How do pilots use stopway, EMAS, clearway and displaced threshold? I noticed in Why is “clearway minus stopway” used in V1 adjustments? that a stopway and an EMAS are both indicated by yellow chevrons:

Same Opa-Locka stopway on the left, and San Diego EMAS on the right. Source: Google Maps

I believe the EMAS could somehow damage the aircraft (e.g. the nose gear). This would be acceptable as this is a last resort choice to prevent exiting the runway in an overrun, and likely more serious consequences.

EMAS in use. Source: flysfo.com

In the other question it is mentioned that a stopway mustn't damage the aircraft. So my first question was What is the difference from a regulation point of view? And how the pilot can know if this is a stopway were braking is desired, or an EMAS where thrust reversers might be hazardous.

However I thing it could be interesting to open the scope and get a more complete view, so my questions are more:

How do pilots use non regular runway portions such as clearway, stopway, EMAS, displaced threshold, and possibly more of this kind if it exists?
Is there some regulation which limits them for taking off, taxiing, or landing?

This is a loaded question.  Every regulation in aviation seems to be written blood and the need for runway safety areas (RSA) is no exception.
RSAs are defined in AC 150/5300-13A

Runway Safety Area (RSA). A defined surface surrounding the runway prepared or suitable for reducing the risk of damage to aircraft in the event of an undershoot, overshoot, or excursion from the runway.

RSA's were developed for specific reasons and are discussed in section 307 of the AC.

In the early years of aviation, all aircraft operated from relatively unimproved airfields. As aviation developed, the alignment of takeoff and landing paths centered on a well-defined area known as a landing strip. Thereafter, the requirements of more advanced aircraft necessitated improving or paving the center portion of the landing strip. While the term “landing strip” was retained to describe the graded area surrounding and upon which the runway or improved surface was constructed, the role of the landing strip changed to that of a safety area surrounding the runway. This area had to be capable under normal (dry) conditions of supporting aircraft without causing structural damage to the aircraft or injury to their occupants. Later, the designation of the area was changed to “runway safety area” to reflect its functional role. The RSA enhances the safety of aircraft which undershoot, overrun, or veer off the runway, and it provides greater accessibility for fire-fighting and rescue equipment during such incidents.

Runway safety areas surrounding a runway is typically twice the width of the runway and 1000' longer than the runway on both ends.  The 1000' of additional length is referred to as a runway end safety area (RESA).  Objects inside the RSA must have specific function and be frangible (fall down) if hit by an aircraft)

AC 150/5300-13A Figure 3-5
Let's talk about runway end safety areas (RESA).  The 1000' feet of additional space beyond the end of each runway is now mandatory.  Every airport must have a RESA at the end of the runway.  The only exception to that rule is runways with an EMAS installed.  The 1000' is not an arbitrary number either.  Through analysis of aircraft overrun incidents from 1975 to 1987 it was determined that approximately 90% of the overruns stopped within a 1000' past the end of the runway at speeds less than 70 knots.  See AC 150/5220-22a for reference.
There are airports that cannot comply with the RESA requirement due to topography, roads, railroads, houses, etc.  In these situations, the FAA has established a concept called declared distances that will push the RESA onto the runway.  This will limit the accelerate-stop distance available (ASDA) and landing distance available (LDA) values.  Airports that cannot comply with the RESA standard are limited to a runway length which is available and suitable for preflight planning purposes.  It would be impractical for the FAA to tear up perfectly good runway.
This means pilots must reference declared distance information from the current chart supplements booklet to take advantage of runway safety protections.
Take a look at KSAN runway 09 end.

Google imagery from KSAN Airport
A 1000' RESA lands in the middle of shopping center.  In this case, the RESA is moved onto the runway.  The pilots must reference the chart supplements to determine usable lengths for takeoff and landing.  Here is the declared distances from the chart supplements booklet.  The runway length is 9400' but the ASDA and LDA values 1,121 feet shorter due to no space for a RESA at the end of the runway.

Chart supplements information for KSAN
Other parts of a RSA include a runway protection zone (RPZ).  This area extends up to 1700 feet past the end of the runway and can be as wide as 500 feet depending on the type of aircraft the runway was designed for.  A little history on RPZs

Approach protection zones were originally established to define land areas underneath aircraft approach paths in which control by the airport operator was highly desirable to prevent the creation of air navigation hazards. Subsequently, a 1952 report by the President’s Airport Commission (chaired by James Doolittle), entitled The Airport and Its Neighbors, recommended the establishment of clear areas beyond runway ends. Provision of these clear areas was not only to preclude obstructions potentially hazardous to aircraft, but also to control building construction as a protection from nuisance and hazard to people on the ground. The Department of Commerce concurred with the recommendation on the basis that this area was “primarily for the purpose of safety and convenience to people on the ground.” The FAA adopted “Clear Zones” with dimensional standards to implement the Doolittle Commission’s recommendation. Guidelines were developed recommending that clear zones be kept free of structures and any development that would create a place of public assembly.

AC 150/5300-13A Figure 3-17
Take a look at KSAN runway 9 again and you will see that the runway does not have space for a runway protection zone at the end of the runway.  A RPZ is mandatory and so the RPZ is moved onto the runway.  The takeoff runway available (TORA) is also 1,121 feet shorter than the runway for just that reason.
For takeoff performance calculations, pilots are required to ensure the airplane takes off and climbs to at least 35 feet within the TODA distance to achieve the designed safety in the RPZ.

Clearways are a special type of RPZ that will not allow any obstacles other than lights that are less than 26 inches in height.  The clearway must be at ""least 500 feet wide centered on the runway centerline and the length may not be more than 1/2 the runway length."

A clearway increases the allowable aircraft operating takeoff weight without increasing runway length.

In other words, takeoff distance available (TODA) is increased beyond the runway when a clearway is installed.

Displaced thresholds are created for four reasons that are beyond the power of the airport owner / operator.

A means for obtaining additional RSA prior to the threshold.  See
paragraph 307.
A means for obtaining additional runway object free area (ROFA) prior to the threshold.  See paragraph 309.
A means for locating the RPZ to mitigate unacceptable incompatible land uses.  See paragraph 310.
Mitigation of environmental impacts, including noise impacts.

Let me answer your questions to the best of my ability
What is the difference from a regulation point of view?
A stopway is designed to allow an aircraft to stop during an aborted takeoff.  Interestingly enough the AC 150/5300-13A does not say it is designed for runway overruns during landing or undershoots on the opposite runway.  By design it will increase the ASDA value for the runway
An EMAS system replaces a stopway and is usable for undershoots while landing on the opposite runway and overruns during both takeoff and landing and is not intended to meet the definition of a stopway.  An EMAS will not increase the ASDA value for the runway

How does the pilot know if this is a stopway where braking is desired, or an EMAS where thrust reversers might be hazardous.
The chart supplements book contains information on all EMAS systems.  Looking at the declared distances for the airport will indicate the presence of a stopway when the ASDA value is greater than the runway length.  Take a look again at KSAN and you will see a note for an EMAS off of runway 27.

Chart supplements information for KSAN
Stopways are a little harder to notice but can be spotted by noticing the ASDA value is greater than the runway length.

How do pilots use non regular runway portions such as clearway, stopway, EMAS, displaced threshold, and possibly more of this kind if it exists and is there some regulation which limits them for taking off, taxiing, or landing?
What are Runway Declared Distances?
This is the easiest question of the bunch.  Pilots are required to use the applicable declared distances for takeoff and landing performance calculations.  By design declared distances take into account all of the airport design standards such as clearway, stopway, EMAS and displaced thresholds.
Declared distances bridges the gap between runway design standards and aircraft performance.

§91.103   Preflight action.
Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. This information must include—
(a) For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts, fuel requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which the pilot in command has been advised by ATC;
(b) For any flight, runway lengths at airports of intended use, and the following takeoff and landing distance information:
(1) For civil aircraft for which an approved Airplane or Rotorcraft Flight Manual containing takeoff and landing distance data is required, the takeoff and landing distance data contained therein; and
(2) For civil aircraft other than those specified in paragraph (b)(1) of this section, other reliable information appropriate to the aircraft, relating to aircraft performance under expected values of airport elevation and runway slope, aircraft gross weight, and wind and temperature.

The AIM has information concerning runway lengths.

4−3−6. Use of Runways/Declared Distances
4-3-6(c)(1) Declared distances for a runway represent the maximum distances available and suitable for meeting takeoff and landing distance performance requirements. These distances are determined in accordance with FAA runway design standards by adding to the physical length of paved runway any clearway or stopway and subtracting from that sum any lengths necessary to obtain the standard runway safety areas, runway object free areas, or runway protection zones. As a result of these additions and subtractions, the declared distances for a runway may be more or less than the physical length of the runway as depicted on aeronautical charts and related publications, or available in electronic navigation databases provided by either the U.S. Government or commercial companies.
4-3-6(c)(2)(c) When considering the amount of runway available for use in takeoff or landing performance calculations, the declared distances published for a runway must always be used in lieu of the runway’s physical length.
4-3-6(c)(2)(d) An aircraft is not prohibited from operating beyond a declared distance limit during the takeoff, landing, or taxi operation provided the runway surface is appropriately marked as usable runway.

AIM Figure 4-3-6
How do you use declared distances for multi-engine pilots?
How do runway declared distances affect my takeoff distance?
The short version is aircraft utilizing balance field length calculations typically provide a single distance for takeoff that must be lower than both the TORA and ASDA value.
Aircraft with unbalanced field length calculations typically provide separate performance calculations for accelerate-go and accelerate-stop. The TODA and ASDA values must be greater than the calculated accelerate-go and accelerate-stop distances, respectfully.

TL;DR version
Pilots using applicable declared distances are afforded designed runway safety area protection.  Pilots who choose not to adhere to runway declared distances risk getting outside the protections designed for the runway.


What are the pros and cons of adding a gearbox to larger jet engines? What are the merits and demerits of adding a gearbox to larger jet engines like the Trent 900.  If its about torque, why not use a magnetic gearbox?  What are the demerits of using magnetic gearboxes in a geared turbofan engine?

One major benefit is that gearing slows down the fan
tips below supersonic, giving a major reduction in noise and drag.  The newer massive turbofan jets are ever improving in efficiency, and, with gearing, are taking a page out of the turboprop book to do it.


What is GPS HIL in layman's terms? GNSS Horizontal Integrity Limit/ Horizontal Protection Level is a measure of GNSS position error/integrity that's very important in RNP operations and RAIM, but it has an obtuse definition in aviation regulations like DO-229D that's hard to apply in practice:

  [HPL] describes the region assured to contain the indicated horizontal position. It is a horizontal region where the missed alert and false alert requirements are met for the chosen set of satellites when autonomous fault detection is used.

Is there a simpler definition that is equivalent for most equipment? It seems like a 1 - 10-X% accuracy bound, given pessimistic assumptions about satellite availability, but given the description it's hard to be sure?

The true position of an aircraft in flight can be measured, but the accuracy of any measurement is limited. The actual measured position is the actual true position plus the actual measurement error. Each error of position measurement is 3dimensional. If observed over a long time, the distribution of the errors will have a shape and size that is characteristic for the measurement method.

For GNSS receivers, the measurement of the latitude and longitude measurements depend on each other, while the vertical measurement of altitude does not correlate much with the horizontal measurement. This is why the usual model to describe is a cylinder:

Image source: ESA

The Horizontal Protection Level (HPL) is simply a horizontal cut through the cylinder where the aircraft is located with an acceptable level of probability.
The cross section of a cylinder is a circle, and the radius of this circle is the horizontal performance requirement.

The HPL is just a geometric definition. It is useless without acceptance levels and performance requirements, which are not part of its definition. Those emerge from the performance of an GNSS augmentation system like WAAS for GPS or EGNOS for Galileo, and the requirements for the use in aviation. Here below is a table of GNSS augmentation performance requirements by FAA for different phases of flight:

Image source: ICAO


How much noise does flow separation cause? I recently found the following image showing the different sources of noise in vehicles. I notice that Aerodynamics is actually quite a big part of vehicle noise, as shown below by the blue line:

Image source

I can imagine this is partly because of the flow going over the car. However, I think a part of this noise also comes from separating flows (for example at the rear window).

I was wondering if it is possible to reduce the aerodynamic noise of vehicles by applying separation control.

As such, I'm wondering:

How much noise does a separating flow generate?

I'm guessing this highly specific to the local geometry and velocity, but I would already be very happy with some examples.

Flow separation makes a lot of noise. Usually, it is masked by engine noise and/or damped by insulation. Any pilot of a light plane may climb to a safe altitude and then idle the engine, start a glide, and then slowly pull the stick until the wings start to stall. He will hear a lot of noise, and feel a strong vibration, too... The cause is the turbulence associated with the flow separation.


How far should the two propellers on a twin engine plane be apart? I was wondering if there are any specific ways to calculate the appropriate distance between two propellers for a twin engine twin fuselage planes like a Twin Mustang plane?

I'm assuming that you want to minimize efficiency losses due to propellers competing for clean air. I do no know what the optimal distance is but looking at a few practical examples it seems that as long as the propeller disks aren't overlapping you should be alright.

Here is a B 29 superfortress front view you can see the propeller disks are tangential to each other. The B 17 has a similar set up.

Here is a Tupolov bear as a more modern example there is more space between the propeller disks here than on the b 29. I would say this is probably because of the significant difference in horse power between the bears engines and a b 29's.

I hope this helps shed some light on what you were looking for. If you need more information your best bet is to look for a NACA paper on the topic. If there is research on this (and published in english) they are likely to be the ones who have done some.


What happen to schedule flight when airport close for undertermined duration? very similar to What happens to incoming flights when the airport shuts down

In the event that an airport shuts down for undetermined period, flights that already airborne would be divert to other nearby airports. What about planes those are still on the ground? Would they proceed to takeoff to land at a diversion or would they simply cancel the flights?
What about next day if the destination airport still close? Would they cancel all flights until airport reopen?

If an airport is shut down, all flight operations are ceased, with maybe the exception to police, state or medical flights. Scheduled, non-scheduled and general aviation flights will be grounded until the airport is reopened.

Flights will be cancelled or the passengers will be bused to airports in the vicinity, from where flights are able to depart, e.g. passengers that were scheduled to depart from Dortmund Airport would be bused to Paderborn Airport. But since the reason for a shutdown usually involves public safety, passengers will be rather evacuated and the flights cancelled, rather then moving them to another airport.


Why is the IATA Airline Accounting Code abbreviated as PAX? I'm dealing with some configuration files used in a software system. There's a single configuration file for each airline, e.g. like for Cathay, below:

"IATA": "CX"
"PAX": "160",
...

My understanding is that PAX is used to indicate a passenger count, is that understanding incorrect?

I figured out that the PAX is referring to the IATA Accounting Code for the airline:

But why is IATA calling this 'ACCOUNTING CODE(PAX)', when apparently PAX is used to refer to 'passengers'? Is it because this is specifically the accounting code for passenger transactions?

It is called PAX because this is the accounting code for passenger operations. IATA has two kinds of these codes called Accounting Code for passenger operations and Prefix Code for cargo operations.

Accounting or Prefix codes
Airline accounting codes and airline prefixes are essential for the identification of passenger and cargo traffic documents, processing of passenger accounting transactions, cargo transactions and other commercial/traffic purposes.

(iata.org)
An airline can have both codes if they are operating both passenger and cargo flights, as seen in the following list of requirements to obtain such codes:

For a 3 Numeric Accounting Code (Passenger Operations)

Valid Air Operating Certificate (AOC).
Certificate of incorporation / Company Registration, with shareholders name.
Confirmation issued by the data aggregator (i.e. OAG, Innovata)

(only if a scheduled airline)

One of the following criteria must be meet;

Passenger Bilateral Interline Agreement with an IATA code holding airline
Confirmation from BSP (IATA Billing and Settlement Plan)/ARC (Airline Reporting Corporation)

For a 3 Numeric Airline Prefix Code (Cargo Operations)

Valid Air Operating Certificate (AOC).
Certificate of incorporation / Company Registration, with shareholder names.
Satisfy requirements to publish schedules in airline guide publications (only if a scheduled airline)
One of the following criteria must be met;

Cargo Bilateral Interline Agreement with an IATA code holding airline.
Confirmation from CASS (IATA Cargo Accounts Settlement System)
Letter of confirmation from a Freight Forwarder that will be issuing AWBs on your behalf

If applying for both codes, both requirements for each code will need to be met.

(portal.iata.org)
In your example, Cathay Pacific has both an Accounting Code and a Prefix Code of 160 because they operate both passenger and cargo flights.


Why are there no supersonic propellor driven aircraft? Pretty self explained in the title.

Yes, I realize there is no widespread demand for them; this is not what I'm looking for in an answer.

I'm looking for an answer that covers more why they can't be built (or aren't practical to). I know that jet engines may generally be better, but I've recently been doing reading on aircraft like the Thunderscreech and it's made me curious why exactly it won't work.

The NASA has done research on the supersonic propeller at the end of WWII, which can be found here and here.

The main reasons that we don't see any supersonic propellers are the following:

The supersonic regions at the blades create tremendous forces which will tear the propeller apart. Thus the design needs to be such that these forces can be mitigated. This is also the case for jet engines, which is why the ducts are designed such that the airflow into the engine is slowed down to subsonic speeds.
The developments in jet engines were going at such a fast rate that the propeller was soon surpassed and was written off. However, since turboprops are much more efficient than jet engines they might pop up on the research radar in the near future.


Is the Bill Of Sale required for deregistration? Is the Bill Of Sale required for deregistration?

What are the FAA and EASA regulations applicable?

In the US you don't need a bill of sale because the aircraft may not have been sold. The FAA's definition says:

  Deregistered Aircraft An aircraft that has been removed from the U.S. Civil Aircraft Register at the owner's request. Aircraft are
  generally removed for the following reasons: exported, destroyed,
  salvaged, dismantled, or permanently retired from service.

There would be no bill of sale for a destroyed aircraft, for example.

If you're asking about handling the FAA registration when you sell an aircraft, according to AOPA's guide you have to sign and return the current registration certificate, and the FAA will issue a new one to the buyer.


Does the wake from horizontal stabilizers merge with the wing wake? There is already a long series of questions about the downwash and tip vortexes with nice images, but I'm going to add another one...

Large airliners (A380, B747-8) have horizontal stabilizers competing with small Boeing wings, and definitely larger than business jet wings.

Source

How does the tail wake look like when the horizontal stabilizers produce significant lift? Does it merge with the wake from the wing or is there a second wake above the first one?

Edit: I've found this image:

Source

Which shows the tail vortexes below the wing vortexes, and apparently larger than them.

Yes, when viewed from far enough away.
Close up, both will have their own developing wake. The boundary layer leaving wing and tail will leave a speed discontinuity, and the downward moving wing wake will be complemented by a tail wake, which will slow down this downward movement directly behind the tail, and increase it left and right of the central tail wake. Normally, the horizontal tails of transport aircraft produce a considerable downforce during landing to compensate for the backward shift of the center of pressure when the high lift devices are employed.

Aircraft model flying through illuminated smokescreen (picture source)
This animated GIF shows the wake of the tail as a darker box inside the bigger wing wake. It forms two small vortices which rotate against the rotation direction of the wing wake and get spread out when being absorbed by the wing wake.
Friction will soon dissipate the much weaker tail wake, so at some distance all what is left is a single wake which looks slightly distorted around its center, when compared to the wake of the isolated wing.
Fun fact: The negative lift on the tail can even contribute thrust.


How do banner tow planes coordinate with air traffic control? I tried searching with terms I think were correct around the net, but no satisfying results.

I have seem many times small planes circling around when there is some special event going on. They have advertising banners trailing behind them. For busy airspaces like the San Francisco bay area where you just have to glance up to spot a plane, how does this work with ATC?

Do these planes have to stay under certain level that is not controlled by ATC or ATC just allocates them a block of area and declares it off limits for others?

Do they have to declare their intention of circling special event areas given the security concerns and large gathering of people?

An aircraft conducting a banner towing operation must have prior approval (written letters of authorization) from any ATC authority they will be conducting operations prior to the banner tow operation. A copy of this letter must be carried on board the aircraft. The local FSDO must also be involved (which will handle the 7711-2 application).

The first thing you need to do is to file Form 7711-2 "Certificate of Waiver or Authorization Application" detailing all regulations which will be violated (minimum safe altitudes/separation, etc).

From the INFORMATION FOR BANNER
TOW OPERATIONS FAA/FS-I-8700-1:

  Conduct all banner tow operations in VFR weather conditions defined by Title 14 of the Code of
  Federal Regulations (14 CFR) part 91, section 91.155. Operations shall be conducted only between
  the hours of official sunrise and official sunset.
  The certificate holder shall obtain the airport manager’s approval to conduct banner tow operations
  at each airport of intended operation.
  Notify appropriate airport officials in advance when banner tow operations will be in close
  proximity to each non-towered airport.

  ...

  Operations outside the geographic area of the issuing FSDO will be coordinated with the appropriate
  jurisdictional FSDO in advance and the operator will comply with all special provisions imposed by
  that office.


Where can I find an aircraft's year of certification (airworthiness certificate)? Is there a way to pull a list of all certified aircraft (of course only valid certifications) including the year of certification please?

For example I am actually trying to identify when CRJ200 PF was certified ?

thx

The FAA has a listing of all of the Type Certificate Data Sheets for certified aircraft.

So the first thing you need to do is determine the manufacturer. According to Wikipedia, “The Bombardier CRJ100 and CRJ200 are a family of jet-propelled regional airliners, based upon the design of the Challenger CL-600 business jet.” So look up Bombardier on the FAA site, and then open up the models made by Bombardier.

There are lots of CL-600 variants that all use the TYPE CERTIFICATE DATA SHEET NO. A21EA. The TCDS lists the years for each variant. The CRJ200 PF is a marketing variant of one of these, so you’ll have to do some research to find out which marketing variants match the TCDS but this should get you started.


Are there aircraft that fly without fuel or electricity? I was browsing through Wikipedia when I saw this:

  An electric aircraft is an aircraft powered by electric motors. Electricity may be supplied by a variety of methods including batteries, ground power cables, solar cells, ultracapacitors, fuel cells and power beaming.

This led me to wonder whether an aircraft could stay airborne/take off without fuel or electricity. (Other than gliders)

Yes, there are so many sources of energy you can use.

In the simplest form we have Buoyancy, Human power, Fly wheel, Rubber band.

More complicated mechanisms include compressed air, steam, hydrogen peroxide, which you can either use directly as a rocket/jet, or drive a piston engine or turbine to further drive a fan or a prop.....

Or, if you prefer, you can never go wrong with nukes

(Although one could argue nuclear and peroxide(and other mono-propellants) are fuels)

Here I'll just present my favorite out of all the possibilities.

Picture credit: TIHOOD


What is this biplane from an old photograph? Copyright photo by Real Photographs No 334

Gloster Gladiator, also on YouTube.

(Answer taken from comment by mins.)


How come planes can endure more positive than negative g's? I.e. how come V-n diagrams are not symmetric? In this question A380 reverse thrust on only half the engines some doubts were raised about the strength of structures in certain directions.
Specifically, Peter Kämpf states:

  Aluminium and Carbonfiber are almost as good in compression as in
  tension, so the direction of the load is secondary. This is not true
  if buckling stiffness is not sufficient, but in case of wing in-plane
  bending, buckling is of no concern.

This made me wonder:

How come V-n diagrams are not symmetric?

From the image it can be seen that the structure at 150 knts can only cope with -1.8g, but +3.8g.
Where does this difference come from, is it coming from difference in buckling stifnesses in different directions?

The lines start at zero load factor because with no speed there is no lift. If you move further right, the upper line is determined by the maximum lift, while the lower line is determined by the minimum lift. Both have the same value only for symmetric airfoils - regular airfoils are optimized for creating lift in only one direction.

The upper and lower maximum load factor limits of the v-n-diagram are mostly determined by maximum gust loads in level flight, and in this condition they are represented by lines emanating from +1 g, such that the distance from +1 g in terms of positive and negative load factors should be the same. Add to this that your wings will create approximately 50% more force until they reach their maximum lift as compared to the minimum ( = maximum negative) lift (the details depend on the airfoil, of course), and then your load factor limits will be 1 + 1.5$\cdot$gust load factor in positive and 1 - gust load factor in negative direction.

For an example I have uploaded the polar of a supercritical airfoil which I calculated years ago with Mark Drela's ISES. It's the best I could find quickly - most polars only show the positive maximum lift, not the limit at the opposite end.

As you can see, the maximum $c_L$ is +1.3, while the minimum $c_L$ is only -0.8.

Let's look at a practical case: Utility category airplanes must be certified for +3.8 gs and -1 g. In level flight a positive vertical gust (updraft) might add +2.8 g. The same gust strength in negative direction (downdraft) will cause a load change of only -1.9 g (because the wing will stall earlier), which, when added to the regular 1 g at level flight will translate into a -0.9 g load factor. Close enough for limiting the negative load factor at -1 g.

At higher speed the gust will not stall the airfoil in either direction, and now we can simply assume that a gust will produce a positive load of 1 + gust load factor and a negative load of 1 - gust load factor. Let the gust load factor be 2.8, and your limits will be +3.8g and -1.8g, like in your example at 150 kts.

So far, I have looked at the rationale behind the load limits for certification. But also in real life there is a difference between positive and negative load factors: The wing spar has to carry the bending moment due to lift minus the wing weight. If it would need to carry the same aerodynamic loads in both directions (up and down), the wing weight would reduce the total positive load, but would make the total negative load greater. This is why the structure cannot endure the same load factors in both directions: You need to give the wing some margin to carry its own weight in addition to the aerodynamic loads.

Things look differently if you take the v-n-diagram of aerobatic category airplanes. Now you cannot readily assume that the plane will only fly straight, but you need to assume that it will be hit by a gust while flying upside down. Add to this that the symmetric airfoil will create the same lift in both directions before it stalls, and your envelope needs to be limited at ±6 g, making the envelope symmetric.


How can bird hazard be avoided? How do airport authorities deal with with birds? Which procedures have acutually been used in order to minimize or even avoid birds on airside and landside? Is there any procedure that crew can perform in order to minimize the danger caused by birds?

Airports are responsible for bird control and should provide adequate wildlife control measures. Some major airports are provided with an ornithological department that has ravens or similar birds trained to drive away other birds from the airport premises.

However, this is not a 100% efficient solution and flight crews have procedures that must follow if birds are reported.

If large birds or flocks of birds are reported or observed near the runway, the flight crew should consider:

Delaying the takeoff or landing when fuel permits. Advise the tower and wait for airport action before continuing.
Take off or land on another runway that is free of bird activity, if available.

To prevent or reduce the consequences of a bird strike, the flight crew should:

Discuss bird strikes during takeoff and approach briefings when operating at airports with known or suspected bird activity.
Be extremely vigilant if birds are reported on final approach. If birds are expected on final approach, plan additional landing distance to account for the possibility of no thrust reverser use if a bird strike occurs.

References: http://www.birdstrike.org
http://www.boeing.com/commercial/aeromagazine/articles/2011_q3/4/


What fuel would a Bell Huey helicopter use in 1964? What type fuel would a Bell Huey have used in 1964? If that matters, let's say for a medical evacuation situation

In 1964, the Huey would use JP-4 or JP-5 .

When fitted with models T53-L-5 or T53-L9, the Huey would burn JP-4.
With engine variety engine T53-L11 it would burn either JP-4 or JP-5. The JP-5 type fuel was mainly used for Navy operations.


Are conditional line-up clearances still valid if the referenced traffic initiates a go-around / missed approach? Suppose you are the captain of Big Jet 345:

  Big Jet 345, behind landing Boeing 757, line up runway 27, behind

  Behind landing Boeing 757, line up runway 27, behind, Big Jet 345

Now suppose the landing Boeing 757 executes a go-around. Does the conditional clearance allow you to line up and wait after the Boeing 757 flies over the touchdown point?

This may sound obvious, but you should probably ask ATC.

In the sentence given it specifies that you should line up behind the Landing B757, not the Going Around B757. This sounds pedantic, but the situation has changed.

The chances are the ATC is still expecting you to be the next aircraft on the tarmac, but if you're in any doubt whatsoever, do not put your aircraft on a live runway (or anywhere else you can reasonably expect another aircraft to want to be in the next 5 minutes) without explicit, unambiguous permission.


What if traffic should give way to me but doesn't appear to be? Let's say I'm flying a GA aircraft VFR, and I don't have TCAS or similar. I see another aircraft on a converging course, and it must give way to me. (Suppose it has me on its right.) It doesn't appear to be changing course to avoid, so what should I do?

Obviously I shouldn't just wait for us to collide, but at the same time, I don't want to take action that will negate its avoiding action. (e.g. If I climb to avoid, and he climbs to avoid because he was expecting me to hold course, we will both still collide.)

The question seems to relate mostly to uncontrolled airspace, but I'd appreciate an answer that also covers controlled airspace possibilities.

Whether you have the ROW or not, it is your responsibility to "see and avoid" even if the other pilot isn't. This is the aviation analog to defensive driving; call it "defensive flying".

There are no hard-and-fast rules for collision avoidance maneuvers. You basically have six options and their combinations, any of which will put you at a different point than you would be at the expected intercept (collision) point: climb, descend, turn left, turn right, speed up, slow down.

There was a study conducted by students at the University of Illinois at Urbana-Champaign, results available here, which might be helpful. The primary purpose of the study was to determine the usefulness of a computer traffic display in aiding the pilot to spot and avoid the traffic, but a secondary goal was to determine the most likely (and safest) collision avoidance maneuvers when presented with "intruders" on a collision course in each of 12 basic intercept paths (overtaking, crossing, or approaching, from the left or the right side, and climbing, level or descending). Among the lessons learned were:

Pilots (CFIs were used) were most likely to maneuver purely in the vertical to avoid traffic, moving opposite the vertical direction of the plane in sight and preferring to climb if the intruding traffic was holding altitude.
Despite the pilots' preference for the vertical, the maneuvers that cleared the "conflict" in the shortest time were in the horizontal plane, either turning opposite the plane's relative direction of travel to move behind, or slowing to let the traffic pass in front.
Pilots tended to do what was "easiest" at the time the conflict arose, especially if the intruder was sighted late (because the traffic didn't appear on the computer display; another of the variables they tested). Thus, single-axis maneuvers were most common (not counting the use of throttle to adjust power while performing a maneuver, such as cutting power to dive or increasing it to climb or turn).

Taking all this under advisement, the maneuver most likely to avoid a collision with another plane in otherwise clear skies is a level 30-45° turn in the direction of the intruding aircraft's tail, coupled with a reduction in airspeed if the intruder is on a crossing or approaching route (if he's coming up behind you, maintain airspeed). If the other pilot sees you and reacts at the same time, his most likely move will be a climb, which is fine; if he doesn't see you or react at all, you'll pass safely behind him at the same altitude hopefully avoiding his wake (if he's bigger than you).

However, there's some interesting game theory here. Any maneuver I tell you to make, except one, will keep you on a potential collision course if the other pilot reacts in the same way at the same time. As you supposed in your question, If you both climb, or dive, or speed up, or slow down, or try to turn behind each other, you'll crash (or at least get way too close for comfort). So, anything I tell you to do because it's unlikely the other pilot will do the same will be self-defeating, because eventually other pilots will do the same thing because it works.

The one move that won't result in a collision if mirrored is a 90° turn in the same direction as the intruder's movement across your vision. If he's on your left moving right, turn right 90°. If he's on your right, turn left. If the other pilot mirrors your maneuver, worst-case (an aircraft overtaking you directly from behind who turns the same way as you) you'll end up on parallel flight paths at whatever distance you first noticed each other. Best-case, you'll be heading away from each other and after a couple of minutes you can both reverse your turn and continue along your original heading.

But, this move is the worst thing you can do in several scenarios if the other plane holds its course. In high-offset crossing routes (close to 90°), turning away from the intruder will keep you out in front of him and probably too close for comfort, especially if he's faster than you (turning the crossing-route collision course into an overtaking collision).

Lastly, any formulaic maneuver we dream up in a two-plane scenario is going to break down when you add more planes, or restricted airspace, or weather. The maneuver may work in cross-country flight, but when dealing with merging Victor airways near a population center, there will be too many aircraft for any single avoidance maneuver to guarantee you'll get out of trouble without getting into more.

So, ultimately, your call.


Could the Wright brothers fly across the US today? If the Wright brothers were still alive (and in very good health for their age), could they fly one of their aircraft across the United States today?

Specifically, I'm looking at the Wright Model B, a commercially-produced biplane with a maximum speed of 45 mph, a range of 110 miles, and no radio on board.  It was originally produced in 1910, while the first flight across the US (with plenty of stops) was in 1911.

Could a pilot with a Wright Model B use modern airports?  Could they navigate?  Could they keep to their designated airspace?  Could they do all they needed to do to fly in an FAA-approved manner?

It's possible, but it would be difficult under today's regulations.

Restrictions (regulations):

Avoid any controlled airspace that requires talking to ATC
For the sake of argument I'll pretend we have no radio on board, so no class B, C, or D airspace.
(You COULD call the controlling agency and coordinate with them, but let's just pretend we don't have a cell phone either.)
Avoid any airspace within a mode C veil
Because presumably we don't have a transponder on board we can't cross mode C veils.
Avoid any restricted/special use airspace
Duh.
Comply with any other restrictions noted on the chart
I did this in 10 minutes - I may have screwed up a little.
Fuel Reserves
This is the one that makes it tough.
With no wind 110 miles at 40MPH (the cruise speed) is ~2.75 hours endurance - I assume that's to empty tanks (which is how it's usually quoted for aircraft).
The FAA requires at least a 30 minute reserve per FAR 91.155, which means we can fly for 2.25 hours (90 statute miles, 78.2 nautical miles) before we need to land. All legs need to be under that. (It's possible a flight like this could get a waiver from the FAA, but let's assume nobody applied for one.)

Restrictions (Other):

Refueling
Where possible legs should end at airports that have fuel available.
(This isn't a hard "must" since presumably the Wright 1B can burn whatever kind of gasoline we can find once we're on the ground).
Airports
I'm excluding private / restricted airports from consideration as landing spots (again, we'll pretend our pilot has no cell phone and therefore can't coordinate landing access at these fields).

Simplifying Assumptions:

Simple fuel burn
Not having numbers for this aircraft I'm assuming fuel burn will average out such that the aircraft's endurance on all legs is about 2.75 hours (78.2 nautical miles with no wind). This simplifies the planning
There is no wind
(Or if there is, it's always a tailwind.)
There's an aviation GPS (or something like Foreflight) onboard
Frankly I wasn't going to spend an hour looking for landmarks.
You could probably manage the flight by dead reckoning if you had to though.
The Wright Model B can climb high enough to clear any obstacles/terrain
Again, not having numbers for the aircraft (service/absolute ceiling) I'm just making the assumption to simplify things.

So if we put all that together can we plan this flight?
What do you think I did with the first half of my lunch hour?

This is one possible route - there may of course be others

I believe I met all the restrictions, if I screwed up I'm sure someone will edit the flight plan (or come up with a different route).

A Note on Performance
As I mentioned in the assumptions I didn't have performance data available for the 1B when I laid out this route. Some folks helpfully pointed out in comments that there are flying replicas of the 1B.  These don't appear to be "exact reproduction" replicas, but I was able to find some performance data on them.
Given the maximum altitude in the performance figures (2,000 feet MSL) it would probably not be possible to fly the route plotted above with the reproduction equipment available (several legs are well above 2,000 feet MSL), and I would assume the original 1B had comparable performance.


Can a commercial airliner be too heavy to take off? According to this question's answers, MTOW (or MTOM) is the Maximum Take Off Weight, which is everything up to and including trip fuel. Then there is one step above that, MRW, or Maximum Ramp Weight, which is MTOW plus fuel used to taxi out to take-off.

Can a plane be given too much roll-out fuel, so as the plane is actually too heavy to take off, without having to do perhaps another lap around the airport?

My thoughts are that there are simply no scheduled flights which require a total amount of trip fuel that would make roll-out fuel cause the plane to be too heavy for take off.

EDIT: Although (in a comment) I am asked to possibly change the title of the question to fit more closely (include fuel), after considering it, I've decided to leave it alone. It is unlikely that a plane would be loaded to the point that it is too heavy to take off, before fuel is added. I believe it would be a 100% certainty that it was the addition of fuel that will make (all)(commercial) aircraft go beyond MTOW. There might be some edge cases of contents (payload) being too heavy, but if that were the case the plane would not even be considered for take off (without fuel).

It is possible to arrive at the runway with too much weight to takeoff, but this result is generally a mismanagement of fuel.  The most likely scenario this happens is when you are going to be at MGTOW for takeoff but need fuel to get to the runway (putting you over MGTOW at the gate) and are anticipating a long taxi or long lines at a de-ice pad.

If the long taxi doesn't materialize this can result in getting to the runway with too much fuel.  Recognizing this, fixing it is often as simple as taxiing with both engines instead of just one.  If you are really overweight you just ask to get put somewhere you can wait while running both engines and wait for the weight to come down.  There is really no benefit to taxiing around the airport versus just waiting in one spot to burn fuel.


What is the difference between experimental and amateur built aircraft in the US? What is the difference between experimental amateur and amateur built aircraft in the US, or are they the same?

If not, is there a difference re specifications, inspections, engines, passengers, etc.?

The FAA provides pretty clear definitions and/or explanations:

Amateur built:

  Title 14, Code of Federal Regulations (14 CFR), part 21, section
  21.191(g), defines an amateur-built aircraft as an aircraft "the major portion of which has been fabricated and assembled by person(s) who
  undertook the construction project solely for their own education or
  recreation."

They define Experimental as a category, since it has to do with how the airworthiness cert is issued:

  A special airworthiness certificate in the experimental category is
  issued to operate an aircraft that does not have a type certificate or
  does not conform to its type certificate and is in a condition for
  safe operation.  Additionally, this certificate is issued to operate a
  primary category kit-built aircraft that was assembled without the
  supervision and quality control of the production certificate holder.

And further

  Special airworthiness certificates may be issued in the experimental
  category for:

  Operating amateur-built aircraft: to operate an
  amateur-built aircraft in which the major portion has been fabricated
  and assembled by persons for their own recreation or education.
  Operating kit-built aircraft:  to operate a primary category aircraft
  that was assembled by a person from a kit manufactured by the holder
  of a production certificate for that kit, without the supervision and
  quality control of the production certificate holder.

So... All amateur built aircraft are experimental (flown under an experimental airworthy type certificate) but not all experimental's are amateur built, for example a pre-production aircraft may need to be registered as an experimental for test flights before a type certificate is received.


What are IFR departure categories? I'm looking at the takeoff mins and DPs for Reno/Stead (RTS.)  It lists takeoff mins for Cat A and B, Cat C and D NA:

  TAKEOFF MINIMUMS: CAT A,B only, CAT C,D NA. Rwys 8,14,  1300-2 or std.
  with a min. climb of 400' per  NM to 6500.  Rwy 26,  1900-2 or std.
  with a min. climb  of 410' per NM to 7200.  Rwy 32,  2300-2 or std.
  with a  min. climb of 420' per NM to 7200.
  (Source)

What are the departure categories?  I can't find any mention of them in the instrument flying handbook.

The categories are actually approach categories that are also used for departures. From the AIM, 5−4−7. Instrument Approach Procedures

  Aircraft approach category means a grouping of aircraft based on a
  speed of VREF, if specified, or if VREF is not specified, 1.3 VSO at
  the maximum certified landing weight. VREF, VSO, and the maximum
  certified landing weight are those values as established for the
  aircraft by the certification authority of the country of registry. A
  pilot must use the minima corresponding to the category determined
  during certification or higher.

  Category A: Speed less than 91 knots.
  Category B: Speed 91 knots or more but less than 121 knots.
  Category C: Speed 121 knots or more but less than 141 knots.
  Category D: Speed 141 knots or more but less than 166 knots.
  Category E: Speed 166 knots or more.

These categories are used to determine visibility and ceiling minimums for an approach and determine the protected area for circling approaches. As you can see in the departure minimums you quoted, they are also used for departures.


Where does the APU draw its intake air? In an airliner, where does the APU draw its intake air?

Is it a similar location for all airliners, or do different options exist?

The APU is usually located at the rear of the aircraft, in the tail, so the intake is generally somewhere on the side of this location. Aircraft place the inlet in different places though, and some even put the APU somewhere different. For some examples:

737 intake, the small NACA inlet at the bottom

E145 (the place they don't want you to put de-icing fluid)

B777 (the scoop that opens upwards)

A330 (a scoop on the underside of the tail)

B727 (inside of the wheel well)

Here is an interesting thread including other examples.


Did we get closer to another plane than we were supposed to, or was the pilot just protecting our delicate sensibilities? Yesterday, April 28, 2019, I was flying on Alaska flight 557 from LAX to PDX.

About an hour into the flight (near the California/Oregon border) I was looking out the window and saw a jet travelling the opposite direction from us.  It was travelling exactly the opposite direction of us and I saw it when it was ~45-60 degrees forward of us.

Within a couple of seconds of my seeing it, we banked sharply to the right.  It was not a violent turn; An answer to this question describes true evasive maneuvers as, "those of you not strapped down would have been hurled to the ceiling or slammed to the floor and your stomach would be heaving in a different direction from the rest of you." - and we didn't have anything like that.  I'm not sure I would have even noticed the turn had I not been looking out the window.

However, it was a pretty sharp mid-flight maneuver, and because I was over the wing, I didn't get to see the other airplane at closest approach because the wing blocked my view.  I would estimate that it was about 3-5000 feet away from us.  I felt like he was at pretty close to our altitude, but again, as the linked question says, that's hard to say for sure.

The linked question points out that distances and altitude differences are hard to judge.  That's fair, so I'll offer the following bona fides:

I live about half a mile from a commercial airport, perpendicular to the end of the runway, so I have a good idea of what jets that are half a mile away from me look like.  I would estimate that the other jet was a bit but not a lot further away than that.
If two jets pass by each other at 1/2 mile, and you can see another jet that is 60 degrees in front of or behind you, and he, like us, was travelling 480 mph, he would have been in my field of vision for 6.5 seconds.  That sounds about like what I remember.  At 3 miles, that number turns into 40 seconds.  I don't remember the exact amount of time, but my initial estimate before I did this math was 8 seconds.

I could imagine our pilot banking the plane simply to lessen the odds of the passengers noticing a safe encounter, as even a safe encounter leads to awkward questions on sites like this.

So, my question: Did we have a near miss, or was this a standard close-but-intended encounter?

From the flightradar24 playback, it appears to have been an encounter with Etihad Airways 171.

Your flight (Alaska) was at FL360, while the opposing was at FL370. Therefore, there was 1000 feet of vertical separation between them, which is typically considered safe when operating with RVSM, Reduced Vertical Separation Minima rules (see other answers).

I also looked up the LiveATC recordings archive (Seattle Centre Sector 14 high, 28/04 2000Z), and found a clip that I think corresponds to the event:

  Alaska 557, can we take a heading right of course to avoid some wind?
  Affirmative
  Ok, deviation approved [...]


Why doesn't temperature affect Pressure Altitude? In this picture:

it states the tops and bottoms of the 3 columns of air have the same pressure.
This explains the error in altitude indications given in a non-standard temperature.
Pressure only drops 1 inHg per 1000 ft. when temperature is standard.
Assuming that the bottoms of the column of air are at sea level, why aren't pressure altitude readings (setting altimeter to 29.92) affected by the True altitude formula, TA = IA + (4ft. x (1000s of ft) x (OAT - ISA))?
I was always told temperature does not affect pressure altitude readings because the atmosphere is not a fixed volume of air. If temperature increases, it will also expand in volume, like how the picture explains.
I could see how pressure altitude wouldn't be affected by 4ft. per 1000ft per (delta°C ISA) only if the picture assumed the bottoms of the pressure started at ground level.
Or does it affect pressure altitude, just very slightly and non-significant? Not as much as if you were in a fixed volume of air...

The picture you have displayed is correct. But, your understanding of what it is saying is incorrect. The picture is explaining the reason your Indicated Altitude will change with temperature for the same True Altitude. And, your True Altitude will change with temperature (a potentially dangerous situation) for the same given Indicated Altitude.
Your misunderstanding may stem from the fact that the Indicated Altitudes and the field level barometric pressure (or at least the Altimeter Kollsman Window) setting are the same in all three temperature scenarios. This is not the case for the pressure at 10,000 feet MSL True Altitude. The atmospheric static pressure at altitude for the three scenarios is not given. And, they can not be equal to 29.92.
The static atmospheric pressure is higher for the cold scenario and lower for the warm scenario at 100,000 feet MSL True Altitude. You would think that this would be the opposite way around. And, it is for air confined in a container. But, not for unconfined air or air confined in different sized containers.
Atmospheric air will become less dense and rise when warmed. This will create a partial void of air below it. This partial void is an area of low pressure since the surrounding air has yet to move in to fully replace the vacating air. If the air were to be cooled, it would sink onto the air below it. This would create an area of high pressure as the existing air has not moved outward in sufficient quantity yet.
How does this affect the different types of Altitude? Like this:

True Altitude is the height above MSL measured in actual feet of distance.
Pressure is just a measurement of the amount of air interacting with the measurement device and the average amount of energy each air particle has. Temperature will affect the amount of energy possessed by each air particle proportionately. This will either cause the  pressure to change proportionately. Or, it will cause the volume and density of the air parcel to change proportionately.
Barometric Pressure (Altimeter Setting, Kollsman Window Setting) is just the static atmospheric pressure at field elevation adjusted to show what the pressure should be at Mean Sea Level.
Indicated Altitude is just the reading you receive from your Altimeter. Your altimeter is just a very accurate pressure gauge (a barometer) calibrated to show the height above a specific reference line of pressure. The pressure and density of air at lower altitudes are greater than they are at higher altitudes. This is due to the sheer weight of the air from above pushing down and compressing the air below. The amounts of changes of air pressure and air density are known. This is based on observationally, scientifically and mathematically derived formulae and estimations that are based on the International Standard Atmosphere. On an ISA day, that reference line is equal to the Mean Sea Level. That is not always convenient since the atmosphere is not always at standard pressure and temperature at Mean Sea Level. So, most altimeters can be adjusted to account for non-standard barometric pressure.
Pressure Altitude is just the height above the mathematically derived line representing where the International Standard Atmosphere pressure of 29.92 inches of Mercury should be felt. Pressure Altitude is the height in feet you would feel the same pressure on a non-standard day as you would on an ISA standard day in feet MSL.  If the atmospheric pressure at MSL (or the barometric pressure at field elevation) is not standard, the two beginning levels will not be in the same place. You would have to make an adjustment to the height of MSL to derive the Pressure Altitude.   The pressure of air is derived from its volume and energy content. Temperature is a factor in this only if the air is confined or in a container.
Density Altitude is just the height above the mathematically derived line representing where the International Standard Atmosphere density. Density Altitude is the height in MSL where you would feel the same density on a non-standard day as you would on an ISA standard day.   If the atmospheric density at MSL is not standard, the three beginning levels will not be in the same place. You would have to make an adjustment to the height of MSL to derive the Density Altitude.   The density of air is derived from its weight and volume. Both pressure and temperature are factors in this only if the air is unconfined or in a container.

You derive Density Altitude by adjusting Pressure Altitude by atmospheric temperature. You derive Pressure Altitude by adjusting the True Altitude by the atmospheric pressure. You have to have each to get the next.
Case in point. If the air were confined to nice, neat, little columns with defined and rigid lateral boundaries and adjustable vertical boundaries, the average pressure in each container would remain the same. The heights of each column would be different based on temperature. For extremely tall columns, the pressures at the bottoms would all be equal. And, the pressures at the top would all be equal. But, the rate at which the pressures would change with height would be different. Since Indicated Altitude is just another way to represent the static atmospheric pressure at altitude, the Indicated Altitude of 10,000 feet MSL would be at different True Altitudes based on temperature.


What do these symbols indicate on the ATC display? I just got found ATC controller display on the internet and could you tell me what are these symbols indicating? For example the ones I highlighted in red?

The white squares are aircraft - it's course is indicated by a line. Then there is a datablock showing Callsign "FWA170C", its altitude F053 = Flighlevel 53 = 5300ft, climbing to an assigned flightlevel 190 = 19000ft.
A = altitude - below a defined transition level
F = flightlevel (steps of 100ft) - above a defined transition altitude

Transition altitude and level depend on the location and weather.

Then you have the airports, navaids, nav-fixes and the control zones showing.


What are these 4 red spots on the A-10? What are these 4 spots on the wings and fuselage of the A-10? I can't seem to find a closer shot of their wings but each spot looks like a small target with a dot and an outer circle, mostly in red, but some are in black.

I am fairly sure that these are the fuel hatches. They are placed right over the wing and main fuselage fuel tanks. (The hatches are where the fuel is put into the craft, not drawn out for sampling). During ground fueling, the hatches are used to refill the tanks.


How to deduce the dynamic general equations for a non-symmetric level turn manoeuvre? I'm currently studying flight mechanics on a subject at my engineering degree and I'm trying to solve some standard case exercises with the general equations and diferent reference frames.
I've been able to solve multiple exercises on different looping manoeuvres enclosed in the vertical plane but I can't deduce the general equations for a horizontal plane.
$$ T
\cos\varepsilon\cos\nu - D - mg\sin\gamma-m\dot{V}=0\\
T\cos\epsilon\sin\nu-Q+mg\cos\gamma\sin\mu+mV(\dot{\gamma}\sin\mu-\dot\chi\cos\gamma\cos\mu)=0\\
-T\sin\varepsilon-L+mg\cos\gamma\cos\mu+mV(\dot\gamma\cos\mu+\dot\chi\cos\gamma\sin\mu)=0
$$

So starting with the above and taking into account some simplifications I get to an intermediate state which is quite similar to the solution for the problem which is the following:

$$T\cos\nu-D=0\\
L\sin\mu+T\sin\nu\cos\mu=\dfrac{W}{g}\dfrac{V^2}{R} \\
L\cos\mu-T\sin\nu\sin\mu-W=0$$

My question is: How is it possible that the Lift term appears in the second equation if the starting equation didn't consider it? And also, why the trigonometric relations for the thrust change?
(This results are for a non-symmetric manoeuvre).
I can't get in my mind why the general equations used in all the books can't give in a direct way the desired result without adding new terms.

Reference frame for the equations is wind-axis.
The angles used are:

$\nu =$ Thrust side-slip angle

$\varepsilon=$ Thrust angle of atack

As we are using wind-aixis reference frame:

$\mu=$ velocity roll angle

$\gamma=$ velocity pitching angle

$\chi=$  velocity yaw angle

$W=mg$, $T=$ thrust,  $D=$ drag, and $Q=$ lateral aerodynamic forces

Your equations seem to be in wind-axis, and look a little weird from my literature (referencing Stevens and Lewis, Aircraft Control and Simulation). I'm more used to specifying mechanics from the body-axis.

Legend: $\theta$ is Euler pitch angle, $\phi$ is bank angle, $\psi$ is yaw angle, $p$ is body roll rate, $q$ is body pitch rate, $r$ is body yaw rate, $\alpha$ is angle of attack, $Y$ is aerodynamic side force (in stability-axis), $u$ is body forward speed, $v$ is body lateral speed, $w$ is body vertical speed.

A. Thrust aligned with body-axis

I will assume:

Thrust is aligned with the body-axis.
All aerodynamic forces are aligned with the stability-axis (see this question for the rationale).
No wind, so that the velocity in body-axis is the relative air velocity ($\alpha=\tan^{-1}(w/u)$,$\beta=\sin^{-1}(v/\sqrt{u^2+v^2+w^2})=\sin^{-1}(v/V)$).

For the general 6-dof, we have:

$$T-D\cos\alpha+L\sin\alpha-mg\sin\theta=m(\dot{u}+qw-rv)$$
$$Y+mg\cos\theta\sin\phi=m(\dot{v}+ru-pw)$$
$$D\sin\alpha-L\cos\alpha+mg\cos\theta\cos\phi=m(\dot{w}+pv-qu)$$

In a coordinated turn, the ball is centered, which means that the gravity component cancels out the centripetal force, and the aerodynamic forces in the y-axis must be zero.

Furthermore, in the inertial frame, we should only see a non-zero yaw rate ($\dot{\psi}$) for a steady turn. So translating this back into body-axis, we have:

$$p=-\dot{\psi}\sin\theta$$
$$q=\dot{\psi}\cos\theta\sin\phi$$
$$r=\dot{\psi}\cos\theta\cos\phi$$

To make the matter somewhat clearer, we can choose to make small angle assumptions on $\alpha$ and $\theta$, and $u\approx V$, and eliminate all second order terms. This brings us to:

$$T-D+L\alpha-mg\theta=m(\alpha V\dot{\psi}\sin\phi- \beta V\dot{\psi}\cos\phi)$$
$$mg\sin\phi=mV\dot{\psi}\cos\phi$$
$$-L+mg\cos\phi=-mV\dot{\psi}\sin\phi$$

From geometry, a particle tracing out a constant circular path with a rate of $\dot{\psi}$ will have a radius (i.e. turn radius) of: $R=V/\dot{\psi}$. So the second equation is now:

$$tan\phi=\frac{V\dot{\psi}}{g}=\frac{V^2}{gR}$$

We can define a stability-axis load factor ($n_{z_s}=\frac{L}{mg}$), which would closely approximate the body load factor for small AOA. The third equation can be expressed as:

$$n_{z_s}=\cos\phi+\frac{V\dot{\psi}}{g}\sin\phi=\sec\phi$$

At this point, we've completely reproduced the performance equations relating load factor, bank angle and turn radius from the 6-dof equations.

B. Thrust asymmetric with body axis

Let's say that the thrust vector is angled with the body axis by a pitching angle of $\epsilon$ and a yaw angle of $\nu$.

So in the body-axis, the thrust vector is:

$$\boldsymbol{T_b}=\begin{bmatrix} \cos\epsilon\cos\nu & -\cos\epsilon\sin\nu & \sin\epsilon \\
\sin\nu & \cos\nu & 0 \\
-\sin\epsilon\cos\nu & \sin\epsilon\sin\nu & \cos\epsilon \end{bmatrix}
\begin{bmatrix}T \\ 0 \\ 0 \end{bmatrix}$$

We now have modified 6-dof:

$$T\cos\epsilon\cos\nu-D\cos\alpha+L\sin\alpha-mg\sin\theta=m(\dot{u}+qw-rv)$$
$$T\sin\nu + Y+mg\cos\theta\sin\phi=m(\dot{v}+ru-pw)$$
$$-T\sin\epsilon\cos\nu + D\sin\alpha-L\cos\alpha+mg\cos\theta\cos\phi=m(\dot{w}+pv-qu)$$

Again assume that the ball is centered, thus $T\sin\nu = -Y$. The conclusion from the second equation (relating bank angle to yaw rate and turn radius) would be the same as before.

The third equation can be reduced to:

$$\frac{1}{mg}(T\sin\epsilon\cos\nu+L)=\sec\phi$$


Is there any flight school that uses jets as part of their training program? Is there any flying school out there that use "jets" as part of their training program? I mean like a Cessna Citation or Phenom.

Yes, Lufthansa flight training in Bremen uses the Cessna Citation CJ1+.

D-ILHA
D-ILHB
D-ILHC
D-ILHD
D-ILHE

The KLM flight academy used to have Cessna Citations, but I think they no longer use them as part of the training.


Is there any benefit to folding wings on commercial aircraft? This video shows NASA researching folding wings, in what looks like a model of an airliner. What would be the benefit to this technology?

It would allow an aircraft to have a wingspan of >80 meters yet still be able to be serviced at a standard airport gate.

There are a variety of benefits to longer wingspan, but the major drawback is that commercial passenger airports are designed around that 80 meter box.


What is the most effective way for a VFR pilot to scan the instruments during manoeuvres? May I ask your opinion on what is the best and most effective pattern for a VFR pilot to scan their instruments during manoeuvres?

A VFR pilot shouldn't really be "scanning" the instruments in the sense that an IFR pilot does; he should be scanning the sky for traffic (see my first answer) while using his peripheral vision to maintain attitude.  Yes, he should periodically (and briefly) check the instruments to make sure nothing is amiss, but then go back to scanning for traffic.  I wasn't taught any particular "scan" for that, just to look at whichever instruments seem most useful for what I'm doing at the moment.

If you're having trouble holding proper altitude and airspeed as a VFR student pilot (from a comment to other answer), you may be spending too much time looking at the instruments rather than not enough.  That may seem counter-intuitive, but the key to both is attitude.  Get the right attitude, using the artificial horizon or other instruments at first if necessary, then look outside at the real horizon (in particular, the relation of your nose to it) and then just maintain that picture while you do your traffic scan.

The only time a VFR pilot is supposed to be "scanning" the instruments is during hood training.  For that, I was taught the "T" scan: assuming you have a six-pack in the standard arrangement, you focus on the AI (top center) and then briefly look left at airspeed, then back, then down at heading, then back, then right to altitude, then back.  Repeat until the hood comes off.


Is there a relationship between control surface deflection and a particular turn radius or bank angle? I am making a project which includes automation of aileron, rudder and elevator deflection.

Is there a quantifiable relation which can tell me the amount of deflection required for any radius of turn if the other parameters are put constants.

You need the ailerons only to bank the aircraft; once the bank angle is reached, the aileron deflection is mostly close to zero. I assume we are talking about stationary turns, so speed and aircraft mass will not change significantly over the duration of the turn.

While turning, several moments need to be balanced to keep the roll angle constant, and a good design does this without requiring aileron input:

The rotation around the vertical axis causes more airspeed over the outer wing, increasing its lift. This causes a rolling moment into the turn.
The rotation around the vertical axis causes a sideslip condition at the vertical tail which causes a yawing moment against the turn.
The inertial forces try to pull the wings level. This causes a rolling moment against the turn.

However, the elevator needs to be held at a slightly more negative angle than in level flight to pull the required load factor $n_z$. In a turn, the load factor is proportional to the bank angle $\Phi$:
$$n_z = \frac{1}{cos \,\Phi}$$
Radius $R$: $$R = \frac{v^2}{g\cdot tan\,\Phi}$$
Angular velocity $\Omega$ (rad/sec): $$\Omega = \frac{v}{R} = \frac{g\cdot tan\,\Phi}{v}$$
The amount of elevator deflection needed depends on the stability margin (expressed as $\frac{c_{m\alpha}}{c_{L\alpha}}$) of the airplane, its pitch damping (expressed as $c_{mq}$) and elevator effectiveness (expressed as $c_{m\eta_H}$).


Who checks the instruments and avionics before the crew boards an aircraft? Before the crew boards the aircraft for a commercial airline flight, is there anyone who checks the instruments and avionics system? I'm sure the engines are checked  but what about the avionics systems, instruments, sensors,etc.?

There was an accident due to an incorrect reading of the pitot sensor, is there somebody to check it?

In general, nobody else does.

When pilots arrive to an aircraft for the first flight of the day, extra checks are performed by the crew to verify aircraft systems are all working properly.  These checks are done once per day and subsequent flights will perform abbreviated checks instead.  A visual walk around inspection is accomplished before and after every flight.

Maintenance will check on airplanes at required intervals but outside of specific checks (associated with the carriers approved maintenance program) the only time they'll check something like a pitot tube is if the crew notes a problem and writes it up.  At that point maintenance will address the issue to return the aircraft to airworthiness.


Can the overwing exit slide be used when ditching in an A320? I want to ask if an overwing exit slide in an Airbus A320 can be opened at all when landing or ditching. Is the exit still usable? Or it is blocked and we have to move the passenger to another one?

And in ditching is the water level one of the reasons why it will not be opened and the reason the exit is blocked? If it was the case, why to consider the primary exit in ditching is the over wing exit? If it is deployed we will not use it in ditching.

The over overwing exits are secondary exits in a ditching and they should be used only if it becomes absolutely necessary to use them. The reason is because, the escape slides of the overwing exits are just slides and not rafts as they cannot be used as long term flotation devices. Moreover, unlike the slide rafts, the escape slides on the overwing exits cannot be detached from the aircraft. If the aircraft sinks, it takes the slides with it. The rafts can be separated away from the aircraft and can be used as small dinghy to hold the passengers. Furthermore, the rafts also have a loop to which you can attach the survival kit.

Here you can see that the A320 has four slide rafts (fwd and aft doors) and two overwing escape slides.
If the usage of overwing exits become necessary then they can be used in a ditching. In the Hudson landing, they used the overwing exits because the aft exits were rendered useless due to the considerable amount of impact damage received by the aft fuselage of the aircraft. Nonetheless, there are ditching related safety devices in the overwing exit. This is because in a ditching, the wing may get slippery. So, there are life lines that can be attached to assist passengers to escape the aircraft over the wing. This is what that yellow hook you see on the A320 wing is used for. So, yes wing exits can be used in a ditching, but they remain as secondary exits as long as all the other four exits are in working order.


What is the late BF109's (G models) internal fuel capacity? What is the late BF109's (G models) internal fuel capacity? I've been trying to google the answer for a few hours with no luck, perhaps someone here has the right source

The BF109G could carry 400 liters of fuel internally, and up to two 300 liter drop tanks externally.

You can also find the information in the flight manual, but you have to be able to read German. It's on page 7, under "Kraftstoffanlage".


What device in western countries allows ATC to get clearances or search flight plans automatically? In Korea, there is a device called 'Flight data terminal' which enable air traffic controller to get clearance or search certain flight plans automatically. But I found that there is no 'FDT' in western countries. I believe there must be some devices whose functions are similar to FDT of Korea, so I want to know the name of that device.

The European equivalent would be the Flight Data Processing System (FDPS). The FDPS receives flight plans over the Online data interchange (OLDI) / ATS Message Handling System (AMHS) from the Integrated Initial Flight Plan Processing System (IFPS) which is operated by EUROCONTROL. In addition local flight plan can be added to the FDPS.

Aircraft operators file their flight plan with the IFPS, which checks the flight plan for correctness (syntax errors, route errors, etc) and determines whether the plan is acceptable to the air traffic service providers. If necessary, plans are rejected or modified. Once the plan is acceptable, it is distributed to all Air Traffic Control units (ATCU) along the route.

In the ATCU, the FDPS will receive the flight plan and store it in its flight plan database.

It must be noted that the FDPS is much more than just a flight plan database. It is at the heart of the air traffic control unit. It correlates flight plan data with actual radar tracks, updates flight plan with inputs from air traffic controllers and it supports local flow management functions, conflict detection systems and much more.


Which regulations require the ARROW documents? In the US, a common mnemonic for the documents that must be on board an aircraft is ARROW:

Airworthiness Certificate
Registration Certificate
Radio Station License (international flights only)
Operating Handbook
Weight and Balance

Which regulations state that these documents must be on board?

It is in several places:

Airworthiness Certificate  FAR 91.203
Registration Certificate FAR 91.203
Radio Station License (international flights only)
Operating Handbook FAR 91.9
Weight and Balance FAR 23.1589

CFR 91.9:

  (a) Except as provided in paragraph (d) of this section, no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards, or as otherwise prescribed by the certificating authority of the country of registry.

  (b) No person may operate a U.S.-registered civil aircraft -

    (1) For which an Airplane or Rotorcraft Flight Manual is required by § 21.5 of this chapter unless there is available in the aircraft a current, approved Airplane or Rotorcraft Flight Manual or the manual provided for in § 121.141(b); and

    (2) For which an Airplane or Rotorcraft Flight Manual is not required by § 21.5 of this chapter, unless there is available in the aircraft a current approved Airplane or Rotorcraft Flight Manual, approved manual material, markings, and placards, or any combination thereof.

CFR 23.1589:

  The following loading information must be furnished:

  (a) The weight and location of each item of equipment that can be easily removed, relocated, or replaced and that is installed when the airplane was weighed under the requirement of § 23.25.

  (b) Appropriate loading instructions for each possible loading condition between the maximum and minimum weights established under § 23.25, to facilitate the center of gravity remaining within the limits established under § 23.23.

FAR 91.203

  (a) Except as provided in § 91.715, no person may operate a civil aircraft unless it has within it the following:

  (1) An appropriate and current airworthiness certificate. Each U.S. airworthiness certificate used to comply with this subparagraph (except a special flight permit, a copy of the applicable operations specifications issued under § 21.197(c) of this chapter, appropriate sections of the air carrier manual required by parts 121 and 135 of this chapter containing that portion of the operations specifications issued under § 21.197(c), or an authorization under § 91.611) must have on it the registration number assigned to the aircraft under part 47 of this chapter. However, the airworthiness certificate need not have on it an assigned special identification number before 10 days after that number is first affixed to the aircraft. A revised airworthiness certificate having on it an assigned special identification number, that has been affixed to an aircraft, may only be obtained upon application to an FAA Flight Standards district office.

  (2) An effective U.S. registration certificate issued to its owner or, for operation within the United States, the second copy of the Aircraft registration Application as provided for in § 47.31(c), a Certificate of Aircraft registration as provided in part 48, or a registration certification issued under the laws of a foreign country.

The other "R" for the radio station license was in the FCC documents, but since it is no longer required, it does not appear. If you are operating within the United States, the acronym is AROW. Outside of the United States you would have to see the Canadian, Mexican, or other countries requirements. Here is the Canadian information as an example.


What is this plane flying in overlapping circles pattern doing? I have seen this Beechcraft Super King Air coming from France near Valenciennes and flying in circular patterns over a zone of Belgium for 2 days in a row now.
What is it doing, some kind of aerial survey ?

It's acting as a television broadcast relay for the 2020 Tour de Wallonie cycling race, taking place in Belgium from August 16 through August 19.

The flight paths you posted correspond roughly to the race routes for stage 2 (August 17, Frasnes-lez-Anvaing to Wavre) and stage 3 (August 18, Montzen to Visé).

Here you can see a photo of what one of these broadcast planes looks like, with retractable underbelly antenna:


May someone please suggest EHA design procedures for AFS? Are usual electro-hydraulic actuator designs for aileron control employable for aeroelastic flutter suppression? If not, where can I find design procedures for this specific case?

This 1986 USAF experiment might help.

  The purpose of this test was to demonstrate in flight for the first time the
  feasibility of powering a primary flight control surface with an
  electromechanical actuator (EMA) in place of the standard hydromechanical
  actuation system. An advanced development model model EMA drove the left aileron
  on a specially modified C-141A aircraft and was to duplicate the functions of the
  standard hydromechanical unit. Lockheed-Georgia Co. (GeLac) was the prime
  contractor with Sundstrand Corp. as the subcontractor.

  [...]

  The C-141 aileron is statically and dynamically stable with
  the critical flutter parameters being tip weight and actuator stiffness. If
  either parameter were not present, the damping would still be sufficient within
  the aircraft normal operating envelope. Laboratory studies had shown that the
  stiffness or spring rate of the EMA was identical to the hydraulic unit. All
  else remaining unchanged, the structural damping of the modified aircraft was
  expected to be the same as that of the baseline aircraft. The baseline aircraft
  has a flutter margin more than 20% above the normal operating limitations of the
  C-141A, and well above the military specification (MILSPEC) requirements.


What happens when all electrical systems in a helicopter fail? I was thinking of asking this question at Worldbuilding, because it is for a book I am writing, but I hope this site will fit better. You can migrate this question if you find Worldbuilding more appropriate.

Let's imagine a flying helicopter, something like Eurocopter EC135. What happens if all electric equipment suddenly stops working? The reason of this failure is not important, just imagine all electricity is "gone" without any warning: all screens are black, all lights are gone, all communication is cut, GPS not working anymore etc.

I suppose the main engine is still running, no reason for sudden falling, right? But... is the pilot still able to fly it? Is it probable he would land successfully? Does the helicopter need any electricity to stay flyable?

The reason for the failure is important actually. If all the electrical systems on an EC135 helicopter fail in your classic EMP scenario then the helicopter has to make an emergency landing as the jet engine is run by a computer system which requires electricity. A power failure of that system would most likely cause the engine to revert to manual backup, which means it's still running but you need to get it down ASAP. It's also possible the engine could fail entirely, in which case the helicopter would have to autorotate, i.e. land without engine power, which is survivable, if hazardous and extremely exciting.

If you are asking about a more straightforward electrical failure of flight instruments and comms with the engine still running then the pilot would continue to fly the chopper and use backup instruments to complete the flight. Even fully "glass cockpit" aircraft have a set of "steam gauge" instruments, some which require no power whatsoever, like an altimeter and airspeed gauge which use air pressure measurements, a magnetic compass for navigation, etc. Some will also have a backup Attitude Indicator which is powered by an isolated battery system and would give the pilot attitude reference even in cloud or poor visibility. So it's less of an event that you might imagine, although instrument failure is always an interesting experience, trust me.


What are these lines on the fuselage of a 747? Have a look at this picture:

It's from Airliners.net (though I've modified it a lot) and shows some lines on the fuselage. What are they? Are they Lightning Diverter Strips like in this question ?

No, they are just the boundaries between skin panels. See below for a picture of the 747-8 fuselage during assembly.

[

Boeing 747-8 front from side (picture source)

And this is how the panels for the cylindrical section look like before they are joined:

Boeing 747-8 fuselage panels. The original picture (source) is named "wing panel skins", but these are really fuselage parts.


Are there any Navions on floats? I have a friend that is considering putting his Navion on floats. A huge challenge. I recall having seen a photo of a Navion on floats, an old black and white photo, but I can no longer find it. If we can find it, it would be very helpful as he might be able to look up the N number and get FAA records on the engineering, etc.

Can anyone help in find information on Navion float conversions?
Any thoughts on a Navion on floats?

It can be done in theory, as can most airplanes if you develop the attachment fittings and the airplane has a reasonably slow takeoff and landing speed.  The Beech 18 has long been used on floats in the bush.

Notwithstanding the fact that it was done once upon a time on a Navion, in the absence of a pre-existing STC, and access to the particular floats covered by it, the costs would be staggering unless you put the airplane into the Experimental category and even there it would be only slightly less than staggering.

I don't see any signs of a float kit that was ever developed for the Navion for Edo or Wipline, and I assume it's a certfied category aircraft, so I'm going with starting from scratch, which means staggering, which means "fuggeddaboudit".

As an ex bush pilot, as far as doing well as a float plane, several comments:

As a thing, in general, low wing float planes suck.  The wings get in the way of docks.

The takeoff and landing speed needs to be reasonably low, ideally below 50 kt.  There is a bit of a hydrodynamic "wall" you hit around that speed while aquaplaning and if you can't lift off before that speed you zoom along seemingly forever building that last few knots, not to mention the concrete like character the water starts to take on.

To have good utility, unless you base it at a lake and only fly to other lakes, the floats should be amphibious, but amphibs on a 4 place airplane leave you with a 2 place airplane (even though you've removed the landing gear).  Straight floats have only a minimal effect on useful load (because credit is taken for the lift generated by the floats plus the removal of the ldg gear), but amphibs are brutal because the weight of landing gear and pumps is ballast.  In the bush you don't see that many working airplanes with amphibs for that reason unless they really need it.

Hull insurance on a straight floatplane is somewhat higher than wheels, but on an amphib, the premium will melt your eyeballs.  Because, maybe sooner or maybe later, just about every single amphib out there will get landed wheels down on water, eventually.

The floats are destabilizing in yaw, and the Navion has a rather smallish rudder/fin, so it will almost certainly need a ventral fin.  Expect to add it to the STC development work.  Only a few sea planes have gotten away with not adding extra fin area.

So, bottom line is, unless you can find an installation STC, and can locate a set of floats covered by the STC, making it just bolt it all together, rig, make a log entry, and fly, it's a gargantuan task that will quickly bring your friend down to earth unless money is no object.


Why are airplane passengers boarded from front to back? Last time I boarded a flight (Boeing 717 with Delta, with assigned seats), the passengers were split into 4 groups and allowed to board the plane in an order that filled seats from front to back. I can understand why first/business class could go first, since they pay more. But the rest of the passengers pay the same rate.

Wouldn't it be more efficient to let the passengers that sit in the back board first? Or maybe even to just let everyone board in random order.

A number of airlines (including Delta) use a 'zone boarding' procedure. In short, the first/business class board first, followed by 'blocks' of passengers, usually from rear to front (In your aircraft, this was apparently done the opposite way).
However, it is important to point out that the back-to-front is not very efficient, atleast if you take into account the time taken to seat everyone. Experimental evidence indicates that the back to front method is one of the least efficient of all the boarding methods. The table below shows the time taken for 72 people to board a (mock) airplane using various methods.

Table from Experimental test of airplane boarding methods by Jason H. Steffen and Jon Hotchkiss
The basic problem in following back-to-front method, according to the author is that it is a serial process:

The passengers would rush into the cabin, proceed toward the back—and come to a screeching halt as the first one or two passengers stowed their luggage. The first 30 passengers (the back five rows) would take up nearly the entire length of the cabin. The rest of the line has simply moved from the airport gate into the jetway or cabin—and it moves no faster.
... In this case, only one passenger at a time is seated. The aisle in the airplane isn’t used effectively.

There has also been studies on optimal boarding procedures, which indicate that optimal procedure is different from what any airline follows.

There was a mythbusters episode that simulated boarding an airplane using various methods in vogue. Making allowances for the lack of scientific rigor, the results of boarding 173 passengers were pretty much the same- back-to-front is the slowest method.

Image from mythbustersresults.com


What are these light like panels on the overhead bins of Boeing 737? These light like panels are seen in older Boeing 737s. I've never seen them turn on. Could someone enlighten (no pun intended).

They are indeed emergency cabin lighting. See, for instance, this photo of a similarly configured 737 interior.

(Łukasz Stawiarz - JetPhotos.net)


Are there any civilian powered-lift aircraft besides the AW609? I was looking at the difference between rotorcraft and powered-lift and every example I saw was a military application (Osprey or Harrier or F35)

The FAA defines powered-lift:

  Powered-lift means a heavier-than-air aircraft capable of vertical
  takeoff, vertical landing, and low speed flight that depends
  principally on engine-driven lift devices or engine thrust for lift
  during these flight regimes and on nonrotating airfoil(s) for lift
  during horizontal flight.

I was wondering if there were any small, personal powered-lift aircraft that one might get their private pilot license in the way people get a ASEL certificate in a 172.

I know there is the AW609, but that is targeted towards the business market with a very specific niche.

I suppose some kinds of roadable aircraft aka 'flying car' designs would qualify under the powered lift category.  One example which nearly escaped the prototype stage was the Moeller SkyCar.

But beyond the Agusta AW609, I cannot think of any other powered lift category aircraft which are, or may be soon, available for sale to the general public.


Is it safe to use a parallel runway's PAPI/VASI? Many airports have parallel runways but only one runway has a PAPI/VASI. If both runways start at the same point and have similar touch-down points, is it safe to use the parallel runway's lights for the approach and landing?

Per the AIM (2-1-2 - Visual Glideslope Indicators)

  The visual glide path of the PAPI typically provides safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 4 SM from the runway threshold.

(Deviations from that are supposed to be noted in the Airport/Facility Directory, for example if the clearance path is offset from the centerline, or theoretically if you could use a parallel PAPI...)

A few miles out you're probably within the 10 degree arc, so the PAPI will be useful, but as you get closer that arc narrows, and as Lnafziger mentioned there might be an obstacle in your way (like the FAA-Standard 50-foot tree right at the threshold line).
Also as abelenky pointed out you're not supposed to be using parallel PAPIs/VASIs for approach guidance - It's a good cross-check, but not a primary reference.


What is the name of the maximum altitude at which a helicopter can fly? What is the name of the maximum altitude at which a helicopter can fly?

I recall it as "vertical limit", but I can't find a Wikipedia page for it other than a movie of the same title, which seems to concern mountain climbing altitudes.

Like with fixed wing aircraft, it is called the ceiling. Usually two ceilings are distinguished;

service ceiling, where the aircraft can still achieve a positive rate of climb of either 100 fpm (propeller) or 500 fpm (jet).
absolute ceiling, the theoretical altitude at which no positive rate of climb can be achieved. In other words: the maximum altitude at which the aircraft theoretically can fly under maximum engine power.


What is the maths behind the descent rate calculation? The descent rate calculation states that descent rate is calculated by 'groundspeed / 2 * 10'.

Another document stated that the ground speed should be multiplied by 5 (or more accurately 5.2) to acquire the descent rate. The 5.2 value is found by finding the gradient for 3 NM for 1000 feet (based on the 3:1 glide ratio), which is 5.2% (found using tan of 3 degrees). The document can be found here: https://www.ivao.aero/training/documentation/books/SPP_APC_Top_of_descent.pdf

My question is: How was the formula created? It's interesting that I can't find any info on this on the internet. Can someone show the maths behind this formula?

From Gypaets' answer
$$DescentRate = 0.0524 \cdot GroundSpeed$$
But the Ground speed is in nautical miles per hour [NM/h], and the descent rate is in ft/min.
So we have
$$DescentRate \left[\frac{ft}{min}\right] = 0.0524 \cdot GroundSpeed\left[\frac{NM}{h}\right]   $$
With $6076.12 \left[ft\right]$ in 1 $[NM]$ (yay for imperial units) and $60$ $[minutes]$ in 1 $[h]$ we get a conversion factor:
$$ 1 \left[\frac{NM}{h}\right]= \left[\frac{6076.12~ft}{60~min}\right] = \frac{6076.12}{60}\left[\frac{ft}{min}\right] \approx  100\left[\frac{ft}{min}\right]$$
This leaves:
$$DescentRate \left[\frac{ft}{min}\right]  \approx 0.0524    \cdot GroundSpeed \left[\frac{NM}{h}\right] \cdot 100_{(NM/h~to~ft/min)} $$
Further approximating it to:
$$DescentRate \left[\frac{ft}{min}\right]  \approx 5 \cdot GroundSpeed \left[\frac{NM}{h}\right]  $$


What is the purpose of a reverse-flow orientation for turbo-prop aircraft? If I decide to utilize a PT6 (ignoring for now the cornucopia of variants) as the turbine engine I will be using on my newly designed turbo-prop aircraft, do I then decide how I will orient the engine or is the this something that is engineered into the engine and thus a consideration when deciding which we choose?

Source (adapted)

What compels an aircraft design team to utilize a reverse-flow (turbine ahead) turbine engine orientation? Is the reverse-flow a design of the engine, or maybe an option?

What are the benefits/ drawbacks of reverse-flow designs to the design engineers, mechanics, flight crew, and/or airlines?

Are you talking about the reverse flow of the combustor or the reverse flow of a PT-6 installed in a tractor configuration (puller)?

The reverse flow design of a PT-6 using a power turbine separate from the gas core offers several advantages:

simplified gas core and power turbine without the additional complexities of nested spools.

modular gas core, power turbine, propeller gearbox and accessory gearbox for ease of maintenance.
design facilitates ease of installation in a pusher configuration e.g. Beech Starship, Piaggio P180 Avanti without complicated and heavy propeller drive trains.
Engine exhaust from a pusher configuration additionally provides propeller deicing without additional electrical or chemical deicing boots.
the reverse flow of the tractor layout allows for additional FOD protection vis a vis an intertial separator prior to air entering the first stage of the compressor.  This makes the engine more adept to operating from unpaved airstrips or ones covered with rocks, ice or other debris.
separate gas core and power sections reduce spool inertia in the gas core, making the core - and the engine - more responsive to throttle inputs from the flight crew or autothrottles.