What repairs or modifications can be done without approval/certification? I realize that this is likely to depend on jurisdiction (EASA or FAA would interest me the most in that case), but is there any common-sense kind of line that you don't cross until you've at least checked that it's okay?

I mean it's obviously okay to put checklists in a side-pocket, and it's obviously not okay to replace the avionics. Can I replace the PTT button on the yoke? Or if I don't touch the wiring and simply add some plastic on top give it a better feel?

This answer applies to FAA certified aircraft.  For experimentals, there are really no restrictions.  I mean, you can build the airplane from scratch so replace what you want...  but for certified aircraft:

The following is copied and pasted from the AOPA website:

FAR Part 43 specifies who may do what to an aircraft in the way of maintenance, repair or alteration. It requires that only properly certified mechanics work on aircraft and "okay" them for return to service. However, it does allow preventive maintenance to be performed by a certificated pilot, holding at least a Private certificate, on an aircraft owned or operated by that pilot, provided the aircraft is not used in commercial service. The responsibilities for a pilot performing preventive maintenance are very similar to those imposed on the certificated mechanic performing other duties. The FARs require that anyone who works on an aircraft must have the appropriate maintenance and service information available. This means quite simply that before you set about performing preventive maintenance items on your airplane, you must first have the proper maintenance manuals available.

A list of "preventive maintenance" allowed is specifically listed in FAR 43 appendix A (4) c and is copied below:

  Preventive maintenance. Preventive maintenance is limited to the
  following work, provided it does not involve complex assembly
  operations:

  (1) Removal, installation, and repair of landing gear tires.

  (2) Replacing elastic shock absorber cords on landing gear.

  (3) Servicing landing gear shock struts by adding oil, air, or both.

  (4) Servicing landing gear wheel bearings, such as cleaning and
  greasing.

  (5) Replacing defective safety wiring or cotter keys.

  (6) Lubrication not requiring disassembly other than removal of
  nonstructural items such as cover plates, cowlings, and fairings.

  (7) Making simple fabric patches not requiring rib stitching or the
  removal of structural parts or control surfaces. In the case of
  balloons, the making of small fabric repairs to envelopes (as defined
  in, and in accordance with, the balloon manufacturers' instructions)
  not requiring load tape repair or replacement.

  (8) Replenishing hydraulic fluid in the hydraulic reservoir.

  (9) Refinishing decorative coating of fuselage, balloon baskets, wings
  tail group surfaces (excluding balanced control surfaces), fairings,
  cowlings, landing gear, cabin, or cockpit interior when removal or
  disassembly of any primary structure or operating system is not
  required.

  (10) Applying preservative or protective material to components where
  no disassembly of any primary structure or operating system is
  involved and where such coating is not prohibited or is not contrary
  to good practices.

  (11) Repairing upholstery and decorative furnishings of the cabin,
  cockpit, or balloon basket interior when the repairing does not
  require disassembly of any primary structure or operating system or
  interfere with an operating system or affect the primary structure of
  the aircraft.

  (12) Making small simple repairs to fairings, nonstructural cover
  plates, cowlings, and small patches and reinforcements not changing
  the contour so as to interfere with proper air flow.

  (13) Replacing side windows where that work does not interfere with
  the structure or any operating system such as controls, electrical
  equipment, etc.

  (14) Replacing safety belts.

  (15) Replacing seats or seat parts with replacement parts approved for
  the aircraft, not involving disassembly of any primary structure or
  operating system.

  (16) Trouble shooting and repairing broken circuits in landing light
  wiring circuits.

  (17) Replacing bulbs, reflectors, and lenses of position and landing
  lights.

  (18) Replacing wheels and skis where no weight and balance computation
  is involved.

  (19) Replacing any cowling not requiring removal of the propeller or
  disconnection of flight controls.

  (20) Replacing or cleaning spark plugs and setting of spark plug gap
  clearance.

  (21) Replacing any hose connection except hydraulic connections.

  (22) Replacing prefabricated fuel lines.

  (23) Cleaning or replacing fuel and oil strainers or filter elements.

  (24) Replacing and servicing batteries.

  (25) Cleaning of balloon burner pilot and main nozzles in accordance
  with the balloon manufacturer's instructions.

  (26) Replacement or adjustment of nonstructural standard fasteners
  incidental to operations.

  (27) The interchange of balloon baskets and burners on envelopes when
  the basket or burner is designated as interchangeable in the balloon
  type certificate data and the baskets and burners are specifically
  designed for quick removal and installation.

  (28) The installations of anti-misfueling devices to reduce the
  diameter of fuel tank filler openings provided the specific device has
  been made a part of the aircraft type certificate data by the aircraft
  manufacturer, the aircraft manufacturer has provided FAA-approved
  instructions for installation of the specific device, and installation
  does not involve the disassembly of the existing tank filler opening.

  (29) Removing, checking, and replacing magnetic chip detectors.

  (30) The inspection and maintenance tasks prescribed and specifically
  identified as preventive maintenance in a primary category aircraft
  type certificate or supplemental type certificate holder's approved
  special inspection and preventive maintenance program when
  accomplished on a primary category aircraft provided:   (i) They are
  performed by the holder of at least a private pilot certificate issued
  under part 61 who is the registered owner (including co-owners) of the
  affected aircraft and who holds a certificate of competency for the
  affected aircraft (1) issued by a school approved under Sec. 147.21(e)
  of this chapter; (2) issued by the holder of the production
  certificate for that primary category aircraft that has a special
  training program approved under Sec. 21.24 of this subchapter; or (3)
  issued by another entity that has a course approved by the
  Administrator; and   (ii) The inspections and maintenance tasks are
  performed in accordance with instructions contained by the special
  inspection and preventive maintenance program approved as part of the
  aircraft's type design or supplemental type design.

  (31) Removing and replacing self-contained, front instrument
  panel-mounted navigation and communication devices that employ
  tray-mounted connectors that connect the unit when the unit is
  installed into the instrument panel, (excluding automatic flight
  control systems, transponders, and microwave frequency distance
  measuring equipment (DME)). The approved unit must be designed to be
  readily and repeatedly removed and replaced, and pertinent
  instructions must be provided. Prior to the unit's intended use, and
  operational check must be performed in accordance with the applicable
  sections of part 91 of this chapter.

  (32) Updating self-contained, front instrument panel-mounted Air
  Traffic Control (ATC) navigational software data bases (excluding
  those of automatic flight control systems, transponders, and microwave
  frequency distance measuring equipment (DME)) provided no disassembly
  of the unit is required and pertinent instructions are provided. Prior
  to the unit's intended use, an operational check must be performed in
  accordance with applicable sections of part 91 of this chapter.


What are the pros/cons of low/forward powerplants on helicopters? (Original)

The double-decker Westland Wessex has a pair of side-by-side Gnome turbines low and forward (blue rectangle above).

What are the pros and cons compared to the center-high more typical placement of nowadays?

Of the cons is perhaps the longer shafts I drew above, which are concluded based on pictures that reveal the orientation of the engines and pictures of a partition between (but aft of) the two cockpit seats.

I searched for clear cutaways on Google and Flight's archive. Also checked the Wikipedia page regarding the engine placement.

The Wessex is developed from the Sikorsky H-34 that had a radial engine in the same location.

The radial was put down there to keep the center of gravity low with a heavy piston engine while leaving a decent size space for payload on the center of gravity below the rotor head.

The compactness and lighter weight of turbines made it possible to mount them up at the rotor head, resulting in a cascade of benefits, and as usually happens, the configuration hits a sweet spot where all the competing compromises are in the best possible balance, so the turbine engine/transmission behind the rotor head becomes almost universal.

In the case of the Wessex, the turbine engines' location is an artifact of its radial powered ancestor and it likely would never have been designed that way if it had a turbine at the start.


How are procedures for curved-runway operations different from those for straight runways? Runways having a significant curve between the two ends aren't exactly common, but they do exist, one good example being Elk City Airport's runway 14/35.

When operating to or from an airport with a curved runway, what does one have to do differently than with a straight runway?

I know that KAVX has quite a hump in the middle of the runway which does not allow for departing aircraft to see all the way down the runway, and I'd imagine that the procedures are the same as they would be for Elk City Airport. The Facilities Directory/Chart Supplement for KAVX says:

PILOTS CANNOT SEE ACFT ON OPPOSITE ENDS OF RWY DUE TO GRADIENT, MUST ANNC TAKING ACT RWY ON UNICOM PRIOR TO DEP

Essentially, communicate your intentions on the common traffic frequency. Where you are taxiing, what runway you are using and when you're about to take off. Also be vigilant watching for traffic that may be using the opposing runway.
On a curved runway, Your main concern is that someone else would be approaching or using the opposite runway while you are using the other end. This is even recommended in the Chart Supplement for Elk City, which says

LAND RY 14 TKOF RY 35 WHEN WIND CONDITIONS ALLOW

As far as actually taking off on a runway that is not straight, you'd need to take into consideration obstacles around the runway environment. In the case of Elk City, I'd hold off on rotating until after the bend so that I can climb straight out and get above tree level prior to making a turn.  It appears as though that is in line with the Chart Supplement instructions, as landing RWY14 would give you the longest length to land and start to slow before you had to make the turn, and taking off on RWY35 would have you turning prior to rotation speed (or at least shortly thereafter).


How many versions of the P-51 dorsal fin fillet are documented? How many different versions of the P-51 Mustang DFF are there?

A quick search of Google Images seems to show only three major variations on the tail for production P-51 variants:

Razorback (all P-51A, B, and C variants; no dorsal strake and a higher rear fuselage line):

Bubble canopy without the strake (seen on early D-variants)

With the strake (seen on later production D variants, integrated fully into K and H models and retrofitted to earlier Ds, sometimes to the Razorback B/Cs):

There is some difference in the prominence and exact shape of the fin fillet as the design continued to be developed; for all B/C/D variants it was a thin piece essentially bolted onto the strakeless frame. For the H variant in the bottom picture, it was integrated more fully into the fairing of the vertical stabilizer.

There's one more I've seen and I'm not sure if there's just the one example, but there is a P-51 "XR" variant, "Precious Metal", with dual counter-rotating props and further aerodynamic refinement, including a fairing behind the modified bubble canopy that narrows into a continuous strake along the aircraft's rear spine:

Other custom racing variants have existed over the years, all heavily modified from USAF production variants.


Is it possible to Fly Aircraft on Mars? I have been fascinated with the thought of flying all kind of aircraft on Mars. To begin, I don't know much about the fundamental things or requistes for flying. Is it possible with the the things we currently have? What kind of infrastructure would be needed to fly there? Assuming GPS navigation is already set up there. What would be the design of the aircraft and the runways? Would it be like we have on Earth or completely revolutionised Idea? Kindly not mention the costs of flying there.

you're in luck, somebody did the calculation/ simulation.

Mars: To see what happens to aircraft on Mars, we turn to X-Plane.

X-Plane is the most advanced flight simulator in the world. The product of 20 years of obsessive labor by a hardcore aeronautics enthusiast who uses capslock a lot when talking about planes, it actually simulates the flow of air over every piece of an aircraft’s body as it flies. This makes it a valuable research tool, since it can accurately simulate entirely new aircraft designs—and new environments.

In particular, if you change the X-Plane config file to reduce gravity, thin the atmosphere, and shrink the radius of the planet it can simulate flight on Mars. (Note: Thank you to Tom J and the folks in the X-Plane community for their help with aerodynamic calculations in different atmospheres.)

X-Plane tells us that flight on Mars is difficult, but not impossible. NASA knows this, and has considered surveying Mars by airplane. The tricky thing is that with so little atmosphere, to get any lift, you have to go fast. You need to approach Mach 1 just to get off the ground, and once you get moving, you have so much inertia that it’s hard to change course—if you turn, your plane rotates, but keeps moving in the original direction. The X-Plane author compared piloting Martian aircraft to flying a supersonic ocean liner.

Our Cessna 172 isn’t up to the challenge. Launched from 1 km, it doesn’t build up enough speed to pull out of a dive, and plows into the Martian terrain at over 60 m/s (135 mph). If dropped from four or five kilometers, it could gain enough speed to pull up into a glide—at over half the speed of sound. The landing would not be survivable.

so, you would need runways that look at each other, as turning is almost unfeasible, and these runways will have to be really long, as you have to get to Mach 1 to take off and you have to decelerate from that same speed once you touch down.
GPS would not be really needed.


How many variations are there of the Avro Lancaster? How many different variations of the Avro Lancaster are there?

There were twenty-three different variants, according to Wikipedia:

British-built variants (13)

Ten combat variants (B.I, B.I Special, B.I (FE), B.II, B.III, B.III Special, B.IV [Lincoln B 1], B.V [Lincoln B 2], B.VI, B.VII)
Two reconnaissance variants (PR.I, GR.3/MR.3)
One SAR variant (ASR.III/ASR.3)

Canadian-built variants (10)

Two combat variants (B.X [later 10S/10U], B.XV [Lincoln XV])
One dual-purpose combat/reconnaissance variant (10BR)
Three dedicated reconnaissance variants (10AR, 10MR/10MP, 10P)
One SAR variant (10S&R)
One trainer variant (10N)
One drone-mothership variant (10DC)
One jet-engine testbed variant (10O)

Plus the Avro Lancastrian, a commercial airliner derived from the Lancaster B.X (the first few Lancastrians were direct conversions of existing B.Xes, although later batches were built as airliners from the start).


What licenses and/or training should one obtain to be able to fly a drone in California? The FAA will open up to flying civilian drones in 2015. Should we get pilot licenses to be ready for this? if so, is there a difference between plane or helicopter pilot license?

Links related:
NASA Helps Draw Up Rules for Flying Drones in the U.S
FAA making plans for drone flights in U.S.
U.S. colleges begin offering more drone piloting programs to keep up with domestic drone boom
California bills tackle drones, personal privacy
Aviation schools prepare for boom in demand for drone pilots

From the second link you posted:

  Until regulations establish who can fly a drone and where, Huerta said, the FAA will license drone operators on a case-by-case basis.

It's doubtful that getting an airplane or helicopter pilot certificate will aid legally with the transition. It could obviously help with the concepts, but until the FAA releases an NPRM (Notice of Proposed Rule Making), the best we can do is guess.


Could an airliner get better fuel efficiency at higher altitude? By higher I mean like 60k feet instead of 30k.
Seems like the rate limiting step is engine performance at 60k feet.
Are people working engines that can operate at higher altitudes? How close are we to good performance at high altitude (60k feet).

For example: Proteus high altitude aicraft

There are several factors to take into account to explain your question, but it is a nice one.

In a cruise flight the aircraft force balance determines that the lift compensates the weight of the air plane and the engine thrust compensates the drag.

So, assuming the weight is given (which varies along the flight) the lift is determined to ensure the air plane is not falling. The lift influences the drag, the more the lift the more drag (actually a lineal variation with the variation of the square of the lift). And so, the engine compensates the drag.

So... engine thrust depends on the weight, essentially to the aerodynamic efficiency. So, my first answer, the more efficient the aerodynamic of the air plane, the higher it can fly. So, the engine is not the only factor.

However, you are highlighting an important point, the performance of gas turbine based propulsion. The problem of this propulsion is the need for an external oxidant. Essentially, the engine needs the oxygen of the atmosphere to be able to work. So that limitation requiring oxygen will make it impossible to reach much higher flight levels.

Another option is to change the propulsion concept and use an independent engine where not only fuel is carried but also oxidant is carried in the plane. The normal answer to that one is using a rocket engine. For example, the Bell-X (first manned A/C to flight faster than speed of sound) was having a ceiling of +90000 feet using rocket propulsion.


Why do some T-tail aircraft have a protrusion on the top front of the tail? Aircraft like the Tu-154 and VC-10 have a "point" on the T-tail, while others like the 727 do not. Is this structure a shock body, or otherwise related to the tail's aerodynamics? And why is it only found on some designs?

Tu-154

VC-10

727

It's a "bullet fairing".  Sometimes you get the pressure fields of the vertical and horizontal surfaces in alignment so the lowest pressure zone of the vertical fin is merged with the lowest pressure zone of the horizontal tail right at the intersection of the surfaces.  It results in a more extreme pressure recovery aft and can cause flow separation and vibration, and sometimes shock wave effects at high speed.

The bullet effectively moves the pressure field of the vertical surface forward to bring it out of alignment with the one of the horizontal surface.  It's usually an add on resulting from interference issues that are discovered in the wind tunnel, or during flight testing.


Can I fly from the UK to Spain on an NPPL(A)? I have a UK-issued NPPL(A) with microlight rating, can I fly my own aircraft to Spain on this?

The NPPL is a UK only license and is not recognized by other countries, however there is a letter of agreement between the UK and France that you can fly there provided you have a medical. There is no such agreement with Spain, however you can contact their version of the CAA and maybe get permission, I'm not sure what hoops you would need to jump through on that.


Why do flight times differ between traveling East versus traveling West? Why does it take longer to fly East to West than West to East?
Which factors affect this?
Does Earth's spinning affect the time difference? Maybe the air circulation?

As Robbie's answer implies, the answer is wind - Trade Winds govern what happens on or near the surface and were historically important for sailing ships, and today in aviation we deal with the the Winds Aloft at whatever altitude your plane is flying.

As an example, consider two hypothetical flights at 30,000 feet with the winds shown below:

With these winds a flight from A to B (East-to-West) will be fighting headwinds the whole way. My handy flight planning program tells me that at 500 knots (airspeed) you'd be in the air for about 5 hours 30 minutes.

Traveling in the opposite direction from B to A you'd have a tailwind, and with the same 500 knot airspeed you would make the trip in roughly 4 hours.

The winds aloft vary seasonally, which can affect flight times for summer versus winter trips. According to one of our folks who is regularly up at those altitudes even the daily variations can be noticeable, and may make the difference between being able to make a nonstop trip or having to stop for fuel on the way.

Pilots and flight dispatchers will often review the wind data prior to flight and try to select an altitude that affords a "good ride" (free of turbulence) and favorable winds (either a tailwind or the lowest headwind they can find).


What are effective ways to spot the aircraft ATC specified? When ATC instructs me something like "There is a Skyhawk on your 2 clock, 7 miles, 6500". I am not able to spot the target at least half of the time after several ATC reports its position until ATC says "not a factor" or gives me a new heading or altitude assignment.

I am wondering if there is any effective ways to get the aircraft spotting skill? Or knows my limit that it is nearly impossible to see it if it beyond a certain range and give up searching. When entering busy airspaces, the aircraft looking is taking a large portion of cockpit time.

(Daytime flying only. Peripheral and night vision is different and I have zero practice of night flying.)

The highest resolution part of the eye is the fovea, and it's surprisingly narrow. If a small, slow-moving object is outside this area it probably won't be seen. If you scan from say 20 degrees left of an object to 20 degrees right of it you will also miss, because the eye tends to jump in steps and we only see a small fraction of what is actually in front of us.

So I was always told to gaze steadily, in ten degree steps, for a few seconds at each area. A grid of search areas both above and below the horizon should be checked. You'll only recognise an object when your fovea is virtually on it.

Only look for a second or two at each are because any longer and the vision "bleaches" and you are even less likely to recognise anything in that region; just keep moving on to the next.
The narrow 10 degree steps are that size because that's the region
of acceptably sharp vision. (I suspect it differs between individuals)
This was what I was taught for general lookout, though I suppose it should apply to a specific search area given by ATC too.

Apparently these tips were all derived from RAF training for this sort of thing, but I don't have any notes on that.  In any case I suspect it's more practice than bookwork anyway.

One of my gliding instructors liked the spotting game. One point for every aircraft I spot before him. He had one dodgy eye and of course still won by an appalling margin... (I've also heard some play this game for beers, though frankly none of my instructors would ever be able to drive home.)


What if the tower Is obstructed by clouds? I know towers use radar to watch aircraft, obviously. But what about ground controllers? What if their view is obstructed by a low cloud level/fog?

Is there such a thing as ground-based traffic tracking? I’m not a pilot so bear with me if I sound naive.

If cloud ceiling or visibility falls below certain minima, the ATC tower will initiate "Low Visibility Procedures (LVP)". These are different from airport to airport and depend largely on the available equipment.

Some airports have surface movement radar (SMR), also known as ground radar, which will let air traffic controllers monitor aircraft on the ground on a dedicated radar screen. At airports with SMR, ground movements are virtually unaffected by LVP.

At airports without SMR, controllers will rely on their mental image of the traffic situation to control aircraft on their ground. (Note: controllers do this even if visibility if OK. You could ask a controller to close their eyes at any point during their work, and they would still know what was going on outside the windows). Obviously, the controller will need to update their mental picture as planes move around. With limited visibility and no SMR, this will mainly be done by pilot reports. Basically, the controller will ask the pilot to inform them when they pass or reach certain parts of the aerodrome, such as a certain taxiway or runway.

One additional piece of equipment that is very common to use during LVP is stopbars. Stopbars are a row of red lights that span across a taxiway and can be switched on and off by the controller. During good visibility conditions, controllers will visually scan the runway area to make sure no aircraft inadvertently enters the runway without permission. Since such visual scanning is not available during low visibility, turning on stopbars near runway holding points serve as an extra reminder to pilots that they have not received permission to proceed.

Low visibility procedures can also include special rules or procedures that come into effect if the visibility becomes really, really bad. For example, where I work, if visibility falls below 200 metres, only one aircrat is allowed to move at the entire airport at a time. So if one aircraft is moving around, all other aircraft have to wait at the gate until that one aircraft is in the air. Obviously, this requires quite a bit of planning work from ATC, but safety always comes first.


Why am I not getting the "TO" VOR flag as I think I should? I would appreciate some insight as to what I’m doing wrong or missing.
I just completed a XC flight practicing VOR/GPS Navigation. I was inbound to KLOL from KRNO with the lovelock VOR frequency (116.5, 040 Radial) dialed in. I was southwest of the VOR on a heading of 030 and at an altitude of 9500.
The issue is, I could not get the VOR to designate a  “TO” flag unless I turned the OBS to the reciprocal of around 220. This radial should indicate a “FROM” flag.
This is so confusing because I’ve cross-checked this on multiple simulators just to make sure I wasn’t going nuts. Dialing 220 should indicate “FROM” but it indicates “TO”.
Can anyone help me figure out what I did wrong?

A quick review of the US Chart Supplement shows that the Lovelock VOR (LLC) is unusable at your current altitude and position. The VOR is 3.6 NM North by Northwest from the field. Your aircraft is 24.5 NM South by Southwest of the field. Your aircraft would have to be at or above 9600 feet MSL to receive a useable signal from the LLC VOR. This makes any reading you receive from your Nav radio receiver OBS or CDI suspect.

Source: skyvector.com

The probable reason for the VOR indication to work in a sim is that the sim does not replicate real world radio telegraphy. It is only basing the VOR CDI display on geographic position and magnetic variation.
Something of which to take note is the VOR equipment elevation of 4760 feet MSL, versus the highest point Southwest of the VOR at 6348 feet MSL. There is also a microwave tower West of the VOR. These things should be taken into consideration in flight planning.
If you were to use actual IFR charts, routes and procedures, you would notice that you are not allowed to fly below 10,000 feet MSL to still guarantee that you receive the LLC VOR signal on the Victor airway from the FMG VOR to the LLC VOR. As a matter of fact, prior to the HIXUP waypoint, the minimum enroute (IFR) altitude using GPS is 10,300 MSL. The Minimum Obstacle Clearance Altitude of 9500 feet does not guarantee signal reception.

Source: skyvector.com


Could a Dyson fan scale up to be used as a bladeless aircraft engine? Dyson has been making bladeless fans for a few years now that accelerate a consistent stream of air without exposed blades.

If this concept were applied to aircraft engines, it could potentially reduce the number of bird strikes, engine complexity/part count, danger for ground crews, etc. That said, it has not been done (or has it?). What are the major roadblocks prohibiting engineers from scaling this technology to large aircraft applications?

No. Not a useful propulsion engine.

The first problem is power. The air stream from Dyson's fans is weaker than what you can get from a conventional fan the same size, and jet engines need a very powerful stream. You'll notice they're quite heavy as well; Dyson AM-06 has a thrust-to-weight ratio of just 0.06, 100 times less than a jet engine.

The second reason is they're very inefficient at high speeds. Dyson's fans use the Venturi effect, which is also used in aircraft evacuation slides, to turn a narrow stream of fast air into a wide stream of slow air. This happens through friction simply pulling slow air alongside the fast stream.

Current airliner engines do the same thing, but better. There, high-energy air spins a turbine, which then spins a fan. The conversion efficiency of this process is 3x-5x better and produces uniform velocity - important when you're close to the speed of sound. The fan approach also results in a smaller, lighter engine.

Jet engines imitating Dyson's fans would need cores and core intakes as least the same size as current ones. The reason Dyson chooses to protect their intake with a grate and Rolls-Royce or GE don't is Dyson fans produce on the order of 50 W of power, jet engines 50+ MW. No one cares about a few watts, they do about a few megawatts, which translate into a couple ocean tankers full of oil over a plane's lifetime.

If you want, you can protect a jet's intake with a grate too - see F-15SE, Su-57 (PAK-FA) with radar blockers, Mig-29's "dirt runway" top intakes. This has nothing to do with using an ejector or not. Dyson's design does remove the slow fan, but at the cost of a lot of weight and efficiency, and it's core damage that is the worst scenario in bird strikes.

The third reason is that Dyson's fans would not scale. To fly at Mach 0.8, the ejector stream would have to be highly supersonic, which is a problem in itself. To use them for hovering, where they are reasonably efficient, you'd face the problem of Venturi effect fading with distance - requiring an entire grate of ejectors, not one simple ring. Helicopter blades do the same thing better, while being far lighter and easier to fold.


What is the maximum crosswind limit for a C150/2 aircraft? What is the maximum crosswind limit for a C150 or C152 aircraft?

Does this change depending on the class of licence?

Are there exceptions for emergencies?

Section 4  of the C152 POH lists the demonstrated crosswind component as 12KIAS. The 150 had a few variants so finding a published number is a bit more tricky. The Aerobat's are sometimes listed as 13KIAS, sometimes 15KIAS - but in general its the same sort of range as the 152(ish!).

You will only ever see "demonstrated" next to these numbers, it is not the maximum possible - I regularly hear of people landing 152's over that 12KIAS.

The number does not change due to your license privileges, it changes based on what the pilot is comfortable with /able to handle safely. Personally I would be wary of any crosswind over about 9/10KIAS.

In an emergency almost everything is an exception. Except aviate.


What is the difference between an aileron and a flap? I have already been searching Google for the difference between an aileron and a flap, but I am not much satisfied, so now I am asking here on SE.

What is the difference between an aileron and flap? Especially, how do they differ in their shape and position?

An Aileron is used to control the roll of an aircraft. Ailerons are found on the trailing edge of the wing, typically closer to the wing tip.
Ailerons will move in opposite directions to each other, as one goes up, the other goes down.

Flaps are used to increase the amount of lift that a wing produces by increasing the camber and surface area of the wing. Typically they are located near the root of the wing. Flaps on each wing are moved together, both extend and retract at the same rate.

Flaps are generally more complex depending on type. The basic flaps will just pivot down from the lower edge of the wing. Modern airliners have a fowler flap which both pivots down and extends back from the lower edge of the wing.


Are the current seat belts used in commercial airlines safe enough? I find myself thinking often, if the seatbelts in airlines are designed just to keep the passengers in seat or to really act as a safety belt like in cars, because in cars which go at 300kmph speed, you have the 5 point seat belt. Why isn't similar approach used for airlines, where the risk is too high.

Plus articles like these, suggest heavier / obese passengers are at more risk.

For a proper answer we first need to define what "safe enough" is. If you want a significant reduction in risk over current standards, improving the restraint will not be enough.

Your observation is absolutely correct: The lap belt is the minimum the airlines get away with, and you would be much better protected in some kinds of accident by a proper 5-point harness. But fitting the harness alone will not achieve much: To stay in place in a crash, all seats need to be reinforced, so they can tolerate the increased loads at the shoulder belt attachment points. This will add weight and cut into the profits of airlines, so it will only happen when it is mandated.

Please read this answer for more details. It concerns GA aircraft, but much applies to airliner seats as well. The better the restraints are, the more deceleration load can be survived. Note that the points in the Eiband diagrams shown in this answer are from tests with additional leg, chest and arm restraints. If all you have is a lap belt, you might probably be able to tolerate only half as many gs.

The better alternative to a 5-point harness would be to turn around all seats. This would help most to reduce injuries and improve chances of survival in a crash landing.

Now I have to contradict @FreeMan: While the brace position will put all the load on a small strip around a person's hips and lets the arms flail forward, a properly secured torso can take 10g for a duration of more than a second and up to 40g momentarily without ripping the head off. See below the famous sequence of Dr. John Stapp in a ride on his rocket sled "Sonic wind":

Dr. John Stapp in a deceleration test (picture source)

He clearly had his head bobbing about, but even though he lost dental fillings and suffered hemorrhage in his eyes, the head stayed intact.

In the end, all what the lap belt is really good for is to keep you in your seat with negative acceleration due to gusts. This is by far the most common situation when a restraint is needed. The classical brace position (torso over legs, head down) is impossible anyway in economy class due to the ever reducing seat pitch.


If the APU is switched off but the APU bleed is on, will the engine bleed valve close automatically? On he A320 family aircraft, if the APU is switched off but the APU bleed is on, will the engine bleed valve closed by the Bleed Monitoring Computer (BMC)?
This what I understood after going through the APU chapter of the FCOM. Just wanted to confirm because the way I understand it is that the APU bleed valves will not open since it requires a minimum of 8 PSI, so the engine bleed valve should be open.

The answer is in the FCOM:

So, the ENG bleed valve closes if:

Reverse flow detected
ENG 1 starter valve not closed
APU bleed valve open
Bad things (Overpressure / Overheat / Leak)
ENG BLEED switch is off or FIRE pb pushed

So, if APU is not ON, the APU BLEED valve is closed, and then the condition 3 is false. If all the others conditions are also false, then the ENG valve would open.


Does ELMS inhibit cabin pressure alarms on the 777, and would the MEC Override Vent be stuck open following an electrical failure? I found this article rather interesting, but like most things on the internet, they can be wrong. I couldn't think of a better site to address this question. This user says:

when ELMS takes over power supply it shuts down the Air Cycle Machine (ACM) and the Air Supply Cabin Pressure Controller (ASCPC). Cabin pressure alarms in the cockpit also lose power.

The user follows up with this later on:

In addition to loss of electrical power from the cabin pressurization system electrical smoke in the Avionics Bay or MEC likely tripped open a vent called the MEC Override Vent, which simply allows electrical smoke to be pushed out by cabin air pressure. Once open this vent needs electrical power to close again, so if an electrical failure followed, it would be left limp and open.

I look forward to reading your answers about this, Thank you!

Generally, the post you quote from does not look like a credible source. For starters, it says things like:

Electrical failure shut down the Air System Cabin Pressurization Controller (ASCPC) and Air Cycle Machine (ACM) which on a Boeing 777 are all electric. Unlike most other airliners the B777 does not use engine bleed air.

This is completely wrong. The 777 uses engine (or APU) bleed air to operate the PACKs. The author might have mixed this up with the 787, which uses electrically powered compressors for cabin pressurization instead of bleed air.

Bleed air can be supplied by the engines, APU, or a ground air source.
Bleed air is used for:

air conditioning
pressurization [...]

(Boeing 777 FCOM 2.40.1 - Air Systems - Bleed Air System Description)

The vent in the electronics bay exists and it will indeed open automatically to vent out smoke:

The forward system reconfigures automatically to an override mode when:

[...] smoke is detected in the forward equipment cooling system or the forward equipment ventilation system [...]

In the override mode when the FWD CARGO FIRE ARM switch is not ARMED, the vent valve opens, both supply fans shut down,
and the forward cargo heat valve closes. [...] Cabin differential pressure draws air through the flight deck panels into
the E & E equipment compartment to create a reverse flow of air across the equipment, then through the override valve
to an overboard vent.

(Boeing 777 FCOM 2.20.12 - Air Systems - Air Conditioning System Description)
With an electrical failure it is plausible that this valve could no longer close, therefore preventing cabin pressurization.

The ELMS (Electrical Load Management System) described in the post will shed loads in this order:

The load shedding is galleys first, the utility busses. Utility busses are followed by individual equipment items powered by the main AC busses.

(Boeing 777 FCOM 6.20.1 - Electrical - System Description)
The FCOM indeed does not specify the order of these "individual equipment items". Since we don't know what exact failures occurred on MH370, it is impossible to say which systems were shut down. However, during normal operation there are two AC busses (left and right) powered individually. No single point of failure could shut down both PACKs.
The post further claims that

Cabin pressure alarms in the cockpit also lose power.

This cannot be related to the ELMS, which only controls the AC power distribution. The EICAS alerts are however powered by the DC system (via the flight instrument busses), which can be powered independently of the AC busses in standby operation:

The main DC electrical system uses four transformer-rectifier units (TRUs) to produce DC power. The TRUs are powered by the AC transfer busses. [...]
The standby electrical system can supply AC and DC power to selected flight instruments, communications and navigation systems, and the flight control
system, if there are primary electrical power system failures.
The standby electrical system consists of:

the main battery
the standby inverter
the RAT generator and its associated generator control units
the C1 and C2 TRUs.

(Boeing 777 FCOM 6.20.13 - Electrical - System Description)
The author of the post further claims that no warning is given to the pilots because the SMOKE / FUMES REMOVAL checklist in the QRH (linked in the post) shows UNANNUNCIATED. This is however the wrong checklist for the case described earlier. The unannunciated here means that this checklist is for when the pilots recognize smoke or fumes in the flight deck before any annunciation. The correct checklist for the open vent in the electronics bay is this one (and it is annunciated on the EICAS):

[] EQUIP COOLING OVRD
Condition: The equipment cooling system is in override mode.

Wait 2 minutes. This allows time for any smoke in
the system to clear.
EQUIP COOLING switch . . . . . . . . Off, then AUTO
The EQUIP COOLING OVRD message blanks.
Wait 1 minute. This allows time for the system to reset.
Choose one:

EQUIP COOLING OVRD stays blank: ■ ■ ■ ■
EQUIP COOLING OVRD shows again:
Note: After 30 minutes of operation at low altitude and low cabin differential pressure, electronic equipment and displays may fail.

(Boeing 777 QRH 2.19)

Another weird claim from the post is:

The brand new Boeing 777X model suffers the same vulnerability.

I wonder how the author wants to know this. The 777X is not in service yet and the author claims to be an aviation enthusiast from New Zealand. Only a Boeing engineer could possibly know about such system details of the 777X.


During an instrument approach, what are the obstruction clearance given? I was wondering wether each segments of the approach has different minimum obstruction clearance? (E.g. initial, intermediate and final) From both terrain and man made obstacles.

If possible i would like it to be from ICAO, hence PANS-OPS. But any TERPS answers i would happily accept.

The FAA lays this out in Order 8260.3c the three main relevant sections for requirements, level flight and climbing/decent segments are:

  2-1-2. Required Obstacle Clearance (ROC). This order specifies the minimum measure of obstacle clearance considered by the FAA to supply
  a satisfactory level of vertical protection. The validity of the
  protection is dependent, in part, on assumed aircraft performance. In
  the case of TERPS, it is assumed that aircraft will perform within
  certification requirements.

...

  2-1-3. Level OCS. The level OCS concept is applicable to “level
  flight” segments. These segments are level flight operations intended
  for en route, STAR, feeder, initial, intermediate, and NPA final
  approach segments. A single ROC value is applied over the length of
  the segment. These values were determined through testing and
  observation of aircraft and pilot performance in various flight
  conditions. Typical ROC values are: 1000 feet (2000 over designated
  mountainous terrain) for en route, STAR, and feeder segments, 1000
  feet for initial segments, 500 feet for intermediate segments, and
  250-500 feet for final segments.

...

  2-1-4. Sloping OCS. The method of applying ROC, in segments dedicated
  to descending on a glidepath or climbing in a departure or missed
  approach segment, requires a different obstacle clearance concept than
  the level OCS because the ROC value must vary throughout the segment.
  The value of ROC near the runway is relatively small and increases
  throughout the segment.

The document is lengthy and lays out various formulas and charts, to keep form copying the whole thing here please reference the document directly for anything more specific.


Are there take-over requests from autopilots? I am thinking of the driver take-over request in automated driving, when the system limits are reached and the back-up driver has to intervene / drive manually. Is there something similar in aviation, e.g. autopilot is engaged and has reached its system limits? Maybe you can give me some examples.

Edit: The reason why I am asking is, that there is a lot of concern about take-over situations in the automobile industry because cars are getting more and more automated. Since automation has a longer tradition in aviation than in automobile industry I assume there is a thing or two to learn from you guys. So basically I want to know what take-over situations there are and what is done to make take-over easy for the pilot (airplane or helicopter pilot).

I assume in your question the autopilot is engaged. When the auto-flight system reaches the limits of its capabilities it simply disconnects. On Boeing aircraft you get a
> AUTOPILOT DISC

Warning Message on the EICAS and the siren sounds. Now it is all manual flying for the pilots.
An example would be turbulence exceeding the auto-flight system capabilities to maintain the intended trajectory.
After the question was clarified:
The big difference between flying and driving are

system redundancy - in an aircraft, everything important is available two times, the very important stuff even three times. If there is a technical problem system performance normally degrades accompanied with appropriate annunciations to the pilots.
the environment you are operating in - in the air there is no road to follow or you fall off a cliff. There are mountains, yes, but in cruise flight (similar to driving on the highway) where your vigilance is lower the mountains are below you. In the end, the airway is an imaginary thing. An imaginary line drawn between two waypoints. You won't crash (immediately) if you deviate from it. Even your surrounding traffic is miles away laterally. When the margin for error gets smaller pilots are way more vigilant. During departure/arrival/landing, even when flying fully automated, the concentration is fully on the aircraft. So deviations from the intended trajectory are noticed early and can be acted upon quickly. This even goes so far that with most commercial operators there is a sterile cockpit rule below 10,000 ft where there is no communication in the cockpit which is not relevant to the current situation.
the system sophistication - the feat car manufacturers are trying to accomplish is way bigger than an auto flight system for an airliner. The margins for error are way smaller, yet the precision needs to be way higher. In aircraft the autopilot is basically a glorified feedback loop. And even if the autopilot system fails spontaneously due to technical problems the aircraft initially keeps flying without any intervention and only slowly deviates from its current trajectory as aircraft are designed to be aerodynamically stable.
training of the operator (pilot/driver) - commercial pilots train for abnormal situations in full flight simulators every six months. Drivers, well, don't. Their last training was most probably when making their drivers license many years ago. Another thing is vigilance and planning ahead. Pilots are trained to anticipate what is coming next. You try to get a mental picture of the traffic around you and where conflicts may arise. And as your aircraft is moving typically pretty fast and there are no brakes you can slam you are flying in a rather defensive way.

And I even have a real world example where the auto flight system performed flawlessly yet human intervention was required:

What you see here is a blurry photo of the incorrect turn construction of a departure. The departure trajectory is supposed to be a left turn to the next waypoint (white star). The flight management system constructed a right 270° turn (magenta line) to match all the constraints of the waypoints (flyover, etc) where a 70° left turn would have been the correct behavior. The aircraft was flown manually to adhere to the departure procedure.
In this case no system degradation or warnings were present. You can see that the Flight Director (FD) on the PFD on the right commands a right turn (vertical magenta line). The autopilot simply follows FD commands and would therefore fly this (wrong) turn.


Why does the Falcon 900 have anhedral wings? Why does it have anhedral wings and not "normal" wings? Many other similar aircraft with low-wing have dihedral wings.

Source: DassaultFalcon.com

Edit: This is about the Falcon 900, which apparently has a low-wing design and it's not used for cargo like the An-225

For the same reason why the Lockheed F-104 Starfighter had such a pronounced anhedral: It is the size and location of the vertical tail.

Lockheed F-104 Starfighter (picture source).

In both cases, the vertical tail is large relative to the wing and fully above the roll axis. In a sideslip it produces a high rolling moment, so any more rolling moment from the wing would reduce the handling qualities of the aircraft.

Especially in case of the F-104, the raised position of the horizontal tail shifts the center of pressure on the vertical tail upwards, exacerbating the offset location of the vertical tail.

The rear-mounted engines on the Falcon 900 move the center of gravity backwards, so the wing is more backwards than usual for aircraft with wing-mounted engines. Therefore, the part of the fuselage ahead of the center of gravity is large, requiring a larger vertical tail to overcome the destabilizing yawing moment of the fuselage.

The same is true for the Tupolev 134 and 154, and - surprise! - they also have no dihedral, even though both are low-wing configurations.

Tupolev 154M of the Polish Air Force (picture source)


Do "air ferries" for civilian vehicles still exist? In the 1950's and 1960's, there were vehicle (and passenger) air ferries operated by planes such as the Bristol Freighter. Mostly across the English Channel (England to France), by companies like Silver City Airways and Channel Air Bridge.  In other words, your car travelled with you on the same plane.

On that route, sea ferries (and hovercraft) eventually killed them off financially.

Do similar scheduled air ferries, for civilian cars and their passengers, still exist anywhere in the world?  If not, why?  Is the reason just financial, or are there no suitable planes any more, or did new safety or security rules make it impossible to operate them?

They would seem well suited to short hops like the Scottish islands, islands off British Columbia or Alaska, Indonesia, the Caribbean islands, and so on.  Especially in locations where the sea crossing is rough and unreliable.

There are a number of suitable airplanes - C-130 Hercules, C-17 Globemaster, C-5 Galaxy, AN-124, up to the rather monstrous An-225 Mriya. Cargo versions of airliners don't usually handle vehicles - they are designed for palletized cargo while the above cargo planes have ground-level ramps.

If you want to fly with your car somewhere it's just a matter of calling someone who owns one of these airplanes and putting down your no-limit credit card.

As you surmised, the reasons they don't operate scheduled service is financial - boats are much cheaper, and not enough people want to go where a boat is impractical.


What approvals do I need for a helicopter landing? I have a horrible conflict; my sons are graduating on the same day at about the same time in different states. One in East Greenbush NY the other in Beverly MA.

I am interested in hiring a helicopter to transport us from NY to MA. My question is if I receive permission from the schools to land what other permits or steps would I have to take?

If you charter a helo, most likely they’ll fly you from KALB to KBVY, then provide you additional ground transportation to and from these airports.  As to landing directly onto school property, that would probably be at the discretion of the school itself; my guess is that they would frown on it unless it was an emergency, as helicopters are a noisy and somewhat dangerous nuisance to have around.


Has anyone researched or built an aircraft that controls pitch and roll by pumping liquid within the airframe? I am confident I have seen an article couple years ago about a "static surface aircraft" (or at least a concept of it) with no control surfaces, which uses a "wet mass" to adjust its roll and pitch.

The container within its CG is filled with a fluid which is then transferred (or sucked) to the wing tips (to control roll) and along the fuselage (to control pitch). I'm not sure about the yaw control - it should be elevon-like.

Having spent half a day online, I have been able to only find a DEMON UAV from BAE systems, a "flapless" aircraft which uses flow injection above the control surfaces for maneuvering. That is not the same.

My question - is there something fundamentally wrong with a concept I have described?
Were there any experimental aircraft made?

The aerodynamic forces resulting from surface deflections are orders of magnitude larger and faster (in their rate of change) than the gravitational forces obtainable by shifting the centre of mass.

Additionally, as OP seems to realize, yaw control would not be feasible with this method.

So overall it would not be impossible, but it has no clear advantages to outweight the heavy disadvantages. I am also unaware of any prototypes or tech demonstrators using this method.


Do flight regulations prohibit sleeping on the floor of an airliner? During a recent trip in a Finnair A350, a couple traveling together was occupying 1 row of three Economy Comfort seats. During the 12 hour flight, one of the couple stretched out on the seats, the other one on the floor in between the seat rows, leg room being sufficient to allow this.

A flight attendant was overheard stating that sleeping on the floor was not allowed due to safety regulations. What safety regulation would prohibit this?

update

During cruise condition, no Fasten Seatbelt sign. EASA regulations. Yes you're out of your seat but we're allowed to walk around aren't we. Where is the hard, written, safety regulation?

That depends on the air carrier and the regulatory body they're certified by. Finland is part of the EU so I'm assuming that Finnair's certificate is under EASA aviation safety regs. Specifically, a quick Google search finds:

CAT.OP.MPA.165 Passenger seating:
The operator shall establish procedures to ensure that passengers are seated where, in the event that an emergency evacuation is required, they are able to assist and not hinder evacuation of the aircraft.

Finnair would also write their own SOPs to ensure they meet all the EASA regs.


What are some of the more common procedures when faced with a hung landing gear? A hung landing gear is a potentially disastrous situation for a pilot flying a general aviation piston aircraft. During "shop talk" I've heard people say that the best thing to do is cycle the gear. During my multi-engine check ride I was told emphatically by my examiner that cycling a hung was the wrong thing to do.

What are some of the more common procedures suggested in POH/AFM documents for this situation? Can any deeper understanding be extracted from the common procedures?

As referenced in a comment, the generally accepted thing to do is to refer to the aircraft emergency checklist/AFM to see what it says to do.

This will vary by aircraft design, but usually involves testing the indicator lights, and then activating alternate means of extending the gear as needed.


How high can I fly a kite above my farm? This idea is inspired by this question.

Suppose the OP decides to fly some kites or helium balloons above his farm to keep other pilots from flying near it. Regulation-wise, how high can these objects go?

It depends how big the balloon or kite is. Balloons and kites are governed by 14 CFR 101, but specific regulations only apply above a certain size. 101.1 says:

  a) This part prescribes rules governing the operation in the United
  States, of the following:

  (1) Except as provided for in §101.7, any balloon that is moored to
  the surface of the earth or an object thereon and that has a diameter
  of more than 6 feet or a gas capacity of more than 115 cubic feet.

  (2) Except as provided for in §101.7, any kite that weighs more than 5
  pounds and is intended to be flown at the end of a rope or cable.

However, note the reference to 101.7, which says (in part):

  No person may operate any moored balloon, kite, amateur rocket, or
  unmanned free balloon in a manner that creates a hazard to other
  persons, or their property.

That means, if your balloon or kite is too small to be governed by part 101 then there are no specific restrictions on how you operate it, but you still can't fly it in a way that puts other people in danger.

If part 101 does apply to you, then you have to follow the rules in 101.13 and 101.15:

  §101.13   Operating limitations. (a) Except as provided in paragraph (b) of this section, no person may operate a moored balloon
  or kite—

  (1) Less than 500 feet from the base of any cloud;

  (2) More than 500 feet above the surface of the earth;

  (3) From an area where the ground visibility is less than three miles;
  or

  (4) Within five miles of the boundary of any airport.

  (b) Paragraph (a) of this section does not apply to the operation of a
  balloon or kite below the top of any structure and within 250 feet of
  it, if that shielded operation does not obscure any lighting on the
  structure.

  §101.15   Notice requirements. No person may operate an unshielded moored balloon or kite more than 150 feet above the surface of the
  earth unless, at least 24 hours before beginning the operation, he
  gives the following information to the FAA ATC facility that is
  nearest to the place of intended operation: [contact details, time, altitude etc.]

There are more requirements in 101.17 and 101.19.


Can an A&P who is also a private pilot receive compensation for conducting maintenance test flights? Related to this question.

Suppose a repair is made to an airplane and a maintenance test flight is required. Suppose the A&P who works on the aircraft is also a private pilot. That person performs the test flight and then signs off the repair.  (assume USA)

A private pilot can't fly for compensation or hire.

Can the mechanic bill for the time she spent flying?  Are maintenance test flights considered incidental to a mechanic's business?

Yes, the mechanic can fly the aircraft, according to this FAA legal interpretation (Williams, 2014):

  The scenario you present is a mechanic who, as part of his duties,
  conducts flight tests after performing maintenance on the aircraft,
  and does not carry passengers or property for compensation or hire.
  The mechanic holds a private pilot certificate with a valid third
  class medical certificate. This situation is covered under §
  61.113(b), which states that, "[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." As these flight tests are
  incidental to his employment as a mechanic, the mechanic is not in
  violation of § 61.113 when conducting these flight tests


How much power is needed by aircraft IFE systems during flight? How much power is needed by aircraft In Flight Entertainment systems during flight if they operate all the devices connected in the cabin?

I don't have specifics but lets extrapolate for a minute (using the Boeing 777-300 for size filled with lets say 500 seats). Assuming you are talking about IFE systems where there is a screen in every seat then you will most likely have screens similar to this. While not exactly what the airplane uses I would think they are similar. The specs for that screen claim it takes <= 8W. Lets round it out and say it takes 8w. Looking at our 500 seats thats 4000W of power. I can only assume there is a computer or two of sorts running those displays, lets say they have 500W (typical desktop supply on the more powerful side) and there are 2 of them. Thats another 1000W so you are at 5000W there. Assuming you have 120V power P=IV thats about 41 Amps of current you will draw from the system. I am running this assumption that all the screens are on at all times as I assume the system is built for that.

Cabin lighting is tough as I have no idea how many bulbs they have in there. I know that each seat has its own little lamp so you are looking at 500 little lamps running in the 1W-10W range. So maybe another 2000W for the individual lights. Overhead is tough since you cant really see the individual bulbs. It should also be noted that LED's are becoming more wide spread and draw way less power than traditional incandescent bulbs which will greatly reduce the amount of power drawn by the interior lights.


Is my company EASA 147 approved? How to get an EASA licence? I am a bit stuck with my career and just need some advice.

I am currently a technician at Trans Maldivian Airways (Twin Otter). I would like to work in an airline in the future. Is this organization EASA 147 approved?

If so, what are the necessary steps I should take to get the license? If not what should I do? I did not do any basic training and I am completing modules conducted by SR Techniques.

I am not sure what you should do, but this company is not EASA 147 certified. Source


Are there any safety data on the aircraft used for skydiving? I am planning a (first) skydive, a tandem jump with an instructor. However, I have not picked which school I will use yet.

I am convinced about the safety of the jump itself, but cannot find reliable data on accidents that have occurred during the actual flight.

How safe are aircraft that are used for skydives? What are the statistics compared to commercial aviation?

You didn't mention any particular country, but for the US I found an NTSB report called On the Safety of Parachute Jump Operations. It's from 2008 so some of it may be dated, but it says that no reliable data exist (emphasis mine):

  According to USPA safety records, from 1992 through 2007, about 30
  parachutists per year were killed in jumping mishaps. Safety Board
  accident data show that, for the same time frame, about five
  parachutist fatalities per year resulted from accidents involving
  parachute operations aircraft. Direct comparisons of associated risk
  are difficult to calculate due to the likelihood of multiple
  parachutists being carried on each flight and a lack of departure data
  for parachute jump operations. The Safety Board notes that the FAA
  does not have data on the number of parachute jump operators or the
  number and type of aircraft used in parachute jump operations in the
  U.S. The absence of these data precludes any calculations of safety
  statistics for parachute jump operations, including accidents rates.

Based on that information, you have 5 fatalities per year related to aircraft, and 25 that are not. So the aircraft should be the least of your worries.

Here are some key points from the rest of the report:

  a segment of U.S. general aviation operations, which, according to
  data compiled by the United States Parachute Association
  (USPA),[1]transports parachutists on 2.16 to 3 million jumps
  annually.[2]

  [...]

  Since 1980, 32 accidents involving parachute operations aircraft have
  killed 172 people; [6]most of whom were parachutists.

  [...]

  The investigation identified maintenance discrepancies on the airplane
  and deficiencies with the pilot's performance of emergency procedures;
  these issues prompted the Safety Board to examine accident reports for
  parachute operations to determine if such safety issues may be
  widespread. The results, discussed in this investigation report, show
  that these issues were present in many accidents

  [...]

  The Safety Board's review of parachute operations accidents since 1980
  identified the following recurring safety issues:

  Inadequate aircraft inspection and maintenance;
  Pilot performance deficiencies in basic airmanship tasks, such as preflight inspections, weight and balance calculations, and emergency
  and recovery procedures; and
  Inadequate FAA oversight and direct surveillance of parachute operations.

Anecdotally, skydiving is indeed associated with poor maintenance and hiring low-time commercial pilots. It's one of the few commercial activities that doesn't require an air operator certificate (see 14 CFR 119.1(e)(6)) so it can operate under part 91, without the more stringent rules and requirements of part 135. That also means there are no minimum hours required for the pilot as long as he holds a commercial certificate, and it's a very sought-after job for commercial pilots who want to build hours without instructing.

However, anecdotes tell you nothing useful at all about the overall safety of the industry, or about the safety of an individual skydiving operation. Some research is good and I think you can look for some common sense things that you might look for in any business: professional location, good customer service, good online presence, good reviews etc. But trying to quantify the risk in a meaningful way is extremely difficult, and you still have to balance it against the reward and against the risks of whatever else you would do that day instead of skydiving.


Should I open a door or window when there is smoke in the cockpit? Let's say when flying, I encounter smoke and the smell of something burnt in the cockpit. Should I open the door or a window to clear the smoke?

My thoughts: the smoke may be toxic; opening the door brings in fresh air and avoid incapacitation. But, if something is burning, opening the door also brings in plenty of oxygen, and the fire will spread very rapidly.

I'm asking about GA planes.

If possible, you should do whatever the operating handbook for your aircraft says but don't hesitate to do something different if you think it's necessary (more on that below).

I checked a couple of POHs that I have to hand and they don't mention the doors specifically, but there is a slight difference in what they say about cabin ventilation.

The C172S checklist emphasizes avoiding drafts, including shutting air vents and ventilating only after fighting the fire:

  ELECTRICAL FIRE IN FLIGHT

  Master Switch -- OFF.
  Vents, Cabin Air, Heat -- CLOSED.
  Fire Extinguisher -- ACTIVATE.
  Avionics Master Switch -- OFF.
  All Other Switches (except ignition switch) -- OFF.

  WARNING

  AFTER DISCHARGING FIRE EXTINGUISHER AND ASCERTAINING THAT FIRE
  HAS BEEN EXTINGUISHED, VENTILATE THE CABIN.

  Vents/Cabin Air/Heat -- OPEN when it is ascertained that fire is completely extinguished.
  [...]

The PA28 checklist on the other hand says that the vents should be open:

  FIRE IN FLIGHT

  Electrical fire (smoke in cabin):
  Master switch....OFF
  Vents....open
  Cabin heat....OFF
  Land as soon as practicable

But practically speaking, fire in the cabin is a really extreme situation and it's hard to say that you should always follow the checklist (if you even physically can). For example, if the cabin fills with smoke and you can't see anything at all you might have to try to clear the smoke somehow just to keep control of the aircraft, even at the risk of feeding the fire. The Piper POH acknowledges that the pilot is the best person to decide what to do:

  The procedure given is general and pilot judgement should be the
  determining factor for action in such an emergency

For a real-life account of a cabin fire in a C172RG, see this AOPA Real Pilot Story. They had to open the door to be able to see and land, which reinforces the point about doing whatever you have to do in an extreme scenario.


What is the difference between ground speed and airspeed? What is difference between ground speed and airspeed? Is ground speed used only for takeoff or is it used for flight too?

The ground speed is the speed the aircraft is making over ground below.

The indicated airspeed (IAS) is the speed shown on the airspeed indicator. This will be different than the ground speed for various reasons, such as wind and the attitude of the aircraft. For example, if the aircraft is diving then the IAS will be greater than the ground speed. In fact, if the aircraft were diving straight down, then the ground speed could be 0 while the IAS was hundreds of knots per hour.

The indicated airspeed is the usual measure used in flight.

The ground speed can be calculated to estimate the time of arrival of the aircraft at some destination.


Would this hovercraft be stable? Would this two-rotor hovercraft design work? The bold black line is weighted metal on the lower to stable it. If it helps, this is a human sized hovercraft.

Would it work if:

prop1 lift > prop2 lift
prop1 lift = prop2 lift
prop1 lift < prop2 lift

The difference between prop1 and prop2 lift should be in a range of 0-30%

NOT TO SCALE, assume that lower weighted bars are equidistant from middle of hovercraft.

Yes - it can work. Colin Furze (UK inventor & TV personality) built an essentially similar device. Skip to about 1:40 to see some of the problems he had.


How are landing minimums decided? How are landing minimums decided for a flight? Does the captain make the decision depending on weather conditions or is it preset for each airport?

The terms you are looking for are Decision Altitude (DA) and Decision Height (DH). If no visual reference to the runway is established at the DA or DH, a missed approach has to be initiated. So based on the weather and the certification of the airport (CAT I / CAT II / CAT III), the pilot will make the decision to land or not land at the DA/DH.

(Image Source: SKYbrary)

Decision altitude (DA) is referenced to mean sea level and decision height (DH) is referenced to the threshold elevation.
The DH for Category II and III approaches is invariably assessed by reference to a radio altimeter and never a barometric altimeter; therefore the minima can only be expressed as DH and not DA. For approaches with DH of 200ft or higher, radio altimeter reading would be unreliable due to the unevenness of the terrain; therfore a barometric altimeter is always used and the minima may be expressed as DH or DA.
The required visual reference means that section of the visual aids or of the approach area which should have been in view for sufficient time for the pilot to have made an assessment of the aircraft position and rate of change of position, in relation to the desired flight path. In Category III operations, the required visual reference is that specified for the particular procedure and operation.
For convenience where both expressions are used they may be written in the form "decision altitude/height" and abbreviated "DA/H"

Related Videos:
CAT II ILS Approach LGTS
Related Questions:
Is it legal to land in bad visibility conditions without ILS?
Are zero visibility landings practical and desirable for commercial aviation?
How can landing in zero visibility be safe?


How are extreme winds aloft handled and how do they affect flight? I'm looking at forecasted winds aloft on SkyVector for early next week. Specifically, I'm looking at the Pacific Ocean (routed between California and Hawaii) and notice that there are some barbs showing almost 150kt winds at FL300.

Being someone who only has experience flying in lower altitudes with wind speeds I can fathom, this brings up a few questions for me:

Is there a maximum or safe winds aloft value / crosswind for say, a 737 to fly?
How is it reasonable to deal with wind speeds this high when they're other than a direct headwind or tailwind? What if it is a direct crosswind, how is it possible for the airplane to fly without significant navigation issues (or maybe safety issues?) at velocities that high.
In general, how does the significant wind speeds found in the upper altitudes affect flight (contrasted with typical general aviation flight)

Is there a maximum or safe winds aloft value / crosswind for say, a
  737 to fly?

Crosswind limits are in place for landing not flying. Cross wind limits have to do with how effective the control surfaces are which allows you to fly the plane in such a manner where the fuselage is aligned with the ground track. At altitude winds simply either add to your ground speed or count against it.

  How is it reasonable to deal with wind speeds this high when they're
  other than a direct headwind or tailwind? What if it is a direct
  crosswind, how is it possible for the airplane to fly without
  significant navigation issues (or maybe safety issues?) at velocities
  that high.

Winds are not always a direct head or tail wind (for that matter they often are not) thus you simply need to figure out your course correction. You can check out this video on how to do so. Keep in mind that you are flying through the air and thus moving with it, on the ground you feel wind because you are stationary and it is moving around you.

  In general, how does the significant wind speeds found in the upper
  altitudes affect flight (contrasted with typical general aviation
  flight)

Its all relative but in general it simply effects time in transit (ground speed). However keep in mind that the planes that fly up there are often faster so 150Kt headwind on a plane that can cruise at 550Kts at FL300 is not all that different from a 35 Knot headwind on a plane cruising at 140kts at 5000ft.


When to start descent entering a racetrack under NORDO? Scenario:
I am flying in IMC, and communications fail completely. IMC persists up until destination, where I will be conducting the following instrument approach:

I am flying direct to ZUNAD from the north, approaching it on a track of 200°. When within the prescribed MSA, I descend and maintain 4,300 ft. At the moment I reach ZUNAD, I will be performing a teardrop entry into the racetrack/procedure turn (heading of 211° after ZUNAD for one minute, then right turn direct to ZUNAD).

Question:
Can I start descending to 2,600 ft just after passing ZUNAD, entering the procedure turn on that heading of 211°, or should I wait until I cross ZUNAD again and become established on the racetrack pattern?

You can descend from 4300' to 2600' as soon as you pass ZUNAD, as long as you remain in the protected airspace of the hold at ZUNAD.

It is the same situation if you were "Cleared for an approach" in a non-radar environment.


How to make use of linear acceleration and gyroscope data? This is strictly not aviation related so please feel free to move it to the correct section.

I have a 9 axis IMU, which gives me yaw, pitch, roll, magnetics, gyros, accels etc.

I currently make use of the roll, pitch and yaw (true) however I want to learn how to use the rest of the data. I know that the raw magnetometer data can be used to judge when the true yaw is not accurate enough and even correct it. I'm reading up more on that subject at the moment.

However what I can't find much resources on is on how to make use of linear acceleration and angular acceleration. I have successfully converted the data from raw units to g/s.

How do I obtain the acceleration of my craft with the data?

You integrate accelerations to get speed and integrate speed to get position. So if you have angular speeds or even orientation, I don't see any use for angular accelerations. That does not mean the unit does not use them internally when calculating the angular speeds and/or orientation.

The linear accelerations can be used for dead reckoning. Airliners, and increasingly any plane with glass cockpit, have inertial navigation system that integrates the accelerometer and gyroscope data to keep track of position. It used to be primary means of navigation over ocean before GPS and now it is still used as backup if GPS signal is lost and for compensating errors by cross-referencing.

The lateral acceleration is also shown by the slip-skid indicator (used to be accompanied by turn rate in turn indicator, but glass cockpits often only have attitude indicator provided it is non-tumbling and maintains precision at unusual attitudes; see also When/How may I replace the Turn Coordinator with an Artificial Horizon?).


Do carriers such as Janet Airlines carry ADS-B transponders? I was doing some casual browsing and came across some videos related to Janet Airlines. This is something I remember hearing of many years ago but this happened to jog my memory.

What jurisdiction would such an airline fall under? From the Wikipedia article:

  Due to the secretive nature of the airline, little is known about its organization. It is operated for the USAF by infrastructure and defense contractor AECOM through AECOM's acquisition in 2014 of URS Corporation, which acquired EG&G Technical Services in 2002, as derived from URS's history of providing this service to the Air Force and job openings published by URS.

If it's strictly military (all staff appear to require clearances, after all), would such planes be fitted with ADS-B transponders by regulation? If so, couldn't they just be looked up on websites like Flightradar24?

Also, if an emergency occurred on board, what special treatment (if any) would they be provided if they landed at a civilian airport?

You can just look them up. Here's a screenshot from Flightradar24 taken at about 1410 UTC on 22 May 2017.

I imagine in an emergency they'd be given priority just like any other aircraft in distress. The crew might have specific orders covering that situation that requires them to head for a military base. Their operation is so secret, though, that I doubt we'd find out unless a emergency occurs.


How is "wing thickness" defined? In the answers to this question about wing thickness, there were many references to wing thickness as a percentage (ranging from 6.5% to 13.5%).

What is that a percentage of?

The wing thickness is basically the distance between the upper and lower surface of the wing (or airfoil).

`

Source: NASA.

The wing thickness is usually given as a percentage of the wing (or airfoil) chord(the distance between the leading and trailing edge). This is to make it a non-dimensional quantity for ease of comparison across different scales.


When should a transponder be used? When should a transponder be turned turn on?

On the ground?
Always in flight?
Only when required: during radar service (flight following), above 10,000ft MSL, inside the Mode C Veil, or on IFR flight?

Should Altitude Mode be used whenever the transpoder is on?

At least in the United States the FAA recently (I think in 2012?) changed the recommendation for transponder operation in the AIM.  It now reads:

  Civil and military transponders should be turned to the “on" or normal altitude reporting position prior to moving on the airport surface to ensure the aircraft is visible to ATC surveillance systems. IN ALL CASES, WHILE IN CONTROLLED AIRSPACE EACH PILOT OPERATING AN AIRCRAFT EQUIPPED WITH AN OPERABLE ATC TRANSPONDER MAINTAINED IN ACCORDANCE WITH 14 CFR SECTION 91.413 MUST OPERATE THE TRANSPONDER, INCLUDING MODE C IF INSTALLED, ON THE APPROPRIATE CODE OR AS ASSIGNED BY ATC. IN CLASS G AIRSPACE, THE TRANSPONDER SHOULD BE OPERATING WHILE AIRBORNE UNLESS OTHERWISE REQUESTED BY ATC.

(Cribbed from Chapter 4-1 of the AIM)

So, basically "Turn it on before you taxi, and turn it off right before you shut down the engine. Always use the Altitude mode (Mode C) unless ATC tells you otherwise."

In practice having the transponder on while on the airport surface doesn't do much unless your field has something like ASDE-X which plots aircraft transponders on a screen in the tower, but it generally doesn't hurt anything and it ensures you don't forget to turn the transponder on when you take off.

Operating your transponder while on the ground may cause "ground clutter" on nearby radar station's displays (possibly setting off the conflict-alert system) - this is why many of us were taught to set our transponders to standby mode while on the ground. In practice this usually isn't an issue, and if it is a problem local ATC will ask you to "squawk standby while taxiing" to resolve the issue.
If anyone gives you a hard time about it copy the number and politely quote the AIM.


What is the typical temperature of an airliner's hull during flight? Some high-speed military aircraft like the SR-71 had real heating problems, but airliners also travel almost at the speed of sound, use most of their fuel to make up for frictional losses, so I would presume that their hulls heat up. They are also cooled by the airflow, but at what temperature does equilibrium set in during cruise? I remember that airliners don't seem to be very hot when you touch them after landing, but they have had time to cool down in the slow winds during descent.

There are two primary factors that affect the skin temperature of an aircraft in flight: the air temperature, and the speed of the aircraft.

The air temperature where airliners cruise is relatively cold, around -54 °C at 35,000 feet.

As a body like an aircraft moves through air, it compresses the air, which causes the air temperature to rise. The maximum temperature rise will be if the air is completely stopped, such as at a leading edge. This is called the total air temperature, and the amount that the temperature rises is called the ram rise.

Using a simple formula to find the ram rise:

$$RR = \frac{V^2}{87^2}$$

… where $RR$ is in Kelvin, and $V$ is the true airspeed in knots.

Using a typical airliner cruising speed of 500 knots gives a temperature of 33 degrees. This brings the total air temperature to -22 °C, which is still quite cold. At places other than the leading edge, the temperature rise will be less. This is why cargo holds will need heaters to be safe for live animals, even being insulated and pressurized. Airliners just don't fly fast enough to produce a significant amount of heating.

On the other hand, the SR-71 could fly at over 1,910 kts, which gives a ram rise of 482 °C. The air doesn't get much colder as you climb to the altitudes where the SR-71 flew, so this gives a total air temperature of over 400 °C. Speed makes a huge difference.


How can I calculate turbofan efficiency as a function of turbine inlet temperature? I know that increasing the turbine inlet temperature (TIT) increases the overall efficiency of the jet engine. So I wanted to find the overall efficiency as a function of TIT. I used the equations from this website. But the efficiency seems to go down as I increase the TIT. I have attached the pictures of the functions I used to get the graph.

I assumed a compressor pressure ratio of 30, a fan pressure ratio of 1.5 and a bypass ratio of 8.

stages of the cycle the way I defined it as
1-2 is inlet
2-3 is compressor
3-4 is combustor
4-5 is a turbine
5-6 is afterburner(I didn't use it so 5 and 6 are same)
6-7 is the nozzle

I have also found another picture from this website that showed the similar result with efficiency going down as TIT is increased

Can someone please tell me what I did wrong? Or if you can provide a similar graph with similar assumptions that would be great.

First, you should state whether you are designing an engine (increasing the TIT) or if you are doing an off design calculation for an existing engine.

In the case of design we gas turbine performance engineers call this design point analysis, increasing the TIT indeed would increase the efficiency, but this would require an increase of the pressure (OPR, Overall Pressure Ratio) as the pressure ratio is a parameter in the thermodynamic efficiency equation. A rise in compressor exit temperature by the increased pressure ratio requires raising the TIT to be able to add power/heat to the cycle. See e.g. the following example:

When increasing the pressure, the exit temperature of the high spool speed compressor also increase and results in an even higher amount of cooling flow required to cool the turbine. Using simple formulae is possible, but not preferred, specific software exists to do this for you.

If you are doing an off design analysis, so basically you have a frozen design and want to see the effects of TIT on efficiency, this can only be done with a gas turbine simulation program. To do this you would require the off design characteristics of the turbomachinery components, which are highly classified data.

Looking at the formulae you posted, I assume that you are looking at various designs. Please download a free copy of a gas turbine performance simulation tool and it will tell you the answer in minutes. E.g. this tool or this tool are free to use. There are probably much more tools.


Are elevator trim tabs required for an aircraft equipped with movable horizontal stabilizer? The Bombardier C-Series aircraft has a movable horizontal stabilizer. It also has Trim Up/Down (discrete) switches in the cockpit.

Is the aircraft also equipped with trim tabs?
If so, when pilot adjusts the trim using the trim switches, which surface moves - horizontal stabilizer or trim tabs?
If an aircraft has both trim tabs and movable stabilizer, when are the trim tabs used for trimming?

Is the aircraft also equipped with trim tabs?

From the images available online (this is a youtube screenshot, click it to see the larger version), no. And see point 3 on why I was not expecting any different.

  If an aircraft has both trim tabs and movable stabilizer

I do not see the need of such a solution, a trimmable stabilizer is already optimal, adding trim tabs would increase the complexity of the system with no significant benefits, as the use of tabs increases drag, something that a THS does not.

I do not know of any aircraft that uses both THS and tabs, but, should one exist, I presume one would use the tabs only if significantly faster than the THS actuation system, allowing the aircraft to be trimmed more rapidly, but afterwards the THS would take care of the trim allowing the tabs to go back to neutral and reducing drag.

This solution would be hardly beneficial, since commercial aircraft (as the one that prompted your question) do not preform manoeuvers that require such fast (and eventually frequent) re-trimming.

In addition, as GHB has pointed out in the comments, the elevator is already able to take care of fast transients, the trim tab would only provide unneeded complications (in the design, the maintenance, the control).


How did the B2 Bomber achieve yaw I came across this diagram of the B2. I was wondering how it achieved yaw. If I'm correct usually the rudder on the tail would do this, but the B2 does not have a tail. Does it have no need for yaw, or does something else act as the tail?

They use differential breaking. The elevons are split, and can open up both above and below the wing to increase drag on one side, yawing the plane.


Since there are no toilets on smaller aircraft, how do you deal with the inevitable? How do you handle business on a small plane on long flights? For example a cross country in a C-172.

The other answers are good, but don't touch on one key method...

Prevention.

Small aircraft like a Cessna 172 have a limited cruise time, about 4 hours maximum. They are small enough that they get relatively uncomfortable after 2-3 hours, and if flying in turbulence or challenging conditions, flights can be relatively short.

The best way I've found to avoid the problem is to make sure to use the facilities as close to departure time as possible and to limit my intake of fluids in the hour or so leading up to a flight.

The other option you have is to land and use the "facilities". Many unmanned airports that have terminals (like KMNM) have a keypad access and facilities inside. Airports are pretty common and you usually aren't more than 30 minutes away from an airport with a bathroom.

Just as a personal account of this, I was doing night training at my local field (Class C) and it was late (10:00 PM or so). One gentleman came on the radio and asked the tower if the FBO was open so he could use the facilities. The controller responded that the FBO was closed but he could taxi him to a quiet corner of the airfield for a few minutes. The pilot gladly took him up on the offer.


Do military pilots have flight & rest hours regulation? I have read that civil pilots have stringent regulations regarding flight hours and hours of rest between flights.

What about military pilots? Does it change between wartime and peacetime? Between type of aircraft (transport vs combat)?

Yes, they do. My experience is with the U.S. Air Force, so my answer will be from that perspective, but other air arms have similar regulations.

USAF

From the 11-202V3, Chapter 9, Crew Rest, Fatigue Management and Flight Duty Limitations:

9.4.3 Augmented Aircrew

  A basic aircrew supplemented by additional aircrew members to permit in-flight rest periods IAW paragraph 9.4.8. If the basic aircrew requires only one pilot and a second qualified pilot (includes pilots enrolled in an AETC formal aircrew
  training course) is designated an aircrew member to augment pilot duties, the crew can be considered augmented.

9.4.6 Flight Duty Period

  FDP begins when an aircrew member reports for a mission, briefing, or other official duty and ends when engines are shut down at the end of the mission, mission leg, or a series of missions. FDP for UAS ends at final engine shut down, final in-flight handover briefing, or final crew swap, whichever occurs last.

Table 9.1 (Maximum Flight Duty Period in hours by aircraft type)

9.8 Crew Rest

  Aircrew require at least 10 continuous hours of restful activities (including an
  opportunity for at least 8 hours of uninterrupted sleep) during the 12 hours immediately prior to the FDP. To ensure individual accountability and mission reliability, crewmembers should be officially notified prior to entering a crew rest period. A crew rest period cannot begin until after the completion of official duties.

So you can see from the chart that it depends on the type of aircraft, and the number of qualified pilots on board. But there are of course exceptions (e.g. the B-2 Spirit has been known to fly missions up to 44.3 hours), especially in wartime. All Air Force flights' risk is determined prior to the mission, and in training things like crew rest are instant no-flys, but when the needs of the mission dictate, pilots may have to overfly when they are the only or best option, or when exceptional circumstances dictate.

Also, from the Navy (I searched for other regulatory publications from other countries, but couldn't find any):

US Navy

From the OPNAVINST 3710.7T Chapter 8:

8.3.2.1.2 Flight Crew

  Ground time between flight operations should be sufficient to allow flight crew to eat and obtain at least 8 hours of uninterrupted rest. Flight crew should not be scheduled for continuous alert and/or flight duty (required awake) in excess of 18 hours. If it becomes necessary to exceed the 18-hour rule, 15 hours of continuous off-duty time shall be provided.

8.3.2.2.a Flight Time

  Daily flight time should not normally exceed three flights or 6-1/2 total hours flight time for flight personnel of single-piloted aircraft. Individual flight time for flight personnel of other aircraft should not normally exceed 12 hours. The limitations assume an average requirement of 4 hours ground time for briefing and debriefing


Where is the term *pro rata* defined as it is used in 61.113(c)? You've just received your private pilot certificate and your friends want to share the operating expenses of a flight with you.  There's a mother, a father, and their 6-month old baby. Do you split the cost of the flight among three people or four?

Obviously, the answer depends on the definition of pro rata, but I can't find the definition of that term anywhere in the FARs. This term is used here:

  (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.

Where is the term pro rata defined as it is used in 61.113(c)?

pro rata in law generally means according to a calculation or apportionment formula - in the context of the FARs that formula is generally assumed to be $\left(\frac{1}{nOccupants}\right)$ as Hugh noted.
I actually went on a dive through FAA counsel opinions on how they deal with the pro rata bit and found nothing applicable to this situation, so what follows is an interpretation crafted out of my own slightly deranged mind, but it seems sensible to me.

  Interestingly while digging around I found nothing in the FARs or interpretations that would seem to preclude a more complex formula for pro rata share than "divide by the number of people in the plane", but neither is there anything I can find to support doing so, and I imagine it would be much harder to justify to your local FSDO if questions came up.
  For the sake of simplicity (and our collective sanity) let's stick with "simple division" as the formula.

The FARs specify that the pilot may not pay less than their pro rata share of operating expenses associated with the flight.  So, if we have 4 occupants of the aircraft (Mom, Dad, Baby, and Pilot) and they go for a hundred-dollar hamburger the simple division method says pilot cannot pay less than one-fourth of the operating expenses associated with the flight.  If we say the expenses work out to be \$100 (for the sake of easy math) the pilot has to pay at least \$25.

The FAA doesn't much care where the rest of the money comes from because it's implicit in the regulations that the pilot isn't keeping it (the money would be going into the hands of the FBO for fuel, oil, ramp fees, etc.) -- Mom & Dad could pay $37.50 each (covering themselves plus the baby) or split it up between themselves in any other way they wish and this is still acceptable under the regulations as long as the pilot has paid their pro rata share of the expenses.

The pilot can certainly pay more than the simple-divison pro rata share of expenses (and generally that's the most equitable option - figure out who's paying, divide by that number, and make sure the pilot is in the "paying" group to stay on the right side of the regulations).
In your example you would split the cost up among the three adults (each paying $33.33, and the pilot generally kicking in the extra penny).

The same logic in both of these arguments would apply if we weren't talking about a baby, but rather a third friend that you all decided to treat to a trip.


Are jet streams a net benefit in time and fuel savings? Suppose a plane has a cruise speed of 400 knots  TAS. In a 4000 nm route we would have a round trip of 20 hours. If there was a jet stream of 100 knots in either direction, we would have 4000/500=8 hours in the tailwind direction and 4000/300=13.3 flying into the jet stream for a total of 21.3 hours. Now clearly, airlines are smarter than this and plan flightpaths, altitudes and speeds that maximize tailwinds and minimize time spent flying against the wind. The question, is to what extent does this strategy help? Does it simply offset the time lost compared to flying at the same speed in both directions? Or does it help even more than that. In other words, would a hypothetical windless world hurt the airline industry?

Yes, Jetstreams are a net benefit on longer flights because it is easy to minimize headwinds and maximize tailwinds for both directions.

Longer flights can detour hundreds of miles in order to take advantage of more favorable winds and still result in a net gain.

I frequently fly from Toronto to Hong Kong. We always fly a polar route YYZ-HKG as it is shorter, but usually take a HKG-YYZ North Pacific route over Alaska to take advantage of the prevailing winds.

This daily flight is always scheduled at 15 hours 40 mins for Toronto to Hong Kong over the pole but only 14 hours 45 mins returning via a longer route over Alaska.

The longer flight routing over Alaska is a net benefit in time and fuel due to the prevailing westerly winds over the North Pacific.  This type of flexibility is not available on shorter flights.

YYZ-HKG 6,787nm non-Stop 15:40

HKG-ANC-YYZ 7,050nm non-Stop 14:45


Does the co-pilot still remain in control of the plane if an engine fails during takeoff? If an engine fails after $V_1$, how long does the copilot remain in control if he was the pilot flying? What is prioritized before the captain taking control of the aircraft?

The operating procedures for the four airlines I worked for (2 commuters and two 747 carriers) all called for the flying pilot (which would be the first officer if it was their leg) to retain control of the airplane until all relevant checklists had been accomplished.

That said, it is, of course, the captain's prerogative to take control at any point. That would, I think, be very unwise to do in the case of an engine failure during takeoff unless the first officer was really screwing up.

The greater workload in the 747 during emergency/abnormal procedures lies with the non-flying pilot and the flight engineer (old 3 man cockpit 747-100s and -200s).

The recommended procedure at my last two airlines was, if the captain was flying at the time of the failure, to hand control to the first officer after all relevant checklists had been completed, to thus enable the captain to give his full attention to how best to proceed.

My personal and observational experience is that there is little difference between captains and first officers at the 747 level insofar as control manipulation during go/no go situations on the runway in simulators. In fact, I could point you to an accident resulting in the total loss of a 747 when the flying pilot was the Captain, and he elected to abort 30 knots after $V_1$, thus insuring the aircraft would leave the runway.