What are the FAA regulations concerning controlled descent of a light payload? I'm part of a High Altitude Ballooning club. Our main goal for this year is to achieve controlled descent of our payload. We plan to use Magnus force cylinders to go about this. I have found nothing in FAA documentation that specifically mentions something of this sort requiring extra clearance, but am still somewhat worried about putting the payload 100,000 feet up and then dropping it down in a controlled manner without being absolutely certain, as an object falling out of the sky in a directed manner could obviously garner concern if people didn't realize what it was. Does anyone know if there are specific regulations for this sort of thing, and whether there are or not, what should I look into doing? Thanks for the help

The FAA FAR says the following on the matter,

Sec. 91.15
Dropping objects.
No pilot in command of a civil aircraft may allow any object to be dropped from that aircraft in flight that creates a hazard to persons or property. However, this section does not prohibit the dropping of any object if reasonable precautions are taken to avoid injury or damage to persons or property.

As long as you take precautions not to hit anything you are ok. All things considered you are somewhat at the mercy of the FAA here, if something were to go wrong it would most likely be considered your fault.
After some looking around there are some other things to consider. Since you are using Magnus Force Cylinders to control the decent depending on how you look at it these can be considered a "Parachute" by the FAA definition

Parachute: means a device used or intended to be used to retard the fall of a body or object through the air.

Likewise what you are doing may also be considered a "Parachute Drop"

Parachute Drop: means the descent of an object to the surface from an aircraft in flight when a parachute is used or intended to be used during all or part of that descent.

Another interesting point is that from 100,000 ft you will be busting through the Class A airspace here in the US (and likely class E). For that you may want to read up on parachuting in controlled airspace.
Again similar to the dropping, parachuting must be done with caution

§105.5   General
No person may conduct a parachute operation, and no pilot in command of an aircraft may allow a parachute operation to be conducted from an aircraft, if that operation creates a hazard to air traffic or to persons or property on the surface.

Again a lot of this is open to interpretation, since you have no (presumed) way of controlling the vehicle on the decent I would say it does not fall under what the FAA considers a UAS/UAV. You may want to reach out to the FAA directly about doing something like this from the kinds of altitudes you intend to.


How accurate is the inflight location information? I'm wondering how accurate the location information displayed on the in-flight entertainment system is. As I recall, it always shows quite direct routes, such as this:

However, I'm wondering how accurate this information is. I can image that because of ATC the route will not be as smooth as displayed above. Does it simply show a predetermined route as function of time?

More towards a specific case, would the people onboard the Malaysia Airlines MH370 be able to see the changed course of the aircraft?

The route is actually quite accurate; it is derived from the navigation system of the aircraft. You can determine your departure and arrival routes pretty well from the inflight entertainment system if you are familiar with the routes on the airport you are flying.

In the image in your question you can see a slight course change East of Newfoundland. This is where the aircraft entered its oceanic track.

If the system was operating on MH370, it would have shown the course change as well.

Below you see what the IFE showed on 11 september 2001 when aircraft heading towards the USA were not allowed into US airspace after the attacks.

Source: airliners.net


Is baggage always offloaded when a passenger does not travel? For terrorism concerns I think many airlines offload checked in baggage if a passenger somehow does not end up travelling on a flight.

How strictly are these rules followed? e.g. If a connecting passenger with a tight connection cannot make it to the gate in time will the airline actually send in a ramp guy into the baggage hold to remove specific pieces of baggage? How feasible is it to do thing when the bags are in pods or the Unit Load Devices? Do they have to remove the load device from the hold before they can extract a specific bag?

How does the gate delay of just waiting for the errant, late passenger compare to the time & effort needed to find & offload his bags?

PS. Since bags do get misrouted I'm sure at least some bags fly without a passenger owning them on board.

Normally, baggage takes much longer to switch flights than self-loading cargo, so your scenario is highly unlikely.

In the event of a passenger missing and his/her baggage already on board, all bags need to be unloaded until the orphaned bag is found. When ULDs are used, those must be unloaded first and are then unpacked, mostly on the apron next to the aircraft.

Waiting for the missing passenger is an open-ended game. At some point, you must decide on a course of action with a fixed exit so you can move on.

Normally, every airline is required to unload an orphaned bag. I am sure some are more strict about this than others.


What safety precautions are taken for an airline prototype test flight? Regarding the software, the equipment and the personnel.
Can the crew jump out of the plane with parachutes or is it a bad idea?
Additionally, if you would compare the safety of today and the 1970/80s what would be the difference?
Thanks in advance.

The bail-out procedure is usually only available on the first and second prototypes, which are the riskiest because they are usually designated for testing aerodynamics, dynamics, performance and flight controls, as well as for envelope expansion. Obviously, it's only used as a last resort when recovery is deemed impossible.
In an efficient and professional flight test organization, each flight test is planned out in advance. The test requirements and procedures are written by engineers to ensure that they can be carried out successfully and safely, with clear pass/fail criteria, as well as abort criteria should airplane deviate from safety thresholds.
The crew, including pilots, flight test engineers, and ground telemetry engineers, are briefed on the test procedures and the applicable flight envelope and systems restrictions on the test day. Flight risks are identified and treated accordingly. For example, if a stall test is planned, the risk to spin/deep stall may be high enough to warrant the arming of the spin chute.
The restrictions are some of the most critical technical documents to ensure the safety of flight. They contain the following:

Limit the flight envelopes, and expand only insofar as the planned procedures can be carried out successfully;
Outline systems limitations and defects, and procedures to go with them;
Performance penalties, including takeoff/landing speeds/distances, that may be impacted by the non-conformant systems or failures;

Any non-remote failure or combination of failures would have been checked out in a pilot-in-the-loop simulator with the best-known flight dynamics and systems models/rigs. The results of the evaluation would be a major driver in adding/revising/confirming the restrictions and the Airplane Flight Manual under development.
Another layer of defense lies in the onboard flight test engineers, who will be monitoring the critical flight parameters relevant to the test. They direct the flow of the testing and have direct line of communication with the pilots. For critical flights, ground telemetry personnel will also be monitoring the parameters. Should the parameters fall outside the abort thresholds, immediate abandonment of the test procedure will be called and the pilots will initiate recovery.


What is a "confidence maneuver"? Order JO 7110.65T Section 6 Part 5-6-1 says

  Vector aircraft:
  a. In controlled airspace for separation, safety, noise abatement, operational advantage, confidence maneuver, or when a pilot requests. Allow aircraft operating on an RNAV route to remain on their own navigation to the extent possible.

What is a confidence maneuver?

As quoted from the entry in the Pilot/Controller Glossary:

  CONFIDENCE MANEUVER− A confidence maneuver
  consists of one or more turns, a climb or
  descent, or other maneuver to determine if the pilot
  in command (PIC) is able to receive and comply with
  ATC instructions.

This could be useful if the controller suspects a hijacking, hypoxia, radio failure, or other situations that would compromise reception and execution of ATC instructions.

Perhaps the best example of an implementation of this would be when ATC suspects a partial aircraft radio failure; a confidence maneuver vector might enable ATC to determine that the pilot was still able to receive instructions, though aircraft radio transmission might be compromised.


What might this P-68 be doing? Right now (28 May 2020, 0910 UTC) this Partenavia P-68 is repeatedly flying, alternately, northbound and southbound over Rome, Italy, in regular straight paths about 45 km long, some 400 meters apart. Flightradar24 gives for it just the model (no callsign, not anything). Yesterday morning it was doing the same, for at least six or seven runs.

What might it be doing? Is this the same kind of flight as in this other question? I can't say, since the flight pattern is somewhat differen: for one, the parallel paths there are some 4-5 km apart, while in this case they are less than 0.5 km.

According to the pattern and altitude, this aircraft is probably doing aerial photography or 3D mapping (or both !) for services like Google Maps or Apple Plans.
The Partenavia P-68 Observer is actually made for this kind of missions. According to this link, the Italian State Police uses it too.

Since it's happening over Rome, it could be on an archeological mission too, but that is speculation.


Intercepts and aerial combat in IMC (or my no-fly zone is full of clouds?!) If a reasonably modern fighter was placed into a situation where they had to engage in aerial combat while in IMC (say if radar picked up non-squawking aircraft coming from a hostile military airbase toward a no-fly zone that you're patrolling, and said no-fly zone and its immediate vicinity are full of clouds), could it be done?  What techniques would be used?  Or would the fighters seek to meet each other away from the cloud cover, since aerobatic maneuvering in IMC is generally not a good idea?

Furthermore, if it was an unknown (not necessarily known-hostile) aircraft incoming, could it be intercepted in IMC, or would the intercept have to wait until the unknown aircraft emerged into VMC?

In the first scenario, where it sounds like you're assuming that the intruder aircraft is known to be hostile even without seeing it, a shot with a radar missile would be unaffected by the IMC, and that scenario is a pretty straight-forward kill.

The hard part of IMC for a modern fighter aircraft isn't killing the target, it's getting the positive ID on it that's necessary before shooting in order to assure the chain of command that you aren't, in fact, about to kill a neutral or friendly aircraft who's wandered into the wrong place at the wrong time with the wrong squawk.  THAT is where VMC becomes necessary, in most cases, to get the required visual ID on the target.

Using radar alone, an interceptor could close to some reasonably short distance (say, inside a mile, with some altitude separation as well), and if the unknown aircraft enters VMC even briefly, then the intercept could be completed to the point where one interceptor makes the visual ID.  With the aircraft being known to be hostile, that interceptor could break away, and a wingman, maintaining position further back, could then take the shot with a radar missile.

Presumably, the "bad guy" has some mission to complete, and most of those (though not all) tend to need VMC to accomplish -- dropping bombs or taking photos or whatever.  So chances are probably pretty good that the intruder is going to get to VMC eventually.  (Or, if he drops bombs off of radar/GPS, then that act itself might be sufficient confirmation of hostile intent that the interceptors would be cleared to engage, ensuring that the bandit doesn't live to ever repeat that mission.)


Is it required to report climbs and descents within a block altitude assignment? The following is assuming US FAA and IFR.
This question stems from a question on CRUISE clearance. Section 4-4-3.d.3 of the 2021 AIM says that in a CRUISE clearance

Climbs/Descents within the block is to be made at the discretion of
the pilot.

I've never been given a CRUISE clearance, but I have been given a Block altitude assignment before (e.g. 8000-12000). I could climb and descend to my heart's content without telling ATC every time I changed altitude within my assigned block. In fact, I've been voluntarily given a block altitude assignment by ATC just to shut me up after asking for too many altitude deviations for weather.
The AIM says about CRUISE clearance,

However, once the pilot starts descent and verbally reports leaving an
altitude in the block, the pilot may not return to that altitude
without additional ATC clearance.

Some of my fellow pilots interpret this to mean that you must report to ATC when you descend, but the way I read this is that you don't have to report leaving any altitude in a Block until you are finished with that altitude or the block, and once you descend AND report leaving an altitude, then that signifies to ATC that they can assign that vacated altitude or block to other aircraft. However, none of this appears to says to me, that you have to report descending within the block if you intend to climb back up in the block later.
In other words, don't report to ATC that you're descending until you are done with the block. For example, if I'm given 8000-12000. And I start my final descent and I know I'm not going to be climbing back up then I'll tell them Cessna 123 10000 descending 8000. Then ATC can assign the 10000-12000 block.
Questions:

When given a CRUISE clearance (which includes a block altitude assignment from MEA to CRUISE altitude) where does it say that a pilot must report altitude changes (climbs or descents) within the block altitude. If not, then where does it say you don't have to report altitude changes.

Is there an FAA publication that provides more information on Block altitude assignments and Cruise clearances besides the AIM?

When given a CRUISE clearance [...] where does it say you don't have to report altitude changes.

In my opinion, it say that by implication in the text you quoted, emphasis mine:

The pilot may level off at any intermediate altitude within this block of airspace. Climb/descent within the block is to be made at the discretion of the pilot. However, once the pilot starts descent and verbally reports leaving an altitude in the block, the pilot may not return to that altitude without additional ATC clearance.

I read that to mean, and as a controller I was taught that that means, you can climb and descend to your heart's content while operating on a cruise clearance. Only once you report leaving an altitude are you required to remain below that altitude; therefore by implication you are allowed to return to that altitude so long as you don't report leaving it, and therefore by further implication you are not required to so report in the first place.
The AIM references the Pilot/Controller Glossary term "cruise" which contains the same exact verbiage.
The 7110.65 contains instructions to controllers that further this interpretation, particularly 6–6–2c under the Non-Radar section and 5–6–6a under the Radar section, which say that controllers cannot use Mode C altitudes to guarantee vertical separation if one of the aircraft involved is on a cruise clearance—because the aircraft is allowed to climb or descend without notice.


Why are aerial taxis multirotored, instead of a single rotor? source -- image shows Volocopter's design

I find that in the designs of aerial taxis, particularly in Volocopter's design, the design consists of a system of multirotors.

What is the main reason for not substituting this bunch of rotors with fewer bigger blades (helicopter)? As far as I know, a helicopter is energy efficient for horizontal displacement, and the multirotor is at hovering. Does a quadrotor taxi provide any other dynamics advantage?

There are a few main reasons most electric air taxi concepts have multiple rotors.

1) Mechanical simplicity.  Helicopters are controlled by varying the angle of attack of the blades as the rotate, and the mechanical mechanisms to do this (swashplates) are complex and expensive to build and maintain. The thinking is that with electric motors, you can stabilize the vehicle using differential thrust and eliminate the complexity of those systems.  This has implications for vehicle cost.

2) Noise.  One of the main reasons there aren't any helicopter airlines around now (and there used to be) is that helicopters are very noisy.  Noise in rotorcraft is related to a lot of things, but one of the main drivers is blade tip speed.  With more, smaller rotors, you can have lower blade tip speeds for the same disk area, thereby reducing noise.  Whether this has the potential to reduce noise enough to make a significant difference has yet to be conclusively demonstrated, mostly because there's no clear definition of "enough noise reduction".

3) Safety.  Another argument commonly made for eVTOL air taxis is more motors = more safety, because if one motor fails you have lots of others to keep you in the air.  The validity of this argument depends on how much redundancy you have in the rest of your powertrain, but it principle the opportunity for more redundancy offers a pathway to improved reliability.  There are new failure modes introduced by this multitude of rotors and in general these vehicles have no autorotation capability, making a total power failure much higher consequence; all of which needs to be taken into account.

4) It looks cool There's probably more to this argument than it gets credit for.  Most of the investment and momentum behind the air taxi concept is coming from Silicon Valley and not the traditional aerospace players (who, it must be said, are started to get onboard - especially Airbus). This creates pressure to develop a product that looks and feels revolutionary, to raise the billions required for aircraft development.  Public acceptance of these systems will also be an issue, and public opinion in many large cities is pretty anti-helicopter.

From a performance standpoint the big difference between most multirotor concepts and current helicopters is that lots of multirotor concepts are battery-powered (for noise, local emission, and infrastructure flexibility reasons). Batteries are much worse than avgas from a energy/weight standpoint.  A hybrid-electric multirotor would have broadly similar performance to a hybrid-electric helicopter, assuming they had the same disc loading.


How to find the measurement of how far Tail plane to Center of gravity of the aircraft? How do you find the measurement of Piper Archer Tail Plane distance to the center of the gravity.

Google really doesn't help me... maybe you guys know some website that has databases of small aircraft.

Thank you very much and best regards,

First you calculate the position of the CG, then you do a simple arithmetic calculation based on the station of the tailplane.


Why don't we fly helicopters with yokes? Both yokes and sticks are common in fixed wing aircrafts, with yokes on mainly passenger-carrying aircrafts and sticks mainly on gliders, aerobatic aircrafts and fighter jets.

However I have never seen a helicopter with a yoke-style flight control. Why?

Well first off, a helicopter doesn't have either a yoke or a stick; it has a cyclic.

Second, the original use for a yoke or a stick was to provide a pilot with a mechanical advantage in actuating the airplane's control surfaces against the force of the relative wind.  Helicopters never needed this as the cyclic actuated the swash plate on the rotor mast, changing the pitch of the rotor blades as they passed over.

Third, helicopters demand a little more 'hands on' attention when flying them as opposed to airplanes.  The helicopter pilot is required, particularly in hovering, to make constant adjustments to the cyclic, collective, throttle (if not equipped with a governor) and anti-torque pedals.  Therefore a yoke style cyclic is not useful to a helicopter pilot.

A cyclic does not necessarily need to take the form of a traditional joystick as in the example from an MD900 (Top) and an R22 (bottom).


What is this high flying aircraft over Pennsylvania? Yesterday afternoon I photographed a Boeing 777-300ER flying over my home, according to radar data it was at approximately 32,000 ft. In the photograph there is another aircraft present, it is much smaller and higher in altitude (40,000-50,000 ft) and it is a small aircraft, possibly a drone or military. It did not appear on any flight tracking sites. I usually see military traffic flying in that particular route and heading. I have numerous "raw" images of this particular aircraft.

I originally though it may be an L-39 although that particular aircraft does not have a T tail design and I think that it would struggle at that altitude. The photographs were taken at 1545 EST over the LVZ VOR.

The aircraft was flying an almost perfect east to west heading usually reserved for military traffic. One interesting note is that it was not leaving a contrail. I routinely photograph B-52's, tankers, and fighter aircraft transitioning over my home at or about that altitude and they almost always leave contrails.

Using the location you gave, I tracked back aircraft in that area at that time, and found a scenario that fits with your photo:

(Source: Flightradar24)

So, judging by that, the jet in question is actually a Learjet 31, as said by John K.

Here are some blueprints, and the dimensions are similar:


What is the maximum legal flight time for single pilots under Part 91/135 operations? I'm referring to FAA Part 91 and 135 operations (or similar,  EASA) and the maximum duration of one single flight (not the maximum duty time per day / week / month). If any, what are the legal flight time limitations for single pilots? In other words, which flight time requires more than one pilot?

Short answer: no limit for private Part 91 operations, otherwise 8 hours.

The only Part 91 regulations I can see on this are in Subpart K - Fractional Ownership Operations. There's too much information to quote here, but see 91.1057, 1059, 1061 and 1062. For a single-pilot operation the basic limit is 8 hours, per 1059(b):

  (b) Except as provided in paragraph (c) of this section, during any 24
  consecutive hours the total flight time of the assigned flight, when
  added to any commercial flying by that flight crewmember, may not
  exceed—

  (1) 8 hours for a flight crew consisting of one pilot;

There's no restriction for typical private GA pilots, apart from 91.13 on careless or reckless operation. Flying while very tired could easily be seen as reckless if it affects the safety of a flight.

As for Part 135, the regulations are in Subpart F—Crewmember Flight Time and Duty Period Limitations and Rest Requirements. Again, there's too much to quote but the basic limit for a single pilot is 8 hours, per 135.267(b):

  (b) Except as provided in paragraph (c) of this section, during any 24
  consecutive hours the total flight time of the assigned flight when
  added to any other commercial flying by that flight crewmember may not
  exceed—

  (1) 8 hours for a flight crew consisting of one pilot;

Your second question about when an additional pilot is required is a bit unclear. A second pilot is usually required because of the type of aircraft or operation, not the length of a flight. But I know very little about Part 135 so I may be wrong; in any case, I think it would probably be better as a separate question.


How much does an ILS approach cost? A statement in this question, asking how to pay fees for using the airport services, without being at the airport, inspires me to ask a question.

Quote:

  (Yeah I know... you gotta pay for an ILS approach... yuk.)

How much does it cost to do an ILS Approach (for the pilot when he pays the bill)?
How much does it cost to do an ILS Approach for the airport (Electricity, Staff, Maintenance, Chart-making, ...)?
Is this listed as seperate item on a bill or is it included in the airport fee?
If it's included, how much would it be?
What percentage is to cover maintenance cost and what is the payment for the controllers?
Are there differences between aircraft size?
Are there differences between ILS Category?

I am asking this question for any country in Europe, because, as Dan Pichelmann pointed out, in US ILS Approaches are still free.

Would appreciate answers.

For New Zealand1, the Airways Pricing Framework is a document which describes how the prices are set but not the actual prices themselves (that is in a different document that it appears you have to sign up to receive). Some excerpts:

Consistent with international practice and ICAO guidelines, Airways uses aircraft weight as the basis for its charges.
En-route charges also vary with distance flown. Intrinsic to the formulae is the principle that prices should be
transparent and practicable. A simple pricing system lowers Airways’ costs and those of its customers.

For IFR approaches:

For aircraft flying IFR, the greater of the Minimum Price or:

for aircraft weights under 5 tonnes = Base Rate x MCTOW / 5
for aircraft weights 5-30 tonnes = Base Rate + Weight Rate x (MCTOW – 5)
for aircraft weights above 30 tonnes = Base Rate + Weight Rate x 5 x Square root of (MCTOW – 5)

» where the Minimum Price, Base Rate and Weight Rate are provided by the relevant price table.
Price tables provide the prices for each service and location. Price tables are provided in Airways’
standard terms and conditions
» where MCTOW is an aircraft’s maximum certified take-off weight measured in tonnes.

There are also different formulas for aerodrome services, en-route domestic, and en-route oceanic service.
More information can be found at the New Zealand Service and Pricing Framework page.
1. Yes I know that New Zealand is not a country in Europe.


How can the landing gear fit in the small room in the engine bay on the Tupolev Tu-144? I recently went to the museum in Sinsheim, Germany, where a Tupolev Tu-144 is on display. I noticed that the landing gear of this plane is actually way wider than the space it has available when retracted. How can this work? Does the gear fold before retracting?

Sadly, I wasn't able to find any video footage of the TU-144 retracting its gear. Please take a look at the picture I took to understand what I mean:

The Tu-144 uses much smaller wheels than comparably-sized subsonic aircraft. This makes it possible to rotate the gear bogie sideways towards the middle of the aircraft, so it can be stowed vertically inside the wheel well. Your picture already hints at that:  Note that the gear strut is offset inside the wheel well, so it would leave more space on one side for the gear bogie.

Tupolev Tu-144 landing gear (picture source). Note the big drums of the wheel brakes: They were needed to stop the aircraft - the engines had no thrust reversers! Inside are stacks of disc brakes to absorb the energy that comes with a landing speed of 270 km/h. Also note the unusual sideways arrangement of the scissors link: This way it did not interfere with the rotated wheel bogie. Next clue: The big hydraulic cylinder on the left was used to pivot the bogie around an axis parallel to the direction of flight.

Picture of a photo from Tu-144 landing gear test, including finger print (picture source). This shows the gear in mid-sequence: The bogie is already rotated and lies sideways, with the gear strut between the wheels. Now the strut pivots forward and up into the wheel well.

Requiring complex motion adds more failure modes: On its 59th flight, the XB-70A suffered a malfunction of the left gear which left the bogie in the upright position. If you want to know how it was supposed to work, watch this video from 14:47 on. The picture below is taken from this video.


What are good study guides/practice tests for the airframe maintenance certificate? I am approaching my 18 month mark on the job. Wanting to get my A license first. I have done all kinds of airframe work in this time period. Wondering if anyone has suggestions for the names of the good practice tests books for general and airframe. I have the FAA books on all 3 subjects just no study guides or practice tests. Any suggestions?

I used the Dale Crane series of study guides from ASA years ago, available from either of those two links as well as many other places.

Here is the specific study guide for Airframe, but you will also want the General study guide. These are for written test prep, but might also include Oral and Practical (O&P) test prep.

Image from mypilotstore.com product listing

There are also other options out there. Gleim offers an AMT test prep course, as does ASA in their AMT Prepware, but I don't know that I have any experience with either one. I definitely used one of the digital test prep packages out there, but I can't remember which one. I do like the digital tests, especially since that is probably how you will be taking the writtens anyway.

I also studied the Jeppesen textbooks in addition to the FAA textbooks you mentioned.

You will also want to study the Practical Test Standards (PTS) for your O&P test prep.


What is the rejected takeoff procedure for a blown tire? When I got a tire/wheel issue during takeoff, how should I execute the rejected takeoff procedure? Is it different than the typical rejected takeoff procedure for an engine out that is applying the max brake?

With smaller planes, if you blow a tire on takeoff and have enough runway left to abort, then you should do so. Staying on the ground can be a much better option than a go-around and landing with a flat. Chop that throttle and “fly” the aircraft until it comes to full stop. That said, there will be certain issues to consider based on which wheel is the problem.
On a tricycle gear plane, popping a main will generally cause the plane to pull in that direction, and standing on the brakes aggressively can make it worse. It may require more gentle braking to maintain directional control and avoid going off the side of the runway, and this will, of course, increase stopping distance. If it’s the nose wheel that goes, directional control may be erratic and it might help to hold aft yoke to take some weight off the front gear as you apply brakes. If the plane has differential braking, you might be able to steer the plane with more authority by using stiffer pressure on one brake-side or the other.
If you’re in a taildragger, you may be straight out of luck. Keep those brake inputs punchy, and hopefully you can avoid a ground loop.
Most modern airliners have multiple tires on each landing gear strut, and the tires are designed to handle the load if one of the tires is compromised.
If the pilots know a tire has failed during takeoff at low speed, they will abort the takeoff using a prescribed procedure. At high speed, they will typically take off, perform a go-around, and return to land for a safety inspection.


How does the mixture of an engine affect the engine's operation? I know that in most piston aircraft that there is a mixture control for the engine. My question is, how does the mixture control affect the engine's operation and what type of situations dictate a particular mixture setting? Would an incorrect mixture setting be detrimental, a minor effect or nothing at all?

Simple Answer: Running the engine lean or rich at different altitudes.

Longer Answer: There are a couple of reasons you want to adjust the mixture of a aircraft engine.

Since air density changes with altitude, it's a good idea to be able to change the fuel/air mixture at different altitudes.  If you did not adjust the mixture at high altitudes you may not get full power because the air is thinner and now there is same amount of fuel being mixed with less air.  All the unburnt fuel can cause issues like loss of power and/or fouling of plugs.
Being able to lean the mixture at higher altitude lets you save fuel, so you can go further on a full tank.  (hence saving money)
Running a engine rich can help cool engine.  Fuel acts like a coolant in this manner.  Typically on climbing you want to run the engine a bit rich because your going slower and less air is able to help cool the engine.
Traditional piston powered aircraft engines are shut off by pulling the mixture to the off position.  This starves the engine and burns off remaining fuel in the cylinders.

This topic can also bring up other discussions.  Like EGT, CHT, running an engine rich of peak or lean of peak, monitoring fuel flow rate with a flow meter, and fuel injectors on fuel injected systems.

Hope this helps.


How to demonstrate that an elliptical circulation distribution can be induced by an elliptical chord distribution? I intend to demonstrate that a wing with an elliptical chord distribution, without torsion ($\alpha(z)=\alpha=\text{const}$) and constant section ($\beta(z)=\beta=\text{const}$, and $a_{2\text{D}}(z)=a_{2\text{D}}=\text{const}$), can induce an elliptical circulation distribution.
Well, for an elliptical chord distribution, the chord is defined by:
$$c(z)=c_C\sqrt{1-\left(\frac{z}{s}\right)^2}$$
where $c_C$ is a constant.
On the other hand, the circulation distribution is defined by:
$$\Gamma(z)=\frac{1}{2}a_{2\text{D}}V_\infty c(z)\left[\alpha+\beta+\alpha_i(z)\right]$$
So, by substituting $c(z)$ on $\Gamma(z)$, we get:
$$\Gamma(z)=\frac{1}{2}a_{2\text{D}}V_\infty \left[c_C\sqrt{1-\left(\frac{z}{s}\right)^2}\right]\left[\alpha+\beta+\alpha_i(z)\right]$$
which can be written as:
$$\Gamma(z)=\Gamma_C(z)\sqrt{1-\left(\frac{z}{s}\right)^2}$$
where $\Gamma_C(z)=\frac{1}{2}a_{2\text{D}}V_\infty c_C\left[\alpha+\beta+\alpha_i(z)\right]$
So, to demonstrate that an elliptical chord distribution can induce an elliptical circulation distribution, we would also need to demonstrate  that $\alpha_i(z)=\alpha_i=\text{const}$, to make $\Gamma_C$ a constant.
I don't know how to do this last step. How would you do it?
Note that:
$s:=$ semispan of the wing,
$z:=$ transversal coordinate of the wing, it goes from $-s$ to $s$,
$\alpha:=$ geometric angle of attack,
$\alpha_i:=$ induced angle of attack,
$\beta:=$ symmetric of the null lift (geometric) angle of attack,
$a_{2\text{D}}:=$ airfoil lift coefficient slope,
$V_\infty:=$ freestream airspeed.

First, let's transform the coordinates to polar coordinates for simplicity by introducing a variable $\theta$ such that:
$$z=-s\cos{\theta}$$
In this coordinate, the chord distribution is then:
$$c(\theta)=c_C\sin{\theta}$$
Let's write the unknown lift distribution of the bound vortex as a Fourier sine series, again in the $\theta$ coordinate:
$$\Gamma(\theta) = \sum_{n=1}^{\infty}A_n\sin{n\theta}$$
Through Biot-Savart, the induced AOA can be computed from the trailing vortices, such that:
$$\alpha_i(z) = \frac{1}{4\pi V_\infty}\int_{-s}^{s}{\frac{(d\Gamma/d\zeta)}{z-\zeta}d\zeta} = \frac{1}{4\pi V_\infty}\int_{0}^{\pi}{\frac{\sum_{n=1}^{\infty}{nA_n\cos{n\theta_0}}}{\cos{\theta_0}-\cos{\theta}}d\theta_0} = \frac{1}{4V_\infty}\sum_{n=1}^{\infty}{nA_n\frac{\sin{n\theta}}{\sin{\theta}}}$$
Now collecting everything together and put into your original equation, we have:
$$\Gamma(\theta) = \frac{1}{2}a_{2D}V_{\infty}c_C\sin{\theta} \left[ \alpha - \beta - \frac{1}{4V_\infty}\sum_{n=1}^{\infty}{nA_n\frac{\sin{n\theta}}{\sin{\theta}}} \right] = \sum_{n=1}^{\infty}A_n\sin{n\theta}$$
The key, at this point, is to realize that each $\frac{\sin{n\theta}}{\sin{\theta}}$ is linearly independent to the others, so in order for the other terms to satisfy the above relation for all $\theta$, they must be simultaneously zero. That is,
$$A_n = \begin{cases}
      A_1 & n=1\\
      0 & n>1\\
    \end{cases}$$
So now the circulation and chord distributions have the same form, which are elliptical.


Who designed and built Rans S-7 airplane? I read in the Washington Times, that a man named Swingle, who has no knowledge and experience in aircraft design, built one which he called a bush airplane. But I read in Wikipedia, that the RANS S-7 series seems different as it was built by a company, Rans Inc, seems after the founder name, Randy Schlitter.

Does anyone know the complete story about the aircraft, the engine specification, the size, the weight, the dimension, etc, of that Rans S-7 as mentioned in the Washington Post article? It is interesting as it can land in a savanna.

The Ran's S-7 is a kit plane. The article didn't clearly state it, but the gentleman from Ohio bought a Rans kit and assembled it himself, he didn't design the aircraft, he put a kit together.


How are naval jets moved around below the deck of a carrier? There are many kinds of jets on an aircraft carrier. I'm curious how they're moved around below deck. They have to be moved around for storage and to get to and from the large elevator that takes them up to and down from the flight deck.

So how are they moved? Is there some tug? Or something powering their wheels? I really hope they don't have to use their jet engines below deck, as that seems very dangerous to me.

As Simon pointed out, they use tugs. Obviously the engines are not started below the deck as it would have potentially deadly consequences.

The tugs are either electric or powered by a diesel/JP-5 engine. For example, the USN uses the A/S32A-32 towing tractor (also called spotting dolly SD-2), among others.

Image from zone-five.net

This tug is powered by a diesel engine and controlled using a joystick. In order to be useful in the confines of the deck, the tug can rotate with a zero turning radius. The operation is pretty much similar to the other tugs- the tug is moved so that it lifts up the nosewheel, facilitating the aircraft movement.

The French, on the other hand use remotely controlled mototk tugs on board de Gaulle.

Image from mototok.com


Were planned release dates skipped in 2020 for the VFR sectional charts for Juneau Alaska and Dutch Harbor Alaska? Were planned release dates skipped in 2020 for the VFR sectional charts for Juneau Alaska and Dutch Harbor Alaska?
On February 3 2021, the FAA's "Raster Charts" webpage listed a March 26 2020 date for the latest edition of the Juneau sectional, and a February 27 2019 date for the latest edition of the Dutch Harbor sectional.  These dates seem unusually old.  (And interestingly, at that time, the links to those editions didn't even work.)
There was a rather significant airspace change at PASI at Sitka Alaska (which is located on the Juneau chart), effective November 5 2020, which appears to coincide with what should have been a planned release date for this chart.  The E2 Class-E-to-surface airspace at Sitka was changed from an "L" shape with arms to the northwest and southwest, to a nearly circular shape with a very large rectangular E4 Class-E-to-surface "extension" projecting toward the northwest.  As of February 3 2021, the current VFR sectional products available online still showed the old airspace configuration, while the new airspace configuration could be seen by going to the  LAANC map and typing "PASI" in the search window and enabling the E2 and E4 layers.  (Images of each attached below-- screenshots taken February 3, 2021.)
It seems odd that such a major change in airspace configuration would not have been covered by new edition of the VFR sectional chart.  Was a release of the Juneau chart planned for November 5, 2020, and then skipped for some reason?
Bonus: if so, for what reason?
The rather low "edition numbers" shown on the current edition of the FAA's "Raster Charts" webpage for many of the Alaska charts does suggest that they generally been released only about half as frequently as most other charts.  So maybe these long intervals have been planned, or at least did not come as a surprise.
Basically, in a nutshell, this question can be re-stated as "Did the latest editions of the Juneau and Dutch Harbor VFR sectional charts prior to the 2-25-2021 update show an 'expiration date' that was earlier than 2-25-21?  And if so, why was the previous planned update skipped?"
A note in closing -- The FAA's "Aeronautical Chart Bulletins" webpage is currently a good resource for seeing a list of significant changes that have occurred since the last publication of any given VFR aeronautical chart.  Also, as of February 3 2021, this webpage indicated that the Dutch Harbor chart was actually last updated on Feb 27 2020 rather than February 27 2019, so the 2-27-2019 "latest update" date on shown on the "Raster Charts" webpage on 2-3-21 may have been a typo.  That doesn't change the basic thrust of this question-- was a planned update in 2020 missed?

The FAA has just switched to a 56-day release cycle (double AIRAC cycle) for all VFR sectional charts. In the process of aligning the release cycle, they may have skipped an update. However, the chart of Dutch Harbor was on a cycle of one year before, and would have been due on 25th of February anyway. Juneau was also on a one-year schedule and would have been due on the 25th of March. It is very unlikely that a release would have been skipped.
The story behind the switch to the 56-day release schedule can be found in this FAA briefing. See Milestone #2 below, which may be the reason for skipping a release.

Background/Discussion: The lifecycles of FAA-produced Visual Flight
Rules (VFR) Charts vary from 168 days to two years and at one time
various charts did not update for years longer (Helicopter and Grand
Canyon for example).
Extended and unsynchronized lifecycles create an
undue burden on the NAS and on chart users. The NOTAM System must
carry many facility NOTAMs until consistently charted. As a result,
chart users are burdened with numerous NOTAMS and difficulty arises in
identifying pertinent NOTAMs and correctly applying them. Numerous
changes are alerted in Chart Supplement Chart Bulletins that many
users either do not know exist and/or do not find readily accessible.
Unsynchronized chart dates lead to inconsistent data capture on
overlapping areas, adjacent charts and other chart products.
Producing
56-day VFR Charts will provide significant relief to a number of these
issues. The NAS picture will be consistent with that reflected on
Enroute, Terminal and Supplemental products. NOTAMs will be
significantly reduced as charts will capture changes with every 56-
day AIRAC cycle. Chart Supplement Chart Bulletins will no longer be
necessary.
Planned Actions: Update the VFR Sectional, Terminal Area,
Flyway Planning and Helicopter Route Chart series on the 56-day AIRAC
cycle. Implement this effort across a series of milestones:
Milestone
#1 will synchronize the cutoff for VFR Charts with other aeronautical products. (June 18, 2020)
Milestone #2 will eliminate 28-Day AIRAC
date VFR Charts to align with airspace amendments and will stage
charts for 56-day AIRAC date production. (September 10, 2020)
Milestone #3 will realize full implementation of the 56-day update of
VFR Charts and elimination of supporting Chart Supplement Chart
Bulletins. (February 25, 2021)

And more history can be found here: VFR Chart Print Schedule Realignment and Synchronization


Are there any current projects/plans for a VTOL passenger airliner? I was very surprised to see there's a seemingly underway project for a VTOL "business aircraft" that seats a few people.

http://xtiaircraft.com  , https://www.startengine.com/xti-aircraft

They assert they've done a 65% scale test.

I realize historically there have been a couple military transport-sized VTOL aircraft, and there's one or two small ones today.

Is anyone contemplating a regional airliner or even full-size airliner VTOL concept?

US patent 9,475,585 describes a Tilt-Rotor Vertical-Lift Aircraft. This patent was awarded to Boeing on October 25, 2016. The subject aircraft may be anything from a personal aircraft to a regional commercial aircraft for at least 100 passengers.

The two tilt rotors (36) are powered by a number of turbine engines (40) which are fix mounted under the wings. The novelties claimed by this patent are about the transmission of power from the power plants (engines) to the rotors.

Figure 1 - in vertical mode:

Figure 2 - in horizontal mode:

Images source: United States Patent and Trademark Office, www.uspto.gov

Of course, the filing of a patent is an evidence that a company is spending at least some limited resources to the subject. However, this does not mean that Boeing is actually developing such an aircraft.


Garmin 530: What is NXRG telling me? I have a Garmin 530 in a Cessna 550.
It has a constant display of NXRG:x:xx in the upper right corner of a map page. It changes color (yellow and green are common) and the value of x:xx changes to some sort of code (see pictures)
Any idea what this is telling me?

It looks like the "weather product age" for NEXRAD weather data, i.e. how old the current data you're seeing is (see Pilot's Guide, p.13). The number is contextual, based on the weather information type:

The age of the displayed weather product—or the effective time of
Winds Aloft predictions—is shown in the upper right corner of the
display. For example, if NEXRAD is displayed, “0:05” indicates that
the data are five minutes old. If Winds Aloft predictions are being
displayed, “10:00” indicates the effective time for the displayed
prediction is 10:00 AM.

In the first image, the data is 15 minutes old, in the second it's 6 minutes old.
The information and images on p.72 show that NXRG is "Region NEXRAD" and NXCO is "CONUS NEXRAD". P.70 also mentions NXRD, which seems to be just "NEXRAD" and it's used when no data is available.
As for the color, the manual says:

When the age of the displayed XM Weather product reaches one half of
its expiration time, the color of the displayed time changes from
green to amber

NEXRAD data is good for 30 minutes per the Guide, and that matches with the color change at 15 minutes in the first image.
Note: although the manual talks about SiriusXM providing NEXRAD data, ADS-B radar data is also from NEXRAD. Presumably the display uses the same abbreviations, regardless of which service provides the NEXRAD data.


Can a lost aircraft get a DF Steer? When I got my pilots license in 1975, a lost airplane could call almost any FSS and get a DF (Directional Finder) steer. The range was probably upto 30mi. I would request a practice one every 3-4 years. The last practice DF steer I did was 15-20yrs ago.

Can you still get DF Steers (or an equivalent) from FSS?

Direction finders outside of Alaska were decommissioned in 2007 as GPS and and ADS-B, as well as older technologies, have made the DF services obsolete. The DF services in Alaska were decommissioned in 2013.


Commercial aircraft minimum and maximum climb angle and rate? Is it possible for a commercial pilot to set a minimal rate of climb - for example, 350' NM climb rate, target heading of 200 degrees and target altitude of 2000 feet above MSL - before getting radar vectors from ATC when they hit the target altitude?

You are asking several different questions, but I can answer the first part easily enough.

First, let's distinguish between climb rate and climb gradient:  climb rate is expressed as feet per minute, climb gradient is expressed in feet per nautical mile.

The autopilot I am familiar with can be programmed for a target climb or descent rate, heading and altitude.  With ground speed and some math a FPM rate could be set that will achieve a desired gradient, but I am not aware of any systems where this can be actually set.

737 takeoff and climb performance will vary greatly depending on weight and other variables.


How do the Tiger Moth's anti-spin strakes work? As originally designed, the DH.82 Tiger Moth had unpredictable spin characteristics. Many aircraft were lost because spin recovery took too long (i.e. too much loss of height). Many examples of the type have been retrofitted with anti-spin strakes, which extend forward along the top of the fuselage from the empennage. It's shown here on two DH.82a's.

The anti-spin strakes don't prevent spinning completely, but they make the spin more manageable and more predictable. Some operators of the type nowadays haven't added the strakes, because they have found their aircraft to behave itself in the spin even unmodified. There's a theory that the unpredictability of the type was the result of variations in material and construction quality in wartime.

How do the strakes help? What aerodynamic effect causes them to help spin recovery?

The vertical tail of the Tiger Moth is located a bit aft of the horizontal tail due to its sweep, such that the vertical will be in the wake of the root of the horizontal in a typical spin attitude (around 45° angle of attack). I would strongly recommend to fit the aluminium anti-spin strakes - those pilots who had no problem without them flew the Moth at a forward location of the center of gravity, which helps to end the spin. A lighter forward passenger/pilot will make the aircraft behave a lot differently; in spins small differences can translate in a markedly changed spin behavior.

Cut-away drawing of the Tiger Moth's tail. The anti-spin strakes are the parts marked 16.

A spin can be ended in two ways: Either the rotation rate is stopped by neutral rudder or a rudder deflection against the spin, or the separated flow on the wing is reduced by pitching down. The first way works better for aircraft with long fuselages and low wing span, and the second is preferred in aircraft with big wings like gliders. In the end, a combination of both works best and some aircraft need their own technique to end a spin safely.

Generally, it helps to have as much of the vertical tail exposed to undisturbed airflow as possible. Ventral fins are a tremendous help in upright spins but useless in inverted spins. Strakes or fillets ahead of the vertical tail are very effective, especially in fast spins when the angle of sideslip at the tail is high. In the 1930s, Arado in Germany built a range of airplanes where the vertical tail was positioned ahead of the horizontal tail, for the express purpose of making spins easier to end.

Arado 79 in flight (picture source)

The anti-spin strakes produce a vortex at high angle of attack, similar to that on a delta wing. This increases the dynamic pressure on the vertical tail and makes it more effective. Since every bit helps and the spinning characteristics can vary strongly with c.g. position, it would be careless to leave them off.


Does a request for passengers to open vents indicate pressurization issues or equipment failure? This occurrence was a year ago, but it kept bugging me until this day. I am a frequent flyer and this happened only this one time. While the plane (a Swiss A320) was still by the gate and the boarding just completed, the attendants asked the passengers to open the overhead vents because (not sure about the exact term) they have cooling difficulties. At that point it sounded reasonable, but it was around 09:00 in the morning and it wasn't a particularly warm day, it was 20°C at most outside (history says that the maximum temperature that day was 25°C). Roll-back and lift off were briefly after the boarding was complete.

Does a request like that indicate a failure or pressurization issue? I believe we were safe, just curious.

I have occasionally asked passengers to do the same thing.
I have also asked for window shades to be lowered.

The reason is usually because the APU was not working and the ground air conditioning was not doing a good job or was unavailable.

Without the APU the aircraft's airconditioning can not work and engine starting relies on a ground air source to provide air pressure to spin the engines for start up.

When using ground air for starting, the ground air conditioning  is disconnected first and it takes very little time for the cabin to become uncomfortably warm.


What are the financial implications for Lufthansa (and other airlines) of keeping the back row of their A320neo free of passengers? After the recent EASA airworthiness directive concerning the potential for weight and balance problems with the A320neo, Lufthansa announced it would no longer sell seats on the back row of those aircraft.  What are the financial implications for airlines of not being able to fill an aircraft?

Not being able to sell seats on the last row would (in Lufthansa's case) theoretically mean a 3.3% loss of revenue: LH setup for A320neo is 180 seats, 6 seats in last row.

But, only theoretically, because seat occupancy rate for Lufthansa Group was  81.4% (2018). It is very unlikely that all of the flights operated with A320neo would fly 100% fully booked. In a non fully booked flight, the last row would obviously be the first one to be left empty. The actual loss of revenue would be way less than 3.3%, but how much, it is impossible to say.

Anecdotally I'd say that it is a blessing the last row is out of service for now, this Business Traveller article will give you an idea  why: no window, seats do not recline, legroom is smaller...

World Airline News: Lufthansa Group becomes the largest airline group in Europe with 142 million passengers in 2018


What would be the power requirements and performance of a Scroggs-type delta-wing aircraft with a 250 cm span? Roy Scroggs, a tailor, patented in 1917, US1250033, and in 1932 US1848578, a Delta Wing plan form machine 'Flying Dart', flight tested

              with an OX-5 engine, they say anything would fit an OX-5 powered airplane, as in Besler Steam Airplane, it had same Leading Edge swept, 60º, as Handley Page HP 115 of 1961, that tested the Concorde wing (

             )
The page of an study from the French ONERA about vortex over a Delta plan wing is an experiment conducted with the type of pointed wing in the description by Jones, and in the Langley tests on A Lippisch DM-1, but it's not sure if flow will be identical on a truncated point Delta, as used in first Saab 'Draken'.??

I wonder what the power requirements and performance would be of an Ultralight Airplane with a wing span of 250 cm, maximum width allowed on the road, and a total weight less than 299 kg. 115 kg empty weight is the class limit for Ultralight

First, thank you for unearthing this unorthodox design!

However, it shows that paper airplanes don't scale well. Nevertheless, it follows the same laws of physics, so the same equations should apply for a quick performance evaluation. What have we got?

A flat plate airfoil. Maximum lift coefficient will be between 0.7 and 0.8, so minimum speed at a given wing loading will be quite high.
A sweptback delta wing of low aspect ratio, so the lift curve slope will be low. For the same lift coefficient it needs much more angle of attack than a regular airplane. Since upper side flow is separated, airfoil drag will grow with the square of the angle of attack, and the low lift curve slope ensures that drag will be needlessly high.
A big fuselage with a lot of wetted surface area.
A massive separation area at the back which will produce a lot of drag without any benefit, except for improved directional stability.

Let's start with induced drag. The low aspect ratio ensures a nearly elliptic lift distribution, and lifting 300 kg with 2.5 m of wing will create $$D_i = \frac{2\cdot(m\cdot g)^2}{\rho\cdot v^2\cdot\pi\cdot b^2} = \frac{180000\cdot g^2}{1.225\cdot v^2\cdot3.14159\cdot 6.25} = \left(\frac{g}{v}\right)^2\cdot 7483\;N$$
At 20 m/s flight speed this will equal 3,600 N of drag and at 40 m/s flight speed a quarter of that (900 N). Multiply by speed to get the power needed to overcome just induced drag: 36 kW at 20 m/s and 18 kW at 40 m/s.

But what speed is achievable? We need to guess the wing area in order to find the stall speed. I assume 4 m chord and 1 m span at the leading edge, so the wing area is 7 m². Using a maximum lift coefficient of 0.75, this means you cannot fly slower than 30.24 m/s. Whoa! That is 58.8 kts or just below the 61 kts limit for the old FAR 23.

Let's add some safety margin and continue with 40 m/s flight speed, which corresponds to a lift coefficient of 0.43. Now to the angle of attack - this requires to know the lift curve slope. As a slender body it will be slightly below $\pi\cdot\frac{AR}{2}$, and with an aspect ratio $AR$ of below 1 this is maybe 2.2 per radian or 0.04 per degree. At $c_L$ = 0.43 this is 11°. Multiply the weight with the sine of 11° and you get the cost for flying a fully separated top wing: 506 N. Dragging this through the air at 40 m/s needs another 20.2 kW.

Now to the wetted surface: The vertical surfaces add maybe another 4 - 5 m² to the 14 m² of the wing. The Reynolds number is 11$\cdot 10^6$, so the friction drag coefficient is as low as 0.003 if the surface is smooth. Since the upper wing shows separated flow, I will continue with 15 m² surface area. At 40 m/s this equates to 44.1 N of drag, needing 1.76 kw of power.

The fixed and unfaired landing gear will be another source of drag; here I simply double the friction drag in order to account for it, too. I expect that a detailed drag analysis will not change the result substantially.

Your idea of filling the separation area with a ducted fan is probably costing even more performance. Please consider that now you have a high-speed stream of air flowing through a duct running along the length of the fuselage. Better to narrow the fuselage in the rear half so it ends in a vertical rudder.

If we now assume that you avoid any boattail drag this way, flying straight and level at 40 m/s will need a total of 42 kW. Add 50% for manoeuvring and climbing (those extra 21 kW translate to a climb rate of more than 6 m/s - looks OK) and a propeller efficiency of maybe 75% (look at this answer - that could be as low as 60% in reality!), and you end up with an engine requirement of 84 kW or 112.6 HP. It looks like you need a Rotax 914 or similar engine, the mass of which will eat up one third of your budget.


Which operating systems do entertainment systems run on? Which operating systems run the In-Flight Entertainment Systems on commercial passenger aircraft?

According to this article, Linux is at least one of the main contenders in the space, Wikipedia also makes a lose reference to Linux and cites this article as the source. Here is some photographic evidence that its Linux as well. Although I'm sure it varies by maker it seems that Linux is at least one of the main players.


How do pilots maintain awareness of other airplanes during taxi? If I compare taxiing of airplanes with, for example, driving cars, drivers in the latter case regularly check the positions of their cars relative to others by using the different available mirrors. However, that is not an option in airplanes.

Just thinking about all potential possibilities, I imagine that airplanes probably rely on the airport control tower for making decisions that require the knowledge of the relative positions of other airplanes. Also, collision–prevention devices provide part of that information.

My question is:

How are airplane pilots aware of other nearby planes during taxi? Do they need that information, or is not useful for them as instructions are sent by the control tower?

At a large airport, all aircraft movements are coordinated by the ATC tower on the ground frequency. Aircraft should never move without authorization from the controller. The tower will issue instructions to aircraft that might look something like this:

  Taxi to Gate 1 via Alpha, Alpha 1, Lima 3, cross runway 24, hold short Delta.

These names correspond to markings on the ground that match up with the airport taxiing maps. By talking with the pilots, the controllers are able to build up a map of where aircraft are. It also helps that they can look out the window and see the aircraft on the ground.

At airports without a tower, taxiing isn't much of an issue. There aren't many planes around, and there's generally only one runway and not many taxiways. Nevertheless, aircraft taxiing when there is no ground controller comply with "see and be seen" by looking outside and turning on aircraft lights. Furthermore, if the aircraft has a radio, it should self-announce its movements on the ground.


How are batteries cooled in passenger aircraft? What sort of systems are used to cool batteries in the air? Liquid cooled? Air cooled?

I am interested in lithium chemistry batteries in the form of either pouch cells or 18650 batteries inside of boxes placed in the fuselage or wing.

As far as I can tell, current aviation lithium batteries do not use active cooling.

I know the True Blue Power TB17 (Robinson R44 & R66, Bell 505 Jet Ranger X) and TB44 (Cessna Caravan, DHC-6, DHC-8) do not require active cooling.

I haven't seen any easily accessible info on the Saft batteries for the A350.


What is the meaning of first flight and introduction in aircraft production? They are info from wikipedia (here and here). I don't know many about the B-52 Stratofortress, but I'll take another case. The N-250 I remember its first flight which was performed with large scale, watched by Indonesian's former President and many other high rank officers. I remember the date, or at least the exact year. It was 1995.

Then my question is, if 10-Aug-1995 was its first flight which was performed with great fully, then what is the meaning of introduction (15 June 1997 in this case)?. If it was widely open to public when performing first flight, then why does an airplane needed to be introduced?

The first flight of a new aircraft type refers to the first time the aircraft is flying during the development and testing phase. If the testing goes smoothly, it might be that no more changes are necessary and the aircraft can be delivered to customers as it is. But if problems show up during these test flights, changes might be necessary before finishing the final design.

The introduction refers to the first flight by a customer (an airline for commercial airliners or a military unit for military aircraft). This is also referred to as entering service. This could happen in the same year as the first flight (e.g. Boeing 737 Classic series in 1984) or many years later (e.g. Concorde in 1976, 7 years after the first flight in 1969).

Another term commonly used is the launch of an aircraft type, which refers to the start of the development program.

The IPTN N-250 you mentioned was never introduced into service. Wikipedia claims the 15 June 1997 as introduction date, but on this day the aircraft was shown at the Paris Air Show:

(image source: airliners.net, taken by Peter Vercruijsse in Paris - Le Bourget on June 15, 1997)

The image description says:

  "Gatotkoco", the prototype N-250 returning from a demonstration flight at the Paris Air Show. The N-250 programme is currently (early 2000) on hold due to a lack of finance.

This does not count as introduction and is therefore a mistake in the Wikipedia article.


In the Philippines' Civil Aviation Regulation Part 7, what does this part mean? In the Philippines' Civil Aviation Regulation Part 7 it says

  individual certificate of airworthiness of the first production aircraft under the type certificate

I want to know what does "first production aircraft under the type certificate" means.

"first production aircraft" indicates the first aircraft built as part of the "production" run (as opposed to the ones built for the test phase, that are not part of the "production").

"under the type certificate" indicates that the type of aircraft has achieved certification and can be legally flown in the Philippines.

All together it identifies the first production built aircraft of a certain type after the certification was provided (in this case for the Philippines).


Is a "T" (Tango) prefix required before the registration number for Part 135 flights? After September 11th, the FAA required all Part 135 air carrier flights to prefix their registration number with a "T" and use the "Tango November" prefix on the radio.

Every once in a great while (about once to twice a year) I still hear someone doing this, but surely there are more 135 flights than this.

Is it (or was it ever) required to use the "T" prefix for Part 135 flights?

Since you're asking if it's required then I believe the answer is no.

First, just to include the information from another answer, the AIM 4-2-4 only says "should", not "must" (my emphasis):

  4. Air Taxi or other commercial operators not having FAA authorized call signs should prefix their normal identification with the phonetic
  word "Tango."

  EXAMPLE- Tango Aztec Two Four Six Four Alpha.

Second, the FAA's Joint Order defining ATC regulations says in section 2-4-20 (my emphasis):

  Air taxi and commercial operators not having FAA authorized call
  signs. State the prefix “TANGO” on initial contact, if used by the
  pilot, followed by the registration number. The prefix may be dropped
  in subsequent communications

That's the only mention of this prefix in the entire ATC regulations, therefore it's safe to say that controllers don't need the prefix and aren't required to do anything when they hear it.

On the AOPA forums there are a couple of unsupported comments that the prefix was used to give commercial flights priority in the past, and that it's still used for gathering statistics on flights today (although it seems like a very unreliable mechanism for that).


Can longer paths consume less fuel than the (shorter) great circle path? Is the most fuel-efficient route between points A and B always along a great circle ?

Although somewhat counter-intuitive, this comment on an aviation blog seems to suggest that longer paths (in terms of geographic distance covered) can save fuel:

  Oceanic Flights these days are not restricted to the old “defined
  great circle routes”. Modern computerised flight planning systems
  definately take weather into account, and go searching for the best
  winds (tailwinds) or least adverse (headwinds). Particularly in the
  case of westbound flights across the Indian Ocean, where headwinds are
  often ferocious, the tracks actually flight planned, and actually
  flown, are often a long way off “great circle” routes.

That depends how you define longer in aviation. As you can look at it geographically or on the clock.

The hard answer is no, the most fuel efficient route is the one that has the aircraft in the air for the shortest amount of time. If you can take advantage of a big tail wind 20 miles south of the geographically shortest route or at a slightly higher altitude you may burn a bit of fuel getting there but on long haul flights you can make up for the burn, and even gain quite a bit by taking advantage of the winds

Similarly headwinds can really kill your efficiency even over short distances.


Why use Mach number for describing the speed of aircraft? What does Mach speed mean for describing aircraft speed if the speed of sound changes with temperature?

The aerodynamics change with Mach number.

At low Mach numbers (< ~0.3) , air is considered incompressible; it has constant density along the stream line.

At higher Mach numbers, air is no longer incompressible; the density changes as the air passes over the aircraft. The compressing and expanding of air changes the way the air flows, and consequently it changes the performance of the aircraft.

At Mach numbers approaching 1, parts of the flow around the aircraft may breach the sound barrier. This leads to trans-sonic effects such a shock waves which affects the performance of the aircraft even more.

For subsonic aircraft the maximum speed is typically expressed by two numbers: the maximum calibrated airspeed and the maximum Mach number. The first is related to the dynamic pressure the flow of air creates and is typically the limiting factor at lower altitudes. The Mach number is related to trans-sonic effects and is typically the limiting factor at higher altitudes where are is colder and the speed of sound is lower.

For the pilot it thus important to know both the airspeed and the Mach number.


Is ear protection necessary for General Aviation aircraft? What would happen if someone flew a brand new Cessna Skylane/Caravan or a Robinson R22 without using earplugs or headphones? Would they get hearing damage or it would be just a little bit loud where communication with co-pilot need constant yelling? How serious ear damage is?

This study on cabin noise with experiments in a Cessna 172s and a Piper PA-44 got the following results (noise comparisons are mine):

Peak:

Without headset: 101.3 dBA = rock concert (not front row though)
With headset: ~88 dBA* = vacuum cleaner (old bag-style ones, not Dyson...)

Average:

Without headset: 86.26 dBA = heavy traffic (by the side of the road)
With headset: ~73 dBA* = cloth dryer

Those value are not terrible per-se but on the long term ear damage is very likely.

*The study found that a headset reduces the loudness by 13 dBA in average. The reduction should be even higher with a noise cancelling headset.


How do pilots stay disciplined and use checklists, even after they have become routine? I originally asked the same question on Space Exploration but will repeat it also here:

Before every takeoff and every landing, there are several routine checks which need to be done in order to provide the highest maximum safety to passengers.

But after certain number of repetitions, these tasks can feel as tedious especially if you are flying a plane which goes in "turns"

(Real example of what I mean is commercial line between Prague (PRG) and Frankfurt (FRA) where plane lands, people go out, new people go in and plane goes back. And so on)

How do pilots and other personnel make sure that they actually do go through the check every single time without "It was OK last time, so it will be ok this time. Skip it and say it is ok" ?

You stay vigilant by having seen things go wrong.

Like Jamiec mentioned the importance of a proper preflight is drilled into you by your primary instructor from day one in light aircraft, and that mentality carries through all the way up to heavy transport-category aircraft: You want to find any problems you can while you're on the ground, because if you take a problem into the air with you it's a decision you can quickly come to regret.

Personally I've found all sorts of "interesting" things on preflight inspections of light aircraft, including (but not limited to):

Mud wasps building a nest in the pitot tube
Mud wasps building a nest in the fuel drain
(still don't know what was up with that)
Missing screws from a fairing
Flat-spot on a tire
A tennis ball stuffed in between two cylinders
(a common flight instructor trick to see if students are doing a thorough preflight)
Position light lenses installed backwards
(another common CFI trick, but this one was actually a maintenance shop screw-up)
Various light bulbs burned out
Water in the fuel after a heavy storm.

I've also heard some scary stories:

Migrating colony of bees hanging out on the tail of the aircraft
(described as "The tail was literally dripping bees")
Flight controls rigged backwards
Big gouge in the wingtip
(acquired by the previous pilot scraping the tip against another plane's tail taxiing in on the ramp)
The ever-classic "ran out of fuel because you didn't visually check the tanks"


Do pilots eat the same food as passengers? I imagine it might be hard to find a time when pilots can eat, but when they do, what do they eat?

Yes, commercial pilots eat the same meals that the passengers do. They may have extra snacks and such that the passengers don't, but that's it.

It's actually quite easy to find time to eat, since the majority of the actual control manipulation is handled by the autopilot. If the autopilot isn't available for whatever reason, one person can fly while the other eats.

Fun fact: Most airlines have a policy that the pilots must eat different meals, so that if there was a bad batch of chicken that gave everyone who ate it food poisoning, then the pilot that had the fish can still fly and land the plane.


On coaxial helicopters, how exactly does the yaw mechanism work? This question asks how coaxial helicopters achieve yaw. The accepted answer correctly states that this is done by increasing pitch on one rotor while decreasing pitch on the other rotor, which leaves lift the same and creates a yawing moment.

The post became active again on 20 July, when @Andy Ewen asked how the mechanism works exactly:

  ..a lot of the answers are stating the obvious but fail to explain HOW. Yes a torque differential between the rotors will effect a yaw but the real question is how is this achieved?

The post was deleted and not entered by OP as a separate question, hence this question. How is this achieved, exactly?

Mechanically it's simple, and ingenious.
The following is from a 1966 patent titled: Coaxial rigid rotor helicopter and method of flying same (US3409249A) by United Technologies Corp. (Of course this is not the only way, but it's one way as invented by a major aerospace company over 50 years ago.)
I've done the laborious reading referencing numbers and text, and I'll summarize it here.
Swash control

(Don't mind the steering wheel, it's the inventor's idea of pushing the cyclic left/right.) I've added an arrow pointing to 274 in the illustration, it's a wheel, and it's the key.
Using the collective (254) translates that wheel forward and aft, which moves the rigging of both swash plates up/down collectively.
But using the anti-torque (yaw) pedals, rotates that same wheel by way of cable 328. The wheel rotation would move the rigging for each rotor opposite each other.
Below is a simplified elevation view for the effects of translation and rotation of the wheel on both swash plates:

Swash mounting
For yawing, the summary is that the up/down translating parts do not rotate. It is the attachments from plates to rotors that do rotate and are on bearings. Basically two of the same but in a concentric manner.

The two main element per rotor are bearings that permit the vertical translation of the fixed portion, and the rotation of the attachments to the rotor. Focus on labels 136 and 140 (added arrows for easier finding) for the upper rotor, and here's the quotation:

(...) Bearing 136 is positioned between ring member 132 and fixed housing 52 so as to prevent rotation of ring member 132 about the axis of rotation 28 but to permit translation of ring member 132 along axis 28. Swash plate mechanism 130 also includes inner gimbal ring 133 which is pivotable about axis 134, outer gimbal ring 135 which is pivotable about axis 137, and ring member 138, which is supported from ring member 135 by bearing 140 for rotation with blades 96 about axis 28.

(Emphasis mine.)


The FARs "require" the wearing of parachutes for certain types of maneuvers. Is parachute training required? FAR 91.307 (c)  requires that each occupant of an aircraft must wear an approved parachute during the execution of certain types of maneuvers (e.g., more than 60 degrees of bank or
or 30 degrees pitch, etc.).  Is there a legal requirement that those occupants have any specific training in parachute operations or jumping?

No, no training required. But I tried to train my aerobatic students.

I was trained. Working as a CFI I told my students how to adjust the straps, where the D ring was and how to pull it after exiting the aircraft.  I suggested how to end the ride down with minimal damage to themselves.

As far as when to pull the pins on the door and depart is concerned.  If they hadn't heard me say "Jump" the noise of the air rushing in through the hole caused by my missing door and the lack of my butt in the seat - was a reminder that is was time to leave.


Does the DA-42 automatically lean to clean fouled spark plugs? The DA-42 has an automatic run-up method. Specifically, the pilot in command is to hold two buttons (one for each engine) until the run-up is complete. Since the DA-42 has no manual mixture control, does it also automatically lean the mixture when foul spark plugs are detected?

Depends on the variant.  Most DA-42s are powered by turbocharged Diesel engines and do not have spark plugs.  And yes the DA-42 uses an automatic run up cycle in order to test the Engine Control Units (ECU).  The test button is depressed and held while the automatic ECU cycle runs on both ECUs for each engine; the pilot simply monitors the engine gauges for signs of abnormalities.

Now the DA-42L is an exception to this rule as it is powered by Lycoming IO-360 gasoline engines.  It makes use of more conventional run-up procedures.


Do flights of a specific callsign always depart and arrive at the same airports? I've been doing some research using flight data, but I'm not particularly versed with aviation. From a quick look, it appears that, say, a flight with callsign SAA203 will always be departing from Johannesburg, South Africa and arrive in JFK Int'l airport.

Is this sort of thing always the case, are callsigns only changed when a flightpath is retired, or can a given callsign correspond to multiple flightpaths?

You may be confusing callsign (with can be multiple things) and flight code/number as FlightAware may display one or both of these things depending on whats applicable. FlightAware tracks publicly available filed flights at a variety of levels depending on what callsign you search/are looking at the answer may change. For example

American Airlines runs flight AA66 (AAL66) from JFK to BCN and the code AA66 is used to identify that flight (AA67 is the return flight). This code may also be used for a code share. Generally these codes stay fairly consistent unless there is an overlap (see ymb1's) comment for how dupes are handled.

Generally non scheduled commercial and private traffic the flight files with their tail number, for example in the US tail numbers are often 5 (or possibly 4) digits and a preceding N. So N12345 may file for a flight from anywhere to anywhere they want to go. This history log is a good example of a charter plane that seems to fly out of KDYL to lots of places.


Why don't we treat all takeoffs as short field in GA? Depending on the airframe, there are a number of techniques to reduce the Take Off Distance required. For example, deploying flaps.

What advantage is there to NOT using short field take offs, even when runway length is sufficient? Surely it's always advantageous to require the minimal amount of runway, thereby adding a larger margin for error?

Short-field take-off techniques often achieve a shorter ground run by hurting climb performance. While having more runway is great for safety, planning to use less of the runway is not a huge benefit: you always plan to have enough runway left if you need to abort during the take-off roll. It's much better to have more height quickly in the climb-out: it gives you more margin against obstacles after the runway's protected area, and it gives you more height to land in case of an engine failure after take-off (EFATO).

The numbers for a normal take-off optimise for a good rate of climb, which has the greatest benefit to safety. A short-field take-off gives you an extra option when the runway length is too short for that - at the cost of some margin if there's a problem in the climb-out.


Does a hold-entry count as a hold for instrument currency? So in looking at the instrument currency requirements for the FAA (6 approaches, holds, intercepting & tracking courses), I'm having difficulty nailing down what constitutes a hold.
Based on AIM 5-4-9(a)(5) where it talks about HILPT, it sounds like all I need is to do the hold-entry and get established inbound, which feels a bit odd since for a parallel-entry since that's nearly equivalent to a procedure turn (which I believe wouldn't count as a hold).

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

Based on the above, I assume if I fly a HILPT as part of an approach in actual/simulated instrument conditions, I can count that as a hold. Following that logic, would flying the hold-entry at a missed approach fix also qualify as flying a hold? Or does that excerpt above only apply to a HILPT?
Is there any official guidance/interpretation provided in regards to this?

The entry of a hold is sufficient for the holding procedures task on the instrument rating practical test in the US and for execution of an instrument approach procedure that begins with a hold, so it follows that it would also be the appropriate standard of completion for currency purposes regarding the required holding procedure.
I think the text you quoted in the question serves as a sufficient source by itself.


Is flutter speed always smaller than divergence speed for aircraft? In aeroelasticity, there are three main phenomena that one should take care of: divergence, aileron reversal and flutter. Each of them has an associated speed at which the phenomenon might start to occur.

During wind-tunnel tests it is possible to increase the flutter speed to have access to the divergence speed first by using some small masses smartly placed on the wing. This is due to the fact that usually flutter speed is smaller than divergence speed.

Is it always the case for aircraft (without additional masses on the wing)? If not do you have any example? If yes do you have an explanation why or a mathematical proof of it?

Flutter speed will usually be smaller than divergence speed. Flutter will appear first because as a phenomenon, by definition, describes the state of the deformation of the wing where it deflects for example up and down in a vibrating fashion. Divergence on the other hand is when the moments from the aerodynamic forces acting on the wing are larger than the restoring moments due to structural stiffness thus resulting in failure.

For the sake of simplicity -since the entire calculation is pretty lengthy- let's imagine an airfoil at an angle of incidence θο that's been twisted by an angle θ due to aerodynamic loading. This additional angle θ is used to measure the twisting strain (dynamic) energy 0.5*K*θ^2 where K is the stiffness of the airfoil - much like a spring's K constant. An increase in speed will increase angle θ and the corresponding strain energy stored in the structure. When the speed reaches the divergence speed the restoring forces are smaller than the aerodynamic forces and the angle θ becomes infinite but since infinite is impossible in reality, the structure fails.

Very early airplanes (Wright, Langley) had major divergence problems and where unable to fly although they had airfoils capable of generating the lift necessary. The same airplanes with stiffer wings in later designs where able to fly. Modern airplanes due to proper design and stiffer materials have divergence speeds higher than flutter speeds. Divergence is a measure of the overall stiffness of the structure and is also used in order for the aircraft to get certified.


Can anyone identify the plane in this old photo? It belonged to my uncle. May have been 1930s vintage.

It's probably a Stinson Junior. Built in the late 1920s and early 1930s.


How are bird strikes tested in helicopters? Bird strikes are pretty well tested for planes, but what about helicopters?
Do they happen as frequent as planes and if so, what would be the possible outcomes?

Do helicopter emergency procedures include a "bird strike" event?

Do they happen as frequent as planes?

Here is a link to the Federal Aviation Administration's Wildlife Strike database. Here you can search all the recorded wildlife strikes in the USA, and filter them by various things, including Engine Type.

To get a good idea of how many helicopter bird strikes occur in comparison to other aircraft, we can compare how many bird strikes occurred in turboshaft (Engine Type F) engine aircraft to the total number of bird strikes.

From January 1, 1990 to January 1, 2017...

  California
   - There have been 31 turboshaft engine wildlife strikes, accounting for 0.22% out of the total 13,698.

  Texas
   - There have been 46 turboshaft engine wildlife strikes, accounting for 0.30% out of the total 15,520.

  Florida
   - There have been 22 turboshaft engine wildlife strikes, accounting for 0.20% out of the total 11,119.

This data would suggest that roughly 0.25% of all wildlife strikes are on helicopters.

Taking another piece of data from the FAA, we find that the ratio of rotocraft to general aviation aircraft in 2015 is 9,766 to 199,927, meaning that helicopters account for roughly 4.66% of total aircraft.

Combining these two pieces of data, we can see that since 0.25% of all wildlife strikes are on helicopters, but helicopters account for 4.66% of aircraft,  helicopters encounter wildlife strikes at a rate of ~18.64 times less than general aviation aircraft.

(Disclaimer: Data used above is rounded and averaged. This is a ROUGH estimate!)


Why there are more requirements for being PIC of the airliner above FL200? From another answer:

  Because there are first officers who legally can't be PIC of an
  airliner above FL200...

Why more experience is required to fly the airliner above I assume 6096 meters? I would expect, taking off and flying close to terrain should need more experience.

Why more experience is required to fly the airliner above I assume 6096 meters? I would expect, taking off and flying close to terrain should need more experience.

I'm unaware of any regulation that requires a minimum number of hours to be a captain or first officer above FL200. That doesn't mean there aren't such, just that I don't know of them.

It's not that that taking off and flying close to terrain requires more or less experience, but that safely operating at high altitude typically involves a different set of knowledge and experience than operating at low altitude. A seasoned bush pilot who does only that would be ill equipped to suddenly become the captain of a 747 at 35,000 feet, just as the 747 captain who had never been a bush pilot would be ill equipped to scud run through a valley to land on a remote airstrip.

Part of the difference between two such pilots is, of course, a matter of a propeller airplane versus a jet, a slow airplane versus a fast, and the differing complexities of their aircraft. In addition to those differences, though, the environment that they typically operate in and indeed the altitude itself makes things different. The nature of the emergencies they can possibly face are also different.

Offhand I can think of three things the typical low altitude pilot doesn't have to contend with that the high altitude pilot does. There are certainly more.

Oxygen considerations, in other words what you need to do if you suddenly don't have it at a breathable pressure. Probably never going to happen, but the high altitude pilot trains for it.
Regular operation in or close to the coffin corner. If you're unfamiliar with the term,  Wikipedia has a reasonable explanation as well as
this question.
A whole different situational awareness environment than the low altitude pilot. For example, I used to do a flight from Sao Paulo to Miami. Two other carriers had flights scheduled that went out immediately before us, also 747s. Everybody was always heavy, which meant the first guy out got the highest cruise altitude available for the weight we were all at approximately, the second guy 2,000 feet below that, and then us sucking fuel 4,000 feet lower than the first. However, I knew that if I could open up the distance between myself and the second guy, I could get a clearance through the second guy's altitude to the first guy's altitude since there was enough time/distance between us. So what I would do was to climb at best angle rather than best rate. Then, if the weather was good (i.e. no turbulence) and I had the engines for it, it took very little fuel burn before I would able to get 2,000 feet higher if I was willing to accept slightly lesser protection from the top of the coffin corner. Sometimes that would work out, sometimes not, but it always got us at least up to the first guy's altitude. And on rare occasions, it meant we reached Miami before either of the other two.


What instrument can be used to check that constant attitude is maintained? In Sporty’s training, the following question came:

One way to determine that you are maintaining a constant attitude
is to occasionally check:
A. The vertical speed indicator
B. The tachometer
C. The altimeter

My answer is A, but sporty’s app says I’m wrong and correct answer is C.
Could someone please confirm the right answer and explain why?

Multiple choice questions are rarely about picking the only correct answer but instead often challenge you to pick the most correct answer out of a choice of 2 or more potentially correct answers.
I think that is the case here. While the VSI may well indicate to you that you are climbing or descending, it is unreliable for monitoring as it will be affected by small fluctuations such as up/downdrafts and lags quite a bit behind actual control input.
The altimeter, on the other hand, is quite stable and does not fluctuate quite so readily. If you're scanning and over a period of a minute your altitude has increased by 100 ft you can be pretty sure you're climbing - in that time the VSI may have indicated a climb, a descent and another climb etc. If you had scanned it while in a short-lived descent you might be fooled into thinking the long term affect was a descent. It was not - you were climbing overall.


How far would a landing Airbus A380 go until it stops with no brakes? If an Airbus A380 lands with all brakes disbled, including reverse thrust, wheel brakes and any other measures it has to stop or slow down. Then how long would it take it to reach a complete stop.

This is a very hypothetical question. If the aircraft has no means to slow down it has to lose all kinetic energy through rolling friction and air resistance. Both of these are very small (and get smaller as the aircraft gets slower) and will not have too much effect on a heavy aircraft like the A380 with an enormous amount of kinetic energy. Therefore the aircraft will continue to roll way beyond any runway or proper landing surface.

For high speeds, the air resistance will have the bigger impact on slowing down the aircraft (air resistance is about proportional to the square of the true air speed). Once the aircraft gets slow, the air resistance gets very little and rolling friction (highly dependant on ground surface) will be the bigger force to slow down the aircraft.


How is MEF calculated for Canadian VNC? According to the VNC, the MEF represents the highest feature in each quadrangle. It refers to

AIM RAC 5.4 and CAR 602.15(2b) which basically says "lower than 500 AGL (CAR 602.14(2b)) ok, when for aerial application or aerial inspection, photography, ..."
AIM AIR 1.5 which is about "Pressure Altitude" which I guess is because the heights are ASL

Now, the sample quadrangle here shows a MEF of 2700'. Looking at that quadrangle, the highest obstacle I would say is the mountain in the very east, north of 50°35' which is 2290' high. I wonder where that difference comes from.

I think that both figures, 2700' MEF and 2290' are ASL. Therefore it can't be the difference between ASL and AGL.
It always seems to be ~400' more than the highest feature.

According to Aeronautical Information Circular 26/11 VFR Navigation Charts—Clarification of the Maximum Elevation Figure the

  The MEF is calculated by taking the higher value of:

  the top elevation of the highest obstacle plus the vertical accuracy (variable) of the terrain
  source data; or
  the elevation of the highest terrain plus 328 feet plus vertical accuracy of the terrain source
  data.

So the 2700' could come from 2290' plus 328' rounded up to next hundred feet.


Do you ask ATC for HILPT? This specifically pertains to VOR approaches, but I guess it can apply anywhere else that has a hold in lieu of procedure turn (HILPT) also. There are numerous examples but let's try one: KUKI VOR-A.
If you were approaching from say the North (thus a teardrop entry is most suitable), does the hold constitute your course reversal, or must you conduct the procedure turn to get established for a simple ASEL? 5.3 miles out seems pretty good to get distance to get established, but maybe I'm missing something as an early instrument student? Do you have to contact ATC to let them know this is the way you'd conduct the reversal?

Typically, the way that it works in my local area is that the pilot would request the full procedure when wanting to use a course reversal. This would be interpreted by ATC to mean the pilot was going to fly direct to the IAF requested by the pilot when requesting the IAP. ATC would then vector the pilot in a manner to get the pilot to intercept the course at the most advantageous angle. The pilot may request to self vector, though. The pilot would then fly outbound on the IAP for the PT.

The PT has to be done along the outbound course. Though there is not a specific distance the pilot must fly in order to do the PT, it has to be flown in such a manner that the aircraft does not exceed a specific distance. The pilot can, however do the PT in as little a space as that provided by a hold.

If the pilot chooses to use the hold as a course reversal instead, they would request the hold first. They would follow that request up either with another radio call or within the same radio call with stating the intent of using the IAP to approach for a landing, touch and go, low approach, etc.

If the pilot does not make their intent clear when requesting the approach ATC will ask for the pilot to state their intentions. On a slow day, they may just ask you to report the FAF when inbound for a landing.

Remember though, the procedure for using an IAP would be to have your aircraft established on the lateral guidance, fully configured for a landing, at or prior to the FAF. That would preclude the possibility of flying directly to the FAF from any other angle or direction, then descending down for a landing. Because of that, ATC would be expecting you to do some type of course intercept or course reversal on the intermediate leg.


What would it take to pressurize a cabin with surface pressure? At cruise level around 10000 meters the cabin pressure is lower than surface pressure. The only reason for this, is to reduce stress on the structure of the plane, or fuselage, right?

My question is this:

Given the current state of technology, if manufacturers were to produce passenger aircraft, massive or robust enough to allow cruise flight with cabin pressure equal to surface pressure, then how much would the gross weight of the aircraft increase? How much would the range of the aircraft decrease or how much less cargo could it carry?

I suppose that the current planes could also fly at surface pressure, but the level of safety would decrease, due to increased forces on the structure. So, the question really is: Suppose we want to fly at ground pressure with the same levels of safety, how much would the gross weight increase, how much less cargo could a plane carry?

Many thanks.

Not much. The current requirement for 8,000 ft equivalent pressure translates into 8.11 psi at 43,000 ft. Boeing studied the benefits of lower pressure and found that going below 6,000 ft equivalent pressure brought no additional benefits.

The full pressure differential between sea level and 43,000 ft is 12.3 psi or just 52% more than that at 8,000 ft. This would require a heavier fuselage, but would not be impossible to do at all. Statistical methods give a mass factor for the fuselage pressure differential of $(1 + ∆p)^{0.203}$ which yields 1.0933 for 8.11 psi (∆p = 0.552 atm) and 1.1314 for 12.3 psi (∆p = 0.837 atm). Increasing the pressure to its sea level value would increase the mass of a typical airliner fuselage by 3.5%.

If we use the volume of the cabin, we can also calculate how much heavier the air is: The A330-200 has a cabin volume of 372 m³, and with the density of air at 8,000 ft of 0.9633 kg/m³, this computes to 358.35 kg. Compared to the mass of the same volume at sea level (455.7 kg), the difference is roughly equivalent to the mass of a single passenger (not counting the amenities carried along for her/him, too). In other words: The added mass of air for sea level pressure will make no difference if one passenger more misses her/his flight that day.


Are the captain's and first officer's brake pedals always mechanically linked? I heard that for Boeing and Airbus aircraft, the pilot's and copilot's brake pedals are mechanically linked, is that true?

Why did they make that design decision? What's the advantage? Do all kinds of passenger aircraft have the same design?

It is cost effective for one. With an unlinked system, you now need to resolve disagreement between inputs some other way. Software has its own challenges. It's also instant, non-verbal communication between captain and first officer. A pedal moves and the other's pedal has already moved. No confusion or pilot effort to communicate it.


Why keep the doors open for aircraft in boneyards? Photo by Bastian Ding from airliners.net

The image above shows Boeing 747s stored in a boneyard.

Why are the aircraft left with the doors open? Won't this increase the probability of further damage and/or faster corrosion?

Scrapped aircraft are often cannibalized for parts, it's possible that the parts that were needed from this specific aircraft were the doors.

The photo provided in the question points to Victorville  boneyard, and some detective work using the partially visible registration indicates the 747 in the picture to be G-BNLU. Some digging on the reg shows us it was withdrawn in 2014

  Withdrawn British Airways Boeing 747-436 G-BNLU positioned Cardiff-Wales – Victorville this morning as BA9156.

It seems that at various times there have been 7 BA 747's stored at victorville

  747-400s; G-BNLA, B, C, D, G, H, U

And at least one has visited Victorville for a refit

  I was on airliners.net reading some posts/threads and I read one: G-BNLV is back from the desert!!

(Both above quotes from this thread)

Which lends weight to my original assertion of cannibalization, however nothing concrete as to whether U provided new doors to V.