Why is ARTCC room lighting in the US dim? I have made several trips to US ARTCC centers and they had very dim lighting. I was told the lighting, carpet and wall colors where all decided on by the (PATCO) union contract with the FAA.

This week I was watching a BBC documentary and the British air route control room (NATS) was brighter than a normal office.

What is the justification between the two lighting preferences.

Dimly lit ARTCC room, even the display and control area use dark trim.

Brightly lit British NATS room, note the bright display and control area.

The FAA set out the ARTCC Facility Design Guidelines in this document. In short they are dark to minimize glare.

  295. TRACON OPERATIONS ROOM. Lighting intensities in the TRACON operations room are usually kept at a very low ambient level, less
  than 5 foot-candles (fc), in order to prevent glare and reflection
  detracting from the target viewing on the radar displays. The design
  shall consider incandescent lighting with pinhole covers or framing
  capabilities in lieu of fluorescent lights. These incandescent lights
  can be aimed exactly where needed and, unlike fluorescent lights, can
  be dimmed to low light levels.

Its possible the British have no such requirement (under EASA or ICAO) or that the photo was simply over exposed and the room appears bright.


How are compressor blades connected to the shaft in turbojet engines? The below figure is about rotor and stator blades of compressor . How these are connected to the compressor shaft in jet engines ?

There are three primary ways that blades are connected to the shaft

Circumferential dovetails  Here is a nice site demonstrating it.  Includes STL files so you can 3D print your own demonstration part.
https://cults3d.com/en/3d-model/tool/jet-engine-component-1-1-axial-compressor-circumferential-dovetail-slot-type
Axial dovetails Here is a video demonstrating blades with an axial dovetail being assembled.  This particular video is a turbine, not a compressor, but in theory the same method can be used.

Blisk "Blisk" is a contraction of "bladed disk". The blades and the disk are physically welded together (or in some cases machined as one piece out of a solid block of metal).  Here's a wikipedia article on blisks
https://en.wikipedia.org/wiki/Blisk

Each of these methods has advantages and disadvantages in terms of weight, cost, vibration, etc.  Which one is picked depends on the circumstances.  It is also common to see multiple different methods within one compressor. For example the LEAP-1A HPC has a 10 stage compressor.  The forward stages are blisks, and the aft stages are circumferntial dovetails.


How can I legally land VFR in class D airspace with low and few clouds? This question is a bit specific because it applies to an actual situation I'm observing for a flight I'm looking to make tomorrow.

I'm a Non-IFR rated pilot looking to fly class D airspace. My destination airport is anticipated to have clouds (FEW @ 1,000 ft). In this case, it seems like it would be pretty easy for 1 single cloud's position to make it impossible for me to land at the airport despite being able to (likely) safely land. For example, if the cloud were over the middle of the runway, but I had plenty of runway at my landing end, it's technically possible that the requirements for distance from clouds could keep me from landing here.

I realize the example is trite, but hopefully this illustrates my point.

What is the appropriate way to handle this situation as a pilot?
I'm calling up tower before I have a visual on the airport (which would be the case in this situation) would they likely deny clearance to land due to knowing that a singular cloud sits out there and would cause a bust the visual flight rules or might they clear me without regard to the rules?
What is considered cloud clearance in this situation? I realize clearance is easy to determine if you are directly above, below or adjacent to a cloud, but more commonly you'll be at some sort of angle to the cloud as in the picture. Shown are two ways to consider cloud clearance (in red and blue lines)

What is the appropriate way to handle this situation as a pilot?

First, tell tower about the problem.  They may be able to assign you a different runway, have you loiter (circle) for a minute or three, etc.  It's likely not the first time this has ever happened.

If necessary ask the tower for a Special VFR clearance.  That changes your cloud clearance requirements dramatically in your favor.  Note that the tower is not allowed to offer this clearance to you - you have to explicitly ask for it.

  I'm calling up tower before I have a visual on the airport (which would be the case in this situation) would they likely deny clearance to land due to knowing that a singular cloud sits out there and would cause a bust the visual flight rules or might they clear me without regard to the rules?

J. Hougaard answered this part in the comments - the tower is likely not checking how far you are from a single cloud.


What factors determine where an aircraft can dump fuel? An aircraft flying over a densely populated area–far away from the sea and mountains–declares an emergency, request fuel dump, and a landing as soon as possible. How does an air traffic controller know where it is safe/possible to dump fuel?

If this is regulated, then by whom or what is it regulated?
If it's not regulated, by what criteria does an ATC use to determine an area for dumping?

Fuel dumping was regulated by FAA Order 7110.65P - Air Traffic Control, which was canceled in 2006. FAA has the following to say regarding fuel dumping:

  ...If the need arises, aircraft are instructed by Air Traffic Control to dump fuel at high altitudes as far away from the airport or any populated areas as possible.

At present, there are no hard and fast rules (at-least in US, for other countries, see below) regarding fuel dumping and it is left to the air-traffic controllers to guide the aircraft.

The main criteria in determining an are for fuel dumping are:

-Altitude In general, fuel jettisoned above 5000 ft will vaporize before reaching the ground. Due to this, some manufacturers recommend fuel dumping above 5000 ft. In general, the ATC will guide the aircraft to an altitude where it can dump fuel so that it vaporises before reaching the ground.

-Atmospheric conditions The evaporative characteristics of the fuel dumped depends on the altitude and the atmospheric temperature. The aircraft fuel tends to vaporise faster in a warm day.

-Aircraft separation The ATC will try to keep a minimum lateral separation (~5 miles) between the aircraft dumping fuel and other aircraft and also some vertical separation (~2000 ft, according to Order 7110.65P).

Except in case of safety emergency, the fuel dumping is carried out at high altitudes.

Note: Some countries do have fuel dumping regulations, like Switzerland, which says,

  The choice of the dumping area is determined by the urgency of the incident, the actual flight path, meteorological conditions and the general air traffic situation. The aircraft is led to a selected area by the air traffic control to dump fuel. At the minimum speed of 250 knots at an altitude of 6,000 ft, but usually with 350 knots at 14,000-16,000 ft fuel is dumped ... There exist no predefined dumping areas ...


What aircraft looks like a cross between a Cessna and a glider? I always like to look at flying machines overhead.  One day I saw something I've never seen before.  It looked like a cross between a Cessna and a glider.  It was powered, but I heard no sound from it (but I might not have anyway due to ambient noise).  The wings were about twice as long and half as wide as a regular Cessna.  Any idea what that was?  It looked like it was built for pure fun.

Updates in response to comments:

It was not a glider; it had a front engine and high wing like a Cessna.  But it was not a Cessna either.  The wings were about twice as long as a Cessna, and about half as wide.  On the other hand, the wings were about half as long as a glider, and twice as wide.

It was almost directly overhead, about 1,000 feet.  I looked intently since I love aviation in all forms and I'd never seen anything like it.

Whatever it was, it looked like it would be a lot of fun.

If it matters, it was near downtown Seattle about 2 years ago.

As you describe it, a motorglider would fit the bill. There are several types around, the most popular being the Grob 109 and the Hoffman Dimona.

Grob G-109 (picture source)

[Hoffmann H36 Dimona (picture source)

Other possibilities include the Valentin Taifun (the only one with a tricycle landing gear) or the Scheibe SF 36. All of those are of composite construction, but there are also earlier types with wooden wings and a steel tube fuselage, like the Scheibe SF 25 "Falke".

While a Cessna is a high wing plane, all motor gliders are low wing (well, except for this one here). Would a cross between a Piper and a glider describe what you saw even better?


What does the lift coefficient take into consideration for flaps? Angle of attack increases lift for two reasons, Camber and increased flow deflection, What reason does the lift coefficient use? Both?

The lift equation is:

$$ L = C_L \frac{\rho \times v^2}{2} A , $$

where $C_L$ is the lift coefficient, $\rho$ the density of the air, $v$ the relative velocity and $A$ the wing area. The idea behind the lift coefficient is to combine all aerodynamic effects related to the shape of the aircraft into one dimensionless number, which can be experimentally derived as a function of the angle of attack:

(example lift curve from Wikimedia)

When extending the flaps, two things can happen:

The shape of the wing changes, i.e. wing camber is increased. This will modify the lift curve:

(image taken from this answer)
The total area may increase (e.g. for Fowler flaps, see also this question: Does deploying flap change the aspect ratio of the wing?).

So the $C_L$ is taking the change in camber into account, but not the change in area, which will also contribute to increased lift.


Could a light helicopter pilot land a transport-category helicopter? Related question, but not a dupe as that's about starch-wings and the gap between light fixed-wing planes and fixed-wing transports does seem larger than the similar gap in rotorcraft...

Let's say our good friend Simon, with his considerable amount of cyclic-time in small-to-modest helicopters, is onboard an S-76 (or other similar large helo) and both the pilots find out that the fish was a bad choice of preflight meal.  How much assistance would he need from someone on the ground with time-in-type in order to get the helicopter on the ground safely, assuming this was in VMC?

This is based on knowledge and a little experience. I have flown a Wessex to a hover and they are big, heavy, powerful beasts. If your example

  our good friend Simon

refers to me, then I must also state that I only have about 130 hours so limited hours is more accurate :)

It is said that if you can fly one helicopter, then you can fly another.  Indeed, I learned on the R22 and it's a "fact" (insofar as if enough people repeat something enough times, it becomes a "fact") that if you can fly the R22, then you can fly anything because it demands careful handling and has very small power margins.  I have never heard a really experienced pilot refute that.

If we assume that you have enough fuel and that there is no complex fuel system which requires switching of pumps to keep the engines fed, then yes, you could land anything with one notable exception.

Nearly all helicopters have a couple, either manual or automatic, between the demand for power (how much pitch you are asking for) and the engine power output.  Raise the collective and the throttle is automatically opened and vice-versa.  This is certainly true about transport category aircraft.  On something like early Hilliers, I would need to learn pretty fast that as I increase pitch, I must roll on throttle otherwise, I will stall when I try to climb or raise the lever to come into the hover.  This is practised during PPL but I must admit, I've never used manual throttle control since I got my license.

Another area of concern would be over controlling but that's easy to deal with.  I am now thrust into the pilots seat of a type I don't know and I am not licensed for.  I am going to land on the nearest safe spot.  I'm not going to do anything fancy whatsoever so, if I need a descent, I will lower the lever gently and use the cyclic to maintain my speed. Then I'll climb a little by gently raising the cyclic until I start to climb.  All helicopters fly nicely at about 60 kts so I will pitch for that speed. The only thing I need to look at to ensure the limits aren't busted is airspeed.  Any helicopter pilot would get the feel of this in very little time as would any fixed wing pilot.  It's just a question of how heavy the controls are and how much they physically need to move but that's quickly explored by starting gently and using just enough to do what you need to do.

Let's assume that the subject craft does have automatic throttle control.

I will also assume that we are in VMC otherwise, we are all going to die.

There are only two other areas of concern that I can think of and that's the type of the landing gear (skids vs wheels and how many) and the height of your seat above the ground.

One major difference between rotaries and fixed wing is that there is no stall speed and all helicopters can land with the same forward speed and rate of descent.  I can, if I want to, bring the craft to a hover and stop to have a good think about what comes next.  To come into a hover is also easy.  You can do it by the numbers but the practical way is to keep your speed over the ground so that the site picture is apparently a fast walking speed and keep the landing spot in the centre of the window.  if the landing spot moves up, decrease your rate of descent and vice-versa.  Do this, and you will arrive close to the spot at a sensible speed and with a low rate of descent.  Vortex ring state won't be a concern for me.  I won't know at which speed I will lose translational lift but it will be somewhere between 10 and 15 kt, so I'll be waiting for that little shudder to start and the nose to swing a little, ready to bring in power and pedal.

I believe that most, perhaps all, wheeled transport helicopters have wheel brakes, but I will have no clue how use these.  So, I am going to land zero-zero and ensure that I am directly into wind and on a level surface.  The next think is how will I know when I've landed?

When I first landed a B206, it was on my conversion course so I already knew how to land smoothly.  All I had to do to deal with the extra height I was sitting above the ground was "feel" the aircraft down.  It can be surprisingly difficult to know when a helicopter is fully on the ground and not flying it all the way down is one way to get into trouble.

I would deal with this by feeling for the first contact and then smoothly, but not too quickly, lowering the lever.  This does two things.  It ensures a firm contact and removes my biggest landing worry in an unfamiliar type which is dynamic rollover.  It won't be pretty and I might even get a blade strike somewhere but with power now off, we'll all walk away.

So in summary, I wouldn't need any assistance but, if I can figure out where the transmit button is and how to tune the radio, I will try to get some anyway.


What does it mean when autoland is fail passive / fail operational? The below explanation is what I've got from the internet about fail passive and fail operational:

Fail operational - Where you have 3 autopilots engaged, such that any single failure will result in the remaining 2 autopilots being able to safely land the aircraft. That is if there is a failure autoland remains operational.
Fail Passive - Where you have 2 autopilots engaged, such that a single autopilot failure will result in the disengagement of both autopilots with no significant deviation from the established flight path. In this case the pilot must manually take control and go-around/land. (avsim.com)

Can someone confirm whether the above explanation is correct?
I've read that the A320's Autoland is fail operational but that does not match with the above explanation (since the 320 only has 2 AP's hence making it fail passive).
And also (if possible) can someone give examples of aircraft whose Autoland is fail operational/passive?

The quoted explanation about "fail operational" and "fail passive" is correct, in that "fail operational" means the system will continue to function after an failure, and "fail passive" means the system will not misbehave after an failure.

The exact number of autopilots required to make this work, however, is debatable; and much depends on how you define it.

Let's take the Boeing 777 because it is easy to begin with. It has three autopilots. It will say "LAND 3" or "LAND 2" respectively. In a system of three, a failure can be detected if one disagrees with the other two. In a system of two, it is uncertain which one has failed, so all units come offline.

Now here comes the interesting part: what if I can distinguish a failed unit from a functional unit, without using another functional unit? In other words, what if I have something that can monitor the existing units, but is incapable of functioning the same as one of the monitored units on its own?

That is how fail operational can be implemented with two autopilots. For example, the Flight Management and Guidance System (FMGS) on the Airbus A320 can switch from "Dual Mode" to "Single Mode". The FCOM does not detail how it does that. (A320 FCOM - Aircraft Systems - Auto Flight - General)

But the FCOM does state a "CAT 3 DUAL" automatic landing is fail operational

  the remaining part of the automatic system allows the aircraft to
  complete the approach, flare and landing

while a "CAT 3 SINGLE" landing is fail passive:

  there is no significant out-of-trim condition or deviation of flight
  path or attitude, bu the landing is not completed automatically

 A320 FCOM - Procedures - Normal Procedures - Landing Categories

The Boeing 737 has 3 inertial sources but only 2 autopilots. It implements fail operational on the inertial sources but fail passive on the autopilots.

  If a failure is detected, the flight controls respond to the A/P
  commanding the lesser control movement. If a failure occurs in one
  A/P, the failed channel is counteracted by the second channel such
  that both A/Ps disconnect with minimal airplane maneuvering and with
  aural and visual warnings to the pilot.

Boeing 737 FCOM volume 2 - Automatic Flight - System Description


On modern commercial airliners, how much of the flight could be fully taken care of by the auto pilot? If one wanted to, how large part of the flight could a modern commercial airliner do completely on its own? That is, if the pilot only was allowed to set things up and then leave the cockpit, from where (taxiing, take off, et cetera) and for how long would the airplane be able to handle things itself before things went out of hands?

This should apply to the most advanced modern airliners. Older aircraft may not have all of the same automation available. The autopilot can take care of most tasks between takeoff and landing.

The pilots have to take care of starting the airplane. This includes turning on electronics, bringing up the aircraft systems, and starting the engines.

Taxiing is pretty much on the pilot, there is no automatic taxi yet on commercial airliners.

Once the aircraft is lined up with the runway, the pilot can hit the TOGA (Takeoff/Go Around) button. The plane will automatically apply the right amount of thrust for takeoff. The pilot will then rotate the plane (lift the nose) at the rotation speed (calculated before the flight), and the plane lifts off. Shortly after that, the pilot will engage the autopilot.

If the autopilot is set up to follow GPS waypoints and proper altitudes, it will be able to take care of the climb, cruise, and descent portions of the flight. The autopilot can follow the best speeds and fly through each waypoint in the flight plan.

Once the aircraft is approaching the runway, the pilot will tune the proper ILS frequency for the runway into the navigation radio. They will then engage the Approach mode, which captures the localizer (lateral navigation left/right to align with the runway) and glideslope (veritical navigation up/down to have the proper approach path). The pilot then needs to deploy the flaps and landing gear as the plane slows down for landing.

In the lowest visibility conditions, the plane is capable of the approach and touchdown on the runway all by itself. The pilot will then apply reverse thrust and brakes as needed to slow down.

Now that the plane is back on the ground, it is once again the pilot's job to exit the runway and taxi to the gate. Shutting down the engines and then the electronics will also be up to the pilot.

What is the autopilot still missing?

Responding to ATC (readback clearances, change frequencies)
Reacting to nearby traffic
Following ATC instructions (climb/descend, turn, slow/accelerate)
Reacting to emergencies or system failures
Controlling lights, flaps, landing gear

This is of course a high level view and there is so much more that goes into the flights.

Also, keep in mind that we have the technology to do much more. It just hasn't made it into service for one reason or another (lack of development and testing, not seen as important, etc.). We have UAVs that are much more automated than this. However, they are still working on how to effectively avoid other aircraft.


Is the aircraft neutral point a function of the tail incidence angle? While using XFLR v5 for a basic analysis I am facing this issue. For a fixed configuration I varied the tail incidence angle and XFLR is displaying a change in the Neutral point location. But as per theory neutral point location is not dependent on the tail incidence angle at all. I was hoping if someone could help me with this issue.

I have done some homework and I will explain why the Neutral point does not vary with the tail incidence angle.

The above equation is the fundamental equation defining the location of the neutral point.

We can see that the Neutral point is a function of the following factors only,

Aerodynamic centre
Tail volume (Horizontal tail sizing and Arm length)
Tail efficiency factor (Ratio of dynamic pressure at the tail and at the wing),
Lift curve slope for the wing and HT (CLalpha - which is fixed and not dependent on the tail incidence),
Downwash effect
Fuselage moment contribution

So none of these factors are dependent on the tail incidence angle and hence there musnt be a change at all. What shocked me the most is the fact that errors in variable quantites can be accounted for but errors in quantities that shouldnt vary is very confusing. It is a very standard statement that '' Static margin or ultimately the Cmalpha shouldnt get affected by the change in tail incidence''
This is the information I could get about it.


Callsign includes the term 'with Kilo' ; What does that signify? In FS-X I sometimes see with Kilo at the end of a Call-sign. For example the one from last night had

  Mike Sierra Alpha Bravo with Kilo

What does With Kilo mean?

What that probably means is that the pilot is reporting that they have ATIS information kilo. Automatic Terminal Information Service (ATIS) is a radio broadcast on a specific frequency (often a local navaid like a VOR) which a pilot dials up to get weather and airport information before joining one of the airfield's frequencies. Each time the information is updated in a day the next letter of the alphabet is used; "information Kilo" means the information has been updated 11 times that day.

If the tower had to relay weather, runway in use and other instructions to everyone pilot who joined the frequency it would take loads of their time; ATIS is instead there so controllers can spend their time controlling. When a pilot introduces his/herself on frequency at an airfield they announce the latest ATIS they have so that the controller knows they have up to date information and they don't need it relayed.

From a phraseology standpoint just saying "with kilo" is okay. I usually say "with information kilo" because it makes sure that kilo isn't confused as being part of my callsign.


How does the ADS-B compact position report NL() function work? I'm trying to decode ADS-B messages for a school project, and I cannot reproduce the results of the NL() function as described in this document. I've seen the same formula in several other documents. Also in this document is the reverse of this function - the NL is input, and the latitude "boundary" is the result. I cannot solve that either.

I've tried radians and degrees for the trig functions and several different calculation tools, and my result is never close to correct.

The "known" good inputs and result are from this document. I've also seen these inputs and results elsewhere, but no details about the equation itself.

The summary of the "known" good data set is:

$rLat = 10.2157745361328$

$NZ   = 60$

$NL   = 59$

The equation is:

$$
NL = int \left( 2 \pi \left[ arccos \left( 1 - { 1 - cos \left( {\pi \over 2NZ} \right) \over cos^2 \left( {2 \pi \over 180} \mid lat \mid \right) } \right) \right] ^{-1} \right)
$$

Can anyone help me understand this calculation?

Compact Position Reporting (CPR) is a way of reducing the number of bits needed to transmit position whilst maintaining high position resolution (~5.1 meters for airborne encoding). Ordinary encoding would require 45 bits, but CPR uses 35 bits thus saving 10 bits. To do so, the world is divided up into a number of zones, both for latitude and for longitude and the position within the zone is encoded. Since transmitting the zone numbers would cost as many bits as that would have been saved a clever trick is used. Two types of encoding are used, each with a different number of zones. From the difference in zone coordinates between the two types of encoding one can determine which zone the aircraft is in. Therefore one needs to receive an even and an odd encoded message within 10 seconds from each other. Once the initial position decoding is successful every subsequent position message will give the updated position.

In CPR decoding, you first determine the latitude of the aircraft based on a pair of odd and even position messages received within 10 seconds from each other.

Latitude is always encoded in the same number of zones between the equator and the poles (15 for even encoding, 14.75 for odd encoding). Due to the roundness of the earth the numbers of zones used for longitude encoding depends on the latitude. Longitude even encoding uses 59 zones at the equator and only 1 at the poles. Odd encoding uses always 1 zone less, except near the pole where 1 zone is used like in even encoding. The number of longitude zones used for even encoding can be found by the $NL()$ function.

The transition latitudes, i.e. where the number of zones for longitude encoding change, can be calculated by the inverse $NL()$ function. This function can be used to create a lookup table of transition latitudes which is more efficient to use than the original $NL()$ function.

Without knowing anything about your implementation it is difficult to assist further, the formula is depicted correctly in your question. Note that input latitude is given in degrees, but the trigonometric function are assumed to work on radians hence the $\frac{\pi}{180}$ factor.

Edit: on further inspection I noticed a mistake in the formula: it should be :

$$
NL = int \left( 2 \pi \left[ arccos \left( 1 - { 1 - cos \left( {\pi \over 2NZ} \right) \over cos^2 \left( { \pi \over 180} \mid lat \mid \right) } \right) \right] ^{-1} \right)
$$

(note that the conversion from degrees to radians is corrected)

For those that really want to understand CPR coding and decoding in detail, you'll have to obtain a copy of RTCA document DO-260B or Eurocae document ED-102A (unfortunately they're expensive, I think about $700) and read Appendix A.1.7 and Appendix T.


What airspeed is required at sea level to create the same aerodynamic pressure as cruise altitude? I would like to know what speed would be required, at sea level, to exert the same aerodynamic pressure as experienced at cruise altitude.
For example, if an airliner were traveling at 500kn at 35,000' what speed would you travel at sea level to experience the same forces on the air frame?

You are looking for the equivalent airspeed. Here is the definition from Wikipedia:

Equivalent airspeed (EAS) is calibrated airspeed (CAS) corrected for the compressibility of air at a non-trivial Mach number. It is also the airspeed at sea level in the International Standard Atmosphere at which the dynamic pressure is the same as the dynamic pressure at the true airspeed (TAS) and altitude at which the aircraft is flying.

$$ \text{EAS} = \text{TAS} \times \sqrt{\frac{\text{density at altitude}}{\text{density at standard sea level}}} $$

At standard sea level, EAS is the same as calibrated airspeed (CAS) and true airspeed (TAS). At any other altitude, EAS may be obtained from CAS by correcting for compressibility error.


When can spoilers be used on airliners? On airliners, are spoilers used in any part of flight other than landing?

Spoilers have many uses, but first I want to distinguish types of spoilers.  Airplanes will typically have ground spoilers and flight spoilers and they work like they sound.

Ground spoilers only open up on the ground -- these are usually much more detrimental to lift than the flight spoilers.
Flight spoilers open when actuated by the pilots

Another type of spoiler is the spoileron, which is used on some airplanes like an aileron, that is to bank the airplane by destroying lift on one wing.
Since you ask about use in the air, I will focus on flight spoilers.  When would I use flight spoilers?

I want to descend faster
I want to slow down quicker
I want to descend and slow down

I want to descend faster
This can be broken down into three categories

I screwed up and I need to make a crossing restriction
The anti/ice system turned on (more on this below)
I am initiating an emergency descent (abnormal)

The bit about a/ice comes from the fact that on many airplanes when a/ice is on there is a high demand for bleed air.  In the EMB-145 the FADEC bumps up idle thrust quite a bit to meet this demand and if you did not anticipate this in your descent planning, we were authorized to use our spoilers in icing conditions to aid in the descent.  This could be interpreted as an "I screwed up" case, but really isn't in my opinion.
I want to slow down faster
If there is a charted speed restriction, this may be useful.  Particularly if you have just prioritized the descent to meet a crossing restriction and now need to bleed off speed.
You might need to start descending out of 10k feet ASAP, and need to be at 250 kts to do so, and in this case spoilers can be useful.
I want to descend and slow down
In a jet, this can be hard when clean.  Often the choice is descend or slow down.  When you need to do both, spoilers can be a great help.

In the case of landing or rejected takeoff, all of the spoilers (including flight spoilers) should deploy automatically on most airplanes when the thrust levers are moved to idle, there is weight-on-wheels and you are above some threshold speed.
In addition, spoilers are useful in some airplanes for roll control, in addition to airplanes with pure spoileron roll control.  I didn't spend much time on this topic as like the ground spoilers in landing and RTO, these are passive from a pilot point of view -- you aren't specifically controlling these spoilers, the flight control system is doing it for you.  In any case, the spoilers used for roll control are quite important during flight.
As you can see, spoilers have many uses in flight and not just for landing.


What does the pressure distribution over a glider's wing look like? Can someone explain the design of glider wing airfoils and the subsequent pressure distribution over them?

I hypothesize that:

The pressure distribution should form a resultant force in the forward, upward direction, since two components of force are required to maintain equilibrium in the flight of a glider: a) lift - in equal opposition to weight, and b) a forward component of the total reaction generated by the airfoil - in opposition to drag.
Thus I conclude that the angle of attack of a glider airfoil relative to flight direction would be negative, in order to achieve a forward component opposing drag; although it would be positive relative to airflow, such as to generate low pressure over the wings. Either that or the camber is designed such that the two mentioned criterias here, (a) and (b), are upheld.

Should there not be any opposition to drag, I would expect to see the glider decelerate in the forward direction, until the airflow stalls over the wings, and the glider loses lift and falls.

I am also curious to know about the various designs of glider airfoils: a) what are the criterias defining them, and b) how do they differ from those of powered aircraft, if there are any differences at all?

The pressure distribution over a glider's wing is no different from that of a well-designed aircraft. A glider can maintain flight by flying slightly downwards, so the direction of motion is not straight but slightly down. Doing this in rising air will result in sustained flight.

Look at the sketch above: The flight path angle $\gamma$ is negative and in still air the flight path vector $\text{x}_k$ is parallel to the direction of the airspeed. Due to the inclination of the flight path, the lift vector is tilted forward such that its horizontal component is exactly opposite to the drag force. This is shown on the right where I moved the vectors into a closed sequence which demonstrates that all forces balance.

From the viewpoint of the glider, the lift is pointing straight up and drag directly backwards, but the weight force is slightly tilted forward. In a way, it seems that the thrust of a glider is its weight force.

Now let the whole air packet in which the glider flies move up. The glider will still sink down within this air but relative to the ground it will gain altitude if the upward air velocity is high enough.


Effect of gravity vs airmass on a falling object Let's say you were drifting along in a hot air balloon at a ground speed of 50 knots at an altitude of roughly 10,000' MSL/AGL.  The airmass is uniform, moving at the same speed at all altitudes.  In your hand is a streamlined, very dense object.  Picture a 5 pound chunk of lead shaped like a torpedo.

If you were to drop this object (over an unpopulated area of course!) would it continue to track along the ground at the exact same speed as the airmass/balloon, or would the vertical acceleration due to gravity overcome the horizontal inertia, slowing the groundspeed and causing it to arc towards a trajectory more perpendicular to the ground?

In other words, would the lead impact the ground directly beneath the hot air balloon, or at some point "upwind"?

My gut tells me that it would fall almost straight down immediately, with only some slight sideways drift, but I don't know how to quantify that hunch.

FYI, this question has its origins in the discussion here:  Force Balance From Wind

This answer assumes that the wind is uniform in direction and speed, from the balloon all the way down to the ground.

The object will impact the ground directly below the balloon, not "upwind" of the balloon.

As the falling object accelerates vertically, the trajectory of the falling object as viewed from the ground reference frame continually becomes more and more perpendicular to the ground.  Yet the horizontal components of airspeed, force, and acceleration are all zero throughout the entire fall, so the falling object remains directly under the balloon.

As viewed from the airmass reference frame, the trajectory of the body is purely vertical, i.e. completely perpendicular to the ground, throughout the fall.

The horizontal component of the object's groundspeed is constant throughout the fall, and equal to the wind speed.

Now imagine simultaneously dropping a low-density object and a high-density object from the balloon.  Both would be directly below the balloon at the moment of impact, but they would impact at different times.

For more, see Force Balance from Wind

Also, note that saying the object will tend to fall straight down relative to the earth, rather than relative to the balloon and the airmass, is essentially saying that the earth is a privileged reference frame, which goes against the laws of physics.


When is a 100-hour inspection required if alternating commercial and private use? First, a setup rehashing common knowledge: A plane owner, who's also a CFI, gets an annual done on his Cherokee and teaches out of it for 100 hours in three months. He flies it to a repair shop 3 hours away for a 100-hour check. After the 100 hour check is complete, he can legally use it to teach for 97 hours before the next 100 hour is due (if he doesn't reach a required annual first). This is because there's a 10 hour window past the 100 hour limit to fly a plane to a place where it can receive its 100 hour service, but that window doesn't add to the time of the next 100 hour time requirement for commercial use.

Now to my questions. In the above scenario, does the 10 hour window even apply to the owner? He's flying his plane non-commercial, not for hire, so in that capacity he should be able to fly it as long as he likes (until the next annual is due, of course).

What if the owner in the above scenario teaches out of his plane for 100 hours after the annual, stops teaching and flies his plane personally for 50 hours, then decides he wants to teach in it again? Can he get a 100 hour check to get the plane legal for commercial use? Is the next 100 hour due in another 50 hours? What if instead he flies it personally for 100 hours after the 100 hour is due? Does that mean he has to get two 100 hour checks done in a row to use it commercially again? Or does he have to get a full annual to reset the 100 hour clock?

This FAA legal interpretation covers a lot of scenarios and it looks like it answers yours too. Although it refers to rental, not ownership, the result is the same because rental time isn't instruction or carriage for hire.

First, what the regulation says (14 CFR 91.409(b)):

  Except as provided in paragraph (c) of this section, no person may
  operate an aircraft carrying any person (other than a crewmember) for
  hire, and no person may give flight instruction for hire in an
  aircraft which that person provides, unless within the preceding 100
  hours of time in service the aircraft has received an annual or
  100-hour inspection and been approved for return to service in
  accordance with part 43 of this chapter or has received an inspection
  for the issuance of an airworthiness certificate in accordance with
  part 21 of this chapter. The 100-hour limitation may be exceeded by
  not more than 10 hours while en route to reach a place where the
  inspection can be done. The excess time used to reach a place where
  the inspection can be done must be included in computing the next 100
  hours of time in service.

The key phrase from the interpretation is this one (my emphasis), which really just restates the regulation in a simpler way:

  if [you are] going to operate the aircraft to provide
  flight instruction for hire, then the aircraft must have had an annual
  or 100-hour maintenance inspection within the preceding 100 hours of
  time in service.

Now we can compare your scenarios to the ones in the interpretation. I won't quote the document here, but scenarios 1 and 6 together cover your cases.

In the above scenario, does the 10 hour window even apply to the owner? He's flying his plane solo, not for hire, so in that capacity he should be able to fly it as long as he likes.

Correct. If the aircraft isn't going to be used to do any paid instruction or carry paying passengers then he can fly the aircraft himself, rent it out, lend it to a friend etc.

What if the owner in the above scenario teaches out of his plane for 100 hours after the annual, stops teaching and flies his plane personally for 50 hours, then decides he wants to teach in it again? Can he get a 100 hour check to get the plane legal for commercial use?

Yes, in fact he must. The aircraft requires a check within the last 100 hours of operation to be legal for flight instruction for hire, or carrying paying passengers.

Is the next 100 hour due in another 50 hours? What if instead he flies it personally for 100 hours after the 100 hour is due? Does that mean he has to get two 100 hour checks done in a row to use it commercially again? Or does he have to get a full annual to reset the 100 hour clock?

The 100 hour clock is reset by a 100 hour inspection or by an annual, he doesn't need a second check. But note that if the CFI does get an annual, he still has to deduct any 'overtime' from the 100 hours:

  You may perform an annual inspection rather than a 100-hour
  maintenance inspection when the aircraft reaches the 100-hour
  limitation under§ 91.409(b). However, if you perform an annual
  inspection on an aircraft that has exceeded the 100-hour limitation,
  you are still required to subtract the excess time from the next 100
  hours of time in service.

As for going over the 10-hour excess time, the interpretation covers an equivalent scenario (scenario 6) where the aircraft is flown to 112 hours legally by renters, inspected, and then used for paid training again. The explanation is poorly written in my opinion, but it confirms that the aircraft needs an inspection before any paid training can take place - which makes sense - and the next inspection after that must be made within 88 hours - which makes less sense.

Extending that forward, it would mean that if you fly to 199 hours, you need an inspection - either 100 hour or annual - to make the aircraft legal for paid training and the next inspection would then be due in 1 hour! I don't know if that's really the intended result of the interpretation because it seems to conflict with the regulation's wording about "within the preceding 100 hours of time in service". And what happens if you rent the aircraft out for 299 hours before using it again for training?

Maybe I'm just misreading or misunderstanding things completely, but it looks like the interpretation leaves a couple of loose ends and the only definite, official way to get them answered would be to ask for another interpretation.


Where can I find a free list of ICAO and IATA airport identifiers? Is there an open source or free comprehensive (or close to it) list of ICAO to IATA airport identifiers? The official list from ICAO costs hundreds of dollars. I suppose such a list could be scraped from Wikipedia.

It depends on whether it should be reliable enough to be used operationally. If yes, I don’t know one and would to the best of my knowledge advise spending some sort of money. If no, maybe openflights.org could help?


What priviliges and limitations does an Aircraft(General) mechanic have versus an A&P? The FAA provides practical test standards for Airframe, Powerplant, and General mechanic certificates. Mechanics seem to demonstrate a preference for Airframe & Powerplant, so much that "A&P" is common shorthand for "aircraft mechanic".

That being the case, my questions are:

What can a mechanic who is only "general"-certified do and not do, compared to an A&P?
Is there any real-world benefit in holding a general mechanic certificate?

None. It is required to pass your written general to move on to obtain your Aiframe/Powerplant certification via an Oral & Practical exam. There is no general certification.

If you're looking for a way to work without certification, you can work under a 145's certificate without any.


What airfoil design is needed for a 4 m wingspan soaring plane? I’d like to build one that is heavier than a F3J plane and it will be similar to NASA’s soaring plane of the "Autonomous Soaring Plane" project. What kind of airfoil do I need? Simply scaling a normal airfoil would have bad results.

First for those who wonder what F3J is: This is the FAI model aircraft category for thermal soaring.

Quick answer: This answer describes what resources are available on the Net.

Your choice of airfoil depends on the wing loading and the size of the model, because those will determine the Reynolds number of the flow over the wings. Soaring flight requires high lift coefficients, but maybe you also want low drag for sprints between thermals or to avoid being blown away by strong winds.

The description of the NASA Autonomous Soaring Plane gives 15 pounds of mass and a wingspan of 170 in. It was based on a model glider by RnR Products, and there I found the aspect ratio of 19.8 and the wing area of 1545 sq.in. These numbers are not very consistent, but close enough to get an idea.

Thermals are strongest in their center, so it is desirable to fly as tight a circle as possible. Low wing loading $\frac{m}{S}$ and a high lift coefficient $c_{l_{max}}$ drive the minimum turning radius $r_{min}$ down (at a given density of air $\rho$), and the formula is:
$$r_{min} = \frac{\frac{n_{z_{max}}}{\sqrt{n_{z_{max}}^2 - 1}}}{c_{l_{max}}\cdot\frac{\rho}{2}\cdot \frac{S}{m}}$$

Here $n_{z_{max}}$ is the maximum load factor, and the picture below shows that little is gained by increasing $n_{z_{max}}$ beyond 3. The little DFS Habichts help to illustrate the bank angle.

With a wing loading of 6.8 $kg/m^2$ and a mean wing chord of just 23 cm the flight speed at a $c_l$ of 1.2 is 9.5 m/s. At sea level in a standard atmosphere the Reynolds number would be 150,000. The wingtip flies at a Reynolds number of below 100,000. In circling flight with a bank angle of 60° (equivalent to 2g, so you need twice the lift), the Reynolds number would increase to 212,000 for the mean chord and to 140,000 for the tip. If this sounds a lot to you, it isn't. This is a flow which needs highly specialized airfoils.

My recommendation is to try the UIUC airfoil database and select a specific model airfoil with low drag at high lift coefficients and Reynolds numbers down to 100.000. It should have high camber and a thickness of around 12% to keep wing weight down. If you have the lower range of Reynolds numbers covered, you need not to worry about the higher range. You might even consider to use different airfoils over the wingspan, depending on the minimum local Reynolds number. Ideally, you'll find a set of airfoils which have been optimized for exactly this purpose, like the DAE11 - DAE21 - DAE31 airfoils of the Dedalus human powered aircraft.


Do any airplanes really have this piece Tom Cruise is hanging onto in this movie? The piece Tom Cruise is holding onto on this moving plane seems useless as a component, maybe even inductive of drag. Is this a real airplane component, or just a film prop?

I don't know the model of the airplane; I'm hoping maybe the shape is recognizable to some of you, or maybe it's even a "no-brainer".

The plane is an Airbus A400M Atlas, a four-engine turboprop military transport aircraft.

I'm referring to this page, and there the stunt is well described.
About the door, here's an explanation:

  Visible in the released image, the A400M's new side door deflectors were added to the development aircraft fleet after initial tests with the ramp and side doors open resulted in high noise levels and turbulence inside the cargo hold, says Fernando Alonso, Airbus Military's senior vice-president flight and integration test centre.


What is the average time taken to load and unload the luggage? I was wondering, how are Lufthansa able to unload luggage (LH 760) of 500 passengers and load the luggage (LH 761) of another 500 passengers, in just a 2 hour gap for return leg of 7000 KM FRA-DEL journey.

What is the average time taken to complete a typical loading and unloading operation for a fully loaded A380? Some simple maths in this case shows its about 14.4 seconds for unloading and loading, pretty very high.  But that's assuming that no time is spent in any  task other than handling luggage, which is pretty foolish.

Bonus Question : How are the handlers able to complete this operation that fast?

Passengers' luggage is not loaded in an A380 by one suitcase at a time. That would be very time consuming.

After passengers check in the luggage and head towards the gate where the superjumbo is parked, their baggage is started to get stored in unit load devices1. And after that, those ULDs are loaded into the airplane:

Image Source

According to Airbus, the A380 can store 38 LD3s. Volume of a typical suitcase/bag (dimensions: 32"H x 12"W x 21"D) is less than 5 cubic feet, so 30 suitcases can easily fit in a single LD3.

Now let's talk about your questions about loading and unloading times. As A380s mostly fly on international routes, passengers are required to check in several hours before a flight's departure. But once they check in their luggage, the process of loading those LD3 starts, even if the airplane has not yet arrived at the gate. As soon as the airplane reaches the gate, unloading and loading processes start. These two processes are not as time consuming as they may appear2.

Passengers' checked in luggage is not loaded like in this manner (picture below). On a wide-body like an A380, this is the case of carry-on baggage which stored in the underfloor area, instead of overhead bins.

Image Source

1: A380 uses LD3, whose capacity is 159 cubic feet.
2: Note that after an LD3 is unloaded from an airplane, it might take another hour or even more for the passengers to get their luggage at the baggage claim area.


How do tugs push back the Antonov 225? How do tugs push back aircraft with 2 nose gears such as the Antonov 225?

Quite simple ― use a (special) towbar! Aircraft with such unique front wheels (like the Antonov An-225 Mriya and Lockheed C-5 Galaxy) carry their own towbar around, which is then attached to the tugs for movement.

For example, here is the Galaxy's towbar:

From left to right: 68th Airlift Squadon loadmasters, Senior Airman Katy Mackey, Master Sgt. Kevin Foerster, Senior Master Sgt. Dustin Burleson, Airman 1st Class Brandon Stone, and Master Sgt. Alfonso Cervantes unload an aircraft tow bar off C-5A Galaxy upon arrival to Cairns, Australia on May 5, 2012. The tow bar was used airport officials to move the Air Force's largest transport aircraft in place to load the U.S. Coast Guard's HH-65C Dolphin helicopter. (U.S. Air Force Photo/Maj. Tim Wade)

And here's that of Mriya:

AN-225 towbar being removed from aircraft; screen grab from this youtube video.

And here's a Galaxy with a towbar:

Troops from the 439th Maintenance Squadron prepare to tow a C-5 Galaxy into Westover's Regional Isochronal dock, May 22, 2013, to test the newly-constructed mobile tail enclosure. Crews broke ground April 1, 2012, for the $5 million MTE, is a moveable structure on rails that will protect maintenance troops from harsh New England weather. The MTE is the largest structure of its kind in the Air Force. (U.S. Air Force photo/SrA Kelly Galloway)

This video shows Mriya's towbar in use.


Is an additional rotor useful on a coaxial rotor configuration? I can understand coaxial rotors cancelling the need for a tail rotor, however, I am curious as to if the second rotor is needed to actually maintain the same pitch or could be just used to offload the primary disk in a powered auto-rotate capacity?  That would just create more drag I assume.

You could use the second rotor to provide anti-torque function only, as Arthur Young did when developing his helicopter test models at Bell during WW2.  In that case the upper rotor did all the lifting and the lower one had blades that were at 90 degrees and just made drag to generate a cancelling torque.

But that is really inefficient, and Young quickly moved on to using an anti-torque tail rotor (with a decently long arm to minimize the thrust it had to make), not wanting to go the whole-hog coaxial route, with all its mechanical complexity.

So if you want to have a coax machine to do away with a tail rotor, you might as well design it so both rotors are lifting (to realize the efficiency you are seeking by going with co-ax in the first place) and you can easily get yaw control by using a mixing system operated by the anti-torque pedals that adds collective pitch to one rotor and decreases collective pitch to the other rotor equally, in a way that the total lift is unchanged but a yawing torque can be created and varied.  And there you go.


What does flight categories "C", "G", "T" etc. mean? In a flight database that I'm working with on a project, there is a column of data called "flightCategory" with values "C", "G", "T", etc.  Any idea what those actually mean?  From what I understand, the database is from FAA.  But I'm not 100% sure.

I got the answer.  'C' is commercial, 'G' general aviation, 'T' taxi, etc.

Update:

http://www.faa.gov/air_traffic/publications/atpubs/fss/AppendixA.htm, under section "Type of flight", it lists

  S  if scheduled air service

  N  if nonscheduled air transport operation

  G  if general aviation

  M  if military

  X  if other than any of the defined categories above.

But types C and T isn't there.


Are the ICAO phonetic numbers used anywhere? I ran across a table of ICAO (NATO) approved phonetic number pronunciations. As early as I can remember (50+yrs) in the United States "nin-er" is the only one I ever remember hearing in aviation and I don't recall hearing it in the last 30yrs. I recall hearing "Fife" but I don't remember where - perhaps ham radio operators.

I have never heard "tree" (three), "Tousand" (thousand), or "Fower" (four). If I heard ATC say, "maintain 'climb to nin-er humndred'", I would be very surprised. And if they said, "maintain 'tree tousand'", I would think they needed retesting for ICAO English language requirements.

Is there any country, military, or agency that regularly uses the full ICAO (NATO) approved phonetic number pronunciations? Is it taught to any pilots?

source

Is there any country, military, or agency that regularly uses the full ICAO (NATO) approved phonetic number pronunciations? Is it taught to any pilots?

Yes, pretty much every country in the world. As you mostly have experience flying in the USA, where the native language is English, you may not be used to hearing these pronunciations so much. People whose native language is English tend to pronounce words [and numbers] as they would in normal speech. In most of the world, however, English is by no means the native language, so controllers and pilots alike will use the pronunciation guidelines created by ICAO to ease understanding across multiple dialects and accents.

As an example, the Danish aviation regulations has an exact copy of the table you present in your question, and it is used by everyone.


What is Brake To Vacate (BTV)? Emirates has this feature on many of its A380s. From what I've read, the feature decreases the amount of runway an aircraft uses after landing. It also helps the aircraft achieve a certain exit way. Is this feature unique with only Aibus aircraft? How is it set up on an aircraft and how does BTV work?

According to the Airbus website, Brake to Vacate is a feature installed on newer A-380s and also on the new A-350XWB that allows the pilot to select which runway exit s/he needs to use, and the system will brake hard enough, but just hard enough, to slow the plane to taxi speed by that turnoff.  This minimizes time on the runway.  The following quote is from the Airbus website.

  Brake to Vacate allows pilots to select the appropriate runway exit during the approach to landing, and regulates the aircraft’s deceleration after touchdown – enabling it to reach any chosen exit at the correct speed under optimum conditions, no matter the weather and visibility.

To my knowledge, Airbus is the only aircraft manufacturer to incorporate this feature - to date.

This feature does not reduce the amount of runway the aircraft uses.  Maximum Braking is still maximum braking.  It does however, optimize the braking so that the aircraft gets to the taxiway intersection sooner (doesn't brake too hard too soon, keeping speed up) and also prevents overshooting the intersection requiring a relatively slow taxi to the next turn off.


Do I Set the Parking Brake On the Ramp? Next week I am flying to an airport and going to have dinner. But I've never stepped out of my aircraft except at my home airport!

When I park on their ramp, do I keep the parking brake on?

I assume you're talking about a light GA airplane (Cessna/Piper singles or twins).

The short answer is "Maybe, but you probably shouldn't.": The parking brake should only be used for as long as necessary to get wheel chocks in, and should then be released.

Aside from making it inconvenient for the local ramp personnel if they need to move/tow your plane, setting the parking brake has a few other downsides which are related to the way the parking brakes work on your typical light aircraft.

When you set the parking brake you're doing two things:

You are pressurizing the hydraulic lines that run to the plane's brakes.
You are doing something to prevent that pressure from bleeding back out.
(Exactly how you accomplish this varies depending on the plane - the "parking brake" on a Piper Cherokee is a tab that prevents the brake handle from returning to the "released" position, maintaining pressure in the cylinder. I think the Cessna 150 pressurizes and then turns a valve.)

Because of how the parking brake works it has two common failure modes when it's set: Pressure can bleed out or it can blow out.

Bleeding Out happens because fittings, seals, hoses, etc. in the brake system aren't perfect. Hydraulic fluid will escape past whatever little opening it can find, and eventually there will be insufficient pressure in the system to keep the aircraft from moving.
If you happened to be parked on an incline steep enough to get the plane rolling it will then go off on its own down the hill just as if you hadn't set the brake (and you will be very confused when you get back to where you left it).

Blowing Out typically happens on hot summer days when there aren't many little openings for pressure to leak out through: 5606 Hydraulic Oil (the stuff in the brake lines) expands as it gets warm, and with the parking brake set it doesn't have anywhere to go (it can't get back to the main brake reservoir). If you land at 11:00 (local time), set the parking brake, and go have a nice leisurely lunch there is a good chance that when you return to the plane at 13:00 or 14:00 you will find that the hydraulic fluid in your brake system has blown out of whatever the weakest point in the system is (often the seals on the toe brake cylinders, sometimes around the calipers, occasionally a hose fitting fails).
This means you're going to have a mess of hydraulic fluid to clean up at best, and at worst if you're on a hill you're in the same situation as above (the plane has gone rolling away), only now there's hydraulic fluid all over as well (sometimes in a little red trail to wherever the plane has wound up).

So bottom line: Try to avoid leaving the parking brake set for extended periods of time, especially if there might be a temperature increase while it's set.
Instead bring your chocks with you (if you own your own plane, or even if you're a renter, pick up a set of "travel chocks" - they're right at or just under 1 pound, you won't even notice them) and chock your wheels when you leave the plane. Ramp personnel will be able to spot the chock easily, and they're unlikely to fail.

Ideally you would also tie the aircraft down if possible, but some ramps don't have tiedowns (and others are bring-your-own-rope).


How do visiting foreign pilots access Duats or Duat? I'm visiting the US and will get my foreign licence verified, but this means that I won't have a US license or medical. I understand that it is a requirement to sign up for Duats and Duat?!

Any idea or suggestion on how else to use it?

I've just arrived back home after being in the US for some months. I was required to have a FAA class 3 medical, because I did some flight training there, and luckily the one I've received is also is a student pilot certificate with the number on it you require to register for DUAT. Some of my colleges didn't have this number and so they were not able to register until getting there FAA pilot certificate. This will be send to your home adress, most probably when you are home again. In the US you'll only get a temporary certificate (peace of paper). The only number you'll find on it is your current license number.

Now what you can try: One of my colleges simply wrote an e-mail to duats helpdesk where he described his situation, giving all the information they require on their registration page with his foreign license number and attached a photography of his license and a proof that he'll be in the us for the next months. Less than 24 hours later he had a log-in. We had a student Visa, but if you don't have something like this, just try it without it, or take a photography of something else looking trustworthy.

Good luck and enjoy your trip!

Edit: I was just looking for the e-mail address, but for any reason my browser refuses to load duats website. As far as I remember, you'll find it at the registration page. If someonewho can access the website likes to add the e-mail adress please feel free to do so, I would appreciate your help.


Is it legal to build and fly an international aid drone? Is it legal to build and fly a scale 1m:20cm Boeing C-17 for use in flying from the U.K. to other countries to deliver aid in places that are hard to reach?

For example, on top of a large hill where it is hard to get aid workers on foot up there, or too expensive to air drop supplies to people on top of the hill.

Is it legal to build and fly a scale 1m:20cm Boeing C-17 for use in flying from the U.K. [...]

Building an aircraft is likely not regulated (intellectual property laws still apply), it's probably like building a car in your garage, however using an aircraft, specially outside your own property is regulated. Drone use, in UK, is regulated by CAA as for any aircraft, the main reference is:

Air Navigation Order 2016 and Regulations (CAP 393).

Article 23 (Exceptions from application of provisions of the Order for certain classes of aircraft) specifies that some aircraft are excluded from the scope of the order, this includes:

  any small unmanned aircraft.

So some drones can be used quite freely. Indeed you are always responsible of what happens with your drone. Some articles still apply and in particular art. 94:

Art. 94 - Small unmanned aircraft: Need to fly safely, and can't drop anything that can endanger persons or property. Must maintain direct, unaided visual contact with the aircraft. Unless authorized by ATC, weight is limited to 7 kg when inside A, C, D or E airspace, when close to an airfield, or when flying higher than 400 ft.

This article alone prevents free use in your case.

Source

For the sake of reference, let's look at the other articles:

Art. 91 - Dropping articles for purposes of agriculture etc. and grant of aerial application certificate: This is not allowed without authorization.
Art. 92 - Mooring, tethering, towing, use of cables, etc.: Use of cables being a hazard for other aircraft, some cases are prohibited, e.g. using cables in a controlled airspace, or near an airfield.
Art. 95 - Small unmanned surveillance aircraft: Not applicable.
Art. 241: Endangering safety of any person or property: Don't, even recklessly or negligently!
Art. 239 and 257: Power to prohibit or restrict flying: You may be prohibited to fly if circumstances call for; Art. 265: Offences and penalties: How you'll be fined if you do something not allowed.

For uses not covered by art. 23, CAA says:

  If you want to use a small unmanned aircraft or drone outside of the
  operating limits set out in the Air Navigation Order then you will
  need Permission from the CAA, even if your activity is non-commercial.
  Applications for this type of Permission are considered on a case by
  case basis.

Permissions are granted on a case by case basis, they may be valid for one flight or for a period of up to 12 months.
An operating manual must be prepared and submitted to the CAA, and a designed pilot must be assessed by CAA as having the competences required to fly the missions.

In addition, as mass increases, regulation becomes more stringent:

  Unlike small drones, unmanned aircraft with an operating mass of more
  than 20 kg are subject to the whole of the UK Aviation regulations (as
  listed within the UK Air Navigation Order – ANO), although they may be
  exempted from certain requirements by the CAA.

  Unmanned aircraft with a mass of more than 150 kg are also subject to
  additional certification requirements as determined by the European
  Aviation Safety Agency - EASA.

In the UK, "large" drones

  are not currently permitted to fly in any non-segregated airspace [...]
  without specific permission from the CAA.

Flying from the U.K. to other countries [...]

UK is not part of the Schengen Area, flying to a Schengen Area country will be considered as if flying to a foreign country.

Flying to (or over) any other country requires to follow local laws, which vary, but likely include:

Getting an authorization to fly a drone from the local agency equivalent to CAA. Regulations may be more limiting than in UK.
Getting a specific authorization if the pilot is a foreigner. In some countries this may be not allowed at all.
Getting an authorization to use a camera. Some countries don't welcome flying cameras, some just exclude their use at specific locations.

ICAO Appendix 4 to Annex 2 of the Chicago Convention (Remotely Piloted Aircraft Systems) lists the few agreed principles between ICAO members, including:

  An  RPA  shall  not  be  operated  across  the  territory  of  another  State,  without  special  authorization issued by each State
  in which the flight is to operate [...]
  An  RPA  shall  not  be  operated  over  the  high  seas  without  prior  coordination  with  the  appropriate ATS authority.

To deliver aid in places that are hard to reach, for example, on top of a large hill where it is hard to get aid workers on foot up there [...]

UPS-backed Rwandan blood deliveries (source)

Why not launching your drone close to the destination, instead of flying from the UK, think about aspects like:

The ability to maintain a radio link with a significant data rate for the camera. This can be difficult without using a satellite.
A drone limited range, even if fuel is used in place of batteries.

More on unmanned aircraft in UK airspace:

Drones are administratively known as UAS (unmanned aircraft system) and SUAS for the small ones.
CAA site
Unmanned Aircraft System Operations in UK Airspace – Guidance (CAP 722)
The Regulatory Framework for RPAs (EASA)


How is an Airbus A380 fuselage joined and fastened together? An Airbus A380 fuselage is manufactured in three different parts and then assembled together:

(Images courtesy of Airbus S.A.S 1994)

The fuselage functions under extreme conditions: low pressure outside and normal pressure on the inside (normal for humans, that is), and wind drag at near Mach 1 speeds.

How are the three parts joined together to complete an airtight unit? Does one fit into the other in a male-female configuration and how are they held together? Is it nuts and bolts, rivets, screws, airtight glue or a combination of them all?  Pictures would be greatly appreciated.

With approximately 19,000 rivets.

This picture is of the wing attachments, but the fuselage joints use the same attachment method.


Why are passengers not given the option of shoulder harnesses? From this question:

  In airliners, shoulder harnesses are not installed for passengers because:

  it is not mandated by law
  it is too much for average passengers to deal with
  it requires money to install
  it is superfluous in a crash when compared to the same safety from a lap belt

  Flight crew is required to use the shoulder harness (when installed) as it is the law (14 CFR 91.105): [...]

How is 4 true? Why would shoulder harnesses be obligated for flight attendants in their jump seats, but not for passengers?

Against 1 and 2, should shoulder harnesses be installed, at least to enable passengers to decide to use them or not?

Against 3, do the safety benefits not outweigh the costs?

I'll address these one by one.

Should shoulder harnesses be installed, at least to enable passengers to decide to use them or not?

No. They would not serve a significant purpose to improve safety in those seats, and they would add weight and increase maintenance costs for airlines.  Keep reading, and this will come to light collectively with my full answer.

Why would shoulder harnesses be obligated for flight attendants in their jump seats, but not for passengers?

Those seats aren't lined up in rows, therefore there is no seat in front of them that they would hit and be stopped by.  Think of it like a school bus with no seat belts; the passengers will be stopped by the seat in front of them in a low-force crash, but the bus driver wears a seat belt because there is a steering wheel and windshield in front of them, not a padded seat.

How is 4 true? (It is superfluous in a crash when compared to the same safety from a lap belt)

Essentially, if there is a crash that will kill people, the shoulder harness will not be the thing that makes a difference.  The lap belt isn't really even there for crashes.  Extreme turbulence could throw someone up out of a seat; a lap belt is sufficient to prevent this.

A shoulder strap is designed to reduce impact with an object on board a vehicle. A car, we can safely assume, will remain in one piece if it hits a concrete wall.  Airplanes do not have structures designed to withstand impacts like that. If a plane disintegrates in a crash, the passenger, packaged along with the lap belt, shoulder strap, and all, will come to impact the external object directly due to structural failure.  No seat belt can save you from a total structural failure.

Do the safety benefits not outweigh the costs?

Since there really is no safety benefit whatsoever in adding them in the seats that don't already have them, no.  It would be security theater that costs airlines a lot of money.

Regarding Pilots

Notice I highlighted the low-force impact statement up above in regards to buses.  Let's say there is a low-force impact in a plane such as a taxiing crash that jars everyone on board. The passengers will hit the seats in front of them, not that the seats are even necessary to prevent injury.  However the pilots, on the other hand, have a lot of hard instrumentation in front of them such as throttle quadrants, and other things you don't want accidentally shoved forward during a ground crash.

It appears that very little actual research has been done on this subject. For example, this European Transportation Safety Council report states,

  Many proposed safety measures require further research before their benefit to cabin
  safety and the optimal design can be firmly established. In most cases, the availability
  of accurate, validated analytical models is indispensable.

It also states,

  It must be emphasised that these [death count] figures are at best estimates, since insufficient detailed
  accident information is available.

and,

  A fundamental limitation to this process, however, is the lack of adequate accident
  information for a sufficient number of accidents to allow full cost benefit analyses to be
  performed. The absence in many accident investigations of detailed information on
  injury mechanisms and cause of death makes the precise estimation of the potential
  benefits of any one measure very difficult.
  The Cherry study (1995)*
  , one of few studies which have performed a detailed trade-off
  concerning the full range of possible survivability measures, provides insight into
  available options. However, the small number of accidents available for investigation
  in such studies means that the basis for determining priorities still relies heavily upon
  best expert judgement rather than a truly numerically-specific approach.

...and lastly,

  Three-point lap and shoulder harnesses:
  As mentioned above, passengers who are restrained by a lap belt only and who do not
  take up a brace position prior to impact, are likely to suffer serious injuries due to the
  flailing motion of the upper body. As with rearward facing seats, the provision of
  three-point shoulder harness restraint systems would prevent this situation. If all
  passenger assumed the brace position prior to impact, the additional benefits of a threepoint
  shoulder harness would be small. In reality, however, for a variety of reasons,
  occupants generally do not assume a proper brace position, so a three-point lap and
  shoulder harness would be likely [to] improve occupant protection substantially.

So, after reading this document, I did not find any numerical evidence contained within to support its claims, and it even states that it has very little research to go on and appears to be written in an almost purely speculative and subjective manner, which leads me back to the original point above...

A shoulder strap will not save you from a structural failure, and if the plane bumps into something while rolling wheels-down on the ground, the seat in front of the passenger will absorb their impact.


Why did the Mercure use cascade-type reversers? There are three main types of jet-engine thrust reversers:1

Target-type reversers are seen on most civilian turbojets and low-bypass turbofans;2 they have the instantly-recognisable buckets that swing out behind the engine to deflect its exhaust (from both the engine core and - if present - the bypass duct) forwards.
Clamshell-type reversers, seen on some turbofans (both low- and high-bypass) have (as the name suggests) clamshell-style doors that open up from the engine cowling to deflect air forwards.  Clamshell reversers on low-bypass turbofans (“hot” clamshell reversers) generally deflect both the core and bypass air, while those on high-bypass turbofans (“cold” clamshell reversers) usually only bother deflecting the bypass air (which reduces maintenance costs and makes the reverser mechanisms last longer).
With cascade-type reversers, seen on most high-bypass turbofans, the entire rear portion of the cowling slides rearwards, diverting the engine’s bypass air forwards through the resulting gap.

Turbojets and low-bypass turbofans generally3 use target or hot-clamshell reversers, as much of the engine’s thrust (or all of it, for turbojets) comes from the core airflow, and said airflow thus has to be deflected forwards (along with the bypass air, if any) in order to produce net reverse thrust.  In contrast, high-bypass turbofans, the vast majority of whose thrust comes from the bypass air and only a  small portion from the core airflow, can get away with only deflecting the bypass air and leaving the core airflow alone (and thereby saving on maintenance, because jet engine core exhaust is really really hot and filled with delightfully corrosive combustion [by]products); as a result, they mainly use cascade or cold-clamshell reversers.

Enter the Dassault Mercure (an unsuccessful French jetliner from the seventies strongly resembling a longer, shorter-ranged 737-200), which used a pair of low-bypass JT8Ds, and, yet, if this photograph of a landing Air Inter6 Mercure is any indication...

...used cascade reversers.7

I’m having trouble seeing how this would work; for the engines to actually produce reverse thrust, rather than (an albeit diminished net amount of) forward thrust, would seem to require - for the reasons stated above - the use of target or hot-clamshell reversers, which redirect both the core and bypass airflow, rather than cascade or cold-clamshell reversers, which redirect only the bypass airflow.

What am I missing here?  Did Dassault have some magic trick up their britches, were the Mercure’s reversers meant merely to reduce the amount of forward thrust generated (and not to produce actual reverse thrust), or is that picture not what it looks like?8

1: For diagrams of the various types of thrust reversers, see the thrust-reverser tagwiki.

2: Low-bypass turbofans (seen on most narrowbodies designed from 1960 through 1980) have a bypass ratio less than 5:1, and generate the majority of their thrust from the engine core; high-bypass turbofans (seen on all widebodies except for one early Soviet design and on most post-1980 narrowbodies) have a BPR equal to or exceeding 5:1, and get most of their thrust from the bypass air.

3: For obvious reasons, I am ignoring jets that don’t have thrust reversers (such as essentially all fighters, early Caravelles, the BAe 146,4 and the F28).

4: I am aware that the BAe 146 uses high-bypass turbofans; footnote 3 applies to all jets, not just turbojets and low-bypass turbofans, but I couldn’t think of anyplace better to put it.5

5: Hey, I can nest footnotes!

6: The type’s only customer (Dassault sold them nine production Mercures, then refurbished the prototype and sold that to Air Inter as well).

7: (Image originally by Eric Salard at Flickr, via Dura-Ace at Wikimedia Commons; shrunken by me.)

8: Well, it’s definitely a Mercure either landing or rejecting a takeoff (as evidenced by the extended spoilers), but maybe what appear to be cascade reversers aren’t what they seem to be?

Did Dassault have some magic trick up their britches

It was an era of innovations. Have you seen the Vickers VC10 thrust reversers? The clamshell / target doors can be made internal within the nacelle. Literature is lacking on the Mercure, but there is a nice hint from a cutaway drawing:

Source: Air Enthusiast magazine, via aviadejavu.ru

The highlighted item relates to the exhaust cone, and it's labeled "Thrust-reverser cone." I will use a different patent (for now) for illustrative purposes only:

Above shows a nacelle that cascades, revealing vane panels to direct the gases forward, and blocker doors that pivot radially inwards.
The Mercure's thrust reversers were supplied by Snecma, now Safran, and indeed I found a Safran patent for a thrust-reversing cone of similar embodiment that was filed in 1974 (the year of Mercure's entry into service). It does not have cool drawings, but the text is clear:

The jet propulsion nozzle 7 is here of the needle or plug type, or in other words provided with a central body 30 [i.e. cone], and can be closed off completely by means of flaps (not shown) which seat (in the closed position) on said plug or central body 30. [emphasis mine]

Jumelle, Louis Francois. "Jet engine nacelle with drag augmenter auxiliary for thrust-reverser system." U.S. Patent No. 3,941,313. 2 Mar. 1976.


What is the "on condition" concept of aircraft maintenance? "On-condition" appears to mean that a component should be "fit until failure" or that the maintenance should only be performed upon failure of the component.

This seems problematic.

Can someone help me to understand why some components are handled this way and not as part of a regular inspection schedule of some kind?

I'm not a maintenance guy, but you may be mixing 'inspection' and 'maintenance' together here.

An inspection helps you decide if maintenance is needed or not. For example, inspecting the tire tread before every flight, or checking the cylinder compressions every 100hrs. If the inspection shows that the condition of the item is still within acceptable limits, then you don't need any maintenance yet. This is the 'on condition' or 'condition-based' approach, at least as I understand it.

Another approach is to do planned maintenance at fixed time intervals whether it's 'necessary' or not. For example, replacing engine oil every 50hrs, or replacing the entire engine every 2000hrs. In this case it doesn't matter what the item's physical condition is, you perform the maintenance even if everything looks good.

FWIW, some people strongly prefer the 'on condition' approach, especially for piston engines (see this book, for example). But even they probably replace their oil at more or less fixed intervals.

If you want something more official, I found an FAA definition:

  On Condition Item (Oc)

  A primary maintenance process requiring repetitive inspection or test
  to determine the condition of units, systems or portions of structure
  to assure continued serviceability. Corrective action is taken when
  required by item condition as determined by analysis of inspection
  and/or test results.

The key point as I understand it is that you base the decision to do maintenance (or not) on the physical condition of the item.


Is it possible to use reverse thrust while airborne? I play a flight-sim called X Plane. The other day while I was approaching an airport a little too fast and knew I couldn't slow down in time. I decided to use the reverse thrust while I was still in the air and this helped dramatically and I was able to land safely.

But now I'm curious - Would using reverse thrust in a real-life Boeing 747 have the same effect, would it cause the plane to crash, or go out of control?

Commercial jets are not designed to use reverse thrust in flight. With engines mounted under the wing, the turbulence can affect the lift over that section of wing. Tail mounted engines could interfere with the tail. This, in addition to the huge increase in drag, is what causes loss of control, as in the incidents that RedGrittyBrick mentions. Speed brakes are designed to provide the needed drag for emergency descents or otherwise slowing down faster. If the pilots find themselves too high/fast for an approach, and deploying spoilers/gear/flaps won't fix it, then they should go around for another approach.

The loss of control is more of a risk when a thrust reverser deploys only on one engine. Other risks are still there, since those thrust reversers are designed to deploy in landing conditions, not flight conditions. Notable exceptions listed on Wikipedia include the Hawker Siddeley Trident, though it also mentions that the capability was not often used.

Military aircraft, such as the C-17, can be different. They tend to make extremely steep descents more often (called a tactical descent/approach), so thrust reversers can be used in flight.

I did some testing with the stock 747-400 in X-Plane. Deploying the thrust reverser only changes the force applied by the engine, but doesn't seem to affect the air flow. So the loss of lift is not reflected by the model.


where can i get a aviation map of korea with the moes, and highways and vectors ive been searching for a aviation map of South Korea and cant find anyone that sells it. does anyone know where I can find one for flight planning

Those are available in section ENR 6 of the South Korean AIP. Direct link.


Why do the Cirrus SR-20 and SR-22 have the CAPS (parachute) system? Cirrus touts the parachute as an added layer of safety. The parachute has obvious marketing value, but is the parachute's added safety a spin on the airframe's shortcomings? CAPS is not an option when buying a Cirrus, so what's the real reason for it?

Why do the Cirrus SR-20 and SR-22 have the CAPS parachute? Can a Cirrus SR-20 or SR-22 be certified to fly without it?

Briefly, without the CAPS the aircraft could not be certified because it wouldn't meet the spin recovery requirements of 14 CFR 23.221.

You can read a lot of detail in Cirrus's own CAPS Guide but their design premise is that pilots are bad at recovering from spins, especially close to ground. Cirrus wanted to make a safer aircraft that could recover even if the pilot has no spin training at all, so they implemented two safety features: a "cuffed wing design" from NASA and the CAPS.

Normally, the Cirrus would have to comply with 14 CFR 23.221(a):

  Normal category airplanes. A single-engine, normal category airplane must be able to recover from a one-turn spin or a three-second spin,
  whichever takes longer, in not more than one additional turn after
  initiation of the first control action for recovery, or demonstrate
  compliance with the optional spin resistant requirements of this
  section.

But, rather than comply directly by demonstrating the spin recovery, Cirrus asked the FAA to certify them based on the wing design and CAPS instead, as the CAPS Guide explains:

  Given that Cirrus had demonstrated enhanced low speed handling
  characteristics that will help pilots to  avoid inadvertent spin entry
  and the presence of CAPS, the FAA granted Cirrus an Equivalent Level
  of  Safety (ELOS) for the spin recovery requirement of the
  certification regulations. This ELOS is accepted  by all civil
  aviation authorities that have certified the Cirrus SR20 and SR22

The CAPS also has some other benefits, such as being easy to use for an untrained passenger (think pilot incapacitation). That might be an important "why" reason and selling point from a Marketing perspective but it isn't directly relevant for certification.


Testing control surfaces pre flight; what feedback does pilot recieve? During taxi / pre-take off I see a lot of commercial airliners test the deflections of their various control surfaces like the rudder, ailerons etc.

What's the feedback received in this operation i.e. The pilots themselves cannot visually verify the full deflections achieved on command, right? Unlike on (say) a carrier etc where there's a spotter on the ground to confirm.

Just curious, what is the failure mode to be revealed in this sort of test. Is there some sort of internal avionics indicator that would tell the flight crew if the control surface was not reacting to the inputs as expected?

According to this PDF from Airbus (see section "The importance of the pre-flight, flight controls check"), the PF (pilot flying) moves the sidestick around in a defined manner while the PNF (pilot not flying) watches the ECAM F/CTL (flight control) page and calls out "full up", "full down", etc. (Actually the procedure is described in the A330 SOP but the linked document explains it in a comprehensible fashion.)

Source

The ECAM F/CTL page displays the actual position of the control surfaces. This video from Captain Joe explains the behaviour of the sidestick in an Airbus and shows how the control surfaces can be checked on the ECAM F/CTL page (from approx. 1:40 to 2:15).


How to reverse course when there is no published course reversal? Coming from the SW on the RNAV RWY 15 KONO, how do I align myself with the final approach course?  There is only one IAF and no published course reversal.  Is it up to me how I get established inbound?
[RNAV 15]

If the approach doesn't contain a published course reversal (ie PT barb or Hold-In-Lieu), the approach must be flown straight in. In this case, you will either get vectors-to-final or you will get cleared via one of the feeder routes.


Why does the stall angle decrease as camber increases? I have a rough idea about why $C_{{l}_{max}}$ increases with increase in camber.
But I can't explain why the stall angle decreases simultaneously.

At the same angle of attack, a cambered airfoil has a larger suction peak on the upper side (toward the leading edge), and a larger associated pressure recovery (toward the trailing edge).

Larger pressure recovery is equivalent to larger adverse pressure gradient, which leads to easier onset of boundary layer separation and stall.


Can planned runway closures prevent a plane from leaving an airport? I was on a flight recently where, due to the long runway at my airport being repaired, we had to fly to another nearby airport to get enough fuel for the rest of our trip.  We couldn't take off with enough fuel for even a two hour flight because of the runway closure, and this was at a major GA airport.

I'd imagine there are runway closure regulations to prevent this kind of thing from causing serious logistic issues, but do planned runway closures ever make a trip impossible even with refueling?  Considering factors like airspace restrictions, distance, heavy cargo, etc.  it's easy to imagine that a flight normally possible could become impossible due to a planned runway closure, even if you try to refuel at the nearest allowed airport.  What airport regulations are there to mitigate this and how big of an issue is this? For example, can an airplane ever be stranded while airport construction is occurring? How are airports required to notify pilots in advance of planned closures and are there regulations to prevent stranding airplanes or causing logistic issues by closing the only long runway at a critical airport?

Note: I'm not concerned with weather-related closures here, but rather planned runway closures.  My question is aimed at GA where things are more flexible, but applicable answers from commercial aviation can be accepted too.

There is actually a really good example of this...

In 1994 it was decided that the infamous Meigs Field would be demolished and turned into a park. (I say infamous because for all of us young flight simulator aficionados this is the home airport of Microsoft Flight Simulator).

On a Sunday night, March 30, 2003, the Mayor Daley of Chicago ordered the runway bulldozed by gouging huge X's into the runway itself. This was done in the middle of the night with many aircraft still based on the field. No notice was given to the FAA or the owners of aircraft still on the field. In fact, an inbound flight had to be diverted by air traffic control because of equipment on the runway.

You can imagine what kind of excrement storm this stirred up. In the morning of March 31, 2003 at a press conference Daley defended his actions by saying that it would have saved the city of Chicago years of court battles over closing the airport. Luckily the aircraft at the field were allowed to depart from the 3000' taxiway that ran adjacent to the runway.

In this case, the worst the FAA could do was fine the city of Chicago \$33,000 (\$1,100 per day) for closing an ILS procedure without a 30 day notice. Later it was found that they misappropriated FAA funds to demolish the runway and build the park and that had to be paid back, but there were no legal implications of this. The airport was not under federal funding and the city was technically within its rights to close it.

You can read more about it on Wikipedia

The point is that airports are often owned by the city in which they reside, or sometimes the state, at least in the U.S. The FAA releases many guidelines for airports to make them safe, and even has an "airport certification program" for certifying part 139 operations, however these are done through "orders" and guidelines, not much in the way of FAR's.

ATC, if federally operated, must comply with the regulations that apply, including giving NOTAM information for planned closures, or even NOTAM's for closures that are not planned, such as runway debris or accidents closing runways.

So really when you get down to it, the city that owns the airport can close runways (or the entire airport) whenever they want, and yes this may strand aircraft. Usually if the airport is closed unexpectedly and aircraft are still there, they will be allowed to take off from taxiways or grass strips. Worst case scenario the wings will have to be removed and it will need to be trucked out, at least for GA operations.

Depending on the Ops Spec for the airline, it may also allow the aircraft to take off from a taxiway. Usually something like that is done without passengers on board though.

So to address your specific questions...

Is an airport required to give notice to pilots (or aircraft owners) about planned construction? No, there is no requirement for this. Usually what happens is airports don't give adequate notification and it agitates owners, but it all works out in the end.

For example, can an airplane ever be stranded while airport construction is occurring? Yes, at Meigs originally owners had to fight to be allowed to take-off. Many aircraft where going to be scrapped as they were too expensive to move by truck, and owners didn't want to pay. The city didn't want to pay, and the insurance company didn't want to pay, so that would have kicked off a big set of lawsuits for the city.

Closing runways can't always be avoided, for example when there is an accident, weather (flooding, snow, ice), earthquakes, etc. It happens and the system "works" around it when it does.


Is it possible to design a helicopter with fixed rotor blades only (no blade angle/flap/pitch)? I am not familiar with helicopter rotor design but I wonder if it is possible to build a working/flying helicopter with fixed rotors that cannot change the blade angle, flap, pitch or adjust blades otherwise?

I am curious whether the changes in rotation speed would suffice for controlling the aircraft. I guess the cheap RC helicopter models may use such simple design, but is it possible to scale that up to 1:1?

I mean propellers that are solid state and cannot be adjusted in any way except changing their rotation speed, like plastic props used in RC modelling. I do not mind if the whole helicopter design is a traditional main rotor + tail rotor or a coaxial rotor design.

I am interested in 1:1 scale size (at least the Mosquito personal helicopter size). Has anyone tried such simple design?

Also I consider electric propulsion where the RPM changes may be quicker that with internal combustion engines.

Scaling laws are your enemy here.

Model helicopters can be controlled with changes in rotational speed, but for full-sized helicopters the energy needed to quickly change the speed of their rotors relative to the energy needed for lift creation is far too high. In detail:

The moment of inertia of a scaled-up rotor changes with the fifth power of length. The mass of the rotor changes with the cube of the linear scale, and the moment of inertia adds another factor proportional to the square of the linear scale.

A bigger object also needs slower changes, but time scales only with the square root of the linear scale. Next, the engine power available for speed changes will scale with the 3.5th power of scale*.

This still leaves a deficit of one power in the engine power available for speed changes when the helicopter is scaled up.

Lift asymmetries in forward flight can be dealt with by adding a second, counter-rotating rotor, but scaling laws can not be designed out. As Jan Hudec points out, you need to repeat the same trick for forward-backward lift shifting, so four rotors would be the minimum to control this type of helicopter in all directions.

* Proof: Thrust must exceed weight, so thrust goes up with the third power of scale. Rotor disk area scales only with the second power of scale, so a higher acceleration through the rotor disk is required to create more lift per rotor area. If we look at the power required in the static case
$$P_{min} = \frac{\eta_{Prop}}{T_0}\cdot\sqrt{\frac{\frac{4\cdot T_0}{\pi\cdot d^2}\cdot g}{2\cdot\rho}}$$
and insert the scaling factor in all scaleable variables, a power of 3.5 remains for the minimum power $P_{min}$. This is more than the increase in static thrust because the efficiency of the rotors declines with higher disk loading.


Would "wind turbine generators" in the bypass stream save fuel for jetliners? What is the location of an aircraft's alternator, in a large airliner like a Boeing 747 or Airbus A380?

How much power does it produce in kilowatts?

And what is the possibility of installing it with fan blades? To act as a windmill/wind generator at the point where air is slowed down in a bypass turbo fan engine. I mean, incorporate it into the engine design so that it slows down the air to generate electricity, rather than using the motion of the engine.

The aim would be to reduce the amount of fuel required to generate electricity.

There are a few Alternators on big planes.

Most large aircraft have an APU which is often in the back of the aircraft. It is effectively a small turbine directly bolted to an alternator. It provides power while the plane is on the ground (and the engines are off) and can also be used in flight if need be to supplement the main system or in the event of a main engine failure.

The engine alternators are generally mounted and driven directly by the turbine (via a transmission) in this case near the compressor stage. You can read more in this thread and check out this video for a nice overview/explanation of jet accessory drives. You can also see where in this picture,

(source)

As mentioned in the comments you can have a Ram Air Turbine driven by airflow but these are presumably not as efficient as directly mounting it to the engine.