilliant.

And here it is in action where the eccentric blade disc can be clearly seen.


How much fuel aircraft should carry to complete flight plan? Here is the question I was looking for (it didn't answer my question though), but this is specific to Boeing 787.

Is there any regulation to carry certain amount (may be %) of fuel aircraft should carry when its flight plan is prepared?

Note: We had argument that aircraft should carry 150% of fuel of it's planned travel, then someone bought argument of hijacking planes and said that 15 to 30 minutes of extra travel time fuel they have to carry.

This may vary elsewhere in the world but according to the FAA FAR Sec. 121.639

Fuel supply: All domestic operations.
No person may dispatch or take off an airplane unless it has enough
fuel--

(a) To fly to the airport to which it is dispatched;
(b) Thereafter, to fly to and land at the most distant alternate airport
(where required) for the airport to which dispatched; and
(c) Thereafter, to fly for 45 minutes at normal cruising fuel consumption
or, for certificate holders who are authorized to conduct day VFR
operations in their operations specifications and who are operating
nontransport category airplanes type certificated after December 31,
1964, to fly for 30 minutes at normal cruising fuel consumption for
day VFR operations.


What's the difference between "HAND OFF" and "HAND OVER"? I think "HAND OVER" is a whole process of transfering radar idenrification between 2 controllers, and "HAND OFF" is a term used by the transfering controller(not receiving controller) when doing HAND OVER.

Am I right?

In the U.S. Air Traffic Controllers initiate handoffs and receive handoffs.  Perhaps the term "hand over" is general term applied to the process of making/receiving a "handoff."

Here is the definition of "Handoff" from the Pilot/Controller's Glossary in the FAA JO Order 7110.65W, Air traffic Controller's handbook:

  HANDOFF
  −
    An  action  taken  to  transfer  the  radar
  identification  of  an  aircraft  from  one  controller  to
  another  if  the  aircraft  will  enter  the  receiving
  controller’s airspace
  and radio communications with
  the aircraft will be transferred.

I am unable to find the term "Hand Over" in the 7110.65W.


How does an airline decide on an engine? How does an airline, when buying aircrafts, decide on which engine to use? In many cases, although there are several options to choose from, the engines do not differ much in their operating parameters.

As an example I would take the Boeing 757-200. This aircraft was able to be equipped with Rolls-Royce RB211 and Pratt&Whitney PW2000. Both engines have very similiar performance ratings and also do not differ much in their physical parameters (e.g. diameter, weight).

From this perspective, it seems to me, that engine decisions are mostly driven by business consideration (e.g. sales discounts, maintenance contracts...)?

I think you are answering your own question. It all boils down to money. Every factor of the aircraft buying process will be driven by money. They are, after all, a business. Some decision driving factors may include:

The acquisition cost.
The operating cost.
Fuel efficiency. Fuel costs the airline money
The reliability. Down time for the aircraft loses the airline money.
The liability. Is it going to breakdown midflight and cause death and lawsuits?
Manufacturer support. Will they get help if problems arise?
Is their an adequate supply chain of parts?
Airline’s specific history with that engine.
Does the airline already have mechanics certified and experienced for that engine?
Do they already have parts and spares of that engine?
It is easier to maintain only one type/model of engine across their fleet than several.
Tax incentives.
National loyalty for some airlines.
Brand loyalty for other airlines.
Kickbacks
TBO. Maintenance costs money.
Core resale value.
Possible advertisement opportunity.
Contractual agreements.
Politics (both internal and external)
Etc.


Is it safe to takeoff with some ice and snow on the wings? I took a look at the post 'What things can a passenger look out for, to indicate an emergency?', and remembered this video I've seen.

Obviously, video uploader claims that this take off was unsafe due to some ice and snow on the wings. Was he right? Were the pilots really breaking any regulations?

It appears that there was a considerable amount of contamination, either snow, ice, frost, or a mix thereof, on the wing when the takeoff roll started, and that is not considered safe under any current standards I'm aware of.

There are markings on the top of the wing for the 737 Next Generation series that define an area where cold-soaked fuel frost is acceptable up to a defined thickness, but the area covered by the contamination in the video extended beyond those markings, so even if it was CSFF (which I doubt, given what's shown late in the video), it was still more than what's allowed.

Late in the video with the aircraft flying, we see that much of the ice is no longer present, which means that it detached from the wing at some point.  If it was dry snow that blew off in the first 10 or 20 knots of the takeoff roll, that's no big deal, but you don't see the ice gone until late in the video -- this isn't simply dry snow.  Plus, you still see significant patches of ice adhering to the wing at the end of the video -- which suggests that it isn't CSFF nor dry snow, but ice.

The current accepted standards of safety in commercial aviation don't permit taking off with any ice adhering to the wing, and from what is shown in the video, it certainly looks like that's what was done here.  (Disclaimer, I'm no expert on watching u-tube videos of ice-covered wings, so there may be more going on here than is apparent on first or second viewing.)  IF that's correct, then I'd have to agree with the title of the video, that this was unsafe.

The standards of safety allow for a lot of margin, so that when mistakes get made they are still likely to be survivable, and it looks like that's how things turned out here.  Things were done wrong but everybody made it out okay.  But... what if one more thing had gone wrong?  What if they'd lost an engine at rotation?  Would the aircraft have been able to climb out with one engine & the wings in this condition?  Or would these guys have been headline news of a crash out of Sarajevo that killed all on board plus how many more on the ground?

No, this looks pretty far out of bounds to me.


Why do airlines have intermediate stopovers with no passenger boarding? I fly regularly KLM 573 from Amsterdam to Dar es Salaam. This flight does a stop over in Kilimanjaro International Airport and no passengers are boarded, but passengers are disembarked.

There are also other flights of other airlines that I know of that do this (Turkish airlines, Swiss International).

Why is this done? Wouldn't it be more of an advantage to pick up some more passengers in a short intermediate flight in order to maximize profits?

Or does the hassle of loading/unloading luggage and passengers make it less viable?

DeltaLima is correct but there is a little more to the story which he hints at in his link. This topic is known as Freedoms of the Air. There are five official in total, each dictating in what way an airline may operate in a foreign country. What KLM has done is a:

Normal stop for those getting off.
Technical stop for the onward passengers.

Both are less controversial than what would essentially be letting a foreign operator offer flights in your country, which would not help local carriers ( and which would constitute Cabotage as DeltaLima says).
The technical stop is defined in the second freedom of the air:

Second Freedom of the Air - the right or privilege, in respect of scheduled international air services, granted by one State to another State or States to land in its territory for non-traffic purposes (also known as a Second Freedom Right).

The Third and Fourth Freedom states that the airline can load and unload passengers in a foreign country for transport to and from the carrier home country:

Third Freedom of The Air - the right or privilege, in respect of scheduled international air services, granted by one State to another State to put down, in the territory of the first State, traffic coming from the home State of the carrier (also known as a Third Freedom Right).
Fourth Freedom of The Air - the right or privilege, in respect of scheduled international air services, granted by one State to another State to take on, in the territory of the first State, traffic destined for the home State of the carrier (also known as a Fourth Freedom Right).

(Needless to say, 3 and 4 go hand-in-hand)
Source: ICAO
See also this Boeing document for easier reading.
The other option, aside from not doing it for legal reasons, is that KLM cannot justify the trouble and cost of doing it.

Setting up more domestic presence (websites, additional staff, pricing in regard to competition) in a foreign country is a somewhat complicated business.
There would be additional waiting time on the ground when stuff was loaded and paperwork sorted out.
Furthermore, I imagine that KLM would like to block the free seats for the complete leg as long as possible (which would generate the greatest revenue), so the actual number of available sub-segments for booking would not be that great.


What is "Block burn" and how is it calculated? I have heard a couple of times the term "block burn" in the aviation industry but I am not sure to what it exactly refers. My second question is how is it calculated? I have also heard it depends on seasonal data

I have no idea and no connection with the aviation industry so I looked it up. I found

Block Fuel / Ramp Fuel / Total Fuel On Board
Block fuel is the total fuel required for the flight and is the sum of the Taxi fuel, the Trip fuel, the Contingency fuel, the Alternate fuel, the Final Reserve fuel, the Additional fuel and any Extra fuel carried. Source: Skybrary.aero.

That in turn led me to look up 'aviation block' and I found

Perhaps you’ve noticed that flights flown on different airlines between the same airports take different amounts of time. You might reasonably ask: why would different flights, departing from and arriving to the same airport take different amounts of time? The total amount of time a flight takes — from pushing back from the departure gate (“off-blocks”), to arriving at the destination gate (“on-blocks”) — is called “block time”, and airline block times vary for the same routes. Source: FlightStats.

I guess that block burn is the amount of fuel burnt between the departure gate and the destination gate.

My second question is how is it calculated?

Start fuel - end fuel, I guess. This can then be tabulated and used for future flight block burn calculations.

I have also heard it depends on seasonal data.

Many operational factors will vary by season so this seems reasonable.


How close are we to replacing pilots with computers? Recently someone on another thread recommended the following video:

Andrew Godwin - What can programmers learn from pilots? - PyCon 2015

where the speaker, at about ~3:14, talking about pilots mentions:

  not to the point where we can replace them with computers, because we're not there yet

which got me thinking:

How close are we to replacing pilots with computers? (like totally)

As a person that "tries to replace pilots with computers" I personally say: not even close.

The processing power (certified for flight, not the latest pentium sitting under your desk) is too behind, in particular concerning the point here below.
Synthetic vision is still extremely lacking. This is currently the biggest hurdle to overcome. While pilots can look out of the windows and assess the situation (with some limits, admittedly), computers still have several problems with it, starting from a general lack of cameras and going all the way to the daunting level of processing power required.
Ability to adapt is still a long way to come. Computers are "fundamentally stupid", they do what they are told (programmed) to do, they are not capable of adapting to an unforeseen (and never experienced before) emergency. There are several people working in machine learning and the field has advanced significantly in the latest years, but good luck certifying those programs.


What does the ‡ symbol in the Chart Supplement (A/FD) designate? In the Chart Supplement there is occasionally a ‡ symbol after the operating hours for control towers (and other time information) like what's shown below.

What does the ‡ symbol represent?

The ‡ symbol in the A/FD specifies that the location observes daylight savings time.

This is from the A/FD legend, which can be found online by going to the online digital A/FD and searching for an airport.  The A/FD Legend link will then be at the top of the search results (unfortunately the link changes every cycle so I can't include an exact link).

  6 TIME CONVERSION

  Hours of operation of all facilities are expressed
  in Coordinated Universal Time (UTC) and shown as ‘‘Z’’ time. The
  directory indicates the number of hours to be subtracted from UTC to
  obtain local standard time and local daylight saving time UTC–5(–4DT).
  The symbol ‡ indicates that during periods of Daylight Saving Time
  effective hours will be one hour earlier than shown. In those areas
  where daylight saving time is not observed the (–4DT) and ‡ will not
  be shown. Daylight saving time is in effect from 0200 local time the
  second Sunday in March to 0200 local time the first Sunday in
  November. Canada and all U.S. Conterminous States observe daylight
  saving time except Arizona and Puerto Rico, and the Virgin Islands. If
  the state observes daylight saving time and the operating times are
  other than daylight saving times, the operating hours will include the
  dates, times and no ‡ symbol will be shown, i.e., April 15–Aug 31
  0630–1700Z, Sep 1–Apr 14 0600–1700Z.


How often are heavy aircraft brake pads changed? How often are Boeing 747-800 and Airbus A380 aircraft brake pads changed?

The 747-800 uses carbon brakes made by the Goodrich company and according to this article,

  The entire industry is leaning towards carbon brakes, Honeywell
  executives assert. Lufthansa Technik also sees a trend towards carbon
  brakes, as the mean time between repairs (MTBR) for carbon brakes is
  1,500-2,000 cycles, compared with some 1,100 cycles for steel brakes.

Also of note, take a look at this video on the testing of the brakes.


Are there cases where a double horizontal stabilizer is useful? I was watching Agents of Shield recently, and in it the team fly a plane that's claimed to be a modified C-17 Globemaster. It has two extra engines, rotary turrets, and, according to the wiki, a pair of half-length wings at the rear of the fuselage, seen here:

(image courtesy of Agents of SHIELD wiki)

To me, it also kind of looks like a second horizontal stabilizer. Certainly some of the modifications to this fictional plane are pure flights of fancy, but is there any basis behind this one? Is there any reason why this feature would be useful? Have there possibly been any experimental or production aircraft with something like this? Or is this pure "cool factor," with no real basis in aviation?

The main aerodynamic purpose of the horizontal stab (or certain canards) is to provide longitudinal stability.

If the rear wing with the 5th and 6th engine flies "up," like the main wing, then it will counteract the longitudinal stability of the horizontal stabilizer. If the rear wing flies down, like the h-stab, then it is just extraneous, since the h-stab can be made as large as necessary.

If all you want to do is to add extra engines, they can be mounted on the main wing, like in the eight-engine B-52 bomber:

or the six-engine Antonov An-225 cargo jet:


Can the emergency slide be re-used after it has been deployed? Can the emergency slides be re-used and re-packed after they have been deployed, assuming no damage is done?

For example, I heard of a case where the slide was accidentally deployed due to opening of the main door when it was "armed". This resulted in the slide partially deploying and landing on the air bridge.

Sure. In fact, the emergency slides have to be removed from aircraft and tested periodically under present regulations.
According to Lufthansa Technik:

Under current regulations each emergency escape slide must be removed from the aircraft every three years and checked in the workshop.
The slide is tested by "flat firing" the slide on the floor; the test confirms that the slide inflates properly within two to ten seconds, depending upon the aircraft and type of slide.
The inflated slide is also checked in the workshop at over-pressure to test that seams retain their integrity under extreme loads. The slide is also tested for its ability to remain properly inflated for several hours.

This testing cycle varies according to the OEM/operator. For example, according to Boeing, the B747-400 slides have a 12 year testing cycle. In addition, they are checked regularly depending on various factors like its age etc. According to Udo Janssen, Lufthansa Technik’s director of emergency equipment,

At approximately 15 years of age, the first signs of aging appear with the materials—porosity of the fabric, seam peal, or pack board delamination. That is the reason why, after 15 years, the OEMs change the inspection schedules from three-year intervals to yearly cycles.

During these tests, the slides are usually inflated either fully or partially. So, the undamaged slides can certainly be reused.


How do power and thrust curves compare? I would like to really understand why when talking about jets we care about thrust but when talking about propeller aircraft we care about power.
(THRUST)="Just a force"
(POWER)= work/time = force x velocity
I know that even though propeller aircraft are called "power producers" and not "thrust producers" as jets, any aircraft needs Thrust because that's what overcomes Drag. The difference is that a prop aircraft uses the Power of the engine to turn the prop while a turbine engine produces Thrust by itself.
I also know that total drag curve comes from induced drag (decreases with airspeed) and parasitic drag (increases with airspeed), so that is exactly what thrust needs to overcome. The total drag you get at a given airspeed is equivalent to the thrust you need to stay level. That makes a lot of sense.
I have no problem with jet theory when thinking about that and the Thrust required / Thrust available curves.
Why is it different for prop aircraft? Why is the power curve important? I mean, aerodynamically. Because I've seen that total drag curve is also the same as Power Required Curve and I don't understand why.
My first thought is:
Engine power is important because that is what the prop will use to rotate and generate Thrust. (Propeller efficiency is directly related with HP and other prop aerodynamic factors). However, even with the most powerful engine, if prop efficiency is poor because of the other factors, we won't get too much thrust and that's the only thing that matters. And one more time, thrust is what makes any aircraft fly forward, so total drag is thrust required, not power.
Vx speed is found where the greatest difference between thrust available and thrust required is. Greater excess thrust equals greater angle of climb. (Got it!) that's very logical for me.
But: Vy is where the greatest difference between Power Available and Power Required is found.
What?! Why?! How can the power the engine produces relate with airplane's aerodynamic?? It has nothing to do with that. Vy is best rate of climb, the airspeed at which the airplane will get faster to an altitude. I think that the reason should be related with a thrust/drag ratio.
On the other hand, I know that the Power Curve results from multiplying each thrust value times each airspeed value of the thrust curve. That's the fact, just let me explain why it doesn't make any sense to me...
Power=force x velocity, and we can apply that in different ways. If we were talking about electricity we could say Power is measured in Watts, and Watts= Voltage x Current. Because we are talking about prop aircraft, we should use a power unit like HP (for reciprocating engines). HP= Torque X RPM.
Multiplying the Thrust Curves to get Power Curves would mean that Power= Thrust x Airspeed
What kind of power are we getting when multiplying thrust times the airspeed at which the airplane is flying?
Wouldn't that be something like "Aircraft power = thrust x airpeed" or in other words "the amount of power needed to stop that airplane"? Nothing to do with the engine (which is really the reason why a prop airplane is called "power producer")
I'm very confused, even tired of not understanding the exact reasons behind this after reading what should be sufficient. I think I know what power and thrust are, but I just can't understand the way they relate, and to be more specific, how does excess power affect the aircraft flying in real life, aerodynamically. Why to talk about Power instead of Thrust in any case, jets or props. (It's clear there's a good reason not to, and that's what I want to finally understand). Maybe more realistic examples or comparisons instead of graphs and curves would help.
(But those are not a problem either in case you want to try.)
I'm a student pilot and I hope I was clear enough with my doubts and explanations.
(Also with English since Spanish is my native language)

Aircraft power curve
(a.k.a “polar”—a completely illogical name because somebody long ago plotted them in polar coordinates, which makes no sense, but the name stuck)
This is just the power balance of the aircraft: the power provided by the propulsion system minus the power taken away by drag.
You can divide the values by velocity (true airspeed) to get a force (thrust - drag) curve instead. But usually just the power curve is plotted and lines through origin are used to read the interesting force maxima.
Two useful observations can be made about meaning of the power and force here:

Excess power is linearly proportional to sustainable climb rate, simply by $P = m g v_v$ (where $P$ is power, $m$ is mass of the aircraft, $g$ is gravity and $v_v$ is vertical velocity).

Excess thrust is linearly proportional to sustainable angle of climb. Well, actually there is some tricky trigonometry involved, but at low angles (non-aerobatic aircraft only do very shallow climbs and descents, below about 10°) you can approximate $\sin x \approx x$ and $cos x \approx 1$ and say that $T = m g \gamma$ (where $T$ is thrust, $\gamma$ is flight path angle and $m$ and $g$ as above).

This is true independent of what kind of propulsion, if any, the aircraft has. Power curves work the same for propeller, jet and rocket aircraft and gliders alike. Just the function describing power available for given speed differs by the propulsion type.
Kinds of power
A propulsion system is a device that converts one form of energy to another with some efficiency. So in has input power ($P_{in}$)—which is the rate at which energy comes in—and output power ($P_{out}$)—which is the rate at which it provides the desired energy. They are related by efficiency ($\eta$: $P_{out} = \eta P_{in}$). The rest of the energy—because energy is always conserved—is wasted (often as heat, but in aircraft propulsion the energy given to the reaction mass, the air, is also wasted).
Powered aircraft usually use internal combustion engines consuming hydrocarbon fuel, so the input energy is fuel flow times heating value of the fuel.
The output power of the whole propulsion system is then the energy given to the aircraft (to replace the energy taken away by drag), and this is always thrust times velocity. They are related by the propulsive efficiency, which varies with velocity, and varies differently for different propulsion systems.
When propeller is used, you can split the system in two parts, with their own separate efficiencies: The engine burns fuel, drives the shaft, and wastes the rest of energy as heat of the exhaust gases. It's output power is the torque times shaft speed (the RPM). The propeller then takes this power as input and accelerates some air to produce thrust. But doing so it has to sacrifice some energy to that air (its kinetic energy increases), so its output power is lower than that of the engine.
Note to units

Power=force x velocity, and we can apply that in different ways. If we were talking about electricity we could say Power is measured in Watts, and Watts= Voltage x Current. Because we are talking about prop aircraft, we should use a power unit like HP (for reciprocating engines). HP= Torque X RPM.

Power is always the same dimension, and therefore its basic unit is always Watt. This is a derived unit composed as $\mathrm{W} = \frac{\mathrm{J}}{\mathrm{s}} = \frac{\mathrm{kg}\ \mathrm{m}^2}{\mathrm{s}^3}$. Power is voltage times current for electricity, and the units work out, because $\mathrm{V}$ is just $\frac{\mathrm{kg}\ \mathrm{m}^2}{\mathrm{A}\ \mathrm{s}^3}$ (and Ampere is a base unit).
For fuel, power is heat value, in $\frac{\mathrm{J}}{\mathrm{kg}}$, times flow rate, in $\frac{\mathrm{kg}}{\mathrm{s}}$ and we are at Watt again.
And of course torque in $\frac{\mathrm{kg}\ \mathrm{m}^2}{\mathrm{s}^2}$ times angular velocity in $\frac{1}{\mathrm{s}}$ gives you Watt again. (watch out here; it requires angular velocity, in radians per second, not revolutions per second, but radian works as dimensionless here (metre per metre), so this is prone to error by $2\pi$ that dimensional analysis won't catch).
A horsepower is not an independent unit, just a funny multiple of Watt. Multiple different multiples of Watt, actually, because there are some variants.
Engine power as function of velocity
Piston engine power grows with RPM, then plateaus (at the expense of declining efficiency) and then you hit the maximum permitted RPM.
A constant speed propeller allows running the engine at the optimal RPM, and it's efficiency only decreases slowly with airspeed. Therefore a piston engine with constant-speed propeller produces relatively constant power over the design range of the aircraft, while the thrust declines about inversely proportionally to velocity. Thus it makes most sense to give power as the main figure describing it.
With fixed pitch propeller, you are limited by not being able to reach the optimal RPM at low speeds, and by having to throttle the engine to avoid exceeding the maximum RPM at high speeds, so the power declines faster as you get away from some optimal design speed. That's why fixed propellers are only used on slower planes where it does not matter that much. The power curve is still flatter than the thrust curve (dividing by velocity), so it still makes more sense to give power as the main figure though.
With turbojet engines on the other hand the available thrust remains roughly the same. It first declines with speed somewhat similarly to a propeller, but then the ram pressure starts increasing the effective pressure ratio and the available thrust starts growing again. That's why jet engines are generally rated with thrust, not power. But it isn't really constant over speed, just like the power isn't really constant for a piston engine and propeller.
And this carries over to turbofan engines, that are actually somewhere between. Their thrust decreases with speed, though slower then for propellers, and their efficiency increases. It is an oversimplification to rate them with just static thrust, but it remains the primary value given.


If a pilot has the wrong altimeter setting, will his transponder mode C altitude be off too? Just wondering if the transponder mode C reported altitude will be off if the pilot accidentally has the wrong altimeter setting.

No your altimeter setting has no effect.

The altitude signal for mode C comes from a separate pressure altitude sensing "blind" encoder that only supplies the transponder, or an equivalent device integrated into the transponder itself, or a pressure altitude signal coming from an Air Data Computer on a larger aircraft.  It reports pressure altitude to a resolution of 100 ft.  So as you are climbing between 1000 and 1100 ft, ATC's indication will roll over from 1000 to 1100 at somewhere around 1050ft, from 1100 to 1200 somewhere around 1150 ft, etc.

So if you make the wrong altimeter setting and level at a cleared altitude and the pressure altitude reported by your transponder is off by more than 1 or 200 feet from the pressure altitude they expect to see, ATC will inquire about your altimeter setting.


What role, if any, does visual aesthetics play in the design of modern airliners? Another way of asking the question:

  Are there any distinctly identifiable features of particular modern airliners that are there for design reasons that have less to do with engineering than with appearance?

or:

  Could one look at at a modern airliner, and point out something in its design, however small or large, that is there because "it looked good"?

To be clear about a few points:

By modern I mean since the 707.
In visual aesthetics I only want to include physical form - contours, placement of parts, proportions etc - and specifically want to exclude livery, colour, and so on.
I'm not interested in inessential matters like the design of the interior, but in the airframe, engines and so on.

I'd be pretty surprised to discover that any aspects of design allowed aesthetics to trump engineering consideration, but perhaps there are examples where aesthetics played a part because the choices, from an engineering point of view, were equally viable.

A friend of mine, who did the design of the Gulfstream G650 canopy, designed the cockpit windows on that jet after the lines of an Aston Martin sports car.  I suspect there are a few other features like that in various aircraft.

That being said, despite the aircraft design mantra of 'if it looks good it will fly good' most the the design choices made in aircraft is very utilitarian.  Aerospace engineers - and in particular the management at the major OEMs - are some of the most boring, unimaginative SOBs you will ever meet.  They generally leave creativity to the marketing departments and make every effort to pound flat any nail that sticks out.

The only exception to that rule that I can think of was Burt Rutan of Scaled Composites, who when his own way and designed unique planes as virtual works of art - but also were highly functional with great performance and capabilities.  From the Vari-EZ to Spaceship One, that guy is in a league of his own.


Couldn't airplanes have more emergency exits? Being near an emergency exit improves considerably the survival chances after an accident. Why not put one exit at every 5 rows?

Money.

Doors cost (and weight) a lot more than plain aluminum panels. And the exit row on larger planes usually consumes one row of seats. So lets say we are on a 767 and take out every 6th outer row, that's 5 extra exit rows and 20 fewer paying seats, or $6,000 less per flight which quickly adds up to nearly the cost of the aircraft itself over its service life. And that's quite a lot of money for something that will very likely never be used. Remember that exit doors only help if the plane crash-lands in a mostly upright position. Severe crashes often add large exits by splitting the fuselage open, and lawn-dart mode accidents don't leave too many survivors.

The flying public has indicated that they are very interested in ticket price, but somewhat less interested in the safety factor. The current accident rates appear to be acceptable to those paying for the service.


What is this helicopter (and probe) in the film "Act of Valor"? In the film Act of Valor, two helicopters are used to airdrop troops and their boats onto a river. (Clip here.)

Firstly can you identify the aircraft?
Second, what is the extremely long probe on the front? It looks to be half as long as the actual helicopter!

My initial guess would be some type of Chinook and refueling probe but that's purely guessing. Can anyone verify or correct?

By U.S. Navy photo by Mass Communication Specialist 3rd Class Robyn Gerstenslager [Public domain], via Wikimedia Commons

Yes, it looks to be a Boeing CH-47 Chinook. Above is a photo from Wikipedia showing an Army Chinook with a Navy SWCC boat attached to the external cargo hook, looking almost exactly like in the movie.

And yes, the probe is the refueling probe. It needs to stick out from under the rotors, to prevent the rotors from accidentally cutting the fuel hose. (Although it doesn't prevent this from happening.)


What uses for flight did early aviation pioneers envision? Between 1903 and 1914, what did the aviation pioneers think flight would be used for, besides military purposes? Did they envision anything like crop dusting, commercial transportation, charting terrain in the wilderness, scientific study of the atmosphere, etc.? Even just pure entertainment flights?

I did read this little article about the Wright Bros thinking it would actually deter war, but it didn't mention if they had thought of some alternative use to warfare.

There are of course many aviation pioneers from those days. Did any of them envision uses besides war? It would be really interesting to see what they came up with and if it turned out that way.

"Airship" originally meant any large aircraft, whether lighter or heavier than air. Ballooning was already a popular sport among the rich when aeroplanes first flew. Most pioneers seem to have taken it for granted that aircraft - both airships and planes - would be used for private and commercial travel as well as warfare. Airmail was perhaps the most discussed niche role. A few might have had other niche purposes in mind but on the whole they were content just to get the thing flying and find a buyer or sponsor. A V Roe built the first plane with an enclosed passenger cabin in 1912, the first year a mail package was delivered by air.

J W Dunne was one of the few influential pioneer aviators from a military background and argued for a variety of specialist types for different military roles. He was also a friend of writer H G Wells. Together they envisaged total war with vast airship fleets capable of wrecking whole civilizations and hoped that the threat of this would put an end to ground warfare as such. When Wells wrote "The War in the Air" (around 1908?), Dunne sent him some of his research materials which found their way into the story.

Rudyard Kipling (of Jungle Book fame), though not an aviator himself, wrote a novel about a commercial transatlantic mail airship, "With the Night Mail" in 1905.


Are there any data on the safety rate of gliders vs single-engine GA aircraft? Can anyone point me to statistics on the safety record of gliders vs. single engine general aviation aircraft?

I had three days to burn so I took a look.)

Comparative data was very difficult to find beyond accident counts, so determining relative safety is problematic. No one that I could find tracks or estimates the number of flights/hours for gliders, even the Soaring Society of America, so this is all interesting but essentially meaningless. Even if such data existed, the difference in use models would cause problems making a fair comparison. So now that I've told you this was a waste of my time to compile, I will make you waste your time to read.

If you could extrapolate single mode pilot certificate counts to a common usage basis, flying a glider is 2.5x safer than flying an airplane, but of course you can't.

NTSB accident count for 2017 shows 56x more airplane accidents and 90x more fatal airplane accidents than glider accidents.

271 fatal and 972 non-fatal GA airplane accidents, total 1243
3 fatal and 19 non-fatal GA glider accidents, total 22

US Civil Airmen Statistics shows 18x more airplane only pilots than glider only pilots, with 40-80% of both numbers muddied by multiple certificate pilots.

14k registered glider only pilots
24k registered glider pilots with multiple certificates
260k registered airplane only pilots, excluding ATPs
190k registered airplane pilots with multiple certificates, excluding ATPs

AOPA had a report for 2009 for all general aviation where the accident rate per 100k hrs is 7.2, and a fatal rate for the same of 1.33.


How are Rolls-Royce engines different to others? I heard that Rolls-Royce engines has 3 engine spools.
Are they different in design compared with GE, PW engines?

thanks

Yes, RR engines typically have 3 spools while GE and P&W generally have 2.  There are several design tradeoffs.  Briefly:

3 spools are easier for the aerodynamic design. For example, compressor stall can happen when the front stages of the compressor are pumping more air than the back stages are able to accept.  On a 2 spool machine, the front and back stages are all on the same shaft going the same speed.  However, on a 3 spool machine, the front and back stages are on different shafts.  So one shaft can speed up or slow down to better match the stages.  To work around this issue, 2 spool machine usually need to have more variable geometry (such as variable stator vanes) than 3 spool machines.

2 spools are easier for the mechanical design.  Every spool needs to be supported by bearings.  More spools means more bearings.  Bearings have to be supported by frames and cases.  More bearings means more frames (or more complicated frames).  Every spool has critical speeds. So more rotors means more possible critical speed issues.

There is not a clear winner.  2 spools are better for some things but 3 spools are better for the other.  Each company is going to tell you that theirs is "the best", but really they are about even overall.


What do you do when your engine quits right when the airplane starts off the ground? This has been one of my fears in flying (a plane the size of Cessna 152). I sort of know what to do when the engine quits on you when you are a few hundred feet off the ground, although it is definitely not easy to manage. However, lets say you are just past the rotation speed and have very little runway left. Is there anything you can really do other than cut power, retract flaps and try not to set your brakes on fire?

Edit: I am assuming that I am barely 10 feet above the runway. I suppose this is a more specific version of the general case of engine failure at lift-off.

The first and perhaps most important thing to do is NOT turn around. Generally speaking you won't have the airspeed/altitude to make a full 180 and return to the field. While it can be done, it's advised to continue forward and put the plane down as you would in any emergency. Trim for best glide and pick a landing spot (limited options in this case).

In some cases with small plane/long runway situations you will be able to execute something like a short field landing with the remaining runway but that is very situationally dependent. When I flew out of KPNE in a Warrior 24 was 7000ft; if you lost an engine at rotation you had plenty of runway. At DYL where I fly now that's not really the case. Every airport is different but a good deal of the airports I have flown out of recently have had long fields at either end of the runway giving maybe an extra 1000 ft or so. Airports in populated areas may have roads you can touch down on.

You should always consult the POH of the specific aircraft in this case for proper emergency procedures.

Specifically to the 152 point, the take off distance is around 1400 ft. full loaded if memory serves. Unless you are training on 2000 ft strips you should have no problem getting the plane back down with remaining runway at all but the shortest of fields. If you are only 10ft up you should be able to put the plane down fast, albeit a bit hard, but fast none the less. For what it's worth Cessna landing gear can take quite a beating. Once you have touched down it would be advised to retract your flaps, this will increase the load on the gear (by reducing your wings' effectiveness) and increase brake effectiveness. You should take care to not lock the brakes as well.

Side Story: This happened to a buddy of mine in his Archer a bunch of years back (I'll try to find the incident report). The plane was fresh out of annual and something was not hooked up correctly and shook loose on take off causing the engine to cut out around 100ft or so. There was a corn field dead ahead and he was able to put the plane down smoothly. Thankfully no one was hurt and he simply owed the farmer for the corn he took out on landing….


Is this plane landing or departing? I have a picture of Air Force One I took fairly up close several years ago.

Unfortunately, I don't remember if that was on arrival or departure.

Is there anything visible in the airplane's configuration (flaps, angle of gear?) that would indicate if this is arrival or departure?

The plane is probably taking off.  The flaps are hard to see but they don't quite look to be extended enough for landing (Looks like flaps 20).  On a 747 they extend to around 45 degrees (flaps 30, but they curve around more than that) for landing and have a huge, unmistakable profile.  Further, we know it's KBFI and we know the plane is on 31L from the photo.  Looking at the area we can deduce... (click for bigger)

...that the plane is about 3500ft into the runway proper, and 4500ft if we count the displaced threshold (and just off the ground) with the face of the southmost Jorgensen Forge building visible in the background (along with the green GA hangars).

At 3500-4000ft into the runway, hovering over the last markers in the TDZ, this seems quite late to be a landing.  It might be a very deep float, but I would expect more precision from an Air Force pilot flying the CINC around.  Air Force One is heavier empty, but probably overall lighter than a loaded 747-200 (and has powerful engines), so a 4000ft takeoff run for a light 747-200/VC-25 is sensible and probably more likely than an extremely late landing.
The flaps are more than minimum for takeoff, but seemingly less than normal for landing. Maybe 31L was running shortened that day?  Entry at B10 onto the displaced threshold would also give them an extra 1000ft - V1 just past the aim point and rotate near the end of the TDZ markers seems sensible enough.

EDIT
After running a series of simulations, it seems difficult for the VC-25 to be able to takeoff from where we see it, even when starting from B10. The VC-25 is 525,000lbs empty.  With only 100,000lbs load (fuel+people) it can takeoff by B5 at flaps 20, but only by lifting off below V2 (no wind).  This has to be a landing (confirmed by the newly discovered set of photos), but it is a very late landing indeed.
It also seems that military aircraft of the United States are exempt from the requirement to execute a missed approach in the case that they can't make the landing within the TDZ by DA/DH (using "normal" maneuvers), so perhaps the pilot just didn't care and bobbled it in anyway.  The plane did touch down in the TDZ, but just barely.


What do pilots do on a windshear alert after V1? What is a pilot taught to do, when a windshear is detected and the planes speed is above V1 and before Vr? I can't think of what is safer.

Rejecting, with the risk of overshooting the runway.
Taking off, with the risk of the windshear stalling the plane and dropping it on the ground. If the height of the aircraft was low it probably would just overshoot the runway. If the aircraft already gained some altitude, it could crash.

As well, are there any differences in procedures if the alert occured

After V1 but before Vr
After Vr

V1 is the calculated decision point at which takeoff must continue. Unless the aircraft is suffering a catastrophic failure, the pilot should not abort takeoff after V1.

The danger when taking off during windshear is the sudden lost of airspeed may result in the airplane settling back on the ground after it has become airborne. The technique, therefore, is aimed at gaining ground clearance in the shortest amount of time possible. In general, this involves:

Apply max thrust
Delay rotation
Once rotation is initiated, quickly pitch up to gain altitude

Below is an extract from the Boeing 777 FCOM about taking off when windshear is suspected (my emphasis):

  Takeoff with less than full rated thrust is not recommended (...)
  Use the longest suitable runway (...)
  Consider increasing Vr speed to the performance limited gross weight rotation speed. (...) If windshear is encountered at or beyond
  the actual gross weight Vr, do not attempt to accelerate to the
  increased Vr, but rotate without hesitation.
  (...) Minimize reductions from the initial climb pitch attitude until terrain and obstruction clearance is assured, unless stick
  shaker activates.
  (...) Stick shaker must be respected at all times.


When was the first THS (Trimmable horizontal stabilizer) used and on what aircraft? When was the first THS (Trimmable horizontal stabilizer) used and on what aircraft? Has any UL or GA trimmable stabilizer?

If the question is understood to encompass any form of horizontal stabilizer which may be adjusted in flight (with or without a separate movable elevator), then the answer would appear to be Sir George Cayley's 1849 full-sized glider which briefly took flight-- see http://www.flyingmachines.org/cayl.html.  The Wright brothers also used all-moving horizontal surfaces on their early gliders and airplanes, but located in front, as canards.

However, a comment has clarified that the question is meant to only encompass a horizontal stabilizer which may be adjusted for trimming the aircraft, with an attached elevator for pitch control inputs.

According to page 9 of the book "Aces Wild" by Al Blackburn (see this Googlebooks link), the first use of an in-flight-adjustable horizontal stabilizer was in 1929 by Clarence Gilbert Taylor in his B-2 "Chummy", which eventually evolved into the Taylor Cub and then the Piper Cub, all of which used the same stabilizer trim system.  Naturally, all these aircraft featured an elevator attached to the adjustable horizontal stabilizer.

The same source says that many old Waco biplanes used the same feature.  In this photo of a 1936 Waco biplane, the slot associated with the adjustable horizontal stabilizer is clearly visible.


Where to find information about number of seats knowing the aircraft Registration ID? Let's say I have an aircraft registration id (not sure about exact name) like LN-DYO. Where can I find an information about configuration of the aircraft - i.e. number of first class seats, business class and economy class seats? I would like to have some automated solution (API? parsing of web-pages?) to get this data for a number of aircraft.

The usual way would be to find out which airline operates that aircraft. Usually Google will give the answer. Otherwise planespotters.net will help. In this case it is Norwegian.

Then seatguru will show you what the interior configuration is.

I don't know whether these website have public API's that could help you and I think that is a bit off topic for Aviation.SE.


Why/how is a downplane parachute configuration aerodynamically stable? One of the most dangerous situations possible in skydiving is a so-called downplane, where both the main and reserve chutes deploy, and they shift outwards to the sides of the parachutist until essentially side-on, like so:

(Image by the United States Navy, via Wikimedia Commons; this is actually a simulation of a downplane, with two parachutists and only one parachute per parachutist, rather than the real deal, which would involve both parachutes deploying from a single parachutist, but it illustrates the configuration very nicely.)

This reduces the total cross-sectional area (as seen by the airflow) of the parachutist-parachutes assembly, causing said assembly to accelerate downwards to greater-than-optimal speeds, which is why a downplane situation is dangerous.

However, it is far from obvious how a downplane would be aerodynamically stable; even when virtually edge-on, each of the open parachutes still has a very high drag coefficient,1 a fairly low mass, and (as a result) a very low ballistic coefficient,2 while the skydiver attached to the parachutes has a fairly low drag coefficient, a much higher mass (relative to their parachutes), and, consequently, a very high ballistic coefficient.  As such, the parachutist should tend to trail ahead of the two parachutes, with the aerodynamic forces on the latter wrenching them up towards top dead3 center, unless the whole shebang is spinning rapidly enough about its vertical axis for the outwards centrifugal force on the parachute canopies to overcome the upwards drag force on said canopies, which would require a spin rate high enough to be lethal even without taking parachute malfunctions into account.

What is it that overcomes these aerodynamic forces on the parachutes and renders a downplane aerodynamically stable?

1: Albeit much lower than when face-on.

2: A measure of the relative unaffectedness by aerodynamic drag of an object moving through an atmosphere of given composition.

3: No pun intended.

It appears that each parachute will tend to adopt a position where a line drawn from the skydiver through the center of pressure of the chute is aft of a line drawn through the skydiver perpendicular to the relative wind, by an angle equal to the L/D ratio of the parachute.  The higher the L/D ratio of the parachute, the closer to "straight overhead" the chute can be, in the reference frame of the falling skydiver with his body positioned horizontally as per the photo.  Much as the higher the L/D ratio of a kite on a string, the closer its steady-state position can approach a position straight "overhead" the kite flyer.  But a stable downplane should be possible even with chutes with a rather poor L/D ratio-- the chutes just wouldn't be positioned nearly opposite each other as is the case in the photo.  This would be analogous to a kite with a poor L/D ratio flying in a position that is far from "overhead" the kite flyer.  The speed of such a downplane would tend to be lower than the downplane illustrated in the photo.


What are the 2 protrusions next to the fore ground lights on the Tu-22M3? Here's a reference image :

What are those 2 spokes coming out next to the ground lights ?

They appear to be pitot tubes, part of the air data system.


What is the trend of gender distribution among pilots? Are there any statistics on the distribution of pilots between the two genders? Specifically, has the ratio changed over the past decades (I'd expect female pilots to be getting more common)?

I'm aware that the number will vary between countries. I'm more interested in the trend of certain group(s) that are statistically significant to an area (e.g. all commercial carriers in the United Kingdom / all PPL holders in the United States).

At least for the FAA, you can get the U.S. Civil Airmen Statistics as a download that covers from 2005 to 2014. It includes data based on gender and license type. I'm not sure when they will update for 2015. If you download the 2010 one, it has data back to 2001, so about 13 years of data.

Here is an example of the data provided:

Similarly for the UK, you can download statistics from this website. I haven't downloaded them but it looks like what you are looking for is there.

You may be able to find similar data for Canada, Australia, and some other relatively "open" countries.


How is the ALSF-II approach lighting system built and powered? The ALSF-II approach lighting system includes lead-in groups, a decision bar, red side bars and sequenced strobes:

ALSF-II approach lights for KRFD - Chicago-Rockford Intl (source).

Does anyone know the number and type of lights used, how they are arranged (distance and slope) and how much power is required to feed the full system?

The specifications for an ALSF-2 (and other approach lighting systems) can be found in FAA JO 6850.2B - Conveniently titled "Visual Guidance Lighting Systems."
As an FAA order these are obviously US-specific, but other jurisdictions' guidance is probably similar.

The ALSF-2 is a High Intensity lighting system, so lights used in the system are defined in the FAA order as follows:

  High Intensity Systems.

  Specification FAA-E-2408b, 300-watt, 20A, PAR-56 lamps for steady-burning, aboveground, white lights with Specification FAA-E-982 lampholder.
  Specification FAA-E-2408b, 500-watt, 20A, PAR-56 lamps for steady-burning, aboveground, colored lights with Specification FAA-E-982 lampholder.
  Specifications FAA-E-2952 or FAA-E-2491 approach lights, 500-watt, for all semiflush lights.
  Specifications FAA-E-2628b or FAA-E-2689a for all sequenced flashers.

From the number of required lights we can then derive the total system power used for an FAA-Specified ALSF-2 lighting system -- As I'm not fond of doing math it's fortunate that some manufacturers have already done this for us, and a full system (with all the flashers) requires approximately 104kW (varying slightly depending on input voltage). Actual utility power consumption will vary based on the efficiency of certain components but will likely shake out to something around 104kVA since the incandescent lamps have a power factor close to 1.0.


Could an aircraft 'hide' in the aircraft shadow of another aircraft without being detected or noticed? I just finished reading an interesting post where the author suggests that the missing Malaysian Airlines flight 370 could have 'hidden' under the cover of Singapore Airlines flight 68 to fly to a covert airstrip.

I've read multiple thrillers where submarines have hidden behind the acoustic signal of large cargo vessels to mask their sound over sonar arrays, and this (at least in the book) sounds plausible. I also read another book where a bomber (flying under the identity of a commercial jet) masked a business jet to get it into an area without detection. Naturally, both examples are taken from fiction, but I'm wondering:

Would there be any hints now in retrospective to suggest they were being followed? Their transponder was off of course, but I'm wondering if for instance there might be some radio interference or static from such as large aircraft behind them? Are there every any issues when refueling aircraft do this sort of thing?
What is the resolution of radar? Would one be able to notice the two blips on the screen unless they were literally under or beside each other, or would it still appear as one dot on secondary radar if say they were 200 meters behind and below?

Radar resolution is defined in terms of degrees of arc (or alternatively in steradians/solid angles) and as such, the further away from the radar, the larger volume is being sampled.  At altitude and some distance from the radar you should have a bit of leeway on how loose of a formation you can fly and show up as one contact on the radar display.  I'm not giving credence to the theory presented, but I am saying it is plausible that one aircraft could fly a formation with another and be detected as one airplane by a radar.

If the transponder is off, the aircraft you are following will not see you on TCAS  and if you are behind them you will be visually undetectable by the crew or passengers.  If you fly above them you will be clear of their wake, so I would put behind and above the best position to shadow.  A lateral offset might be safer, but if you stray too much, you might wander into the FOV of the cabin.
I can't see any way the following airplane would cause nav or com interference in the followed airplane.

The biggest threat to being detected in this scenario are being seen by other airplane.  If ATC calls traffic and you see two planes in formation instead, you would probably say something.  In the case of the airplane you refer to however, it was night and if you turn all of your position lights, beacons, strobes, tail lights and if there is no moon out you might escape visual detection by a third party.


Why did the pilot inform ATC that he is going to autoland? I was listening to ATC and I heard the pilot say that they are going to autoland. What is the purpose of providing this info to ATC?

From what you said, I'm assuming that the pilot had informed that he/she is going to autoland under VMC.
The main reason is that the autoland procedure requires accurate guidance and the ILS signals may be disturbed by the traffic (both surface and air). So, the pilots want to inform the ATC that they want undisturbed signal. From a Flight Operations Information leaflet from CAA, Qatar:

Most ILS installations are subject to signal interference by either surface vehicles or aircraft. To prevent this interference ILS critical areas are established near each localiser and glideslope antenna.
The ILS sensitive area is protected from all surface vehicles and aircraft when ILS Category II or III operations are conducted or anticipated.

These disturbances may happen when Low Visibility Procedures (LVPs) are not in force and may cause problems for the approaching aircraft:

When the LVPs are not in force, ILS beam bends may occur because of vehicle
or aircraft interference. Sudden and unexpected flight control movements may occur at a very low altitude or during the landing and rollout when the autopilot attempts to follow the beam bends.

Due to these reasons, it is better for the pilots to inform the ATC about their intention to autoland so that appropriate measures can be taken or if it is not possible, the same can be relayed to the approaching aircraft.

The ATC should be informed about the intention to conduct an autoland. Such
information should not be taken as a request for or expectation of the protection of the ILS but is merely given to enhance the possibility for ATC to inform the flight crew of any known or anticipated disturbance.

Also, the ATC has to adjust the aircraft spacing if autolands are being conducted, which may affect the operations.


Do aircraft use the majority of their fuel to overcome friction? It was asserted (tangentially) in this question that airliners use most of their fuel to overcome frictional losses.

Is that a true statement?

If so, approximately what percentage of fuel is used to overcome friction?
If not, what is the major use of fuel? (Beyond the obvious 'to run the engines'.)

No, the majority of the fuel is wasted on inefficiency of the engine.

Internal combustion engines like turbine engines are not exactly energy efficient. Most of the fuel is wasted by running the engine. Only about 35% to 40% of the energy from the fuel is converted to propulsive energy.  The rest of the energy from the fuel (~ 65%) is lost on heating up the atmosphere directly, excess kinetic energy in the exhaust stream, internal drag & friction of the engine and producing noise.

The remaining ~35% the energy is there to overcome the work done by drag.

This drag can be split into lift induced drag and parasitic drag.
It can also be split into pressure drag and friction drag.
For simplicity assume that all the lift induced drag is all pressure drag, and all parasitic drag is friction drag.

Aircraft usually cruise near the speed where drag is lowest. In such a situation, 50% of the drag is induced drag and 50% is parasitic drag. In practice cruise speed is a bit above the minimum drag speed, so the parasitic drag exceeds the induced drag. If our earlier assumption is correct, then over 50% of the drag would be friction drag.

That would bring the total estimates to:

65% wasted
20% friction drag
15% pressure drag

For example the GE90, the engine fitted on most Boeing 777s, produces a thrust of 70 kN in cruise flight of 250 m/s at a fuel consumption of 1.08 kg/s.

The propulsive power delivered by the engine is $70 \cdot 10^3 \cdot 250 = 17.5\cdot 10^6 \textrm{W}$.

Jet fuel has a specific heat of $43.15 \cdot 10^6 \textrm{J/kg}$
The energy consumption of the engines is thus:

$1.08 \cdot 43.15 \cdot 10^6 = 46.6 \cdot10^6\textrm{W}$

That gives an efficiency of 37.6%. This may seem poor but it is one of the most efficient engines available today.

Data sourcePDF for thrust, speed & consumption:


Why aren't there brake lights on aircraft? Why don't aircraft have brake lights so you can see when an aircraft in front is slowing down?

I know there are air traffic controllers to control aircraft but they cannot do much about an aircraft's speed on the ground, it is down to the pilot.

They simply aren't necessary.

Brake lights are on road vehicles because often they travel at relatively high speeds, and follow relatively close to one another. If a driver suddenly slows, the brake lights help provide a visual cue (which grabs the attention of other drivers, and is visible from quite a long distance) that the vehicle intends to slow or stop.

In aviation, no aircraft should be traveling on the ground (taxiing) at such a velocity that stopping in a short distance is a problem - nor should they be following another aircraft too closely (regulations/airport rules govern both taxi speed and following distances). Taxiing aircraft are either in communication with an air traffic controller, or each other, making the need for sudden stops, change in speed or direction highly unusual. In addition, there is a higher degree of professionalism within the aviation community than your ordinary automobile driver; pilots pay closer attention to what their and other aircraft are doing; i.e., you won't find a pilot with a Big-Gulp in one hand, a shaving razor in the other, head facing the back seat passengers, all while attempting to pilot the aircraft!

In short, brake lights wouldn't be necessary on road vehicles either under the same conditions - but as it is, they assist in preventing collisions in numerous situations. In aviation, these sorts of collisions do not occur often due to the factors above, and therefore are not necessary.


Which Navigation Specifications support an RF leg? I am studying FAA's rules concerning navigation specifications and the utilization of RF legs in an Instrument Flight Procedure. However, I am having trouble understanding if an RF leg is supported by RNAV procedures (RNAV 1 specifically) or only by RNP procedures. After some search in FAA's IFP coded database (CIFP file), I realised that only SIDs labeled as RNP 1 support RF legs, at least as far as FAA's procedures are concerned. However, an introductory page on FAA's site, concerning RNAV and PBN procedures, includes the RF as a general RNAV leg type.

Am I missing something? Could someone point me in the right direction?

EDIT: I think the question that pretty much sums up my confusion is if it's possible for a SID or STAR with only an "RNAV 1", instead of "RNP 1", requirement to contain an RF leg. Because so far I have only encountered RNP 1 SIDs with RF legs, such as STAYY ONE

First is understanding the difference between RNAV and RNP.  This related question: What is the difference between RNAV and RNP? provides a basic answer to that part of your question.

To your specific question, RNAV procedures predate the acceptance of RNP standards. Since RNP standards have been established as the basis of navigation, you should expect that all procedures published in the future would be RNP procedures.

As a reference, I can point to RTCA Document DO-236C, Minimum Aviation System Performance Standards: Required Navigation Performance for Area Navigation (MASPS). This document describes how RNP standards will be applied in the airspace. That covers airspace design, procedures and equipment used to fly within RNP airspace. Performance Based Navigation (PBN) adds aircraft specific performance requirements to the RNP concept.

Definitions from DO-236C which references ICAO Doc 9613:

  RNAV system (as defined by ICAO Doc 9613): A navigation system which
  permits aircraft operation on any desired flight path within the
  coverage of station-referenced NAVAIDs or within the limits of the
  capability of self-contained aids, or a combination of these. An RNAV
  system may be included as part of a flight management system (FMS).

  RNP system (as defined by ICAO Doc 9613): An area navigation system
  which supports onboard performance monitoring and alerting. An area
  navigation system capable of achieving the performance requirement of
  an RNP specification is referred to as an RNP system.

  PBN (as defined by ICAO Doc 9613): Area navigation based on
  performance requirements for aircraft operating along an ATS route, on
  an instrument approach procedure or in a designated airspace.

Also from DO-236C, section 3.2 Path Definition Requirements, we find:

  3.2.1.1 Navigation Database Flight Path Legs for Terminal Area Procedures

  Permissible leg types for the definitions of the RNP flight paths for
  all navigation database procedures (e.g. SIDs, STARS, Approaches
  including missed approaches), with the exception of airways, are
  limited to the following:

  Permissible Leg Types          ARINC 424 Leg Type
  - Track to Fix leg                      TF
  - Radius to Fix leg                     RF
  - Initial Fix                           IF
  - Hold legs                        HM, HA and HF
  - Fix to Altitude leg                   FA
  - Direct to Fix leg                     DF
  - Course to Fix leg                     CF

  Note 1: RNP procedures that require the repeatability and predictability of
  a specified ground track should be constructed using IF, TF, and RF legs only.

  Note 2: If the FA, DF and CF types are used, they may introduce less
  repeatability and predictability.

As you can see from the above, RNP procedures are built using RNAV leg types. RF legs are an RNAV leg type unlike the similar AF leg which is a DME arc that can be flown with a DME.

Realistically, you will only find RF legs within SIDs, STARs, and IAPs as that's where they are needed. They are useful when you need a large change of direction which is common in the terminal environment but not so much while enroute.


What are these pipes on an Avro Vulcan? As you can see above, there are two small pipes next to the main engine exhausts on this Avro Vulcan(the one at Duxford). I'm curious what these pipes are/what they are for. Are they fuel dump pipes? If so why have two right next to each other?

Although it is difficult to say from old photos, the tubes doesn't seem to be visible on the prototype or early Vulcans.

Another Vulcan, XH558 started life as a B2 and are fitted with Olympus 202 engines. Looking at a photo of it there are what appear to be intakes on each engine, as seen here. I don't know what engines the Duxford Vulcan has, but according to Wikipedia the 202 was the definitive version for the Vulcan, with the exception of some aircraft which received the 301. As far as I can tell, one of the features with the 202 was that it had a redesigned oil separator breathing system.

Such features require air inlet as well as an outlet for the vented gases, could this be related to that system?


How to become Hybrid airship Pilot? Are Hybrid Airship pilot different from other aircraft or helicopter pilot?

Yes, they are different.  A hybrid airship has the characteristics of an airship, but it also generates lift based on its aerodynamic shape (like a powered aircraft wing).

The FAA defines an airship as having both "Lighter than Air" and "powered aircraft" characteristics.  A hybrid airship falls under the characteristics of an airship, in this sense.  However, as with any aircraft, a specific type rating may be required for a hybrid airship.

Therefore, the path to certification as a pilot of a hybrid airship will likely be very similar to, but distinct from, a typical pilot.  In particular, it may be added on as a rating to an existing pilot certificate.

https://www.faa.gov/training_testing/testing/test_standards/media/FAA-S-8081-18.pdf


Why does placing one hand on the head track stabilize you during turbulence? At 0:40, Lufthansa Capt. Joachim Schwarzenberg advises

"Whenever we get turbulence and that can always be the case during 11 hours 40 on
such a long flight - that is also the flight time -
The safest thing to do while in the cabin
is to be one with the plane.
That means if you can just support yourself on the the head track, then you are
with one hand, firmly connected, it's a straight line to the floor and you
can hold yourself really well.

If you just hold onto the seats like that,
you will always be levered out and fall back down. So just remember this,
with this you even have one free hand with which you can perhaps
maneuver the cart a bit.

What's the physics behind this? Please explain in simple English. I never studied physics.

He's just saying that you can brace your torso, and transfer the airplane's movements into your torso better so you don't sway around relative to the floor, by holding something rigid with your hand anchored at or just above shoulder level.
If you've ridden in a subway car that is rocking back and forth while standing up, holding on to a vertical post, you've probably noticed it's better to hold the post with your hand about level with your head, vs holding it down at your waist.  With your hand up high the car's motion is easy to transfer to your torso so you can stay more rigidly connected and you move as if you were part of the car.  Hold it down lower and you notice your torso tends to rock about the lower anchor point and your upper body sways more relative to the post, and this makes it a lot harder to stabilize yourself.


Do Diesel engines have a mixture option? Consider the DA-42, it has no mixture control. Is that because it is run on Jet-A/diesel? Or is the mixture control automated?

For fuel, any fuel, to burn, it must be mixed with suitable amount of air. Neither too little nor too much would burn. Spark-ignition engines pre-mix the fuel with air, so they must do so in the right ratio, hence the need for mixture control (which might be automated, but it must be there).

However, compression-ignition (Diesel) engines are different. They inject fuel directly into the cylinders and as the fuel spreads from the injecting nozzle, it mixes with air and ignites at the moment it is sufficiently mixed. The cylinders always take full charge of air, otherwise the compression would not heat the air enough to ignite the fuel.

At low power, the flame is only small around the nozzle and at the large power it expands to fill the cylinder, but either way there is a point where the mixture is just right and the fuel ignites. Therefore compression-ignition engines don't need mixture control. The power lever simply controls the fuel flow into the engine and there is no throttle on the air intake (so calling power lever ‘throttle’ is inaccurate for Diesels (and turbines)).


What are the differences between FADEC and EEC systems? Can anyone differentiate FADEC and EEC system in an aircraft Engines?

As I was working related to Engine controlling. I got confused of FADEC and EECs.
As per some of the doc. I read like EECs are a part of FADEC.

The EEC is the Engine Electronic Controller, the digital processing heart of the Full Authority Digital Electronic Controller. Kind of like the microprocessor in a digital computer. From The Jet Engine by Rolls Royce, 5th edition:

The EEC is dual redundant with all subs-systems such as sensors, cables etc duplicated, so that a single fail leaves the system fully operational. It is housed either in the airframe, or like in civil airliners on the engine, leaving it in need of protection of extreme circumstances:

Temperature - ice and tropical heat.
Electromagnetic radiation - lightning and airport radar
Engine vibration

The FADEC monitors inputs such as:

Shaft speeds
Engine temperatures
Oil pressures
Actuator positions
Power setting

and then sets fuel flow, variable stator vanes, and air bleed valves.


Does a flight cycle require a minimum duration? For medium/long-haul pressurized airliners that are used on short routes.

How is a cycle calculated?

Wouldn't the short flights impact the maintenance schedule due to the frequency of pressurization cycles?

Much of the wear on an engine happens during startup, so while yes it does have a significant impact on maintenance costs, it's rather unavoidable unless the operator chooses to avoid shutdown between flights (as some do, e.g. skydiving and ag spraying)


Is there an offline airplane route software similar to the in-flight entertaiment map? Regarding the software that displays on a video the map with flight information for passengers, I would like to know:

1) The software from various airline companies seems to be more or less of a standard. So they should work in a similar fashion. Which input is needed in order to make it work (i.e., altitude, lat/lon coordinates, temperature)?

2) Is it possible to acquire one version of this software and run it offline as a simulation, giving as input the needed information?

3) Is there a freeware solution to this? I'm more interested on information like the geography, cities, countries and borders.

1) The software from various airline companies seems to be more or
  less of a standard. So they should work in a similar fashion. Which
  input is needed in order to make it work (i.e., altitude, lat/lon
  coordinates, temperature)?

"Inputs" from the aircraft devices, like pitot, anemometer, gyro, etc. ? I don't know. DeltaLima answered that for you. What you see on the screen is definately a software rendering, that means an operating system is running, and displays a frame on that screen device. The graphic is software-generated (the map, the plane, its orientation, the text, the sun, the clouds, zooming, etc.)

So, at some point, the inputs signals (altitude, cruise, heading...) has to be converted in computer bytes that will be handled by hardware devices of a computer, buffered in memory, then used by "some software" in the way they have been designed for.

Option 1 :

There's a central Operating System (OS) that holds all the computable datas and feeds all onboard software on demand including FMS, IFE, etc.

analogic device -> convert to computable data (bytes) -> central OS
                                                        / | \
                                                      /   |   \
                                                    /     |     \
                                    Cockpit softwares    IFE    Cabin Softwares

Option 2 :

There's no central OS, but multiples ones, and a direct star-type (tree) data pipeline.

analogic device
 |_ convert to computable data (bytes)
     |_ some software on some OS
     |_ some software on some OS
     |_ IFE softwares on IFE OS
     |_ some software on some OS

Option 3 :

IFE Software is a included in one OS that also run other softwares

analogic device
 |_ convert to computable data (bytes)
     |_ OS1 (cabin)
     |   |_ IFE softwares
     |   |_ Inflight intercom software
     |_ OS2 (cockpit)
     |   |_ Front Panel softwares
     |   |_ BlackBoxes softwares
     |_ HUD software (of packed software in hardware)
      ...
      ...

There are other Options, each one could be better called "onboard System"

By the way, if, by "inputs", you meant "how to make that tiny plane move along the map", there are thousands of ways doing it, but the schemas is the same :

draw a map (use some gree/blue/brown color to make it look good enough)
draw a path using points locations on a X-Y (invisible) grid and line segments
slam a top view of a plane on all of that at a precise X-Y location (and don't forget to rotate the plane icon in the correct heading or your passengers will start to panick)

No matter how beautiful the flightpath could be rendered, remember it's a computer generated graphic, and doesn't need to be accurate at all. For example, refreshing could be set at an interval of 5 seconds instead of real time (5 seconds is good enough even for steep turns on final) The map resolution doesn't require a milimetric precision. 1000ft or 500ft lateral precision could suffice, and even if the displayed (text) altitude is in feet, the 3D rendering doesn't care about that at all : it uses a fraction of that altitude, then accordinly shifts the position of the aircraft model on the screen to give you the impression the aircraft is at an higher altitude...

That the logical way the flightpath software requires. Accuracy and physics computations are not required, unless you want to create a game or even better, a simulator (in terms of reproducing nearly-real behaviour in a virtual world) GoogleEart's Flight game for example isn't as precise as many other games out there (Lock On, X-Plane...)

But for all of those, the "inputs" are all binary datas stored in memory and used as variables by the software. Turning a plane isn't dependent on a heading value. It's one block of the software code that reads the heading variable, then rotate the object (the plane) by the corresponding angular value, then another block of the software code draws (renders) the object on a screen buffer. Finally, the screen buffer is passed to the displaying device (your IFE screen) and each pixel of that screen shows what has been calculated by the software for the human eyes.

In the end, what you see on a screen - ANY screen wether it's your TV, the IFE, your computer screen when you read this answer, your phone screen - is a series of slideshows pictures rendered by the screen device one image after another. But it's done so fast that the human eyes (or brain actually) think what is shown is really moving. It's not, but looks like.

  2) Is it possible to acquire one version of this software and run it
  offline as a simulation, giving as input the needed information?

I tend to say yes ! but wait !

Good luck finding that software though. You should ask someone working for an IFE system provider for aircraft manufacturer.

And note one thing : Such softwares could be packed in some hardware components having an inbuilt memory card, this preventing anyone from copying that very software while it is successfully loaded in the IFE OS just like any other software loaded from disk/CDs/USBs... Of course you can't unplug the hardware device from the IFE hardware motherboard, and plug it on your computer motherbord, that wont make it.. Just like your phone (wether android or iphone or whatever) the firmware is burried deep in one hardware component. You can't easily copy a firmware from an iphone to a nexus.. :P

But at one point, those softwares has to be created on a computer, then, have their "saved as files" state in the computers of the enterprises creating them.

As you could have guessed, chances to get a copy of such software is pretty.. non existent, not because it's nearly impossible, but because such software are copyrighted, and/or the (hardware) system supposed to work with aswell. A flightpath IFE software developped by a company may fail to work on your computer if you don't have the same OS architecture as the company's, and/or even some hardware devices that may be required to input or output valid binary datas read/written by the software.

Someone who has a copy of such software wont tell you he has...

I can tell you the Air Austral IFE is Linux based Operating System. The flightpath map displayed, the movies/music/games entertainments are all running on that OS. While the IFE on some Air Madagascar planes could be Linux based aswell, the softwares (the rendering and graphic layout) are different, meaning that those are not the same softwares as the Air Austral ones (or other versions)

  3) Is there a freeware solution to this? I'm more interested on
  information like the geography, cities, countries and borders.

An authentic flightpath software like those onboard aircraft ? Nope ! Never seen one in the items library of a store, and never found a page using google of a page "FlightPath Software Download".

A software that shows earth, oceans/lakes, country boundaries maybe ? Yes !

GoogleEarth/GoogleMaps
Nasa Worldwind
Bing Maps
Many little and less widely used software on SourceForge using rendering libraries and web hosted databases
...

A software that allows you to draw/show paths (and objects if possible)

GoogleEarth
Cesium
Nasa WorldWind
Marble
...

A standalone software that shows you (simulated) realtime flight of an aircraft over a map or 3D Earth ?

Anyone who tried creating such software ended making it a web-based application that you can access only through a navigator (like FlightRadar) Otherwise, it would be the decision of an enterprise or organism to hire developpers to produce such software for internal business purposes ONLY !

display aircraft on a radar screen
display meteorogical objects evolution on a map
display satellites movements at a space center on a large screen
(^^ purposes like that that has nothing to do in public domain)

That's exactly what IFE hardwares/softwares is about : have a bunch of engineers/programmers, build the devices/softwares, sell them to airlines/aircraft manufacturers. Panasonic, Thales, LiveTV of JetBlue, Rockwell Collins... Don't expect them to upload their baby on a website and allow you to download them..

So far, I said "anyone who tried..." ... ... failed ! Because building such software, to be accurate enough and interresting for you and me, would require a massive amount of datas :

flightpaths are not straight lines from airport to airport. You can spot this with FlightRadar, then you'll need each airport data, with their SID/STARS; you'll need waypoints, you'll need routes (those you can see on a real jepessen map) etc.
of course, you'll have to maintain those datas up to date.
those datas are NOT freely available, so if you're a developper that paid acquiring them (or a company that employs developpers) you should find a way to make profit on it. That's what Microsoft made with Flight Simulator, what Lockheed Martin is doing with Prepar3d, X-Plane, etc. Games are selling well, but a simple "show my flight plan" software isn't interresting enough to make profit on it. For you or me perhaps, but not at all for average people.
And because the datas has to be updated, a standalone application that doesn't connect to the web would prove impossible to achieve, as it will be obsolete soon enough and would require anyway an internet connexion and mostly a registering (payware) for stream updates. Most applications that does this are web-based applications, not downloadable ! This is even more not standalone if you are thinking of displaying an actual, flying, aircraft (like FlightRadar) - And you'll have to purchase access rights on some radar centers... and implement the programatic logic to handle those streams of datas at runtime.
What about maps ? If the plane is flying above the city of New-York, what are you going to display ? A greenish-brown landscate ? A text showing "New-York" ? What about the shores (or how the software knows there is nearby ocean and land ?) Yes, you must have a landclass/waterclass database. The way the datas are stored highly depends on the way the software displays them. You need raster (images) tiles of the earth if you want photoreal-like terrain, or vector-based datas for computer generated landscapes. The later is lighter in terms of required disk space, but vector-based datas ar good for flat terrains (projections) To have datas for mountains, valleys, etc. you'll need anyway discrete values of land elevation around the globe. The disk space used quickly rockets... So don't expect from someone the task to compile all those datas for you.. and there are awfull voids here and there (in far far away land on this earth) that you can't retrieve freely on the web (well, there are 100 meter resolution terrain elevations available for free out there, but higher resolutions are very hard to get for the entire planet)
That's why on flightplans IFE, you can't zoom in and see roads on the map ;)

I've started developping my own "show aircraft routes and display realtime flying tiny aircraft over a map" years ago, still, it's stucked as a "Work In Progress" due to the massive amount of new issues occuring and the interlacing complex features I would like it to have (Compatible with the game simulators mentionned above)

There's almost one new created airline every week, one new aircraft delivered every day, updating the - offline - database of that program occurs on a daily basis, weekly at longest, and I still need internet for that ! So, the day I may release that application would never come before I die. Just to pick an example, the application is developped as a Windows Forms interface. There's a better interface provided by the dotNet Framework called WPF. Upgrading the application to this new architecture would be a must before releasing it, and I have no time to do that. The database weight several Gigabytes (as expected : Maps and graphics...)


What dialogue would a crop duster typically have with ATC? By Stefan Krause, Germany (Own work) [FAL], via Wikimedia Commons

What is the exact dialogue a crop duster pilot will have, if any, with ATC on a routine flight?

The actual operation of a crop duster airplane will almost invariably happen in uncontrolled airspace. In the US, controlled airspace does not start until 700, 1200, or in a very few select areas 14,500 feet above ground level; below that the airspace is Class G, uncontrolled. Crop dusters operate at a few hundred feet above ground level or lower (a quick google shows altitude as low as a few tens of feet AGL). Even if they wanted to talk to ATC at those altitudes, radio reception would be all but impossible.
When not actually working on a field crop dusters must adhere to the standard minimum altitude rules (500 feet AGL over non-congested areas, or 1000 feet above the tallest obstruction within 2000 feet over congested areas). But even if they enter Class E airspace, which is controlled, they do not have to contact ATC unless they want to receive an instrument flight rules clearance.
There are three times when a crop duster would have a dialog with ATC: when they want to come into a controlled airport to land, when they want to transition the airspace close to a controlled airport (where the controlled airspace extends to the surface), or when they want to operate over a field within the controlled airspace near an airport. For the first two situations they would communicate with the tower just like any other aircraft; for the last situation it might sound like this:

Duster: Podunk Tower, hello, Air Tractor 123AT is eight miles to the east, we'd like to operate over a field inside the Class Delta airspace two miles east of Podunk Airport.
Tower: Air Tractor 123AT, Podunk Tower, the Podunk altimeter 2992, proceed as requested and remain east of runway 18/36.
Duster: Proceed as requested, remain east of 18/36, Air Tractor 3AT.


When can I request flight following? I'm a student pilot doing all VFR flying and making flight plans for training. I've heard that most people don't file a flight plan for VFR outside of training though, and instead request "flight following" from nearby ATC.

When can I do this in flight? Which ATC can do this for me?

As SkipMiller said, you can basically request flight following at any time and any certificate level - student, sport pilot, private pilot - the service is available to anyone.

Also:

We're told that FF is "workload permitting".
I used to think that meant they'd give you services when they can.   But I was wrong about that. Instead, once they accept you, you're in the system, and get full services.   If they get too busy, they'll tell you and kick you out of the system.  ("Radar Services Terminated; Squawk VFR")

FF depends on radar services.   When flying rather low and near mountains, its easy for them to lose you.

As for when you should request it:  You can request it at anytime.
Personally, I wouldn't be in a hurry to request it as soon as you depart.   Wait until you're established on course, in a cruise-attitude (instead of a climb), and everything is settled and running smoothly.  Then know your position, and how you're going to report it.  Know where you're going (both by name and ICAO identifier), and try to anticipate any questions they might ask.

Look for the Center/Approach/Depature where you are  (look in your AF/D for an airport close to you), and call up with:

You:   "Seattle Center; November 12345: VFR, with request"
translation:  Calling Seattle Center, this is N12345.  I'm VFR (so you haven't heard from me before... don't be surprised!), and I have a request.

Center:  "November 12345: Say request."

You:  "November 12345 is SkyHawk, 10 mi. South of Harvey Field, 4,500 feet.  Request VFR Flight Following to Friday Harbor"

translation: I'm a Cessna Skyhawk, my location and altitude will help you find me.  I'm asking for FF to this other airport."

Center:  "N345: Squawk 4532 and Ident."

You: (Set your transponder to 4532, press the Identify Button), and say "4532 and Ident, N345"

Center:  "N345: Radar Contact, 11 mi. south of Sierra Four Tree, at 4,500.  Traffic at your 1o'clock, 5 mi. North Bound, Altitude indicates 3,000."

translation:  I found you on my radar scope, and am describing the position I see you. (If you disagree, speak up!).  You have traffic ahead and slightly to your right.  Their transponder indicates 3,000 feet, but I cannot independently verify that.


When the angle of attack is increased does the air flowing below it slow down So the air above the wing flows faster. So it creates low pressure above the wing. The air flow below the wing, is it slowed down by the increased angle of attack or does it stay the same? So is the higher pressure on the bottom of the wing relatively higher then the bottom or does the airflow on the bottom slow down beucase if the increased angle of attack?

In high alpha flight it is not uncommon to have compression below the wing, which would increase the pressure, and act in concert with the Bernoulli Effect on the top of the wing.  The effect on the underside of the wing could also correctly be called a form of Bernoulli Effect.

There need not be any compression on the underside for there to be lift on the top side of the wing.  However in higher angles of attack there is compression, which supplements the lift.


What's that in front of the overhead panel? There is that thing I have see a few pilot using it. it can be pulled outside and then inside. what's that and what's the use of it?

That's where the analogue/backup compass is stowed. The compartment can be opened downward if you ever need to use the compass, as seen in this image:


Why do some airports have to put 2 jetbridges on one aircraft? At a gate in Denver Int'l there is a United plane with 2 jetbridges.

Why do some airports have to put 2 jetbridges on a plane? Is it necessary?

It is not strictly necessary. But it is done in order to save time.

More points of passenger loading leads to faster loading, potentially reducing delays, airport charges etc.
In some cases, there is a seperate jet bridge for first/business class.
For large aircraft like A380 etc, is quite common to use multiple jet bridges as use of a single one may lead to quite large loading time.


Is there something like a table of aircraft required runway lengths? I'm looking for a chart showing the minimum length a runway can be for various aircraft to land and take off.

Does something like this exist?

Such table would not be useful at all. As the required runway length varies with the aircraft weight, pressure altitude, temperature, aircraft configuration, runway slope, condition (wet, dry), wind, etc.

Examples:

A 7000-foot runway can handle a 747, but listing the 747 under aircraft that can takeoff from 7000' runways does not say how big the weight penalty will be.
A 7000' runway at sea-level is longer than 7000' at a high altitude airport.

I'm afraid you won't find such list.

Related:

For designing a runway, what are the largest cargo airplanes in use?
How can a Boeing 747 takeoff from Princess Juliana 7,546 ft runway?