Why is this VDP not authorized? I have to admit that I’ve always kind of struggled with the Visual Descent Point (VDP) concept. Looking at the Terminal Instrument Procedures (TERPS) definition:

  “The VDP is a defined point on the final approach course of a
  non-precision straight-in approach procedure from which normal descent
  from the MDA to the runway touchdown point may be commenced, provided
  visual reference is established.”

Fine, I take that to mean that if I start down from Minimum Descent Altitude  (MDA) too far after passing the VDP then my descent won’t be “normal”. What I don’t get is when the VDP is “Not Authorized”. Take a look at the RNAV (GPS) Z RWY 24 approach for KTTN. Included in the notes is the statement: “VDP NA with Northeast Philadelphia altimeter setting”.

What does that mean? Why is the VDP not authorized now that the MDA is 60 feet higher? If I didn’t want to descend too late before, I certainly don’t want to go past the VDP when I’m 60 feet higher! Is the note just telling me I better have the required visual references in sight so I can start down BEFORE the VDP? That might not be possible if visibility is at the 1 mile minimum.

@voretaq7:

I understand the implications of altimeter setting from a different airport and how your actual altitude could be higher than indicated.

I guess I'm hung up on what it means to "use" the VDP. Assuming that you use the Dive-n-Drive technique (rather than a constant descent rate), then your statement "Fly the approach until you have the runway environment in sight and then figure out your own glide path intercept based on the visual references you have" is what you are going to do regardless of what altimeter setting you use. In that case, what does it mean to "use" the VDP? In a light piston aircraft with airspeed under control, I may prefer to wait until the VDP and make a steeper than normal descent even if my actual altitude if higher than indicated. That way, in poor visibility, I avoid obstacles that may exist below the MDA prior to the VDP. So exactly what is the FAA saying I'm not authorized to do while using the PNE altimeter setting?

The key is in the part of the procedure description I've highlighted:

When local altimeter setting not received use Northeast Philadelphia altimeter setting -- you're using the altimeter setting for an airport 15 miles away.

15 miles may not seem like a lot of distance, but it's enough for there to be a notceable variation in altimeter settings. The FAA assumes this error will be in the least favorable direction (i.e. your altimeter will indicate you're higher than you really are), and accordingly they take some precautions when you're using another field's altimeter setting.
In this particular case:

The decision altitudes (DAs) are higher.
Baro-VNAV (vertical guidance for your descent based on your altimeter) is not authorized.
The use of the charted Visual Descent Point (VDP) is not authorized.

The VDP is telling you "If you are on the approach path and remain at the MDA until over this point on the ground you'll be on the glide path to the runway" (or alternatively "You can plan a constant-rate descent that intersects the MDA over this point and you'll be on the glide path to the runway").

Using the charted VDP is specifically not authorized in this case because the nominal descent angle you will have passing through it counts on your altimeter being accurate and your aircraft being at the MDA. Since the MDA has changed and we're using a remote altimeter setting the location of the VDP isn't going to be what's shown on the chart. (For example, if you're 60 feet higher than you "should" be & everything else is perfect the VDP moves further away from the airport to provide the same glide path at a higher altitude).

Rather than charting several visual descent points (which would be futile anyway as you can't know the altimeter error portion of the equation) the FAA just says "Don't use it: Fly the approach until you have the runway environment in sight and then figure out your own glide path intercept based on the visual references you have."


Why don't nonrigid airships have multiple gas cells? Nonrigid airships (blimps) differ from rigids and most semirigids in having the entire envelope form a single large gas chamber, rather than dividing the lifting gas among several redundant gas cells.  Having only one compartment for the entirety of the airship's lifting gas raises the specter of an envelope rupture causing the loss of the airship's entire gas load,1 resulting in ungood things happening to the airship and its occupants.

In contrast, having multiple discrete gas cells (either by using a number of separate internal gasbags contained within the outer envelope, or else by dividing the envelope itself into compartments using gastight septae), in the fashion of all rigids and almost all semirigids, would allow the airship to remain airborne even if one or two2 of the gas cells were ruptured and completely deflated,3 and would allow gas cells of uncertain structural integrity to be filled only partially (to reduce the stress on the cell walls, and, thus, the likelihood of a complete rupture) while still maintaining full inflation on the known-good cells.  In addition to the obvious safety benefits, the use of multiple gas cells would also allow better control of the envelope's shape (by allowing different gas cells to be inflated to different pressures to - for instance - stiffen the parts of the envelope experiencing the greatest loads), and would allow minor to moderate maintenance and repair work to be done on the envelope and/or individual gas cells without having to deflate the entire airship.

So why don't nonrigids have multiple discrete gas cells, rather than a single, undivided envelope?

1: This would be exacerbated by a nonrigid airship's need to maintain a considerable positive internal gauge pressure in order to prevent the aerodynamic forces on the airship from distorting its envelope; this positive internal pressure would greatly accelerate the escape of gas from the envelope, and the tension forces on the envelope resulting from said positive internal pressure would tend to produce severe tearing emanating from the site of any rupture (think of what happens when you pop a party balloon).

2: Or, potentially, more, depending on the size of the airship and the number of gas cells contained therein.

3: Note that this does not necessarily mean that the airship will remain capable of forward flight (although, depending on the circumstances [primarily which gas cell(s) lose pressure, and where within the envelope they happen to be located], it very well may), only that it won't be in danger of plummeting to the ground in the event of a rupture.  If a gas cell near the middle of the airship were to lose pressure, this would likely cause the envelope to distort to such a degree as to render controlled forward flight impossible, as @A.I.Breveleri correctly points out - but the key is that the airship would still have one or more intact gas cells providing a considerable amount of residual lift, allowing a controlled forced landing.4

4: This would be an especially great advantage in the case of a major rupture occurring at altitude (where the undivided envelope of a typical nonrigid could easily lose its entire gas load during the time needed to descend to ground level), and even more so if the temperature gradient of the ambient air is greater-than-adiabatic (in which case you lose lift as you descend even if you aren't progressively losing gas).

With the loss of one cell you also lose the same fraction of lift. Unless you can drop an equal amount of ballast quickly, having some more gas cells isn't much of an advantage – the ship still falls out of the sky.

The Zeppelins could lift up to three times their empty weight simply because they became more efficient by growing larger. Blimps are small, so their lifting capacity is restricted. Carrying so much ballast would require a much bigger blimp.


How much pressure do boost and jettison fuel pumps produce? What is the pressure output of a (boost) fuel pump on a Boeing 767 and/or 777, compared to a heavy-duty jettison fuel pump.

I looked up a cannister boost pump and jettison fuel pump on the Eaton website and found a cannister boost pump for the 747 that puts out 28,000 Pounds Per Hour, and a jettison pump also for the 747 that puts out 40,000 PPH.  Safe to say jettison pumps generally have a higher output than engine boost pumps, for obvious reasons.


Is autorotation possible in a tandem rotored helicopter? I just wonder, whether a synchronized autorotation is possible in case of turbine failure (one or both gas turbine engines). All Gearboxes obviously must turn not to desynchronize -> lethal

On the Chinook, the sprag clutches that allow the drive system to freewheel when an engine fails are between each engine's step-down transmission and the "combining transmission" that receives torque from each engine and sends it to the front and rear rotor transmissions.

This means that the entire drive line between the rotors always remains engaged and in sync regardless of whether any power is being supplied. If one engine fails, it's simply disconnected from the drive system by its sprag clutch with the remaining engine doing the work, like any helicopter.  And if both engines are shut down, same deal; both engines are disconnected by their sprag clutches and the still interconnected rotor system will autorotate with the correct blade intermesh maintained.

So the Chinook can loose one engine and continue flying (more or less), or lose both both engines and glide to land like any multi-engine helicopter.  If you loose one of the gearboxes or drive shafts in the interconnected system however, now you have an unpleasant situation.


What are the implications of Visual Descent Angle Not Authorized (VDA NA)? On some non-precision approach plates, there is a VDA/TCH mark. My understanding of it is information-only. If you pass its starting fix at the charted altitude and maintain the given descent angle, the airplane will flying over the runway thresh hold at TCH.

However, I noticed one NOTAM mentions this information is not authorized, e.g. E16 RNAV (GPS) RWY 32 (on Nov 2019).

!FDC 9/9659 E16 IAP SAN MARTIN, San Martin, CA. RNAV (GPS) RWY 32, ORIG-C... GELVY TO RW32: 3.37/45 NA. 1903201729-2103201728EST - (From FAA website on 2019/11/22)

Given "GELVY TO RW32: 3.37/45" is still one spatial path for the non-precision approach, and the LNAV approach is still available. There are no airport elevation and re-defined fix height. So my questions align with,

1) Why am I not authorized to fly "GELVY TO RW32: 3.37/45", if my airplane is capable to maintain descent angle and have runway environment in sight right above MDA.

2) Are there any additional procedures to follow even for flying VDA/TCH at an airport when are authorized?

E16 RNAV (GPS) RWY 32

--

This NOTAM is a Flight Data Center (FDC) NOTAM which is used to amend published Instrument Approach Procedures (IAP).  That means this NOTAM is effectively amending the procedure as the FAA hasn't had the opportunity to change the procedure yet.  This is probably due to a new obstruction that has been placed in the decent path.  Perhaps a new cell phone tower has been erected.  That is why it is always a good idea to check NOTAMs especially when flying under IFR.

EDIT:  To clarify a comment I made to OP, the MDA usually requires 350 feet obstacle clearance along the final approach segment.  However, when flying a glide path, the Required Obstacle Clearance (ROC) increases the farther away you are from the threshold (see graphic from Code 7700 Website).

The ROC is based off of the Obstacle Clearance Surface calculated for the approach.  Notice that if a new obstacle is erected somewhere along the glide path it is possible for the MDA to still be satisfied but the glide path ROC may have to change.  That is probably why the MDA is not changed in this NOTAM but the glide slope is Not Authorized.

Quote from 7700 website:

  (1) If the OCS is penetrated, the OCS slope may be adjusted upward, thereby increasing the glide path angle. The glide path angle would increase because it is dependent on the required slope.


Can you be a pilot after being diagnosed with Generalized Anxiety Disorder? Went to my primary care physician who referred me to the psychologist. Went in for two evaluations. The only thing that had been written on my medical record was anxiety, no medications of any sort had been prescribed and the psychologist asked that I enrolled in anxiety classes in college (this was during my freshman year) I am a sophomore now.

Was wondering if this diagnosis of anxiety could prevent me from obtaining a third class medical, although it is not listed as anything that requires an FAA decision especially if no medication has been taken or prescribed.

The first thing is to determine if you were evaluated for anxiety, or diagnosed with an anxiety disorder.  Your primary physician's office can answer that because it will be in their records.

Often (not necessarily applicable in your case) symptoms which do not require ongoing therapy or medication may not have hard diagnosis.

Avoid assuming that you have a disqualifying condition.  Contact your physician and ask if you have that diagnosis.  It might help to explain why you are asking, specifically that you would like to fly and get an FAA Medical, so that they know the context of the question.

You might also want to read this FAA writeup on Item 47:

https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item47/et/

As a final note, as an instructor I have had several students over the years who had serious, diagnosed psychiatric issues.  Most of them got effective help. A few became ineligible for a FAA medical. One refused to seek treatment as they were concerned about losing their medical. (I discontinued providing instruction, which aggravated the problem.) However, I know of no pilot or pilot wanna-be who had to take a class on anxiety or anger management, or personal relations, or similar to be denied an FAA medical on that basis alone.

In your case, the anxiety may have been situational, and developmental (as an adolescent) and clarifying whether you have a diagnosis (as opposed to just an evaluation) before you spend the big bucks for an AME exam would be appropriate.


Why mount multiple autocannons on a fighter or CAS aircraft as opposed to a revolving barrel auto-cannon with a higher rate of fire? Why would one design an aircraft with multiple chain guns instead of a single large rotary cannon, like the GAU-8 Avenger, and similar weapons?

Image source

Same difference as between a shotgun and a rifle: if you need to hit a moving target, like a clay trap target or pigeon or aircraft, it's best to spread the projectiles out so that there is more of a chance that the target meets them. If however the target is (almost) stationary, nothing beats lining up carefully and inflicting the maximum damage with the projectile.

Heavy machine guns are mounted on swivels to create an effective area instead of a line, and only one bullet would be required to stop a soldier. A trap shooter swivels while overtaking the spinning disk, thereby spreading out the spray of shot. But an A-10 lining up for a tank kill wants to maximise impact upon this one tank only - just the one bullet landing anywhere on an armoured tank may not do the job.

When multiple cannons/machine guns are mounted across the wings, the aircraft is set up for dogfighting. Which they are not designed for anymore.


Time to switch instructors? or not? To give a bit of background before I get into my scenario, I recieved my PPL in Canada two years ago, and then my night rating about 10 months after that. I was able to remain current but due to financial reasons I only just recently was able to go for my CPL.

The instructor I have now was just randomly assigned to me, and took me up to show that I was able to do upper airwork. Needless to say my skills had eroded, which wasn't all that surprising - so it took a few lessons to get all that rust off. Then we decided to practice diversions, which again my skills were eroded.

Now I have been studying all these maneuvers at home and playing them over in my head to get all the steps down pat, which I know isn't the same as flying. Having said that, I am not flying that regularly either which is down to my schedule and things pop up sometimes on my 4 days off so I do take full responsibility for that no doubt.

My instructor isn't all that encouraging though, he basically is trying to tell me without saying it, "stop wasting your money and stop flying". He doesn't try to really help, he basically criticizes me, which I am able to take, and he's not wrong on what he is saying -  but that's it, he doesn't really go much further than that.

He also has mentioned that my walkarounds are taking too long and that I am not fast enough at it, and I should be quicker with checklists, when all I am doing is being methodical and sure that I am not leaving anything out. Another thing is, half the time we don't do a briefing/debrief so the first time we practiced diversions again, we went up without a CPL diversion briefing and then we came back and he basically told me that wasn't up to CPL standard and this is how we do it.

So shouldn't he have done a debrief so I could know that? Another thing is he was late for a lesson by a half hour, but gave me flack for being 5 min late... I do feel frustration with him but I am not one to talk openly about that frustration so maybe I should grow a pair and talk to him about it? Before switching instructors?

Sorry for this being long but thanks to anyone who has tips or criticism.

It's your money. Spend it on someone you are comfortable with can have a good rapport with.


What Height Atc radar reads from pilot selection Just want to know whether ATC radar always reads aircraft height with respect to standard altitude setting or will read the change in height if we select QNH instead of standard 1013 hPa (QNE)?

The altitude reported by the mode C of the transponder is based on the standard altimeter setting (29.92 in the United States)


How can this STOL plane fly so slow? This plane's ground speed looks slower than a person's walking speed, maybe 10km/h!? It can not be possible that an airflow of 10km/h around wings keep plane in the air.
What is the key for such a slow flight?
a) head wind
b) blast from propeller make additional lift at wings
or
c) maybe propeller upward thrust component help to lift plane in the air

Yes, yes and yes:

At that event the winds were 12-15kts.
There is some lift increase from propeller wash impinging on the inboard wing and flap. But most airplanes benefit from this (my own PL-2 has flaps that go all the way under the fuselage and the sink rate difference power on and power on is a lot).
Propeller thrust is contributing to the total lift as soon as the thrust line is tilted above horizontal, as a vertical component is added to the thrust vector. With a slatted wing allowing the wing to operate at up to 25 degrees AOA with the associated deck angle, engine power is starting to contribute a significant part of holding the plane up (if a 300lb thrust force is inclined 25 deg, the vertical thrust or "lift" component is about 130lbs), which is why it plummets the instant the power is removed (to better imagine the effect, just imagine you cankeep pitching the plane's deck angle to 90 degrees, where ALL of the lifting force is coming from the prop).

So, an ultralight like that should have no problem slowing to 21 or 22 kt in that configuration (a Zenith 701 can maintain control down to about that speed although its published stall speed is 30 mph or 26 kts), dropping another knot or two as it gets into ground effect, add in the head wind that was present, and you're down to a ground speed of a person running.
The headwind is kind of "cheating" in terms of absolute performance, but keep in mind that it's a competition between aircraft in those conditions on that day, so the headwind isn't a factor in the relative performance of the competitors, except to the extent it's varying at the time and small variations in wind speed are probably enough to give one plane a victory over others with more or less identical STOL performance.


Why is the nose cone of SU-34 white? The title says it all.

Can be clearly seen for example in this image:

(image source: Wikimedia)

The rest of the jet seems to have a camouflage.

It is all part of the camouflage.

The blue parts on the bottom make the aircraft hard to identify from below against a blue-background (sky). The dark parts on the top make it difficult to identify from above against a dark background (ground).

The white parts make the aircraft's size/shape difficult to determine. This helps to confuse the enemy by making the aircraft seem farther away than it really is.


What is the speed during push-back? What is the usual or maximum speed during the push-back procedure of large commercial aircraft (say, B737, B787)? Is it fixed or dependent on the aircraft type or weight or anything else? Is it different for towbarless vs. towbar procedures?

There is no regulatory guidance on how fast (or how slow) an aircraft must move during the pushback. Furthermore, there are many opinions (see below) on how fast an airplane moves during pushback.

If you watch a pushback, you will notice that ground personnel known as wing-walkers* will walk alongside the aircraft, at the wingtip, during pushback.  The normal speed of humans walking is 3-4 mph, which can surge to 5-6 mph for short distance.

The speed is not fixed. It is dependent on all the factors you mentioned plus the experience of the tug driver and ground crew as well as size of the airplane and its weight. It takes longer to accelerate a large airplane to this speed, and it is harder to slow down a large airplane.

* ICAO Annex 2 Volume 5 (Appendix 1-5) and SA CATS 91.05.1 (5)

See also:

airliners.net / Pushback-speed Limitations?
pprune.org /  Pushback and Towing - Time


Tips for the private pilot check ride I am 17 and am going to be taking my check ride for my private pilot's license very soon. What tips do you have before I go up? (Oral exam and check ride).

I am more looking for personal experience and tips from people who have taken the check ride. I know what goes on during the check ride already, I'm looking for things people know would be useful from their own experience that they want to pass along.

Do NOT worry about getting an unsatisfactory result!!  It just does not matter.  There will be no record of it anywhere but in your memory.  It's not noted on your certificate and, really, nobody will care.  The PPL is a license to learn and that is what you'll be expected to do after you pass.  The checkride merely assesses basic requirements.  Now, if you want to be a professional pilot...it still doesn't matter.  Nobody will care if you made a dumb mistake on a PPL ride and had to go back and demonstrate a maneuver again.  Anyone who does is not worth working for anyway!

Think about it, worst case you have to go flying again (that's a pretty good "worst case").  The only downside I see is having to pay the examiner fee again.

Ok, but real advice...
1.) Get sleep the night before.  You'll be nervous, but sleep anyway.  You already know everything you need to know to pass, a few more hours of studying won't make or break the ride.

2.) It's ok to say "I don't know the answer, but I know where to find it," and then look it up.  You can't say it for every answer, but it's not a deal breaker to not know something.

3.) At least one experienced pilot (your CFI) thinks you're ready to be a PPL.  If you took a stage check with an evaluators at a flight school, two experienced pilots think you've got what it takes.  CFIs don't sign off on a checkride if they think the student will fail.

4.) Be able to explain why the plane is legal to fly.  One of the examiners I used loved to ask the students to prove that the plane was legal.

5.) Be able to explain why you're qualified to take the exam.  The same examiner would routinely ask students to prove that they were qualified to take the exam.

The only way this ends is with you earning a PPL.  If it takes two rides, so what?  You've already done the hard work.  Just go flying with the examiner and show him/her what you've been showing your instructor for the past few hours.

Good luck.  Don't sweat it.


What is the relation between a helicopter's length and rotor diameter? I was looking at a couple of helicopters on Wikipedia (specifically the Boeing A160, the Robinson R22, and the Sikorsky S-46) and I noticed the main rotor diameters seem to be pretty similar to the helicopter length (see below).

Is there a reason for this, or is it just coincidence? I thought it might be that helicopters are just long enough for the tail rotor to not interfere with the main rotor, but that doesn't seem to work out, because the rotors aren't quite centered over the helicopter.

Helicopters' length and main rotor diameter legend:

                Length     Rotor Diameter
Boeing A160      35'0"        36'0"
Robinson R22     28'8"        25'2"
Sikorsky S-64    70'3"        72'0"

Important.  I am a helicopter pilot, with no expertise or experience in design so I can give you reasons for this, but not design detail.

Most design decisions are compromises.  Helicopter rotors are definitely compromises.

What is the aim of the rotor design?
To have the smallest possible rotor to achieve the performance requirements of the craft.

What limits the smallest size?
Let's assume that the blades are as efficient at generating lift as you can make them.  There are only 2 ways to increase lift for any given blade at any given angle of attack.  That is to increase the length of the blade or to move it faster through the air, i.e. to make the rotor spin faster.

What limits the speed at which the rotor can rotate?
As the blade tip speed gets faster, drag increases with the square of the speed.  Increased drag means increased power required which means heavier engine and heavier gearbox.  As speed moves to a high percentage of supersonic, turbulence and therefore drag increases enormously.  The longer the blade, the lower the possible rotor RPM since the tip approaches supersonic speed more quickly.

Why not just increase the length?
Because the blade becomes increasingly difficult (and expensive) to manufacture to handle the loads on the blade and the heavier they become requiring more robust and heavier rotors hub assemblies.

The inner part of the rotor also produces little lift since it is moving relatively slowly and since lift decreases with the square of the speed, the lift generated falls away rapidly as you move to the inside portion of the disc.  As you increase the length of the blade, without being able to increase the speed of the disc as above, the area of the disc which is "useless", increases as a proportion of the overall disc size.  Therefore, more power is needed to rotate the increasingly large useless area of the disc.

The lower the disc loading, the more efficient the helicopter is in the hover.
The disc loading is the ratio of the weight of the helicopter and the area the rotor disc describes as it rotates.  The disc loading should be as low as possible to reduce the required strength, and thus weight, of the blades especially as the weight of the helicopter increases under positive G which in turn increases the disc loading.

Non-performance considerations.  Parking; hangar space required; ability to operate in confined areas.

Given these (and other design parameters), the rotor sizes you quote will have been arrived at by factoring each of the variables to find the best compromise, according to the designer, between them to achieve the desired performance goals.

Therefore, I don't believe that there is a relationship between the fuselage length and rotor size, possibly with some influence from the need to park and hangar the resulting craft.

[EDIT]
I've been hoping that some better informed answers would be added.  As there are none, I'll continue with my simple pilot guesswork.

What is the aim of the fuselage design?
To have the smallest possible fuselage to achieve the performance requirements of the craft.

What limits the smallest size?
How many crew?  How many PAX?  Level of comfort (utilitarian - R22, or comfortable - Long Ranger).  Fuel load.  Engine and gearbox size.  Cargo and other payload.  Baggage stowage?

What limits the maximum size?
Weight.  Profile drag.  Cost to manufacture.

Non-performance considerations.  Parking; hangar space required.


What is the purpose of the Dash 8’s “TOUCHED RUNWAY” warning light? The DHC-8-400 (and possibly other DHC-8 variants) has (or, at least, had in late 2007, according to Appendix G of this AAR) a warning light labelled “TOUCHED RUNWAY”.
The extract of the DHC-8-400’s QRH quoted in Appendix G of the aforementioned AAR mentions this warning light at the end of the landing-gear abnormal-procedures section, and says what to do if the light illuminates, but not what the light actually indicates:

”TOUCHED RUNWAY”
(Warning Light)

Do Not Start APU
Advice [sic] ATC for Runway Inspection

Note: Continued flight operations require maintenance approval.

The landing gear of a DHC-8-400 (or, indeed, of any aircraft so equipped) routinely touches the runway, and the ramp, and the taxiways, and the hangar floor, all the time during routine operations - indeed, touching the ground (including, but not limited to, the runway) is literally the primary, and very nearly the entire, purpose of landing gear!  So what does the “TOUCHED RUNWAY” warning light indicate that is severe enough to warrant possibly grounding the airplane?

The light is a tail-strike indicator.

  Touched Runway system

  The  Touched  Runway  system  provides  a  warning  light  in  the  flight  compartment.  It  illuminates when the aft fuselage makes hard contact with the runway on take off or landing. The system consists of a frangible1  switch located at the bottom of the aft fuselage, activating the warning light. The system is powered from the 28 Volt DC right main bus. Once activated, the frangible switch can not be reset but must be replaced by maintenance personnel. Source: Smart Cockpit.

1 frangible
/ˈfran(d)ʒɪb(ə)l/,
adjective

able to be broken into fragments; brittle or fragile.
"the frangible skull of an infant"
denoting ammunition designed to disintegrate into very small particles on impact.
    "frangible bullets"

Figure 1. Source: ATSB.au.

Figure 2. Source: ATSB.au.

Links:

Tail strikes during landing involving Bombardier DHC 8 402, VH-QOT and VH-QOS.
AAIB Bulletin: 10/2017 G-ECOJ EW/G2017/01/03.


What is altitude above surface / ASFC? ASFC is an acronym frequently seen in official European publications, e.g. used by the French AIS:

Also in some ICAO ones, e.g in Annex 4 (Aeronautical Charts) to the Chicago Convention:

  The airspace is shown only from the surface to the higher of the
  following two levels: 1500 m/above mean sea level (AMSL) — 600 m/above
  surface (ASFC).

What is ASFC compared to AGL? Is ASFC also used over water?

As best I can tell, ASFC is only used in France and is synonymous with AGL.

First, it isn't in ICAO's list of abbreviations or the FAA's PCG, but it is in the French AIP in section GEN 2.2:

  ASFC / Au dessus de la surface / Above surface

The AIP also lists AGL, but it doesn't explain the difference:

  AGL   / Au dessus du niveau du sol / Above ground level

Second, the AIP uses both terms in a seemingly interchangeable way. For example, in ENR 1.2 (VFR rules). Compare this from 4.7...

  Come over the aerodrome, perpendicular to the runway at 2000 ft AGL,
  lights on, then join the circuit for landing

...with this from 4.10:

  Fly over the runway at 2000 ft ASFC, perpendicular to the runway
  heading with landing lights switched on,

I can't see any reason why there would be any difference in meaning in those two phrases, and the airports in those sections are not particularly near the sea.

Finally, if you consider Wiktionary a valid reference, the definitions for ASFC and AGL are almost the same and they're both stated as the 'opposite' of MSL:

  AFSC (Aviation) Désigne une hauteur au-dessus de la surface du sol ou
  de l'eau par opposition à une hauteur AMSL, dont la référence est le
  niveau moyen de la mer.

  AGL (Militaire) Above ground level : « Au-dessus du niveau du sol »,
  altitude relative au sol, par opposition à l’altitude absolue, mesurée
  par rapport au niveau de la mer.

Although this is a guess, I suspect that ASFC is simply an example of French phraseology that has now been superseded by English but hasn't been updated everywhere. I can't find ASFC used anywhere in a non-French context.


In a flat spin, does the F-16 use its rudder deflection against the rotation for recovering? If the H-tail is used in recovery from the flat spin, is the rudder used for stopping the yaw or beta of the F-16?

I know that it is surely used for inverted flat spin, but I believe that the rudder is blanked by the H-tails in upright spin and is not effective.

It is not possible to have the rudder deflection because the huge amount of AOA and control law take that in consideration and cancel (fadeaway) the pilot rudder inputs.Activating the MPO the slabs moved  max in order to get the nose down to lower AOA and after that we can get responses from the rudder .https://www.flightglobal.com/f-16-spin-recovery-technique-invented/15027.article


Can water landing be simulated? Is is possible for a flight simulator software to simulate the real time scenario of landing an aircraft on a water body. There are instances of this (Ethiopian Airlines Flight 961, US Airways Flight 1549) and the results were catastrophic/great  based on the type of water body they landed on and the situation which brought them there and several other parameters.

But I want to know if it is possible for a complex computer program to create this scenario effectively and thereby better equip the pilot ?

Technically yes, but I do not know of any simulator which includes this. The water forces can be calculated in the same way as the air forces, so I see no reason why it should't be possible.

Historically, model tests were made to check that a new airplane would behave well when landing on water. The simplest tests would use a catapult and launch the aircraft model into a lake, and more thorough tests use water tanks where the airplane model is pulled along the water surface while being suspended on a rig. This allows to measure forces, while the catapult launch will only show the dynamics of a water landing. Results like these could be used to calibrate the computer model, so you can be sure it behaves like the real thing.


Is there a simple relationship between angle of attack and lift coefficient? Is there an equation relating AoA to lift coefficient?

I have been searching for a while: there are plenty of discussions about the relation between AoA and Lift, but few of them give an equation relating them.

I know that for small AoA, the relation is linear, but is there an equation that can model the relation accurately for large AoA as well? (so that we can see at what AoA stall occurs)

I am not looking for a very complicated equation. Can anyone just give me a simple model that is easy to understand?

(Of course, if it has to be complicated, then please give me a complicated equation)

In the post-stall regime, airflow around the wing can be modelled as an elastic collision with the wing's lower surface, like a tennis ball striking a flat plate at an angle. Lift and drag are thus:

$$c_L = sin(2\alpha)$$
$$c_D = 1-cos(2\alpha)$$

I superimposed those (blue line) with measured data for a symmetric NACA-0015 airfoil and it matches fairly well. I don't know how well it works for cambered airfoils.


Is it possible for Mig 21 at corner speed to extend the flaps to minimize the turn radius? Or this is not an option? The corner speed is around 330knots if you want to turn better than the enemy is possible to lower the flaps?

Not really.
First, the 'legal' reason: the flight manual doesn't offer this method. So you are not supposed to do it.
Second, there is a technical reason: MiG-21 had so called 'floating flaps' (as they call it), which are held down only by hydraulic pressure. The pressure is set such that the air dynamic pressure would retract the flaps as the airspeed rises above certain point even if the pilot forgot to do it, preventing their damage. I can't find the official threshold, but from memory the flaps would fully (or almost fully) retract at 600 km/h. This is a bit more than 330 kt, but anyway this leaves only marginal available extension at the optimum speed. (Full extension limit was around 340 km/h, but we are not talking about full extension in any case).
Now, what if we did it anyway? Floating flaps make calculations uncertain, but we only need to know if flaps would improve things. For that, we need to know if the turn1 is limited purely by the available lift or by something else. This 'someting else' could be thrust, structural load limits or available elevator deflection.
For MiG-21 (and most fighters), elevator becomes limiting only at supersonic speeds, and structural limits at high subsonic speeds (above the optimum turn speeds).
Thrust is important: we can be pretty sure that flaps will increase drag more than they will maximum lift.
Now, I don't want to post a graph for every statement I make, but all the data is taken from the official flight manual for MiG-21bis (the latest major modification of the fighter). I believe it can be easily found in English, at least for the export versions.
At low altitudes, where the turn radius is actually minimal, the data shows that the available load factor significantly increases with thrust (e.g. 2.5G at max military power vs 3.5G full afterburner at M=0.5,2 which is approx. 330 kt), and the turn radius decreases (~1200 m vs 800 m in the same conditions). This confirms that it is thrust that actually limits (the steady state) performance. Thus, flaps will not help. This is a rather typical situation.
However, turn radius keeps decreasing at lower speeds. (At low altitudes. At higher altitudes, it has a minimum at M=0.5 or more). The official data starts at M=0.5, but if I extrapolate a bit, the speed at which it stops being thrust-limited seems to be quite low. There is a chance that we'll get an optimum somewhere between M 0.3 and 0.4, but it will be a very low-energy turn.
Arguably, if we want to out-turn an enemy, we need the maximum turn rate (= minimum turn time), rather than the minimum radius. This optimum is at much higher speeds (around M=0.8-0.9)3, and there it is also mostly thrust-limited. There is no talk of flaps at such speeds anyway.

1 Of course, we are talking about steady turn. If you just want to turn around the quickest way, you are better off doing a chandelle, an unsteady maoeuvre.
2 At H=1 km (3000 ft), weight 7500 kg (fairly low but reasonable), with two missiles.
3 But this optimum is quite shallow, with little difference in the range M=0.6-0.9 at low altitudes. At higher altitudes, the optimum shifts clearly towards M=0.9. But all this only with full afterburner.


Can a VFR flight reference a waypoint in communication? Can a VFR flight reference an IFR Waypoint when communicating position to tower or centers?
For example: “N1234 at 3500’ at FERMY, request blah blah blah?”

Thanks
RHD!

****Adding additional circumstance after the last two responses. Apologies for not being able to comment inline but apparently given the length of the below text I must edit my original post. Sorry for any confusion. ***

After some thought on the answers I want to add a little more to the discussion and my situation that prompted the question. I am using more of an EFB solution as you can see from the screen shot. This is a heavily trafficked area of SoCal as well as multiple airspace’s under multiple controls butted up to one another. I use a display on FF which very clearly defines those airspace’s without a lot of study. Aeronautical map to be exact and then Jeppesen when necessary. This map is super clean and minimizes head down time when head up is critical. I was in a particular area where I was not 100% sure on the closets VFR reference point. What however was very clear was one of the primary IFR waypoints (just using FERMY in this example only). The amount of time for me to be able to reference my altitude and FERMY was less than two seconds. On the other hand, switching to VFR sectional refinding myself, finding nearest VFR point and communicating, was infinitely longer. Hence the prompting of the question. I see the importance of other VFR pilots also knowing my position is of course most critical in an uncontrolled or fringes of controlled airspace at same time I further expect Tower or Center to also reference my nearest landmark. So now a bit more info and two “needs” (tower knowledge of my location and of course fellow traffic) does this change the discussion at all?

J. Hougaard is correct. With Tower, Approach and Center, yes you can use waypoints in communications. Be prepared for them not to know immediately where a lesser used waypoint is. I have had Center not know where particular Class G airports in their jurisdiction were. Some know the names by heart, but not the airport codes.

When it comes to communicating with FSS, best practice is to reference your position by distance and direction from a VOR. Especially on your initial call. If you are on a flight plan, reference the points in your flight plan. Referencing an airport will also work.

When communicating over CTAF, it is best not to use waypoints. Instead, use distance and direction from the airport. Even if you are flying IFR or you are on an IAP. Otherwise reference your position by very well known Visual Reference Points. Preferably ones that are charted on your sectional. There are a lot of non-instrument rated pilots who may also be flying. A waypoint may not mean anything to them. Lack of ATC will mean lack of separation control unless you communicate in a way that is universally understood using the lowest common denominators.


Why do ground crews rotate a radial engine's propeller before a motor/cartridge start? In footage from WWII you often see the ground crew rotating the propeller of a radial engine a number of times before the pilots start the engine.

I know it's not the same as hand-starting (hand-propping).

I read somewhere (but questionable source) that it has to do with the oil sitting down in a radial engine.

As far as I know, the oil surrounds the cylinders on the outside. If the oil is cool and not yet expanded, what will a few turns do to it?

Radial engines - especially older large-bore designs like you find in WWII era warbirds - can suffer from a phenomenon known as hydraulic lock.

Basically while the engine is off and cooling some oil from the crankcase seeps past the piston rings in the lower cylinders, and collects there. When you try to turn the engine over with this oil in the cylinder the bottom piston contacts the oil (which is an incompressible fluid), and can't complete its travel down into the cylinder.
The stresses in the engine build until something - usually the connecting rod for that bottom piston - fails, resulting in an expensive repair bill and a grounded warbird.

To avoid this aircraft that are going to sit for a long time usually have a spark plug removed from the bottom cylinder and a hose run to an oil jug to collect the seepage.
In addition to this (or in place of it for shorter-term storage) the ground crew usually rotates the propeller through by hand enough times to ensure the bottom cylinder has gone through a compression stroke.

If there is oil in the bottom cylinder the crew will feel the hydraulic lock as extra force required to turn the propeller. They can then stop and remove a spark plug to drain the oil from the cylinder before attempting an engine start.

A similar phenomenon exists with rotary engines as Simon described in his answer, and the engine is pulled through for the same reasons.


Does Wing Area vary with angle ot attack? For a very basic airplane, say like Cessna 150 is built with Wing Area (S)=15 meter squared (say it 15m*1m). In another part said that the Lift (L)=0.5*rho*(V)^2*Cl*S. Mean, Lift is affected by the wing area. Yes, it is clear. My question, should I consider the wing area as fix area during the take off, cruise, and during landing? If angle of attack of the wing is 15 degree during take off, what is the wing area?

From the Lift formula above that is written here, S (wing area) is planform (projected). Where it to be projected? If like above, if during the take off the Angle Of Attack is 15 degree, what is the wing area? Very appreciate if explanation provided with reference.

Wing area does not change with angle of attack. The only way wing area can change in flight is if there are devices on the wing that can extend and retract, making the wing longer, shorter or wider.


Why don't Transport Category aircraft have a listed Vy? I was talking with a pilot about an inability to maintain the targeted climb rate in a particular situation and asked him what the Vy was for the jet.  He curtly replied "Vy is only for Part 23 aircraft." (FYI for those outside the US:  Part 25 aircraft are commerical planes, while Part 23 are usually general aviation planes. You can find more details here.)

Yet, I know for a fact that there is a maximum excess thrust speed, because at a certain speed drag is at a minimum. This should be close to Vy.  I also know that rate of climb is frequently listed for these aircraft. However, the optimal speed for gaining altitude isn't usually listed for commercial aircraft like it is for GA aircraft.   In fact, many of the v-speeds like Vmca and Vdec are harder to find for larger aircraft.

Why is this?  I can think of several possibilities:

Commercial aircraft speeds are defined by ATC and operating procedures, not by performance considerations
Commercial aircraft have enough thrust that climb performance limits isn't an issue (which I doubt from my experience).
Commercial aircraft use other parameters for similar purposes like rate of climb, v2, or long range cruise speed
Jets don't list this speed but propeller planes do

Large commercial jets operate within a much wider range of weights than most GA aircraft do, and since Vy varies with weight, it wouldn't make sense to publish "a" single Vy speed for them. The crew can get a best rate or best angle of climb speed from the FMC (which "knows" the current weight of the aircraft, based on current fuel & an entered Zero Fuel Weight).

From an empty aircraft with minimum fuel to a loaded aircraft with max fuel, the weight probably won't quite double for most commercial jet aircraft, but the one might be 170% or more of the other. With that much range, any single Vy you publish would be way far off in a lot of cases. On a GA aircraft, without an FMC and operating in a much narrower weight range, publishing a single speed makes much more sense as the delta between published and actual becomes smaller and the consequence of being a couple knots off is probably slight.


May planes be flown above the maximum certified altitude? Let's take the 737NG as an example. The 737NG has a maximum certified altitude (MCA) of FL410.

However, looking at the MCP, the maximum altitude that can be set is 50,000ft. And the pressurization panel can be set to 42,000ft.  All allowing to fly above FL410.

Please note that I am getting this information from FSX with the PMDG 737. Though a simulator product, it claims to be very accurate model of the plane.

Also, although I am not sure, higher altitudes = fuel savings right?

So this rose the question: Can/May I fly above the maximum certified altitude?

Can I fly safely with an 737NG at 45,000ft for example?

Related: What determines the maximum altitude a plane can reach?

The Max Certified Altitude is the highest that the manufacturer has test-flown the aircraft to. (And the 100ft simply makes cruising at FL410 legal.)

If you want to take the airplane above the MCA, and you can actually get it up there, then you now become a Test Pilot, but without the Test Pilot pay and insurance cover. Good luck!


How do commercial pilots send distress signals? If a commercial jet is in trouble, how does a pilot send a signal indicating distress? Does it take long?

For instance, behind reception desks in many institutions and executive offices, there's a hidden red button that, when pressed, calls security or the police. (I know this since I sit at such a desk.) Do commercial airliners have a similar switch, or do they need to radio in for help? What happens when such a transmission is received?

There are three common ways to send a distress signal (roughly in order of preference):

Over the radio, to whoever you are currently talking to.
Key the microphone and announce to the world Mayday, Mayday, Mayday, the flight's callsign, and a description of the emergency. This is generally the way an emergency is declared, particularly for commercial (airline) service, as they're generally always in contact with an ATC facility
Over the radio, to anyone monitoring the "emergency" frequency.
The VHF frequency 121.5MHz is reserved for aircraft emergency communication. It is monitored at most air traffic control facilities, as well as by many airliners and other pilots with multiple radios in their aircraft. If you're not able to make contact with the facility you're currently talking to in (1) above (or if you're not currently talking to an ATC facility).
Using the aircraft's transponder.
Three transponder codes are reserved for unusual/emergency situations:
7700 for general emergencies
7600 for loss of communication (radio failure)
7500 for hijacking or other unlawful interference
All of these transponder codes alter the way the aircraft's radar target is displayed, to alert the controller to the possible problem (exactly how the display is modified depends on the radar equipment the controller has, and can range from additional text in the data block, like RDOF (RaDiO Failure) for code 7600 to changing the color of the displayed block on newer systems.
Bret detailed some of the procedures around these codes in his answer, and more information is available from the FAA, though you'll have to dig through a few referenced documents to put it all together.

Note that sometimes the order of preference changes - For example if a pilot is being threatened by a hijacker they may quietly set their transponder code to 7500 without saying anything on the radio to alert the hijacker.


What temperature are Pitot Tubes heated to? What temperature is a pitot tube usually heated to prevent ice?

And are pitot tubes always heated to the same temperature, is there any difference between aircraft (say, a C172 and an A321)?

This page talks about the Pitot probes that operate at temperature range -65°C to +70°C. They are FAA TSO-C16 and Military Approved. It is probably unwise to heat them more during normal operation. This is not very hot but +70°C would already burn the skin. The probes are used at Pilatus PC-12, Bell 212, Bell UH-1 Special, Cessna Caravan, Diamond DA42, IAI Heron and Quest Kodiak.

This contradicts another source where heater temperatures of 200 °C are reported, and also this industrial Pitot device (while not used on the aircraft) is rated up till the 200 °C, so the design itself allows the temperatures that high. However the heating device is only part of the probe and should be hotter than the tube it is heating up.

This answer says there are significant differences between Pitot heat systems, and some on the light aircraft are rather "anemic". Hence it may be that some models are heated and operate at much higher temperatures. There is also a phrase "plastic cover could melt" there. Plastic melts well over 150 °C.


What if all passengers pay to check in extra baggage? Suppose a given flight is fully booked and everybody shows up. Not only have they all brought the allowed fully loaded carry-on & checked-in luggage weight but exceed the free-limits. They are all willing to pay extra for, say, an additional 10 Kg per person. Let's assume average weight for all passengers.

Will this cause the flight to go over the Maximum Take-Off Weight? If so, will the flight depart?
What are the measures taken for the passengers & their cargo for such flights? Are they divided to take separate flights?
What if everyone has 20 Kg extra? How about 30 Kg? Is there any limit to it?
Does it add if everyone is overweight?

I am asking this in a general context of a non-budget airline.

To answer the questions as asked,

We won't depart over the maximum takeoff weight. We'll do something to bring the takeoff weight down to not exceed the limit.
Generally, people fly as scheduled if at all possible, and as much as possible their bags go on the same plane that they do, and other cargo is a lower priority. There are exceptions; passengers might be denied boarding when the plane is simply too heavy with every one and every thing on board, but this is a last resort and not particularly common.
Total weight is total weight, and the more of it there is, the more limited your options become.  This is explained in more detail below.
If the people are overweight, it's probably not a factor in the numbers, because for scheduled commercial flights, most airlines use average numbers for passengers and their carry-on bags.  So it doesn't matter if they're all skinny or all heavy, they all count for the same "200 lbs".  For military charters and sports charters, actual weights are used, and some non-US carriers may use actual weights as well.

Okay, that's the what; let's discuss the "why":

There are a lot of "it depends" elements here, but in most cases, what happens is that the amount of other freight that can be carried gets reduced, and in the worst case some of the bags stay behind.  But that's probably fairly uncommon.  It's a very worst-case scenario when you can't even take all the passengers -- pretty rare, in my experience.

Your maximum takeoff weight is limited by one of three limits:

a takeoff limit (how much the airplane can weigh to take off & climb out while meeting all of the various requirements),
an enroute limit (essentially, if you lose an engine at some/any point enroute, can you clear all of the terrain along the way to get to a suitable landing site), and
a landing limit (your expected landing weight is no greater than the maximum allowed landing weight).

In practice, the enroute limit is pretty rare, and if the departure runway is long enough, the landing limit is usually the most restrictive.  So, most of the time, your limit boils down to: basic weight of the aircraft, plus cargo, plus passengers, plus landing fuel, can't exceed the maximum certified landing weight.  The aircraft weighs what it weighs, and a full load of passengers is essentially a given weight (most flights use an "average" weight value rather than actual passenger weights).  So the interesting variables are the landing fuel, and the cargo weight (bags plus freight).

If it's a good weather day and no alternate is required, then the required fuel for landing is one number -- let's say 5,000 lbs in a 737, assuming a fairly "best case" sort of day.  (Various operators may have slightly different numbers, but this is a high-level explanation, not way down in the details.)  But if the weather is bad, that number can go up: allowing fuel for holding, as well as for a possible diversion to an alternate.  Depending on how bad the weather is and how far away the alternate, minimum landing fuel might be 8,000-10,000 lbs for a 737, or more.

Thus... my maximum landing weight is 144,000 lbs for a 737-800.  If the airplane and the people weigh 125,000 lbs, I have 19,000 lbs left over.  If my landing gas is 5,000, then I can take 14,000 lbs of bags/cargo/whatever -- which is a lot.  If the weather is crummy at the destination and instead my min landing gas is 12,000 lbs, then I'm limited to 7,000 lbs of bags.  If today's flight had 6,000# of bags and 3,000# of cargo, it all goes in the first case, but not in the second, and it's usually easier to let the freight take the next flight than the bags -- it gets expensive to deliver bags that the airline didn't get on the same plane as the passenger!

There can also be instances where the max takeoff weight is more limiting... a high & hot airport and/or short runways can limit how much weight you can take off with.  So perhaps "today" where I'm departing, the best that I can do (after considering current winds & temperature and the various runways available) is a max takeoff weight of 165,000#.  If I'm burning 25,000# of gas getting where I'm going, then I'll land at 140,000# -- max landing weight (144k) is no longer the limit, max takeoff weight is.  And the computation now looks at the various weights plus min TAKEOFF fuel compared to the max takeoff weight, rather than weights plus min landing fuel compared to the max landing weight.  But the basic process is essentially the same.

Okay, disclaimer, there are various other things than can come into play that I've glossed over for the sake of simplicity -- max ZFW and improved climb and wet landing runways and plenty of other stuff.  If you're studying for your dispatcher license, this is NOT the answer to address all your what-if's.  It's just an overview.


What is this dome used for? I have seen this dome on the top of some 737-800 airplanes and am curious to know  what is it for. Is the a communication antenna for the satellite connection and in-flight internet that some airlines are providing?

That fairing covers an antenna for a satellite-based Wi-Fi system.


What are the relations between stability, controllability and maneuverability? As preparation for my CFI checkride I have been trying to understand aerodynamics very well. One of the things I’m struggling with is stability

If I have a stable aircraft, this means is less controllable and less maneuverable, right?

Do this means an F-16 is poorly stable but very controllable and maneuverable? And a Cessna or a B737 are stable with less controllability and maneuverability?

Thanks for your help guys

a control system is "stable" if, upon a perturbation (like a gust or up/downdraft), the system will naturally return to its unperturbed state with your hands off the controls.

a plane exhibits "neutral" stability if, upon a control input from the pilot or a gust perturbation, the plane will not right itself if the pilot takes his or her hands off the controls, but neither will it diverge and fly itself into a steeper turn, roll, or pitch attitude hands-off.

"negative" stability means the moment you take your hands off the controls, the plane will by itself pitch up or down, roll left or right, or skid one way or the other. it cannot be flown hands-off unless it has an artificial stability augmentation system built into its control hardware.

A control system is "controllable" if pilot input is successful in recovering from a perturbation. But without pilot inputs, a "controllable" system will not necessarily by itself recover from a perturbation.

Maneuverability refers to the airplane's overall sensitivity to control inputs from the pilot and the effectiveness of the control surfaces over their control range.

An airplane that is highly maneuverable MIGHT be unstable- that is, it MIGHT  not fly hands-off because of how sensitive it is to control inputs or gusts. In general, a high degree of maneuverability usually is associated with marginal stability.


How are landing aircraft handled during an emergency runway closure? A Hypothetical scenario

  A landing aircraft at a busy airport such as London Gatwick LGW
  has an issue during landing that requires the immediate closure of the
  runway.

My understanding is that there could be several aircraft lined up on approach to land at busy times and more circling waiting to land.

If such an incident as the one described above were to happen how would ATC handle the other aircraft?

Obviously they will almost certainly need to be diverted, would they contact each aircraft individually to give instructions starting with the closet to landing and work back or is there a quicker way to give mass instructions to divert all aircraft?

As a tower controller, in case of an unexpected unusual situation for an aircraft on final approach, this will be my list of priorities:

Clear the runway of other traffic
Determine if fire and rescue services need to get involved
(Call fire and rescue services)
Call approach and ask them to stop inbound traffic. In case of other traffic on final behind the emergency, coordinate missed approaches
Instruct other aircraft on final to go around, in accordance with the coordination with approach

The above points will take me no more than 30 seconds to get through. This takes care of the most immediate priorities. I will then await the landing of the emergency plane, and coordinate with fire and rescue as appropriate.

As for departing traffic on the ground - aircraft on their gate will be instructed to stay there. Aircraft taxiing to the runway will either continue to the runway holding point or be turned around to a gate, if available - this depends on whether I expect the runway to be closed for a long time (say, more than 20 minutes). The same, more or less, applies to VFR traffic in the control zone intending to land. They can hold in the air if I expect to reopen the runway shortly, otherwise they might have to find an alternate; I will coordinate any diversions with approach.

Once I have a hold of my own traffic, I will call the operational supervisor and inform them of the situation. They will take care of stopping additional inbound traffic if required, and coordinating with adjacent units and sectors. I might also call approach again directly to let them know how the situation is developing.

It will be up to approach, in cooperation with the supervisor and based on the information I provide, to determine if aircraft on initial approach should be diverted, or if they can hold in the air awaiting a runway reopening. Each individual aircraft will require individual handling, to determine if, where and how they want to divert.

Once the runway is reopened (after fire and rescue have finished their work, the emergency airplane has been removed, runway inspection carried out and so on), I will coordinate with approach and the supervisor to start inbound traffic again (possibly with a reduced rate), and start getting my own departures rolling again.

As you can see, there are a lot of "if's" in the above. A lot of decisions have to be made, and the basis for making said decisions changes depending on the situation. There is no set checklist or rulebook for when something like this happens, because the required actions will vary. But that is what we get paid for after all - as an air traffic controller you have to be creative and flexible, especially when unusual situations occur.


co-pilot incapacitation: land alone or with a passenger-pilot? Pilots are trained to safely fly the aircraft in case of co-pilot incapacitation:

  "A commercial aircraft can be landed with one pilot at the control and
  Delta pilots are fully trained to do so if the situation were to
  occur." (Delta representative)

  FAA AC 25.1523-1 requires all aircraft to be capable of operation
  by one pilot only from either seat, so just one pilot can safely fly
  the aircraft - albeit under increased workload. (source)

So why would a pilot in such a situation elect to ask over the PA system "are there any non-revenue pilots on board, please ring your call button" and then land the plane together with this unknown person (a military pilot in this case) ?

This happened on United Airlines Flight 1637. Sure, if it turns out right (which it did in this case), it's certainly pleasant to have a helping hand. But there are all sort of things which could go wrong (“At the beginning, I interrupted her flow of operations, but we figured everything out extremely quickly."). Personally, I'd much rather prefer not being interrupted and distracted when I have to concentrate in this critical moment. Why take any risk at all when one pilot should be able to safely land alone?

There are risks either case. There are no hard rules for or against calling a pilot from the cabin for help; it is up to the pilot to evaluate the situation and select the best course of action.

The risk of landing solo is greatly increased workload, which increases the chances of human error. There are quite a few things to attend to when flying an airliner (compared to a small aircraft). It gets worse when you're in busy airspace.

The risk of asking someone to help is the uncertainly of whether this person will do more harm than good. There would be differences in flight experience and operation procedures. However, Crew Resource Management and handling ATC radio applies to pretty much all types of flying.

Historically there had been examples of either choice, and they both turned out fine.


Are the single-engine Piper Malibus required to have a black box? Is the single engine Piper Malibu required to have a black box?

The short answer is that it probably does not require a "black box".

What you refer to as a "black box" is actually 2 things (and Orange!) a Flight Data Recorder and a Cockpit Voice Recorder. The rules on when they are required is broadly similar, however the data required to be captured by the FDR varies.

For the CVR:

  Fixed-wing aeroplanes with a maximum take-off mass of more than 5 700 kg and for which the certificate of airworthiness is first issued after 1 January 2003 shall be equipped with a CVR with a recording duration of two hours

For the FDR:

  [...] depending on the maximum certificated take-off mass and the date of first issue of the individual certificate of airworthiness. For example, provision 6.3.6 of Annex 6, Vol. I states that, all aeroplanes of a maximum certificated take-off mass of over 5,700 kg for which the individual certificate of airworthiness is first issued after 1 January 2005 shall be equipped with a Type IA FDR

The Piper PA-46 (aka Piper Malibu) has a MTOW ranging from 4,340lb(1,969kg) to 6,000lb(2,721kg).

Speculation about the recent incident, and the specific model intentionally left out!


Can paragliders in the US communicate with ATC? I am a private pilot looking to get into paragliding. After talking to some of my friends who do paragliding in the San Francisco Bay area and watching YouTube videos I noticed some fly through places like VPMIN (which is near SUNOL). That's an extremely busy intersection, sometimes right in the altitude ranges I normally fly through them in my powered aircraft. From this I had a few questions:

Is it possible to get the equivalent of flight following or at least call up ATC to let them know you are there, if you are planning on flying at higher altitudes? I am used to doing this for a D airspace if I am flying only just over or near it if they are not busy.
If so, what would the phrasing of that sound like when you don't have a callsign?
14 CFR 103.17 says that I require prior authorization to enter class B, C or D airspace. What does this look like? Can I take a handheld radio and ask for permission on the tower frequency? Or is this something I'd need to get through written permission from a FSDO or the tower directly?

Where noted, the information in this answer is from Advisory Circular 103-6, which was issued in 1983, but which apparently is not actually obsolete.

  Is it possible to get the equivalent of flight following or at least call up ATC to let them know you are there, if you are planning on flying at higher altitudes? I am used to doing this for a D airspace if I am flying only just over or near it if they are not busy.

It's certainly legal to call up ATC while you're flying an ultralight, whether it's Part 103 or not. The relevant FCC regulation, 47 CFR § 87.18(b), says that aircraft are "licensed by rule and [do] not need an individual license," and ultralights are aircraft, so an airband radio on an ultralight counts as being licensed.

Advisory Circular 103-6 also recommends that ultralight pilots contact ATC using the ordinary radio frequencies (but I believe it was written when all airband radio users needed individual licenses).

I don't know whether or not ATC gives flight following to ultralights. Advisory Circular 103-6 says that separation services "will not be available to ultralight pilots." But there's no harm in asking.

  If so, what would the phrasing of that sound like when you don't have a callsign?

There's the tricky bit.

The regulation governing this is 47 CFR § 87.107(a), which states that you should identify using one of the following four options: your "aircraft radio station call sign"; the aircraft type and registration number; your radiotelephony designator and flight number; or a temporary identifier for "organized flying activity."

However, if you're flying a Part 103 ultralight, then in all likelihood, you don't have any of those.

Advisory Circular 103-6 states that "ultralight operators should state the word 'ultralight' followed by the call letters assigned by the F.C.C. on your radio license, i.e., 'Ultralight 12593U.'" Assuming you don't have a radio license, it seems like the best you can to is to simply use the word "ultralight" as your call sign.

  14 CFR 103.17 says that I require prior authorization to enter class B, C or D airspace. What does this look like? Can I take a handheld radio and ask for permission on the tower frequency? Or is this something I'd need to get through written permission from a FSDO or the tower directly?

Advisory Circular 103-6 says, "Requests for authorization to operate an ultralight vehicle into [controlled airspace] should be made by writing, telephoning, or visiting the air traffic control facility having jurisdiction over the airspace in which you wish to operate. Requests for such authorization via air traffic control radio communication frequencies will normally not be accepted, since it may interfere with the separation of aircraft."

That said, I'm not aware of any special legal meaning of the phrase "prior authorization." So on the off chance that ATC does tell you that you're allowed to enter the airspace, presumably you can do it.


Why are some aircraft windows painted over? I have seen that some aircraft have some of their windows painted white. As you can see in this picture, this A340 has many windows painted white.
Why is it that?

Source

If you look at the seating chart for that plane, you'll notice that those windows match the location of toilets and galleys.

Note that the exact position of toilets and galleys may change during the lifetime of an aircraft, so it's easier to have all the windows installed by design, and just obstruct some that are not used. Even if it were just obstructed from within, I suppose it's better if in an emergency, if emergency personnel had to look inside the plane (to check for people still trapped inside), they would be able to identify quickly those windows that do not need looking through.


What does "E" stand for in a polar curve? In the following polar curve, there is a symbol "E" with the number 33.5 next to it. What does this mean?

E is used as the symbol for L/D in German. Normally, a symbol description will call it "Gleitzahl" (glide ratio).


What's the minimum roll rate a commercial airliner would have with maximum aileron deflection? If the maximum aileron deflection possible was commanded on a commercial airliner, how fast would the aircraft roll?

I don't think there's many reasons to bank a large aircraft quickly, but what I want to know is whether it's even possible to roll it at rates such as 10-15 degrees per second or more.

The achievable roll rate depends on altitude. At sea level, big aircraft have very low roll rates, because their roll damping is very high due to the large wingspan. Roll damping goes up with the square of the wingspan, whereas the aileron moment grows linearly with wingspan.

If the aircraft flies high enough, the roll rate will go up inversely to the change in density. This is because the flight speed increases inversely with the square root of density, so the same roll rate will cause less change in the local angle of attack on the outer wing (which is the mechanism which causes roll damping). Thus, in 12 km altitude the roll rate will be twice of what it is at sea level (at the same CAS). That is why large airliners have special high-speed ailerons at midspan: They suffice for control, and using the outboard ailerons would stress the wing a lot more. Also, outboard ailerons on high aspect ratio wings cause considerable torsion, such that the wing twist from aileron deflection will reduce aileron effectiveness. Inboard ailerons are much less affected by this effect.

I would wager to say that any airliner will be perfectly capable of 15°/s roll rates if you deflect the outboard ailerons (without overstressing the wings).

The high altitude research airplane Strato 2C had a roll rate during approach of only 2°/s! This was no real problem, because the large wing (56.5 m wingspan) would not be affected by gusts when the aircraft flew lower than approx. 30 m. The turbulence is so small scale close to the ground that the gusts would average out over the large wing, and the aircraft calmed down when sinking below 30 m, even in gusty weather. At 18 km altitude, however, it handled almost like a fighter aircraft.


Do aircraft designers gather real data to confirm their design (CFD, wind tunnel) data? What  tools and techniques are used to get real data test to confirm the values that are obtained by computational fluid dynamics (CFD) calculations and wind tunnel testing?
Is this standard procedure for all aircraft before going into production?

What tools and techniques are used to get real data test to confirm the values that are obtained by computational fluid dynamics (CFD) calculations and wind tunnel testing?

During development wind tunnels and model tests confirm the validity of CFD results.
Usually one prototype is used for stress testing with special rigs which simulate flight loads. This testing will cover the full life of the aircraft, measured in flight hours, and will accelerate ageing by using higher than usual loads.
Once you have a flying article, test flying is used for validating the design. A new design is first flown by a certified test pilot and normally instrumented with telemetry so engineers on the ground can follow what happens during the test flight. While the first flight is done at low speed, successive flights will expand the flight parameters (speed, load factors, rotation rates) until the whole operational envelope has been covered. This is called envelope expansion and will eventually cover stalls, spins, overspeed and flutter conditions. Military aircraft will also test all planned external loads and their separation in flight.

Is this standard procedure for all aircraft before going into production?

Yes, this is the certification process. Unless a design is certified, it may only be used in a limited way. Commercial use of an aircraft requires a certification.


Does a no-touch policy really work? In Boeing 787 and Airbus 350 aircrafts, more than half of the aircraft body is made of composite material. The composite structure of the fuselage does not indicate the damage when the body is contacted and damaged by the ground support equipment. That's why an airline company I’m familiar with issued a statement for the entire fleet to the ground staff indicating "do not touch the aircraft while servicing" (a no-touch policy).

How can the passenger mobile stairs be aligned safely from the ground without contacting such high aircraft passenger doors?  Wouldn't it be possible for passengers to fall down from the gap between the aircraft and the mobile stairs, especially in windy weather?
What else can be done not to damage composite structured aircraft fuselage?

Jet bridges are operated just next to the point at which passengers will enter the aircraft. They have proximity sensors that tell the operator if they getting too close. And the bridge doesn't have to physically touch the aircraft as long as the gap on the walkway is small enough to not pose a danger to the passengers, it just needs to get close enough so that the end of the bridge can extend like an awning and cover the entrance. The parts that do touch the aircraft are usually made of material that will not damage the surface of the airframe.


How do I calculate the required heading for an aircraft carrier with an angled deck to sail into the wind? The natural wind is from 360 degrees at 10 knots. The desired relative wind down the angled deck is 10 degrees left of the ship’s heading at 30 knots.

What heading and speed must the carrier go?

A carrier heading of 010 degrees at a speed of 20 knots would give you an acceptable solution.  You could perform some vector addition to compute the resultant wind and perhaps optimize this somewhat, but in reality the winds are generally not constant enough to make minor adjustments worth chasing.

Even if the winds were calm and the ship was making all 30 knots the crosswind component is almost negligible, and well within limits for any carrier based aircraft.  This happens a lot.  There is a bigger negative effect from  turbulence caused by the island structure when the ship has to make wind than any effect of increased crosswind.


How long does it take to refuel a big jumbo jet? How long does it take to refuel a big jumbo jet? What about a smaller A320?

It depends on a number of factors like:

the aircraft size and variant
the range required
the aircraft load
equipment available
Ground crew proficiency

...among others things.

This figure from the 737 Airport Planning document gives 9 minutes for the fueling time for a Boeing 737-600:

Image from B737 Airplane characteristics for Airport Planning

The following image shows the time taken for refueling a Boeing 747-8 Jumbo to be 44 minutes:

Image from B747-8 Airplane Characteristics for Airport Planning


Is the APU classified as a component of Airframe or Powerplant? In the classification of systems and components on the aircraft - is an APU classified under the Airframe or the Powerplant?

I was a tech writer in another life.  Under ATA100/2100, the Air Transport Association system of categorization of systems for maintenance manuals, the APU is Chapter 49 (Airborne Auxiliary Power).
Power Plant chapters are 70 and up. (Some OEMs also use a equivalent numbering convention for engineering drawings to align them to ATA100/2100, where, say, if Flight Controls are Chapter 27, flight controls related drawings would have "27" at the start of the drawing number with the applicable sub-system numbering as appropriate - makes finding drawings in a database quick and easy).
Airframe systems are Chapters 20 thru 50.  So from that standpoint, its Chapter 49 designation makes the APU an airframe system, not a Powerplant (which only refers to propulsion engines per ATA), as far as the industry is concerned, and I think you are pretty safe to go on that.


Why are 3- or 4-seat gliders so rare? Sailplanes capable of climbing in rising air (not troop transports, which can only descend after the towrope releases) have one or two seats.  I know of only one type with more, the Schweizer SGS 2-32 "2½ seater."  Even experimental one-offs like the Perlan series have at most two seats.
Ignoring social aspects such as marketing, class associations, and racing leagues, what are the technical difficulties in making/flying/maintaining a sailplane with more than two seats?  Frontal area, if seated abreast?  CG range, if seated fore-aft?  Something special about mass or wingspan that doesn't apply to powered airplanes?

Because much of the fun in being in a sailplane, is in actually flying the sailplane.  It's not a means to get from point A to point B, it's a means to enjoy the magic of flight, much of which involves seeing the sailplane respond to your control inputs.
Once you start getting more than two occupants, most of the occupants won't get to do much of the flying.
It's kind of like asking, "why aren't there more saddles for horses that can handle 3 or 4 people?"
As an aside, raw novice passengers tend to be at high risk for airsickness when subjected to prolonged thermal turns in turbulent conditions, especially if they get to do little or none of the actual flying.  Three or four non-flying passenger seats would potentially equate to a lot of clean-up afterwards.
I guess it's all a little subjective-- a commercial pilot friend of mine regularly gives 15-to-60 minute semi-aerobatic rides in a glider with room for two passengers squeezed in side-by-side on a seat in the back (Schweizer 2-32), with controls for the pilot only, and most of his passengers love it (and most don't get sick).  But being seated tucked in close to a friend for a little while feels different than riding on a "bus" with, say, four or more strangers-- and in that particular case the very same glider can have the second control stick re-installed in the back and be used for student instruction with one rear-seat occupant and one front-seat occupant.  A bigger "bus" with more ample seating for multiple passengers probably would be a poor candidate for a training glider.


Can time logged in foreign aircraft be applied towards an FAA certificate or rating? Does time logged in these foreign-registered aircraft (cross country, etc) count towards US certificates or ratings? Or is it flight experience that should be excluded from an 8710?

Yes, it counts: the FAA doesn't care where flying hours are accumulated provided that the US written and/or practical test requirements are met. I learned to fly in South Africa then applied for an unrestricted FAA license (i.e. not a foreign based license). The FSDO told me that I could count all my time in SA (cross-countries, night flights etc.) towards the FAA license requirements, but I would still have to pass the FAA written and practical tests like any other student pilot.

One practical issue in this situation is that hours may be logged slightly differently in different countries, by regulation or simply by local practice. The two examples I encountered were that PIC time is (was?) defined differently in SA and the US, and the number of landings is not relevant in SA for currency so no one logs them.


What are the airflow patterns of a helicopter when operating in ground effect? When operating in the air cushion region of approximately 8 inches and below to the ground what pattern does the downward flow of air flow?

What happens at a height of 8 inches and below in the hover in ground effect is a function of rotor diameter: everything is relative. Ground effect becomes noticeable at about one rotor diameter from the ground surface, so if your rotor is 8 inches in diameter there is not yet a significant change of the downward air flow.

If we limit ourselves to discussions of flow as a function of rotor diameter, we can see the following happen as illustrated in the above figure, from J. Gordon Leishman, Principles of Helicopter Aerodynamics:

Out of Ground Effect, the ground has little or no effect on the rotor outflow. The spiralling lines in the figure are the blade tip vortices.
In Ground Effect, the rotor downwash appears compressed and spread out. One way of understanding how ground effect affects lift, is by considering that the static pressure underneath is increased and contributes to the lift.

The spiralling blade tip vortices are compressed and spread out as well, and this has a large effect on wake fluctuations, particularly noticeable for a ground observer. What exactly happens regarding spiralling gusts is not yet fully understood - from Prouty, Helicopter Performance, Stability and Control, page 68:

The wake in ground effect is not really a steady flow..., but a flow with large scale fluctuations that can be felt as gusts by an observer standing near the helicopter. Reference 1.21 speculates that these fluctuations are associated with the vortex that is made up of the individual vortices from the blade roots.This vortex apparently writhes like a pinned snake along the ground, causing the entire wake to shift and wobble.
Pilots occasionally report that when hovering in ground effect, they experience random yaw disturbances. This is probably due  to the effect of the root vortex as it writhes near the tail rotor.


How could so many drones establish contact with ATC? India has brought out best set of drone regulations on the basis of No Permission No Take-off (NPNT).
But how can the ATC establish contact with so many  drones that will be unpredictably asking for take off.
Also how can they be monitered through a controlled airspace? Will it be miNiaturr ADSBs fixed or something else?

I'm not sure about everywhere but in the U.S. there is an app called "Airmap" Link to webpage. It's built for commercial drone operators but it can also be used by people flying for fun.

There is a flight plan portion of the app that allows you to file for a flight. You specify time of takeoff, radius you'll fly in, altitude and aircraft. This is then submitted for approval from the FAA.

It takes a matter of seconds and your approved, or not depending on the situation. It also has a map portion that displays the other approved flight plans in the area, if the pilot made his public, so you could even use this to join other's flying at the park if you see a flight pop up or something like that.

This could be a viable answer for India as well, coupled with a mini ADS-B, like CrossRoads mentioned, could prove even better.


Is there a way to obtain real-time METAR data? I know that METAR data are available at hourly intervals from the US National Oceanic and Atmospheric Administration (see e.g. the report for Karpathos Airport, Greece ).  However, I would have thought that at the age of the internet it would have been possible to obtain (near) real-time data regarding an airport's weather.  Is such a service available?  Is there a better (more frequently updated) internet-accessible source for global METAR data than NOAA?

You might know this already, but if you want to get an AWOS/ASOS report minute by minute, you can call most of the automated sites. In the US the phone number is listed in the A/FD.


What is the weight limit for a pilot to eject from an F-100? What is the maximum weight for a pilot to use the ejection seat in an F-100 fighter?

Firstly, welcome to Aviation Stack Exchange! As for your question, I actually could not find the exact model used for the F-100 series (sorry), but as far as I can tell most American first and second generation jet fighters were installed with Martin-Baker Mk.1-3 ejection seats. These were some of the first examples of explosive charges being used as the main propellant, and for the sake of a shorter answer I will assume you understand their basic operation. The Martin-Baker website states that the for the given size range of crew (between the 5th and 95th percentile), the seat could manage to lift a 224lb pilot/aircrew at a maximum of over 400 knots indicated airspeed.

[Edit] I want to address @GypsyRanger's answer: I think we can all assume that the pilot being ejected from the fighter has undergone and passed Air Force criteria for qualification to be a fighter pilot. I personally think his question is simple but a good one because he is just asking the weight limit, and in terms of mass this shouldn't be too hard to answer. I myself couldn't find the exact model, but all main-stream American jet fighters of the F-100's era were fitted with Martin-Baker seats ranging from the Mk.1 to the Mk.3. If you take the time to look at the specifications for each and compare, or knew beforehand you'd know that the improvements between each model were mostly pertaining to reliability and safety for crew, something that they were lacking in at the time (the firing mechanism was practically the only thing changed throughout). Really though, don't be too quick to criticize if you won't put in the time to read it or because it's a short question.


Are solid fuel rocket engines designed differently and how? How do solid fuel (Hydrazine, UDMH) and oxidizer (N2O4) differ in design from cryogenic rocket engines such as LH2 and LOX?
Are there differences related to temperature, material design, turbopumps, turbopump bearing seals, etc?

Yes, solid fuel rockets are very different from liquid fueled rockets. A solid fuel rocket is basically some solidified rocket fuel and oxidizer wrapped in a non-combustible cylinder (hence the name). Once it's lit, there's no way to throttle it or shut it down, it just burns until all the fuel is consumed. On the other hand, in a liquid fuel rocket (cryogenic or not), liquid fuel and oxidizer are pumped into a combustion chamber to be burned. Liquid fuel rockets can be throttled or shut down by controlling the fuel pumps, and can be re-lit once shut down (assuming its igniter is reusable).

(It's important to note that the examples of "solid" rocket fuels you gave aren't actually solids. They're liquids, just like cryogenic fuels are. A solid fuel would be something like the ammonium perchlorate and aluminum powder used in the Space Shuttle Solid Rocket Boosters.)


What factors lead to mounting engines towards the rear of aircraft Some aircraft have engine beneath the wings and some have at the rear of the aircraft.

What are the factors that are considered while deciding where to mount an engine?

Is one configuration advantageous over other?

I am just a Flight Sim enthusiast so everything I say should be heavily scrutinized, but there is a flightsim that features the A-10C which has an engine configuration just like you describe as you can see in the picture.

The (ingame) flight manual has the following to say about the engine configuration:

  Engines
  All versions of the A-10 have been powered by twin TF-34-GE-100A engines that are mounted high
  on the rear fuselage between the wings and the rear stabilizers. The unusual placement of the
  engines provides several distinct advantages:

  The high mounting reduces the likelihood of the engines ingesting Foreign Object Debris
  (FOD) when operating from rough, forward bases in war-time.
  Engines can remain running when aircraft is being rearmed and refueled. This leads to
  faster mission turn-around
  Ease of servicing the engines
  Reduced IR signature from below due to the shielding of the horizontal stabilizer.

Another related thing I found was how they combine with the leading edge slats, it says.

  Added leading edge slats for improved airflow to engines at higher angles of attack

As most of these reasons are in a military setting I cannot comment on the advantages for civilian aviation.


What is the average speed used by modern jet fighters when in dogfight? I am asking this question pertaining to a game I'm designing.

It is well known that many modern jet fighter aircraft can fly at supersonic velocities however I read that this top speed is hardly ever used in combat situations, owing to things like larger turn radius etc.

Can someone tell me a rough estimate of what is the range of speeds most dogfights take place at for modern world jet aircraft?

Modern Air Combat Maneuvering takes place between about 350 to 600 KIAS; There is no specific speed but each aircraft has a specific optimal cornering velocity which gives it the greatest rate of turn in order to maximize its maneuverability.  Pilots will seek to maintain this speed when entering a merge as it can give them the greatest maneuvering advantage in order to turn inside on opponent or for jinking to evade a cannon or a missile shot.  As an example, the Lockheed Martin Block 50/52 F-16C has a cornering velocity of 420 KIAS.

Traditionally air combat has been about energy management.  Fighter pilots have something in common with economists in that they are engaged in the art of managing the flow of currency; in the case of the pilot that currency is energy and not money.  The total energy state of a fighter is:

current energy state = energy in - energy out.

The current energy state is the sum of the kinetic energy, proportional to the square of the velocity of the jet and the potential energy of the jet, which is proportional to its height above the ground.  Energy leaves the system in the form of parasite and induced drag acting over a distance as well as loss of altitude, which is proportional to the flat plate area of the jet, load factor, AoA, etc.  Energy enters the system at a rate proportional to the amount of jet fuel burned; this supply is limited to the fuel onboard which again affects the mass of the jet, the induced drag, etc.

So keeping this in mind, a good fighter pilot will seek a way in which he/she can maneuver through space, gaining the best speed and turning performance for the least amount of energy consumed, in order to land in an advantageous position to employ the weapons against an enemy jet.  These kinds of speeds vary between if the jet is on the offensive or defensive in relation to a threat.

So a pilot maintaining that optimal energy state is in the best position to attack, or defend against an attack, and a pilot in a very low energy state is very vulnerable - "low and slow, you're outta dough" - and could be quickly killed in a multi-jet furball.

The cornering velocity is preferred for this reason if maneuvering is anticipated (a given if the jet is about to enter a merge).

With the advent of terminal homing, beyond visual range missiles allowing pilots to stand off from the fight and shoot a threat before it could get close enough to turn with them, higher speed cruise, along with a capability to maneuver well at those higher speeds has become an advantage.  It allows a pilot to more quickly close with an enemy aircraft into the missile's 'no escape' zone, fire, and then turn and dash from the threat, minimizing their presence in an enemy's 'no escape' zone whereby enemy missiles simple don't have the available energy to catch you.  This was the basis for supercruise - supersonic cruise without the use of afterbruners - on the ATF / F-22 program.  Combined with good frontal stealth to minimize the detection range by enemy fighters, supercruise could give a Raptor jock a major advantage in the BVR areana - near invincibility in BVR engagements against non stealthy fighters, if the published results of the Red Flag and other military exercises are to be believed.


What are these on the F/A-18F's wingtips? At 5:34, former TOPGUN instructor Cdr E. Vincent Aiello (the narrator) says

  Looks like you've got [I can't decipher] Xes.

What words was he speaking?
Is he identifying the missile-looking object marked by my red arrow below?

He says:

  Looks like you've got some AIM 9Xs on the wings

Yes, the AIM 9 is a commonly carried short range air-to-air missile, with the 9X being a particular variant.


Why don't passenger aircraft use the trijet configuration anymore? As a kid I distinctly remember seeing aircraft like the bright blue KLM MD-11 having the prominent third engine on the tail.

https://commons.wikimedia.org/wiki/File:KLM_MD_11_AMS.jpg

However, I don't think I've seen a plane in the past few years (besides maybe a few smaller private jets) that has a engine on the tail - let alone a trijet configuration.

What's with their disappearance?

The fewer engines an aircraft has, the lower are its operating cost. Engines are the most maintenance-intensive part of an aircraft, and doing a hot section inspection on two large engines costs less than doing it on three somewhat smaller engines.

When the tri-jets were developed, no sufficiently large and powerful engines were available. They were already cheaper to operate than the four-engined aircraft, and too large to have sufficient power with just two. Now, with engines which can deliver a static thrust of more than 100,000 pounds, everything below a Jumbo Jet or an A380 can be powered with just two engines.

Another reason is increased engine reliability: With three or four engines, an engine failure is less of a problem than with just two engines per airplane. Previously, route planning had to keep a maximum distance of 60 flight minutes to a diversion airport. In 1964, this was waived for three-engined aircraft, but twins were still bound to this restriction. With more experience and better engines, this rule has been relaxed for twins gradually to 120 (1985), then 180 (1988), and now 370 (2014) minutes for the Airbus A350 XWB, and twins have become much more versatile for their airlines.

Some of the old tri-jet designs were quite popular with operators: The last Tupolev Tu-154 was built only in 2013. But besides the Dassault Falcon 900 and 7X business jets, I don't know of any trijet which is still in production.