Does FAR 91.155c apply to class E surface extensions? Federal Aviation Regulation (FAR) 91.155 says under (c):

  Except as provided in §91.157, no person may operate an aircraft
  beneath the ceiling under Visual Flight Rules (VFR) within the lateral
  boundaries of controlled airspace designated to the surface for an
  airport when the ceiling is less than 1,000 feet.

Does this regulation apply to class E surface extensions to class D airspace?

For example the class E extensions at KSTS. Specifically, suppose the ceiling is 900ft (agl) in this class E extension and vis is 10 nm. As a VFR helicopter, can I fly through this airspace at 400ft (agl) (3 -  5/1/2 being met)

FAR 91.155(c) uses the phrase “within the lateral boundaries of controlled airspace designated to the surface for an airport” to describe the airspace where a Special VFR clearance is required to operate under Visual Flight Rules below a ceiling of less than 1000’ AGL.
The FAA often uses the phrase "surface area" to refer to the controlled airspace that actually surrounds the airport for which it is designated, specifically excluding any surface-level Class E "extensions".  An argument can be made that in the context of interpreting the meaning of the FARs, this is the most correct understanding of the phrase "surface area".  This interpretation is based on the difference between the language used to describe surface-level Class E "extensions", and the language used to describe other surface-level Class E airspace, in the "Airspace Designations and Reporting Points" document, current edition FAA Order JO 7400.11E.  For more on this, see the related ASE question What indication has the FAA given that phrases like "surface area of Class E airspace designated for an airport" do or don't include E4 "extensions"?.
But the phrase "surface area" does not appear in FAR 91.155(c).
However, the phrase "designated for an airport" does appear in FAR 91.155(c).  An argument can be made -- again, based on  based on the difference between the language used to describe surface-level Class E "extensions", and the language used to describe other surface-level Class E airspace, in the "Airspace Designations and Reporting Points" document, current edition FAA Order JO 7400.11E -- that this phrase excludes surface-level Class E "extensions".  Again, for more on this, see the related ASE question What indication has the FAA given that phrases like "surface area of Class E airspace designated for an airport" do or don't include E4 "extensions"?.  According to this interpretation, FAR 91.155(c), which contains the requirement that the ceiling be at least 1000' AGL, would not apply in the surface-level Class E "extensions".
However, one problem with this argument is that FAR 71.71(b) seems to either 1) use the phrase "designated for an airport" in its description of all surface-level Class E airspace, or 2) omit any reference to surface-level Class E "extensions" at all, in which case it seems the "extensions" might be construed not to legally exist at all. Obviously, the latter interpretation is somewhat problematic.  This seems to imply that the phrase "designated for an airport" should not be construed to exclude surface-level Class E "extensions".
It's also unclear as to whether or not SVFR should ever be authorized in surface-level Class E "extensions".  FAR 91.157(a) uses the phrase “within the airspace contained by the upward extension of the lateral boundaries of the controlled airspace designated to the surface for an airport” to indicate where a SVFR clearance may be authorized.  Again, just as with 91.155(c), the phrase "surface area" is not used in the regulation, but the phrase "designated for an airport" is.  So the language for the two regulations is quite parallel.
Therefore it seems that if the 1000' ceiling requirement is construed to apply in the surface-level Class E "extensions", then it should be permissible to authorize SVFR flight in the surface-level Class E "extensions", and if it is construed not to be permissible to authorize SVR flight in the "extensions" by virtue of FAR 91.157(a), then the 1000' ceiling requirement ought not apply there either.
(Note that there are sometimes other operational reasons unrelated to FAR 91.157(a) why SVFR flight is not authorized in some specific surface-level Class E "extensions"-- one such case is noted in the second-to-last paragraph of this 2010 response from the FAA ATO Western Service Center.)
The last paragraph of this 2010 response from the FAA ATO Western Service Center (same link as immediately above) concludes that due to the wording of FAR 91.157(a), SVFR should not be authorized in surface-level Class E "extensions".  This implies that the 1000' ceiling requirement ought not apply in surface-level Class E "extensions" either, due to the parallel construction of the language of FAR 91.157(a) and FAR 91.155(c).
One problem with this 2010 response from the FAA ATO Western Service Center is that is contains the passage "The language in FAR 91.157 exactly matches the language in FAAO 7400.9T par 6002.".  This is not actually quite true, because FAAO 7400.9T par 6002. contains the phrase "The Class E airspace areas listed below are designated as a surface area for an airport."  As we've already noted above, neither FAR 91.157(a) nor FAR 91.155(c) actually contain the phrase "surface area".
FAA Order 7110.65Y, entitled "Air Traffic Control", states in section 7-5-1 that Special VFR flight will only be authorized "within the lateral boundaries of Class B, Class C, Class D, or Class E surface areas, below 10,000 feet MSL."  As noted above, there are many instances where the FAA has used the phrase "surface area" to refer only to the controlled airspace that actually surrounds the airport for which it is designated, specifically excluding any surface-level Class E "extensions".  So this passage could be construed as guidance that Special VFR flight should not be authorized in surface-level Class E "extensions".  If this guidance is just based on FAA policy but doesn't accurately reflect the meaning of FAR 91.157(a), then it perhaps it should not be construed as "releasing" the surface-level Class E "extensions" from the 1000' rule, even though, as argued above, the wording of FAR 91.155(c) is very parallel to the language of FAR 91.157(a).
In actual practice, controllers will often authorize SVFR flight in surface-level Class E "extensions".  For more on this, see this related ASE answer.  (And controllers generally use the word "surface area" in its most logical sense-- meaning the entire column of controlled airspace that is in contact with the earth's surface, including any surface-level Class E "extensions".)
The truth is that the FAA is deeply divided as to whether phrases in the FARs like "surface area", "designated for an airport", and "surface area of controlled airspace designated for an airport" should or should not be construed to include surface-level Class E "extensions".1  Ambiguity around this issue has existed ever since the 1993 "alphabet" airspace re-designation.2  There's some consideration of a future rule-making effort to address this issue.3  It's possible that the language in AIM 3-2-6, as well as in the legend of the Chart Supplements, that reads "Surface area arrival extensions become part of the surface area and are in effect during the same times as the surface area" will be changed in the future to avoid implying that all regulations that apply to the core "surface area" should automatically be construed to apply to the surface-level Class E "extensions" as well.4
Due the confusion around this issue, whenever a pilot is issued a SVFR clearance for a given controlled airspace, he or she should verify whether or not it includes any adjoining "extensions", in any case where that might be a factor.  It would also be wise to ask the controlling agency for any given airspace whether they construe that the limitation against operating below a ceiling that is less than 1000' AGL applies in the "extensions".  The "safe" course of action, naturally, would be to assume that it does.
Footnotes:
1,2,3,4) Source-- comments made by high-level FAA staffers during April 2021 airspace charting meeting.
Related ASE questions and answers
A: Does an SVFR clearance extend to Echo surface extensions?
A: Does an SVFR clearance extend to Echo surface extensions?
A: In the US, in actual practice, workload permitting, will ARTC facilities grant SVFR clearance for surface-level Class E “extensions” (E4 airspace)?
Q: What indication has the FAA given that phrases like "surface area of Class E airspace designated for an airport" do or don't include E4 "extensions"?
A: What indication has the FAA given that phrases like “surface area of Class E airspace designated for an airport” do or don't include E4 “extensions”?
A: Is the official weather report for an airport in Class D airspace controlling for its Class E surface extension?
Q: Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?


How do airlines manage routes when respective aircraft undergo B,C or D checks? While playing some airline management simulation games, I found all these checks to be some real kind of mess. If suppose I have a fleet of about 10 A-320s then if one them goes for any check, then I would end up losing about 10% of my earnings. How do real world airlines make up for these absent aircraft? Like, consider an A380. It takes more than 2 weeks for a C Check to complete (>1 month for a D-Check), and it certainly translates into a big financial loss. How do airlines operate such routes routes in the mean time?

Essentially they plan on some fraction of the fleet undergoing some sort of maintenance check at any one time, so they build their flying schedule around the remaining fraction.  And then there is some amount of flex due to things needing unscheduled maintenance or coming out of maintenance early.

What makes the task easier is the fact that maintenance needs can be forecast fairly far in advance, and so the schedules can be built around a knowledge of how many aircraft are likely to be available.

As an illustration (not necessarily representative of any particular airline's actual numbers), let's say you have a fleet of 200 aircraft, and you know that on average each aircraft will be down for two 2-week heavy maintenance checks each year.  That works out to essentially one month out of 12, each aircraft is down, or a little under 10% of the time.  Add in a little time for shorter maintenance visits (but still longer than an overnight), plus an allowance for the fact that some aircraft just need unscheduled work, and the maintenance planners may end up telling you to plan on 175 aircraft available each day.  So that's what you build your schedule around.

Now let's say that one aircraft takes a birdstrike & an engine needs to be changed.  That is now a hole in the schedule.  It can be covered by cancelling a flight (undesirable, but always an option).  If an aircraft is finished with maintenance ahead of schedule (say it was scheduled down all day for some work, but the work is actually done by noon), that aircraft may be able to be put into service.  Perhaps it's possible to delay some sort of minor maintenance a day (not a heavy check, but something quicker) and essentially create one aircraft-day of capacity, and push the check off to a weekend day when the schedule uses fewer aircraft.  Or maybe the schedule was built with one or two aircraft available as spares that day.

Depending on a variety of factors, spares may or may not be available, or even deliberately built into the schedule at all.  Having an A-380 sitting around unused all day is an EXPENSIVE insurance policy against something unforeseen happening, but cancelling a flight on something that big is an expensive event when it happens!  If you operate all out of one giant hub and you know that your fleet of 500 aircraft (flying 450 lines every day) is likely to have 2-4 aircraft every day go to the hanger for unexpected maintenance, it's probably a good financial decision to allocate two or three of those lines as dedicated spares.  If your aircraft operate a point-to-point schedule, it's harder (or unfeasible) to keep a spare aircraft at every airport you serve, "just in case" something happens to break there.

There are complicated decisions that airlines will continuously evaluate to find what balance works best for their particular operation.  In some cases, it may be possible to substitute an aircraft from a different fleet for a broken jet... an MD80 goes to the hanger, and a 737 with a reserve crew flies the rest of the day that the MD80 would have flown.  Or maybe a 757 broke, and the decision is to use the 737 to cover the flight, and re-accommodate the extra passengers that the 757 could hold that the 737 now can't.  That's a tactical decision that the airline's operations center will make, considering the availability of both aircraft and crews, as well as the passenger loads.  (They also may pull a "healthy" 757 off of its less full schedule to fly in place of the broke 757, use a 737 that wasn't going to be very full to cover that 757's route, put an RJ on the 737's route that day, and cancel the RJ's flights "due to maintenance."  And if that inconveniences 4 flights of 40-50 people who mostly just get delayed a few hours, that's probably a better plan than stranding two flights of 200 people who'd otherwise have no way to get where they're going until tomorrow or later.)


Why depict TRSA on a map? Participation in TRSA services is completely optional. The depicted airspace is all still class E, and you can fly straight through it sans radio or transponder without violating any regulation.
Obviously, if you do talk to them, they can provide radar services, but this is no different from any other class E airspace owned by an approach facility, including (notably) the class E above and below the depicted TRSA boundaries.
So, why bother showing it at all?  And even if there’s a reason to show it, what’s the point in such complex configurations that have zero impact on either pilots or ATC?

I think - and I may be wrong - that your question assumes that ATC services are the same in a TRSA and in class E in general. Or perhaps that TRSA Service and flight following give you exactly the same thing.
In fact, TRSA service is slightly different: it provides everything that Basic Radar Service does (e.g. safety alerts, sequencing), plus separation services for all participating aircraft. Usually, ATC doesn't provide any separation service to VFR traffic in class E.
The ATC Orders (JO 7110.65) sections 7-6 and 7-7 cover Basic Radar Service and Terminal Radar Service; you can read more details there. Since the ATC services available in a TRSA aren't the same as those available in general class E airspace, that seems to me like a valid reason to chart it.


Where can I find detailed dimensions of aircraft panels? I'm thinking of building some of physical aspects of a flight simulator, such as the overhead panels and pedestal.

Is there a publication available where I could find detailed dimensions of cockpit panel sizes of say Boeing 737 and A320s? I've found some pictures online but they don't quite have the detail I would like. Google images shows a few results with detailed dimensions, so I'm wondering where they got theirs from... actual measurements perhaps? (there are photos of measurements, but i'd like something maybe a little more exact)  Is there maybe a standard size of these panels, also on the larger jets?

Sort of thing I'm looking for:

There appears to be some (free) quality materials accessible through the download section of Open Cockpit's Website, including CAD (.dwg) files and drawings such as this 737 Overhead Panel.

(seem to have at least partially answered my own question, but a clear technical drawing if somebody could provide/suggest a source of one would be greatly appreciated)


Why aren't there aircraft with forward-mounted vertical stabilizers? Many aircraft have the horizontal stabilizers mounted in front of the main wings (this is called a canard configuration); however, to the best of my knowledge, there don't seem to be any aircraft with vertical stabilizers in front of the wings.

Why is this?

From the image you can see that a vertical stabilizer mounted behind the aircraft CG imparts a restoring moment to a yaw disturbance which increases as the yaw movement increases. If the fin were placed on the nose of the aircraft, ahead of the CG, the moment would amplify the yaw disturbance, which is destabilizing.

An actively controlled rudder could be located ahead of the CG, but cost and complexity normally limit this to things like missiles.


Are airliners' pilots trained to safely ditch an aircraft? After reading this question and these two answers it is clear that ditching is taken into account, at least for biggest airliners (and with reasons as it occured several times in aviation history).

Pilots are trained to face many technical problems that may lead to an accident (engine flame-out, cabin fire, partial loss of hydraulic power, partial loss of flight computers,...).

But, many airlines pilots do not posses the qualification (nor the training) to pilot specific categories of aircraft such as fighters, gliders or seaplanes. Thus it makes sense to assume they are not trained to fly in formation or land on water.

Is an airliners' pilot trained to ditch as he is trained to deal with technical emergencies? If not, what is its knowledge of such situation (only theorical, practice once on simulator,...)? Is there differences between country's regulation?

This is a very dated answer now, but for what it's worth, prior to my retirement in 1999 from a U.S. airline, we did ditching scenarios in 747-100/200 sims during initial training and then occasionally during recurrent training. Proper execution included being on-speed for your weight, nose attitude at touchdown (5 degrees up as I remember), aircraft configuration (gear up but I don't remember the flap setting), determination of wave direction if possible, and landing parallel to the wave action. It was a relatively easy scenario for the pilots but a busy scenario for the flight engineer. He had to position valves properly at the right time, including making sure the pressurization outflow valves were closed to prevent fuselage flooding.


When do pilots engage the autopilot in airliners? I may be wrong but I learned that in regular airliners, pilots always takeoff manually.

After taking-off and going to a positive rate of climb:

When do pilots engage the autopilot?
Is there a minimum altitude to engage it?

The minimum altitude for autopilot engagement is generally the acceleration height or around 400' AGL though this can vary between operators.

The question of when the autopilot is actually engaged is a more complicated question and is subject to pilot preference.  Personally, I generally hand flew until the first level off or until climbing and accelerating through 10,000 MSL.  Others may turn it on as soon as allowed and most fall somewhere in the spectrum between the two.


Can the fuel on the wing cause the aircraft to destabilize? If fuel is stored in the wings, which are in constant movement during the flight, can the fuel unbalance the aircraft?

Yes it can. Source: I'm a pilot.

Most aircraft (even many small general aviation ones) have balance parameters where the fuel quantity in each side cannot/should not exceed that on the other side by greater than a certain amount.

Note that this is usually caused by fuel consumption in flight, not sloshing as you asked.

Also, (as in your question) fuel can slosh between tanks in most aircraft through the vent line that often connects one tank to another such as in light Cessnas. However this is usually only a small quantity and furthermore the aircraft is usually in level flight so it's not really a problem.

Fuel sloshing inside of one tank could potentially imbalance the plane a bit but I've never ran into any real effects of this nor heard anyone mention it. Furthermore, most aircraft have some sort I baffles in the tanks (usually wig ribs) that prevent much sloshing, whether by design or not.


What is this clock-like device? Whenever I watch cockpit footage of test flights there is always an added device with big clock-like digits centered above the glareshield.

They come in different shapes as shown below. What are they called and what are they for?

I'm thinking it's to timestamp the multi-angle video cameras, but I highly doubt that's the answer.

Images linked to sources.

From YouTube

After scouring the internet, the device seen in the first two pictures is indeed a clock.

In the linked video the display does count up like a clock. In the beginning of the video the narrator says, "it's just after 4 AM in Seattle," and the displayed time is 04:17:58.

Watching the maiden flight of the A350, no similar device is found.

I then turned my attention to the FAA's Flight Test Guide For Certification Of Transport Category Airplanes, there's no mention of such a device being mandatory.

Closest thing I found is a requirement to video record and timestamp spin tests in light aircraft.

The timestamping theory would make sense if the video recording of the cockpit is high speed, which would be overkill for any scenario really.

Time synchronization for the flight test instrumentation data acquisition is a real, and complicated thing.

My theory, showing the pilots the master clock—if that's the case—would help the pilots note the time when a situation arises so the engineers can check the relevant data.

It might also have other functions as recording total elapsed time of the entire flight test program for the airframe it's installed on.

I've also looked into trajectory guidance systems for test pilots based on true airspeed/pressure measurements being fed to the pilots, but such systems turned out to look completely different than a seven-segment display.

Over to you.


How do symmetrical airfoils generate lift? It is widely understood that the curved shape of a typical airfoil (such as a Clark Y) causes a pressure difference that creates lift. How do symmetrical airfoils do this when the top and lower surfaces are the same shape and length?

By using a non-zero angle of attack.  When the trailing edge is pointed downwards, and assuming the airstream leaves the trailing edge smoothly, the exiting airstream is deflected downwards.  This causes lift via conservation of momentum.  Increasing the angle of attack will increase your lift until such time as the airstream over the trailing edge becomes non-smooth.  (When this happens, you're close to stalling.)

(Image from this page, which unfortunately appears to be down)

As you can see from the above graph, a symmetric airfoil at zero angle of attack generates no lift;  see this site from NASA as well as the above Wikipedia page.


What are the mandatory elements of an ICAO flightplan? I need to write a software parser for ICAO flightplans, and in particular I need to parse FPL messages.

What are the mandatory elements included in a flightplan document? For example the image below illustrates a typical flightplan form:

Also the above form contains special sequences such as <=. What is the signification of this sequence? Does it correspond to a newline in the generated flightplan text format?

A corresponding textual representation of a flightplan is also shown below:

(FPL-REU974-IS
-B77L/H-SDE1E2E3GFHIJ4J5M1RWXYZ/LB1D1
-LFPG1845
-N0490F310 OKASI UL612 MILPA UM730 TOP UL50 ELB UL12 VELAD UM728 NERAR UP3
RCA/N0489F350 UR611 TIKAT UG300 MAV UM665G ITLOX UM665 UVESO/N0486F370 DCT DENLI
UR780 MIDRI UR780G UVENA
-FMEE1036 FIMP
-PBN/A1D1L1S1 NAV/RNP10 DOF/121114 REG/FOLRA EET/LSAS0039 LFFF0039 LIMM0048 LIRR0111
LMMM0218 HLLL0237 HECC0343 HSSS0425 HAAA0545 HKNA0700 HCSM0701 FSSS0745 FMMM0900
SEL/CGFR ORGN/RUKOUU PER/C SRC/RQP RMK/ADSB ACARS EQUIPPED TCAS EQUIPPED)

So basically I need to write a program capable of parsing the previous textual format and validating it against any errors and or missing elements.

About the special characters at the beginning or in the body of the form: They are:

Formatting characters inserted when sending the FPL with a teletype interface on the AFTN network. e.g. < is a carriage return, = is a line feed

Routing indication, e.g. FF is the priority level for a message of type FPL.

These characters are not part of the flight plan data of course.

Parser assumptions

All fields from 7 to 18 are mandatory and included in a Filled Flight Plan message (FPL). Being mandatory doesn't prevent some field to be filled with some dummy value, e.g: Field 18 may contain "0" to indicate no information is provided.

Field 19 can have survival items and remarks left blank. Field 19 is not part of the FPL message, but of the SPL message. The latter is transmitted to other ATS units by the ATS unit having registered the flight plan only in specific situations, e.g. when the contact has been lost with the aircraft (ALERFA).

ATS consistency
While they are mandatory, some fields are used only in specific conditions, in particular the ones related to navigation capabilities.

Example: Not all approaches or routes are PBN required. Not mentioning some navigation capabilities may not be a problem if the capability is not required by an ATS unit to provide the desired routing, but if you use a RNAV approach, the flight plan will be rejected.

For more information on the combinations that are consistent, see the interactive Eurocontrol Flight Plan Guide for IFPS (Integrated Initial Flight Plan Processing System). Example:

When PBN is specified in the item 18 of a flight plan, it indicates the Performance Based Navigation (PBN) levels and/or the Required
Navigation Performance (RNP) levels that can be met. It can only be
present if the aircraft is PBN approved which shall be notified by the
letter R in the equipment of that flight plan.

**Filling instructions**
The content of the ICAO flight plan is detailed in appendix 2 of ICAO Doc 4444 (PANS-ATM) and a filled sample is provided (page 361), but filling instructions are also available separately, e.g.:

ICAO Flightplan Form Basics
Flight Plan Filling at SKYbrary (Eurocontrol)

Note that FAA and ICAO flight plan forms have been different in the past, and while FAA is pushing for the adoption of the ICAO form, it seems the FAA form is still used for US domestic flights.


Is this a type of navigation aid? I saw this contraption on the southeast corner of Eastern West Virginia Regional Airport, Martinsburg, WV (MRB). My first thought was this was some kind of NDB antenna but not sure.

If you go to www.skyvector.com and zoom in to MRB
(easy to enter a flight from KOKV to KMRB to find it quick)

Select the World VFR view, and you will see no navaids at that location.
Select the Enroute L-29 view, and you will see no navaids at that location.

So no, it is not a type of currently used navigation aid.

If you peruse the Instrument approaches for KMRB at Airnav.com  https://www.airnav.com/airport/KMRB

you will also not see that structure mentioned.

Airport phone numbers are listed, you could call up and ask what it is.


Why do most aerobatic aircraft have conventional landing gear? I was browsing images of aerobatic aircraft on Google and noticed that the vast majority of them have conventional "tail-dragger" landing gear.

Is there any practical reason why this is the case, or rather an aesthetic preference?

The tailwheel is much lighter and smaller than a nose wheel. That means reducing airplane overall weight and drag (because the landing gear is usually fixed). And it's probably cheaper, too.


Do we fly full size aircraft with video game style joysticks? Are there planes with electronic joysticks as shown below?

RC airplanes are incredibly effective at using this technique. For actual planes it would remove the need for rudder pedals and a stick along with potentially being easier to get used to.

Are thumb controlled sticks used in aviation? or is there a reason to why they aren't used?

They are used, they are just bigger joy sticks than used for RC flying.

A current example is the Airbus A320 (and related family) of passenger aircraft.  A short video of the joystick in action(called "side stick", start at about 1 minute in).  There is no direct mechanical linkage between the stick and the flight controls.

(For the A330, but basically the same).

For more detail, you can download this (slightly out of date, but with enough information to be useful) Flight Controls lesson for the A320 here.

  I am more curious about thumb controlled flying as you could control
  everything from what essentially looks like a video game controller.

@Rory Alsop noted that ...

  ... even video game controllers are terrible for this. The bigger the stick the better fine control you have over it. This is why for flight
  sims for PC's and consoles, keen players buy proper joysticks -
  otherwise they are twitchy and hard to handle

Video game controllers require two hands, have poor sensory feedback (as compared to a stick type controller) and are not as ergonomically effective as a multi-axis stick.  Also, there are some "push buttons" on a control stick that allow moving a finger or a thumb to activate other functions, like the "take control" button in the side stick(For swapping control between left seat and right seat pilots).  On some sticks you'll also have the "push to talk button" for the radio, as has been done for decades.  It's an efficient use of the hand, without having to move the hand for multiple tasks.


Is mode C required for CVFR in Canadian Class B airspace? (This is in reference to Canadian Airspace)
Can you fly in Class B airspace under CVFR (Controlled Visual Flight Rules) without a transponder with Mode c (altitude encoding) capability?

To enter Class B airspace you'd require ATC clearance to begin with, I'd assume if you didn't have a transponder with Mode C, they wouldn't clear you, but I'm not certain.

I'd assume aircraft flying under IFR would have this transponder with Mode C capability, but aircraft that typically fly VFR may not.

The vast majority of GA airplanes have Mode C transponders and when you ask for the clearance, you will be given a transponder code to squawk.  If you don't have one, you have a problem and you probably won't get a clearance except in special circumstances.  Not only do you need a  Mode C transponder, it has to be calibrated and certified every 2 years by an AMO.

You could call Terminal while still clear of the Class B, tell the controller you are no-transponder would like to go from A to B, and see what happens: the controller may let you transit by reporting position at specific points if the path is out of the way.  Or maybe not.

Better yet, call the applicable ATC unit on the phone and find out if you can get permission to transit Class B non-transponder for a particular reason.

As a general practice however, the answer will almost certainly be no.  Just go around or under.


In EASA, what is Panel 12? Is this just the same as Panel 10? IN EASA safety approval guidance, particularly CM – SWCEH – 001
Development Assurance of Airborne Electronic Hardware, the entity charged with making sure that a system meets applicable requirements and guidelines (especially concerning safety) is called "Panel 10."
However, in section  5.2 "Background" there is a list of panels, and there, Safety is listed as Panel 12.  (Immediately after this list comes most of the assurance-related material, which extensively speaks of Panel 10.)  Yet no other mention of Panel 12 is made in this document.
Is this just a typo, where they meant Panel 10, not Panel 12?

Reading through CM-SWCEH-001, the Background section is identifying the EASA system panels, one of which is identified as the primary panel for certification requirements for the system being developed. My understanding of Panel 10 is that it serves as a secondary panel for some of those requirements.

The document defines Panel 10 as:

  The EASA panel in charge of software and AEH aspects of certification.
  This panel includes at least one software and AEH expert (the
  coordinator) and, depending on the size of the project, may include
  additional software and AEH experts.

I would say that it is not a typo, with Panel 12 being the System Saftey panel.


Which came to be first - bigger airplanes, or longer runways? I'm generally speaking about airports with runways long enough for airliners, be historic or still in use. In order not to turn this question to a chicken-egg discussion, here are my points:

Would making an airport(s) before making the actual airplanes be
feasible and cost-efficient ?
Will new(and more runway-length
demanding) airplanes be able to take-off from shorter runways,
because there are no other options ?

I'm generally interested in historic terms, which came to be first - bigger airplanes, or longer runways ?

It is the larger aircraft that came first. Historically, the runway length (and design) of an airport has depended on the aircraft operating there (among other things), though this is changing. For example, the Prague airport site:

  The main runways – RWY 04/22 and RWY 13/31 – were continually lengthened during post WW II operations which kept them in line with the demands of the aviation industry until the mid 1960s...

The runway required for the aircraft depends on the take-off weight and the lesser runway length restricts the payload or range. As a result, for economical operation, the runway needs to be longer.

However, there are other constraints to consider:

For large aircraft, the runway (and taxiway) width, apron and parking space are important considerations. In most cases, lengthening the runway will be easier than taking care of these other constraints.
In the end, airports have to weigh the benefits of letting heavier aircraft operate against the resources required for runway lengthening. For major airports (like Heathrow, for example), the cost of runway expansion will run into the billions.
Unless the aircraft is going to be operated regularly (which depends on how many airports it can land), there is no point in lengthening the runway in an airport.
The economic operation of the aircraft has to be considered. For example, the A380 was designed around a 80m 'box', which the airlines had decided is the maximum size they can operate economically.
A bigger aircraft does not mean more runway required. For example, the A380 requires (slightly) lesser runway compared to 747-400.

If it comes to that, aircraft requiring more runway can takeoff from smaller ones. For example, a Boeing Dreamlifter once took off from a 6000 ft runway (it normally requires > 9000ft).

The airports with longest runways have them for different reasons- the Qamdo Bamda Airport (5500m runway) has a long runway due to its elevation (>4300m above MSL), while the Ramenskoye Airport as a long runway (5400m) due to the aircraft operated there; it was a test facility, for among other things, the Soviet Buran spacecraft.


Can passengers tell (without GPS etc.) where the aircraft is heading to? I was watching Mayday Varig Flight 254 and at minute 38 it said that some passengers noticed that the plane was flying in the wrong direction. This accident took place in 1989, so my question is: without 'modern' aids like GPS, smartphones, in-flight entertainment system maps etc., can a passenger really notice where the aircraft is heading to?

(I suggest you watch that minute of the video if you have the time. It will help to understand the question.)

can a passenger really notice where the aircraft is heading to?

A wide variety of observable phenomena and general attentiveness can lead to an approximate understanding of which direction the aircraft is heading in.

Passengers can rely on visibly observed phenomena such as stars, moon, sun, ground topology, or major landmarks (interstates, cities, facilities etc.). General familiarity with flight routes and runways, coupled with attentiveness to significant changes in roll, pitch, and yaw can bolster an understanding of the flight's direction.

Items such as a compass (built into Casio calculator watches?) could also be used to get an approximation of direction. They may be affected by other instrumentation and mechanical features along with being really cheap.

Some passengers will be able to note which runway they took off from and a divergence from a typical path. While still ascending they can more easily notice landmarks that are likely familiar, and recognize that no significant change in direction has happened since orienting themselves.

It's possible too that cognitive bias may be another explanation. The media, and documentaries like this, seem to embrace an event as predictive or accurate despite a long history of inaccuracy or patterned behavior. That passenger who makes 98% incorrect assertions of plane direction is only recorded or listened to after the fact and appears to be 100% accurate in their vastly under sampled assertion set. How does it go? A broken clock is right twice a day?

Also, thanks to all the comments, tried to cover most of those notes/ideas here.


Does the power behind the engine make any difference to how strong the thrust is? What difference does horsepower make? If the engine can spin the propeller fast enough, why does it need power behind it?

You ask:

  If the engine can spin the propeller fast enough, why does it need power behind it?

Good question. However, the answer is in the if of your question.

A propellor does work - it pulls (or sometimes pushes) the aircraft through the air. In order to move the aircraft at a useful speed (or even at all) it has to spin pretty fast.

The faster it spins, the more work it has to do. That work requires power. If the engine doesn't have enough power, it can't spin the propellor fast enough.

So yes, though the power and the speed of the spin are not the same thing, you won't get the spin without the power.

If you consider a car, the engine has to spin the wheels fast enough to move it along at the desired speed. And what makes it possible for it to spin the wheels fast enough is power. Otherwise, the wheels won't turn fast enough (or at all), and the car won't move fast enough (or at all). It's the same in the case of an aeroplane.


What is the difference between "x" and "+" configuration in missiles? What is the difference between "x" and "+" configuration tail fins, and what are the advantages of each in free flight? (for example JDAM missiles)

Mounting missiles below a wing or stocking them in weapon bays is much easier with X-Configured missiles. Look at these photos:

K-5M Missile Source

AIM-120 Missile Source

"+" mounted missiles would need more complex hard points and larger weapon bays.

Once fired the configuration doesn't matter anymore as all four control surfaces are continuously used to guide and stabilize the missile along its 3d trajectory.

If the missile only moves in the horizontal or vertical plane, the X configuration is better. For a fixed force F the angle of attack of the control surfaces ($\alpha_{cs}$) is smaller and can therefore be set faster, making the missile more agile. Assuming* a linear relationship between the the control surface force and its angle of attack:

$$\alpha_{csx} = \frac{F}{q \cdot S \cdot C_{L\alpha}}\cdot \frac{\sqrt{2}}{4}$$
$$\alpha_{cs+} = \frac{F}{q \cdot S \cdot C_{L\alpha}}\cdot \frac{1}{2}$$

For a quadratic relationship* between the drag ($D_{cs}$) and the angle of attack of the control surfaces there is no difference in the total drag.

$$D_{cs+} = q \cdot S \cdot (4\cdot C_{D0}+2 \cdot C_{D\alpha} \alpha_{cs+}^2) = 4\cdot q \cdot S \cdot C_{D0} + \frac{1}{2} C_{D\alpha} \cdot (\frac{F}{q \cdot S \cdot C_{L\alpha}})^2$$

$$D_{csx} = q \cdot S \cdot (4\cdot C_{D0}+4 \cdot C_{D\alpha} \alpha_{csx}^2) = 4\cdot q \cdot S \cdot C_{D0} + \frac{1}{2} C_{D\alpha} \cdot (\frac{F}{q \cdot S \cdot C_{L\alpha}})^2$$

*If someone has better assumptions for lift and drag please comment or correct the post.


Why was Air India flight AI101 diverted to SHJ 5 times in the past few days? Air India flight AI101 using a 777-300ER on multiple westbound and eastbound routes was diverted to SHJ airport in Sharjah, UAE. I am curious if there is a specific reason. It cannot be a coincidence 5 times to the same airport.

Link to flight history: https://www.flightradar24.com/data/flights/ai101

Is it possible that they don't have the range to get to JFK without stopping for fuel due to the Pakistan Airspace Closures/Restrictions. Looking at the dates, it seems that the flights started diverting when the India/Pakistan tensions flared up a week ago (~Feb 28).

https://www.flightradar24.com/blog/tensions-between-india-and-pakistan-affect-air-traffic/

Going to Sharjah for the diversion avoids the Pakistani airspace as seen below:

https://www.flightradar24.com/data/flights/ai101#1fb4a663


Can the design for neutral stability reduce trim drag? If one were to design an aircraft to have neutral longitudinal stability would this reduce the required horizontal stabiliser surface and hence trim drag?

Terminology first: Trim drag is the drag component added by adjusting the incidence of the horizontal tail rsp. the deflection angle of the elevator for trim. The increased parasitic drag of a larger tail surface itself is already part of the aircraft's zero-lift drag.

Sizing criteria for tail surfaces

The horizontal stabilizer surface must be dimensioned with these criteria in mind:

Sufficient static longitudinal stability. To achieve this, the tail volume (tail area times lever arm) must be high enough. Use similar aircraft and copy what has been found to work well.
Sufficient pitch damping. This is driven by tail size times the square of the tail lever arm.
Sufficient control power at the most forward cg location over the whole speed range.
Sufficient control power at the most forward cg location over all load factors (including pitch damping effects).
Sufficient control power when flaring in ground effect (which reduces elevator effectivity)
For T-tail configurations: Sufficient control power over all sideslip angles. Sideslip produces a strong pitch-down moment in T-tail configurations.
For gliders: Sufficient compensation for the force of the tow line, both at the beginning of a winch launch (tow line horizontal) and at the end (tow line vertical).

The other criteria (upper and lower limits on stick force gradients over speed and load factor) can be tailored with elevator chord, so the horizontal tail surface is not directly affected.

In the end your horizontal tail will be as large as you want your cg range to be wide. Operators like wide cg ranges, so the small drag penalty of a bigger tail surface might be worth it.

Wing airfoil

Also, wing airfoils with a high pitching moment (think rear loading, i.e. high camber in the rear part) will need a bigger tail surface due to the larger shift of the center of pressure over speed, but have less drag and a higher maximum lift than comparable, old-fashioned airfoils (think NACA 4-digit range), so the wing can be smaller and has less drag, which easily compensates for the increased tail surface.

Do not optimize each surface separately

If your wing has already an optimized lift distribution, adding more lift in the same Treffz plane will spoil the end result. In the end, it does not make much of a difference at which position in streamwise direction lift is created, only the sum of it counts. Therefore, it might be better to have as little tail loading as possible in the design point.

If you take the mass of the wing structure in consideration, your optimum lift distribution over the wingspan will change to a more triangular shape, and now it might even make sense to create a small downforce on the tail to reduce the downwash angle in the center section. A lighter wing will require less lift and help to reduce drag.

Think of it this way: The triangular lift distribution produces a higher downwash angle at the tail, and any downforce there would actually point slightly forward, creating induced thrust. Effectively, it helps to equalize downwash over span in the Treffz plane of wing and tail.


How can I calculate the glide time for a B737 with engine failure? We talked today in our flight school about the following scenario: if I climb in my 737-800 to FL100 and then have a dual engine failure, how many seconds would it take me before I reach ground?

I'm assuming:

I want maximum glide time (not distance)
I'm within 10NM of the departure airport
Flaps 15
Gear extended
No speedbrakes

For reference consider TACA Air Flight 110, a 737-300 that lost both engines at FL165, on approach to New Orleans in a very heavy hail/thunderstorm.

No exact listing of how long 110 stayed in the air with no power, but the Mayday/Air Disasters show on this incident hints that it was in the vicinity of 13-15 minutes, which indicates a drop rate of around 1100-1300fpm.

A heavier example was BA flight 9 a 747 that lost all four engines due to flying into a cloud of volcanic dust at night at FL370. This led to the classic announcement:

Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get them going again. I trust you are not in too much distress.

Fourteen minutes later at FL135, they got a restart. At that descent rate, they would have had maybe another nine minutes before hitting the ocean.


What rating can I add to a commercial certificate with the least time/effort? I have an FAA commercial certificate with ASEL, AMEL, ASES, Glider and Instrument ratings (alongside specific type ratings). What additional certificate or rating will require the shortest amount of training to add?

It could be anything from sport pilot through ATP certificate, for any class: weight shift, multi engine seaplane, gyro-copter etc.

Jack Brown's Seaplane Base offers single engine seaplane ratings at private and commercial level.  It takes 2 full days and costs between 1400 USD and 2300 USD depending on your choice of training aircraft.

From their website:

  SES Rating

  We offer three options of planes for your SES training at the private
  or commercial level, both of which include: 1.5 hours of ground
  instruction, 5 hours of dual instruction, the check ride and the
  examiner’s fee.

  Training in the Piper J3-Cub on floats,  1,400.00.

  Training in the Maule M-7 on floats,     2,300.00.

  Training in the Super Cub on floats,     1,850.00.

  If additional flight instruction hours are required they are billable
  at the hourly rate of the aircraft (listed below).

They are located in Winter Haven, FL.


Are gyroscopic effects of tail rotor noticeable with hover spot turns? I have a question of the book  "The foundations of helicopter flight" by Simon Newman.

The question is from page 186:

1) How can we feel gyroscopic effect of tail rotor with hover spot turns?

The tilt and the gyroscopic effect cause the helicopter to hover with a slight bank in a no-wind condition, a compromise that is acceptable. It should also be noted that a crosswind can exaggerate the bank, eliminate it, or even cause the helicopter to bank in the opposite direction.

In helicopters, the controls are rigged is such a way that when forward cyclic is applied, the helicopter moves forward, likewise for aft, etc.  To accomplish this, the pitch horn is offset 90º to the rotor blade.  The controls still tilt the swash plate in the same direction as the control input is made, but due to the pitch horn placement, the input to the blade occurs 90º earlier in the plane of rotation. The tail rotor as a gyroscope is rather insignificant

http://books.google.co.in/books?id=lTkiuG4RaFIC&pg=PA410&lpg=PA410&dq=gyroscopic+effect+%2B+tail+rotor&source=bl&ots=0t9R_FBArG&sig=pWRaKnWgjGAqkmeePDrmmclx7UA&hl=en&sa=X&ei=rSHhU7jSBMG0uAS9ioDIDQ&ved=0CD8Q6AEwCQ#v=onepage&q=gyroscopic%20effect%20%2B%20tail%20rotor&f=false

Also,  speed decreases all the way from the start of the approach to the hover point, and the power, controlled by the collective-mounted throttle, decreases during the first half of the approach, and then increases during the latter half - as the helicopter nears the hover spot and loses translational lift.

In a stable, no-wind hover everything is in equilibrium. The engine is providing just enough power to keep the main rotor turning at just the right rpm to hold the height over the ground and to keep the tail rotor spinning at just the right angle to counteract the torque of the main rotor. When you push one or the other of the tail rotor pedals forward, you upset this balance and must do something to compensate in order to hold the same hover height.

In a hover, the torque of the main rotor tries to turn the fuselage to the right and therefore pressure on the left pedal is required to keep the nose straight. Forward left pedal means the tail rotor blades are biting the air at a greater angle of attack and therefore producing more lift. If you add even more forward left pedal to initiate a left hovering turn, you increase the tail rotor blade pitch angle even more. This requires more power from the main gearbox and, if engine power remains constant, the only way the gearbox can satisfy this increased demand for power from the tail rotor is to allow main rotor rpm to decrease.

The tail rotor provides horizontal thrust but only to the right (nose left).  The tail rotor counters the torque on the fuselage caused by the engine driving the main rotor


Could you help me identify this plane (miniature model)? please help me identify this model.
Thank you

Both the Sopwith Camel and the Nieuport 11 mentioned elsewhere had rotary engines with a rounded cowling, but the model in the photograph appears to have a square cowling. This suggests it might be a Royal Aircraft Factory S.E.5 or S.E.5a which had a V8 engine.

Wikimedia Commons


Why do shockwaves progressively move aft as speed increses? As an airfoil moves from subsonic to supersonic, the shocks that develop over the surface move progressively toward the trailing edge. What is the physical explanation for this behavior?

As a side question, what determines where the shock (and hence location of minimum pressure) is located?

The answer is deeply rooted in the theory of compressible fluid dynamics, so for a fully satisfactory take on the matter you might want to refer to a textbook on that topic (such as Thompson or Shapiro). I will try to give a qualitative explanation.

For our discussion here, let's consider a shockwave as the way to abruptly slow down a supersonic flow and recover pressure; abruptly, because, since disturbances cannot propagate upstream in a supersonic flow, the flow has no way to "know" that the disturbance is coming and it isn't able to "smoothly" accomodate it (as it happens in subsonic flow). A disturbance here is, for example, the presence of the airfoil and its effect on the velocity and pressure fields.

Let's have a look at your picture. In a) the flow is subsonic everywhere and we have no particular issues with that (although we might want to consider some compressibility corrections).
Now, the flow accelerates over first portion of the upper surface of the airfoil, so the speed of the flow there is greater than the speed of the free stream flow (and greater than the speed on the lower surface, so we can have lift).
We can see that for free stream Mach numbers $M_\infty$ (ie flight speeds) close to 1 the flow over the upper surface can actually reach local Mach number $M$ of 1 and even above, because of that acceleration.
This is exactly what has happened in b): here $M_\infty$ is greater than the critical value (usually given as 0.8) and there is a supersonic bubble right there in the middle of the upper surface.
The flow downstream, however, is still subsonic, therefore it has to slow from the supersonic condition it reached and to do so a shockwave appears. This shockwave usually interacts with the boundary layer, adding a very high adverse pressure gradient to the one already experienced towards the trailing edge, so the boundary layer will most likely separate, leading to stall.

As we increase the flight speed, more and more of the flow over the airfoil becomes supersonic, also on the lower side, therefore the shockwaves "travel" downstream until, close to $M_\infty = 1$, the whole flow on the airfoil is supersonic, as in d).

As you can see from c), the shockwave on the lower side actually overtakes the one on the upper side. This is because the lower side is usually "flatter", so the shockwave appears later (ie at higher $M_\infty$) since it experience less acceleration (which is due to the curvature), but it also experience less deceleration towards the trailing edge and the local flow will be supersonic over a longer distance along the lower surface.

For even higher flight speeds, a detached shockwave appears in front of the airfoil: the purpose of this wave is to "turn" the flow around the airfoil. As the flow is supersonic, this turning of the flow can't happen "smoothly", but like we said it is the shockwave that abruptly accomplishes it.
The flow behind this curved shock is still supersonic (except for a region right around the nose of the airfoil) so later downstream we once again find the shockwaves which help the flow go back to its undisturbed free stream conditions.
The detached wave significantly increases drag; in some application this is optimal (eg in the atmospheric re-entry of a spacecraft), but it is detrimental for supersonic flight. This is why supersonic airfoils are designed to have a sharp trailing edge, so that the turning of the flow can be accomplished by oblique shocks attached to the edge, resulting in less drag.

As to answer your last question: where does the shockwave position itself? The answer lies in the boundary conditions, that is to say the conditions that have to be restored downstream of the airfoil: these will be the free stream speed and pressure.
Without going into much details about the variation of pressure with velocity in compressible flows, let's just say that the shock position is such that afterwards the flow has enough "space" left to recover subsonically. So, say you have to recover to a pressure of 1 to the freestream pressure of 10 (random numbers with no meaning) at a certain distance downstream from the airfoil: if the shockwave increases the pressure to 6, it will be positioned in such a way that after the shock (where the flow is subsonic) there is enough space for the pressure to increase "smoothly" (subsonically) by 4 and restore freestream conditions at that distance.
The increase of pressure across a shockwave is given by the shock strenght and can be seen as proportional to the Mach number, so at higher Mach the shock is stronger, the pressure recovery is higher and the shock will position further downstream, since the flow will have less pressure to recover subsonically and can do so over a "shorter" distance.


Are high bypass turbo jet engines suitable for tail and body mounted engines Are high bypass turbo jet engines suitable for tail and body mounted engines.  If not what are the drawbacks, danger if so, are there any anycraft with any such setup?

it depends on what you call 'high-bypass'. The RB.211 engine was tested in a tail mount on a VC-10:

For tail-mounted high-bypass engines, the engine mount gets long, which means it gets heavy.

Tail- and bodymounted engines in general have drawbacks that also apply to high-bypass engines:

the high position means maintenance access requires special equipment and takes longer
for bodymounted engines, engine choices are limited by the amount of space available (unless you redesign this part of the fuselage, which can get expensive)


What does 3Q8 mean in the aircraft model Boeing 767-3Q8? I have aircraft types like Boeing 767-3Q8, Boeing 767-33A, Boeing 767-3P6ER and many others. I know what ER means. But what is coded as 3Q, 33A, 3P6 etc.?

How can I convert it back to more common types like Boeing 767-300? Just replace last two symbols with 00?

Those are Boeing's customer codes. They denote which airline the aircraft was originally built for, not necessarily the airline that owns/operates the aircraft currently. For example, Southwest's customer code is H4 but they operate some 737-7BD's, which are from the AirTran acquisition. In your case, the Q8 means it was originally built for ILFC, a leasing corporation.  A full list is available here:
http://en.wikipedia.org/wiki/List_of_Boeing_customer_codes

Your assumption about replacing the customer code with 0s to get the plain old model is correct.


what's the difference between priority and sequence valve in aircraft? What roles do they play during retraction and extension of a landing gear ?

A priority valve will manage the flow in a hydraulic supply that feeds two different circuits such that if the input flow, that is normally enough to satisfy both circuits' demands, drops below a threshold, the valve will starve or cut off the low priority circuit in favour of the high priority circuit to keep it supplied.  So if I have two subcircuits in a system running on the same source, and I determine that one is critical to safety, I'll put in a priority valve to make sure the critical circuit continues to get pressure if the inlet flow is not able to supply both.

Not to be confused with shuttle valves in brake systems that block off one inlet when pressure is applied at the other inlet.

Sequence valves require a mechanical condition (or electrical condition in the case of a solenoid sequence valve) to be satisfied before supplying or cutting pressure to a circuit.  Like to control gear doors that need to be timed to open or close when the gear legs are at position X or Y.


What does AO2 in the remarks of an ASOS/AWOS mean? I occasionally see AO2 in the remarks of an automated weather report. What does the AO2 mean?

METAR KSLC 280453Z 00000KT 10SM FEW042 SCT055 BKN080 04/02 A2981 RMK AO2 CIG 037 NW RNWY SLP087 T00440022

The AO2 notation means the station is automated and has a precipitation
discriminator. AO1 means automated but no precipitation discriminator. The precipitation discriminator will be able to sense the difference between rain and snow.

The METAR format is documented in the Federal Meterological Handbook No. 1 in Chapter 12. This particular notation is:

  12.7.1 c.
  Type of Automated Station (AO1 or AO2).
  AO1
   or
  AO2
   shall be coded in all METAR/SPECI
  from automated stations.  Automated stations without a precipitation discriminator shall be identified
  as
  AO1
  ; automated station with a precipitation discriminator shall be identified as
  AO2
  .


What is the straight-and-level altitude record for a heavier-than-air winged/lifting-body aircraft? There are many variants of the flight altitude record. The highest on the list is SpaceShipOne but rocketry isn't really "flight" in the sense of aerodynamic lift. What is the highest altitude for which:

The flight at a reasonably constant speed and altitude "straight and level". It is not in free-fall, so the "cabin" feels about 1g.

It is "heavier-than-air" and supported by lift rather than buoyancy. The engine thrust's vertical component is much less than the weight of the aircraft, so the wings or lifting body have to support the craft.

The speed is slow enough that centrifugal effects are negligible (i.e. it is not in orbit). This is the case below about 2.5 km/s (about mach 8).

The highest on the list that may qualify is in a Mikoyan-Gurevich MiG-25 at about 36000 meters. However, it is not clear if this was at the top of a parabolic arc initiated at a lower altitude. The highest (including unmanned) that surely fulfills the above requirements is the Helios HP01 at almost 30000 meters.
Helios HP01, although very light, is a very low-power craft that only uses propellers. One would think (sc)ramjet-powered craft would win due to the high speeds needed to generate lift in such extremely rarefied air. Is this the case?

As of writing this, the official (as verified by FAI) "altitude in horizontal flight" category record goes to the SR-71 on 28 Jul 1976 at an altitude of 25 929 m (85 069 ft).
Second place is 24 463 m (80 259 ft) in a YF-12A, and third place is 22 670 m (74 377 ft) in a E-166 (modified Ye-152).

For more: www.fai.org


Are life jackets mandatory on planes that will never fly over water bodies? Supposing I'm a regional carrier and my routes never pass over water bodies (sea or lakes which are over a certain size). Am I obliged to carry life jackets on my plane?

Assuming you are asking about civilian flights operated under FAA rules, part 91 rules (14 CFR §91.205(b)(12)) advise that approved and serviceable flotation devices are required to be carried for each occupant during flight where such flight takes place over water outside power-off gliding distance to shore. "Shore" has a specific definition.

If the aircraft is operated [for VFR flight during the day] for hire over water and beyond power-off gliding distance from shore, [it must carry] approved [and serviceable] flotation gear readily available to each occupant and, unless the aircraft is operating under part 121 of this subchapter, at least one pyrotechnic signaling device. As used in this section, “shore” means that area of the land adjacent to the water which is above the high water mark and excludes land areas which are intermittently under water.

These provisions are extended to VFR flight at night and IFR flight in 14 CFR §91.205(c) et seq.
Part 91 subpart F stipulates the requirements for large/turbine-powered multiengine operations (where such rules exclude flights for the purposes of common carriage). In summary, §91.509 requires approved flotation devices when operated more than 50 miles from the nearest shore, and liferafts, survival kits, etc for flights operated more than 30 minutes flying time or more than 100 nautical miles from the nearest shore.
Most "commercial" flights in large aircraft are further regulated in terms of equipment by sections under part 121, part 125, part 135, etc. with similar equipment requirements to those noted above (links take you directly to relevant sections of the code for extended overwater operations under each part).
If operating a commercial air tour compliant with part 136, and such tour is to take place over water beyond minimum gliding distance in a non-compliant aircraft except for the purposes of takeoff and landing, then the code in 14 CFR §136.9 is more strict: occupants must wear life jackets until at least the period when the flight ceases to be over water.

(a) Except as provided in paragraphs (b) or (c) of this section, the operator and pilot in command of commercial air tours over water beyond the shoreline must ensure that each occupant is wearing a life preserver from before takeoff until flight is no longer over water.
(b) The operator and pilot in command of a commercial air tour over water beyond the shoreline must ensure that a life preserver is readily available for its intended use and easily accessible to each occupant if:
(1) The aircraft is equipped with floats; or
(2) The airplane is within power-off gliding distance to the shoreline for the duration of the time that the flight is over water.
(3) The aircraft is a multi engine that can be operated with the critical engine inoperative at a weight that will allow it to climb, at least 50 feet a minute, at an altitude of 1,000 feet above the surface, as provided in the Airplane Flight Manual or the Rotorcraft Flight Manual, as appropriate.
(c) No life preserver is required if the overwater operation is necessary only for takeoff or landing.

In summary, for FAA aircraft operating solely over land, the regulations noted above and by Ralph J's comment proscribe that the required equipment to be carried is minimal.
Of course, what the letter of the law says, and what's a good idea to carry, may in some cases be different things -- I'm thinking here about good practice to carry additional life preserving equipment when operating a GA aircraft for an extended time over water.


What is the origin of the "Pickle" switch for release of ordnance? I am looking for proper proof of the theory that it is called so due to the Norden sight of the B17, which was said to assist the bomber in putting a bomb into a pickle jar, and hence it stuck.

The accuracy of the Norden bombsight was often exaggerated, but it was never claimed it could put a bomb into a pickle jar. The exaggerated claim from the Norden Company was that a bombardier using it under "ideal" conditions could put a bomb into a pickle barrel from 20,000 feet AGL. In reality it could barely get within 100 ft of the target from 10,000 feet AGL. (AGL = Above Ground Level) Some sources claim that it's called a pickle switch because a control handle with many switches almost feels like a pickle with all its bumps, but that would imply the name was given considerably later than WW2.


Where to find information about aircraft type knowing the flight number and date? Having flight date and exact flight number, I would like to know aircraft type (like Boeing 737-400). Is there any service where I can get such information in bulk (for hundreds of flight dates and flight numbers)? I know that flightradar24 provides us with similar data, but it doesn't have any API to get such information for many cases.

FlightAware will give you all the info and has an API.


What is the difference between saturated and unsaturated adiabatic lapse rate? I'm having trouble understanding the difference between saturated and unsaturated adiabatic lapse rate.

I know the unsaturated adiabatic lapse rate is approximately 5.4 degrees per 1,000 feet in which a "dry" parcel of air cools at that rate. What does the unsaturated adiabatic lapse rate depend on? Why is the unsaturated adiabatic lapse rate lower than the saturated lapse rate?

I searched and found that the unsaturated adiabatic lapse rate is lower due to the air parcel releasing its latent heat, which causes the air parcel to cool slower, but I don't get it. When a "dry" parcel of air is cooling adiabatically, are we assuming 0% moisture?

The difference between a unsaturated and a saturated adiabatic lapse rate is that in the latter the water vapour has to change state from gaseous to liquid.
When air rises it expands due to the lower pressure of the ambient air at higher altitude. By expanding, the air parcel is doing work on its surroundings. Since no heat is transferred to the air parcel (by definition of being adiabatic expansion) but work is being performed, the temperature has to drop. Thus a rising parcel of air cools down.
Cooler air can hold less water vapour than warmer air. If the air parcel contains water vapour, at some point during the cooling the maximum relative humidity is reached. At that point the air is saturated with water vapour. If the air continues to cool, the water vapour content has to change from vapour to liquid. This is called saturated adiabatic cooling.
The process of condensation of the water content is exothermic; when the state changes from gaseous to liquid, heat is released to the air in the parcel. Therefore the lapse rate (temperature change with altitude) of a saturated adiabatic process is less than an unsaturated adiabatic process. The heat released from the condensation process reduces the lapse rate.


Why does an aircraft's nose tend to pitch downward at higher bank angles? In the usual aircraft configuration, the center of lift is located behind the CG producing negative pitch moment (the horizontal stabilizer counteracts it by producing downforce - positive pitching moment). If the aircraft rolls to one side the vertical component of lift on the wings would decrease, so by that logic the aircraft should pitch up.

Why does it pitch down? What am I missing?

The answer is that the aircraft doesn't actually pitch down. When banking (or rolling) into a turn, the angle of attack (or the angle between the center of the wing and the flight path of the aircraft) stays the same. Assuming no correction to maintain altitude is made, the aircraft will continue on the same angle of attack, just banked over by some amount. Due to the bank, the lift produced by the wing is no longer vertical, instead, it is directly perpendicular (at least for our purposes) to the wings. Therefore, if the airplane is in a 30 degree bank, then the lift vector will also be 30 degrees from vertical. Doing some vector analysis, then you can determine that if the angle of attack hasn't changed the new vertical component of lift will be about 86% of what it was in level flight. Therefore, the plane would begin losing altitude. This altitude loss is what you see as the airplane pitching down.


Where do I start learning about Avionics programming? I am a student in his last semester going for a B.S. in Computer Science. I would like to eventually transition into the space exploration industry (NASA, SpaceX, Boeing, Lockheed Martin, etc). I know nothing about avionics and i would like to learn more about the subject, specifically the software side. I have found little information online. Please give me reference material (books, websites, etc.) to learn about this area. Your point of view and additional information is strongly welcomed.

Ok, I was posting this as a comment but was becoming ridiculously long...

I worked for most of my professional life in fields that are somehow related.
I can see that there are three areas of study that will help you a lot here.

First: programming languages. Knowing a language used in the industry is a plus.
Now I am working in the automotive/transportation industry; I am not working on safety critical material, so we just use standard C/C++. Even at that level a good knowledge of low-level programming and software (how to write a simple driver, how to interact with a device using ioctl, etc..) are very useful.

Before that, I worked on a field related to programming languages and compilers, especially on the simulation and analysis of concurrent code. Among the others, I briefly interacted with people working for Airbus (professors that are in academia, but help to build real software).
They still see and use a lot of Ada out there, so.. knowing that is good :) I also know for a fact that Java is also used, together with special tools for verification of the code.

Which bring us to the second: everything related to the verification of software, both from a theoretical and a practical point of view, will help you hugely in this industry. Study and practice with runtime monitors and model checkers, at least. Learn about various static analysis techniques, like abstract interpretation. Take classes about that, if you can at your school.

And third: study and practice with embedded systems and with the (more rare) real-time OSes and how they work (and how you do program them).
Get yourself an arduino or a netduino (not a raspberry PI - too high level, too many resources there!) and practice with them. Lear about uboot.


How can reducing power too quickly on a piston engine damage it? In many places, it's been stated that you should reduce power slowly to prevent engine damage.  Depending on who you talk to, some say you should reduce the manifold pressure by 1 inch per minute, others say two. However, I'm not sure just how reducing power quickly will damage an engine, and if you do, what would happen. Could someone explain?

The main concern cited in regards to reducing power too quickly is that you could shock cool the engine.  A sudden decrease in power, particularly at high altitudes where it is cold can cause a rapid decrease in temperature of the engine which can cause damage to the cylinder heads.

However the theory is very controversial because there is no evidence that the cooling causes a problem, and in fact the engine cools much more quickly when you shut it down at the end of a flight.  A very good article going into more specifics about cooling of aircraft engines is here:  the physics and metallurgy of "shock cooling".

One of the more interesting points that it discusses is that only about 12% of the heat generated from combustion ends up making its way through the block and is dissipated by air cooling (cooling fins).  This means that most of the heat is already going somewhere else anyway (the largest part goes out the exhaust), and the "air cooling" doesn't make that big of a difference anyway.

As always, be sure that you follow all recommendations and limitations from your POH or engine manufacturer in regards to engine cooling, CHT's, etc. since they could have procedures for other reasons as well.


How much clearance is provided when taking off over a 50 foot obstacle? When performing a takeoff over a 50' obstacle, how much clearance is provided between the obstacle and the aircraft and where can that be found?

Calculated figures for take-off distance required (TODR) are to only just clear a 50-foot obstacle at that distance (with gear down), and figures provided by aerodromes for take-off distance available (TODA) are the measured distance to the obstacle, with no extra clearance added.

If there's any uncertainty when they measure TODA, they'll give the most pessimistic value. The obstacle may be further away than the given TODA but no closer. Measuring distances is easy with modern equipment so it's likely to be an exact figure. However, it's rare for the first obstacle to be exactly 50 feet high. If the obstacle is (say) only 30 feet high, you get 20 feet of separation for free.

Be sure to apply the standard safety factor (e.g. 1.33) when comparing your calculated TODR with the published TODA, to ensure you get plenty of separation over the obstacle. As StephenS points out, if there are any significant obstacles in your take-off path, it's good practice to go for a best-angle climb until you overfly them.


What weather should we expect when temperature and dew point are similar? What should i expect during my flight planning when i see both temperature and dew point are the same?
I understand there will be fog but what else? could it mean icing? any difference between 20/20 and 04/04 for example to expect?

Both 20/20 and 4/4 will probably result in fog or thick haze/mist.
4/4 is a problem because it tells you that besides the airport being likely fogged in, the freezing level is only a couple thousand feet above the airport and there is very likely icing at that level if there is any cloud up there. Only airplanes capable of flight in icing would be coming and going, if at all, depending on the actual runway visibility.
20/20 is also likely fogged in, but the freezing level is up at 10000 ft so that's not a problem.  15-20C is a sweet spot for carb icing, so saturated air at that temperature is a major concern.
The other thing to take into consideration is temperature tendency.  Generally, a zero spread like that in the morning means you can expect to wait a couple hours and the fog will lift.   On the other hand, a spread approaching zero in late afternoon is a big red flag.
When I was bush flying on floats in Northern Ontario, the dew point spread was the most important bit of data when checking weather.  A spread of one degree in the morning when departing on a trip was no worries because it would only improve (absent frontal conditions etc) as the day warmed up. On the other hand, a tight spread in the afternoon might mean making a customer wait at the lodge until the next morning rather than risk getting caught out scud running home at 500 ft, with clouds forming all around as the spread became zero, necessitating a diversion to the nearest lake on the route.


Will the blade angle of a constant speed propeller be at its least angle (fine pitch) during full throttle and prop full? During low power settings, low throttle setting and prop full during taxi, the blade angle will be at its finest pitch. As we increase the throttle for take-off, will the blade angle remain in its finest pitch to cater for increasing RPM ?
Will the propeller be at its finest pitch at full throttle & full prop setting ?

Prop full forward means fine pitch, so when the throttle is pushed full open the engine can spool up to its maximum rated RPM and thereby develop maximum power for takeoff. The fine pitch stop is set so as to prevent the engine from overspeeding at full throttle conditions.
With the throttle still wide open, deepening the pitch angle (pulling back on the prop control) will increase the torque load on the engine and cause it to slow down.
With the engine thus slowed down to a lower RPM setting and the throttle still wide open, pulling back on the throttle will cause the prop governor mechanism to decrease the prop pitch, so as to automatically maintain that RPM setting.


What is the airspeed velocity of an unladen swallow? I'm considering the airspeed velocity of an unladen swallow because the swallow may present an opportunity for the observation of nature to lead to better design in aviation. Many technologies built by humans are inspired by designs in nature.

If one were to set out to determine the airspeed velocity of an unladen swallow, how might they go about this?

In general, the method of getting the airspeed of any bird is pretty much the same:

Measure the ground speed of the bird.
Measure the wind speed in the area.
Calculate the airspeed of the bird from these two values.

The following excerpt from Air speeds of migrating birds observed by ornithodolite and compared with predictions from flight theory by C. J. Pennycuick et al. published by the Royal Society details one such method:

  We measured the bird's air speed, for comparison with the predictions of theory, in two stages. First, we measured the ground speed vector, consisting of the bird's speed relative to the observer's position on the shore and its track direction, i.e. the direction in which the bird was moving over the ground, measured clockwise from true north. We also measured the wind vector consisting of the wind speed and the direction from which the wind was blowing, and then obtained the air speed vector (air speed and heading direction) by vector subtraction of the wind vector from the ground speed vector

Other researchers have used  Doppler radar for the same purpose and in case of high flying birds, one can simply fly along with the birds at the same speed and measure the airspeed.


Do airliner cabin filters trap viruses or other pathogens? I understand that half the air in an airliner is re-circulated (per How much air is recirculated (vs. bleed air injected) in modern airliners cabin?). Of this 50% re-circulated air, what it's the chance that viruses pass through its filters?

Disregarding possible recent developments due to the COVID-19 outbreak, were filters normally designed to remove viruses or sterilize the air somehow?

Modern airliners use HEPA filters to filter the air before re-circulation. This will remove almost all airborne pathogens like viruses:

  The overall risk of contracting a disease from an ill person onboard an airplane is similar to that in other confined
  areas with high occupant density, such as a bus, a subway, or movie theatre for a similar time of exposure.
  anywhere where a person is in close contact with others.

  That said, the risk on airplanes is probably lower than in many confined spaces because modern airplanes have
  cabin air filtration systems equipped with HEPA filters.

  HEPA or high efficiency particulate air filters have similar performance to those used to keep the air clean in
  hospital operating rooms and industrial clean rooms. These filters are very effective at trapping microscopic
  particles as small as bacteria and viruses.

  [...]

  Air filters can remove very small particles such as bacteria and viruses. Virtually all viruses and bacteria are
  removed; even the most difficult particles in the range of 0.1 to 0.3 micron are filtered out with an efficiency level
  of of 99.995%. Contrary to popular belief, very small particles below 0.1 micron are easily filtered out by the
  mechanism of diffusional interception.

(IATA Briefing Paper - Cabin air quality - Risk of
communicable diseases transmission, emphasis mine)

The following image shows the location of this filter in front of the re-circulation fan for a Boeing 737:

(Boeing 737 NG FCOMv2 2.30.5 Air Systems - Air Conditioning System Description)


How can a passenger determine airspeed without a handheld GPS? This question is in the context of being a passenger on a commercial airliner, where you're in the cabin and the cockpit door is locked.

In another question, someone posited that if an airliner had reduced its airspeed by 60%, he'd be quite concerned.   I asked "How would he even know?"

How would a passenger on a commercial airliner, who is reasonably technically savvy but not a pilot, be able to discern airspeed?

This is old school. The person does not have any modern smart devices.  Or does, but their battery ran down.  (Not looking for a product reco for a gadget or app, there's another answer for that.)  The person could probably improvise a plumb bob, stuff like that.

Would anything change if the passenger has a clear view of the ground, relevant maps with scales, and a stopwatch (but not any wind data)?

It is impossible for a passenger to determine the airspeed to any reasonable accuracy (otherwise Birgenair 301 and Aeroperu 603 would not have crashed).

From my personal experience, it is not possible to receive GPS signal using a handheld-device in the passenger cabin. Even if it works, winds aloft at cruising altitude are often in the range of 100~200 knots. That throws the calculation completely off even if ground speed is known.

The only reliable way is to refer to the entertainment system, which obtains its data from the cockpit and is therefore accurate. However, the interface is usually programmed to display measurements in other units; the indicated airspeed has to be calculated from the displayed values manually.

Here are some ways you can guess the airspeed to a certain extent:

If you do not notice any significant airframe vibration, you can
assume the airspeed is somewhere between the stall speed and the max
airspeed.
If you can tell the flaps position from observation, you can also correlate that with the usual flaps extension speed of the model
you're flying, which should give you ~20 knots of accuracy.
If you are familiar with the SID or STAR of the airport, and you know planes normally pass a certain point at a certain speed.
If you have a handheld ATC receiver, sometimes ATC will issue speed instructions to planes during approach.


What is the temperature of the air leaving the combustion chamber of a CFM56-5C? What is the temperature of the air leaving the combustion chamber of a CFM56-5C? I was wondering as I could only find out that the fuel burns at around 1500 Celsius but this can't be the same as the air temperature because the air/fuel ratio isn't 1:1.

Quick answer: At the design point considered, which is assumed to be takeoff conditions, a CFM56-5C combustor raises gas temperature to 1360°C (the share of the compressor in this raise is about 600 °C).

This is a common value found in modern turbine engines, a balance between fuel consumption reduction and turbine material capabilities (nickel super-alloy, more on that here and here).

Turbine entry temperature (TET) varies with thrust. Takeoff TET is maximal and top-of-climb TET is about 100°C less. Takeoff TET cannot be allowed for a long time, due to the damages which would be incurred by the high-pressure turbine guide vanes and blades.

Some details about turbine engine principles follow.

Station numbers

In turbine engineering, to facilitate description and comparison, steps in the Brayton cycle are identified by a station number.

(Source)

Additional stations are defined to reflect specific needs (e.g. for the cold flow of a turbofan). The full standard is known as ARP 755, see this old but free description.

The exit of the combustor (which is also the turbine nozzle guide vane leading edge) is station 4. In this nomenclature, Tn is the temperature at station n, Pn the pressure, etc. As an example, the sensor seen in the fan inlet of many turbofan engines is commonly referred as T12 or P12T12 sensor.

Gas temperature and entropy

Thrust which can be produced by the engine depends on the turbine inlet temperature (station 4), which is limited by materials.

There are two means of raising the temperature. The compressor raises the temperature by increasing air pressure, the combustor raises it by fuel combustion at (ideally) constant pressure. The later increases entropy due to the breaking of hydrocarbon chains.

This is visible on a so called temperature-entropy (T-s) diagram, e.g. this one for the CFM56-7B:

CFM56-7B T-s diagram. Source

We can see the compressor work between stations 0 and 3 (with no change in entropy in a perfect cycle) and the (ideally) isobaric raise in temperature and entropy between 3 and 4 as fuel chemical potential energy heats air.

The area under the curve is representative, along with the mass flow, of the net work of the engine (energy produced by the turbine minus energy consumed by the compressor), hence its efficiency. The area depends on two main factors:

How much pressure (and temperature) is raised by the compressor.
How much entropy (and temperature) is added by the combustor.

The goal is to achieve the desired turbine temperature with the highest efficiency. By increasing the pressure ratio of the compressor (the height of the left vertical segment) less entropy has to be added by the combustor (horizontal segment). This means less fuel.

There is a specific PR value, around 30-35, for which the area under the T-s curve is maximal. This value is indeed targeted by the engine designer. Looking at the previous diagram (oblique lines in kPa), we can see the PR used is around 30.

CFM56-5C

Four CFM56-5C were used to power the smallest A340. A340 manufacturing has been stopped, as 4 engines are no more a good option in the era of high fuel prices.

Your question indeed boils down to: What is T4 for the CFM56-5C?

From this document (in French):

Pour une approche analytique de la dynamique du vol

which is a thesis by Elodie Roux, this table on page 198:

tells us the T4 temperature is 1633 K, that is 1360 °C.


Is the Beechcraft Bonanza Jaguar edition different from any other A36? I've seen a few Beechcraft A36 Bonanzas with special Jaguar marketing. Some have special paint or interiors. During some hangar talk I've heard it said that the Jaguar edition is faster. Does it actually have any differences that impact performance?

@acpilot is right- the Jaguar version of Beechcraft Bonanza differs only in the paint job and interiors. AOPA had run an article when the Jaguar versions were introduced:

Like the Jaguar edition of the Beech King Air C90B offered last year, the Bonanza and Baron will have specially outfitted interiors and unique paint schemes.
... Seats in the Jaguar airplane will use the same frames but have new cushions tailored to look like those found in the Jaguar Vanden Plas luxury car. ... tastefully wrapped the yokes in leather.
On the outside, a special paint scheme has been designed to set the Jaguar airplanes apart from standard Bonanzas and Barons.

and also,

The new soundproofing Beech plans for the Jaguar airplanes appears to work well in the rear of the airplane.

Looks like the only differences were the paint and interiors designed by Jaguar specialists:

Jaguar Cars' automotive stylists designed the paint and interior for these packages. Inside, they applied more and finer hardwoods — including a polished Jag-logo inlay on the right yoke — better carpeting, and the finest leathers from Jaguar's own vendors. Outside, the Jag-edition Bonanzas ... get a distinctive four-color metal-flake paint scheme finished off with Jaguar Cars' stylized leaping-cat insignia leaping from the vertical stab and rudder.

These are the only differences and everything else is the same. The performance changes if any would come from these- which I doubt. Around the same time, the Continental engines were refined (they were the same 300 hp though), which might have made the aircraft appear different, though there are none.


How is the Flight Plan Data transferred into an aircraft/plane? I know that pilots have to fill the ICAO standard flight plan and send it to the relevant CAA to be checked, updated if needed and finally approved before the flight takes off. what I am looking for is to understand how does the  aircraft receives that acknowledged flight plan data. I know that some airlines receive the acknowledged flight plan from CAA's and then send it to the aircraft via ACARS so the aircraft, is this the most common option or there are other option for the aircraft to receive the acknowledged Flight Plan? Please let me know.

First, as other answers have stated, you're not actually required to file a flight plan unless you're flying IFR. That having been said, if you do file a flight plan, there are several ways you can get it programmed into the airplane:

You don't

The flight plan is never loaded into the navigation system at all. It's either on paper or loaded into a tablet, and that's it. This is pretty common amongst small-aircraft private pilots.

Manually

The flight plan is printed or loaded into a tablet to get it out to the airplane, where it's then manually keyed in to the on-board navigation system. This was at one time the only way of loading a flight plan, and is still pretty common across all types of aviation.

Bluetooth

This is a pretty new option for the higher-end GA aircraft and charter aircraft. The flight plan is transferred from a tablet, laptop, or smartphone to the onboard navigation system via a Bluetooth connection.

ACARS or other data link

Yes, ACARS is used by the big airlines to transfer flight plans to aircraft. Note, however, that some commercial aircraft don't have the capability to automatically transfer the flight plan to the navigation system(s), it's printed out by the in-cockpit printer and keyed in to the navigation system as described above.


Does MMO (limiting Mach number) assume any maneuvering limits? This answer to a question about emergency descents notes:

  [Y]ou can accelerate descents by banking the aircraft
  into a turn. This allows you to increase angle of attack, thus
  increasing drag to keep speeds down, while rotating the lift vector
  away from the vertical so it's not working against you. The
  combination allows for higher descent rates with the same MMO/VMO
  limits.  Some operators train for this, but my impression is not many....

Banking seems like an obvious way to increase drag and accelerate descent when the only objective is to get to a lower altitude (e.g., due to rapid decompression).  So does forward slipping.  Is either ever indicated in manuals or emergency checklists?

I was wondering if such maneuvers might actually be contraindicated: Isn't MMO determined by the stress limits of the airframe?  If so, does MMO (in theory, if not in practice) assume some limit on angle of attack, and would MMO decrease at high angles of attack or slip?

The problem is that in a deliberately entered spiral dive it is very difficult to keep things in check.  In an idle descent, pitch is your only speed control (well... really, in the end, pitch is your speed control all the time; any glider pilot understands that), and in a spiral dive trying to slow down by increasing pitch is trickier because a lot of the pitch input just steepens the spiral and you just pull more G instead of slowing down.  Which is the whole reason spiral dives are to be avoided in the first place, especially in the IFR world.

In a jet in an emergency descent you will generally dump flight spoilers with the engines at idle and push over to accelerate to MMO/VMO.  An attempt to maintain MMO/VMO in a spiral dive turn would probably end poorly.  If you are diving straight at VMO, spoilers out, and want to get down faster, depending on the airplane you might get a faster descent by slowing to gear extension speed and extending the gear, but I don't think most manufacturers recommend that and it's not something I was trained to do (on RJs).

Sideslip doesn't come into it as sidesliping swept wing aircraft deliberately is very dangerous (it doesn't take much skid/slip to make a swept wing airplane want to roll on its back), and nasty dutch roll situations can result.  In any jet, once you are off the ground, the yaw damper system takes care of adverse yaw and any random disturbances, and you never touch the rudder pedals unless an engine quits.  It's generally feet on the floor after the initial departure profile until final approach.

In any case, in an emergency descent you are way above maneuvering speed so pulling too hard will fold the wings before stalling AOA is reached and trying to get more descent rate by spiraling would be suicidal.


How does ATC deal with a crew who is not capable of a clear pronunciation? It probably is common guesswork to think that in nowadays' World we all speak English no matter what our mother tongue is. This should be even more the case with Civil Aviation, where everything is in English and the staff is hired also based on its linguistic capabilities, yet the question arises:

How does the ATC deal with a crew who is not capable of a clear pronunciation? The opposite might also happen.

What to do in such cases?

There is special phraseology snippets that allow information to be transmitted over the frequency with more accuracy, slower, repeated or worded differently.
ATC may also query other company traffic to relay information in another language or they might use the ACARS/CPDLC system to transmit a text message, should both parties be capable.

SAY AGAIN
„Repeat all, or the following part, of your last transmission“

(Source: AIP Germany GEN 3.4)

WORDS TWICE
„Request: Communication is difficult. Please send every word, or group of words, twice.
Information: Since communication is difficult, every word, or group of words, in this message
will be sent twice.“

(Source: AIP Germany GEN 3.4)

SPEAK SLOWER
„Reduce your rate of speech“

(Source: AIP Germany GEN 3.4)


Are steam gauges more reliable than glass panels? I have always had a deep appreciation for technology and the future and I encourage that technology should move us forward whether that be in aviation terms or otherwise but one question has been on my mind for a very long time and that is why we have computerized gauges and not the old fashioned ones with the gauge hand behind glass. In the event that a plane loses power, wouldn't it be better to have physical gauges because if the plane loses power, those critical gauges on a screen will disappear. Is it just me or does it not make a huge difference? I suppose an old-fashioned glass gauge will stop too, just the same as a glass cockpit gauge?

Thanks. This is a question I have always wanted to ask someone who has the expertise to answer it.

Most aircraft using electronic displays have double (and sometimes triple) redundant power supplies to keep the electronics alive in cases of power failure. The mechanical gauge panels of the not so distant past did not have these same levels of redundancy built in.

Beyond power considerations, glass panels also contain features like weather radar, collision avoidance, and navigation that further increase the reliability and safety of the system as a whole.

That said, it's fair to say that glass panels are more reliable. The funny thing is, critical mechanical gauges are still included on most panels as last resort backups.


Are fly-by-wire fighters protected in AoA? When thinking about fly-by-wire, I always think about civilian aircraft (Dassault Falcon 7X, Airbus A350...) for which protections are implemented to ensure the aircraft stays in its designed flight envelope (load factor limits to avoid overstressing the airframe, AoA limits to avoid stall, bank angle limits to avoid inverted flight...). All these restrictions help maintaining the aircraft in a manageable situation while in flight. Some (e.g. pitch or bank angle limits) are OK for airliners but counterproductive for fighters. Other are clearly applicable to both (e.g. load factor. You don't want to overstress your airframe or risk a G-LOC).

My question concerns AoA protection. For fighters, I imagine this protection can avoid loss of roll control while stalling. Yet, some fighters are able to fly at AoA obviously beyond stall angle (e.g. during a cobra), suggesting this protection is not present.

Do fly-by-wire fighters have an AoA protection? If so does it prevent stall? (I can imagine a protection triggered only if a limit is reached for at least a certain amount of time, or a limit beyond stall angle but not far beyond.) Does it have to be deactivated for manoeuvre such as the cobra (I expect every system to be able to be deactivated on such aircraft)?

Brief answer: Yes, but the protection does not always work.

Most modern fighter aircraft have an AoA limiter. That is different from a stall warning – in case of the McDonnell Douglas F-4 the limit was only 23 degree, below the stall limit. The reason for the limit was the loss of directional stability above 23 degree AoA.

In case of the JAS-39 Gripen the limiter worked in a straight pitch-up but when the pilot repeatedly pitched up during a flight display over Stockholm, the dynamic response overpowered the AoA limiter and the aircraft stalled. It fell like a stone into a public park, miraculously without loss of life.

In another accident the JAS-39 FCS software got confused after the controls could not follow the change in angle of attack quickly enough when one aircraft flew through the wake of another, its adversary in an air combat exercise. This caused the safe limit of 20 degree to be exceeded and the aircraft became uncontrollable.