How does the cabin pressure controller work in a large commercial airliner? The cabin pressure controller controls the pressure in the cabin in relation with aircraft altitude, and a manual control is possible using the overhead panel:

A320

Air Conditioning and Cabin Pressure panels on an Airbus A320 (source: Olivier Cleynen on Wikimedia)

B737

Pressurization panel on a Boeing 737 NG (source: B737.org.uk)

Overall how do the controller and the related equipment work in a commercial airliner, e.g:

What is the source used for pressure reference?
How outflow and relief valves and packs are related to the controller?
When and how is used the manual control of the pressure?

The System you are referring to is described in ATA chapter 21. I will report here an example for A320

An overview of the system is reported below (from the ATA21 report):

  What is the source of pressure reference?

In flight the outside pressure signal can be come from either:

The Air Data Reference System (ADIRS), for the pressure altitude.
The Flight Management and Guidance Computer (FMGC), for the landing elevation.

If FMGC not available, uses the landing elevation from the ADIRS and the landing elevation

  How the different valves (outflow, relief) and the packs are related to the CPC?

There are two independent safety valves controlled by two independent Cabin Pressure Controllers (CPC) and actuated by three independent motors.
 The pressure in the cabin is controlled only with these valves, while the temperature of the cabin is controlled by mixing the air from the packs with the one of the cabin. In particular the valves are opened and closed to keep the desired pressure profile according to the logic dictated by the different flight phase. .

Different constraint drive the controller:

Cabin pressure at cruise altitudes is limited to an equivalent ISA pressure of 8000ft, due to structural fuselage requirements. By providing higher pressures levels (equivalent to lower ISA equivalent altitudes, e.g.: sea level) the fuselage would overstrain. A (very) simplified example  of this is a balloon in a vacuum chamber.
Maximum descent rate is kept under 750 ft/min for passenger comfort. Otherwise your internal ear starts hurting.
At take-off on ground the cabin is de-pressurized till -0.1 psi with a max rate of 400ft/min to avoid pressure surge at rotation

  When and how is used the manual control of the pressure?

Manual control of the pressure is used when both the CBC controllers fail or when the crew uses the cabin press control panel, that you showed. In case of aircraft ditching the inlets are closed as well with a ditching button (first image, right in the CABIN PRESS panel)


Why pets are allowed only on select flights? If the baggage compartment is always pressurized, why pets can be brought only to select flights and not all flights?

The USDOT has a list off things related to this matter here but there are many factors.

International Travel: Since flights often go between countries that also means they cross jurisdictions. Many countries have varying laws on importing and exporting different animals. As such airlines may not always allow you to carry animals since it may not be legal.
Contamination: Animals can carry a wide variety of disease and other things. An airline my chose to not carry animals to avoid any potential issues. Even if in the cargo hold it can not be guaranteed that the animals fur wont come in contact with another passengers baggage. If that passenger had an allergy to that type of fur they may later have an issue.
Food: Placing an animal in the baggage hold prevents anyone from effectively feeding the animal which the DOT does seem to have some regulations on for longer flights.
Temperature: Although it is pressurized the baggage compartment is by no means warm. This prevents a potentially dangerous situation for animals as well.

As for bringing an animal on the plane (aside from service animals which are not considered animals). It would seem that the FAA leaves this specific matter up to the airlines. According to this document when it comes to

What are the FAA rules regarding traveling with pets in the passenger cabin?
The Federal Aviation Administration (FAA) allows each airline to decide if they will allow you to travel with your pet in the passenger cabin. If an airline does allow you to bring your pet into the cabin, we consider your pet container to be carry-on baggage and you must follow all carry on baggage rules (14 CFR part 121, section 121.589):


Would more throttle when using reverse thrust reduce stopping distance? If more throttle is applied after engaging the reverse thrust, would it shorten the braking distance?

Broadly speaking, yes.

The standard method of operating reverse thrust on jet aircraft is to use the reverser levers, which are actually thrust levers as well.  As you pull the reverser levers up, you increase engine thrust.  Many aircraft types will have prohibited areas between idle reverse and full reverse thrust which should be avoided (for things such as blade flutter).  Importantly, reverse thrust is not considered when evaluating aircraft landing performance - it largely used to reduce wear and tear on the aircraft for reasons of economy of operation, usually idle reverse thrust is ample for this purpose.   As you suggest, in an emergency full reverse thrust can be used to reduce or prevent a runway overrun.

With propeller aircraft, turbine or piston, you may enter the 'beta' mode (if equipped), creating reverse thrust and selecting appropriate engine power as desired, though as with jets, there may also be prohibited engine speeds which may be passed through on the way to a higher speed, but not left at that level.


How small can turbojet engines be made whilst remaining fuel efficient, light, cheap, and producing enough thrust to carry a human, gas, and casing? I've seen many videos of small turbojet engines (small enough to hold in your hands) that produce 30-40 pounds of force. If you mounted a couple of these on a small craft, that wouldn't even support human + gas, and especially wouldn't support a fuselage or any other casing.

What size is efficient with gas but still produces a lot more than 40 pounds of thrust?

An extra question you don't need to answer: what is an effective way of tuning fin direction on the exhaust end of one of these engines? Basically, how can I twist a knob and make the fins tighten or twist in a direction I want the thrust to move in?

The figure of merit here is thrust to weight ratio (https://en.m.wikipedia.org/wiki/Thrust-to-weight_ratio)  For a good turbojet, you get about 5:1. So a 100 lb engine could produce about 500 lbf of thrust. Modern High bypass turbofans are significantly more fuel efficient than turbojets, but the thrust to weight ratio is still about 5:1. So calculate how big your human is,  how much gas you want, and divide by 5


Why do airlines require passengers to return to their allocated seats for landing? Airlines which allocate seats often make announcements prior to landing to request passengers return to their allocated seats. What is the motivation for this requirement, especially since I have never seen the requirement rigorously enforced by the crew (by requesting sight of the boarding pass).

The requirement is not simply a polite way of requesting standing passengers return to their seats – for two reasons:

Crews are typically explicit in their language when giving directions, such as requiring standing passengers be seated. It is clear from the phraseology and emphasis given in the announcements that returning to the allocated seat is a critical component of the request.
On a recent long-haul flight, a couple seated in my row were offered to relocate to vacant seats in an exit row for the duration of the flight, provided they returned to the allocated seats for landing. (They were not, at the time, standing.) Furthermore, in the event, only one member of the couple returned; the other remained in the non-allocated seats (an example of non-enforcement).

Some possible motivating factors I have considered:

Weight distribution – ensuring the flight envelope of the aircraft is not exceeded during critical phases of flight. However, I have encountered this situation on wide-body jets on long-haul flights (e.g. A346, A388), where a handful of passengers, of nominal mass, being situated elsewhere in the plane does not seem cause for concern.
Collection of personal effects – if passengers relocate after takeoff, they may leave personal belongings at their original seat, unwittingly or not.   A requirement to return to the original seat may:

trigger passengers to locate & take with them items left/forgotten at their original seat, reducing the cost of the airline returning these to passengers later.
improve the efficiency of disembarking by avoiding passengers who need to move against the flow to collect belongings elsewhere in the aircraft.

However, I have encountered this after long-haul flights with tens of hours of turnaround time on the ground, so eliminating a few minutes from the disembarking time of some passengers does not seem a high priority (and, in any event, the effect of reducing the overall exit time would be in the noise and difficult to quantify).

Limitation of privilege (hence, revenue protection) – passengers in a higher cabin tier may benefit from certain privileges upon landing, such as the possibility to disembark the aircraft more quickly. However, crew are normally hot on ensuring passengers do not self-upgrade to a higher cabin, so this would not seem to apply.
Emergency preparedness – for example, ensuring there is a sufficient cabin crew to passenger ratio in all areas of the aircraft to meet emergency / evacuation requirements. Such ratios may be upset in the event passengers relocate far from their original seat. (If so, why is this not an issue when in the cruise?)
Passenger identification – air crash investigators often use seating manifests to identify remains of deceased passengers, so this requirement could be to ease any future investigation in the event of an incident on landing. (Similarly, what about the rare likelihood of an emergency which rapidly develops while in the cruise, without opportunity for passengers to relocate?)

None of these reasons seem to entirely justify the requirement for this routine request or its existence across all manner of aircraft types.

My questions

What benefit do airlines or the wider industry gain from this requirement?
Why is it not rigorously enforced by crews?
How do airlines which do not allocate seats to passengers satisfy the same requirement when there is no published seating manifest in advance of passengers entering the aircraft, or why are they exempt from such requirements?

Its a matter of legal requirement (under the FAA, and I presume the EASA has a similar reg). Strictly speaking its really more important that the passenger returns to a seat. Generally you are asked to return to your seat as it can be assured its empty and available for you. Under FAA regulations you are required to be wearing a seatbelt for landing and thus must be in a seat

  14 CFR 121.311 - Seats, safety belts, and shoulder harnesses.

  (b) Except as provided in this paragraph, each person on board an
  airplane operated under this part shall occupy an approved seat or
  berth with a separate safety belt properly secured about him or her
  during movement on the surface, takeoff, and landing. A safety belt
  provided for the occupant of a seat may not be used by more than one
  person who has reached his or her second birthday.

Weight and balance is important but not on a single passenger level i.e. on an airliner of decent size if a single passenger moved around it would be ok. If half the plane was empty and the passengers rearranged them selves there might be an issue.

  How do airlines which do not allocate seats to passengers satisfy the
  same requirement when there is no published seating manifest in
  advance of passengers entering the aircraft, or why are they exempt
  from such requirements?

They are not exempt from the requirements but there are enough seats for everyone on the plane and as noted above its really important that you are belted in so taking an available seat will do in this case. On these flights generally speaking, you take a seat prior to takeoff and that somewhat becomes your seat for the flight. In my experience there is little if any mid-flight seat swapping.

  Furthermore, in the event, only one member of the couple returned; the
  other remained in the non-allocated seats (an example of
  non-enforcement).

As noted above the policy is to be belted in, so the regulation was indeed enforced. The other member of the couple may have remained in the seat if they were the only person capable of preforming the exit row duties.


What happens if a private pilot's license isn't used for some time? I have a question about the currency of a Private Pilot's License: if someone obtains a PPL but doesn't fly for a period of time, is there a time after which some conditions or restrictions are imposed?

I'm mainly interested in Europe and the US.

In the US (under the FAA) there are 2 things that must be maintained (lets assume this is a VFR license).

First there are some basic flight requirements. You don't need an instructor to complete these. It basically boils down to 3 take offs and landings every 90 days to be current to cary passengers. Here is the full legislation.

  Sec. 61.57

  Recent flight experience: Pilot in command.

  (a) General experience.

  (1) Except as provided in paragraph (e) of this section, no person may
  act as a pilot in command of an aircraft carrying passengers or of an
  aircraft certificated for more than one pilot flight crewmember unless
  that person has made at least three takeoffs and three landings within
  the preceding 90 days, and--

  (i) The person acted as the sole manipulator of the flight controls;
  and (ii) The required takeoffs and landings were performed in an
  aircraft of the same category, class, and type (if a type rating is
  required), and, if the aircraft to be flown is an airplane with a
  tailwheel, the takeoffs and landings must have been made to a full
  stop in an airplane with a tailwheel.

  (2) For the purpose of meeting the requirements of paragraph (a)(1) of
  this section, a person may act as a pilot in command of an aircraft
  under day VFR or day IFR, provided no persons or property are carried
  on board the aircraft, other than those necessary for the conduct of
  the flight. (3) The takeoffs and landings required by paragraph (a)(1)
  of this section may be accomplished in a flight simulator or flight
  training device that is--

  (i) Approved by the Administrator for landings; and (ii) Used in
  accordance with an approved course conducted by a training center
  certificated under part 142 of this chapter.

  (b) Night takeoff and landing experience.

  (1) Except as provided in paragraph (e) of this section, no person may
  act as pilot in command of an aircraft carrying passengers during the
  period beginning 1 hour after sunset and ending 1 hour before sunrise,
  unless within the preceding 90 days that person has made at least
  three takeoffs and three landings to a full stop during the period
  beginning 1 hour after sunset and ending 1 hour before sunrise, and-

  (i) That person acted as sole manipulator of the flight controls; and
  (ii) The required takeoffs and landings were performed in an aircraft
  of the same category, class, and type (if a type rating is required).

  (2) The takeoffs and landings required by paragraph (b)(1) of this
  section may be accomplished in a flight simulator that is--

  (i) Approved by the Administrator for takeoffs and landings, if the
  visual system is adjusted to represent the period described in
  paragraph (b)(1) of this section; and (ii) Used in accordance with an
  approved course conducted by a training center certificated under part
  142 of this chapter.

Every 2 years you will also need a flight review which is administered by an instructor.

  Sec. 61.56

  Flight review.

  (a) Except as provided in paragraphs (b) and (f) of this section, a
  flight review consists of a minimum of 1 hour of flight training and 1
  hour of ground training. The review must include:

  (1) A review of the
  current general operating and flight rules of part 91 of this chapter;
  and

  (2) A review of those maneuvers and procedures that, at the
  discretion of the person giving the review, are necessary for the
  pilot to demonstrate the safe exercise of the privileges of the pilot
  certificate. (b) Glider pilots may substitute a minimum of three
  instructional flights in a glider, each of which includes a flight to
  traffic pattern altitude, in lieu of the 1 hour of flight training
  required in paragraph (a) of this section. (c) Except as provided in
  paragraphs (d), (e), and (g) of this section, no person may act as
  pilot in command of an aircraft unless, since the beginning of the
  24th calendar month before the month in which that pilot acts as pilot
  in command, that person has--

  (1) Accomplished a flight review given
  in an aircraft for which that pilot is rated by an authorized
  instructor; and
  (2) A logbook endorsed from an authorized instructor
  who gave the review certifying that the person has satisfactorily
  completed the review. (d) A person who has, within the period
  specified in paragraph (c) of this section, passed a pilot proficiency
  check conducted by an examiner, an approved pilot check airman, or a
  U.S. Armed Force, for a pilot certificate, rating, or operating
  privilege need not accomplish the flight review required by this
  section. (e) A person who has, within the period specified in
  paragraph (c) of this section, satisfactorily accomplished one or more
  phases of an FAA-sponsored pilot proficiency award program need not
  accomplish the flight review required by this section. (f) A person
  who holds a current flight instructor certificate who has, within the
  period specified in paragraph (c) of this section, satisfactorily
  completed a renewal of a flight instructor certificate under the
  provisions in Sec. 61.197 need not accomplish the 1 hour of ground
  training specified in paragraph (a) of this section. (g) A student
  pilot need not accomplish the flight review required by this section
  provided the student pilot is undergoing training for a certificate
  and has a current solo flight endorsement as required under Sec. 61.87
  of this part. (h) The requirements of this section may be accomplished
  in combination with the requirements of Sec. 61.57 and other
  applicable recent experience requirements at the discretion of the
  authorized instructor conducting the flight review. (i) A flight
  simulator or flight training device may be used to meet the flight
  review requirements of this section subject to the following
  conditions:

  (1) The flight simulator or flight training device must be
  used in accordance with an approved course conducted by a training
  center certificated under part 142 of this chapter.

  (2) Unless the
  flight review is undertaken in a flight simulator that is approved for
  landings, the applicant must meet the takeoff and landing requirements
  of Sec. 61.57(a) or Sec. 61.57(b) of this part.

  (3) The flight
  simulator or flight training device used must represent an aircraft or
  set of aircraft for which the pilot is rated.

The license its self (as the laws currently stand) is good for life, barring you having it revoked for some reason you will not need to fly your check ride again (unless you go for something like an instrument rating or a higher license).

Until recently here in the US you also needed a valid medical certificate. However recent regulation change has altered that a bit. You can read up on some of the changes here as they are still in progress.

On a bit of the more practical side there are some things to consider. For example many people here in the US rent aircraft. Your local flight school or rental facility may impose other rules on flight currency for you to be allowed to rent a plane. Likewise if you own a plane your insurance company may require certain experience or other things in order for you to be allowed to fly your plane. Generally this is based on your experience as well as time in type.


Where can I find more information about that glass board in old aircraft carrier operations centers? When I was a kid, I used to read this comics about aircraft pilots in the 50's, and in the operations center of their aircraft carrier, they had operators using markers on a glass wall to keep track of operations. Any idea how that was called and where I can find pictures of it? Is it still in use today, or is it now all computerized?

Perhaps you're referring to the status board (still in use):

(navy.mil)

  Air Traffic Controller 3rd Class Jeoffrey Keever writes the status of each aircraft on the status board in Carrier Air Traffic Controller Center (CATCC) aboard USS John F Kennedy (CV 67) during flight operations.

Windows also seem to work:

(navy.mil)

Also the low-tech but dependable Ouija board is still in use:

(navy.mil)


Can a wide body airliner land safely with a full fuel tank? Can a commercial double-aisle jet aircraft (e.g., 777, A330) land safely with a full fuel tank (minus the fuel spent on taxing and takeoff)? Has that ever happened?

Can a wide body airliner land with a full fuel tank?

Yes! But it is safer to land an aircraft below its published MLW.

Wikipedia has the relevant specifications for the B777 and the A330

Using the B777-200 as an example.

Maximum take off weight: 545,000 lb / 247,200 kg
Maximum landing weight: 445,000 lb / 201,840 kg

So this particular aircraft may have to drop roughly 46,000 Kg of weight if taking off at its maximum before it can land safely. That's not to say it's impossible to land without doing so, but it's certainly not advisable.

When an emergency presents itself, what is "advisable" is getting on the ground as quickly as possible, and if that means landing overweight then so be it. There have been plenty of times when an overweight landing has caused no damage - and even if the aircraft is damaged by an overweight emergency landing, that's still often a better outcome for the people on board than would be the case if the aircraft waited to get below its MLW before landing.

However, with that said, just because you are taking off with a full load of fuel it does not imply that you must be at MTOW. You could be taking off with a full load of fuel but no cargo/passengers, in which case it is entirely possible that you may be below MLW. And in which case the answer would be yes, it's entirely possible to land with full fuel tanks.


Compression and tension members of a biplane wing I get why the upper wing of a biplane is a compression member (because the flying wire is attached to it at an angle) but what I fail to understand is why the lower wing is the tension member of a truss of a biplane as explained here. So my question is why is the lower wing of a biplane referred to as a tension member of a struss?

It's not a tension member in that sense.  This is a pin jointed truss with flexible tenion-only diagonals.  The lower wing is a non-cantilevered beam, that is, supported at both ends, so it will bow up in the center under load with flight loads, and this applies a modest tension load at the root (as well as pulling the bottom of the interplane strut inboard, to the extent that deformation occurs in the main spar beam).   If the lower wing's spar had perfect rigidity and didn't bend at all, there would be no tension load at all at the wing root; it would be all vertical shear.

If you thought of the lower wing as a sheet of fabric, and imagine that the interplane strut at the outer end was rigid vertically, you'd have basically an upside down hammock, and when you lay in a hammock, the attachments are under tension (of course, the outer interplane struct not being rigid vertically, the hammock would collapse straight up - in the biplane's case the lower "hammock" is a semi-rigid length of lumber that only deflects slightly so the outer interplane strut doesn't have to be vertically fixed).  So the extent of any tension load at the root fitting for the lower wing, it's only to the extent that there is a hammock effect happening as the spar deforms.

To get the lower wing to work in tension as part of rigid truss system with the upper and lower wings integrated into it, the X of diagonal wires have to be replaced with rigid struts that can take compression.  The rigid strut running down from the upper root to lower tip would be in compression, sharing load with the other one in tension, and this would make the lower wing a tension member in the system.  But with tension-only flying wires, that doesn't happen.

Clear as mud?


Can I get an EASA Class 1 medical if I have monocular vision? I have monocular vision (amblyopia). In the USA I can get an FAA first class medical via a SODA waiver. Can I get an EASA Class 1 Medical issued with the same monocular problem? I would be applying for a medical in Ireland.

If I absolutely can’t get an EASA Class 1 medical, then will European airlines hire ATPs with a US FAA first class medical, or do EU airlines all require EASA Class 1 Medicals?

The Irish Aviation Authority's aeromedical site directs you to the underlying EU regulations (Part-Med), which say:

  Applicants for a Class 1 medical certificate shall be required to have
  normal fields of vision and normal binocular  function.

That seems to rule out monocular vision completely, which is very strange (to me) considering that the FAA is very clear that binocular vision isn't needed to fly safely. But medical issues are complicated, so I would definitely consult an aviation medical specialist in Ireland before making any decisions.

As for using an FAA medical certificate instead of an EASA one, that should really be a separate question. However, it's highly unlikely to be possible: generally speaking, your pilot's license/certificate and medical have to come from the same country.


Are there any accurate books that help with identifying aircraft when planespotting? I want to start planespotting and I'm looking for the best and mosts accurate registration book.

I want this book to be:

accurate
checkable (to check planes I have seen)
have almost every plane
codes (IATA | ICAO)

If anyone knows a book I would love to hear it!

The best option is probably Jane’s Aircraft Recognition Guide. It is hard to find, but it has a large number of planes and has multiple editions.


How unusual is the 737 MAX 8's crash history? The Boeing 737 MAX 8 is getting a lot of bad press at the moment,  but people's instincts when it comes to probability are generally terrible, especially when it comes to risk assessment.

Compared to other models, how unusual is it for there to be two crashes in half of a year, of rather young planes? How much total flight time has the model had? How statically signification is it?

Historically, it's not unusual at all to have many accidents of an aircraft type in relatively short order, especially when the type is still new and hasn't had a lot of operating hours across the fleet to detect and work out teething problems.

BUT, and that's a big BUT, in recent history that's been happening less and less as testing and certification programs have gotten ever longer and stricter (in large part as a result of those earlier crash series).

As for the 737Max, according to Wikipedia some 350 have so far been delivered (out of over 5000 on the order book) over the space of only 2 years (yes, they're that new). Of those 2 have gone down. That's not a particularly high number historically, but as said in recent history people have come to expect nothing bad to ever happen because there have been so few accidents overall and most of those easily explained by external factors (MH17 being shot down, for example).

So this number is both highly unusual, in that it's not something that's been seen in recent memory, and rather normal, in that in the history of aviation it's not unusual at all.


What is the meaning of the letters on the side(s) of WWII British aircraft? WWII British Spitfire and Hurricane had identification letters on the side of fuselage. Do they have a specific meaning? How are the letters chosen?

Spitfires had a few different markings, but primarily there were two. One, written in smaller, often black, text was the aircraft serial number and stayed with it for its entire life. The other, usually either side of the roundel was the squadron and airrcraft id:

Image source

XT was 603 Squadron. So if a Pilot of that squadron was told to go and "Fly Delta" he would know to go to that specific aircraft. Aircraft would have been lettered in sequence, Alpha, Bravo, Charlie etc.

There were some exceptions; to wit

  ...Thus the famous Douglas Bader was allowed to have the letters "D-B" painted on the side of his Spitfire VA, because he commanded the Wing flying from Tangmere Aerodrome. Bob Stanford-Tuck, commander of the Biggin Hill Wing had a Spitfire with "RS-T" on it.
  source

Hurricanes followed the same standard


Anyone able to help identify what aerofoil this is? Firstly, apologies for the potato quality of the image below. I am attempting to determine the qualities of a VTOL and cannot find any data online. If anyone knows what aerofoil this could be that would help a bunch! (the green line is the upper edge and the yellow line is the lower edge)

Try contacting the local FAA Flight Standards District Office (FSDO-'fizzdoe') for help. They may be able to tell you how to get a copy of the aircraft's certification documents which may indicate the airfoil used. Mention the aircraft's N-number: N301XZ. To locate the nearest Flight Standards District Office, see here:

https://www.faa.gov/about/office_org/field_offices/fsdo/


Does the a320 neo have anything like MCAS? I am trying to book a flight that will be on an A320 NEO.

Does this have any 'new' systems or features, like the MAX MCAS system?

I'm asking this question also because one airline has just grounded it's NEOs...

Different airplanes, different systems; however, all modern airliners have computer assisted flight controls to some degree.  These include stall protection of various types, of which Boeing's MCAS is one.  Airbus uses different methods of stall protection, but there's still a computer involved.

Do you need to worry about the same issue?  No.  Part of Boeing's problem was that they didn't tell people about their system and pilots weren't trained.  Had the pilots known about the system and how to disable it, the crashes probably would have been avoided.


Does pilot-controlled lighting work if you are interrupted by another voice transmission? This question is in the context of pilot-activated runway lighting, which involves clicking the microphone e.g. 7 times to turn on the lights at night. I was wondering what happens when you are clicking the radio button, which typically takes several seconds, and suddenly someone else starts transmitting on the same frequency while you are still clicking? Does that mean your attempt has failed, since the other person's transmission is often continuous? To what extent is the receiver on the ground able to discern between the two signals? Does it depend on our relative proximity to the airfield? Or is this nothing I should worry about?

From a technical standpoint, it's extremely difficult to tell two different signals on the same frequency apart. So, if someone steps on you while you're trying to turn the lights on, then the ground equipment can't tell the difference between their radio and yours. So, unless the other radio is far enough away that it doesn't register on the PCL receiver at all*, it won't activate. You'll just have to try again when the other pilot's done talking.

In general, it's usually nothing to worry about, because the other pilot(s) nearby will hear you clicking, and know to avoid using their radio until you're done.

* Many airports turn the sensitivity on their PCL down so that distant planes on the same frequency won't interfere with a local pilot trying to land.


Aviation ebook for beginners? I'm new to aviation but I am very passionate about it. I'm just 14 years old, so please help me in finding a good e-book about aviation for free.

I don't know how to search with Google about it.

Although this is a question based on opinion, it might perhaps have some value as a community wiki so I've marked this 'answer' as such. I also borrowed one of Manfred's links. Feel free to append stuff to the list.

In terms of free download, I can definitely recommend the FAA Airplane Flying Handbook which can be found on the FAA web site. There are also a number of other handbooks there which are great reads. To be honest, I find this the best introductory book I know, free or otherwise.
If you're out for a good reference book, something like Anderson's Introduction to Flight will be good, but bear in mind this is hardly an easy read but does cover virtually everything you will need to know. An older edition seems to be available online.


Going from VFR in Class B to IFR If I departed a heliport in Class B airspace, on my way out can I tell approach that I want to cancel my VFR flight plan to pick up an IFR flight plan?

I figured I could because Approach will be controlling me while I'm in the Class B airspace but I want to make sure before I request it.

There are several ways to do what you are requesting.  One way is to follow the guidance in the Airman's Information Manual, para. 5-1-7 (AIM).  This guidance describes how to use a "Composite Flight Plan."  With this procedure you are filing a VFR flight plan and an IFR flight plan simultaneously, and in your case with the intention of using the VFR Flight Plan first.
Although the description in the AIM describes a flight in which the pilot is not already talking to ATC (as you plan on doing because you will be in Class B airspace) the general procedure is clear.  Depart the airport, open the VFR Flight Plan with the nearest FSS (or other facility), and at the appropriate point where you planned to begin the IFR portion of your flight and while in communication with ATC in the Class B airspace, request the IFR clearance.
After picking up your IFR clearance make certain that you cancel your VFR flight plan (you can ask the IFR controller to do this for you, but if you have a second radio you may just want to call the nearest FSS and cancel it yourself).
A second, perhaps more efficient method to accomplish what your question suggests is to: (assuming you are departing from an airport near or within Class B airspace)

File an IFR flight plan with a starting point at or abeam whatever location/fix etc. you want to begin the IFR route.
Obtain a VFR clearance into the Class B airspace from ATC (you won't have a VFR Flight Plan, but you will be receiving flight following and thereby realizing essentially the same benefit).
At the appropriate point as filed in your IFR Flight Plan, request the (IFR) clearance from the controller you are in communication with.
In this case you won't have a VFR Flight Plan to cancel.

I'm not suggesting that you should not have a VFR Flight Plan if you will be traveling anything other than a short distance before you start flight following (or a Class B clearance) from ATC.  But, if you are departing an airport near the Class B airspace and will be talking to ATC shortly after takeoff the benefits of having a VFR Flight Plan may be essentially irrelevant if you are already talking to ATC receiving flight following or Class B service and will be transitioning to an IFR clearance.
Lastly, if your only intention is to get an IFR clearance while you are flying along VFR, see "How do you request a "pop up" IFR clearance?" which has already been answered in this StackExchange. But since your specific question indicates that you are interested in a procedure where you have filed an IFR and/or VFR flight plan before departing I hope my comments help your understanding.


Airbus Beluga, what is aft of the cockpit? In the Airbus Beluga (and Beluga XL), the main cargo deck runs the full length of the aircraft, starting just above the cockpit. Is there more usable space behind the cockpit? Or are there fuel tanks here?

In the attached image of a Beluga, there appears to be large door immediatly forwards of the tailnumber, and a smaller door aft.

Image taken from Airbus Beluga promo site

On the Beluga, the area behind the cockpit bulkhead 6 is unpressurized. It contains avionics (A19), the nose wheel and the crew entry hatch (17). It is connected to the forward underfloor cargo bay. That area is unchanged from the A300: it's where the passenger luggage is usually kept. Aft of the wing is another cargo bay.
The same goes for the Beluga XL: underneath the floor, it's identical to a normal A330.

This article indicates the underfloor cargo areas can be used:

... the Beluga XL can carry two A350 wings with additional space for other small components and cargo pallets underneath the main hold floor.
Underneath the freight area is room for 14 LD3 containers as well as a bulk cargo compartment in the far aft.


What is the technique or procedure to disable/disengage the MCAS on Boeing 737 Max 8 & 9 Aircraft? What is the technique or procedure to disable the MCAS and manually fly the Boeing 737 MAX 8/9 Aircraft?
To clarify my question, what I'm asking is can the pilot disengage the MCAS and if so, how do they do that? Is it just flipping a switch or popping a breaker, or is it a complicated set of procedures?
UPDATE: The answer to this question explains how to disable/disengage the MCAS from pitching the nose down.
UPDATE: This video is the most concise answer to my question that I have found. It shows a crew in a full motion simulator like the Boeing 737 Max 8 that crashed in Ethiopia, then it shows the proper technique to disengage the MCAS and manually trim up in the same scenario.

MCAS doesn't have its own on/off switch
It is a fly-by-wire feature designed to account for a particular flight regime that would not (or was not expected to be) encountered very often in normal operations, and is intended to account for some of the aerodynamic effects of the LEAP-1B (CFM International) engine installation for this model.  Its activation requires a number of preconditions, but we'll get to that in a moment.
A concise description of the system is found here.  The observation was a follow up to an observation that the MCAS isn't an anti stall feature like a stick shaker, but rather ...

Just about everything you have read in the media is wrong.  MCAS is not stall protection.  MCAS does not counter the additional thrust of the more powerful engines. It is only there because the larger engine nacelles of the B737 MAX cause an aerodynamic pitch up moment at high angles of attack that did not meet FAA longitudinal stability and stick force certification standards.  The easiest fix was to automatically apply a little nose down trim at high angles of attack.

A few things that should disable it (with caveats)

Lower the flaps. It is intended to work only if the flaps are up.

Turn the Stab Trim switches to OFF.  This disables the horizontal stabilizer's trim completely, and reverts to manual trim (there are two guarded stabilizer trim switches in the aisle stand, see Windshear's answer).  This means that the pilots must move/rotate the trim wheels in order to apply pitch trim during flight, though the Max trim wheels being of a smaller diameter raises a training and effectiveness problem1 that deserves its own question and answer.

The manual pitch trim procedure appears to be what a few crews did prior to the LionAir crash in October 2018.  It is unclear how many of the crews knew that it was MCAS that was malfunctioniing, versus any other trim or pitch anomaly.  The previous LionAir crews on the accident aircraft ended up flying to their destination manually. (Original source is the Preliminary Report from that accident).

... pilots encountered problems involving the AoA as well as the pitot tube used to measure airspeed.  In a flight in the same plane the day before, to Jakarta, the pilot experienced many of the same symptoms as the pilots on flight JT610: the stick shaker activated during rotation, an indicated airspeed warning alert appeared, and the aircraft began automatically pushing the aircraft nose down.
The pilot, after determining that his flight display system was malfunctioning, ran a runaway stabilizer non-normal checklist which led to the MCAS being disconnected when the stabilizer trim switches were turned off.  The copilot flew the rest of the flight using manual controls and without autopilot.
That Jakarta flight was using an angle of attack sensor that had been replaced after the previous Lion Air flight to Denpasar experienced problems. {snip} However, it is not clear whether the pilot communicated that he ran a runaway stabilizer non-normal checklist during the flight, which might have alerted the airline’s engineering staff that there was still a problem. (source)

Enable autopilot.  It is supposed to only work if the autopilot is off.  But...CAVEAT

That last part is a little bit complicated: the autopilot may not stay on if it - the autopilot system - keeps getting spurious signals from the AoA sensors, or if the pitot static system is providing bad data to the FCCs.
How do you know that you need to disable MCAS?
A related question is "when do you know that it's time to turn off Stab Trim switches?"
The problem for a given crew is: how do you know what sub-system is giving you trouble?  The AD released in December of 2018 updated the Runaway Stabilizer procedure.  Since there are other malfunctions possible in the trim system for pitch, such as a trim runaway, the same (or similar) symptom may manifest during malfunctions with different causes.  (See the example above).  If additional symptoms are present, such as a stick shaker activating from an erroneous AoA indication or some other fault, which problem do you solve first?
Which problem are you having?
Are you having both problems, or even something else?
That concern, the relationship between different potential failure modes, gets to the heart of

What is in the pilots manuals?

What training the crews do, or do not, get on this sub-system?

The MCAS is only supposed to activate under certain conditions (in theory): high angle-of-attack, flaps-up, flight with autopilot off.  This includes high angle of bank flight in such conditions.

###CAVEAT
Take a look at that last bullet in the lower right of the figure.  It's only partially correct.  When the pilot overrides with yoke trim, MCAS will try again five seconds later (after the pilot has stopped) unless the triggering condition, or signal, goes away.

"In the event of erroneous AOA data, the pitch trim system can trim the stabilizer nose down in increments lasting up to 10 seconds," Boeing explained to operators in a bulletin issued last November, following the JT610 accident. "The nose down stabilizer trim movement can be stopped and reversed with the use of the electric stabilizer trim switches but may restart 5 sec. after the electric stabilizer trim switches are released. Repetitive cycles of uncommanded nose down
stabilizer continue to occur unless the stabilizer trim system is deactivated." (source)

It is this system behavior that is believed to have ultimately overcome the best efforts of the pilots in the LionAir crash.  They were airborne for about six  minutes before they were no longer able to overcome the horizontal stab position with their trim controls.  (Caveat: current as of early 2019.  When the final report comes out this may become a lot clearer, and may need revision).
There is an easy-to-understand video of the relationship between the jack screw and the horizontal stabilizer function here.  Whenever the jack screw is moving the horizontal stab, a cockpit cue that this is occurring is the rotation of the manual trim wheels (seen at about 3:40 in the video).
Why is this activating during takeoff/departure?
That MCAS appears to activate(sometimes) during routine flight regimes is believed to be catching some crews by surprise - and not just the two accident crews.  There is a recent article in *Atlantic* that excerpts some NASA reports by aircrews in the US about some cases of unexpected / odd pitch behavior in this model aircraft.  As of mid 2019, the AoA signal (be it from signal error or a faulty AoA probe) has been identified as a part of the problem in this unexpected activation during takeoff and departure.

1 Note from @user40476, slightly edited:
If you are a bit late to switch off both CUT OFF switches, the deflected angle of the THS will create strong forces on the trim screw, more particularly if simultaneously you hold the yoke to maintain an acceptable pitch.
Critical Flight Safety Issue Follows
In these conditions, it becomes very hard to move the trim wheels manually. This is a major problem; the trim wheel diameter in the 737-MAX is smaller then the trim wheel of the previous models: 737-100, 737-200 etc. This smaller diameter reducing the efficiency of the pilot force on the wheel handle. (Less leverage for the same amount of pilot force applied).
Important Note: this answer is based on information available before the deep dive into the MCAS system that was required to recertify the 737 Max.  It will probably require revision when the final recertification process of the 737 Max is completed.


What ATC entities does a commercial airliner communicate with? As a private pilot, I am familiar with tower, ground, approach and departure control, but I am aware that there are other entities like clearance, pushback and center. If I were flying a commercial airliner, what is a complete, ordered list of entities (and a brief description of roles) I might talk with over a flight between two class B airports?

This answer details the procedures used in the US. Other countries will be similar, possibly with different names for some positions.

When preparing for a flight, after their flight plan has been filed, the pilots will first talk to the clearance delivery controller. This controller clears their planned route and altitude. At larger airports this may be done via text rather than voice. The pilots may also call their company dispatch to get the route or fix any problems.

If there are significant delays in effect at the airport, the pilots may have to talk to the metering controller. This controller is responsible for holding aircraft at their gates. Weather at departure or arrival airports may reduce the number of aircraft the airport can handle. There is no sense in sending the aircraft onto the busy taxiways if they will just have to sit there and wait for weather or traffic before they can depart.  The metering controller will eventually hand the pilots off to the next controller when the aircraft is finally cleared for departure.

Again at larger airports, the next contact will be with the ramp controller. This controller is responsible for a ramp area near the terminals. The controller will let the pilots know when it's safe to push back, and which way they should turn at the end of the push back. After starting their engines, the pilots will receive instructions for exiting the ramp.

Once pilots reach the edge of the ramp area, they will call the ground controller. This controller is responsible for managing traffic on most of the taxiways. The pilots will receive instructions for taxiing to their departure runway. If this route takes them across an active runway, the ground controller will have to clear this with the tower controller, or possibly have the pilots switch to the tower controller for permission to cross the runway. At small airports, the ground controller handles all of the previous positions as well.

Upon reaching their departure runway, the pilots will switch to the tower controller. The tower controller is responsible for the active runways. Busy airports may have multiple tower controllers managing different runways. The tower will clear the pilots for takeoff, ensuring proper separation between any other arriving/departing aircraft.

Shortly after the aircraft starts climbing, the tower will hand the pilots off to the departure controller. Depending on the location and traffic levels, this could be the same controller and frequency as the approach controller. This position is part of the TRACON (Terminal Radar Approach Control) facility. High traffic areas will have their own separate TRACON facility, while in lower traffic areas this will be combined with a tower location. In other countries this is referred to as the Terminal Control Center (TCC).

The approach controller's responsibility is routing aircraft leaving airports in the area to avoid conflicts between aircraft, but often the pilots will just fly the published departure procedure. The departure controller receives reports of weather such as precipitation or icing and passes this on to other aircraft.

Upon reaching a certain altitude, the departure will hand the pilots over to the center controller. This position is part of an ARTCC (Air Route Traffic Control Center), often abbreviated to "center". The US has 22 ARTCCs, each further divided into different sectors. Sectors are consolidated between controllers depending on traffic levels. Other countries refer to this as an Area Control Center (ACC).

The center controller is responsible for traffic at higher altitudes, primarily enroute traffic. The aircraft may pass through multiple centers, and each center may have different sectors controlled by different controllers. The pilots will be handed off between these controllers. Pilots must request altitude or course changes (for efficiency or weather reasons), and controllers may issue changes for traffic reasons. Controllers also handle pilot reports of conditions such as turbulence.

If the flight is crossing large areas of ocean, the flight may be handed over to an oceanic controller. These controllers do not always have radar coverage of the aircraft they are controlling. They rely on the aircraft following their published routes and altitudes, and providing regular position reports. The lack of radar means there are also more strict rules about deviations from flight plans.

As the pilots get closer to their destination, they will start on their arrival procedure. This usually specifies altitudes and possibly speeds, so the pilots will need to plan when to start their descent in order to meet these restrictions. The center controller will know the procedure and instruct them to follow it, and possibly issue deviations as traffic requires.

At some point before arriving, the pilots may also contact their company at the arrival airport. They may need to coordinate passenger needs such as wheelchairs or medical/security issues, or communicate maintenance needs. They will also coordinate what gate they are scheduled to use. This can also be done via text, such as through ACARS.

When descending out of center's airspace, pilots will be handed over to the approach controller. This position is part of a TRACON and handles arriving traffic. Depending on the location and traffic levels, this could be the same controller and frequency as the departure controller. The pilots will continue to follow the arrival procedure, again with any deviations issued by the controllers. The departure controller receives reports of weather such as precipitation or icing and passes this on to other aircraft. The controller may also issue information about weather observed on radar, although each aircraft also has its own radar onboard. The approach controller will then provide vectors to the pilots as needed to get them to an approach procedure. The approach controller will then clear the aircraft to fly a certain approach to a certain runway.

Once the aircraft is established on the approach a few miles from the runway, the pilots will be handed over to the tower controller. The tower will clear the aircraft to land. If the aircraft has to go around, the pilots are sent back to approach to be sequenced back onto the approach. The tower controller also receives reports of wind shear and at what altitude pilots break out of the clouds, to pass on to the next aircraft.

After exiting the runway, the pilots will change to the ground controller. As before, the ground controller issues taxi instructions to get the aircraft to the appropriate ramp.

Before entering the ramp, the pilots will call the ramp controller. The ramp controller must see if the aircraft's scheduled gate is available. If not, the aircraft will have to wait on a taxiway somewhere. Once the aircraft's gate is free, the ramp controller allows the aircraft to enter the ramp, and park at the gate.


For a same propeller solidity, what are the tradeoffs between blade activity factor and blade number? In order to absorb more power for a given prop diameter, we can design the propeller with a higher activity factor-- basically what amounts to wider blades-- or we can also design it with more blades. Both increase the solidity, and thus the ability to produce more thrust, but what drives optimal design? Longer chords mean more drag on an individual blade, but more blades mean more disruption of the airstream. Why and when choose one over the other?
Low blade count, low activity factor:

Low blade count, high activity factor:

High blade count, low activity factor:

High blade count, high activity factor:

One way look at it is your engine is power and prop is load.  The amount of thrust you get will depend on the efficiency of the propeller x engine power output.
So, if one is going for the best fuel economy, the two blade is most efficient, but if you want the more thrust from a larger engine, you either increase the number of blades or increase the chord of the blades.
Both approaches reduce efficiency but increase thrust output, resulting in increased performance.
More high aspect blades, as in a helicopter, will be more efficient at lower airspeeds, but will suffer structural issues (bending) as forward airspeed increases.
Fewer low aspect blades offer a much higher forward speed range but will create a lot more blade interference turbulence at lower airspeeds.  These are commonly seen on turboprop freighters such as the C-130.
It is extremely important to evaluate the design speed envelope of the aircraft when choosing, as forward airspeed reduces interference turbulence.
I took the liberty of adding the A6 Intruder jet aircraft to your list, and found the expected improvement in higher airspeed performance, but a take off run almost 5 times that of the A2D-1 Skyshark.
Enough said there.  Contra rotating coaxial props, and keeping prop speeds below supersonic, also help improve efficiency.


Why does the F-22's wing give it such great maneuverability? An F-22's wing is much different than a wing like the one on the F-16.

This an F-16 wing design:

(Source: www.aviastar.org).

This is an F-22 wing:

(Source: s3.zetaboards.com)

There is a great difference between the 2 wing designs. The F-22 is a very maneuverable aircraft and can out perform almost all the current fighter jets. The YF-23 has a very similar wing design and is considered to be one of the most maneuverable aircraft of all time.

So why does this wing design give the F-22 and YF-23 such good maneuverability?

The YF-23:

(Source: en.wikipedia.org)

The wing design is different between F-16 and F-22 (which is similar to YF-23) because the requirements were different.

The wing of F-22 (and that of F-23) were designed with stealth in mind, with the wing (and control surface) edges parallel to each other. There was no such design requirement in case of F16.

F-16 is a highly maneuverable aircraft in its own right. However, there are some reasons the F-22 is more maneuverable (i.e. it is super maneuverable) compared to the F-16, most of which are unrelated to wing design.

In general, lesser the wing loading, higher the performance. F22 has a lesser wing loading compared to F-16 (377 kg/m² vs 431 kg/m²). Though this figure will vary depending on various conditions, the F-22 has a lower value, helping in maneuverability.
The F22 has thrust vectoring, which basically acts to increase the control authority and also helps in controlling in high alpha region where the conventional controls would've become unusable.
The F22 is maneuverable in the post-stall region, something the F-16 is not capable of. This helps the F-22 in performing maneuvers like the Cobra and Kulbit, which is not possible in F-16.

As a side note, the F-16 VISTA technology demonstrator (which had thrust vectoring) is considered super-maneuverable on par with THE F-22, though it had the same wing.


What's the best way to get started flying? I'm considering flying.  I'd like to find out what is the best way to start.

I find climbing into the aircraft a good first step ;) Sorry, couldn't resist!

The best way to start is to find and visit a local airfield near where you live.

Most local airfields have some level of training taking place, and if the closest to you does not then another, perhaps slightly farther afield, will do.

Visit one of these flying schools and ask to speak to an instructor, a CFI, or an examiner. They will give you more details such as the aircraft they fly, the typical syllabus and the expected costs.

From there, you might like to start with a "trial flight" - typically 30-45 minute flight where you get to take controls and get a feel for piloting an aircraft.

Good luck.


Why would the propeller of a lightsport plane or ultralight w/ Rotax engine be connected to the engine through a clutch, and not turn at low rpm? Why would the propeller of an ultralight or lightsport plane be connected to the engine through a clutch, and not turn at low rpm?

I've often witnessed the engine start of a Bailey-Moyes Dragonfly (link to flight manual, links to cool you-tube videos but not showing engine start #1, #2) and the prop did not turn until the motor rpm was increased substantially above idle.  It was clear that some sort of automatic clutch was not engaging until the engine rpm was increased above idle.

It would seem that any sort of clutch that would allow the engine to run without the prop turning would add un-necessary complexity.  So why was this feature incorporated into the drive train of some versions of this aircraft?

I'm rather sure I was told the answer to this once, but I've forgotten.

I know that the aircraft in question was powered with a Rotax engine, but several different Rotax engines have been used on this type of aircraft, and at present I'm not able to identify the specific one I witnessed where the prop was not turning at idle.  It seems likely that many other aircraft powered by the same engine would use the same gearbox with the same automatic clutch feature.

Centrifugal clutches are mainly used to provide a compliant connection between the engine and prop to absorb power pulse peaks, as well as allow the engine to be automatically disconnected from the drive system at idle.

The big bugaboo of reduction drives over the years has always been torsional resonance resulting from the flywheel - the prop - being driven through a springy drive path by strong pulsating power impulses.  At RPMs where the pulse/feedback frequency matches the natural frequency of the drive system/prop, you get massive resonant torsional vibration, which at minimum is unpleasant and at maximum can trash the gear train.

Over years various attempts have been made to tame this phenomenon in a practical way.  It's not actually a good idea to use a centrifugal clutch in a normal aircraft.  If the engine quits, the prop can freewheel and this turns it into a very powerful airbrake. It's also a reliability issue, being a friction device in a critical power path.

That said, a coupling that has been used with some success, and even certified at one time, was the Flexidyne Dry Fluid Coupling, which works like a centrifugal clutch but uses steel shot encasing a wavy plate in the housing to act a bit like a fluid torque converter.  The FAA certified Molt Aerocar used a Flexidyne to connect the Lycoming to the prop down a long drive shaft (which suffers from the same kind of torsional resonance problems).  Problem is, Flexidynes get really hot, and you still have the windmilling problem (Molt Taylor used the Flexidyne in several of his homebuilt concepts but he never really addressed the freewheeling prop issue) and a propeller brake might be in order if you want to be able to glide (or a feathering or folding prop).

You see centrifugal clutches used in paramotors, mostly because it allows the motor to be running at idle without the prop turning, a handy feature for a paramotor.  I wouldn't be surprised if the Dragonfly's engine is actually using a Flexidyne instead of a friction clutch.

The most common compliant coupling between motor and prop however, is rubber.  Most commonly a rubber drive belt system, used everywhere on ultralights and some automotive aircraft conversions.  Or as successfully used by Rotax, a rubber coupling in the gearbox itself. Rotax, after a lot of effort, was able to create a rubber drive isolator that would be effective in a given engine's operating range.  This would have taken a massive engineering effort over the years to perfect.


Why is there a difference between GPS Speed and Indicator speed? I just played with flight simulator and noticed that the GPS shows different speed from the speed indicator in the cockpit. Also, GPS speed is higher than the Indicator. Any Idea why?

The speed indicator in the cockpit shows indicated airspeed. Indicated airspeed is usually different than GPS speed, due to wind and aerodynamic effects.
GPS speed is your speed with respect to the ground. If you are standing on terra firma it reads 0. If it reads 100 knots you will be 100NM away from where you are now in one hour, so long as you keep flying in a straight line.
Airspeed is the speed of the aircraft relative to the surrounding air. So if you are standing on terra firma with 20 knots wind blowing in your face, your airspeed will be 20 knots. If you travel at 100 knots airspeed against a 20 knots headwind wind, your ground speed is 80 knots. If you do 100 knots airspeed with 20 knots tailwind, your GPS speed reads 120 knots.
But even in calm wind conditions the airspeed indicator will read differently than the GPS speed . This has to do with the way airspeed is measured.
Airspeed is measured with a pitot tube. A pitot tube has two pressure measurement ports. One that measures the total pressure $P_t$. This port is facing the incoming airflow. The other measures the static pressure $P$ and is placed perpendicular to the airflow. The difference between the two pressures is called impact pressure (pressure rise due to the airflow impacting the pitot tube) and is denoted $q_c$.
The impact pressure is related to the speed of the airflow the pitot tube is exposed to. If the flow is considered incompressible (which is an acceptable approximation for speeds up to 200 knots) the impact pressure can be derived from Bernouilli's equation.
$q_c = \frac{1}{2}\rho V^2$

$q_c$ is the impact pressure in Pa
$\rho$ is the density in kg/m3
$V$ is the true airspeed in m/s

The airspeed indicator is calibrated for standard sea level conditions, where $\rho$ is 1.225 kg/m3. In reality the aircraft will fly at altitude and therefor the actual density of the air is lower. Therefor the indicated airspeed will be lower as well. For example if an aircraft flies 75 m/s (about 146 knots) at 6000 ft the density will be 1.02393 kg/m3.
$q_c = \frac{1}{2} 1.02393 \cdot 75 ^2 = 2879.8 \textrm{ Pa}$
The equivalent airspeed at sea level for the same $q_c$ is:
$V_{EAS} = \sqrt{\frac{2 q_c}{\rho_0}} = \sqrt{\frac{2 \cdot 2879.8}{1.225}} = 68.6 \textrm{ m/s}$
Your airspeed indicator will read only 68.6 m/s (133 knots) despite the fact that you are moving with 75 m/s (146 knots) with respect to the air.
Conversion of true airspeed to the equivalent airspeed can be done directly by:
$V_{EAS} =V\cdot \sqrt{\frac{\rho}{\rho_0}}$

$V_{EAS}$ equivalent airspeed (m/s)
$V$ true airspeed (m/s)
$\rho$ actual air density (kg/m3).
$\rho_0$ density at standard sea level conditions (1.225 kg/m3)

The effects of the lower density on your aispeed indicator become more pronounced the higher you go. Once you go faster than about 100 m/s true airspeed the effects of compressibility can no longer be ignored and the above no longer applies. Airspeed indicators are corrected for effects of compressibility and therefore don't use the equivalent airspeed but instead use calibrated airspeed for calibration.
$V_{CAS}=a_{0}\sqrt{5\left[\left(\frac{q_c}{P_{0}}+1\right)^\frac{2}{7}-1\right]}$

$V_{CAS}$ is calibrated airspeed
$a_{0}$ is the speed of sound under standard sea level conditions (340.3 m/s)
$P_0$ is the static air pressure under standard sea level conditions (101325 Pa)
${q_c}$ is the impact pressure

The impact pressure is also a bit more complex for compressible flow:
$\;q_c = P\left[\left(1+0.2 M^2 \right)^\tfrac{7}{2}-1\right]$

$P$ the static pressure
$M$ the Mach number

Effectively, the higher and faster you get, the greater the difference between the indicated airspeed and the true airspeed.
For example, Mach 0.8 at 40000 ft in no wind will result in a GPS speed of 489 knots, but a calibrated airspeed of only 242 knots, which is less than half.
Therefore at high altitudes and speeds, the indicated airspeed will be lower than the ground speed / GPS speed, unless you have extreme headwind.


What's the purpose of yawing? I've never understood the purpose of yawing, i.e., rotating around the vertical axis by activating the rudder. Provided that airplanes have ailerons that allow banking (used for turning), why do they actually need to yaw? Furthermore, I've read that yawing induces an undesired banking because of the different lifts generated by each wing, due to the fact that one wing "feels" a higher airspeed than the other (a similar effect as a car's wheel spinning faster than the other during a turn). So, if yawing is so "useless" or bothering, why do airplanes have rudders? Moreover, could an airplane takeoff, fly and land without rudder?

From a totally practical standpoint, let's say you're in a small tricycle gear aircraft with a freely castoring nose wheel (or a tail dragger) and you're starting your takeoff roll in a calm wind. When you bring the power up, the aircraft is going to want to turn left (why is another question), in other words to yaw about its vertical axis in a counter-clockwise direction, and head for the grass off the left side of the runway. You counteract that adverse yaw by using right rudder to keep the airplane straight. Initially you might have to use some right brake as well until there's sufficient air moving past the rudder. If you had a steerable nose gear, you wouldn't need the right brake.

You reach flying speed, apply up elevator, and lift off. As the airplane rotates about its lateral axis, there'll be some additional adverse yaw as a result of that rotation (again another question). Even if you had a steerable nose gear, that would now be useless as the nose gear is no longer on the ground. Your means of continuing to fly straight ahead is to counter the adverse yaw with rudder, and you would continue to use right rudder as you climb out. If you don't, you'll start turning left.

You reach the altitude you want, level off, and trim for level flight straight ahead. Then you decide you want to turn left. You start the turn briskly with left aileron, but you forgot to use any rudder. If you were looking at the ball on the bottom of the turn and bank indicator, you would see it shoot left. If you had used left rudder while initiating the turn, that wouldn't have happened. You would have started a coordinated turn.

Now you're coming back to the airport, and there's a crosswind from the left. You decide you want to counter that crosswind by slipping into it. In other words, you want the airplane to travel sideways at a speed that matches the crosswind while still having your nose pointing straight down the runway. So, you lower the left wing and to keep the airplane from turning, you use right rudder to keep the airplane aligned with the runway. You match the crosswind by adding or decreasing your bank.

There are other uses of rudder, and especially in aerobatics.

I once flew a few loads of skydivers. The jumpmaster sat behind me, and to help him in positioning for the drop zone, he wanted flat turns. In other words, he wanted the airplane turned while keeping the wings level. So, if he wanted a left turn, that meant left rudder and right aileron. Uncomfortable from a pilot's standpoint.

Finally, back in the 1960s when I was working on my instrument rating, I had an instructor who taught that the best way to track a localizer in close was to use rudder only for small corrections. Personally, I don't like that method, but it's one way of doing things.

A useful thing, the rudder. You need to be able to directly control movement about all three aircraft axes.


If AWOS reports IFR conditions but I can see at least three miles, can I take off or land? The uncontrolled airfield where I have my airplane gets foggy in the morning occasionally, but there have been times when there is just a little fog where the AWOS station sits so it reports 1/4 mile visibility and undetermined ceiling, yet the runway farthest from it is clear and there are no clouds. My flight instructor and ground school instructor said you must always comply with the AWOS reported conditions, yet my flight examiner (I just got my private pilot license) said a pilot can overrule the automated station if it is clearly wrong. Machines can break and are limited to where their position is.
FAR 91.155 talks about visibility, but doesn't mention how it is determined. Flight visibility is determined by the pilot, so I interpret this to mean he can overrule the AWOS if it is clearly wrong.

(d) Except as provided in §91.157 of this part, no person may take off or land an aircraft, or enter the traffic pattern of an airport, under VFR, within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport—
(1) Unless ground visibility at that airport is at least 3 statute miles; or
(2) If ground visibility is not reported at that airport, unless flight visibility during landing or takeoff, or while operating in the traffic pattern is at least 3 statute miles.
(e) For the purpose of this section, an aircraft operating at the base altitude of a Class E airspace area is considered to be within the airspace directly below that area.

Another question about (e), after reading it about 5 times: my airport is class G up to 700 feet, then turns into class E above that. Does (e) mean that if I am at 700 feet AGL, I am still in class G? Of what significance is this?

In the specific case that you mentioned (VFR at an uncontrolled field), you can take off or land because the only legal requirement is to maintain VFR cloud clearance and it's your responsibility at the pilot to do that. The possible downside would be that if you have some kind of accident or incident and the FAA or NTSB investigates, they will take the AWOS reports as the reference for weather conditions at the time. If weather or visibility was relevant to the accident then your decision might be questioned, unless of course there are witnesses who can confirm the actual conditions.

In the case of a controlled field and VFR, ATC will base their actions on the reported conditions so they would tell you that the field is IFR only. One 'workaround' that could be useful is an SVFR clearance, which allows you to operate VFR in an airport surface area even below VFR minimums. You have to request it because ATC can't offer it although they may hint strongly at it to help you out: "the field is IFR, is there anything you'd like to request?" But ATC may not issue an SVFR clearance if the reported visibility is below 1 mile, so in the scenario you mentioned it wouldn't help you. (And note that you need an instrument rating for SVFR at night.)

Under IFR the picture is different. A part 91 IFR flight can legally depart in zero visibility so there would be no issue there, provided that you get your clearance on the ground first, before entering IMC. Legal in this case obviously isn't the same thing as safe, though.

I deliberately didn't answer your second question because I think it would be best for you to submit it as a separate question.


Is there a minimum start altitude for autorotation landings? If a helicopter is flying relatively low, say for sightseeing, can it still land using autorotation if required?

What about if there was an issue during a routine landing? Is there any cutoff point where autorotation is no longer feasible?

What you're looking for is the height/velocity curve, some times called the 'dead man's curve'. This shows the altitude and speed requirements for a safe autorotation, plus the height and altitude conditions under which an autorotation is probably not possible.

A lot of variables go into this, and the h/v curve is specific to the particular helicopter, and in particular, whether the helicopter has a high inertia rotor system or low inertia rotor system.

For example, the Robinson R22 has a low inertia rotor system, meaning that the rotor blades are fairly light, and thus don't have a lot of inertia to remain spinning in the case of engine failure. A similar size helicopter, the Enstrom F28, has a high inertia rotor system, so the h/v curve for the Enstrom looks quite different from the Robinson, but is somewhat similar to another popular high inertia helicopter: the Bell 206 JetRanger.

As the article notes, Robinson doesn't recommend a climb out under 45 knots speed, while Enstrom allows it at 17 knots. This limitation is governed by the h/v curve, not performance. While the Robinson could climb out at lower airspeeds, it wouldn't be safe in the event of engine failure.

Disadvantages of a high inertia system are that it uses more fuel, and is slower to accelerate under power in low rotor speed conditions (which are also potentially deadly).


How would fighter jets make contact with a previously hijacked aircraft? For example, a plane is hijacked but civilians regain control, they know how to change the plane's frequency but no procdeures - i.e. dont know guard frequencies. There are fighter jets alongside who do have contact with ATC. What could the jets/ATC do to let them know what frequency to use?

Nothing. There is no possible world in which someone has the necessary training, knowledge, and experience to operate the complex communication equipment, yet doesn't know 121.5.


Is it possible to disengage only one axis of a two-axis autopilot? Take GFC700 for example, when autopilot (or flight director) engaged, the lateral mode falls into

ROL, HDG, GPS, VOR, VAPP, LOC, BC, ...

and the vertical model has to fall into

PIT, ALT, FLC, VS, VPATH, GS, GP, ...

When disengaged (or temporarily by CWS), a pilot has to hand-fly both axes.

I am wondering if this is universal across all autopilot systems. Is there any autopilot that I may engage one axis and hand-flying the other. e.g. The autopilot only holds altitude and I may roll the yoke without any counter pressure. Are there regulations or purely from technical consideration?

Some autopilots found on advanced aircraft can be engaged on selected axis only, for example Boeing 737, 747-200 & MD-11. There are three autopilot indicators on the Boeing autopilots: auto throttle, roll and pitch. Each can be in a different mode.

Here a Boeing 737's autopilot roll mode is set to Heading Select (HDG SEL) while the Pitch is flown manually (CWS P):

The pilot can pull or push the yoke, and the autopilot will roll the aircraft automatically. If the pilot steer the yoke left or right, the roll mode will change to CWS R.

In this image below, the pilot is manually Rolling the aircraft (CWS R), but the autopilot pitch mode is set to Vertical Speed mode.

Later models, such as the Boeing 777, does not have this feature - both pitch and roll modes must be engaged together.


Why was the P-51 Mustang not adopted by the U.S. Navy? I've heard from many WWII aviation hobbyists and WWII vets that the P-51 was essentially the pinnacle of U.S. piston-engine fighter design; it was fast, maneuverable, long-range, well-armed, allowed superb pilot visibility, etc etc.

So, why did the Navy never adopt it? It seems there were flight tests of the P-51D as a carrier fighter, modified with a tailhook for wire capture landings, but the Navy never pulled the trigger (so to speak). What were the primary reasons behind this decision?

The biggest driver behind the use of the P-51 Mustang in naval operations was the need for B-29 escorts while bombing Japan. No naval fighter at the time had the range to accompany the B-29's so the P-51D was selected to determine if it could be a suitable carrier operator.

The test project was named "Project Seahorse", and one aircraft was selected and specially modified to cope with carrier landings.

Navy Concept Image in Livery (Image Source)

The modifications included:

"Fin Fillet Extension" which enhanced low-speed operation.
Tail hook (for obvious reasons)
Catapult hook
High pressure tires
Higher pressure in the shock absorbers
Reinforced airframe

The modified P-51D started testing in September of 1944 under test pilot Robert Elder. The tests were carried out at Mustin Field in Phillidelphia on a modified runway fitted with a catapult and arresting cables. Throughout September 1944 to October 1944, 150 launches and recoveries were made on this modified runway. One big concern was that the aircraft would need to land around 90mph and the stall speed was 82mph, not much of a margin.

In late October 1944 the next stage of testing started, carrier landings/launches at sea. Lt. Elder made all the carrier landings at 85mph and was pleased with its handling characteristics, but there were issues:

Stall speed margin was extremely low, too low for safety
Rudder control at low speed and high angles of attack was inadequate
Landing attitude had to be very carefully controlled to avoid airframe damage
Go-arounds required slow throttle advancement. The extreme power of the Packard/Merlin engine meant that a high-power fast throttle advancement could put the aircraft into a roll or snap-roll. At low speeds this would prove a fatal mistake.

Only 25 launches/recoveries were made in the suitability trials and Lt. Elder did not believe that the Mustang had a place in carrier operations.

It was a moot point anyway. By early 1945 Okinawa and Iwo Jima were won by the allied forces. Each island had airfields that were taken over and provided a close base of operations for aerial attacks on Japan. In August 1945 Japan announced its surrender and it was official September 2, 1945. The P-51 wasn't required to be used from a naval platform anymore.

The project wasn't forgotten though. North American presented the NAA-133 based on the P-51H, which was a carrier operations "Mustang". It didn't go any further than the design stage though. In 1947 a P-51H was acquired to test new catapult equipment. Either way the war was over by that time and we didn't have to put any more effort into modifying the aircraft for carrier operations.

Here is my main source


Why is it runway "1" instead of "01" in America? In the case of a runway with a magnetic heading of 10° in America the runway number ("1") isn't hugely distinguishable from the runway centreline IMHO, (for example see Washington Airport and San Francisco Airport).

Is there a reason why the USA doesn't add the leading zero like the EU (example Brussels Airport and RAF Waddington)?

Does the ICAO make any recommendations about this?

Indeed USA deviates from ICAO:

5.2.2.4 Zeros are not used to precede single-digit runway markings. An optional configuration of the numeral 1 is available to designate a runway 1 and to prevent confusion with the runway centerline.

Source: USA AIP - GEN 1.7 Differences From ICAO SARPs
5.2.2.4 in ICAO SARPs Annex 14 (Aerodromes) is as follows (emphasis mine):

5.2.2.4 A runway designation marking shall consist of a two-digit number and on parallel runways shall be supplemented with a letter. On a single runway, dual parallel runways and triple parallel runways the two-digit number shall be the whole number nearest the one-tenth of the magnetic North when viewed from the direction of approach. On four or more parallel runways, one set of adjacent runways shall be numbered to the nearest one-tenth magnetic azimuth and the other set of adjacent runways numbered to the next nearest one-tenth of the magnetic azimuth. When the above rule would give a single digit number, it shall be preceded by a zero.

Shall in ICAO legalese denotes a standard.
The aforementioned optional configuration for "1" covers your concern regarding the centerline:

The numeral "1", when used alone, contains a horizontal stroke, as shown, to differentiate it from the runway centerline marking.

Source: FAA AC 150/5340-1
The rationale is not in the AIP; it's not always given. Deviations from SARPs are also very common, that's why there's an AIP section dedicated to them.


Why was Concorde's cockpit so complex? Source

Why was this cockpit much more complex than any other modern day aircraft or a fighter jet? It looks to have many more buttons and controls, and very small (interesting) screens. Also, its steering was much different than you would see in any other aircraft.

Why was this cockpit much more complex than any other modern day aircraft

Firstly, as others have noted, you imply Concorde was modern when you compare it with "other modern" aircraft. OK, it was a "jet-age" aircraft, but it wasn't a 21st Century design. it was designed before "glass cockpits" were possible, in the 1960s. There were no real multifunctional displays then, so there had to be a switch or dial for every possible action and every possible parameter the pilots might need to know about.

The main difference is probably the flight engineer's panel on the right. Modern aircraft have two pilots in the cockpit and no flight engineer. I imagine that increased automation in engine controls mean that the engine management by the crew is much simpler and requires fewer controls and dials. These are now typically located in the center of the main instrument panel above the thrust levers etc.

For comparison, here's (a somewhat poorly stitched panorama of) a 747 cockpit

Image by Eric Long, National Air and Space Museum, Smithsonian Institution

and a rather better photo of a 747-300 cockpit (though lower central controls are obscured) ...

Image © aroosh

  or a fighter jet?

A lot of the controls and instruments are duplicated in a two-pilot cockpit. In a fighter jet, you only see one set of instruments and controls. Also a one-engine plane will have a quarter the engine controls of a four engine plane. Fighters probably lack an APU.

Although fighters have additional switches etc for armaments, airliners have additional switches etc for passenger related facilities (seatbelt lights, a/c? etc), security (cockpit door), cabin-crew comms and so on. They also may have more fuel tanks and maybe more means to move fuel around in flight to trim the aircraft.

  It looks to have much more buttons and controls,

Modern glass cockpits just hide all that complexity, just imagine you could rotate 90% of what you see out of view.

  and very small(interesting) screens.

There are no screens at all. There is a colourful moderately-complex artificial horizon instrument which also shows aircraft attitude and a few other things. The visual part is essentially mechanical rather than created by a light-emitting digital display.

  Also, its steering was much different than you would see in any other aircraft.

The shape of the control yoke may be slightly unusual but it operates the same was as any more common yoke design. You push it forward and back to control the pitch using the elevator (or elevons) and you rotate the top part left or right to control roll using ailerons (or equivalent control surfaces). There are buttons on the had grips to control a few functions. I think the shape was partly to make it easier to get in and out of the seat.

Heres a similar yoke design in an Embraer ERJ-145LR

Image © Micheal Catchpole


Is an engine surge classed as an engine fire? Sometimes flames come out from the exhaust due to bearing distress or turbine blade fracture.

Can such flames/fire be considered an engine fire?

If the fire is momentarily and stops by itself: No, this is not an engine fire. Flames can come out of the engine at both ends in a compressor stall (also called surge - watch the movie which is linked in the question!), but that is no engine fire. See this question for another example where spectacular flames develop, yet the engine is not on fire.

If the fire can only be stopped by shutting off the fuel supply or the engine itself: Yes, that is an engine fire. I guess you refer in your question to this bulletin on PW4000s, where the No. 4 bearing overheated due to insufficient lubrication. In that case the oil itself overheated and burned, but this still makes it an engine fire.


How reliable is keeping flight maps on an iPad in the cockpit? Are flight maps no longer kept on a shelf in the cockpit as a back up in case the iPads malfunction? One story that I managed to research highlighted that this was under debate to rely only on a tablet. For such important documentation, am I to understand that this is due to each airline's discretion?

Electronic flight bags are plenty reliable.   I carry a primary and spare iPad mini on long-distance flights, in addition to my iPhone, all of which are loaded with ForeFlight.  I also carry a USB cable and car cigarette lighter adapter with me so I can power the tablets while in flight. I reason that the risk of a failure of both iPads combined was a failure of my iPhone is so low that it’s not even worth worrying about.

Keep in mind paper charts carry their own risks with them.  They’re bulky and take up a lot of space.  You can forget to pack the right ones, flashlights can run out of power making them useless in the cockpit at night, etc.

Airlines are going to have their own SOP’s for what shorts and other navigation aids are available to their flight crews, but by and large most airlines are going over to EFBs, in fact beginning to issue them to their pilots, primarily due to the reduction in weight and other costs associated with traditional printed charts and other resources.


What are these beams sticking out of the Su-17's nose? As visible in the image above, there are these 2 beams sticking out of the Su-17's nose. One is longer and one is shorter.
What are the purpose of these beams and exactly what do they do?

conical nose reminded of its predecessor as much as the MiG-21, and ended with two long poles, one of which contained the very classic Pitot tube and the second a fire control calculator.

Source :https://www.avionslegendaires.net/avion-militaire/sukhoi-su-17-20-22-fitter/

  Two protuberances extended the nose: a Pitot tube and above all a pole supplying measurements to an ASP-5ND fire control system

Source:https://aviationsmilitaires.net/v3/kb/aircraft/show/2208/sukhoi-su-17-otan-fitter


Are there any ducted propeller or fans without a shaft in the centre? Are there any propeller or fan designs that hold the propeller or fan in the duct and do not have a boss or propeller shaft? This could reduce the drag of the  centre. Are there any other advantages?

Perhaps an aeronautic version of one of the Voith maritime systems? This one appears to be electrically powered.
http://www.voith.com/en/products-services/power-transmission/voith-inline-thruster-voith-inline-propeller-11014.html (watch the "installation" video).
Also, this video explains the concept a bit (for maritime applications)

I suppose if you could arrange a lightweight frictionless magnetic ring bearing (possibly integrating electric drive), and/or peripheral drive linking system, it might be worth it if you needed to have two or three smaller fans beside each other, driven by a single core, rather than a singe large fan, in order to reduce fan/nacelle height. (imagine a B52 nacelle with one side shortened to just a fan cowling) I doubt that this would reduce overall drag, though, but I am intrigued by the concept of the greatest chord of the blades travelling the fastest.


Does/did Russia or the Soviet Union ever fly rocket planes? Did Russia or the Soviet Union ever have their own experimental or military rocket planes (other than the Buran), or did their military merely use jets and other non-rocket aircraft? America flew those many experimental X-planes, did the Soviet Union have any similar planes? Afaik all MiGs are jets.

Yes
First, we should clarify the fact that a "rocket engine" is a variant of a jet engine. A rocket engine is usually understood as a jet engine that requires external supply of all components of combustion, including the oxidizer.
In a way, that makes things easier, and this is why rocket engines were commonly used at the early stages of jet propulsion development.
Early examples include rocket boosters for traditional piston-driven airplanes. This method is still in use to shorten the take-off distance (down to zero in some cases), but early on it was tried for "regular" emergency power and, of course, research. (Ram jets also had some limited use then).
The first Soviet 100% jet was BI-1 (БИ-1) in early 1942.

wiki Commons
BI-1 had a rocket engine burning kerosene and nitric acid. Even though the airplane was designated as "fighter" and had a space provision for guns, it was really a research ariplane, with the maximum time under power of only a few minutes (it never reached even two minutes in real tests).
The first one was corroded away by the acid. The third one (BI-3) was lost, and the test pilot Bakhchivandzhi died, presumably due to Mach tuck, which was not understood then.
In the later times, during the "true" jet era, there was much less cooperation between the aviation and space industries than in the West. This is one of the reasons why "rocket planes" were a rarity in the USSR, even for research.


What options do the crew have when passengers go berzerk? In one recent incident with an American Airlines flight from São Paulo (GRU) to New York (JFK or LGA, dunno), the crew decided to land in Brasilia (BSB), Brazil because one couple was fighting (source in Portuguese).

In this case, the crew decided to make a landing in an airport outside their flight plan, and remove the fighting passenger couple from the aircraft. Because of Brazilian regulations on the crew working hours, the aircraft was then grounded for the day.

In the scenario where:

passengers aboard an international flight (during flight) begin fighting between themselves (the shouting at each other, possibly bare-fist only kind of fight) and refuse to heed the flight crew's warnings and requests (but not in a life-threatening way), what other options could the crew have besides the one used in the incident above?

See Chapter 4 of this IATA document for flight crew management of unruly passengers.

http://www.iata.org/whatwedo/safety/Documents/Guidance-On-Unruly-Passenger-Prevention-And-Management-1st-Edition.pdf

In general, they will weed a lot of the negative behavior out on the ground prior to boarding by looking for signs of agitation or aggressiveness towards other passengers or crew.  Should a passenger becom unruly while enroute, the following is generally done.

Assess the situation and level threat:  what's happening? who is doing it? what are their grievances? Are the legitimate e.g. A family member having a medical emergency or trivial e.g. Passenger in 22B is drunk and aggressive?

If there are other than legitimate reasons for the disruption, action in taken using the use-of-force continuum:

Physical presence - flight crew will be nearby watching subject.

Verbal commands - confront subject.  Inform them of both the airline's and Law Enforcemnt's zero tolerance policy toward their exhibited behavior.  Inform them if they continue with this behavior the aircraft will be landed, they will be placed under arrest by LE on the ground, and that penalties for their actions are severe.  Try to calm them down as well, but do NOT serve them alcohol, even if requested.

If behavior continues, quietly inform the cockpit crew of the disruption and they will make arrangements to divert to nearby airport and inform local airport police and other LE agencies to be ready on the ground.

If passenger has become so unruly that they are posing an immediate threat to other passengers around them, physical force can be used to restrain them by the flight crew.  This poses a high risk and should only be done as a last resort to regain control of the cabin.  If there is a federal Sky Marshall(s) on board they can assist the crew here as well.

Restraints such as handcuffs and the waist belts may be used to immobilize subject until LE can take over.  Divert will become urgent.

Electro Muscular Disruptors - flight crews are now being equipped with and trained on the use of the TASER EMD systems to immobilize unruly passengers in order to restrain them.

If subject's actions pose an immediate threat to life and limb of passengers and threaten the safety of the aircraft and crew (VERY low probability but it is is a contingency), deadly force may be used to neutralize the threat.  Near as I know some Capt./FOs do carry firearms as do Sky Marshals.  I'm not aware of guns being issued to flight attendants.


What is the height requirement for pilots in the Philippines? I am not an airline pilot nor do I work in the industry but I'm looking forward to. I live in the Philippines, a part of South East Asia.

My question is: what is the current minimum height requirement in the Philippines to be a private airline or commercial airline pilot?

I was at a Aviation School seminar a few months ago and one of the guest asked the host if height still mattered and the host answered "not anymore because airplane pilot seats are now adjustable". That didn't really convince me because they might be biased considering they are looking for students.

There's no minimum height stated in the Philippines Civil Air Regulations (section 2.10.2.2) for any class of medical (you need a class 1 medical for a commercial license). However, Philippine Airlines apparently requires pilots to be at least 5'4" / 162cm.


Should I record my helicopter and autogyro time in separate logbooks? I have been flying autogyros for some years now, and I am out to do my license on UL helicopters.

I bought a new logbook to log all time in helicopters separately from autogyros. Is that correct?

In a few days I will also be taking some lessons in an R22. That's not even UL anymore. Do I have to get another logbook for all flying of non-UL aircraft? Would I log it all in the same logbook?

In the United States, except for that time which is used for certification or currency, the FAA permits you to log your time however you like, or even not log it at all.  That means that you can do pretty much whatever you feel like.

That said, here are my personal recommendations in order of how much I support them:

Get a digital pilot logbook. Log everything in it.
Get a professional pilot logbook with plenty of space for various categories and classes of aircraft. Copy all of your records from your old logbooks into it. Archive your old logbooks in a safe location. Use your new logbook for everything from here on.
Get a professional pilot logbook with plenty of space for various categories and classes of aircraft. Don't copy all the records from your old logbooks into it, just carry forward the totals. Archive your old logbooks in a safe location. Use your new logbook for everything from here on.
Get one logbook for each category/class of aircraft you intend to fly. Log your time in whichever logbook is appropriate. Remember which logbook is which. Keep them all easily accessible rather than storing them in a safe location. Worry about whether you lost one. Have a complicated system of adding up your totals from various logbooks. Make it difficult to look up flights chronologically. Feel sad.