Flying VFR in uncontrolled airspace, what to do if one spots an apparently out-of-control fire on the ground? Suppose I'm flying VFR in class G (uncontrolled) airspace, monitoring the local CTAF frequency while doing so. Maybe I'm alone in doing circuits around the local airport, or maybe I'm practicing navigating by landmarks, or maybe I'm on a cross-country flight from A to B. Either way, there is no one else in the immediate vicinity making themselves known on the radio, and (unlike in controlled airspace) there's no obvious ground station that I can call and expect to get an answer from.

Now, I, or someone else onboard, spots a fire on the ground some distance away.

A good first step then seems obvious, to go closer to get a better look. Now suppose that, on closer inspection, this does indeed appear to be an out-of-control fire with no firefighters on site. This could mean either that nobody yet knows about it, or that rescue services have been alerted but are still on their way.

It could be a structural fire, or a forest/field/grassland/etc. fire. To the extent that this makes a relevant distinction, it'd be great if answers addressed both types. (Both of these have happened recently in my immediate area, though I don't think they were initially reported by aviators.)

For me, a thousand feet or more above ground, what's the next step?

The aircraft isn't in any immediate danger, so from the perspective of the aircraft and its occupants, it's not an emergency or even urgency situation. However, there's certainly risk to property, and possibly people, on the ground.

Should I dial in 121.5 on the radio and call mayday? Or pan-pan on 121.5? Or should I use some other frequency, such as that of the local area control if I were to climb straight up into controlled airspace? (They would also be monitoring 121.5, so I would effectively be reaching the same people.) Mayday, pan-pan, or not? Or something else entirely?

Not doing anything in particular and just going on with my day doesn't seem like the right thing to do in such a situation.

Looking at my radiotelephony textbook, urgency traffic (pan-pan) includes situations relating to the safety of a "vehicle" (not just the aircraft, but specifically including any aircraft) or for a person onboard or within sight, but that do not require immediate assistance. Emergency traffic (mayday) includes situations involving "serious and/or immediate danger" (unspecified as to what) where immediate assistance is required.

I'm interested primarily in answers pertaining to the EU.

This has happened several times and each time I was able to reach a local approach facility.  Prior to GPS, I would circle above the event, and approach would get a pretty good fix.  One time it was a propane facility near the uncontrolled airport I was flying out of at night.  Shortly there after, when the flames shot above 4500 feet, the tower saw it form 20 miles away, visually.

One of the more interesting events was one early spring, when I was crossing the Finger Lakes in New York, and saw two snowmobiles go through the thin ice.  I hung around for the recovery, and everyone was pulled out of the water alive.  In that instance, (Rochester) approach kept asking for updates, as they were talking with the fire departments, who were trying to find the best ice for their approach to the snowmobilers.

In my experience, I have always been able to reach approach.  However if approach was not available, enroute or FSS, and as a last resort, local unicoms.

When flying for the state conservation department, we did radio in fires, as part of the job expectation.

For those looking for more guidance, might I suggest something like:

Cessna345: Approach, Cessna 12345, 20 miles south, near Geneseo VOR, with two snowmobiles through the ice on the lake, 5 miles southeast of the VOR.  Three souls observed in the water.

Apch: Cessna 345, squawk 4311, ident, say altitude.  How long ago did this happen.

Cessna345: About 2 minutes prior to my call up. 1500.

Apch: Any other snowmobilers in the area?

Cessna345: No, not at the north end of the lake.

Apch: Fire is being dispatched from both sides of the lake, would you say the swimmers are closer to the east or west shore.

Cessna345: East shore, advise fire that I am circling above the swimmers, with landing lights on.

and so on.

Addendum: The question asked about uncontrolled airspace, and while there may be uncontrolled airspace even in areas of radar and ATC coverage, it is useful to discuss what to do when ATC coverage is more sparse.  The objective is to communicate to authorities so that fire services can be dispatched to control the fire, and alert people who might be in harms way.  My suggestion, as a CFI and as someone who has flown the northeast corridor as well as rather desolate portions of the earth, is to establish communication with anyone on the ground as soon as practical.  If you can reach any FSS or ATC facility, I would contact them first.  If unable, and if nearby (considering your altitude) I would try airports with unicom/multicom frequencies listed.  You might alter your flight to get you closer to civilization and potential contact points. In Northern Canada, as an example, there are many well equipped airports which are not charted, but support mining operations. I carried a list of their frequencies shared with me by regional pilots.  Barring that, I would make calls on 121.5.  There may not be any facilities around which are in range for 121.5, but there are likely airlines and military flights which monitor 121.5, particularly in cruise. It is not uncommon to use other aircraft to relay information, and short concise messages help.  If one has HF or a SATphone, then the radio game is different.  In extremely sparse areas, a fire may only be of advisory interest, so do not expose yourself to increased risk to report it.


Can PC joystick simulate aerodynamic lock in spin? I never explored joysticks for playing simulators on PC. Can some kind of joystick simulate aerodynamic lock during spin? You do hands off control stick and it stays there, won’t center as usual. I understand that force feedback is often included in such products, but can force feedback override auto centering?

Yes there are PC joysticks that can remain in an off center position: the active feedback joysticks, without the force feedback switched on. The stick feels pretty light in that situation and kind of remains where you put it, almost like a helicopter cyclic stick with the trim button released.

When switched on, the force feedback can act like a passive spring and accepts some input parameters for varying the feel. The neutral position can be varied, the return position of the spring. All pretty course, not bad for the money, although the stepper motor produces grainy feedback forces.


Why is the planned Kingdom Tower Skydeck unsuitable for use as a helipad? Why is the planned Kingdom Tower Skydeck unsuitable for use as a helipad? Originally the skydeck was supposed to be a helipad, but this idea was subsequently rejected and the feature was repurposed as a "sky deck" when it was discovered that it was not usable as a helipad, recalling another failed aviation docking boondoggle, the airship mooring mast on the Empire State Building.

A quote from The Guardian:

  A Starship Enterprise-like circular helipad, 30m across, protrudes out at level 157. This was originally designed to provide fast access to the penthouse, but the wind makes it a dangerous place to land, so instead it has become an observation deck – the world’s highest at 630m.

link (emphasis by me)

Helicopter prefers steady wind condition in order to land safely and comfortably. The nature of wind at such height is gusty and turbulent due to proximity to the building itself. It would be unsafe and very uncomfortable to the rich man who rides the chopper for 'quick access' to the penthouse on that floor. The highest helipad now is at 438 meters high at that is at the TOP of the building.


What are the advantages and disadvantages of the MiG-29's horizontal stabilizers (not what do they do)? The MiG-29's tail axes are located fairly close to the leading edge, and rotate along an axis oblique to the chord. What are the possible consequences to this arrangement (e.g. actuator torque, flutter potential)?

There is nothing too special about the MiG-29 stabilator.
The "slanted" (swept) axis of rotation is fairly common: as far as I remember, all MiGs that had a stabilator had this arrangement.
This has primarily structural advantages: it is easier to integrate the shaft (or axle) along the structural elements of the stabiliser, making it lighter. Also, the hinge moments are more consistent along the shaft. (For the straight shaft on a swept stabiliser, there will invariably be twisting forces that must be absorbed by the structure. Say, the root section may experience positive moment with respect to the shaft while the end section may have negative moment).
Also, as Charles already noted, a swept axis may allow to move the stabilator a bit further back (while keeping the same overall hinge moment), increasing its lever arm and thus efficiency. This is because the attachment point at the root can be closer to the leading edge. But this is only a gain when the actuator cannot be moved further back for some design reasons (like on MiG-29).
On the other hand, the leading edge may interfere with the fuselage when deflected, necessitating a "stump" at the root (which you can also see on most jet MiGs). At the same time, you need larger deflection in order to achieve the same aerodynamic effect (see also this answer).
The perception that the shaft is too close to the leading edge is a bit of an illusion. In fact, it is just a bit forward of the 1/4-chord line: exactly where it should be, as can be seen in these diagrams.


Which radio frequency is used during a flight interception? What kind of communication do the intercepting and intercepted aircraft use? Is it the usual air-to-air frequency or the international emergency frequency?

An interception with an aircraft that's either on an unknown frequency, or non-responsive etc will be conducted on the emergency frequency of 121.5. Likewise, a pilot would be expected to tune into that frequency if they found themselves the subject of an interception.

There is no other standard "air to air" frequency that's likely to be utilised. I'm aware that some countries have special frequencies reserved for formation flight etc, but most pilots wouldn't have those memorised and wouldn't be expected to use them.

However, if the aircraft is/was communicating on a known frequency then there'd be no reason that an interceptor couldn't use that.


Are there any standards on the dimensions of PFD symbols? Are there industry standards on dimensions of PFD symbologies like heading, airspeed and altitude?

I want to design a 15 inch screen and wonder if there are any standards or regulations regarding the design of those information displays.

Yes there are standards. There are industry standards which not regulatory standards, but they have been deemed acceptable by the regulatory agencies (e.g. FAA). So following them is usually accepted without issue.

The FAA also provides guidance in the form of an Advisory Circular, AC 25-11B Electronic Flight Displays.

You have two separate things to address; the actual display hardware and the displayed content.

The standard for the hardware is SAE Aerospace Standard AS8034B, Minimum Performance Standard for Airborne Multipurpose Electronic Displays.

The rest is covered under a group of SAE Aerospace Recommended Practice (ARP) documents. The top level is ARP4102, Flight Deck Panels, Controls, and Displays. Under it are several Volumes and Appendices.

ARP4102-7, Electronic Displays, covers the general requirements for what must be displayed.

ARP4102-7 Appendix A, Electronic Display Symbology for EADI/PFD, covers the details for the PFD. Appendix B covers the EHSI/ND and Appendix C covers the Engine displays.


What is that round antenna(?) on the bottom of a Piper Comanche? Does anyone recognize this round object under the belly of a PA-24?

From a Comanche parts catalog, it's the ADF loop antenna (item 45) minus the aero cover (30):

http://www.aeroelectric.com/Reference_Docs/Piper/pa-24-180-250-260-400_pcv1998.pdf


Could flywheel type gyros stablize a plane? An aircraft carrier has massive spinning gyros to keep the ship upright against waves. Do planes of any type have gyros like those used in satellites? Not instrument gyros. In the picture below spinning this one when suddenly stopped could move the plane in flight significantly allowing it to correct from a flat spin? It would spin in the event of a flat spin and stop suddenly to correct it, but it would not spin in normal flight. Or it can be used to shoot backwards momentarily. Can they be used this way for more control of the plane with the fins?

I actually have a lot of experience in the shipboard systems that you are talking about.

First, the gyro's do not keep the boat upright, they counter the rolling effect of waves but they cannot completely remove them. Gyro's of all designs work on the principle of conservation of angular momentum. That means that a spinning object will tend to impart a force 90° opposite of the force applied to it to conserve angular momentum.

In order for this to have a tangible effect on something of significant mass, the gyro itself (more specifically, the flywheel) must also have a significant mass. In shipboard systems this means that they usually use many (for an aircraft carrier, I would assume dozens even) of these devices that spin a flywheel weighing in the magnitude of tons. That is a lot of mass to be moving around!

So the first issue you have is to get the mass spinning fast enough to have an effect. Getting something that large spinning takes significant amounts of energy and time. Getting something that large to stop spinning can be equally problematic. Yes, you could use brakes (and many do), but you need to dissipate a lot of energy (heat).

So, taking into account that these gyros don't change speed very fast, and that they very heavily counter forces, you have a number of problems off the bat:

You have to carry a LOT of extra weight.
You need to have a lot of extra fuel/motors/generators to get the mass spinning.
Once spinning, the mass will counter changes in momentum, this will make the aircraft difficult, if not impossible, to bank (aka: turn).

So could they be used to correct a flat spin? Not really. In order to counter the flat spin you'd have to have a gyro mounted 90° to the angle of the spin, and then change the momentum of the gyro to counter the spin. Flat spins are not (apart from what Top Gun may have you believe) impossible to recover from given altitude and control authority. This happens in the world of aerobatics quite frequently (and on purpose).

Can they be used to control the plane? Again probably not. You are talking about changing the angular momentum of a huge mass very quickly. This would work for the braking side, but not the speed-up side. That means you'd have an aircraft that can perform a maneuver once in one direction, then have to fly off while the aircraft builds up gyro's again.

By the way, spacecraft use control moment gyros that work by using gimbals to rotate a gyroscopic flywheel to impart a rotational force on the spacecraft. These work because of a reduced gravity/drag in the operational environment of the spacecraft itself. The masses don't have to be as big as they would on earth.


Why don't black boxes have their own GPS? In too many cases of unfortunate incidents, hunting for FDR (or CVR also) is a major challenge.1 There are many or all answers recorded on that device.

Why a locator (GPS linked) cannot be included in the black box? It has its battery which runs for several days and very rigid outer shell.

Ordinary cell phones are GPS enabled which pinpoint their location with the accuracy of a couple of feet. So why there cannot be a more sophisticated technology added to the black boxes?

1: I am aware that most of FDRs/CVRs are eventually recovered.

First let's and define what "too many cases" means in terms of cold, hard, unfeeling numbers (as best we can):

Wikipedia has a list (admittedly incomplete) of crashes where the CVR/FDR was not recovered. There are 16 crashes listed. I'll further add Air France 447 (which took "a long time" to find), and MH370 (which is currently unrecovered), bringing the total to 18.

As Wikipedia admits their list is incomplete I'll double-and-round that in the name of being pessimistically conservative and say that since 1965 there have been 50 cases where it has taken "a long time" to recover the flight recorders (or they were never recovered).

In a single year there can be over 100 "incidents". Even if we assume the CVR/FDR data wouldn't be useful for all of them there are still many hundreds (if not thousands) of incidents since 1965 where the cockpit voice recorder and/or flight data recorders have been recovered along with other wreckage or damaged airframes - often within a matter of days or hours (as soon as investigators can get to the wreckage). That's a pretty good track record.

One could certainly argue (legitimately) that "one unrecovered flight recorder is too many", and indeed the goal is to always find the recorders and analyze their contents.
If we're being realistic about this though we're going to have to accept the fact that sometimes you're just not going to recover the recorders: Aircraft crashes are messy, high-energy affairs and often involve inhospitable recovery environments like "the bottom of the ocean".

  If someone has better statistics close at hand I would love to review them and update this answer. Otherwise, it should be obvious that the above is an extremely rough off-the-cuff estimate, and should not be taken for any research or investigative purposes.
  In case it's not obvious - well I just said it.

Now, to the meat of your question:

Theoretically you could include a locator beacon in the CVR or FDR - incorporating a 406MHz ELT into the black box design is possible (you could even add a GPS to encode the device's location, though it would be of limited additional value with the inherent location accuracy of the 406MHz locator signal and satellite search system).

So why don't we do it?

As Lnafziger pointed out, airliners are already required to carry emergency locator transmitters - in any case where such a beacon would function including one in the CVR/FDR would be redundant with existing equipment in the aircraft.

Further practical problems arise when you consider the kind of abuse a "black box" is subject to -- These things need to survive a crash (up to 3400 Gs), crush forces, fire, and immersion in water under pressure.
Your typical distress beacon requires an antenna and a view of the sky, both of which would be in serious doubt after a crash:  The black box may be inside or under wreckage, required external antennas may have been torn off or burned away, and distress beacon signals are unlikely to be received if the recorder is under water (this is why current generation recorders have sonar "pingers" to assist in locating them).

  To easily illustrate the sort of problem radio devices have with "stuff" between them and the sky, try this experiment: Take your cell phone, wrap it in aluminum foil to simulate the skin of a plane, put it in a zip-lock bag, and take it to the bottom of a pool. I bet you won't be able to get a call on that phone.

Given the numerous failure modes (all of which are fairly high-probability in a real-world crash scenario), and the fact that we usually have a pretty good idea of where an aircraft is when a crash does happen, there isn't much to be gained by including additional locator technology in the CVR/FDR designs at this time - it just adds more components that would need periodic testing and recertification to ensure they are functioning properly and would activate appropriately in the event of a crash, while not appreciably improving our odds of finding the recorders.


Are any agile (aerobatic) private jets produced? If you look at the car industry there are luxury comfort brand like Rolls Royce or Bentley but super expensive racing cars are probably even more popular. They offer limited comfort, are not practical, almost not usable on normal roads, not very reliable and offer terrible fuel consumption. But still everybody dreams about them and a lot of companies try to manufacture.

Business jet can offer luxury and comfort but what to do if you want some excitement or performance? Why are there no jets with massive after burning engines with thrust bigger than weight that can climb straight up and do several G? Something like a cross-breed between a Gulfstream and an F15? Maybe it's good business case to manufacture something like this?

The reason these aren't built is that there's no market for them. Sure, there's loads of people who would love one of these (including me) but they would be incredibly expensive to buy and operate, far out of reach for anyone but the extremely wealthy.

At the airfield I fly from there are Jet Provosts, a 50's era jet trainer, available. These old, not particularly fast or agile jets cost about 1000 USD per  hour to fly. I've seen Mig-21 (certainly fast with lots of Gs) training for about $4500 per hour, which gives you an idea of the running costs for a fast, exciting jet.

The existing market of people who can afford this is already supplied by military surplus jets. These run from trainers like the L-39 and Gnats to fighters and bombers like Migs, an F-104, hawker hunter, there's even a privately owned Harrier. These don't cost that much to buy considering what one would cost new, and there's plenty of them on the market, so there's no call for new builds.


What is this device on the nose of an MD-11? In the following photo there is some sort of cover or opening (for an optical device I assume) on the nose cone.

What is this and what is the system behind it?

(link to source)

Enhanced flight vision system

or a different angle

wiki says:

  An Enhanced flight vision system (EFVS, sometimes EVS) is an airborne system which provides an image of the scene and displays it to the pilot, in order to provide an image in which the scene and objects in it can be better detected.


How long to keep ASRS report? After submitting a NASA ASRS report, it is returned to the submitter along with the tracking number.  For how long should that packet be retained (in case it is needed during an FAA enforcement action)?

Generally the FAA inspectors are supposed to complete their EIR within 75 days of the date they learn of the violation, and regional review should be completed 15 days after that - so you should theoretically hear something from them within 90 days of a violation.

The NTSB's rules of practice governing certificate actions (referenced in that same FSIMS order - 2150.3B) says they can't suspend or revoke your certificate if the violation took place more than 6 months prior to their notifying you (the "stale complaint rule") so generally if you haven't heard from them after 6 months you're probably in the clear and won't need your ASRS stub anymore, but there are exceptions to this that are easy for the FAA to leverage, so holding on to the stubs longer isn't a bad idea.

Personally I believe in holding on to the ASRS stubs forever - I have mine (all 3) in a folder in the back of my filing cabinet, even though the newest one is almost 3 years old now and I'm fairly sure the FAA doesn't care about any of them, but if they do come after me for any of those incidents I know I did the right thing and I can prove it.

More importantly for me though it's a reminder that the point of the ASRS program isn't to be a get-out-of-jail-free card for when we screw up: That's the carrot used to entice us into filing them, but these reports are supposed to serve as an educational tool for other pilots and for us.
Any time I feel the need to file another ASRS report I take the time to look at the ones I filed previously - If I'm making the same mistakes multiple times that's a clue that I should be getting time with a CFI and working on those areas of operation.

Knowing my insurance policy on those incidents is still good if someone dredges them up later is just a bonus, and the stubs don't take up that much room.


Why most of the supersonic or fighter aircraft use all-moving control surfaces? What are the advantages of using all-moving control surfaces? can someone give explanations based on aerodynamics?

The biggest two reasons to have a stabilator (the most common all-moving control surface) are stability at supersonic speeds and increased maneuverability.

As an airfoil approaches its critical Mach number, the diverted flow moving past the wing's leading edge, because it has to move faster than the wing itself to follow the contour, starts to exceed Mach 1 and then decelerates below it, causing a transsonic shockwave to form behind the wing's leading edge. This shockwave causes boundary separation of the airflow at the trailing edge of the wing, where traditional elevator surfaces are placed. This reduces the wing's lift and also the effectiveness of elevator surfaces, a phenomenon known as "Mach tuck". By instead moving the entire control surface, this problem is avoided as the entire airfoil, regardless of the quality of the flow of air over any point of it, is used to direct airflow and thus rate the aircraft's nose.

Second, and more intuitively, the larger the elevator surface, the more air it redirects and thus the more force it places on the tail section, in turn allowing the pilot to pitch the aircraft at higher rates. The ideal endpoint of this line of thought is that the entire stabilizer also becomes the elevator surface; a "stabilator".

Both of these considerations are critical to the design of fighter jets, which as of the fourth generation were almost all capable of Mach 1 (and a few could exceed Mach 2), and which also have to be highly maneuverable even as the moment of inertia of the airframe in the pitch plane increases (an unavoidable side effect of wrapping an airframe around two high-performance jet engines traversing the length of the fuselage).


Can a plane turn around like on this photo? I've never seen a plane do such a maneuver, have you?

Is this photo just a hoax?

hoax, totally. that plane is travelling at about 550MPH and the forces required to turn it 180 degrees with a radius of ~two wingspans would destroy the plane and kill everybody in it.


In a B737 NG, when a TO is flown with an Assumed Temperature N1, is the subsequent CLB N1 also adjusted (lowered) accordingly? The Title is my question. Because I think that if one uses a very high Assumed Temperature, the subsequent Max CLB N1 maybe higher that the TO N1.

Possibly, but not necessarily.
The climb thrust can be selected on the FMC N1 Limit page. The choice is between CLB, CLB-1 and CLB-2. The climb thrust is then reduced according to the selection:

7 - Climb (CLB)
Push – selects full rated climb thrust limit. [...]
8 - Reduced Climb (CLB–1 and CLB–2)
Push – selects the associated reduced thrust climb mode.
CLB–1 provides a climb limit reduced by 3% N1 (approximately 10% thrust).
CLB–2 provides a climb limit reduced by 6% N1 (approximately 20% thrust).
Deletion results in the selection of CLB thrust.
Manual selection of a climb thrust rating overrides the automatic selection.

(Boeing 737 NG FCOMv2 11.40.47 - Flight Management, Navigation - FMC Preflight)
When a takeoff thrust derating or an assumed temperature is entered, the FMC automatically selects a corresponding climb derating. And yes, the climb derating is computed such that it is below or equal to the takeoff thrust:

Derated Thrust Climb
Two fixed climb thrust derates can be selected on the N1 LIMIT page. CLB–1
provides a climb limit reduced by 3% N1 (approximately 10% thrust). CLB–2
provides a climb limit reduced by 6% N1 (approximately 20% thrust). The
reduced climb setting gradually increases to full rated climb thrust by 15,000 feet.
In cruise, the thrust reference automatically changes to CRZ. The reference can be
manually selected on the N1 LIMIT page.
Use of an assumed temperature reduced thrust takeoff or takeoff derate affects the
FMCs climb derate computation. If a reduced thrust takeoff has been specified on
the TAKEOFF REF page, the FMC will re-compute CLB-1 and CLB-2 values as
required to avoid a climb N1 value greater than the reduced thrust takeoff N1
value.

(Boeing 737 NG FCOMv2 11.32.4 - Flight Management, Navigation - Flight Management Computer; emphasis mine)
However, if the pilots manually select CLB after the automatic selection of a derated climb thrust, then the climb thrust can actually increase over the TO thrust.


Why is it the ATC recording of Ethiopian Airlines Flight 302 is not yet available online? I understand sites like liveatc.net constantly stream the conversation between the ATC and pilots. Why is it that there's no such recording for Ethiopian Airlines Flight 302 yet?

From LiveATC FAQ:

  LiveATC provides many of the major airport feeds on the network but most of the feeds are provided by volunteers. For this reason we sometimes have only limited control over where (and when) new feeds come online.

The coverage is not global, and in some countries (e.g., UK) it is illegal to broadcast it (that's why you can't find any UK airport on that site).

Officially, CVR/ATC recordings (transcripts are a different matter) of accidents are not made public, unless there is a civil lawsuit (jurisdiction dependent). See: Does the NTSB provide CVR audio recordings alongside transcripts in accident reports?


How should I operate within the dashed magenta lines next to Class D airspace? I am unsure of how to operate within this area (red dashed line) without connection to ATC.  It appears to come off of class D airspace.

Can anyone provide an explanation of what this area is and how to operate within it?

The area inside those lines is class E from the surface.


How can I reduce the responsivness of my homebrew brake system? I have a hydraulically actuated aircraft brake system.
Each main landing gear are equipped with brake disk hydraulically operated. The actuation is realized independently for each wheels by means of the correspondent control valve which controls pressure delivery to the brakes. Each brake control valve is connected to each pedal brake. When the pedal brake is depressed, the control valve will open and deliver a variable pressure to the brake adjusted by the pedal angel.
The problem is the Brake is too responsive. When the pedal is depressed slightly, the aircraft suddenly stop.

What is the main problem? Is it the hydraulic flow to the brake disk too high?
Can I install a "restrictor valve" from the brake valve to disk to restrict the flow and make the brake smoother?
if so, how can i determine the size of the restrictor valve?

or the pressure to disk brake is too high?

the function of accumulator is for emergency

the pressure to disk brake is too high?

That is sure, that is the only parameter that can influence how much braking authority you are using.

Given the schematic you posted, my otherwise uninformed opinion (as I don't have pressure measurements, or other data), is that you should investigate your brake valve.

It is probably not providing a sufficient pressure drop even when slightly open. This could be due to the valve model.

Yes, your suggestion to have a restrictor valve (or an O ring inside the pipes) should be a suitable approach, but it depends on the solution you are looking for.
The pressure will drop when the brake fluid is moving, but the equilibrium state will not change, if you keep your pedal slightly depressed your aircraft will still come to a complete stop, simply it will do so slightly later.

If your intention is to have the braking authority controlled by the pedal, what you really want is to change the pressure reaching the brake disk with the pedal.
No static solution is viable in that case: you will need a valve that lets you control the pressure received by the brake plate with the pedal deflection, i.e. you probably have to change your brake valve, or you have to install a system that dynamically adjusts the pressure downstream of the brake valve.


In general, how do aircraft handle differently in inverted flight versus in upright flight? Inverted flight is flight with a roll angle between 90° and 270° (although it classically referred specifically to flight with a roll angle of 180° - i.e., upside-down).  In what ways, in general, does aircraft handling in inverted flight differ from aircraft handling in upright (non-inverted) flight?

Partially inspired by reading about the crash of Alaska Airlines Flight 261, including how the pilots apparently tried (albeit unsuccessfully) to recover their airplane from its final dive by rolling it inverted.

Typically, unless the CG is quite far aft (as is often the case with aircraft designed for aerobatics), lots of forward stick or yoke will be needed to keep the nose high enough for sustained inverted flight. With inadequate forward yoke or stick input, the airspeed may increase very quickly as the flight path curves earthward and altitude is rapidly lost.

This orange radio-controlled model glider doesn't even have ailerons, and it has a flat-bottomed airfoil, yet it may be flown in sustained inverted flight.  (Roll control is challenging-- inverted, the ample dihedral is very destabilizing.)  With the right technique, nearly any aircraft would likely be controllable in sustained inverted flight.  Getting there safely from upright flight, and getting back safely to upright flight afterwards, may be another matter, especially if the roll rate is sluggish.

Obviously, whether or not the engines will receive adequate fuel and lubrication to keep running during sustained negative-G flight, and what will happen to the flight controls if they do not, will vary from one aircraft to another.


What does "With One Minute Weather" Mean? Yesterday I was listening to LiveATC at McClellan Field (KMCC) since many CAL Fire Tankers are stationed there and there's a lot of activity recently.

As the tankers returned from their bombing runs, they called McClellan Tower and reported they had the "One Minute Weather".

Most seemed to be flying VFR if that matters, although the Tower was handing out Squawk codes to those that requested them (on departure, probably for better TCAS reporting, coordination and general awareness I presume).

I'm unfamiliar with the weather report "with one minute weather", what does it mean? Is it a quick way to report they have the latest ATIS information?

It's used at uncontrolled airports to tell approach controllers that you've got the AWOS/ASOS there. I believe the tower at KMCC is temporary (probably for firefighting).

The AIM 4-3-26 is snappily titled Operations at Uncontrolled
Airports With Automated Surface Observing System (ASOS)/Automated Weather Sensor System(AWSS)/Automated Weather Observing System (AWOS), and says:

  If ATC service is required for IFR/SVFR approach/departure or
  requested for VFR service, the pilot should advise the controller that
  he/she has received the one−minute weather and state his/her
  intentions.
  EXAMPLE− “I have the (airport) one−minute weather, request
  an ILS Runway 14 approach.”

It's also in the Pilot/Controller Glossary:

  ONE-MINUTE WEATHER− The most recent one minute updated weather
  broadcast received by a pilot from an uncontrolled airport
  ASOS/AWSS/AWOS.

And this from the ATC Orders 5-10-2:

  Automated weather observing systems may be set to provide one minute
  updates. This one minute data may be useful to the pilot for possible
  weather trends. Controllers provide service based solely on official
  weather, i.e., hourly and special observations


Why has the European Union banned several airlines? The European Union does not permit the entry of several airlines in any of its member states. It does so to ensure the safety of its own airfields, as it feels that management of several airlines is not caring enough. How is this justified?

No such ban is implemented by any Middle-East or American country, which have a very good safety record. What are the EU's views on banning airlines?

I think the policy is completely justified. An analogy: You wouldn't allow an unsafe and unapproved car onto a highway in Europe where it presents a unjust danger to everybody else.

You have to remember that the European Union is a fairly compact bunch of nations: To get to Paris from Southeast Asia or Africa, you're probably looking at overflying at least two or three other countries. Thus, a single flight will have wider implications and involve multiple nations. The policy keeps everybody somewhat happy that they have safe airlines in their airspace. It also keeps their own citizens off the airline in question.

I do not think that it is a question of 'caring'. If they do not feel that the airline can safely fly, they ban it. Note that a fair number of the EU blacklist are automatically banned by country if they have insufficient oversight. It's also not a permanent 'thing' or sentence. Garuda Indonesia was on the EASA blacklist for two years until they brushed up, and are now back flying into the EU. Perhaps it might even have been good, since it pushed the company to improve their standards?

Here is a recent quote on the Iraqi Airlines ban:

  ATW understands from unidentified sources that 600 non-EU airlines had applied for TCO authorization. Most had been granted with few problems, but a small number of airlines were subject to greater scrutiny because of their perceived high-risk status. Source

While perhaps less prominent, I think the United States will quickly block any unsafe airline from coming in, although perhaps on a more case-by-case basis. I believe there are other hurdles, such as airport security requirements, that have to be settled to fly into the United States and can act as barriers. I believe the same applies for any other nation.

Other countries say no as well, just perhaps not being as 'vocal':

  Some Thai-registered airlines earlier faced flight restrictions by Japan, South Korea and Indonesia, following an audit of Thailand's air operations by the UN-based International Civil Aviation Organisation. In June the agency raised a red flag over aviation safety standards and gave the country until November to tackle the issue. Meanwhile, the US Federal Aviation Administration (FAA) last Friday gave Thailand 65 days to address shortcomings it had found. Source


Why don't ailerons affect pitch? Why don't ailerons affect pitch, or do they?

I'm told spoilers can affect pitch if not placed in the right spot.

On a classic standard wing configuration, why don't ailerons affect pitch as they are at the trailing edge
and would create a moment around the spar which I'm told it usually located at 25% chord
in ultralights.

Two reasons:

Because they don't have a very long moment arm.
Because their movement works in opposite directions to each other, any pitching moment one side might cause is cancelled out by a pitching moment going the other way from the aileron on the other wing.


What is the working principle of anti-explosion fuel tanks? I recently read a question about Anti Explosion fuel tanks which are self sealing. But the technology seemed to be too old after a bit of research, and that it was difficult to apply this age old technique to pressurized fuel tanks at high altitudes. What are the modern technologies being used for auto - sealing of fuel tanks after being hit by enemy fire to avoid detonation?

Modern military fuel tanks use the same basic technology to seal the tank after a puncture as WW2 aircraft did, which is the use of a laminated rubber-textile material, which tends to retain its form after being torn. The main difference between modern tank liners and WW2 liners is that the modern liners use more sophisticated materials so they can achieve the same benefit using a much thinner liner (hence less weight).

Bullets hitting a tank do not cause "detonation" unless they generate a spark and the fuel-air mixture in the tank is in ignition range. Also, most aircraft explosions are not detonations, they are deflagarations. The liner does nothing to prevent this. The main functions of the liner are to prevent fuel from leaking out of a punctured tank and to maintain the integrity of the tank in a low-altitude mishap or crash. The main test for a liner is the "drop test" in which the liner is filled with fuel and dropped from a height of about 50 feet.

The advantage of pressurizing a tank with air (inerting) is that it increases the critical temperature of an explosive mixture. If the critical temperature of the mixture is above the ambient temperature, then the tank will not explode spontaneously when sparked. A modern variation on this is called "nitrogen inerting". The idea with that is to pressurize the tank with nitrogen. This makes the tank spark proof.

Note that inerting technologies do not prevent a fuel tank from blowing up if an aircraft is hit with ordnance. The reason for this is that typically the way an aircraft blows up is that damage from the ordnance starts a fire. The fire then rapidly evolves fuel-laden gases into open compartments of the aircraft. As soon as these gases reach the ignition mixture, the fire deflagarates the mixture, causing an explosion. Inerting does little to prevent this.

Inerting is very useful, however, because it can prevent a plane blowing up due to lightning or problems with electrical wiring or static electicity buildup.


How to land the aircraft when the flight deck is full of smoke? If a fire occurs in flight, the crew will likely try to land on a diversion airport. However landing presupposes seeing the primary instruments, switches and controls.

Source

In case the fire is not extinguished in time, how would the crew manage smoke in the flight deck to be able to land safely.

Smoke is a real challenge on an aircraft. The first course of action, other than extinguishing the source of the smoke, if possible, is to evacuate the smoke. In some aircraft windows can be opened. Some have a system to vent the smoke outside. In the crash of SAA flight 295 it was mentioned that the smoke evacuation procedure on the 747 Combi was to open the entry door in flight.

When UPS Flight 6 had an onboard fire the smoke evacuation system was inadequate and the pilots were unable to land safely. They were unable to see any of the instruments or the runway. It ended in disaster. Many lessons were learned from it and advances were made to help deal with smoke in the cockpit.

There are three distinct problems with smoke:

Smoke inhalation Having an adequate supply of breathable air or oxygen is key. On UPS 6 the captain's oxygen supply ran out. He attempted to get to another mask, but succumbed to smoke inhalation before he could get there. There can still be plenty of oxygen in smoke-filled air, but smoke contains many toxins that quickly damage the lungs making it impossible to get the oxygen into the blood. Some toxins damage the hemoglobin in the blood so that it can't pass oxygen to tissues. Some types of material can even produce cyanide when burning.
Eye irritation. I was in a house fire once and I can tell you that my biggest problem was the eye irritants in the smoke. Even a moderate amount of smoke contains enough irritants to be debilitating. The smoke in my house was nowhere near being thick enough to prevent seeing through it but my eyes teared up and there was an almost irresistible reflex for them to close. It's very painful and it takes a lot of effort to keep them even partly open. Finding the fire extinguisher was a difficult task. One of the lessons learned from the UPS accident was that pilots needed to have protection for their eyes also. The best solution is to have full face oxygen masks similar to what firefighters wear.
Opacity Since a cockpit is enclosed, if smoke builds up faster than it can be evacuated then it can become thick enough to prevent seeing through it. I've read stories of pilots of light aircraft actually sticking their head out the window to land. Seeing instruments is also a problem. One development made in the wake of UPS 6 is the Inflatable Vision Unit. This is a transparent inflatable bag that fills up with clear air and displaces thick smoke to allow pilots to see instruments and out the window.

source
I'm not sure how many aircraft are equipped with such a system, but combined with oxygen and eye protection it could make a big difference in a severe smoke situation. (As was apparently experienced by Santa this Christmas Eve!)


Can wing-tip vortices be reduced/eliminated with a rear-facing propeller near the wing-tip? Let's say we have a propeller-driven aircraft in the pusher configuration (rear-facing propellers). If we could somehow put an engine at the wing tip (ignoring structural concerns), and maybe make the propeller rotate in the opposite direction of the way the wing-tip vortex wants to spin, would this eliminate or at least drastically reduce the wing-tip vortex?

Yes. From an aerodynamic standpoint it makes some sense to use the wingtip vortex in combination with a propeller.

In this article by Sinnige et al., the researchers modeled and tested a propeller in various positions along a semispan, concluding that there were real gains to be had due to the increased span efficiency. Up to 15% less drag was measured when the propeller was positioned at the wingtip compared to a conventional mounting:

  By positioning the propeller at the tip of the wing, the slipstream interacts with the flow around the wingtip, thus affecting the roll-up and downstream behavior of the wingtip vortex. PIV measurements downstream of a propeller–wing model showed that this leads to a reduction in overall swirl with inboard-up rotation, for which the swirl in the slipstream is opposite to that associated with the wingtip vortex. At the same time, the system performance was found to improve due to a reduction of the wing induced drag, leading to the conclusion that the decrease in swirl causes a reduction in downwash experienced by the wing.

  Apart from the change in drag, the interaction of the wing with the propeller slipstream also modifies the wing lift. The locally enhanced dynamic pressure increases the lift over the spanwise part of the wing washed by the slipstream, which is amplified by the induced swirl for the case with inboard-up rotation. As a result, a strong spanwise variation in lift occurs with the propeller on. The induced velocities caused by this lift gradient lead to a spanwise shearing of the slipstream. With outboard-up rotation, the swirl in the slipstream acts to locally oppose the increase in wing lift due to the propeller-induced dynamic-pressure rise. Compared to the inboard-up rotation case, this leads to a reduction in wing lift at a given angle of attack, thus also a reduction in maximum lift coefficient. Furthermore, the direction of the spanwise shearing of the propeller slipstream is inverted on both sides of the wing.

  To quantify the potential aerodynamic benefits of the wingtip-mounted configuration, a direct comparison was made with a conventional configuration, with the propeller mounted on the inboard part of the wing. The increase in wing lift due to the interaction with the propeller was 1 - 4% smaller for the wingtip-mounted configuration than for the conventional configuration. For the latter, the enhanced dynamic pressure and swirl in the slipstream acts over double the spanwise extent, and on a part of the wing where the section lift is higher than for the wingtip-mounted configuration. At higher angles of attack, the lift advantage for the conventional configuration could be further enhanced
  by the local angle-of-attack increase in proximity of both sides of the nacelle.

  In terms of drag performance, on the other hand, the wingtip-mounted configuration showed superior performance. At a wing lift coefficient of $C_L = 0.5$ and a thrust coefficient of $0.09 < C_T < 0.13$, the drag reduction amounted to about 15 - 40 counts (5 - 15%) compared to the conventional configuration. The aerodynamic benefit of the
  wingtip-mounted configuration further increases with increasing wing lift coefficient and propeller thrust coefficient, leading to a drag reduction of 100 - 170 counts (25 - 50%) at $C_L = 0.7$ and $0.14 < C_T < 0.17$. An analysis of the wing performance confirmed that this drag benefit is mostly due to a reduction of the wing-induced drag. Compared to the conventional configuration, a relative increase in span efficiency of up to 40% was measured for the wingtip-mounted configuration. Although the exact drag benefit will be specific to vehicle design and operating conditions, it is concluded that the interaction between the propeller slipstream and the wingtip vortex leads to a clear drag reduction for the wingtip-mounted configuration.

Keep in mind this is purely aerodynamical, of course, and from a structural standpoint things might not be so clear-cut. While weight in the wings helps alleviate the bending stresses generated by lift, a large mass at the tip can lower the first bending eigenfrequency to unacceptable levels, risking a coupling of the wing oscillations with some other mode in flight or on the ground.

As far as I am aware wingtip fuel tanks have mostly been used on relatively low aspect ratio wings, which lends some credence to the magnitude of this problem.


Can high-bypass turbofans cruise at high altitude? They have talked for years about re-engining the B-52 with something more modern than its TF33-P-3/JT3D turbofans, which are fairly low-bypass (1.42:1 for the JT3D).

Modern engines are much higher bypass - like the GE Passport at 5.6:1, similar to the CF34 - in the same weight class and thrust as the TF33.   A larger engine like the LEAP has an even higher bypass ratio, e.g. 11:1.

Now, the B-52 has a published operating ceiling of 50,000 feet.  The 737, A320, Bombardier RJs etc. have a ceiling of 41,000.

However the KC-135s, re-engined with semi-modern CFM56 high-bypass turbofans, have a ceiling of 50,000 feet.

So I am confused. Does the bypass ratio have an impact on the practical ceiling of the aircraft?  Could the B-52 fly to current spec with engines like the GE Passport?

A side question... the TF33 claims a specific fuel consumption of 0.56 lb(lbf-h).  I can't seem to find that figure on the most recent high-bypass turbofans.  Is it inapplicable to high-bypass turbofans?  If not, is there a viable way to figure what a modern engine would do to the B-52's range?

Yes in principle, but some modifications are advisable.

What limits the maximum operating altitude of a jet engine (besides the thrust needed to climb up there) is the length of the combustion chamber and the absolute pressure of the air entering it. Since the atmospheric pressure drops with altitude and the compression ratio of the compressor stays constant, the absolute pressure in the combustion chamber drops with altitude.

For combustion to take place, first the fuel droplets injected into the air stream need to evaporate. This is made easier by higher temperature and pressure, and the lower both are, the more residence time of the fuel-air mixture (caution, PPT link) in the combustor is required for good combustion. Longer combustors have higher pressure losses and weigh more, so engine designers try to limit their length.

Just throttling down can already cause the ignition to stop at high altitude. If a flame-out occurs, the engine cools down quickly and a restart at a lower altitude might not be possible. Turbofans suitable for high altitude operations use special measures to stabilize the flame. When they are in place, there is no reason the B-52 can't continue to fly at 50,000 ft.


What is P-Factor in Propeller Aerodynamics? What is the P-Factor when we're talking about a Propeller Aerodynamics ?

Thanks

If the airflow is parallel to the axis of rotation of a propeller, the resulting thrust force will also be parallel to the axis of rotation and act on the center of the propeller disc.

If, however, the airflow hits the propeller at an angle of less than 90°, the resulting force will tilt towards the flow direction and shift away from the center of the propeller disc in a direction orthogonal to the directional change.

Example: You fly in a single-engined plane, the two-bladed prop is spinning clockwise when seen from the pilot's view and you push the left pedal such that the aircraft flies in a sideslip. If both propeller blades are level, nothing much changes, but if the propeller turns another 90°, both blades will see very different flow conditions (see the sketch below):

For the upper blade, which moves from left to right, the sum of circumferential speed ($\omega\cdot r_{Prop}$, red) and air speed ($v_{\infty}$, blue) is bigger than that of the lower blade (black arrows) and hits the blade at a larger effective angle of attack $\alpha_{eff}$. Thus, the lift force created by the upper blade is much bigger, and as a result it will act at a point on the upper half of the propeller disc.

The same happens when the plane flies at a high angle of attack and high power (ground run of a taildragger, or climb) and the airflow hits the propeller disc slightly from below. Now the thrust force will move to the right and tilt slightly downward. This will cause the aircraft to  turn to the left and must be compensated with right rudder.

This effect is sometimes called p-factor, but this is not a factor in an equation, but something you need to factor in when flying at high angle of attack. Note that the rotational component of the prop wash will cause a similar effect when it hits the rudder at an angle, adding to the leftward tendency of the plane.


How does auto-trim work on fly-by-wire aircraft? As I understand, you trim to reduce the effort needed to maintain the stick in the right position. Thus, you may reach steady flight before moving the trimming wheel.

In fly-by-wire aircraft (to fix things, let's consider an A320), there is no such effort to maintain as you use sidesticks. Moreover the elevator may move almost constantly (and thus always apply some effort) to compensate turbulence (enhance stability feature).

After reading this question, I understand that trim is achieved by moving the stabilizator and that in normal law it is done by the computer (we actually see the trim wheel moving alone)

My question comes in several parts:

In flight in normal law, how and when does the computer decide it must trim the plane?
What does it take into account to trim the plane (speed? flaps configuration? average position of the elevators for the last few seconds? a mix of all? I guess average position of the elevator in a sliding time window is enough)
Does it anticipate the trim (e.g. trim before or while changing the flaps configuration)?
What happen on the ground? For example during the take off roll, I don't think there is enough data to feed an auto-trim system, but I may be mistaken.
What happen if not in normal law (I guess auto-trim would be one of the feature unavailable in alternate law)?

EDIT: althought the question may seem similar to this one, it differs as my question address the decision process used by the auto-trim system to command the flight control surface, and not the flight control surface itself (the use of stabilisator as trim in the A320)

In fly-by-wire aircraft (to fix things, let's consider an A320), there is no such effort to maintain as you use sidesticks.

Let's be clear: there is no such effort on the pilot side, but the forces on the surfaces are still there and are taken care of by the electro-hydraulic actuators.

  In flight in normal law, how and when does the computer decide it must trim the plane?
  What does it take into account to trim the plane?

I will answer these two together. And let's remember what written above: the actuators are taking care of the control surfaces loads, this means that part of the actuator authority is being used to control a static load.

In an ideal situation all the authority (coming from hydraulic pressure or coil current) can be dedicated to control transients: gusts, configuration changes, turn entering, turn leaving. If you are allocating part of this authority to keep level flight, a gust (for example) that otherwise would have been easily compensated for, will lead to a momentarily loss of coordination, reducing the comfort of the passengers.

That is what (mostly) you use to trim the aircraft: if your actuator is constantly (or on average over several seconds) applying a certain force in a certain direction, the system will use the trim functionality to remove said force while not altering the flight equilibrium.

  Does it anticipate the trim?

I have no public reference for this.

  What happen on the ground?

Usually you leave the aircraft with no trim.

  What happen if not in normal law (I guess auto-trim would be one of the feature unavailable in alternate law)?

Unless you are outside of normal law for actuator-related issues (power/hydraulic losses, for example) I see no reason why trimming would be unavailable, all that is required for trimming, as said above, is the average load on the actuators and trimming actuation capabilities.


Are regulations covering private jets different from those covering commercial jets? Do private jets have relaxed FAA regulations (and regulations imposed by any other aviation agency) when compared to commercial jets? If yes, which aspects of aviation are these relaxations are pertaining to?

Technically no, but in the spirit of your question, yes.

All aircraft, including those operated for private and commercial purposes, are governed by 14 CFR 91 - General Operating and Flight Rules.

14 CFR 119 specifies additional regulations that govern certain types of aircraft and operations, including larger private aircraft and commercial operations:

14 CFR 125 covers larger (airline style) private aircraft
14 CFR 121 covers the airlines
14 CFR 135 covers commuter and on demand (charter) commercial operators

So it isn't that private aircraft have relaxed regulations, it is just that they aren't required to comply with the additional regulations that govern the airline and charter operators.

There are many, MANY additional regulations that commercial operators have to comply with, including operational and maintenance regulations.

A few example:

Pilots flying commercially have strict limits on the time that they are allowed to fly or be on duty.  Pilots of private aircraft don't have any limit, other than not to fly if it would be unsafe.
Commercial pilots are subject to more strict medical requirements.
If an aircraft has to divert due to a mechanical problem, it must be reported to the FAA if being operated commercially.
There are strict limits on how far that a commercially operated aircraft may be from a suitable airport, but there are no such limits for privately operated aircraft.
Passengers must be screened and must be checked against government maintained no-fly lists for commercial flights.
An aircraft used for commercial purposes is required to be inspected more often.
With certain (very limited) exceptions, commercial aircraft are required to be operated by a company (certificate holder) with required management personnel such as the Chief Pilot and Director of Maintenance, while private aircraft can be managed by one person (even the pilot).

See the online eCFR for the specific regulations that fall under each part.


Was the runway upgrade at Mataveri Airport on Easter Island really related to the Lee Correy novel "Shuttle Down"? This answer to the question Could the Space Shuttle have landed on any long runway other than those specially reinforced at Kennedy (TTS), and Edwards (EDW)? says:

The Mataveri Airport on Easter Island was a planned abort site for the Space Shuttle. Since the Space Shuttle has no means of propulsion, you might want to have a fairly tight mesh of potential landing sites in event of an emergency.
As a nice side-effect, the long runway allowed for larger passenger aircraft to service the island, which boosted tourism. A nice win-win situation.

What caught my eye is the comment:

The runway improvement happened only after the problem of an unprepared emergency landing there occurred... in a novel. But then none of the Vandenberg launches for which it would have been a launch abort site ever ultimately happened.

followed by this comment:

He's probably talking about Shuttle Down by Lee Correy. https://en.wikipedia.org/wiki/Shuttle_Down

Question: Is this timing factually correct? If so, was this coincidental, or is there in fact some causal aspect to the relationship?

As much as I enjoyed reading the novel after reading the Wikipedia article about Mataveri Airport I am somewhat disappointed by my answer. The novel was published in 1980 and the official agreement between the United States and Chile was not signed until 1985 there is circumstantial evidence that the novel did not play a causal role.

In Glynn S. Lunney's Oral History from NASA's Oral History Project. Link to Full Text It appears that from very early on in the Air Force's involvement with the Shuttle Project that Easter Island was identified as a possible abort landing site. They didn't like it because of the short runway but they thought about it. Because this is an oral history it is hard to pin down exactly when these thoughts were happening but the context makes it look like it was quite early.

Naturally all of the news articles from 1984-1987 about the extension I found never mention the novel. Nor does the official text of the Agreement.

It was a fun little novel though. Which strangely enough foresaw most of the logistical problems that would arise from having a NASA retrieval crew on Easter Island. Especially the water and sanitation limits.

Having kept looking for a bit I found an interesting declassified memo from 1966! The Air Force has been considered their own manned space flight program launching from the Western Test Range heading south and using Easter Island as a possible abort landing sight. Another memo from 1967 says it got so far as actual discussions with the Chilean government. Even though these documents were classified it is clear that the idea of using Easter Island as an emergency landing site did not come from the novel.


What changes are needed for a piston-prop aircraft to withstand saltwater environment? I'm interested in WW2-era piston-prop aircraft. I want to know what changes are needed to make the aircraft withstand saltwater corrosion. Presumably these are different and more expensive than the normal land versions of aircraft, or they would make them that way in the first place.

I'm not interested in the usual carrier modifications, like tailhooks and wing-folding. For this question, I'm only interested in withstanding saltwater corrosion.

I have heard that aluminum resists saltwater corrosion very well. Not so sure about steel or wood. Are there differences in the air intake? What about certain delicate instruments like a pitot-static tube?

Edit: I was envisioning any combat aircraft that fight over the ocean, but especially the more exposed stuff like low-level torpedo bombers and seaplanes since they land directly on the water. Carrier aircraft is fine too.

There is no way to fully protect an aircraft from the effects of salt water corrosion, even when any aluminium is treated with protection products like Alodyne. In fact, there is no way to prevent corrosion from happening anywhere unless you protect the item in question. Corrosion can affect an aircraft even in the dry climates.

Even if it is not landing or taking off in salt water, just being close to a body of salt water will cause corrosion. All you can do is be very proactive in washing the aircraft with clean water after every day, and using products like Corrosion-X to coat surfaces with a corrosion protection film. Even WD-40 will do a great job of this, because it is not a lubricant, it is designed as a hydrophobic [W]ater [D]isplacement product. You need to protect both exterior and interior areas, even inside the wings. Just ask any mech who has worked on aircraft for any length of time at a location near salt water.

Tailhooks and wing folding do nothing about corrosion, it just helps get the aircraft on the carrier and allows for efficient use of the deck areas.


Where does the air enter the passenger cabin? After passing through the packs and turbines, where does the air get into the cabin? On the 737-800, for example. I don't see on the roof any grill to let the air enter the cabin, look:

Source: Airliners.net

Where does the air enter the cabin? According this graphic, the air enters through the roof and exits through the wall:

It looks to me in your top image that the air vent is right there at the center of the ceiling.

It looks like a linear slot diffuser running the length of the cabin.  Similar to this


Does an aircraft's nose landing gear extend on take off? Something I noticed while flying - while on takeoff it feels as if the plane is tilting upwards even though the plane is clearly still on the ground with all sets of landing gear.

Does the nose gear extend immediately upon acceleration to perhaps generate more lift? Or maybe it's just an illusion caused by the acceleration. (I've only noticed this on large aircraft - like for example: Airbus A320 or Boeing 737.)

No, the gear doesn't actively extend, and any passive change to the strut extension during takeoff is likely to be imperceptible.

What you are perceiving during takeoff is the somatogravic illusion. It is a physiological sensation, not a physical change. Rapid acceleration, as during a takeoff roll, causes the inner ear to report what your brain assumes is your head tilting back.

The otolith organs in your inner ears sit in fluid and detect the tilt of your head. Acceleration and pitching up (or tilting back) cause the exact same movement of the otoliths. Because the otoliths are pushed backwards by the fluid, just like they would by you tilting your head back, it feels like a climb.

When an airliner is taking off, you have limited outside references to the horizon and your inner ear takes over the task of orienting you. You might notice it in smaller aircraft if you closed your eyes; in very small aircraft, the acceleration may be too slow to trigger the illusion.


Why does the F-111 sometimes squirt a giant fire plume behind it? (NOT afterburners!) As seen in multiple pictures:

First, this one, it appears the aircraft is spraying copious amounts of fuel into the exhaust!

Surely this provides no thrust, not in the way an afterburner (which the F-111 has!) does.

Is it perhaps as an alternative to flares for anti IR missiles? It seems logical, but I don't think so, because I've seen it on takeoff too!

At any rate, it is QUITE badass!

EDIT: YouTube video!

EDIT: Can any other aircraft perform this?

The F-111 has, like many aircraft, a fuel dump port so it can get rid of a lot of heavy fuel rather quickly. Most aircraft have the dump ports on the wings, the F-111 designers put it in the tail between the engines. End result is if you dump fuel and briefly light the afterburner you will ignite the liquid fuel in your wake creating a rather spectacular trail of fire.

Aerodynamically it's completely useless, financially it's very expensive, you'd only do it in combat if you were suicidal as it greatly increases your IR signature right where you don't want it, but at an airshow it does look totally badass, especially as the afterburner is adding a lot of noise at the same time.

I would expect any pilot who does a dump-and-burn outside of an airshow (or an emergency) will have his own tail set on fire by the air wing's commanding officer.

The SR-71 had a similar issue - it leaked like a sieve on the ground. Rotating for takeoff would occasionally set fire to the JP-7 on the runway leaving a burning trail behind it much like the Road Runner.

Reply to the video:
watch the takeoff section carefully. You can clearly see the afterburners come on before the fuel dump starts.

Reply to about half the comments:
Highly unlikely they designed it to do this. The F-111 was one of the earlier swing-wing planes, that meant that you can't put much on the wings. And as the bigger tank is in the fuselage anyway, someone would have looked at the space between the engines and thought it was just right for a dump pipe. The flame effect was probably discovered later.


Is using flaps the same as increasing the AOA? The purpose of trailing edge flaps is to give the aircraft more lift at lower speeds.

But do simple flaps beneficent more than increasing the angle of attack?

The image looks like part of the wing just had it's angle of attack increased, and the other part did not.

Also considering flaps lower a wings critical angle of attack, and increasing the lift coefficient are they really just another way of changing the angle of attack?

If so why do smaller planes use them instead of setting up the landing gear to takeoff/land with greater angles of attack?

The ultimate goal is to reduce the landing speed and takeoff run. Not to get the higher angle of attack. The speed without flaps would not be low enough even at higher critical AoA. The key is to generate the most lift as possible, with all means available.


How to start deriving longitudinal equations of motion for an aircraft? I hope this is a relevant place for me to ask a math question regarding aircraft design.

I am trying to understand how one would implement a controller to control the pitch angle of an airplane for a small exercise. I understand the control part and its implementation. What I do not grasp is how one acquires the longitudinal equations of motions (which are then used for the control part) which serves as the starting point. What is the starting point or what are the principles used to derive these equations? If I know how to derive these equations for a very simple case, then I know I have to linearize the equations and then apply control theory to it.

For example, how are the left and right hand sides of eq. 4.70 from pp. 164 of the following book book is derived?

I will appreciate a simple explanation of the above case.

Edit:

I am attaching two screen shots of two sets of equations from two sources. Links to the books are included below. Both sources state these are longitudinal equations of motion although their general form differ from each other.
I think I got to understand one point: these equations were derived considering translation motion on the x and z planes and rotation about the y axis (so stated in the first book) Thereafter, I don't understand the procedure.

1st set of equations from book 1:

second set of equations from source 2:

    book1: pg. 164 of Morris, Introduction to Aircraft Flight Mechanics: Performance, Static Stability

    source 2: pg 3 of this online note

Note: Answer in progress!

Part 1
(Unfortunately I'm only familiar with #1 and #3 at the moment, not #2)

(Footnote: This might be a bit simpler than your case, but hopefully it you'll be able to fill in the remaining gaps)

From this, you can some the forces up according the direction of the velocity or the lift  vector. Doing this horizontally, you get equation 1, and likewise for vertical direction your equation 3.

To make this simpler to handle, we use small angle approximation consider $\cos(0)=1$ and $\sin(0)=0$. This simplifies down to:

$$V:0=T-D$$

$$L:0=mg-L$$

(i.e. thrust equal to drag, lift equal to weight)

Part 2:

This is basically the equations of a kinetic diagram of the Free Body Diagram above, where there can be a change either in airspeed of altitude. What your second equation says is that excess thrust (T-D, Thrust-Drag) can:

be used to increase altitude: $m\times{g}\times\sin(y)$

and/ or

be used to increase airspeed: $m\times{v}$


Is it really required for a pilot to have good eye sight? My basic knowledge says that it is not necessary for a pilot to have good eye sight,  he can use spectacles.

In an article I came to know that :
The United Kingdom Civil Aviation Authority state the following:

‘An applicant may be assessed as fit with hypermetropia not exceeding +5.0 dioptres, myopia not exceeding -6.0 dioptres, astigmatism not exceeding 2.0 dioptres, and anisometropia not exceeding 2.0 dioptres, provided that optimal correction has been considered and no significant pathology is demonstrated. Monocular visual acuities should be 6/6 or better.’

*Above eye problems are high level of eye defect.

• We should be worried on normal eye problem a serious problem to become a pilot ?

Here are the guidelines regarding medical qualifications (including eyes) for obtaining a U.S. medical certificate:

From the FAA's "Guide for Aviation Medical Examiners" (Link is here)
From FAR Part 67- MEDICAL STANDARDS AND CERTIFICATION (Link is here)

Hope this helps.


Do I have to do all exercises during a checkride, even if I did them in a previous one? I am currently a private pilot with an instrument rating and multi-engine rating.  I own and regularly fly my own twin engine airplane and have been thinking about getting my commercial rating.  Part of the PTS requirements for the commercial multi-engine include the emergency procedures for engine out/emergency descents, etc.

Since I have already had a check ride (multi-engine rating) that included ALL of these maneuvers, do I still have to perform these on a commercial multi-engine check ride?

Yes, if this is your initial rating on a Commercial certificate, you have to do all of that rating's required tasks. A checkride for a given certificate is always self-contained. In the case of an additional Commercial rating (ASEL, for example) you can refer to the appropriate "Additional Rating Task Table" and you'll see that some areas are already covered by the existing Commercial rating.

If you look closely, you'll notice that the PTS standards for the same maneuvers are more precise for Commercial than they are for Private. Notice that Steep Turns differ in both bank angle and execution technique:

Commercial (from FAA-S-8081-12C)

  Task A: Steep Turns (AMEL and AMES)

  References: FAA-H-8083-3; POH/AFM.

  Objective: To determine that the applicant:

  Exhibits satisfactory knowledge of the elements related to steep turns.
  Establishes the manufacturer’s recommended airspeed or if one is not stated, a safe airspeed not to exceed VA.
  Rolls into a coordinated 360° steep turn with at least a 50° bank, followed by a 360° steep turn in the opposite direction.
  Divides attention between airplane control and orientation.
  Maintains the entry altitude, ±100 feet, airspeed, ±10 knots,
  bank, ±5°; and rolls out on the entry heading, ±10°.

Private (from FAA-S-8081-14B)

  Task A: Steep Turns (AMEL and AMES)

  References: FAA-H-8083-3; POH/AFM.

  Objective: To determine that the applicant:

  Exhibits satisfactory knowledge of the elements related to steep turns.
  Establishes the manufacturer’s recommended airspeed or if one is not stated, a safe airspeed not to exceed VA.
  Rolls into a coordinated 360° turn; maintains a 45° bank.
  Performs the task in the opposite direction, as specified by
  the examiner.
  Divides attention between airplane control and orientation.
  Maintains the entry altitude, ±100 feet, airspeed, ±10 knots,
  bank, ±5°; and rolls out on the entry heading, ±10°.


What is a vortex generator? I saw a vortex generator mentioned in an aircraft listing.

What is a vortex generator?

To be more general, a vortex generator is a small angled plate installed on an outer surface of an aerodynamic body. The angle of the plate causes the air to swirl, creating a vortex behind it. This effect allows the air flow to remain "attached" to the surface even at points where the flow without a vortex would separate from the surface.

One of the most common uses of vortex generators is on aircraft wings forward of the ailerons. When the aircraft wing stalls, the flow detaches from the wings. This means that the flow will detach before it reaches the ailerons, making them ineffective. The use of vortex generators helps the ailerons to provide control even if the rest of the wing is stalled.

Source

Of course, these also add drag, even when the wing is not stalling, so they are only added where needed.

They are also used in other places, such as the engine, as in Farhan's comment above, and also on the tail of the 737.


How are flaps controlled? I can understand what function(s) the flaps serve, but how are they controlled from an internal perspective? Does flipping the switch send signals to an electrical servo? Or is it hydraulics? How are these devices attached to the main wing body, and if they use hinges (which they probably do) where do the hinges connect to? Do these devices have "Control Horns" and "Push-rods" like RC Planes? This can also be generalised to apply to ailerons and rudders too.

EDIT: I'm primarily referring to small GA planes like the C172 and the PA-28 - So while I'd like to hear about air-liners too, I primarily want to know about its implementation in GA aircraft.

Flaps have different actuation mechanisms from primary flight controls. Flaps deflection brings a shift of pitching moment with it, and it is done slowly to give the pilot time to adjust the aerodynamic trim. Usually with electrical screwjacks, with a fine pitch that stops the forces on the flaps from feeding back into the motors.

Yes flipping the switch switches the electric motors on. Most jetliners use Fowler flaps, which ride out on their little rails attached to the wing, and clad with an aerodynamic fairing at the trailing edge. This picture (source) shows the rails, flaps, and screwjacks when completely extended.


Are there safety countermeasures for test flights that simulate crashed flights? This question is based on this episode of Air Crash Investigation concerning crash of Lauda Air flight 004.

It discusses a test flight that simulates the crashed flight (41 minutes and 20 seconds into the video), in order to determine the effects of a sudden unintended reverse thrust deployment at higher altitudes and speeds, than those of the original test flight (which tested the deployment with the Boeing 767 at around 10,000 feet).

However, since there seemed no preventives or recourses for this test flight, was this test flight as dangerous and likely to crash as Lauda Air Flight 004? If so, was it a forlorn hope or suicide mission?

ACI did mention that this test flight was conducted with the 4-engined DC-8, instead of the 2-engined B767, so is ACI implying that the greater number of engines on the DC-8 was a corrective?

The test was flown on a DC-8-72. This model aircraft is certified to have its inboard thrust reversers deployed during flight, which means that the test was either within standard operational guidelines or not too far outside them (it's possible it's not supposed to have reversers deployed at Mach 0.8, but it's allowed to have them deployed at speeds over 190 knots per @UnrecognizedFallingObject's comment, thrust reversers are allowed up to Mmo). In addition, both inboard thrust reversers were deployed; the TV show is wrong when they claim that there were 3 normal engines and one reversed one. As the test found, there was some buffeting, but there wasn't the need for too much lateral control input, because of the symmetry (there was a bit of asymmetry when deploying reverse thrust, but not once both were deployed). Also, crucially, the flight crew was prepared for this, and they had the outboard engines fully spooled up (so while there was high sink rate at high speed, they had the power to come out of the dive safely). The test protocol had them maintaining airspeed, idling the reverse thrust engines before the end of the reverse thrust run, and then having engines at full thrust already to pull up.

In short, the reason it wasn't a suicide flight was that the flight crew was prepared, the plane could take some degree of reverse thrust in flight, the reverse thrust was symmetric, the outboard engines were both spooled up and pitch was adjusted to maintain airspeed, and in general it was a controlled test environment. The TV show implies it was to see if it was possible to recover. That was not the purpose of the test; they set up the test so they knew they could recover, and the purpose was to see the effect on airflow over the wing in as controlled an environment as possible.

Source: NASA report on the test flight


What are the effects of the Boeing 787's very flexible wings? I recently came across this picture of the Boeing 787 series aircraft's incredible wingflex:

I suppose this is a consequence of using very light CFRP wings, but how does the wingflex itself improve the 787's flight performance? Do the benefits/drawbacks also apply to the 747-8 (which IIRC also uses CFRP wings)?

From here:

  The amount of flex is really a product of the material. The wing requires a specified ultimate strength; with metal, that translates into a given amount of flex. This can be varied within limits, but it is really the material, its stiffness to yield point ratio, and its fatigue properties, that control how much flex you are going to end up with. CFRP is a very different material, and has much less stiffness for the same yield point, and has essentially no fatigue problems. This is beneficial in that it provides a smoother ride in turbulence; the wing acting essentially like a giant leaf spring. There is some lift lost due to the nature of the curvature, though. However, this is relatively small.


Does cargo balance affect fuel efficiency in commercial aviation? Positioning cargo such that the center of gravity of the plane is within a certain range is essential, but is there any advantage to having the center of gravity closer to some ideal point within the acceptable envelope?

Would additional control surface drag be caused by cargo loaded right on the edge of operating standards?

Would finding an optimal loading be computationally complex? How many cargo pallets/containers fit in a large cargo aircraft?

Positioning cargo such that the center of gravity of the plane is within a certain range is essential, but is there any advantage to having the center of gravity closer to some ideal point within the acceptable envelope?

There is no one ideal point for all large cargo aircraft as defined by a center of gravity (cg) expressed as the percent of the mean aerodynamic chord (%mac). There are a lot of aircraft model and operational variations. The general idea for large aircraft like the 747 is to put the c.g. as far aft as possible while keeping undesirable operational characteristics within reason. The farther aft the c.g. is the lower the fuel burn because as you move the c.g. aft (toward the center of lift of the wing), the pitch down moment of the wing lift decreases and thus the tailplane has to supply less downward force, which means there will be less overall drag and fuel efficiency goes up (the aerodynamicists here can probably say that more succinctly).

The operating envelopes of the airplane define how far aft you are allowed to put the c.g. There are multiple constraints insofar as determining the aft most limit. Two obvious ones are controllability in engine-out situations and in turbulence.

One doesn't always try to put the c.g. just forward of the aft limit, though. There can be other considerations. For example, on 747-100/200/400 aircraft at typical weights, the aft c.g. limit is 33.0%mac, but a common aiming point for the zero fuel weight c.g. is 26.6%mac. While I don't know all the reasons for using 26.6%, one is that that is the location of the wing gear, so if for some reason you couldn't extend the body gear, the aircraft might sit on its tail when landing depending on how much fuel you had left and how far aft of 26.6% you are.

Loadmasters for a given aircraft are a good source for what the usual aiming point is for the c.g.

  Would additional control surface drag be caused by cargo loaded right on the edge of operating standards?

Yes, if you had the c.g. up against the forward limit, the tailplane would have to generate a greater downward force than otherwise, and that would mean more drag. Also, on wide-body aircraft, if you were up against the maximum lateral imbalance moment, you're going to have aileron drag that you otherwise would not have.

  Would finding an optimal loading be computationally complex?

Not really, especially if its the case that all pallets/containers are going to be off-loaded at a single destination. If there's more than one off-loading destination it gets more complicated since you'd want those pallets getting off first to be positioned such that you could move them to the cargo door without having to move pallets not getting off.

There might be other constraints as well. For example, let's say you had a 30,000 lb pallet to be put aboard a 747-100/200/400. The only area that can take that kind of weight in a single size M pallet is over the wing box. That limits you to using one side of three side-by-side position pairs. Let's say you put that pallet on the left side of the aft most side-by-side position pair. That's fine, but you have now limited the right side to a max of 6250 lb.

You also have to ensure that you don't violate cumulative loading limits from the front of the aircraft to the middle and from the aft to the middle, and a few other things besides.

Computer programs for doing weight & balance for large cargo aircraft have been able to handle all of these things since the 1980s. I wrote a DOS application in 1988 that did all these things and was eventually used by three cargo carriers. It was finally phased out in 2016.

The algorithm it used was straight forward. Sort the pallets by weight and allocate from heaviest to lightest. Put the heaviest in the position closest to the target c.g. Then put the next pallet either aft or forward of the previous depending on which will produce a c.g. closest to the target, and so forth. After each position allocation, it checked to see if any limitation had been violated. If so, it reallocated until there were no violations. Even on slow computers of the DOS era, it never took more than a few seconds to complete.

  How many cargo pallets/containers fit in a large cargo aircraft?

Depends on the size of the containers and the size of the aircraft. There are a lot of choices. Go to this ULD sizes page to see common sizes. For 747s carrying civilian cargo, size code M is probably the most used on the main deck, with either 29 or 30 positions. For military cargo size code B was that size I mostly saw on the 747 main deck, usually with 33 aboard.

The lower holds on 747s had a lot of variability insofar as the ULDs used down there.

If you want to explore 747 cargo position configurations, go to this 747 weight & balance page. The POSITION CONFIG menu will allow you to select different configurations between 30, 29, and 33 main deck positions. After selecting a configuration, you can scroll down to see the arrangement (or press F6, either the key of the left nav button).


Help in decoding this ATC instruction with landing clearance? I was reading the FAA ATC phraseology document (FAA JO Order 7110.65W) and wanted to see if I could get help on decoding what this phrase meant (from the same document):

“American Two Forty−Five, Runway One−Eight, cleared to land, number two following a United Seven−Thirty−Seven two mile final. Traffic will depart prior to your
arrival.”

Does this mean:

A) American 245 is sequenced to land after the United 737, and the United 737 will vacate the runway before the American lands?

B) American 245 is sequenced to land after the United 737. After the United lands, a different aircraft will use the same runway to depart before the American lands?

B. After the United 737 lands another aircraft will take the runway and depart prior to American 245 landing.
They may not call out what type/make/airline the departing aircraft is. I’ve heard them say ”Company departing prior to your arrival” if the traffic is the same airline though.

FAA JO Order 7110.65W
3−10−6. ANTICIPATING SEPARATION
a. Landing clearance to succeeding aircraft in a landing sequence need not be withheld if you observe the positions of the aircraft and determine that prescribed runway separation will exist when the aircraft crosses the landing threshold. Issue traffic information to the succeeding aircraft if a preceding arrival has not been previously reported and when traffic will be departing prior to their arrival.


What would happen when the fuel tank of a Cessna 172 became (partial) vacuum during horizontal flight? Let's say we are flying a piston engine high wing airplane (Cessna 172) that uses a carburetor.

What would happen when the fuel tank of a Cessna 172 became (partial) vacuum during horizontal flight?

The 172S POH, the current version in production indicates:

FUEL VENTING
Fuel system venting is essential to system operation. Blockage
of the system will result in decreasing fuel flow and eventual engine
stoppage. Venting is accomplished by an interconnecting line from
the right fuel tank to the left tank. The left fuel tank is vented
overboard through a vent line, equipped with a check valve, which
protrudes from the bottom surface of the left wing near the wing
strut. Both fuel filler caps are also vented.

FUEL SELECTOR VALVE
The fuel selector valve should be in the BOTH position for
takeoff, climb, landing, and maneuvers that involve prolonged slips
or skids of more than 30 seconds. Operation from either LEFT or
RIGHT tank is reserved for cruising flight.

NOTE
When the fuel selector valve handle is in the BOTH position
in cruising flight, unequal fuel flow from each tank may
occur if the wings are not maintained exactly level.
Resulting wing heaviness can be alleviated gradually by
turning the selector valve handle to the tank in the "heavy"
wing. It is not practical to measure the time required to
consume all of the fuel in one tank, and, after switching to
the opposite tank, expect an equal duration from the
remaining fuel. The airspace in both fuel tanks is
interconnected by a vent line and, therefore, some sloshing
of fuel between tanks can be expected when the tanks are
nearly full and the wings are not level.


What are the busiest airways? Wikipedia lists the busiest city to city routes.  But for instance (nb: this is purely speculation), flights originating in Boston would transit through much of the same airspace to get to LA as a slightly shorter flight originating out of DC.

What are the busiest actual air routes (airways) (irrespective of origin/destination cities)?  Total aircraft count, as well as passenger- and cargo-based metrics appreciated.

Is there a breakdown of aircraft volume transiting between and within the 22 area control centers in the United States?

The best map I've found so far came from this joint publication comparing the US and EU in air traffic management, but this does not show traffic flow between areas:

As originally phrased, I realize such a graph could get very much "into the weeds".  I'm rephrasing the question to start high-level and then work down (if possible).

For example, a flight from Tucson to LA involves a handoff from ZAB to ZLA, such that a numerical representation (aka directed graph) might look like this:

        In
        ZLA ZAB
Out ZLA  X   X
    ZAB  1   X

Adding flights from Tucson to Phoenix (within the same ARTCC) and from LA to Tucson would result in this:

        In
        ZLA ZAB
Out ZLA  X  *1*
    ZAB  1  *1*

Ultimately, this matrix would be 22x22, but since not all ARTCCs can handoff to all others, many cells would be zero.

You can use Flightradar24 which will shows air traffic in real time where you can check which airlines are the busiest. Flightradar24 is using the callsign of the flight and compare it with big databases of airline and airport schedules to find the matching flight number, so not all airlines are submitting their schedules.

You can choose Airline fleet database in Data/History where you can check a comprehensive guide about the fleets of the world's airlines. Once you select an individual airline to view, you'll get its entire fleet. However it won't give you exact number, but list of all airplanes flying per airline (e.g. EasyJet).

To display the number, either you should request that information from the author of the site, or there are few workarounds.

Technical analysis of the busiest airline

When you open the page with specific airline (as suggested above, e.g. EasyJet), you can type the following command in JS console (e.g. in Chrome - More tools and choose JavaScript Console):

$("#listAircrafts li").length

and it'll print you the number of flying planes (sometimes less, because of the pager).

Or use Yahoo Developer Console and type the following query:

select * from html where url="http://www.flightradar24.com/data/airplanes/ryanair-ryr/" and xpath = '//*[@id="listAircrafts"]/li'

And in Tree View, you'll see number of flying planes at the moment (e.g. count: 323) based on Flightradar24 database.

To combine all lists together, you need a script as below.

In example the following *nix command (it'll take few minutes to run):

$ time for uri in `curl -s http://www.flightradar24.com/data/airplanes/ | grep -o 'data/airplanes/.*-[^"]*'`; do curl -s http://www.flightradar24.com/$uri | grep -o '/data/airplanes/.*-[^"]*' | wc -l; echo $uri; done | paste -d" " - - | sort -nr | head -n20
521 data/airplanes/airbus-aib/
484 data/airplanes/china-southern-airlines-csn/
411 data/airplanes/china-eastern-airlines-ces/
404 data/airplanes/lufthansa-dlh/
341 data/airplanes/air-china-cca/
324 data/airplanes/ryanair-ryr/
306 data/airplanes/british-airways-baw/
259 data/airplanes/turkish-airlines-thy/
254 data/airplanes/air-france-afr/
246 data/airplanes/emirates-uae/
214 data/airplanes/easyjet-ezy/
193 data/airplanes/saudi-arabian-airlines-sva/
186 data/airplanes/air-canada-aca/
184 data/airplanes/air-berlin-ber/
179 data/airplanes/netjets-nje/
176 data/airplanes/aeroflot-afl/
171 data/airplanes/qantas-qfa/
169 data/airplanes/tam-linhas-aereas-tam/
163 data/airplanes/cathay-pacific-cpa/
157 data/airplanes/sas-sas/

It will scan over 800 different airlines from the web and it'll print sorted list of the 20 busiest airways according to Flightradar24 database at the time of scanning. Tested on Linux and OSX.

Technical analysis of the busiest route

In order to calculate the busiest city to city routes, it's more complex that above example and you'll have to write similar script (or spreadsheet) of fetching all departures/arrivals of each airport (e.g. LGW) from available Airport database over world airports page, extract data from the tables, consolidate the airport/destination and sum it up in similar way.

Example extraction from table for LGW airport:

Extraction formula which I've used to list all departures from London Gatwick in Google Spreadsheet:

=ImportHtml("http://www.flightstats.com/go/weblet?guid=34b64945a69b9cac:4bf2fb3c:1246346ea7d:4597&weblet=status&action=AirportFlightStatus&airportCode=LGW&airportQueryType=0%22", "table", 0)

So theoretically you can extract all departures of the airport per Sheet (it's like over 3000), group Destination (so you know at least the busiest destination per airport) and sum it up, do some consolidation between Sheets plus some magic, and viola. That's why it's better to write some script:) If I'd have too much time on hand, of course I could do it.

So in other words, the busiest air route would be the airport which will have the highest number of the same Destination city (if I'm correct).

You can always simplify the work by choosing top 20 airports to give you some idea how does it work (instead of checking all of them).

Conclusion

Maybe it won't answer your question directly (which route is the busiest), but it's an idea how to extract the data of the busiest airlines and similar statistics. As it seems it takes a bit knowledge and time how to do it.

If you find any easier way of extracting that data or different database, let me know:)

Summary of the busiest airline

So based on above data (and ignoring Airbus), it's:

18:00 UTC/GMT (Friday)

China Southern Airlines (484)
China Eastern Airlines (411)
Lufthansa (404)
Air China (341)
Ryanair (324)
British Airways (306)
Turkish Airlines (259)
Air France (254)
Emirates (246)
EasyJet (214)

The data is indicative and it depends on the time of day and week, so I'm not warrant of any correctness of it as this is only the example.


Is there any technical reason that prevents installation of a jet blast deflector at Princess Juliana airport? A jet blast deflector (JBD) or blast fence is a safety device that redirects the high energy exhaust from a jet engine to prevent property damage and injury.

Regarding the incident on July 13, 2017 at Princess Juliana Airport, I see no jet blast deflector installed. Is there any technical reason that prevents installation of such a safety device?

An immobile jet blast deflector could not be built far enough away from the runway end to be safely clear of the landing path. Large airplanes like 747s must touch down pretty close to the near end of the runway, which is right at the edge of the  beach, a blast deflector would be a serious hazard if an airplane came in a bit too low. Here's what I'm talking about:

A static deflector would be extremely close to the path of the landing gear.

It could theoretically be possible to install a retractable one, however sand does not make a good building surface and therefore it would be real engineering challenge.

It seems much more likely that the authorities, if they do anything, will install more fencing or other barriers to deter people from getting so close rather than install a blast deflector. This would be cheaper and achieve the same effect.