On old sectional charts, what was the purpose of the domestic ADIZ regions and what was the difference between a "Defense Area" and an "Open Area"? Looking at an old US sectional chart from 1956, I noticed a few oddities around where Air Defense Identification Zones (ADIZs) were placed.
Compared to modern airspace where the US ADIZ is strictly off the coast and along the borders, there appear to have been additional land-based ADIZs dividing the country up into three parts. There was also a large ADIZ centered over Albuquerque. They also seem to have made a distinction between a "Defense Area" and an "Open Area".
What was the purpose of having an ADIZ inside the country? What's the difference between an "Open Area" and a "Defense Area"? And just what was so special about Albuquerque?

Originally they were zones to protect Americas nuclear testing areas and other key military interests. The Albuquerque area was likely there to protect Los Alamos Laboratory and other related nuclear assets of the era.
This report prepared for congress (on a slightly different topic) has some notes on this in the "History" section.
They explain an ADIZ as:

An ADIZ is a designated area of airspace over land or water within
which a country requires the immediate and positive identification,
location, and air traffic control of aircraft in the interest of the
country’s national security.

Which does not necessarily limit it to border monitoring. The modern ADIZ is large a border related zone but that was not always the case.

In 1948, the U.S. Air Force designated several offshore areas as
“active defense areas” or “defense zones.”3  From these, the first
ADIZs in the world were established in 1950, under an Executive Order
directing the Secretary of Commerce to exercise security control over
aircraft.4 Various defense zones were redesignated as ADIZs.5  The
present-day U.S. ADIZs, including the contiguous U.S. ADIZ, the
Alaska ADIZ, the Guam ADIZ, and the Hawaii ADIZ, are codified in Title
14, Part 99, of the Code of Federal Regulations, along with the
procedural requirements for flights operating in these designated
areas. They are predominantly located over water and typically do not
extend to the shore, leaving a narrow strip of sovereign airspace
parallel to the coastline that is not within the ADIZ.

The citation for the above paragraph explains it better (bolded for emphisis)

At the time, U.S. ADIZs included offshore regions stretching from
Maine to North Carolina in the Atlantic, and from the U.S.-Canada
border to waters off the Baja California in the Pacific. Additionally,
several over-land areas were designated as ADIZs, mostly along the
west coast and south of the U.S.-Canada border, but also above
interior lands around Albuquerque, NM, and Knoxville, TN, as part of
national security efforts to protect key nuclear research facilities
in these regions. The over-land ADIZs no longer exist. For a time,
portions of the special flight rules area (SFRA) around Washington,
DC, established after the 9/11 attacks in 2001, were designated as an
ADIZ, but this airspace is no longer referred to as such.

This map just pre dates the deployment of the Distant Early Warning System in the north and various Nike Missile Sites that were put on either coast but you can see how the American costal strategy was shaping up in a post WWII country which is interesting.
As radar became more prevalent at local facilities (think class B/C/D approach control as well as regional centers) the need for specialized interior radar was far less and those duties could be off loaded to the local facilities


What is "scintillation" and are "qualified pilots" aware of it? This answer to Has great eyesight been necessary for astronomers? mentions Astronomer Jocelyn Bell Burnell's recounting of a likely first visual observation of a pulsar. This can be found for example in Nature's Air force had early warning of pulsars

Wikipedia's Crab Pulsar includes this passage:

  Jocelyn Bell Burnell, who co-discovered the first pulsar PSR B1919+21 in 1967, relates that in the late 1950s a woman viewed the Crab Nebula source at the University of Chicago's telescope, then open to the public, and noted that it appeared to be flashing. The astronomer she spoke to, Elliot Moore, disregarded the effect as scintillation, despite the woman's protestation that as a qualified pilot she understood scintillation and this was something else. Bell Burnell notes that the 30 Hz frequency of the Crab Nebula optical pulsar is difficult for many people to see.

Question: What might "scintillation" be in this context, and are "qualified pilots" generally aware of it?

"Scintillation" is the flickering of starlight due to the turbulence in the Earth's atmosphere through which the light passes. It is also known as stars "twinkling."

The current version of the PHAK discusses a number of nighttime optical illusions, but not scintillation. It does discuss, however, autokinesis, which is a less well-known but similar illusion. I don't think it would be outrageous for a pilot who knows about scintillation to connect the two. After all, a pilot can discern the difference between a ground-based light source and a star because the star will scintillate and the ground-based light source will not. Maybe the PHAK should include it, given its interest in identifying false horizons created by lines of ground lights.

Someone knowledgable who observed the visual flicker of the Crab Pulsar would be able to easily tell that it wasn't scintillating because scintillation is random, whereas pulsar flickers are more precisely timed than atomic clocks.


How do the vortices of a fixed wing and horizontal stabilizer interact? What interaction of vortices between the fixed wing and horizontal stabilizer?

How do the vortices affect the flow of the horizontal stabilizer upon leaving the wing?

when will the downwash effort affect the flow, apart from not having clean-flow?

Does the downwash decrease dynamic pressure the reduce the lift?

Does the Airflow be affected after leaving the wing?

The vortices coming off the ends of the wing are outside the width of the stabilator or stabilizer/elevator, thus there would be little interaction.

In my plane for example, the wings are 35 feet 6 inches wide, the stabilator only 11 feet 10 inches.
Thus the end of the wing is 17.25 feet from centerline, the end of the stabilator at 5.9 feet, thus 11+ feet of clearance.


Does a "climb and maintain" instruction override a "climb via the SID" one? This question pertains to the SNSHN THREE SID out of Ontario, CA (KONT).

Let's say I was originally cleared to "climb via the SNSHN departure except maintain 8,000". Then the clearance is amended after departure to "climb and maintain FL 240".

My question is, am I still required to cross NLAND at or above 14,000, as depicted in the SID?

If the controller issues a "climb via" SID with an interim altitude of 8,000 and then subsequently amends the altitude and states:

"Climb via SID and maintain Flight Level 240" then the altitude crossing restriction to cross INLAND at or above 14,000 still applies.

However, if the controller does not use the words "Climb Via," and instead states:

Climb and maintain Flight Level 240" then the altitude crossing restriction to cross INLAND at or above 14,000 is cancelled.

The words "Climb Via" are essentially the same as "comply with all SID restrictions."  If a new altitude is issued without the "Climb Via" verbiage, then (unless the altitude crossing restrictions are restated) climb unrestricted to the new altitude is expected.

From FAA JO Order 7110.65W, para. 4-5-6 and 4-5-7 (Air Traffic Controller's handbook):

  6.
  When an aircraft has been issued an interim
  altitude  and  after  departure  ATC  can  subsequently
  clear the aircraft to climb to the original top altitude
  published  in  the  SID  instruct  aircraft  to  “climb  via
  SID.” When issuing a new altitude and compliance
  with  published  restrictions  is  still  required  instruct
  aircraft to
  “climb via SID
  except maintain (altitude).”

  PHRASEOLOGY
  −
  CLIMB VIA SID.
  CLIMB VIA SID except maintain (altitude).

  EXAMPLE
  −
  1. (An aircraft was issued the T
  eddd One departure, “climb
  via  SID”  in  the  IFR  departure  clearance.  An  interim
  altitude of 10,000 was issued instead of the published top
  altitude of FL
  230; after departure ATC is able to issue the
  published top altitude): “Climb via SID.”
  NOTE
  −
  In Example 1, the air
  craft will track laterally and vertically
  on the Teddd One departure and initially climb to 10,000;
  Once  re-issued  the  “climb  via”  clearance  the  interim
  altitude is
  cancelled aircraft
   will continue climb to FL230
  while complying with published restrictions.
  EXAMPLE
  −
  2. (Using Example 1, after departure ATC is able to issue
  an altitude higher than the published top altitude):  “Climb
  via SID except maintain flight level two six zero.”
  NOTE
  −
  In Example 2, the air
  craft will track laterally and vertically
  on the Teddd One departure and initially climb to 10,000;
  once issued “climb via” clearance to FL260 the aircraft
  will  continue  climb  while  complying  with  published
  restrictions.

  NOTE

  1.
  Considering the principle that the last ATC clearance
  issued has precedence over the previous, the phraseology
  “maintain  (altitude)”  alone  cancels  previously  issued
  altitude  restrictions,  including  SID/STAR  altitude
  restrictions  unless  they  are  restated  or  modified,  and
  authorizes  an  unrestricted  climb  or  descent.  Speed
  restrictions r
  emain in effect unless
  the controller explicitly
  cancels the speed restrictions.
  2.
  Restate
  “climb/descend via” and then use “except” or
  “except  maintain”  phraseology  to  modify  published
  restrictions  or  assign  a  new  top/bottom  altitude.  Use
  “resume” phraseology with “maintain” to rejoin a route
  and assign a new altitude
  where
  compliance with published
  altitude restrictions is not required.

[all preceding emphasis is mine]

Also see AIM para. 5-2-8.

Lastly, here is some good guidance regarding "Climb/Descend Via"
Climb/Descend Via FAQ


How does a supersonic jet engine differ from a subsonic jet engine? All jet engines have the same method of air flowing into the engine, which is compressed and ignited.

What can engine designers do to make an engine design create more thrust? For example, what is different when comparing the Olympus engines on the supersonic Concorde to the CFM56 engines on a 737?

Thrust is air mass flow multiplied by the speed difference between flight and nozzle speed of the engine. To increase thrust, subsonic engines try to maximize mass flow (by increasing the bypass ratio) while supersonic engines rely more on increasing the nozzle speed (by using afterburners).

The core engines do not differ much - after all, the intake will make sure that air reaches the engine at a speed of Mach 0.4 to 0.5, regardless of flight speed. The main difference is in their bypass ratio. The slower the design speed, the bigger the bypass ratio may become. At very low speed, the ungeared, shrouded fan is exchanged for a geared, free spinning propeller, in other words, the jet changes to a turboprop. The intake and nozzle, however, are very different indeed.

The optimum bypass ratio changes continuously, but since the drag coefficient drops after crossing Mach 1, airplanes are either designed for a maximum Mach number of 0.9 or less, or 1.6 and above. The corresponding bypass ratios today are up to 12 for subsonic engines, and less than 1 for supersonic engines. This produces a sharp boundary at the speed of sound, and many military engines designed for supersonic flight lost their afterburners and were fitted with a big fan to become the engines for subsonic transport aircraft. Examples are:

The Pratt & Whitney J57 turbojet (installed in the F-100 and F-102 fighters, among others) became the JT-3D turbofan which powered the Boeing 707 or the DC-8.
The core of the General Electric F110 (installed in the F-15 and F-16 fighters, among others) became the CFM-56 turbofan which is used in the Boeing 737 or the Airbus A320.

The differences between sub- and supersonic engines grow bigger the more you move away from their core. High-pressure compressor, combustion chamber and high pressure turbine look and work the same, but the low pressure compressor of subsonic engines swallows a lot more air and has a much bigger diameter. Supersonic engines in turn mostly have an afterburner. The biggest difference, however, are the intakes (large pitot intake with blunt lips for subsonic aircraft versus adjustable spike or ramp intakes for supersonic flight) and the nozzle (fixed for subsonic flight versus a complex, adjustable convergent-divergent nozzle for supersonic flight). This is due to the very different air speeds and the much higher exit velocities required for supersonic flight.


Is there a way to avoid the effects of turbulence? I am trying to determine the plausibility of a larger, broad question using a modified plane equipped with a modified E-fan and external electric ultra light weight rail. The power would be collected from the rail by Laser Induced Plasma Channel. The problem is to stay a safe 3-7 meters from the sky rail during flight because of turbulence.

Is there a plane or guidance system that can ensure a smooth and straight line of flight without any shift in position because of turbulence?

There are currently no production anti-turbulence devices or control systems that I know of. It should however be noted that auto-pilot (to an extent) will hold a course in turbulence within a margin but will or may constantly be auto-correcting.  However there is some research going on at RMIT into the matter and it looks like they have at least a small working prototype. The issue you have in the matter is positive control, to avoid turbulence and/or be ready to correct for it before it happens you need to be able to see it/predict it ahead of time. There is some more research going into Laser based Radar systems for detecting clear air turbulence but as far as I know nothing has made it to market. So yes it may be/is almost possible but the systems are still in research and development at best.


Why is the autopilot called "George?" The autopilot of an airplane is frequently referred to as "George" (for example, in this answer). When did this nickname enter common usage, and what is its origin? Please cite sources if possible!

The first "practical" autopilot was invented by George DeBeeson (the patent can be found here, updated here) - This seems to be the most likely reason for the informal name "George" for the autopilot system on aircraft.

Autopilots are also sometimes called "Otto" (as in Otto the Autopilot from Airplane!, and our very own chat bot, but this seems to be less common than "George".


Is it legal to fly GA aircraft in temperatures above what is shown on the performance charts? Most Cessna aircraft have performance charts the range from 0 to 40 Celsius. I've had a CFI tell me that the FARs prohibit flight if the OAT exceeds 40C or whatever is shown on the performance charts. Is that a true statement? I have not found anything in Part 91 that addresses this.

Yes, it is legal, disregarding any catch-alls such as 91.13 reckless operation or ones pertaining to pre-flight planning data like takeoff distance.

It is simply left to the pilot's good judgement for a go/no go decision depending on whether or not the flight can be completed safely.

Edit: Re-reading this answer much later, I would like to emphasize, "disregarding any catch-alls".

With regard to the catch-alls such as 91.13, this could very easily be considered illegal, but no rule with a statement clearly identifying taking off with temperatures higher than those on the charts as a prohibited action exists to my knowledge.  Do not do it.


What is the approximate range of the Pelegrin Tarragon? I recently read about the Pelegrin Tarragon ultralight aircraft made in my country, and got interested in it.

Is it possible to have a reasonable estimate of the average distance you could cover in such plane, taking into account that it has a cruising speed of 270km/h, a  96l fuel tank and the engine it uses (a single Rotax 912ULS) is listed as using 15l/h at 5500rpm (75% power)?

Unfortunately, the manufacturer's page doesn't list any max distance or indeed any technical specs, and Wikipedia entry doesn't list much more either

According to the manufacturer, it has a range of 1,300km.


What is the tolerance of SSR against signal frequency shifts? I know that the Secondary surveillance radar (SSR) interrogates at 1030MHz, and the reply is at 1090MHz.

What happens if the radio signal sent to the plane is less than/more than 1030MHz?
Also what happens if the radio signal with which the plane responds is less than/ more than 1090MHz?

With respect to the radar frequency drift, I am afraid you are asking an impossible question, the interrogation frequency is continuously auto monitored, any drift tendance is electronically prevented. However should this occurs, the aircraft transponder has a sharp filter limited just to light Doppler effect, beyond that the transponder will not answer to the received signal.

I do understand a drift in the aircraft transponder, that is a frequency drift in the aircraft transponder answer, that’s not a problem; even though it is quartz generated, that is nearly impossible to drift, the ground radar accepts a frequency drift of + or - .5MHz, beyond that the received signal by the radar could be interpreted as a response to a lobesides  signal received by the aircraft transponder, and may get mutually eliminated.

However the radar memorizes all present mode A received information, if the received signal concerns an aircraft identification not received previously, the radar will accept the signal and not reject it as being a response to a lobesides signal.

If the frequency drift is important, this is equivalent to having lost the transponder. The total loss of transponder information may sometimes be mitigated by the availability of primary radar data. However, if false primary tracks appear too often, a “real” track may be considered to be fake. This is especially true when no other data is available (e.g. information from the previous sector).


Has a pilot ever been disciplined for taking a guest for a flight in a single-seat fighter aircraft? I recall reading of a spitfire pilot who was suspended for taking a member of the WAAF up for a jaunt to impress her. She supposedly sat in the pilot's lap throughout the short flight and they were caught when they landed and a member of the ground crew noticed her alighting. I specifically remember the author referred to her as "a uniformed lovely" in his recounting.
I've spent some time googling around and rummaging in my library but to no avail. Can anyone identify this specific incident (ideally the exact account) and/or have there been other incidents that are similar?

According to the book "A Spitfire Girl" the pilot's name was Flight Lieutenant Edward Gordon Brettell DFC of "Great Escape" fame, among other things, and he was court-martialed for flying his Spitfire Mark Vb of 92 Squadron to a dance with a WAAF on his lap. Squadron Leader Tony Bartley DFC helped defend him during the court-martial.
The man was a colorful character, to say the least. In one of the many references to him on the Internet I found this:

He had flown his girlfriend, a WAAF based at Tangmere, in his single
seat Spitfire to RAF Biggin Hill for a squadron party. Unfortunately
for him, the station commander who was there when they landed took a
dim view of his actions and reported him. Among the charges at his
later court martial was endangering the King's aircraft (King George
VI was then on the throne). He called upon his friend, a Battle of
Britain ace with a Hatfield-link, Anthony Charles Bartley (41816) for
help.
Tony Bartley was acting as a test pilot for Supermarine at the time.
He later revealed in his autobiography that he asked Jeffrey Quill
(Supermarine's chief test pilot) and Joseph Smith (Supermarine's chief
designer after Reginald Mitchell's death) for their help. Joe Smith
even went so far as to draw up some mathematical equations alleged to
prove the aircraft wasn't in any danger, which Bartley presented at
the court martial. Although the clinching argument was when asked by
the prosecution how he could prove it, Bartley admitted to having
committed an identical offence previously. Now faced with the prospect
of having to prosecute two badly needed officers with a war on, the
charge was dismissed. Although Gordon Brettell was transferred away
from the squadron.


What is the exact responsibility of the Landing Signal Officer on an aircraft carrier? From Youtube:

There are three LSOs apparently working at the same time, providing indications to the pilots:

What is the exact role of the LSO?
Why three? All of them holding a wave off switch.
What is the reason to have pilots guiding pilots rather than a computer?

An Landing Signal Officer (LSO) is a naval aviator with additional specialized training to better facilitate recovery operations on the ship.  LSOs provide guidance for aircraft making approaches to the carrier.  They monitor the approach and remain in contact with the pilot during the approach by radio.

Carrier approaches or 'passes at the boat', while analogous in technique to an approach to land at a terrestrial airport, require much more precision and have far less margin for error due to the landing area's small size (75 x 600ft). And the requirement that the jet must impact the deck on speed and on angle of attack within a small area to snag an arrester wire and trap successfully makes this even more difficult.

The Navy has adopted this policy of the landing signal officer as well trained LSOs can quickly dissect problems with the approach and alert the pilot to correct prior to the pilot even becoming aware that there is a problem developing.  Particularly insidious errors like settling in the groove or settling at the ramp leading to a dangerous rampstrike or liquid landing can be spotted by the LSO before the pilot even realizes its happening.

In addition to forcing each pilot to perform at their best, the LSO grades each pass.  Multiple LSOs observe the approach and comment on the elements of the approach e.g. Long in the Groove, a little fast, low at the ramp, etc.  These are used to assign the following grades to a pass.

OK UNDERLINE - perfect pass, only awarded in extreme circumstances or
emergencies. Worth 5 points.
OK - excellent approach. On lineup, speed and glidepath with minimal
deviations, each corrected for quickly.  Hook snagged the 3-wire.
This is the best grade assigned for normal operations. Worth 4 points.
(OK) - A fair pass, exaggerated deviations with delayed corrections,
but approach was safe and conducted properly.  Worth 3 points
OK-BOLTER - an an OK or (OK) pass where the tailhook did not snag a
cross deck pendant.  Worth 2.5 points.
NO GRADE - Approach was safe but had gross deviations and
unacceptable corrections. Worth 2 points
WAVEOFF - Approach terminated, either by the LSO or the pilot for a
variety of unsafe reasons e.g. foul deck, PIO, etc.  worth 1 point.
CUT PASS - Unsafe approach attempted by the pilot, generally after
refusing to comply with a waveoff instruction.  If you survive it,
you can probably expect to have your wings clipped in a Field Naval
Aviator Evaluation Board.  Worth 0 points.

Grades do matter.  A single bad landing or a bolter will get you a razzing by your squadron mates; habitual bad landings and low grades will get you a FNAEB and most likely reassignment to flying helos or to shore based aircraft.

At least four LSOs will be on hand to observe and grade landings.  This 'Wave Team' will consist of a Controlling LSO, who monitors glideslope and speed, ultimately assigning the grade, a Backup LSO, generally more senior than the Controlling LSO who monitors lineup and assists with grading, and a Deck Status LSO, who monitors the condition of the deck in order to provide a waveoff alert to both the Controlling and Backup LSOs.  A fourth LSO, the Airwing LSO 'Paddles CAG' will be on hand to observe and supervise the whole operation and mentoring junior level LSOs.  There are two Paddles CAGs on every cruise and at least one is on the platform for every recovery.

In the photo above you have a group of LSOs observing approaches during a recovery.  The wired wands that two of them hold are controllers for the waveoff and cut lights on the IFLOLS optical landing aid system to the left of the landing area.  These give visual cues of mandatory instructions from the LSO for a waveoff or for the pilot to cut their engines on the approach.  Each LSO is noting where the aircraft was during the approach vs where it should have been to get a consensus as to what grade and comments to assign to an approach.


How old is too old to become a pilot? What is the highest age at which you can decide to become a pilot for a major airline, a pilot for a cargo airline, or a private pilot?

I'd like to know for Canada or France mainly. But I wonder whether these countries will have rules that are too different from the US and EU.

First up, commercial pilots (both major airlines and cargo airlines): It depends on the country and airline, but the retirement age for a pilot is generally 65 in most countries, and almost always somewhere between 55 (e.g. British Airways) and 65 (standard in much of the U.S.)

There is no set last age at which you could be recruited, so in theory it's just before those ages, but in practice you're unlikely to be hired by a company if you can't work there for at least 5 years.

If you're not yet a qualified pilot, though, you'd have to account for this time too (no company is going to hire you and train you just in time to retire). In practice, therefore, the likely realistic age is at least 10 years prior to the retirement age for the country/company in question, and likely 15.

And if we move into pure conjecture for a moment, I'd hazard that you'd find it quite hard to find a company willing to take on an untrained pilot much after their early-mid 40s.

As for a private pilot: As long as you can pass the medical you can fly and, indeed, learn to fly, at any age. There's no maximum age, although as you'd expect most (but certainly not all) people start to struggle with passing the medical sometime in their 70s. By 80, there aren't too many pilots still flying around.


What is the difference between a glider and a sailplane? The words "glider" and "sailplane" seem to refer to similar or the same type of aircraft. In particular, the Wikipedia articles "Glider (aircraft)" and "Glider (sailplane)" seem to be describing the same kind of aircraft.

What is difference between a glider and a sailplane, if any?

The sailplane article is focused around sport and recreational planes. The aircraft article describes a wide variety of aircraft, not simply planes, like hang gliding and paragliding.

Which makes sense - one is about aircraft, so it has the aircraft moniker. The other is specifically about planes, which are a subset of aircraft, and thus have the sailplane moniker.

There was an idea of merging them in 2011, but it failed.


What are the differences between a GPS coupled autopilot and a GPSS autopilot? I'm trying to understand the differences here between an autopilot that is "coupled" into a GPS/NavCom like a Garmin 530W and what GPSS and altitude hold (like in an S-TEC 50 autopilot) have to do with this. Can anyone explain this to me? Maybe there is no difference, I really need this explained.

Pugz provided some very good information back on September 29th.  As I recently installed a Garmin GTN 650 and add S-TEC GPSS to my 35 year old S-TEC 60-2 autopilot I thought I might respond also.  As I did this installation myself I am quite familiar with the wiring involved which helps in understanding how the autopilot responds so differently to GPSS (GPS Roll Steering) than it does to the CDI (Course Deviation Indicator).  First we need to understand that after installing GPSS the autopilot has two completely different interfaces.  When in NAV mode the autopilot responds to the CDI for lateral guidance (and the CDI glide slope if the autopilot has that capability like my 60-2 does.)  When in HDG mode the autopilot would normally respond to the Heading Bug on the Directional Gyro but if GPSS is installed the autopilot actually has two separate functions while in HDG mode:  1) Follow the HDG bug on the DG; 2) Follow the GPS Roll Steering commands that are provided by the GPS via ARINC 429 output that is routed to the autopilot GPSS module and converted into Heading Commands as if the HDG bug were providing them.  In order to implement this the GPSS module has a switch to change from HDG mode to GPSS mode.  As far as the autopilot is concerned he is just getting heading commands from a HDG bug on the directional gyro.  The autopilot has no idea that he is being driven buy the GPS while in GPSS mode.  Just imagine that a very skilled pilot is operating the HGD bug on the DG and the pilot knows exactly when and how much heading change to make in order to turn smoothly on the next route segment or intercept that route segment if off course. This is exactly what is happening except that the very skilled pilot happens to be the GPS receiver.  The GPS knows exactly what heading changes need to be made and when to make them in order to guide the aircraft around a procedure turn and intercept the final approach course.

The new Garmin GI-106B CDI that I installed along with the GTN 650 still has some very important functions.  After the GPS has guided the autopilot (via GPSS) through the entire route and possibly a procedure turn course reversal and intercepted the final approach course I switch the autopilot from HDG mode to NAV mode in order to engage the autopilot on the CDI.  Now if I am flying an ILS or RNAV LPV approach the autopilot has both vertical and lateral guidance via the CDI.  The CDI will either be getting input from the ILS signal or from the GPS depending on what has has been selected on the GTN 650.  Both autopilot interfaces are still important (HDG/GPSS & CDI) but the autopilot CDI interface is used only for the final approach where vertical guidance is needed.  Most of flight is best flown with the autopilot engaged in HDG mode either flying on the actual heading bug (being vectored) or with GPSS engaged and the GPS is turning the virtual heading bug for you in order to fly the programmed route.


What does “to the numbers” mean in landing clearance? Last night I was left downwind, abeam the tower, on my second circuit of the pattern. The controller said “helicopter xyz, cleared for the option runway 24, to the numbers”. I already had been given a restriction to stay east of rwy 18; as there was an airplane in right traffic there. What is the significance of “to the numbers” in this clearance? Is he just telling me not to land long?

Typically it's phrased as "direct to the numbers" and means you should proceed in a straight line from your present position to where the runway numbers are painted on the pavement. This instruction can be issued to fixed-wing aircraft as well, but perhaps not from as wide a range of starting positions. It relieves you of any previous restrictions.


What is the behavior of false glideslope signals? I know that an ILS transmits not only the correct glideslope but also signals that can be interpreted as a false glide path. But I'm not familiar with the details of these erroneous indications. What causes "side lobe" or "mirror" false glideslopes? How many are there, where are they located, and what sensing do they cause in the aircraft? What is the typical behavior of a glideslope signal outside its usable range, or is it completely unpredictable?

The glideslope system is an analog system, and as such, it's subject to aliasing, resonances, heterodyning, and eight other technical terms I pulled out of my ass.

Maybe a diagram will help:

false glide slopes

In plain English, above the "real" glideslope, there are false glide slopes caused by your equipment locking onto the wrong phase of the signals. If you lock onto the wrong lobe, it will still take you to the runway, but at a much higher rate of descent than you planned for. Maybe steeper than you can manage safely.

Assuming the correct lobe is the bottom-most one in the system (see diagram), you'll be ok as long as you intercept it from below. If you intercept from above, you could lock onto the wrong one, and then you're gonna have a Real Bad Day.


How does Integrated Modular Avionics (IMA) improve reliability and obsolescence mitigation over the federated architecture? I've been researching this question on why IMA is more reliable, and the common answer seems to be because of the robust partitioning which is reliable and can prevent software fault propagation.
But how is it more reliable? Wouldn't sharing of hardware resources create more dependencies for these systems?
How does IMA prevent obsolescence comparing it to federated architecture?

Software faults are not included in reliability calculations because a software fault is a design issue. Developing SW in accordance with DO-178C (or predecessors) is intended to ensure that these faults are minimized. The reasoning that it's not measured as reliability is that when there is a SW fault it's not a broken box on the plane that has to be fixed, that fault is a potential failure on every aircraft that has the same system.
Swapping out a unit for a SW fault doesn't solve the problem. It's going to take a service bulletin (SB) with new SW deployed to the fleet to fix it.
So reliability is about hardware failures. Basically, parts break. Some break more often than others. The more parts you have, the more likely something will break. So making things more reliable is about minimizing parts and using the most reliable parts you can. But there are limits to what you can do. A power transistor will be less reliable than a resistor, but if you need it, you have to have it. But having one or two instead of 3 or 4 will improve reliability. I suggest a read of MIL-HDBK-217 which is the industry standard for predicting reliability.
So an IMA improves reliability by reducing the number of Line Replaceable Units (LRUs). Fewer LRUs means fewer cables, connectors, power supplies, and processors. An IMA can run multiple functions on a single processor card instead of having a dedicated unit for each function. All that means fewer parts to fail and higher reliability.
Aside from parts count, the biggest drivers of electronics failures are heat (high temps and high temperature swings) and vibration. Which is why some manufacturers perform Highly Accelerated Life Test (HALT) to identify weak points in the design early.
Nothing will solve the issue of parts obsolescence. Parts will go obsolete. It's a huge problem in aviation where products hang around for 20 or more years. An IMA does help manage the obsolescence issue. It does it by having a bunch of common processor boards. Not only do IMAs have fewer total parts, they have fewer unique parts which mean fewer parts that can go obsolete. Fewer parts going obsolete will mean less work to replace them.
It's still a complicated process to deal with, but if a part becomes non-procurable on an IMA processor board you'll need to modify the board design to use a new part. That can be a fairly straight-forward part replacement (equivalent part) to a major redesign of the circuit board. In the end, the new board has to be equivalent to the old one. That way it can be swapped out without impacting anything else (software or hardware).


Are drones used in firefighting, agriculture and pest control? Well, as the question says I am interested in the use of drones in agriculture.

Are there any drones designed to carry a tank of some chemical or water?

How large are those tanks?

I have seen that airplanes are used in agriculture and in extinguishing forest fires. They can carry tanks containing 500-2000 kg (or more) of chemicals/water.

I once worked in the UAV company, which was contracted to supply a system to identify trees. To achieve this, all you need is a good camera and an image recognition software (now to be easily written using .NET).

I have not heard about drones carrying such large amounts of chemicals, so sorry about that. In this part of the world (eastern Europe) we have enough of our own, conventional planes which do the job just fine (like PZL-106 Kruk). I guess buying drones to do that would not be economical (again I'm just speaking for my country)


Is there a website similar to FlightRadar24, but showing general aviation? As far as I am concerned, FlightRadar24 reads out transponder responses.

As most engine driven aircrafts have at least a mode C transponder, is there a site that displays such traffic as well?

Yes, and no.
FlightAware (and I believe FlightRadar24) will show General Aviation aircraft (I panned around a bit and found N802AF, a Pilatus, buzzing around over Bethlehem, Pennsylvania just now).

The catch is most of these systems are fed with ATC data, and generally only pick up flights that are either on an instrument flight plan, or which have picked up flight following & been entered into the ATC system by the controller who set up the strip.

Most light GA aircraft are flying around VFR (transponder code 1200), and don't show up on these flight tracking sites. Similarly if you're assigned a "local" transponder code rather than a system-wide one  you typically won't show up on the tracking sites either (this is often the case when you're flying VFR and go through Approach/Departure for Class C or Class B transitions/arrivals).

As more of the fleet is equipped with ADS-B this coverage may improve, as anyone can set up an ADS-B receiver and skim the traffic data. That data is currently only broadcast when a "participating aircraft" (ADS-B Out equipped) is in the area though...


If the profile of a wing pulls a plane up, why can planes fly inverted? I'm simplifying here, but every introduction to flying shows us that the profile of a wing leads to lower pressure on the upper side of the wing, hence the wing and the plane attached to it will be pulled up.

All right.

How does that explain a plane flying inverted? If the explanation was right, the plane would pull itself towards earth.

Normally, an airfoil is optimized for best lift/drag (L/D) efficiency for a certain flight profile (usually a compromise). Since most of the time for most aircraft inverted flight is not an issue, you get an airfoil that is optimized for upright flight, and this is best achieved with asymmetric geometries.

However, depending on the angle of attack any airfoil can (and will) generate "negative" lift, only much less efficiently so, than for the optimized regime,  resulting in increased drag.

The desired angle of attack for conventional aerodynamically controlled aircraft is maintained by the elevator. For symmetric airfoils commonly used for aerobatic planes, the performance for upright and inverted flight is quite similar. For 99% of all other airfoils inverted flight will work up to a certain point, depending on the available power, CG, the maximum lift and rudder forces availabe before stall. As a result, for some aircraft, a stable inverted flight cannot be maintained, while for others it could be (but with varying penalty to performance, stall speed etc). The aerodynamical possiblity of inverted flight is of course limited by structural and other considerations.


Can someone/something other than the pilot trigger the ejection seat? Let's say there was a two-person jet (take the F-15 for example) that was involved in some sort of accident in the air that incapacitated the pilot (unconscious but still alive) and left the aircraft unflyable. Could the copilot eject his fellow pilot in an attempt to save his/her life from the inevitable crash that would eventually take place?

Is there some sort of system in the aircraft that would do this automatically?

Seems like an messy problem to have. On one hand you don't want to be blasted out the windshield accidentally by your copilot or faulty computer system but on the other hand it sure would be nice to survive in the off chance you are unable to exit the plane yourself.

In a word, yes.

There is a switch which controls this and the default position is "both".  If any handle is pulled (pull down over the face or the one between your legs), then both seats fire.  If solo, the switch is turned to "solo" so that the rear seat is not ejected and the front seat gets to leave a little bit quicker.  If the switch is left on solo, and both seats are occupied, then each crew member can eject on their own.

You would also have if set to "solo" with an untrained passenger in the back.  You wouldn't want someone getting a bit excited and firing them both out of a perfectly working jet.

See this question about what happens, and this one to understand why you won't hit the canopy.

As far as I know, there is no computer controlled ejection system.  I don't think anyone would trust it to know better than the crew when it's time to bail out.


From an ATC perspective, what is an "arrival gate"? I have seen reference to ATC assigned "arrival gates".
As a passenger, an "arrival gate" is something like B12 or D37, but I'm quite certain that's not what this is referring to.
From an ATC perspective, what is a flight's "arrival gate"?

Different ATC facilities need a standardized way to manage handoff of traffic between them and make sure traffic headed in different directions doesn't conflict at the border, especially at the interface between Approach/Departure and Center where traffic is climbing or descending and therefore can't be separated by cruise altitude like en route traffic can.
The standard way this is done in the US is to establish "gates", which are fixes/waypoints on the airspace control boundary, and each is designated for arrivals (descending) or for departures (climbing).  Note that this boundary is not related to airspace class and is not charted, though you can often deduce where it is based on traffic patterns and SIDs/STARs.
Here is a conceptual diagram of the ATC gates for an airport in "south flow", meaning aircraft use the runways in the southerly direction:

Source: here
The black crosses in the corners are the arrival gates, and the white crosses on the sides are the departure gates.  When the airport is in north flow, the diagram is flipped vertically.  For airports that are oriented east-west, the diagram will be rotated 90 degrees for east or west flow.  Most traffic will use a runway on the same side as its arrival gate, but there are crossover paths for when Approach needs to rebalance traffic or some gates are closed due to severe weather.
When a gate is "open", there is an agreed maximum rate or minimum spacing that the sending facility can send aircraft through it, hence the term "metering fix" on the diagram legend.  If the sending facility exceeds this rate, the receiving facility may "close the gate" until they can sort out the resulting mess, which means the sending facility will have to slow down, reroute or hold traffic until the gate reopens.  Nobody wants that.


Why were rotary vane compressors never used in jet engines? It seems like a rotary vane compressors have ideal characteristics for a jet engine. They can generate high pressure ratios (up to maybe 10-12) compared to older axial compressors and I think they can have a high flow rate at ~90% energy efficiency. They also seem simpler to construct/cheaper than axial compressors.

I understand that modern axial compressors can generate a higher pressure ratio, but historically why didn't rotary vane compressors have a place over at least centrifugal compressors in earlier jet engines?

The most important characteristic for a jet engine compressor is high mass flow rate with light weight and if possible small size. For the same size, the flow rate can be increased by operating the compressor at higher rpm. But sliding components don't allow that.

Only the axial and centrifugal compressors can achieve sufficient flow rates, so they are used. Centrifugal compressors achieve higher pressure ratio for weight, but are larger, so they were used in many early designs and now remain in small turboprops while larger engines use axial compressors for their compactness.


Lighter than Air Aircraft Given the fact that Helium is now readily available (as compared to times when Zeppelins were around), why isn't Lighter Than Air Aviation used for cheap travel?

There are many factors that have kept Lighter Than Air Aviation out of the mainstay,

Speed: Airships are not exactly the most efficient means of moving through the air. As such their speed is far more limited than their heaver than air counterparts. For what its worth the main advantage of air travel in the modern world is speed. Its better to fly to Europe in 8 hours from New York than take a 3 week boat trip.

Size: Rigid or even Semi Rigid airships are not small vehicles. They require very large hangars to keep them protected from the elements considering they are fabric covered.

Capacity: The largest airship ever made was the Hindenburg class of airships. Coming in twice as tall and 3 times longer than a modern 747 and in its biggest configuration only able to cary 73 passengers compared to 550 for the largest configuration of the smallest 747 built. Granted the Hindenburg was not laid out like a modern airliner (it was more like a cruise ship) considering the slow speeds it would need to be that way even today.

Even with Helium being easier to come buy, its just not efficient to fly such a large craft for so few people.


Why did my transatlantic flight meander off the great circle? I recently flew commercial to Scotland and was tracking our progress on my iPad using Foreflight. I made a direct-to line that followed the great circle route, but noticed that we meandered off of it quite a bit.

The only explanation I can think of is that the crew was trying to take advantage of favorable tailwinds by following the jet stream. Is this assumption correct?

And if so, can an autopilot be programmed to follow a route dictated by a winds aloft forecast?

Most flights across the Atlantic don't fly direct great circle routes; they use the North Atlantic Track system, which is an array of "lanes" you might say, usually 60Nm apart, like one of those slot car racing places with 6 or 8 lanes of cars.  Just about everybody that can make the trip non-stop will be in the tracks at various altitudes. Off each coast are an array of fixed entry point fixes called Oceanic Entry Points as jumping on or jumping off points.

The north/south position and the precise routing of the tracks is set up each day, with the focus on eastbound traffic in the morning and westbound in the evening, and are moved up and down the take advantage of winds or weather, especially jet streams.

Jet streams flow along air mass boundaries at the top of the troposphere and change constantly as air masses move.  The tracks are set up to try to exploit or avoid them depending on whether they are favourable or not (as well as other weather systems).


Why is the clearance delivery frequency included on an approach plate? Approach plates include frequencies in the order that pilots will require them, reading from left to right.

The example below from McClellan-Palomar’s ILS or localizer/DME approach to runway 24 is a fair representative. On the far right hand side just above the overhead view is the clearance delivery frequency of 134.85.

Talking to clearance delivery prior to departure is common, but when would a pilot talk to clearance delivery on arrival? What is the purpose of including this frequency on the approach plate?

The FAA Aeronautical Chart User’s Guide: Terminal Procedure Publications in section “Bottom Briefing Strip (Communications Information),” page 15 in the revision effective 29 March 2018, explains:

The communications briefing strip contains communication information when available, in separate boxes, listed from left to right in the order that they would be used during arrival …

Clearance Delivery (CLNC DEL) frequencies; where a Control Tower does not exist or is part-time, a remoted CLNC DEL may be listed …

Relevant to the briefing strip in the question, this section adds

Note: Part-time operations will be annotated with a star. Check Chart Supplement for times of operation.

According to the Chart Supplement for McClellan-Palomar, the tower is indeed part time.

AIRPORT REMARKS: Attended 1500–0600Z‡ …
COMMUNICATIONS: …
    TOWER 118.6 (1500–0600Z‡)

Other use cases when having the clearance delivery on the approach plate is convenient are obtaining a new clearance during a brief stop and closing an IFR flight plan through clearance delivery, either local or remote, when the tower is closed.


How do I pay fees if I don't even land at the airport? So let's say I'm going from Wellesbourne (EGBW) to Coventry airport (EGBE) and at Coventry I do 1 ILS approach and go missed and return back to Wellesbourne.

Even though I never put a wheel on EGBE how will they collect the fee for doing the ILS approach? (Yeah I know... you gotta pay for an ILS approach... yuk.)

I fly in France and I had the same question. Apparently they use the aircraft registration to identify the owner. If you rented the plane from a club or renting company, the bill is going directly to them, otherwise they are going to try contacting you. If for some reason they didn't get your registration or if the airport was uncontrolled then you don't pay the fee. That's how it works over here, however I can't say if the same would apply in the UK.


Can I get a medical after having had a seizure eight years ago? In 2010 I had a seizure (as of this writing that would be 8 years ago.)

I was a CFI/Commercial Multi pilot, and the FAA took away my medical. I have never piloted since, though I've missed it tremendously.

At the time I was told that I could not obtain a medical again unless it was after 6 years being seizure free with 2 off medication. I have been off medication for 1 year and have had no problems.

I recently got a battery of tests (EKG, MRI, CAT Scan/CT Scan) etc and found no seizure activity.

Have the rules changed in nearly a decade for this? Should I see an AME or would it be a waste of time? I know there is a pilot shortage now, so I'm wondering if it has gotten more lenient.

This is something only an authorized AME can answer for you and it there is no harm in talking to one or two of them. You can find a little bit of info here and a copy of the seizure questionnaire here but that appears to be something an AME would fill out so its contents are not really useful on its own.

  At the time I was told that I could not obtain a medical again unless
  it was after 6 years being seizure free with 2 off medication. I have
  been off medication for 1 year and have had no problems.

If you were explicitly told this when the FAA pulled your medical then you still have another year to go at which time you can reapply for a medical.

In terms of regulations §67.401 Special issuance of medical certificates allows the FAA to issue medical certificates to airmen who can demonstrate "a Statement of Demonstrated Ability (SODA)" which is at the discretion of the flight surgeon. In short the regulation reads, if you can show that you are fit to fly and we agree we can issue a medical as we see fit.

What has changed quite a bit is the big overhaul that included the Basic Med requirements which do include some notes on special issuance cases that you may be able to operate under.

For you it also depends on what kind of operations you want to do since you are a CFI/Commercial. If you just want to get back in the air it may be a bit easier to do that.

From what I can tell it looks like you can get it back but you will need to talk to an AME.


Is there any obvious warning when auto-pilot is disengaged or when the mode changes? Under the investigation section of the First Air Flight 6560 incident, it describes the catalyst for the accident:

  The approach was entirely flown on autopilot, which was correctly set to capture the localizer signal and track along the runway centreline (VOR/LOC capture mode). However, an inadvertent movement of the control column by the captain during the turn onto the final approach track caused the autopilot to disengage from VOR/LOC mode and revert to maintaining the current heading, resulting in the aircraft rolling out to the right (east) of the runway centreline.

My question: Is there any obvious warning (on common commercial aircraft, i.e. 737, A320) when auto-pilot is disengaged or when the mode changes?

I would have expected there to be an audible notification, some flashing light or something to make it as apparent as possible that something has changed, if it's as easy to change as 'nudging the stick'.

The Boeing 737 allows a mode called control wheel steering (CWS). The A320 doesn't. For what is CWS, see: Is it possible to disengage only one axis of a two-axis autopilot?

The wording on Wikipedia doesn't emphasize this point; however, the final report does.

  The pilots may also manually control the aircraft in a normal manner with the control wheel and column (control wheel steering [CWS]) without disengaging the pitch or roll axes of the autopilot system. Pilots can then assist the autopilot system in flying to a selected heading or course. Use of CWS does not disengage either channel of the autopilot system. The autopilot system was modified from the original design to allow for the use of GPS guidance for the course signals to the autopilot (section 1.6.10).

Note that Wikipedia says "(...) disengage from VOR/LOC mode (...)".

Therefore, for First Air Flight 6560, the autopilot was not disengaged.
Switching to CWS is not aurally annunciated. See also: Why are callouts of changes in the Flight Mode Annunciator not automated?
Autopilot disengagement is accompanied with aural and visual warnings. See: Why is an auditory alarm necessary when the autopilot disengages?

(All bold emphasis mine.)


What is the optimum speed for takeoff flaps? I took a 737 rating written test yesterday and one of the questions was:

What's the optimum speed for takeoff flaps?

V2
V2 + 10
V2 + 15
V2 + 20

Anybody knows the answer? I did some research and couldn't find it.

I assume the question means optimum climb speed.

From the Boeing 737 NG FCTM (3.30 Takeoff and Initial Climb):

  V2 + 20 is the optimum climb speed with takeoff flaps. It results in the maximum
  altitude gain in the shortest distance from takeoff. Acceleration to higher speeds
  reduces the altitude gain. If airspeed exceeds V2 + 20 during the initial climb, stop
  the acceleration but do not attempt to reduce airspeed to V2 + 20. Any speed
  between V2 + 15 and V2 + 25 knots results in approximately the same takeoff
  profile. Crosscheck indicated airspeed for proper initial climb speed.


How can the runway allocation process be optimised? I would like to write a programme that would be able to find the optimal arrival sequence for a given list of aircraft on a given airport.
By optimal I mean in terms of delay, fuel burn and runway throughput

Before this, I'm trying to collect information on the matter because I'm totally novice. I have a few questions

Do air traffic controlers only use the First Come First Served (FCFS) principle to assign runways to aircraft or are there other algorithms ?

I've read that this principle can prove inefficient because, for example, it doesn't consider aircraft "size". I've read that a sequence of 5 small aircraft followed by 5 large is better than one alternating 10 large and small aircraft because less spacing required. Is it true ?

Do you have other examples showing that the FCFS is not optimal ?

When is a runway allocated to an aircraft ? When it reaches the Initial Approach Fix ?

Thanks a lot for your help!

Sorry for the mistakes, english is not my native tongue

This question is extremely broad. At airports where there's multiple runways, there are numerous factors influencing which aircraft get which runway. Factors include, noise sensitive areas(so one runway should be favored over others), runway length/operational necessity, and configuration.

When an airport has multiple runways usually the tower will decide which are being advertised as arrival/departure runways. At which point the approach control will sequence to those given all the restrictions. Runway assignment usually occurs upon the aircraft entering the approach control's airspace. Once assigned to a runway, it's up to the controller to decide on the sequence, factors include airspeed, distance, and somewhat weight category. If you have multiple heavies coming in, it's often better to group them, than mix small-heavy, BUT you need to have the volume to be able to setup that kind of mix, to minimize space.


What is the meaning of nose-art on the Tu-160 bomber? The BBC reports another Tu-160 interception on 15 Jan 2018 and it's clear that there is a large message painted on the side of the bomber.

Looking at the Wikipedia page, it seems this style of nose-art is common among the Tu-160 community; the style is similar, but whatever it says, they're all different.

It would be interesting to know what's being said here, and who is making the choices. Official propaganda,  or personal messages?

(source: BBC)

(wikimedia.org)

Most of the Tu-160 in service are named, much like the B-2 bombers are.

The one in the image is S/N: 7-02 "Василий Решетников / Vasily Reshetnikov" named after a WW2 pilot.

You can find the names of the other ones on the Russian Wikipedia.


Why don't we have yokes that look like steering wheels? This question came across my mind when I was thinking about cockpit design vs car design: why don't we have yokes that look like steering wheels?

The first advantage I can think of is more gestures to hold the yoke. You can hold a steering wheel in many ways, e.g. 2 & 10 o'clock, 3 & 9 o'clock, top, bottom, one hand, both hands etc. And one can still pull or push the yoke even if it's circular.

Secondly, in most (if not all) of the yokes, full aileron deflection is achieved when the yoke is rotated approximately 90 degrees. Would it be beneficial if it's 180 degree instead, allowing more fine control?

We Do! It just has been a while since anyone has built a plane like that.

Many early planes did, notably the curtis biplane comes to mind

As closed cockpits came into be and the modern control set up we see something like a car wheel.

  The cockpit of the Reliant SR-6A shows the love and skill that went into the restoration.

source

Yokes then evolved to have a more cut down top like the one seen here (in my favorite plane) the Spartan Execuitve This plane was built in the 30's

Even later than that the Ercoupe has a somewhat rounded control wheel.

Also of note the Piper Pacer and Cessna 140 had rounded yokes. After that period most of the big makers moved to the yoke we know and love today. Piper would have a closed top yoke on their early Comanches through the early 60's as well. It should also be noted that early planes (wright flyer etc) had stick like controls. I would assume this was to allow the cable to be mounted far from the pivot for torque reasons although Im not sure (this was for sure before trim).

Remember in an airplane its all about weight so trimming it where ever you can is worth it.

In a plane the maximum deflection of a yoke is often no more than 90 degrees so having a full wheel (which allows a hand over hand car style turn) is not necessary.

Orientation is a bit of a concern when flying on instruments but many race cars have center marks on their steering wheels for a similar reason.

For what its worth formula 1 steering wheels see about as much travel as a yoke and are similarly shaped. Some even have more buttons than a cockpit.

source


Why has flight UA106 such a strange predicted flight path? I was looking at the predicted flight path for UA106 from IAD to MUC and noticed this odd pattern. Why would it do this? I understand that most flight paths are not straight and there are airways that most all flights follow, but this path makes two less than 90 degree turns. Wouldn't it be simpler to go straight to the Belgium point rather than go to Poland, then back to Belgium, then back again to Munich?

As @mins suggested, it seems to be a wrong longitude of a waypoint in the Shannon Control area. I assume it is a hemisphere error (they used East instead of West).
If the longitude of the waypoint is mirrored with respect to the Greenwich meridian, the resulting path gives a more likely route to be flown:


Is there any System to warn of Runway Incusion? From what I learn, in large towered airports, the control of who enters and leaves the runways belong to the Control Tower Operators.

And that got me thinking:

Is there any Equipment or System in large airports to warn the tower of something/someone entered or is crossing the runway?

Yes, there are several systems.

The simplest are REALLY BIG WINDOWS (and binoculars):

When the entire wall in front of you is a big expanse of glass looking out over the runway there's a good chance you'll notice something trying to roll onto the runway.
Many runway incursions are detected visually.

Really big windows don't work as well when you have multiple runways and larger airport complexes though, so we have some technological solutions too. The most common is Automated Surface Detection Equipment (ASDE), the one being deployed today is ASDE-X.
This is basically "radar on the ground" which interrogates aircraft transponders and shows the controllers which aircraft are where on the airport surface:

There are also systems on the ground designed to prevent incursions, but those are mainly for use by pilots.
These include Runway Status Lights, taxiway guidance lights (which include "stop bars" that light up on hold-short lines), and "runway guard lights" (which may be mounted either in the pavement or alongside the taxiway/runway intersection).

Many of these systems can be controlled from the tower, either by automatic systems or manually by the controllers.


What does this symbol on this Aerodrome Chart mean? Does anyone know what this symbol on aerodrome charts is?

It is the Aerodrome Reference Point, ARP.

As per ICAO annex 14 vol 1, chapter 2.2:

  2.2 Aerodrome reference point

  2.2.1 An aerodrome reference point shall be established for an aerodrome.

  2.2.2 The aerodrome reference point shall be located near the initial or planned geometric centre of the aerodrome and
  shall normally remain where first established.

  2.2.3 The position of the aerodrome reference point shall be measured and reported to the aeronautical information
  services authority in degrees, minutes and seconds.

The FAA likes to use the term "Airport Reference Point"

Please see the Jeppesen AWM introduction - airport chart legend (pdf). Chart on page two has the symbol with refrence number 17, and on page three this is explained as:

  17 — The geographical location of the Airport Reference Point (ARP) is depicted when known.


What lights does the Cessna 172 light rheostat control? I am part of a team developing a Cessna 172 P model for FlightGear, an open source free flight simulator. We are now programming how the panel and radio lightning rheostat should work, but we found a lot of unclear and/or contradictory information about it online. Our main problem is to understand how the radio light knob (labelled as RADIO LT) work in these older models of the 172.

The POH from 1982 states the following:

  The engine instrument cluster (if post lights are installed), radio equipment, and magnetic compass have integral lightning and operate independently of post or flood lightning. The intensity of this lightning is controlled by the inner knob on the light dimming rheostat labelled RADIO LT; rotate the knob clockwise to obtain the desired light intensity. However, for daylight operation, the compass and engine instrument lights may be turned off while still maintaining maximum light intensity for the digital readouts in the radio equipment. This is accomplished by rotating the RADIO LT knob full counterclockwise. Check that the flood lights/post lights are turned off for daylight operation by rotating the PANEL LT knob full counterclockwise.

This makes it look like the RADIO LT knob controls both the brightness of the radio digital readouts (i.e. the frequency digits) as well as other types of lights (radio cluster buttons and compass), but I found out that other renowned simulations of the 172 for other simulators do not dim the digital readouts with that knob. It also seems strange to me that one would be able to dim the radio digits under any condition, let alone turn them completely off.

So does anyone here have experience with these models of the 172? Would anyone be able to describe how to best model the behaviour of the radio lights?

This depends more on the radios installed than the plane its self, older era planes may have had King radios with analog numeric readouts. These radios are generally back lit and controlled by what ever rheostat controls the panel those radios generally look like this

(source)

later planes may have had digital readouts which in some cases had another control to dim the intensity. This is often because in a sense the lights are always on you may need to control them with out turning on or dimming the panel. As a matter of fact you generally want them to work opposite, during the day when the panel is dim or off you want the radio lights to be brightest they would then be dimmed in the evening as you bring the panel lights on. Those radios often looked like this,

(source)

The dim function may appear on units like the DME and Auto Pilot if they are similarly lit.

Its been a while since I have night flown with one but if memory servers the newer GPS units like the GNS430/540 have backlit buttons that come on when the panel lights are activated. These units also tend to have separate ways to control the screen brightness/contrast

(source)

You may have more luck referencing the manuals for the radios them selves than the POH for the plane. You should design for the types of radios you are putting in (looks wise)


What types of antennas are used in a Piper Seneca PA34-200? What types of antenna are used in the Piper Seneca PA34-200 and where are they are located? The manual is not giving the specific answer to the question. Also, what is the frequency range of the antennas?

There can be quite a few antennas:

VHF Comm
VOR
Localizer
Glide slope
DME
ADF
Transponder
Marker beacon
GPS
ELT with integral GPS receiver
ELT
FM Receiver

You can search for antenna at a site like chiefaircraft.com to see what they look like and the frequencies they are designed for. Or go to a manufacturer website, like COMANT Industries, for the same.

Some may have multiple functions in one antenna.

Typical locations:

Top of fuselage/wing, (VHF comm, GPS)
bottom of fuselage (belly), (transponder, marker beacon, VHF comm)
top of tail, (VOR, glide slope)


How can I find traffic patterns that pass over my house? I live in Atlanta, GA well north of the airport and typically there is very few large, commercial aircraft that pass overhead. But there is an on-going security issue at the airport today and there are some really low-flying commercial jets passing from east-west over my house at altitudes that look like they would be on final approach (if they weren't 40 miles north of the runways anyway). There is a military airport near by and we frequently have C-130's landing but they don't come from that direction.

So I really have no idea what those planes were doing or where they were going, and in the 5 years I've lived here there have never been commercial planes that flew that pattern. At another place I hang out, close to the airport, I've noticed that air traffic passes over when there are storms at the airport.

I would imagine this is a "something is wrong at the airport" pattern as opposed to a normal operating pattern, and it may even be something that was specific to that particular aircraft for some reason.

Is there any way to look up what patterns would pass over a given location under what situations? Or more likely -- how can I look up what patterns are around an airport and how those patterns change with conditions (weather, emergency, traffic, etc)?

Its not that easy for a non-pilot to do it, but there are about a dozen "Arrival Procedures" that show specific routes into ATL.

You can also see on the Atlanta Area Chart how some of the traffic might flow near your house.

The easiest thing to do, if you can pick out some of the aircraft, is to look up their flight paths on Flightaware:


Is there a best number of wheels per bogie? I understand the need of having more wheels when the aircraft is designed to be heavier. The number of wheels per bogie and the number of bogies differ from an aircraft to another. For example, there are some main landing gear compositions (from the lightest to the heaviest aircraft):

A320/B737: two 2-wheel bogies
A330/A340/B767: two 4-wheel bogies
DC10/MD10: two 4-wheel & one 2-wheel bogies
B777: two 6-wheel bogies
B747: four 4-wheel bogies
A380: two 4-wheel & two 6-wheel bogies

Given those examples, I guess the maximum number of wheels per bogie is 6 and thus given the number of wheel of the B747's main landing gear, it could have been composed of fewer bogies with more wheels on each (e.g. three bogies: two with 6 wheels and one with 4 wheels). So I wonder if there is an optimal number of wheels per bogie, and if for a given number of wheels it is better to add bogies with fewer wheels per bogie.

The answer depends on who you ask. The structural engineer would prefer a single wheel, and as few legs as possible, while the aerodynamicist would vote for 8 or 12 wheels, because then the bogie has less frontal area and can be accommodated even in thin wings.

Generally, less than two wheels would compromise redundancy, and more are needed to reduce local ground pressure. Remember that the A-300B was initially not allowed on some US airports because of a slightly higher ground pressure. See this answer for more.

Modern designs use two wheels per strut for redundancy when the aircraft is light enough and replace them with a bogie with as many wheels as necessary to carry higher aircraft masses. The A-340-200 has gained a central strut with two wheels (A-340-200/300) rsp. a 4-wheel bogie (A-340-500/600), while the equally large, but lighter A-330 uses just the two 4-wheel main gears without the central gear. Airbus could have used two six-wheel bogies, but preferred to keep commonality with the A-330 gear.

More than 6 wheels per bogie is very unusual, but there are exceptions: Since the Tu-144 had no thrust reversers, all braking had to be done by the wheel brakes. Additionally, the bogies needed to fit between the intake ducts inside the nacelles, so the final design used 8 wheels with the large housings of the disc brakes sticking out towards the center of the bogie. As @Zeus points out in the comments, these were more precisely 4 dual-tire wheels per bogie: The two tires on each side were mechanically linked.

Tupolev Tu-144 landing gear (picture source). This particular aircraft is parked in the back yard of the Aviation Institute in Kazan. If you want to know how this 8-wheeled monster would fit inside a supersonic airliner, read the answers to this question.

XB-36 (first prototype of the B-36) taking off (picture source)

Convair experimented with different tire sizes for the B-36 and even a tracked version. The initial single wheel design resulted in the biggest aircraft tire ever produced, but in the end the conventional (but novel at this time) 4-wheel bogie was preferred because the single wheel had too much ground pressure for most US airbases. Earlier airplanes had used 2-wheel bogies (Tupolev TB-3, Junkers G-38) or a pair of wheels left and right of the strut (Douglas DC-4). Very early large aircraft had to use what was available, so the Caproni 42 bomber of 1918 below had as many main wheels as the TU-144 half a century later (picture source). The Zeppelin Staaken giant aircraft of WW I used the same number of main wheels on a single axle for soft field operations.

When Air India ordered their first A320s, they were afraid the main wheel pressure would be too much for some Indian airfields. Airbus produced a version with a four-wheel bogie instead of the usual two-wheel main gear of the regular A320. When they later ordered the A321, India seemed to have improved their airfields, because the newer planes use the regular two-wheel gear which is mechanically simpler and needs less maintenance.

Air India A320 (picture source)


Why was brown chosen to represent the ground side of an attitude indicator? Is there any particular reason for having the ground represented by brown on an artificial horizon or PFD?

Blue represents sky, brown represents earth, which will be used for easily identifying the aircraft attitude (along with line of origin). Using blue to represent the sky makes conventional sense. But why is brown used? Is there any scientific reason for using brown instead of another color?

The answer to the specific question of "why PFD's (glass cockpits) use this standard" is because their old style gauge cockpits used it before them. The glass cockpits of today are made to be similar to the older gauges so as to avoid confusion in their operation when moving from one type of aircraft to the other. This has been shown to be an issue in the past in the difference between American and Russian attitude indicators as such instrument operation strives to be at least somewhat uniform.

Now as for the more general question "why are attitude indicators Blue/Brown?" there are a few reasons. First off some types of color blindness cause issues with the blue/green mix making it a combination to avoid (some info on color blind flying). Second, and perhaps as important is that blue and brown sit basically on opposite sides of the color wheel making them very contrasty while blue and green sit right next to each other on the wheel. This ensures accurate viewing in most lighting situations.

There are also other attitude indicators like those commonly used in military aircraft which have had different colors

(source)

The oldest examples are completely void of any color (you can see why they introduced color)

(source)

For what its worth some modern flight displays now include terrain data and are capable of showing many other colors to outline it as can be seen here on this Garmin unit

(source)


How do airline pilots maintain night currency? Does flying as an airline pilot under 14 CFR 121 provide different ways to maintain night currency? Suppose a pilot were to bid only day trips and end up flying only during the day for over 90 days. Under the recency of flight experience requirements in 14 CFR 61 that would mean a pilot might not be night current anymore but do 121 operator's op specs have some way around this?

The night currency requirements are in 14 CFR 61.57, which does provide exceptions for pilots flying for an air carrier:

  Except as provided in paragraph (e) of this section, no person may act
  as pilot in command of an aircraft carrying passengers [at night]

61.57(e)(2) has this exception for part 121:

  (2) This section does not apply to a pilot in command who is employed
  by a part 119 certificate holder authorized to conduct operations
  under part 121 when the pilot is engaged in a flight operation under
  part 91 or 121 for that certificate holder if the pilot in command
  complies with §§121.436 and 121.439 of this chapter.

121.436 has general PIC requirements for part 121, and 121.439 has recency requirements, which are 3 takeoffs and landings in the last 90 days in the same aircraft type, or an equivalent simulator.

So part 121 pilots need three takeoffs and landings in type in the last 90 days, with no specific requirement for them to be at night. That's all based on just reading the regulations, someone who's actually been there and done that could probably add some more information.


What are hydraulically powered and electrically controlled actuators? I thought that the actuators are hydraulically controlled when the hydraulic fluid changes their position, but some aircraft (Bombardier, for example) has hydraulically powered and electrically controlled actuators.

What does electrically controlled means?
How does hydraulics power the actuator?

As wikipedia mentions, "Electro-Hydrostatic actuators" (EHA) are self contained, the only input they need is electrical power and commands.

The electricity powers up the hydraulic pump that is used to move the actuator piston, while the electrical commands are used to select what the actuator does through the use of a valve.

  What does electrically controlled means?

Means that the position (and thus the action) of the valve is controlled via a solenoid. The following scheme shows a valve with two solenoids. The valve has three positions, indicated by the three squares. Depending on the electrical control signal, the current in the solenoids changes and thus moves the selector (the block with the three squares) laterally.

Image source

  How does hydraulics power the actuator?

Through a pump. Where the fluid goes is selected by the electrically controled valve, but the piston of the actuator is moved by the hydraulic fluid.

In the image below, if the valve of the image above is in the central position, the actuator does not move.
If it is in the left position, the actuator retracts.
If it is in the right position (with the two arrows crossing) the actuator extends.

Image source


How do stealth aircraft reduce the Heat Signature? According to the wikipedia article, a stealth plane requires the following features in order to reduce its radar signature and thermal detection:

  Reducing thermal emission from thrust
  Reducing radar detection by altering some general configuration (like introducing the split rudder)
  Reducing radar detection when the aircraft opens its weapons bay
  Reducing infra-red and radar detection during adverse weather conditions

How do aircraft actually achieve reduction in their thermal emission from thrust?

The short of it is that it's really hard to hide the heat signature of a device that is powered by burning large amounts of kerosene and shoving those gases out behind it. IR stealth is therefore a secondary concern (or lower) to designers of stealth fighters, primarily because the IR signature only matters at much closer ranges where stealth technology itself has reduced value (you can hide from radar, and camouflage to an extent, but you can't disappear entirely from visual range).

However, there are some things that can be done to make an aircraft less than blindingly obvious to IR sensors. Here are a few:

High bypass. Not all of the air that enters a turbofan engine's intake enters the actual combustion chamber. Bypass air helps to cool the hot combusted air before it exits, reducing the IR signature.

The A-10, not a "stealth" aircraft in the slightest, nevertheless operates in situations where MANPADS (shoulder-fired SAMs) are a big threat, so to reduce its IR signature it uses some of the highest-bypass turbofans ever put on a military single-seater, at a 6:1 bypass ratio. These high bypass engines, however, reduce performance at high altitudes and high airspeeds; neither disadvantage is a problem for the low, slow A-10's mission profile, but for a more high-performance air superiority fighter this is a big deal.

High-performance jet engines in fighters tend to be relatively low bypass compared to airliner engines for this reason. The F-15 and F-16 were powered by a P&W turbofan with just 0.36:1 bypass ratio, however this only increases IR signature by requiring higher fuel flow rates for the same thrust at lower speeds (lower bypass also reduces the effect of afterburners because there is less unburned bypass air to feed the additional combustion).

The F-22 mitigates the efficiency losses of a turbofan with a variable bypass intake system, allowing it to function as a turbofan with similar bypass to other fighters (about 0.3:1) at low speeds and altitudes, but converting to a near-turbojet configuration (almost zero bypass) at high altitudes and supersonic speeds, which is more fuel-efficient than an afterburner (and so allows the F-22 to supercruise).
Exhaust baffles. The thing designers typically want to avoid at all costs is exposing the actual point of ignition and primary combustion in a jet engine to the ground; this makes the hottest part of a plane's visible IR signature within the plane itself instead of the stream of hot air behind it, allowing easy targeting by IR SAMs. Imagine being an SA-13 "Gopher" mobile SAM launcher and having these twin fireballs from an F-15E for a target:

To hide this massive heat source, stealth aircraft are designed with exhaust vents that mask the exit point of the engine's exhaust from observation by the ground. There's really not a lot you can do design-wise to mask the IR signature from directly behind the aircraft; it's the pilot's job to ensure nobody ends up at that angle within missile range.

Northrop is a fan of directing exhaust out over the top of their fuselage designs. Here's the B-2; you can see the heat plumes of the exhaust trail, but the source of actual combustion is well within the engine housing, and with the aircraft at any altitude the exhaust vent itself would be totally obscured:

Here are the exhaust channels of the YF-23, which incorporated lessons learned from the B-2; notice the similarities in the strategy for directing the exhaust out over the top of the aircraft's trailing edge:

The F-22 Raptor uses a similar theory of tucking the engines way back behind exhaust ducts, but these ducts can move to vector thrust or open to allow afterburners, so for greatest effect the ducts are placed to the rear instead of over the top of the fuselage as Northrop's designs tend to:

EMR-absorbing materials. A basic part of stealth design is the use of materials that absorb radar, and designing the aircraft's surfaces with angles that minimize the number of surfaces providing a direct return at any angle, while remaining aerodynamic. Other materials can absorb other frequencies in the EMR spectrum including IR; the Space Shuttle's lower and leading surfaces were covered in special ceramic tiles that could absorb enormous amounts of thermal energy while being cool to the touch. A similar material, not quite as effective but also less delicate, is used to protect the exhaust ducts of stealth fighters, and this has a secondary effect of lowering the radiant heat signature of the engines because the exhaust nozzles stay cooler. The radar absorbing material used elsewhere has some capacity for absorbing heat on leading edges, which helps avoid good lock-on by all-aspect IR missiles, but it's not the material's primary job.

In summary, designers do try to minimize IR signature, but tactically, if an enemy can launch an IR missile at you you have already failed at being stealthy. An infrared missile launch requires the launcher to tell the missile where to look, and that means they must at least be able to look at you themselves (using helmet-cued AA missiles), if not point the missile itself or the tracking radar at you. The idea of stealth is to minimize the amount of time the enemy knows that you exist by being invisible on radar, so they can't see you coming until they spot you visually, at which point they're either already dead or have mere seconds to react. Then for a ground run it's "one pass and haul ass" to avoid reprisals from anti-aircraft systems, while for an air-to-air engagement the first plane to launch a missile has an extreme advantage (and thus the advantage starts with the first plane to know where the other one is).


What is the thing in the middle of the turbofan? I have been understanding more about engines lately, but I can't figure out what the section in the middle of a turbofan is for:

What benefit does this part provide to rotating the air? Is it some kind of separate fan or something?

egid is right. It is called spinner.

The spinner basically covers the part of the hub where the compressor blades are attached and reduces drag.

Source: b737.org.uk

It also serves other purposes:

Diverting the airflow efficiently in the center of the engine so that the airflow is smooth over the compressor blade hub

More importantly, the spinner serves to divert the rain and (more importantly) hail impinging on it towards the bypass fan and away from the 'core' of the engine, reducing chances of engine flameout.

The second point an important design parameter for the spinner. According to AGARD-AR-332, Recommended Practices for the Assessment of the Effects of
Atmospheric Water Ingestion on the Performance and Operability of Gas Turbine Engines,

  An effective way to remove a sizable amount
  of hail from the core is to optimize the spinner shape
  to deflect hail upon impact directly towards the fan
  duct.

The spinner of the CFM56 engine was modified in response to the engine flameout experienced in Garuda Indonesia Flight 421. The shape was changed into a conelliptical profile.


Are there commercial airplanes that are still flyable without any electricity? I have seen the first episode of Revolution yesterday and there are all kinds of airplanes just falling from the sky because of complete loss of electricity.

I know most if not all modern planes use fly-by-wire systems.

I thought about this and the the question occurred:

Are there any still commercial airplanes in use that are still flyable with complete loss of all electric systems?

Do some commercial airplanes still have mechanical backup mechanisms to manoeuvre?

Are there any still commercial airplanes in use that are still steerable with complete loss of all electric systems? Do some commercial airplanes still have mechanical backup steering mechanisms?

Yes and Yes.

On most(*) Airbus aircrafts,

  In case of a complete loss of electrical flight control signals, the aircraft can be temporarily controlled by mechanical mode.

This is called MECHANICAL BACKUP and is the lowest level of control law (after Normal, Alternate and Direct Laws)

The aircraft can be steered:

  Pitch control is achieved through the horizontal stabilizer by using the manual trim wheel.
  Lateral control is accomplished using the rudder pedals.

The pilots are notified with:

  A red MAN PITCH TRIM ONLY warning appears on the PFD.

But:

  Both controls require hydraulic power.

This means that if the aircraft looses BOTH electrical and hydraulic power, is no more controllable.

Usually there are pressurised hydraulic reservoirs that allow to have a minimum of hydraulic power even if there is total loss of electrical power, but if there is substantial damage to the aircraft that has severed the hydraulic lines, this is no more applicable.

(*): beyond the A320. Functionalities vary in the following manner: (emphasys mine)

  Primary Flight controls:

  Back-up Control Logical evolution of A320 / A340 / A340-600 family:

  Full Fly-By-Wire, with a “Back-up” as an additional precaution to keep control of the aircraft during temporary loss of:

  all Primary Flight Control computers
  all Electrical power supply

  A320 : full FBW controls, mechanical Back-up (Pitch Trim & Rudder)

  A340/A330 : like A320, additional Yaw Damper to improve Dutch Roll
  damping even in Back-up mode (BYDU with hydraulic micro generator)

  A340-600 : like A340 for pitch, Rudder becomes fully Electrical (BPS + BCM : Back-up Power Supply + Control Module)

  A380 : like A340-600 for Yaw control + BPS+BCM also power:

  Electrical Pitch Back-Up (elevators) linked to side-stick
  Electrical Roll Back-Up (ailerons) linked to side-stick
  Pitch Trim (Wheel is replaced by Switches)

For the A380, in particular:

  Active Stability Control functions:

  All levels of control laws (Normal, Alternate, “Direct” and even Back-up) include a Yaw and Pitch damping function


Is defacing the airline logo of a wrecked airplane illegal? I was listening to episode #25 of the Hello Internet podcast where Brady Haran mentioned that it's not unheard of for airline employees to rush to their own airplane's respective accident scene to deface the logos and registration numbers painted on the airplane's wings and fuselage. This is apparently done to reduce the damage to the airline's reputation. Below is an picture of the same from an alleged account of Thai Airways defacing the logo on a crashed (but still very intact) airplane.

So is there any law regarding whether this can be done? Could defacing the logo end up hampering the air crash investigation?

In the US (you tagged your question FAA) it would most likely be illegal. 49 CFR 830.10 says (note that the NTSB investigates US accidents, not the FAA):

  (b) Prior to the time the Board or its authorized representative takes custody of aircraft wreckage, mail, or cargo, such wreckage, mail, or cargo may not be disturbed or moved except to the extent necessary:

  (1) To remove persons injured or trapped;

  (2) To protect the wreckage from further damage; or

  (3) To protect the public from injury.

It seems highly unlikely that painting over logos would be justified for any of those reasons. On the other hand, this wording leaves the question open of what might happen after the NTSB takes custody, and in theory an airline could do it with permission.

Personally, I find it hard to see how this would help the airline because the story would be all over the news anyway, but laws and attitudes vary widely in different parts of the world.


ICAO and EASA classification of instrument approaches ICAO distinguishes approaches operations based on DH between 'Type A' (DH >= 250 ft) and 'Type B' (DH < 250 ft), which are further divided into subcategories. From the Annex 6 — Operation of Aircraft Part I:

a) Type A: a minimum descent height or decision height at or above 75 m (250 ft); and
b) Type B: a decision height below 75 m (250 ft). Type B instrument approach operations are categorized as:

Category I (CAT I): a decision height not lower than 60 m (200 ft) and with either a visibility not less than 800 m or a runway visual range not less than 550 m;
Category II (CAT II): a decision height lower than 60 m (200 ft) but not lower than 30 m (100 ft) and a runway visual range not less than 300 m;
Category IIIA (CAT IIIA): a decision height lower than 30 m (100 ft) or no decision height and a runway visual range not less than 175 m;
Category IIIB (CAT IIIB): a decision height lower than 15 m (50 ft) or no decision height and a runway visual range less than 175 m but not less than 50 m; and
Category IIIC (CAT IIIC): no decision height and no runway visual range limitations.

Instrument approach procedures are further classified as follows:

Non-precision approach (NPA) procedure. An instrument approach procedure designed for 2D instrument approach operations Type A.
Approach procedure with vertical guidance (APV). A performance-based navigation (PBN) instrument approach procedure designed for 3D instrument approach operations Type A.
Precision approach (PA) procedure. An instrument approach procedure based on navigation systems (ILS, MLS, GLS and SBAS CAT I) designed for 3D instrument approach operations Type A or B.

If I understand correctly, EASA would like to implement similar concept (as stated in 'Notice of Proposed Amendment 2018-06(C)'). On page 51, there is a summary table with classification of approaches:

From the table above, how can Category I/II/III approach be 'Type A'
approach (green rows)? I thought that from the definition, only 'Type B'
approaches have subcategories.
What kind of approach would be LIRN ILS Z RWY 06 (see the chart
below)? What kind of planning minima should I use?

First, you're reading the EASA table wrong. Type A approaches are not all the green rows, they're the vertical column that says "Type A, 2D or 3D" that covers all the specific column of all the green rows and the blue also. On the right side of that column, you see Type B approaches, divided to subcategories. All of those being 3D approaches.

Second, the approach you are asking about is a precision approach. Type B 3D approach if we want to use the new terms. It's an ILS-approach, it has a vertical flight path guidance. You should use precision approach planning minima. It does have a higher minima than ILS usually does. The higher minima is most likely because of nearby high terrain influencing the go-around requirement.

I would say it's Type B 3D because it's Cat 1 ILS, therefore it's a precision approach and it must be a precision runway. The lowest possible DH for Cat 1 ILS is 200ft. With these facts I would place it in the given category. Although this particular approach minima is higher, it is not because of the approach it self, but rather because of obstacles.


What aircraft design elements contribute the most to sustained flight? If I wanted to design an aircraft for autonomous operation and maximum endurance, what design philosophies provide the greatest benefit?  I'm imagining a powered glider.  Does not have to be highly maneuverable.

I'm interested in relative proportions, wingspan, length, center of gravity, center of pressure, wing placement, dihedral/anhedral, engine placement, fuel type, etc.

Is there a "sweet spot" for center of gravity relative to center of lift so as to maximize stability?
Since it will be mostly autonomous (computer-controlled), can I design for less inherent stability?
What engines/fuel types are the most efficient?

Natural stability would be highest on the list for me. Look at free flying model airplanes for inspiration. They have their own characteristics:

Very low wing loading for minimum sink speed
High natural stability, and consequently a very narrow speed range
High aspect ratio wing, thin airfoil with high camber
Extremely short fuselage ahead of the wing (no payload to carry)
Extreme fuselage length aft of the wing which provides ample aerodynamic damping
Strong dihedral of the outer wing.

This in combination means that your control software can be very simple. Relaxed stability will require many sensors and built-in redundancy, and the more parts you need to add, the more possibilities of failures you will end up with. In contrast to that, the laws of physics never fail, use them to your advantage. See below for an example which I copied from the Wikipedia page on free flight models:

For airfols, c.g. location and all other details I recommend to look at several free plans until you see a common pattern.

Regarding the type of fuel: Depends how noisy and messy you tolerate the engine to be; some people will only fly electric while others are happy with two-stroke engines.


What is the correct name of this aircraft subsystem in English? I would like to know what the correct name of this aircraft susbsystem is in English:

(Source)

name: пилотажно навигационный комплекс
+/- literally translated it could be something like: flight navigation system.

I am looking for some sort of blockdiagram of this system of either an F-35 (my favorite) or otherwise a boeing airplane. A blockdiagram which components are used and how they communicate with each other. E.g.:

(Source)

Could anybody suggest me some good places to look for?

From the product page and Google translate:

  Newton is designed for use in unmanned aerial vehicles (UAVs), civil and special purpose. Designed to determine the parameters of flight and navigation and automatic flight control UAV, payload control and to ensure information exchange with the ground control station (NPU).

  Support RTK technology for high-precision positioning according to the satellite radio navigation systems (SRNS)
  The high accuracy of the orientation angle according to the SRNS
  Possibility of interconnecting with foreign strapdown inertial navigation system (SINS) on the fiber-optic gyro (FOG)
  Possibility of controlling any types of payloads including mode gyrostabilization
  Available in a block of flight and navigation built-in radio for transmission of telemetry and control commands
  The presence in the radio unit built ground goniometric RTK-receiver of the SRNS signals

It's an FMS (Flight Management System) with a capability to connect to an INS.

As for diagrams for the F-35, the general public doesn't know what the F-35 cockpit looks like, let alone schematics for avionics.


What percentage of professional pilots end their career early for medical reasons? As an amateur pilot I'm aware that I can lose my medical at some point and have to give up flying.  For a professional, losing a medical can end their career. I know several people who wouldn't even get a PPL with their medical history. Are their any figures on the number of CPLs/ATPLs that lose their livelihood for this reason?

(US-based answer)

The problem with answering your question is that it isn't all clear what "losing a medical" actually means. If a pilot is denied a medical, the FAA will obviously know and you could probably get that data from them somehow, even if it takes an FOIA request. But what if you just decide not to renew because you know you'd fail? For all the FAA knows, you might have retired, changed career or even died.

If we assume you do mean "denied" then the only specific number I could (quickly) find for denials was from 1978:

  The annual denial rate based on airman applicants is 7.9 per 1,000
  airmen. By class of certificate applied for, the annual denial rate
  per 1,000 applicants is 4.5 for the first class, 6.0 for second
  class, and 10.2 for third class.

You could apply those rates to the number of airmen certified each year to get an estimate of the absolute numbers, but obviously using a 40 year-old report may not be accurate today. And determining how medicals 'map' to pilots may not be easy.

If you want a better answer, you'll have to define exactly what you're asking. To get an accurate number (whatever that means for your purposes) you might have to look for some specialized actuarial or medical research on this.