How is an out-of-trim condition (in relation to weight distribution) detected on the ground? My question relates to Captain reports Out of trim
and
this answer.

How is an "out-of-trim" condition like the one mentioned in the linked question detected on the ground? I.e "out-of-trim" in the context of weight distribution or balance of the aircraft and not control surface trim.

The most likely scenario, where you have an unforeseen deviation from plan at the last minute, is pax loading where due to a statistical fluke there is an uneven distribution of pax in the cabin, say because a lot of them didn't show up and the no-shows tended to concentrate toward one end.

When the FAs inspect the cabin after boarding, they do a pax count and one thing they are looking for is a minimum number of pax in each cabin weight and balance zone.  If the FA sees something that is out of whack, like the front half of the cabin near empty with a crowd at the back, they will let the Capt know, and if necessary will start going around to pax to request them to change seats to address the under filled zones.

For cargo, the crew has to trust the people that loaded the cargo weight and balance wise.  For fuel, it's mostly about making sure the fuel load indicated in the cockpit matches the fuel load paperwork and the weight and balance load sheets and trip requirements.

In a line operation, the crew doesn't have to do any of the actual dirty work, they are just presented with the information prepared by specialists and review it to make sure it jives with expectations and requirements.


Why do airlines park their planes out in the middle and ferry passengers to the terminal by bus, even during non-peak hours? There are numerous occasions, especially during late night flights, when hardly there is rush at the airport, the pilots park the airplane out there somewhere, and ferry the passengers by bus. Is it a big trouble to take the plane to the aerobridge and then take the plane to the parking spot?

An airport will have a menu of charges for the services it provides to airlines.

Here is one Schedule of Charges for London Heathrow, for some of these services. Probably you can find further examples via their Conditions of use page.

Some of these charges are unavoidable - landing fees, for example - but others will be subject to agreement.

An airline can save money by opting for a cheaper option in certain cases.

If you've ever watched successive plane-loads of Ryanair customers climb out of their 737s into horizontal rain to trudge across 100m-wide puddles to the terminal, and each subsequent shipment of shivering human cargo queue at the steps as the wind whips the standing water up to knee-level, while every other airline during the same period uses a bus to deliver its passengers, you'll have had a very visible indication of they way airlines can choose to pay for particular services - or not.


What is the FAA's official stance on logging illegal flight time? To preface my question, I want to discuss the reality that with the number of people and flight operations, there are surely cases where pilots have mistakenly flown under conditions in which it is not legal to do so.

Possible examples:

Students soloing after endorsement expiration.
Pilots flying without realizing their medical has expired.
Non-instrument-rated pilots inadvertently flying into IMC.
Carrying passengers without landing currency.
Acting as PIC beyond BFR currency.

Barring any discussion or speculation about punitive actions for the above listed items, what would the FAA's stance be on logged time?  Would it be logged as valid pilot time regardless of it being illegal, or does the fact that it is illegal make it null and void as logged pilot time?

For example, in the first scenario, if a student solos without a current endorsement, would it be able to be logged as PIC solo or would it not exist in the eyes of the FAA as it pertains to flight time and the flight would be considered to have been performed with a complete lack of an acting PIC?

There are probably many answers, depending on the specifics of the situation. But at least one of your scenarios has a certain and definite answer.
I don't think that the FAA has ever issued a legal opinion on this topic, and I kind of doubt they would, but we might be able to piece some answer together.
But first let me address a couple of misconceptions you might have about logging time. In the title and first paragraph of your question, you simply ask about logging time, or logging pilot time. At the end, you ask about PIC or solo time. These are all different kinds of time.
You also wonder whether a pilot could log time, or does the FAA consider that flight to not have had a pilot-in-command. Those are totally different things. Logging pilot time, logging PIC time, and BEING PIC of an aircraft are all different things and don't really have much to do with each other. There are situations where you are PIC and cannot log any time. Other situations where you are not PIC and can log PIC time. Still other situations where you are PIC and can log pilot time, but not PIC time.
To determine whether you ARE ACTING as PIC, you need to look at FAR 1.1: a Pilot in Command

Has final authority and responsibility for the operation and safety of the flight;
Has been designated as pilot in command before or during the flight; and
Holds the appropriate category, class, and type rating, if appropriate, for the conduct of the flight.

That's a totally different section from the regulation that instructs you on how to LOG PIC time, which is FAR 61.51(e):

(1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-
(i) ...when the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated...

In other words, BEING PIC and LOGGING PIC are completely different criteria. And those criteria for logging are that the pilot is rated, not that the pilot is current.
But there is ONE part of 61.51 that does require currency: Let's start with a student who solos after the expiration of their endorsement. FAR 61.51(e)(4) says:

A student pilot may log pilot-in-command time only when the student pilot -
(i) Is the sole occupant of the aircraft or is performing the duties of pilot of command of an airship requiring more than one pilot flight crewmember;
(ii) Has a solo flight endorsement as required under § 61.87 of this part; and
(iii) Is undergoing training for a pilot certificate or rating.

So for certain, that student cannot log PIC time.
But now, notice that this is the only place anywhere in 61.51 where currency is required. They make a point of it for student pilots but it doesn't show up anywhere else. So I would be tempted to say that a private pilot can log a flight legally that you weren't allowed to make due to currency. And about generally breaking the rules, I am tempted to add to your list: "I flew to my local uncontrolled field and made right turns in the pattern instead of left turns in violation of 91.126(b)." Do I still get to log the time, even though I flew the wrong pattern? Or what if I accidentally violated an ATC instruction? I think I still log that time. After all, making mistakes and learning from them is what "aeronautical experience" is all about.
So in that same vein, what if I flew out of currency and filed an ASRS report? What if I flew out of currency and didn't file a report? I think it's all the same; I think that breaking a reg doesn't invalidate the time.
There are some FAA opinions that back me up a little bit. In Walker, the FAA gives an opinion about a non-instrument rated pilot who manipulates the controls of an airplane in IMC. Because that pilot is manipulating the controls of an airplane in which they are rated, they log PIC time according to 61.51(e)(1)(1). In that opinion, the flight is legal because their instrument rated friend is occupying a pilot station and acting as PIC (But the friend doesn't log time, even though they are PIC, because they are not manipulating the flight controls).
Perhaps more importantly for your question, that pilot also logs instrument time according to 61.51(b)(3)(2) because the time was acquired in IMC. So a non-instrument rated pilot CAN log instrument time, without a CFII on board, even though he has no instrument rating.
So I think that in general, inadvertently breaking a reg doesn't affect logging, but that is different from saying that such a flight is a very smart or safe thing to do, and if you do log it, you're admitting to a violation in an official record. Also not smart.


What is the wingtip station number on a Boeing 747? In the figure we can see the station line even though it is not clear. I'am using that picture just for an example to make the question clearer.

Main question

What is the station number for wingtip on a Boeing 747? (fuselage station and water lines)(If possible the butt lines too)

I tried searching the internet for the station number and couldn't find what I'm looking for. Or am I looking at the wrong place to find it? Where to find the number if you don't have access to the aircraft maintenance manual?

For the wing tip station , just divide the wingspan by two and multiply by 12.  The stations are in inches.  For a 747 with a 195' 8" wing span, the tip station is 195.66 divided by 2, times 12 = 1173.96, so the tip will be Station 1174.

For X and Z you need to know where the datum point is longitudinally and for the X axis, and what the waterline is that defines the Z axis.  Waterline is often the cabin floor.  X datum on a jet is often the forward pressure bulkhead surface.


Where does one request a VFR transition route through class B? Other than staying outside class B until being cleared in, is the point where one requests a transition route important? For example, the SFO B coastline transition is shown as starting up at San Rafael in the north. But one could also fly as far south as SAU below 5000 or Lake Merced below 3000 outside the Bravo before having to ask for clearance. So my question is whether the intent is that one should start at the mapped limits of the transition routes or whether one can ask for them anywhere as long as you're outside the Bravo?

Vaguely related question: the FAA presentation on the latest version of the SFO B shows that the intention for the coastline transition is "at or above 3500". Is this documented somewhere other than in this random PDF from a 2-year-old presentation?

There's an AOPA Air Safety Institute video, "Ask ATC: Am I Cleared for Class B?":

In this and other "Ask ATC" videos, they point out that if you're in VFR flight-following, ATC will not clear you for Class B without your requesting it, even if your current flight path will obviously enter that airspace.
If you are getting ATC VFR flight-following, you should make the request in the course of normal communications, but no later than the point where you can easily divert if clearance is denied.
If you are not talking to ATC, you must first get their attention ("November 12345, request"), then on acknowledgement (when they'll probably abbreviate your call sign, which means you can, too), give your aircraft make/model (which tells ATC your capabilities), relative position (which tells them where to look for your radar return), altitude(s) (level/climbing/descending, which they won't get directly from your transponder), and intentions (your request). This, too, you should do well before the point when diverting around the airspace becomes inconvenient.
(If you're squawking 1200, they'll give you a squawk at the same time, probably an altimeter setting, and possibly altitudes and vectors through the Bravo, so be ready with your lapboard or tablet. Don't hesitate to ask for a re-read, or even to ask them to speak more slowly—in another "Ask ATC" video, they say that controllers often accelerate their speaking pace over the course of a shift without realizing it, they know that VFR pilots aren't as practiced in ATC comms, and they'd much rather you ask for them to repeat more slowly than for you to make a guess.)
So long as you're already handed-off to (if flight-following) or have made contact with the ATC with jurisdiction over the Class B, you can theoretically do it as early as you like.
So there's a bit of a trade-off: later makes it harder to divert, but easier for ATC to have awareness of you. Earlier makes it easier to divert, but ATC may not be ready to clear you if you're far enough out that the traffic situation may change significantly before you enter the airspace.
(Since you're probably significantly slower than most of the aircraft in the Class B, that makes it even more likely that the situation will change.)


Can a wind tunnel simulate airflow when a vehicle goes around a curve? In real life, airflow in a turn is curved, how does a wind tunnel simulate this condition?
If we just yaw the test object at some angle in wind tunnel, do we simulate the airflow in correct way?

Wind tunnel is a tool to interrogate aerodynamics, not to investigate flight dynamics (which relies on aerodynamic results to predict vehicular dynamics). As explained in this answer, the additional aerodynamic effects from induced airflow due to rotation can be lumped into dynamic derivative coefficients. Some examples include:

Pitch damping: $C_{m_q}$
Lift due to pitch rate: $C_{L_q}$
Roll damping: $C_{l_p}$
Cross yaw derivative: $C_{n_p}$

etc. Note that the rates in these derivatives are expressed in dimensionless rates to maintain similitude, which is accomplished by dividing the body rates by $bV_\infty/2$, where $b/2$ is half span and $V_\infty$ is freestream speed.
To estimate dynamic derivatives in wind tunnel, the forced-oscillation method is typically applied. The model is excited in a single axis by a small amplitude sinusoid at representative range of dimensionless rates and reduced frequency. This paper provides a good introduction to the data collection and analysis.
Rotary balance tests can also performed in wind tunnel to measure the effect of sustained rotary motion whose angular velocity is coincident with the air velocity vector. These tests are mainly to explore spin characteristics, which occur at very high angles of attack and sideslip. Forced-oscillation method would not be adequate in these conditions.


In general, what are the RPM ranges/differences between the various compression stages on a 2 or 3 spool (LP,IP,HP) turbojet/fan engine? I have a general interest in jet engines and am pretty new to the topic so I wanted to toss this question into the wind as I don't have any previous experience or knowledge to pull from and haven't really found a similarly posted question anywhere else.
In the small amount of reading that I've done when looking at the RPM ranges for the various compressors (LP,IP,HP) generally the LPC spins the slowest and the HPC usually spins the quickest and, if the engine has one, the IPC has an RPM range that falls between the two.
So my question is what sort of speeds or fluctuation in speeds for each shaft could we expect during takeoff/flight/landing? For example does the LPC fluctuate more or less than the HPC/IPC or do they remain fairly constant while in flight?

RPM does not generally fluctuate in flight, or on the ground for that matter.
For 'fan' RPM, 100% N1, is somewhere between 2000 to 4000.(aka LP stage)
For 'core' RPM, 100% N2, is somewhere between 9000 to 14000.(HP stage)
The 3rd spool (IP stage) RPM would be in between the LP and HP nominally around 7000.
These are ballpark figures.


What is the difference between a VOR and a VORTAC? Confused about the difference between a VOR and a VORTAC?

A VOR ground station (VHF Omni-directional Range) provides azimuth information to aircraft equipped with a VOR receiver.

A TACAN facility (Tactical Air Navigation) provides azimuth and distance information to the facility in slant range (known generally as DME) using the UHF (Ultra High Frequency) band to TACAN equipped aircraft (normally military aircraft).

A VORTAC (VHF Omni-directional Range/Tactical Air Navigation) combines a VOR ground station and a TACAN ground station into a single facility.

If a VOR equipped aircraft is also equipped with a separate DME unit it will receive distance information between the TACAN ground station (at the single combined facility) and the aircraft.

More technical and expanded information can be reviewed beginning with section 1-1-3 in the Aeronautical Information Manual (AIM)


Could a C-130 Hercules be built using WW2 technology? I'm looking at this as a "time traveller carrying only designs in his head" scenario.

Obviously turboprop engines are out of the question, but how close in capability would it be possible to get a C-130-style aircraft for use by June 1944 if our hypothetical time traveller arrived at Boeing or Lockheed in September 1939, and was able to prove his bona fides and be put to work with adequate resourcing?

It's possible to get something in the vicinity of the C130 during WW2. The C130's predecessor, the Fairchild C123, was powered with two WW2 era P&W R2800 radial engines, each producing 2000 hp. Presumably, the design and number of engines could have been scaled up.

Remember that a defining characteristic of the C130 isn't it's payload, it is the rough field landing capability, which includes STOL. I've been in a C130 when it was practicing short field landing and takeoff, and the experience was... dramatic. When it hit the runway, it really did hit the runway... with a bang.

A piston powered transport with somewhat the same capabilities of the C130 was produced in the 1950's, the Blackburn Beverly, used by the RAF. The Beverly was built with WW2 technology, and was powered by WW2 vintage Bristol Hercules and Centarus radial piston engines.

The Beverly was abandoned in favor of the turboprop Armstrong-Whitworth Argosy, when it became available, just as use of the C123 was phased out as the C130 became available in sufficient numbers. The greater power and substantially lower maintenance requirements of turboprops made them the logical choice when they became available.

Given that the C130 was initially produced with Allison T58 turboprops, at 3500shp, a four R2800 C130 would have had a power deficit. The larger P&W R4360 at 3000 hp could be used, although it was still having development problems during the war.

A WW2 vintage C130 would have had longer takeoff and landing, and a lower payload, due to the lower power available and the heavier weight of the power plants, but it was possible with the technology of that day.

Would it have been produced? Given that WW2 had its own unique requirements, probably not. Aircraft production was centered around warplanes and transports with long range, such as the Douglas C54. By the end of the war, the Allies had prepared field construction down to a fine art and the teams in place to build those fields quickly in both theaters, so the need for a large transport with rough field capability wasn't as evident.

Where the C130 really became valuable is in lower intensity conflicts that followed WW2, where expert runway construction teams aren't available on short notice, and the front lines of combat aren't nearly as well defined.

So, to a degree, the changing nature of armed conflict defined the need for the C130.


What is the purpose of this helicopter fin antenna? I'm an airplane guy, but I've got a quick helicopter question. I've seen a few helicopters with what seems to be a fin shaped antenna on the middle of the fuselage just above the windshield. I've also seen them just below the cockpit. And sometimes there's two antennas, one above, and one below.

(source)

Just curious what its purpose is?

The antenne balise de detresse is the one I'm curious about:

It can be quite difficult to see as the big fin in the first photo is a wire cutter and it seems that the arrow points to that.

The second photo shows it a little more clearly.  It is a wire cutter.


Was ATC overstepping its boundaries when advising a pilot to ignore a cell warning? I found a clip on YouTube (via an article on Jalopnik) of an Aer Lingus pilot departing from JFK. Due to a weather cell showing up on his instruments, he can not make the left ATC asks him to make.

ATC advises him that the weather is not as bad as the pilot makes it out to be.

  ATC: "Shamrock 104 heavy, it's light. I have 6 categories of weather here, it's the lightest category. I've had no adverse ride reports south of the airport by 10 miles."

He then is put in a holding pattern (while departing) until the situation is resolved. He is then told that the last 6 craft departing had no problem following that heading.

  ATC: "Shamrock 104 heavy, you're gonna go the way the last 6 GREKIs went while you did this overhead Kennedy."

Was ATC overstepping its boundaries advising a pilot to ignore a weather warning?

The controller didn't overstep his boundaries, and he didn't tell the pilot to ignore a weather warning.

Shamrock demanded something that's extreme for the NYC airspace: runway heading for 15 miles. Usually asking for right or left deviation is sufficient, and that appears to be what the previous Delta departure did.

Once Shamrock declined an easterly heading, the controller had no choice but to vector them in a temporary hold. The controller was frustrated because the previous departures had been accepting turns to the east and his radar didn't show signs of significant precipitation. He also astutely pointed out that this weather was 5 miles from the runway departure end. Aer Lingus should have been able to paint that on their radar or see it with their eyes before they departed. Their clearance was to the GREKI fix so they knew they'd be heading that way after departure. That doesn't mean Shamrock was wrong. After all, they are flying in actual, and the controller is sitting in a room at zero knots, but in the incredibly dense NYC airspace, it can create an emergency if you have to deviate that much.

The controller was harsh and made his frustration evident in the way he chose his words. The pilot stroked his ego by saying his boss would call the controller's boss.

Once you strip away the emotions, the pilot and controller did their jobs. The pilot kept his airplane clear of weather that he determined to be dangerous. The controller did the only thing he could to keep the Aer Lingus flight out of that weather and away from conflicting traffic.


How do aircraft batteries power the engine/APU? I fail to understand how do batteries power up the jet engines/APU. Are they responsible for starting up the Ignition that ignites the air-fuel mixture? Or is there some other function which I'm missing out?

Yes battery power will supply both the APU's igniter system and its starter/generator (a single motor that switches to generator mode after start, similar to turboprops).  So you need the APU to start the engines (notwithstanding other bleed sources) but you need the battery to start the APU (or an external DC power source - the APU will be fed from a DC bus; whether the bus is being energized by a battery or a DC ground cart, the APU doesn't know or care).


On a METAR, what does DSPTD mean? KDEN is currently reporting the following METAR:

SPECI KDEN 090325Z 34031G37KT 10SM -PLRA FEW015 OVC036 08/03 A2992 RMK AO2 PK WND 35037/0325 RAB04PLB25 TS DSPTD P0000 T00830028 $

I have no idea what DSPTD stands for. My best guess is "dissipated". I have been unable to find anything online, can someone help confirm this?

This is a METAR with the addition of U.S. Observations, and according to the details of the abbreviations used there is no such value as DSPTD.

I suspect you are right, that it should have been DSIPTG - which does indeed mean "dissipating". The full decode of the Remarks section of your example METAR is as follows

A02 - automated station with precipitation descriminator.
PK WND 35037/0325 - Peak wind 350 degrees at 37 knots between 03 and 25mins
RAB04 - Rain began at 04mins (You can infer the hour from the main report)
PLB25 - Ice pellets began at 25mins (Again, inferring the hour from the report)
TS DSPTD - Thunderstorms which dissipated
P0000 - Trace amount of  hourly precipitation

I should add that I'm by no means an expert at decoding this part of a METAR, I made judicious use of this page.


Is there any reason to have ADS-B out that is not based on GPS? The ADS-B system is only as accurate as the location data source it uses. In the US the 2020 ADS-B mandate requires that horizontal location data be from a GPS source with minimum performance standards set out in 14 CFR § 91.227.1

The aircraft in the Lamia crash in Colombia had ADS-B out that was based on an inertial system resulting in their ADS-B track being off from their actual position. It was off by 2 km when the flight began and drifted further during the flight, possibly being off by as much as 4 km by the time of the accident.2

Although ATC radar will still get an accurate location from the transponder, other aircraft might be using the data for traffic advisories through a system like ATAS. Using a system that could be sending inaccurate data has the potential to be dangerous.3 No info would be preferable to incorrect info. Is there any reason to install an ADS-B out system that does not use a GPS data source?

1ADS-B Frequently Asked Questions (FAQs)

2Satcom Guru: LMI2933 LAMIA AVRO RJ85 Medellín Deadstick

3At this point there is no reason to believe inaccuracy of location data had any bearing on the LMI2933 accident.

There are still quite a lot of aircraft that do have ADS-B based on inertial navigation position.

The reason for this is quite simple; they don't have GPS or the GPS is not connected to the transponder. Somewhere during the lifetime of the aircraft the transponder has received an update or has been replaced and is now transmitting ADS-B messages, based on the only position source available to the transponder; the Inertial Navigation System. That is fully legal, but it does not meet the ADS-B requirements of the various ADS-B mandates around the world.

Is this a danger to the safety of flight when ADS-B IN based systems like ATAS are used?

No, not at all. ADS-B IN systems do not use the data from these aircraft as the ADS-B messages contain several quality indicators that must meet certain conditions before a track is being displayed in the cockpit. Transponders transmitting INS positions indicate that the position integrity and accuracy is very low. In addition the source integrity level (SIL) will also be set to 0. Each of these indicators will result in the track not being displayed.


Do 'threshold' and 'end of the runway' mean the same thing? While I studied aviation, I got confused by these two words.
Can anybody explain whether they're the same or not, and if not, what is the difference?

For the simple case, yes.   The threshold will be the end of the runway.  The AIM has a graphic showing standard markings past the a normal threshold.

However, the airport operator may decide that aircraft should not land at the end of the runway.  This may be temporary (perhaps for construction), or permanently (for obstacle clearance or noise abatement).  In such cases the threshold is moved and marked away from the end of the runway.  When permanent, this is called a displaced threshold and will reduce the landing distance available (LDA) to less than the length of the paved runway.


How much do propellers stutter? A photo in EAA's monthly magazine shows one propeller blade as a dozen distinct images rather than the usual smooth motion blur.  One explanation (this answer appears to have been deleted) for this is that a propeller at nominally 2300 rpm actually varies +-200 rpm as each cylinder fires, so when it's slower, it captures more sunlight glint.
Edit: this question is about propellers, not about a photo.  The photo is only a motivation, perhaps an incorrect one, for the question.
Is this plausible?

Piston engines have flywheels.
A 400 rpm change happening 2300 times per minute is a 17% change happening 38 times per second.  Jerry Lee Lewis would say that's a whole lotta shakin' goin' on.
Onboard GoPro videos with rolling shutter artifacts show the blades "bending" from root to tip smoothly, not jaggedly.

We can count more than 15 blade-images in that short arc of revolution of the propeller, so there's no way that each one corresponds to an individual firing of a cylinder.  Perhaps there is a resonant vibration involving a slight twisting of the blade, and the sun angle is such that this produces a strobing effect.
The suggestion of a 300 rpm variation between each individual firing of a piston is completely implausible.
Some sort of camera artifact seems a possibility.


Radius of Turn Query I am making a project related to flight paths. If we are given two points in space (lat,long) and the flight headings(angles) that the flight should attain at that points.

By using the radius of turn formula, I checked whether the flight can reach the next point or not, but how can I check whether the flight can reach both the points with the specified heading or not??

Please help me out.. Thanks in advance...

Sorry for the ambiguity in the question. In the figure attached, if I need to go through points 1, 2 and 3 so on which are few points in the flight path. And if I am given (lat,long,heading the flight should attain at that point) for each point, I need to find out whether points can be reached or not. Also please suggest me the solution if I need the same heading at all the three points (say x).

And the flight should not take more than 1 turn i.e. loops are not allowed (flight should always move towards the destination).

Now, i need to head from source to destination along points 1,2,3 with same heading(q) at these three points. For example take q as the angle between source and destination. Now i want to move towards destination i.e by not turning back and no loops. Just want know whether its feasible for flight with specific radius of turn to reach the next point or not.

Or what should the minimum vertical distance and horizontal distance between the points be in order to satisfy both the points.

But we can't determine the minimum radius exactly right?? In the figure 3, point 1 can be reached with the specified heading with distance below 2 * rmin. So the condition be like delta(x) > rmin definitely because it can't reach close neighboring points but what should be next condition to check whether it can reach with required heading or not. If it is like delta(x) > 2 * rmin then figure 3 would contradict it, right?

The difference in headings gives you the number of degrees you need to turn. The distance between the two points then becomes a secant to the turning circle which should give you the turn radius by applying some basic geometry. I assume that the turn starts on point 1 and ends on reaching point 2. Like this:

Now you first need to calculate the turn radius, using the equation for secant length: Start with the difference between the two headings and call that angle $\varphi$. Then the difference between two points $s$ is $$s = 2\cdot r \cdot sin\frac{\varphi}{2}$$
Since you know $s$, you can calculate the turn radius $r$ by a simple transformation: $$r = \frac{s}{2\cdot sin \frac{\varphi}{2}}$$
Now you need to check whether the airplane will be able to turn with that radius. This depends on wing loading $\frac{m}{S}$, density of air $\rho$ and maximum lift coefficient $c_{L_{max}}$, and the equation for the minimum turn radius is $$r_{min} = \frac{2\cdot m}{c_{L_{max}}\cdot S \cdot \rho}$$
Compare both values of $r$ and check if $r > r_{min}$. Then the turn is physically possible.
Now I only hope that this is really what you asked. Your question leaves a lot of room for interpretation.

EDIT: @amarender has updated the question. Now the heading is identical at all intermediate points, and below is one of many possible solutions (blue line):

I indicated with pie segments where the turns are; of course, the one single turn condition has to be interpreted as one turn per intermediate point. The sections between the turns are straight, and all bring the aircraft closer to the destination if the heading at the intermediate points is identical to the heading from target to destination.
When do we have a condition where a solution is not possible? Only if the points are too close together to satisfy the condition of the minimum turning radius. By rotating the coordinate system such that the desired heading at the points is parallel to the x axis, this is easier to show:

The distance between two points in the direction of the desired heading $\Delta x$ must not be smaller than the diameter of the minimum possible circle ($2\cdot r_{min}$) using the equation above. The green line above is for $\Delta x > 2\cdot r_{min}$, and the red line for the boundary condition $\Delta x = 2\cdot r_{min}$. To be precise, the equation above does not put a limit on the maximum load factor $n_{z_{max}}$ - if this needs to be considered, the minimum radius is:
$$r_{min} = \frac{2\cdot \frac{n_{z_{max}}}{\sqrt{n^2_{z_{max}}-1}}}{c_{L_{max}}\cdot \frac{S}{m} \cdot \rho}$$
Things get more complicated when the heading at the points is different from the heading from the source to the destination. Then $\Delta y$ becomes important as well, and when it gets large relatively to $\Delta x$, the straight connection between turns will point away from the target very soon.


Why do we call moving an aircraft on the ground "taxi"? We all know what "taxi" means to general public -- a car which carries you from A to B in exchange for your paying a fare.

"Taxi" also means to drive an aircraft on the ground. Why do we call it that? What's the reason & history behind the term?

This online etymological site suggests that an airplane moves slowly across the field in a similar fashion to how a taxi-cab driver would slowly make his way down a block looking for fares, and the term is borrowed from that behavior.


Validity of Volga-Dnepr An-124 Grounding in US Around June 10th, a Ukranian court issued an order grounding 5 of Volga-Dnepr's An-124 cargo planes, citing maintenance checks conducted without OEM (i.e., Antonov) authorization. According to FlightAware, one of those planes (tail no. RA-82078) has been sitting on the ramp at Huntsville International since June 26th, after landing in the U.S. for the first time since the court issued the grounding order. Has the FAA grounded that plane in response to the Ukranian court order, or are Volga-Dnepr leaving it there for other reasons? It's definitely not a grounding of all An-124s, since Antonov Airlines continues to operate An-124s in the U.S.

It only makes sense USA enforces the action of Ukraine, if it wishes Ukraine does the same in the future (as noted by @JuanJimenez). Luckily, those countries (states) already agreed to the following terms as part of joining ICAO:

4.2.1 State [Country] of Design
4.2.1.1 The State of Design of an aircraft shall:
a) transmit to every Contracting State which has in accordance with 4.2.3 a) advised the State of Design that it has entered the aircraft on its register, and to any other Contracting State upon request, any generally applicable information which it has found necessary for the continuing airworthiness of the aircraft, including its engines and propellers when applicable, and for the safe operation of the aircraft, (hereinafter called mandatory continuing airworthiness information) and notification of the suspension or revocation of a Type Certificate;
Note 1.— The term "mandatory continuing airworthiness information" is intended to include mandatory requirements for modification, replacement of parts or inspection of aircraft and amendment of operating limitations and procedures. Among such information is that issued by Contracting States in the form of airworthiness directives.
Note 2.— The Continuing Airworthiness of Aircraft in Service (Cir 95) provides the necessary information to assist Contracting States in establishing contact with competent authorities of other Contracting States for the purpose of maintaining continuing airworthiness of aircraft in service.

(Source: Annex 8 to the Chicago Convention; bold emphasis mine.)
That's the legalese for when a country that has designed a plane, finds an issue (e.g., the alleged unauthorized maintenance making those affected not airworthy), shall notify the other contracting states (other ICAO member states).
If any state wishes to ignore that it has been notified that certain planes are not airworthy, will surely have consequences, but this is a better fit for Law.SE.


What's that rattling noise from parked jets? While walking around the airport on a windy day I occasionally hear a tingling or rattling noise from the engines of the parked jets. You can see the fans rotating in the breeze. What’s causing the noise? I should add that the aircraft are not in use, just parked with the engines uncovered.

It's fan or compressor blades rattling loosely in their blade roots as the engines windmill in the breeze.  The blades are attached to a hub or disc, and the retaining systems for the blades have to allow for thermal expansion, and also allow for a little bit of sideways compliance as the blades spin around, so they are a loose fit when cold.  Compressor blades are usually in a kind of interlocking socket and fan blades are often mounted on pins that allow a bit of freedom of movement.


How did the De Havilland Mosquito compete with contemporary jets? During the Second World War, the British De Havilland Mosquito light bomber achieved success in raids through its sheer speed. Traveling at up to 392 mph, it could outrun virtually all piston-engined interceptors, removing the need for it to carry defensive weaponry. Later in the war though, German jets like the ME-262 could travel at speeds in excess of 500 mph, seemingly making the Mosquito obsolete. How did the Mosquito compete with these jets successfully, despite the obsolescence of its only major advantage?

The Mosquito was a great aircraft but it was not faster than Germany's Messerschmitt ME-109 and Focke-Wulf Fw 190 piston powered fighter aircraft.

It also did not successfully compete with the jet powered Messerschmitt Me 262. The limited numbers of ME-262 were probably the only reason the Mosquito could survive in the same airspace.

On 26 July 1944 the first aircraft to be shot down by a ME-262 was in fact a Mosquito: Mosquito Operational History

"a 262 A-1a, caught and severely damaged the Mosquito in a pursuit. The Mosquito, which managed to escape into cloud, later crashed at its destination airfield in Italy, and the airframe was written off"


Is there a preferred turn direction for helicopters? If I have a requirement to fly a helicopter in a circle or racetrack over a point of interest that's stationary or moving relatively slowly, is there any reason to prefer left or right turns?

I'm not concerned about visibility and I'm not asking about turns in a landing pattern: I'm asking if - all other things being equal - there's any mechanical, aerodynamic or procedural reason that pilots would prefer to turn in one direction over the other.

Most helis make CW turns because the pilots sit on the right and it is easier to judge position and drift when you can look out the window directly.  Turning CCW is no problem however but it takes a tad more concentration.

one drawback of CW turns from the right seat is that the ALT and ASI would be out of your field of vision, so you'll have some head turning to peek at them. In a CCW turn, its easy to glance at the instruments in the center console.


How to measure the Aircraft cabin air quality? Is there any tool or mechanism to do quantitative analysis of aircraft cabin/cockpit air quality?

A few years ago, the Australian Civil Aviation Safety Authority convened an  Expert Panel on Aircraft Air Quality.

From page 138 of the report they discuss the available monitoring devices. From my brief readthrough, there were no real monitoring devices for this purpose at the time (2009) however research was being conducted.


Can an aircraft re-pressurize at high altitude? When parachute jumps are performed from 32000 feet (or between 28000 - 30000 feet), once the jumpers are let out from the aft (cargo area), does the aircraft need to change altitude (e.g. descent)? Can the crew not pressurise the aircraft by simply closing the door?

In particular, I am talking about wide body aircraft with cargo deployment facility.

Pressurization is controlled by two processes: air in and air out.  Air is constantly being let out of the cabin through (at least) 2 outflow valves, typically located at the aft limit of the pressure vessel.  Air is let into the cabin through the air cycle machines (a.k.a the "packs") which are provided with very hot and high pressure air from the compressor stage of the engines and eventually output into the cabin through the air conditioning vents.

During normal cruise flight, the mass flow rate of air into the cabin is constant (because the flow rate through the engine compressor is constant), thus pressurization is maintained by actuating the outflow valves.  Open them up a little more to raise the cabin altitude, close them up a little more to descend the cabin altitude.  Note that while maintaining a constant cabin altitude the outflow vales are partially open -- the incoming air is more than adequate to pressurize the airplane.

When a main cabin door or something bigger is opened, the airplane will no longer maintain pressurization and everyone must don oxygen masks to avoid unconsciousness.  With a planned cabin dump, masks will be donned before the cabin is evacuated, which will happen before any doors are opened.  As noted by others, the pilot oxygen is fed from cylinders of pure oxygen and will last a long time.  Passenger emergency oxygen is from chemical oxygen generators and lasts 12-15 minutes.  I'm not sure what type of oxygen masks the HALO jumpers would wear, but presumably they have portable oxygen for the jump not related to the airplane oxygen facilities.

When all of the jumpers are away the doors are closed and once again the airplane is capable of pressurization.  The outflow valves will be commanded closed and the cabin altitude will start descending.  Once the cabin altitude is back down to normal levels, the crew will remove and stow their oxygen masks.

There is no need to descend to accomplish this because the air provided by the engines is much higher pressure than even sea level air.  Re-pressurization is accomplished by closing up the airplane and letting air accumulate in the cabin, thus raising the pressure.  Once the target pressure is realized (~8000 ft), then the outflow valves partially open to stop descending the cabin and to maintain the target pressure.


How significant is antenna drag on light GA aircraft? Antennas sticking out of an aircraft obviously increase profile drag, but the folks who design antennas have done a lot to improve aerodynamics: High performance aircraft can have antennas mounted inside of fiberglass components like wingtips, and flush-mounte antennas are available for transponders and DME equipment.

For slower light GA aircraft more aerodynamic antennas are also available (e.g. blade-style transponder antennas are available which produce about 80% less drag than older spike-and-ball style antennas), measured at 250 MPH.

Since the average light GA aircraft has a VNE below 250 MPH and isn't generally covered in antennas, how significant is the antenna drag on a typical light GA airframe?  For example, would stripping the ~6 pounds of antenna drag from your average Cessna make an appreciable difference in airspeed?

From an aerospace engineering perspective:

The drag coefficient ($C_D$) of a round antenna is can be estimated by around $.5$ depending on shape, while for an streamlined shape it's around $0.045$.

(Source)

Drag is defined as:

$$D=\frac12C_D{\rho}V^2A$$

Thus, say you have a 0.01 m wide antenna 0.25 m long, for an aircraft moving at 50 m/s. At sea level conditions, air density $\rho=1.225 \mathrm {kg/m^3}$. Say that $C_D=0.5$. If my calculations add up, it's around $1.9 \mathrm{N}$.

Say you have the same antenna, for the same aircraft aircraft moving at 50 m/s. Air density is $1.225 \mathrm{kg/m^3}$, but this time the antenna is streamlined with $C_D=0.04$. This results in a force of only $0.15 \mathrm {N}$.

(Updates: Originally the formula included $\frac12$ twice which was wrong, and that the force was given in kg, rather than newtons; my apologies.)


Violation class bravo airspace I was flying under class bravo airspace at 1800 feet which was the legal altitude 1800 and below but my transponder is off by 200 feet so they thought I was 2000. when I landed and i had to talk to the tower. He did not say anything except be careful and turn your altimeter down next time and be careful. nothing else happened but am I OK? did the get my n number ? i never gave them my name or info.

You're probably fine.  File a ASRS form all the same though.

The feds tend to focus on safety of flight issues or gross violations that indicate general incompetence.  Some guy flying below a B shelf doesn't rise to the level of incompetence (because it's not).  Worst case, you caused a resolution advisory for an airliner which, in the grand scheme, is not a huge deal (for you, legally) if you were following the rules (sounds like you were).

If you get a letter, call an aviation attorney.  I doubt it will come to that though.

Keep on flying.


Which countries in Europe allow for the use of Pilot-Controlled-Light? In Europe is very uncommon to see this feature at airports due to the local regulations in different countries, but still some are allowed and use this system. What countries allow for its use? Please name at least one airport for each country which uses it.

Sweden has numerous airports that use pilot controlled runway lights. Such lights are typically turned on by making a long (10 seconds or longer) transmission on the airport frequency, though variations exist.

Some examples of airports in Sweden that use PCL are:

ESSD Borlänge/Dala Airport
ESGE Borås
ESSU Eskilstuna/Kjula
ESNG Gällivare
ESSG Ludvika
ESKM Mora/Siljan
ESND Sveg
ESGT Trollhättan/Vänersborg
ESKC Uppsala/Sundbro

For clarity's sake: This answer is not meant to imply that other countries do not allow for PCL, nor that all lighting on the airports listed is pilot controlled.


What does RPM mean in a propellor aircraft, compared to a jet aircraft? What is the practical significance of speed RPM in a propeller aircraft for a pilot? I am not able to correlate it with RPM in jet engines?

RPM in a propeller aircraft is typically under 2400, as the prop spins at the engine RPM speed. Above 2700 the tips of the propeller begin going supersonic and make more noise than anything.

Jets engine spin much faster, as discussed here
Which are typical rpm values for aeronautical turbines?


Could in flight folding wing tips lead to a safer airliner design? As a spin-off to the recent success of the Boeing 777x maiden flight, the effects of folding the wing tips in flight were considered.

Folding them down in cruise, like the XB-70 should increase yaw stability and create a slight anhedralling effect, which reduces Dutch Roll tendency.  More importantly, it would shift the Center of Pressure forward, eliminating the need for downforce from the tail.  This creates a desirable, fuel saving, staticly nuetral configuration.

But the real safety improving benefit would be to fold them down on approach to landing, requiring downforce on the tail to balance the lifting forces.

Would this not create a safer, staticly stable configuration, where approach speed can be trimmed?

A few issues make fold-up wing tips unfeasible:

Weight and complexity of a mechanism and control system for it.

Shifting CP forward makes the airplane less stable statically. In any case, if you want to reduce trim drag, just move the C of G aft to unload the tail to get the same result, and use computers to artificially induce static margins, which is already done.

The stall speed reduction from the extra wing area is quite small.  A wing tip that added  10% to wing area when dropped would only drop the stall by a few knots.  The stall speed reduction from adding flaps dwarfs the reduction you get from adding area.

At high altitudes, you want the extra span so you wouldn't want to retract the tips anyway.  On an airliner that cruises sub-sonic at high altitudes, there's no benefit to reducing span.  On sub-sonic airplanes, where you clip off the wing tips, it's to improve speeds at low altitudes (like the clip wing Spitfire, done to improve performance below 20000 ft - for the very high altitude versions used to take on JU-86s, they added span).

The only practical reason to have folding wing tips on an airliner is to reduce span on the ground, as an alternative to winglets (which are used to gain some of the benefit of added span without taking up space or adding to bending loads on the wing), but a winglet is a much cheaper solution.

Which, as always, is why you haven't seen anybody do folding wing tips in the last 60 years, whereas winglets are everywhere.


Is it fairly common for student glider pilots to have wing tip strikes, especially in gusty cross wind conditions? Is it fairly common for student glider pilots to have wing tip strikes, especially in gusty cross wind conditions?
I understand gliders are landed level, slow down and then the wing drops onto a wing tip wheel or skid plate when coming to a stop.
Which begs the question, are gliders more prone to wing strikes by student pilots prior to or after landing due to the mono wheel arrangement and low wing tip clearance, or have poor cross wind landing ability in gusty conditions (say 10-15mph gusts above the headwind) when compared to a tail dragger or tricycle wheel arrangement?
Yet thousands of gliders around the world are used every week with the mono wheel arrangement, with a mid wing arrangement that is only 2-3' off the ground.
My gut feeling says no, as gliders have been around probably for 100+ years and they would have changed from mono wheel to a tail dragger, at least on the trainers by now if wing strikes were common among student glider pilots. This is probably due to the lateral stability of a long wingspan and the mid wing arrangement means the glider is landing in a nice stable pillow of air in ground effect.

Most gliders have dihedral, giving more wingtip clearance than you probably are envisioning.  Many glider pilots routinely use the wing-down (slipping) method of crosswind correction.
As far as general handling while landing in gusty crosswind conditions, most tailwheel airplanes sit in a much more nose-high attitude than most gliders, and have the landing gear much further forward ahead of the CG, and therefore are much more prone to ground-looping.  And groundloops often involve wingtip contact with the ground-- on the downwind side.
On the whole the crosswind limits below which a safe landing without damage to the aircraft can reasonably be expected, are likely higher for most gliders than for most tailwheel light airplanes.
As for the part of your question contained in the actual title-- no, it is not common for student glider pilots to strike the wingtip into the ground before the main wheel touches.


What is a fuel tank float valve and how does it work? This report on dodbuzz mentions a 'fuel tank float valve'. Neither google nor StackExchange seem to know what it is. What is it, why is it necessary?

I don't know about the fuel float valve of the F35A. A float valve is basically the principle used in toilet flush: A device that:

senses liquid level in a tank, and
open/close a valve according to this level.

The device may rely on a float acting on a horizontal lever, or it may be a float sliding vertically along a rod.

There are several float valves on this schematics of the Boeing 737 fuel system:

Source

If this doesn't work, the tank may be reported as always full, as for the F35A of your report.


Why is Thunderbird 5's number upside down? Why is Thunderbird 5's number written upside down?

This is because Thunderbird 5 is the opposing solo, and spends almost all of its time inverted.

Apparently though, this plane's number was not always painted upside down:

Just guesswork on my part, but maybe the Thunderbirds did not fly inverted maneuvers before the F-16s?


How is the compliance time in this AD interpreted? Within 25 flight hours (FH) after the effective date of this AD, or
  within 100 FH since the last inspection, whichever occurs later, and
  thereafter at intervals not to exceed 100 FH

Do we have the same condition in both states of above? If our A/C inspected since the last inspection in 100 FH over or less because of this state "whichever occurs later", we must comply for 100 FH grace period and 25 F/H is omitted?

Break down the timeline logic.  The key word is "later".

AD released today.

Last inspection may or may not have been done 50 hours ago, which pre-AD was voluntary or part of a non-mandatory maintenance program, or part of some recommended Service Bulletin, that is now being mandated, or maybe it was never done at all.  Assume it was done 50 hours ago.

Which requirement is later?  25 hours from today, or 100 hours since the inspection done 50 hours ago?  100 hours from the last inspection is still 50 hours out from today, so it is later than 25 hours from today, so do it in 50 hours.

Say last inspection was 90 hours ago.  Hundred hours later comes up in 10 hours.  But the AD says whichever is LATER.  25 hours from today is the later than 10 hours from today, so that applies.

Or inspection has never been done before.  25 hours from today.

In no case do you have to do it in less than 25 hours.  It's more or less the same as that other one you posted about landings, but with a bit different wording.


Is it possible to turn and safely land an aircraft with a malfunctioning rudder? Is it possible to turn mid air, and land a jumbo Boeing 747, Airbus A380 or any aircraft if the vertical stabilator is jammed in a position that allows it to fly straight at cruise altitude and speed, assuming everything else works including the horizontal stabilators?

If the rudder is jammed in the neutral position (as stated in your question), then landing is easy. You will just land using ordinary techniques. The plane may feel sloppy, and passengers sitting at the back will complain about feeling dizzy, but the aircraft is easily controllable and landing would not be any problem.

Now things are different when the rudder is jammed to one side, for example in American Airlines Flight 96. The crew faced major controlling issues with a full right rudder, engine failure and very high sink rate. But even then, the pilots managed to land successfully.


Is it legal to use handheld radios to listen to aviation frequencies in the USA? Is it legal to use handheld radios to listen to (general aviation) airport frequencies in the USA? Can I go to an airport with a handheld radio and listen to their frequencies?

Your receiver must comply with USC 47 302a, the law that says, "you can't interfere with other equipment".

USC 47 301 in general is all about "transmission of energy", or broadcasting.
And it really is beyond the scope of government to say you can't stick a piece of metal in the air and process the signals it receives, provided you don't cause interference to anyone else.

Assuming your radio is receive-only, you really won't have a problem with that. (short of a total malfunction!).


Where should I enter the pattern when instructed to report a 2-mile left base? Say I'm flying heading 275 and am headed in to land on runway 16 at a towered airport in Class D airspace. I'm 8 miles to the east and have been cleared: "report 2 mile left base runway 16". Should I go for a standard 45 degree traffic pattern entry to downwind at midfield or should I fly straight to the base and report when 2 miles east of the runway?

In this case I went straight for the base and reported and didn't get yelled at by the controller but I'm curious what the correct thing to do is in this situation.

I'm not asking what a 2 mile base is, I'm asking where I should enter the pattern if instructed to report on 2 mile base.

I'm assuming you're more interested in the base-or-downwind question rather than the where-is-the-2-mile-base question.

Theoretically you're supposed to fly the published procedure unless told otherwise. In this case the procedure would probably be a standard traffic pattern.

Being told to 'report' means only that, you should report it when you're there.

This is not to be confused with the (in my experience) more common instruction "Enter and report a 2 mile base for runway 16", in which case you head for the base and not the downwind, and you report it when you get there. To argue ad absurdum, the clearance "Cleared touch and go, after the touch and go, make left traffic, report mid-field downwind" doesn't mean you should head straight for the downwind.

As always, when in doubt, ask.


Which Velocity is used to measure Dynamic Pressure? Suppose an airplane is flying in windy conditions. Now, for the calculation of the dynamic pressure should I use the relative velocity or the absolute velocity as the free stream airspeed?

You should use the speed of the air relative to the object.

Take the extreme example of a stationary wind turbine. It obviously experiences aerodynamic forces and dynamic pressure, yet always has an absolute speed of zero.


Why was the F-117 retired so quickly? Why was the F-117 retired after so few years in service (Approximately 25 years) while other military aircraft are in service for many decades? Many of the 60 built should still be air-worthy.

For example, the F-15, F-16, and F-18 models have been kept in service for 40 years.

Several reasons can be found for its early retirement:

the aircraft was instantly obsolete after one was shot down over Yugoslavia by a 30 year old SAM system
Maintenance was pretty expensive and difficult (and according to some involved large quantities of highly toxic chemicals that are still causing health problems for the people involved)
Few military reasons to keep it in the existing threat environment. An F/A-18 is cheaper to operate than an F-117 for bombing missions against insurgents and terrorists.
Politics. Retiring the F-117 could have been intended as a step towards asking for funding for more F-22s, claiming that the USAF was now without a tactical stealth aircraft for the ground attack mission (the F-22 at the time was envisioned as a multi role aircraft, having a secondary ground attack function like the F-15 and F-16).
The F-15 and F-16 have been kept in service through extensive replacement and upgrade programs for older models. There never was an upgraded F-117 proposed or built. The F/A-18 E/F are effectively a completely new aircraft and shouldn't be considered the same type as the older A/B.


Can you help me to identify a Boeing 727 maintenance task involving a safety risk for a research project? I need help identifying a Boeing 727 maintenance task that would be suitable for a research project on improving maintenance instructions.

Ideally, the task should meet the following criteria:
- the task should take about 1 hour to complete in a base maintenance environment;
- the task should have a safety risk that is prone to human error (for example, potential to do an incorrect installation of a component).

This is for a research proposal to improve the quality of maintenance instructions. I have a commercial aviation training school that is interested in participating. They have a 727 which is a type I've never worked on and I don't have access to any of the 727 manuals either.

I'm trying to table several options that I can put to the school. What I have so far is removal/installation of an AC generator or perhaps the generator constant speed drive. Further suggestions would be very much appreciated!

It's been a while since I worked the 727. It was a very forgiving airplane, so you had to do a lot to make a critical safety error from a maintenance perspective.

However, I do remember elevator position transmitters being a major pain to adjust. Although the manual wasn't necessarily bad, I never felt comfortable with the adjustments because of how sensitive they were. The manual made it sound so easy, when in all reality, I would have felt better if there was some note that said something to the effect of "this may take a while." Plus, you always had Skydrol dripping in your face when doing it off a lift in the howling wind.

Even tightening the bolt of the transmitter down was enough to bring it out of tolerance. So, ordinarily, you had to rig it out of tolerance, then hope that the tightening of the bolt brought it in tolerance. Sometimes it'd take 5 minutes. Other times it could take all night.

There is also a "dog bone" that attaches between the transmitter and the flight control surface. Sometimes the bearings in that dog bone would develop slop, and cause autopilot issues as well.


When did ATA introduce ATA Chapters? When did ATA introduce the ATA chapters and since when was it used by all manufacturers?

Thanks!

ATA100 was introduced as a publications standard in the late 50s for manuals and was in wide use by the late 60s.  Some manufacturers organized their engineering drawing numbering systems around ATA100 (ex.: flight control systems drawings numbered with a "27" or landing gear with a "32" prefix), but not all.


What are the trim settings on ferried aircraft? Sometimes an aircraft or spacecraft is ferried on top of a carrier aircraft. Do these "piggy back riders" have their flight surfaces controlled (possibly remotely) during the flight? If not, how are they trimmed?

In case of the Short Mayo Composite, controls of the payload aircraft were locked in neutral position until separation from the carrying aircraft in the air.


What callsign should an ultralight use? I plan to operate an ultralight aircraft domestically (in Oregon, USA) in uncontrolled airspace and will not venture out of the country nor will I come near the Canadian or Mexican borders.

I have searched a bit and found that as long as I'm going to be operating domestically, I don't need an FCC license, however in AC 103-6 it states

  c. Traffic Advisory Practices at Uncontrolled Airports.

  In all radio communications, 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".

How can I use FCC call-letters if a license is not required domestically?  Since ultralights aren't required to be registered, I won't have a tail number to use either.  Do I just make something up like "ultralight whisky bravo" (my initials)? I do have an amateur radio license, but I'm guessing that isn't relevant here.

One of the suggested communication strategies for uncontrolled airports is to announce the type of aircraft and color. e.g. “Brown and white Cherokee entering downwind”.

Rather than using your initials, which like the tail number, don‘t really give any information, why not use your color or some distinguishing feature. e.g “Red tricycle ultralight” or “Blue weight-shift ultralight”.

Anyone out there would have a better chance of knowing what to look for and seeing and avoiding you.


Why was the Vulcan bomber used for the Falklands raid? There is a lot of information about this complex operation. But can anybody explain why they chose to use an aircraft? They could easily shoot cruise missiles from a ship or ballistic missiles from a nuclear submarine. The easiest and quickest option would be just to shoot an ICBM directly from the UK using a conventional warhead. Just put the coordinates in and task done. No risk to anyone! I think the UK had all the needed technology by that time.

This is borderline as an aviation question but I will answer it anyway.

They didn't use those weapons because they did not have them at the time:

Conventional cruise missiles did exist but most were nuclear, and the UK didn't possess any conventional ones.

ICBMs with conventional warheads did not and probably still do not exist because they are not a good idea:

Their capacity is low: A sub launched ICBM has somewhere around 2.5 to 3 metric tons' throw weight, much of that would be taken up by warhead guidance, thermal protection and other necessities so your actual warhead would be maybe 1000kg, or 2200lb. That's not that big a conventional bomb, and it could only launch one. A fighter bomber could drop 2 of those. The Vulcan bombers on the raid carried 21 1000 pound bombs.
They aren't accurate enough: a nuclear weapon can be a bit off and still destroy its target utterly, a conventional weapon needs a great deal of precision. The Polaris missile had an accuracy of 3000ft (900m). That's okay for a nuke, it' still ruin someone's day, but completely inadequate for a 2000lb bomb. More modern ICMBs have more like a 100 meter accuracy, which is a lot closer but still not good enough for a conventional bomb
They are expensive: that's a lot of cash for a 2000lb bomb that probably will miss
Launching one could start WW3: If you launch an ICBM someone is going to see it and if they think it might be directed at them a retaliatory strike could be the answer. The world has come perilously close to this more than once, it simply isn't worth the risk!


How do I optimize a turbofan engine to fly lower and slower instead of higher and faster? I was reading something about someone who was doing this and I'm intrigued, but I have no idea what you actually do to optimize the engine to be better at lower altitudes and lower speeds?

As a summary, the engine generates thrust by changing the impulse (momentum) of the air. Please refer to this: NASA Genera Thrust Equation

So to optimize aircraft performance, the main options you can play with are that depend on your aircraft operation:
V0: flight speed
p0, r0: inlet pressure and density (function of altitude)

And the variables that depend on your engine design:
Ve, pe, re: exhaust velocity pressure and density (depend on the thermal cycle and actual operating condition of the engine)
A0, Ae: Inlet and nozzle areas (engine geometry, sizes derived from the design point)

Now what you need to see is that there is no single best option, aircraft design is an optimization problem, eg finding compromises. Flying lower and slower is actually an attractive option for greener aircraft, as it enables technologies that reduce drag, such as ultra high aspect ratio wings, laminar airfoils, boundary layer ingestion, electric propulsion and a few more.

Whether optimizing a turbofan for lower altitudes make sense can only be seen by comparing the wins against the losses, and it is hard to say absolute truths as it depends on many variables.

Now about the actual "how-to" optimize a gas turbine, essentially the key variable of the engine is the pressure ratio, PR, so how much it compresses the inlet air. For a given flight condition (thrust, speed and altitude) , there is an optimal pressure ratio. From that the number of compressor and turbine stages can be calculated (also if you need a multi-spool engine, do you use an intercooler, etc.), and also the geometrical dimensions of the engine. And this goes back to the comment I've made that it is a compromise. Building a very heavy, expensive, hard to maintain engine will not be a good choice as what you win by increased engine efficiency you will lose on the flight efficiency.

But suppose as an academic exercise you just want to alter an existing engine design to move its design point to a lower speed and altitude, then you need to change the design pressure ratio, and follow up with any internal changes (add/remove stages, change inlet, nozzle, etc.)


What is this object on the tail of an F-16? Source: skytamer.com

What is the object on the tail of this F-16 (next to the serial number)?

Source: primeportal.net; cropped

That's the cooling-air outlet that is aft of the cooling inlet. In between is a power amplifier for the radar-warning system.

  Source: amazon.co.uk (one of the product images); cropped

  118: Cooling-air ram air intake
  124: Radar-warning system power amplifier

Related: What is the device at the tail of the F-16 Block 60?


How to land using horizon? source

I recently heard pilots discussing a landing technique that some instructors are now teaching.

To assist new pilots in flaring, they instruct the pilot to adjust their attention toward the far end of the runway or horizon. There was some discussion that it won't work for a pilot short in height. As they look toward the end of the runway or horizon they are suppose to use some type of reference, such as "the horizon expanding".

What is this technique for landing and how is it suppose to help?

Update: According to the "Rod Machado" YouTube video provided below, it is the runway width that is the primary reference, not the horizon or end of the runway. The pilot is viewing the end of the runway for peripheral vision of the width.

I think the GIST here is:

Look far ahead. Don't look at whatever is directly in front of you.

It's the same as driving. If one looks at the piece of concrete just meters ahead, then the barricade will "pop out in front suddenly" or the bumper of the car is "in your face out of nowhere".

Our peripheral vision will guide us to wherever we want. It is natural and in-born, biologically. You just need to know where to look.


How to get the correct speed/power on downwind? (Note: in this example I'm taking speeds from a Cessna 172)

I was taught that on downwind, you fly at pattern altitude at a normal power setting until you beam the numbers, at which you reduce power (to 1800 RPM.. ish) and start your descent. I was also told that the speed of each leg of the descent should be 80 (downwind), 70 (crosswind), and 60 (on final), and you add 10° of flaps each leg.

I'm running into two related problems:

On downwind, my airspeed can be 100-100 knots. This means I float for awhile at pattern altitude after beaming the numbers to get my airspeed down before starting the descent. I can't extend flaps until I'm under 80 knots and in the white arc.
My goal is not to add power after I've taken it out. Idea is to control the landing enough that I can still make the runway during an engine out. If I reduce the power a lot to hit 80 knots, I end up having to add a bunch of power on final to make the runway. If I keep the nose high and drop airspeed after beaming the numbers, I end up floating too far away before starting my descent, causing me to fly a larger pattern, and the need to add power to make the runway.

How do I control the speed and power setting to have a graceful pattern and smooth power setting while landing?

I spend most of my flying time in C172s of various models as well as 152s, PA-28s and the like. In most C172s you can extend 10° of flap at 100kts, or even 110kts in some models. The white arc is usually for 20° of flap and above and that's 85kts not 80kts, but you should check the POH to be sure or it may be written on the flap handle placard. 10° of flap will certainly help, but it's more your technique that seems to be the issue here.

Your goal to not add power after you've taken it out is what is the biggest reason for your float, and isn't really constructive. It's normal to reduce throttle to meet a particular airspeed and then throttle up again, if you don't you are relying solely on drag to slow you down, which as you have discovered takes time. Cessnas are draggy beasts because of their low wing loading, wing struts and big rivets, so you can kinda get away with it, but if you tried that in a PA-28 you'd float much, much farther as it is less draggy, so it's not a good habit to get into as you'll be carrying too much extra speed throughout the approach.

You're never going to hit on the perfect throttle setting that will carry you around the pattern and touchdown at just the right point, there are too many variables to factor in like wind direction, wind speed, rising or falling air, etc. Fixing your throttle forces you to fly a specific pattern for the specific conditions, which won't be the same pattern as everyone else, and it will be different every time. There's no benefit to doing it.

The moral of the story is don't be afraid to use the throttle as necessary to control your energy, that's what it's for. When you need to reduce speed throttle back more, then increase again when you get to your target airspeed. In the approach make throttle adjustments required to maintain the descent rate you need, if you start to get a bit low add some, if you get to high pull it, and practice practice practice.

Don't worry about engine failure in the pattern either, if your engine quits you most likely have enough energy to make the field, just clean up and fly your best glide speed. Try it with your instructor: throttle back to idle at downwind and fly a curved approach onto the runway, you'd be surprised how much energy you have at the end.


What is the most economical way to store a small aircraft in a place with severe weather? I'm interested in possibly owning a small aircraft sometime in the future.  In the interest of finding out how much money it would cost, I recently called a local FBO and asked about a hangar rental.  I was told that it starts out at over $300 per month and that there is an 18 month long waiting list to get one!  I am talking about an older used piston engine plane, not a private jet.

I'm quite aware of the fact that it is money, rather than aerodynamics that keep a plane in the air, and I'm getting the impression that it takes a lot of money to keep a plane on the ground, too.

The only other thing I know of is to tie it down, which I was told costs $150 per month at this same FBO.  The issue I have with that is concern about the weather.  I live at high elevation; the summer sun is very intense, thunderstorms and hail and common in the summertime and winter brings plenty of snow; sometimes up to two feet at a time.  Temperatures fluctuate from about 0 to 100 degrees Fahrenheit.

I was wondering if there are ways to effectively protect an aircraft from the elements while it is tied down, or if there may be some more cost-effective storage solution than a rented hangar.

Location matters.  Where are you located?  A hangar is not as important in a dry climate like Las Vegas as it is in, say, Miami.

It may make sense to pay more for a hangar.  Leaving a plane exposed to the elements you describe (0° - 100°, snow, wind, sun) will do damage over time.  The plane won't corrode into a heap but little things will start to require extra attention.  Those little things will add up at annual time.  It's unavoidable.  Having the hangar is another layer of protection that, in my opinion, is well worth the cost.  If a hangar is simply unworkable then think about a covered tie down. A covered tie down plus a decent cabin cover can accomplish about 75% of what a hangar offers at half the price.  You won't have complete protection from hail, vermin, or thieves but that's not a deal breaker.  Just lock the doors and keep the insurance up to date.

Are you considering a simple plane like a 150 (all metal, "affordable"), a tube and fabric plane, or something with more complexity like a Bonanza or Mooney?  Maybe a C-150 with rough paint, a worn interior, and old avionics that aren't worth stealing will do just fine outside.  If you buy something with good paint and interior (or fabric covering) you'll want to protect it.  New P&I costs thousands and thousands of dollars so it's much cheaper to keep a pretty plane pretty than to make an ugly plane pretty.  The costs to re-cover a plane in fabric can cost tens of thousands depending on the amount of fabric and complexity of the paint scheme.  Other airplane-specific considerations like corrosion on Mooney's steel structure (see Mooney Service Bulletin 208) or a Bonanza's magnesium control surfaces should be factors in your decision as well.  Finally, when you go to sell the plane a buyer will likely feel much better about a plane that was hangared than one that was parked outside.

One piece of (unsolicited) advice: draw up a conservative budget assuming that costs will be higher than expected.  Budget for a hangar, $1M smooth insurance, and a tough annual during the first year of ownership.  Multiply this number by 1.5 at the very least.  This is a "bad case" first-year cost (don't worry, it gets better as you settle into ownership).  If you can absorb that cost without feeling any pain then you're ready for ownership.  If you can't...who cares?  Buy the plane anyway!

We can give you a more complete answer if you know the answers to the following questions:

where are you based?
what kinds of planes are you looking at?
what is the current condition of this hypothetical plane?
what's your maximum annual ownership budget?


What is the type of the seaplane at the end of runway 18L on Schiphol Airport? From 47 to 52 seconds into this video we can see a seaplane parked in a small pool of water. What type of plane is this and when did the plane fly for the last time?

To clarify, it's a Fokker F-27 Friendship 500.

Manufacturered in 1971, PH-NIV has photos of it on Wiki:

Registration details here

As to how it's in Amsterdam Schipol:

  towed to entrance at Oude Meer nr Schiphol East 12.07.12 as PH-NIV in
  old Fokker proto cs owner Coöperatieve Vereniging Anthony Fokker
  Logistics UA moved to permanent display location 13.03.13 on poles in
  a lake with nose up,

So it's been there since March 13, 2013 (the same day the current pope was inaugurated, incidentally).

Before that, it was registered with several companies during its service:


What are heat detection sensors and how can they cause a speed error? From this news article on Saratov Airlines Flight 703:

  A report handed down by Russian investigators has blamed human error for the crash of Saratov flight 703, saying the pilots didn’t switch on the heat detection sensors on the plane.

Heat detection sensors sounds wrong as cause of de-icing failure.

Is it a bad translation of the sensor's name? What would be the correct name? Else please explain how the failure to turn on a heat detection sensor cause icing speed error detection.

It seems that the pilots didn't activate pitot tube heaters but the investigation is not completed yet.

"Pitot tube, also known as Pitot probe, is a flow measurement device used to measure fluid flow velocity."

So detection sensors in your question refer to pitot tubes and failure to turn on their heaters in icing conditions can cause incorrect airspeed indication. This in turn may lead to incorrect decisions from pilots or autopilot.


Who is responsible - CFII or the Private Pilot? Here's the scenario: There is a Private Pilot working on their instrument rating. Alongside with him is their CFII. Let's say it is just a normal VFR flight, and they're getting back to their home airport after a training flight. Now, after the first radio call, ATC instructs them "NXYZ, Squawk 1234 and ident - remain outside (Airport) Class Charlie".

Even though you just need Two-Way Radio Communications to enter Class C, ATC has strictly advised them to remain outside of it.

Now, for some reason, the airplane goes well inside Class C airspace. After a few minutes, ATC gives a call saying "NXYZ, cleared into Class C, enter left base Runway 18. Possible pilot deviation, advise when ready to copy down a phone number"

The question is - since both the Private Pilot and the Instructor are logging the flight time as PIC, who is responsible to answer? And if a deviation is given - who among the two gets it?

There is a contradiction in your question.

You say both the student and instructor are logging PIC.  This is fine, but the authority for this to happen depends on certain things.

The instrument student logs PIC under 61.51(e)(1)(i)

  (1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-

  (i) When the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, or has sport pilot privileges for that category and class of aircraft, if the aircraft class rating is appropriate;

They are acting as PIC as the sole manipulator of the controls and must be rated for the aircraft.
The instructor logs PIC under 61.51(e)(3)

  (3) A certificated flight instructor may log pilot in command flight time for all flight time while serving as the authorized instructor in an operation if the instructor is rated to act as pilot in command of that aircraft.

This only applies on instructional flights, where the instructor is providing instruction and is rated to act as PIC (e.g. if the instructor lacks a medical and could not act as PIC, they could still provide instruction if the student is the PIC, but the instructor would not be able to log PIC).

The reason I say this is a contradiction is that you claim

  Let's say it is just a normal VFR flight, and they're getting back to their home airport after a training flight.

This makes it sound like it is not a training flight and in that case only one of the pilots could log PIC using the sole manipulator rule in the absence of instruction taking place.

It turns out the above isn't directly important, as logging != acting PIC, and the acting legal PIC is what matters from an authority and enforcement perspective.  What the above logging issue gets at is hinting at who might be the legal PIC absent the two pilots agreeing who would act as the legal PIC.

In the case instruction is taking place even though the student is logging PIC  the instructor is also logging PIC and is the "ranking" pilot in the flight and may be viewed as the legal PIC.  In the case of a non-training flight (which would be hard to justify if you both logged PIC), then it comes down to the question -- who agreed to act as the legal PIC?  Either of the student or instructor could act as the legal PIC, but on a non-training flight only the one of you actually manipulating the controls could log PIC.  If there was no agreement prior to the flight over who is the legal PIC, the FAA will still probably decide the CFII was the legal PIC or the FAA may decide to go after both of you.  I believe there is precedent for this in enforcement action, but I don't have any cases handy to reference.

What should you do about this?  Both the student and the instructor should fill out a NASA ASRS form and preserve evidence that you submitted it within 10 days of the event.  If the deviation was not willful and the controller decides to pursue action, this will protect you from enforcement.


Is there anywhere I can find examples of letters seeking interpretation of FARs, sent to the FAA Office of Chief Counsel? Is there anywhere I may find examples of letters seeking interpretation of FARs, sent to the FAA Office of Chief Counsel?

What is the appropriate salutation, if one is needed, on a letter to the FAA Office of Chief Counsel?

Should the actual letter (not the envelope) be sent to the "Chief Counsel" or to the "Office of Chief Counsel"?

Should anything in the way letter is addressed, or who it is addressed to, signal that I specifically am seeking clarification of an FAR and not raising some other legal issue?

Related:

How can someone get clarification from the FAA on the intent of a regulation?

https://www.faa.gov/about/office_org/headquarters_offices/agc/key_officials/media/AGC_Org_Chart.pdf

The FAA posts the original submission along with the interpretations, at least for recent interpretations. There's a lot of variation in who they're addressed to; many of them are follow-ups to previous contact with the FAA, presumably with the local FSDO.

This one (Standel-West Coast Aviation Services, 2019) might be useful as a starting point, it simply uses the salutation "To Whom It May Concern" and it has the full mailing address in it. It also uses very specific wording about the scope of the request:

  This letter is a request for interpretation and clarification of 14
  C.F.R. § 135.267(b).


What is the difference between a published and unpublished TFR? On this article about Sporting Event TFRs on the Flight Service website, they mention unpublished TFRs:

Play Ball! Be Aware of Sporting Event TFRs June 26, 2016 when you ask
the specialist for TFRs along your route of flight or request an
online briefing, you may expect the specialist to provide unpublished
TFR information that is not associated with the “blanket” sporting
event TFR. Ensure you check your route of flight for the possibility
of a Sporting Event TFR or published TFR.

What is the difference between a published and unpublished TFR?
From the article I would infer that Sporting Event TFRs are considered published, but I don't think they are published anywhere else but in the NOTAM. Appearing in a NOTAM is not considered as being published, right?
Where are the published TFRs being published now? NOTAMs used to be published in Notice to Airman Publication (NTAP). But, from these notes on the FAA website it seems that NTAP is being retired. So, where would the NOTAMS be published moving forward?

It looks like you have two questions: what's an unpublished TFR, and where are NOTAMS published?
First, unpublished TFRs. I can't find any FAA information on "unpublished TFRs" and I suspect it was just poor phrasing from FSS. I read the article you linked and it's unclear what they really meant, at least to me. Having said that, you could interpret "unpublished TFR information" in two ways:

Unpublished information about TFRs
Information about unpublished TFRs

I believe the intention was #1. There's a blanket 'stadium TFR' NOTAM but it doesn't include key information, like when the TFR is active for a given stadium. That's because games schedules change and the FAA doesn't keep track of them; it's up to the pilot to know if there's a game going on or not. For that reason, the stadium TFRs are very unpopular with pilots.
But, FSS might still tell you if a stadium TFR is active. Especially for major, high-profile events like the Super Bowl. There's no guarantee that they can or will, though, especially since FSS has become more centralized and less local.
Second, NOTAMs. The FAA currently publishes them here: https://notams.aim.faa.gov/#News
I say "currently" because the FAA seems to like moving things around and breaking links. But as you can see from that site, you can search yourself and there's also an interface that other systems can use.
Finally, that brings me to the practical answer to both your questions: just use your favorite flight planning app. I use Garmin Pilot, which displays current and future TFRs, and it keeps track of sporting event schedules. It also has NOTAMs, of course. Foreflight or other alternatives would do that too, I'm sure.
The stadium TFRs are usually easy enough to work around because - except for really big events like the Super Bowl - you can fly through them anyway if you're talking to ATC. So if you can get flight following (always a good idea) then you're complying with the TFR requirements.


Which avoidance maneuver is best when seeing crossing traffic on approach to a runway? Let us say I am in final landing and I saw another aircraft is crossing the runway while I am still in air, should go around be my best choice?

If I touched down and then I saw the traffic, how could I make the best decision to avoid the conflicting traffic, increase throttle to go around, or increase brake force to stop before the impact, or decease the speed and try to exit the runway at a high speed?

When you are on short final and something is on, is entering, or even seems to be entering the runway, you execute a go around.

As for the second part of your question, given the loose parameters I'm afraid there is an infinite amount of different scenarios, and therefor I can't provide a comprehensive answer.


Are high lift wings bad for faster speeds I notice a trend in many aircraft designs. If the aircraft was designed to go slowly but have shorter takeoffs/landings they use airfoils with a high lift.

However for long endurance flights they use a flatter airfoil that produces less lift.

To my understanding the reason for this is because you never get anything for free. When a wing produces lift, it is trading the forward movement of the plane for vertical movement.

I understand that at higher speeds the high lift wing would fight horizontal movement too much and so they chose the flatter airfoil.

However my question is what if you change the angle of attack for the high lift wing? Pointing the front of the wing downward, thus making its lift more of a forward direction.

Would this somehow still be less efficient than a flatter airfoil or do they just chose the flatter foils for design purposes and structural reasons?

Every airfoil has a range of lift coefficients where the flow around the wing is most favorable. Airfoils with high camber shift this range to higher lift coefficients. Now the question comes down to: At which lift coefficient will the aircraft operate most efficiently?
The efficiency of transport aircraft is maximized when none of the three parameters payload, range and speed can be changed without reducing the product of the three. As it turns out, wing weight has a big influence on this, especially for large aircraft: A heavier wing will reduce the possible payload. It is better to limit wing span such that the ratio of wing span to chord is between 7 and 10: This will limit the bending moment at the wing root and allow to build the wing lighter. At this aspect ratio, the optimum lift coefficient for best transport performance is around 0.4 to 0.6, a number at which the low camber airfoil will feel right at home.
At such a low lift coefficient, however, the high camber airfoil, on the other hand, will experience a strong suction peak on the lower side of its nose. At high flight Mach numbers, this will lead to locally supersonic flow and a big increase in drag as well as cyclic loads on the wing (buffeting).
Now you could correctly argue that the wing could be much smaller with a high camber airfoil for the same lift. Yes, but the wing needs to adapt to take-off and landing conditions, too, and needs to have enough volume to contain the trip fuel. And for this landing condition the wing of an airliner will even have more camber than your example airfoil:

Typical landing configuration of an airliner wing, from an article by A. M. O. Smith, McDonnell-Douglas, in Journal of Aircraft, Vol 12 No 6, 1975.


Can APU start in-flight using RAT or battery power? Is it possible for a passenger jet to start its APU using power from the RAT? If so, are there plausible benefits to doing so (like supplying hydraulic pressure to the wheel brakes)? Do modern passenger jets frequently (ever?) operate with the APU not running?

On the 737, the APU is typically started from battery power; this is normally done on the ground, but it could be started this way in flight as well.  (The 737 doesn't have a RAT.)  The APU is typically operated only on the ground for short-haul flights, although there are cases such as a generator that failed in flight when it's started & used in the air.  It's also used in cases of a "bleeds off takeoff" to provide air conditioning and pressurization when the engines aren't supplying bleed air (to increase power for a hot, high, and/or heavy takeoff).

But yes, it's more common than not for modern passenger jets to fly with the APU off on moderately short legs.

The exception to this is that some jets are required to run the APU during long over-water (ETOPS) legs, so that if one generator fails, the APU's generator is available without the question of "will the APU start after having been cold-soaked at altitude for so long?"  So in that case running it for much of the flight is common.

As far as the APU vs a RAT, the APU is almost always going to be a bigger generator than a RAT, so it can power more electrical systems on the aircraft than a RAT.  These would probably include electric-motor driven hydraulic pumps, which again will probably have more capacity to provide hydraulic power to flight controls & other things than a RAT would alone.  Plus, an APU can provide pneumatic power (bleed air, i.e. pressurization) than a RAT can't.  The other side of that coin is, a RAT is typically able to produce power more immediately after it's called on than an APU, which takes some tens of seconds to start up.


Do aircraft automatically send a message to the ground if there is a catastrophic failure? For example, if there is a engine failure, it will be displayed on EICAS as a CAS message. As per my knowledge, the pilot will initiate the contact with any ground station nearby for guidance to land safely. Iis there any equipment in the aircraft to send the distress automatically when there is any major failure?

There is nothing formally standardized as far as I know however newer Rolls Royce jet engines (and presumably those from other major manufacturers) do have a continuous inflight data link that reports engine data in real time to their reporting centers. You can read up on it here as well as this discussion with lots more info.

  Aerospace Operations Centres are able to track the health of thousands
  of engines operating worldwide by using onboard sensors and live
  satellite feeds. Rolls-Royce are world leaders at equipment health
  management (EHM)

The centers are potentially able to detect certain emergencies remotely based on the parameters reported.

Since you note the pilot making contact presumably with the radio: Pilots can report an emergency without the use of a radio by Squawking 7700 on the transponder as well.


What is an afterburner and how long can a jet fly on afterburner? I heard this word so many time in military documentary about jets, especially fighter jets, but I don't fully understand what it is or how it works. In a documentary from the Discovery Channel, all but one fighter needed to engage afterburner to reach supersonic speed. Could you tell me why is that?

The documentary also states that a fighter jet rarely engages this system. If the afterburner system can make a jet fly faster, why don't they use it all the time? Is that because of the airframe cannot handle supersonic airflow for a long period of time?

An afterburner is a secondary combustion system which burns additional fuel downstream of the combustion chamber, to further increase thrust at the expense of much higher fuel consumption.

This is the Pratt & Whitney F100 afterburning turbofan, variants of which power the USAF's 4th-generation fleet of F-15s and F-16s:

The final spoke-looking thing just beyond the turbine fins, plus all the space between the turbine core and the exhaust nozzle, is the afterburner. In this area, fuel is sprayed directly into the exhaust stream from the turbine core, where the heat from the air leaving the core is enough to ignite it. This additional pressure adds to the thrust produced by the turbine.

As I said, though, the tradeoff is increased fuel consumption, sometimes usually dramatically so. The F-16 at full military power and low altitudes burns about 8000 pounds of fuel an hour, which with a full droptank configuration gives it about 2 hours' flight time. Cruising at higher altitudes, that flight time can be further extended as both the higher altitude and the lower throttle setting (about 80%) reduce fuel flow rate by up to 40% versus low-altitude flight.

In full afterburner at low altitudes, the F-16 can burn in excess of 64,000 pounds an hour. At full throttle, a U.S.-variant F-16 with maximum external fuel stores has about 20 minutes until it's on emergency reserves (which would only last an extra minute or so at full afterburner). The speed gain is minimal; the F-16 cruises at between 450-550 knots, while full afterburner only increases that to about 700-800 knots with a typical underwing loadout. So, burning 8 times the fuel, you get around a 50% speed boost.


Calculation of temperature correction for altimeter I try to calculate the correction of cold temperature for altimeter , i use for this the equation 24 of the Engineering Sciences Data Unit (ESDU) publication but it give me very high number .
if i take for example the given conditions
altitude of aircraft 1000 ft
0 ft for aerodrome altitude
t0 288 K
temperature deviation from the ISA = 259.9812
L0 = 0.001981
the result is 599777.4389 ft is too big , the expected result is 60 ft So where is mistakes ?

EDIT :
So i corrected the ISA dev according to what Ralph said but the result still incorrect i joint the step of calculation :

the expected result is 60 ft

Finaly i have found the answer the error is on all book that published the equation there is the true equation


What happens to Flight Testing Aircraft after Testing is over? Are aircraft used for flight testing typically sold to Airline customers after their use for flight testing is over?

e.g. The aircraft shown in this SE Aviation Question:

Why are these windows on some airplanes red?

Sounds like a lot of money to waste so I expect they would be sold for some revenue but to what end use is the question.

It depends. In most of the cases, the aircraft have been instrumented and pushed so much that it not possible to modify them for commercial flight. In these cases, they are either preserved or continued to be used as test aircraft. In other cases, the aircraft are modified and delivered.

Boeing 747- The first ever Boeing 747 was used exclusively as a test aircraft and was later handed over to museum. On the other hand all the 747-8s were converted back after test flights and delivered to customers.
Boeing 777- The first 777s were considered production models, not prototypes and were delivered to customers after testing.
Boeing 787- It is kind of a mixed bag here- The first three 787s are in museums across the world (two in the US, one in Japan). Boeing is still using one as a testbed, while one more is in storage. Another aircraft used for testing was later modified and sold to the Mexican Air Force.
Airbus A350XWB- Right now, Airbus is holding all the five testing aircraft and using them for testing or demonstration flights.
Airbus A380- Airbus has all the test aircraft.

You can check out the production lists of various aircraft here


What is an aileron bushing? What is an aileron bushing,and what's its use?

Bushings are a type of bearing that has no rotating parts. They are among the oldest bearings known.

There is nothing special about it being for ailerons, except that is will be installed on the hinge of an aileron.