Airbus control architecture - where does the actual autopilot live? I'd like to ask for confirmation about the A320 (and, generally, Airbus family) control architecture. The book Aircraft Systems provides the following
overview of A3XX computing architectures:

Focusing particularly on the A320 family, are the ELACs and SECs merely actuator controllers for the control surfaces, or do they also carry the autopilot flight control algorithms? Or is the "autopilot" a separate entity, which feeds desired control surface positions to the ELACs and SECs (i.e. these latter are simply "slaves" to the autopilot)?

This picture from an A320 Operating Manual makes it seem that ELACs and SECs are autopilots themselves (i.e. there is no separate entity that is the autopilot that feeds them signals):

However, the same manual has another figure which makes it seems that indeed there is a separate autopilot entity:

If the autopilot is indeed a separate "master" entity which feeds desired
control surface position signals to the ELACs and SECs, is this a concept that generalizes to the rest of the Airbus family? Where does the autopilot software then live?

Short answer: Autopilot is a feature of the Flight Management And Guidance System (FMGS), and in particular each of the two Flight Management And Guidance computers (FMGC) manage its autopilot.

  Are the ELACs and SECs merely actuator controllers for the control
  surfaces?

Correct, but they are reconfigurable in case of failure of one of the SEC, ELAC or FAC. In addition the ELACs are used to detect the excursion off the flight enveloppe (e.g. alpha prot). They inform the FMGC of such situations.

  It seem that ELACs and SECs are autopilots themselves

No, AP is a separate function of the FMGC (and of the FAC).

FAC, ELAC, SEC are flight control computers, but are not equal.

FAC (Flight Augmentation Computer) in particular is devoted primarily to rudder control, and all the associated functions (e.g. yaw damper). It is a main component of the autoflight system.
Ailerons and elevators are directly controlled by the Flight Management and Guidance System (FMGS), which includes the autopilot.

Autoflight system presentation by Airbus:

  The auto flight system (AFS) installed on the aircraft is made up of
  two types of computers :

  the flight management and guidance computer (FMGC)
  the flight augmentation computer (FAC)

  and two types of control units :

  the flight control unit (FCU)
  the multipurpose control and display units (MCDU).

  The functions of the FMGC are :

  autopilot (AP)
  flight director (FD)
  automatic thrust control (A/THR)
  flight management.

  The functions of the FAC are:

  yaw damper
  rudder trim
  rudder travel limiting
  calculation of the characteristic speeds and flight envelope monitoring
  acquisition of the yaw AP order.

Redundant FMGS are divided in two functions: Command (issue commands to flight controllers) and Monitor (monitor the result of the commands, e.g. by analyzing air data and inertial data to detect anomalies).

The FMGS has different functions:

It uses the navigation database containing aerodromes, waypoints, navaids, procedures, etc, for the routing of the aircraft.
It takes into account aircraft performance data to manage the vertical aspects of the route.
It controls navaid receivers (VOR, DME, ILS, etc) and use navigational data.
It receives air data (from pitot, static pressure sensor, pitch angle probe) and inertial data.
It monitors the progress of the aircraft on the route programmed into the flight plan.
It issues flight guidance cues using the flight director indicators on the PFD.
It takes into account short term instructions entered by the crew using the FCU, and long term instructions entered using the MCDU.
It manages flight control laws and laws reconfiguration after controls failures.
It is coordinated with the Autothrust system which, with the FADEC, control fuel flow and engine thrust (FMGC is interfaced with ECUs/EECs).

The manual way of controlling the aircraft is:

FMGC gives instructions to the crew using the flight director cues and the yaw cue.
The pilot follows the cues with the controls (rudder pedals, side stick)
Pilot commands are taken into account by the flight control computers (FAC, SEC, ELAC) which determine the way control surfaces will be moved, possibly limiting the deflection ordered by the pilot to maintain the aircraft within its flight envelope.
FAC, SEC and ELAC orders are sent to respective actuator controllers.
Two notes on this transmission:

There is a final control function on the actuator, to allow actuator redundancy for control surfaces, e.g. for elevators:

  Each servojack has three control modes: Active: The jack position is
  electrically-controlled, Damping: The jack follows surface movement,
  Centering: The jack is hydraulically retained in the neutral position. (Source)

ELAC, SEC and FAC can be reconfigured according to law degradation status, the outputs of these FCC can be sent to different actuators, so the electrical circuit between an FCC output and an actuator input includes some switching circuitry.

Because of the two notes above, sending an electric order to the actuator doesn't mean the actuator will move the control surface, it depends on the current mode.

When the autopilot (AP) is engaged:

The cues displayed by the FD and yaw indicators are converted directly into orders to the flight control computers. So AP is just automating what the pilot would have done when following the cues.

While in cruise only one AP can be engaged, landing may requires the two AP for automated approach and landing.

FMGS computer location

Source of all images: A320 family ATA-22 Autoflight Maintenance.


How does the Pseudo-Satellite Zephyr land? I don't see how the Airbus Pseudo-Satellite Zephyr solar plane can land safely.

It this video, it is "thrown" to take off, but no gear or something similar is visible. Will it just land on its belly?

This video shows, I think, landing footage, but only the runway is visible.

After some power googling...

https://www.airforce-technology.com/projects/zephyr/

  Launch and recovery The air vehicle is launched by hand. Recovery is
  by belly landing as the air vehicle has neither landing gear nor
  landing parachutes.

https://www.ainonline.com/aviation-news/defense/2016-07-11/solar-powered-pseudo-satellite-display-farnborough-2016

  It is hand-launched by a five-man ground crew, and recovered by belly-landing.

http://en.ruvsa.com/catalog/zephyr/

  Launch: hand launch Recovery: autonomous belly landing

It has two-bladed props, so they can be positioned to avoid a ground strike.


Why are aircraft tires not pre-spun prior to landing to preserve them? Why has someone not designed a landing wheel with a fin or fins on it so that the air will start the wheels turning before the wheels touch the ground? Wouldn't that preserve the tires longer from wear? Or would it make the control of the aircraft more dangerous in some circumstances, such as rain or snow, to have the wheels already turning when landing? If so, perhaps the fins could be manually or computer controlled for various weather conditions.

This has been researched over the years, but it seems that the solutions did not find wide application. The oldest I could find is from 1941 (see page 112 in the September 1941 issue of Popular Science), and there have been several attempts to implement a spin-up turbine. See “Wheels with wings” on NewScientist Blogs or “Spin Wheels Before Landing”, a discussion thread on Eng-Tips forums, for more. The biggest problem seems to be the inertia of the spinning wheel because it makes the aircraft react in funny ways if the pilot wants to correct his approach.

The rough field package on the Cessna Citation 500 uses this technique (for the nose wheel only) to protect the fuselage from debris which could be kicked up by the wheel spinup.


Does international mail go in passenger planes? I have a shipment from Canada to South America coming, and it's curious that the "priority" FedEx option takes 6 days to arrive, when there are daily flights between the two destinations.

So I'm assuming mail does not go in airliners.

Am I right, and if so, what's the reason for that? It seems it would be extremely more efficient at least for small shipments.

So I'm assuming mail does not go in civilian aircraft.

Like many thing in aviation it depends. For shipping it will depend on where you are shipping to and from, how big the item is and the chose method of shipment. Both FedEx and UPS (who are private shipping carriers) operate large fleets of cargo airplanes. In many cases a shipment may end up on one of their own cargo planes. However their planes, like passenger planes run routes that may be pre-decided. As such passenger airlines sell the leftover cargo space to anyone willing to buy it. You can find a nice blog post on how it works here. UPS/FedEx may pre-broker a deal to buy a certain amount of cargo space per year from an airline to obtain a better rate or they may buy it on demand as needed.

Now Air Mail is a bit different as its offered (here in the US) by the government postal service. Technically the USPS no longer offer airmail service as it was once called but does still offer domestic and foreign guaranteed time shipping. All of these items are moved in cargo space on Commercial Passenger Planes or by under contract by FedEx as the USPS no longer operates any aircraft.

  Am I right, and if so, what's the reason for that? It seems it would
  be extremely more efficient at least for small shipments.

Like most things in aviation low cost will always beat out marginal efficiency. If FedEx can ship a package at a significantly reduced rate but in turn it will take an extra day or two to arrive than many customers will see a value add in that. In the same vein it would be very efficient to fly every passenger in a small plane to an airport closer to their final destination and have the plane depart when the passenger needs to, however the cost of that simply would never work out.


Does anyone know of sources for ATA 206? I have been seeing references to 206 ATA recently. However, it appears to be so new that very little Google indexed information is available.

Has anyone dealt with this particular  ATA chapter, and if so are there any publicly available resources?

Please note: I am not talking about USS Pinola (ATA-206).

Airlines for America (formerly known as Air Transport Association of America (ATA)) maintains a website for their publications and subscriptions. You can access all/several of their specification documents.

Spec 100 (Manufacturers' Technical Data) can be downloaded from this page, by just paying an exorbitant a minimal fee of $650.

I am not sure which spec contains Chapter 206.


What might a pilot mean by "uncontrollable"? The air safety reports from FlyDubai aircrew leaked to the Guardian contain some alarming stories about crew rostering, tiredness and duty times, but another one caught my eye, a description of an encounter with severe clear air turbulence on a flight from Moscow to Dubai (search for 511 VKO-DXB):

  Aircraft was uncontrollable at time for 10-15 seconds every now and then. Total duration probably around one and half minute.

What does the pilot mean by uncontrollable? That the aircraft wasn't responding to commands and the crew were helpless passengers, at the mercy of the weather, and that everyone survived simply because it didn't go on long enough to tumble the plane out of the sky? Or that it was just being a bit difficult?

"Uncontrollable" is a technical term (actually, in literature it's more often called "loss of control"). It means the aircraft is not responding to at least one normal command. Be it elevator or ailerons or rudder etc.

Really, really good AND lucky pilots can sometimes still control aircraft that's uncontrollable. Either by using another control surface to influence the control desired (eg. by using rudder to get out of a bank) or by using non-primary surfaces like trim tabs or flaps.

When no control input will influence what the aircraft is doing then it's called total loss of control (or totally uncontrollable).


How to calculate coefficient of drag for a particular shape? While working on my project I gave my RC plane's nose a particular shape. It doesn't resemble any simple shapes for which coefficient of drag is provided on Internet.
I don't know simulations.  Also I don't have any wind tunnel facility for my project.  So is there any other way,  any website or any formula for computing coefficient of lift and drag?

There are essentially only two ways to do this.

First you can build a wind tunnel, run experiments and measure the forces involved.

The second is to run a computer simulation. There is software that will do this, but it is complex professional grade engineering software. Free applications are available, but I can't vouch for their effectiveness. You can search for "computational fluid dynamics software" to find options. Adding "free" to that will find you a few cost-free options.

Be aware that setting up and using this software is a complex task that involves creating a CAD model of your shape. You can definitely do the calculation if you are interested, but it's not a simple or quick task.


Does ATC provide ILS frequency and course setting for the runway in use? I'm just from FSX background and not familiar with real procedures. In real world situations, when the pilot is vectored to the runway, does the ATC provide the pilot with the runway frequency and course setting or does the pilot have to know these already from somewhere (logs, FMS, etc)?

I mean in a real world case does ATC say for example "Expect ILS runway 24 left" or do they tell the pilot the nav frequency and course setting too? Or does the pilot obtain the setting for approach like the FSX GPS?

If possible please provide me with a sample communication for landing between ATC and Pilot. (Really curious)

When nearing their destination, pilots will be checking weather and airport information. This will let them know which runways are being used for landings and what type of approaches are being used. ATC will also tell each aircraft what runway and approach they can expect in advance, as in your example, "Expect ILS approach runway 24 left".

Once the pilots know the runway and approach, they can reference the corresponding chart (like the ones in this question). Pilots are required to have these charts available, traditionally paper copies but more recently being replaced by electronic copies. This will give them all of the information about the procedure, including the localizer frequency. Besides programming the frequency, the crew will also review the other important requirements of the approach and landing.

ATC does have access to this information as well, and can provide it if they feel they need to confirm the pilot has the right frequency, or if the pilot asks.


Why is a strake placed on the fuselage in front of the tailplane on the Hawk aircraft? Why is a strake placed on the fuselage in front of the tailplane on the Hawk aircraft?

You may have noted that the tailplane of the Hawk is a full-flying surface, also called an all-moving surface. When the stick is pulled aft, the leading edge will align with the strake, forming in effect a leading edge extension. This will produce a vortex over the lower surface of the inner tailplane and prevent early flow separation at the tailplane root at low speed.

The obvious next question is: Why is it not part of the tailplane itself? Adding it to the tailplane would increase drag and produce nonlinear control forces. Since it was added later in the life of the design, fixing it to the fuselage allowed to keep the tail surfaces and their actuation unchanged.

Note that early Hawk versions (Mk.1, Hawk 50) lacked this detail. In flight testing, it was found that the Hawk would suddenly nose-dive with full flaps and gear up. This was dubbed "phantom dive". Cutting back the flaps solved that behavior, but later, heavier versions of the Hawk needed more lift, so a different fix had to be found. From the Hawk story by Harry Fraser-Mitchell:

  It was shown with the half model of the Hawk at Hatfield that high
  local downwash at the tail, coupled with the very large nose down
  pitching moment induced by the flap, was causing the tailplane to
  stall on its lower surface, so that it could no longer provide
  adequate balancing power. It needed more lift, extended to higher
  angles of attack.

  In the case of the F-4K Phantom aircraft this was achieved by
  installing a fixed leading edge slot to the tailplane, harking back to
  demonstrations of such devices by Handley Page on wings in the early
  Twenties! A fixed slot with its associated drag was not an option on
  the Hawk although a cambered tailplane was tried on the model with
  some success. Removal of the outboard vane of the flap reduced the
  flap pitching moment to such a value that the standard tailplane could
  cope, so this was the quick solution for the RAF. However, for the US
  Navy VTX project, (and for later combat versions of the Hawk) the
  maximum possible lift was required, so that at least the outer flap
  vane had to be replaced. The dive phenomenon had to be fixed.

  An example of the cross-fertilization of knowledge due to the matrix
  working of the design department now occurred. Barry Pegram, then
  Section leader of the Fluid Dynamics section of the Aerodynamics
  Department, had been working on the adoption of leading edge root
  extensions (LERX) for the “Harrier” wing, and this work had shown that
  these devices extended the lift of the wing to higher angles of attack
  by virtue of the non-linear lift developed by the vortex flow they
  created. He proposed that these should be added to the tailplane of
  the Hawk model, but this would have had a serious effect on the
  tailplane hinge moments. The author, who was working with Barry in the
  V/STOL tunnel at Hatfield, suggested that the ‘tailplane canard vane’
  (TCV), as it was called, could be fixed to the fuselage at such a
  position that it was lined up with the flow at normal conditions, but
  with its trailing edge adjacent to, with a small clearance, the
  leading edge of the tailplane at its maximum nose down position.

  Experimenting showed that these vanes could be made quite small and
  they gave a complete cure to the problem in the wind tunnel, with very
  little drag in the normal flight regime. To prove the concept in
  flight, some temporary vanes were manufactured which could rapidly be
  fitted to one of the test aircraft which had flaps with the full vane.
  First, the aircraft was flown without the TCV to establish the
  conditions under which the ‘Phantom Dive’ occurred on that particular
  aircraft. On a later flight, the TCVs were fitted and the aircraft
  flown again to the identical conditions as before. Despite every
  attempt by the pilot to instigate the phenomenon, it did not occur –
  the vanes were a complete success, even though they looked
  inconspicuously small for such a large effect.


Why are cambered airfoils used for horizontal stabilizers in some designs? From what I know, usually NACA9/12 or similar symmetrical airfoils are used for the tail.

Still some aircrafts use highly cambered airfoils for elevators.

What are some advantages and disadvantages of this configuration?

It's done to get a little more lift coefficient, and hence more tail downforce power, at low speeds and there is a drag penalty to take depending on how much camber.  The Zenith STOL family are the extreme example, and being draggy flying lunchboxes anyway, the penalty is minor in relation to the benefit and allows a smaller, lighter tail unit than would be needed otherwise.

Some high performance and transport aircraft have cambered airfoils for the tail but the amount of camber is subtle (a bit more curvature on bottom than top) and you can only tell if you can see the actual airfoil profile, or examine the surface up close.


An airplane has an engine that pushes its flight. What force pushes a glider to fly? An airplane has an engine that pushes its flight. What force pushes a glider to fly?  Is it gravity? I think the flight of a glider is driven by gravity, but some people disagree with me. They say gravity acts vertical, it has no component in the horizontal direction. Am I wrong?

Please note that this question is not specifically asking about what (thrust-like) force acts opposite to the drag vector.  The direction of a glider's flight path as viewed from the earth may not necessarily be opposite to the direction of the drag vector-- for example, the glider may be travelling horizontally over the ground at constant altitude, or may be rising straight up in ridge lift or wave lift-- and this question may be construed as asking what force is pushing the glider along the direction of the flight path as viewed from the surface of the earth.

Airplanes do not fly because of their engines. Airplanes and gliders both fly because their wings turn thrust into lift and drag.

That simplistic answer, of course, just begs the question "how can you generate thrust without an engine?"

A glider is constantly trading altitude (potential energy) for airspeed (kinetic energy). Energy over time equals force, which in this case we call thrust. Airplanes do the same thing when descending. Both can also trade energy in the opposite direction, but only briefly until the wings stall.

The big difference is that an airplane can also turn fuel (chemical energy) into thrust, which allows sustained level or climbing flight. Gliders don't have that option.


What are the main obstacles to becoming IFR-rated in USA? Compared to getting a PPL, is it hard to become IFR-rated in USA, and if yes, why?

I recalled from the late 90s and early 2000s a statistic that said there are two GA accidents every three days.

And from a quick research into VFR into IMC, it turns out "nearly half of all weather-related accidents happen as a result of continued VFR flight into instrument meteorological conditions (AOPA)."

Revisiting the former statistic, it turns out for GA, "There is one fatal accident involving LOC [loss of control] every four days." And "a failure to recognize deteriorating weather continues to be a frequent cause or contributing factor of accidents (FAA, 2018)."

Combining the AOPA and FAA figures, and sad as it is, one can say that once every week or two, a fatal GA accident happens due to entering unanticipated IMC.

I'm hoping for an answer based on studies or experience (which may even draw from knowing VFR-only pilots who did not become IFR-rated, an experienced CFII for example). The reason I ask, I'm looking for some explanation to that statistic, by starting with the obstacles to getting IFR-rated.

The problem is an instrument rating is expensive, time consuming and requires much more - expensive - proficiency related activity. If you are only flying 20-50 hours a year like most PPLs, it's pretty hard to come up with a "business case" to spend the 10-15 grand for getting one if you're not doing serious travel regularly, just from the standpoint of return on investment, let alone staying proficient.

In other words, the majority of PPLs simply don't fly enough to justify an IR.  The majority that do usually have their own a/c and use it a lot on business, or it's a stepping stone on a career progression.  And even if you have an IR, if your airplane doesn't have airborne weather radar and equipment for flying in icing, you are still pretty limited in your travel at certain times of the year (generally, to under the freezing level and far away from convective weather unless you like taking chances).

If you study a lot of VFR/IMC accidents you find that it's mostly people doing VFR travel for extended distances and time frames.  A light aircraft being used for travel in VFR weather is a very unreliable travel method and pilots have to accept that; too many don't.

So the big problem is people don't allow for weather delays in schedules, so they push weather to get home.  If you travel places VFR for time frames beyond the next day or two (about the limit you can depend on forecasts most of the time) you have to treat it like flying standby on the airlines; always ready to wait a day or two to get where you're going.  When you build this into your planning (like planning to be home 3 days before you have to return to work instead of the day before) you can relax a bit, and the risks of getting caught in a get-home-itis trap go down dramatically.


Why don't Russian aircraft sell as much as their European/American counterparts? Are there any reasons other than political why Russian jets don't sell?

For a case study, let's compare Sukhoi Superjet and Mitsubishi  Regional Jet. Despite being delayed several times, Mitsubishi has secured more orders than Sukhoi. Similarly, Embraer and Bombardier aircraft sell much more than the Sukhoi Superjet. Many new airlines continue to go to with Embraer and Bombardier. Despite promising lower running, maintenance, purchasing costs, why doesn't this aircraft secures orders?

If you take out the political angle (which is by far, the most important), there are a number of reasons for this.

Basically, the Russians have a serious image problem. Russian (and Soviet) aircraft have a reputation for poor quality, reliability and safety issues. This will take a long time to fix. In contrast, Japanese have no such problems (In fact, the MRJ boasts of 'legendary Japanese reliability')
It is not easy to make airlines switch from an existing aircraft. Most airlines have a huge system built around the aircraft they operate (In fact, quite a few regional carriers operate only a single aircraft type). It would take enormous amount of investment in time and money to shift to a new aircraft and it would take a large incentive for them to put their eggs in a new basket.
US is probably the most important market at present and operating there gives other airlines a lot of confidence to buy the jet. If you see the orders for MRJ, most are from US (In fact, almost all orders are from either US or Japan). The Superjet, in contrast, hasn't even applied for FAA certification as far as I know.
Promising and delivering lower costs are completely different things. Airlines are more prone to believe companies that have a proven track record of manufacturing civil aircraft than a newcomer.
The Superjet is the first airliner to be developed in Russia since the end of cold war. As such there are questions about its industrial capability and quality control processes. Mitsubishi, on the other hand is engaged in a number of aircraft projects (it makes more than a third of 787 structure).
Sukhoi has to build a supply chain and support system from scratch (Superjet has a number of foreign components). Again, in the extremely cost sensitive airline industry with tight schedules, there is a perception that the Russian aircraft will not be supported as well as their western counterparts (For example, Boeing boasts of a >99% dispatch reliability for 737)


Can TCAS give an RA for one aircraft and a TA for another? I am an air traffic controller and I had the following situation. Traffic maintaining FL360 and below him traffic at FL350 requesting FL370. Once they crossed each other I gave clearance to climb FL370 with 5.1 nmi separation. The guy read back the clearance and said he received a TCAS RA, the guy at FL360 said he received a TCAS TA. Does this make sense?

It's hard to give a definitive answer without more information.  My go-to for TCAS details is the FAA's Intro to TCAS II. In general, an RA will try to coordinate with the other aircraft, but such coordination doesn't require the other aircraft also issue an RA, it only listens for other RA "intent" messages and makes sure it doesn't issue a conflicting RA.

Here's some possibilities:

A marginal RA encounter.  Each airplane has slight differences in calculation , so, as the FAA manual linked above reads, "In a majority of the TCAS/TCAS encounters, the two aircraft will declare the other aircraft to be a threat at slightly different times"
The TCAS of one aircraft was set to TA-ONLY, although this normally only happens if the airspace is busy
One had an inaccurate pressure altimeter reading
Thresholds are larger at higher altitudes and this could have contributed to the higher altitude pilot receiving only a TA
One airplane was running TCAS I instead of TCAS II and couldn't get RA's.  This is probably not the case if the aircraft was commercial.
They're running different versions of TCAS with slightly different algorithms


What's the preferred approach for a passenger jet? I seemingly can't find an answer to this quite obvious question:
What's the preferred approach procedure for a passenger jet at a modern airport fully equipped for precision ILS (both aircraft and airport): ILS or visual approach?

If it's ILS, what would cause a visual approach to be flown (except for the ILS not working of course)?

If it's visual,

a. why? (ILS seems more secure from my naive standpoint)
b. what would be the cause to do ILS instead? Bad weather / sight for instance?

Is the decision made only by the tower or does the captain of the aircraft have any saying in it?

I'll give the answer from an ATC perspective. A visual approach is the most preferred approach, since we can get aircraft to follow each other, and don't have to worry as greatly about aircraft getting too close. The rules say we can compress under certain conditions to 2.5 miles on ILS or radar separation approaches, but timing wise, for the runway to be clear, you can often need less separation between aircraft to maximize its usage. With the visual approach, you're vectoring to keep aircraft closer so they can see each other and follow in closely to each other to the runway.

In most ATC facilities, the Tower decides what runway to use, and the approach control calls the type of approach generally on offer(this can vary depending on facilities and how they agree to run things). A pilot can always request a different approach... they might be delayed, sometimes significantly if they insist on something way out of the loop.


Do TSA regulations allow CFIs to start training non-citizens before the TSA has approved their training request? 49 CFR 1552.3 says (emphasis mine):

(4) TSA has informed the flight school that the candidate does not
pose a threat to aviation or national security, or more than 30 days
have elapsed since TSA received all of the information specified in
paragraph (a)(2) of this section.

This one implies we can't train until we hear back from the TSA for aircraft that are in "Category 1—Regular processing for flight training on aircraft more than 12,500 pounds".
However, the section on "Category 3—Flight training on aircraft 12,500 pounds or less" says:

(4) The flight school begins the candidate's flight training within
180 days of the date the candidate submitted the information required
under paragraph (a)(2) of this section to TSA.

So that tells me that as long as the information is submitted, we can begin training a non citizen immediately (for less 180 days).  What is the point of this?  Where is the security?  Is this correct? Or is it just another confusing regulation?
What is the current industry practice? Do CFIs provide the training in this situation? Or are more TSA checks initiated?

This is addressed in the AFSP Candidate FAQ, which confirms that you can start training in category 3 as soon as all information has been submitted:

How long should I expect to wait after I have submitted my training event request?
[...]
Candidates in Initial, Instrument, and Multi-Engine training (category
3) may begin training as soon as AFSP receives all required
information, including the candidate's passport, fingerprints, the
fee. You and the provider will be notified once AFSP receives the
fingerprints and you have been granted Permission to Initiate
Training.

That's also what the regulation says, but the FAQ may be a little clearer.


What is the relationship between blade inertia and rotor kinetic energy? As far as I know:

High blade inertia provides good pilot intervention time (the time
between recognizing engine fail and pushing the collective down).
High kinetic energy allows for a soft touch down after flare in
autorotation.

What is the relationship between blade's inertia and rotor kinetic energy?

The relationship between blade inertia and rotor kinetic energy is:

$$K = N\frac{1}{2}I\omega^2$$
$$I = \int mr^2dr$$

Where:

$N$ is the number of blades
$I$ is the moment of inertia of a blade
$ω$ is the rotational velocity (rotor rpm)
$m$ is mass
$r$ is distance from hub along the blade

For a fixed RPM increasing the moment of inertia of the blade increases kinetic energy of the rotor. An increase of the moment of inertia can be obtained by increasing the mass of the blades (inefficient, rotor gets heavy and requries more power from engine, less payload, etc.) or by placing relatively small masses at the tip of the blade.


What type/model of plane is this? I came across this photo but it doesn't have any other info. What type of plane is it? Also, is it some sort of seaplane perhaps? I say seaplane because it was tagged with the word "seaplane". Seems Cessna-ish to me but I'm clueless beyond that. Is it possible to identify the exact model?

It looks like a Cessna 208 Caravan to me:

These are single-engine high-wing turboprops, useful for a variety of cargo and passenger-hauling tasks. Here's what a 208 in seaplane configuration looks like on the outside:

Your photo looks like an older plane with the original radio stack and no glass, unlike these newer cockpits. In addition, somewhat startlingly, the right-hand control column and yoke have been removed, but they bothered to keep the copilot's 6-pack. That's odd, from my sensibilities, and it tells me the plane was altered in the cheapest possible way for use as a pure short-range passenger ferry. The right-hand seat can now accomodate an extra passenger (and becomes the best in the house for enjoying the view), without the possibility of that non-flier binding up the pilot's controls.


What is a "slender delta" wing? I am curious about delta wings. I read some articles and found the term "slender delta". Please help me to understand this term.

A slender delta wing is a delta with low aspect ratio.

The use I have seen is in the study of vortex lift, which is present at high angles of attack.

What is vortex lift?


From which aircraft are these parts (plane crash on "Dallas" TV series)? I'm trying to identify the aircraft in this scene from episode # 014 <2.09> entitled "Survival" of the classic "Dallas" TV series (filmed and broadcast in 1978), which featured the debris after a plane crash.
The footage was reused in 1984 as "a day for night" shot for another plane crash in a "Falcon Crest" episode, so this is the last aircraft missing in the "Falcon Crest" database I'm programming.
Please note:
I am not sure if the production company used parts of a real aircraft to stage the scene or if this is a complete mock-up.  The "SF" logo (for "Southfork Ranch" on "Dallas") is definitely a prop the movie studio’s art department added to the debris.
I have no idea if it is possible to get any clues from the debris about the make and model these parts might have come from  --  if these were real airplane parts at all.
Any input is appreciated.  Thank you so much for taking a look!

I think, based on that tail section, that it looks a lot like a Stinson 108-3.  They had large metal tails with horizontal corrugation.
The position of the rear nav light and trim tab (just above the light) allows for enough room below the light for the six rows of corrugation that I count in photos of other 108-3s.
The position of the tail wheel fits, too.  It is not too long but it is easily noticable and not buried in, or up close to, the tail.
The wings are metal with fabric covering.  108s were all metal and covered with fabric, except the tails.
The only thing that does not seem to match is the wing rib.  The Univair website images for 108 wing root ribs have a very similar outline but do not have what appear to be four holes near the rear edge.  They have a single large hole instead.  Univair may be selling improved parts, however, and the rib in the video may be a factory original -or- a field manufactured piece as part of a repair that does not match the original.


If the previous 100 hour was overflown but not for hire, is the time still subtracted from the next 100 hour? A rental plane at a local FBO had an annual inspection at 2345 hours on the Hobbs. The next 100 hour inspection wasn't completed until 2450.

If the current hobbs time shows 2547, would it be legal to take the airplane for a 2 hour flight lesson with an instructor?

Also, does the legality of this situation change depending on whether the 5 hours between 2445 and 2450 was with an instructor or not?

According to FAR 91.409 b, the 100 hours can be overflown by ten hours in order to fly the plane to a place where the inspection can be performed, but this time must be included in the next 100 hour period.

If the five hours over the designated 100 hour time limit was for hire (ie not flying the airplane to somewhere the inspection could be performed) then they were technically illegal. And no, that wouldn't change the fact that you must count those hours in the current 100 hour cycle.


Can a gyro-copter soar? If one centers the gyro-copter in a thermal and then simulates a hover facing headwind; can the gyro-copter climb up like that ?
Is it technically possible or is it advisable....

Any aircraft, from a helicopter to a 747, can soar.

All it has to do is enter and maintain its position in rising air. How the pilot accomplishes that would be based on picking a strategy for staying in the rising air, and using his skill to do it.


Do commercial flights continue with an engine out? Do commercial flights continue with an engine failure? If you look closely at the attached picture it seems that one of the engines has a much smaller contrail than the other three. This seems to suggest that the aircraft is flying on three engines with the one at reduced (idle?) power. Is this normal?

The image looks like four engines running at the same cruise thrust. The wake vortex is blowing the exhaust of the inboard engines down and the exhaust of the outboard engines out and in the perspective of this image this makes the lower two streams look merged while the upper ones further apart. Close behind the engines it is clear there is four of them and all have similar strength.

That said, a four-engine aircraft may continue on three engines as far as it has enough fuel and there is no other damage (so not if the engine flamed out after a big bang). With one engine out it can't maintain as high altitude, so it has to drift down to lower altitude where it flies slower and thus has shorter range. However if they have enough contingency fuel, they can continue to destination. Or return back to departure point, or proceed towards the destination, but land somewhere short. The dispatcher will consider the repairs, taking care of the passengers, rebooking them, the next flight the plane was scheduled for and other things and tell the pilots which is the preferred option.

In contrast a two-engine aircraft shall land as soon as possible. One engine out of two means there is no redundancy left and that is an emergency and shall be handled as such. Note that as soon as possible does not necessarily mean closest airport—the aircraft will cover over 100 NM during normal descent from cruise altitude, so if there are more options in about 150 NM, the pilots and dispatcher still get to choose.


Does intake mass-flow rate vary linear proportional with turbine fan speed? Is jet turbine intake mass-flow rate linear proportional with its fan speed (N1)?

Not linear, because the back side of N1 will influence the flow. Not only that but the flow is non linear with respect to rotation in most axial flow compressors.

Is there a specific engine or cycle that you are wondering about, because that changes the answer to your question?


Is there a real temperature change along a streamline when its velocity changes? Stagnation enthalpies are given as

$H_T=H+\frac{v^2}{2}\ $

Along an adiabatic inviscid steady flow streamline Stagnation Enthalpies are said to be constant.

$H_{T1}=H_{T2}$

$H_1+\frac{{v_1}^2}{2}\ =H_2+\frac{{v_2}^2}{2}\ $

$H_1-H_2=\frac{{v_1}^2}{2}\ - \frac{{v_2}^2}{2}\ $

$H_1-H_2=\frac{{v_1}^2-{v_2}^2}{2}\ $

Stagnation temperatures are  also constant

$T_0=T_1+ \frac{{v_1^2}}{2CP}$

$T_0=T_2+ \frac{{v_2}^2}{2CP}$

$T_1+ \frac{{v_1}^2}{2CP}=T_2+ \frac{{v_2}^2}{2CP}$

$T_1-T_2= \frac{{v_1}^2}{2CP}- \frac{{v_2}^2}{2CP}$

$T_1-T_2= \frac{{v_1}^2-{v_2}^2}{2CP}$

In both of these equations there is derived a notion of a static enthalpy and static temperature at a point of interest along a streamline. These can be different by the value of the flow velocity v

This is stated to be applicable to compressible and incompressible flow

Is it correct to say that there is a real temperature change $T_1-T_2$ along a streamline when its velocity changes?

Don't know what you mean by real temperature. You will certainly experience a change of static temperature in an adiabatic flow if the velocity changes.
Stagnation enthalpy describes the total energy contained in the fluid which comprises inner (thermal) energy, kinetic energy (and potential energy which is often neglected). Stagnation enthalpy is constant for an adiabatic flow with no energy exchange. Thus, thermal and kinetic energy are antagonistic in the sense that increases of the kinetic energy need to be countered by reducing thermal energy in order to keep a constant value of total i.e. stagnation enthalpy, and vice versa.
The stagnation temperature of a fluid is a virtual entity, temperature entities that are observable i.e. measurable are static temperatures. However, in a stagnating point the static temperature ideally features the value of the stagnation temperature.
Back to your question: If you measure temperatures in an adiabatic flow at points of different flow velocities, you will experience different temperature readings. Your measurement setup has to ensure that your readings are not falsified by slowing down the fluid at the points of measurement.


What ISA temperature to use in the density altitude calculation? In the density altitude formula: DA = PA + [120 x (OAT - ISA Temp.)], should one use the ISA temperature at the field elevation or the ISA temperature at the pressure altitude?

Calculating Density Altitude

Density altitude in feet = pressure altitude in feet + (120 x (OAT - ISA temperature))

Altimeter Pressure altitude is determined by setting the altimeter to 29.92 and reading the altitude indicated on the altimeter.
OAT stands for outside air temperature (in degrees Celsius).

ISA stands for standard temperature (in degrees Celsius).

Keep in mind the standard temperature is 15 degrees C but only at sea level. It decreases about 2 degrees C (or 3.5 degrees F) per 1,000 feet of altitude above sea level. The standard temperature at 7,000 feet msl, therefore, is only 1 degree C (or 34 degrees F).
For example, the density altitude at an airport 7000 feet above sea level, with a temperature of 18 degrees Celsius and a pressure altitude of 7000 (assuming standard pressure) would be calculated as follows.

18 – 1 = 17
17 x 120 = 2040
2040 + 7000 = 9040 feet Density Altitude

This means the aircraft will perform as if it were at 9,040 feet


How are APUs started? How are jet engines started? says that engines must be started from bleed air, which can come from the APU, another engine, or a huffer cart, or from windmilling.

As far as I understand, APUs are also jet engines. How are they started? In the air, they must be able to start when both engines are out, so are they able to windmill start? On the ground, can they connect to a huffer cart?

APUs are like small jet engines, small enough to be started electrically. So you would use the power of the battery or an electric ground power cart to spin up the APU by its electric starter motor, and then introduce fuel into it once its spinning fast enough, just like a jet engine is started. Depending on the design, the electric motor will then either act as a generator to supply electrical power back to the aircraft or decouple when a separate generator is used.

The APU will spin up, and besides spinning the electric generator, some pressurized air will be 'stolen' from its compressor to supply "bleed air" for engine starting, the air conditioning packs, etc...

Big APUs like on the Boeing 777 have actually two methods of starting: They have both an air-driven and an electric driven starter motor. The method of operation is as follows: When the APU is started with the engines off, electrical power from battery or ground connection is used. After the flight, the APU will be restarted before the main engines are turned off. In that case, the APU will be started by the air-driven motor rather than the electric motor, with pressurized air supplied by the still-running main engines.

EDIT to answer question in comment:
Depending on size, the APU will take something between 30seconds and 2 minutes to start. The big APU of the 777 will deliver electrical power after 2 minutes or so, small units you are likely to find on regional jets can do that after perhaps 45 seconds. Then, it takes an additional 2-4 minutes until you can extract bleed air from it. That is because taking air from the compressor increases the exhaust gas temperature of the APU, and you want the APU to warm up evenly. The same is true for the shutdown process: You close the bleed-air valve and then let the APU continue to run for another two minutes or so to cool down, then shut it off completely. This lowers the thermal stress on the unit. On modern planes like the 777 this process is automated: You turn the APU selector switch to OFF and that will close the bleed air valve, initiate a 2 minute cooldown period, and eventually turn off the APU completely. The only way to shut it down immediately is in fact the APU FIRE handle.
So, you will turn the APU on typically while you are taxiing in after landing. Because of course you want it to be up and running and ready to take over the air conditioning by the time you are at the gate.
Some APUs like those found on the MD-80s have two settings for bleed air extraction: NORM and ECON. ECON takes less bleed air, thus not increasing the exhaust gas temperature of the APU too much. On particularly hot days, using the APU bleed in ECON might help not overheating the APU if it is to be used for an extended period of time.


How does a self-centering rudder affect left-turning tendency? In this answer to a question about controls, Peter Kämpf mentions the Klemm 35:

  ...the rudder has two narrow strips which are deflected slightly to the left and the right, respectively. This increases the force gradient over deflection for the first few degrees when the rudder is moved away from its centered position.

How does this interact with left-turning tendency coming from the engine slipstream? Normally, small movements of the rudder are needed to counteract the effect of the slipstream on the fin, so increasing the force required for small movements would seem to hinder rather than help the pilot.

On the other hand, I'd expect the right-pointing strip to be in the lee of the fin (as the slipstream passes left-to-right over it), which would reduce the force on it, letting the rudder move a little to the right on its own, which is exactly what you want.

What actually happens? Does the neutral position of the rudder change at different power settings when flying straight and level? Does this arrangement reduce your foot workload compared to other aircraft?

First, "adverse yaw" refers to the increased drag of a down aileron (and reduced drag on an up aileron) -- which mean that as you deflect the ailerons to roll left (in order to turn left), the adverse yaw makes the nose yaw right -- exactly the opposite of what you want. Therefore you balance any application of aileron with just the right amount of rudder to counteract the adverse yaw. This is called "coordination".

For any control surface (like rudder or aileron) there is a small "dead zone" around neutral, where movement of the surface does not have an appreciable aerodynamic effect. Those narrow strips reduce the size of that dead zone and improve control. Therefore they help, not hurt.

What you're talking about is what the FAA (and others) call "left-turning tendency". When flying straight and level, the engine power affects the amount of rudder required, and significantly so. At high power more right rudder is required, and especially so at low speeds like climbing. At low power settings less right rudder is required, especially at high speeds -- so in a descent many aircraft require left ruder to straight. (Of course this is most applicable to single-engine airplanes where the fin is in the propwash.)

To help the pilot with the forces required, surfaces have trim tabs -- see Why Pitch Trim Up/Down & Roll Left/Right switches on yoke or control stick?

(Incidentally, many older small English engines like the dh Gipsy engine, https://en.wikipedia.org/wiki/De_Havilland_Gipsy_Major, turn the opposite direction so airplanes like the Tiger Moth that use that engine have a right-turning tendency and require left rudder.)


How do the Beech Bonanza's ruddervators work? How do the Beech Bonanza's ruddervators work? When the yoke is pulled completely back, is it possible to use rudder?

In the Bonanza, a mechanical mixer controls ruddervator movement based on pitch and yaw commands. Here's a typical V-tail mixer (this is not of a Bonanza though):

(source: eaa1000.av.org)
There are two rods extending off to the left of this photo that connect to the actual ruddervators. Rightward motion of the top rod (due to either rightward motion of the entire mixer assembly due to a pitch command, or clockwise rotation of the assembly due to a yaw command) will deflect the ruddervator one direction; leftward motion deflects it the other direction. Similar for the other ruddervator connected at the bottom.
I can't completely answer the second part of your question, whether yaw authority is reduced when pitching or vice versa. It depends on where the limit stops are installed in a Bonanza. If the stops are set on the ruddervator side (left side in photo above, so that the mixer's range of motion is limited by its leftward connections), the amount of available rudder will be reduced when pitching. (Sorry I can't answer that part of the question, but I thought the information about the mixer would still make a useful answer.)
The airplane is obviously designed so that sufficient authority is available in all situations. (This means making the two fins of the V longer than those of a traditional horizontal/vertical stabilizer design so that similar control surface area is available.)


Are mode C altitude returns valid for aircraft separation? According to FAA JO 7110.65 5-12-8 'Validation of MODE C READOUT', Mode C is valid if there is less than 300 feet deviation from the pilot reported altitude.
If ATC instruct 'A' aircraft to maintain 5,000ft, and its Mode C indicate 4,900ft on radar, and ATC instruct 'B' aircraft to maintain 6,000ft and its Mode C indicate 6,000ft, are A and B vertically separated?
By looking radar, it is 900 feet separation, but pilot reported altitude is 1,000 feet separated.

Yes, they are separated. Both according to mode C (in your example, there is 1,100 ft between them - not 900) and in general. It is normal for there to be small deviations in mode C in the range of 100 to 200 ft. If I have two aircraft crossing each other, supposedly with 1,000 ft in between, but the indicated (mode C) separation is slightly less, I will certainly ask the pilots if they are indeed at their assigned altitudes. If they confirm, then all is well. A pilot report generally overrules mode C (to the extend where there is even a procedure for asking the pilot to turn off mode C reporting if there is a discrepancy between pilot report and mode C).


Why doesn't Ketchikan, AK have a control tower? Why doesn't Ketchikan International Airport (PAKT) in Alaska have a control tower?  The special flight rules applicable to the area (14 CFR 93 Subpart M) seem to make it clear that traffic management is an issue, focusing mainly on being in contact with the Ketchikan flight service station when it is in operation.
The now uncommon situation of an On-Airport Flight Service Station as noted in AIM 4-1-3 would seem to be in force here, but in Ketchikan, it appears that under the SFAR, seen in Ketchican FSS Information, participation is mandatory.
With mandatory participation, what separates Ketchikan from an airport which would normally be served with a control tower?  Does it not quite qualify based on traffic?

A tower can only control what it can see, visually or with radar. The traffic in that area is at low altitude and landing or taking off many places that are not the central airport, much is VFR and not inside the space of a class D tower.


Were my airplane's wheels under-inflated? I recently took a flight on a (Lufthansa) Bombardier CRJ900 aircraft. As I was about to embark, my eyes caught this image:

And the aircraft wasn't even loaded with the passengers yet. If I saw this in a car, I would assume a flat tire or other loss of air pressure...were these wheels under-inflated?

It's absolutely normal. Above is how the manufacturer even depicts the nose tire in the airport planning manual (.pdf, page 42).

The pressures are checked by line engineers typically before leaving the hub, as well as an inspection by a flight crew member before every flight.

While not available on the CRJ900, there are many jetliners that have tire pressure sensors. See:

Do airliners or business jets have brake temperature sensors? (image of such cockpit display)
How do tyre pressure sensors in aircraft work? (how they work)


How to achieve shorter taxiing time by elongating the airfield What about doubling the length of airfields in order to shorten the time it takes for a plane to roll on the ground after landing and before takeoff. The plane could take off from the middle of the air-lane and when it lands it can turn off in the middle, in order to minimise the driving time to and from the terminal. Why don't we see this and what does it take to achieve it?
I had expected a calculation as an answer to this question. Taxiing takes 23 minutes. In Sweden savings for private travel is evaluated to €4 per hour and $20 for business.

The cost is that it would required a runway twice as long.

Airports already take up enormous amounts of land. Designers try to build airports near major centers, so taking up twice as much valuable land for longer runways near a major population center is a huge cost.

The longer runways also need to be cleaned, maintained, and snow-plowed.

That is a lot of cost and difficulty just to reduce taxi-time by a couple minutes.   After one has taken a 2 hour cross-country flight, 5 minutes of taxi-time is not a point of concern.


Would turbulence created by two jumbos less than 100ft apart cause both of them to crash? In a scene from Spider-Man 2 (2014), which you can see in this video, two jumbos almost collided. At the last possible moment, the pilots were able to save their planes, but both planes came to within 100 feet apart from each other (I guessed the distance). Both planes survived.

I wonder in real life with real science and no Hollywood involvement, could any plane survive this close encounter with another jet?

The probability of two jets surviving such a close encounter are extremely remote.

Setting aside the fact that it is difficult to imagine two aircraft flying in the same altitude in opposite directions (commercial aircraft are separated by 3 miles laterally and 1000 ft. vertically) ,if the scenario unfolds as in the movie and the horizontal separation between the aircraft on approach is as shown, the pilots would not have time to react and take the necessary evasive actions.

Assuming that the jets are cruising towards each other at 900 kmph, the combined speed is around 1800 kmph, or half a kilometer per second.

If the TCAS is not working and the aircraft come within five km (the distance in the video is considerably lower, less than a km) of each other, the pilots have less than 10 seconds to get out of each other's way.

The civil aircrafts are not designed for such rapid roll rates. The inertia of the aircraft (especially the 747) will limit it.

Another thing to note is that the modern flight control systems will not allow airline pilots to carry the maneuvers shown in the flight. The pilot can override the Flight control Computer.However,in this case, they would not have time to react.

If by some miracle the aircrafts cross each other, they will fly right into the other aircraft's wake turbulence, which will have disastrous consequences, especially for the smaller aircraft.

Sources: airpower.maxwell.af

In case of small aircraft flying behind a heavy jet, FAA regulations require a minimum separation of 5 miles, lesser than which the effect of the wake turbulence (wingtip vortices) can have serious consequences.

Source: Aeronautical Information Manual

FAA conducted a test on the effects of wake turbulence by flying a 737 behind a 727, which shows the loss of control associated with flying in the wake of another aircraft.

Once (if) the aircraft pass each other, they should be brought to level flight as quickly as possible (whether it is possible or not is another question) to prevent stall. In this critical juncture, if the aircraft wings encounter wake turbulence, the control of the aircraft will be loss, resulting in stall.

Finally, in case two aircraft do approach each other in the same altitude in opposite directions, there are laid down procedures to follow. None of them involve the stunt shown in the movie.

When two aircraft are flying head on, each must move to their right.

Source: planefinder.net

If two aircraft are at the same height and on converging courses, the aircraft with the other on its starboard side has to give way.

Source: planefinder.net


How much runway is needed for comfortable operations in a PC-9? I am familiar with simple single engine props and twins and am thinking of moving up to turboprops like a Soccata TBM 700 or Pilatus PC-9.

How much runway do aircraft like these need to operate comfortably? (think grass strips with trees at the ends). By "comfortably" I am not talking about test pilots in perfect conditions. I am talking an amateur pilot on a windy, rainy day with enough runway that he won't be shaving bird nests out of the trees on takeoff.

TBM quotes the distances for the 700 at

  Take-off: 2,133 ft (650 m)

  Landing: 2133 ft (650 m)

And Pilatus for the PC-9

  Take-off distance over 50 ft obstacle at sea level: 1,300 ft (397 m)

  Landing distance over 50 ft obstacle at sea level: 2,255 ft (687 m)

The PC-9 and TBM 700 are very different beasts (did you mean PC-12?)

comfort is about you the pilot and there are some pilots who operate right down to book minimums. Like anything else in aviation the pilot is the ultimate decider and you can operate both of these planes off a 2256 foot strip in clear weather. I'm not sure I would. I would think 3000ft. is enough to comfortably fly either of these planes. The FBO I rent from at KDYL flys King Air 200's out of there all the time and they only have 3000 ft there. For planes like this, considering their common missions I would also look for a strip with a solid IFR approach, sells Jet-A on the field, enough ramp room to fit your plane, and taxiways wide enough for your wing span as well as sufficient runway length. Its also going to take a lot more than "familiarity" with single engine prop planes to move up to a turbo prop.


Why doesn't F-15 have a protruded cone at its rear like what the Su-35 has? Why doesn't F-15 have a protruded cone-like structure at its rear like what the Su-35 has?

Left one is Su-35. Right one is F-15.

This is Radar Warning Receiver.

Where is F-15's RWR?

As @RalphJ notes, it is not required. It is a design choice based on various considerations. The 'cone' in the Su-35 houses the RWR and the drogue chute. In case of F-15, however, the drogue chute is not used and the RWR antennae are located elsewhere (in the wing and vertical tail tips, to be exact).

The image below from a BAE systems document shows the integration of AN/ALR-56C Radar Warning Recievers in the F-15 A/E aircraft.

Integration of AN/ALR-56C Radar Warning Receivers on F-15; image from BAE systems


How close are planes allowed to fly next to each other? I have a question - how close are planes allowed to fly when their paths are about to cross? I am sure there are proximity warnings and what not but I also know those accidents happen, even if not that often.

I was on board of a KLM flight from Amsterdam to Madrid and sometimes in the later part of the flight, if I recall correctly, another plane, flew just below us. Of course, I imagine human vision, mine included, is probably not the most reliable source. However, I saw the plane and in less than 1 second it speeded right below us, so I imagine that it was quite close. However, I felt no turbolence after it passed.

Given that description, can you let me know your thoughts - how close in reality it was? Of course if it helps, I can give you the flight number and day.

Your plane was at least 300 meters above the aircraft you saw.

The limits are determined by the altitude and capabilities of the aircraft.

Up to 29,000 ft - 300 meters vertical separation
29,000 ft and above - 600 meters
29,000 - 41,000 ft (where there is RVSM (Reduced Vertical Spacing Minima)), the minimum separation is 300 meters, but the aircraft have to be equipped with specific instruments. Most modern airliners are equipped to fly in RVSM approved airspace.
41,000 feet - 60,000 ft, 300 meter RVSM
60,000 feet and above, 1.5 KM irrespective of RVSM

You won't feel turbulence unless you are flying behind an airplane, or you fly into an airplane's wake.  Turbulence happens in disturbed air and this is usually behind the airplane's wingtips.

All modern airliners are equipped with TCAS (Traffic Collision Avoidance System); which consist of visual indicators on the relative position of nearby aircraft.

Here is an image from flightgear wiki that shows how this looks on some modern airliners:


Why do countries place limits on what foreign-registered aircraft can do? Just read in local news Israeli regulator is giving a hard time on a company operating regularly out of Israel a plane with foreign (US) registration.
The company wants US registration to get better freedom to fly to various countries. This I understand. But what difference does it make otherwise? Why would the regulator care, and make it difficult to operate regularly without local registration? Are such limitations common in other countries?

Perhaps the biggest reason for this is that countries have different standards of safety.
One example, is a few years ago, Cessna recommended that basically all their piston aircraft have a thorough maintenance inspection known as a SID once they reach 20 years of age. The FAA didn't feel that these inspections justified the fairly considerable cost. Other countries though - Australia, NZ, Germany come to mind - felt the manufacturer knows best, and made the inspections mandatory.
This is just one example of the broader problem of differing standards throughout the world. When an aircraft gains Israeli registration, it must comply with all local laws and airworthiness directives, giving authorities confidence that their standards are being met. Being locally registered also makes it easier to track movements and to target inspections. There could also be tax implications too, as it would become a local asset.


How is the amount of time for an A check or daily maintenance determined? How can the time for daily maintenance or A Check be calculated for different aircraft types?

Is there any exact formulation depending on the aircraft specifications?
 P.S.,I'm very new to the aviation field.

This answer is not specific for A-checks, but covers the whole maintenance effort.

Try Eddins-Earles, Mary: Factors, Formulas and Structures for Life Cycle Costing, Eddins-Earles, 89 Lee Drive, Concord MA 01742, USA, 1981

It's a bit dated, but has a wealth of data.

Another source would be Fabrycky, Wolter J.; Blanchard, Benjamin S.: Life-Cycle Cost and Economic Analysis, Prentice-Hall International. ISBN 0135383234.

Also, the white volume (I think it is No 8) of Jan Roskam's collection is a good start. Roskam, Dr. Jan: Airplane Design, Roskam Aviation and Engineering Corporation, Ottawa, Kansas 66067, USA, 1990.

Generally, this is not exact science, so exact times cannot be expected. With experience, each operator will be able to estimate how long things take, but you do these checks to find possible damage which needs to be taken care of. A lot depends on the training and experience of the maintenance crew. The best way to approach this is with statistics.


For how long after the last A380 delivery does Airbus have to provide spare parts for it? After Airbus's announcement that they plan to discontinue A380 production in 2021 after the last orders are filled, how long will they have to guarantee the availability of A380 spare parts?

When a company decides to terminate the construction of a specific airplane, then this company needs to follow some conditions. In the contracts between Airbus and airline companies, there are many conditions concerning multiple aspects.

There are conditions for example about:

spare-parts availability
transfer knowledge about specific features of the airplane
training (not for all the occasions)
and more (we are not in a position to know them all and in detail)

These conditions are discussed in the beginning, before the signing of the contract. Of course, conditions may differ from one contract to the other, but I think you got the point behind this idea.

So there is no way that someone will tell you what will happen between Airbus and their clients because this information is confidential. As soon as, the clients of Airbus do not sue them, then their contracts are including mechanisms about this.

Lastly, these contracts most of the time are including basically conditions about safety or financial sections. There is coming the role of ICAO, IATA, EASA, FAA and more. These organizations are responsible for managing properly also the sector of safety/security. The fact that spare-parts availability is playing vital reason in the safety of the passengers among the world, then it is 100% sure that they also know about it and they know how to handle it.

Hope that I helped.


What are the role and responsibilities of "fleet captains"? I understand that fleet captains are usually experienced airline captains that take over this management position and deal with training, staffing and administration of a particular aircraft type (or family). Can someone elaborate on the actual duties of fleet captains?

Besides the respective responsibilities, do they to a certain extent have directive authority over all pilots flying the respective aircraft types (like being their direct boss)?

A fleet captain basically deals with fleet specific issues. For instance if a new procedure is introduced in the company how is this going to be implemented on the fleet. The most recent example in my company has been the implementation of "RNP" approaches (GPS only approaches) that was introduced across the company but what does it mean for our fleet; where is this displayed on our specific aircrafts what calls should be made depending on the various cues we getting our aircraft etc...this is the kind of answers the fleet captain would have to give to the Chief Pilot in the this example the training department would be heavily involved as well with the respective CFI's(Chief Flight Instructors) again fleet specific. Depending on the company structure the fleet captain might be associated with daily issues or even disciplinary procedures in association with CP, HR etc...
Hope that helps :-)


On the V2533 engine, what protections do the FADECs provide against uncommanded unstow? An uncommanded reverser unstow at high power is quite a problematic event for a flightcrew to handle, at minimum.  As a result, engine and airframe builders put protection mechanisms in to prevent this -- such as auto-restow functions, and on the CFM56-5, code in the FADEC that automatically rolls back the engine to idle upon detecting an uncommanded unstow.

However, I have not seen any documentation for the A320 family with IAE V2500 series engines that details what the FADECs on those engines do in case of an uncommanded unstow of the reversers.  (The A320 FCOM on Smartcockpit only covers the CFM56-5 equipped versions of the A320 family.)

Can anyone fill me in on this?

Not from an FCOM, but from an A319/A320/A321 IAE V2530-A5 training manual, it's the same thing as the CFM:

  Inadvertent Stowage/Deployment

  In either case the LVDT [Linear Variable Differential Transformer] sensors would detect a movement the EEC
  would execute auto−restow or auto−redeploy.

  If the reverser travel exceeds 15% of its travel from the fully stowed position
  then the EEC will command idle.
  Following restow, full power is again obtainable.


What United States state and federal agencies generally participate in aerial weather modification? Also wondering which agencies regulate weather modification activities? Any idea where I can find more information about this?

The North Dakota State Water Commission runs the North Dakota Cloud Modification Project, which primarily seems to work at reducing hail damage to crops during the thunderstorm season, and has been active (perhaps not continuously) since 1975.

They've got a section on program evaluations; a peer-reviewed article published in 1997 states:

  [...] the expanded 13-year NDCMP data base showed a 45% decrease in losses in the target area (Smith, et al., 1997).

Their website has a ton of information; a company called Weather Modification, Inc. is the contractor for ND State and does a lot of other work as well. Either the state or WMI would probably be able to provide additional data.

It may also be worth noting that Russia does lots of weather modification work as well (perhaps more when it was the Soviet Union). No idea how successful any of it is.


Is it illegal for Joe Public to listen to ATC in the UK? I recall that in the UK (unlike in the rest of the world) we have a law forbidding the listening to of air traffic control, dating back a century, to the days of paranoia over spies!

What is this law, exactly? Is it illegal for a member of the public to listen to live ATC in the UK? Are there any exceptions?

It seems like something of a grey area, but some sources claim that listening to a delayed feed (or historical recording) works around this law; is this true?

Yes, it is illegal.

The UK has some very strange ideas about Radio, which bear no resemblance to the reality of physics and how radio actually works. Foremost among those ideas is the idea that you are only legally allowed to listen to transmissions intended for "general reception":

  The services that can be listened to under the definition of general reception are:

  licensed broadcasting stations;
  amateur and citizens' band radio transmissions; and
  weather and navigation transmissions

  Radio scanners should not be used to listen to any other radio services, including illegal radio stations (pirates) (by virtue of the fact that they are not licensed radio stations).

Aviation-band transmissions are not on Ofcom's list, so even though they are broadcast entirely "in the clear" and anyone with an appropriately tuned AM receiver could hear them you are legally prohibited from listening to them.

Providing feeds to LiveATC would also appear to be a violation, though it's not clear to me that listening to LiveATC streams would put the listener in violation of the law.

From the same Ofcom site:

  … it is illegal to listen to anything other than general reception transmissions unless you are either a licensed user of the frequencies in question or have been specifically authorised to do so by a designated person.

and

  … it is also illegal to tell a third party what has been heard in a transmission a person has listened to illegally.

So anyone providing UK aviation band transmissions to LiveATC may be in violation of both of those laws, but I'm not certain what that means for LiveATC listeners (that would be a question to ask Ofcom).


What are the pro/cons of polyhedral cranked wings? Dihedral wings seems to be very common (almost if not all low-wing airliners, many modern gliders,...). Polyhedral seems to be less common and mainly found in relatively old aircraft (F4 Phatom, F4U Corsair, DR400,...). By polyhedral, I mean at least 2 dihedral angle with a sharp discontinuity between both. I don't include wings whose diheadral angle varies smoothly along the wingspan (such as this B787).

But I was surprised to discover that this design (polyhedral with sharp angle between the distinct diheadral sections of the wing) was elected in at least 2 project whose first flight was in the last 10 years (namely the solar impulse and the qinetiq zephyr). I do realize that both examples I gave have similar missions (stay airborne as long as possible, and thus fly slowly; gather as many sun-energy as possible, and thus fly as horizontally as possible) and may thus have similar design.

Given recently-designed aircraft with polyhedral wing exist, what are the pro/cons of such design over well spread dihedral wings and over the smoothly varying dihedral angle?

EDIT: note that the polyhedral does not necesseraly increase the dihedral angle as we go away from the wing root (Be 12, Habicht,...)

While dihedral wings offer increased stability in the roll axis, they also decrease the lift that the wings provide. A polyhedral wing provides a compromise: a steep dihedral at the tip of the wing in order to maximize stability, and a shallower dihedral angle closer to the root in order to maximize lift.

Therefore, a polyhedral wing allows the best of both worlds for a wing design. Other applications of a polyhedral wing are utilitarian; the gull wing on the Vaught F4U Corsair is designed so that the landing gear is positioned close to the ground while maintaining roll stability and aerodynamics.


How do I get flight numbers? Flight AWE685 goes from Seattle to Philadelphia.

What exactly is that AWE685 identifier called?  Every flight seems to have a unique name.  I'm trying to learn more about flight data but it's tough when you don't know what terms to Google for more in-depth results.

Apologies if this question doesn't have a simple answer.  I'm trying to learn about HTTP requests, so I'm teaching myself by pulling flight data from websites.  Also, aviation data is new to me, so I don't realize how easy/difficult of a question this is.

These are colloquially called "flight numbers," though technically that term refers to just the numerical portion. Pretty much all travelers will use this name for them.

According to Wikipedia, the International Air Transport Association (IATA) officially uses the name "flight code" to refer to the whole portion. Unfortunately, the cited IATA document is behind a paywall, so I can't independently verify that.

In particular, the type of flight code in your example is of the ICAO variety and is also being used as the callsign for that particular flight for radio communication purposes. In the U.S., it is customary to use the airline's callsign plus the flight number as the callsign for a particular flight. Some other countries use the Aircraft Registration Code (commonly called the "tail number") of the aircraft instead of the airline flight number as the radio callsign. General aviation aircraft (which don't have airline flight numbers) will also normally use their tail number as their callsign.

When used as a call sign, a flight code will use the ICAO code for the airline. However, for purposes of airline reservation systems, it's common to see the flight number listed with the airline's (2-letter) IATA code rather than its (3-letter) ICAO code.

When a flight number is used as a callsign and is spoken on the radio, the airline's callsign will be spoken instead of the letters in the flight number. For example, your example of AWE685 will be pronounced "Cactus Six Eight Five" on the radio, since "Cactus" is the callsign for U.S. Airways.

For reference, the use of "AWE" and "Cactus" for U.S. Airways is a relic of when U.S. Airways merged with America West Airlines. They kept the name of U.S. Airways, but the ICAO code and callsign of America West (whose main hub was in Phoenix, AZ, hence the "cactus" callsign.)


Are rhumb lines ever used as leg paths for RNP/RNAV? Are rhumb lines ever used by an FMS as leg paths for RNP/RNAV? If so, what arinc 424 leg type would use them?

No. The FMS does not use rhumb lines.

All RNP/RNAV flight path legs are geodesics. The only exceptions are RF legs (a constant radius circular path about a turn center) and hold legs (a closed racetrack pattern).

To quote RTCA DO-236C, Minimum Aviation System Performance Standards: Required Navigation Performance for Area Navigation:

  RNP Routes and user-preferred trajectories are assumed to use a series
  of fixes. The desired path is defined by a series of geodesic tracks
  joining successive fixes.

It also includes the following definition:

  GEODESIC LINE [Bowditch]
  A line of shortest distance between any two points on a mathematically
  defined surface. A geodesic line is a line of double curvature and
  usually lies between the two normal section lines which the two points
  determine. If the two terminal points are nearly in the same latitude,
  the geodesic line may cross one of the normal section lines. It should
  be noted that, except along the equator and along the meridians, the
  geodesic line is not a plane curve and cannot be sighted over
  directly.


Can you identify this airplane? Im thinking the window sequence and the shadow (possible a prop?) Might be your best help. My dad bought this photo and him nor I can figure it out. I work at a dang airport, too! TIA.

It's most likely a Boeing B-29 Superfortress. It was a strategic bomber used by the US in the Pacific theater of World War II. The lower row of four windows and then another further aft matches pictures of the B-29. The "U.S. AIR FORCE" markings are a post-WWII style.

Source

It's also possible that it's a B-50 Superfortress. This was an upgraded version of the B-29 with new engines and other changes that are hard to see in the picture. Only 370 were built. Although it's not clear when the picture was taken, and only 5 examples of the B-50 still exist. The B-29, on the other hand, has way more.


How did War Emergency Power work? Someone can explain how WEP (War Emergency Power) worked on the planes of the Second World War? And if it was really effective during a combat?

Generally, War Emergency Power was a power setting that was available, but exceeded the engine's long term running condition rating.  It was usually specified in manifold pressure, and primarily applied to supercharged or turbocharged engines (which was most of the high performance piston engines by the end of the War).

The way it works was much like how it works in modern jets (where it often specifies afterburner operation): There was a stop on the throttle and a warning mark on the manifold pressure gauge that warned the pilot not to exceed those settings, as well as a specification in the manual for the longest permitted time in War Emergency Power setting.  To engage this setting, the pilot either had to manipulate the throttle lever in an unusual direction (pull up, push sideways) or break an actual wire with a push strong enough not to be done by accident, in order to bypass the stop.  In aircraft where it was used, the wire served to notify ground crews that WEP had been used.

Once engaged, War Emergency Power would give anything from 10% to 20% more total horsepower (in most cases, though the last version of the P-51 got roundly 60% increase), and a significantly increased rate of engine parts wear and risk of failure (blown gaskets, thrown connecting rods, even holed pistons from detonation if the fuel wasn't quite up to spec).  This doesn't seem like much, but 20% additional power would amount to 10 knots or more of additional level flight airspeed, or several hundred feet per minute of increase in climb rate -- it could make all the difference in air combat, when fighters of one force were often quite closely matched to those of the other in terms of performance.


Is it always the case that any one STAR leads to all the runways? I was making an addon for a flight simulator and I am having a problem figuring this scenario out:

Let's take CYOW - Macdonald Cartier international.

It has 6 runways: 04, 07, 14, 22, 25, 32.
It has 5 STARs : CAPTL4, DEANS8, LEAMY3, MEECH1, RIVER2.

For this specific airport every STAR can be used to approach runway 07,14,22,25 and 32. (Runway 04 isn't used for arrivals at all.)

I was wondering if this was the case for every airport or is it different? I'm not sure if my wording was right. I'll try to clarify it to the best of my abilities if further clarification is needed.

Some STARS are designed for specific runways (i.e. not all runways for the airport).

For example, shown below is the BASET FIVE ARRIVAL to Los Angeles.  It is designed for runways 6L/R or 7L/R: (not for runways 24L/R or 25L/R)

page 1:

 page 2:


Considering all US untowered airports, what is the furthest distance that E2 airspace (dashed magneta line) projects from the airport? Considering all US untowered airports (50 states), what is the furthest distance that E2 airspace (dashed magneta line) projects from the airport for which it is designated?

Measure from the middle of the airport, or if the airspace is officially defined from a navaid or other feature that lies on the airport, measure from that navaid.

Example of E2 airspace -- KONP-- http://vfrmap.com/?type=vfrc&lat=44.580&lon=-124.058&zoom=10

On this airport, only the inner circle is E2 airspace.  The outer projections are E4 and don't count for this question-- http://vfrmap.com/?type=vfrc&lat=38.894&lon=-119.995&zoom=10

Beware these 3 airspaces, they are special anomalies, they appear to be all E2 but the projections are actually E4 (see related question Why are KACV and KTLV depicted differently on sectional charts than KSGU, KBIH, and KTPL, even though each is E2 w/ E4 extensions? ).  To my knowledge these are the only 3 of this kind:

KSGU -- St. George Regional Airport, UT -- http://vfrmap.com/?type=vfrc&lat=37.036&lon=-113.510&zoom=10

KBIH -- Bishop Airport, Bishop CA -- http://vfrmap.com/?type=vfrc&lat=37.373&lon=-118.364&zoom=10

KTPL -- Temple, Draughon-Miller Central Texas Regional Airport, TX -- http://vfrmap.com/?type=vfrc&lat=31.152&lon=-97.408&zoom=10

Except for these three anomalies, you can generally assume that a dashed magenta line surrounding the airport whose approaches it protects, with no inner dashed magenta line, denotes E2 airspace.

Don't be shy about posting the longest answer you've found -- if someone else posts longer no big deal.

Give you best guestimate by measuring on sectional, or check this document for the actual airspace description-- E2 airspaces are listed on pages E-2 through E-141 and have "E2" in the heading, like this:

"ANM OR E2 Newport, OR
Newport Municipal Airport, OR
 (lat. 44°34'49"N., long. 124°03'28"W.)
Newport VORTAC
 (lat. 44°34'31"N., long. 124°03'38"W.)
Within a 4-mile radius of the Newport Municipal Airport, and within 3.5 miles each side of the Newport VORTAC 357° radial extending from the 4-mile radius to 7.9 miles north of
the VORTAC."

In any case of doubt, use the document linked above to definitively determine for which airport the E2 airspace in question has been designated.

State whether measuring in nautical miles or statute miles

The document above uses nautical miles (p. A-2).

Best candidate so far--

Sheridan County Airport-- Sheridan, Wyoming-- KSHR
Page E-92 in the "Airspace Designations" document

The E-2 airspace extends 17.6 (nautical) miles southeast of the airport-- and also 16 miles northwest of the airport  -- last amended 5/31/12

http://vfrmap.com/?type=vfrc&lat=44.769&lon=-106.980&zoom=10


How do pilots calculate the temperature to put Into the FMS for an FLX takeoff? I recently read an article about derated takeoffs and I understand the concept, but how do pilots know what temperature to put into their FMS if they want an FLX takeoff? Some people say it's a rough estimate like ~50-60 C, but is this true? If it is gauged by some external factor, what is it?

For Airbus Aircraft you use a tool from Airbus where you put in data like wind, air temperature, pressure, weight, runway characteristics (length, heading, elevation, etc)  and other elements that calculates the flex temperature. It also gives you some other parameter like required runway length among others.


Is the angle of attack equal to zero when the plane is on the ground with wings level? I read in the internet that when an airplane stands at the airport (horizontal) it has zero degree aoa. The captain must pitch up the plane during cruise to generate an amount of lift and when the airplane pitches the relative wind also changes, and this will affect the angle of attack. This is really confusing me

You're right to be confused. The AoA can be almost anything, depending on wind direction. Normally, a wing has some camber so the lift it creates in flight is possible with an AoA of 0°. Normally, the wing is mounted at an incidence of a few degrees so the fuselage remains horizontal in flight. With this incidence and horizontal wind, the AoA at rest is just this incidence angle. But if the aircraft experiences tailwind, the AoA can be near 180°. If heated air below the wing rises up as a thermal, the AoA can be momentarily around 90°. In almost all cases, flow speed is much lower than that required for flight, but there are exceptions.


How did the windshield technology evolve? I would really appreciate it if someone could please explain the differences and similarities between the cockpit windows of a Boeing 747-400 and Douglas DC-3.

I am just trying to figure out how the technology would have evolved, what aspects would have remained and what would have changed. Literally just a brief comparison - nothing technical.

I have been unable to find information specific to the two models. I have found out the basic information with regards to a cockpit window, but I am unsure as to whether it applies for a Douglas DC-3 as well.

The two biggest differences both relate to their widely different cruise speeds: the 747 at 500kt and the DC3 at 180kt. The 747 is also pressurized and the DC3 is not.

The 747 is curved for aerodynamics.

It is also much stronger.

PPG Cockpit Windows

The DC3 windshield is weaker and flat. There are two major versions of the DC3, one with a wide flat pane and another that splits it two, though with no attempt at airflow improvements. It seems the smaller pane of the split version could be opened. It also apparently leaked like a sieve.

Birdstrike protection testing was mandated after the DC3 went out of production.

  Section 25.775 requires windshields and their supporting structure withstand, without penetration, impact with a four-pound bird at VC (design cruising speed) at sea level. This regulation has been in place and is unchanged since part 25 was introduced in 1965.

You have undoubtedly heard of the NASA chicken gun, a compressed air device for accomplishing this test. Used by the British it on a train, it caused an extraordinary amount of damage to the cockpit being tested and even went through the rear wall into the passenger compartment. When enquiring of NASA as to the cause, NASA replied "Defrost the chicken".)

Mythbusters chicken gun


Is the SEPECAT Jaguar's design aerodynamically inferior to more modern jets? If we compare the SEPECAT Jaguar's design with the latest jet fighters, what aerodynamic shortcomings do we find in its design? (I'm only asking about aerodynamics, not AESA radars, electronics suites and so on.)

For instance, in what way is the Jaguar inferior to the SAAB JAS 39 Gripen, PAC JF-17 Thunder, or the HAL Tejas? Is it inferior at all?

Only aerodynamics? Then the answer is simple: It lacks artificial stability.

In a paper by Ray Whitford on fighter design he published a comparison study between the conventional Jaguar and an advanced version optimised for relaxed static stability. The improved version is slightly unstable at subsonic speeds and much less stable at supersonic speeds, resulting in much less horizontal tail downforce and reduced size of all lifting surfaces.

Both configurations have the same airfield and combat performance! However, the smaller surfaces and the reduced trim drag improve performance noticeably. Note that this optimization was for the ground attack role; an optimized fighter version would had maintained a larger wing and horizontal tail for higher agility.


why there is APU bleed air supply? Does someone know anything about APU bleed air supply in this pic?

The APU is an alternate source of electrical power and also bleed air.  Since it doesn't have any function to generate thrust, it burns considerably less fuel than the engines do, and is intended primarily for ground use, although most APU's can also be operated in flight for things like a second source of electrical power if an engine generator has failed, or a source of bleed air if the bleeds are closed on the engines in order to generate more thrust.

In that diagram, what you're seeing is a portion of the pneumatic system, showing that the bleed air from the APU can be routed to both air conditioning packs (on many aircraft the APU can power both AC packs on the ground; on some aircraft it can only power one at a time), as well as to the engines, where it provides air for starting them.

On some aircraft, the bleed air from the APU can do other things, like pressurizing the water supply, and while it isn't operationally useful, it can generally supply bleed air into the anti-ice ducting for the leading edges.  In practice, though, that's only done when the engines are running, due to the greater volume (and temperature) of hot bleed air that the engines can produce compared to the APU.


To what extent does pressurisation increase the rigidity of an airframe? A vessel such as a balloon or the rubber air-cell of an inflatable boat will become more rigid when pressurised.

The same must happen to the fuselage of a pressurised aircraft - but to what extent?

Unlike balloons and inflatable boats, aircraft are not flaccid when unpressurised...

I imagine that the effect must be so tiny as to be not just utterly negligible, but literally impossible to measure; is it possible however to calculate theoretically (and if so, of what order is it likely to be)?

Disclaimer: I am not a pilot, nor do I have anything with planes. I am a mechanical engineering student, so I do know quite a bit about the strength of materials.

What you should know is that whenever something is filled with air, that air is trying to achieve a state in which it has the lowest pressure, meaning it is trying to increase in volume. This is the reason balloons are roughly round, because a sphere has the largest volume for the lowest surface area. The same pretty much applies to planes. What generally happens when you bend a tube (and a fuselage is in essence a big tube) is that two sides are getting closer, making it easier to bend because the second moment of area decreases. This does however mean that the hull becomes less round, thereby decreasing the volume. The air inside will try to prevent this volume change,  which makes it harder to bend the tube, which means the stiffness increases. Note however that more stiffness does not necessarilly mean it is also stronger.


In what situation could the maximum ramp mass limit the allowed take off mass? I’ve been pondering this for the longest time, but have been unable to come to a conclusion.

@vasin is correct. I'll put some actual numbers in a scenario.

A 747-481F has a max ramp weight of 913000lb, a MTOW of 910000. That 3000lb difference between max ramp and MTOW has been the same for 747s since the -100 airplanes.

The 3000lb is usually sufficient to cover the taxi fuel, but not always. Think having to taxi out at JFK when departures are heavy and the runway in use is the one farthest away from your ramp. Or, same thing at Honolulu and because of your weight you need the reef runway.

The dispatcher/load planner for the flight believes in following the rules, and he believes the taxi out will consume 4000lb. Thus, he has to use 909,000 as the max takeoff weight. Thus the max ramp mass has limited the MTOW

This kind of thing happens most on freighter flights because they're loaded as often as possible right up to their max zero fuel weight, that's where the money is. So let's say it's a freighter flight, JFK to Tokyo Narita. With the airplane near MZFW, you can't load enough fuel to get to Tokyo, but if you stretch a string on a globe between JFK and Narita, it goes almost right over Anchorage, and Anchorage is pretty much at the halfway point. Indeed, Anchorage has been used as the refueling stop for freighters for years and for pax aircraft as well, but especially for freighters.

Anyway, the load planner will put as much cargo aboard as possible to put the actual takeoff weight right up against the MTOW allowed.


Why can't an airplane stall at zero G? You may be surprised to find out that an airplane can stall at any attitude if the critical angle of attack is exceeded, but it cannot stall at 0 G.

This quote found in the April 2014 issue of Flying magazine, but it seems counterintuitive to me.

Why can't an airplane stall at 0G?

At 0 G the plane does not need to generate any lift, therefore there is no critical angle past which the airfoil cannot generate the lift required.

In addition, a sustained 0 G maneuver is a parabolic arc, which means that in theory your flight path should keep your angle of attack at zero the entire time (in a theoretical, symmetrical airfoiled aicraft). You can't stall because your AoA is constantly 0 degrees and cannot exceed the critical angle.


Lockerbie bombing - amount of debris (confusing numbers) As mentioned on Pan Am Flight 103:

  ... In total 4 million pieces of wreckage were collected and registered on
  computer files. More than 10,000 pieces of debris were retrieved,
  tagged and entered into a computer tracking system.

This is a bit confusing, at least to me. So which one is the actual number? Or if both sentences are correct, what is the difference between them?

Pieces of wreckage implies a large 'section' of plane, whereas debris suggests miscellaneous smaller items and bits of metal etc.

I agree it's potentially confusing, however, and likely arises from two people editing the same section without adjusting the context.

I'd say that 4 substantial sections of plane were found, along with a large amount of smaller debris scattered around, totalling around 10,000 pieces.


When are you allowed to use a call sign that is not the aircraft registration? Some General Aviation pilots use their aircraft registration as a call sign, like C-ADYDJ for example. I've heard some use their aircraft type then some numbers like Cessna 45G. Then the typical airliners who use their company name then flight number, like ACA783.

When are you required to use your aircraft registration, and when are you allowed to replace it? If you are allowed to change it, can anyone use whatever call sign they want or is it limited to airlines only?

For the US, this is covered in AC120-26L, or in a more human-interpretable way from an NBAA article.

  When are you required to use your aircraft registration

By default unless you have a callsign

  Can anyone use whatever call sign they want or is it limited to airlines only?

What you use must be registered. For international flights if you fly frequently enough you can get a 3 letter ICAO designator (SWA, DAL, UAL, etc.)

There are national callsigns which are detailed in that letter, and local callsigns which may apply only to your tower, TRACON, or center depending on who you talk to and what their own rules for issuing a letter of agreement to use it are.