Are the flaps of a Cessna 414A fully extended at 15 degrees or at 45 degrees? When are the flaps of a Cessna Chancellor fully extended? At 45 or 15 degrees? Also, what are the range marks of its tachometer with Continental TSIO-520-NB engines?

A Cessna 414A with the TSIO-520-NB is listed here, from a high-res cockpit photo both questions can be answered.

The flaps extend to 45 degrees
The TSIO-520-NB's red-line is 2700 RPM.


What is it like flying in class B airspace? I'm a student pilot at a class C airport in the USA. Last weekend I did pattern work. Mostly touch and goes, but it was busy and my approaches were less than perfect so there were some go arounds and some 360s for traffic.

Being in the pattern on a busy day was a little stressful. I was constantly reading things back, changing traffic direction, switching runways R/L, etc.

I am curious to know what it's like flying in class B airspace. Are traffic patterns different from class C? Are there additional skills that pilots must have? For example, I know that I'm not even allowed to be in class B airspace as a student without a class B endorsement.

On my first cross-country as a student (dual), we actually transitioned through the class B airspace just north of us, flew to a smaller airport north of town, did a landing there, followed by flying back to the class B and landing at the primary airport there before returning home.

Basically, I had a few key experiences:

The controllers work quickly and expect you to pay attention.  More than once, as a rather inexperienced pilot, my instructor had to help with the radio, either in understanding the instruction, or helping reduce my confusion by handling communication.
Even on a slower Sunday, the center was training a new controller, so there were times the person training had to step in to clear up some of the radio congestion -- we almost had to turn away from the class B, since they hadn't yet assigned us a beacon and cleared us through the bravo.
We got vectored around pretty quickly... which, basically threw out all our flight planning (we were expecting this to happen anyway).
Talking to approach to land, they told us to expect the visual approach to one of the parallel runways, and the tower controller didn't toss us any curve balls there.  Although, with the headwinds, even with a fair amount of power, we weren't moving very quickly, and probably got cleared to land a bit too early (thankfully, the airspace wasn't busy... but there were a few jets waiting for us to land and taxi off).
Ground control and clearance delivery was combined, and they were pleasant enough to give us progressive taxi without asking (I was expecting to write furiously), and also let us taxi to depart off the intersecting runway.
Departing after cleared and returning home was pretty uneventful.  At this point, I was out of the way for most traffic.  Much more like being under regular flight following.

Granted, it's not like I was flying into ORD -- it was a pretty slow day at an airport that isn't busy much to begin with -- but I have a feeling if you've been used to flying from a Class C airport, not much will feel different for the most part, especially at one of the smaller Class B airports (and for the bigger ones especially -- DEFINITELY get to know the airport diagram beforehand).

To answer some of your specific question, the A/FD will list traffic patterns (probably going to be opposing right/left traffic for parallel runways so people don't end up head on at each other) ;) Controllers will guarantee separation from all aircraft, so you'll be assigned a heading and altitude (maybe "at or below"), and possibly a speed.  So really, if your radio communications are good and you're able to fly straight and level, you won't have many problems (it just comes down to obeying clearances, and not violating any airspace).  You're right that you would need an endorsement to fly solo into a Class B airspace, but this would not apply if you were dual with your instructor, since they are PIC.


Would this "being paid while flying" scenario be considered "flying for compensation"? The difference between a private and commercial pilot's license hinges on this critical ability to expressly receive pay for flying; a PPL is allowed to fly "in furtherance of a business" but cannot be paid to fly a plane, while a CPL can. That brings up an important question; in today's corporate world, there often isn't a strict "hours for pay" exchange; you get a salary, for which you perform the duties of the job (which do not necessarily mean being there 8 hours a day). So,  what's the difference between being paid while flying in furtherance of a business, and being paid for flying?

A simple example (I hope): I'm a salary man, and my workplace happens to abut a public air park in Dallas. A coworker of mine needs to get to Waco to have a short face-to-face meeting with a client (teleconferencing won't do), and my boss knows I'm a PPL and own a fairly speedy Cherokee 235 (cruising speed 135 mph). The forecast for tomorrow is perfect flying weather, so he proposes this deal; I commute to work in my plane tomorrow instead of driving. After morning coffee and e-mails, my coworker and I will head over to the air park and fly out from there to Waco in my plane and be picked up by the client. We'll have the meeting, be driven back to the airfield, and I'll fly us back to Dallas so he can drive home.

For this, I'll get paid for the workday as I normally would, no vacation or other leave time required to be used. My boss also suggests that I can expense my fuel costs and any landing fees, like I would be able to do with my gas and parking fees if I drove. My boss gets two people face-to-face with the client faster than if we drove, with less time off our normal duties than if we flew on a regional jet (and much cheaper), and I get paid to fly my plane without being explicitly hired to do so.

The questions:

Can I accept the deal at all, or will the fact that I'm technically being paid while flying be considered the same as being paid for flying even though no additional money specifically for my yoke time is changing hands?
What portion of my out-of-pocket costs can legally be expensed?

All my fuel and landing fees incurred between taking off from and landing back at my home field (which I otherwise would not have incurred)?
100% of costs from when I take off at the air park near work to when I return there (the portion of the flight in furtherance of the business)?
50% of "non-commuter" flight costs (gas to and from Waco and the landing fee there, but not the fees at the air park or gas to and from my home field)?
No expenses allowed (because that would be "compensation for flying")?

Would any of this change if I were an hourly employee doing this "on the clock" as opposed to being salaried?
Would any of the above answers change if my boss wanted me to rent a speedier plane (that I was rated for of course)? Would I be able to expense some or all of the rental?
I'll try not to make this an off-topic "legal advice" question: if I refused the deal because I thought it would violate the restrictions of my PPL on flying for pay, and I was summarily fired, should I be talking to a lawyer about a wrongful termination suit?

The short answer is that you'd need a commercial certificate, and potentially a commercial operator's license, to do what you're describing. Standard disclaimer: IANAL, and if you wanted to do anything like this, you really should find an aviation lawyer and get answers from them in writing!

The rules that cover this are contained in FAR 61.113, quoted in relevant part:

  §61.113   Private pilot privileges and limitations: Pilot in command.

  (a) Except as provided in paragraphs (b) through (h) of this section, no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft.

  (b) A private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if:

    (1) The flight is only incidental to that business or employment; and

    (2) The aircraft does not carry passengers or property for compensation or hire.

  (c) A private pilot may not pay less than the pro rata share of the operating expenses of a flight with passengers, provided the expenses involve only fuel, oil, airport expenditures, or rental fees.

To point 1, the answer is no. You're being compensated for your time, which is spent flying. If you were alone, 61.113(b) would allow you to be compensated - but that only applies if the aircraft does not carry passengers. Since the 61.113(b) exclusion doesn't apply, you're stuck with 61.113(a)'s prohibition of flying for compensation or hire.

You make an interesting point at the beginning about salary covering strange hours. If you really were paid just for your productivity, and you had an arrangement where you could just go take a couple of hours off in the middle of the day to go flying (or any other personal activity) without burning leave or affecting your pay, you could claim that you weren't being compensated for your time. I might write to the local FSDO for clarity on that before actually doing it, though.

If you were an hourly worker (#3) and were not paid for the time you were flying, that would eliminate some of the compensation. Note, however, that the FAA constructs "compensation" very broadly, to include good-will from others. If you made this flight in order to make your boss happy, you're being compensated! The source of the incentive to fly would be important: if you and a co-worker had to get to a destination, and you suggested, "Let's fly there!", you're under much better grounds than if your boss told you to.

The second point would depend on your normal work situation. Let's look at two portions of the flight:

The portion from home to work, and from work back home: In this case, you could be compensated for the flight under 61.113(b) - both in salary and costs, as long as your employer has a policy of reimbursing staff for their commuting costs.
The "non-commuter" costs: You could ask for 50% of the costs of the flight under 61.113(c) (see Mangiamele interpretation) - but from your co-worker, not your employer. Where they get that money is up to them. One important point: 61.113(c) requires "bona fide common purpose" -- you and your co-worker must each have a reason, beyond the flight itself, for going to the destination airport. If you weren't required to meet the client (or do something else that requires you to physically be in Waco at that time), you could not even share the costs of flight. Note that you can't be paid or reimbursed for your 50% — you have to eat that cost yourself.

To #4, the owner of the plane doesn't matter that much here, for a private pilot. The question of who provides the plane becomes very important in common carriage, but that's a different question.

To your last point, I'm not a lawyer - but I imagine that being fired for refusing to take an illegal action would be wrongful termination.

Further Reading:

An FAA Article on cost sharing

Mangiamele Interpretation: a letter from the FAA Office of Legal Counsel discussing this topic


Why are the throttles of aircraft such as the Twin Otter placed on the overhead panel? Some aircraft such as the DHC-6 Twin Otter, have their throttles on the overhead panel:

Is there a reason that they are not on a center console between the pilot seats or mounted to the panel like on most airplanes?

It seems like it would be more comfortable for the pilot if he didn't have to reach up to change the power settings.

I think it was for two reasons:

It makes for straight path for the controls to reach the engines, as all of these are fly by cable. Many of these aircraft where also designed for harsh climates, so I imagine it's an advantage to have less pulleys and other things which might rust and require maintenance.
There is very little space to place the throttles further down, especially with the control column mounted on the DHC6 Twin Otter where it is. If you did want a pedestal, you'd have to seperate the control columns, requiring further mechanical components, and you'd have to route the engine cables upwards, both of which would be undesirable.

As you mentioned, there are downsides. Commonly mentioned ones are:

It is not particularly comfortable to have you arm raised for an extended period of time, and you lose some sensitivity in it.
You hope that the other pilot used his deodorant that morning.

Other somewhat similar aircraft which use this configuration are the PBY Catalina and Grumman Goose. Another one is the Avro York heavy transport aircraft.


Why does Vx have a relationship with thrust but Vy has a relationship with power? https://www.boldmethod.com/learn-to-fly/performance/vx-vy-altitude-and-where-they-meet/
After I watch this article, now I understand the relationship between altitude and the rate of climbs.
But I wonder why Vx has to do with thrust and Vy has to do with power.
Could you explain them for me?

The angle a plane can climb at is entirely dependent on excess thrust.  With props, maximum thrust can be at a lower airspeed than Vbg, so even if the plane is not at its optimal wing AOA (more drag), the maximum line between drag and thrust is where you get your best climb angle, Vx.
That's the easy part.  How can a plane climb faster when it is climbing at a lower angle?  By going faster!
The formula for Power is Force (thrust) x Velocity
When you see this graph, note that the maximum distance between Power and Drag is Vy.  This plane will fly higher and farther for a given amount of fuel than at Vx.


Are pitot systems protected from ice? Aircraft use pitot tubes or pitot-static tubes. Do these have some kind of anti-ice system? If so, how? And if not, why not?
I'll just point out that it doesn't seem trivial to de-ice such a thing. A simple heating element at the front would melt the ice but then the water will travel through the tube and probably quickly reform somewhere else. So the entire tube could be heated, but then, that will drastically alter the ambient conditions that the pitot is trying to measure.

You can see an example sketch of a heated pitot tube in the FAA Handbook of Aeronautical Knowledge:

As you can see, there are two heaters that heat the entire tube and (ideally) stop ice from forming in the first place (anti-ice, not de-ice).


Is 1 propeller always more efficient than 2? Based on other answers I've read here (1) (2) (3), a single large blade propeller is the most efficient type of thrust you can get.

There are 2 reasons for this (as I understand it). Firstly, because each blade on the propeller causes wing-tip vortices when low pressure air meets high pressure air.

Secondly, each blade on the propeller adds surface area to the aircraft increasing parasitic drag.

So my question is what if both propellers are surrounded by a duct? Assuming it's a perfect fit, the duct will neutralize wing-tip vortices, so now all that's left is parasitic drag.

Now couldn't you just use 2 propellers that equal the surface area of a single large propeller and get the same efficiency with no added parasitic drag?

On a similar note, could you use just 1 small propeller surrounded by a duct and reach similar efficiency (if not better) than a large propeller surrounded by the same duct?

I say "if not better" because the smaller propeller would have less surface area, thus less parasitic drag.

Ducts are only used for highly loaded propellers of a very small radius, namely the fan stage of turbofan engines. For lower disk loadings a shroud or duct would create more friction drag than it saves in efficiency.

If the tip Mach number of the propeller is low enough (say below Mach 0.9), then the single propeller of maximum diameter will be the most efficient way to create thrust. This condition is met when both flight speed and thrust per propeller disk area (disk loading) are low.

As the aircraft gets faster, the tip Mach number can best be limited by reducing the propeller diameter. Now more blades will be needed in order to create the desired thrust, and interference between them will reduce efficiency. Also, the higher disk loading will result in more swirl losses, and now it becomes attractive to run a second, counter-rotating propeller behind the first. The two can be either close together or - even better - on opposite ends of the aircraft.


To receive an SVFR clearance, does the airport need to be reporting IFR conditions? If conditions at a towered airport are not IFR, can pilots request a special VFR clearance? For example, at a Class D airport, ceiling 1300 broken, 10 sm visibility is technically too low to remain in the pattern (assuming a 1000 foot AGL pattern and maintaining at least 500 feet below clouds), yet it is not IFR.

With a Special VFR clearance, the pilot would be able to maintain a 1000 foot pattern and remain clear of clouds. If the pilot requests SVFR, will the tower grant it?

A Special VFR (SVFR) clearance may be issued to a pilot when:

The weather is below VFR weather minimums, as reported at the intended airport
The pilot is able to remain clear of clouds
The pilot has at least one mile flight visibility (other than helicopters) at all times
The pilot is operating (or wants to operate) within the lateral boundaries of the airport surface area
The pilot specifically requests it.
The airport is not among those listed in 14 CFR Part 91, Appendix D (except helicopters)

If the weather is not reported at the airport, the pilot must tell ATC that they are "unable to maintain VFR" and request SVFR.

Side note:  The weather conditions that you describe above are technically "Marginal VFR" and not IFR.  It would be a perfect situation to operate SVFR though.


What is the 'optimal' taper ratio? I mean the optimal taper ratio for an unswept trapezoidal wing for minimising induced drag.
I see a lot of places recommending a value of 0.45 to give as close to an elliptical distribution, therefore maximising Oswald efficiency (to 1). However, Hoerner (Fluid-Dynamic Drag, chapter 7-2) has this plot which suggests the optimal taper ratio is about 0.356 (graphical line fit).

Similar graphs are produced in this paper: Induced Drag of High-Aspect Ratio Wings
Tommy M. Chen and Joseph Katz
This exact taper ratio is used by BAe regional jets also.
I haven't read about this thoroughly enough. Maybe this value considers root chord and wing area to be fixed, therefore as taper ratio is decreased the aspect ratio must increase to maintain a constant area. The increased AR (really the increased span) reduces the induced drag.
Does anyone know the answer? I'd really like to be able to justify my taper ratio for an aircraft design assignment.

The excerpt you posted mentions a further modification of the Oswald efficiency/taper ratio curve which is not applied to the graph in the excerpt. With that modification (which I believe is included in the following pages of the book), the optimum point may move to 0,45. For an assignment, the other places you found 0,45 from and the BAe wings are sufficient motivations to set it at 0,45 IMHO.
I'd like to mention that taper ratio is not the only way to adjust spanwise lift distribution, you can change the airfoils (which you mentioned you have excluded from your design) or you can add twist to the wing so that the wingtips work at a lower AoA. This has the added benefit of making the wing root stall before the wingtips where the ailerons are located.


Has Air Traffic Control ever had to talk a first time pilot through a landing due to an emergency? This question deals with the plausibility of the Hollywood cliché of a passenger on a commercial jetliner landing a passenger plane.

My question is related but broader, and less hypothetical:

Has anyone ever found themselves in an emergency with no piloting experience (e.g., the amateur pilot of a small plane dies or is incapacitated, and the only other person in the plane has never flown anything before) and been talked down by Air Traffic Control?

The answer is yes.  One example was on April 2, 2012.  Helen Collins, an 80-year old Grandmother was forced to take the controls of her husband's CE-414 and land it at Door Country Cherryland Airport (KSUE) after her husband had a massive heart attack at the controls and died.  She managed to circle the airfield and call 911 on a cell phone.  The emergency dispatcher contacted the FAA who got in touch with ATC.  A KSUE based private pilot named Robert Yuksonavich took off and joined her in formation, talking her through what was about to happen and flew her wing on several practice approaches prior to the landing attempt.  On landing the Cessna 414 skidded off the runway and came to a stop in the grass, breaking the nose gear off.  Helen survived with only minor injuries; her husband was pronounced dead on the scene.

A brief piece by the CBS morning news featuring commentary by Capt Chesly Sullenberger about the incident.

This is the full ATC of the accident


How does jet training work for private pilots? Are there jet trainers? For a private pilot (not an ATP) that wants to get ratings for jets, how does that work?

What kind of training aircraft is used typically?

There is no FAA requirement for any specific pilot certificate level beyond Private to get a type rating in any jet. In fact, many owner/operators of small business jets (CJ, 500s, Phenom, etc) only have a Private certificates.

See 14 CFR 61.31

The only FAA requirements are that you have a Private certificate with multiengine and instrument ratings. Additionally, a High Altitude Endorsement is required to take the actual type checkride unless you meet the grandfather requirements of the HAE. RVSM is NOT required to take the checkride, but it is required before flight into or through RVSM airspace.

You can enroll in a simulator based Part 142 course (think Flight Safety, Simcom, LOFT) and complete your entire training in a Level C or D full flight simulator, but once you complete your training you will have an SOE limitation on your type rating. This is per 14 CFR 61.64. This regulation says you must have 25 hours of Supervised Operational Experience in the aircraft before you can act as PIC in that aircraft unless you meet specific requirements including total time, time in multi-engine turbine (including turboprop) aircraft, military training, etc.

You can enroll in a part 61 course and complete your training in the actual aircraft and once you pass the type rating, you would not have the SOE limitation under 14 CFR 61.64 since you took the actual checkride in the aircraft as opposed to an FFS.

You can enroll in a Part 142 initial hybrid program that offers simulator training for the first part and when you have complete the sim portionof your training they move you to the aircraft for the final training segments and checkride. This also eliminates the 61.64 limitiation on your certificate.

Three things to remember: First, ALL type ratings are done to ATP standards regardless of certificate level and Second, SOE or not, insurance companies rule on how much time you will need to fly with a mentor pilot before going out on your own and finally an in-aircraft checkride for your type rating will be far easier than an in in-sim checkride.


How to navigate an aircraft without GPS? In case of loss of GPS: how can an aircraft not only be navigated but navigated so precisely that it can pinpoint its destination airport ?

(case in point: Finland and Norway are telling airline pilots to be ready to fly without GPS )

The question you should be asking is rather, how did airliners navigate before the widespread adoption of satellite-based navigation systems such as civilian GPS?

One can navigate by way of landmarks (as is typical in low-altitude VFR general aviation), but more typical in commercial aviation in the absence of GPS would probably be to navigate by either inertial navigation, or by radio beacons. There are or have recently been several systems that can be lumped together as "radio beacons", such as for example NDB, VOR/DME and ILS, which are used for different purposes, and have different strengths and weaknesses. Until recently, another such system was LORAN.

Major airports typically offer a number of radio beacons that can be used for locating the airport, and there are normally waypoints, sometimes associated with radio beacons of their own, along which a route can be flown even without external references (such as in instrument meteorological conditions, IMC). 757toga's answer to this question shows what such a navigation system for long-distance flight can look like.

GPS does make it easier to fly the most efficient route possible under current conditions, but it is hardly required in order to fly some route from one airport to another. Being prepared to fly without GPS might, in the simplest of cases, simply mean that you plan for a slightly less direct route and treat your non-GPS navigational aid equipment as required, possibly even primary, rather than secondary or nice to have, since you know there's a clear risk of losing GPS through no fault of your own or of the onboard equipment.


If stealth aircraft are invisible to radar, then how does their own Air Force manage them or see them in flight? Air traffic controlling is a significant deal when it comes to air forces. If a stealth aircraft like the F22 is almost invisible as said, it has cross section of very small metal ball. Then, how does US Navy/Air Force see their own aircraft in the air.
Possibly GPS/datalink?
As often said, stealth are not invisible but harder to detect, even then it will create huge problems for operating airforce to effectively see thier own aircrafts in the air.

Like most military aircraft, the F-22 has a military equivalent of a transponder, an IFF system (Wikipedia):

Identification, friend or foe (IFF) is a radar-based identification system designed for command and control. It uses a transponder that listens for an interrogation signal and then sends a response that identifies the broadcaster. It enables military and civilian air traffic control interrogation systems to identify aircraft, vehicles or forces as friendly and to determine their bearing and range from the interrogator.

Depending on mission profile the F-22 may also carry a radar cross section (RCS) enhancer to hide its stealth capabilities and make it more visible on radar.
Usually the main system for creating situational awareness during military operations and training is the Link 16 military tactical datalink. This system is carried by all modern NATO military aircraft, though F-22 will be getting the full feature Link 16 system including transmit functionality during 2021  . Link 16 also utilized by other branches of the military forces.


How is collision avoidance regulated in controlled airspace in Canada? According to CAR 302.31(3) "Compliance with Air Traffic Control Instructions and Clearances"

  The pilot-in-command of an aircraft may deviate from an air traffic control clearance or an air traffic control instruction to the extent necessary to carry out a collision avoidance manoeuvre, if the manoeuvre is carried out

    (a) in accordance with a resolution advisory generated by an ACAS; or

    (b) in response to an alert from a TAWS or a Ground Proximity Warning System (GPWS).

I know that even in controlled airspace with separation/conflict resolution, and without equipment mentioned in (a) and (b) it is the responsibility of the pilot to avoid collisions. Is that covered by a different CAR?

You are correct, it applies when operating in the vicinity of an aerodrome:

  Division V — Operations at or in the Vicinity of an Aerodrome

  602.96 (1) This section applies to persons operating VFR or IFR aircraft at or in the vicinity of an uncontrolled or controlled aerodrome.

  (3) The pilot-in-command of an aircraft operating at or in the vicinity of an aerodrome shall

    (a) observe aerodrome traffic for the purpose of avoiding a collision;

Also this part:

  Part VI — General Operating and Flight Rules

  602.19 (1) Notwithstanding any other provision of this section,

    (a) the pilot-in-command of an aircraft that has the right of way shall, if there is any risk of collision, take such action as is necessary to avoid collision; and

    (b) where the pilot-in-command of an aircraft is aware that another aircraft is in an emergency situation, the pilot-in-command shall give way to that other aircraft.

The way I'd interpret the above is vigilance in see-and-avoid is always there, unless of course you don't have ACAS and TAWS and flying IFR in instrument meteorological conditions (IMC).


How to reduce altitude in a passenger jet without gaining forward speed in an emergency? Assume the pilot is flying too fast and high for an emergency landing. What movement of the control surfaces must they apply to land the aircraft safely on the runway? I heard this type of manuever is also used in gliders and light aircraft

Ah that's a good question indeed. You asked

  How to reduce altitude in a passenger jet

Normally most of the passenger jets have spoilers They are effective and can be deployed at any speed.

Now what happens in case you don't have spoilers for any reason. I was discussing the subject with a pilot many years ago and he told me the trick you mentioned: you apply rudder to one direction (I assume opposite to the engine rotation to avoid unpleasant surprises). That increases dramatically the forward surface of the plane against the relative air flow. That results in increased drag and thus speed loss.

But yaw causes roll (and vice versa). Also the wing of the side you are yawing to, has less lift because it is shaded from the forebody of the plane. This is where the aileron is needed. You need aileron to maintain lateral stability and prevent the aircraft from rolling. See the image bellow. The orange lines denote the area of increased drag by the fuselage. The green area is the "shaded" area of decreased lift of the wing.

Top view from wikipedia. Derivative work by me.

According to that pilot, this is more effective than spoilers. But there is a trap: You need to be careful not to yaw the plane too much because the shaded wing will loose too much of its lift and will result in capsizing the plane.

EDIT: Finally, you mentioned emergency. There are different types of emergencies. Pressurization is an emergency situation but does not affect aircraft control (at least not directly). Hydraulics problems or engine loss is an emergency as well. But that will affect the way you will handle the aircraft. Here I cannot help you. A trained pilot perhaps can answer, though I believe that the answers will vary depending on each planes flight manual.


Why do commercial flights turn / bank so sharply? When I take commercial flights, or you see turns in the vapour trails, they turn very sharply. What's the reason for this - wouldn't it be more efficient to turn gradually?

Airplanes are expected by air traffic control to turn at a "standard rate of turn" which is 3 degrees per second.  This will provide a 90 degree turn in 30 seconds.  A standard rate is used so that controllers can anticipate how long it takes for an airplane to turn to a heading and they can line them up easier.  It also makes the turn happen in a smaller amount of airspace so that two airplanes can be flying in the same general vicinity without getting too close.

Unfortunately, at the speeds that jet airplanes travel this would mean a very high angle of bank.  A standard rate turn at 200 KT TAS is about 30 degrees of bank and jets can go much faster than this, which would require even higher bank angles.  They actually limit it to 25 degrees of bank when using a flight director, mainly for passenger comfort.

It can be impressive when looking out the window and seeing the ground, but don't worry, the airplane is more than designed for it!

This is used mainly at lower altitudes where there are lots of airplanes.  Once they are up high and airplanes are further apart (and the turns are also usually smaller) they  can bank even less (by using a "half-bank" mode) which adds to passenger comfort.


What can cause the engine temperature to be high in piston engines? What can cause the engine temperature to be high in piston engine aircraft?

Low oil quantity, improper cooling, running excessively lean of peak.  Excessive boost from a turbo or supercharger at high altitudes where sufficient cooling is not possible.  Ther are quite a few reasons.


Are there any supersonic aircraft with strictly mechanical controls? Are there or is it possible at all to create a supersonic aircraft with strictly mechanical (human powered without boosters) controls?

I know there was an attempt: Bede BD-10 but it never reached supersonic speed.

Have there been successful planes/designs that implemented it?

There's one I can think of immediately, and that's the granddaddy of them all, the X-1. The X-1's control system was unassisted and it had no hydraulic system. The only part of the control system that was assisted was the horizontal stabilizer, which was operated using high-pressure nitrogen gas.

I think most of the early supersonic test airplanes were mechanically operated .


How much effect does the nose design of the plane have? Boeing 747 nose

Which looks like a goose head

which, for me, much uglier than 737

which has a head similar to

which is of course, much better looking from my point of view. Why are there different designs of the nose for planes by the same manufacturers? What effects do the different designs have?

Good question! The raised cockpit and the hump behind it make the 747 look like the goose. Raising the cockpit allows the hinged nose to come up to load freight. The raised area behind the cockpit was initially a lounge, and was then used for seating or cargo.

How the 747 Got Its Hump, Smithsonian Air and Space

Boeing 747-8F:
Photo by Olivier Cleynen


What's the possibility of a commercial airplane crashing due to a computer error? In line with this great question, what's the possibility of a commercial airplane crashing due to a computer error? Or are there already known cases of this? As a passenger, should you be worried about this possibility happening to you someday in the future?

First; let's be honest.  No one really knows what the exact probability is.

But we do have a design certification system that requires developers to apply various development assurance processes to meet specific safety standards for the design. The primary requirement is covered by §25.1309   Equipment, systems, and installations.

That has a lot of words about identifying potential faults and mitigating the associated hazards. But there are no numbers. As with most rules, the FAA conveniently provides an Advisory Circular to help you show compliance with the rule. In this case, its 25.1309-1A - System Design and Analysis.

The acceptable standard for critical faults (those with a potential catastrophic result) is found at the bottom of para 10.

  (3) Extremely Improbable failure conditions are those having a
  probability on the order of 1 X 10^-9 or less.

So, if the developers do their job to the standard and the standard (and the methods used to evaluate it) are accurate the answer to the question is:

The probability is less than once in every 1 billion hours of operation.

As a point of statistics, that number applies to the cumulative hours of all aircraft of that design.


Can throttle control be considered as a primary flight control? My flight instructor asked me if throttle can be considered as a primary flight control?

14 CFR 23.673 - Primary flight controls defines primary flight controls as:

  Primary flight controls are those used by the pilot for the immediate control of pitch, roll, and yaw.

While a throttle could be used to effect changes in aircraft attitude (depending on configuration and other factors), the effect could hardly be called immediate/direct. So, throttle could hardly be called a primary flight control; and as @Ron pointed out, there are gliders.

Note: I'm aware that aircraft have been controlled solely using throttle. But it is an exception rather than the norm.


Can a helicopter stand on the ground upside down on its rotor head? From what I understand the rotor head needs to be strong enough to hold the craft weight hanging below it, and sounds pretty strong. The blades however look quite fragile (for a piece of metal).

In short, can a helicopter do something like this?

I found source of this GIF image: Escape to Witch Mountain (1975). This scene is around the 1h 19m mark. All hail @Peter Kämpf for identifying this copter as Hughes 500 which led me to list of copters in movies.

In the scene with humans and the Australian helicopter, a trained eye can spot the lack of a "green screen effect" (it's a 40-year-old movie!) so it seems this Hughes 500 was really put upside down! (Should we investigate it further to Movies.SE now?)

Followup on Movies.SE

Stand on its rotor head? yes, maybe. Spin? not for long.

The rotor hub and blades are quite strong and can take the helicopter weight at-least temporarily (leaving aside the balancing issue). The blades are designed to overcome stresses in flapping and can take the load. The rotor hub however, is not designed to take loads in this attitude (it is designed to lift the helicopter, and not push it) and its capability is an open question. You could put the helicopter upside down, but its going to be a brief affair with no guarantee that the parts will ever work again properly.

However, in case you want to spin the helicopter, you run into a number of issues. You could clamp the blades down and try to spin, but the rotor hub will struggle to take the load. The load path from the rotors to the fuselage is designed to take lifting loads and not this.

Helicopters are not designed for sustained inverted flight and as a result, the systems are not designed for anything like this. For example, the gearbox lubrication system isn't going to work for long in the upside down condition. The rotating control rods aren't going to take the gear box weight, let alone the helicopters'.

But first, the dynamic loads- helicopter systems below the rotor hub are not designed to take rotating loads, let alone the horribly unbalanced one like a fuselage. Even the lightweight helicopter blades are balanced to prevent and unsafe vibrations -in a case like this, the rotating fuselage would most likely tear apart the helicopter before anything else.


What is the cause of tire marks at the extreme ends of runways? At LAX, planes (usually) take off from east to west. On the west end of the runways there are dark tire marks.

What is the cause of thesey tire marks? Failed take offs? Late landings? Something else?

See Google Maps of LAX

The marks are left by the tires of landing planes when they touch down -- that is, ordinary routine landings.

The wheels of a landing aircraft do not start rotating before they hit the runway -- so right at the moment of touchdown, the wheels will at first skid along the runway surface until the friction between tires and runway has delivered enough angular momentum to the tire to spin it up so it matches the ground speed of the landing plane. Once that happens, the wheel will roll normally.

This skidding causes the skid marks you have observed.

Even if the runway is usually used in the east-to-west direction, there are still enough days where landings are from the west that both ends of the runway will collect tire marks. How many days that are doesn't really influence how black the runway gets, only how long it can go between having the rubber buildup cleaned off.

At the few airports that are really only used in one direction (such as the famous Princess Juliana Intl Airport at St. Maarten, which does not even have charted approaches from the east due to terrain obstacles) you will find the tire marks only at the touchdown end of the runway.


Does anyone have free plans for a ultralight? I am looking for free ultralight plans for a beginner. I have been wanting to fly but I don’t want to spend thousands on a license so ultralight is the next best thing.

Your best bet is a Sandlin Goat, with free plans for download and quite a few built.  It's a soaring glider but some have added motors, although that eats into the useful load.  A motor would have to be a 2 stroke to have adequate power for the weight, (you want about 25 hp) and it would be best to use an off the shelf paramotor engine.  I would just purchase an old used paramotor cage/motor to get the motor/reduction drive/prop and rebuild the motor.  A goat itself is still going to cost you at least 5k to build from scratch, probably at least half that in the cost of fabric covering process, before the motor.  Then of course you have to engineer a way to attach the motor with adequate structure that can handle several Gs, doesn't screw up the weight and balance, etc etc etc.

Aviation, even at that level, ain't cheap.

But before all that, you have to get training to avoid killing yourself, so save up a couple grand first and go to an ultralight flying school for lessons.


What is the relation between manifold pressure, RPM, and power, in a constant speed prop? I know that there are similar topics here, one is mine even, but still I have few questions about constant speed propeller. My questions:

Why if we decrease RPM and maintain throttle lever setting the power output decrease?
Sounds like very basic knowledge but I heard a lot of versions and I want to reassure. Is tachometer on constant speed prop reading engine rpm or prop rpm?
If we move prop lever we are changing blade pitch and then rpm adjust to it or we are changing engine rpm and blade angle adjust to new rpm

1. Why if we decrease RPM and maintain throttle lever setting the power output decrease?
Power is energy per unit of time, and since there is fewer revolutions, there is fewer power strokes to release that energy. There is less contention for the air from intake manifold so the manifold pressure will increase a bit and each power stroke will deliver a bit more energy, but not nearly enough to compensate the overall lower number of power strokes.
For this reason, manifold power can only be related to power for constant RPM, and it's still complicated by other things, especially the density altitude. Fuel flow is a better indicator of power as long as you keep the engine properly leaned.
2. Sounds like very basic knowledge but I heard a lot of versions and I want to reassure. Is tachometer on constant speed prop reading engine rpm or prop rpm?
Usually propeller, but may depend on the aircraft. But it does not really matter, because the gear ratio is always fixed and because the pilot does not have any other use for the value than comparing it to some nominal values in the operating handbook, which are aircraft-specific anyway.
In one aircraft the POH might say that maximum RPM (more can't be selected anyway) is 2500 and most efficient for cruise is 2100, but on another aircraft it might say that 2750 is for take off, but for 2 minutes only, 2600 is maximum for continuous operation and 2300 is most efficient. If it instead said 3130 and 2625, it would make no difference.
Because of this, turbine RPM is only reported in percent, which sometimes extends to the propeller on turboprops too. It is still aircraft-dependent, because some engines go up to values like 102.5% and the spread between maximum and most efficient also varies.
3. If we move prop lever we are changing blade pitch and then rpm adjust to it or we are changing engine rpm and blade angle adjust to new rpm
You are setting the desired RPM, which the governor will try to attain by adjusting the propeller pitch. If the propeller is too slow, the governor decreases the pitch, thus reducing the thrust and associated resistance until the engine can keep up, if it is too fast, it increases the pitch until the propeller absorbs all the power the engine is providing. If the throttle is too closed, even the finest possible pitch might have too much drag and the RPM will be lower than selected.
There were some variable pitch propellers where the pilot directly controlled the pitch, but the governor is a fairly simple hydromechanical device (weight on spring measures the centrifugal force and directly controls hydraulic valve that adjusts the pitch) and results in so much more practical handling that it quickly prevailed.
This is further complicated in beta range (reverse thrust) where the power lever switches to controlling pitch directly while throttle is controlled by another governor to maintain RPM. But you'll mostly encounter that on turboprops.


What is the difference between "amended" and "revised" clearances? Reading the ICAO Phraseology Reference Guide I saw the term amendment applied to clearances, and I got a bit confused about how to differentiate it from a revised clearance. What does each one mean? Are there any examples?

An amended clearance usually indicates something has been added to it, but the original content remains the same. Revised usually means the clearance has had modifications to the original content, including possible additions and deletions.


What is the brace position for cockpit crew? I have read a number of times the CVR transcript of US Airways 1549. Just before impact, they say:

  we're gonna brace

I know what is the brace position for passengers, but I'm not sure about how cockpit crews would adopt it. For Airbus aircraft (as this flight was) I think it could be done more or less the same way as passengers, but what about in Boeing or other yoke-equipped cockpits? Wouldn't the brace position interfere with critical flight controls?

You don't brace -- you're still operating the aircraft!  The pilot seats have shoulder harnesses; in many cases you can lock them, plus they also have inertial reels that keep you from slamming forward at an impact.  Additionally, the pilots can presumably see the moment of impact coming, and tense for exactly that moment in a way that passengers cannot.


Can time spent in consumer flight simulators increase the safety of flying light sports aircraft for licensed pilots? I've asked this question to my flight instructor, who believes flight simulators do a very poor job of modelling flight physics for very light airplanes, which makes them useless for preventing accidents.

Considering most accidents are caused by loss of control this explanation does make sense. On the other hand, flight sims might help in dealing with engine failures.

I intend to fly in a plane derived from Zenair CH-701.

Perhaps yes, but it's not easy to qualify objectively.

Simulating a light airplane may require a different approach in some areas, but it's not inherently difficult compared to 'heavy' ones.

However, the truth is, nobody cares that much, so there is much less investment in such simulators. A decent FTD (flight training device, something a step lower than what is legally called a 'simulator' (FFS)) will cost easily several times more than an ultralight, while the risk benefit is arguably lower (compared to real flight).

Secondly, type-rated simulators are rarity even on the 'proper' GA market; typically FTDs are 'generics' that aim to simulate a representative 'class' of aircraft. This makes fair comparison difficult, especially by real pilots who have most experience on a single/few real types.

Then, there are technical features that are even more important for light (and GA) airplanes than for big ones. One is a good visual system: in real visual flying, you obviously use it more, and having a single monitor stuck in front of you will hamper you more than you might think.

Second is control loading: on light airplanes you get airspeed and trim feedback right at your fingertips. There are no cheap solutions to this. You may argue this is not 'physics', but it actually is, this is all part of a feedback between the airplane and you being the part of control system. Lack or poor quality of these things (which is more than common on the simulators used for light planes) will substantially affect subjective and objective qualification of the flying qualities/handling of the simulator.

There are areas where even expensive FFS suffer. A typical example is ground handling. Or, speaking about 'loss of control', many regimes that result from it, notably stall and spin, are actually difficult to simulate well, and are often not required for certification.

That all said, it's an overstatement to say that simulators are 'useless for preventing accidents'. Flying is more about thinking ahead, planning and situation awareness than any specific piloting skills, and even a game simulator can teach you some of that.


Do airports have their own incident/accident investigation departments? Do airports have their own incident/accident investigation departments? or they are restricted to the NCAA/Safety department only?

More often than not, the accident investigation boards in Europe are a governmental unit independent of NCAA. The Board should be able to criticize and put requirements on all units involved in an accident/incident. This obviously include the CAA.

Departements and organizations are free to do an accident investigation. Availability to an accident site may be limited, though.
E.g. IFALPA have a structure of their own Accredited Accident Investigator, available for any relevant investigations.


If the the body and it's wing is mostly covered with solar panels and flies with electric motors, is it possible for that aircraft to fly? First before I say anything else, this is indeed a stupid question.
It would be most likely heavy, bulky, and expensive.

But theoretically, is it possible to fly with only Solar energy?

What does it take to accomplish such task? The total cost? Probable shape and size? The power required to lift off such a stupid aircraft?

What does it take to lift off with a single average man piloting the solar-powered aircraft? Without a man?

If you did calculate the amount of power needed, for both lifting a man and not lifting anything but itself, what else could you used that energy for?

Not a stupid question at all! This was one of the goals that solar impulse I and II set out to show. one thing to keep in mind is that its of course only possible while the sun is shining. It was able to do it but the margin of error was fairly small,

  During the day, the plane flies only by the energy from the sun. But
  in the morning and evening, when sunshine is not so strong, and
  especially at night, it must tap into its reserve of energy stored in
  its batteries. So every evening, the pilot must make sure that the
  plane’s batteries are 100% charged so that it can fly until the next
  sunrise.

Solar impulse ran on 8HP motors which is not much more than the Wrights first powered aircraft with a cruise speed of 56MPH it was not a terribly fast aircraft either but proved the concept was possible at a small edge of the spectrum.


What do the partially filled circles on skyvector mean? What does a partially filled weather status circle signify on Skyvector.com ?

It's an indication of how much of the sky is under that weather condition: IMC, marginal VMC, VMC.


Can I have two speeds on one motor? I am designing an aircraft and it is my first that will use a combustion engine rather than electric, so I am curious, if I had a single engine in the fuselage and gear shafts to the wings that drove propellers, how would I achieve different speeds on the propellers? The 'plane' itself is more similar to a VTOL so the different speeds are needed. I would be fine with a solution that used smaller electric motors in it's mechanism.

Or maybe I'm approaching this in a terribly inefficient way and there's a much better method to what I'm trying to achieve, I just feel stuck after battling it for a few days.

The aircraft itself will look similar to this:

The short answer is you probably wouldn't do it this way: Designing a drive system which allows you to split the work force between two output shafts at an arbitrary ratio (effectively an active differential) is pretty complex, and failure-prone. The failure of the differential would be "problematic" (both rotors stop), and the failure of a single drive link would likely be catastrophic (one rotor stops in the VTOL configuration you have an extreme wing-over from the imbalanced thrust).

The generally preferred design for this type of aircraft has two full engines mounted on the wings (for example the V-22 Osprey).
Similar results can be achieved by vectoring thrust from a jet engine (as in the Harrier "Jump Jet"), which can be done with a single engine.


How would an Inverted Delta Wing planform behave, Straight part forward? Are there wings shaped this way? There is info about straight edge wings, swept back wings, swept forward wings, delta wings.
Is there also info about a Delta wing with a straight leading edge and a tapered trailing edge, the point rearwards, like a manta ray?

To answer your second question first: Yes, these are mainly used for ground-effect craft. The idea is to have positive angle of attack, a tapered wing and a trailing edge with constant, low distance from the ground. This question covers their sweep angle.

The RFB X-114 ground-effect craft. Forward is right.

The wing would behave just like an ordinary, forward swept, low aspect ratio wing. It would have a small lift curve slope and a lousy stall behavior, because the low tip chord will make the tips stall first, causing the whole wing to roll. Unfortunately, the low leading edge sweep will prevent vortex lift, which is a typical feature of regular delta wings, to develop, so the stall angle will be only little higher than that of a straight wing with the same aspect ratio.

Manta rays are more diamond-shaped, so their "wing" has positive leading edge sweep and almost zero quarter-chord sweep. Their stall behavior would also be nasty if they were rigid, but the wings are actually fins and used for propulsion, not lift, so stall does not mean that the fish plunges to the ground. The picture above shows an Atlantic manta and was shamelessly copied from Wikipedia.


Why does it take so long to develop a passenger aircraft? I was researching about the Boeing 737 MAX, and came across some information on a Business Insider page:

  But in the 2010s, Boeing tried to replicate the success of the 737NG with the 737 Max. But this time, it wasn't simply competing with Airbus; it was playing catch-up. Boeing began to discuss a successor for the 737 as early as 2006, looking at both putting new, more efficient engines on an existing 737 airframe, or starting from scratch with a brand new airframe. Boeing knew that Airbus was similarly exploring an A320 replacement, but both companies were still in early stages.It was still trying to decide in 2010, when Airbus launched the A320neo family (neo = new engine option). The jets used the original A319, A320, and A321 airframes, but used new engines that offered a 15-20% increase in fuel efficiency, consequently lowering operating costs and giving the planes longer ranges. Airbus has since released two longer-range variants of the neo family — the A321LR and A321XLR.

Then the article began talking about how it could take up to 10 years for Boeing to create the new aircraft, so instead of creating a completely new airplane, Boeing decided to just add bigger engines.

Now my question is, why does it take so long to develop a new passenger aircraft?

It's similar with military aircraft. In a mature field it becomes ever harder to create something that is clearly better than what we have already.

Since every new development costs so much, the consequences of failure are immense. Therefore, management will try to lower the risk of failure which again drives up development cost and time. It is a self-reinforcing spiral.

Add to that the fact that we now have only two major civil aircraft producers which both are heavily backed by their respective governments and are too big to fail. This creates political interference which makes major decisions even more complex and precludes bold, risky decisions. Only the most safe* option will be chosen after years and years of deliberations.

And I refuse to believe that we don't know enough yet in aerodynamics or materials science. When a wing test lets the wing break at a load factor of 1.54 (where 1.5 is the goal) on the first try, we are pretty good already. Same for performance: New models hit their predicted fuel consumption within 2%! And regarding the many subsystems: COTS. Of course, if you insist on re-inventing the wheel all over again for a new airliner, then those 10 years are acceptable.

* "Safe" meaning the one promising the highest bonus to management for the time they hold their position, and with their current state of incomplete knowledge. Sadly, the ethos of companies like Newport News Shipbuilding, whose motto was: 'We will build good ships here — at a profit if we can, at a loss if we must, but always good ships.' has been lost to the Harvard MBA culture with its focus on short-term results.


Is an Aileron Roll Easier Done Opposite The Rotation Of The Plane's Propeller? We all know helicopters have tail rotors because they would spin out of control thanks to Newton's third law.

That got me thinking, would a single propeller plane have an easier time doing an Aileron roll opposite the rotation of the propeller? And do light aircraft require any special tricks like having one wing longer than the other or the ailerons being tilted in the rest position?

To be clear, I really don't know any more about aviation than the average person. The question just crossed my mind and I didn't find anything googling around.

Yes: Rolling one direction easier than the other, as you mentioned, newton's laws are at work here.

Special Tricks? Also Yes.  There are several design strategies to deal with asymmetries of thrust from propellers.  Bear in mind that these thrust asymmetries are not always at work, so any design feature is a trade off.  The propeller must be running, angle of attack is a factor, etc.  I have heard of asymmetrical wing incidence used, but more often a slight offset of a tail-plane, such as the vertical stabilizer is used.


Why is the A320 pre pressurised before take-off? I know this question has been asked, but I still haven't understood the answer. In the A320 the cabin gets pre pressurised before takeoff as we apply takeoff thrust. What I don't understand is what is the exact reason behind this. A little technical answer will be much appreciated.

In general, you want the cabin to be

pressurized in flight, and
not pressurized on the ground

If the system followed only & exactly that logic, at the moment of liftoff it would start pressurizing immediately, with the goal of overcoming the sudden change in pressure due to the aircraft's rapid climb away from the ground, but not more than that so that you don't pressurize below ground level all at once.  In practice, that ends up being a pressure "bump" right at (or slightly after) rotation, which is undesirable since it is at least noticeable and potentially uncomfortable or startling.

To prevent that pressure bump, the pressure controller is programmed to slowly pressurize the cabin slightly while the aircraft is still on the ground, so that at liftoff it is essentially maintaining the differential it has, rather than starting pressurization all at once.


Is it possible to land a commercial aircraft with an elevator trim stuck at a high degree? I know this is not practical (considering there is normally not much use to use up to 30 degrees of elevator trim), but if you were on a Boeing 777 or 737, or similar, and the elevator trim was set into said position, and stuck there, would it be possible to safely land said aircraft in that condition?

From the Boeing 737 emergency procedures:

After all attempts fail to free the stabilizer...

  Anticipate higher than normal elevator forces during approach and landing.
  The thrust reduction at flare will cause a nose down pitch.
  Note: Elevator control is sufficient to safely land the airplane regardless of stabilizer position.

Note on terminology: Most jet-liners (including the 777 and 737 as the question requests) use a trimmable horizontal stabilizer (THS), in which the pitch trim is achieved by positioning the whole rear wing up/down -- as opposed to using trim tabs.

(airteamimages.com) THS of an Embraer ERJ-190.


Why are the wings of some planes changing width? I was travelling recently in a Boeing 737 and I noticed one thing that I didn't understand. After the takeoff the wing flaps started retracting into/under the wing, making it narrower. The opposite happened before the landing.

You can see what I mean in this video:

The question is:
Why are the flaps hiding into/under the wing?

I understand that the bigger wing area is better during takeoff and landing. But why is the wings' size reduced during the cruise? Shouldn't bigger wings provide better lift during the entire flight?

Some clarification after comments:
I'm asking specifically why are the flaps retracted and not just remain parallel to the wing

Well, yes, bigger wings to provide better lift, but the also produce more induced drag in the process.

The wings on an airliner are optimized for cruise in high subsonic and transonic flight where a slender, swept wing works well.  While this is great for cruise flight, the trade-off is this style of wing requires a very high approach speed for landings which in turn require very long runways to accelerate the airplane on to reach rotation speed for takeoff or to decelerate the aircraft on once it has landed.

The Boeing Company successfully addressed these problems in the early 1960 with the development of the 727 airplane as a regional airliner.  It made use of a type of flaps called Fowler flaps (see Fig 1) in concert with leading edge extensions.  Fowler flaps. These style of flaps consist of a series of segments attached to tracks or support linkages running chordwise, allowing the flaps segments to extend and retract by rolling along said tracks.

Fig 1. Typical Fowler flap installation

When deployed these give the effect of changing the airfoil shape from a slender, slightly cambered airfoil into a wide airfoil with a large camber.  Fowler flaps have an additional advantage to them in that partial deployment creates a large increase in lift with limited additional drag, very useful for takeoff, while when fully deployed they create a lot of drag in addition to higher lift.


How to understand "Stage length, for payload calculations includes 85% wind"? Reading "Long Range Aircraft-AEA Requirements".

In appendix, Para 1.2 "Definitions and specifications", the definition for "Stage Length" states

  Stage length [...] for payload calculations includes 85% wind.

What does that mean?

The document AEA Requirements Long Range Aircraft is related to airline fleet planning, and the calculation of the fuel needs. Note that it is dated Dec. 1987. More on airline fleet planning.

85% wind

For this planning the document from the airlines association recommends to assume the wind that has a probability to occur of 85%. That means: assume you will find this wind on your route 85% of the time. The wind force itself is determined talking into account statistics for the regions overflown.

Stage

The flight profile is provided on the document itself, defining "stage" as start of climb to end of descent, excluding initial climb:

Planning profitability

Knowing how much fuel will be required and by deduction how much payload can be transported allow airlines to estimate the airline costs and revenues on a given route with a given aircraft. This is important for planning aircraft acquisition and replacement, as well as the route catalog.


Questions about go around safety When I perform a go around, how it is guaranteed there will be no traffic on my go around route for both controlled or uncontrolled airport?

At a controlled airport, the tower will route you or other aircraft as needed for seperation. If IFR, you will have a clearance to follow if you have to go around, either from ATC for that area, or as published, and once following the clearance you will go back to ATC for further information.  At a non-controlled airport and IFR, the same will apply. If you land, you call and cancel the clearance, if airborne and you are talking to ATC and have visual to land, you may be able to cancel while airborne.

VFR is similar - either tower will direct you as needed, or you see and avoid when non-towered.   If you use flight following, you will be talking to ATC until you get near the airport, they will often advise you of any nearby traffic before cutting you loose for your own approach and landing, with their last direction being something like "Nxxxx, airport is at your 12:00 and 8 mile, you have traffic at 1:00 and 5 miles, squawk 1200, frequency change approved."


Is there a way, by which an airline or ATC would be alerted, if both pilots are asleep or incapacitated? There are various questions around, which deals with what happens if both pilots are incapacitated, but my question is different.

I want to ask, is there a way by which an airline or ATC is alerted that both pilots are asleep or incapacitated, more like a camera which tracks eye movement, which would alert the pilots or cabin crew or ATC.

No there isn't. The only indication ATC has is if the pilot doesn't respond to radio calls but that can also be because of other issues like a radio malfunction.

There is not much ATC could do anyway if pilots are non-responsive.


Where can I find articles about Handley Page multi element segmented airfoils? Can anyone direct me to a source containing the complete article on Handley Page's 6 and 8 element airfoils from Flight magazine Feb 24, 1921 (PDF) or further more detailed information on this subject.

The images look a lot like the ones in:

A.M.O. Smith, “High-Lift Aerodynamics”, 37th Wright Brothers Lecture, Journal of Aircraft, Vol. 12, No. 6, June 1975

The  classic paper on multi element airfoils, great read!


How does an aircraft form wake turbulence? This question discusses how wake turbulence can affect planes flying in formation.  It got me wondering, how do aircraft (the wings in particular) form wake turbulence to begin with?  It can't be as simple as tip vortexes right?

As a follow up, how can you design an aircraft to minimize wake turbulence?  And what are the trade offs in doing so?

Origin of the vortices

Wake turbulence is easy to understand once you know how a wing creates lift: By deflecting the air flowing across it downwards. In this answer, I had used the simplification of just accelerating downwards all the air flowing through a circle with a diameter equal to the wingspan, and leaving all other air unaffected.

This helps to understand the principle of lift creation, but is too simple, of course, because the downward movement of air will create a void above it, and the air below has to make place for that downward moving streamtube. Also, the pressure field around the wing will affect the air in the vicinity of the streamtube as well, and in consequence air from below will be pushed sideways already by the wing, and the air above will start to flow towards the low pressure area over the wing. This sideways movement will become more pronounced aft of the wing, such that air will continuously be pressed outwards below the wing's wake, move up left and right of it and inwards above the wake. The inertia of the downwash keeps it moving downwards for several minutes, continuously displacing the air below it and sucking more air into the space above, and that will result in two vortices swirling behind the wing. This is the rolling up of the wake (see the sketch below, taken from this source).

The vortices are just a consequence of the downward movement of the wake, and this in turn is a consequence of lift creation. Please note that the cores of the vortices are closer together than the wingspan! This by itself should make clear that they are not caused by air flowing around wingtips, a hard to extinguish misconception. The table below gives calculations of this vortex spacing.

The table is also from the Carten paper of 1971; note the inclusion of Boeing's 2707 project!

Strength of the vortices

If we again come back to the simplified streamtube approximation, lift is proportional to the mass of air flowing through it per unit of time times the deflection angle. If lift is equal to the aircraft's mass (as it should be), heavy aircraft need to either accelerate more air (wider span) or accelerate air more (higher deflection angle) than light aircraft at the same speed. A higher deflection angle will produce more powerful vortices. For that reason, a heavy aircraft at low speed and with a small wingspan will produce the strongest vortices.

Since more air flows through the streamtube at higher flight speed, flying faster will require less deflection, making the wake vortices weaker. If the aircraft climbs, air becomes less dense with altitude, and less mass flow over the wing is available, so the vortices grow stronger if the flight speed does not change. Normally, aircraft accelerate when climbing, and the vortex strength will stay the same if the aircraft flies at constant dynamic pressure.

Vortices can be avoided in three ways:

Infinite wing span (meaning infinite mass flow, so no deflection is necessary for any lift)
Infinite speed (again, gives infinite mass flow)
No weight of the aircraft. Flying a zero-g parabola does indeed produce almost no wake turbulence.

End of the vortices

Inertia will keep the wake moving downwards and the vortices spinning, but friction will let those air movements die down within a few minutes. If the aircraft flies high, the wake is dissipated long before it hits the ground. The wake of low flying aircraft, however, does hit the ground and is deflected. The vortex tube now acts like a wheel and starts moving outward, and if there is a sufficient crosswind, the windward vortex can be arrested as in the right sketch below (also from the Carten report).

Photographic evidence

There are far too many pretty pictures around of wake vortices to not include some, so I will add a few here:

You can see that the outer contrails of this Boeing 747's engines wrap around the contrails of the inner engines. This shows how the air is pushed down in the wake of the wing and that the centers of the vortices are slightly inboard of the outer engines.

The condensation traces originating at the winglet tips of this A340 move in- and upward, again showing that the vortex does not originate from the tips but forms behind the wing and with a distance between the two vortex cores of substantially less than the wingspan.

These two pictures show how the downwash of the wake is cutting a furrow in the clouds.

KLM MD-11 on a moist day, flaps set for landing (source © Erwin van Dijck). One, it shows how insignificant the tip vortex is compared to vorticity shed at the flap tips, and Two it shows how the tip vortex moves inward and starts to be sucked into the wake vortex. Note also the tip vortices from the tail!


Are altimeters calibrated to ISA geopotential altitude or ISA geometric altitude? Altimeters convert a pressure measurement to an indication of altitude. When set to standard pressure setting (1013.25 hPa / 29.92"Hg), they assume the atmosphere is according to the ICAO Standard Atmosphere (ISA) and indicate the altitude accordingly. However, ISA has two altitude definitions; geometric altitude and geopotential altitude.

The ICAO Standard Atmosphere is a model of the atmosphere up to 80 kilometres high, based on the perfect gas law and the hydrostatic equation.  In order to deal with the effects of reduction of gravity with height, it uses the concept of geopotential altitude H:

$$H= \frac{1}{g_0}\int_0^hgdh$$

with:

$h = \textrm{geometric altitude}$
$H = \textrm{geopotential altitude}$
$g_0 = 9.80665\textrm{ m/s, mean gravitational acceleration at mean sea level}$
$g = \textrm{local acceleration of gravity (height dependent)}$

Gravity is given by :

$$g = g_0 \left(\frac{r_e}{r_e + z}\right)^2$$
with:

$r_e = \textrm{the radius of the earth}$

And thus the relation between geopotential altitude and geometric altitude is given by:

$$H = h\frac{r_e}{r_e+h}$$
And
$$h = H\frac{r_e}{r_e-H}$$

In the ISA model, the properties of the atmosphere (pressure, temperature, density) are all calculated with respect to geopotential height.

For a geopotential height of 12 500 meters (41 010.5 ft), which corresponds to a geometric height of 12524.6 meters (41091.3 ft), the ICAO atmosphere gives a pressure of 178.648 hPa.

My question is: what will a perfectly calibrated altimeter indicate when the pressure is 178.648 hPa? Does it indicate 41 010.5 ft (the geopotential altitude) or does it indicate 41091.3 ft (the geometric altitude)?

You might say that the difference is "only" 80 feet, but for RVSM operations that is quite significant.

The ICAO standard atmosphere (as described in ICAO Doc 7488) does not give the answer (at least I couldn't find it). And it includes tables for every 500 meters of both geopotential and geometric altitude, so that does not make it easier.

I'd like to know which altitude is indicated on an altimeter (ISA geopotential or ISA geometric) and where (in which official document) this is specified.

The TSO for Air Data Computers is TSO-C106. It specifies for the minimum performance standard "SAE Aerospace Standard 8002, Air Data Computer - Minimum Performance Standard."

From AS8002:

  3.6 Altitude Reference:

  Calibration of the static air sensing mechanism for pressure altitude
  outputs (including baro-corrected if supplied) shall be to the
  geopotential altitude tables of U.S. Standard Atmosphere, 1976.

While this is a US standard, the FAA asserts it is in compliance with ICAO Doc 7488.

For RVSM, additional requirements are levied against the installation primarily focused on reduction of static source error (SSE). That guidance is available in AC 91-85A.

It's important to remember that absolute accuracy at altitude is not as important as everyone adhering to the same reference.


What deviation from the official flight path is allowed during takeoff and landing? Our local airport is currently going through CAP1616 and permanent airspace change consultations.

Considering take off and landing flight paths:

what degree of deviation is allowed from the official flight path by aircraft while under 7000 feet (2133 meters)?
what would be a typical distance travelled before reaching the aforementioned altitude?

A potential 3rd question relates to finding the designated flight paths but I believe this is answered in other questions.

Instrument flight and visual flights have very different standards and expectations regarding flight paths, and aircraft being guided in real time by ATC in a radar environment are different again.
For instrument path design, I believe what you are looking for is called a TERPS design standard(terminal procedures specifications). In the USA most of this is contained in FAA orders 8360.3 and 8360.19 the CAA, EASA or ICAO probably have some equivalent. However IFR path design mainly considers only ATC controlled vs uncontrolled airspace and restricted areas, not much weight is given to the various classes of controlled airspace. The different classes of controlled airspace exist primarily around ATC workloads.(traffic density) TERPS are mainly concerned with obstacle clearance, availible navigation and equipment failure contingencies.
This is not specific to the UK, but planes have the same physical limits everywhere so standards are similar. The industry standard final approach for instrument flights is 3 degrees or 318 feet per NM, steeper only when required for physical obstacle clearances. The obstacle clearance on approach generally changes from 1000ft in the initial segment to about 250feet at the missed approach point.(dependent on the exact form of navigation)
The standard minimum expected climb performance is 200ft/NM but the obstacle evaluation surfaces are only 152ft/NM (40:1) up to the en-route obstacle clearance. These climb slopes are reduced at high altitudes but that is not relevant to an airport in the UK.  Also EASA and the FAA have slightly different methods for setting the details, like where the slope starts, but the end result is similar. Normal climb performance in modern aircraft is usually above 400ft/NM not withstanding engine failure, or mechanical trouble like stuck flaps, lightly loaded jets can climb much steeper slopes.
As for lateral clearances, this is a bit complex and based on the type of navigation, a localizer/ILS final will have a wedge of plus or minus 3 degrees to either side of the center path and the wedge will be 700 feet wide at the runway threshold. This is usually up to about 1000ft above the airport. there are wide safety buffers either side of this 6degree wedge. With other forms of final guidance the path may be over a mile wide at its most narrow.
The initial segment and low routes are most often plus and minus 4NM from the center path, plus a 2NM obstacle safety buffer [12 miles total width].
WAAS(SBAS) enabled GPS nav can allow terminal area paths of plus or minus 1 mile from center-line(they still require a large safety buffer beyond this), reducing to 0.3miles on final and with some equipment a narrowing wedge similar to the affore mentioned LOC/ILS.


Why don't we have video recording of runways takeoffs/landings? When planes crash at airports, it seems the only video available is amateur footage several miles away with terrible quality.

Why don't we have video recordings of all takeoffs and landings at the airport?

Because video is mostly useless for investigation.

The investigators need to know the exact flightpath, which is already recorded by the ATC radar and by the flight data recorder, they need to know whether and which systems failed, which is recorded by the flight data recorder, and they need to know what the pilots were doing, for which they have cockpit voice recorder and the radio communication is also recorded in the ATC facility (tower).

Video would be worse for determining the flight path than both ATC radar and FDR and while ATC radar does not have attitude, FDR does and again more precisely than video. Plus video might, depending on angle, have external damage, but that can generally be determined by examining the wreckage quite fine.

So video would add very little information over the existing recordings and thus it is not cost-effective to add it for just this purpose at all airports (it may be used if it is installed for security purposes).


How will a prolonged series of steep turns produce a stall in subsequent level flight? In Stick and Rudder, the author warns pilots against the unreliability of judging airspeed and hence “buoyancy” — his term for how far the airplane is from aerodynamic stall — by throttle position, engine noise, and nose attitude.

  Perhaps the most deceptive of these factors is g load. When an airplane, flying at a certain speed, goes into a turn and loads itself down with g load it assumes larger Angle of Attack and this gets closer to the stall. That has been described earlier in this book. But it isn’t the whole story. At the larger Angle of Attack, the wings have more drag, and thus the airplane will slow up, unless the throttle is opened wider. The airplane assumes a still higher Angle of Attack and gets still closer to the stall! Few pilots realize how strong and dangerous this effect is.

Langewiesche, Wolfgang. “The Flying Instinct.” In Stick and Rudder: An Explanation of the Art of Flying, 58. New York: McGraw-Hill, Inc., 1944.

He then gives a surprising example.

  The average small airplane, fully loaded and with its throttle set at cruising, is actually unable to hold indefinitely any turn banked much more than 45 degrees! The effect just described will slow it down gradually, as it circles, so that the pilot’s stick comes farther and farther back; until finally, after perhaps twenty turns have been completed, it will stall: stall, mark you, out of level flight with cruising throttle!

ibid.

Why doesn’t nosing over to leave the steep turns for straight-and-level attitude with open throttle produce sufficient airspeed to avoid the stall?

A prolonged series of steep turns will not produce a stall in subsequent straight and level flight.

  "after perhaps twenty turns have been completed, it will stall: stall, mark you, out of level flight with cruising throttle!"

In this case "level flight" means not climbing or descending while still in a steep turn.

Stopping the turn by rolling level would unload the wings and prevent the stall. Nosing down would also unload the wings and increase airspeed, also preventing a stall.


Why does strong shock wave-boundary-layer interaction produce a bubble reattachment? The picture represents a lambda type shock wave, separating the boundary layer at its foot. Separation causes a recirculation bubble to appear. I understand why separation has happened, but what is the exact reason for a bubble reattachment?

The picture is from the book called Shock Wave-Boundary-Layer Interaction by Holger Babinsky and John K. Harvey, Cambridge University.

After the rear shock leg, the subsonic flow inside the boundary layer decelerates further, which causes an expansion of the streamtubes and therefore reattachment. Note that with the presence of the supersonic tongue, the deceleration into the subsonic regime happens somewhat "slower" inside the boundary layer than outside (especially above the slip line).


Is AD compliance ever physically verified when maintaining an aircraft? As we all know around here, national aviation authorities put out Airworthiness Directives mandating certain changes be made to aircraft during their service life so that the aircraft can stay airworthy.  The paperwork for these ADs is part of the aircraft logs, and thus stays with the aircraft for the life of the aircraft.

However, just because an AD is marked as complete and closed out in the paperwork does not necessarily mean it has actually been completed.  This was a causative factor in the Omega flight 70 mishap, where an engine fell off a 707 shortly after rotation and damaged the plane to the point where it could not climb out.  The investigation revealed that although the applicable ADs were marked complete, the upgraded part required to be installed to close the ADs out had not been installed on the mishap aircraft.  Instead, a prior owner had marked the AD at the time complete when it had not actually been fully closed out.

How can an aircraft owner ensure that the ADs that the paperwork says have been closed out on an aircraft have actually been closed out and not simply pencil-whipped?  Are such verifications ever performed during maintenance or inspections (including pre-/post-sale inspection), or is the paperwork trusted absolutely?  Furthermore, how can an inspecting mechanic accurately determine the completion status of ADs?  (For the 707 AD in question in the Omega 70 mishap, this could be done with a small template and some mechanic time inside the pylon, but I suspect some ADs aren't that easy...)

I can only speak for commercial aviation, but in my experience, we generally have 100% RII buyback on initial AD compliance issues. For example, if we have to run a new wire bundle or reroute a wire bundle as part of an AD, it has to be "bought off" by either a QC inspector or an RII-qualified mechanic. In these situations, I would say that the work is done properly 99% of the time. Rarely would someone put their name on something that's done incorrectly if they don't have to go back and do the work themselves. The response is generally "Call me when you get it right."

Where I think the FAA severely lacks oversight, in my opinion, is future compliance in upholding the standards of the AD. On the initial AD, you're not allowed to deviate one iota from the original without a very special process put in place. But what happens when you deviate 10, 15, or 20 years down the road?

Hypothetical scenario: An AD is written to reroute a wire bundle from other wire bundles because of some safety issue. The AD is complied with and life goes on. Twenty years later, a mechanic disassembles all the wiring in the area for "X" maintenance issue. He turns it over to the next shift to reassemble it. Next shift has no idea how it goes back together. It's not marked as AD wiring. There are no instructions on how it all goes back together (save for the AD paperwork from 20 years ago), so the mechanics put it back together per the standard wiring practices manual. They bundle and clamp. Bundle and clamp. They do a beautiful job, but guess what? It violates the purpose of the AD from 20 years prior. Do you think the FAA follows up on that? Nope. The company? Nah. They have paperwork showing the AD is complied with. So it's up to each mechanic to determine if what they're working on is part of an AD (even one from 20 years ago), despite no special labeling or instructions, and maintain that AD compliance. As we mechanics joke, "It'll all come out in the investigation."

My experience is that as time goes by, the integrity of many AD's slowly dissolves. That being said, if we as A&P's even smell the faintest whiff of an AD, our antennae perk up and we are very careful to maintain that compliance. AD  violations are the surest way to get a nice letter in the mail from Mr. FAA.


Help in understanding this velocity triangle of a propeller I was reading a research paper and have had difficulty understanding something. How did the author get tan(phi) in these terms?
This is something I've been trying to figure out for a long time now.

There is an obvious error in this paper. Just look at the final formula, and remember that for small angles $\tan(\phi) \sim \phi$. The formula says that if you increase $\phi$, $v_2$ decreases. Of course, the opposite happens.
By (trigonometric) definition,
$$\tan(\phi) = \frac{v_2}{v_{propeller}}$$
Therefore,
$$v_2 = v_{propeller} \cdot \tan(\phi)$$
The rest follows; the result is similar but you have multiplication instead of the fraction.
P.S. You can get a hint that this is a low quality paper by the fact that they obliviously confuse upper- and lowercase $v$ (on the picture and in the formulae). In math/science, case matters! Sometimes even the script matters.


Why aren't there V-tail airliners? Since a V-tail is lighter and generates less drag than a conventional empennage, why has this solution been put away from production?

Controllability and redundancy. Airliners are certified according CFR 14 Part 25, which specifies that upon engine fail the aircraft must still be able to fly and climb: it must have more than one engine.

After an engine has failed, the rudder must be deflected in order to compensate for the asymmetric thrust of the remaining engine. With a V-tail, this means that after engine fail, there is less pitch authority: pitch and yaw surface deflections are coupled. A V-tail has two control surfaces that combine aircraft yaw control and pitch control, which goes well until one of the surfaces hits a stop.

Reduced pitch control due to an engine failure would be unacceptable for an airliner. For a single engine plane with the engine in the centreline, this yaw trim condition would not happen.


Need some help with a seemingly simple question An aircraft flies from A to B, distance 155 nm, in 1 hour and 23 minutes. If there is a tailwind of 12 kts the TAS is?

Try this: (a small amount of rounding, not considering instrument error -basic)

Speed = Distance x 60/Time (in minutes)

Speed = 155 x 60/83(minutes)

Speed = 112 nmh

Speed of 112 nmh consists of 100 kts TAS and 12 kts Tailwind.

Then, TAS = 100 kts.


GA Headsets - is there a standard for the replaceable microphone? I've noticed that on many (but not all) different types of GA headset, the microphone seems to be somewhat modular, with two holes at the end for the microphone boom to insert into, and two screws at the front that seem to be able to be used to both hold it in place on the boom, and also fasten the two parts of the plastic microphone assembly in place.

Example microphone modules:

Is there some standard for microphone modules, or is what I'm noticing just coincidence?

Background: One of my headset microphones no longer works due to being ... unintentionally regurgitated upon - I'm wondering whether I can just buy one that looks similar.

It's not a coincidence, the connection is a modular microphone standard called U-172/U. The pins it connects to are the U-173/U standard.

You can't just get any microphone that has that connector though, it's not aviation specific. You need to get a microphone which has the right impedance and is designed to work with the voltage on an aircraft communication system. There's plenty of options, some which give better noise cancelling properties than others.

All you need to do is get the parameters of your hurl-covered one and get one with the same parameters.

There's information on aviation connectors and standards here, and here.


When do carriers overhaul their flight schedules with flight re-numbering? A (US domestic) carrier can obviously stop flying a flight, or some legs of that flight, for a host of reasons. But - occasionally it makes more significant changes, like re-numbering many flights, or changing a bunch of routes on offer etc.
My question is: Are there rules, or is there an established custom, regarding when this happens? Specifically, do operators always align these changes to the beginning of years, quarters, or months? Or do they just happen at arbitrary times and not even bunched together?
I'm interested in the period between 2000 and the present time.

At my carrier, there are no rules along the lines asked about; the rules that apply are generated by the Schedule Planning department, and will change as they see fit. They produce many schedules each year, and how much "this" one differs from the previous one depends on lots of factors regarding fleets and markets and priorities. Some things are seasonal, many aren't.
The change-over dates are similarly "whatever makes the most sense" as the schedules are being built. One carrier may be on a 6-week cycle, with another on a calendar month cycle; ours seems to change at not entirely regular intervals. Some schedules are longer than others - mid June thru mid-August may be one fairly constant schedule, but November & December may see 4 distinct schedules, as travel fluctuates around the two major holidays.
Increasing automation over the last 20 years has probably contributed to this variability.
There may be some "sacred cows" in the schedule, that flight 1 always is the first departure from (big east coast hub city) across the country to LAX or SFO, perhaps, or flight 711 always serves Las Vegas (dice roll of 7 or 11 is a winner), etc. But much of the schedule is, whatever makes sense to the planners this month or this quarter or this year.
The closest you'll come to having predictable guidelines would be to study one airline's schedules over time & observe enduring patterns... but even those may not be written in stone.


is it possible that setting a lower airspeed makes a steeper climb? I'm now studying a Flight Management System (FMS), and it says that when the FMC predicts that the airplane will not reach an ALT constraint, the CDU will display "UNABLE NEXT ALT" and then we have to manually set a lower airspeed to provide a steeper climb.
But, I've learned that when we pitch up, the aircraft slows down because of more drag.
I also remember that when an aircraft increases speed, pitch goes up because of the increase in thrust and more lift from the wings.
So why is a decrease in speed needed to make the FMC altitude constraint, rather than an increase?

I think you have it backwards, it is not that a slower airspeed produces a steeper climb, it it that a steeper climb, given the same power, will cause a slower airspeed.
If the only constraint you're setting the FMS is the airspeed to maintain for a constant thrust, then it will pitch up more, increasing the rate of climb, which will slow the airspeed.


Why are the Convair 880's yokes shaped differently from each other? Looking at this picture of a Convair 880's flight deck...

(Image originally by the San Diego Air & Space Museum at Flickr, via Wikimedia Commons)

...the captain's and first officer's control yokes have quite different shapes; the captain's yoke is round, like that of an automobile or a 1930s propliner, while the first officer's yoke has the familiar W-shaped yoke, complete with buttons on the yoke's horns.

Why the difference between the two yokes?  Is it to optimise the captain's yoke for the duties of a pilot flying, and the first officer's yoke for the duties of a pilot monitoring?  Or something else?

My guess is that this is a relatively odd situation, where one yoke had already been replaced by a newer one (on the right), whereas the other still is the original.

If you look at the two images below (from Airliners.net), both yokes are the same.

It seems as if the right one has some more controls on the yoke (e.g. for radio settings, trim controls, or something else) and is simply an upgrade to the older model. If the old one still worked, I can imagine an airline waiting for a regular service inspection or overhaul before replacing it, rather than removing parts that are still fit to fly.


Why don't the A380 and A350 have trim wheels? (wikimedia.org) A350 thrust levers without the flanking trim wheels.

Why don't the Airbus A380 and A350 have trim wheels?

On the other fly-by-wire Airbus aircraft the trim wheels are there for manual trim in case the aircraft went into direct law since the Airbus sticks do not have a trim control.

Were the trim wheels replaced by another interface? Or is the manual trim option completely removed due to a certain [backup] technology?

Left: Standard Airbus sidestick on the A350 with no trim control (wikimedia.org). Right: Trim wheels on other Airbus aircraft (wikimedia.org).

The question stems from this comment:

  I don’t think [having trim controls] is strictly speaking necessary. It used to be the mechanical backup for FBW failures on early Airbusses, then it was kept a while for commonality. I am not sure whether the A350 still has it?

(Source)

Both the A350 and A380 have alternate pitch trim control rocker aft of the flap lever in the cockpit to replace the pitch trim wheels near the throttle quadrant.

OPINION: I'd guess this was done simply in a continuous effort to improve the flight deck, reduce clutter and reduce weight. As a pilot myself, I’m not thrilled with it from a kinesthetic standpoint, as the wheel is much more natural to use.


Why don't most fighters have thrust reversers? With the exception of the Panavia Tornado, fighters do not have thrust reversers. Why is this? Why does the Panavia Tornado have them?

Thrust reversal is a complex system (equals money) and it uses significant amount of fuel (also equals money). It is not a very efficient means to reduce the speed of a landing aircraft either, and other methods (e.g. brakes or drogue parachutes) are much better suited.

The biggest advantage of thrust reversal is that it cancels out the idle forward thrust working against the aircraft. Canceling out idle thrust isn't an issue on most fighters, as they have an engine nozzle that is open at ground idle to prevent any thrust from being produced. This nozzle probably also makes it a bit difficult to integrate Thrust reversals, but the Panavia Tornado proves it can be done.