Could the CVR and FDR record to the cloud? Another enthusiast question. I watch a lot of the National Geographic Channel's "Air Crash Investigation", for better or worse, and it seems accident investigators make tremendous use of the Cockpit Voice Recorder "CVR" and Flight Data Recorder "FDR" to determine the chain of events leading up to- or the root cause of an accident.

One of the more recent episodes of ACI (Season 12 Ep. 13) was about Air France 447, the worst disaster in French aviation history. That investigation spent two years and $50 million just locating the CVR and FDR which were ultimately found resting 4 kilometers beneath the mid-Atlantic. Even after the recovery, there were concerns one of the drives had failed.

That ACI episode also mentioned that the Airbus A330-203 in that accident came equipped with a system which periodically transmitted maintenance data to a remote Airbus location in Paris to alert ground crews of possible maintenance issues with inbound aircraft.

Given that Airbus already uses similar technology for maintenance data (and I think I recall hearing Boeing does too), I was wondering if either Airbus, Boeing, or the FAA, plan to facilitate or mandate that the CVR and FDR record to the cloud or a remote location either in lieu of or in addition to the physical devices installed in commercial aircraft. I would think this would be an accident investigator's dream come true, with almost instant access to vital investigative information, while drastically reducing instances of going without these crucial tools when the physical devices are unrecoverable.

So, does anyone in the know have any idea if there are plans for CVR and FDR data to be transmitted and recorded to the cloud or a remote location?

The basic problem with transmitting CVR & FDR data to the ground from flight is the sheer amount of data that is generated by today's sophisticated airplanes.  There are hundreds of parameters being recorded many times per second plus the voice channels.  Today's airliners record 500 GB of data on each flight.  Take this and multiply it by the thousands of airplanes that are in flight at any given moment, and you can see that there would need to be a lot of bandwidth available for all of it to be transmitted wirelessly.  There would also need to be a world-wide standard developed and hardware deployed so that an airplane can transmit the data no matter where they are.  Airplanes operating in remote locations would have to use satellites, which are relatively low speed and expensive to deploy/maintain/operate.

In short, it just isn't practical with today's technology.


Why is subsonic lift at 25% of chord? I pretty much understand the way a wing works and the different ways of explaining it, what I don´t understand is why the lift on a subsonic wing manifest itself at the 25% chord....

The 50% chord would seem more logical if You ask me....

If I was told that the lift IS NOT at the 50% chord and were told to make an (uneducated...;- ) guess as to where it then would be, I would probably guess at the 75% chord rather than the 25%....

As a plane like the Dash 7 which has VERY efficient flaps has its nose pressed down if the flaps are deployed at too high a speed, or, as a wing-shaped leaf would turn nose down at first....

I understand that the lift manifests itself at the 25% chord, I just haven't got a clue as to WHY....???

I just asked a kind of similar question about the lift-shift that occurs at supersonic speeds. I was thinking of asking this question together with that, but I guess it's more of a question of its own....

Lift isn't at 25% of chord, the aerodynamic center is. Lift acts at the center of pressure, which depends on the wing's camber and angle of attack.

Broadly speaking, you can split lift into two constituents, one from camber and one from angle of attack. Deploying the flaps on the Dash-7 changes both camber and wing chord, and of course shifts the center of pressure back.

Changing the angle of attack will add a pressure change over chord which has its center at the quarter chord. The reason has to do with the strong local curvature near the leading edge which causes strong suction peaks. For a more mathematical explanation see the work of Birnbaum. Or read this answer.


Has a scheduled passenger flight ever stalled because of shifting cargo? Has any scheduled commercial passenger - not cargo - flight ever experienced a stall due to cargo shifting, like the National Airlines Flight 102 did, back in 2013?

Please note I am specifically asking about scheduled airline flights with passengers on board, i.e. not cargo flights. No incidents involving tanks or other military equipment.

Yes, a LET-410 crashed in the DR Congo, apparently because a crocodile escaped. Passengers trying to escape the animal apparently caused enough of a load shift to result in a crash.

Not a shift, but Air Midwest Flight 5481 crashed due to a combination of a  weight and balance error coupled with a misrigged elevator.

In general, it's harder to have a significant load shift on a passenger aircraft since it's easy to check the distribution of passenger loads, people are well restrained by seat backs, and unless something else is catastrophically wrong (fire), passengers don't all get up and move to one side of the aircraft.


Why are empty pylons weighed down? (airplane-pictures.net) Airbus A330 no engine option.

Why are empty pylons weighed down?

The plausible answer is to maintain the correct center of gravity. But why not just load ballast pallets in the forward cargo compartment, like those used on tail heavy planes on ferry flights?
On airliners.net there is a theory (plus debate) that states another reason is to relieve the load on the wingbox, which I would imagine would also decompress the landing gear (I don't see how).
Lastly, I remember on a TV documentary it was stated that the reason is so the wing would not deform upwards (again I don't see how).

Your reason 1 is correct. Without the ballast the aircraft would become a taildragger.

Why not pallets? This would produce the same center of gravity location, but a different mass distribution. Clearing this configuration even for being loaded and pushed around is more effort than simply placing the ballast where the mass of the engines would go. Now all clearances are valid and the aircraft can be handled much as one with the engines in place.

Next, engines are only installed shortly before delivery or first flight. The cost of capital is too high to install them any sooner.

(airbus.com) Example of clearances that would be affected by non-standard mass distribution.


What is trimming the fuel tank? In a recent news article on an Airbus A400M crash, it has the following line:

  Sources have told Aviation Week that aircraft MSN23, destined for Turkey, featured new software that would trim the fuel tanks, allowing the aircraft to fly certain military maneuvers.

I understand what trimming is, but what does it mean to trim the fuel tanks?

Just like normal trimming. However trim the fuel tank use aft fuel tank to achieve the trimming effect. Fuel is pumped between main tank and aft tank to shift CG around to a desire position during flight.

Fuel tank trimming has additional benefit of keeping the airplane in "clean" configuration, creating less drag compare to normal trimming.


Should the pitching moment be up or down? I had a question regarding the direction of the pitching moment.

To make sure we are on the same page, here is what I know so far (please correct me if I am wrong).

Lift acts through center of pressure
Normally moment is taken around Aerodynamic Center because then the moment does not vary with angle of attack.
In a cambered airfoil, the aerodynamic center and center of pressure are not at the same place, so the lift created also generates a moment at the aerodynamic center.
In a symmetric airfoil, the aerodynamic center and the center of pressure are at the same place, so you do not have a pitching moment.
Location of Aerodynamic Center is fixed for an airfoil, it does not change with speed.

I am trying to understand the concept of longitudinal static stability and in all the diagrams, the pitching moment is shown to be nose up.

But I would imagine that the center of pressure is further downstream on a airfoil than the aerodynamic center, so shouldn't the pitching moment be nose down? As shown in this picture

Thanks for your help,

All points you mention are correct (for the nitpickers: Point 5 is only true below transsonic speeds). That the pitching moment of the wing is drawn nose-up is probably because it is positive this way - nothing more. The sketch you posted in your question is rather poor, with the center of gravity located behind mid-chord when it should be closer to the aerodynamic center.

Indeed, if you have positive camber, the center of pressure of the wing is behind the aerodynamic center, so the wing's pitching moment around the aerodynamic center should be nose-down. However, if you assume the center of gravity of the isolated wing to be at mid-chord, the center of pressure is normally between the quarter chord and mid points, so the wing all by itself will pitch up because it pitches around the center of gravity. The moment depends on the reference point.

Did you look at this answer for an explanation of static stability yet? Let me know if something is left unclear.


Advantages of square over circular engine nozzle? The F-22 has square nozzles, while the Russian Sukhoi PAK FA has circular nozzles.

There are both 5th generation planes, but with different nozzles, why?

Circular nozzles have these advantages:

They can be swiveled in any direction, so both pitch and yaw moments can be produced. Square nozzles only allow to create pitch forces, because their panels can only be moved around one axis. When moved differently in two-engined aircraft, limited roll moments are also possible.
Round nozzles are lighter. As long as exhaust gas pressure is higher than outside pressure, a square nozzle will be subject to bending loads across the width of its panels. This will make a square nozzle much heavier than a round nozzle.

Actually, square thrust vectoring nozzles have just one advantage: They can be made to reflect radar waves in a few well-defined directions, while round nozzles will scatter them all around. This makes square nozzles the preferred choice for stealth aircraft, regardless of thrust vectoring.

Engine nozzles of the F-22 (picture source). Note the serrated rear edges of the thrust vectoring panels.

Engine exhausts of the B-2. Since the B-2 uses four non-afterburing engines, fixed nozzles are used. Their location helps to protect the airplane from detection by infrared (IR) sensors, but makes thrust vectoring impracticable.

Engine nozzles of the YF-23 (picture source). The lower part is longer to shield the hot exhaust against IR sensors from below.

If the goal is to mostly reduce radar reflections in the forward hemisphere of the aircraft, round nozzles can be tolerated. Only when the aircraft needs to be protected from radar-guided missiles fired from behind will the square nozzles give a clear advantage. It seems that the people behind the Sukhoi PAK FA (and other stealth fighters like the Chinese J-20) do not worry so much about this detail.

Sukhoi T-50 (prototype for the PAK FA program) from below (picture by Dmitry Pichugin)

Chengdu J-20 rear view (picture source)

However, even Lockheed-Martin and Pratt & Whitney now place maneuverability and weight over stealth in their nozzle design for the F-135 engine of the F-35 strike aircraft. Note the serrated edges on all contour steps. This helps to reduce radar returns, but is much less effective than a square nozzle. The benefit is less weight and better maneuverability.

F-35 with the F-135 nozzle visible (Picture source).


How can a SID's MEA be above its top altitude? The SID below has a Top Altitude of 5000 feet, but its Minimum Enroute Altitude (MEA) is above 5000 feet. Why?

I am referring to the SID depicted below, from FAA's SID charts (plate and departure route description). As one can see, the Top Altitude is 5000 for this particular SID. Nevertheless, if we take a look at the MEAs of its transition route, we notice values much greater than 5000 feet (8000, 11000 and 15000 feet).

Could someone explain to me the reason behind this?

Top Altitude is the initial climb altitude for a 'climb via SID' instruction, unless otherwise is stated.

  TOP ALTITUDE– In reference to SID published altitude restrictions the charted "maintain" altitude contained in the procedure description or assigned by ATC.

Initial climb altitude/level is not directly related to the MEA. It has more to do with radar acquisition, noise abatement, and clearing obstacles.

  MINIMUM EN ROUTE IFR ALTITUDE (MEA)− The lowest published altitude between radio fixes which assures acceptable navigational signal coverage and meets obstacle clearance requirements between those fixes. The MEA prescribed for a Federal airway or segment thereof, area navigation low or high route, or other direct route applies to the entire width of the airway, segment, or route between the radio fixes defining the airway, segment, or route.

Source: FAA AIM


Why do the jet turbines spin while the engines are turned off? Why do the jet turbines spin while the engines are turned off? Is this as a result of the wind? Or are the turbines deliberately spun using the APU? If so what is the reason behind this?

After shutting down they still have momentum. Or like you said, because of Windmilling - freely turning when the wind impacts the compressor blades.

The APU can, but more often than not doesn't, rotate the engines (overly simplified, not to go into unrelated details).


How do airlines pay air crews for an aborted flight, in general? I was watching this Swiss Air video. It's a flight from Zurich to Shanghai. Shortly after take off they have high engine oil temp in engine 3 and end up shutting it down. They declare a pan-pan-pan, dump fuel and return to Zurich. It's pretty uneventful, engine shut down aside.

Now, as I understand it, an air crew's pay begins upon push-back, and ends at gate arrival. At the very end the PIC states that for the passengers, Swiss Air has another plane which will be departing in two hours, but with a new crew. Assuming this crew gets no other flights for the day, did they just get only 1 - 1.5 hours pay for the day?

NOTE: even though this is a Swiss Air flight, I am not concentrating on that one airline. I'm curious if there are general rules for flight pay that all/most airlines follow.

How the Swiss Air pilots got paid would, of course, depend on Swiss Air policy. I suspect pay policies vary greatly between airlines and countries, but for what it's worth below are the pay policies for the four airlines I worked for in the 1980s and 1990s. At all four I would have been credited with only the time from push back until the parking brake was set on return insofar as flight time was concerned, but as you will see that wouldn't have made any significant difference in my pay.

commuter #1 no union -- a straight salary but with an hourly addition if your flight time went over a minimum, which it never did.

commuter #2 no union -- a straight salary regardless of the number of hours flown, but they never abused that.

747 freight carrier no union -- a straight salary plus an hourly addition if your flight time went over a minimum, which it occasionally did.

747 passenger carrier in-house union -- flight time hourly pay with a guaranteed minimum. You always went substantially over the minimum. They tried to get you as close as possible to the regulatory max of 1000 hours a year. Additionally, they had a policy that whenever your duty time (as opposed to flight time) went over 16 consecutive hours, you got paid for each hour over that at a rate of 1.5 times your regular hourly flight time rate. Also, you were paid half your regular hourly flight rate while deadheading. Then, if you had less than 8 hours (I might not be remembering that number correctly) between assignments, your duty time continued. My first assignment for this airline was a 32-hour duty day. I operated from JFK to AMS (Amsterdam), so my duty time started at show time, 2 hours before departure. At Amsterdam 5 hours on the ground then commercialling (riding in the back on another airline) to SIN (Singapore) and then to CGK (Jakarta) positioning for a Hajj flight. Crew scheduling regularly abused pilots, but nobody complained because you were being so well paid when they did abuse you.

The breakdown for hours at the flight time rate for that trip was approximately:

7.5 hours operating time JFK-AMS
8 hours deadheading pay AMS-SIN-CGK (half of 16 hours riding in the back)
24 hours extended duty pay (32 hours duty time minus 16 hour threshold times 1.5)

So, 39.5 pay hours at the regular new first officer rate of 55 per hour = 2,172.50, which looked pretty good to me since I had come from a carrier than paid me a straight 4500 per month salary as a 747 captain.

I can't remember all the flight time/duty time details, but back then at least the international rules were much less restrictive than the domestic rules.

Also, back then it was common practice to do things like scheduling a flight for, say, 11:59 for regulatory purposes, when everyone knew it would go slightly over the 12-hour international rule of the time.

It may be worth noting here, that the mind-set of the crew, at least the cockpit crew, is totally different from that of passengers. The passenger wants to get from point A to point B, whereas the crew is simply 'at work' regardless of whether they go anyplace or not. Consequently, at least in my experience and opinion, delays aren't nearly as frustrating to crew as they are to passengers.


What is this pusher airplane? I am attempting to identify this aircraft.

The pictures appear to have been taken around 1960.

It is the only Bede XBD-2, from the early '60s.

According to Wikipedia it was an experimental aircraft with STOL capabilities.


Who bears responsibility when an aircraft takes off from the wrong runway? On occasion, an aircraft is cleared for takeoff on one runway, but actually departs from another runway.  This has resulted in embarrassment as well as catastrophe.  When this occurs, are both the pilot and the air traffic controller at fault?  Or is it only the pilot who is at fault?

It depends. There could be any number of reasons for such a mistake, and it is rarely the mistake of any one single person.

Within aviation, we don't really talk about responsibility the way you seem to imply in your question. In many other industries, when a mistake happens, an investigation  is initiated with the purpose of finding and punishing the responsible party. In aviation, it is believed that no one makes mistakes on purpose; if a plane takes off from a wrong runway, no one meant for it to happen.

So accident and incident investigation in aviation does not focus on finding someone responsible. Instead, the investigation focuses on figuring out how a similar incident/accident can be prevented in the future. That is why ICAO Annex 13 says:

  The sole objective of the investigation of an accident or incident shall be the prevention of accidents and incidents. It is not the purpose of this activity to apportion blame or liability

If someone takes off from another runway than intended, the investigators will not just look at who made the mistake, but rather why the mistake was made. There could be any number of reasons for this. Very often, there are hidden latent threats somewhere in the system.

Maybe the lights at the airport were not sufficient, maybe the signs guiding the aircraft to the runway were misleading, maybe the taxiway layout is confusing, maybe the ground radar was inoperative when it should have been working, maybe the airline had scheduled the crew in a way that imposes fatigue in the cockpit, maybe the procedures are insufficient - I could go on.

The point here is, these potential causes are all things that can be changed in order to prevent the same incident from happening again. You can put up better signs or repair the ground radar, etc. Whereas, if you simple decide that the pilot or controller is to blame and then fire them, without removing the latent threats, then it's more than likely that another pilot or controller will make the same mistake in the future. What are you going to do then - fire them as well?

The whole idea is, instead of focusing on punishing people for their mistakes, if you try to understand what caused them to make those mistakes, you will not only learn much more, but you will also encourage people to report more incidents, that may not otherwise have been reported. We call this Just Culture, and it is all part of the reasons why aviation remains to be one of the safest ways you can possibly travel.


Are there a toilet and (small) kitchen in the Su-34? It seems that there are a toilet and small kitchen in the Su-34. The Su-34 is a medium range fighter-bomber with a range of action of 4000km able to transport 8 tons of bombs and missile.

I know that the pilots enter from the bottom and they sit side by side (so there is some space). Some people say that there is a toilet, some other comforts (microwave,bed) and others say that there is just this:

Is that a toilet? Can you confirm if the Su-34 really has those features?

Yes, the Su-34 does technically include a food ration warmer, a "sanitary container", and some room that allows for sleeping.

However, all three are much less impressive than the terms might suggest:

The food ration warmer is not a microwave. It's just a small can heater:

There is also some dedicated room for extra cans.

The "sleeping room" is just a bit of room where one could fit a sleeping sack.

One can lay down their head and torso on the entry hatch and fit their legs between the seats. This may come in handy for really long missions, likely with in-air refueling. This is more of a side effect of having an entry ladder and a hatch than a deliberate amenity.

The "toilet", or "sanitary can" as it's called, is exactly as illustrated in your question. Its interface technically supports both methods, but there's no record or hint of anyone ever using any but the first.

The reason for these is that the Su-34 is meant to be a long-range bomber with enough air-to-air capability to fly unescorted. So, even though based on a modified fighter platform, it was fitted with minimal amenities. However, these amenities are more of a "tick the box" type.

P.S. To correct some premises, ~8,000 kg is the payload limit for most of the Su-27 family, but not the -34. The Su-34 is significantly above that, with a maximum payload of 10,400 kg with maximum fuel or 12,500 kg with reduced fuel. In practical usage, it's an attack aircraft/bomber that can defend itself and operate against extensive air defenses.

To have an idea of where such a concept comes from, look at the Tu-22M. While a strategic bomber by role, it's rated up to Mach 2 and 2.5 g, has basic defensive armament, and is meant to engage aircraft carriers. So the VVS idea of a bomber from the 1970s on has been less of a bomb truck and more of an enlarged fighter with a large payload of guided munitions.

The Su-34 is a further development towards a fighter-like bomber direction. It's a heavy fighter platform with added wing area, range and payload to match older bombers. To narrow down its role, consider the F/A-18 for a comparison as an exemplary fighter-bomber that you'd see deployed on A2A missions as easily as A2G. The Su-34, OTOH, is more of a fighter-based bomber that doesn't need a fighter escort, but complements the base models for A2G and leaves A2A missions to Su-30/Su-35 variants.

P.P.S. I've taken the liberty of editing out your 2nd image, as it's from a space station.


Do F-22 and F-35 use force sensing flight sticks like F-16? Do F-22 and F-35 use force sensing flight sticks (as opposed to flight sticks that actually deflect and sense movement), like F-16?

They move, pretty much like an F-16 stick.
From this MIT lecture "F-22 Flight Controls", Lt Col Randy Gordon, F-22 test pilot (from the transcript):

It's a side stick.
Initially it didn't move.
Eventually they decided, I'll put in some deflection.
So I can go a half inch left, a half inch right, about a quarter inch
forward, I go about a half inch back because normally I really want to
get the nose going this way.
There's some deflection to give you feedback that you've input
something on the stick, but not so much deflection that it gets in the
way of everything else you're trying to do.


Why was the B-52's wet wing more susceptible to fatigue than its dry wing, and not less? After years of carrying all its fuel in the fuselage, the B-52 transitioned to a wet wing (where the wing structure is used as one or more fuel tanks) with the B-52G.

This caused severe problems with metal fatigue in the wing structure (the wet wing increased structural stresses by approximately 60% compared to the A-F's dry wing, according to Wikipedia), which was already an issue due to the increased aerodynamic stresses associated with a recent switch from a high-altitude to a low-altitude nuclear mission profile (the high-altitude mission profile having become unsurvivable due to advances in Soviet SAM technology).

However, storing fuel in the wings of an aircraft normally decreases the stresses on the wing structure (by putting as much of the aircraft's weight as possible in the part of the aircraft that generates the lion's share of its lift), alleviating fatigue and increasing the aircraft's fatigue life.  What made the B-52 different in this regard?

Earlier B-52s did not carry all their fuel in the fuselage. They also carried their fuel in the wings using rubber bladder-type wing tanks.

The new B52G “wet wing” was a weight savings measure which also increased the fuel capacity over the bladder-type in-wing tanks. The metal fatigue of the new wing was due to a poor structural design which was supposed to save weight.

http://www.joebaugher.com/usaf_bombers/b52_15.html

  The B-52G had a lighter structure than previous versions in order to save weight, but it carried more fuel. This meant that fatigue problems resulting from the structural flexing generated by the stresses of low-level flying and midair refuelling manifested themselves earlier in the life cycle of the airframe. This was especially the case in the region of the wing structure where most of the weight savings had been achieved by using an aluminum alloy. Fatigue cracks got so bad that stringent flying restriction had to be imposed, pending modifications. In May of 1961, a program was approved in which the wings were modified and strengthened as part of the regular IRAN schedules for the aircraft in the B-52 fleet. The project was finally completed in September of 1964.

Early B-52B,C,D fuel chart showing multiple wing tanks.


Can an online course replace "ground school"? I just found an ad for a "Learn to Fly Course."  Can this course be used INSTEAD OF taking "ground school" at a flight school?  On their site it says:

  Get Your Written Test Endorsement   "... We’ll even give you the
  flight instructor endorsement to take the written test—right from the
  course! You can take this endorsement to the FAA testing center, and
  log it in your ForeFlight logbook."

This seems odd.  The flight school I'm looking at charges $1,000 for a few MONTHS of "ground school" (meeting once per week).  This online course is 25% of that cost and I can study with it 24/7.

What am I missing here?

Note:
This question was reported as a duplicate.  Someone previously asked IF ground school is necessary.  That is NOT what I'm asking here.  What I am asking here is for a COMPARISON between ONLINE ground school versus IN PERSON ground school.  I would like to know if there is some intrinsic value of doing ground school in person versus online or, in other words, if one can adequately replace the other.

Here in the states this depends on if you are training at a part 61 school or part 141 school

Strictly speaking there is no ground school requirement for a part 61 school and you are even allowed to study the material on your own. However your instructor must endorse you for the written test so many schools prefer to know that you did at least some ground school usually from them. Online is more than acceptable in this case (especially if they provide you with the endorsement) however its best to talk to your instructor before doing so and make sure they are ok with it.

  §61.103   Eligibility requirements: General.

  (1) Conducted the training or reviewed the person's home study on the
  aeronautical knowledge areas listed in §61.105(b) of this part that
  apply to the aircraft rating sought; and

  (2) Certified that the person is prepared for the required knowledge
  test.

  (e) Pass the required knowledge test on the aeronautical knowledge
  areas listed in §61.105(b) of this part.

For part 141 it depends what they got approved in their curriculum. You can find the full regulation here.

  §141.55   Training course: Contents.

In the 141 case you most likely can not complete the training on line due to the fact it wont fall under their approval.

Also of note from this FAA doc

  Note: If you are enrolled in a part 141 school with test examining
  authority, the school will administer the knowledge test during the
  curriculum.

Its important to note that it does not matter if you are training at a part 61 or part 141 school you end up with the same PPL.

You can find 100% of the information you need to pass the written test for free in the FAA's published handbooks particularly this one.

On a bit of a personal note, I started at a 141 school that shut down about half way through and finished my PPL at a part 61 school (with the same instructor). At the 141 school there was a rigid curriculum and almost always a half hour to hour of ground instruction prior to our flight as dictated by their approved curriculum. At the 61 school I was allowed to work the material at home before hand and come in mainly for my flying but 15 min of discussion usually occurred prior to my flight anyway. I did at least 50% of the ground material on my own and passed the written without any issues but its important to understand what you are undertaking if you go the self study route.


What is the vocabulary used by fighter pilots used to communicate? As far as I understand, fighter pilots or more general military aircrews will use a dedicated phraseology to communicate with each other, which is different to communicating to ATC.
Is this phraseology standardized across different air-forces or even within NATO?
Are there any public documents on this phraseology?

There are NATO standard terms.  For example the MiG-29 is known as a "Fulcrum." That's not the Russian name for it but the "NATO reporting name" which you can look up on Wikipedia.

There are also some standard (but not codified) terms such as "angels" meaning "thousands of feet."  And there are some standard terms such as "bent" meaning "inoperative" but I don't know how much those are used any more.

Within a certain operating area or task force, there may be specific code words used that may change from day to day.  These would not be known to anyone outside that area or task force.


Does anybody know that why C172S POH doesn't have normal & soft field landing distance chart? Thank you for reading my writing.

I found out that C172S, C172P model POH doesn't have normal landing distance & soft field landing distance chart or table. It has only short field landing distance.

Does anybody know the reason?

Thanks.

Typically light GA aircraft do not list normal landing distances or soft field distances in AFMs.  Looking at the POH from a 172S

Look at Note 3, which refers to typical soft field conditions.  It indicates that a 45% increase in the short field figures is representative of soft field landing distances.

As a “normal” landing distances vary depending on how aggressive one applies stopping techniques on the ground this distance is going to vary depending on how the pilot flies the approach and landing.  Unless a specific procedure is described for this, as in the case for short field operations, there’s no way to draw up definitive performance tables for this.  In addition, the critical value here is if the pilot has enough runway available to fly the approach and stop the airplane in the minimum distance required.  If in doubt as to how much runway one will need during landing, the pilot should plan on using a short field procedure and use the published tables accordingly.

For general operations, I find an approximate 30% increase in the figures listed in these tables will provide a good margain for error and offer a conservative margain for landing figures.

Example: grass field, 4120 ft ASL, local altimeter setting of 29.83” Hg, 82° F (28°C), still air.

Pressure altitude is 4210 ft.

Using an E6B, the density altitude is 6,500 ft

Select 7000 ft from the table, 10°C column.

This gives a 730 ft landing roll from the table and 1585 ft distance to clear 50ft obstacle.

Increasing the ground roll figure by 45% for soft field gives 1059 ft ground roll and (1585-730) + 1059 = 1914 ft to clear 50 ft obstacle.

Increase by 30% for safety margin gives 1376 ft ground roll and 2488ft to clear 50ft obstacle.


Which manuals should I study before flying to France, Portugal and Switzerland? I am from Brazil. My crew and I will fly to France, Portugal and Switzerland. I am accustomed to flying to the USA, but it will be my first time to Europe, and I am studying the differences. Which documents and manuals do you recommend that I study and read? (Note: I want names not resource location)

For common procedures and or VFR rules you want to check the respective countries' AIP:

Switzerland   http://www.skyguide.ch/en/services/aim-services/
the other countries you mentioned can be found from this link collection http://www.eddh.de/equipment/ais.html

you may want to check the website of Eurocontrol here you can find IFR standard arrivals and departures

No warranty! Please prepare your flight carefully.


How to guess the actual name of the SID, waypoint, etc., if you have never seen it when told by ATC? Sometimes it's very tricky as those identifiers are not normal words. For example how to find a way-point you have to go direct to if it's not on the flight plan? SID and STARS can be reviewed before clearance but some airports have a very big list.

Can anybody give any good advice on this? How do you deal with this situation?

The naming is simple, from ICAO Annex 11:

  2.1.2 The basic indicator shall be the name or name-code
  of the significant point where a standard departure route
  terminates or a standard arrival route begins.

So check where your route terminates/begins. I'm suspecting you are asking in the context of flight simulation, because otherwise you can look up the preferred routes of your area of flight. They are usually published.

If that's the case, you need a charts subscription, and to view the page where all the departures or arrivals are charted on one page (there is usually one for airports with many procedures). And check which direction you are coming from / going to, this will make it much easier. Example below is from VATSIM Germany (in this case the charts are free).

Alternatively, based on the wind pick a departure/landing runway, and see which procedures include that runway, that will narrow it down nicely. The same is true when you listen to the ATIS. So when the ATC says it, you will have a narrow list to look at and match.

You can always ask the ATC to spell it out in phonetic alphabet as well.

  Say again waypoint/procedure in phonetic alphabet.

And as @Terry explains here, if all the communications are in a language(s) you speak, it will help you anticipate what the ATC will ask you to do.

  For example, if two airplanes preceding you are being rerouted for some reason, [you will be] prepared for the reroute when it comes through to you.


What's that "frame" in the windshield of some piper aircraft for? I often asked myself what that "frame" on/in the windshield of some Piper Aircraft is. Below is a photo:

What I thought it could be, is a "runway alignment help" for the pilot. But I have no idea.

Thanks for all answers.

As Thunderstrike suggested, these are windscreen heaters commonly marketed as "hot-plates".

The Piper Aztec I flew had one of these. When I first started flying the aircraft I expected some difficulty in seeing through or around it, as it was directly in my view. However, when actually flying the aircraft, I hardly noticed it was there.

As with all the electric windshield heat that I am familiar with, it is intended to be used as an anti-icing measure, not a de-icing measure. This means that the plate is heated so that frozen water that strikes the plate should melt and flow off, and liquid water should not freeze but should flow off. The heat is provided by fine, high resistance wires running vertically between two plates of laminated glass. The wires are visible if one focuses on them, but as with looking through a window screen, the wires disappear when one focuses on the distance.

See the following close up of a heated windshield employing the same type of heating elements:

Source: own work

These hot plates are available for multiple makes and models of aircraft, both as a replacement heater for aircraft with inoperative windshield heat such as the Piper Navajo, and for aircraft without installed windshield heat such as the Piper Aztec.

For this classification of aircraft, in order to meet flight into known icing conditions (FIKI), windshield heat is needed to provide an adequate view for taxi, takeoff, approach, landing, and certain maneuvers. Having an adequate view is helpful at any stage of a flight. However, for the practical purpose of anti-icing, windshield heat is arguably most important—and required—during the landing phase. See 14 CFR 23.775(f):

  (f) Unless operation in known or forecast icing conditions is prohibited by operating limitations, a means must be provided to prevent or to clear accumulations of ice from the windshield so that the pilot has adequate view for taxi, takeoff, approach, landing, and to perform any maneuvers within the operating limitations of the airplane.


Has the "Foote takeoff" technique really existed, and how did it work? Reading The Crash Detectives: Investigating the World's Most Mysterious Air Disasters by Christine Negron, I came across the following description, in relation to some early de Havilland Comet accidents, notably G-ALYZ at Rome (Oct 26, 1952):

  Pilots were instructed to nurse the plane off the ground by raising,
  lowering, and then slightly raising the nose again at takeoff speed, a
  technique called the "Foote takeoff"

I was quite puzzled by this.

Has such a technique really existed? "Foote takeoff" returned
literally two search results, one pointing to the book mentioned
above, the other to another book on the Comets.
What exactly is the point/purpose of "raising, lowering, and then slightly raising" the
    nose? Why not simply rotating at VR?

The 1952 takeoff accident you read about was piloted by Captain Harry Foote. The technique got its name after the accident, which Captain Foote was blamed for (Comet! The World's First Jet Airliner, page 125).

Pushing the nose down is not standard though, rather a corrective measure to over-rotation past 6°. The article quoted below covers the proper technique and the 1952 accident:

  The B.O.A.C. Training Manual recommends the following take-off technique:

    At 80 kts. the nose should be lifted until the rumble of the nose wheel ceases. Care should be taken not to overdo this and adopt an exaggerated tail-down attitude with a consequent poor acceleration.

  (...)

  Take-off tests by the manufacturers have shown that a constant 6° incidence of fuselage during the ground run gives good results for distance run and for climb-away behaviour. They have also shown that an increase of incidence to 9° results in a partially stalled wing inducing high drag which appreciably affects the aircraft’s acceleration, and that the symptoms are noticeable to the pilot as a low frequency buffet. The aircraft recovers from its semistalled position if the nose is pushed well down. [emphasis added]

  (...)

  It was the opinion of the investigators that the accident was due to an error of judgment by the captain in not appreciating the excessive nose-up attitude of the aircraft during the take-off.

  (flightsafetyaustralia.com)

As @RAC said, VR didn't exist. Judging by the historic FAA regulations, VR and the takeoff speeds in general for Part 25 came about in the mid-60s.


Could the Boeing 757 replace the Boeing 737 Max 8/9/10? The "Baby Boeing" 737 started life in the 1960s with roughly half the thrust and around 60% of the weight as the 757. In stages the 737 grew into a capacity squarely in the range of the 757. Originally, it prospered as a smaller regional jet. The Max 10 essentially will be a 757.

Is it possible the longer 757 airframe is a better match for the LEAP engines? Does the older, more forgiving AR 8 wing make it a safer aircraft?

Seems (forgive me) like comparing the graceful look of a thoroughbred, built for what it does best, compared to an overloaded old quarterhorse. Is the 757 worth another run?

(Own work; adapted scaled drawings via boeing.com)
It's no coincidence the fuselage widths match, the 757 borrowed the 727's fuselage, which width-wise is the same as the 707 and 737.
@Brilsmurfffje and @CarloFelicione already raised good practical points, namely the indirect airline costs and why airlines would favor the 737 over a 757 re-engine, and the reboot costs.
If we look at the two planes from a pure engineering viewpoint, the 757 makes for a lousy substitute.
The MTOW is 27 tonnes heavier, but we'll gloss over that and say Boeing will certify it at a lower weight.
Bad wing (for the mission)
The 757 as shown above has a lot more wing. The wing areas are 185.25 $m^2$ and 127 $m^2$, for the 757 and Max, respectively. (45% more wing.)
Bigger wing is higher empty weight, i.e., the plane has more material, and subsequently the associated manufacturing costs. 13 tonnes of more stuff not counting the re-engine – newer engines are heavier. As for using CFM LEAP, between the highest 737 Max thrust and lowest 757 thrust option, the 757 has 13 kN more, so we're okay there.
Those 13 tonnes at approx. \$1,700/kg OEW:unit cost correlation already make the 757 some 22 million USD more expensive without taking into account the development cost associated with a re-engine. Unlike MTOW, there is no workaround for that.
Secondly, the 757's bigger wing is really bad for the cruise economy of the 737 missions. Low wing-loading is good for maneuvering and for using short runways, but cruise economy comes from aspect ratio and – ideally if it won't impact too much the takeoff performance – high wing-loading.
The 757 needed such a wing for fuel carrying reasons (volume and MTOW), after all it's suited for transatlantic operations using older engine technology. But when that much fuel is no longer needed (re-engine), the physical big wing remains.

Now, much like how the A330neo complements the A350, one could argue a re-engined 767 could complement the 787, but like also how the A330neo ended up badly for the A350-800, a 767 re-engine could be troublesome for the smaller 787s.


Is it plausible to forget the cockpit unlocking code? Is it plausible for a pilot inside the cockpit to be incapacitated and that at the same time the pilot locked outside simply doesn't remember the code or the procedure for entering the cockpit?

The code would also be shared among the purser and/ or the other flight attendants, so the answer is no. I believe however that they tend to keep the same code for a few days within the same crew to make remembering it easier.


What is the difference between the Bell 412 and the Bell CH-146 Griffon? What is the difference between the Bell 412 and the Bell CH-146 Griffon?

Fundamentally, the CH-146 is a Bell 412EP, which you can still buy from Bell today.

Some features on the CH-146 you won't find on civilian counterparts:

Weapons.  The CH-146 has attachment points for weapon mounts that aren't typically found on the Bell 412.
Wescam T-16D-A Thermal Imaging System. This wasn't a production addition to the CH-146, but it appears be common on these helicopters.  Similar aftermarket systems might be in use on Bell 412s in police use.
Wire Strike Protection System - some civilian helicopters do have this, but they're particularly common on the CH-146 and other military helicopters.
A Canadian Forces paint job.


How does aspect ratio affect the stalling angle of the wing? I have been trying to find a clear answer for this but haven't been able to do so. From what I understand this is linked to induced drag but I'm not able to link it.
Could someone shed some light on this ?

Any finite span wing creates a wingtip vortex which causes an induced downwash profile that is maximum at the wingtips, and gets less as you move further inboard (towards the wing root). This is due to the vorticity causing a upwashing outboard of the wing tip, and a downwash inboard of the wing tip. If we took a theoretical wing where the aspect ratio is high enough that the span is 'near-infinite', there will be no tip-effect (vortex) induced downwash at the center (root).
Lower aspect ratio means that there is more induced downwash further inboard, and this local downwash actually helps to keep the airflow attached becuase the local flow is already flowing downwards along the later surface of the wing. You can also think of it as reducing the local incidence angle because the air is already flowing downwards.
Most wings are designed to stall first at the wing root, and for rectangular wings this is inherit due to the downwashing profile described above. For other wing shapes, designers will include "wash-out" to ensure that the root stalls first (Why does a rectangular wing stall first at the root?). Because the root is separated first, if we take away the section of the wing near the root (hence decreasing aspect ratio), the area that would have already separated is now removed, and the wing will be able to operate at a higher angle of attack.
Therefore the stall angle would increase if aspect ratio is decreased (ceteris paribus!). This is assuming that the wing is operating in the longitudinal plane only. Any asymmetrical movement (rolling and yawing), will mean that the wing could possibly stall at the tip.


Why don't all wind tunnels use magnets to suspend models? NASA and the French aerospace agency have conducted research into magnetic suspension and balancing systems (MSBS) to suspend models during wind tunnel tests, like this system in South Korea.

Where did the NASA and ONERA research lead?
If MSBS reduces interference from the springs and arms that usually hold models, why don't all wind tunnels use this technology? What are the disadvantages?

Also, can somebody create a wind-tunnel or wind-tunnel-testing tag?

Two reasons:

When a model is suspended in a magnetic field, and then the wind tunnel is switched on, you'll see a change in the force along 'y-axis' (The lift forces) and change in force along 'x-axis' (The drag forces). Hence, you'll need a complex mechanism for sensing this forces, and changing the magnetic field in such a way that the change in forces is compensated by the 'change in magnetic field' so that the model does not translate in any of these directions and stays static. Then you'd measure the change in magnetic field to measure the forces, and hence the system becomes expensive and cumbersome.
For pressure measurements, you'd have to use wireless sensors on the pitot ports, as you dont want tubes dangling form the suspended models. This makes the process more cumbersome and expensive

This is why the magnetic suspension is not used every where, as the cost to accuracy ratio in normal wind tunnels is much less than the ratio in magnetically suspended models of magnetic wind tunnels


Is a degree from an overseas institution likely to be a barrier to employment with a major US airline? I'm currently enrolled at a university in Jamaica. However, on my school break I often come to the US for flight training. I would like to know if a major US airline would employ me after completing my degree, given that it is an overseas degree?

Without a considerable amount of time as PIC of a turbine-powered aircraft, I expect your chances would be slight.

Once your other qualifications, logbook, and resume are competitive, I doubt that where you went to college will matter very much.


Why does a turbulent boundary layer cause more friction drag than a laminar boundary layer? From what I understand, friction is caused by viscosity and a bigger Reynolds number signifies lower viscosity.

Thus, a higher Reynolds number(i.e. turbulent flow) results in lower friction.

But, turbulent boundary layer is said to have a much steeper speed gradient at the aircraft skin, causing much more friction drag.

These two statements seem contradictory. What am I missing here?

No, a higher Reynolds number only signifies a lower ratio of viscous to inertial forces. Since you increase the Reynolds number by either increasing speed or length, both will drive up the inertial forces, making the friction forces relatively lower.

Let's do a Gedankenexperiment: Consider an infinitely thin flat plate which moves through air in its lengthwise direction, so there is no pressure gradient along the flow path. The friction force caused by the boundary layer is F. Now add some length at the trailing edge of the plate. The added surface will add some more drag F', so the total drag will be F + F', both being positive. Since the length has increased, the Reynolds number of the flow has increased in the same way, but so has the friction force.

What has decreased is the coefficient of friction, however, because the thicker boundary layer towards the end of the flat plate will cause less friction force per unit of length. The coefficient is calculated by dividing the force by the dynamic pressure and the surface area, and since the surface area has increased by more than the drag, the coefficient of friction is lower.

You can repeat the experiment with a flow speed increase, and now the friction force will go up, too. So both ways to increase the Reynolds number will increase friction drag. Again, the drag increase is lower relative to the increase in dynamic pressure because the boundary layer at the higher speed is thinner, and again only the coefficient of friction is lower.

Only now, when that is out of the way, I want to answer your question directly: If you compare fully turbulent boundary layers, an increase in the Reynolds number will lower the coefficient of drag but will increase friction drag as outlined above.

Now compare two similar fully laminar flows at two different Reynolds numbers, and again the flow with the higher Reynolds number will experience more friction drag. The different speed profiles of their respective boundary layers will only be significant when you compare a laminar flow with a turbulent flow at the same or similar Reynolds number. In the range of Reynolds numbers typical for aircraft the turbulent flow will cause more friction drag.

If you now repeat the initial Gedankenexperiment with a laminar boundary layer and add some length at a point where the local Reynolds number is safely above 500,000, the local flow will already have transitioned to turbulent and the added length will add a fully turbulent portion. Now it can happen that the added surface will experience more drag per unit of area than the forward, mostly laminar surface. The result is both a higher friction drag and a higher coefficient of friction.

If you allow me to copy the illustration from this answer here, the effect can be easily seen:

Friction drag coefficient over chord for an E502mod airfoil at 3° AoA. Blue: Top surface, Red: Bottom surface.

Now this plot uses a real airfoil with a changing pressure coefficient over length, but with a flat plate the plot would look similar. The much higher local speed gradient at the surface of the boundary layer in the rear part will add much more drag per length and the total drag will increase disproportionately. However, a drag decrease with increasing Reynolds numbers is nowhere to be seen.


Does the aerodynamic center always have to lie on the chord line? A lot of resources online state that the aerodynamic center is the "point on the body of an airfoil with respect to which the moment coefficient does not change with angle of attack." However, does this necessarily imply that the aerodynamic center must lie on the chord line? Of course, we can resort to thin airfoil theory and prove that it lies on the chord line, but what about for highly cambered airfoils?

This answer (Why does the aerodynamic center exist?) explains the existence of the AC, but resorts to inviscid, incompressible, thin airfoil assumptions. What about in general though? So, is the aerodynamic center present on the chord line in general for all flows? If not, when does it deviate from chord line and why?

No, there is no reason why aerodynamic center (AC) have to lie on the chord line. As the OP correctly pointed out, Thin Airfoil Theory (TAT) result indicates that the AC:

Exists, and
Lies on the chord line 1/4c away from the leading edge.

However, this is only because the TAT makes the fundamental assumptions that the airfoil is thin, the mean deviation of the camberline is small relative to the chord, and small free-stream incidence (AOA). As shown in the diagram below, the vortex sheet is assumed to lie on the chord line instead of the mean camber line. (I should mention, however, that the slope of the mean camber line is accounted for in the theory to construct the tangent boundary condition on the airfoil). And, of course, TAT doesn't account for drag.

(Diagram cited from Anderson, Fundamentals of Aerodynamics.)

The vertical offset is small, however, at least until the drag rise associated with flow separation or when flow incidence becomes large. If there is a large vertical separation between the center of pressure and the chord, then AC will not exist and this manifests as nonlinearity in the Cm curve.

I've included the pitching moment coefficient about 1/4 chord of NACA0010, Clark Y and NLF(1)-0115 analyzed with Airfoil Tools, which were analyzed with xfoil using panel method + boundary layer equations. The plots included Reynolds number of 500,000 and 1,000,000 with Ncrit transition of 5 and 9. Note that AC exists locally where Cm has a constant slope.

For NACA 0010, AC exists up to 10 deg AOA at 1/4c; near stall, the drag rise occurs and the Cm becomes nonlinear. For Clark Y and the NLF, the AC is pretty close to 1/4 for small AOA, then shifts to a point further aft until drag rise.

Therefore, while the concept of AC is useful for theoretical derivation of stability relationships in linear aerodynamics, it's not a good enough for precise modeling. In engineering modeling, we generally measure the pitching moment (from wind tunnel) at 1/4c, and account it as a function of AOA.


What ICAO codes are reserved for TIS-B use? Using my ADS-B receiver, In the past few months I've seen a lot of what I think are TIS-B contacts.  They seem to cycle through a few different ICAO ID prefixes, but I see a lot that are of the form (in hex) 29xxxx and 31xxxx. E.g. 298c12 and 318512.  I'm looking for a specification of exactly which ranges of ICAO codes can be used for TIS-B.

In this answer I'll assume you are analysing ADS-B data on 1090 MHz, which is the defacto global standard. I am less familiar with the ADS-B on UAT (987 MHz) which is used in addition to 1090MHz in the USA, but I assume the same logic applies.

There are no ICAO addresses assigned to TIS-B targets.

If an aircraft has an ICAO-address which is detected by the surveillance sensors (e.g. Mode S radar, multilateration system) and the aircraft is not transmitting ADS-B, then a TIS-B target will be created with the ICAO 24 bit address.

If an aircraft has no ICAO-address, (i.e. it has a Mode A/C transponder / ATCRBS) and is not transmitting ADS-B, then a TIS-B target will be created with a 24 bit address that consists of the Mode A code (first 12 bits) and a unique surveillance system track number (last 12 bits). Primary radar targets are allocated a "Mode A code" of all zeros.

To determine whether you receive an ADS-B message or a TIS-B message you should start looking at the Downlink Format (DF, first 5 bits of the message) if the DF = 17, then it is an ADS-B message. If the DF = 18 then you look at the control field (CF, bits 6-8). CF = 0 and CF = 1 are ADS-B messages. CF = 2,3 & 5 are TIS-B messages. CF = 6 are ADS-R messages. CF = 4 are TIS-B / ADS-R system status messages.

The TIS-B messages contain an ICAO/Mode A Flag (IMF) bit which indicates how to interpret the 24 bit address. The location of this bits varies by message type (e.g. position, velocity) and replaces a bit in the ADS-B format that has no meaning in TIS-B.


Is ground school required to get a Private Pilots License? I know that there is a written exam that you are required to take, but do you have to go to a class in order to study for that test?  If I'm really good at just learning from a book, can I just learn that way, maybe take a couple practice tests and then take the exam?  Or are they going to need proof that I went to some certified class?

More subjectively: Assuming it's allowable, is it a bad idea?

In Canada, you are required to have 40 hours of ground school instruction. See Canadian Aviation Regulations 421.26 (3)(a):

  completed a minimum of 40 hours private pilot aeroplane ground school instruction on the following subjects ...

Ground school instruction is defined as (CARS 400.01):

  classroom-type instruction generally given to one or more persons and covering an organized program of lectures, homework or self-paced study that adheres to an approved training program.

So, you can learn by self-study, but it needs to be an approved training program. This would mean that a flight instructor would need to sign off on the self-study program.

The FAA says:

  If you are unable to attend a ground school, the self-study method can be satisfactory, provided you obtain the proper study materials and devote a reasonable amount of time to study.

The regulation is at Title 14 Code of Federal Regulations, §61.35(a)(1):

  Received an endorsement, if required by this part, from an authorized instructor certifying that the applicant accomplished the appropriate ground-training or a home-study course required by this part for the certificate or rating sought and is prepared for the knowledge test ...

Because in both cases an instructor must sign off on your preparedness for the examination, and passing the examination demonstrates that you meet the standard, in my opinion, the only thing that would make self-study a bad idea is if self-study is not an effective learning method for you, which could delay your training.


Does P-Factor increase with thrust? I was trying flightgear simulator since I am not a pilot (but have completed ground school) and one thing I have noticed is that the P-Factor increases with thrust applied whether taking off or in cruise flight.

Is this realistic? Does P-Factor vary based on thrust?

Yes, it should. In the end, p-factor is just a funny word for the out-of-center shift of the thrust vector, and if the vector is larger, the effect should be equally larger.


Declaring an emergency - protocols for commercial aircraft I am researching for a book and would like to know how a commercial aircraft would signal that his aircraft has an emergency.  Not mechanical or violence, but possible biological contamination.

What is the protocol for such an event and what such dialog might exchange between the pilots and ATC?

Any advise would help.
Thanks!

Michael

The procedure would likely be the same as any other medical emergency: get the plane on the ground (which is a thing that pilots are good at doing, and have the training and skills to do) so that the medical crews can handle the medical emergency (which is a thing that pilots are not good at doing, and have neither training nor skills to do)

The initial radio call might be something along the lines of "Mayday mayday mayday, Oceanic 201 requesting immediate vector to LAX for a medical emergency, multiple passengers"

"Mayday" indicates several things all at once.

"Everyone else currently on this radio frequency, shut up."
"I am in the middle of an emergency, therefore I am now the most important person in the sky."
"I will do whatever I need to in order to keep this plane safe. Air traffic controllers, you will get everyone else out of my way."
Saying it three times has no relevance other than to make sure that it's heard and the number three indicates distress in general.

"Oceanic 201" is the callsign of the aircraft.
"Requesting" is used to tell ATC that the crew requires action from them, in this case a vector to a suitable airport.
"for a medical emergency, multiple passengers" prepares the emergency crews for whatever situation they're about to have dropped in their laps.

For further examples of cockpit-to-ATC communication under critical circumstances, you might find it helpful to read the cockpit voice recorder transcript of United flight 232, or other in-flight emergency transcripts.


Why is there always a fire truck present before refuelling? Whenever I fly within Europe, I notice there is always a fire truck present for refuelling before takeoff.

Is this standard procedure for every flight in commercial aviation? If yes, is this a global thing or just a European one?

As far as I know it is not mandated, but ICAO (for which many aviation authorities derive their regulations) states in Annex 14 Section 9.6 Ground servicing of aircraft:

  9.6.1 Fire extinguishing equipment suitable for
  at least initial intervention in the event of a fuel
  fire and personnel trained in its use shall be
  readily available during the ground servicing of
  an aircraft, and there shall be a means of
  quickly summoning the rescue and fire fighting service in the event
  of a fire or major fuel spill.

and

  9.6.2 When aircraft refuelling operations take
  place while passengers are embarking, on
  board or disembarking, ground equipment shall
  be positioned so as to allow:
   a) the use of a sufficient number of exits for
  expeditious evacuation; and
  b) a ready escape route from each of the exits
  to be used in an emergency

So you've probably been more aware of this if you were actually on the aircraft as it is being refuelled.


Why do we not have autonomous helicopters? We see a lot of fixed wing autonomous UAVs. What is preventing this in the case of helicopters?
I know the helicopter flight dynamics are complicated. But what exactly is the complication in this case?

Don't we? Most consumer and commercial UAV are helicopters.

If you mean military-only models, consider what jobs military-only helos do. It's troop transport or close combat - both necessarily manned functions. Commercial drones suffice for non-military-specific jobs.

If you wonder why they have 4 rotors rather than 1-2, it's lower complexity - quads can use simple fixed rotors and blades, and only vary power on each rotor. Larger drones with turbine power may well go to 1-2 rotors.


How can air travel be so safe if the aircraft skin is only 1-2 mm thick? Aircraft skin is not very thick at all, yet air travel is the safest form of travel. All aviation professionals know why, but most occupants of an airliner are not professionals. How can it be explained to members of the general public that 1 mm is enough to:

Keep the air pressure in.
Keep the wings from breaking off.
Transport the passengers in greater safety than when they travel in their car.

I've used examples like "you can stand on a full beer can but not on an empty one". What are the secrets of aeroplane construction that makes such a seemingly flimsy construction so safe?

Update

How is a stressed skin construction explained to the general public? Lots of non-experts get quite alarmed when they are thinking of crushing a beer can.

Simple maths. Cut a cabin in two, lengthwise, and check the forces involved. The halves are held together by 4mm of aluminium, and need to withstand a pressure differential wrt to the outside over the diameter of the cabin.

Let's assume that we have a wide body plane of 6m diameter (larger than a Boeing 777), and a pressure differential of 1atm (of course, usually a plane only maintains up to 0.8atm and does not fly in a vacuum, but let's have some safety margin).

The resulting tensile stress is then about 150MPa. Aluminium only yields at 275MPa.

Other forces are carried by struts, spars and in the case of the fuselage, stringers. The skin transfers shear forces between those perpendicular stringers, but I do not think those forces are significant compared to pressure loading.


Did large winglets contribute to the spin behavior of the SB 13 tailless glider? The SB-13 swept wing tailless beauty was developed in the early 1990s as a small recreational glider with relatively large upright winglets.  The design proved very spin prone.

It occurred to me these vertical "winglets", set upright, would generate a yawing "lift" component in side slip.  Since these are set behind the CG, the plane would spin INTO the slip (as the change in relative wind increased their AOA).

This phenomena seems to have similarities to excessive spiral instability in a conventional wing/tail design.  Would reducing the size or shape of the winglets help cure this tendency?
Or lengthening the nose a bit?

Probably not. Spins usually start from a stall, not a side slip, and yaw stability generally improves spin resistance and recovery.

For model flying wings, removing the tip fins usually makes spins far more likely and much harder to recover from. The usual explanation is that the end plate effect delays the stall at the wing tip.


How are aircraft shipped to their customers? This is sort of the inverse of this question.

I was looking at the Boeing facility in Renton, WA in Google maps, and I realized, the airport is across the (Cedar) river from what I assume to be the construction facility. The Boeing facility in Everett, WA is also across Highway 526 from the airport. That prompted this question: How is an airplane that just finished getting built (in any facility) delivered to the airline that bought it?

This question is targeted at large passenger aircraft being delivered to airlines.

They are flown to their customers by either Boeing or pilots from the given airline.

As for the Boeing factory its self, the Everett Factory users Paine Field as their runway. If you look closely there is a bridge that crosses the highway and connects the plant to the main ramp of the airport. This appears to be painted for car traffic but is also used for aircraft. The Renton Factory lies adjacent to Renton Municipal which it uses to fly the aircraft in and out there is also a small bridge connecting them over the river.

Similarly the main airbus factory is located next to Toulouse–Blagnac Airport. Bombardier lies next to Montréal–Pierre Elliott Trudeau International Airport.


What do firefighters do on ordinary days? Some not very busy airports can have no even a minor incident for years and accident probably won't happen in a major airport during several decades. Training of course is done sometimes. I don't know how often though. This has to be the most boring or the best job if you wan't nothing to do. I think you can spend all your career without putting out single real fire or doing real rescue.
So what do firefighters do day to day?

Calling them "firefighters" is accurate but they can respond to all sorts of incidents, not just fires (in the USA, even outside airports it's common for firefighters to respond to purely medical emergencies). On top of that, there's also training, maintenance and keeping physically fit.

This is from a firefighter at Hobart Airport in Australia:

  The aviation firefighters do more than wait for airplane fires, they
  also attend to other incidents, such as motor vehicle accidents, fuel
  spills, hazardous material incidents and first-aid in the terminal.

  [...]

  "A lot of our working day is routine and there are different types of
  things that we need do every day regarding our equipment, servicing
  all of our equipment, checking it over ...," he said.

And this is from one at Heathrow:

  We don’t really have an average day. We attend to all sorts of
  incidents. We attend to anything that is life-threating at the airport
  or on the roads around it; this could include a heart attack air or
  land-side, a drug mule incident where a passenger has transported
  drugs within their body and has ended up in a serious condition, or a
  car crash that we have to cut a victim out of.

  We all have set duties to do every day and night including practical
  and theoretical training, testing and inspections, and cleaning of
  vehicles and equipment. The crews have to keep physically fit so we
  give them time for physical training and provide facilities to do
  this.


What is the wing span in aspect ratio's calculation? We all know that the aspect ratio of an airplane is calculate as:
$$AR=\frac{b^2}{S}$$

Where:

$AR=$ Aspect ratio

$B=$ Wingspan

$S=$ Wing's area

In an airplane, wing span is the distance from tip to tip of the wing. That means the fuselage also calculated. Below are two picture of two different kind of airplane: Boeing and Cessna. As you see, the wing is placed in different position. The Boeing is below of the fuselage so it look like integrated to the wings. But the Cessna is placed on top of the fuselage, make the fuselage is like the separator of the two wings rather the integrator.

But in another time, what we call wing is a thing that is attached to the fuselage. The picture below shows what the wing span is. The fuselage itself is not considered as part of wing.

To avoid miscalculation, I would like to know what is exactly b in that equation. For this case, just consider the wing shape is fully rectangle. Appreciate if with reference.

b is the width of the wing's projection on the horizontal plane, from tip to tip. The wing's vertical position on the fuselage does not influence b. This may or may not include winglets and ideally should be clarified when b is specified.

Calling one half of the wing a wing is sloppy use of language. Ideally, a wing half should be called that, and not be confused with a wing.


Is aerodynamics study compulsory for building a plane? I want to make a plane like a trike. I have a design and some knowledge about plane requirements.

You don't need to know much aerodynamics to build a plane if you follow plans for an existing design that somebody else has engineered and validated, and you don't make any modifications.

If you are trying to design and build something new, even if superficially similar to existing aircraft, then yes you will need to study aerodynamics and other aspects of aeronautical engineering. This doesn't necessarily need to be formal academic study but there is a substantial body of knowledge that you will have to learn in order for your project to be safe and successful.


Why does the co-pilot sometimes keep a hand on the throttle as well as the pilot? In this YouTube video of a takeoff and landing in a Dash-8, you can see the pilot, while landing, keeps his right hand on the throttle levers.

The co-pilot keeps his left hand at the base of the throttle levers during this time. This happens at 3:38 in the video. I assume this is to ensure both pilot and co-pilot agree when lowering the throttle? I'm just guessing, though.

Why is this, and are there other similar events that happen during a flight?

The pilots were probably executing a Cat II coupled or monitored approach. The PF is flying the plane (via autopilot, usually), while the PNF had his hands at the base of the throttle ready to take over to initiate a manual go around (or land in some cases, this varies from airline to airline).

There is a thread regarding this on this on airliners.net. It gives one version of the procedure:

  At my airline we use this procedure for Cat II approaches. The FO always flies the approach... well the autopilot flies it and the FO monitors the instruments, ready to perform a missed approach if the approach becomes unstable. The Captain at the 500 to minimums call places their hand near the base of the thrust levers, under the FOs arm, and focuses outside looking for the runway. If at any point prior to minimums the captain gets the runway in sight, they call "landing, my controls" and move their hand up to the thrust levers, bumping the FOs arm and hand up and off of the thrust levers. If at minimums and the runway is not in sight the FO performs the missed approach.


Why do GA pilots in Europe operate N-reg (US) aircraft? When I read articles or blogs online about GA flying in Europe I get the impression that it's not unusual for European GA pilots to have FAA licenses and fly N (US) registered aircraft.

I've never seen any numbers mentioned so I don't know how common this really is, whether they hold only FAA licenses or also European ones etc. But in general, as a European GA pilot, what is the benefit of operating an N-reg aircraft rather than a locally registered one?

It's usually cheaper to go to the US and earn an FAA license and then fly N-registered aircraft in Europe than it is to get a European license. However, an N-registered aircraft needs to be maintained to FAA standards by FAA licensed mechanics.


What are the dimensions of the parking apron? What are the approximate dimensions of the apron aircraft zones, ramp, aircraft stands such as Airbus A380, Boeing B737, F16.

The Apron Planning and Design Guidebook is used in the US. The goal was to provide a one stop shop for all the relevant information. The FAA maintains a list of standards.

Further, there is special CAD software for the design of airports. This includes the turn radius planning for a large number of aircraft.

Finally, because of the complexity and the large number of regulations there are companies, that specialize in airport planning and design.

Or you could always just wing it like the Germans and be ten years late and six times over budget and still incomplete ...


How is taxi speed measured? What is the maximum taxi speed and who defines it? has a lot of interesting thoughts and facts about what maximum taxi speed is admissible or practical. It brings me to this new question: how does a pilot know how fast he/she is going when on the ground, apart from just looking out the window?

Afaik most planes only have an airspeed indicator, which I suppose is not of much use while taxiing due to surface winds being in the same order of magnitude as ground speed. Also I wonder if an ASI has any usable accuracy near the bottom of its range. The same might be true of GPS speed indication.

Did some more research and found out GPS is much more accurate than I thought it was. http://www.ncbi.nlm.nih.gov/pubmed/15519597 and other sources find it better than 0.5 ms-1 most of the time. I guess that is better than what can be calculated from wheel speed, especially with big, fast wearing tyres.

Some aircraft have a "taxi speed indicator". Here's one I found on ebay for an Airbus:


Why do farmers register their fields as airports? (this seems to be primarily a US phenomenon)

So in the vicinity of my parents' place (in a rural area in Indiana), there are several registered airports within several miles' radius.  I remember when I was a kid, there were a few farmers in the area who liked to fly ultralights, and I wonder if some of these might be for that.  And some of these are listed as having certain aircraft based there.  For many of them, however, looking at their fields on Google Maps there is nothing to indicate that it is ever used for anything but growing crops--in some places there is no obstacle-free area even reasonably close to the listed runway dimensions.

What's going on here?

Just spoke to the farmer that owns Graham Farms Airport (SN72), a grass strip in a cornfield near the sprawling metropolis of Harris, Kansas. Here it is on the sectional:

And Google Earth:

He has a Cessna 182 there. He told me he had it registered as an airport back in the 1970's, like Dave said, in case someone had an engine failure or something, atc could vector them there. He also occasionally allows people from nearby Garnett Municipal Airport (K68) to practice grass strip landings there.

He got an unexpected benefit from having it registered with the FAA several years back when the power company was planning to run a high tension line right across his landing strip. The power company refused to work with him on it so he called the FAA. Since it is officially an airport federal regulations forced them to run their line around it.

Aviation trumps power company profits!


Why do piston engines in aircraft burn fuel at a higher rate than a comparable car engine? I've never understood why piston powered plane engines burn such a large  amount of fuel per time period than car engines.

Can anyone elaborate on this?

I know that a C172M will burn ~5-9+ gph at 2200-2550 RPM between 2k-12k feet based on the POH.  This gives a decent idea of the fuel burn in a very narrow RPM range at various altitudes.  According to the POH, she came with a Lycoming 0-320-E2D. Wikipedia states that the 0-320 provides 150-160HP using a 5.23l engine.

My car on the other hand has a 2l 4 cylinder engine. At 70mph in top gear @ ~2300rpm she gets about 30mpg for a calculated 2.33gph. To me highway speeds at constant RPM provides comparable engine conditions to that of cruise phase of flight.

5.23l / 2l = 2.61

2.61* 2.33mpg = ~6gph

Does that basic analysis hold? Is the larger displacement the main factor in fuel consumption difference between the two? I consider this figure of ~6gph close enough to the 5-10gph listed in the POH for such a back of the napkin calculation if the analysis is more or less correct.

This leads to a follow up question: Is there a reason for the large displacement and low HP? For comparison a 5.7l truck engine from the 70s output 250HP for a gain of 100HP for .47l additional displacement when compared to the Lycoming. I'm in no way very knowledgeable about engine's but am guessing the answer lies in engineering trade offs for making the engine lighter or out of a different material for aviation use or for higher compression ratios for the fuel. Any detailed input would be appreciated.

I know that Volkswagen and Subaru engines have been used for aircraft.  Although my research has been very light, it still looks like the fuel consumption is in the same range.

Going back to my car vs the C172M, or the EcoTec vs Lycoming, 173hp@ 5500rpm for the EcoTec and assuming a (most probably false) linear fuel consumption based on RPM,

5500rpm /2300rpm = 2.39

2.39 * 2.33gph (@2300rpm) = 5.56gph

for comparable HP.

If my analysis provided here is close to the true answer, then I think I've cleared up my misunderstanding by writing out this question.  However, I would like someone more knoowledgeable about such things (possibly an A&P who is also a gearhead) to pipe in and verify or enlighten my analysis.

Thanks!

As others have noted, airplane engines and car engines have very different duty cycles.  An airplane engine will typically run at full power for a few minutes during takeoff & climb, then at a large fraction of max during level flight, which may last for hours, and be throttled back only during descent and landing.

An auto engine, by contrast, only operates at full power for a few seconds, as you for instance accelerate up that freeway on-ramp, then it will be throttled back to produce the small fraction of full power that's needed to maintain freeway cruise speeds¹.  Since the power output is proportional to fuel consumed², your car engine uses much less fuel.  Even though it might be rated to produce the same max HP as the airplane engine, in normal operation it produces much lower HP for the vast majority of its operating time.  You can see this in operation if you drive a car with a real-time fuel consumption gauge.  For instance, my Insight hybrid shows ~25 mpg when accelerating or climbing mountains (using near full power), but 75 mpg or better cruising on a level interstate.

Also note that the actual fuel economy of an airplane isn't that much different from say your average SUV.  I don't have the exact figures any more, but I once calculated that my Cherokee 180 got about 18 mpg.  When you figure that it's going twice as fast, and on longer trips can shorten the actual distance travelled by going in a straight line instead of having to follow roads, the comparison isn't that bad.

¹This, incidentially, is why hybrid cars can use electric assist to get much better mpg - the gas engine can be just big enough for efficient cruise, while acceleration is provided by the electric motor.

²To a first approximation.  It's a lot more complicated in the real world.  Look up BSFC maps if you're curious.


Does the radar altimeter's position affect its accuracy? I have seen the location of the radar altimeter is different between Airbus and Boeing. Airbus has it almost at the tail, Boeing has it forwards. I would like to know which one gives the height more accurately?

In the aircraft I fly, the radar altimeter (aka radio altimeter) is calibrated for the installation, and the calibration compensates for the flight attitude of the aircraft at touchdown.  The radar altimeter is considered radio navigation avionics, and in many cases is required equipment.

So in theory, a flight attitude other than a normal approach attitude may cause some error.  However, since the primary use is during approaches, the consequence of this error is negligible, assuming flaps and gear extended.

In practice the avionics tech verifies that the altimeter reads a certain reading on the ground, and that reading is within spec for the installation. Practically, this means that the radar altimeter does not always read "0" when the aircraft is on the ground in a taxi or parking mode, however it is normally close.

My assumption in answering this is civilian aircraft, using normal low level short range radio altimeters, as opposed to delay Doppler or synthetic aperture radar which are used for other types of navigation applications.


How and why would one call the cockpit of an A330 inside its nose gear bay? According to this A330 call panel diagram,

there is an option to call the nose gear bay with the MECH button. Where is the connection for this in the nose gear bay, and what would it be used for? The closest I can find is in this video, where some connections to call the cockpit of a Boeing 777 are shown in the forward avionics bay, presumably to help with communication among maintenance personnel. Whether these jacks are similar to the MECH channel on the A330 I do not know.

The fact it's called the MECH channel is a pretty big hint that yes, this is for maintenance personnel.

Ant it's not just the nose wheel bay, there are service interphone connections in several locations.


What materials are used to build a military runway? What type of matrix should be used on a military runway used by C130 aircraft?

I believe C-130 was designed to be operated from unprepared runways for takeoffs and landings. One of the reasons for India to buy it and deploy it to forward operating base.


In this F-104 V-n diagram, why does the stall speed (in terms of IAS) decrease with altitude in some parts of the flight envelope? (This question has been edited to reflect a change in perspective: based on answers to the related question What is causing these "corners" on this F-104 V-n diagram?, I now believe that the curves on the upper left edge of the envelope are intended to represent the stall speed throughout their entirety, both above and below the distinct "corners".  If the aircraft is being limited by something other than the actual stall along some portions of these curves, then it would be helpful to clarify and explain that in an answer either to the present question or the one linked above.)
In this V-n diagram for an F-104 (source: this Wikipedia link), why does the stall speed at any given G-loading (in terms of IAS) decrease with altitude-- at least in the part of the envelope that is below the sharp "corners"?
And why is the opposite is true for data points above the "corners"?
For example-- (numbers are approximate)--
Below the "corners"--
20,000', 5G, 415 knots IAS, versus 30,000', 5G, 375 knots IAS
30,000', 3G, 330 knots IAS, versus 40,000', 3G, 295 knots IAS
60,000', 1G, 175 knots IAS, versus 70,000', 1G, 140 knots IAS
Above the "corners"--
30,000', 5G, 375 knots IAS, versus 40,000', 5G, 475 knots IAS
And why do the curves cross each other?
(For example, at about 350 KIAS and 3.5G, the 40,000' curve crosses the 30,000' curve.)
Related ASE questions and answers-- but some of which seem to suggest the opposite relationship should be the case (at least for the "below the corners" cases)--
Why does indicated stall speed change? (see question and all answers)
What causes a slight increases in indicated stall speed with altitude? (see question and all answers)
How does the IAS stall speed vary with increasing altitude? (see question and all answers)

As an airplane approaches Mach 1, all pressure changes grow with the Prandtl-Glauert factor of $\frac{1}{\sqrt{1-Ma^2}}$. Therefore, the lift curve slope increases so the wing produces more lift at the same angle of attack and dynamic pressure the closer its Mach number is to 1. On wings with thicker airfoils and higher aspect ratio the maximum lift coefficient drops in the transsonic region; however, thin wings of low aspect ratios are unaffected by this.
NACA TN 3469 by Edward Polhamus compares wings with varying sweep angle, thickness and aspect ratio. The plot below shows that the Prandtl-Glauert effect is strongest for unswept wings and the transsonic lift bucket disappears for thin wings with an aspect ratio of 4 and lower. The F-104 had a 3.36% airfoil and an aspect ratio of 2.45.

This effect also shows up in the maximum lift; the plot below is from Sighard Hoerner's Fluid Dynamic Lift, chapter 4. It shows how the Mach number affects maximum lift: Small leading edge radii show a loss of maximum lift at moderate Mach numbers but perform well at transsonic speeds.

The indicated stall speed decreases with altitude because the lower temperature lowers the local speed of sound and brings the airplane closer to Mach 1 and thus to higher maximum lift. This effect is limited to subsonic speed close to Mach 1 which explains why those corners only show up when the indicated airspeed correlates with Mach close to 1 at that particular altitude.


Why was the Boeing 377 "Stratocruiser" frequently landed nosewheel first on touchdown? Why was the Boeing 377 "Stratocruiser" frequently landed nosewheel first on touchdown? In the mid-1950's I had often observed Northwest Airlines' B377's frequently being landed that way at the old Minneapolis-St. Paul airport.

A family friend and PanAm First Officer who frequently flew the SFO-HNL run in B377's told me that (as best as I can recall now) the reason for landing the B377 in that configuration had something to do with help in "setting or unlocking the nosewheel steering" for directional use when the aircraft was fully down on the ground.

As the B377 was Boeing's prototype for the "Stratocruiser", I've wondered if their wartime B-29 "SuperFortress" also was, or could be, regularly landed nosewheel first as well?

And then, during WWII, were there any other tricycle geared two- and four-engined "heavies" that were also meant to be, or could be, landed nosewheel first?

Apparently, the nose first landing was necessitated by the aircraft's tendency to enter into a stall if the nose was brought up too far up. According to one of its pilots:

No amount of heaving back on the pole would induce the mainwheels to make contact first. Various explanations were offered for this peculiarity... Others pinned the blame on the pernicious lift-spoilers.
Why build a splendid wing and then fit lift spoilers? The story was that the Civil Aeronautics Administration (CAA: the FAA-to-be) would not give the type its Certificate of Airworthiness because a wing was apt to drop when the aircraft stalled. The CAA wanted the nose to drop first, and the only swift remedy was to destroy an area of lift near the fuselage.

A similar discussion can be found here. However, this seems to have changed later. From the same article:

Ironically, after BOAC had operated the type for about nine years it was decided that lift-spoilers were not necessary, and they were removed. I was then flying later types, but those who were still on Strats told me that it was then a much better-behaved aircraft.

Another thing that supports this theory is that the military version, the C-97 Stratofreighter seems to have landed normally, according to its pilot:

The control wheel is eased back at 90 mph to clear the nose wheel from the runway. The airplane will fly itself off at 100 to 120 mph depending on the load.

and

Normally the nose wheel is kept off the ground for the first thousand feet, but it can be dropped immediately for cross-wind landings.

So, this seems unique to the Stratocruiser (and its derivative, the Super Guppy). B-29s as far as I know, landed main wheels first.


Are turbine and compressor blades and vanes cast or forged? I was wondering how blades and vanes are typically made in commercial jet engines. Would you typically use investment casting to make compressor blades or just in the turbine section to accommodate the cooling channels?

Also, how much does a first stage high pressure turbine blade cost? Are they more expensive on the newer engines, for example, the LEAP vs. CFM56?

As a summary,

The fan blade is made by shaping molten titanium in a hot press. When removed, each blade skin is welded to a mate, and the hollow cavity in the center is filled with a titanium honeycomb.

The compressor blades are made by casting

Turbine blades are made by forming wax copies of the blades and then immersing the copies in a ceramic slurry bath. After each copy is heated to harden the ceramic and melt the wax, molten metal is poured into the hollow left by the melted wax

Please refer to the following website, it is very interesting for the manufacturing process of the main engine parts:

http://www.madehow.com/Volume-1/Jet-Engine.html

Concerning the fan blades:

  Each fan blade consists of two blade skins produced by shaping molten titanium in a hot press. When removed, each blade skin is welded to a mate, with a hollow cavity in the center. To increase the strength of the final product, this cavity is filled with a titanium honeycomb.

Concerning the compressor blades:

  Casting is used to form the compressor blades. In this process, the alloy from which the blades will be formed is poured into a ceramic mold, heated in a furnace, and cooled. When the mold is broken off, the blades are machined to their final shape

Concerning the turbine blades, it is multi-process:

  Turbine blades, however, are made by a somewhat different method than that used to form compressor blades, because they are subjected to even greater stress due to the intense heat of the combustor that lies just in front of them. First, copies of the blades are formed by pouring wax into metal molds. Once each wax shape has set, it is removed from the mold and immersed in a ceramic slurry bath, forming a ceramic coating about .25-inch (.63-centimeter) thick. Each cluster is then heated to harden the ceramic and melt the wax. Molten metal is now poured into the hollow left by the melted wax. The internal air cooling passages within each blade are also formed during this stage of production.

  The metal grains in the blade are now aligned parallel to the blade by a process called directional solidifying. The grain direction is important because the turbine blades are subjected to so much stress; if the grains are aligned correctly, the blade is much less likely to fracture. The solidifying process takes place in computer-controlled ovens in which the blades are carefully heated according to precise specifications. The metal grains assume the correct configuration as they cool following their removal from the oven.

  The next and final stages in preparing turbine blades are machine-shaping and either laser drilling or spark erosion. First, the blade is honed to the final, desired shape through a machining process. Next, parallel lines of tiny holes are formed in each blade as a supplement to the interior cooling passageways. The holes are formed by either a small laser beam or by spark erosion, in which carefully controlled sparks are permitted to eat holes in the blade.

The cost of old models parts could be very expensive because they are manufactured upon request, that was the case for Concorde engines.

The financial aspect of the question is beyond my scope


Should I mention an altitude restriction from the previous controller during an ATC handoff? I was flying my first solo cross country today with VFR flight following heading east at 5,500 ft. As I approach my top of descent (TOD), the controller nonchalantly said, "[call sign], you can descend to 4,500, if you want." So I replied that I would descend to 4,500. I got handed off to the next controller and told him, "[call sign] level at 4,500." He got somewhat annoyed that I wasn't at an odd-thousand-plus-500 foot altitude heading east, so I told him I would continue descending to 3,500.

My question is, how should I have handled this? Should I have told the new controller I was restricted at or above 4,500 even though the previous controller didn't explicitly say I was restricted (recall she just said, "you can descend to 4500, if you want").

There is a bit of a misunderstanding as to what happened here

  Should I have told the new controller I was restricted at or above
  4,500 even though the previous controller didn't explicitly say I was
  restricted (recall she just said, "you can descend to 4500, if you
  want").

You were not restricted to anything (assuming you were within any airspace limitations), flight following is not the same thing as being vectored. Sometimes on flight following you will hear something like

  VFR Altitude At Your Discretion

When you are on flight following you are subject to ATC vectors when they are issued in controlled airspace (A,B,C,D and E) but you are also free to maneuver within the VFR regulations so long as you are not asked to hold a course or avoid a certain area or move for traffic etc.

  you can descend to 4500, if you want

This was not an explicit instruction and not one you needed to comply with nor the floor to which you could come down to technically. They were saying there was no apparent traffic conflicts and if you (for what ever reason) wanted to come down you were clear to at least 4500 ft.

However there are some cases under flight following where you should comply with instructions. Im actually not sure what the legality is on this since you technically don't need to take FF in which case "see ad avoid" is your responsibility. But on any note I have received something like

  Turn left 20 degrees for traffic climbing out of 2500 for 8000

In my experience flying trainer sized stuff in the congested north east corridor, flight following (which ultimate often comes from approach control in this area) will vector you out of the way for jet traffic. Strictly speaking this has occurred in class E airspace where VFR aircraft are largely free to do as they wish.

You may have also been handed off to an angry controller, but you should stick to VFR cruising altitudes when possible as per § 91.159.


Southwest corner of LAX has peculiar airplane parts, what is this area? In the Southwest corner of LAX (at the intersection of Imperial Highway and Pershing Dr.) there is a strange looking area that appears to have some abandoned airplane parts. Also, it looks like a road-striper had a good time one day doing donuts around one of the artifacts. Anyone familiar with this area and what it is used for?

See Google Maps

It is an aircraft fire simulator. They use it for training emergency response personnel and vehicles.

You can see them training on one in this YouTube video

Source: Leipzig Halle Airport


Is there a difference in use of external lights for taxi in/out or takeoff/landing? Will there be a different light pattern (like turning on/off different exterior lights) between taxi in and taxi out, and between takeoff and landing?

The use of beacon, strobe and navigation lights is already covered in this question: When to use beacon, anti-collision, strobe, logo, and navigation lights?

Taxi: Additionally to the navigation and beacon lights, the pilots always turn on the taxi lights during taxi. This is not only to see the taxiway in the dark, but also to signal other aircraft and ground vehicles that this aircraft is currently moving or about to start moving. The use of runway turn-off lights depends on the visibility. In the dark, they are typically turned on, but there is no need for them during daylight. The details may be airline specific as well. There is no difference between taxi out and in.
Takeoff and Landing: In general, all aircraft external lights should be turned on whenever an aircraft is on a runway. This is to increase visibility to other aircraft. There is one exception to this rule: the landing lights are typically only turned on when takeoff clearance has been received (meaning they are left off when receiving a line up and wait clearance). Again, there is no difference between the takeoff and landing roll. Some airlines use the taxi light switch as a reminder for being cleared to land during approach, but it will be on when landing.