How is a turbine engine rotated for starting and inspections? I'm doing an assignment for my Level 3 Aeronautical Engineering course and stumbled on this question and I can't seem to answer it (we have had no teacher for 4 months and therefore we have to learn by ourselves):

Name and explain the type of coupling between the main engine rotating
assembly and the accessory gearbox and therefore how a gas turbine
engine is rotated for:
a) engine starting
b) internal inspection (boroscope)

Any help is greatly appreciated.

On the CFM56-7B engine powering the Boeing 737 NG family, the starter and the handcranking input are part of an accessory gearbox which role is to support components rotating with the high-pressure shaft. This gearbox is located outside of the engine core.

Other engines have a similar design, but the accessory gearbox location may vary, e.g. on the CFM56-5B powering A320 family and 5C powering A340, accessories are at the 6 o'clock position because clearance between nacelle and ground is sufficient.

Accessory gearbox on the CFM56-7B

The accessory gearbox (AGB) is located on the side of the fan containment case.

CFM56-7 exploded view. Source

It is a set of drive pads hosting accessories, including:

The handcranking mechanism used to turn the N2 shaft during borescope inspection (the N1 shaft can be rotated by moving the fan blades manually). The handcranking drive pad is visible on top on the picture below.
The starter, which is the large assembly at the bottom of the picture.

CFM56-7: Handcranking pad and starter, source Youtube

During borescope inspection, a square drive socket attached to a breaker bar is  inserted into the handcranking drive pad, or a pneumatic motor is used.

Handcranking drive pad (cover removed). Source: Youtube

Alternatively on other CFM56 engines the core can be turned directly from a pad on the TGB (see below).

AGB to core shaft

There is a gear train within the AGB with its input gear used to transmit movement between the AGB and the engine core.

The AGB is connected to the N2 shaft by two bevel gear gearboxes:

The transfer gearbox (TGB) fixed just aft of the AGB, on the fan frame case. A horizontal shaft links the AGB input gear and the TGB. A radial shaft is also connected to the TGB.
The inlet gearbox (IGB) fixed close to the No 3 bearing, in the fan frame hub. One bevel gear is coaxial to the HPC shaft, the other is coaxial to the radial drive shaft.

Let's remove some components to better see the link from AGB to high-pressure shaft:

CFM56-7B AGB, horizontal and radial shaft, TGB, IGB and engine shafts. Taken from this answer

The radial drive shaft runs within the 9 o'clock strut of the fan frame.

The described mechanism is bidirectional, the AGB is normally driven by the HPT shaft, but when using the starter or the handcranking mechanism, the pads rotate the AGB input gear using the gear train, and the input gear then drives the intermediate shafts and gearboxes.

Pad use

The accessories have allocated pads on the AGB, the ones mentioned have been highlighted in green:

Accessories and their allocated drive pads on the AGB. Source CFM56-7B manual

Rpm ratio of the gears

Data taken from the engine manual:

N2 is 14,460 rpm
Radial drive shaft spins at 1.343 N2 (19,418 rpm)
Horizontal drive shaft at 1.301 N2 (18,811 rpm)
Starter shaft at 1.002 N2 (14,494 rpm)
Handcranking shaft at 0.986 N2 (14,260 rpm)

Also: Actual photos of the gearboxes in this answer.


Why are there vortex generators under the Boeing 737's cockpit windows? What is the purpose of the vortex generators located right in front of the Boeing 737's windshield?

Apparently, they are there to reduce the cockpit noise. From b737.org.uk:

  Notice the 10 small vortex generators above the radome. These reduce the cockpit noise from the windshield by 3dB.

According to this document, the VGs, along with other improvements like damping/insulation changes, window frame improvement and ECS improvements contribute to a total noise reduction of 3 dB (at 35k ft and Mach 0.78). Though their exact impact is unknown, the reason for VGs are there is to reduce cockpit noise.


What would have been the other stops of Amelia Earhart's ill fated last voyage? Having just watched Amelia - A tale of two sisters, I wondered whether, had she landed successfully on Howland Island, what, or where, would the remaining subsequent stops for the rest of her equatorial journey, in 1937, been?

Were there any other stages that would have been as equally, or more, dangerous, and liable to failure, or was the stage at which she tragically failed the most dangerous of all of the journey's stops?

This image from the Wikipedia page, Amelia Earhart, implies that she would have flown on to Honolulu, but the text doesn't state that fact explicitly:

This table from Wikipedia shows the final two planned legs of her flight being:

  July 3, 1937 Howland Island   to  Honolulu, Hawaii     1900 NM  Planned
  leg

  July 4, 1937  Honolulu, Hawaii to Oakland, California  2400 NM  Planned
  leg


What is this feature on a Sukhoi Su-27? Most but not all Russian Su-27's (and variants like the Su-30, -32, -33) have a device that looks like a headlight in front of the cockpit. What is it?

It's the sensor of the IRST (InfraRed Search and Track) system.
An IRST allow an aircraft to search and track aerial or ground targets using passive infra-red radiation only thus reducing the probability of being discovered (for example using a Radar Warning Receiver).

The Su-27 can use it's IRST to track a target at very long distance and engage it using IR homing AAMs like the R-73 "Archer" or the R-27T / R-27ET "Alamo" without using its radar.

Nowadays, many current fighter aircrafts use some sort of IRST, for example the Eurofighter Typhoon.


What is an example of a quantitative analysis for the lift using Newtonian mechanics? There are several different ways of explaining how an airplane generates lift. The simpler qualitative explanation uses Newtonian mechanics (the third law is invoked to explain how the wing pushes air down and is in turn pushed up by the air) whereas the more quantitative explanation uses aerodynamics and fluid mechanics.

I have been looking to find a simple model of an airplane wing that uses Newtonian mechanics to come to an approximate quantitative description of airplane flight. Everything I have found so far (such as this article) is merely qualitative.

The governing equations of fluid mechanics, Navier-Stokes equations, are derived based on Newtonian mechanics (plus thermodynamics). The circulation theory of lift is derived using a simplified form of N-S equations. It's powerful because it's predictive for important things like lift and induced drag. The Newtonian explanation is not that useful because it's not predictive. Good for party talks, but poor for engineering.

That being said, if you couple it with the concept of control volume and mass conservation, you can derive something. Take a look at NASA Memo 1-16-59L. To summarize, as air moves past the wing, it gets deflected, so the lift in the vertical direction (normal to the incoming flow direction) is:

$$L=\dot{m}\Delta V$$

where $\Delta V$ is the portion of air that was induced across the wing interface in the vertical direction, $\dot{m}$ is the total mass flow rate of air through the wing. That's the Newtonian part of the story.

Now from the conservation of mass, what comes in = what goes out. So we can express mass flow rate as, assuming the wing is like a giant circle with diameter equal to its span (note that this assumption is the major pitfall of this analysis, since there is no reason the stream-tube has to be the diameter of the wing):

$$\dot{m}=\rho A_iV_{i}=\rho\pi(\frac{b}{2})^2V_{\infty}$$

where $b$ is the wing span, $V_{\infty}$ is the freestream airspeed, $\rho$ is air density.

As for the change in vertical airspeed, we can parametrize it by assuming the whole stream tube gets deflected by the wing through an angle $\epsilon$. Therefore, $\Delta V=V_{\infty}\sin \epsilon$, and:

$$L=\frac{\pi}{4}b^2\rho V_{\infty}^2 \sin \epsilon$$

That's pretty close to the lift equation that we know. In fact, if you express drag as the loss of horizontal airspeed, apply small angle approximation to the second order, then normalize the lift and drag by $\frac{1}{2}\rho V^2 S_{ref}$, you get (with $S_{ref}$ being the reference wing area, $A$ being the aspect ratio):

$$C_{D}=\frac{C_L^2}{\pi A}$$

That's the induced drag expression for an elliptical lift distribution that we would get from the circulation theory of lift. But that's pretty much as far as you can go. You have no way of estimating $\epsilon$ from first principle, so the theory isn't all that predictive.


Why isn't KTEX's runway designation 10/28 instead of 9/27? Why is the marking on the runway written as (9/27) Telluride (KTEX), Colorado, USA. whereas the direction is 284 degrees? Shouldn't it be (10/28) instead?

That direction (284) is the true heading, but runways are numbered according to the magnetic heading.

  Runways are usually numbered according to their direction, more precisely called runway magnetic bearing or QFU (see Q codes). (How are runways numbered?)

For KTEX:

  276 magnetic, 285 true
  096 magnetic, 105 true

While 276 should be rounded to runway 28, it could be a recent change that the magnetic heading changed to 276 from say <275. There is a process to go through, so a recent change in magnetic variation does not mean the renumbering will swiftly follow.

  Every five years, the FAA reevaluates shifts in the pole—its magnetic variation—and makes changes to runways and flight procedures as needed. (How do airports determine when they should change their runway numbers?)


Does the A380 have more than one auto-brake disengage switch? I know that the A380 has low/med/high RTO auto-brakes. What I'm not sure about is if there's a switch near the thrust levers that can disengage the auto-brakes, other than the switches located on the brake panel.

To put it another way, the A380 has a brake panel where the switches allow you to engage/disengage auto-brakes (either low, med, or high RTO). But in addition to those, is there any other switch that can do the same thing without the pilot needing to take his eyes away from the view outside?

The A380 has one Takeoff Autobrake setting which is RTO and five Landing Autobrake settings which are BTV, LO, 2, 3 and HI. Some may read that as four plus the BTV, which is a variable deceleration compared to fixed deceleration. As you have noted, these are selected from the Autobrake selector switch.

It is possible to disarm the Autobrake using a number of actions. One or two which have been mentioned already.

The Autobrake selector switch is set to Disarm.
The Brake pedals are depressed with a higher input than the Autobrake setting.
The Spoilers are retracted.
The Autothrust instinctive disconnect pushbutton switch is pressed. These are located at the ends of the Throttle control levers.
The RTO Arm pushbutton switch is set.

FCOM Reference for anyone interested - FCOM/DSC/32/10/30/20/00004244.0002001


Why both ICAO and IATA headquarters are located in Montreal? Montreal is not large city like Paris and New York, nor a important place in aviation history like Kitty Hawk(Wright brothers first flight) or Friedrichshafen (Zeppelin airship first flight). Why Montreal is being chosen as the headquarters of 2 biggest aviation organization.

ICAO is headquartered in Montreal because that was the result of a vote by the founding members (PICAO is Provisional ICAO):

  Why was Montreal selected? While insisting on the excellent
  hospitality offered since of the beginnings of PICAO by the federal,
  provincial and municipal authorities, the delegates described Montreal
  like a roundabout of the international means of communication and a
  strategic centre with a formidable economic, scientific, technical and
  aeronautical expansion being felt for a few years. One insisted on the
  vast spaces of the Canadian territory, offering unlimited
  possibilities for the scientific and practical experiments in the
  field of aviation. Moreover, PICAO was to be established as close as
  possible to the central head office of the United Nations.

And IATA is in Montreal because its founding statutes said that it must be in the same location as ICAO:

  Article II of the IATA 1945 Statutes states that “The Head Office of
  this Association shall be maintained in the city in which the
  headquarters of the International Civil Aviation Organization is
  located.”; this article was later amended to leave an opening for a
  possible other place as determined by the General Meeting


Is the Dassault "ministop" related to the Dunlop Maxaret ABS? Dassault fighters e.g. Ourargan and Mystere had Anti-lock devices called "Ministop" on main landing gear brakes.
Anybody has a picture / drawing / detailed description ?
Is the Ministop related to the Dunlop Maxaret ABS ?

This 1953 issue of Flight International mentions the Messier Ministop, it seems it was shown publicly for the first time at the Salon de Paris, July 1953:

  A particularly interesting development was the new anti-skid device which is being marketed under the name of Ministop. The device consists of an accelerometer—a free mass rotating with the wheel—together with a centrifugal governor and an associated electrical circuit. The general principle of operation is very similar to that of both the Dunlop Maxaret and the Westinghouse Decelostat ...

From that wording I'd say Ministop is unlikely to be a license-built version of Maxaret.


Which aircraft are required to have a black box? When is an aircraft required to have a Cockpit Voice Recorder or a Flight Data Recorder?

Cockpit Voice Recorders
Required for:

large 4-engined turbine-powered planes
large 4-engined pressurized planes
multiengined turbine-powered planes seating 10+ passengers
multiengined turbine-powered rotorcraft seating 20+ passengers
multiengined turbine-powered planes and rotorcraft seating 6+ passengers and requiring two pilots

Relevant regulations: 14 CFR 121.359, 14 CFR 125.227, 14 CFR 135.151

121.359(d) No person may operate a multiengine, turbine-powered airplane having a passenger seat configuration of 10-19 seats unless it is equipped with an approved cockpit voice recorder
125.227(a) No certificate holder may operate a large turbine engine powered airplane or a large pressurized airplane with four reciprocating engines unless an approved cockpit voice recorder is installed in that airplane and is operated continuously from the start of the use of the checklist (before starting engines for the purpose of flight) to completion of the final checklist at the termination of the flight.
135.151(a) No person may operate a multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration of six or more and for which two pilots are required by certification or operating rules unless it is equipped with an approved cockpit voice recorder
135.151(b) No person may operate a multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration of 20 or more seats unless it is equipped with an approved cockpit voice recorder

Flight Data Recorders
Required for:

Multiengine turbine-powered airplanes or rotorcraft seating 10+ passengers
Multiengine turbine-powered airplanes or rotorcraft seating 6+ passengers and requiring two pilots
Large airplanes meant for use either over 25,000 feet
Large turbine-powered airplanes
Turbine-powered transport category planes

Relevant regulations: 14 CFR 91.609, 14 CFR 121.343, 14 CFR 121.344,
14 CFR 135.152

91.609(c)(1) No person may operate a U.S. civil registered, multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration, excluding any pilot seats of 10 or more that has been manufactured after October 11, 1991, unless it is equipped with one or more approved flight recorders that utilize a digital method of recording and storing data and a method of readily retrieving that data from the storage medium, that are capable of recording the data specified in appendix E to this part, for an airplane, or appendix F to this part, for a rotorcraft, of this part within the range, accuracy, and recording interval specified, and that are capable of retaining no less than 8 hours of aircraft operation.
91.609(e) Unless otherwise authorized by the Administrator, after October 11, 1991, no person may operate a U.S. civil registered multiengine, turbine-powered airplane or rotorcraft having a passenger seating configuration of six passengers or more and for which two pilots are required by type certification or operating rule unless it is equipped with an approved cockpit voice recorder that: (1) Is installed in compliance with § 23.1457(a)(1) and (2), (b), (c), (d)(1)(i), (2) and (3), (e), (f), and (g); § 25.1457(a)(1) and (2), (b), (c), (d)(1)(i), (2) and (3), (e), (f), and (g); § 27.1457(a)(1) and (2), (b), (c), (d)(1)(i), (2) and (3), (e), (f), and (g); or § 29.1457(a)(1) and (2), (b), (c), (d)(1)(i), (2) and (3), (e), (f), and (g) of this chapter, as applicable; and (2) Is operated continuously from the use of the checklist before the flight to completion of the final checklist at the end of the flight.
121.343(b) No person may operate a large airplane type certificated up to and including September 30, 1969, for operations above 25,000 feet altitude, or a turbine-engine powered airplane certificated before the same date, unless it is equipped before May 26, 1989 with one or more approved flight recorders that utilize a digital method of recording and storing data and a method of readily retrieving that data from the storage medium.
121.344(a) Except as provided in paragraph (l) of this section, no person may operate under this part a turbine-engine-powered transport category airplane unless it is equipped with one or more approved flight recorders that use a digital method of recording and storing data and a method of readily retrieving that data from the storage medium.

Exceptions: For aircraft manufactured before August 18, 1997, the following aircraft types need not comply with this section: Bell 212, Bell 214ST, Bell 412, Bell 412SP, Boeing Chinook (BV-234), Boeing/Kawasaki Vertol 107 (BV/KV-107-II), deHavilland DHC-6, Eurocopter Puma 330J, Sikorsky 58, Sikorsky 61N, Sikorsky 76A. [src: 14 CFR 135.152(k)]
Additionally, the NBAA has links to summaries, but I do not have an account with them and was unable to retrieve the data.


What are the most efficient layouts of multiple runways? Many airports have more than one runway. How should runways be built in order to achieve maximum usage and minimum delays?

Many major airports have most, if not all, parallel runways. Examples include LAX, DFW, and ATL.

In fact, Chicago O'Hare has been undergoing some major runway improvements, mainly to make the runways more parallel. This figure shows the before (mid-2000s) and after (completion date TBD) layout of ORD. Eventually, ORD is slated to have 6 parallel E-W runways, along with 2 SW-NE runways.

However, a crossing configuration is very common at airports with only 2 runways. Here is one example:

Are parallel runways more efficient, and smaller airports simply don't have space for them? Ideally, how should runways be configured?

Edit:

Additionally, what if we assume...

Case 1 - That wind isn't a factor?

Case 2 - That the airport location has exceptionally variable winds?

Case 3 - That space/airport footprint is an issue?

In order to increase the number of operations that can be handled at a runway, you want them configured so as to allow "simultaneous independent approaches," which means that the 2 (or more) runways can be operational without the need to coordinate between them.

The biggest factor is the distance between the two runways. The greater the distance between them, the less impact they have on each other, not just in terms of number of operations per hour, but also in terms of visibility minima for instrument approaches.

The other factor that needs to be considered is the wind, and as you can see from the Chicago airport layout, there are parallel groups of runways that effectively form a triangle, such that there is never a crosswind component that exceeds 30 degrees. The layout at Las Cruces, NM, which is usually very windy, shows the format better than Chicago, even though they are single runways:

The last issue is the type of radar available, and the faster the radar sweep, the less delay there is between the position of the aircraft and their depiction on the radar screen, allowing the controllers to closely monitor the approaches.


What is the difference between a Sub-Charter Flight and a Codeshare Flight? What are the main differences of this two types of flights?

Sub charter is not used nowadays as a word expression. It's now called wet lease or ACMI. An ACMI specialist airline does not fly its own regular schedule, but usually flies for other airlines on shorter/longer notices (couple of flights or whole schedule). When WOW air started in Iceland, its schedule was flown by a Lithuanian ACMI operator. HiFly flies for Condor its service from Munich this winter, because Condor's 767s are undergoing heavy maintenance. Thomas Cook of UK is a permanent wet leaser to Condor (they are in the same holding). They provide aircraft and pilot crew, but Condor does fuel, maintenance and cabin crew. In the HiFly example above, HiFly provides full ACMI (aircraft crew maintenance insurance) for Condor.


How close is this Su-27 to the aircraft recording the pass? There is footage of an intercept of a US Nay recon aircraft being intercepted by a Russian Su-27:

(still from the BBC video article, who look like they got it from the US Navy directly)

which was reported on the BBC, CNN and elswehere.

I am not familiar with the proportions of the intercepting plane, but it looks like it passed very close to the recording aircraft!

Is there a good way to estimate how close it was, to within a rough ballpark? Tens of meters, a hundred meters, three hundred meters?

The CNN article reports that

  Officials so far, have not been able to estimate how close the Russian aircraft came to the US plane, but described the flight behavior of the Russians as the key factor in making the determination the encounter was unsafe.

but

  The US crew reported turbulence following that initial interaction in which the direct pass occurred. [During the second pass the Su-27] applied its afterburner while conducting a banking maneuver, which is believed to have caused a vibration that was experienced by the American crew.

On a related note, there was also a report of an Su-27 coming within 5 feet (!) of another aircraft earlier in the year; so it seems that this is not a one-off occurrence.

It looks like it's maybe 50-75 ft away from the camera, but you would have to know whether the camera's focal length is neutral, magnifying or wide angle, so it's really a wild guess.  There's not enough detail on the host aircraft to be able to scale it that way.


Why is there a GPS/RNAV waypoint co-located with a VOR? There is an RNAV waypoint named STYCK co-located at what appears to be the exact location of the LOA VOR (coordinates match precisely as well). Why would the creation of a waypoint be necessary if IFR GPS/RNAV units/databases can take both VOR names and waypoints? Why not just use the VOR name that has existed there for over 50 years? Such a thing is regularly done in IFR SIDs and STARs when loading them into a GPS/FMS.

In the US, the FAA has done this alot, as in their long term plan to phase out a lot of the VORs. Doing that, they're preemptively just adding a Fix for procedures on top of the VOR so they don't have to update all the procedures when the VOR is decommissioned.


What is the minimum altitude for dumping fuel? In this question, a comment mentioned that if a 4-engine airliner suffers a 3-engine failure shortly after takeoff, the only way to stay aloft may be to dump fuel.

What is the minimum altitude which fuel dumping is possible? Possible here means, the fuel will not cause a hazard to the airplane or anyone on the ground.

Is the altitude MSL or AGL? (i.e., is it "it takes 2,000 feet for the fuel to fall before it evaporates", or "the atmosphere pressure at 8,000 feet makes fuel evaporate a lot quicker, so you can do that if you're at 8,000 pressure altitude even if the ground elevation is 7,000 feet"?)

The altitude appears to be above ground level. From FAA Order JO 7110.65W Air Traffic Control:

Section 4. Fuel Dumping
9−4−3. ALTITUDE ASSIGNMENT
If an aircraft is dumping fuel in IFR conditions, assign an altitude at least 2,000 feet above the highest obstacle within 5 miles of the route or pattern being flown.

The wording says 'above the highest obstacle', indicating AGL. The CAA Manual of Air Traffic Services is much more explicit:

13.3 Controllers are to recommend to flight crew that jettisoning of fuel should be carried out above 10,000 feet agl. Exceptionally, if fuel dumping at this level, or over water, is operationally impracticable or inconsistent with safety, fuel may be jettisoned above 7000 feet agl in winter and above 4000 feet agl in summer.

This indicates that the altitude requirement of dumping fuel is from the from the first consideration i.e. it takes x feet for the fuel to fall before it evaporates. Swiss regulations go into this at a little bit of detail.

Generally, air masses are only moved vertically very slowly, usually at a settling rate of approximately 60 centimetres per second. In addition the upper limit of the planetary boundary layer (PBL) at the altitude of
approximately 3000 ft over ground renders the air flow from the upper to the lower layers more difficult. Therefore the chance that even a small quantity of fuel reaches the ground is estimated to be unlikely.

Again, it says 'above ground' indicating AGL.


How can we determine the maximum camber and thickness for airplane wings? I want to know if there are any standard factors for determining maximum wing camber and thickness for heavy and light airplanes?

I'm using an optimization process to find the best wing shape to reach the best aerodynamics. E.g. in cruise mode to find the maximum lift-over-drag ratio, maybe choosing a thinner camber or thickness has a higher CL over CD ratio, but may lead to problems with structural limits.

Can anyone help me with some good references on the appropriate limits of changes in both maximum thickness and camber?

Camber pushes the lift coefficient operating range up and increases the pitching moment of an airfoil. It is advised to use lots of camber if you need to create lots of lift at low speed and have no need to fly fast. Conversely, high speed aircraft use uncambered wings. Flaps add camber - this makes them so effective for lowering the minimum speed of heavy aircraft.

Comparison of the same baseline airfoil at different camber values (picture source). This is taken from NACA Report 824 which later was turned into one of the most important books for aerodynamicists.

Wing thickness helps to build a lighter wing but will increase friction drag due to higher supervelocities caused by the displacement effect of the thick wing and cause earlier flow separation because the boundary layer is more stressed. In the end, you need to find a compromise: A 15% - 16% thickness is quite normal for GA aircraft, and high aspect ratio wings like those of the B-24 and the B-29 had a root thickness of  22%, but tapered the thickness down towards the outer wing as soon as practical. The tip thickness of both was just 9%.

The maximum lift will peak around 12% to 15% relative thickness. Below I copied figure 85 from NACA Report 460 to illustrate the point:

Now this was all subsonic aerodynamics. Once you move closer to the speed of sound, the supervelocities can cause pockets of supersonic air which end in a local shock. Therefore, the optimum thickness is reduced as the cruise speed approaches Mach 1, and wing sweep is added to cheat a little and keep thickness higher. Modern airliners use airfoils of around 13% relative thickness, and supersonic wings rarely use more than 6% relative thickness at the root, tapering to 2% to 3% at the tip.


What procedures exist to take control from an "unsafe" pilot? I was reading up on the Garuda Indonesia Flight 200 crash and a few questions came to mind, in summary the captain (PF), conducted an unsafe approach in which he did not heed multiple warnings from both the aircraft and the copilot (PM), and landed 860m past the threshold and at a speed of 221kts.

The wiki article also states: "The copilot failed to take control of the aircraft ...  as required by airline policy". This just got me wondering, what policy/procedures exist in outlining how to take control of an aircraft from an "unsafe" pilot. I know the procedure under normal circumstances is "my aircraft/your aircraft". But how would this be accomplished in a situation similar to Flight 200, where it seems the captain would have of been reluctant to hand over controls given his blatant disregard for all other safety measures.

This is a true "nightmare scenario" and really approaching -- if not beyond -- the limits of the realm of CRM.  The assumption of CRM is that while pilots can get task saturated, focused on "making it (the approach) work out", and otherwise lose track of the situation, everybody is willing to listen to reason, if it is just presented with sufficient clarity.  If a pilot is so far gone beyond that point that he is absolutely determined to take his approach to its completion, you're approaching a different scenario.

Let's stipulate at the outset that this sort of a scenario is incredibly rare. Good pilots can get so focused on making things work that they lose situational awareness, but a clear statement like "we're 40 knots fast & two dots high on glide slope, GO AROUND" will typically snap pretty much everybody out of it.  The captain who is so wrapped up in his authority that he's willing to ignore an FO's repeated direction to go around is pretty rare.

That said... in the nightmare scenario, the FO's options become:

Keep making callouts, more directive, more urgency, yell louder.
Tell ATC that "we need to go around" on the hope that ATC directing "Flight 123, go around, fly runway heading, maintain 3000 feet" may accomplish what the callouts didn't.
Raise the landing gear.
Push the power up or otherwise fight for control of the aircraft.
Attack the flying pilot, perhaps with the aircraft logbook (metal cover) or a heavy flashlight or some other improvised weapon.

At this point, the FO is in the awful spot of having options that have a limited chance of success and in several cases, huge risk of making a bad situation even worse.  There is no "policy" solution to this sort of a scenario.  That a captain would have ignored repeated GPWS callouts and FO callouts is beyond the realm of what policy ever imagines.

As I said before, this sort of scenario is almost unimaginably rare.  Pilots just don't often reach the level of being an airline captain without sorting out the need to accept a "Go Around" callout from their First Officer.  Are there arrogant pilots out there?  Absolutely.  Arrogant enough to get to the situation mentioned in the OP?  Very, very, very few, and very far between.


How is the B737NG Autopilot controlling pitch? In particular, does the Autopilot in a B737NG control the pitch only via trim adjustment, or first via the elevators and then trim?

This is from the B737NG airplane manual. Boeing doesn't offer the technical drawings in the pilot manuals, one would have to have access to the maintenance manuals. Boeing is very sticky about their material being published on the internet.

Autopilot Flight Director System (AFDS)
The AFDS is a dual system
consisting of two individual flight control computers (FCCs) and a
single mode control panel. The two FCCs are identified as A and B. For
A/P operation, they send control commands to their respective pitch
and roll hydraulic servos, which operate the flight controls through
two separate hydraulic systems.

This is a brief explanation of an autopilot system such as on the B737 from this website.

Aircraft with hydraulically actuated flight control systems have
autopilot servos that are electro-hydraulic. They are control valves
that direct fluid pressure as needed to move the control surfaces via
the control surface actuators. They are powered by signals from the
autopilot computer. When the autopilot is not engaged, the servos
allow hydraulic fluid to flow unrestricted in the flight control
system for normal operation. The servo valves can incorporate feedback
transducers to update the autopilot of progress during error
correction.


What happens to used deicer fluid? I noticed several tanks at BWI that store waste deicer fluid. They're in the foreground of the picture; the tanks in the background store Jet A.

What do airports like BWI do with deicer fluid after they collect it? This question is similar but it only partially answers my question. Is the fluid treated the same as household wastewater?

Generally it enters the ramp drainage system and flows out with the rest of the runoff. Sometimes its recycled and sometimes its just filtered out of the runoff water and disposed. The EPA has a lengthy report on it you can find here various airports have different methods for recycling it or filtering it out as well as water drainage systems that vary in complexity and scope. The report sheds some light on the various systems involved at different airports.

Longer blurbs are available in the report (see section 7-1) for deeper descriptions.

Ultimately the components of De-Ice fluid break down fairly rapidly when released.

  When released into the environment, both ethylene glycol and propylene
  glycol are expected to partition to surface or groundwater. They are
  expected to rapidly biodegrade and not to persist in the environment.
  Biodegradation rates depend on temperature and oxygen conditions and
  glycols biodegrade more slowly under anaerobic conditions. The
  half-life of ethylene glycol and propylene glycol in water under
  aerobic and anaerobic conditions, and in soil are shown below. Note
  that these data were not conducted under the same laboratory
  conditions and may not be directly comparable (5).

Smaller fields or those that can not afford complex systems may allow it to flow into installed drainage systems right off the ramp. The small field I fly out of has no formal system to dispose of it.


How do helicopters avoid colliding? When helicopters fly over a city, how do they avoid colliding with each other? For example, after a shooting or accident, both police and news helicopters could head to the same spot.

Just like other aircraft flying VFR, see and avoid. Helicopters fly slower, which gives them more time to see and be seen.

They also have transponders and ADS-B requirements so it will be possible to see them electronically too (with TCAS today and ADS-B in in the near future).

While helicopters could technically have no transponder and hence no ADS-B requirement, operating inside big cities leads to the under class B veil, which ends up forcing transponder / ADS-B requirements anyway. What I really mean is there's little logic in owning a helicopter that can never go into the big city, those are usually expensive enough to warrant being able to go anywhere, unlike some old cheap piston planes.


Why do fighter jets still have guns/cannons? I noticed that the "new" F-35 still has a GAU-22/A cannon installed in it -- albeit with only  182 rounds (more with ammo pods).

Why do fighters still have cannons? The day of dogfighting is long over, now it's just fire some missiles and forget.  Even if they expended all their missiles, 182 cannon rounds is only 6 seconds of firing  (I think the GAU is rated to 1800 rpm).

The only reason (and I'm not sure if I should answer my own question) is that they need something to shoot warning shots over the bow of another airplane. But that seems an awful amount of weight for this rare occasion. And it'd mean loading tracer rounds.

Or is just a vestigial organ, like the sabres on the side of full dress military uniforms?

The idea that missiles will be all a fighter aircraft needs was prevalent in the late Fifties. The McDonnell-Douglas F-4 Phantom II carried initially only missiles, but at the start of the Vietnam war this turned out to be inadequate. The long-range missiles back then were rather unreliable, and in a real conflict things turn out always different than anticipated. As von Clausewitz said, the plan is the first casualty of war.

F-4s frequently found themselves in close-combat situations for which they were inadequately prepared. Even today, a gun gives the pilot a lot more options, and if the situation is unclear, close-up visual inspection before shooting is still vital to avoid politically embarrassing situations.

From the F-4C on, F-4s were equipped with a gun. First in external pods, from the F-4E as an internal gun. What also helped to make the F-4 more effective was better training for pilots and ground crew, so the missiles were in better shape and better applied.


Is there any load and balance and attitude that can put positive G on one wing and negative on the other? I got caught in gusty cross wind on the  final approach to Catalina airport last week and decided to add power and push for quick turn to come back over laterally sliding runway in a Cessna 172N. Later I was thinking back about the distribution of wind and lift pressure on the wings and could imagine a loading that would be directed upward under my left wing but changing downward on at least part of my right wing. Imagine that you're viewing the plane from behind and see it like a catamaran banked into 30' angle. And a horizontal line not necessarily passing through center crossing it as the sea water level. Is it possible and what to do to handle it?

Just imagine an aerobatic aircraft going straight up and rolling at the same trime - sure it will have positive lift on one side and negative on the other while accelerating into the roll or when stopping the rolling motion. Note that during a constant rolling motion while in a vertical climb the overall rolling moment and the overall lift both are zero.

Also, wing twist will cause very little lift or even a small downforce at the wingtip at low angle of attack. I remember that the wingtips of the SB-8 and SB-10 gliders would point downwards from the negative lift at high speed. The high aspect ratio glass fiber wing would bend a lot and indicate the local lift with a local change in curvature.

However, if you were flying an approach, the aircraft should have flown too slowly to allow for that condition, unless it also started to roll violently from the lift asymmetry. If you had to apply full aileron to counter a gust-induced rolling moment, that very aileron deflection would avoid any negative lift on one of the wingtips. This only leaves the possibility that you had negative lift for a very short moment and over a small part of the wing when the gust hit you and before you countered the rolling motion with the ailerons.


What does “Ground loops are costly. Fly them until they stop” mean? In one of the earliest scenes of William A. Wellman's 1942 film Thunder Birds, a sign can be seen in a room of a USAAF base (some relax or briefing room, apparently), which says:

  Ground loops are costly. Fly them until they stop.

I am not entirely sure about its meaning. I know what a ground loop is, but in what sense “Fly them until they stop”? Is it an advice not to use brakes too soon after landing?

It just means "pay attention to what you are doing" until you are no longer moving.  "Fly them" means "keep actively controlling the plane as if you were still in the air". Don't start daydreaming just because you're on the ground, in other words.

Especially with the taildraggers of olden times;

They are dynamically unstable turning-wise while rolling along the ground (because the CG is behind the fixed traction points; try driving a car backward really fast) and require careful attention to staying directionally aligned even while moving slowly.  Taildraggers with locking/free swivelling tailwheels (which you tend to see on the larger ones) are even more demanding, and are basically like a shopping cart rolling backwards (the kind with fixed back wheels, not the 4-wheel caster kind) once the tailwheel is unlocked for taxiing, and need to be steered with brakes alone, which requires quite a bit of concentration.
They like to tip forward under hard braking so keeping full up elevator while taxiing is a requirement to minimize this tendency
Strong quartering winds, if present, are trying to tip you over while 3 point on the ground and you have to learn to apply appropriate amounts of aileron to counteract this tendency.

A lot of stuff to keep in mind.  The tendency of a new pilot, when they had a successful landing, was to breath a sigh of relief and relax during the rollout when dropping below, say, 30 kt where rudder power fades away, or during taxi, forget they were in a backwards rolling shopping cart that is trying to switch ends continuously and let their mind wander, and oops.

Tricycle gear airplanes are nowhere near as physically demanding, but still you need to pay attention to what you are doing so it still applies in the end.


How do airliners get from the factory to the client if the aircraft does not have the required range? Today I flew on an Embraer 190 of Kenya Airways. Checking in the tech specs this aircraft has a range of roughly 2900 km. Considering it is built in Brasil, I was wondering how do they deliver it to Africa since they would have to cross the Atlantic Ocean which I suppose is more than 2900 kms of range it has available.

Do they add temporary tanks and, of course, by flying the aircraft empty get more range out of it?

Sometimes they do add temporary tanks. Here's a picture of what Hawaiian Airlines had to do to get their fleet of 717's over the Pacific because they did not have the range.

I don't have the answer to your question specifically, but I would guess they either add temporary tanks and go from SBNT-GUCY which is not much further than max-range, or take the long haul through the US and Europe.

There's a Cranky Flier blog post about this.


What is the first fighter jet which was built with twin engine and tail configuration? What is the very first fighter jet that pioneers the twin engine and twin vertical stabilizers over the engine just before the exhaust (like the F-14, F-15, F-22, Su-35, etc)?

One of the first was probably the unconventional XP-79.
https://en.wikipedia.org/wiki/Northrop_XP-79

It never entered service of course, but does meet your criteria.

Something that kinda meets your criteria would be the F7U Cutlass. Twin tails and twin rear mounted engines though the tails were in separate tail booms outboard of the engines, a similar configuration to that of the DH Sea Vixen and Venom of roughly the same period.

These did enter service.

Then there is the XF-90 which has twin rear mounted engines with a single vertical stabiliser over them.
The Soviet La250 and Tu28 had similar configuration but came later.

This also did not enter service.


Does ATC prefer ILS over RNAV? Listening to APP for several major (US class B) airports, it seems that every flight is vectored to intercept the localizer.  Is it really possible that 100% of flights filed an ILS approach?  If so, why?  It seems like at least some (perhaps small) fraction would have filed an RNAV approach.  Can someone with only GPS still "intercept the localizer" by flying the given vector until the runway is in sight and then get cleared for visual approach, so actual ILS doesn't matter?  Or does that case just never come up because ATC knows (via the equipment code in the flight plan) who has ILS equipment available and makes them use it even if that's not what they filed?

As egid pointed out, pilots typically do not file a specific approach as part of their flight plan. ATC will decide what runways and approaches are in use based on the weather. As the pilots are on their descent to the destination, they will be told which approach to expect. Pilots can always request something different but ATC is trying to get everyone to their destinations as safely and quickly as possible.

It's easier to space and sequence aircraft if they are all on the same approach, rather than trying to get aircraft on multiple approaches to mesh together just right. It's also easier to sequence them if they are all on the same approach course along the localizer, where an RNAV approach may have multiple initial fixes that follow various paths to get to the same final approach fix.

An ILS approach gives ATC more control over the spacing and sequencing of aircraft onto the final approach course. Aircraft can be vectored in anywhere along the localizer. RNAV approaches have more locations where aircraft can join them, which may be inconvenient depending on the direction from which an aircraft is arriving. Not all aircraft may be able to join an RNAV course by vectors, but pretty much any airliner can intercept an ILS localizer.

The same benefits can apply even in visual conditions. The localizer provides a common reference that all pilots can join and follow while they can maintain visual separation from each other, allowing closer spacing of aircraft. It's easier to say "join the localizer" than "join the RNAV RWY 17 final approach course."


Were early military planes not pressurized? I just heard that  1930s-40s planes such as the B-17 were not pressurized. Is this true? If yes, then how did the military men survive at heights of 30k ft?

There were a few problems:

Pressurization (while not impossible) was difficult requiring extra effort. It also increased weight and complexity.
Pressurization was still a relatively new technology at the time. For reference, the first pressurized commercial aircraft, the Boeing 307 Stratoliner, made its first flight later the same year (1938) as the B17. Note that it was developed from the B17.
There was an incredible amount of openings on early planes for gun turrets, bomb bays, etc. Sealing these off airtight would have been a impractical nightmare. You would traverse the bomb bay move to the back and front of the plane.
It's also better from a reliability standpoint- it's pretty easy to damage and make a hole in the fuselage, but everybody having their own oxygen masks removes that single point of failure.
While perhaps (I imagine) not incredibly comfortable for long duration missions oxygen masks worked fine.

30,000ft corresponds to around 9,200m, although that altitude is a ceiling defined by Boeing. With full load, they never achieved those altitude and hung around a lot lower. While I can't verify it, these forum posters appears to suggest that 19,000ft-28000ft with bombs was more common.

To do the math, the partial pressure of oxygen at sea level is around 0.21 bar. If you're being fed 100% oxygen through your mask, this is the same pressure as at 11,000m.

Photo by Margaret Bourke-White, Sept. 1942, from the LIFE Archives.


Can a Cessna 162 Skycatcher be flown IFR in IMC? This question is similar to these questions:

Are there any LSA aircraft that can be flown IFR in IMC?
What are the FAA requirements for an aircraft to be IFR certified?

Unfortunately I couldn't find a definite answer to the following question:

If a private pilot is instrument-rated, can he/she file an IFR flight plan and fly IFR in IMC in a Cessna 162 (Skycatcher), assuming the C162 is equipped with the optional autopilot? (is it really a requirement to have a functioning autopilot for IFR in IMC?)

As far as I know, the Skycatcher has all the required equipment for IFR, including a "real" Continental engine (unlike most other LSA's using Rotax engines)

Not in the US. The C162's POH says:

  The Model 162 Skycatcher is not equipped or certified for IFR flight

That means that under 14 CFR 91.9 it may not be operated IFR. But, FAA Order 8900.1 allows an exception for aircraft not certified for IFR to be operated under IFR in VMC only:

  A.    IFR Training in Visual Meteorological Conditions (VMC). Instrument flight training may be conducted during VMC in any aircraft
  that meets the equipment requirements of part 91, §§ 91.109, 91.205,
  and, for an airplane operated in controlled airspace under the IFR
  system, §§ 91.411 and 91.413. An aircraft may be operated on an IFR
  flight plan under IFR in VMC, provided the PIC is properly
  certificated to operate the aircraft under IFR. However, if the
  aircraft is not approved for IFR operations under its type
  certificate, or if the appropriate instruments and equipment are not
  installed or are not operative, operations in Instrument
  Meteorological Conditions (IMC) are prohibited. The PIC of such an
  aircraft must cancel the IFR flight plan in use and avoid flight into
  IMC.

An autopilot isn't required for IFR flight in the US (see 14 CFR 91.205(d)) and the question you linked. I didn't check the full equipment list to see which required instruments are missing from the C162, but even with full IFR equipment if it isn't certified for IFR then it can't be operated in IMC per the regulations above.


Why was Energy Maneuverability theory not applied to the F-14? In John Boyd's (declassified) 1966 Energy Maneuverability [PDF] report, studies were done on the F-4 and on the MiG-21 and those studies were applied to the F-15, F-16 and F-18. My questions:

Why wasn't this theory applied to the F-14?
Was this due to the fact that it was a carrier-based aircraft?
Or did it have to do with the variable sweep wings that would change how the energy bleed changed with changes in the sweep angles at different speed?

The F-14 was developed well before the theory of Energy Maneuverability was published, but improvements were made in F-14s till the late 1980s. With the early development of F-15s the Energy Maneuverability theory was utilized to improve its performance but same wasn't done or at least mentioned anywhere.

The Energy Maneuverability theory is primarily a conceptual design framework. Its role is to be a guideline in creating the requirements for your aircraft.

This is something well above the manufacturer's level of responsibility. The requirements are created by the buyer, like the US DoD; the manufacturer's job is to design a machine to meet them, with some leeway. And not all modern fighters are based on the E-M theory.

It's not impossible to use a new design framework if you were doing a Hornet to Super Hornet kind of 'Hollywood remake'. But otherwise, an aircraft is created to do a job, and that general job persists through upgrades. Every design choice is a compromise; to get more of X, you need to lose some of Y. Only with a major technological leap could you fit more of X without that loss.

The F-14's job was to maintain long-range CAP around the CVBG. It needed to detect incoming Soviet aircraft at the longest possible range and intercept them before they could launch their missiles.

The USN had very good reasons to dedicate their top fighter to this role. While the Soviet Navy (VMF) has never been a force the USN had to reckon with, the Soviet Naval Aviation (AVMF) has. Its workhorse was the Tu-22, a supersonic bomber with AS-4 missiles; they're large enough to take out a carrier, and, impacting at Mach 3.5-4.5, outside the realistic capabilities of contemporary SAM, AAM and CIWS to intercept. With a standoff range of over 300 nmi, AVMF bombers would be out of the reach of the Californias at the time of launch. This left CAP essential to carrier survival.

For this job, a fighter needs several things. It needs the range and endurance to patrol far enough from the carrier to help. It needs a powerful long-range radar to spot it before launch. It needs good supersonic speed to have a shot at a Mach 1.8 aircraft. It needs to carry heavy long-range missiles to reach the target.

You'll notice that dogfighting a Mig is not on the list above. It's certainly within the F-14's role, just not as critical as fleet air defense. Attack roles in the 1970s have been mostly filled by Skyhawks, Intruders and Corsairs. The F-14's design, including its swing wing, was a product of its high speed interception requirements, combined with low-speed needs of taking off with limited power and maintaining long patrols.

Even if the E-M theory was fully developed and accepted at the time, it's not likely that following it would have improved the F-14's performance without compromising its primary role. With the end of the Cold War the requirements changed, freeing up the F-14's carrier slots for multiroles with an offensive focus.


Can a modified aircraft be imported and certified in the US? Aircraft can be brought into the US and be made airworthy by FAA standards. What about aircraft legally modified in other countries?

For example, there is a new STC to put a Rotax 912 into Cessna 150s approved by the EASA. Can that STC be made legal in the US even though no similar STC exists here?

If yes, is this just due to relations between the EASA and FAA, or can this be done with aircraft coming from anywhere?

Well, pretty much anything can be given a US airworthiness certificate provided it's not literally falling to pieces.  You could certificate such an aircraft as a Special Airworthiness Certificate in the Experimental category -- Specifically one of:

  Experimental -- Research and Development
  To conduct aircraft operations as a matter of research or to determine if an idea warrants further development.  Typical uses for this certificate include new equipment installations, operating techniques, or new uses for aircraft.

or

  Experimental -- Showing compliance with regulations
  To show compliance to the airworthiness regulations when an applicant has revised the type certificate design data or has applied for a supplemental type certificate or field approval.

If your goal is to ultimately get this aircraft a Standard airworthiness certificate you would probably want the latter, to allow you to conduct test/certification flights in the modified aircraft.
To then get a standard airworthiness certificate things are a bit more murky. You could get a US STC based on the European STC & using this aircraft as the example for conformity inspections and flight testing, but that would require going through the STC process.

The other option would be the 337 process, in which case you are also going to need an A&P mechanic (preferably one with Inspection Authorization) and the cooperation of your local FSDO to approve the modification as a "major alteration" (FAA Form 337 - Instructions here).

As you alluded to in your question, something like installing a Rotax engine in a Cessna 150 is a "Major Modification" that has no "FAA Approved Data" (STC procedure/drawings/etc.) to include with the 337, so you would need to submit "Acceptable Data" for your modification (the European STC is a good starting point) and work with the FAA to obtain approval for the modification.

This is something you would want to talk to the FAA about before purchasing an aircraft with such a modification (there's a good chance they may not approve the modification, which would leave you with an unairworthy aircraft, or one restricted to the Experimental category).


How come the hover efficiency for tiltrotors is better than tiltwings? How do you compare the hover efficiency of tilt-rotor and tilt-wing aircraft? The Wikipedia page Tiltrotor mentions:

Tiltrotors generally have better hover efficiency than tiltwings (...)

But I was expecting just the opposite because of the downward thrust loss due to wing blockage on tilt-rotors.

Your expectation is correct. A tiltwing has a lower drag penalty in hover. The XV-15 had a penalty of 635–680 kg, while a tiltwing would have 23 kg, for the reason you mention.

A tilt-rotor's wing stays horizontal while the nacelles tilt. In the hover, therefore, the wing is in effect a flat plate immersed in the rotor downwash. Kocurek puts the resulting vertical drag penalty on the XV-15 at 635kg-680kg. The similarly sized TW-68's wing tilts with the engines so that its aerofoil always points into the propeller wash. Kocurek estimates the vertical drag penalty at just 23kg.

The sentence on Wikipedia unfortunately lacks the context of the reference (Flight), which is down for maintenance, but the web archive version is available (PDF).

He explains the designer's dilemma: "You want low disc loading to get high hover efficiency, but you want high disc loading to match the propeller to your cruise conditions (...)"

The issue at hand is that tiltwings use propellers, while tiltrotors use, well, rotors – their big size lowers the disc loading, which improves the overall hover efficiency. For more context, a tiltwing was considered for the program that produced the V-22 Osprey. The argument in the article is that a tiltwing would offer an overall better "system" when cruise is considered, "but the long hover times required by some missions favoured a tilt-rotor."

A tiltwing with propellers; source: wikimedia.org

All quotes are from the linked Flight article.


How many plane crashes are prevented by pilots? Statistics about plane accidents consistently show pilot (or other human) error as the leading cause of crashes. With current advances in technology, it is therefore tempting to strive towards replacement of pilots with automated systems. However, I have never seen a tally of how many plane crashes are actually prevented by pilot skill, that would otherwise have resulted in loss of life. Are there any statistics available on this subject?

Any manually-flown landing would meet your requirements. If the pilot does nothing on final approach, the plane will almost certainly come to a fiery end.

Landings that were very, very close to a crash aren't reported all that often - if you made some monumental screwup and managed to salvage it, would you write it up for the FAA? Not many people report almost-car-accidents or red light violations either.


How airplanes of new generation communicate with ATC over remote areas? (North Atlantic Region) How new airplanes get in contact with ATC while flying in remote areas? Do they use VHF datalink (VDL) ?

Planes in the North Atlantic with the latest equipment as you ask would use VDL only within line-of-sight. Otherwise they would use satcom or HFDL (HF data link) for data comms.

(Click for full map) VHF coverage for FL 300, the lower the plane, the smaller the areas.

Data communications will be via CPDLC or ACARS. For voice communications there is also a satcom voice option. There is also ADS-C for tracking, which is mandatory for certain flight levels.

Pilot-to-pilot voice communications to relay information or during emergency is also available on 123.45 and 121.5.

Further reading and source: ICAO NORTH ATLANTIC OPERATIONS AND AIRSPACE MANUAL


What happens to the fuel lines when a jet engine falls off? Going off this question, what happens to the fuel lines to the engine when it falls off? Does it automatically shut off or do the pilots have to manually do it?

Engine separation won't cause automatic closure of valves, but the resulting low pressure will illuminate lights (including the Master Caution light) on the panels and display messages on the displays.

The pilots will have to react to the engine separation, the same way than for an engine fire or severe malfunction. This non normal procedure includes shutting down the fuel line by setting the engine start lever to CUTOFF or triggering the fire bottles on the affected engine.

There is a spar fuel valve (or fuel shutoff valve) fixed to the wing and to the fuel tank, which stays on the wing in case of separation. This valve is to prevent leaks due to a broken line. As the hydraulic power may be missing after the engine damage or separation, the valve is controlled by an electric motor with a backup battery and a double wiring redundancy.

Example on the the B737 NG:

(Shut-off valves framed in purple, source)

Non-Normal checklist used: ENGINE FIRE or Engine Severe Damage or Separation (NNC 8.2 of the Quick Reference Handbook).

(Click to enlarge, source)


What does a fuselage frame structure of a non-pressurized transport aircraft look like? What does a fuselage structure of a non-pressurized transport aircraft look like? I can find loads of examples for pressurized fuselages, but almost nothing for non-pressurized ones. The DHC-5 Buffalo comes to mind, but I can't tell how the fuselage frame is made, e.g.- how the I-beams in the floor are laid out, etc.

A pressurized aircraft structure differs from non-pressurised in that the fuselage center area, including the cabin and baggage compartments, are built as a pressure vessel.

Except for:

strengthened frame and windows
forward and aft pressure bulkheads
pressurization systems

the aircraft structure and design not related to the pressure vessel (like the floor) remain unchanged.

There are many examples of non-transport civil aircraft that have pressurised and non-pressurized versions.  For example, a Beechcraft "P-Baron" or a Cessna P210 Pressurized Centurion has smaller windows and different cabin doors you can easily observe.  Yet, the design principles of the aircraft structure, besides beefing up the pressurized areas remain the same.

Most non-pressurized transport aircraft are utility or military in nature, as is the DeHavilland aircraft you mentioned.  Design considerations for these aircraft, like the floor you mentioned, are related to their mission, not pressurization.  That is, unless the floor itself is a pressure vessel wall.


Is there a 3-dimensional airspace viewer? I am using SkyVector to have an idea of what the airspace looks like in terms of waypoints and airways.

I was wandering if anybody knows a website that displays such information but in 3D (or 3D + time) in order to navigate through the airways and check out some information as viable flight levels or altitude constraints.

I am imaging of a website/software that allows to navigate like on google earth or cesium and see what the airspace is like (qualitatively at least).

You can download Google Earth airspace files for most countries, and move through them in 3D to explore what they would look like for various areas.  For example, you could see where you would be "under" a Class B shelf, or where you might navigate to avoid B/C/D airspace and "surface airport E airspace" (if you're flying an ultralight, for example).

These files can be downloaded from 3dairspace.org.uk

Here is a screenshot I just captured of the Seattle Class B, looking northwest from the southeast corner.


Was wood used in the construction of the TU-144? This image the Yegoryevsk crash of the TU-144 CCCP-77111 appears to show a part of the wreck made of wood:

(picture source)
The inside looks like wood slats with rafters. Wood is sometimes used in airplane construction and has pretty good constructive properties, so I don't want to dismiss the idea a priori as crazy. Was it the case?

You're looking at a typical metal wing's innards with stringers (small lateral stiffeners made from aluminum angle) riveted to aluminum sheet, and the remnants of wing ribs also attached.  The colour is zinc-chromate primer which ranges in colour from bright green (epoxy zinc chromate), to olive drab, to, that that case, yellow/brown.
There is no wood there.  If any wood can be found in an airplane like the  TU-144, it will be in the interior finishings or panels, or possibly internal bits or fittings that are usually made from plastic, say like a saddle that holds some kind of cylinder in place (in lieu of a plastic or rubber material).  But as far as that picture is concerned, you are definetely looking at metal.


How can I tell a GPS installation is acceptable for IFR use? I am evaluating an aircraft for use under IFR.  I want to know if the GPS that is installed is acceptable for use under IFR.  I have access to the logbooks and documentation.  I want to check:

That the GPS unit itself is acceptable
If the installation is acceptable
If the database is current

Operational considerations and limitations may be discussed, but are secondary to the scope of this question.  Citations to the AIM and AC 20-138 should be in a bulletized summary.

The easiest way is to read the Aircraft Flight Manual (AFM) or Aircraft Flight Manual Supplement (AFMS). If the the GPS was installed at the factory, it will be addressed in the AFM. If it was installed later via an Supplemental Type Certificate (STC), there must be an AFMS to cover the operation of the GPS.

If the GPS installation was not at the factory, there should be an a/c logbook entry showing the installation and STC approval.

As specified in AC 20-138D:

  19-9. Operations manual or AFMS/RFMS.

  An AFMS/RFMS must be provided that contains the limitations and
  operating procedures applicable to the installed equipment
  configuration. The AFMS/RFMS must address the operation of the
  equipment and the related components as they are installed (e.g.,
  remote source selector). An AFM/RFM supplement is required if the
  installation is based on a prior approval that had an AFM/RFM, or if
  there are any limitations associated with the operation of the
  equipment.

The key information is covered by the first sentence -- limitations and operating procedures. If the GPS is not approved for IFR, there must be an operation limitation in the AFM/AFMS that states that (and in all of these cases I've seen, the FAA also required a placard stating "GPS not approved for IFR flight.")

If the information is not included in the AFM or AFMS, I would question the approval of the installation as all installations require the AFM/AFMS.

As for the database, it expires every 28 days. Turn the GPS on. If the database is not present or expired, you will get a message to that effect.


What is different between a Cat IIIA, Cat IIIB, and Cat IIIC ILS approach? In terms of aircraft equipment, approach minimums, procedural differences, and anything else relevant, how do the 3 types of a Cat III ILS differ from one another?

ICAO and FAA CAT III definitions

A CAT III operation is a precision approach at lower than CAT II minima. Sub-categories are listed below.

A category III A approach is a precision instrument approach and landing
with no decision height or a decision height lower than 100ft (30m) and a runway
visual range not less than 700ft (200m).
A category III B approach is a precision approach and landing with no
decision height or a decision height lower than 50ft (15m) and a runway visual
range less than 700ft (200m), but not less than 150ft (50m).
A category III C approach is a precision approach and landing with no
decision height and no runway visual range limitation.

*I've omitted the JAA definitions.

Source Airbus Flight Operations Support documentation.

FAA Reference Material

The below links are to comprehensive FAA publications covering the areas as titled.

FAA AC120-29 for CAT I/II.

FAA AC120-28 for CAT III.

Thanks @Sports Racer for the comment with links to these documents.


What are autothrust and manual thrust on an A320 (or other aircraft)? The accident report on the A319 G-EUOE incident in May 2013 mentions "manual thrust", and implies that using it is very unusual.

The autothrust system failed, requiring the use of manual thrust:

  The autothrust system cannot operate  in N1 mode and so was
  unavailable for the remainder of the flight, which was  flown using
  manual thrust

But the pilot hadn't used manual thrust outside a sim session for seven years (and the co-pilot had never used it outside the sim):

  The commander informed the AAIB that, excluding simulator training, he
  had  last flown the A320-series aircraft using manual thrust seven
  years before the accident

That implies that autothrust is always used in normal operations, and manual thrust is an emergency backup only. What exactly are autothrust and manual thrust and why is using manual thrust so unusual?

Manual thrust means that the engine thrust corresponds directly to the position of the thrust lever.

Autothrust means that a target speed is dialed into the system (using a knob that is usually located on the glare-shield) and the auto-thrust system automatically adjusts the engines to maintain that speed.

Now in an aircraft with classical controls the longitudinal stability means the aircraft tends to maintain speed with pitch and pilots basically need to use thrust to climb or descend and yoke to adjust speed, always making adjustments with the other control as well to avoid oscillations and compensate for the more complex parts of the power-pitch relationship.

Due to this, it is usually recommended to fly either fully manual or fully automatic (autopilot+autothrust).

But Airbus A320 and newer (A319 is just a variant of A320) changes that with the artificial neutral stability in normal control law. Even with autopilot off, the flight computer automatically adjusts trim so that the aircraft flies straight so that adding power makes the aircraft accelerate and reducing it makes it decelerate. However pushing the stick forward to descend will still make the aircraft accelerate and pulling it to climb will make it slow down.

Due to this, Aibrbus aircraft are easier to fly with autothrust always on (except for take-off roll; autothrust is disabled when the power levers are advanced above certain position, which is only done for take-off and in emergency where extra power is needed).


Will the ATC be in constant communication with aircraft? When a passenger aircraft travels at higher altitudes will it be in constant touch with air traffic controller?

Are the altitudes or flight levels assigned by ATC or does the pilot file them as part of flight plan?

While flying over regions with no radio communication, how does one ensure that there are no other aircraft nearby?

Generally speaking airliners are always able to be in contact with ATC, either by VHF (regular radio), HF (usable over longer distances, e.g. on oceanic crossings), or satellite communication (possibly relayed through their company dispatch). It is also possible for one aircraft to relay messages for another (for example if one aircraft's HF radio has failed they may contact a nearby aircraft on VHF to relay messages to ATC).

Because they can usually talk to ATC even when they are out of radar contact airliners can and will provide position reports, and ATC updates their position information the old fashioned way (which we talked about over here). The controllers can then assign altitudes, speeds, and headings/routes in such a way that no two aircraft attempt to occupy the same piece of sky at the same time.  (This is generally the way oceanic routes are handled. There are also air-to-air frequencies for aircraft flying these routes so they can coordinate with each other if necessary.)

In the event an aircraft is out of contact with ATC - whether through a radio blind spot, an equipment failure, or for some other reason - they rely on a combination of lost communication procedures (here's a quick reference from the FAA) and "see-and-avoid" (if you see another aircraft avoid hitting it) until contact can be re-established.
The use of standard lost communication procedures also allow the controllers to continue updating the aircraft's position in a non-radar environment (they can estimate progress based on the standard procedures and the aircraft's prior position reports/speed/wind data). A larger block of airspace will be reserved in such situations to account for any error.


Does engine failure shut off the auto-pilot? After answering this question it got me wondering whether there can be a situation where a complete flameout of engines could cause a serious loss of control if the auto-pilot were to continue to try to maintain altitude despite the loss of power. If it did, presumably by raising the nose and losing air-speed, eventually the aircraft would enter a stall.

Which raises the question, does the auto-pilot automatically shut off in the event of engine failure? Though I suppose it depends on the auto-pilot and the aircraft model.

I do realize the pilot and co-pilot should be very aware something is awry, but I can also see them being rather busy trying to figure out what all the alarms are telling them, and or trying to restart the engines and not notice the AP is setting them up for disaster.

No, there is no necessary connection between the autopilot and an engine failing on any aircraft that I'm aware of -- which is far from all of them!  If you're in an idle descent, one motor failing wouldn't really change the flight characteristics of the aircraft, so in that case there's no great need to get rid of the autopilot.  Also, once you have everything trimmed up (i.e. rudder trim in to balance the asymmetric thrust), it's nice to put the autopilot on to let it keep the wings level & hold altitude for you while the pilots sort out everything that comes next -- checklists, ATC coordination, choosing where you'll land, etc.

What DOES come off almost immediately after engine failure, at least on the 737, is the Autothrottle.  It will sense that the thrust and throttle position are mismatched, and rather than moving the good throttle around when you may not be ready to compensate with the rudder, it disengages.  I'm not certain if that is universally true; the 777 computers are crazy smart, and they may actually leave the A/T engaged in that sort of a scenario (while the A/P flies the rudder for you).

The basic challenge that you mention, an autopilot that will hold altitude even when the thrust is insufficient to maintain airspeed, is a scenario that's not limited to an engine failure.  The automation will have some set of rules as far as when to hold, when to go into reversion modes, and so forth.  And if you get caught in the wrong spot, the automation can bite you.  In the 737, for instance, if you're in altitude hold or glideslope capture, the autopilot will hold that no matter how badly the speed decays. (Stall while on glide path, or follow the speed cursor into the dirt short of the runway... damned if you do, damned if you don't!)  On the other hand, if you're in a vertical speed mode or a VNAV climb or descent, there are speed reversions that will change your flightpath rather than accepting a speed above or below safe limits. If everything has been set up correctly and the Autothrottle is engaged (or the pilot is setting the power appropriately), then everything works really well.  But if enough things go wrong and you aren't paying attention... well, that's when bad things can happen.


Is it legal to give flight instruction in my own airplane without 100 hour inspection if doing it for no charge? 14 CFR §91.409(b) states

  ...no person may give flight instruction for hire in an aircraft which
  that person provides, unless within the preceding 100 hours of time in
  service the aircraft has received an annual or 100-hour inspection and
  been approved for return to service in accordance with part 43 of this
  chapter or has received an inspection for the issuance of an
  airworthiness certificate in accordance with part 21 of this chapter.

What if I want to give instruction to a friend or family and they are not paying me to do it? Would I be exempt from having to do a 100 hour inspection?

I agree with acpilot that if you're merely renting the plane to this pilot then no 100hr is required. Rentals are not "for hire" operations.

I do that with a Cherokee that I rent out. I don’t provide the CFI and I do not fly it for others. Several students have taken their practical tests in the plane and I made sure they could explain the FAR to the DPE and they had no problems.

As several commenters have stated, it gets tricky when you own the plane and provide instruction. The FAA considers lots of things as compensation that you and I would not. Goodwill, logging flight time, paying for gas, or even paying for lunch or a beer.

I found a clarification letter from the FAA at Aviation Banter.
http://www.aviationbanter.com/showthread.php?t=11563&page=2

May 3, 1984
Mr. Perry Rackers
Jefferson City Flying Service

Dear Mr. Rackers
This is in reply to your request of May 1, 1984, that we render an opinion regarding the applicability
of the 100-hour inspections requirement of Section 91.169(b) of the Federal Aviation Regulations to rental aircraft.
Section 91.169(b) of the Federal Aviation Regulations provides that, except as noted in Section 91.169(c),
a person may not operate an aircraft carrying any person, other than a crewmember, for hire, and may
not give flight instruction for hire in an aircraft which that person provides unless, within the previous 100
hours of time in service, the aircraft has received either an annual or a 100-hour inspection.
If a person merely leases or rents an aircraft to another person and does not provide the pilot, that
aircraft is not required by Section 91.169(b) of the Federal Aviation Regulations to have a 100-hour i
nspection. As noted above, the 100-hour inspection is required only when the aircraft is carrying a
person for hire, or when a person is providing flight instruction for hire, in their own aircraft.
If there are any questions, please advise us.

Sincerely,
/s/
Joseph T. Brennan
Associate Regional Counsel

One correction to acpilot about the 100 hours. Once you start renting for hire, you need to do an inspection every 100 hours. The clock doesn’t restart every time you do the inspection or annual. You are allowed a little leeway to ferry the plane to the inspector, but you don’t reset the clock.
The 100-hour limitation may be exceeded by not more than 10 hours while en route to reach a place where the inspection can be done. The excess time used to reach a place where the inspection can be done must be included in computing the next 100 hours of time in service.


What are the minimum hours required for private instrument fixed-wing plus commercial helicopter? I want to get my private pilot plus instrument rating in fixed-wing aircraft for personal use. In addition to that I want to get my private and commercial in helicopters to start a career in flying helicopters.

Does my flight time accumulated in both fixed wing and rotorcraft count towards my commercial rating? As in: 40 hours fixed private, then 40 hours fixed instrument. Then 30 hours helicopter private and 30 more hours for the commercial rating? That would come out to a total of 140 hours. All I would have to have would be 10 additional hours of flight time to qualify for my commercial.

I get that not everyone finishes in the minimum hours on everything, but that aside, am I reading the rules correctly? Or would it be 150 hours in helicopters only?

The 150 hours is flight time which is not category or class specific so hours in both airplanes and helicopters would count towards the 150 hours.  You are missing an instrument helicopter rating.  It is in addition to the instrument airplane rating.

Below I try to sum up the minimum hours required for each certificate and rating if obtained under Part 61.  Part 141 schools require different hours.  You actual experience will vary considerably.  I would first get a private pilot airplane and helicopter certificate and then work on the instrument ratings concurrently.  Afterwards, work towards the commercial helicopter rating.

To get a private ASEL certificate:  You need a total of 40 hours
flying time to that meets 61.109 experience.
To get an private helicopter certificate addon:  An additional 30
hours of training is required.  You will already have more than 40
hours total time.  Total time at this point would be 70 hours minimum plus the flight time for the practical tests.
To get an instrument rating for both airplane and helicopter: You will need 50 hours of PIC cross country time plus 40 hours of simulated or instrument time.  The 3 hrs simulated time required by the PP ASEL should count towards that 40 hours.  You must have at least 15 hours each with a CFII in both airplane and helicopter (total 30) and if they are all cross country flights that will help your cause.  You already started with a minimum of 8 XC PIC hours from your private certificates.  The remaining 12 hours along with 7 hours of simulated time can be accumulated in either airplane or helicopter.  Total time up to this point should be 120 hours plus the flight time for the instrument rating practical tests.
To get a commercial helicopter certificate:  A total of 150 hours total time (all the above counts) and 50 hours of helicopter time.  (You should already have 45).  35 hours of PIC helicopter time (Already have 20) to include 20 hours of training on commercial maneuvers, 10 hours solo and 10 hours of helicopter cross country time.  The way I see it, is the commercial will add an additional 30 hours to your total time giving you exactly 150 hours.


How to choose the right ILS when the runway has more than one? I'm wondering how is the right choose when an runway has ILS x, Y, Z. What should I consider in order to pick one of those for landing?

When an airport has multiple ILS approaches to the same runway (usually labelled ILS-Z, ILS-Y, ILS-X, ...), they all end up using the same ILS for that runway, but they differ in how you fly the approach until final.

Consider e.g. KTUP, which has an ILS-Y and ILS-Z approach to runway 36. Here is the chart for the ILS-Y:

(source)

This ILS approach starts at an RNAV waypoint GAGYE and therefore lists "RNAV 1-GSP required" as a requirement. The ILS-Z approach looks completely different:

(source)

This ILS approach has two IAFs: CEVSI on the OTB 12-DME arc and the VERON NDB. It therefore lists "ADF or DME required" as a requirement.

So, which one should you choose?

During flight planning, you should plan to use the approach that best fits your aircraft's equipment. If your aircraft does not have ADF or DME installed, ILS-Z in the example above would not be possible. On the other hand, if your aircraft is not RNAV approved, you cannot fly the ILS-Y. If you can do both, then file a route that ends up at whatever IAF works best for you.
During the flight, it should be clear which approach you should fly based on which waypoint you end up at. In the example above, if had filed a route to the VERON NDB, then you would fly the ILS-Z. If you filed a route to a beginning of a STAR, then you fly the matching approach from the last waypoint of the STAR (KTUP in my example does not have STARs, but other airports with multiple ILS approaches might). This would usually be the RNAV variant, since most STARs are RNAV anyway.
If still multiple approaches are possible, ATC should clear you for one in particular, e.g. via "Cessna 12345, cleared ILS Yankee approach runway 36".


How does the Coanda effect help some aircraft produce more lift? How exactly does the Coanda effect affect the air stream on the wing of, e.g., an AN-72?

The Coanda effect makes an air stream flow on the curved (outboard) surface object which it has produced from there. How does it help produce lift?

According to Wikipedia, the Coandă effect causes the airflow over the top of the wing to "stick" to the upper surface of the wing and continue to hug the wing surface even as said surface curves downwards.  In normal flight, the airflow remains attached to the wing surface all the way to the trailing edge of the wing; as the upper surface of the wing's trailing edge (and, for that matter, generally the lower surface as well) is angled downward, the airflow over the wing is travelling downwards when it leaves the trailing edge, which, as per Newton's third law, produces an upwards force on the wing (and, thus, the aircraft), which we know as lift.  The An-72's overwing engine placement increases lift at low airspeeds because it causes the engine exhausts to blow over the top of the wing; the high-speed exhaust sticks to the upper surface of the wing thanx to the Coandă effect, and is thereby ultimately deflected downwards by the downwards curvature of the rear portion wing's upper surface, producing good lift even at low airspeeds.

A simple way to think about it would be that the An-72's engines blow air and hot gas downwards as well as backwards, but, instead of doing so via traditional ducting, they blow air downwards by blowing it over the top of the wing and allowing it to stick to the upper surface of the wing and follow said surface down.

Note that this is not the only, or even necessarily the primary, mechanism by which aircraft generate lift; it just happens to be the mechanism that is enhanced by the An-72's engine placement.


What is the easiest way for a new private pilot to visit Manhattan? As a goal, I would like to:

Limit the difficulty of the class B airspace by staying at uncrowded areas
Minimize the time it takes to get into the city

All of NYC's airspace is crowded, so there's no escaping that! :) The controllers are very friendly and accommodating though, so don't be afraid. If they're curt, it's just to keep everyone safe. As for airports, there are 4 GA airport options you're most likely gonna consider:

KLDJ in Linden, NJ. It's a 5m cab ride to the train station into the city. Uncontrolled field, tons of news helicopters based here. It's pretty cheap (around $20/night if I recall) and fairly convenient, but the uncontrolled field is under an 800' Class B shelf at Newark and could be stressful. Expect very bare bones facilities - you can get fuel, but there's no terminal building to speak of.
KTEB in Teterboro, NJ is the GA airport for most jets that come into the city. It's the closest airport to midtown, and you'll pay a very pretty penny here, tie-downs are at least \$50/night, and fuel will be around \$9/gallon. This is a hectic option, but it has a tower and is close to the city, so for a quick overnight stop without fuel it may be the best option. Expect to be the only piston on the ramp.
KFRG in Farmingdale, NY (Long Island). Very busy GA airport abuzz with training. Pretty cheap (~$15/night tiedowns), but did I mention that it's busy? You may burn up 1h of hobbes time on the ground waiting to take off if you depart during peak times. You can catch a cab to LIRR which will get you into the city.
KHPN, in White Plains, NY. Mix of GA, training, and a couple commercial carriers like JetBlue. Prety cheap ($~20/night tiedowns) and a short hop away from Metro-North which will have you in the city in about 30 minutes. Controlled field, at 2500' below the Class B shelf. Fairly busy, but certainly managable with the top notch controllers working NY's airspace.

Whichever airport you choose to go to, absolutely get flight following or file IFR. All of the towers in the area expect you to be handed off from NY Approach and will not be happy if you call them directly out of the blue.


How often does evacuation happen as shown during the pre-flight safety videos/stewardess instructions? I believe it is mandatory for airlines to provide passengers with information about evacuation in case of emergencies. However, pretty much every accident I've ever heard off either happens at the airport (where normal exit routes are available) or in the middle of nowhere (where no passenger makes it out alive).

Is there any statistics on how often do "normal" evacuations happen among Western airlines? The only example I can think off is the Hudson landing of US Airways Flight 1549.

I didn't do statistics, but The Aviation Herald lists units to low tens a year worldwide.

Most of them happen at airport due to fire indication (sometimes even false) or smoke on board.

On the ground, fire spreads a lot faster than while flying, because when flying, the wind is too strong and blowing the flames off. The most notable example would be China Airlines B738 at Okinawa on Aug. 20th 2007, airplane in flames arriving at stand. The aircraft was already at the gate when the flames were first noticed, evacuation was immediately initiated and by the time everybody left, it was already engulfed in flames, about 3 minutes after the fire started. While China Air might not be "western" in strict sense of the world, it is largest airline on Taiwan and follows the same standards.

Another notable accident is Egyptair B772 at Cairo on Jul 29th 2011, cockpit fire.

Here are some recent evacuations mentioned on AvHerald:

Air France B773 at Paris on Jul 28th 2013, evacuation while boarding due to fumes
US Airways B752 at Kona on Jun 8th 2013, evacuation during push back causes 4 injuries
PSA CRJ2 near Philadelphia on Apr 17th 2013, smoke on board, evacuation
Easyjet A319 at Belfast on Jan 6th 2011, taxiway de-icing prompts evacuation

Notice, that they are all smoke or fire events. For some other reasons, see e.g.:

Wizz A320 at Rome on Jun 8th 2013, left main gear did not extend
Alitalia A320 at Rome on Sep 29th 2013, right main gear did not extend

two similar accidents where both aircraft were evacuated via slides. The reason in these, and many other gear collapse incidents, is that they don't want to wait in a damaged plane where there is a risk of fire, plus the difficulty of getting stairs to the aircraft resting in strange attitude.


Why is the DC10/MD11 center engine placed where it is? While reading this question about trijets I started wondering why the center engine in the DC10 and MD11 where placed where they are. Most trijets have the center engine at the very back of the fuselage with the intake in front of the vertical stabilizer. The DC10/MD11 engine is placed above the fuselage at the bottom of the vertical stab.

I'm wondering if there is some advantage to that. Does placing the engine there create an appreciable pitch down moment? And how would that relate to the pitch up moment of the underwing engines? Are there any other aircraft that have this configuration?

There are a few ways the aircraft engines can be mounted on the centerline, each with its advantages and disadvantages.

Image from Stanford University.

One way is to mount them as in DC10, with engine above the fuselage; another one is to use a 'S' shaped inlet and put the engine at the aft of the fuselage like Dassault Falcon 7X.

The main advantage of mounting the engine as in DC10 is that the inlet distortion is minimized and there is no need to cut a hole through the fuselage for putting engine. The main disadvantages are that it increases drag (slightly) and engine maintenance is a mess.

Apparently,the DC10 engineers tried to put all three engines in the wing during design, but were not successful.

Engines mounted in high thrust line like DC10 and Piper PA47 are highly stabilizing as increase in engine thrust causes a pitch down motion as the thrust is increased. This is usually disconcerting to the pilots, who expect the aircraft to pitch up while engine power is increased.

Finally they ended up adding design changes to correct this in PA47 (to make it pitch neutral).

In DC10, a combination of underwing and high thrust line engines would've most probably caused no pitch changes at all. So I guess the main advantage is reducing inlet distortion.

As MD11 was developed from DC10, it simply inherited this design.

Note: As for the pitch down moment being disconcerting to the pilots, it is better if someone corroborates it. It is simply that most aircraft don't do this.


Why do some airlines operate fleets so diversified? When you have a look at the fleets from big airlines like United, Delta, Lufthansa, BA, AF, etc. it seems that they have almost every model Boeing and Airbus released in their fleet. And my question is, why?

What I assume is that such a big variety would increase the costs for maintenance, training, etc.

Thus, for example, why use the A330 as well as the 777? Why operate both the A320 and 737?

For me as a passenger it is comfortable because I like to test and review different aircraft; but for these airlines' Operations divisions it must be horrible!

I know there are probably reasons to do so otherwise they would not have this variety. What are these reasons?

There are two philosophies for fleet selection:

One type / model or one manufacturer approach
Multi manufacturer divide and conquer approach

First of all, a single model fleet is only possible for airlines that operate on sectors of comparable length. You can't do intercontinental and regional flights with the same aircraft model efficiently.

As you observe, there are obviously costs associated with flying different types of aircraft. A single type fleet like for example Ryanair (B738), Southwest (B73*) and Easyjet (A320 family) operate, means the cost of maintenance, training, etc can be kept low. Adding a few aircraft of another type to the fleet would mean additional tools in stock, diversified training and a separate flight crew group and lots of other cost factors.

Aircraft manufacturers know that too. So if you need another 10 - 20 aircraft, your standard supplier will ask a high price for this fleet extension, knowing that the competition is never able to put in a compelling offer when all additional cost are taken into account. Only if the batch size is large enough the competitor might be able to offset the additional costs with a unit discount.

That is where the mixed fleet operator has an advantage. Since the additional overhead costs of a couple extra aircraft from type A or B are minimal, they have a better position while negotiating with the manufacturers.

Single manufacturer airlines usually order aircraft in large numbers, otherwise they would not get a proper deal; multi type airlines can order aircraft in lower numbers.

And then there are politics. Sometimes a national airline will be subjected to political pressure to buy from a certain manufacturer. This is especially the case for airlines operating in the international / intercontinental market. The extra fleet cost incurred will be (partially) offset by deals in another field.


Is it "cutting off" in the pattern when I go before a plane that is going faster than I am but let me in first? While turning from the 45˚ to the downwind leg for a downwind pattern landing in a Cessna 182, a Cheyenne was calling 5 miles out on a GPS approach for a straight in landing.  Clear day, both flying VFR, uncontrolled airport.  He and I had been communicating for 5-6 minutes, and I called my base turn knowing I had entered the pattern well ahead of him and had time to land ahead of him.  The Cheyenne pilot acknowledged me and was good with this.

Seconds before I touched down, I heard from a pilot evidently taxiing to take off from the same runway, "Dude ... you just cut off that Cheyenne ... you realize he's going about 4 times faster than you."

Now aside from his ignorance by not hearing the leadup conversation to our opposite direction approaches, when is a plane in a straight-on landing considered to have the right of way over one "in the pattern" and when, apart from communicating between pilots, is it proper regulation to land ahead, vs. extending the downwind leg and falling in behind him?

I was specifically trained that until you are within 4 miles, you are technically not on "final" during a straight-in approach ... but that common sense must prevail, so even if you reach the pattern first, it may be courteous and safer to allow a faster aircraft in ahead of you.

The Cheyenne would have been "cutting you off", if he hadn't worked it out with the aircraft in the pattern and maintained visual separation.

According to the AIM, 4-3-3, standard pattern entry at an uncontrolled airport is abeam the midpoint in the downwind.

  Enter pattern in level flight, abeam the midpoint of the runway, at pattern altitude. (1,000’ AGL is recommended pattern altitude unless established otherwise. . .)

http://www.faraim.org/aim/aim-4-03-14-189.html


What's preventing aircraft manufacturers to record every single possible value in FDRs? The preliminary report of the ET302 crash included some data from the Flight Data Recorder. However, the position of the trim cutoff switches is apparently not among the recorded values.

Given that storage is so incredibly cheap nowadays compared to the price range of an aircraft, why don't manufacturers decide to record every single possible sensor value (including all switches in the cockpit) into Flight Data Recorders? Is this a purely economic decision to not do too much more than required by regulations? Or is there some other reason for it?

I'm not an expert on FDRs, but I do have experience of hardware and software development in a regulated market (medical devices), so might be able to offer some insight.  Here are a few considerations that occur to me:

Development cost:  Adding storage to a FDR isn't like installing new DIMMs in your workstation.  As well as the design work, the changed device must undergo new verification and validation cycles, the supply of the new components needs to be assured, and the manufacturer must continue to support existing products as well as a new one.  The V&V may well include accelerated-life testing and other expensive activities; it's unlikely to be just a few days' work.
Customer demand: Aircraft operators require an FDR that satisfies regulatory requirements; it's a "tick-box item".  Consequently, that's the requirement that aircraft manufacturers demand of their FDR suppliers.  If there's no demand for extra storage (either for an extended loop time or for a greater number of sensor inputs), then there's no money to be made by offering that as a feature.
Interface limits: I don't know enough about FDRs specifically, but the input interfaces may well have a bandwidth limit which precludes providing more readings without providing further connectors (which then has a big impact on development costs; see above).