Do airline pilots use FD when performing visual landing? Permitting weather, most airline pilots get visual landing clearance in the US, unless they specifically have requested an instrument or RNAV approach due to their company rules or special circumstances. My question is: when they disengage Auto Pilot for visual landing, do they still use Flight Director until short final?

This answer will be quite anecdotal (I have not seen a survey on the question). It will answer the question for "most people I've worked with", and for "my" aircraft (B737NG). Also, the usual disclaimer: different airlines/aircraft manufacturers may have different SOPs/instructions/limitations. Consult your manuals.

In general: most pilots will leave FD on, IF it still provides useful and reliable information, without being an obstruction/nuisance (i.e. when configuring it to give correct guidance would be more trouble than it's worth, given that you already have visual references). This philosophy is also usually what you'll find in an airline SOP, but in more formal language.

I'll try to provide some examples (non-exhaustive) to illustrate this depending on how you were set up before being cleared for the visual approach:

ILS to straight in landing

Leave the FD on until landing (on my aircraft, B737NG, it will disappear at 50 ft RA), both localizer and glideslope will give usable and reliable information to the FD. (Caveat: in visual conditions, ATC might be less strict about avoiding signal interference. They might for instance let an aircraft on the ground taxi to cross your runway while you're on approach, which could cause localizer/glideslope interference).

ILS to sidestep

Most would turn the FD's off. Both localizer guidance and glideslope guidance will be to the "wrong" runway. The FD is likely to be more of a nuisance than a useful tool.

Non-ILS approaches with no centerline offset

The Localizer/LNAV path will give good lateral guidance to the FD. The vertical guidance will depend on the approach and your equipment. If the aircraft generates a good quality vertical path, which crosses the runway threshold at a reasonable height (50 ft), there is no real good reason to turn the FD's off. If all you have is vertical speed (V/S) guidance, it might be more helpful to turn FD's off.

Non-ILS approaches with centerline offset (for example most VOR approaches)

At some point during the approach, you'll want to abandon the approach course, and line up with the runway. Where this point occurs depends on specific approach, and how you intend to fly it.

Example: A VOR approach to runway 36 (runway heading 000) might use a VOR 1 nm east of the runway with inbound course 005. You might want to stay on the inbound course of the VOR until it crosses the extended runway centerline. In this case, most people would keep the FD on until reaching this point, and then turn it off, as it won't give you any useful guidance afterwards.


stall with max power I saw a video of a test flight of a GA plane and it stalled with max power and with a moderate AOA (angle of attack). How can a plane stall with max power (with the wings flying below the critical angle of attack)?

A plane (airfoil) can stall at any airspeed and/or power setting so long as the critical angle of attack is exceeded. Airplanes stalling only below a specified airspeed is a common misconception largely due to the fact planes are usually listed with a “stall speed” below which the aircraft will generally stall in most situations. However if the critical angle of attack is exceeded at a higher speed a stall can also occur. The only way to know the critical angle of attack is from an angle of attack measurement device installed on the airframe it is inherently somewhat different than the aircrafts attitude.


Are there any limitations of diopters (corrected eyesight) in the US? According to FAA standards, there seems to be no diopters limitation for a first class medical.
I'm Japanese. JP CAC limits it. UK CAA also does.
I would appreciate it if you could tell me whether my understanding is mistaken or not.

The FAA bases their eyesight limitations on total acuity and not on diopter correction strength. Although many people equate these as being the same thing, they are not.

Diopter correction is based on focal length. How well an image is focused onto the retina of your eye. An image not being focused on the retina is usually due to a distortion of the cornea. Either it is too curved or not curved enough. The image focal point can be on, prior to (cornea too curved), or after (cornea too flat) the retina.

The cornea might also not be completely spherical. More like a rugby ball and less like a soccer ball. This is called astigmatism.

Sometimes the issue could be with the lens. The stiffening (reduction of flexibility) of the lens due to aging is usually the cause of the need for bifocals and reading glasses. The lens can no longer adjust its own focal length as well as it used to. Making it harder to focus up close.

Misalignment of the focal point with the fovea due to a tilting or shifted cornea, lens, or retina is a prismatic issue. The inability to physically align the eye (lazy eye or amblyopia) can also cause this.

Acuity is based on how well the image can be distinguished clearly regardless of focal length. An image can be focused on your retina (0 diopter correction), and still not be clear or distinguishable. Eye diseases like cataracts (fogging or frosting of the lens), glaucoma (increased internal pressure of the eye pressing on the retina, causing damage), macular degeneration (damage to the fovea of the retina), etc. can degrade your acuity without affecting your focal length. No glasses of any diopter strength will improve acuity in these cases. Even eye injuries like a corneal ulcer or a scratched cornea can negatively affect the acuity of a person with normally perfect vision.

Although all of these issues affect acuity, all of them together add up to total acuity. Using only one measure can not accurately determine a pilot’s ability to see correctly. Diopter correction alone can not tell the entire story.


How are fuel tanks cleaned out? One episode of the BBC series "Engineering Giants" featured a BA 747 undergoing a multi-week "D check". Here the inside of a fuel tank was surprisingly clean and dry (to me):

since elsewhere I've read of technicians having to wear respirators and protective overalls. Presumably the lighter fuel fractions can be driven out with forced ventillation, but is a specific cleaning process required to remove less volatile compounds?

FAA design regulations require that the aircraft be equipped with fuel system drain valves that allow the entire fuel system to be drained.

"Fuel System Drains -
Aircraft fuel systems must be fitted with at least one drain to
allow safe drainage of the entire fuel system with the airplane
in its normal ground attitude."

According to a maintenance person: "The residual is vacuumed or absorbed and the negative ventilation is applied. You can make entry almost immediately, though air monitoring is constant. We keep air moving through the tank anytime there is someone in the tank. "

Doesn't clearly answer the question, but this article discusses the procedures for personal protection while entering aircraft fuel tanks.


What do the components of a shockwave's visual artefacts represent? On a recent flight, I was able to observe visual artefacts over the wing (Boeing 767-300 in cruise).

You can see them in the image below; they look like creases in a surface. They moved forwards and backwards over the wing. Later in the flight they extended to the end of the wing; at this point, they extended no further than a few metres.

I've added red and yellow arrows pointing to their ends - as you can see, one of them appears to fork.

Adjusting brightness and contrast makes the artefacts more visible:

I understand that this artefact is caused by a shockwave produced by supersonic airflow over the forward part of the wing.

I'd be interested to know: what exactly is it that I am seeing?

Is the artefact projected onto the surface of the wing, like a
shadow?
Is the artefact a refractive distortion caused by different air
densities?
In this image, there appear to be two creases, one behind the other -
what do they represent?
What does the fork at the right-hand end of one of the 'creases'
represent?
What do the darker and lighter portions of the 'creases' represent?

What you see are changes in the refractive index of the air, caused by the different pressure and temperature at different places. Sometimes, with the right conditions, there may be zones of transient condensation of water vapor, that add to the effect...


Why aren't "fuel polishing" systems removing water & ice from fuel in aircraft, like in cruising yachts? Should you sump fuel tanks when the fuel system is below freezing? the question

should one sump fuel-tanks before flying, if in freezing-conditions?

but this implies another question that boggles me:
Why don't aircraft have "fuel polishing" systems, to remove water from tanked fuel, especially since the cost of having a line block with ice, is so horribly high?
Cruising boats sometimes have such things, & given the peace-of-mind it'd give, why aren't these devices in play, in aviation??
( btw, it essentially is a filter & water-bypass thingy, so the water goes to the bottom of the glass bowl, & the fuel, above that, goes through the filter, if they combine them, or maybe the water-separator & the filter-unit are separate, in sequence, but both are present, before the fuel goes anywhere near the engine... )
I believe a fuel polishing system is run before firing-up an engine.
This removes all the contamination before the engine's fuel-pump even starts.
edit 2:
Marine Diesels, in the stuff above...
Also, this is in light of some events written about years ago...
1 was a small jet that lost power at high altitude due to slush-ice in fuel,
another was a jetliner that smashed after the same problem, ttbomk...

slush-ice in the fuel clogged something in the fuel-system, causing...

a drop in power, so therefore the crew...

increased thrust, which caused ALL the engines to clog/die, so the new recommendation was...

if in that type, at high altitude, in cold, if power reduces unexpectedly,
then reduce thrust to unclog the lines, & it should clear...

also many apparently have had problems with ice in fuel messing things up for them in piston aircraft...
also I know some are running automotive-conversions,
& if anyone ever has ethanol-blend gas in their aircraft,
& that ethanol has absorbed water, & gets cold, it can separate out,
leaving 2 distinct fluids in the tank:
ethanol-water & gasoline.
( I'm not saying running auto-fuel is legal in an aircraft,
but rather that I know human-nature. )
edit 3:
that link above includes some interesting stuff
also, the whole idea may be bunk,
if the amount of ice-slush in a jetliner's tanks is measured in tonnes, rather than litres,
as no catching-out device is going to handle that kind of volume.
I don't know what volume is involved.

The simple answer is weight/risk/added complexity: the systems are heavier than they are worth for the problems they avoid in aircraft.
While ice blockage has been an issue for aircraft in the past, planes that fly high enough to warrant it have fuel heating systems to avoid this very issue.
The reality is that the chances of water getting into marine fuel are MUCH higher than water getting into AvGas. Water finds its way into airplanes in mainly one way: warm moist air that fills the space in fuel tanks condenses in the cold and the water precipitates out. This often happens over night when planes are not re-fueled after their last flight and left out in the cold. As such its extra important to sump the tanks for the first flight of the day. You can also mitigate this by filling the tanks every night if possible. Pilots are also taught to diligently sump tanks to avoid the issue in the first place.
In my experience, flying in the north east of the US where the air can get humid and the nights can be cool, I've never pulled more than a few bead size drops of water out of the tanks of my archer in the morning. I know of others that have pulled more but not significantly more.
There have been occurrences of a fair bit (hundreds of gallons of water) getting into aircraft tanks but these have generally been caught and handled. On the bright side we have a few nice things in aircraft that make water easy to deal with.

Water is heavier than AvGas so it will pool at the lowest point of the tank which is generally where the outlet/fuel line is connected.
The lowest point of a fuel tank on an aircraft is fairly easy to get to so pulling a test sump of fuel is no problem during pre-flight
It's fairly easy to deal with the fuel once it's in the sump cup on the ramp, chances are you wont anger the EPA all to much.

On the contrary, with marine fuel tanks it can be hard, if not impossible, to access the sump in any reasonable way and once you drain it you run the risk of it getting in the bilge and ending up getting pumped overboard which the EPA will have an issue with.
On a boat you have lots of options for water to get into the tank since there is generally water all around. Maybe it splashed in some gas cans you had on deck, maybe it splashed in during a mid trip re-fuel, maybe it splashed in refueling at a dock, maybe it was raining one of these times or all of these times, maybe the dock kid put the fresh water hose in the fuel inlet in a haste etc. etc. As such fuel/water separators are far more critical on a boat where there is often space and weight to spare and the chance of water getting into the fuel is high.


Is commercial domestic service using foreign registry aircraft allowed in the USA? I recently saw a domestic tour operator using aircraft with foreign registry. The pilots had U.S. CPLs. Can foreign-registered aircraft operate commercially within the U.S.A, in an operation where flights begin and end within the U.S.A.?

Yes, it's allowed under both part 135 (on-demand) and part 121 (airlines); 121.153 and 135.25 both have the same wording:

  A certificate holder may operate in common carriage, and for the
  carriage of mail, a civil aircraft which is leased or chartered to it
  without crew and is registered in a country which is a party to the
  Convention on International Civil Aviation if— [...]

And US pilots may fly foreign aircraft within the US.


Do jets breaking the sound barrier leave shredded metal on the ground? As a kid (1960s and 1970s) we would find shredded metal rolled into a loose ball similar to the shredded paper one might find in an Easter basket, in the hills surrounding our farm. We had the Royal Canadian Air Force (RCAF) based about 60 miles north of us in Moose Jaw, Saskatchewan, and the jets used to fly over the farm quite often. We were told that this metal came from the jets when they broke the sound barrier. I can not find any information to confirm this.

I don't think this had anything to do with military jets breaking the sound barrier nearby; it does sound more like strips of metal recovered from chaff dispensers on the jets; countermeasures systems which eject hundreds of strips or threads made of metal foil used to thwart enemy radars.  Most likely the aircraft discharged their chaff dispensers during training exercises over the farm; you simply recovered some of the metal strips.

Wikipedia

Source


Do different grades of leaded avgas differ in ways other than their lead content? Although only one grade of leaded avgas (100LL, standing for 100-octane, Low-Lead)1 is in common use today, there were formerly a number of different leaded avgasses with higher octane ratings and tetraethyllead (TEL) contents (things like 100/130 and 115/145), catering to the large, high-compression piston engines of decades past; these higher-performance blends are now produced only in small-volume special-order batches for applications where even 100LL doesn’t cut it, such as air races.

Are there differences between the various grades of leaded avgas other than their lead content, or could one convert 100LL into (say) 115/145 simply by adding more TEL?

1: 100LL is only “low-lead” when you compare it to the even-leadier avgas blends of days mostly past; it still has a considerably-higher lead content than leaded mogas ever did.

Gasoline (both avgas and mogas) grades are distinguished solely by octane rating and lead content.

In theory, the octane rating is the amount of actual octane (C8H18) it contains, with the remainder being mostly heptane (C7H16), hexane (C6H14), pentane (C5H12), etc. As you note, a higher octane rating is needed for engines with higher compression ratios.

A century ago, the only way to get high-octane gas was via distillation, and since actual octane is a tiny fraction of crude oil, this was very expensive. It was soon discovered, however, that adding TEL made gasoline behave like it had more octane than it actually did; the higher octane rating you needed, the more lead you added. Leaded gasoline was born, including the 80/87, 100/130 and 115/145 grades of avgas.

However, just a few decades later we discovered how to "crack" long-chain hydrocarbons into shorter ones. Cracking diesel produced (mostly) gasoline--and with a much higher fraction of octane than gasoline distilled directly from crude oil. This allowed creating a 100-octane grade of avgas without any lead, but some old engines actually need a little lead for other reasons, so 100LL was born.

In short, you can take any grade of unleaded gasoline and boost it to any higher grade just by adding enough lead. Start with a higher grade of unleaded, though, and you won't have to add as much.


Is this frost or frozen bacteria in clouds? I was recently flying back from Palma de Mallorca Airport (PMI) to Birmingham Airport (BHX/EGBB) and I had the luxury of sitting at a window seat behind the wing. I think the plane was a Boeing 737-800 via Jet2.

Halfway though the flight I was looking out the window and noticed little specks on the outer window and was trying to work out if it was frozen water or frozen bacteria from the clouds?

Does anyone know what this is or how it forms? Does this happen to the pilot windows also?

If it disappeared after you descended, it was frost specks on the inside surface of the structural* outer panel, forming on dirt particles on the plexi, from the small amount of humidity in the cabin air that migrates through the little vent hole in the inner panel that is part of the interior fascia.

It's not a problem on cockpit windows because they are heated.

*I say structural, because the outer pane of quarter inch thick acrylic has about the same tensile strength as the adjacent much thinner aluminum skin and is part of the pressure hull.


Can cold thrusters/roll posts be used to control/stabilize an aircraft (like a satellite)? Aircraft use control surfaces to control their motion/direction. Would it be a good idea (i.e., more efficient, less weight, better responsiveness, less drag, etc.) to use thrusters/roll posts to control roll, yaw and pitch, like the roll posts an F-35 uses for hover?

this question refers specifically to a continuous flow system like the F-35 roll posts. no rockets no turbojets

There are several ways to do it, rockets or turbojets. Rockets have a problem with fueling them, turbojets are very difficult to find a place for that offers reasonable leverage.
Roll posts on the F-35B are not really thrusters, but rather use redirected engine thrust. They're not light either. Engine thrust at high altitude and airspeed is considerably lower than at sea level, while required control forces are larger.

Short version: The reason why control surfaces are better for control than cold thrusters is Lift coefficient, or more precisely the lift-to-drag or lift-to-thrust ratio.

An engine directed in the direction you want to apply force in has a lift-to-thrust ratio of 1. Each newton of engine thrust, gets you 1 newton of force. To produce 1 kN of force from the roll post, you lose 1 kN of thrust.

An airfoil at some angle of attack has a lift-to-drag ratio generally between 5 and 25. By deflecting an airfoil to get 1 kN of force, you only lose 40-200 N of thrust to drag. Thus, it's a much more efficient way to change your direction.

All in all, using thrusters of either type would result in...

Less efficiency: Thrusters require fuel, control surfaces don't. And if they're rocket type, they even need to carry the oxidizer.
Cold thrusters don't require extra fuel directly, but they "steal" main engine thrust, so you get slightly less efficiency.

More weight: An engine can produce 10 times its weight in thrust for 1 unit weight, but an airfoil at high angles of attack can produce a force 100 times its weight. The big weight problem will the be the added fuel, especially for rocket engines that need a lot of oxidizer. Plus, you still need the control surfaces, because they're the only way to adjust your aerodynamics for sustained flight. Thrusters could only be used to accelerate the initial maneuver.

Better responsiveness: with rockets, but a lot of fuel is required for those.
Worse responsiveness: if you reduce control surface size and use turbojets (they take a long time to spin up). The same if control surface size is unchanged.
Same responsiveness: with roll posts/cold thrusters.

Less friction drag: if control surface size is reduced. But since you still have to keep your control surfaces, just can get them smaller (the largest deflections are used at low airspeeds), not much less. Also, the added induced drag from the extra fuel may make up for it.

Overall: There's a reason that even rockets typically use fins (control surfaces) when possible. The only things an aircraft may need thrusters for is things that can't be done with control surfaces.
For instance, roll posts are used on the F-35B because control surfaces don't work at zero airspeed. Thrust vectoring has enabled some maneuvers beyond the normal angle of attack envelope.

If not for the oxidizer problem, there could be some applications for thrusters for unusual maneuvers, strictly in addition to control surfaces. As it stands, their thrust is too expensive to get, compared to force from the control surfaces and even to main engine thrust.


Can a civilian aircraft pilot see a missile coming? Can a civilian aircraft pilot see a missile coming?

By "civilian aircraft," I mean planes that were not equipped with flares that fire when rockets approach  or any similar anti-missile systems.  If these missiles can be detected, can the pilot take any evasive measures?

Visual detection

To take one example, a vehicle-launched ground to air missile system (e.g. the SA-11) that can reach the cruising altitude of airliners travels at several thousand miles per hour and takes perhaps 30 to 40 seconds from launch to reach its target.

Pilots don't have an especially good view of the ground immediately below and would have a very hard time spotting a missile travelling at those speeds.

Electronic detection

Civilian airliners are equipped with a collision avoidance system called TCAS. However this relies on radio signals from transponders which are fitted to other aircraft. Naturally, anti-aircraft missiles do not have a transponder and do not advertise their presence.

Missile Countermeasures

Anti-missile systems that are available (example) are mainly intended to protect against small infra-red seeking man-launched air-defense missiles (MANPADs) rather than larger more sophisticated radar-homing systems.

Even these systems are not fitted to all civilian airliners, probably only to those that operate into airports where there is a current known risk of MANPAD use by terrorists or other armed factions.

Evasion

Civilian aircraft are not designed for high-G evasive maneuvers and in any case, the missile does not have to strike the aircraft, it detonates nearby based on a proximity fuse and the resulting explosion and high velocity fragments will do enough damage to result in the destruction of the target.


Can a VTOL jet such as the Harrier enter a Vortex Ring State? I'm curious, because they obviously don't have those huge rotors pushing the air away, but they are still getting their upward thrust from somewhere.

My gut says, yes, but it is more difficult. Is this right?

The main problem with VRT is the airflow through the rotor which is disturbed because it is ingesting its own downwash.

The large area of air accelerated downwards keeps being sucked back in to the rotor because the helicopter sinks back into it. In this state the rotor provides very little thrust - it acts as a sort of divide-by-zero state, as the transition between normal flight and windmilling when the air streams upwards.

The flow field of the Harrier is different:

Thrust is produced inside the engine, which is shielded from the effects of aircraft vertical velocity: air is sucked in through the inlet next to the cockpit.
The air stream velocities are higher. Air is accelerated downward in a much smaller area at much higher velocities. There is no fuselage which partially decelerates the airstream, like in a helicopter: the downward flow field is much cleaner.

The defining problem of VRS is the lack of thrust from the rotor at downward velocities, this would not occur with the shrouded jet engine of the Harrier.


Do pilots get more fresh air than passengers? There is a famous air travel myth claiming that "pilots get more fresh air than passengers".

       (source: The pure cure, p.375)

I would like experts to either dispel or confirm this myth, that pilots receive "better air" with higher oxygen levels than passengers, who have to breathe more recirculated air.

Although at first glance it might sound absurd, but when you think about it, it would actually make sense, because:

The worst thing that can happen to passengers is that they get tired. Sure, that may be unpleasant (think of the stale air in a crowded room), but does not pose a health or security risk.
Pilots, on the other hand, need to be wide awake and perform to the top of their abilities, as errors can be fatal. So any negative outside influences on pilot performance needs to be eliminated. In particular, pilot fatigue significantly increases the risk of pilot error.

However "CO2 levels directly affect pilots’ flight performance" as was tested in a study on 30 active commercial airline pilots performing maneuvers under varying carbon dioxide concentrations:

  press release
  Previous research led by Allen and colleagues found that, in office buildings, CO2 concentrations between 1000-2500 ppm – levels once thought to be benign – negatively impact the cognitive function of employees. For the new study, they wanted to determine if higher CO2 levels on the flight deck would impair a pilot’s ability to perform advanced maneuvers and manage emergency situations, such as a single-engine failure during takeoff. […] Average CO2 levels on the flight deck are less than 800 ppm. However, they have been measured as high as 2000 ppm on the flight deck and even higher in the cabin during the boarding process. […] The National Research Council has suggested that current standards for ventilation rates on flight decks may be inadequate.

  background
  On the flight deck […] the average CO2 concentrations are typically <1000 ppm, but the 95th percentile concentration can be as high as 1400 ppm, depending on airplane type.

  results
  Compared to segments at a CO2 concentration of 2500 ppm, the
  odds of passing a maneuver as rated by the Examiner in the simulator
  were 1.52 times higher when pilots were exposed to
  1500 ppm and 1.69 times higher when exposed to 700 ppm.

In light of the above it would make sense to prioritize pilots over passengers when it comes to circulation of fresh air.

I will post the results of my research into this question as an answer below, but would welcome other answers presenting technical evidence and quoting citable references.

scope:
This is not the same question as Q57941.
Q57941 asks if there is airflow between cockpit and cabin (as opposed to be hermetically sealed).
Whereas this question asks if more fresh air from OUTSIDE flows into the cockpit than into the cabin. Also, it addresses a very famous airline myth, and as such it has a valuable purpose.

Taking the B737 as an example, fresh air from the left pack flows directly into the cockpit (green airflow in the diagram), whereas the passenger cabin is served from the mix manifold only (yellow). Therefore

pilots receive 100% fresh air
while passengers receive a mix of 50% fresh air and 50% re-circulated cabin air on average, across all aircraft types

share of re-circulated air (red) in the cabin ventilation air (yellow):

B737: pilots 0% passengers 25%
B757: pilots 0% passengers 50%
B767: pilots 0% passengers 50%
B777: pilots 0% passengers  ?

In a cabin packed with hundreds of people each transforming 21% O2 and 0.04% CO2 into 16% O2 and 4% CO2 (i.e. breathing) and where 50% of this exhaled used air (red) is recirculated back into the cabin (yellow), O2 and CO2 levels are poorer than in the cockpit not supplied with exhaled used air.

The AFA-CWA flight attendants association indicates how much fresh air each person receives:

  How much air is supplied in the economy section? 6-10 ft³/min of outside air to each person which is about half what is recommended in
  buildings and transportation vehicles.
  The cockpit gets 50-100 ft³/min per person of outside air, or sometimes a mix of outside and recirculated air depending on the
  aircraft type. That is up to 20 times more than in the passenger
  cabin.


How to compute drag coefficient for falling book? The book measures 20 x 20.3 x 1.4cm and I'm assuming it's sealed shut so the pages don't flap open. Mass is 450g.

I want to understand how quickly it would fall if dropped straight down from 10km altitude. I've used a value for drag coefficient for a flat plate perpendicular to the air flow that I got from NASA (1.28) but I'm guessing that a falling book would spin round, slowing its fall, so this value is probably not right - is this likely?

So I'm wondering if it's possible to estimate the drag coefficient to any degree of accuracy. I don't have access to a wind tunnel and I'd rather not drop it off a tower as an experiment. :)

You have a very thin book. The answer depends on how you initially drop the book.
1. If you drop it flat about its front
It will very closely approximate a flat plate; in this case, the pressure drag will overwhelm the skin friction drag. Hoerner, Fluid Dynamic Drag has some empirical data on the drag coefficient of a bluff body (near 2.0):

To retrieve the 3D coefficient, dimensionalize it with the frontal area.
2. If you drop it broadside
The skin friction drag would dominate. You can approximate it via the flat plate friction drag. For a single side, the drag coefficient looks like (from Anderson, Fundamentals of Aerodynamics):

3. If it tumbles
Your book may also tumble at some point due to random perturbation about its major principal axis. This changes the drag even further; but once again, Horner has some empirical correction formula.


May an ultralight vehicle pass directly above KEGE at 9200 MSL at 1600Z with no prior authorization without violating FAR 103.17? May an ultralight vehicle pass directly above KEGE at 9200 MSL at 1600Z with no prior authorization without violating FAR 103.17?

http://vfrmap.com/?type=vfrc&lat=39.643&lon=-106.916&zoom=10

The A/FD entry for KEGE says "AIRSPACE: CLASS D svc 1400–0200Z‡; other times CLASS E."

There is more to this question than meets the eye-- KEGE appears to be an oddball case.  More detailed descriptions of the airspace descriptions at KEGE, including the page numbers for these airspace descriptions in the FAA's "Airspace Descriptions and Reporting Points Documents" JO 7400.11C, are given in this related question Can the Class-E-to-surface airspace near Eagle County Regional airport KEGE be ignored when the tower is open?

Please note that this is NOT a question about:

Whether an ultralight needs prior authorization to fly in the airspace above the surface footprint of E4 "extensions" such as at KNYL or KMFR, as per Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?
Whether an ultralight needs prior authorization to fly in the airspace above the surface footprint of the rectangular projection of E2 airspace at KEGE-- this rectangular projection was the subject of another related question Can the Class-E-to-surface airspace near Eagle County Regional airport KEGE be ignored when the tower is open?
Whether an ultralight needs prior authorization to fly over the ceiling of Class D airspace in a case where the E2/E4 airspace designations have been assigned in a more conventional manner, with the footprint of the E2 airspace fully coincident with the footprint of the Class D airspace, such as at KMFR or KNYL http://vfrmap.com/?type=vfrc&lat=42.374&lon=-122.874&zoom=10
Whether an ultralight needs prior authorization to fly in Class E airspace in general

Yes, an ultralight aircraft may fly over KEGE ( http://vfrmap.com/?type=vfrc&lat=39.643&lon=-106.916&zoom=10 ) at 9200' MSL at 1600Z -- i.e. above the ceiling of the Class D airspace when the control tower is open and the Class D airspace is in effect-- with no prior authorization without violating FAR 103.17.  Just as is the case above any Class D airspace with projecting areas of Class-E-to-surface airspace where the airspace designations have been handled in a more conventional manner, such as at KMFR ( http://vfrmap.com/?type=vfrc&lat=42.374&lon=-122.874&zoom=10 ).

The design of the airspace at KEGE as described in the FAA's "Airspace Designations and Reporting Points" document, JO 7400.11C, is unconventional and possibly flawed, as described in more detail in this related question Can the Class-E-to-surface airspace near Eagle County Regional airport KEGE be ignored when the tower is open?.  Here are all of the most plausible interpretations of how the Class-E-to-surface airspace around KEGE is intended to function.  None of these interpretations require an ultralight aircraft to seek prior authorization before overflying KEGE at 9200' MSL when the Class D airspace is in effect.

All of these interpretations address this question -- "During the hours that the Class D airspace is active at KEGE, is there any E2 airspace at KEGE, and if so, where?"   To understand why, generally speaking, E2 airspace, and only E2 airspace, appears to be the best fit for the meaning of "the surface area of Class E airspace designated for an airport" in the context of FAR 103.17, see this related answer Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?

1) The best description of the situation at KEGE appears to be that the airspace has been designated in the same way as the 21 airports described in this answer to a related question What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night? , except that no E4 airspace description has been provided to create Class-E-to-surface airspace in the projection to the east when the tower is open and the E2 airspace is inactive.  according to this interpretation, this omission is accidental.  A careful study of the "Airspace Designations and Reporting Points" document makes it clear that any given block of designated airspace (e.g. E2, E4, or Class D) is intended to become effective or ineffective as a single unit, so when the Class D airspace is in effect at KEGE, none of the E2 airspace is in effect. So technically, as the description has been written, it appears that there is no Class-E-to-surface airspace in the projection to the east when the tower is open. Local ATC treats the airspace as if there is Class-E-to-surface airspace in the projection to the east 24/7, i.e. as if an E4 airspace description had been provided to cover the airspace in the projecting area to the east when the tower is open and the E2 airspace is not in effect.  Naturally, it would be wise for a pilot to treat the airspace in the projection to the east as if it were some form of Class-E-to-surface 24/7, because this is the practice of the local ATC.  Nonetheless, an ultralight overflying KEGE above the Class D ceiling when the tower is open is not within the lateral boundaries of any active E2 airspace, so no prior authorization is required by FAR 103.17.

2) The airspace around KEGE has been designated in the same way as the 21 airports described in this answer to a related question What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night? , except that no E4 airspace description has been provided to create Class-E-to-surface airspace in the projection to the east when the tower is open and the E2 airspace is inactive.  According to this interpretation, this is intentional and is based on the theory that when the Class D airspace is active, only that portion of the E2 airspace which coincides with the Class D is superseded by the Class D, while the rest of the E2 airspace remains in effect.  (KEGE appears to be the only airport in the US where this unusual theory has been applied; normally any given block of designated airspace (e.g. E2, E4, or Class D) is intended to become effective or ineffective as a single unit.)  However, a fundamental characteristic of any given column of E2 airspace is that it contacts the surface.  Therefore when some portion of the E2 airspace is superseded by Class D airspace up to 9100' MSL, all the immediately overlying E2 airspace also detaches from the rest of the E2 airspace and becomes E5 airspace.  When the Class D airspace is in effect, none of the airspace above the ceiling of the Class D can be considered to be E2 airspace.  Therefore an ultralight overflying KEGE above the Class D ceiling when the tower is open is not within the lateral boundaries of any active E2 airspace, so no prior authorization is required by FAR 103.17.

3) The airspace around KEGE has been designated in the same way as the 21 airports described in this answer to a related question What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night? , except that no E4 airspace description has been provided to create Class-E-to-surface airspace in the projection to the east when the tower is open and the E2 airspace is inactive.  According to this interpretation, this is intentional and is based on the theory that when the Class D airspace is active, only that portion of the E2 airspace which coincides with the Class D is superseded by the Class D, while the rest of the E2 airspace remains in effect.  (KEGE appears to be the only airport in the US where this unusual theory has been applied; normally any given block of designated airspace (e.g. E2, E4, or Class D) is intended to become effective or ineffective as a single unit.)  Therefore the airspace above the ceiling of the Class D can be technically be construed to be E2 airspace 24/7.  However, FAR 103.17 does not specifically and explicitly reference E2 airspace.  While in most cases, as noted in the related answer Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?, E2 airspace, and only E2 airspace, is the best fit for the meaning of "the surface area of Class E airspace designated for an airport" in the context of FAR 103.17, any piece of E2 airspace that is not actually part of a column of Class E airspace extending all the way to the ground is clearly an exception to this general principle.  An ultralight may overfly KEGE above the Class D ceiling when the tower is open with no prior authorization without violating FAR 103.17.


Does adding a motorized fan to a hot air balloon change its class as an aircraft? I have seen fans like these for use in ballooning and glider propulsion.

Does adding one of these change the definition of the flight vehicle?  e.g. is it No longer a balloon, but now an aircraft?  Does only the flight elevation and proximity to a controlled airspace matter — or does the capacity of the craft have an impact?

I suppose another dimension of this question regards if licensure changes in such case.

Well, a balloon already is an aircraft, specifically:

  A balloon is a lighter-than-air aircraft that is not engine driven, and that sustains flight through the use of either gas buoyancy or an airborne heater.

So if you were to attach engine-driven propellers to your balloon it would no longer be a "balloon". It would start to sound a lot more like another kind of aircraft -- an airship:

  An airship is an engine-driven, lighter than air vehicle that can be controlled in flight.

So from a licensing standpoint there would appear to be two major considerations: First the pilot of such a chimera would need to be licensed to act as pilot in command of an airship (not a balloon), and second the modification itself would have to go through appropriate regulatory channels, since it is changing the fundamental nature of the aircraft in a way that would almost certainly attract some scrutiny.

Specifically regarding the fans/propellers you're talking about, it looks like those are intended for use as inflation fans to help you out when you're setting a hot-air balloon up - once you've got the envelope inflated and the heater is doing its job you don't really need the fan anymore, and you would leave it with your ground crew.

As far as I can tell they aren't intended for use as engines for moving and steering a balloon - I suppose you could carry one aloft with you if you were feeling bold, but I'm not sure what the impact of doing so would be from a regulatory standpoint when it's not permanently attached to the balloon, and I'm not sure how effective they would be as propulsion with only a few horsepower behind them.


Why does a jet engine acquire a metallic whine when in full power? I had a flight yesterday on an AA Embraer ERJ-190. As the plane idled at the end of the runway there was the familiar high-pitched jet whistle, which increased in pitch as the engine started spinning up. But, when it reached full power, the whistle was joined by a far-lower-pitched metallic whine, which persisted until the pilot throttled down after the initial steep climb.

I've heard this before on some (but not all?) planes. By ear, the whistle was about four an a half octaves above the whine, which is about a factor of 24 (I may have been off by an octave, or another factor of two).

On a past flight I calculated that if the main fan spun so that its outer edge was moving at the speed of sound, the whine would be at about the rotational frequency of the fan. If the fan had 24 blades (or 48 if I have the wrong octave) then the whistle could be the fan blades, and the whine the fan itself.

One explanation could be that there's something asymmetrical about the fan, e.g. one blade is a bit too long and hits the housing when at full power. (Of course, this would make no sense from an engineering and reliability standpoint.)

What causes that far-lower-pitched metallic whine?

Edit: I just returned on a JetBlue flight, but also using an ERJ-190. Where before I was seated in row three, this time I was in row 24 of 25. On takeoff, there was only a loud roar; no "whine" or "whistle". So, it's pretty clear that the noises I'm referring to above are emitted from the engine intake.

And, on this page I found a photo of the ERJ-190's GE CF34-10E Efficient Engine's inlet:

Sure enough, the intake fan has 24 blades. So, my above guess on the frequency ratio between my "whine" and "whistle" has some physical basis.

And, I'd like to respond to a comment by @kevin:

  Could it be that the "whine" always exists in the frequency spectrum, but it's just below our human ear detection threshold (both pitch and amplitude) during low rpm operation?

When the "whine" starts and ends, my impression is that yes, the pitch rises as it initially strengthens, and falls as it finally fails. However, its volume is strongly pitch-dependent, so that it is far quieter when running at 80% of the maximum pitch/RPM, and inaudible below that. It sounds as if that blade which purportedly hits the housing only does so above a certain RPM (again: this is what it sounds like, it almost certainly is not what is actually happening). More generally, my interpretation is that the cause of the "whine" only happens above a certain RPM.

Edit 2: @fooot was kind enough to point out another question that is basically a duplicate. My text and suppositions are (I think) a lot clearer, but the other question links to two videos that demonstrate exactly what I've been talking about:

Airbus A320 with IAE V2500 engine
Airbus A320 with CFM56 engine

Neither of the answers to the other question are correct; one focuses on the fan blade noise (too high-pitched) and the other on pressure equalization vents (not engine-speed related).

I found the following RPM limits for the GE CF34-10E: 6325 RPM and 18018 RPM for N1 and N2 stages. At 100% power, the RPM for the N2 stage is 17160 RPM.

So basically we're looking at a rotational frequency of about 300 Hz. Well above the 20 Hz threshold for hearing, even if not at 100% power.

Where things get interesting is the fact that the human ear becomes markedly less sensitive to sounds below 300 Hz. So when the engine spins up from 200 Hz to 300 Hz, not only will the increased power probably produce more raw noise, it's also at a frequency that's more audible. But exactly how strong that effect is, is hard to describe. There's even a standard for this, specifically aimed at airplane noises!


Is it possible to build a jet engine that utilises all excess heat? Is it possible to build a jet engine that utilises excess heat for thrust or does not produce any excess heat hence no need for cooling which is wasted energy

No, any thermal machine always transfers energy from the heater to the cooler (Carnot cycle). The maximal yield depends on the temperature difference and cannot achieve exactly 100%. It is equal

$$
1-\frac{T_\text{C}}{T_\text{H}}
$$

where Tc is the temperature of the surrounding air and Th is the temperature of the burning fuel. Jet engine as normally understood in aviation is a thermal machine.


Why do many stealth aircraft have a similar shape and design? I have been playing around on a bunch of programs with stealth planes and their general shape. I know that they are required to be flat and have some sort of special material/paint on to 'absorb' the radio waves.

But I have been pondering about the required shape of these aircraft and why the flying wing shape is so widely used (excluding its lift efficiency). Why not some other shape, like a tilted square, triangle, or even a sphere? What makes the general shape of the B-2 and F-117 so common in the design of stealth aircraft?

First of all, the general idea is to avoid reflection of radar energy back to its source. Next, you want to direct the reflected energy into as few directions as possible in order to dazzle any observer with a momentary bright beam, surrounded by as little reflection as possible. That is the reason for the aligned edges and serrated patterns on stealth designs.

Next, there is quite some variety. How about this one (Northrop Battlefield Surveillance Aircraft eXperimental (BSAX), or Tacit Blue; source):

Or this (McDonnell-Douglas Bird of Prey stealth demonstrator; source):

Or this (BAE Taranis UCAV demonstrator; source):

If you think that all stealth airplanes look the same, maybe you are only looking at those which were designed for the same purpose?


How should simulator time be logged in a pilot logbook? In a full motion Level C or D simulator like those used by the airlines and for jet type ratings:

How should a pilot log the simulator time in their logbook?  I.e. Can you log:

Total Time
Instrument Time
Time in Type
Cross Country Time
Night Time
Landings (including night landings)
Dual given/received
Anything else?

You log simulated instrument time in an FFS, Full Flight Simulator.
The relevant FAR's are 61.4, 61.1(b)6.


Would an ASTERIX decoder be "radar data processing" or "surveillance data processing"? I am not an air traffic controller, I am a software engineer. I developed an ASTERIX decoder, the application will just extract all the information and save it in a text file.
I am just wondering how we can make use of the application in a real system.

Is that what we call Radar Data Processing or Surveillance Data Processing?

Edit:
I know that my question was ambiguous.So, I will try to clarify it further.
Is the information extracted from the ASTERIX messages useful for the Controller to conduct his work ?

You would call this surveillance data processing, but typically surveillance data processing involves much more than decoding ASTERIX.

ASTERIX has many formats, not only radar but also multilateration, ADS-B, tracker output etc, hence the more generic term surveillance is used in lieu of radar.


What is the maximum lateral deviation allowed on an RNAV route? If an airliner (enroute via IFR rules) discovers a thunderstorm ahead, how much lateral deviation is allowed before a clearance from ATC needs to be obtained ?
Is the width of an RNAV corridor only for navigation errors or also for intended deviations ?

4 nm from centerline or 8nm total width of airway.
You are not required to instantly turn when transitioning between airways.  Required navigational precision for most enroute segments is 2 nm.  Being conservative and always assuming an operational error of 2nd means any observed deviation of more than 2 nm is a red flag.

Intentionally deviating within the course width is not prescribed within the regulations, but then there's no regulation prohibiting or allowing fly by (fly over is sometimes mandated).


What is the axis of rotation in a high alpha roll? When doing an aileron roll at a high alpha (say 25 degs), which axis will the aircraft rotate about?

Is it the incoming air-stream vector or is it more the body X axis? And does the pitch inertial coupling factor into this or is that an unrelated phenomenon?

I am thinking in terms of high agility aircraft like for example the F-16.

That depends on the control system of the aircraft, in case of fighter jets with fly by wire technology and modern fly by wire airliners the yaw control law usually tries to rotate around the velocity vector, which in calm air is the same as the incoming air-stream vector. (according to my university lectures)

The difference in the target yaw rate (r) is just the body roll rate around the x-axis (p) times the tangent of the angle of attack (with the sign flipped, depending on which coordinate system you use).


Do jet contrails impact weather? Do jet contrails impact weather at the ground?

Short answer

Based on past observations and a study led by Patrick Minnis from NASA, contrails could result in increasing the temperature over the ground by 1°C every 30 years over the US.

From a study by German researchers Ulrike Burkhardt and Bernd Kärcher, the effect of contrails is comparable in other areas with a similar level of air traffic.

Because the air traffic is said to be about to increase very quickly, the effects of contrails on the temperature may increase too.

Contrails and natural cirrus: So similar that studies are difficult

Contrails are like cirrus, and actually some just become persistent cirrus. Sometime it's difficult to tell which one is a condensation trail, which one is a natural cloud. This makes more difficult the study of contrails effects, and introduces many uncertainties that need to be reduced:

(source)

The current studies take into account only the young contrail-cirrus, because they are still relatively easy to differentiate from natural cirrus, due to their linear shape. Most aged contrail-cirrus are not differentiable and are not counted as aircraft generated. This means the current results potentially under-estimate the effects of contrails.

Pertaining to the discussion, contrail-cirrus as clouds:

Induce a cloud-feedback, i.e. the coupling between cloudiness and surface air temperature.
Induce a radiative forcing, they increase the portion of the energy not re-emitted to space. The quantity is expressed in mW/m².

Increasing the air temperature has a link with increasing ground or oceans temperature, but the two notions mustn't be mixed. However cirrus are suspected to play a role in the global warming, because they could introduce a positive feedback into this warming.

Study: Coverage and effects of contrail-cirrus

Global radiative forcing from contrail cirrus published in Nature in 2011 was a study to evaluate the contrail-cirrus coverage, and its impact. Conclusion:

  Aviation makes a significant contribution to anthropogenic climate
  forcing. The impacts arise from [...] and from changes in cloudiness in the
  upper troposphere. An important but poorly understood component of
  this forcing is caused by ‘contrail cirrus’—a type of cloud that
  consist of young line-shaped contrails and the older irregularly
  shaped contrails that arise from them.

The estimated effect is depicted on this map (mW/m²) from the study:

Net effect of contrails (CIC) warming compared to other aviation factors of warming:

(source)

Study: Effect of contrail-cirrus on US climate

NASA conducted a study in 2004: Patrick Minnis, J. Kirk Ayers, Rabindra Palikonda, and Dung Phan -- Contrails, Cirrus Trends, and Climate.

This study was analyzed in Science Daily: Clouds caused by aircraft exhaust may warm the US climate:

  Using published results from NASA's Goddard Institute for Space
  Studies (New York) general circulation model, Minnis and his
  colleagues estimated contrails and their resulting cirrus clouds would
  increase surface and lower atmospheric temperatures by 0.36 to 0.54 degrees Fahrenheit per decade.

Aviation radiative forcing in 2000: An update on IPCC (1999)

This study was included in a new one by R. Sausen et al. in 2005. It shown the radiative forcing by aircraft could have been slightly underestimated:

Source: Aviation radiative forcing in 2000: An update on IPCC (1999) - R. Sausen

The US surface temperature is increasing by 1°C every 30 years: I would say this is very significant for plants, life, water cycle, oceanic currents, etc.

Also look at @Simon good answer about the increase of the difference between night and day temperatures, by more than 1°C, during the 3 days civil air traffic was forbidden on September 2001. This increase seems to confirm contrail-cirrus limit cooling on night time.


May an airline replace an airliner's engines without the aircraft manufacturer's involvement? Around a year ago in our country, there was an advertisement on TV regarding an airliner's program to modernize their airplanes' power plants. This airline has various types of Airbus and Boeing aircraft.

I am not sure whether all the airplanes are using the same power plant brand or not. The advertisement shows that one power plant's manufacturer is GE. So I am not sure what is the meaning of "modernization" in their advertisement regarding the power plant. But instinctively, that should be to replace it with a newer, better version.

So my question is, does the airplane manufacturer allow the airline to replace their own power plants without the airplane manufacturer's involvement?

If the airline owns their airplanes outright, then they don't need permission per-se from the manufacturer, but the new engine would have to be approved by the manufacturer for that type of plane. So the airline couldn't just pick some type of jet engine & decide that they're going to figure out how to mate it to their jets; if that combination hasn't already been tested & proven by the manufacturer, it would void the manufacturer's certifications and render the aircraft un-airworthy. So nobody goes that route.

On the other hand, if the airline leases their jets, they can only do what the owner approves.


What aircraft is in The Do’s music video? There is a band call The Do, in one of their videos there is a plane with a strange configuration of turbines, it looks like a version of a 747.

You can find the video on Youtube "The Dø - Despair, Hangover & Ecstasy"

Does anyone know what plane it is?

This looks like G-BDXJ, a modified 747 that was also featured in James Bond Casino Royale as well as other movies.

Edit: The linked wikipedia page confirms this:

  It was used as a prop in the music video of The Dø song "Despair, Hangover & Ecstasy"


How long can an F-16 stay supersonic? I've been wondering for awhile to myself, how long can one stay supersonic?
How long before one ran out of fuel?
What would the issues of staying supersonic be (aside from control)?

Depends on how much fuel that they have on board.   You're not gonna be able to hold wing tanks or a centerline tank on that jet and still be able to fly supersonic, so we will have to assume that we can only use internal fuel. In a Block 50/52  F-16C, the jet holds about 7200 pounds of internal fuel with the tanks topped off. In full afterburner, the jet's F100 or F110 engine is burning approximately 800 pounds of fuel per minute.   This gives a maximum of approx. nine minutes of flight time in full afterburner.  So you  have at most nine minutes of supersonic dash available to you.

As mentioned above, while an F-16 is capable of a maximum speed of Mach 2, it can't do this unless it's in a clean configuration, that is, it does not have any external stores on the jet which create a lot of parasite drag and prevents supersonic flight with ordnance on board. Typical mission speeds are high subsonic (500-600 KTAS) for cruise and combat maneuvering.  Usually afterburning is utilized for brief periods in order to quickly accelerate the jet, such as to shorten takeoff distances, or to quickly replenish energy which has been bled off during maneuvering.  Supersonic dash can be used to egress a FLOT or airspace deep inside enemy territory once, say a bombing mission is complete and you have been informed by an E-3 that there are enemy fighters scrambling towards your position.  You jettison the external stores, save maybe a pair of AIM-9s or AIM-120s on the wingtip rails, push open the throttle and run like hell - and hope it's enough that you can make it to a friendly airbase or a tanker in time!


Can you identify this jet turbine stage? I was just wondering if anyone could give me any info about this turbine rotating stage I picked up at a yard sale today.

The stage measures 8-1/2" to the outside of the blades. The only markings I can find are TCYC5065 TT6776.0. It has 58 blades on the disk.

What is this turbine part?

This assembly is part of the turbine used to rotate the compressor section of a Pratt & Whitney PT6, a free turbine turboprop. It's known as compressor turbine or just CT.

Where is it located?

The compressor turbine is located at the exit nozzle of the annular combustion chamber, and is the first component which enters in rotation under the effect of the hot gas velocity.

Compressor turbine. Source: P&W Training Manual

As visible, there is a second turbine (made of one or more stages, depending on the PT6 model) further downstream. They appear to be on the same shaft, but they aren't. There are two independent shafts rotating at their own angular speed.

The compressor turbine extracts power to rotate mostly the engine compressor, which role is to feed the combustion chamber with compressed air. The other turbine extracts power used (mostly) for the aircraft propulsion.

What is looks like on the real thing:

Source: AVweb on Youtube

The two shafts can be seen on the picture above, separated by the interstage baffle within the power turbine vane ring assembly.

Turbine blades material

Source

The blades, the hottest parts after the combustion chamber, are made of a nickel alloys. Nickel itself melts at 1,455 °C, and alloys are made more resistant either by solidified directional casting or single crystal growth (see more on materials). In larger engines turbine blades are often maintained below their melting point by circulating air in small internal channels. This is not the case for the PT6, gas temperature is still below the melting point (about 900°C).

Blades are protected by an anti-corrosion coating to delay as much as possible the inclusion of ion-sulfur into a material, a reaction known as sulphidation. Nickel sulphidation forms $\small Ni_3 S_2$ which melts at 635 °C. Sulphidation occurs all the time, but more quickly when flying close to sea water or industrial areas rich in sodium salts which can form sodium sulfate (more here). Frequent water washes of the turbine maybe necessary to eliminate salts.

Looking online for PT6 sulphidation, we can see a large number of investigation reports dealing with engine failures due to maintenance not done according to procedures.

About the P&W PT6 engine

The PT6 is a well known engine, available in various versions, which has been used for 50 years on aircraft and helicopters (but also on IndyCars, hovercraft, "turbotrain", snowplows....).

(source)

The particularity is the free turbine design. On large turbo-engines, the compressor (the low pressure compressor on engines with two or three spools) is on the same shaft than the engine output (which drives the fan, the rotor, the speed reduction gear,etc).

On a free turbine there are two rotating groups that are not linked by a shaft.

(source)

The first group is the gas generator section -- in blue, on the right hand of the images -- with a compressor and a combustion chamber. High pressure gas are sent to the last stage of the gas generator, which is a turbine stage -- the compressor turbine or CT, the one you've got. The CT drives the whole gas generator section and the accessory gearbox.
The energy used to move the generator section is only a part of the available energy in the hot gas (e.g. 66% on a twin PT6T-3D). The rest makes it's way to the mechanically-independent power section composed of one or more turbines, depending on the engine model. The turbines drive either the propeller, the rotor, or anything attached to the power section shaft, directly or via a reduction gearbox.
The gas production section can be spun (albeit at idle) wit the power section at rest (an helicopter turbine can be spun, while the rotor is maintained stationary).


What are the indications that your turbofan engine has "thrown a blade?" In an airliner, such as an A380, what indications do the pilots have that an engine has thrown a fan blade?

Will that always result in destruction (of the engine)?

Turbofan engines are designed and tested to contain a fan blade failure. However, this is a violent event and will cause serious damage to the engine. The engine and surrounding components are subjected to large forces and vibrations, and the engine can ingest debris from the damage to the fan, causing further damage. There will likely be an investigation, and the engine will probably be scrapped due to the widespread damage to different components.

To the pilots, it will seem like a bird strike, but probably worse. There will be a loud noise as the fan blade separates and collides with the fan case and following blades. The fan will then be out of balance, so heavy vibrations will follow as the shaft loses its rotational energy. The pilots will be able to tell which engine has failed by the loss of thrust, as well as the indications of vibration and failure on the instruments for that engine.

If the fan does not get stuck, it will continue to windmill, which will result in ongoing vibration from that engine.


How has afterburner design changed since its inception? I came across a NACA summary paper on the past 5 years of afterburner development and started reading cause it seemed interesting. However, a couple of pages in I scrolled back up and realized that it was written in 1956. How much have afterburners changed since then and would the information contained in the article still be relevant?

This article suggests that they have. To name a few:

alluding to improvements in fuel diffusion
adding additional igniters downstream of the first to even out the burn
vectoring improvements to better keep the superheated gasses in the center and avoid overheating the structure at the sides
introducing cool air in a ring around the superheated exhaust stream to aid in a smaller thermal footprint
incorporation of stealth materials


Don't all airspeeds change with weight? Ok, so I'm a student pilot, and I'm going over the Vx, Vy, Vne, ... etc., and I see that "maneuvering speed" (the speed at which you can safely apply full flight controls) "changes with weight".

Which airspeeds don't change with weight? I can pretty much guarantee the the takeoff speed changes with weight, as would flap operating speeds, never exceed speed, and cautionary zone, because that is just the basic application of physics (inertia).

Why do we treat maneuvering speed as the only variable airspeed?

Your instinct is correct; almost all of the key airspeeds — those at which something special happens aerodynamically — vary with weight.

There's a distinction, though, between "speeds at which something special happens aerodynamically" and "regulatory limiting speeds that prevent you from doing something bad."

For example, VNE is a regulatory value; it is prohibited to exceed this speed at any weight. This value includes a safety margin and is determined from flight test data. Nothing special happens aerodynamically at the published VNE speed. (Thank goodness!) The special stuff, like aeroelastic flutter or structural failure, happens at some speed well above VNE, regardless of your weight (as long as it's within the allowable CG envelope of course).

Another example, VFE, is similar. Nothing special happens at this speed. It's just a safety value: as long as you're below this speed, you won't tear the flaps off the plane if you extend them, regardless of your weight.

Almost all speeds that aren't "regulatory limits" do indeed change with weight. Some examples:

VA design maneuvering speed
VX best angle of climb speed
VY best rate of climb speed
VR rotation speed
VS0 landing configuration stall speed
VS1 "specific" configuration stall speed

For larger multi-engine airplanes that you'll encounter later in your flying career:

V1 engine failure recognition speed (or takeoff decision speed)
V2 takeoff safety speed
VMC minimum control speed

(Note that a lot more factors besides just weight can go into these latter speeds, such as atmospheric conditions and reduced-thrust takeoffs.)

For small airplanes, it is common to publish these speeds as single values, measured at gross weight. For many of them there are also graphs in the performance section that show you how the actual speed varies with weight.

For larger aircraft, the performance graphs (or calculations) are always used. For example, you won't use a single "stall speed" value from a handy table in the "POH" of a 747. In these types of aircraft, key numbers are calculated as needed on each flight for current weight.


How is it possible for manufacturers to constantly get data from their planes all over the world? I've heard that manufacturers (like Boeing and Airbus) constantly get data from their planes. So in the case of an emergency, ATC's or pilots can contact the manufacturers for assistance. How do manufacturers constantly get this data and how is it stored (cause considering the number of planes flying today, it must be a lot)?

How do makers get data from aircraft in flight
The data is usually transmitted using something like ACARS which is a system used in aircraft to transmit data in flight using underlying radio and satellite communications systems.
The communications infrastructure is typically provided by large multinational companies who specialise in this job. See ARINC, SITA, Inmarsat and so on.
Engine-makers and Aircraft makers often offer pro-active maintenance and support services to airlines, operators and lessors which involve their aircraft transmitting such data to the makers.
For example, Airbus has AIRTHM

Airbus Real Time Health Monitoring (AiRTHM) is an advanced service through which A380 and A350 XWB operators can receive guidance on optimised maintenance and real-time troubleshooting actions. As part of this effort, a dedicated 24/7 team takes advantage of the uplink technology to further investigate and anticipate warnings/fault consequences.
The uplink technology allows real-time remote access to aircraft data parameters via the ACARS digital datalink system, enabling Airbus AiRTHM engineers to deliver maintenance and technical advice both in flight and on the ground.

Boeing have AHM

AHM sutomatically monitors, collects and transmits service levels using ACARS through the installed Aircraft Condition Monitoring System (ACMS)

Note that ACARS is a relatively low-volume data transmission system. Makers have explored other underlying communication systems as a way to transmit more data at lower cost.
How is this data stored
It is true that there is a lot of data but Boeing and Airbus are big businesses and are able to partner with major IT businesses.
For example IBM work with Airbus

“Today’s aircraft can generate up to a half terabyte of data per flight, an unprecedented volume and variety of data seen in few other industries,” said Timothy Wholey, IBM global leader for the aerospace and defense industry in its global business services unit.

Note - not all data has to be transmitted in flight. A lot of data is collected and stored in the plane and only transferred when the aircraft is on the ground.
Makers like Airbus and Boeing inevitably are already very heavy users of IT for aircraft design purposes. For example, Airbus use HP Supercomputing hardware


Turbofan engine 2 spool - Turbine drives the compressor or Starter drives the compressor I have read somewhere regarding turbofan engine 2 spool that says

"LP or HP turbine will drive the LP or HP compressor"
"During engine starting, the starter will drive the HP compressor via the gearbox"

So I'm confused on whether the turbine or starter drives the compressor. Is it only during starting the starter will drive the HP compressor and after that turbine will take over?

Thanks

The starter drives the entire HP spool (HP compressor, interconnecting shaft, and HP turbine).  The gearbox in question is the accessory gearbox that runs the various pumps and is driven off the HP spool shaft, which by happy coincidence is on the outside of the LP shaft.  The starter is mounted on that gearbox and is able to back drive the HP spool through the gear train for engine starting.

The LP spool, which is the fan and LP turbine with its shaft running down the center of the HP spool, is just going along for the ride during the start.


Why does the main battery discharge with the alternator running? In my cessna 172S, when engine running at any RPM, the current at the main battery is below zero, indicating that the alternator is not charging the battery or the battery discharges, but the standby battery indicates a current above zero and it is charged by the alternator.

How can this happen?

Our mechanic had a similar issue with a Piper Cherokee where the battery would only charge intermittently.  It turned out there was a bad connection at the Master Switch which ran from the Alternator/voltage regulator to the Master Switch. Most of these types of electrical issues tend to be bad wiring. I would check your wiring thoroughly.


Why does supersonic flight detach airflow from a wing? I've read in several answers to questions that when a wing passes the speed of sound the airflow will become detached from the craft towards the rear quarter of the wing (thus making things like elevators ineffective.)

Why does this happen at Mach Speed?  Can it happen at lower speeds as well (in straight and level flight, ie, not stalled)?

Flow separation happens when the pressure gradient of the airflow along the flow path becomes too steep. In subsonic flow, the oncoming air is first decelerated ahead of the wing, then swiftly accelerated when it flows around the strongly curved nose section of a wing. This acceleration is the consequence of the wing's curvature.
After this acceleration, how will the airflow behave? Will the airflow keep moving in a straight line without further acceleration or deceleration? (which implies that airflow will separate from the wing surface, creating a local vacuum) Or will it faithfully stick to the wing surface? In reality, the air settles at a compromise between the straight path and following the contour, creating decreasing pressure along a surface with increasing curvature and increasing pressure along surfaces with decreasing curvature. More precisely, it is always in an equilibrium between inertial, viscous and pressure forces.
This suction not only bends the airflow into following the wing's contour, but also accelerates the air ahead of it. The lower the pressure, the more the air speeds up, such that the total energy of air (the sum of pressure and kinetic energy) stays constant. Therefore, pressure and local speed change in sync.
When the curvature decreases further downstream, the flow path becomes straighter and pressure rises again. However, the air particles close to the wing slow down because of friction. The layer of air where this slowing is noticeable is called boundary layer. In it, the deceleration effects due to pressure rise and due to friction add up, and at some point the air comes to a standstill relative to the wing. Where this happens, static air will collect and build up, causing flow separation. Thankfully, the exchange of air across a turbulent boundary layer kicks the slowest air particles downstream, so at moderate angles of attack the air still moves along until it reaches the trailing edge. Only when the suction peak around the nose becomes very high at high angle of attack, the consequent steep pressure rise along the remaining flow path overpowers the possibilities of the turbulent boundary layer, the air decelerates completely and the flow separates. This is a wholly subsonic affair.

If the wing moves at high subsonic speed, the curvature-created suction accelerates the flow such that it reaches supersonic speed. Now something odd happens: Supersonic flow accelerates further when subsonic flow would decelerate. This is caused by the change in density which is dominant at supersonic speed. Incompressible (= very slow) flow has constant density, and all speed changes affect pressure. At Mach 1, the pressure and density changes are of equal magnitude, and in supersonic flow the density changes dominate. Now we have a supersonic pocket of air on the upper surface of the wing where speed increases and density decreases downstream, and the surrounding subsonic air sees little change in density. This picture should give you some idea how it looks:
![Lambda shock in high subsonic flow][1]
The whole wing moves at Mach 0.68. Compare the green color at some distance from the wing with the scale on the left side, which gives the Mach number for each color shade. At the airfoil nose, you see a blue area. This is where the air decelerates - it gets pushed together by the approaching wing. Now follow the colors along the upper side - they quickly turn green, yellow and red as the air is accelerated into the low pressure area (remember, low pressure equals high speed, so the reddest area has the highest local flow speed and the lowest pressure). In subsonic flow, the suction peak would be somewhere between 20% and 30% of chord, and the colors would slowly change back to yellow and green if you move further downstream. Now we have local supersonic flow (everything redder than light orange is supersonic here), and instead of slowly decelerating, the air is speeding up to a maximum Mach number of 1.23 at almost 60% of chord length.
This cannot last, and at some point this supersonic pocket collapses. This happens instantly in a shock, and as you know, in a straight shock density increases suddenly and speed decreases such that the Mach number after the shock is the inverse of the Mach number ahead of the shock. In the picture above, boundary layer effects create a lambda shock, which has its name from the Greek letter which looks like the shock pattern here. Aft of the shock, you have subsonic flow again, and a much thicker boundary layer which moves very slowly (blue shade). This is due to the energy conversion through the shock, which converts kinetic energy into heat. But the flow is still attached - even this shock did not cause separation.

If this pressure rise is big enough, the boundary layer will come to an instantaneous standstill, and then the flow separates. This is the shock induced separation you asked about. Unfortunately, the picture above is the best I could find, and I have none with separated flow aft of the shock. But it helps to show that the center of pressure moves aft. This causes a strong nose-down moment. Also, with higher subsonic Mach numbers directional stability decreases. Now even more nasty things can happen: The location of the shock might move forward and back. This changes the size of the supersonic area, causing lift changes. On a horizontal tail, this will also cause pitch changes. If you change elevator position slightly with such a shock on the horizontal tail, the lift change could be severe and in the opposite direction of what you would expect. This causes total loss of control, just when you need the control surfaces to counteract the Mach effects mentioned above. Also, the shock position could oscillate, causing a buzzing sound and, if you are really unlucky, coupling into an elastic eigenfrequency of your structure, resulting in flutter. Not only on the tail surfaces, but also on the wing, affecting the ailerons as well. Now you can start to see what scared the early pioneers about flying near Mach 1 and why they spoke of a "sound barrier".

If you fly fully supersonic, this effect goes away because now the shock moves to the trailing edge and stays there. Now everything will be calm again because the shock location stays fixed. This effect was first experienced and survived on April 9, 1945 by [Hans Guido Mutke in a Me-262][3], which briefly flew fully supersonic in a dive. However, even in fully supersonic flow separation is possible, but then because the air flow will not bend more than what can be caused by total vacuum. In hypersonic flow the density changes become so severe that pockets of "air" are possible which do not contain any air, but a vacuum. But this is more an academic case, except for reentry vehicles with a blunt, rear-facing base.


how are UAV systems (aircraft+ground facilities) fitted with landing aid system? For commercial aircraft, precise landing aid systems (ILS, GBAS) are required for autolanding, but these navigation systems are too expensive to be used for UAV operations. However, a lot of UAV OEMs have claimed and demoed landing the fixed wing UAV at a runway which is typically used for a Part 23 aircraft.

How do these fixed wing UAVs perform and autoland?
What kind of landing aided system are installed on the ground or on board?

Each project will have its own specifications. Military UAVs will have different use cases from civilian ones, and, as the comments mention, unmanned does not mean unpiloted.

Most of current UAVs are remotely piloted, meaning that there is a front facing camera relaying images to the ground, where a pilot will command flight adjustments to the vehicle to keep it aligned, no special equipment involved (except for the air-ground communication apparatus). The aircraft will be equipped with the usual inertial sensor unit(s) and GNSS receiver(s).

For situations where you might have an unpiloted aircraft (that are extremely rare today), it is still solvable by simple INS + GNSS, with the additional requirement that you will have to accurately measure the position of the runway in the GNSS reference system (published charts are not precise enough, as they are created for eye-bearing humans, that can correct the course by sight). This is the method we used and we landed 2 meters from the centerline (the two pilots where there for safety, being it the first attempt).
Other projects might include ground-based aid signals akin to an ILS system.


If I have a VOR receiver and a GPS, which should I use to navigate VOR airways? FAR 91.181a states that aircraft on ATS routes shall be flown along the route centerline. I would like a clarification regarding VOR airways. I have a GPS and a VOR receiver, and usually when I fly VOR airways I set both to navigate the leg I'm on. This gives me two navigation needles and two CDI sources. Usually they both line up very well, especially when close to the VORs themselves. A few times when I've gotten far from the station I've noticed a discrepancy between the the VOR nav and the GPS. I assume this is due to inherent error with the VOR as the aircraft gets farther from the station. When this occurs, which navigation source should I use?
I understand VOR airways have 8nm width to account for VOR error, but again, according to FAR 91.181, pilots must fly along the centerline (as best they can anyway). So will the GPS get me closer to the centerline, or the VOR receiver?

will the GPS get me closer to the centerline, or the VOR receiver?

GPS is usually more precise than VOR. Even when selective availability was used this was true, and that program hasn't been in effect since 2000.
The GPS will also have approximately the same error along the entire airway. The VOR's error will increase with distance from the VOR station.
That said, IMHO there's a difference between "which is more precise" and "which one should I use". Airspace features such as airways increase the chances of a collision by concentrating air traffic. An airway isn't as bad as an intersection or airport, of course, and flying appropriate altitudes for your direction of flight mitigates this risk even more. But I would tend to want to avoid being right on the centerline.
Many GPS receivers (and other RNAV devices) allow you to offset your course, so you can fly the airway that way, with a randomly selected offset that remains within the airway†. Or just use the VOR, and let its natural lack of precision help you to avoid being smack where all the other air traffic that's flying exactly on the centerline is.
† Strictly speaking, one should request the deviation from ATC, to avoid running afoul of FAR 91.181, which requires flying the centerline…it is unlikely they would object, but if they do, then you will find out the safe way


A320: Why do SDACs supply all three DMCs? On the Airbus A320, in the Electronic Instrument System (EIS), there are three Display Management Computers (DMCs):

DMC1 supplies the upper ECAM
DMC2 supplies the lower ECAM
DMC3 is a backup.

There are also two System Data Acquisition Concentrators (SDACs) that acquire system status, process it, and and send system page data to the three DMCs.

Why would it send it to all the DMCs?

The Hydraulic System is displayed only on the lower ECAM which is supplied by the DMC2. Nothing about the hydraulic system is shown on the upper ECAM supplied by the DMC1. So why would SDACs send data to DMC1? I can understand why it would send it to the DMC3 because its a backup but why the DMC1?

Same thing for the Air Conditioning System, Electrical System, etc. None of those systems are displayed on the upper ECAM supplied by DMC1. The only thing displayed on the upper ECAM is engine and MEMO (or emergency stuff in the case of an emergency).

I guess the engine is a system but there is an engine system on the lower ECAM as well. The upper ECAM shows the engine performance and the lower shows the oil, so not the same thing.

The Hydraulic System is displayed only on the lower ECAM which is supplied by the DMC2. Nothing about the hydraulic system is shown on the upper ECAM supplied by the DMC1.

That is not true. If DMC1 or DMC2 fails, DMC3 takes over. But if the display fails, the other display takes over. So the hydraulics page can be displayed on the upper display. It can even be displayed instead of the MFD or even PFD if both ECAM displays fail. Similarly for all the other ECAM pages.


Did these parts come from a T-33 crash? A Lockheed T-33 crashed near my hometown (Outer Cove, Newfoundland) in 1956. This year we have had some very strong storm surges, and a piece of metal has washed up on the shore. I am posting this picture to see if anyone  can tell if it is part of the crashed T-33. Thanks.

It looks like the nose skin panel with the gun ports that some T-33s had.  So I'd be willing to put serious money down on "yes".

Lockheed T-33 Shooting Star ‘69330 / TR-330’ (N651)
Alan Wilson from Stilton, Peterborough, Cambs, UK


The NASA X-57 uses 12 electric motors for takeoff. Does it need 12 control levers or just one? If the NASA X-57 uses 12 motors for takeoff, does it need 12 controllers (like throttle levers), or just one?

The traditional way of engine throttle design was 1 throttle per engine, but what if you have 12 engines? Twelve levers would be unmanageable, pushing a quadrant of 12 levers forward on takeoff.

I suppose that on initial setup, you would need a small dial for each prop to sync rpms. More sophisticated electronics could have a feedback loop to do this automatically.

So... what about just 1 controller, and 2 or 3 backup controllers for redundancy as they are electronic and could easily be blown. I'm thinking of a 3 or 4 position selector switch to choose the active throttle, sort of like choosing between magneto 1 and magneto 2 in a typical GA aircraft.

Yes, you could wire the motors up in banks of 4 and have a quadrant of 3 levers, but my specific question is:

Would having just one active controllers for 12 motors be acceptable?

The need for throttles is to provide a linkage to the carburetor/throttle body in the age when everything was mechanical. The throttle in older airplanes directly controlled the air-fuel mixture allowed into the intake manifolds. If electric motors were used, the throttles would have been attached to mechanical rheostats.

In the age of computer controlled engines/motors, this direct linkage is not necessary. You would essentially just tell the computer how fast you would like to go. The system will take care of the rest.

In most cases, the throttle is retained in the cockpit to provide the human pilot with a familiar interface with the computer. Honestly, in an airplane, where throttle settings and changes are more stable and predictable, a knob or a couple of buttons would suffice. FADEC controlled engines/motors are pretty standard now. The method of inputting your desired controls in a fly-by-wire system is arbitrary. It is just a matter of comfort level with the controls. We might even get to the point of a true GUI cockpit one day.

In the case of a multi-engine electric airplane, you would want at least two controls to account for differential thrust when desired. This is not something that you would absolutely need. But, it would be convenient.

Some very complicated aircraft like the V-22 Osprey rely on the pilot not having direct control over the engine-prop systems. It’s absolutely necessary for a computer system to coordinate the two engines during VTOL operation. The same problem would present itself in a quad-copter large enough to carry human passengers.

As an aside, I vividly remember the first throttle-by-wire car our family ever owned. It was a Hyundai Santa Fe. Though, not difficult to drive. The throttle response took some getting used to. Also, modern electric cars with multiple motors have only one throttle.


What does the term "trimming" most commonly mean in aviation? Why does an airplane need trim, and what does it do during the flight? Does an autopilot adjust the trim automatically?

In short: trimming neutralizes the force required to keep control surfaces in a specific position.

Most (if not all) aircraft have some sort of elevator trim control. For example, when the pilot has to keep pulling back on the yoke/stick during a climb, trimming "nose-up" will neutralize that force. The elevator will then remain in the same position without any force required on the part of the pilot. Trimming is usually done by means of a Trim tab on the control surface and is controlled by a trim wheel.

Elevator trimming is used:

During climbs: to maintain a constant air speed and rate of climb
During descents: to maintain a constant air speed and glide path
During level flight: to maintain altitude and speed

Although elevator trim is the most common, trimming can also be done on rudder (quite common) and ailerons (only on larger aircraft).

Rudder trim is used to maintain coordinated flight without rudder input by the pilot. Many single engine planes with powerful engines require rudder trim to offset the "left-turning tendency" caused by P-factor and propellor wash hitting the rudder. Aircraft without adjustable rudder trim will usually have a fixed trim tab on the rudder.

Most autopilots will control the elevator trim wheel because the servos controlling the elevator could easily be overpowered by the required force.

It's important to note that in most cases (especially on small airplanes) trimming doesn't actually move the control surfaces. It changes the force required to deflect the control surfaces. Although there are many types of trimming devices, the common trim tab makes the airflow do all the work. The trim tab causes the airflow to push the control surface in a specific position. On larger aircraft with hydraulically operated control surfaces, trim tabs are less common (see also this answer to another question)


Are there certification requirements on Dual Inputs? Is anyone of you aware of (certification) requirements or similar for dual input, and the priority management of dual controls?

I only know the Airbus philosophy of summing both inputs and limit them afterwards, but I wonder if there are any requirements on this?

Here's what EASA Certification Specifications for Large Aeroplanes CS-25 says about design for dual controls:

  CS 25.399
  Dual control system

  (a) Each dual control system must be designed for the pilots operating in opposition, using individual pilot forces not less than –

  (1) 0·75 times those obtained under CS 25.395; or

  (2) The minimum forces specified in CS 25.397 (c).

  (b) The control system must be designed for pilot forces applied in the same direction, using individual pilot forces not less than 0·75 times those obtained under CS 25.395.

And in many places the requirements state that it must be demonstrated

  ...that exceptional skill is not required to control the aeroplane

The A320 complies. It is designed for control of one pilot at a time, like all other aeroplanes. There is no requirement for a dual control system to be mechanically linked. The B737 columns and wheels can be uncoupled after an elevator or aileron jams, the remaining control provides input on top of that of the jammed circuit.


How should I refer to a transition through class B or class C airspace? In Seattle, it is common to request a transition over KSEA by asking for either the "Bremerton Transition" or "Kent Transition" (depending on what direction you're travelling). I learned these names from my CFI & have used them with no problem, but I've noticed that on the Seattle TAC they are referenced as Seahawk/Mariner Transition, which refer to which runway numbers to overfly rather than direction (personally, I've never heard these referred to on the radio).

Obviously, "Bremerton" transition refers to transitioning to Bremerton, but I'm curious if this is some agreed-upon lingo or just convention. Could I just as easily ask for a "Port Orchard" transition?

If I were in an unfamiliar area, could I request a transition by referring to any location on the opposite side of the airspace? For example, if I wanted to transition PDX airspace could I request a "Hillsboro Transition"?

Sidenote: I personally love transitioning KSEA. If you haven't done it & are in the area, pick a busy day and request a transition. It's pretty impressive to see the large commercial flights landing right below you. On a non-busy evening, I've heard rumor you can even request a stop\go on 16R

You'll sometimes get radio phraseology different from what is published on charts either due to some holdover from now-superseded procedures (bad form, but it happens) or because of Letters-Of-Understanding that exist between the local Air Traffic Facility and certain operators or interest groups/associations, etc.

If you're going someplace new and want to use a published VFR Transition through class Bravo, the best way to go about it is to use the nomenclature on the charts in order to reduce confusion. Otherwise, it is also acceptable to simply request a VFR clearance through the airspace in a general direction of travel. Depending on your altitude, position and direction of travel, as well as traffic load and any airports you need to get around, ATC will vector you through or around the class Bravo.

The initial call follows the standard procedures outlined in the AIM and the Pilot/Controller Glossary. For example, starting out NE of Orlando class Bravo and asking for a transition to the SW, could be something like:

"Orlando Approach, Husky 123 Alpha Bravo Charlie, 35 northeast of the ORL VOR at 4500, request VFR transition to the Southwest through class Bravo."

If you're near a local landmark, you could use it as a reference to help the controller find your aircraft more easily:

"Orlando Approach, Husky 123 Alpha Bravo Charlie, 2 northeast of Lake Ashby at 4500, request VFR transition to the Southwest through class Bravo."

Generally speaking, if a VFR Transition or flyway is available, the preference is to have VFR traffic use it in order to lighten the controllers' workload, but if you don't have the charts, or would rather not do that for some reason or the other, you don't have to. Just follow the general procedures for transitioning through class Bravo and they'll do their best to accommodate you.


Does it violate any regulations for a bag to sit on the flight deck floor? Pilots who fly the Canadair Bombardier Regional Jet or CRJ aircraft know first-hand how cramped the space on the flight deck is. It's really a business jet cockpit, not the flight deck you'd expect on a transport category aircraft. I have heard that it's not uncommon for pilots to keep a small lunchbox on the floor of the seat next to them.

Some pilots say that a bag cannot be stored there next to the seat and that if an FAA inspector were to see the bag, there could be consequences.

Is there a regulation that storing a bag in this way violates?

There are some relevant links in the Cabin Saftey Index document under "crew baggage" indicating that all bags must be restrained. The document points to

  §121.576   Retention of items of mass in passenger and crew
  compartments.

  The certificate holder must provide and use means to
  prevent each item of galley equipment and each serving cart, when not
  in use, and each item of crew baggage, which is carried in a passenger
  or crew compartment from becoming a hazard by shifting under the
  appropriate load factors corresponding to the emergency landing
  conditions under which the airplane was type certificated.

The question remains if the cockpit is in anyway different than a "crew compartment" but I would say that could be applied to your question.

However if the bag in question is a flight kit then different rules apply which can be found here:

  A. Flightcrew Flight-Kits. Particular attention should be given to
  compliance with part 121 regarding restraints for any baggage carried
  on the flight deck. Flightcrew flight-kits are not items of crew
  baggage. This policy also applies to aviation safety inspectors (ASI)
  and additional flightcrew members. While it is logical that
  flight-kits be placed so that movement is restricted, the FAA does not
  intend that they be restrained in a manner that would interfere with
  the needs and functions of the flightcrew.

I can not find a further definition of "flight-kit" and/or if you can or cant put your lunch in it.


What is static discharging noise and what is its effect on radio communications? What is static electricity discharging noise ?
How does this phenomena affect radio communications ?
Does the discharging happen through lightning and are static discharger  fixed or are they removable - such as telescopic i mean ?

The noise is created by sparks caused by static electricity. As the aircraft flies through the air, it picks up electrons from the air molecules. This extra charge will want to flow back into the air to equalize the charge. Small gaps in the conductive path on the aircraft will cause sparks to form. These sparks cause noise on radio frequencies, which can be picked up by the aircraft radios.
The static sparks will cause noise on the aircraft radios, sometimes a crackling sound.
Aircraft use static wicks on trailing edges to allow the charge to equalize. If components are electrically bonded well, static electricity should not be noticeable, other than under certain circumstances. The wicks are fixed and not telescopic but of course can be removed if replacement is needed.


What is this in the window? Every time I have flown and sat in a window seat, I have noticed this small tube at the base of the window.

It looks like it might be either metal or a small air pocket, but I'm not sure. I've been seeing it for years and always wondered what it is.

What is this "tube" embedded into airline windows, and does it have any purpose?

As pressurized aircraft's windows exist of several layers (usually three) there's this little hole to compensate differences in the pressure between inside and outside the aircraft.
Inside the aircraft the pressure is much higher than outside so without this little hole the windowd layers would be pushed together and break.