Does a previous AFSP approval get invalidated when making a new training request? If I've already been approved, and started training in one school and then create a training request to switch to another school, does the previous approval expire?

In other words, can I be simultaneously approved on two different schools?

I'm considering transferring temporarily to continue flying in a different region, but would like to have the option to return to my original school without yet another training request...

Yes, you can have multiple requests open at the same time. This is from the AFSP Candidate Application Guide (step 7):

  It is possible for a Candidate to have several active training requests at a given time. These requests may be for the same or different flight training providers. Each training request form will be processed separately; AFSP approval is valid only for the Provider listed in the application.


How to find the static stall angle of attack for a given airfoil at given Re? For vertical axis wind turbines applications

I'm wondering how one would find the static stall angle of an airfoil at a given Reynold number?

Is it just the critical angle of attach (AoA) where highest lift is achieved or some value beyond that?
Consider the given graph for NACA0012 (for the use of vertical axis wind turbines) at Re of $3\times 10^5$, what will be the static stall angle in this case?

I found some stuff here and there, yet, I couldn't figure out my issue.
The graphed data were taken from this Ref[i].

From Wikipedia:

  In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded.

Other related questions: 1 and 2.

[i] Sheldahl, R.E. & Klimas, P.C., Aerodynamic characteristics of seven symmetrical
airfoil sections through 180-degree angle of attack for use in aerodynamic
analysis of vertical axis wind turbines , Albuquergue, NM: Sandia
National Laboratories, Report No.: SAND80-2114, 1980.

Being a symmetric airfoil, the NACA 0012 does not have a particularly high maximum lift coefficient, especially at low Reynolds numbers. And yes, 300,000 is considered a low value for the Reynolds number of airfoils. On the other hand, there is no other airfoil that has been tested so much. You will find data all over the place.

Generally, the angle of attack range of interest for aeronautics is where little to no separation of the flow along the surface occurs. This is restricted to a small range around 0° (when the flow is hitting the airfoil more or less head on). Larger separation reduces lift, so right before separation first lets lift drop a little, the stall angle of attack has been reached.

180° polar for several airfoils

But stall is not the end of lift. See above for 2D wind tunnel data collected by S. Hörner in his book Fluid Dynamic Lift. These results have been collected at a higher Reynolds number when the stall angle of attack is shifted to higher values. To be honest, a lot of factors influence this. In your case, even though there is another maximum at about 45°, the stall angle of attack is between 9° and 10°. Not more.


Which engines are Jet-A used in? Is Jet-A used in turbojets or is it just used in turbofans, turboprops, and the SMA SR305-230 for Cessna?

Jet-A is mostly for turbine engines in general. Turbine engines can be fueled with nearly anything that you can spray over an open flame and will burn.

It is not a substitute for avgas, for the same reasons that diesel is not a substitute for petrol. You can fuel a diesel engine with Jet-A under some circumstances.


Is screen burn-in a problem? Screen burn-in can be a problem for older and cheaper monitors.  It can be caused by fixed-width text, fixed-size graphics, and operating for long durations, which are things that are common in aircraft displays.

So is burn-in a problem for aircraft? Have there been hardware or software improvements to minimize burn-in?

I was in the Regional Jet industry a long time and never heard of screen burn-in as a complaint on Rockwell Collins ProLine CRTs.  You mentioned "cheaper" monitors and that may be the key.  CRTs built to an aviation TSO (Technical Standards Order) are by no means cheap.


Which parts of an airplane are made of buoyant material? Which parts of an airplane (to make this question more specific: accessible in the main fuselage where the passengers are aboard) are made of buoyant material.
Imagine a plane is about to crash into the sea, you might wanna hang on to something that could keep you afloat, so here’s a few things that I think are buoyant(based on the floating debris seen after a crash):

The life vest/jackets which we can inflate
Seats
The doors(the ones through which we enter or any other door)

Which things would someone want to hold onto, to increase chances of survival?

Passengers are reminded of #1 & 2 above on every safety brief.
Beyond that, you aren't going to get up out of your seat before the crash and attempt to latch on to some buoyant part of the structure, so it isn't an actionable question in the context it is asked.  (Which is a polite way of saying who cares...)
Stay in your seat until the violent motion stops, then follow the instructions of the surviving crew to evacuate the aircraft in an orderly manner.
Allow women and children to go first if able.  Whatever might be floating after the crash is over is buoyant, and may be used.


How the stabilizer cutout switch functionality has changed from Boeing 737 NG to 737 MAX? The Boeing 737 NG has stabilizer trim cutout switches marked as MAIN ELECT (left) and AUTOPILOT (right). Turning off the right switch disables automatic stabilizer trim in autopilot mode and automatic stabilizer trim by the STS in manual mode. The stabilizer can still be trimmed with electric trim switches on the control wheel or manually with the hand crank. Turning off the left switch disables the electric trim on the control wheel.

The Boeing 737 MAX has stabilizer cutout switches marked as PRI (left) and B/U (right).

With the MAX, Boeing added MCAS to the existing STS functionality. If Boeing kept the cutoff switches functionality intact, then turning off the right switch would disable both STS and MCAS, keeping the electric trim operable. Instead, in case of misbehaving MCAS Boeing requires to cut off BOTH switches without explaining what each of the switches does. With both switches turned off the only option to change stabilizer trim is to use a hand crank.

On the NG, if only the left switch is cut out, does it disable electric trim on the control wheel only, or it completely disables electric assist no matter where the command comes from, so in effect when the left switch is turned off it does not matter what is the position of the right switch?
What is the meaning of the new MAX labels?
What is the exact functionality of these switches individually?
Why the algorithm of turning off auto trim system has been changed?

What do you know, I found the answer to my exact question in the Seattle Times:
First of all, even after two fatal crashes,

Boeing declined to detail the specific functionality of the two switches.

Nevertheless,

The Seattle Times found that the left switch on the 737 NG model is capable of deactivating the buttons on the yoke that pilots regularly press with their thumb to control the horizontal stabilizer. The right switch on the 737 NG is capable of deactivating just the automated controls of the stabilizer.

So far this corresponds to the information I found in the 737 NG FCOM myself.

As Boeing was transitioning from its 737 NG model to the 737 MAX, the company altered the labeling and the purpose of those two switches.
On the newer 737 MAX, according to documents reviewed by The Times, those two switches were changed to perform the same function – flipping either one of them would turn off all electric controls of the stabilizer. That means there is no longer an option to turn off automated functions – such as MCAS – without also turning off the thumb buttons the pilots would normally use to control the stabilizer.

If the above is correct, then not only MCAS, but STS/autopilot as well cannot be turned off on the MAX while keeping electric trim on the control wheel functional.

Peter Lemme, a former Boeing flight-controls engineer, said if the company had maintained the switch design from the 737 NG, Boeing could have instructed pilots after the Lion Air crash last year to simply flip the “AUTO PILOT” switch to deactivate MCAS and continue flying with the normal trim buttons on the control wheel.

(^ bold is mine). This is exactly what I was alluding to in my question. I really want to hear the reasons for the change.

Lemme said he’s surprised that Boeing made the change to take away the functionality that could have allowed the pilots to shut off MCAS without shutting off the electric switches at their thumbs.

Oops.


How does the lift coefficient of an A380 change when flaps are extended? I would like to know the lift coefficient with 10 degrees of flaps extended.

As mostly when questions are vague, the answer is: It depends.

If nothing else changes, the nominal lift coefficient stays the same. A coefficient is referenced to an area, and for aircraft this is the reference area which is derived from the wing area. Regardless of flap settings, the reference area stays fixed, and so does the lift coefficient because neither the mass nor the speed of the aircraft have changed when flaps have been set.

In reality, the aircraft will slow down when flaps are extended, and it can afford to do so because drag is increased and stall speed lowered. Now, with the lower flight speed, the lift coefficient will go up in proportion to the ratio of the speeds before and after squared:
$$c_{L_{flaps}} = c_{L_{clean}}\cdot\frac{v_{clean}^2}{v_{flaps}^2}$$
Again, this assumes the same reference area.

In a wind tunnel where the aircraft model is fixed to a sting and the angle of attack is controlled, setting flaps will increase the lift coefficient by the difference in zero-lift angles of the aircraft with and without flaps, multiplied by the lift curve slope of the aircraft.

$$c_{L_{flaps}} = c_{L_{clean}}+ (\alpha_{0_{clean}} - \alpha_{0_{flaps}})\cdot c_{L_{\alpha}}$$

Note that the lift curve slope increases when setting flaps increases the effective wing area. Again, all is referenced to the unchanged reference area.


Why don't planes use pulsejets? According to my research, a pulsejet's thrust grows as the airspeed increases. Most pulsejets require no moving parts which makes it easier to manufacture them. They are also very lightweight which can have some great effects on aircraft.

They are very slow at zero airspeed but very fast at high airspeeds. Therefore you could simply have a normal jet engine to power the take off and then switch after take off to the pulsejets.

Here is an example where I've labelled a DC-10 of what a pulsejet with jet engine plane could look like:

The plane would taxi onto the runway using the jet engine as power, it'd then line up on the runway. It'd then power its jet engine and take off. Shortly after take off it would switch to the pulse engines and optionally turn the jet engine off.

So why don't planes use pulsejets? Surely they would allow planes to go faster and in turn allow them to reach destinations quicker. Also the pulsejets are easier and cheaper to produce than jet engines and there lighter than jet engines.

2 reasons really:

Airplanes need most of their thrust right when their airspeed is low. (to get more airspeed at takeoff and go-around).
The maximum airspeed in cruise is not dictated by how much thrust the engines can throw out. Instead it's dictated by the aerodynamic forces on the airframe. They cruise right below the speed of sound where the rules of aerodynamics change drastically. Going too fast would rip an airplane apart.


Why doesn't the Concorde have any wing fences? A Wing Fence is a straight, vertical "fence" running from forwards to backwards down the wing.

This MiG-17 has three fences per wing. I've also seen them on delta-winged aircraft such as the MiG-25.

The purpose of the wing fence is to prevent the air from flowing sideways over the wing. Air instead becomes trapped between the fences and flows front to back as normal. This is the ideal condition for creating lift, because the air follows the camber of the wing.

So why doesn't the Concorde have them?

The even more extreme sweep (at first) of Concorde's wing seems to me like it would induce even more sideways-flowing air, meaning it should benefit even more from wing fences.

(I noticed the Tupolev Tu-144 doesn't have them either.)

The main purpose of the wing fence is to prevent the boundary layer thickening in the wing due to the spanwise flow observed in swept wing, as can be seen below.

Image from fuckyeahfluiddynamics.tumblr.com

This is the reason for having wing fence in aircraft such as Mig-25- to avert stall and improve stability. In case of highly swept wing like the Concorde, this is not required as the mode of generation of lift is different- using vortex lift.

Vortices over the Concorde wing, Separation in three-dimensional steady flow, ONERA

In fact, there is a significant cross flow, as can be seen in the following image:

Flow above the Concorde Wing, Separation in three-dimensional steady flow, ONERA

Due to this, the wing fences are not required in case of highly swept wings like Delta and Ogival wings (as in Concorde), where separation leads to vortex lift. Mig- 25 wings, though highly swept, was neither of these- the wing generated lift by conventional manner.


Why is parking brake set OFF before jacking? I have a question about the procedure to jack the aircraft for wheel replacement. According to the manual, it required to set the Parking brake OFF before starting jacking at the Main Landing Gear.

I curiously wonder if the brake is set OFF to let the wheels on the other landing gear could rotate freely on its axle.

Why don't we keep the parking brake ON to prevent the aircraft moving and slip out of the jack?

The wheel is removed with the PB depressurized so that the discs are free to float (both rotationally and slightly axially) when the wheel is being slid off, to prevent any potential binding of the disc projections where they engage the slots in the bore of the wheel as the wheel is pulled out. If the discs are locked in place by brake engagement, any off-axis movement of the wheel unit as it's being slid off could jam it on the discs, making it really hard to pull off.

When the procedure is started, the airplane is chocked at the other gears, so the parking brake is already made redundant at this point.  As a former aviation technical writer in another life (not Airbus), I would say it was done that way for work flow purposes (getting all the cockpit related precautions out of the way before you start the procedure) because you don't need the PB on once chocked, and you're going to have to release it anyway, so it's done during the preparation steps prior to the actual jacking.


Who invented the canard wing? Who invented the canard wing?

I know that early planes like those built by Santos Dumont and the Voisin brothers used canard wings but who invented the canard wing?

Update

The plane built by Hiram Maxim and tested in 1894 had a canard wing for pitch control.

(source)

(source)

Hiram Maxim's plane

So, it is quite evident that this type of wing was not invented by the Wright brothers as some people believe.

Short answer? The Wright Brothers. The term was coined to describe the Santos-Dumont 14-bis, as its design with a box-like array of forward control surfaces looked like a duck in flight, but the very first successful powered aircraft was a similar canard biplane with a pusher engine.

As planes developed after the Wrights' first flight, this design fell out of favor for a number of reasons. To save weight, the horizontal and vertical stabilizers were grouped together so a single set of braces could support them, and when this arrangement was forward of the wings in the most logical pusher configurations of the day, the planes had a general tendency to nose away from the relative wind, which caused issues with takeoff and landing as well as unrecoverable deep stalls as the plane kept its nose high or even swapped ends in a stall.

These behaviors led to the concept that's familiar to us today, of a central barrel fuselage with the engine and prop in front, the pilot behind that and an "empennage" of horizontal and vertical surfaces in the rear. This arrangement allows for better stability and easier recovery from stalls by having the empennage point the nose into the relative wind, much like a weathervane. The downwash of air over the horizontal stabilizers also allowed that stabilizer to have a reduced pitch angle, reducing drag. These and other advantages led to the arrangement becoming dominant in aircraft design as of WWI (with a couple notable derivations in the early war, like the D.H.2 "pusher" which allowed a machine gun to be mounted along the pilot's line of sight before the invention of the synchronization gear) and continued into the second and third generations of the jet era.

The return to a "pusher"-style powerplant with the modern turbojet led to a revisit of the idea of a forward horizontal control surface. The design has a few advantages, especially in combination with a delta wing which became common on the second-generation supersonic jet fighters. Canards provide a lift force in the direction the pilot wishes the nose to go, instead of opposite that direction, so when pulling up, the canard adds to total lift. Canards also allow the primary pitch surfaces to encounter relatively undisturbed air, as opposed to a tail-mounted stabilizer, which increases the effectiveness of the surface. The larger rearward delta wing acts as the "empennage" of a traditional plane would, helping keep its nose in the wind, and the vertical stabilizer remains at the rear of the plane, avoiding the shortcomings of early canard designs.

Several experimental designs were tried as early as the war years, but the Saab Model 37 "Viggen" was the first aircraft of the modern era to use a canard-delta planform configuration, in 1967. This design has since become a favorite of European designers, with the Gripen, Typhoon and Rafale all following this basic configuration. The Russians have incorporated canards into a few of their fighters like the Su-30 to augment a traditional all-moving tail elevator, and the PAK FA has a similar concept with movable "leading edge root extensions". American designers have played with it, in programs like the F-15 ACTIVE tech demonstrator and the XB-70 prototype hypersonic bomber, but the sole production U.S. aircraft to use canards does so mainly for stability; the B-1B Lancer has a small pair of canards linked to the FBW system which dampens oscillations in the forward fuselage.


What could cause the Boeing "Pickle Fork" issues? The Boeing 737-NG has been in the news recently regarding cracks discovered in the "pickle fork" assembly which transfers loads from the wings to the body of the aircraft.  The "pickle fork" was supposed to last the lifetime of the air frame (90,000 cycles), but cracks were discovered in airplanes with less than 30,000 cycles.  Could the cracks be due to an "over G" situation where turbulence or a hard landing could have caused the airplane to exceed its load limit, or is this likely due to a design flaw?

Depends on the crack characteristics, number of striations (individual propagation events) etc., whether the cracks are from a small number of near-yield overloads or many small loads from regular cycles.

This sort of thing happens quite a lot.  You are designing parts at all times to be "just strong enough" for all the various requirements and goals, since every pound over that is considered ballast.  Computer finite element analysis makes it possible to fine tune the structure during design and reduce the fudge factor needed in the slide rule days.

Endurance fatigue testing of the part is used to validate the finite element analysis. A 3:1 safety or scatter factor is applied in the fatigue endurance test.  To be certified for 90,000 cycles, the part had to last 270,000 cycles crack free in the fatigue rig.

As a back stop to all that, you have a structural inspection program to cater to the possibility that the scatter is bigger than expected or the analysis was flawed and wasn't revealed by the original endurance test.  Everything has variability, generally on a pareto distribution (bell curve).

If you only endurance test one or two articles, you can't really be sure where those two parts would fall on the bell curve.  You assume it's near the middle, and the inspection program covers your butt if you are wrong.  Which is the case here probably.   You could test a large number of forks instead of a couple to reduce the scatter factor risk, but $.

You'd need to see the lab reports for the Pickle Forks (I've read many).  There may have been microscopic flaws in manufacture (pits or nicks or voids in a forging) that created crack initiation points.  It  may be a batch issue of a defect like that on x number of parts.  Or the original analysis was off, and the fatigue testing got units that represented the right side of the bell curve (low probability) and gave an optimistic result, so the part was too skinny for the job, from a fatigue perspective, from the get go.


Did the Doolittle raid run their engines over square? My flight instructor made a comment when talking about complex airplanes that "never over-square an engine" is a good rule of thumb but secondary to POH instructions. The POH, (I presume) is the best-informed source of how the engine was intended to operate.

He then went on to give an example: Supposedly, since the Doolittle Raid had to launch their B-25B Mitchels 200 miles further out to sea, they ran their engines over square which changed their fuel consumption such that they were still able to pull of the mission.

So here are my questions:

Did the pilots during the Doolittle raid run their engines over square?
By what mechanism would running over square change fuel consumption that dramatically? Is that unique to the B-25B's engines?
If there is such a big fuel consumption benefit, why is the "never over-square an engine" rule so prevalent? (Seems like this competes with operating the engine at "best economy"?)

Image of B-25B launching off the USS Hornet:

According to this transcript of the actual mission report from one of the pilots, they did indeed run over square

  I flew the last 500 miles into Tokyo at altitudes ranging from 1000
  feet to 4000 feet in order to fly in the thin overcast and clouds to
  avoid detection. I used 28 inches of manifold pressure and about 1370
  RPM and indicated between 150 and 165 MPH.

And for the latter part of the mission

  I made the trip from Tokyo to China at about 500 feet altitude and
  1300 RPM and started at 29 inches of mercury and gradually reduced to
  25 inches as my gas load reduced. I indicated about 160 to 165 MPH.

Question 2: According to this copy of the manual (page 155) the engine is almost always run over square in cruise.

As for question 3 you can find a discussion on operating over square in this question and ill avoid answering it here to keep it form being a dupe.


How do commercial airlines prepare for pilots falling sick during the flight? According to this article, the pilot suffered a heart attack mid-air and a passenger helped in landing the plane safely.

How does commercial airlines prepare themselves for these kind of situations. Do they specifically check if there are any pilots in the passenger manifest and inform the crew and pilots beforehand? Or, do they leave it to the co-pilot to take care of such situations? Or do they fly in a pilot (like mid-air refuel)?

On digging deeper I found that pilot sickness has caused several crashes:

Continental Flight 3407 co-pilot felt ill before crash near Buffalo, transcript shows
Plane damaged, pilot felt sick: fatal Transwest Air crash report
Report into fatal plane crash in NWT shows plane was damaged, pilot felt sick

do they fly in a pilot (like mid-air refuel)?

No, that isn't really feasible!

See answers to Can a passenger jet be towed to safety if it breaks down in midair?

  do they leave it to the co-pilot to take care of such situations?

Yes. In both normal and emergency situations, the co-pilot is able to fly the aircraft, navigate to a nearby airport and land the aircraft without the assistance of the senior pilot.

From Skybrary

  Here are some lines of defense:

  The remaining pilot must assume or maintain control
  Establish a safe flight profile and engage the autopilot; use all possible automation
  Obtain cabin crew assistance
  Inform ATC
  If on an extended-range twin-engine operations (ETOPS)
  flight, the remaining pilot or PIC must assess whether to continue
  the flight, return to the departure airport or divert. The decision
  is based on:

  Weather conditions at the destination or alternate
  Reduction of flight time if diverting
  Workload involved in single-pilot operation
  Familiarity with the alternate
  Condition of the incapacitated pilot
  Availability of medical assistance
  Overall safety of the flight

  Arrange medical assistance upon arrival
  Brief a cabin crew member to assist if required
  Complete the approach and landing using the autopilot as much as possible
  A partially incapacitated pilot should not be allowed to participate in the    subsequent operation of the aircraft, as
  judgment may be impaired
  After landing, seek immediate medical assistance

See also IFALPA - Pilot Incapacitation

  The remaining pilot must first assume command and maintain control of the aircraft. Furthermore the position of essential controls
  and switches should be checked, and in nearly all cases, use of the autopilot should be made and an emergency be declared.
  Use of the autopilot and priority of air traffic service are two obvious and effective ways of maintaining a tolerable level of workload.

  The second step is to take care of the incapacitated flight crew member. The grounds for this are not entirely humanitarian; if left unattended an incapacitated pilot can become a major problem and in any case is a major distraction to the remaining crew. Thus
  the incapacitated pilot must be moved out of the range of flight controls. In all cases, the advisability of removing a pilot (perhaps unconscious) from the seat must be dictated by consideration of the phase of the flight, the crew available, and the contours of the
  flight deck.

  Note: Consideration of the restraint and care of an incapacitated pilot dictates that cabin attendants are at least familiar with the
  operation of harness and seat controls

  Finally, and after the incapacitated flight crew member has been taken care of, the remaining flight crew should re-organise the cockpit work and prepare for landing. Details will depend on many variables including such considerations as the type of aircraft being flown, phase of flight, en route and terminal weather, and many others.

  How does commercial airlines prepare themselves for these kind of situations.

I imagine that it involves the usual measures

make pilots take regular medical tests.
make pilots responsible for reporting own or crew illness, fatigue etc.
prevent pilots eating the same meals in-flight.
write procedures for pilot incapacitation in-flight.
train flight crew to perform those procedures
review and revise the above based on experience of relevant events.

From what I've read, non-pilot flight-crew are often given very basic training so that they understand the basics of flight. For example Transport Canada requires flight attendants initial training to include a pilot-incapacitation drill, an understanding of aircraft parts including rudder, ailerons etc, principles of flight, etc etc.

  Do they specifically check if there are any pilots in the passenger manifest

I believe the airline staff would often be aware of any airline pilots onboard (e.g. dead-heading crew) but not of GA or military pilots flying as normal passengers.


Was there any Hawker Trident installed cockpit voice recorder before BEA Flight 548 incident? After BEA Flight 548 incident in June 1972, all British-registered airliners have mandatory cockpit voice recorders. The TV series Mayday claimed no voice recorders were installed in Hawker Tridents before the report of the incident was released.

9 months before BEA Flight 548, a Chinese Air Force Trident 1E (AP-ATL) crashed in Mongolia. Lin Biao, the second-in-charge in China, was killed as well as his family members in the incident.

The incident itself is still mysterious, but some source claimed that there were voice recorders in the cockpit and the chat inside the plane was recorded.  Many sources cited that the Chinese officers did not know the black box was installed, so the voice recorder was only installed by either Pakistan International Airlines (previous owner of the airliner) or by the manufacturer.

The question is : Were there any Hawker Trident installed cockpit voice recorder before BEA Flight 548 incident?

It doesn't appear that CVRs were installed in any Tridents before the BAE 548 accident.

The accident report noted that CVRs are installed in some British Aircraft, but stays silent on the Tridents:

  This, at least as far as CVRs is concerned, we do not regard as
  satisfactory. ... They are fitted as standard equipment to all BOAC's 747s and most large United States transport aircraft.

If any of the Tridents had CVRs, the report would've surely mentioned it. The Chinese Tridents didn't appear to have CVRs long after the accident. In fact, the accident report of a Trident 2E in 1988 notes,

  The  aircraft  was not equipped, neither was it required to be equipped, with a cockpit voice recorder (CVR).

Based on these, it does not appear that any Tridents were fitted with CVRs before the accident.


What is the history of the "Superbay" at San Fransisco International? The Superbay is a maintenance hangar on the north end of the field at San Francisco International Airport, north of runway 28R and west of runway 19R. On the airport diagram it is not labeled, but next to fire station no. 2.

It is currently used by United Airlines and American Airlines for maintenance. Ground control refers to it as the "Superbay" when giving instructions.

When was the Superbay built? Did it have any uses before the current tenants? Where did the name come from?

Superbay Hangar is a maintenance facility at San Francisco Airport.

About previous tenants and when it was built, this forum mentions that:

  It is the large aircraft hangar built by AA in the 1970's to house the
  747. Both AA and TWA were the first tenants. Now it's UAL and AA. UAL uses it as a line maintenance hangar for the wide-body fleet.

  It sits all alone out towards the bay. When VIP's come to SFO, they
  park next to this hangar due to its isolated location.
  ...
  The SuperBay was built and is owned by the City of San Francisco. It
  is primarily used by UA/AA.

Going through the timeline on SFO's History, the vacant area of this hangar is visible in one of the pictures of 1960s. In later pictures (1981), it appears to be there (shown in the background)1.

Interestingly, more references are found about this hangar in the future development plans of the airport than the history. Examples can be seen here (PDF, p20 and 28) and here (PDF, p6). This site also talks about some future work for Superbay Hangar.

1: I am not 100% sure about direction of the camera, but it might be pointing towards that hangar.


Has the cause of the engine failure of Cessna's 182JT-A been determined? Last August during a certification flight, a Cessna 182JT-A compression-ignition (diesel) engine failed in flight. I've been Googling to find the cause of the failure and the status of the certification process but have failed to find any recent info. Does anyone know what the current findings have been and how Cessna expects to proceed?

Apparently, yes, it has -- see Cessna 182 JT-A Certification 'Imminent'.  As the article reports, the issues appeared to be related to the turbocharger, but I'm not sure how far (if at all) accident reports or details go beyond that.


Why wasn't MH-17 flying at 33,000ft before it entered Ukrainian airspace? I was looking at the path of the MH-17 flight that crashed in the Ukraine on FlightRadar24 and noticed it was flying at FL310 (31,000ft), then because of the Ukrainian NOTAM which went up to FL320 (32,000ft) and below, it then ascended to FL330.

Why wouldn't it be flying at FL330 already from the start? Doesn't a higher altitude mean less air resistance (because the air is thinner) and therefore better fuel efficiency?

This is normal.

A 777 on the AMS-KUL route cannot climb to FL330 right after takeoff - this would only be possible maybe 3-5 hours into the flight.

Airliners fly as high as the available thrust (and ATC) allows, because the thinner air allows to fly at a higher lift coefficient and less drag overall. The limit is given by the combination of available thrust and the actual mass of the aircraft, and it will climb higher during a trip as fuel is burnt off. The maximum range is possible at one particular lift coefficient, and to maintain this during a long trip means to increase altitude, so the lower density compensates the lower aircraft mass. Engine thrust is normally sized during design such that this optimum altitude can just be reached in normal operation.

On eastbound routes in controlled airspace, pilots are encouraged to fly at odd thousands of feet (depending on the local rules), so the climb will not be continuous, but stepwise. See this answer for more on separation rules.

For a rather lengthy answer with more background on the theory how to pick the ideal flight condition for maximum range, see this link.


How does a constant-speed propeller work? My explanation of how a constant speed propeller works has always been a little shaky. I know about the "speeder spring," "counter-weights," and how it utilizes the engine oil pressure, but I'd love to know of a simple and easy-to-understand diagram and explanation that I can use to really understand it, and then teach it to others?

Before we get started, I should mention that the most basic constant-speed propellers were driven by balancing air pressure and centrifugal force. The blades were shaped in such a way, or equipped with a counterweight that would cause the blade to intrinsically move to a shallow pitch. However, when air was moved over the blade, it would begin to overpower the counterweight and push the blade to a higher pitch. It's a pretty ingenious design that meant that the prop would automatically be at a high RPM when the plane was moving slowly (takeoff, landing, climbs),  and would automatically move to a higher pitch when the plane sped up for cruise. There is even a single-bladed propeller that utilized this design very efficiently for light aircraft. The problem is that this type of propeller is not pilot-adjustable, and I am assuming you are wondering about adjustable props, so that's what we'll talk about from here on.
In the first picture, observe that the pilot valve is resting directly on the flyweights (separated by a bearing). The second picture better depicts the valve system. So we see that the speeder spring is pushing down on the top of the pilot valve's shaft, which is in turn resting on the flyweights.
First off, the flyweights are turned by the crankshaft, so any change in engine RPM is immediately reacted to.
There are a few ways that the propeller is attached to the piston, and a rack and pinon type gear system is common and easy to imagine. The rack is fixed to the piston so that when it moves, the prop blade's pinion gear is rotated and thus the blade is rotated. Another common type uses a peg that is offset from the center of the blade's circular base. When the piston moves, it pushes or pulls on the peg and because the peg is offset it causes the blade to twist.
Overspeed: When your airspeed increases.
When the RPMs increase, the centrifugal force causes the flyweights to want to spread apart in order to conserve momentum. Because they're in an L shape and have a hinge in the corner, this causes the lower part to rise up, pulling the pilot valve up and compressing the speeder spring. When the pilot valve is raised, pressurized oil from the pump is allowed to flow into the prop hub through a tube that passes through the center of the hub piston. The oil fills a cavity in front of the piston, pushing it backwards. The prop blade is rotated to a higher pitch (closer to feather) which slows the engine RPM. When the RPM is reduced, the flyweights will be under less centrifugal force, and the speeder spring will push them back to equilibrium (on-speed), pushing the pilot valve back down to block the hub oil tube from gaining or losing oil.
Underspeed: When your airspeed decreases.
When the RPMs decrease, there is less centrifugal force acting on the flyweights. Due to their shape as described earlier, they are no longer able to push up on the speeder spring with the same force as before, so the compressed spring will begin to expand. This brings the top of the flyweights in, and their bottoms down. When their bottoms move down, the pilot valve moves down as well and unblocks the hub oil tube. Positive oil pressure in the hub and the blades' built-in tendency to want to move to a low pitch pushes the oil out of the hub and back into the oil system. The piston moves forward and the blades rotate to a low-pitch condition. The flyweights do not necessarily return to equilibrium, especially if you manually set the spring to maximum compression with the prop lever: you want the prop to stay at minimum pitch no matter what.
Loss of oil pressure:
Oil pressure is constantly pushing against the bottom of the pilot valve, trying to force it upwards. The speeder spring is resisting, and while the flyweights are on-speed, the whole system is in equilibrium with the valve blocking the hub tube. When you lose oil pressure, that pressure is no longer holding the valve up and the speeder spring will win, pushing the valve down and allowing the oil to flow out of the hub. This resets the prop to the low-pitch climb setting, giving us maximum power because that's more useful than maximum speed in the emergency situation that is probably about to occur.
So why do we do this?
All propellers are set at a pitch. Theoretically, a propeller is pitched to move forward a certain distance each revolution, just like a screw moving through wood. But unlike wood, air is fluid and difficult to grip. If you imagine screwing a screw into a board, the only way to make it go in faster is to turn it faster. This is because the screw's pitch is fixed. If you could space out the rungs on the screw (increase the pitch) the screw would move through the wood faster but it would become much harder to turn.
An airplane's propeller works much the same way. When we first take off, we need to impart maximum power into the air and it doesn't matter if we don't move forward very far for each revolution, because we're not going very fast anyway. We just want to move as much air as possible. But we will reach a certain point where the only way to speed to is to increase the number of prop revolutions, and that's impractical with our engines. The only alternative is to change the pitch of the blade. We change it to a pitch which allows us to move forward a greater distance with each revolution, in exchange for less power being imparted into the air each revolution. Luckily, we don't need to pump out so much energy, just enough to keep us from slowing down.
If you like numbers, imagine we have an engine and propeller that theoretically (at perfect efficiency) moves forward 1 foot for each revolution, and it can make 1 revolution per second, giving a maximum forward speed of 1 foot per second. That's perfectly fine when we're taking off: we might be moving forward at 0.5 fps, and we have some air being blown backwards a 0.5 fps. When when we level off at cruise, we're stuck at 1 fps. But we want to go 3 fps and we know our airframe can handle it. The easiest option is to turn the engine three times as fast, but unfortunately that would send some pistons flying out of the cowling. So we have to change the prop pitch to one that moves forward 3 feet for each revolution, that way it's still turning at the same rate, but it will move us forward three times as far. Or more likely we're still going 1 fps but only 1/3 RPM and burning 1/3 the fuel! It's here that you can see the issue: if we're burning 1/3 the fuel, we're only imparting 1/3 the energy into the air through the prop, and there's no way we could climb or accelerate quickly (if at all) at that setting.
A final way to think about it is just like the gears on a car. Your transmission allows you to, at 1500RPM, go 10mph or 60mph or any speed in between. The problem is that if you try to accelerate from 10mph to 60mph while maintaining 1500RPM, it will take a much longer time than if you were to bump it up to 2500RPM. High gears are great for cruising and maintaining speed, but are not great for accelerating. They allow you to keep your RPMs low, your torque low, and your fuel burn low, because you don't need that extra energy. A high prop pitch is exactly the same.
A note about multi-engine aircraft:
They are just the opposite of singles. Where singles require positive oil pressure to increase blade pitch, multis require positive pressure to decrease it. This is because in a multi, you want the propeller to feather automatically if you lose oil pressure (because of an engine failure). This removes a significant amount of drag from that side of the aircraft.
They are equipped with either a spring or a nitrogen charge in the hub that is pressurized, pushing the hub piston back to the feathered position. The prop governor works the same way but the pilot valve directs oil to push against the back of the piston, moving it forward and compressing the spring/nitrogen, moving the prop to a lower pitch.
Some are also equipped with an unfeathering accumulator. This is a bottle with a piton in the top (also charged with nitrogen) that fills up with oil when the engine is running. When you bring the prop out of high RPM, the bottle is sealed off from the rest of the system. If you lose oil pressure, the prop will feather like it's supposed to, but there will still be pressurized oil in the accumulator. That way if you manage to get your engine issues taken care of, you can push the prop lever full forward, open the valve to the accumulator, and the pressurized nitrogen will force the oil out of the bottle to put the whole system under positive pressure for a few seconds. This positive pressure moves the hub piston forward and unfeathers the prop.
Now you might think "If multis feather when they lose oil pressure, why are all those twins out on the ramp sitting there with low-pitched props?" Well, they have centrifugal locking pins that disappear when the engine RPM is high enough. If it gets low, they will fall back down into a groove around the hub piston or its shaft and lock it into a low-pitch state. This is not a fool-proof system, however, because the pins have been known to stick, and people have been known to shut the engine off with the prop lever less than full-forward. In that case you either need to get some strong guys out there to manually twist the prop back, or you need to waste a chunk of your starter's precious life turning the engine over to create oil pressure to unfeather the prop. Most engines can not start in a feathered state due to the huge drag from the blades being perpendicular to their direction of rotation.
On turboprops:
Although it can vary engine to engine, turboprops use similar systems to multi-engine aircraft but at much higher pressures and with the ability to enter beta mode (reverse pitch). That introduces problems mainly in that the engine will very quickly overspeed with the blade pitch is 0 and the prop is generating no thrust/load. I'm not going to attempt to explain it because I've never really worked with one. This guy seems to do a good job, though.


Is the shear centre of a wing the same as its aerodynamic centre? How can the shear centre of a wing be located and is it the same as the aerodynamic centre of a wing?

Lastly, I know how the centre of pressure interacts with the aerodynamic centre but not the wing's shear centre, so how does the centre of pressure relate to the shear centre of a wing during flight?

No. These are very different things.

The shear centre (SC) is a purely mechanical (structural) feature of the wing design. It is a point along the chord such that application of force - no matter what force - causes the wing only to bend but not twist.

Unlike the aerodynamic centre (AC) and centre of pressure (CP), it makes no sense to talk about a single integral point for the whole aircraft. An SC can be found for each cross-section of the wing, and it is the chordwise relation of the SC to CP and CM (centre of mass) of the section that is important to aircraft designers.

Designers can control where the SC will be. If we could make the SC match the point of application of the integral force at this section, we wouldn't need much of the torsional rigidity, and could make the wing lighter.

Unfortunately, this is not practically possible. First and foremost, the CP, the integral point of application of the aerodynamic force in flight, moves forward and backward depending on the angle of attack (AoA). This is just the nature of aerodynamics.

Typically, for a straight wing CP will be behind SC for small angles of attack and ahead of it for large angles. This is rather unfortunate, because this means that at a high G load (esp. at moderate speeds), or in an updraft, the wing will twist to an even higher AoA. This positive twist at the max load (typically 1.5 × rated load) is often one of the critical design cases, so in practice we want SC closer to the forward-most CP location. A clever application of SC can make the wing twist negatively and dampen its own oscillations.

CM of the wing section is nearly always behind the SC. In normal flight, static aerodynamic loads prevail over weight of the wing itself, so this doesn't matter much. However, when we start analysing aeroelastic modes, CM location becomes important. To avoid flutter, a common solution is to move CM closer to SC by installing some dead mass at the leading edge. This often proves to be easier and lighter than increasing torsional stiffness. If we can, we would install some useful mass there, such as an engine.

I didn't talk about AC yet. This is because it has nothing to do here. AC is a very theoretical point introduced for convenience of stability analysis. Any force can be broken into a moment and another force, and we just split lift such that part of it acts at CM, and part at another point. Because CP normally moves linearly with AoA, we can make it such that all changes to lift due to AoA 'kind of' happen at a fixed location. But in reality, of course, lift just increases and moves forward with AoA. The structure and aerodynamics have no idea about our mental exercise.

It is perhaps this fixed location of AC that lets it be confused with SC, which is also fixed. But they have nothing to do with each other. Structural engineers don't need to know about AC at all (they just need to ensure the aircraft CM is in a certain range they are told), whereas flight dynamicists hardly ever talk about CP but always use AC as the reference point (along with CM).


Has research into the aerodynamic properties of non-smooth surfaces suggested any promising directions for future aircraft design? As you might gather from Can planes benefit from Mitsubishi's Air Lubrication System? I'm interested in what possibilities there are for radically different approaches to aircraft body surfaces.

Aircraft body surfaces appear to be as smooth as possible, but not all things that fly well are smooth:

golf balls are dimpled (see the very interesting discussion of Is a golf ball surface a good idea for wings or fuselage?)
birds are feathered
sharks have placoid scales (yes, I am aware that sharks don't actually fly through the air...)

Has scientific or industry research indicated useful possibilities in new surfaces for aircraft body skins - or maybe alternatives to skins altogether?

Non-smooth surfaces are already used, particularly in some Military Aircraft. If you've ever run your hand down the fuselage of an FA-18 Hornet you will find the surface is quite rough, much like the skin of a shark. At lower speeds very little is achieved, however at higher speeds small bubbles of air buildup in the indentations of the skin thereby creating an extremely slippery surface.

Take a look

Take a look here too

I'm certain my terminology is not correct, sorry about that. I would have put this all into comment, but I'm not allowed yet.


Do US military aircraft have tail numbers beginning with "N"? Military aircraft usually display a serial number along with other insignia on the tail or body of the aircraft, as described here.  However military serial numbers are not the same as FAA tail numbers on civilian US aircraft, which begin with the letter "N".

Do military aircraft also have an "N" number, or do US military aircraft simply not have an "N" number?

The 'N' numbers you're referring to are FAA registration numbers. The FARs (Federal Aviation Regulations) specifically mention registration as not being required for military aircraft:

14 CFR 47.3

  (b) No person may operate an aircraft that is eligible for registration under 49 U.S.C. 44101-44104, unless the aircraft—

  (1) Has been registered by its owner;

  (2) Is carrying aboard the temporary authorization required by §47.31(c); or

  (3) Is an aircraft of the Armed Forces

The FAA issues these registrations in accordance with its responsibilities under the Chicago Convention on International Civil Aviation, which required (in Article 20) that:

  Every aircraft engaged in international air navigation shall bear its appropriate nationality and registration marks.

As per the above-cited 14 CFR 47.3, though, the U.S. specifically requires that all eligible aircraft have registrations unless it's either a military aircraft or it has temporary authorization under 14 CFR 47.31(c).


Could a 'wind wall' help to reduce the wind shear problem at St Helena airport? I've seen a fair number of articles online about "The World's Most Useless Airport" (St. Helena, HLE/FHSH), which was unable to open to full commercial flights (as was the intention) due to the wind shear that occurs there. Because of this, only small aircraft are allowed to operate into St Helena.

This may well be a completely impossible idea, but if the issue is wind shear could they not adopt a system similar to this 'wind wall' which they use to protect large cargo ships in canals in the Netherlands?

Obviously we are talking about aircraft here and not ships, but would an approach like this - diffusing the wind either side of the runway threshold - have any effect on the final stage of the approach, to the extent that the wind sheer becomes tolerable for 'standard' commercial air traffic? Obviously large concrete structures wouldn't be particularly sightly, but from a purely practical point of view would something like this alleviate the issue at all?

It's a completely different problem, and I'm afraid something like that would make the wind shear close to the ground actually worse since it is inhibiting air flow within 200 ft of the ground while the wind just above is unaffected.

Plus the additional turbulence created by those thingamajigs sticking up.  Most pilots know how unpleasant it can be trying to land on a runway with a stand of tall trees adjacent to it, with the wind shadow and burble generated by the trees.

The windshear problem for aircraft isn't the wind velocity itself, it's the sudden changes in horizontal velocity at certain levels, which in a large aircraft with a lot of mass, creates large airspeed fluctuations as you climb or descend through, along with vertical flows caused by mountainous terrain can can generate high sink rates that, because of the mass, are slow to be addressed with power.  None of that would be helped by a surface barrier.   All the barrier would do is create an extra nasty shear + turbulence right at 200 ft.


Was a 7300-mile non-stop flight possible in 1979? I'm listening to the On Wings of Eagles audiobook by Ken Follett and found some information about a non-stop transatlantic flight between Teheran (IKA) and Dallas (DFW). GCM says that this is 7,300 miles and Google says that's 11,750 km.

Was there any aircraft capable of performing such a flight in 1979? If yes, then which one?

It was expected to travel with about 10-15 people on board and non-stop flight seems to be essential (at least to the author, because I completely don't understand the reasons why such a flight couldn't take a re-fueling break at some European airport once clear of the dangerous zone of Iran's / Middle East's airspace).

The author's choice of either a Boeing 707 or 727 seems to be completely incorrect, as according to Wikipedia there wasn't any version of either of those aircraft capable of flying 7,300 miles non-stop (or I'm missing something). The longest range mentioned is 10,650 km in the case of the B707-320B.

Even for zero payload, no B707 model is able to fly more than 6000nmi (11111km). B727 even has less range.

However, Iranair planned to run Tehran-LAX flight, which length is 12222km, but never materialized because of 1979 revolution. The flight could have been operated by the 747SP (introduced in 1976), similar to their Tehran-JFK route.


Why don't airliners have bigger cockpit windows? A bigger cockpit window would increase the pilot's vision of a runway. So why can't they be bigger?

Note that this question covers cabin window size already, but this question is about cockpit windows specifically.

The reason is that bigger windows really aren't necessary. They are plenty big for the crew to see the runway just fine. Pilots have more than 180 degrees of visibility, and plenty of vertical visibility as well. Traffic routes and patterns are designed to make it easy for the pilots to see the runway as well. If the runway is behind you, then you need to turn around. If it's below what you can see out the window, you are too high anyway. And if it's above what you can see out the window, you probably have more important issues than finding the runway.

Larger windows can help spot danger like other aircraft, but airliners are almost always flown under Instrument Flight Rules (IFR) where ATC is responsible for keeping them clear of conflicting traffic.

In the past, some airliners did have larger window area. This was more important in an era where instrument navigation was more limited, and the pilots relied much more on their view outside. It was also more common on aircraft with military heritage, where it was more likely for pilots to find themselves relying on visual references instead of navigational aids.

However, modern navigation systems have made larger windows even less useful. The instruments can tell pilots just about anything they need to know about anything they can't see out the windows. The 737 actually started with "eyebrow windows" above the main row of windows. Modern systems have made those less useful, and the extra holes in the fuselage can cause cracks over time. Most 737's delivered today don't have them, and some of the old planes even get those windows plugged.

Aside from the functional reasons for not increasing window size, the same structural concerns of cabin windows will apply here as well.


How long does a runway have to be for an Airbus A380 to takeoff? I have seen several Airbus A380's takeoff on large runways, but how small can a runway get for an Airbus A380 to takeoff fully without overrunning?

Airbus's A380 AIRCRAFT CHARACTERISTICS AIRPORT AND MAINTENANCE PLANNING data says that for an A380-800 at maximum certified landing weight landing at sea level a 7000 ft (~2150m) runway is required to land (in dry conditions, presumably).

"A380 Briefing For Pilots (Part 2)" shows a 3750m (~12,300ft) takeoff requirement when operating at 600,000kg at sea level, or almost 5000m if operating at 5000ft at 560,000kg (presumably a lower maximum weight for the higher altitude).  If you can significantly cut back on the weight (no PAX, no cargo, minimum fuel), the bottom end of the chart says ~1600m (~5280ft) for "I don't know how I got here, but I need to get away".

(Trying to find better numbers seems to be difficult because the computer does the calculations, and one document I found claiming to be an FCOM (Flight Crew Operations Manual) only describes feeding the data into the computer, and fun things like how the plane can audibly alert "Runway Too Short!" when landing, but I didn't find any takeoff or landing charts in the 8,100 page manual).


What does "running torque" mean? I would like to know the meaning of the phrase and especially the meaning of "running torque":

  Torque the inner plug to between 75 and 85lbf.in. Loosen half a turn
  and RETORQUE to between 15 and 20lbf.in more than the running torque.

So how do I find out how much is the running torque?

Running torque is also called the "friction torque". It's the torque required to make the nut or bolt turn while the nut is "loose" you might say.  With a locking nut, the locking feature (normally either a plastic insert, or a distorted bore section of the threads that directly squeezes together on them) takes a certain amount of effort to overcome.

Since torque value is an attempt to measure the stretch in a bolt as the rotary sliding wedge of the threads is applied to pull the two ends apart, any rotational resistance forces that are added, not directly applying the clamping force to the part, will skew the final result.

If you torque to 100 inlbs, and it takes 30 inlbs of torque just to make the nut turn because it's a lock nut, when the wrench trips at 100 inlb you will only have actually applied 70 inlbs worth of "stretch" to the bolt. So if you measure 30 inlb while spinning the nut down before it clamps down, you add that to the 100 inlb value, and run the wrench to 130 and will have the proper 100 inlb application to the bolt or stud.

The proper procedure is to run the nut or bolt down to maybe half a turn to contact (washer still loose).  Measure the torque required just to move the nut the last bit before the nut makes contact, and add that to the total.  If the nut spins freely because it's a castellated nut and has no friction device and you can spin it down all the way with your fingers, don't bother because the value will be too low to measure.

This is the problem with preset click-over torque wrenches that can only measure a limit that is set beforehand, when torquing friction-locking nuts.  When a procedure calls for that running torque part, it's better to use a dial indicating or other continuous indication torque wrench that lets you do the running torque observation and addition to the final value on the fly.

When a torque is for a critical part where precision is essential, it's also important to get to the final torque in one motion value without stopping.  That's because if you stop mid way just below the final value, the torque required to get started again will be high, and may be higher than the final value, and you may get a false "I'm there" indication when you really weren't there yet.  Better to back off half a turn and do it again.

If a torque spec says to lubricate threads, this is critical as well, as the friction of the thread and nut interface itself, while the clamping force is being applied, can skew the final result. On aircraft cylinders, where a precise torque application is vital, it's standard procedure to use lots of the recommended oil on the nut and threads to get the thread friction, and the nut to flange friction, as low as possible.  Piston engine cylinder nuts generally don't use any locking devices (or washers) at all, and totally depend on clamping force to avoid backing off, and if done properly, they never do.

In the procedure you're quoting, the objective is to seat the "plug" for some reason with a larger than final force, then back off and re-tighten to a pretty low value of 15-20 (this sounds like a procedure intended for sealing purposes). Factoring in the running torque will be critical to achieving the 15-20 inlb final value.


Why do different sites list different lengths of the lower deck bulk cargo compartment for the A330-300? From the following two links for Airbus A330-300, the length of "lower deck bulk cargo compartment" has two different values.

a) Air China lists the value as 511 cm

b) Airbus (see pg. 112) lists the value as 404 cm

Why?

Some airlines have different specs. I can't comment on the examples you've given but one example I have encountered is on the A340-300.

The airline I worked for had conventional LD3 loading where the cans were loaded in pairs but for a while we had an A340 leased in from Swiss or Sabena (cant really remember which as it was more than 10 years ago) which had an additional LD3 position on the centreline of the aircraft in the space that would usually be available for bulk loading.

On thing which could affect the size of the bulk compartment is the location and number of toilets on the passenger deck. The plumbing usually lives under the floor.

Note the airbus site mentions that dimensions are approximate.


Why are the colors of the MiG-15's attitude indicator inverted? Why are the colors of the MiG-15's attitude indicator inverted (blue on the ground side, brown on the sky side)?

Source: http://www.warbirdalley.com/mig17.htm

That attitude gyro reacts in the opposite manner to pitch movement (pitch down = horizon line rolls DOWN) compared to the "conventional" manner (pitch down, horizon line rolls UP). This is sufficiently confusing that on similar gyros of American manufacture, the words CLIMB and DIVE are printed on the "ball" inside the gyro case to remind the pilot what the instrument is telling him or her.

The "opposite" reading gyro horizons were commonly used in American fighter aircraft because their construction made them more resistant to tumbling than were the "conventional" reading instruments, which were used in civilian aircraft.

After WWII, those opposite-reading gyros wound up on the surplus market and a number of them were installed in civilian aircraft, including the Beech Bonanza that was carrying Buddy Holly, Ritchie Valens and the Big Bopper on the night of their crash. The pilot had trained in a plane with a conventionally-reading instrument in its panel and the accident report claimed that he was confused by that opposite-reading gyro in the dark, thinking he was trimming for an 800FPM climb when what he was really doing was trimming for a descent- and minutes after takeoff, the plane flew smoothly into the ground and everyone aboard was killed.

I have an example of both types of gyro horizon in my collection, and even when they are not spinning, simply tilting their cases in unison demonstrates the difference: one rolls up, the other rolls down when you pitch them both down.


How are "expect" altitudes on STARs used? STAR charts often have expected altitudes. For example:

This is, of course, different from mandatory crossing altitudes, and it seems a STAR with only expected altitudes would be insufficient for ATC to issue a descend via clearance, though I could be wrong about the second part.

Some charts say "VERTICAL NAVIGATION PLANNING INFORMATION" before the expected altitude, so my assumption is that these altitudes are strictly for planning purposes and allow a top of descent to be calculated.

My questions are:

When you enter the STAR in the FMS, will it pre-populate the expected altitude, and does this show up in the FMS exactly the same as a mandatory crossing altitude?
Are expected altitudes treated as suggestions by pilots or controllers? For example, in the above chart, if you were at JHAWK 15,000ft landing south, and Kansas City Center or Approach told you to "descend at your discretion, maintain 8000", would you (or the FMS) make any attempt to cross RUGBB at 12,000 even though it's not required?
How common is it for ATC to actually issue a "cross [fix] at [altitude]" where the fix and altitude are as expected on the chart? And, if it is common, why wouldn't it simply be mandatory?
Are expected altitudes part of lost communications procedures?
Am I missing anything with regards to the purpose of expected altitudes?

My questions are:

  1) When you enter the STAR in the the FMS, will it pre-populate the expected altitude, and does this show up in the FMS exactly the same
  as a mandatory crossing altitude?

This depends on the model of FMS.  Some of them don't even have Vertical Navigation (VNAV), and it really depends on the exact model.  I will say that three of the most common FMS's that I have personally used (Universal, Collins, and Honeywell) all pre-populate the expected altitude and it shows up exactly the same as a mandatory altitude.

In any case, the FMS is advisory only.  Unless the pilot dials in the actual assigned altitude and selects a vertical mode on the autopilot, it isn't going to descend on its own.  So if ATC doesn't assign the crossing restriction, you may see your VNAV pointer come alive and watch as you fly through the vertical profile without capturing it and it would be perfectly normal.  If I am getting close to the point where I would like to descend to make a crossing restriction and haven't been given lower, I will sometimes ask the controller:  "Do you need me to make the crossing restriction at RUGBB today?".  This gives me an idea of what's to come or prompts them to give me the descent clearance.

  2) Are expected altitudes treated as suggestions by pilots or controllers? For example, in the above chart, if you were at JHAWK
  15,000ft landing south, and Kansas City Center or Approach told you to
  "descend at your discretion, maintain 8000", would you (or the FMS)
  make any attempt to cross RUGBB at 12,000 even though it's not
  required?

An "expect" altitude is just that.  It is an altitude to expect, but it is not always actually assigned.  If it isn't, then you don't have to make it and since your example is at pilots discretion, you could descend at whatever rate you want.  You could cross RUGBB higher or lower than 12,000 ft and nobody would care.

In actual practice, they usually only do this in a few situations:

If they have to hold you up higher due to traffic and you can no longer make the crossing restriction, they will just give you a "descend and maintain" altitude, sometimes with a "good rate" tacked on.
It's a particularly slow time (late at night, etc.) and there isn't much other traffic to worry about.
There is an aircraft at, say 13,000 ft. so they tell you to descend and maintain 14,000 ft with the intention of giving you the crossing restriction once you pass the conflicting traffic.

In this last case, I would get down to 13,000 ft. in time to make the crossing restriction if they gave it to me, but it wouldn't be required.

  3) How common is it for ATC to actually issue a "cross [fix] at [altitude]" where the fix and altitude are as expected on the chart?
  And, if it is common, why wouldn't it simply be mandatory?

Again, this depends on the procedure but it is quite common.  That's why they put them there so that you can plan on what is typically done.  There may be operational reasons (like two different procedures that intersect) which prevent them from issuing it every time, so they can't just make it mandatory.

  4) Are expected altitudes part of lost communications procedures?

Surprisingly, no.  Not unless the controller has specifically cleared you to expect or cross it or "descend via" a procedure.

  5) Am I missing anything with regards to the purpose of expected altitudes?

Not on this one!  In some cases, there is a speed restriction which is listed on a separate line from an expect altitude. In these instances, the speed is required whether or not the speed or altitude was verbally assigned, just by being cleared via the arrival. For example, on the SFO HADLY2 arrival, you are required cross EUGEN at 250 knots, whereas 11,000ft is only required if assigned by ATC.


Does the FAA issue multiple physical certificates for different aircraft categories and privileges? If one holds a private pilot certificate in both airplanes and gliders, does the FAA issue two plastic cards that one would have to carry? What if one has commercial privileges in airplanes, but private in gliders?

What about being private in airplane, but sport in powered parachute? Some schools say that if one already has a private in airplane, then powered parachute at sport level would only be a logbook endorsement rather than a new piece of plastic. I was under the impression that logbook endorsements are generally things like the ability to fly a complex airplane, rather than being a sport level in a different category of aircraft.

One certificate would be issued. Your highest rating would be listed on the front and on the back any lower ratings would be outlined.

Before I had passed my rotorcraft ATP my certificate read:

Airline Transport Pilot
 Airplane Single and Multiengine Land

Commerical Privileges
  Rotorcraft-Helicopter


Which civil airport has the longest runways in total? It's quite easy to google information about which civil airport has the longest runways, but what I'm really looking for (and having a hard time to find) is which airport has the longest runways in total - I mean if you add up all the lengths, disregarding the direction - which one be the winner?

Best I can find, within the US, is KDFW with 80,403' of total length. Second seems to be KDEN with 76,000'. Glanced at KORD, and with mental math it comes up to about 71,000'. Most other major airports are well behind all of these, mainly because they don't have as many long runways as DFW and DEN.

Somebody else can consider Russian, Chinese, and Middle Eastern airports -- I don't have the chart sets handy for those.  May be worth converting this to a community wiki answer if any of those places give interesting results.


Can two aircraft be allowed to stay on the same runway at the same time? My understanding is that the runway should always be cleared, and occupied by no more than a single aircraft for takeoff and/or landing at any given time.

Is there any scenario in which ATC can clear two aircraft to occupy the same runway at the same time? Like clearing them to takeoff one by one: clear the front one to use part of the runway to takeoff first, and then clear the other at the threshold to takeoff.

There is another scenario other than "line up and wait" that the other two answers cover...

A "flight" of more than one aircraft may be cleared as a group to take-off. This can consist of many aircraft sharing the runway during take-off (and even landing).

So you can have multiple aircraft on the runway when:

A "line up and wait" order is issued to line up on the runway after another aircraft takes-off or lands. This is usually done so that the departing aircraft can get prepared while waiting for wake-turbulence to clear.
ATC clears multiple aircraft as a "flight". The aircraft must be part of a coordinated group and a single aircraft is the "lead" aircraft for the flight that receives/coordinates with ATC for clearances. The entire flight group will enter the runway and take off in a pre-coordinated fashion.

There are specialized scenarios as well, for example during Airventure Oshkosh. Aircraft will be required to "land on the dot" and multiple aircraft may be on the runway for take-off at the same time, although ATC coordinates them so that they don't depart at the same time, they are asked to line up "on a dot" (a colored circle on the runway) and will then be cleared to depart from there.

As an extreme example:

116 aircraft lined up on the runway and cleared for take-off at the same time.


Do you have to explain what your emergency is? Story Time:

Let's assume, for the sake of the question, that you were piloting a twin engine plane and the right engine, out of the blue, shuts down.

After realizing it you declare emergency, and explain very briefly to the ATC what is your situation at the moment, and after that you start to work out the checklists (I don't know the right order to proceed on a emergency scenario, but i don't think that it's important to this question).

After that you managed well the situation and safely landed the plane.

So here is my question:

At the moment of the emergency you weren't able to explain with details everything that happened to the ATC.

According to FAA, is it required to detail/explain (maybe file some kind of official document) your emergency to some kind of authority?
If you do have to file an explanation, what information do you have to supply?
Also what would happen if they "didn't believe" that situation was an emergency?

The order is "Aviate, Navigate, Communicate".

As a pilot, your first responsibility is to keep the plane flying. After that it is to avoid hitting something or to avoid getting lost. After that comes communication. There are many instances of in-flight emergencies where the pilots never talked to anybody about it, because they were busy flying the plane...

  According to FAA, is it required to detail/explain (maybe file some kind of official document) your emergency to some kind of authority?

The FAA has many procedures on reporting accidents, incidents, and emergencies. Whether or not you report it depends on what the emergency was. If its a very sick passenger, there may be no reporting required. If your control cables failed, you are required to report it. I'll update this answer with the regulations as soon as I find them all. Quick answer is any time you declare an emergency or "PAN-PAN", call the FSDO and let them know. Also depending on the nature of the accident/incident, you may be required to immediately notify the NTSB. See CFR 49 830.5

  If you do have to file an explanation, what information do you have to supply?

This depends again on the nature of the emergency, and the FSDO/NTSB will ask you for the proper information when you file the report. At the very least they are probably going to want a narrative of what happened, and depending on what took place, you may want to contact your lawyer first. (Note: You may have to contact the NTSB immediately but it doesn't say you need to provide details, just that there was an incident, so the NTSB would be your first call "I had an incident", short and sweet, and the lawyer second.)

  Also what would happen if they "didn't believe" that situation was an emergency?

Its not ATC's responsibility to determine if you are lying or not. When you as a pilot say "emergency" you have their full attention. After you get on the ground and the emergency turns out to be you forgot to call your girlfriend/wife and wanted to get ahead of other traffic, then the FAA will get involved. Until you are on the ground, an emergency is handled as priority, regardless of the reason.

Here you can read a good story about a stupid pilot who abused the "emergency" system by landing on a public beach in New York because of an airsick passenger and an engine that was "running a teensy bit rough". He didn't officially declare an emergency, and I can't find any record of official enforcement action against him for doing that. Note the NTSB did not investigate this "incident".


What are typical naca foils for winglets for ultralights/LSA? What are typical naca foils for winglets for ultralights?

The information I have, is that you would want to have the thinnest symmetrical airfoil, that will work in the specified Re range, eg. NACA009


What causes a run-away propeller? I've never understood this, why can't you just idle the engine and let it slow down?

Often the overspeed is caused by the airflow forcing the propeller to move faster. It's like braking on the engine while going down a steep hill, even without touching the gas pedal you may speed up and redline the engine. Very problematic if you already overheated your brakes in a 18 wheeler.

If you have a variable pitch prop you can feather it to reduce the effect of the airflow. Or just follow the procedures in the overspeed checklist for the aircraft.


Why is the Aerodynamic Centre not affected by changes in Angle of Attack? I understand that the Aerodynamic Centre (AC) is the point in the aircraft where the pitching moment never changes with a change in Angle of Attack (AoA). My understanding of the Centre of Pressure (CoP) is that it is the resultant pressure point in the airfoil and it slides rearward when AoA decreases and vice-versa, i.e. it changes its position with regard to the AoA.

Now the point is, how does the pitching moment (the force arm, i.e. the distance between the CoP and the AC multiplied by the force) remain constant when the CoP itself moves with the change in AoA?

As the pitch of the wing increases moment arm decreases and at the same time lift increase, so the pitching moment stays constant.

In typical airfoils such as the wings of an airplane flying level sub-sonically the pressure center is at approximately 0.44 of the  cord length, and the aerodynamic center is at 0.25 of the cord length.

When the AoA increases the lift increases linearly and at the same time the CoP moves forward closer to aerodynamic center in a way that reduction in the length of the pitch moment arm is cancelled by increase in the force (lift); so the pitch moment is constant.

In fact the location of AC is calculated by finding the point that the decrease in pitching arm is proportional to increase of lift, otherwise one could pick any arbitrary point along the cord and calculate the pitching moment at that point, but it would not remain constant for a different AoA.


Can anyone identify the Make and Model of this nosed-over plane? I've tried to identify this plane by the writing on the plate on the cowling but have been unable to match the logo, and when I've blown the size up the writing is unreadable. It looks something like SCOOTROM with a long tail on the upper part of the "S" and with two straight lines under it.  I think this light crash took place in Wisconsin, perhaps Madison or Stoughton but I don't have a year.

I believe this is a Stinson HW-75 (Also called the 105 Voyager).
I know for sure this is a Stinson aircraft due to the logo which was often rendered on the side of aircraft with a double underline and certainly has the long tail on the upper part of the S as you described:

Logo from the orignal picture, rotated and de-skewed
The identifying features which make me think this is an HW-75/105 Voyager are:

Similar decals down the side of the fueselage as shown in image below
Twin Supports meeting at the main gear roots
Shape of the step for access to the cockpit
Grill both side and below the spinner

source: Wikimedia commons
However there is a slight chance that this is actually another Stinson model such as a 108 or L-5 Sentinal which both share some similarities


What are the relative braking contributions from wheel brakes, spoilers and thrust reversers? What is the relative contribution to braking forces in a typical large commercial aircraft  from the three different devices contributing to braking after touchdown:

Wheel brakes
Speed brakes / Spoilers
Reverse Thrusters

The relative contribution should change with velocity so even nicer if we have the velocity depended thrust contributions. e.g. Reverse Thrusters provide more braking at the initial high velocity part of the roll out.

I'm posting a illustrative (but totally made-up) graph to clarify for what I was looking for:

I am looking for either empirical data or theoretical predictions for the thrust. Qualitatively I'd expect the spoiler contribution to fall off with a square law dependence on velocity. I'd think the reverse thrust offers a somewhat constant component but perhaps higher initially due to parasitic drag by the clamshells? Not sure, and this is what I'm trying to get: A quantitative relationship.

In case the answer will vary hugely depending on aircraft, I'm open to any specific case being illustrated.

Let's use the limiting case of full brakes with anti skid on.

PS. Since spoilers directly add to drag as well as indirectly help braking by dumping lift teasing out their braking thrust contribution might be harder?

Your question shows that you understand the issue already very well, and more detailed fractions of the single components depend on the particular airframe and engine, so my answer will not add much insight.

The only detail I can add is a plot of tire friction coefficient over speed. Unfortunately, I do not know the source of it; I collected it sometime in the past and never found a reason to doubt its validity.

Also, this document might be helpful. Below I copied Figure 3 from it, because it comes closest to answering your question. But keep in mind that the details depend on the particular aircraft and its systems, as well as runway condition, wind speed, tire and brake condition.

Typical deceleration forces during landing roll, from this document. Note that the aerodynamic drag with spoilers plus reverse thrust at high speed produce already more deceleration than what is desired at low auto brake setting.

In order to find the overall contribution of each braking component, compare the areas under their respective plot lines.


What is the difference between instrument privileges and instrument rating? According to FAR 61.153(d), a pilot may use a foreign commercial or ATP certificate as a prerequisite for getting a US ATP.

To do so, an applicant must:

  Meet at least one of the following requirements:
  ...
  (3) Holds either a foreign airline transport pilot license with instrument privileges, or a foreign commercial pilot license with an instrument rating, that... (emphasis added)

What's the difference between "instrument privileges" and "Instrument rating"?

The short answer is that the privileges are what the rating confers, and there are ways to get those privileges other than having the rating.

A commercial pilot licensee in most jurisdictions that follow ICAO certification guidelines may fly small planes for hire, doing service as a courier, air taxi, crop duster, etc. These do not necessarily require flying in IMC or in Class A airspace, and so a CPL holder must also have a separate "instrument rating certification" in order to fly IFR.

ATPL licensees fly in Class A as a matter of course, and that also often requires ascending and descending through the cloud ceiling which is IMC by definition. Therefore, the requirements for an ATPL in ICAO-compliant jurisdictions inherently include those required for the "instrument rating" applied separately to lower certification levels (private/commercial), and the resulting license for an airline pilot confers the same "instrument privileges" that the rating would.

Thus the difference in terminology; an ATPL holder in another country has "instrument privileges" as a consequence of his basic license and so does not need a specific "instrument rating". The same is not true for CPLs and so the law specifically requires the instrument rating as a prereq for a foreign CPL seeking an FAA ATPL.


Why is this plane circling around the Lucknow airport every day? Saw this plane circling around Lucknow airport (LKO).
This is happening every day. Any idea what is happening?

That is a plane being used to train/practice landings.

It is without passengers and one of the pilots is training. There will also be another pilot on board, possibly two, providing support and checking that the trainee is performing their duties according to the manual.


Why don’t aircraft have interlocks to prevent high-lift devices from being retracted when doing so would stall the airplane? Most aircraft have high-lift devices on the wings (such as flaps, slats, droops, whatevs) to allow them to take off  and climb out at a reasonable speed instead of having to accelerate to near cruising speed while still on the runway; this enables the aircraft to use shorter runways, but also places it at risk of stalling if these devices are retracted too early in the climb (example).

Given the danger of retracting high-lift devices at too low a speed, why don’t aircraft have interlocks to prevent this from happening?

Most modern airliners have some form or other of mechanism that does exactly that, mostly for the slats (which are more important in stall prevention, anyway).

E.g. on modern Airbusses, there is a Slat Alpha Lock function which prevents slat retraction at high angles of attack, on the Boeings there is a Slat Auto-Gap function extending slats from mid to gapped position at high angles of attack.

Military aircraft often have automatic slat deployment to aid with high angle of attack manoeuvres, and even some vintage aircraft did have aerodynamically activated slat-like devices for stall prevention.

Any sensible reference suggestions welcome for any of these... cannot post mine.


What regulations apply to changing liveries on private jets in the US? Things like the manufacturer's livery, do they need to follow that?

Anything else that will be required when purchasing a new jet and changing the paint to the new owner's choice and requirements.

The only requirement is the height of the registration number, 12" if flying internationally (from the US anyway), 2" I think if staying domestic, and maybe new weight & balance - but usually a layer of paint and primer is taken off, and a new layer is put on, so the weight change is minimal.  Any control surfaces that were removed may need rebalancing.  Colors & schemes are at the whim of the owner(s).


Why do the A220 cockpit seats have a cutout? Why do cockpit seats on the A220 have a cutout on the bottom cushion? The answers to Aircraft pilot's seats: what is the notch for? explain that these cutouts allow for easier maneuverability of the yoke. However, this A220 cockpit has no yoke. Why does this cockpit have the cutout?

(source: thepointsguy.com)

As we have seen in a previous question, the A220 is a re-branded Bombardier CSeries.

The CSeries started flying in 2013. At the time Bombardier's other commercial jet was the CRJ, that started flying in 1999, 14 years prior.

CRJs do have a yoke:

(wikimedia.org)

If you look closely, you'll notice that the seats look identical, indicating that Bombardier probably decided to cut on costs by simply re-using something they had already (and minimizing the parts they would have to support).

Moreover, this answer mentions the need to have the straps as close to the pilot as possible, and this is achieved with the notch. A redesign of the seats has probably been deemed not worthy of the costs.


What are the most popular areas to do private pilot flight training in the United States? Are there any statistics on the most popular states to do private pilot flight training in the USA or a similar measure?

I know Florida is very well visited, but I was wondering if there were other states which also have high number of students.

The FAA has a document on their website which breaks knowledge tests down by FSDO rather than state, and it gives a good idea of where the most training is taking place.
It is called: 2013 Airmen Knowledge Tests by Region and FSDO, and lists the following Regions/FSDO's as processing the most knowledge tests (in descending order)1:

Southern 28,333
Orlando 9,996
South Florida 5,958
Alabama & NW Florida 4,680
Atlanta 3,882
Tampa 2,504
Western Pacific 18,416
Scottsdale 6,053
Riverside 1,556
San Diego 1,463
Sacramento 1,460
Long Beach 1,327
Fresno 1,270
Los Angeles 1,142
San Jose 1,121
Southwest 15,943
Dallas 2,731
Fort Worth 2,581
Houston 2,438
Oklahoma City 2,347
San Antonio 2,321
Eastern 14,552
Richmond 1,956
Greensboro 1,366
Farmingdale 1,280
Philadelphia 1,198
New York City 1,069
Boston 1,041
Great Lakes 11,860
Fargo 2,120
Dupage 1,414
Indianapolis 1,358
Minneapolis 1,142
East Michigan 1,111
Northwest Mountain 9,784
Denver 2,205
Portland 2,131
Salt Lake City 1,964
Seattle 1,611
Central 9,019
Nashville 4,293
Wichita 1,304
Alaskan 812

Based on this data, I would say that the areas surrounding the Orlando, Scottsdale, South Florida, Alabama & NW Florida, Nashville, and Atlanta FSDO's are the most popular training areas, with the Southern region being the most popular by far.

1 To improve readability, all FSDO's with less than 1,000 tests have been removed.  See the source data for the complete list.


Can a passenger jet be towed to safety if it breaks down in midair? A car can be towed by a tow truck to the repair shop when it breaks down on the highway. Is it possible for a passenger plane to be towed by an emergency tow plane along the air corridor to the next nearest airport assuming it cannot reach there on its own power (example if it runs out of fuel or both pilots are incapacitated)?

Update:
This question actually consist of two parts. Whether it is feasible and whether this is practical. I have seen a small tugboat towing a barge; a man pulling a firetruck. Before writing off this idea completely, can someone address what's stopping a fighter plane from towing a passenger jet if a proper point of harness is installed?

Towing is quite feasible, and even landing while in tow is possible - I've done it myself in gliders. The hard part is catching up with the stricken plane.

To stay with Keegan's Boeing 777: It most likely will travel at Mach 0.8 and somewhere between 30.000 and 39.000 ft when disaster strikes. Let's further assume that power fails instantly, so the aircraft, traveling at 240 m/s, will develop a sink rate of 15 m/s just to continue flying. When it sinks, the increasing density allows it to slow down, so at sea level it will fly at 130 m/s, sinking with 8.125 m/s. For simplicity, assume a linearly decreasing sink rate, and the remaining time aloft will be less than 1000 sec or around a quarter of an hour.

Now the towplane has 15 min to scramble the crew, run up the engines, get take-off clearance and to actually fly an intercept to the stricken airliner. How realistic is that? How many airports are needed to have 777-sized towplanes ready, and how many otherwise unproductive 777s would this scheme need?

A car can stop and wait a couple of hours for the tow to reach it. An aircraft can not.


How big can a pulsejet be? Pulsejets are mostly known for propelling the V-1 flying bomb, and have some use as small remote-controlled plane engines. In either case, the pulsejets aren't particularly big, as far as jet engines go.

How big can a puslejet be realistically made? Assuming that, for some reason, there was a need to power a much bigger plane with pulsejets, at which point would it stop making sense to make the pulsejet bigger, and use multiple smaller pulsejets?

At the point where the structural rigidity needed to overcome the vibration of a single enormous pulse train becomes so heavy that the aircraft can't fly anymore, replace the single large pulsejet with several smaller ones, whose individual pulses are smaller.

Conversely, imagine replacing a car's V8 engine with a single-cylinder engine of the same power.  It would need much stronger engine mounts, flywheel, clutch, transmission, etc.  (Single-cylinder car engines weren't that rare a century ago; good luck finding one today.)

But the main reason that large pulse jets are rare is their low fuel efficiency.  The bigger the engine, the more that matters.

See also: What are the pros and cons of a pulsejet?


How does the FAA decide whether an aircraft is deemed a helicopter? This is a followup to this question.

How does the FAA decide whether a new aircraft will is deemed to be a helicopter for licencing and registration purposes?

Is there a law or regulation? Are there guidelines? Is there any case law where a manufacturer challenged a particular classification?

The definition of a helicopter as well as other aircrafts is provided in 14 CFR Part 1

http://www.ecfr.gov/cgi-bin/text-idx?SID=8403e178a4e1d0f8339151fe2529e600&node=14:1.0.1.1.1&rgn=div5

Manufacturers may seek clarification from the FAA about these definitions if/when there is a requirement .


Why would a Mode-C transponder report a different altitude than an altimeter/GPS? This is related to a small single-engined plane.

On a recent flight, the controller kept telling me that I was 300 ft higher than it appeared on my altimeter and GPS (which were in sync). This was not a problem on the previous two legs of the flight. However, multiple controllers thought that my altitude was 300 ft higher.

Has someone run into this issue? What could be the problem?

It sounds like there was an issue with your altitude encoder

  The transponder depends on an external altitude encoder to provide the
  digitized pressure altitude that the transponder needs for its Mode C
  replies. The encoder is connected the same static air line as the
  altimeter and is wired electrically to the transponder.

  AR-850 The encoder may be either a separate unit ("blind encoder") or
  integrated into the aircraft altimeter ("encoding altimeter").
  Encoding altimeters save space and help ensure that the encoder and
  altimeter agree, but they are fairly expensive.

If you have a blind encoder its possible it can report erroneous information with out affecting other instruments onboard. You should alert your mechanic (or the mechanic that takes are of the aircraft in question) to have this checked.


How are weight ranges mentioned for GA airplanes in TCDS? I'm writing software to integrate a weight and balance chart into my website. Most of the Type Certificate Data Sheets TCDS I've read follow the form:

x to y at z lbs. or less
a to b at c lbs.
Straight line variation between points given.

I want to make sure that I test this against more complex scenarios.  Are there general aviation aircraft that have more than 2 "ranges" or are otherwise exceptional that would make for good test cases?  I am only concerned with GA aircraft at this time.

Are there general aviation aircraft that have more than 2 "ranges"

Yes. I happen to fly one (the PA-28 series, TCDS 2A13).
The loading graphs look like this:

Note also that the aircraft is certificated in both the Normal and Utility category, and the weight/CG ranges are different (Utility being a subset of what's permissible for Normal category operations) - so there are two different operating envelopes that must be considered.


What is the best glide speed for the DC-3 with 2 engines out? What is the best glide speed for the DC-3 with 2 engines out?

I realize we may consider best speed for ground distance traveled or best for duration - and that weight can be a factor. I can't find anything on the web.

Maximum glide angle for the DC-3 with power off, both propellers feathered, gear and flaps up, no wind is computed to be 3.88 degrees. This angle will give the maximum glide range. Depending on the aircraft's weight the following numbers can be applied to give the maximum distance:
20,000 lbs. Gross Wt. IAS 92K   (MPH 106),
23,000 lbs. Gross Wt. IAS 99K   (MPH 114),
26,000 lbs. Gross Wt. IAS 104   (MPH 120),
The rate of sink at 20,000 lbs gross weight is approximately 680 feet per minute (11.3 ft per sec.) at 5,000 ft of altitude.


How quickly could a commercial airline integrate advances in technology into its fleet? How quickly would a commercial airline be able to integrate significant advances in technology into its fleet?

Specifically I am interested in large commercial airlines and advances in technology that would substantially increase the efficiency of fuel consumption in passenger aircraft, but I don't have enough of a background in commercial aviation to make an educated guess and have not been able to find a comparable historical example. If someone could provide me with either it would be much appreciated.

It depends on the advance. Generally, there are three ways how airliners can be improved:

Operations and procedures: This can be as simple as faster turn-around times so aircraft will be more profitable, or as complicated as doing away with airways which would help to shorten trips, but depends on changes in regulations which have been in place for decades.
Better equipment: All parts of an aircraft are designed to be individually replaceable, and swapping old engines for newer, more fuel efficient ones will bring already two thirds of the efficiency benefits of replacing the whole aircraft. Other examples could be less heavy furnishings or more precise instruments. But there are limits, and every change needs to be approved by regulatory authorities.
Newer aircraft models: This brings aerodynamics, engines and equipment up to the status quo, and is done by airlines on a regular basis to improve both their attractiveness and their profitability. Examples are Singapore Airlines, which pride themselves on an average age of their fleet of just seven years, or Vueling, which thanks to a recent expansion has lower seat-mile cost than all their competitors.

Generally, the days of dramatic technology advances are long gone. Today, years of research are justified by single-digit percentage advances, and a new development like the A380 is started with a promise of just 15% less seat-mile cost when compared to airliners which are two decades old by the time the new plane is put into service.

To answer your question directly: Changes which produce meaningful improvements need years of preparation and testing for approval by the authorities. Quick gains are not possible anymore.