Why are birdlike airfoils not used? Here are two airfoils (lets focus on Re 100,000):

SD7043-il which is simple to build and has a glide ratio of about 60
e376-il a birdlike and much harder to build if using paper or similar due to the hollow inside but claims to have a glide ratio of about 105

I have never seen such birdlike airfoils on an aircraft (RC or other). Is it because of construction difficulties?

Early biplanes did use similar airfoils. Not as extreme as the Eppler 376, but still very thin and highly cambered.
When Otto Lilienthal started his glider experiments, he tried to copy storks. He experimented with different airfoil shapes by using exchangeable ribs on the gliders and by testing model wings on a rotation test stand (Rundlaufapparat). There he discovered that thick airfoils with a blunt nose were actually better than the thin, birdlike airfoils he had used so far. But he didn't believe his own results and continued with birdlike airfoils.

Farman-Voisin biplane, 1907 (picture source).
The same happened with all other airplane designers until 1915, when scientific work started to influence airplane designs. The highly cambered airfoil works very well in a very small range of angles of attack when the local direction of flow is parallel to the local contour of its nose. But while birds can adjust the camber and area of their wings, airplanes of those times could not. In order to combine fast flight with high lift for take-off and landing, the thick airfoil is better.
While birds are small enough to structurally get away with thin wings, the much larger man-carrying airplanes need the thicker wings to accommodate their bending loads without bracing. Scaling laws show that loads grow faster with size than the dimensions do and only thicker wings make the unbraced, cantilever designs necessary for efficient transportation possible.

Heron in flight (picture source). This picture shows nicely that 90% of the area is feathers, so a thick wing becomes impossible for birds.
Birds cannot be hollow inside, except for hollow bones. So they have no choice of using thick wings - they have to work with thin wings and adjust camber and wing area to the flight conditions. Being much larger, airplanes need thick wings for aerodynamic and structural efficiency.


What does the area around the fan blades in the engine nacelle contain? I was intrigued to find this picture below. There was so much space around the engine. So what is inside of that extra space? Or is it just a hollow casing?

Image Source

Details about the picture as provided in the image source:

  [Last Year] A Southwest Airlines Co. flight landed safely Saturday
  morning following a major malfunction of one of its two engines during
  a flight across the Southeastern U.S.

  The Boeing Co. 737-700 was flying from New Orleans to Orlando early
  Saturday operating as flight 3472 when it suffered the failure,
  causing the jet to quickly divert to Pensacola International Airport
  in northern Florida at 9:40 a.m. CDT, according to a statement from
  the airline.

  A Southwest spokesman said its initial reports indicated no injuries
  were reported among the 99 passengers and five crew aboard.

Yes a bit of the engine called the nacelle is missing. This is an aerodynamic structure that slows the air down before it enters the compressor, the pointy bit in your photo. In the drawing underneath it states Inlet Cowl. It has some thickness, because it requires a certain nose shape for its function. Mainly a hollow casing indeed, but with a high tech shape.


Where can I get information on ATC facility activity, like the number of flights handled in a month? As a numbers/statistics geek I would like to be able to look up information on how "busy" particular airports or regions are.

I'm sure the FAA collects this data, but is it accessible to the general public?

The FAA's Air Traffic Activity Data System (ATADS) contains broad statistical information on activity in the national airspace system which can be used to get an idea of how "busy" a particular Center, TRACON, or Tower facility is.

The caveat is this data only encompasses aircraft talking to Air Traffic Control, so it won't be able to tell you anything about uncontrolled fields except possibly what you can glean from Center/TRACON activity information for the greater area.

I'm not sure where they get their data from, but Fltplan.com has annual reported data for each airport in their Airports & FBO's database:

For example, this is for KBRY (which is uncontrolled):


Is there a way to fly an UAV over a roadway? With an FAA Section 333 Exemption, they will permit you to fly up to 400' above ground level. But they also restrict you to flying at least 500' away from people and vehicles unless you have their permission. You can't get permission from every vehicle driver that happens to be passing by. Does this effectively mean that there is absolutely no way to fly over a public roadway, or is there another exception or reasoning to be able to do this?

For certain operations the FAA does grant waivers to 14 CFR § 91.119(b) and/or (c). These waivers are generally granted for the purpose of allowing pipeline or powerline patrol, aerial survey, or for other operations that are in the public interest. The waivers are also generally granted to the operators of certified or restricted category aircraft, not UAS.

If you represent an operation for which a waiver would be in the public's interest and can demonstrate that the operation would be conducted safely, you might qualify for a waiver.

However, even for that waiver, you have to demonstrate strong evidence to gain a minimum distance of less than 500 feet:

  3-185 A. Unless it is necessary to
  safeguard human life or it can be determined to be in the public interest and contributing to the public health, welfare, and safety, the 500-foot minimum separation distance from persons on the surface shall not be waived.

Note that 14 CFR § 91.119(a) and (d) are never to be waived.

See this document for more information on the above discussed waiver.

Now, all that being said, I don't know if the above example of a waiver apples directly to your question or not; perhaps 91.119 is not the regulation that you were concerned about. Regardless, that waiver is an example of what can be worked out.

The current UAS issue is uncharted water for the FAA; there may or may not be precedent for an operation or exemption. Bottom line, if you have a really good reason to do the operation you want to do, you might be able to work it out with the FAA. Otherwise, you will have to stick to the rules as they are.


Are virtual winglets a viable concept? Just read this abstract by a Regeneron STS finalist.  Is the idea of a virtual winglet a viable concept? Seems interesting.

Aston Martin do something similar with their 'Aeroblade', which replaces the rear spoiler, so the concept of using air to guide surrounding air is viable. Whether it's more efficient than using a physical object, remains to be seen.


Operating with BasicMed, may pilot use a medication otherwise restricted under Part 67 Medical Regulations? I have a CFI student who is currently using BasicMed to satisfy her FAA Medical Requirement.  She is taking a drug, which the FAA in AME guidance prohibits, and is wondering if she can continue to take that drug.  Going through the regulations, there is no FAR specifically naming drugs, and it appears that for BasicMed, the approval for drug use lies with the examining/issuing physician.

She has gone back to her (issuing) physician and verified that there is no concern with her taking this drug while operating a "vehicle or aircraft" and the physician has confirmed that in the physician's opinion there is no concern.  In her case, her primary care physician (PCP) declined to provide a BasicMed exam, but her endocrinologist agreed to. The drug in question is one the endocrinologist is using to treat her with.

So what we have is a situation where the AME's receive guidance to "Do Not Issue" (DNI) and under BasicMed it appears that the issuing physician can decide contrary to FAA Class 1, 2 or 3 policy.  The question is: Under BasicMed may a pilot be taking a drug, with the approval of their physician, which would otherwise be prohibited under a Class 1,2 or 3 FAA medical?

Addendum: The following is a AC issued shortly before this question was asked:
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_68-1A.pdf

Looking at section 2307 of H.R.636, which is the congressional bill which implemented BasicMed requirements, it is clear that the physician who performs the exam, and provides care to the subject is responsible for determining what drug interactions there might be, as well as the impact of medical conditions, and whether they might be disqualifying.

Armed with this, my CFI student and I called a friend who is with FAA counsel, who does not address airmen issues, but rendered the opinion that BasicMed is separate from FAA Class 1, 2 and 3 medicals.  It is separate from Sport Pilot medicals. It is unto itself. Therefore it is their opinion that it was the legislative intent to create a separate certification process.

Therefore, the examining/issuing physician makes the determination as to any medical conditions or drugs and their impact on flying. He is the subject matter expert, and therefore if full disclosure is made, the airman has operated in good faith.

Of course, we were invited to submit an interpretation request, so that we could get an official response.

When talking with attorneys, and especially FAA attorneys (in their unofficial capacity) there many disclaimers, which include neuro, psych and cardio prohibitions.  And the importance of consultation with the issuing physician when there are medical changes.


What is this instrument? I am looking to sell this instrument, but it has no part numbers or any other identifying marks other than it says "Kollsman" on the back.  Anyone know what it is and what it might be worth?

As the face says, it's a "G meter", aka "accelerometer". It measures vertical acceleration in units of "G" (i.e. acceleration due to gravity, 9.8 m/s^2 or 32 f/s^2).
Price would vary, but here's a site with a similar instrument which sold for $75 when it was in stock: https://aeroantique.com/products/accelerometer-g-meter-1?variant=39681371274


Can TCAS cope with situations involving more than two aircraft? Most of the information I've seen about TCAS talks about only two aircraft being involved.

It's pretty unlikely, although far from impossible that situations involving three or more aircraft may arise.

In such situations is TCAS expected to detect the situation and offer sensible advice still? Or are all bets off and a series of confusing and conflicting advice the most likely outcome?

TCAS can deal with conflicts with multiple aircraft, a so called Multiple Threat Encounter. It will attempt to resolve the conflict but it will be limited in its options.

Examples of a MTE are rare, one case I can point to is this incident involving an aircraft turning into the approach stream between two aircraft instead of following the last in line.

MIT Lincoln lab has reported on MTEs and the TCAS algorithm performance in 2009. They report the majority of MTEs involved three aircraft, but mention one TCAS MTE involving seven aircraft.


Why do Computer Navigation Fixes still exist now that GPS waypoints can be used to define tracks? A CNF is a point that defines a navigation track for a GPS, but why is it used when you there are GPS waypoints that are created to define a track?

From the AIM 1−1−17. Global Positioning System (GPS)

  (2) A Computer Navigation Fix (CNF) is also a point defined by a
  latitude/longitude coordinate and is required to support
  Performance−Based Navigation (PBN) operations. The GPS receiver uses
  CNFs in conjunction with waypoints to navigate from point to point.
  However, CNFs are not recognized by ATC. … CNFs that do appear on
  aeronautical charts allow pilots increased situational awareness by
  identifying points in the aircraft database route of flight with
  points on the aeronautical chart. CNFs are random five-letter
  identifiers, not pronounceable like waypoints and placed in
  parenthesis. Eventually, all CNFs will begin with the letters “CF”
  followed by three consonants (for example, CFWBG).

As an example, the glide slope intercept for an ILS that I fly shows up in the Garmin 430 as a waypoint since the GPS requires a FAF to sequence to the MAP in order to conduct an approach. But it does not show up on the chart. (Remember that an ILS doesn’t have a FAF on the chart.) I have seen them on charts, but none come to mind right now.


Would a slower speed and lower altitude reduce fatal incidents? If it became plausible to fly commercial aircraft much lower in the future (due to developments in technology and airway regulations permitting it), say at a standard height of 5,000ft, but with a slower speed - would that prevent / greatly reduce fatal incidents?

In other words, if an aircraft goes down at 5,000ft and 150mph, it's more likely to have survivaility vs 30,000ft at 500mph.

I'd like to answer this question by debunking the premise of the question: that most plane crashes happen when planes fall out of the sky, and that it's like rock climbing where the higher you are, the more likely a fall will kill you.  While it sounds believable, it's almost entirely false, and since it isn't diving out of the sky that kills you, lowering the altitude doesn't really help flights become safer.

Planes don't need speeds of over 300 mph/500 kmh ground speed to be deadly. A car accident for comparison is generally considered to be very likely fatal above 80 mph/130 kmh  (source: DFT London).  Even plane crashes at takeoff and landing speed of around 150 mph/240 kmh can be difficult to survive just due to physics. Every one to three years there's a plane that crashes on takeoff or landing with almost no survivors like TransAsia 235. The most deadly accident ever happened when two planes collided as one was going about 160 mph/260 kmh and the other was almost stationary!

Even if you could easily survive a 150 mph/240 kmh collision, a ground speed of 500 mph at cruise doesn't mean the plane would crash land at 500 mph. Planes don't just dive out of the sky, gaining speed to 500+ mph/800+ kmh (except in total structural failure and breakup, but then you're a goner even at 150 mph). Even in extreme circumstances like loss of all flight controls in UA 232 the aircraft could slow to about 250 mph/400 kmh before crash-landing.  The "Miracle on the Hudson" aircraft slowed a lot after engine loss as it descended towards the river.  Even the dive of Alaska 261 caused by jammed flight controls could be slowed to about 250 knots using air brakes and flaps.  So the actual crash speed for high altitude incidents is usually less than 300 mph even in catastrophic incidents, which you could easily also achieve after an incident at lower altitudes and speeds.

Any serious changes to aircraft have to make enough of an improvement to be worth the disadvantages involved.  When we're talking about things like making flights slower, that's a serious disadvantage.  Probability per flight hour that an engine or flight controls will catastrophically fail is small but very real number in hazard analysis and so longer flights have a higher chance of an incident.  If the cruise portion of a flight takes twice as long, is that portion now twice as safe per minute to compensate?

Edit: As Martin James and Milwrdfan have pointed out, flying lower and flying slower both increase the amount of fuel you need per trip, which lowers the amount of passengers you can take.  This would increase the number of planes in the air which would probably decrease safety per passenger as well.

Finally, the most dangerous parts of a flight are takeoff and landing. Nearly half of accidents occur during final approach and landing, and only 10% occur in cruise (source: Boeing).  If the past few years are any indication, you're about as likely to have your plane damaged by terrorists as to crash during an incident in cruise.  So you're making every flight lower and slower to help less than one accident per year.

Now that this is the accepted answer, I should point out that Dave has some very good points in his answer about the particular dangers of lower altitudes like weather and glide distance.

So in summary, the premise that cruising at 150 mph and 5,000 ft AGL is relatively safe, while cruising at high speed and high altitude is relatively dangerous, is a faulty assumption. So you don't have much to gain by lowering the speed and altitude.


How would a Flying Fortress behave if it lost its empennage mid-flight? The 1990's movie "Memphis Belle" depicts a Flying Fortress having the whole tail cut by a fighter impact on the rear part of fuselage, as a razor or chainsaw will do, the bomber airplane enters a flat descent with all 4 engines operating.

Is this type of accident possible? How would such a bomber behave with the empennage cut? Is there any way or chance to survive such an accident?

Depends on the extent of the damage as well as what systems are affected.  Lose the vertical fin, it's possible the aircraft could make it home but with limited yaw stability.  Lose the vertical fin and the tailplane, the airplane would nose over and depart from controlled flight due to longitudinal instability.


What are the vertical pieces of metal on the Slingsby Swallow wing for? I was watching James May's Toy Stories, particularly the one where they try to fly a glider across the English Channel.  In the middle of the episode they mention a glider that was used for training in the RAF during the 1950s.  It was called the Slingsby Swallow, and it looks like this:

When I saw those pieces of metal coming out of the wings I was...surprised.  At first I thought they were split flaps but then I found another picture and became even more confused:

The devices are clearly coming out of the top and bottom of the wing, not the trailing edge.

Does anyone know what these are and what they are used for on the Slingsby Swallow (or any other aircraft the employs a similar device)?  My only guess is that they are some sort of spoiler that may reduce lift to help get the glider on the ground...but I'm uncertain.

You're correct -- they're speedbrakes, often referred to as spoilers, and are retracted when striving for efficient flight, but are generally extended in the landing pattern so that you have correction available if you start to get slightly low.  Also frequently extended when the glider is left on the ground to reduce the effect of gusty winds & the likelihood that they would lift a wing.


What is the origin of the term "pax"? Pax in commercial transport is used as something like persons or passengers, in the context of counting people, e.g. 150 pax onboard.

(Amadeus capture, source)

I observed that in German writers tend to use the meaning:

  PAX = Persons approximately.
  (Source: European Union and the Committee of the Regions)

English.SE has a page for What does “pax” mean in the context of the apartment rental? Selected answer:

  Pax isn't exactly shorthand for Passengers. It's short for
  Passengers and Passes.

But the author of the answer agreed that another answer was likely more accurate. The latter has a reference to a magazine, Air Facts: The Magazine for Pilots - 1946:

  Cargo is known as "cargo", but passengers are called "pax" by the
  traffic department, who puts them on and takes them off the airplane
  and "bodies" by the crews who fly them.

Pax could be from passenger as usually assumed in the Aviation community, albeit I don't see why not *pass" instead. I wouldn't be surprised it comes from the merchant navy.

Can we track the use further back to the origin in aviation field?

The 'x' suffix is aviation speak in an abbreviated word called a contraction.  You can think of the 'x' as "cut short" shorthand.  Some are defined in manuals or advisory circulars.  For example, WX is weather as defined in an old advisory circular, AC00-45.
Official or not, a few others that come to mind are:

MX - maintenance
CX - cancel
TX - transmit
RX - receive

Maybe others will chime in the comments with more lore. The -x is also used outside of aviation, and is a common abbreviation marker, e.g. Dx ("diagnosis"), elex ("election"), and Hx ("history").


Is the modelname of a flight management system chosen in accordance with the aircraft it will be used on? I am looking for information about what modules (not necessarly partnumbers) are used in a flight management system of a relatively new airplane.
After having looked around for quite some time, I found this bit of information with a very nice scheme block.

The flight management system (FMS) they are talking about is the 737 FCMS. However it is not totally clear to me (even after having looked around online), whether this is the FCMS is the one being used for Boeings 737.

Is this the case? Or is that number just coincidence?

Yes, this is the system used on the Boeing 737. As the document mentions, it is similar to the system design on the Boeing 757 and 767 models.


Why do some helicopters, e.g CH-53, have some kind of hook thing protruding from the underside of the tail section, what is this for? Why do some helicopters have some type of hook sticking out of the bottom of the tail section, my guess is that it is used to secure the helicopter to carrier deck, but i'm not sure, so I am going to ask in case I'm wrong.

Source: www.b-domke.de

The device is often referred to as a tail rotor guard or tail skid, which hints at its purpose.

Helicopters that have tail rotors that sweep below the tail boom are usually equipped with this guard to prevent the tail/rotor from striking the ground during landing, both during a rolling landing or a vertical landing. It is especially useful for landing off-field where the terrain may not be flat near the tail rotor.

Many rotorcraft, both general aviation, transport, and military have this feature, and it may even be required by regulation (see 14 CFR 29.411 for transport category rotorcraft).

Here is the tail rotor guard on a Robinson R44:

Source: Airport-Data.com

While technically the same as in the original question, I do not believe the R44 rotor sweeps below the vertical fin. The Red/White guard protects the blade while the "stick" on the fin keeps the fin from contacting the ground. It may be possible to contact the rotor if landing on soft earth or tall grass...

You can search through Google Images to find many examples of rotor guards.


Why would an approach be Cat A NA? I was looking at the RNAV (RNP) 6 approach into Gunnison (KGUC) and noticed something quite strange:

If the image isn't clear enough -- the approach is Not Authorized for approach category A aircraft (which of course includes every last helicopter on the planet).  WHY would this be so?  Is there some operational or technical reason a slow-moving category A aircraft or helicopter can't fly this approach, even though their avionics might be perfectly capable of doing so? Or is this some sort of charting error I should bug the FAA about?

Original answer: The speed of Category A aircraft is too low to execute the missed approach.  For this particular airport, it's basically a hole in the ground with steep mountains on all sides. To go missed, you gotta get up in a hurry, and the TERPS data probably indicates a minimum speed is needed.

Edit:  Despite the downvotes and comments stating that my answer was "unlikely", I'm sticking to my guns.

To make sure that I knew what I was talking about, I contacted the FAA's Flight Procedures Standards Branch in OK City and eventually was put in contact with someone who was able to pull up the documentation on this approach.

Listed in the comments of the document he was looking at was this: "Ref 8260.52 CAT A -- final approach speed is too slow for RNP missed approach segment length for obstacle penetration."

Translation: whoever put this approach together did the math that is required, and the formula result was that speeds needed for obstacle clearance are not sufficient when using CAT A speeds.

Note 1: some math and formulas required to build an IAP missed approach procedure can be found in Chapter 4 of 8260.52. (https://www.faa.gov/documentLibrary/media/Order/ND/8260_52.pdf)

Note 2: 8260.52 has since been superseded by 8260.58, which itself has undergone an update and the most current document is 8260.58A.

Gory technical details (or some insight as to why this oddity is the way it is):

The thing that makes this approach special is that not only is it a RNP AR approach, the missed approach requires abnormally precise navigation as well (i.e. RNP values <1.0).  The length of this span of the missed approach (from the MAP to TIPOC) is bounded by the results of formula 4-3-8 in 8260.58A, which is dependent on the true airspeed of the slowest aircraft of the approach.

DMASRNP is the max distance allowed for a given true airspeed (category) to return to RNP 1.0 on missed approach. The longer the distance to return to RNP 1.0, the faster the plane needs to be.

In the case of the KGUC RNAV (RNP) 6 -- the MAP to TIPOC span is 6.7NM along track, which is longer than the formula's results no matter which of the three possible RNPs are applied if you are using a category A airspeed (these results are applied to the whole span as per figure 4-3-5).

Why this formula is needed, and applied to the whole span for that matter, is a mystery, though -- 8260.58A gives no design rationale for this limitation, or why it is pegged to airspeed.  A rationale is that navigation errors are cumulative though -- the slower you're flying, the more time you have to drift off course before you make it to the next "gate" where a higher RNP prevails.

Other approaches (even in similar terrain and with seemingly similar conditions charted) may not have this peculiar limitation, though -- the KRIL RNAV (RNP) Z 26 approach, for instance, also requires RNP < 1.0 on the missed approach, but for a shorter distance -- a mere 3.5NM from the MAP to TEROE, whereas the limit distance for Category A given the RNPs used in the missed approach there is 4NM.

Moral of the story: pay attention to your approach plates!


Why is there a maximum altitude to restart a jet engine? On all the turbojets that I have flown the maximum altitude a pilot can attempt a restart is 30,000 FT MSL.  What factors go in to deciding what the maximum altitude is for an engine restart / relight?

Basically, it gives the pilot the altitude and airspeed at which the engines can be relighted in flight. Based on these values, the pilot has to take a decision to descend etc. A jet engine requires (compressed) air, fuel and a flame source for (re)starting. So air density plays an important part in determining the maximum restart altitude.
In addition, there are other factors at play as well. In case of unassisted (without APU, for example) windmill restarting, the airspeed must be enough to overcome the inertia of the components. In certification memorandum on Turbine Engine relighting in flight, EASA says,

.. as core - bypass ratio of engines continues to increase,  higher  airspeeds  are  generally  required  to  enable  unassisted  windmill   restarting.  The  inertial  effects  because of the increased size, mass,  and number of engine driven gearbox accessories may also contribute  to   increased  rotor  drag  loads,  decrease  starting  performance,  and   possibly  contribute  to  rotor-lock  conditions.

In case a starter is available, the airspeeds required go down (as APU itself is usually a small turbine, the altitude effects are not as pronounced). According to CFR § 25.903 Engines:

(2) An altitude and airspeed envelope must be established for in-flight engine restarting, and each engine must have a restart capability within that envelope.
(3) For turbine engine powered airplanes, if the minimum windmilling speed of the engines, following the inflight shutdown of all engines, is insufficient to provide the necessary electrical power for engine ignition, a power source independent of the engine-driven electrical power generating
system must be provided to permit inflight engine ignition for restarting.

The engine restarting envelope is decided both in terms of altitude and airspeed. It also depends on aircraft. For example, in ETOPS aircraft, the APU must be designed to have airstart capability throughout the normal flight envelope. Regarding this envelope, EASA says,

2 Envelope of Altitude and Airspeed
2.1  Sufficient flight tests should be made over the range of conditions detailed in 2.2 and 2.3, to establish the envelope of altitude and airspeed for reliable engine restarts... The effect of engine deterioration in service should be taken into account.
2.2 Altitude and Configuration. From sea-level to the maximum declared  restarting altitude in all appropriate configurations likely to affect   restarting, including the emergency descent configuration.
2.3 Airspeed. From the minimum to the maximum declared airspeed at all altitudes up to the maximum declared engine restarting altitude. The airspeed range of the declared relight envelope should cover at least 30 kt.


Why are high-g requirements so important for training next generation of fighter pilots? Background

In the development of T-X program, a major step has been the refining of the technical requirements, in particular this "sustained G" maneuver:

  The sustained G maneuver shall be flown with a standard configuration (i.e., clean with no external stores), at or above 80% fuel weight (relative to
  maximum fuel capacity), steady state flight, and standard day conditions. The maneuver will begin in level flight (flight path angle no lower than zero
  and no higher than two degrees nose high), wings level (+/‐ 5 degrees of bank), at or above 15,000 feet pressure altitude, and at or below 0.9M. From
  this point, the pilot shall immediately initiate bank and back pressure to achieve the sustained G. The sustained G must be maintained for a minimum
  of 140 continuous degrees. The pilot may begin reducing the load factor and rolling out after a minimum of 140 degrees in order to roll out at
  approximately 180 degrees of turn. The sustained G Threshold:  ≥ 6.5Gs; The sustained G ≥ 7.5Gs.

seems to be quite challenging for the T-100 from Alenia and the BAe Hawk.

Alenia T-100 is still bidding after changing partner.
BAe, which partnered with Northrop Grumman, discarded the Hawk in favour of a clean sheet design.
Boeing/Saab participate with a clean sheet design.
Lockheed proposing the T-50 after discarding a SkunkWork clean sheet design.
Textron Scorpion seems to have pulled out after the new set of requirements.

Trend
The new requirement seemed to challenge the existing design. The Hawk could be considered "old" (first flight in 1974), the scorpion could be considered "simple". The T-100 and the T-50 starting development mid 90s together with international partners (Italy/Russia,USA/Korea) should though be "modern" trainer. While the T-100 seems to be more challenged, Lockheed considered a clean sheet design as well, so was probably not too relaxed about the T-50 performance .

Question
 - Why is this request for maneuverability so important for the next generation of fighters?
 - Should not be other factors like battle-space management more important?

Two solid reasons: defensive and offensive ACM/BFM remain relevant

I'll address the defensive issue first.  Even if a pilot will never get into a dogfight, the pilot / aircraft still must defeat or evade a surface-to-air or air-to- air missile.  This combines the use of both countermeasures and 3-dimensional maneuvering to cause the guidance system inside the missile to lose it's lock on the aircraft.  To get the turn rate and axis-change-rate needed to deal with modern missiles requires the ability to pull a significant number of g's.  You can look at is as a "purely defensive dogfight" technique.  You fight the way you train, so you need to train for this likely situation.

The offensive high energy, high-g capability has to be retained because in real life, the rules of engagement do not always allow for a BVR (Beyond Visual Range) engagement.  Further that point, even with BVR engagements allowed, if the opponent has good defensive technique versus your missiles you may still get into a dogfight-style of engagement in order to defeat or destroy that opponent.  You have to know how to do that, and train for how to do that.  It is an acquired skill. (The basics of the skill were eloquently laid out by John Boyd, which is where the OODA loop model comes from).

Both the offensive and defensive applications of these maneuvers require skill with and acclimatization with high-g maneuvering.

A related reason to boost the performance of the Trainer

For the last 20 years, it has become fashionable, and sometimes useful, to do a thing called "downloading training" into a cheaper to fly, cheaper to maintain aircraft.  That way you don't wear out the airframes of your very expensive front line aircraft.  (The Navy spent years using the T-2 for spin training for its jet pilots, to include T-2's not used in the Training Command but retained on both coasts as "spin birds").   This concept of "downloading training" sounds nice, but in reality has mixed results.  At the high performance level that front line aircraft operate, some skills are transferable and some are "building block" from one airframe to a more complex airframe. Given how recent this requirement is, I'll see in this requirements crafting something similar to the initiatives that I ran into in the Navy (and in Joint Training) with "downloading training."  The same mind set is at work here: if the spec can be met at a high enough level, the graduate of the advanced jet training will enter the front line units with a higher level of capability.   We successfully down loaded quite a bit of instrument training into the sim in at least one aircraft program I worked on, the T-6.  While that was 15+ years ago, the never ending push to "do it cheaper" has not let up in the DoD. Our efforts to download ACM/BFM into the T-6 for the NFO training pipeline ran into the problem of "not enough energy."  I am not sure if that has since been solved, or abandoned, but I think it's the latter.  (The last time I checked on this was about 6 years ago).

Note: This is an experience based answer, informed by my having both been taught basic one-versus-one maneuvering, and many years later having been deeply involved in training systems development, and training requirements, for US Navy fighter/jet pilots. (They had the same challenges to overcome as their Air Force colleagues in the proposed T-X system).  A more detailed answer would be, roughly, book length.  Chapters 5 and 6 of the link cover Offensive and Defensive BFM basics.

From the introduction to that manual:

  BFM INTRODUCTION
  When the P-80 finally became operational in the mid-1940s, WWII was coming to a close, as was seemingly the age of aerial dog fighting. While these aircraft never took part during operations in Europe, they became an integral part of combat operations in Korea. In November, 1950, a P-80 flown by LT Russell Brown shot down a Russian MiG-15 in the world’s first decisive all-jet aerial battle, acting as a reminder that BFM was still a very real possibility in combat operations. With the maturation of aerial warfare evolving into Beyond Visual Range (BVR), the decades that followed Korea exploded with the development and implementation of long range air-to-air missiles that could potentially eliminate the possibility of Within Visual Range (WVR) engagements. During the Vietnam conflict, however, aircrew often found themselves unable to employ their BVR missiles, forcing weapons employment into the WVR arena, ultimately relying on BFM skills to defeat their opponents. The days of Korea and Vietnam are long past, and we have achieved amazing successes with the accuracy and reliability of our current long-range
  missiles.  As we, and our enemies, continue to improve our BVR capabilities, a combination of electronic attack, theater Rules of Engagement (ROE), switchology failures, or a momentary lack of attention to prescribed air-to-air timelines may ultimately bring us face to face with the enemy in a 1v1 engagement.
  (CNATRA P-1289 (Rev. 01-16))

The airframe may change, but the problem remains the same.


What makes an airplane STOL? I watch STOL pilot champs Zenith CH701 here.

The engine power are: 130 HP, 80 HP, 120 HP and 100HP, respectively. Amazing. As per my observation, the third airplane takes off in a distance shorter than its length. It uses an 120 HP engine. I tried to search over the net how long the required runway is to make it take off. Unfortunately, I could not find it. But I believe that should be longer than its length.

What are the technical requirement to make an airplane able to STOL?

There are a number of factors that can contribute to short take off landing (STOL) ability.

The Zenith page has some information:
http://www.zenithair.com/stolch801/design/design.html

Wing Shape

A more "cupped" wing shape generates more lift at a slower speed, enabling a shorter take off. This sacrifices the aircraft's top speed. Note that this limitation can be mitigated by making the wing shape changeable with slats and flaps.

There are other modifications that can be made to a wing shape to favor STOL characteristics. For example, there are a variety of STOL kits that can be added to existing aircraft. These range from wing tips to other airfoil shape changes.

Wind Speed

By taking off into a higher speed wind, the takeoff distance is decreased. With a strong enough headwind (and a skilled pilot), a STOL aircraft and appear to take off vertically with little or no runway needed.

Power to Weight Ratio

The more powerful the engine is compared to the weight of the overall aircraft, the less runway is required to achieve takeoff speed.


What are packs on aircraft? I've been watching YouTube videos and when they're going through the checklist they say "packs off" can anyone elaborate?

Most jetliners are equipped with "p-a-c-k-s" which stands for
  Pressurization Air Conditioning Kits".

The air conditioning (A/C) packs are usually located at the lower wing/fuselage root fairing beneath the fuselage.

source

On some jetliners (Douglas Aircraft DC-9 Series) the A/C packs are located in the tail, while other aircraft such as the McDonnell Douglas DC-10/MD-11 and Lockheed L-1011 are located in the front of the aircraft beneath the flight deck.

Nearly all jetliners have two packs, although larger aircraft such as the Boeing 747, Lockheed L-1011, and McDonnell-Douglas DC-10/MD-11 have three.


Why does a 3D wing's CL keep increasing even after 50° AOA in XFLR5? Can you please tell why my 3D wing in XFLR5 keeps increasing it's lift even after 50 degree AOA, while it's 2D profile stalls after about 10 degrees ?

More details on simulation setup:

Airspeed is 15 m/s (Re is about 20000-25000)
Wing chord length is 3 cm
Wing span is 12 cm
Wing is straight
Airfoil is symmetric (NACA-0009)

XFLR5 is not made for this kind of calculation. Do not trust the results.
Stall is not the end of lift. See below for 2D wind tunnel data collected by S. Hörner in his book Fluid Dynamic Lift. 3D results would look similar, but with a less steep gradient around 0° and lower peaks.

180° polar for several airfoils


How do you find the difference in degrees between two headings? This may be more of a math question, but it is specific to aviation so here goes:

Given an origin heading and a destination heading (origin heading is the heading you're already flying at and destination heading is the heading that you want to turn to), what are the formulas for degrees of separation between those two headings for a left or a right turn?

So if you are heading 190 and you want to go to 020:

The left turn formula should output 170 degrees.

The right turn formula should output 190 degrees.

Figured it out.

LH turn: [origin hdg] - [destination hdg] (if less than 0, add 360)

RH turn: [destination hdg] - [origin hdg] (if less than 0, add 360)

Edit: for the acute angle between two headings you would just take the lower number between these two values.   There is no different formula.   This is alluded to in this SO post.

By the way, this is not really useful for normal pilots because you can just visualize a compass rose and figure out the different angles pretty easily but I am making a program that will make flying holding patterns a lot easier.   You input the inbound leg course (not radial), the wind (direction, velocity), your true airspeed, and whether you are making a left or right hand turn.   The program calculates what heading you should turn to on the outbound leg and the heading you should then turn to on the inbound leg (assuming standard rate turn).   It also gives you the time to fly on the outbound leg after you reach your heading for that leg.   It even takes into account turning from/to different crab angles (which would make the turns more or less than 180 degrees).


What is the formula for estimating the maximum stationary thrust of a rotor as function of its diameter? I am new! New to this forum and new to aviation (i normally deal with statics) so thanks in advance for beeing patient with me.
Recently i was trying to figure out how much weight a rotor can lift as a function of the rotor diameter.
Therefore I came across this formula.
$$
T_{rotor} =(0.5*P^2*η_{rotor}^2*η_{el}^2*π*d_{rotor}^2*ρ_{Air})^{1/3}
$$
This brings me already quite close to my goal as I now have $ Thrust = f(P^2, d^2)$. Now I tried to relate the engine power to the rotor diameter by using :
$
P=T * {rpm}$  with $ T=I *α=(0.5* m*r^2)*v_{sound}/r $  and $ {rpm}=v_{sound}/(\pi*d)$
Which leads me to
$$
P(m)=(v_{sound}^2/(4*π))*m
$$

From this calculation a few questions arise:

Do you think this is a good estimate (within +-15%)?
Is there a better formula to estimate $I_{rotor}$ than using $I_{zylinder}$?
Is there any formula to estimate $ m_{rotor} = f(d_{rotor})  $

I want to add  that this estimate is for a rough feasability study and not to design a rotor or aircraft. I also know that several of the values in this formulas are a function of altitude and aircraft velocity. Please dont take this into account. At the moment I am only interested in a stationary solution.
Thanks for your help!

The dimensional approach is simple... It can be safely assumed that the lift $L$ is a function of the input power $P$, the diameter $D$ of the rotor and the air density $\rho$.

Thus, $L = f(P,D,\rho)$

where $f$ is a function to be determined.

From dimensional analysis, the lift $L$ can be easily derived:

The variables are Lift $L$, dimensions $MLT^{–2}$; Power $P$, dimensions  $ML^2T^{–3}$; Rotor diameter $D$, dimensions $L$ and air density $\rho$, dimensions $ML^{–3}$

The variables form a non-dimensional product $k$

$k = L^a\cdot P^b\cdot D^c\cdot \rho^d$  where $a,b,c,d$ are numbers to be determined.

Let’s form now a parallel product $k^*$ with the dimensions:

$k^* = (MLT^{–2})^a  (ML^2T^{–3})^b  (L)^c (ML^{–3})^d$

Clearly, $k^* = M^0 L^0 T^0$... We now take the exponents for each dimension:

$a  + b + d = 0 \\
a + 2b + c – 3d = 0 \\
–2a – 3b = 0$

We make $a = 1$, since $L$ is the variable we’re going to solve for.

$b = –2/3 \\
d = –1/3 \\
c = –2/3$

Then,

$k = L^a\cdot P^b\cdot D^c\cdot \rho^d \rightarrow  k = L\cdot P^{–2/3}\cdot D^{–2/3}\cdot \rho^{–1/3}$

Solving for $L$

$L = k\cdot P^{2/3}\cdot D^{2/3}\cdot \rho^{1/3}$

where $k$ is a constant to be determined...


Can Airbus A320 doors be opened mid-flight? Today I learned how airliner doors are typically an outward facing plug and cabin pressure would make them nearly impossible to open mid-flight.
It's easy enough to see that for the shape of Boeing 737 doors, for example.
But looking at this video of the A320 door operation, it doesn't exactly look like it forms a plug.  So if it were unlatched while the cabin is pressured, would it get pushed open?

It's a plug door.  The door nestles behind an array of cleats and a set of L shaped guide tracks and has to move up some distance, as you can see in the video, to clear the cleats and exit the L track.  When it's dropped into the locked position, it's not dependent on any moving parts to resist pressure because it settles behind the fixed cleats in the outer frame.  The cleats in the door bear on the ones in the frame to resist outward pressure and the door is opened by lifting it to mis-align the cleats so the door cleats clear the frame cleats. That makes it a plug door.
It looks like there are other levers and cams to assist with the door pull-in, and probably some form of locking pin(s) to block vertical movement when latched. If the door was, say, 36 inches wide by 80 inches high, at an 8 psi cabin pressure differential, there is about 23000 lbs pushing on it, so you won't be moving it unless you are The Hulk.
The CRJ Regional Jet main pax doors are an example of non-plug doors that just pull in flush on a simple hinge at the bottom, and latching shear pins extend into holes in the door frame.  This door is dependent on the shear strength of the movable pins, and the shear loads when pressurized pretty much weld the pins in place.


Under which conditions is full rated power instead of METO power required for takeoff (DC-3/C-47 with Pratt&Whitney 1830 twin wasp engines)? OK, so my explanation is going to be quite long, but please bear with me. My question is in two parts, but first I'll explain what I know.

I was reading the C-47 Pilot's Flight Operating Instructions and the DC-3 Organisation Control Manual, and they both say that takeoff should be performed at full-rated power.
This link shows a bunch of good reasons why one should always use maximum power for takeoff

[FAA mandatory for commercial operations; P&W endorse it;

  'The distance the pistons travel in the cylinders (stroke) is related
  to the power used. The piston rings, over time, wear a ridge into the
  cylinder wall at the top and bottom of the stroke. If 42" is used for
  takeoff, the bottom ridge will develop further up the piston wall than
  in an engine that has seen rated power for Takeoff. If the time comes
  when full rated power is needed (short runway, engine failure, etc.)
  and a power setting greater than 42" is used, the piston is now forced
  past the ridge in the cylinder created by many hours of using de-rated
  power. Forcing the piston rings past this ridge can cause them to
  break'

;carburator has additional cooling feature past 45"; engines last longer],

but also mentions the fact that full-rated should only be used for one minute at a time (which is apparently one of the reasons some people choose to take off with METO power instead).

One minute sounds like a very short time to me (and to the person defending T/O with METO power), but I'm not a pilot, so I do not know how long a  normal T/O roll with a DC-3 at maximum takeoff power  would take.

The DC-3 performance information sheet (found here) mentions that (at sea level and normal runway conditions) a 1700 ft T/O roll is enough to reach 100 mph (which I am assuming is the minimum takeoff speed ), but it says nothing about how long  the DC-3 would take to reach that.

They also mention that at 5000 ft altitude it'd take a 2300 ft T/O roll to attain that same speed. But that still doesn't tell me how long that would take because I don't know the acceleration rate the DC-3 has. I've checked the charts, but I admit I couldn't conclude anything from them (doc is semi-readable, plus, it might have been way over my head anyway). I'm sorry if this question is stupid, maybe I need to brush off my physics , but I really am not managing to figure this one out on my own ...

I am aware there are a number of variables that come into play here, but I'd be happy if anyone could give me an approximation , or even an example of what conditions need to exist for the DC-3 to take only a minute to do the T/O roll (if one wanted to use full-rated power).
And, more importantly: Would a wet grass runway at an almost 6000 ft altitude airport, plus having the aircraft at maximum takeoff weight (or close to it) justify choosing to take off with METO instead of full-rated power? I mean, such a T/O roll would definitely take over a minute, right?

Thanks a lot

Let's consider your case of a 2300 ft (700 m) takeoff roll. Your link lists the procedure as reducing power upon reaching 90 kt (46 m/s). To make things easier we can assume constant acceleration. That won't be true in real life but it will give us an approximation.

Two basic equations for acceleration, relating distance $s$, acceleration $a$, time $t$, and velocity $v$:

$s=\frac{1}{2}at^2$

$a=\frac{\Delta v}{t}$

Substituting our known values in, we get:

$700\ \mathrm m=\frac{1}{2}at^2$

$a=\frac{46\ \mathrm{m/s}}{t}$

Soving for $t$, we get about 30 seconds (and $a=1.5\ \mathrm{m/s^2}$). Even accounting for acceleration reducing as speed increases, that suggests there's plenty of room to reach 90 knots in less than one minute.

If we look at what takeoff roll would result if we need 60 seconds to reach 90 knots, we get 1380 m, or 4500 ft.

To verify this you can also look up videos of DC-3 takeoffs. Like this one, which seems to take about 30 seconds:

I agree with the comments, piston travel changing significantly with power setting does not make sense.


Why do aircraft cockpit displays use uppercase fonts? I've seen many images of aircraft cockpit displays and instrument or control labels that all seem to use uppercase lettering, even though there seems to be a lot of evidence indicating that mixed case lettering has superior readability. Why is that?

The specific reason all-uppercase was adopted is just historical. Traditional steam gauge faces use capital lettering exclusively. The reason for that is that capital letters are easier to produce with limited tooling. When they were installed in aircraft, this cost-efficient convention was followed.

This pattern is not exclusive to gauges: historically, in Indo-European languages, uppercase letters came first. Bicameral script is a later invention, present only in a few (albeit very popular) language scripts.

Early typewriters were all-uppercase. Upper case persisted in teletype communications and early computers. Mixed case always added complexity, so its adoption in tech took time throughout the 20th century. This made all-uppercase text very familiar to the technically-minded people involved in aviation, right at the time when its conventions were being established.

The reason uppercase hasn't been replaced, even in glass cockpits, is a simple case of getting the best size:readability ratio. Capitals are fixed height and allow for twice larger letters (thus more readable) within the same amount of space.

For the same reason, exit signs in buildings spell "EXIT", not "Exit", most book covers feature all capital letters, and "NO STEP" won't be replaced with "Please avoid stepping here" anytime soon.

Mixed case has superior readability for natural English, but the language used in aviation is a specific lingo with heavy use of abbreviations. The word-recognition advantage you use reading this post would not initially work in reading "ALT" or "HDG". These are new symbols to learn. Once learned, they become more familiar than the original non-abbreviated terms they stand for.

Aviation documentation is written in mixed case, but the use of uppercase in cockpits continues to be beneficial, as uppercase helps automatically emphasize the exact terms as seen in the cockpit and elsewhere.

Will aviation displays ever switch to mixed-case? The process is ongoing, but rather than changing the old function, it's just the use of mixed-case for some new functions. These involve incorporating paperwork into the glass, which uses more natural language, for which mixed case is suitable (and, as Gerry correctly adds, officially recommended).

Aviation-specific, abbreviation-rich jargon is an artificial language, not a natural one, so there's no case for it to switch.


What is the purpose of VFR-on-top? VFR-on-top is an IFR clearance in the US that a pilot can request to allow an IFR flight to use VFR altitudes provided that it can remain in VMC. Requesting and receiving a VFR-on-top clearance doesn't cancel the IFR flight plan.

When is this clearance useful? It allows the pilot a greater choice of cruising altitudes, but why would a pilot prefer to use VFR-on-top rather than request a different IFR altitude? VFR-on-top adds at least one task to the pilot's workload - maintaining VFR cloud clearance - without reducing the IFR workload.

The VFR on top clearance is often given with a block of altitudes.  Such as this from the reference document "Maintain VFR-on-top at or between six thousand and one zero thousand.”  With this clearance the pilot can fly any altitude they want within this block of altitudes without having to contact ATC for further clearance.  This flexibility can be useful with the conditions are such that the clouds come and go as you fly along.  So if you are cruising along at 6500 and encounter a cloud and need to climb to 8500 to maintain clearance you just do it.  No need to contact ATC and wait for them to ensure they can clear you higher while the clouds keeps getting bigger and bigger in the windshield.

Even if there are not cloud issues, the ability to change altitudes may be useful in seeking an altitude with more favorable winds.


Why would the Pakistan airspace closure cancel flights not headed to Pakistan itself? The India-Pakistan feud has heated up again, with Pakistan closing its airspace as a result.
I know many international routes fly over Pakistan, and that the closure would cause issues, but this report surprised me:

Thousands of people were also stranded by affected airlines that not only land in Pakistan, but fly over its airspace -- one of the major routes from Southeast Asia into Europe.
Thai Airways announced that all its European routes "departing near midnight of 27 FEB through early 28 FEB" were canceled "due to sudden closure of Pakistani airspace as a result of tension between India and Pakistan."

Why would the airspace closure force flights over it to cancel entirely? I would think you would just reroute them around it.

To give an example of how flights can be affected by this in ways to make them impossible, Iranian airspace is closed from sunset to sunrise (unless things have changed recently).
Any aircraft that due to the closure of Pakistani airspace would need to cross Iranian airspace and be unable to do so because of that closure now needs to be cancelled or rescheduled.

Also, if the diversion around Pakistani airspace would stretch the endurance of an aircraft beyond what fuel it can carry, it cannot fly the route.

Or the diversion would cause such a delay in the schedule that it causes too much problems with the overall scheduling of the airline. Such things tend to have a ripple effect. One flight gets delayed by several hours, dozens of others get delayed as a direct result, hundreds more can suffer delays in the end.

Also, some airports only operate during daylight hours. A diversion around Pakistan might mean the flight can't make it to one such airports before sunset and thus can't land at its intended destination. Now the airline has 2 options, divert to another airport, arrange for bus or train transport for all the passengers, and in the morning yet another hop to the intended destination to pick up the new passengers, or cancel the flight.


What to do when fuel is exhausted and we are denied landing by ATC? What to do when fuel has exhausted and we are denied landing by ATC?
If we were denied landing it means we are close to the runway, and thus if we are intending for a forced landing, the runway could have been the safest option.  With time being a constraint, what call should be made to ATC?

You should have declared an emergency long before your fuel was exhausted. If you haven't yet, do it now.
Land Anyway
You are authorized to do whatever it takes to get the aircraft down, worry about regulations when you are alive enough to do it. Until then, ATC will clear out anything around you, just say "declaring an emergency" and then fly the plane regardless of what ATC "authorizes" you to do or not.
The literal call to ATC will be:

KXYZ, Unable, emergency, landing now.

But only if you have time to make the call.


Where is the midspan airfoil located on the 737? The 737 has a root airfoil, two midspans, and one outboard. Is the midspan located under the fuselage or between root and tip?

The midspan airfoil is between root and tip, so somewhere along the half span of the wing. Midspan is therefore a misnomer, but sounds better than midhalfspan.


UAV project in aerospace department I am 2nd year PhD student in Physics.

Can you think of any UAV project which won't contribute to army? UAV designing is a career of my dream, but I want to serve the greater good. However, all advances are developing in military field.

One would be the Aurora Flight Sciences Perseus, which started as an unmanned instrument carrier for flights into the south polar vortex, in order to study ozone depletion.

But guess what: Development took much longer than initially expected, and funding gaps could only be filled with DARPA money. In the end, military contracts keep many high-tech companies alive which could not support themselves exclusively with civilian money.

If your field of interest has military applications, it will be very hard to stay true to your ethical standards.

I would dispute your claim, however, that all advances take only place in the military field. Apart from GPS, many advances which make UAVs practical are connected to civilian-driven technological progress. Only when it comes to issues like reserving airspace for UAV operations, the military is in a much easier position than civilian operators which must wait for slow-moving government bureaucracies to adapt to progress. The discussions we had with the FAA in 1990 on how to operate UAVs were surreal.


Does a Type Rating "upgrade" with your license? I believe anything the FAA refers to as a "rating" upgrades automatically with your license. For example, if I get my instrument rating on my Private Pilot License, I don't have to retake the instrument checkride when I get my commercial license in order to fly IFR commercially. This is not true for license classes (single engine land, multi-engine land, single engine sea, multi-engine sea). If I get a private MEL, and then take my commercial checkride in a single engine, I still have to take another commercial MEL checkride in order to exercise commercial privileges in a multi-engine airplane.

The question is, do type ratings work like instrument ratings or like license classes, and what regulations govern this?

The answer to this lies in 8900.1, Volume 5, Chapter 2, Section 18 - Conduct an Airline Transport Pilot Certification, Including Additional Category/Class Ratings.

In most cases, yes the type rating "upgrades" or "elevates" along with your license since the type rating is always evaluated at ATP standards, even if you only have a private or commercial certificate.

Exceptions are type ratings for single-engine airplanes and type ratings that have a "VFR ONLY" restriction.

8900.1 excerpt:

  5-710    PILOT CERTIFICATE LEVEL AND CATEGORY AND CLASS RATING. The following category and class rating(s) for which the applicant has
  qualified on the original or subsequent ATP practical tests are
  entered on the ATP certificate.

  A.    Addition of Lighter-than-Air and Glider Class Ratings. A lighter-than-air or glider category rating may be added to an existing
  ATP certificate; however, the rating may be added only at the
  recreational, private, or commercial pilot certificate level, as
  appropriate to the practical test completed. There is no provision for
  the original issuance of an ATP certificate with a lighter-than-air or
  glider category rating.

  B.    Type Ratings. Type rating tests are conducted to the ATP standard for all grades of pilot certificate. Therefore, all type
  ratings in that category and class of aircraft for which the practical
  test is conducted in are upgraded after successful completion of the
  practical test. For example, a person who holds B-737, DC-3, and SK-62
  type ratings on his or her commercial pilot certificate, and later
  satisfactorily completes an ATP practical test in a CE-750, would have
  his/her B-737 and DC-3 type ratings elevated up to the ATP
  certificate. The SK-62 would not elevate up because the practical test
  was in a multiengine airplane. However, when the person satisfactorily
  completes an ATP practical test in a helicopter, the SK-62 would then
  elevate up to the ATP certificate. Therefore, all of the type ratings
  held on the superseded certificate carry forward at the new
  certificate level within category and class.

  NOTE:  A type rating for a single-engine airplane may not be upgraded
  to the ATP level.

  1)    Except for type ratings and, under some circumstances, the
  instrument rating, other ratings indicated on the superseded pilot
  certificate are carried forward at the commercial, private, or
  recreational pilot certificate level, as indicated on the superseded
  certificate.

  2)    Instrument rating privileges are shown on the ATP certificate
  only if the ATP practical test was conducted under visual flight rules
  (VFR) only, or to retain instrument privileges that were held on the
  superseded certificate for a category of aircraft other than the one
  used for the ATP practical test.

  C.    Type Rating Limited to VFR. A type rating bearing the limitation “VFR ONLY” may be added to an existing certificate other
  than an ATP certificate under the provisions of § 61.63(e). This
  limitation may be added to an aircraft type rating not capable of
  instrument maneuvers or procedures required on a practical test. The
  practical test must be administered under the appropriate ATP PTS for
  an aircraft type rating limited to “VFR ONLY”. A type rating bearing
  the limitation “VFR ONLY” may be added to an existing ATP certificate
  under the provisions of § 61.157(g). The practical test must be
  administered under the appropriate ATP PTS for an aircraft type rating
  limited to “VFR ONLY.”

  NOTE:  There is no provision for taking an initial practical test for
  an ATP certificate in an aircraft that would require a VFR limitation.


Which country has jurisdiction over incidents in flight? If an incident occurs on board an aircraft in flight which could be considered as criminal in one country, what decides which country the incident falls under? For example, if a man was found to be in possession of "virtual" child pornography and not all of the countries involved consider that to be illegal, which country is the one who decides whether the person have broken the law or not?

In my PPL class I was taught a simplified explanation:

If a baby was born (or a crime committed for that matter) on an aircraft, the official country in which it was born depends on wether the aircraft's doors are open or closed (within reasonable limits, so assuming they can't be open in flight).

If the doors are open, the country will be the country where the aircraft is currently located. If the doors are closed, it will be the country in which the aircraft is registered.


What does the condition lever in turboprops control? Turbojet and turbofan engines have just one control lever that controls the thrust by setting the amount of fuel injected.

But most turboprop aircraft have three levers. One adjusts the fuel flow, one adjusts the propeller speed, but what does the third one do? Does it only act as an on-off switch as simulators tend to present it?

Shamelessly quoting from Skybrary: (emphasys mine)

  A Condition Lever is a pilot actuated control which is located within
  the throttle quadrant of a turboprop engine equipped aircraft. It is
  utilised to control some functions of both the propeller and the
  engine. These functions vary from installation to installation.

  Functions of the condition lever can include any of the following:

  Fuel cut-off.
  Propeller feathering.
  Propeller un-feathering.
  Low idle/high idle selection.
  Propeller speed control.


How do electric propeller governors (or electrically controlled governors) work and what are their pros and cons? I am trying to understand why electric propeller governors are not (yet) prevalent given that they offer the ability to control the RPM with high accuracy. What is the typical architecture for an electric governor or electronically controlled governor? What are their pros and con?
As far as I know, there are two types of electric governors:

The governor has an electric actuator in the propeller hub like the Airmaster Governor. This removes a lever, but adds a number of switches in the cabin.

The governor is still hydraulic, but an electric actuator controls its position. (I think the PC-12 and TBM700 work like this?)

I am assuming that option 2 is not ideal as you need a separate actuator to control the governor cable.
I guess I do not understand how airplanes like a PC-12 or TBM700 (that only have a single lever in the cabin) regulate propeller RPM.
Thanks!

They are much more prevalent than you think, and have been in use for more than 70 years. Rotax 912 and 914 engines can be installed with electric governors from MT Propeller. Airmaster sells them as well. You may also be surprised to learn that nearly 90% of German operational Luftwaffe aircraft during WW2 used an electrically-actuated propeller system designed by Dr. Hans Ebert of the VDM (Vereinigte Deutsche Metallwerke, or United German Metalworks). One example of these excellent propeller systems is in the Smithsonian's National Air and Space Museum.
This article does a pretty good job of explaining how they work.


What determines the direction of rotation for counter-rotating propellers? As Wikipedia and other sources make clear, most twins with counter-rotating props are configured with the left (#1) prop turning clockwise (as viewed from behind the plane) and the right (#2) prop turning counterclockwise. But there are significant exceptions, such as the P-38. What the sources do not make clear is the reason for the exceptions. There are a few vague comments about the P-38 having "unsatisfactory" handling as originally configured with the common setup, but nothing that helps me understand what aerodynamic or other issues might make a P-38 or any other plane a candidate for reversing the rotation directions. I realize that there are potential issues with coupling to tip vortices if the engines are near enough to the wingtips. And I assume that there might be effects related to air impinging on the fuselage, or FOD from stuff entrained in the airflow during ground ops, or maybe issues with where ice being slung from the prop blades impacts other structure. But I am wondering if there is a more general aerodynamic principle which drives the rotation direction decision.

Most twin-engine aircraft with counter-rotating propellers have the rotation set up so that the propellers are rotating inward towards the center at the tops of the propeller arc.

This configuration reduces the P-Factor effect at slow speed high angles of attack, and eliminates the "critical" engine that is present on multi-engine aircraft where both engines rotate in the same direction.

Conventional Multi engine propeller aircraft (both clockwise rotation)

The original XP-38 (X=Experimental) had "inward" counter rotating propellers but only flew a few times before it was destroyed in a crash.

There were some tail buffeting problems identified with the XP-38. While trying to solve the tail buffeting problems, various wind tunnel tests were conducted. Some of these tests were done with "outward" rotating propellers.

These tests showed that "outward" rotating propellers did not reduce tail buffeting BUT they did reduce power on/power off pitching moments, and therefore made for a more stable gun platform.

  "The P-38 props rotate in the direction they do for the simple reason it reduced the power on/off pitching moment, thus making for a more stable gun platform" - Kelly Johnson, P-38 designer.

The tail buffeting was eventually solved by fitting large leading edge fillets at the wing/fuselage interface.

The YP-38 (Y=Prototype) and most subsequent versions of the P-38 retained the "outward" counter rotating propellers. This in effect made both engines "critical", but combat performance was more important that low speed performance.

So while most aircraft with counter rotating propellers have "inward" rotation, a few do have "outward" rotation to gain an operational advantage.


How could it be possible to fully prevent wing tip vortex formation? I know that winglets and swept wings are ways to reduce the vortex that are currently in use on many aircraft. Are there any aircraft design concepts out there that completely eliminate the vortex effect?

Wingtip vortices are an unavoidable side effect of producing lift with an airfoil of finite length (thus having "wingtips"). The wing is designed first to have relatively high pressure underneath the wing and lower pressure above it. Second, air passing over the top of the airfoil is directed downwards as it leaves the wing (thus "pulling" the wing upwards by Newton's Third Law). These two characteristics of an airfoil combine to make air around the wingtip want to "spin"; high-pressure air below the wing will "leak" upwards over the wingtip, then be directed back downwards along with the rest of the air, creating the wingtip vortex:

Reducing the pressure differential between air above and below the wing will by definition reduce lift, because it is this pressure differential producing lift. By the same token, reducing the "downwash" off the back of the wing will reduce lift because the force creating the downwash is also lifting the wing. Therefore, conventional wings will produce wingtip vortices by definition.

Theoretical ways to reduce this vortex include:

Make it harder for air to "leak" upward over the wingtip. This is the principle behind the "winglets" you see on many airliners; they prevent air iunderneath the wing being able to move over the top of it, thus reducing the severity of the rotation of the vortex (which reduces drag, which saves the airlines fuel):

Even small aircraft, like this PiperSport light sport, often have little blended winglets to reduce vortex drag, saving as much available power as possible from the limited-horsepower engines of this class:

The A-10's wingtip has a similar idea implemented the opposite way; a slight downward curve to the wingtip holds the "cushion" of higher-pressure air under the wing, reducing the amount of leakage around the wingtip, which lowers the wing's stall speed and also reduces tip vortices:

Don't have a wingtip. "Nonplanar" wing designs, including ring wings, reduce (but do not eliminate) vortex drag compared to conventional wing planforms simply by not providing a single border between lifting and nonlifting surfaces:

This is a concept drawing, but the idea of a tipless closed-loop wing has been incorporated into production small planes, like this Belarussian small single:

Vortex drag is not totally eliminated because there is still a downwash behind the wings relative to the undisturbed air to either side of the plane, but the intensity of the vortex (and thus the energy lost producing it which counts as drag) is reduced considerably.
Reduce the pressure differential at the wingtip. This is a major way that swept, delta and double-delta wing planforms reduce tip vortices. Very simply, most modern wings on high-speed or high-performance jets have a smaller chord length and a thinner cross-section at the wingtip than the wing root. This provides less lift at the wingtip (and the wingtip stalls more easily and thus tends to stall first) than a straight wing with a relatively constant cross-section, but the reduction in pressure differential and downwash right at the wingtip reduces the two primary contributors to wingtip vortices:


What is the origin of the waypoint CLAWW and PAHTI(New England region)? I'm the reading the book "Sayfaring".
There are two waypoints I don't get the origins in the sentences.

1) CLAWW

"Boston has lifted a particularly intricate constellation of itself
into the ether above New England. There is PLGRM, for the
region’s history; CHWDH, LBSTA and CLAWW for its food"

2) PAHTI

"Even the region’s speech –WIKID, followed by PAHTI – seems to be mapped

Read it as "wicked party" and Boston is famous for sea food, including crab claws.  Chowder, lobster and claws.


Relation between Squawk code and ICAO adress I can see in ADS-B downlink format 5 or 21, it is possible to answer squawk code. I am wondering how ATC will know which squawk  code is coming from which aircraft? There is no possibility to encode ICAO address in downlink format 5 or 21 . However, address parity finally result a uncontrollable ICAO address.

The ICAO 24-bit aircraft address is encoded in every ADS-B (Downlink Format = 17) message. It is the primary means of associating messages to the same aircraft in ADS-B.
What you have in your question is not an ADS-B message but a surveillance identity reply (DF = 5). This is the reply to a Mode S radar interrogation. The Mode S radar already knew the 24-bit address of the aircraft when it asked the transponder to send a short (DF = 5) or long (DF = 21) identify reply.
The Mode S radar verifies the aircraft address during the parity check and reports the 24 bit address, squawk code, azimuth, range and additional information to the ATC surveillance data processing system.
The air traffic controllers do not use the 24 bit address; this is only used in the data processing. The air traffic controllers see the position of the aircraft on their display, with a label containing the squawk code and other information.


What permits are needed to operate a human-flying drone in the United States? Casey in Finland.

If Casey Neistat were to be flown with the human-flying drone in the United States, what licenses / permits would be required from the FAA to make it legal?

All aircraft categories in the FAA assume that the pilot is inside the vehicle. Drones are operated remotely by an operator which is not carried in the vehicle, but drones are unmanned. Is there a regulation for "drones which carry person(s) while operated remotely by an operator"?

According to https://www.faa.gov/uas/beyond_the_basics/#55:

  To fly a UAS that weighs 55 lbs. or more, operators will need to use the existing Section 333 exemption process.

The Section 333 page has further links.  Spot checking some of the approved exemptions shows that the exempted status tends to look quite a lot like the 14 CFR 107 (sUAS) rules and include phrases like "carrying no passengers or crew", "weighing less than 55 pounds including payload".

As far as pilot certification would be concerned, exemption 11422 (which is one I spot-checked with) says:

  Under this grant of exemption, a PIC must hold either an airline transport,
  commercial, private, recreational, or sport pilot certificate.  The PIC must also hold a current FAA airman medical certificate or a valid U.S. driver’s license issued by a state, the District of Columbia, Puerto Rico, a territory, a possession, or the Federal government.  The PIC must also meet the flight review requirements specified in 14 CFR §61.56 in an aircraft in which the PIC is rated on his or her pilot certificate.

So, the FAA could decide to issue an exemption under section 333 for such a flight, and declare whatever limitations they wanted (or, of course, reject it outright).  If approved, I'd expect it to come with limitations like:

Must adhere to 14 CFR 107, treating the flight as an sUAS flight even though it exceeds the sUAS maximum weight.
The PIC must be certificated for Remote Pilot (sUAS) or hold an airline transport or commercial certificate with a corresponding class 2 medical and valid government-issued photo ID.

(Every other restriction I could think of is already part of 14 CFR 107, and the carried human would probably be treated equal to a wing walker... and I can't dig up any extra restrictions regarding them)


What is a transmit-only frequency? I found the above in the Jeppesen Airport Chart Legend.

What would be an example of a transmit-only frequency? Is it related to Flight Service Stations? If so, how?

Where can I find an example for transmit-only frequency on a chart?

(skyvector.com) Chart Supplement for Redding Municipal Airport.

An example of transmit-only frequency would be a VOR frequency used for a remote communications outlet (RCO). From the example above, 108.4T is a transmit-only frequency using the voice channel of the VOR.

How to use: How do I contact Flight Service while in flight?


Why does the U-2 use a chase car when landing? Why does the Lockheed Martin U-2 spy plane need a car behind it during landing? Is that to help the pilot in case of excursion off the runway?

It is to help the pilot land the aircraft (the chase cars are also used during takeoff). The U2 is considered notoriously difficult to fly in low altitudes- a tradeoff in an aircraft optimized for very high altitude flight:

Because the U-2 was so specialized, it was amazingly difficult to fly. ... the lower the U-2 flew, the heavier its unassisted controls got, to the point where pilots literally had to brute-force the plane around during take-off and landing.
... landings were the biggest problem. The replacement for Johnson's cart-and-skid ground system was a compact setup — two centrally located landing gear in the fuselage and one detachable "pogo" gear on each wing — that turned the U-2 into little more than a 30,000-pound bicycle. Because of the high-lift wings, pilots didn't so much land the plane as fly it really close to the ground (usually about two feet), stall it, and then fall out of the sky.

The decreased visibility of the pilots, combined with the highly efficient wings and bicycle landing gear meant that unassisted landings are difficult (but certainly possible, as has been demonstrated)- thus the chase cars.
On of the chase car drivers (themselves U2 pilots) describes the drill:

... the objective is ensuring that the pilot safely landing the aircraft... calling him down to two feet... holding them off there and then the plane will just kind of settle down on the ground.


Why is thrust vectoring not used on commercial jets? Is there a particular reason for which thrust vectoring is not used in airliners as it is with military aircraft besides weight and complexity factors?

I understand that on military aircraft maneuverability is a core component but, by implementing this technique also on commercial airliners, wouldn't there be any benefit? For example one thing that comes into my mind would be reduction of stress on the tail of an aircraft at high speed/high altitude turns, thus potentially reducing maintenance.

Another option would be increased safety, whereas if maneuverability would be compromised by loss of the tail of the plane (for example American Airlines 587), you would still have some sort of control, even though reduced, on the plane with directional thrust.

Thrust vectoring is for flying outside the "normal" envelope (which is characterized by attached flow). Airliners should really never leave this envelope, so they are perfectly fine with regular control surfaces.

If you want to add thrust vectoring, it would make most sense if the engines are at the back of the airplane. On most airliners, it is really better to put them on and ahead of the wings, because in this location they help both with flutter damping (mass ahead of the elastic line helps) and bending relief. Putting the engine mass right where lift is created is better than carrying stresses all around the airframe, which would be the case with rear-mounted engines.

The redundancy point is valid, but it would be more helpful to have redundant control surfaces, and this is exactly what airliners have. At some point, every airplane has to come down for a landing, which requires to throttle the engines. No thrust, no control!

Most extreme case: If one tail surface breaks off, I wonder if thrust vectoring would be up to the job of trimming the aircraft even with cruise thrust. Not only have the raw forces to be sufficient, the reaction time to control setting changes has to be quick enough to suppress oscillations. I am sure, however, that thrust vectoring will certainly not suffice in all flight phases.

Thrust vectoring is perfect for situations at high angle of attack where you quickly want to point the nose of your aircraft at your adversary, so you get lock-on first. This is quite different from what an airliner has to do.


What is a "sidestep landing" in an instrument approach? I have never seen a sidestep landing on an approach plate. What is a sidestep landing and when I can chose this approach?

From the AIM 5-4-19:

  5−4−19. Side−step Maneuver

  a. ATC may authorize a standard instrument approach procedure which serves either one of parallel runways that are separated by
  1,200 feet or less followed by a straight−in landing on the adjacent
  runway.

  b. Aircraft that will execute a side−step maneuver will be
  cleared for a specified approach procedure and landing on the adjacent
  parallel runway. Example, “cleared ILS runway 7 left approach,
  side−step to runway 7 right.” Pilots are expected to commence the
  side−step maneuver as soon as possible after the runway or runway
  environment is in sight. Compliance with minimum altitudes associated
  with stepdown fixes is expected even after the side−step maneuver is
  initiated.

  NOTE−
  Side−step minima are flown to a Minimum Descent
  Altitude (MDA) regardless of the approach authorized.

  c. Landing
  minimums to the adjacent runway will be based on nonprecision criteria
  and therefore higher than the precision minimums to the primary
  runway, but will normally be lower than the published circling
  minimums.


Can RVSM safely be further reduced? Since the world population shows no signs of slowing down its rapid increase, it's pretty safe to say that means we can only expect more concurrent flights as time moves forward.

Is it physically possible (with current aircraft models) to further reduce RVSM to say 500ft?

Since automatic altitude maintenance is required when flying in this airspace, I can't see why not.

(ICAO)

In cruise the wake turbulence levels off about 900 feet below the cruise level, which is just enough for another plane flying head-on 1,000 feet below to miss it or encounter the mild part of it. Encountered wake turbulence in RVSM should be reported to ATC, because the wind also affects it, and then the ATC will advise on a deviation for the remainder of your route and for the other aircraft behind you, for example.

Regarding the projected increase in travelers, new airways can be utilized, more use of free route airspace, using bigger (but not too big) planes, as well as improving the throughput of the runways using various technologies (NextGen and SESAR for example).


Who owns B- registration? China or Taiwan? Aircraft registration is unique to each aircraft. Each one begins with country code follow by numbers or characters. However wikipedia says that Taiwan and China both use prefix B. So who actually own the right to use prefix B? If two of them do not co-ordinate the use of prefix them there can be two planes of same registration in the sky. So how things work out here.
https://en.wikipedia.org/wiki/Aircraft_registration
https://en.wikipedia.org/wiki/List_of_aircraft_registration_prefixes

From your second link:

Aircraft registered in the People’s Republic of China traditionally
have had "B-" followed by four digits.
B-0000 to B-9999

Since 2018, the following registration schemes are also in use:
B-000A to B-999Z (General)
B-00A0 to B-99Z9 (General)
B-00AA to B-99ZZ (General)

And for Taiwan:

B-00000 to B-99999 after 1990s

so there won't be any confusion, one has 4 digits/characters after the dash, the other 5 digits.


What is the "off-side engine generator" on an A320? For the A320 family, is the "off-side engine generator" the same as the "emergency generator driven by the RAT"? I can't find the location of the "off-side engine generator" on the A320.

Offside simply means opposite, and it's to do with the AC bus supply priority.

For the A320 the priority is:

Onside, e.g., left engine IDG for AC BUS 1
External power
APU
Offside, e.g., right engine IDG for AC BUS 1, meaning the left engine's IDG has failed or taken offline.


How does a flying wing keep from going into a flat spin when maneuvering? How do flying wings, like the B-2 Stealth bomber, actually keep themselves from yawing out of control without a vertical stabilizer?

For the record, I assume this has to be a simple mechanics process.  Why?  Well flying wings go all the way back to the 30s.  One of the earliest (and my personal favorite) is the N-9M, which was a scale model of the XB-35, a prototype bomber for the allies during WWII.

They didn't have flight control computers back then, and the only control complaints I recall them having is that early versions had a tendency to flip over backwards when approaching stall speeds, well, that and the ground effects were pretty strong. But, no mentions of going into flat spins when going into hard maneuvers (that I recall).

So how do they control that Y axis on flying wings?  Are they perhaps more susceptible to a flat spin than a regular design (even if those risks can be kept to an acceptable minimum)?

Sweepback helps a lot, and the rest is achieved with drag devices near the wingtips.

(Source: aerospaceweb.org)
Did you notice that the B-2 has split ailerons, and they are partially opened during flight? Their drag pulls the wingtip back, and in combination with sweep the forward wing in yaw will have a longer lever arm, so the same drag produces a bigger stabilizing yawing moment.
Differential thrust is not available on gliders, and there are lots of flying wing gliders. Horten III and IV, Fauvel AV-36 and the SB-13 are some examples. The Hortens used speed brakes near the wingtips, and the SB-13 has rudders with differential deflection (70° outwards, 20° inwards) on its winglets to increase the yawing moment.
Directional control is no problem with flying wings, even though directional stability becomes weak at high speed when induced drag is low. Flutter and a low $c_{L max}$ are the real drawbacks. Ground handling, landing characteristics and payload space are others, but can be overcome somewhat.
And flat spins are not possible with flying wings. Their spin modes are all fairly steep due to the lack of a strong inertial moment from the lengthwise distribution of masses.


How were pilots selected and trained before the introduction of simulators? I wonder, how were the pilots selected and trained before simulators were introduced.

The simulators allowed to test the coordination and reaction time of candidates. And they allowed the students to learn to manipulate the planes before they actually flew. And to train the pilots to work in different situations.

So how was it before the simulators?

Almost every pilot learns to fly in an actual aircraft, this is one of the reasons all trainers have dual controls.

My first day out, ever, was in an actual plane, behind real controls, in the sky. No sim-time prior to that. The instructor talked me though takeoff and maneuvers (keeping an eye on everything and operating the rudder). All he did was radio coms, navigation and the approach/landing.

As for whats common:

The vast majority of American WWII pilots are said to have learned to fly in the piper J-3 Cub

The Boeing PT-17 Steraman and AT-11 Kansan were also popular.

In GA where everyone else gets their start the Piper Cherokee and Cessna 150 or 172 rule supreme.

Of course these planes are slow, benign and fairly safe by aviation standards. But what if you have some super fast, one of a kind, high flying, awesome supersonic jet gadget. You surely cant afford to ruin such a plane but still need to train pilots. Well in that case you just build yourself a dual cockpit custom trainer....

Even the space shuttle had a real flying trainer designed to mimic its approach characteristics.

All that being said simulators can be a big help if used properly.


What is the difference between the ILS Critical Area and the ILS Sensitive Area? What's the difference between the ILS Critical Area vs ILS Sensitive Area?

I'm getting multiple conflicting opinions online.

e.g. I can't decipher from this set of definitions how exactly they differ:

  The ILS critical area is an area of defined dimensions about the
  localizer and glide path antennas where vehicles, including aircraft,
  are excluded during all ILS operations. The critical area is protected
  because the presence of vehicles and/or aircraft inside its boundaries
  will cause unacceptable disturbance to the ILS signal-in-space

vs

  The ILS sensitive area is an area extending beyond the critical area
  where the parking and/or movement of vehicles, including aircraft, is
  controlled to prevent the possibility of unacceptable interference to
  the ILS signal during ILS operations. The sensitive area is protected
  against interference caused by large moving objects outside the
  critical area but still normally within the airfield boundary.

All I can grok is that the critical area seems some subset of the sensitive area?

Do I take this to mean no vehicles are allowed in critical area but some smaller vehicles may be allowed in the sensitive area?

Basically, yes- critical area is a subset of the sensitive area. However, the terms 'sensitive' and critical' are used interchangeably in many contexts. ICAO itself acknowledges this in the same section (ICAO Annex 10 Volume I Attachment C):

  Note 1.— The objective of defining critical and sensitive areas is to afford adequate protection to the ILS. The manner in which the terminology is applied may vary between States. In some States, the term “critical area” is also used to describe the area that is referred to herein as the sensitive area.

The determination of the critical and sensitive areas depends on the actual airport and the system in operation. The operator/regulator may simply include the are in critical list if they suspect any interference. For example, Transport Canada says:

  Actual critical areas can be defined only by experimentation and experience. When any portion of a designated sensitive area becomes suspect as a likely source of interference, that portion must be included as part of the critical area.

The main difference appears between the critical and sensitive areas appear to be that the size of the critical area is fixed (for a localizer and glide path antenna in an airport) while that of the sensitive area varies with the category of ILS and the aircraft type. In fact, the introduction of A380 led to a reassesment of ILS protection areas. From Volume I:

  2.1.9.3 The size of the sensitive area depends on a number of factors including the type of ILS antenna, the topography, and the size and orientation of man-made objects, including large aircraft and vehicles. ... . Because of the greater potential of the larger types of aircraft for disturbing ILS signals, the sensitive areas for these aircraft
  extend a considerable distance beyond the critical areas.

Image from ICAO Annex 10 Volume I Attachment C

In operational sense, in critical areas, all the vehicle and aircraft movement is prohibited, while in sensitive areas, the prohibition is limited.

  To protect the critical area, it is necessary to normally prohibit all entry of vehicles and the taxiing or parking of aircraft within this area during all ILS operations. ... With respect to sensitive areas, it may be necessary to exclude some or all moving traffic depending on interference potential and category of operation.


Does official source of data about air routes exists? I'm interested in the information about air routes of all the world. I need information with following features:

it must be official (not stolen, without violating any license);
it should be in digital form;
it should be in WGS84;
it should cover all of the world;
it should be free (no payment);
it shouldn't be detailed (just main routes);
it shouldn't be actual (current), one or two years outdated is appropriate.

I've realised that some kind of this information is published by ICAO at the AIP, but I can't find it.

So my question is: whether such information is available and where I can find it?

Such information is not available, for free, on a world wide level.

If you are willing to spend some money, you should have a look at Navigraph, which provides such information on a world wide level, for hobby use.

However, most countries now make their AIP publically available on the internet. Simply search for "[country name] AIP" to look up an AIP for a specific country.

In any AIP, you want to look at part 3 of the ENR section. Usually ENR 3.1, ENR 3.2 or ENR 3.3. Here is an example of from AIP Denmark: AIP Denmark ENR 3.3 - RNAV routes

This information is digital, official, up to date, free and in WGS84 format. However, you will have to look it up for every country.

If you are looking for a visual overview of airways and RNAV routes in Europe, a good place to start is the Eurocontrol regional charts.

You should also check out SkyVector


Constant TAS versus constant GS: What is the influence on turning circle? Scenario

Lets imagine a 50kts wind from east.
Now lets imagine an aircraft flying at 200kts (True Air Speed) east that make a 1.15G turn -90º to north. Maintaining in all moments the given constant speed.

Now, lets imagine the same flight but with 200kts constant ground speed.

In the first case, the speed is 200kts TAS= 150kts GS, and after the turn TAS=GS=200kts
In the second case, the speed is 200kts GS = 250kts TAS, and after the turn, TAS=GS=200kts

Any mistake until now?

The question:
The question is how that influence the turning circle? In which of the two cases the turning circle is flatten/stretched and in which is circular if any? What is the approximate shape of them?

Further explanation

Considering my very weak understanding, the turning circle G depend on absolute speed (~ Ground speed), and thus, turning with a constant ground speed imply a circular turning. Which is independent of the wind. Of course, the pilot would have to accelerate/decelerate to maintain this speed.
With TAS, the real speed is variable, so in our case, I expect to see a turning circle which is horizontally flatten.

But, using a planning system, the result I observe is the reverse: the circle is constant (independent of wind, circular) on TAS and variable (dependent on wind, shape is not drawn) in GS.

Edited: TAS=GS=200kts: I just realized that it is not really true, cause the aircraft need to head slightly east to compensate the wind, so probably the TAS will be ~206 and GS 200. Even if that do not make a big difference for the question.

If you maintain a constant bank angle (30 degrees for a 1.15 g turn) and maintain constant true airspeed of 200 Knots, your path will be as shown in the chart by the yellow line.

If you maintain a constant ground speed (150 knots) and a constant acceleration 1.15, then your path will be as described by the grey line. It will be as if there is no wind, however it requires thrust variations and bank angle variations.


Why do some commercial flights start off unpressurized? In this video, the B738 starts takes off without the plane's pressurization system engaged.  The video specifically notes that the craft is being pressurized fairly soon after the takeoff has happened.

Is this because of the icing conditions they had on the ground?  Or is there another reason why it would take off unpressurized?

Screen capture for the extremely busy:

The 737 like most modern airliners (notable exception, the 787) is pressurized by bleed air, from either the engines or the APU. Drawing bleed air from the engines reduces the thrust available for takeoff.

From most common to least common, takeoff configurations are:

Engine bleeds on (supplying bleed air to the pneumatic system), APU off. This is a pressurized takeoff & generally the most common scenario.
Engine bleeds off, APU bleed supplying air to the pneumatic system. This also results in a pressurized takeoff, with more engine thrust available. Used when max thrust is desired, typically due to heavy weights, short and/or contaminated runways, close-in obstacles requiring steep climb gradients, and similar circumstances.

In the case that the APU is inoperative but taking off with the engine bleeds off is still required, you get:

Engine bleeds off, APU bleed off. This results in the unpressurized takeoff referenced in the question.  At a suitable altitude (typically 2000 to 3000 feet into the climb, a minute or two after takeoff), the engine bleeds are turned back on & the aircraft pressurizes normally.

This is uncommon, but still considered a normal procedure (not an abnormal one out of the QRH).

Edit:

Link to Pneumatic System description for the 737

Link to PDF discussing pneumatics & pressurization on the 737