Who is the third pilot in this Qantas Airbus 380 long haul flight? In the documentary, Secret Life of the Long Haul Flight (2017), we get a look at a long haul Qantas flight from London to Sydney.

One of the scenes shows the flight deck with three pilots (at least their epaulettes have chevrons on them). What is the third pilot in the middle doing? Just hanging out? If he's on rest, shouldn't he be in the rest quarters and not on deck?

The two stripes on his shoulders indicate he is a Second Officer. They are fully qualified pilots but only act as cruise relief pilots on long flights. New Qantas pilots are  initially employed as a Second Officer.

It is standard practice to have all pilots in the cockpit for takeoff and landing. Their role in these periods is pretty much to just keep an eye on everything in case the other two miss something. Some time after the aircraft reaches cruising altitude one of the pilots will start their break and the second officer will take over.


Do any airbridges move vertically to match arrival/departure halls? One of the things that always baffles me is that airports almost always have the arrivals and departures sections on different levels, but that you exit the aircraft into the departures hall. In some airports this leads to long walks along labyrinthine corridors to customs.

Now it seems to me that one could easily raise and lower the other end of the bridge to match the hall being used. Domestic flights could exit directly onto the arrivals level, and international to the customs. Yes, this would increase the complexity of the bridges, but much less than the reduction in complexity of the rest of the airport layout while eliminating many escalators and elevators.

Does anyone know an airport that does something like this?

JFK's Terminal 7 (British Airways Terminal) had (no more) some gates with this feature. The terminal-side of the bridge moved vertically down for disembarkation, and up for boarding. You can see a photo in this post on flyertalk.com. Below is a comparison for the old/new systems:


What is this 'ball' in front of the cockpit of some fighters, e.g., an Su-57? What is the lump/ball thing visible below and to the left of the canopy in this image of a PAK FA (which became the Sukhoi Su-57), and what is it for? It's also seen on other fighters.

Image source

That is the infrared search and track (IRST). This particular model of an IRST is known as the OLS-50M in Russia and uses quantum well photodetectors.

Radar has two serious limitations, one is that advanced software can jam it, the other is that you give away your position when transmitting radar signals.

An infra-red sensor can be used to find and destroy targets without giving away the position of the aircraft and cannot be jammed. IRST is especially effective at detecting low-flying vehicles like helicopters that would otherwise be lost against a background. IRST can also be used to find, hunt down and kill ground vehicles.


Where is the taxiway between the Boeing factory and Paine Field airport? How do the Boeing aircraft taxi to Paine Field (KPAE) from the Everett Factory? It looks like a 'road' connecting the airport and the factory. Do they use this?

That "road" is in fact a taxilane, and marked as such on the Paine Field side (note the yellow lead lines marked at the bottom of the image below, you would find on a taxiway). It connects the Boeing plant to Paine Field's "Boeing Ramp" where final prep can be completed before the aircraft are flown off to wherever they're going.

The terminology is important here: The bridge acts as a taxilane (a non-movement area not under the control of ATC which connects various aircraft parking areas to the taxiways). Boeing coordinates their own movements between the main plant (north) and Paine Field's Boeing Ramp (south). (The bridge is also not depicted on the airport diagram and may not even have "taxilane" status - as far as ATC is concerned. It's just sort of "there".)


How does an eILS improve throughput (for the A380)? While researching where Heathrow's MLS approachs had gone, the only thing I could find is a topic on Heathrow's new eILS (enhanced ILS). As of the topic's date (Aug 2015) it seems eILS is only available in Heathrow and Zurich (at least for Europe).

While researching what eILS is (was not easy), I found this IATA presentation from 2017 that discusses it. It mentions the following:

  Ability to handle multiple A380s in Wide Area of the DLSA (currently only 1) and retain ILS usage, as no DLSA.

And it shows a diagram that I don't really understand:

I tried to search for ILS DLSA (Dynamic Localiser Sensitive Area), but I couldn't find anything. So, how does eILS do its thing?

The bigger the aircraft, the more disturbance it creates to the ILS signal while moving on the runway (or TWY). Therefore airports have static and dynamic ILS sensitive areas to assure the validity of ILS signal. The eILS has smaller dynamic localizer sensitive areas, and aircraft (A380 in this case) will vacate this area in less time, enabling reduced separation and increasing throughput.

A little something about ILS critical and sensitive areas: Determination of ILS Critical and Sensitive Areas - icasc (.pps)


How could the B-29 bomber back up under its own power? I was watching some footage of the Enola gay

I was interested in the part where the plane was backing up over the bomb (starts around 18:27). It appears to be doing this under its own power with the propellers running. Could the B-29 reverse some propellers to do this?

Some B-29s had reversible pitch propellers. All the B-29s used for the Atomic bomb missions had reversible pitch propellers.

Wikipedia B-29 Variants

  Moreover, engine packages changed; including the type of propellers and range of the variable pitch. A notable example were the eventual 65 airframes (up to 1947's end) for the Silverplate and successor-name "Saddletree" specifications; built for the Manhattan Project with Curtiss Electric reversible pitch propellers.

Army Air Forces tests reversible propellers for B-29 bomber


Why circle an airport after takeoff? (SLC particularly) I left SLC (Salt Lake City) this morning heading to MCO (Orlando). On previous flights, I remember takeoff similar to other airports. We got in the air, gained altitude, and moved to our heading and left.

This time though, we seemed to circle for a while, gaining altitude. I initially assumed it was to gain enough altitude to clear the surrounding mountain. I ruled out equipment problems because we kept climbing.

Pilots who have experience with SLC, is there a certain runway that needs this altitude gain due to the terrain? Would there be another possible reason this happened?

I would assume it was to avoid terrain, traffic and/or the restricted airspace close to the airport, but there is at least one departure procedure from KSLC that calls for a climb in the hold. The SALT LAKE TWO departure includes this:

  Continue climb in TCH VORTAC holding pattern (hold south, left turn,
  341° inbound)

And several other departure procedures call for climbing right or left turns; combined with a few ATC vectors that could easily give the impression of circling.

You might try looking for the actual radar track online if you search flightaware.com or a similar site for your flight. That would let you see what track you really flew.


How different is flying through Free Route Airspace (FRA)? I understand the flight planning and ATC aspects of Free Route Airspace. I'm trying to understand what a pilot does differently while flying in an FRA. Are there changes to standard procedures while transitioning from ATS routes to FRAs and vice-versa?

How does the pilot handle deviations/re-routing from a planned route (typically a straight line between the chosen Entry and Exit points), especially when this can pose risks of conflicting with routes of other aircraft flying in the FRA?

Short answer: We do nothing differently in the cockpit when flying in a FRA. The route segments are filed as a long direct and simply flown like that.
As ususal conflict prevention/solving lies with the controller. Only short term conflict solving lies with the cockpit crew (think TCAS RA). In a FRA this is nothing different. In a "regular" airspace with airways and waypoints the problem is the same. Only are your conflict hotspots concentrated on waypoints where you have crossing or converging airways.  This presents similar problems to the controller.
The FRA I mostly fly through is in south-east Europe (Vienna, Ljubljana, Bratislava and Budapest FIRs). Often the Austrian controller clears us from our western entry point on a direct all the way to the eastern exit point of the adjacent Budapest FIR. So there is some trans-national coordination going on in the background.
From the Eurocontrol Free Route Airspace FAQs:

Have ANSPs developed strategies to mitigate the potentially more
difficult detection of conflicts that comes with FRA implementation?
[...] ATC systems across Europe [...] include conflict detection tools
[...] using aircraft trajectories calculated by the ground system which
are updated in real time as a flight progresses.  [...]  The tools help
controllers identify conflicts well in advance of them occurring [...].
At the same time, the implementation of Free Route Airspace generates a
much better spread of conflicts compared to the concentration of
conflicts generated by the fixed route network.

source: http://www.eurocontrol.int/articles/free-route-airspace, omissions by me
Route deviations from cockpit side (to avoid weather for example) are handled like everywhere else. Ask the controller for an avoidance heading and you're good to go. Possible arising conflicts are then solved by the controller. Same works for conflict mitigation from controller side. You might get a heading until clear of conflicting traffic and then a direct clearance again.
In my experience this works just fine in the daily operation.


Why is the L/D ratio numerically equal to the glide ratio? *L/D is ratio of two forces, lift and drag.
*Glide ratio is ratio of two distances.
Can you explain mathematically how they end up  numerically equal and are they always equal?

The sum of all work done on the airplane must be zero in a glide. That is, the work done by gravity must equal the work done by drag. Note also that lift equals the force of gravity in equilibrium
Work is force times distance. If gravity is X times larger than drag, this means that the distance in vertical direction must be X times smaller than in the horizontal direction.


What are the differences between the CH-46 and the CH-47? The CH-46 and the CH-47 Chinook are very similar-looking aircraft and seem to serve similar purposes - only though for different branches of the U.S. military.

What are the differences between the CH-46 and the CH-47?
Why does the military run both instead of settling on one?

The difference is in mission, and the difference is non trivial.
The twin rotor configuration goes back to the 1960's. ("Flying banana" Piasecki H-21.  The CH-47 replaced it in Viet Nam in 1965).  Chinook became the Army's heavy tactical lift during Vietnam.  Like the C-130, that particular design is timeless.  The CH-47F is the current configuration.  It carries about twice as much as a CH-46 could.  It is also one of the faster helicopters there is (it can fly almost 200kts) though the CH-53E has flown faster.
The CH-46 was an adaptation of the same idea, but made smaller and marinized: it had to meet a host of Marine Corps and Navy requirements to fit on amphibious ships and supply ships. Space and fit are non-trivial limitations when writing requirements for naval aircraft.  (As an aside, the US military no longer operates the CH-46.  It appears that the last CH-46 squadron in the USMC, HMM 774, let go of its last Phrogs in 2015 and is now VMM 774, flying V-22's.  The Navy Sundown for CH-46 was in 2004.)
Not having to take off some power for a tail rotor is an advantage.  The CH-46 mission for the Marine Corps was vertical assault (it carried more than a Huey and predecessors like the CH-34); for the Navy, it was the VERTREP mission.
The payload and maneuvering benefits from the lack of a tail rotor made the VERTREP mission a perfect fit for the CH-46.  One of the challenges in ship borne operations is the ability to run simultaneously resupply by air and ship-to-ship (UNREP) while not being operationally constrained (for the ship drivers) "getting into the wind."  That limitation tail rotor helicopters don't handle as well as the CH-46.  (That point was a core argument against CH-60S as replacement for  CH-46; but that's another matter).  I've flown VERTREP in helicopters with tail rotors; the CH-46 was less constrained than we were.
What about Marine and Navy Heavy Lift missions?
The Marine Heavy lift (analogue to the CH-47 for the Army and Air Force CSAR) is fulfilled with the CH-53, and has been for over 40 years.  The CH-53 can fold its tail to fit on a ship.  Even with folded blades, the Chinook's deck footprint is / was too large(at the time) on the amphibious ships in service.  The Navy VOD (heavy lift) was handled by CH-53's for 40 years.  They have since given that mission to the MH-53E minesweepers.  (Flexible, that's helicopters!)
Smart Requirement Writing led to smart choices
"The Military" would have made a significant mistake "to just make one type" since back in the 60s and 70s, making mission specific aircraft was the way to go.  Quite frankly, it makes for cheaper aircraft to build it for one core mission.  (See the A-10 as a fine example of that).
Note: An early failure in "one size fits all" was the F-111.  A current "one size fits all" example of cost going through the roof is F-35.
At the time the CH-46 and CH-47 were procured, the military was smart: apply the KISS principle to get aircraft that fit mission requirements.  The Army and Navy mission requirements were not identical.
(So how do I know all that?  25 years Navy pilot (helicopters, ASW warfare specialty, did other stuff like Vertrep ...), significant experience in multi-service operations, and a few years having to work in an acquisition job.)


Does a secondary surveillance radar need the support of a primary surveillance radar? ATC technologies are evolving to include other components than primary and secondary surveillance radars, but I believe these two pieces of equipment are still the backbone of ATC. Primary radar (PSR, 2.8 GHz) works usually on higher frequencies than secondary radar (SSR, 1.030 GHz).

Top: M10SR SSR | Bottom: Morava PSR | Right: Sky Search-3000 PSR+SSR co-mounted

Primary radar uses the natural echo reflected by the target to determine its angular position and range, while secondary radar uses the cooperative answer provided by the target transponder. The answer is equivalent to a natural echo, but is delayed by a known time, and is more powerful. It can also contain additional information such as level.

I read that SSR is more accurate in position determination than PSR. Indeed SSR doesn't work without the support of the airborne transponder, and the target can disappear from SSR display when the transponder has failed or has been disconnected.

My questions:

In appearance SSR + transponder can provide information to ATC without the need for a primary radar support. Is it true, if not why?
SSR can technically receive a natural echo on 1.030 GHz before the SSR reply which is sent on 1.090 GHz, is this signal used?
Do ATC systems usually display PSR data for controllers continuously or only on demand (e.g. when a target transponder doesn't answer SSR interrogator)?

SSR can work independently and this is quite common as well. Primary radars cost a lot to maintain, and as more and more planes are equipped with transponders, primary radars are being shut down. Many areas now have secondary radar coverage but no primary radar coverage.

SSR only relies on replies sent as a response to its own interrogations. This works well in theory, but becomes a problem in practise in areas where many SSR units transmit on the same frequency resulting in many overlapping replies. This results in FRUIT and garbling.

For areas where both primary and secondary radar data is used, the data is combined to create individual radar plots that are shown to the controller. The controller typically does not have to worry about the exact source of data, and will not worry about switching on or off individual sources (at least not during normal operations). Modern ATC units receive radar data from many different sources, including both SSR and PSR stations, and process and combine this data to a single representation. This happens by using technology such as ARTAS. On the controller radar screen, aircraft plots will look different depending on their data sources. For example, a PSR-only target may be shown as a circle, an SSR-only target as a diamond and a SSR+PSR target as a square. The exact specifications vary from system to system.


What are the communication procedures for flying from one Class D airspace directly into another Class D airspace? What is the communication procedure for descending through Class D airspace to land at a different controlled airport in a separate class D airspace that is directly next to it, such as Long Beach (KLGB) and Los Alamitos (KSLI)?

I have not flown into this airspace. But, based on the location in question, you probably should be on flight following long before entering the Mode C Veil for the overlying Class B. If not, contact the Approach Control listed for the Class D into which you are flying. They will then coordinate your clearances through the respective airspaces until you are handed off to the final destination Class D controller for landing clearance.

Arrivals into KADS have a similar scenario. When getting your ATIS before arrival, you will be informed on the recording to contact approach on a specific frequency, give your destination as Addison, and that you have information A-Z. You are required to do this in order to land in KADS. You can not enter the Class B or the Class D without doing this first. Approach will handle your transition through any airspaces from there.


Identify canard, low-wing, single pusher-prop plane over Upstate NY Yesterday, August 11, at around 3:30 pm, I saw an unusual-looking plane flying over Ithaca, NY. It seemed fairly small -- approximately business jet sized. Unfortunately, I didn't have time to get a picture, but I remember several distinctive aspects of its appearance:

Canard and seemingly no conventional tailplane
Single pusher propellor
Low, swept wing with winglets. Pretty sure it was tapered.

I only saw the plane from below, so I don't know anything about design aspects on the top side of the plane. I checked on FlightAware and FlightRadar24, and didn't see any obviously-matching flights, but I may have missed something. Based on some googling, what I saw seems pretty close in appearance to the AASI Jetcruzer (picture below), but apparently only five of these were ever registered, all in California. According to that same page, only one remains registered, most recently in Washington. The most recent flight recorded with its tail number (N200JC) by FlightAware is from 2014.

AASI Jetcruzer

Additionally, the wing profile doesn't look quite right to me. Another somewhat similar-looking plane that has a more correct-looking wing is the Beechcraft Starship (picture below). However, I'm quite sure that what I saw only had a single propellor. According to the same website, only one specimen of this aircraft remains registered, and similarly its last flight recorded by FlightAware was in 2011.

Beechcraft Starship

Are there any more likely possibilities for the aircraft I saw than one of these rare and seemingly seldom-flown planes?

There are a number of near-copies of the Long EZ, with nearly identical wing and canard shape; they differ in number of seats, performance, range, and, yes, several of them have retractable gear.  I think there's at least one that's pressurized.

Without a high quality photo (possibly even with one, if shot from the ground), it may be impossible to determine what you actually saw -- but a single pusher propeller, low mounted cranked/swept wing with tip fins, and swept canard originated with the Long EZ (before that, there was the Vari-EZ with unswept canard, and the Vari-Viggen with a different wing sweep profile).


Would a stationary WWII fighter fall on its nose with full throttle and brakes on? Would a stationary WWII fighter fall on its nose with full throttle and brakes on?

It's a general question, but I am interested in the Republic P-47.

(Wikimedia; arrows and CG icon are my additions) P-47 side drawing.

The thrust has a bigger moment arm around the tires contact points compared to the weight. It won't nose over below a certain RPM (it will be specified in the training). Below that RPM:

The weight will counter the thrust
The propeller downwash will produce downward force on the horizontal stabilizer
Applied brakes will resist the rotation of the wheels (airframe rotating around wheels)

From a training video for the comparable big-engined F6F Hellcat, the narrator says:

  You can't gun this engine to full takeoff RPM and manifold pressure while holding the plane with the brakes, if you exceed 2,000 RPM the tail will lift and you risk nosing over.

Answer is yes it can happen.

Note: for comparison, the max RPM is 2,700 for the Hellcat.


What is the form of information stored in black box? Black boxes contain the information regarding to a flight. What is the form of those information? Any particular language log?

There are 2 different black boxes.

The cockpit voice recorder. This holds audio from several different sources, including the microphone for each pilot, the radio and a general cockpit microphone.
The flight data recorder holds at least 88 different parameters including attitude of the craft, engine performance, autopilot setting, pilot input one the controls, etc.


What are the FAA regs regarding landing a helicopter off airport? I have been mulling over getting a Mosquito helicopter, the experimental version with the uprated gas or turbine engine and larger fuel capacity. It's unwise to try to fly any of the Mosquitos without at least a rotary wing solo ticket, and if you have that, you may as well get the better version so you can log the time, and take advantage of the greater range and power. This leads to an interesting question:

What are the regulations regarding where a helicopter can be landed? Obviously, it can be landed in a lot of places, but what does officialdom have to say about where a helicopter can and cannot be landed?

There are no Federal Laws prohibiting landing rotor craft off field.
14 CFR 91.119

(1) A helicopter may be operated at less than the minimums prescribed in paragraph (b) or (c) of this section, provided each person operating the helicopter complies with any routes or altitudes specifically prescribed for helicopters by the FAA;

Part B and C, for reference

Except when necessary for takeoff or landing, no person may operate an aircraft below the following altitudes:
(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000 feet above the highest obstacle within a horizontal radius of 2,000 feet of the aircraft.
(c) Over other than congested areas. An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.

However, state laws, local laws, zoning laws, etc. change from location to location. You need to make sure you plan where you are landing beforehand and check these laws.
For example, in the State of New Jersey, helicopters can only be landed at the following locations:

Permanent public use heliport or vertiport
Permanent special use or restricted use helistop or vertiport
Temporary helistop or vertiport

(Reference)


What makes someone a 'Senior First Officer'? Some airlines have a Senior First Officer rank. Apart from the title and (presumably) the pay, what makes them different from a regular First Officer?

Do they have any differing duties or responsibilities? And do they need to pass some kind of test, or is the rank just given to them after a certain amount of years service?

"Senior," is generally a subjective term.  In order to fly to the lowest authorized minimums one generally needs 100 hours in type, but other than that, one is no longer "green," after accumulating 100 hours in type.


Final 200 feet under autoland How does Autoland work below decision height (200 ft)? Ie, what guides the plane until the radar altimeter notes the jet is at the right height to begin to flare? I've been searching the internet, and it looks like the plane simply holds its attitude for around 100 feet until the RA kicks in.

An autoland can be performed when a CAT II or III ILS (Instrument Landing System) approach is available (bad things can happen otherwise: Why don't pilots always use autoland?). The decision height for these approaches is lower than the usual 200 ft:

Cat I: DA 200 ft or higher
Cat II: DA 100-200 ft
Cat III A: DA < 100 ft
Cat III B: DA < 50 ft

The pilots must have the runway (or runway lighting) in sight when reaching the decision height. Otherwise, a go around must be executed. But this does not mean that the ILS signal is no longer available. The autoland system continues to use the ILS signal together with the RA (radio altimeter) to fly the aircraft. That means the autopilot uses the localizer deviation to control the aircraft laterally (during the approach, the flare and even after landing) and the glide slope deviation vertically until the RA indicates it is time to start the flare (at this time glide slope is ignored).

The exact details will of course depend on the aircraft model. Here is how the autoland works on a Boeing 737 NG (source: FCOM v2 4.20.19 Automatic Flight - System Description):

  500 Feet Radio Altitude

  The pilot is required to check for the presence of LAND 3 or LAND 2 in order to
  continue the autoland.
  If the second autopilot in CMD remains armed and does not engage, LAND 2 or
  LAND 3 does not annunciate. Instead, the amber NO AUTOLAND annunciation
  alerts the pilot that dual control has not been established and the autoland is to be
  discontinued.

  450 Feet Radio Altitude

  The alignment mode is enabled which provides rudder compensation for the
  purpose of decreasing large crab angles produced by crosswinds, and to control
  the adverse moments caused by an engine failure. The automatic correction for
  aircraft crab angle due to crosswinds and engine failure enhances flight crew
  runway perspective and provides optimal aircraft position for initiation of rollout
  control. In a strong crosswind, the airplane does not fully align with the runway
  but lands in a slight crab. Sideslip is limited to 5 degrees. This mode is not
  annunciated.

  400 Feet Radio Altitude

  The stabilizer is automatically trimmed an additional amount nose up. If the A/Ps
  subsequently disengage, forward control column force may be required to hold the
  desired pitch attitude.

  If FLARE is not armed by approximately 350 feet RA, both A/Ps automatically
  disengage.

  Flare

  The A/P flare maneuver starts at approximately 50 feet RA and is completed at
  touchdown:

  FLARE engaged is annunciated and F/D command bars retract.
  FLARE engaged is annunciated and with LAND 3 annunciated, F/D
  command bars center.
  the A/T begins retarding thrust at approximately 27 feet RA so as to reach
  idle at touchdown. A/T FMA annunciates RETARD.
  the A/T automatically disengages approximately 2 seconds after
  touchdown.
  the A/P must be manually disengaged after touchdown. Landing rollout is
  executed manually after disengaging the A/P.

  Rollout

  ROLLOUT arms when LAND 2 or LAND 3 annunciates.
  At approximately two feet radio altitude, rollout activates:

  ROLLOUT replaces the VOR/LOC roll flight mode annunciation
  the autopilot controls the rudder and nose wheel steering to keep the
  airplane on the localizer centerline.
  rollout guidance continues until a full stop or until the autopilots are
  disengaged.


During instrument approach, is an abbreviated racetrack course reversal allowed? I was flying the RNAV (GPS) RWY 33 approach into KFNL during instrument meteorological conditions.  The plate identifies a non-standard 6 NM racetrack reversal at IMOMY:

Denver approach cleared me direct to IMOMY.  I was approaching from the Southwest, but NOT from HYGEN. Thus, I began a circuit around the depicted procedural track. I was cleared for the approach and approved to change to advisory frequency.

At about 4 NM outbound, ATC contacted me* and asked when I planned to turn inbound.  I advised that I could begin inbound immediately, which they then asked (not cleared) me to do, in order to avoid encroaching on departing traffic from KDEN.

During VFR practice approaches (not under ATC), we always shortened the course reversal on this particular approach to save time. When doing the real thing, it was always my understanding that the depicted track had to be flown EXACTLY as published.  Per the FAA Instrument Procedures Handbook:

  A holding pattern in lieu of procedure turn may be specified for course reversal in some procedures. In such cases, the holding pattern is established over an intermediate fix or a [final approach fix]. The holding pattern distance or time specified in the profile view must be observed. For a hold-in-lieu-of PT, the holding pattern direction must be flown as depicted and the specified leg length/timing must not be exceeded. (Page 4-53)

Now, I was also taught that if you have to perform a teardrop or parallel entry, that completed your reversal and no circuits are necessary:

  The holding pattern maneuver is completed when the aircraft is
  established on the inbound course after executing the appropriate
  entry. (Ibid.)

Question 1: Was it appropriate for me to attempt to fly the 6NM circuit?

Question 2: Am I allowed to choose an arbitrary leg distance (or time), as long as the 6NM limit is not exceeded?

*I was already switched over to the CTAF, but still monitoring approach control on the second radio which I always do just in case. Something I picked up from my flight instructor who flew larger planes for a living...

Unless you were "cleared straight-in" for the approach, when IMOMY is your IAF (as it was in this case) you are required to fly the course reversal, even if you can execute a direct entry. This is because the approach does not have terminal arrival areas labeled NoPT. So, yes, it was appropriate to fly the 6nm reversal.

That said, no, you cannot choose a different course reversal, even a shorter distance hold. When a hold is depicted in lieu of a procedure turn (HILO) you are required to fly the hold as shown.

AIM 5-4-6 (4) states:

  If proceeding to an IAF with a published course reversal (procedure turn or holdinlieu of PT pattern), except when cleared for a straight in approach by ATC, the pilot must execute the procedure turn/holdinlieu of PT, and complete the approach. [emphasis mine]

The IFH that you cited in your question has similar wording:

  For a hold-in-lieu-of PT, the holding pattern direction must be flown as depicted [emphasis mine]

Occasionally ATC will act surprised or get frustrated with you for flying a reversal when you're within a 90° turn of the initial segment's course, but unless they specify straight in you're doing the right thing.


What are the rules for close/formation flying of civilian planes? Two recent questions and their answers have raised a further question.

In Are there laws about how close military aircraft can fly to passenger jets, and are they enforced?, we learned that "the military can get as close to other aircraft as they damn well please, through a procedure called Military Assumes Responsibility for Seperation of Aircraft, or MARSA".

In Why are there NASA branded F/A-18s? we see a picture of closely flying planes, and a comment notes "NASA is a civilian agency".

Do the NASA planes fly under MARSA rules or another set of rules for civilian agencies?  Are there other non-military agencies that fall under this rule too?

Pilots are allowed to fly as close as they want to each other as long as all parties agree to it and feel safe doing so.

Air Traffic Control cannot guarantee separation for planes in formation flight,So this will only be done under VFR and in VMC, where pilots can maintain visual separation from each other.

Many stunt fliers are civilian pilots and will routinely fly in close formation as well.

Other notable example of civilian formation flight include Mythbusters testing airplane fuel efficiency in formation and Airbus' publicity stunt with 5 A350s


Why does a phone's flight mode also disable FM radio? I had two phones being capable of listening to VHF FM radio (in Germany about 90 to 104 MHz).
However when turning on flight mode, the radio receiver is also disabled, and I wonder why:
Listening to radio does not transmit any electromagnetic waves (more than when playing some game I guess).
I thought it would be some fun listening to the different radio stations while passing countries from above.

All broadcast-band radio receivers contain local oscillators which are used in their intermediate frequency (IF) circuits to downconvert the (higher) frequencies they receive. These IF circuits are prohibited by law from radiating more than very small amounts of radio frequency power while operating, but to prevent any possible chance of having the airplane's navigation receivers pick up interference from portable radios, they have to be shut off during flight.
This is a minor problem today, but old-school shipboard radio receivers during WWII were supposedly capable of radiating enough power off their IF stages that submarines could tune in on them and use them as homing beacons to track convoys and then sink them.


What is the advantage of the blisk design in the new Trent XWB engine? What advantage does the "blisk" or "bladed disk" type rotor have over the usual rotor system?

Since the blades and rotor disc are a single piece, there are no additional fittings (bolts, screws etc) to attach the blades reducing complexity and weight.  The blade root joints are also a source of failure through manufacturing defects and fatigue cracks.

The disadvantage is that any damage to a blade requires the entire assembly to be replaced rather than a single blade.


What are the advantages of the Riblett airfoil over the Original Pietenpol Airfoil? Some builders have opted to build a Riblett airfoil based wing for the Aircamper rather than using the original Pietenpol wing.  What are the basic characteristics of the Riblett wing which differentiate it from the original wing, and what are the pros and cons in construction and performance?

Assuming that the same wing chord is used for both, one technical difference between the Pietenpol and the Riblett is the depth of the airfoil.  The Riblett that has been used on the Air Camper is the 612 (or sometimes the 613.5), which makes it 12% (or 13.5%) deep.  With a 60" chord, that's a depth of 7 to 8".  The deepest section of the stock Pietenpol airfoil is only 6-9/32", which makes it roughly a 10.5%.  The offshoot is that a taller spar can be used with the Riblett, and in spar strength the height makes a great deal of difference because the section modulus goes as the square of the height and the section modulus is what determines bending strength.  A taller spar can be made lighter with proper design.  Another useful consequence of using the Riblett is that a deeper wing section allows a larger fuel tank to fit in the space between the spars.  The stock Pietenpol wing centersection can accommodate maybe 10 gallons, but the Riblett should be able to fit more up there.

I've attached a graphic overlay comparison of the Pietenpol airfoil with the Riblett GA30U-612; Piet in red, Riblett in white.  The 613.5 is similar but the differences are a bit more accentuated.

For performance differences, I will defer to both a technical treatise by Mike Shuck (on the airfoil list) and the flight comparison between two very similar Piets conducted several years ago and documented in the BPA Newsletter.  Very similar performance in all flight regimes.


How does an AMRAAM communicate securely with the aircraft that launched it? From Wikipedia:

  It also incorporates a datalink to guide the missile to a point where
  its active radar turns on and makes terminal intercept of the target.
  An inertial reference unit and micro-computer system makes the missile
  less dependent upon the fire-control system of the aircraft.

What is the nature of this "datalink"? What is it called, what protocol does it use?

How is this datalink secure?

Do you have a need to know?

Fortunately, there is a simpler answer to your question: the original AMRAAM does not communicate with the host aircraft. Only the host aircraft communicates data to the missile. This data is transmitted in the form of fixed-format messages, repeated multiple times with redundancy.

Security would fall outside the scope here, except in most general terms. In general terms, when secured, unidirectional datalinks use fixed key symmetric encryption. A missile's downlink isn't necessarily secured, as it's only transmitting the enemy's position for guidance correction.

Newer and more complex missiles that do communicate bidirectionally typically use Link 16. That is a secure encrypted protocol. It's well-documented and you can find a fairly good overview of the protocol on the net.


What is the purpose of eyebrow windows? Nowadays they are no longer needed but why do they cover them up like in this photo?

What is their purpose and why aren't they used anymore?

Source

Wikipedia answers this on the Boeing 737 page:

  Most 737 cockpits are equipped with "eyebrow windows" positioned above
  the main glareshield. Eyebrow windows were a feature of the original
  707 and 727. They allowed for greater visibility in turns, and
  offered better sky views if navigating by stars. With modern avionics,
  they became redundant, and many pilots actually placed newspapers or
  other objects in them to block out sun glare. They were eliminated
  from the 737 cockpit design in 2004, although they are still installed
  at customer request. These windows are sometimes removed and
  plugged, usually during maintenance overhauls, and can be
  distinguished by the metal plug which differs from the smooth metal in
  later aircraft that were not originally fitted with the windows.


Is there any comprehensive source for landing fee information? Is there any comprehensive source for landing fee information for US airports?

Airnav and the facility directory do not have landing fee information.

Also, going to airport web sites often is useless. For example, Massport lists landing fees for Hanscom on their web site, but do not list their fees for Logan.

Note that landing fees can be complicated. For example, there can be "landing fees" and "ramp fees" and others. So, usually the fee information is for a bunch of different stuff.

After working on the problem some more I have found there is not really any centralized source for landing fee information. Pretty much the only option is to call the FBO. However, you can get the FBO information from Flight Aware, assuming a US airport. For example, to get FBO information for Logan Airport in Boston, you would use the URL:

https://flightaware.com/resources/airport/KBOS

This tells you that the GA FBO for Logan is Signature and that their number is 617-561-2500. At that point you have to call them to find out more. For example, I did this and the answer was:

\$33 single engine piston landing fee
\$6 per hour parking
\$53.90 general landing fee
\$49.00 handling charge (waived if you buy at least 15 gallons of fuel) \$95 "security" charge
\$5 random bureaucracy charge


Can IATA code for an airport be more or less than 3 letters? I got an exercise where IATA codes are involved - exercise's specification says those codes can be 2-4 letters. After a few minutes of research I see that those codes should be 3 letters, so can IATA code for an airport be more or less than 3 letters?

IATA themselves say it's a three-letter code:

  Airlines and CRSs [computer reservations systems] may request the
  assignment of a unique three-letter code to identify an airport

The UN trade locations coding also says the same thing:

  when a three-letter code is used alone to indicate a location, it
  designates the name of an airport or location as adopted by IATA
  (whose code only has three letters)

According to Wikipedia, IATA has several different types of code that can be from one to four characters, but airport codes specifically are always three based on all the sources I mentioned.


Why does this aircraft land nose first? I've seen almost every aircraft land back gear first to evenly distribute the landing load between more struts.

However, I recently saw this video of a NASA Super Guppy Nose-Wheel land gear first at Mansfield-Lahm Regional Airport:

            .

I couldn't think of any reason a pilot would want to do this so is there any reason as to why they would want to land nose first opposed to the conventional way that I don't know of?

That's pretty much how landings turn out on Super Guppy. The aim is to make a three point landing (main and nose wheels touch down simultaneously), but the Super Guppy is a tricky plane to land. Earlier versions were tricky on takeoff too: during takeoff roll their main gear tended to lift off before the nose wheel, this, ofcourse is far from optimal...

This article will give you a nice briefing on this beautifully weird plane (see page three for stuff about landing).

The ones still flying are fitted with Boeing 707 nose gear, which is shorter, sturdier and placed further behing than the original one. Despite this modification, the aerodynamics of the plane are such that it just wants to plant the nose wheel down first. Searching "Super Guppy landing" on Youtube will yield allmost only nosewheel landings.


How much runway does an amphibious Cessna Caravan require for VFR part 135 operations? I am trying to determine the length required for us to build a simple paved runway for a Cessna Grand Caravan EX Amphibian to depart for water landings and and return (VFR/VMC only, Part 135).

Previous questions about for "runway length required" only refer to Part 135 and Part 91 for Large Transport Category.

The minimum required runway length for a Cessna Caravan is *762m/2500ft. Considering that the Caravan has a stall speed of 60 knots, and for a safety margin, you would approach at 70 knots, this makes sense. Assuming that it slows at a rate of around 1 knot/ 10m, You can do some basic calculations: 70/1, which is 70, resulting in a 700m long runway, plus 62m for a safety margin.

EDIT: But now we're talking about amphibious, so water could help the plane slow down, but at the same time a longer takeoff roll would be required. And it turned out that the website I used wasn't reliable. Sorry about that. Anyways, it is said that an amphibious Cessna Caravan needs a takeoff roll of 2,341 feet/714m. However, the actual requirements force a 3660ft/1116m runway. I didn't get the landing distance required, but I think it's safe to say that the landing would be shorter than the takeoff roll.

*the actual runway length required of a normal caravan is 2,055 feet/ 626m, and you can expect to rotate at 1,160 ft/ 354m.

*Some (incorrect) information was from: http://www.sgl.com/208.html
And more correct info from: https://cessna.txtav.com/en/turboprop/caravan

Please tell me if I should delete the first paragraph.


What are the names and the function of these aircraft components? These images were taken from a Cessna 150 aircraft containing a Continental O-200 engine.

1 - nutplate holding something on the other side of the firewall

2 - starter or master contactor (a relay operated by low-current signal from cockpit switch)

4 - positive heavy-gauge cable to battery or starter

5 and 6 might be the alternator voltage regulator to hold the output voltage at 14.4V

10 - oil filter to remove carbon and other crud from oil

11 and 23 - magneto to provide carefully-timed high voltage pulses at for ignition

12 - alternator to charge battery and run electric instruments / radios

14 - vacuum pump to power gyroscopic flight instruments

15 - carburetor to meter air and fuel

21 - crankcase vent (?) to prevent blow-by gases from forcing oil out of the engine

22 - fuel strainer drain valve to drain water / crud from low point in fuel system

Better pictures would help to identify the other parts!


Does altitude affect how you interpret the attitude of the aircraft? I understand that for any specific aircraft, at a constant power setting, you can use the aircraft's attitude as a proxy for airspeed.

For e.g. In aircraft X, when the dashboard is 1 inch below horizon, at power setting X, means the aircraft will be flying at around speed X.

My question is, if you are much higher in terms of altitude, won't your attitude based on visual reference e.g. How many inches away is your dashboard to the horizon, be different when you are much closer to ground?

Yes, due to the curvature of the earth.  But you'd have just as much variation with a small change in pilot eye position within the aircraft.  The exact "sight picture" of the top of the nose (or the top of the instrument panel) relative to the horizon is not really something that you memorize and use as an absolute reference point with the expectation that it will be exactly the same every time you fly a given airplane.  It's more just something that you keep an eye on to watch for changes.  By the time you've climbed to altitude, you've had plenty of time to (perhaps unconsciously) get used to the resulting slight change in the sight picture between the nose and the horizon line.  All the while, other instruments such as the altimeter or airspeed indicator or vertical speed indicator help tell you whether the place you are putting the nose relative to the horizon, is really the correct place to make the airplane do what you want it to do.  Of course, there many instances where the horizon is not clearly discernible anyway.


If all passengers moved to the back, front or one side, would they crash the plane? all-time classic:

Would the load shift of all passengers herding at the back, front or one side make the plane hard or even impossible to keep in the air ?

Are there any passenger aircraft where this could be a problem ?

scope: Q2507 is about unspecified movement of some passengers ("passengers moving around"). This would hardly be a problem. The scenario presented in this question here is an entirely different one, viz a hypothetical extreme case where ALL passengers gather in 1 spot at the front or back. Also, it addresses a very famous airline myth, and as such it has a valuable purpose.

The issue at hand is known as weight and balance. Most of the larger airliners do not have much of a problem with a large shift in Passenger weight but shifting cargo has indeed caused accidents (See https://en.wikipedia.org/wiki/National_Airlines_Flight_102) which was what happened when a large amount of cargo, not properly secured, fell towards the back of the aircraft during takeoff causing the B747 to crash.

In general, the smaller the aircraft, the more sensitive it is to Moment and Arm changes in its weight and balance. If there is too much weight towards the rear (known as Aft-CG) then the pilot may not have enough down-elevator authority to keep the aircraft from pitching up even further.

A forward-CG problem may also happen where there is too much weight towards the front of the aircraft which may cause the pilot to run out of UP elevator authority during the landing flare, causing a nose-first landing.

Both fore and aft Center-of-gravity issues have caused airline crashes in the past although usually not from passengers but rather shifting cargo not properly secured.

I am not aware of any sideways loading issues that could not be corrected with aileron (assuming both wings are attached). Flying with more fuel in one wing than the other can be tiresome but is usually safe.


When can I descend on a feeder route if instructed “maintain ... until established” AIM 5-4-6 discusses how Approach Clearance applies to feeder routes. It says that when ATC clears an aircraft for the approach, the aircraft is expected to use a feeder route if applicable. My understanding is that this includes the altitude published on the feeder route.
However, if ATC says “maintain 2000 until established, cleared approach” and the aircraft is approaching a feeder route, when would the aircraft descend to a published altitude? On the feeder? Once past the initial approach fix?

Is this something that you have experienced yourself? If so an example would be helpful. Approaching a feeder route and hearing "Maintain... until established" imply two separate situations, to my ear.
From a controller's standpoint, if you are operating on an unpublished route (radar vectors or direct the IAF or similar), we follow the 7110.65 4–8–1b:

b. For aircraft operating on unpublished routes, issue the approach clearance only after the aircraft is:
1. Established on a segment of a published route or instrument approach procedure, or
2. Assigned an altitude to maintain until the aircraft is established on a segment of a published route or instrument approach procedure.

So if you are flying toward the airport but not on any airway or feeder route, you will receive vectors to final, or to an initial fix. Then in accordance with b2 we can say "Maintain 2000 until established on final approach course, cleared VOR runway 18 approach." You descend and maintain 2000, and do not descend any more until you (as PIC) deem yourself established on the published approach segment. (The procedure is slightly different if you are with a Terminal Arrival Area designated for an RNAV approach and above the minimum altitude for that TAA; then we can just say "Cleared RNAV runway 18 approach.")
If, however, you are operating on a published route, such as an airway leading to a feeder route, all we have to say is "Cleared VOR runway 18 approach." You are currently at a safe altitude on the airway, and the approach is specifically designed to give you all the information you need to get from that airway altitude down to 0AGL without running into any terrain. If this involves the use of a feeder route, you are expected to use the feeder route and any altitude restrictions for it.

Essentially: I don't think you would be told "Maintain 2000 until established, cleared approach." Perhaps you would be told "Maintain 2000 until FIXXX, cleared approach" where FIXXX is the beginning of a feeder route and you will intercept FIXXX at an angle of 90º or less; you are then assumed to be established on a published approach segment once you cross FIXXX. Once you are established (i.e. after FIXXX) you may descend in accordance with the published approach procedure.


Why do pilots need the ceiling, time, and dew point in the ATIS? For example:

Ceiling: what is the ceiling? Why do they need to know the ceiling?
Zulu time: what is the zulu time?
Dew point: why do they need to know the dew point?

The ceiling is the lowest altitude where clouds cover more than half of the sky. This is important because climbing above that altitude means you will most likely have to fly through clouds. This makes navigation more difficult and pilots are required to have special training to fly in low visibility. If the ceiling is too low, pilots can't be at a safe altitude above the ground and out of the clouds at the same time. Low ceilings are also critical for landing, and may require pilots to make an instrument approach and landing.

Zulu time refers to UTC time, which is the universal coordinated time. Zulu or UTC time is helpful as a worldwide reference in fields like aviation, to avoid issues like dealing with changing between local time zones. The ATIS will contain the Zulu time that it was updated so pilots know how recent the information is.

The dew point in relation to the temperature gives the pilots information about the humidity, and can affect visibility. If the dew point is close to the temperature, humidity is high, which can cause hazy conditions, or even fog. As with the ceiling, this can warn pilots of possible changes in conditions that will make it harder to see the ground or other aircraft while in flight. In terms of aircraft performance, the dew point is also needed to determine the true density altitude, when combined with the pressure and temperature. A high dew point means a higher density altitude, which reduces aircraft performance.

Dew point is also very important in certain helicopters with carburetors, like the Robinson R-22 and R-44 helicopters, which are subject to carb icing even during take-off because they only use as-required power rather than full throttle. In this case, carb heat needs to be applied whenever the temp/dew point spread is 15C or less. Here is the citation from the R-22 POH:


Is designing a small GA airplane with a wing loading of 20-25 lbs/sq ft a bad idea, or is that wing loading too high? Is designing a small GA plane like the following a bad idea?
This question is not the same asking if a an airplane with a traditional design is safer with a lower wing loading.
This question specifically asks if there are any reasons not to design a small slow landing plane such as a non-USA ultralight with a specific wing loading of 20-25 sq ft, and gives specific design suggestions to counter against popular reasons why an airplane shouldn't be designed at that wing loading.
Is designing a small GA plane like the following a bad idea?
Similar to the Cri Cri but with a wing loading of 20-25lbs/sq ft, slotted flaps, similar 17% airfoil to a Zenith 701, for low a weight spar, wing twist and vg's for better stall resistance,  twin engine, MTOW of 600 lbs, so wing area of 30 sq ft, 15 ft span, 2 ft chord, and a stall speed of 30-45mph (assuming all the math works out)?
This reduces the argument that high wing loading planes must land at a high speed and use low profile wings, which are easier to stall.
It seems many small airplanes are designed in the 10-14lbs/sq ft range, except for the BD5 at 17 lbs/sq ft (popular longer wings), and Rutan's Catbird at 45lbs/sq ft.
Wouldn't smaller wings, smaller spar, lower weight, less drag and less horsepower requirements be advantageous?
Approximate wing loading of various aircraft:
Cessna 172 - 14lbs/sq ft
CriCri - 11
Zenith 601 - 10
BD5 - 17
Rutan Catbird - 45lbs/sq ft

Racing airplanes do that and live with high landing speeds.  25 psf is about the wing loading of a Beech Baron.  The Baron stalls in the landing configuration, gear and flaps down, at 84 mph/73kt.
This mean you fly approaches at 110 mph with flaps.  Not too many GA pilots are safe with an airplane that hot without a lot of extra training and lord help you if you have to put the thing in a field that fast (a single I mean, the Baron being a twin and the expectation of off field landings being low).
You can make the flaps fancier, and maybe get that down under 100 mph, and then add wing slats and maybe get it down to 90, but you just added a lot of weight and cost.  Not worth it for a few knots at the top.


What are the FAA requirements for an aircraft to be IFR certified? As I understand it, the FAA certifies certain aircraft types for IFR flight in general. All aircraft of that type are then certified, not something you have to do with each individual aircraft.

What are the minimum requirements for aircraft to be certified for IFR? Is it all location-sensing equipment?

And a bonus: can I get a single aircraft that is only VFR certified to be IFR certified if I add more equipment?

As you say, the FAA certifies an aircraft for certain "kinds of operation".  For a normal category airplane certified under 14 CFR 23, it basically says that it must be "established appropriate to the installed equipment":

  §23.1525   Kinds of operation.
  The kinds of operation authorized (e.g. VFR, IFR, day or night) and the meteorological conditions (e.g.
  icing) to which the operation of the airplane is limited or from which
  it is prohibited, must be established appropriate to the installed
  equipment.

The installed equipment required for IFR flight (beyond that required for VFR flight)  is listed in 91.205(d) and is mostly equipment used to communicate with ATC and to maintain control of the airplane when flying without visual reference to the ground (so no navigation equipment is specified):

  §91.205   Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.

  ...

  (d) Instrument flight rules. For IFR flight, the following instruments
  and equipment are required:

  (1) Instruments and equipment specified in paragraph (b) of this
  section, and, for night flight, instruments and equipment specified in
  paragraph (c) of this section.

  (2) Two-way radio communication and navigation equipment suitable for
  the route to be flown.

  (3) Gyroscopic rate-of-turn indicator, except on the following
  aircraft:

  (i) Airplanes with a third attitude instrument system usable through
  flight attitudes of 360 degrees of pitch and roll and installed in
  accordance with the instrument requirements prescribed in §121.305(j)
  of this chapter; and

  (ii) Rotorcraft with a third attitude instrument system usable through
  flight attitudes of ±80 degrees of pitch and ±120 degrees of roll and
  installed in accordance with §29.1303(g) of this chapter.

  (4) Slip-skid indicator.

  (5) Sensitive altimeter adjustable for barometric pressure.

  (6) A clock displaying hours, minutes, and seconds with a sweep-second
  pointer or digital presentation.

  (7) Generator or alternator of adequate capacity.

  (8) Gyroscopic pitch and bank indicator (artificial horizon).

  (9) Gyroscopic direction indicator (directional gyro or equivalent).

As far as converting an airplane from VFR to IFR, the Type Certificate Data Sheet (TCDS) must specify that the airplane is designed for IFR flight, and then you could add the missing equipment to make it qualify.


When would CAPT 3 or FO 3 ever be used on the A320? On the Airbus A320, on the very top of the Pedestal and right below the bottom ECAM there are switches saying ATT HDG and the you can either switch it to CAPT 3 or FO 3 same for the other switches in that row AIR DATA, EIS DMC, and ECAM/ND XFR. I think they are for if the Captain or First Officer has custom gear or equipment. Please explain what each switch means, whats it's use, and when would they be used.

"ECAM" is a typical terminology of Airbus aircraft.

From this accident report found quickly while searching for "CAPT3":

The panel:

The explanations:

  Normally all switch are positioned on NORM selection, mean that all of
  the source  are coming from co-location sources (i.e. system 1 for
  Captain, system 2 for F/O and  system 3 is standby).

  In case of
  failure of either of the related system sources for Captain or F/O
  side, they  can alternate it by selecting the switch to either CAPT 3
  or F/O 3 (CAPT or F/O for  ECAM/ND XFR).

The switches are used to designate which input to connect to equipment or display.

When everything is fine, the NORM position links a left side input to a left side equipment, and a right side input to a right side equipment. If an input is not operational, then the switch can be used to select the third input for either the left side or right side equipment.

The equipment and sensors we are talking here are:

Attitude / Heading reference
Air data reference
Electronic Instrument System / Display Management Computers
ECAM and ND XFR used to manage where appear PFD, ND and SD.

Detailed example

The aircraft attitude and heading are sensed using cooperating inertial sensors and air sensors which are combined in an ADIRU. As the attitude determination is key to pilot the aircraft, in particular when autopilot is used, there are 3 redundant ADIRUs on a A320, one for the Capt (#1), one for the F/O (#2) and a backup one (#3). Each ADIRU #n receives data from its ADR #n unit (air data) and IR #n unit (inertial).

The NORM position allow to send the left ADIRU to the Capt panels and the right ADIRU to the F/O panels. This allows the Capt and the F/O to have separate data, and they can compare them in case of doubt. Same for the flight control computers behind Airbus fly-by-wire.

If ADR or IR fails on the Capt ADIRU (#1):

ATT HDG on CAPT 3 position replaces IR #1 by IR #3 on the ADIRU #1
AIR DATA on CAPT 3 position replaces ADR #1 by ADR #3 on the ADIRU #1

If the failure occurs on F/O side, corresponding F/O 3 positions would be used to replace IR #2 and ADR #2 by IR #3 and ADR #3.


Is there a fuel injector cleaner additive available? I have not seen any additives (such as those used in automobiles) to clean and maintain fuel injectors in aviation engines.   Is there a reason for that such as the use of lead in 100LL or something else?   The fuel injectors will eventually constrict or clog as the avgas leaves residual deposits.

Is there some technical reason or is it just that no one has gone through the certification process or at least (like AVBlend or CamGuard) received the "will do no harm" approval from the FAA?

Removing, cleaning, reinstalling fuel injectors is not only expensive but you also risk damaging them and if you have the GAMI injectors you can have quite a bill coming at you.

Fuel injectors in GA piston engines are actually fixed nozzles, so short of fuel contamination, are not so easy to clog,since the only thing that can  be deposited with clean fuel is the blue dye in the avgas.

In 8 years maintaining a fleet of 6 to 8 injected Continental engines, running 200-700 hours / year, I did not see a fuel-deposit blocked nozzle. Deposits did change the flow rate enough for us to routinely clean them ultrasonically (our pilots were cruising lean of peak, and would start complaining), but removing, cleaning and reinstalling the injector nozzles was a routine, straightforward and scheduled event in my experience.

With position tuned nozzles, as current Continental ones are, you need to be careful to get them back to their correct position, just like GAMI ones, but it's not rocket engineering. The torques for installation are in the manuals, and they are not the most challenging item to work on (one b-nut and one pipe thread per nozzle) on the average GA engine. There's no need for special additives.


What is the time-lag between an airline's decision to serve a route and the starting of its service? I was wondering whether there is any literature about the time-lag between the moment in which an airline decides to enter a given route and pays the associated fixed costs and the moment in which the airline starts to sell tickets and fly in that route.
Could you point out some common sense narrative and also some more formal studies (if any)? How does the time lag compare to other industries (e.g., car manufacturing)?

I work for an airline. Normally it takes no less than 6 month from the GO to maiden flight. It depends on many factors, but simplified, it goes like this:
When Commercial teams look for new opportunities, they prepares a "business case" balancing the profitability of the route and costs. Main board evaluates the proposal and gives the GO.
It is very hard to open a new route before 6 months, as all airplanes are assigned to other routes with already-sold tickets. Assigning aircraft into the new route requires a very delicate coordination to maximize each aircraft's utilization and avoid unused ground times.
Having that, you can start to sell tickets. At the same time, legal, maintenance, operations and airports teams have to run to get in place all certifications, personnel, permits, contracts and requires stuff for the route.
(Prior to all this, it is important you have an available slot in the origin/destination airports, otherwise it could take much longer.)


Can radars detect all planes, including military ones? This is with reference to a News Article that I read today. I find it scary that radars would not be able to detect an aircraft. Is it really possible? If yes, how can ATCs manage this situation?

Some military aircraft reflect little enough radar energy to be effectively undetectable. Note that the actual details are likely classified, but even the modern F-22 still has a radar cross-section of about the size of a steel marble. Still, the B-2, an older stealth aircraft, is claimed to disappear from air traffic radar when in stealth mode.

The same article on the B-2 also notes that it has "deployable radio antennas for navigation in civilian skies". When flying during peacetime and outside of an MOA, military aircraft generally have some level of coordination with ATC. If the pilots of a stealth aircraft don't want to be seen, then presumably they would be responsible for maintaining separation from other aircraft, as they cannot be tracked on radar. Of course, there's also plenty of airspace where aircraft don't need to talk to ATC at all (E and G in the US), and the pilot of each aircraft is responsible for maintaining separation.

That said, there are some things in this article that are unclear:

The Etihad aircraft received a TCAS alert for an aircraft that didn't show up for ATC. TCAS intentionally uses the same frequencies and signalling as ground-based secondary radar, so if an aircraft receives a TCAS response it should also show up for ATC. The article does note that the aircraft were "450 to 480km from Mumbai's coastline", so it's possible that the mystery aircraft just had a weaker TCAS response that wasn't received by a distant ground-based receiver.
The article suggests that fighter aircraft don't fly as high as 36,500 feet. A ground attack aircraft might not be able to fly that high, but most, if not all, air superiority fighters have service ceilings of at least 50,000 feet.


Concorde thrust reversers engaged on parked aircraft, but not all engines? Am I correct in interpreting this photo as showing one thrust reverser engaged, while the other is open? Do the thrust reversers fall into place on a fully powered down Concorde? Could this be caused by an engine being removed for display? If so which engine was removed?

Yes the left (#1) reverser is engaged in this photo. G-AXDN is the British pre-production Concorde and has some differences from the final versions. G-AXDN contained internal clam shell reversers, if the GIF at the bottom of this informational page about G-AXDN is any indicator that external engine reverser may still actuate for show and in this case was simply closed while you were there. This video shows the light up ring that they may have used in the GIF (5:02)

This Concorde also has a droop nose that still works. There is also a fairly active effort going on to restore that airframe to have some of the parts work.


Is there an order for the instructions of a go-around? Scenario: Aircraft on final is approaching the threshold. A departing aircraft is slow to roll and ATC must issue a go-around instruction.

ATC: PULL UP AND GO AROUND. TURN LEFT HEADING 360 MAINTAIN 3000'

or

ATC: PULL UP AND GO AROUND. MAINTAIN 3000' TURN LEFT HEADING 360

Is there a correct order to follow for these instructions. Set aside the reason for the go-around is obvious and turning first would appear to be prudent. In simple terms, it there anything that prevents a pilot from turning first, climbing first and then turning, or perhaps making a climbing turn?

* I'm a controller.

Standard ICAO phraseology for ATC commanded go around for callsign XYZ would be:
"XYZ go around (possible reason for go-around)"

XYZ would then acknowledge this:
"Going around, XYZ"

ATC may then give additional instructions in the order it sees fit. If turning is first priority:

"XYZ turn left heading 360, climb and maintain 3000"

In any case the plane would of course be climbing, so if there is a heading to give, it would be logical to command it first.

If for some reason it is imperative to turn the plane away from something as quickly as possible, ATC can command "XYZ turn IMMEDIATELY left heading 360"

Why like this? Because it is imperative that that ATC can be assured as fast as possible that the aircraft will be initiating the go around. Anything other is secondary. The pilot will be preoccupied with the go around procedure for a couple of seconds, and should not worry about heading untill safe climb speed has been established. It is also good practise to keep messages short when something out of the ordinary is happening. Not that go arounds would be that rare, but the pilot might be wet behind the ears, and too many instructions might overwhelm him/her.

In any case ATC must assume there will be some delay in anything an airliner does. There's all kinds of CRM going on in the cockpit to verify everything happens safely.

As to why Canadian phraseology would use the non-standard "pull up" seems strange, but from what I hear Canadians are very nice people so I'll let it slide :)


Is a "stalled" aircraft free-falling? If I was in an elevator in a sky-scraper and the cable broke, I would free fall and feel weightless until hitting the ground. When I cause a stall on an airplane (power-ff) and the wings stop producing lift, why doesn't the same effect occur?

If the cables break on an elevator (and the safety brakes fail), you won't be in true freefall. You'll still have friction from wind resistance, from the guide rollers on the rails, etc. The same is true in an airplane. Even if you're falling straight down, you'll still have wind resistance.

In addition, lift doesn't just drop straight to zero when the wing stalls (no matter what it might feel like to the pilot). Here's the lift-to-angle diagram for a typical wing:

(wikimedia.org)

This wing stalls at about 16° AoA. But notice that the coefficient of lift doesn't simply drop to zero, it just starts descending at that point. So even in a stall, the wings are still generating some lift, just not enough to overcome the weight of the plane.


What would be the designation for 4 parallel runways? If an airport were to have 4 parallel runways (ex if KSEA added another one), what would the designations be. Would it be 34L, CL, CR, and L? I know in Orlando they are separated by the terminals, and thus quite far apart, and they're numbered 17 and 17 and 18, for example. But if they were right next to each other, would that make a difference? Would the two-number system still be used there?

Airports can have a left, center and right runways.  Memphis (KMEM) is a good example.  Airports with four or more parallel runways are left and right with the numbers off by one.  Los Angeles (KLAX) and Chicago (KORD) are good examples of such an arrangement.


Why are accident rates higher on smaller aircraft? This question was raised as part of this discussion.

Why are accident rates higher on smaller aircraft?

It seems the safety record of military, private and small commuter planes is much less safe than that of large commercial operations and I was wondering what factors cause this?

The amount of resources that go into commercial aviation are really amazing -- the amount of time, talent, money, and effort that have gone into making the airlines the safest mode of travel known to recorded history is really extraordinary, and the results reflect that.

Design

Aircraft are expensive, but a part of that expense is the extreme care that has been taken to make them highly reliable, with redundant systems and lots of advance warning systems when something is nearing the point of failure.

Fifty years ago, aircraft were less reliable; the engineers have incorporated the lessons learned.  And, considering how much money an airliner make, airlines are generally willing to pay absolutely top dollar for the very safest design possible.

Small aircraft have also benefited from this learning process, but as a matter of economics, they don't get quite as much redundancy or refinement.  While 99.999% might be "good enough" for the general aviation, the airlines can afford the (high) costs of adding more 9's onto the end of that number.

Maintenance

Again, the airlines can afford a maintenance process and inspection regime that would raise the cost of flying a light aircraft significantly.

Mechanics are trained to uniform standards and work in a carefully monitored environment where parts are exactly tracked and the aircraft have an incredibly detailed history of all that's been reported and fixed over their lifespan.

Manufacturers like Boeing and Airbus can see millions of hours of data and spot trends that are developing to head off incipient problems before they become widespread. This, combined with the way that the aircraft are engineered, makes things really, really reliable.

General aviation maintenance is good -- I'm not bashing that -- but airline maintenance, especially at the major airlines, is amazing.  That's not free, but the results are there.

Pilot experience and training

Light aircraft are often flown single-pilot, by a pilot who probably has under 2000 hours, and who may have flown 200 hours in the past year.

On the other hand, airline pilots are typically hired with at least 1000 to 2000 flight hours, often more, and a captain at a major airline may well have 10,000 to 20,000 hours.  Added to that, the crew has probably flown between 400 to 800 hours in the last year, as well as getting multiple days of training -- both ground school and simulator -- as well as at least one if not two checkrides.

Flying is their profession, not a hobby, and they spend time continuously studying the aircraft, its systems and checklists, the environment, and the regulations.  And, they're trained to work as a crew -- if one pilot is about to make a mistake, the other pilot is there to catch it and keep things on track. Not everybody flying light aircraft has these resources.

All of this is possible because, while it is all expensive, airlines can afford it.

And the records speak for themselves -- one fatality in a commercial U.S. aircraft over the last several years -- which includes many millions of flights.  I don't think any other human activity -- including sleeping in your own bed at night -- can claim a similar safety record.

The relevant point isn't that light aircraft flying is "dangerous" compared to commercial aviation; it's plenty safe by normal comparisons.  It's just that airline flying is so incredibly safe, any other activity will look more risky in comparison.


Why five touchdown zone markings for only one aiming point? RWY 24 at Paris-Orly is a runway sustaining precision approaches. There is an aiming point and five touchdown zone markings.

Orly RWY 24, source: Google Maps

Aiming the visual aiming point, or following the ILS/PAPI glideslope should bring the aircraft on the runway before the aiming point.

Why five touchdown zone markings, in particular the three after the aiming point?

Related, but not duplicates:

What are runway Aiming Point markers used for?
What determines the touchdown zone and aiming point markings on a runway?

From the answer: "Touchdown zone marking" doesn't refer to a marking that would indicate a touchdown zone, which would imply multiple touchdown zones. Instead it refers to all markings in the single touchdown zone, including the aiming point markings.

ICAO Annex 14 specifies the need for 6 pairs of touchdown zone markings for runways with a landing distance available of 2400 metres or more.

As noted in Annex 14, the number of markings relates to the landing distance available.

Presumably, the rule is there to make it easy for a pilot approaching the runway to make sure the runway is long enough if, for some reason, they are uncertain of the runway length. Similar logic could probably be applied to the rule regarding threshold markings ("piano keys"): What does the number of white bars in runway's threshold mean?


Why couldn't the CRJ100/200 be equipped with triple-string autoland? The gold standard for zero-visibility ILS approaches and landings is a triple-string autoland system, where the signals from the localiser and glideslope beams and the aircraft's radioaltimeter system1 are fed into the aircraft's autopilots and control its flightpath directly (with the pilots monitoring the system so that they can execute a go-around if the ILS signal is lost or an autopilot fails), cutting out the human middleman.  For redundancy, each of the aircraftside links in the chain (ILS receivers, autopilots, radioaltimeters, etc.) is present in triplicate, producing three parallel autoland strings, each constantly comparing its inputs and outputs to those of the other two strings, so that a failure in any of the components of the autoland system can be automatically detected and alerted to the pilots.
However, apparently, not all aircraft are capable of being equipped with a triple-string autoland, with the CRJ100/200 series being one of the major exceptions:

Simultaneously, pilot organizations globally were advocating the use of Head Up Display systems primarily from a safety viewpoint. Many operators in non-sophisticated environments without many ILS equipped runways were also looking for improvements. The net effect was pressure within the industry to find alternative ways to achieve low visibility operations, such as a "hybrid" system which used a relatively low reliability autoland system monitored by the pilots via a HUD. Alaska Airlines was a leader in this approach and undertook a lot of development work with Flight Dynamics and Boeing in this respect.
However, a major problem with this approach was that European authorities were very reluctant to certificate such schemes as they undermined the well proven concepts of "pure" autoland systems. This impasse was broken when British Airways became involved as a potential customer for Bombardier's Regional Jet, which could not accommodate a full Cat 3 autoland system, but would be required to operate in those conditions. By working with Alaska Airlines and Boeing, British Airways technical pilots were able to demonstrate that a hybrid concept was feasible, and although British Airways never eventually bought the regional jet, this was the breakthrough needed for international approval for such systems which meant that they could reach a global market.

Why couldn't the CRJ100/200 be equipped with a full triple-string ILS-III autoland system?  Even if it didn't normally come equipped with triplicate autopilots/ILS receivers/etc., those surely could have been retrofitted to the aircraft to give it full ILS-III autoland capability...

1: The localiser beam is used for lateral guidance throughout the entire approach until the aircraft taxis off the runway; vertical guidance is provided by the glideslope beam down to flare height, and the radioaltimeters thereafter.

I have experience on that program and can tell you that:
A:  While anything is possible, this would cost a fortune to implement, requiring a complete avionics overhaul.  For a single potential customer?  Snowball's chance in heck.  The customer would have had to commit to paying the development costs, many zillions, which would also have a snowball's chance in heck of happening.
B: By the mid 2000s, no development money was being allocated for that sort of product improvement on the 200. By then the program funding was generally only to deal with airworthiness issues and upgrades to deal with avionics obsolescence, as development money focused on the 700/900.
C: British Airways aside, there was no demand to speak of from the industry for that kind of capability, that anybody would be willing to pay for. Adding HUGs on the 700/900 to get Cat IIIa cert was more than sufficient.  On the 200, even to do that would have required an avionics suite upgrade that no regional operator would be willing to pay for (again, Snowball's chance in...).  Regional operators run on very thin margins.
In the US, by the late 2000s, Regionals would not even implement optional Service Bulletins unless there was a financial payback of ONE YEAR or less.  That meant that only SBs mandated by Airworthiness Directive were being incorporated.


How are rocket engine nozzles able to survive very high temperatures without melting? The temperature of the gaseous products exiting from the nozzle is higher than the melting point of the nozzle material. So how do the nozzles survive without melting despite exposure to such temperatures? What is the feature which enables them to do so?

There is actually quite a lot of information on the subject in the Braeunig web site Basics of Space Flight. To give the salient points:

Liquid-fueled rocket engines

Both the nozzle and the combustion chamber itself need to be cooled. Although most of the thermal energy produced is ejected with the exhaust, some of it will indeed push hardware temperatures up if not checked. Techniques include:

Regenerative cooling, where the propergols (both propergols, or just the fuel) are pumped through a jacket around the nozzle before going into the combustion chamber. This cools down the nozzle, and heats up the propergols that may be cryogenic in nature. This is what was used in the Saturn Vs' Rocketdyne F-1 engines, and the Space Shuttle main engines.
Dump cooling, similar to the above but the fuel used to cool the nozzle is dumped overboard instead of being fed into the combustion chamber and being used as, well, fuel.
Film and transpirative cooling, where a thin film of coolant or fuel is created near the chamber wall.
Ablative cooling, where part of the combustion chamber or nozzle wall is sacrificed. As the material is melted or otherwise burned away, it absorbs some of the thermal energy, thus saving whatever is behind it.
Radiation cooling, where nozzle design is such that heat has time to be evacuated through the part's exterior wall. This is used mainly in small engines, not main.

Solid-fueled rocket engines

No information available. Nothing. Zilch. Nada.

It would seem that the nozzle and combustion chamber materials just need to be strong enough to withstand the heat from the burning gasses. It is perhaps worthwhile to note that solid rocket engines are designed to burn just one single time, and for a relatively short period of time (even the Space Shuttle boosters were extensively overhauled before being put back into service, with any necessary parts changed). Rocket engines need to withstand working conditions for just minutes, instead of the thousands of hours an A/C jet engine turbine would be expected to work without failure.

It would also be reasonable to assume -though this is strictly something I am making up on the go, with much hand waving- that of the techniques described above for liquid-fueled rocket engines, at least two could be easily adapted to solid engines:

Film cooling, with an extra tank of cooling liquid on board.
Ablative cooling, with some refractive material used to coat the inner surface of the nozzle.


Why does this holding pattern have both minimum and maximum altitudes published? Reference the VOR-A Approach to Stellar Airpark (P19), in Chandler, Arizona (shown below):
When JAROD INT is used for missed approach holding the published procedure calls for the aircraft to climb to 3900 feet.  The terminal transition from STANFIELD [TFD]  to JAROD is a NoPT route at 3900 feet (no holding/course reversal [unless approved by ATC]), and the terminal transition from PHOENIX [PXR] to JAROD is 4700 feet.
Why then is it necessary to publish a hold altitude of (Maximum) 6000 feet and (Minimum) 3900 feet at JAROD when anything other than 3900 feet (missed approach altitude) or 4700 feet ( would seemingly have to be assigned by ATC?
For perspective, I have annotated the position of JAROD and Stellar Airpark (P19) on the Phoenix Terminal Area Chart (IWA R-220, PXR R-150, TFD R-355) shown on the second image below.

So that it keeps you under the shelf of the adjoining bravo airspace and because the decent gradient may be steep enough to require an upper limit. As discussed here:

The instrument approach procedure Holding Pattern In Lieu Of Procedure
Turn (HILPT) is designed to facilitate alignment with the final
approach course. The descent gradient from the HILPT altitude to the
Final Approach Fix (FAF) altitude is limited by TERPS criteria to
permit aircraft deceleration and configuration for the final approach.
Due to a combination of this descent gradient requirement and the
surrounding terrain, it may be necessary to employ a smaller than
desired holding pattern template to define the HILPT protected
airspace. Use of this smaller template may require the designation of
a maximum holding altitude on the 8260-2 Form. This becomes the
maximum altitude the aircraft is permitted to enter the HILPT unless
ATC can ensure obstacle clearance by keeping the aircraft at or the
minimum vectoring altitude (MVA) or the minimum

(source)
(red circle is roughly where the hold is, arrow points to minimum altitude)


Does airspeed come into play with vertical speed, in terms of who will reach the ground first? So let’s say there’s two aircraft, which are the same, and both are cruising at 28,000FT, the only difference is one plane is doing 260 knots and the other is doing 280 knots. If they both pitched down reaching a vertical speed of -15,000FT/Min at the same exact time, would the aircraft going 280 knots still hit the ground first despite sharing a vertical speed the entire time??

No, both would reach the ground at the same time, although the one with the higher airspeed would go farther before hitting the ground, assuming atmospheric conditions are invariant.

On the other hand, if both aircraft have the same flight path angle, the one with the higher airspeed would have a higher sink rate.


Why don't big commercial planes have full aircraft parachutes? On smaller aircraft, like some Cirruses for example, they have parachutes attached to the body of the aircraft that can help the plane get to the ground safely in an emergency.

I'm wondering why commercial aircraft (like, say, a Boeing 737 or Airbus A320) don't do this?  I figure it might have to do with the speed a jet moves at, or maybe the altitude, but I was hoping to get a more complete answer by posting the question here...

The reason for not using full aircraft parachutes can be stitched together by looking at the many related questions. Let me do this for you:

Parachutes will only help when something essential fails at sufficient altitude for parachute deployment. As paul said here, most accidents happen at take-off and landing where a parachute cannot be successfully deployed.
Parachutes big enough to slow down a whole airliner will be very heavy, reducing payload and increasing the number of flights to transport the same number of passengers. The biggest parachutes designed so far were for the solid rocket boosters of the Shuttle, and paul gave their mass a 3 x 990 kg plus 550 kg for the drogue chute. Wikipedia gives the mass of one SRB at 91,000 kg. Scale this for the zero-fuel mass of an A-320 of 62,500 kg, and the mass will be approx. 2,500 kg. That is equivalent to 25 passengers, or 16% of the A-320's capacity. Adding the parachute will translate into 16% more flights, just to compensate for parachute mass. This is most likely underestimating the true impact because I did not add the mass for structural reinforcements.
The opening shock at travel speed would destroy both airplane and chutes. If we want the parachute system to work in as many cases as possible, we need to make deployment possible at up to Mach 0.85, and then the maximum g-load on aircraft and passengers must not exceed 6 g. (See here for Eiband diagrams which give time- and direction-dependent limits for the maximum deceleration a human being can survive). This is possible with staggered deployment of several chutes with increasing size, and by sewing parts of the canopy and the parachute's strings together, so they can rip apart during opening, which slows the unfolding process. But I expect that this will add to the mass of the parachute system. It will certainly add to the mass of the aircraft's structure, which is currently limited to +2.5 / -1.0 g.

By looking at point 2 above alone, it becomes clear that the addition of parachutes will most likely drive up air travel casualties. If we need 16% more flights to make the cruise part less dangerous, and still most accidents happen during take-off and landing (which are now 16% more numerous), we gain little. Crashes now involve fewer passengers, but their number goes up. Tickets will become 20% more expensive at least (more if the parachute system costs something, which is very likely), and we all know how the majority of passengers votes when faced with a choice of dearer, somewhat safer flights and 20% cheaper flights at almost the same accident risk.


Is it possible to build a honeycombed vacuum balloon? Is it possible to build a vacuum balloon with a near perfect void that can lift heavy objects and doesn't collapse and buckle under the atmosphere?

I expect perhaps a honeycombed or lorimerlite lattice infrastructure with toothpick-like filaments spanning across the honeycomb or lorimerlite voids in an alternating double helix pattern. These "toothpicks" would be slightly thicker in the center and thinner at their ends where they connect to the inside of the honeycombed or lorimerlite lattice. This would be made made of titanium. I would choose a toroidal (donut) balloon.

Would this design work, or is there another design that would?

You can load a decent titanium alloy to about $500 \mathrm{MPa}$ (the ultimate compression strength is quoted at least $850 MPa$, but you need to stay below the elastic limit and have some safety margin). That is $5000$ times more than the pressure at sea level. Therefore, the supporting elements have to take about $\frac{1}{5000}$ of the volume. At density about $4500 \frac{\mathrm{kg}}{\mathrm{m}^3}$, the average density comes at least $0.9 \frac{\mathrm{kg}}{\mathrm{m}^3}$. That is just slightly better than the $1.225 \frac{\mathrm{kg}}{\mathrm{m}^3}$ of air, but way worse than the $0.09 \frac{\mathrm{kg}}{\mathrm{m}^3}$ of hydrogen or the $~0.17 \frac{\mathrm{kg}}{\mathrm{m}^3}$ or helium. And this is only weight of the support—for containing vacuum, the skin will be much heavier as well.

Therefore there is no way this could be better than traditional hydrogen or helium-filled aerostats and it's unlikely to get off the ground at all in practice though the above back-of-the-envelope estimate suggests it just barely might.


Why landing gears still need bungee springs? While studying landing gear, I came across this term 'bungee spring' to which there was no definitive explanation in text with regards to its usage.

So in the image, you can see for the jury strut/ drag brace down lock strut there are 2 bungee springs used even after the presence of downlock actuators.
As per my assumptions they must be used to give the jury strut some extra kick while extension and gravity extension and improve redundancy or there's some other reason?

The key to this is the text in yellow in the bottom right-hand corner

Lower torsion link (Disassembled)

The bungee is simply being used to support part of the mechanism that is being worked on. It will be removed when the work is complete and the lower torsion link reassembled.


Deployment of leading or trailing edge flaps - increase or decrease the angle of attack and critical angle of attack? There are a number of similar questions, but I'd like to clarify the increase or decreases between the angle of attack and critical angle of attack. According to this article, "When the pilot lowers the flaps, two things immediately happen: the wing camber and the AOA both increase."
With regards to leading and trailing edge flaps is it accurate to say deployment will increase AoA and the critical AoA?

How does AOA change?
The angle of attack (AOA) is defined as as the angle between the chord line and the relative wind. When flaps and slats are deployed, the effective chord line changes. This is already nicely illustrated for trailing edge flaps in the article you linked:

(boldmethod.com)
As you can see, the new chord line has a higher angle compared to the relative wind, which results in an increase of AOA. Combined with the increase in camber, this will result in more lift (at the same airspeed), which means the pilot will usually reduce pitch to lower the AOA again when flaps are deployed.
I modified this image to illustrate the same for slats:

Now the new chord line is at a slightly lower angle compared to the relative wind, which results in a reduced AOA. The same is true for other leading edge devices (like e.g. Krueger flaps).
How does critical AOA change?
This depends on the exact type of device used. The following graphic shows how the coefficient of lift $C_L$ as a function of AOA $\alpha$ changes with various trailing edge high lift devices:

(HAW Hamburg - Aircraft Design)
For the slotted flap, critical AOA remains unchanged, but for all other types shown here critical AOA is reduced when deploying flaps. Note however that the maximum lift coefficient is always higher. The reason for the change in slope for extending flaps is already explained here: Why does lift curve slope increase when Fowler Flaps are deployed?.
The following graphic shows the same for leading edge high lift devices:

(HAW Hamburg - Aircraft Design)
Here, critical AOA is always increased compared to the clean wing.


How could a wood and fabric aircraft be controlled after a fabric tear mid-flight? This question is specific to wood and fabric aircraft.

What would happen should the fabric for a wing tear mid-flight and what should the pilot do to increase his survivability following such an incident?

For the sake of the question, assume it's bird strike or similar that caused the tear, to one wing only, without any additional structural damage other than to tear the fabric.

I'm aware that for a large tear, the aircraft would spin out, and for a small tear it would have only a small effect(?), so I'm thinking specifically for a tear large enough to have a significant effect, but small enough that the pilot has a chance.

I've found very little about what to do following a fabric tear mid-flight. I found several AAIB reports - but these talk about the damage and what happened, not about what options the pilot had after whatever event caused the damage in the first place.

A wing tear is not something people train for because the impact on the airplane depends on where it is, how big it is, and what other systems have been damaged. If it's just a fabric tear then the damaged wing will produce less lift than the good one, meaning the airplane will want to roll in the direction of the damaged wing. For a pilot to survive there needs to be enough aileron and rudder authority to compensate for this and keep the plane level. So the first priority is to maintain positive control of the airplane and learn how to fly it again by using control inputs against the rolling action. If I feel like I need more aileron power I would decrease speed from cruise in small increments, seeing how a slower speed effects my ability to control the airplane, if it reduces the rolling and gives me better control then I'll keep decreasing speed bit by bit to find a sweet spot. If the damage happens at a slow speed, like in a climb, I would increase speed by increments. I would keep a very healthy margin above stall speed though, as the damage to the wing has probably increased the stall speed of the damaged wing. If the damaged wing stalls then I'm in a snap roll and unlikely to recover.

Once I have control I want to land as soon as I can, and I ideally want a very long runway into wind with emergency services. If I know the area well I probably already know where I want to go. If I can't maintain altitude then I need to find a big field, quick.

Once I've aviated an navigated I will communicate and declare an emergency with ATC and state my intentions. ATC can't help me fly the airplane so I didn't need them before now, but now they can help reduce my workload. If I don't know the area ATC can help me find the best place to go, and they can give me weather information and notify emergency services.

Once I get to an airfield comes the tricky part - landing. It's tricky because I don't know when the damaged wing is going to stall, so I have to keep a lot of extra airspeed on approach and landing without flaps (flaps will change the shape of the wing and the dynamics of the situation in ways I cannot anticipate). This means a faster approach and putting the wheels on the ground at a much faster speed - this is why I would want a really long strip. Once the wheels are on the ground if one wing stalls before the other I can probably control it, and the wheels will help give some stability as well while I gently brake.


Is there a worldwide association for stunt/trick/tournament hang-gliding? I'm wondering if there is any prevailing organized body of sports-people in hang-gliders, other gliders, and/or personal non-powered glide craft in general?

I'm particularly interested in stunts related to gliding, competitions, and how to find people in each locale (presumably) thorough an 'organized' body of sports-people.

FAI (Fédération Aéronautique Internationale)

  – The World Air Sports Federation, is the world governing body for air
  sports, aeronautics and astronautics world records. Its head office is
  in Lausanne, Switzerland.[3] This includes man-carrying aerospace
  vehicles from balloons to spacecraft, and unmanned aerial vehicles
  (such as model aircraft and UAVs). It was founded on 14 October 1905.

FAI is the international governing body for Acrobatics through its FAI Aerobatics Commission("Commission Internationale de Voltige Aerienne" – CIVA).

For Gliding through FAI Gliding Commission("International Gliding Commission – IGC").

For Hang Gliding and Paragliding through FAI Hang Gliding & Paragliding Commission ("Commission Internationale de Vol Libre – CIVL)