Is the bleed air passengers breathe tapped from the engines before or after it comes in contact with fuel? And why? Isn't this unhealthy? Passengers are often surprised to hear that the air they breathe comes from inside the engines.

This sounds unhealthy. Can you explain, why it is not ?
Is bleed air tapped (for cabin pressurization) before or after it comes in contact with fuel inside turbofan engines on passenger airliners ?
And what is the reason for either choice ?
Specifically where is the location in this diagram ? (diagrams in answers would be very welcome)

scope: This question is about the air breathed by humans inside the plane. Q11917 is about de-icing. Neither the question nor the answers in Q11917 deal with the aspect of whether the air would be safely breathable for passengers and crew. This aspect is very well dealt with in the comments and answers below. As such, these questions should remain separate.

The bleed will be tapped from one or two of the 3rd, 4th, 5th or 6th High Pressure Compressor stages.  Usually there are two bleed ports.  The highest pressure port will supply really hot air for things like anti-icing.  The lower pressure port farther upstream will supply air for air conditioning/pressurization and other pneumatics.  Some systems combine the two ports into one system and draw from the low pressure or high pressure one as required.

The air has to come from the compressor, not after combustion, mainly because it needs to be clean ambient air free of kerosene combustion byproducts, and it's plenty hot enough anyway and taking it from the turbine would be way too hot.  The discharge in the last stages of the HP compressor can be upwards of 700-800F at takeoff thrust.

If the aircraft uses a high temperature "evaporative" anti-icing system, it will tap air from hotter stages of the compressor than if there is a non-evaporative system (Evaporative = anti-iced skin temperatures above the boiling point of water.  The leading edge will be over 100 C, like the surface of a steam iron.)

Even if it is taking "clean" air, the bleed flow will have all sorts of charred bits of things from the atmosphere in it; pollen, bits of bugs, that collect and get everything dirty in the ducting and components (at lower altitudes).  Combusted air would be ten times worse, not to mention the carbon monoxide poisoning the passengers and being way too hot to be usable in the first place.


Would it be realistic to live in an airplane? I've been playing with the idea of someday modifying a small airplane to create a sort of flying RV/Camper. The passenger seats would be removed and replaced with a flat, raised surface that would run along the wall to be used for a bed, or a desk during the day. A small chair and portable toilet could be secured below that, with room for food, etc.
Would this be usable in practice? Can a certified aircraft be modified in this way? Is it allowed to sleep in a plane on the apron overnight? Is external power ever available near airplane tie-downs? Etc.
I'm mostly asking about the U.S., but I'd be curious about other countries as well.

Sure, it actually is more common than you might think. While the general notion of a private plane is a small sleek jet to dart about in, plenty of wealthily people own larger jets equipped as you describe. Nick Gleis is somewhat famous for photographing the biggest of the biggest private jets and this article covers a lot of the really cool stuff he has seen.
The FAA does not necessarily mind how you configure interiors as long as you don't try and qualify things as a "seat" for occupancy, takeoff and landing purposes.
Sleeping on the apron is likely more about airport rules than anything else. You would need some kind of an APU to run your electronics as most airports wont want you running your engines all night...
If it does not need to fly this is always an option.
While you likely cant order the cool defense stuff there is nothing stopping you from outfitting a VC-25 similar to Airforce One which is more than livable.


How to find past flight routes between 1977/82 Latin America and the former Soviet Union? I hope now that I am in the correct place to post my question, as I have been kindly accompanied to the exit on travel part of stack overflow. ;)

Is there a way to find past flight routes between Panama City and St. Petersburg (former Leningrad) in the years 1977 to 1982?

To be precise: over which flight route would someone reach to either from Panama City to St. Petersburg and vice versa in the late 1970s?

I would need this information for an historic background check up in my genealogical (family tree) research.

Bonus point: I have heard that especially in Latin America, flights back then would "collect" passengers (part of student exchange programs between Latin America and the former Soviet Union) from capital to capital before the plane would go into the intercontinental flight, e. g. start in Panama City, going to San José, Costa Rica, to Managua, Nicaragua, to Belize City, Belize to ... to Havanna, Cuba. However, I am not sure about this claim.

Here are a series of old Aeroflot schedules. In 1977, from Latin America, they flew two scheduled routes

Lima > Havana > Lisbon > Frankfurt > Moscow
Mexico City > Havana > Lisbon > Frankfurt > Moscow

It seems unlikely there were scheduled stops not listed, as if you're including a 1h10m refuelling stop at Lisbon you may as well list them all :-). Note that most of the international flights (perhaps all the long-distance ones?) went into Moscow; there were a few into Leningrad but all European routes.

However, it is possible that Aeroflot provided a charter-type service to collect foreign students (especially if it was some kind of large-scale state-backed scholarship scheme). In which case... the "hopping" route and then to Leningrad (via a fuelling stop somewhere) seems quite plausible, but finding documentation on it forty years later would be incredibly challenging.


Why does climb gradient at Changi be at minimum of 6 and 7 percent? Changi airport, Singapore, runway 20C and 20R both point into the sea with no significant obstacle to clear. There is no residential area down there. Next land mass is about 15 km away (Batam, Indonesia) so I guess noise abatement is less of a concern. What could be the possible reason for specify climb gradient at 6 and 7 percent?

Geographical location of Changi airport

Singapore is on the Straits of... Singapore. This straits is the southern continuation of the Straits of Malacca, both form an international maritime road between Indian Ocean and Pacific Ocean, on a par with Suez and Panama.

(Source)

To add to the bustle, the Changi Naval Base, opened in 2004, is a mere 2 km East of the runways:

(Source)

If that was not enough, there is a shipping channel at the North of the airport, with two terminals near the runways: A ferry terminal, and a cargo terminal.

View of the waters South of Changi airport:

(Source)

Obstructions and climb gradient

Very large ships, including military ones can be close to the runway ends. When this happens, and to take a long takeoff into account, a large climb gradient is in use.

AIP for Changi includes instruction for obstacle clearance calculation.

On the North the climb gradient is at least 3.3%, but is increased based on ships actual height when ships exceed a specified height, and depending on the runway e.g. for RWY 02C:

  When there are no reports of vessel movement along the northern
  shipping channel, or where the reported vessel height is less than 70m
  (230 ft) AMSL, the aircraft minimum net climb gradient shall be at
  3.3%.

  Where the reported vessel height is 70m (230 ft) AMSL or higher, ATC
  shall advise pilots of the vessel height. Pilots, on receipt of this
  information, shall apply the minimum net climb gradient in
  accordance with the following table.

For RWY 02L, the height threshold is as small as 35 m and the gradient for a 110 m ship will be 10.7%, i.e. the gradient is twice.

On the South, because the traffic is larger and permanent, the guidance is different:

  All departures on Runway 20C/20R shall be on a minimum net climb
  gradient of 5% until reaching or passing 400 ft. Thereafter, the
  minimum net climb gradient shall be 3.3%.

So what happened for this NOTAM to be published, requiring a higher gradient of 6 and 7% for RWY 20C/20R? Note this is only 1 or 2% steeper than it is usually. Different possibilities, no certainty:

The South protected area border is temporarily closer to the coast.
There is a very tall ship in the vicinity.
There is an obstacle on the land.

The general formula used for MOC calculation, for North and South departures:

  For the above calculations, operators shall use the following
  information:

  a. The most penalizing obstacle is a tall vessel which is
  on the extended center line of the runway. (ATC shall advise pilots of
  the height of the tall vessel.)

  b. The required MOC is 0.8% of the
  distance (d) from the departure end of runway (DER) to the obstacle,
  in accordance with Volume II of ICAO Doc 8168 -  Procedures for Air
  Navigation Services Operations (PANS-OPS)  where, in the case of
  Singapore Changi Airport, the DER is defined as the end of the
  clearway.

  c. The distance (d) for departure Runways 02L/02C is
  measured from the DER to the shipping channel north of Changi. The
  distance (d) for departure Runways 20C/20R is measured from the DER to
  the boundary of the restricted waters south of Changi wherein tall
  vessels of height above 49m (161 ft) AMSL are not permitted. The
  distance (d) for the various departure runways is as follows

The procedure above can be used by crews to calculate an optimized climb gradient, in case the default 5% is not retained. This procedure is used to provide pre-calculated MOC for North departures.

Now I want to see the actual departure from RWY 02C! Fly me!


How does the HUD Display System work? I have seen a couple videos of fighter jets and commercial planes with HUD systems and was wondering how do the heads up displays work?

HUD

The most common form of head-Up Display (HUD) is simply an out-of-sight display screen reflected in a transparent flat sheet of glass in the viewers line of sight out the cockpit front window.

The glass sheet is called a combiner. It combines the HUD information with the view out of the aircraft.

There are coatings for glass (E.g.) which allow for reflecting a monochromatic image while allowing transmission of other colors.

The display is obviously tailored for that specific use. It must avoid obscuring the view. Therefore it mostly consists of minimal light-colored lines and numerals/letters against a dark background. The dark background allows the pilot to see through the reflection to brighter objects outside - it's a bit like the matt black upper surface typically found on many car dashboards which prevents distracting unwanted images of the top of the dash being reflected into the driver's view out of the windscreen.

Here's an example from Boeing

A HUD display is visible on the left in the pilot's line of sight. Above it, mounted on the ceiling is the projector unit.

The Projector contains optics to make the pilot's view of the display appear to be at infinity (rather than the few feet away it is in reality). This allows the pilot to read the data while their eyes are focused on far-away real-world objects outside the aircraft (runways, weather, other aircraft etc).

EFVS

Beyond the projection of basic flight instrument data is the use of HUDs for Enhanced Flight Vision Systems (EFVS) which provide a kind of augmented reality display that typically uses external infra-red camera systems to identify landmarks (e.g. runway outlines) that may be obscured to the pilot due to fog etc.


How can the landing gear of an A320 be lowered in the event of a simultaneous hydraulic and electrical failure? What is the process for lowering the landing gear of an A320 when the hydraulic and electrical systems are not operational?  What happens to the aircraft when you lower the landing gear with inoperative hydraulic and electrical systems?

The A320 has an emergency gear extension handle to deploy the landing gear by gravity in case of electrical, hydraulic, or mechanical failure. To force the landing gear to extend, one of the crew must pull the emergency gear extension handle up, then turn it clockwise three turns. The cutoff valve then shuts down hydraulics to the landing gear system and depressurizes it. This allows the landing gear to fall free to the down lock position by gravity.

Source: a320dp.com


What does "wraparound" mean in the context of flight controls? In the references regarding the flight control (for example in F-16) I see the word "wraparound". For example "Rudder coil wraparound", "IBU pitch wraparound", "IBU lateral wraparound"or "AMUX bus wraparound failure". What does this word mean in this context?

Wraparound is a method used to ensure flight control computer (FLCC) commands are reaching the actuators as they were inteded.

To maintain a desired flight condition FLCC calculates necessary control surface movements. These calculations are translated into control signals that are sent to actuators. These signals are periodically monitored by wraparound loop to verify they match the command originally calculated by FLCC.

This is the quickest (and the only viable) way to verify system integrity, since there is no need to wait for aircraft sensors to verify the plane did what FLCC wanted. Should the wraparound signal not match what FLCC commanded, the control reverts to a backup system.

Without wraparound, faulty signals would lead to incorrect control surface movements, that would in turn lead to corrective action by FLCC, and should the fault in the signal delivery persist, the corrective action would of course be also wrong.
Pilot action to supress these incorrect control outputs would be difficult at best, impossible at worst, since commands given by pilot are delivered through the faulty system. In the case of modern, unstable fighter jets, the worst possible outcome is the most likely one.

A diagram of wraparound arrangement can be seen here: NASA technical paper 2857, page 91

Wraparound is pretty well described in this patent application: Failsafe digital bus to analog protocol converter system

  A failsafe avionics interface unit (10) serves as a protocol converter system for translating data for control purposes from a digital communication bus (65) to an analog control channel as an upgrade or interface to an existing analog control system. The avionics interface unit (10) includes digital interface bus logic (101), a digital data processor module (102), an analog interface, and a mode selection circuit (104). Data communicated over the digital interface bus (65) is periodically translated into equivalent analog control signals. For safety purposes, the avionics interface unit (10) ensures the integrity of the system by repetitively looping back or wrapping the digital equivalents of the analog output signals and comparing them to commanded digital control values. The protocol converter system additionally monitors communications over the digital data bus for data continuity. If the difference between a wrapped digital equivalent of an analog output signal and an expected value exceeds tolerable limits or if communication fails, the system disconnects its interface from control using redundant software and hardware and returns control to the analog control system (51).


Why do high altitude air-launch plane designers choose to use two fuselages? We see double fuselages in both the huge Stratolaunch vehicle and in Virgin Galactics high altitude launch vehicle. What about this design makes it desirable?

It is simple to maintain symmetry if the launch vehicle is in the middle, with two fuselages on either side.

With only one fuselage, the departure of the launch vehicle would change the symmetry, and therefore the lateral stability.

One possible exception is if the launch vehicle is directly above or below a single fuselage.  This was done with the M-21 carrying a D-21 launch vehicle, where the D-21 was directly above the centerline of the M-21.


If this is not a Lippisch L-13, what is it? The image comes from a 1956 Nestle, a chocolate maker, sticker album. 'Maravillas del Universo', serie 1. Chapter has 3 pages, and is entitled: 'The sound barrier', signed by the woman test pilot: Jacqueline Cochran. It indicates it's a Lippisch L-13, but it's not, Lippisch L-13 was a rearwards swept Delta design, with a thick Vertical Fin that included the pilot's cabin, it was tested as a glider. Final version had to use a Ramjet, fueled by burning coal in a rotating basket. YouTube video link.

Alexander Lippisch did develop a similar-looking wind tunnel model, see photo. According to his Errinerungen (memoirs), Page 218, this was in 1943 and it was tested in 1944. Dan Sharp; Secret Projects of the Luftwaffe: Vol. 1 Jet Fighters 1939-1945 (Mortons 2020) shows a couple of photos on Page 219 and says that it marked the start of his delta-winged P.12/P.13 project, including the DM-1 glider which was actually built and flown. But this early wind tunnel model had only a thin central spine, with no cockpit and, like all his delta aeroplanes, was designed to fly apex foremost.

The illustration on the sticker or card is, as you note, back to front. Consequently its supersonic performance would be appalling. It is probably based on a photo of the model, with its identification based on remarks about the P.13 (or Projekt 13), but is otherwise total fantasy. Presumably there is no suggestion that the author of the article actually flew it.


How to reproduce NASA/Langley airfoils for general aviation with long chord lengths? I have scaled a NASA/Langley LS(1)-0413 airfoil to a 90 inch chord length, and now the trailing edge is 0.5in. Any longer chord length would have a larger trailing edge thickness.

  (90in*(0.0071-0.0016)=.495in)

This doesn't seem right, I have not witnessed a non-supercritical airfoil with a trailing edge larger than a .25in.

First off, do long chord length wings using the low and medium-speed airfoils have thick blunt trailing edges?

Secondly, if medium speed wings don't have blunt trailing edges how does industry taper the trailing edge? Is it assumed they will be rounded off, or sanded to a point? Should one remove from the bottom concave surface or remove from the top surface? Both will alter the exit angle of the airstream.

Thirdly, is there an ideal length chord for the NASA/Langley low and medium-speed airfoils, e.g. do they really only apply to a 36in chord lenght? Does scale matter?

You are right, such a thick trailing edge is not right. It will add pressure drag unnecessarily – quick fix: Just taper the last 10 or 20 percent of the airfoil such that a thickness remains which is sufficient for structural reasons. You don't want a trailing edge that is as sharp as a knife edge. It has no stiffness left, so it will warp and will easily be damaged.

The more elaborate way: Do as if there would be a hinge at the nose and you close the two sides, just like scissors. That will leave the contour unchanged. The "hinge" location is ideally the center of the nose radius.

Tapering the last 10 or 20% will steepen the pressure rise there and will let the airfoil stall a tiny fraction of a degree earlier than with the unchanged surface contour.


How to calculate the lift coefficient of a multi element airfoil? How to calculate the lift coefficient of an airfoil section with flaps and slats if we know the Cl for the individual elements, like Cl of wing, Cl of slat and Cl of flap?

It depends. Are the c$_l$ values referenced to the local chord? Then you need to convert them to the chord of the full airfoil so they can be added.

I wonder, however, how you can have individual lift coefficients without the total lift coefficient. If the single parts are isolated, their pressure distribution is different from that in the context of the full airfoil. Please check the source of the lift coefficients and make sure that they are representative of the local lift when flown in combination with all other parts.

Normally, what needs to be done is to use a multi-element airfoil code and calculate the lift coefficient of the full wing with all high-lift devices in place.


Why are planes generally painted white? When planes come off the assembly line at the factory, they're green:

So why are most painted white? Surely a darker colour would hide dirt better?

Is there a reason planes are traditionally white?

Here's a clip that shows a Boeing 747 being painted:

White has some significant thermal advantages over color. In most cases, this is probably just a benefit in terms of keeping the cabin slightly cooler. In the case of 'plastic' airplanes (those built with composite construction), some airframes require the use of white paint on upper surfaces to keep some elements within limits. Early Diamond Aircraft designs had a 38° C outside air temperature limit, past which the main spar is not considered structurally sound.

As a result, Diamond would only manufacture aircraft with predominantly white upper surfaces, as darker surfaces could result in significant heat gain.

Avweb has an article on the DA-20 that shows the bright red over-temp indicator that raises the maximum temperature to 55° C, added as a Service Bulletin.


What FAA rules govern tethered, outdoor UAV flight? This question is concerning the possibility of operating an Unmanned Aerial Vehicle (UAV) outdoors—a commercially available quadcopter, for example—but with the distinction of operating the UAV while tethered.

In this letter of legal interpretation, the FAA states, that:

  The FAA has repeatedly affirmed it's position that any vehicle
  designed for tethered operations only, and not for "free flight",
  should be considered a kite.

An applicable kite (over 5 lbs., etc) would be subject to 14 CFR 101.

However, any UAVs which were originally designed for free flight would clearly not meet the "kite" definition—even if operated tethered, since the original design was for "free flight" and not tethered operations only.

This is my primary question: If an UAV were attached to a tether and so operated, would that UAV remain subject to all legal requirements regarding the operation of UAVs?

Additionally, I would be interested in the following:

Is there a letter of legal interpretation from the FAA on this matter, or any other regulatory or guidance material that I am not aware of?

Are there any rules governing tethered aircraft flight, in general, apart from 14 CFR 101?

The FAA's rulemaking document for UAVs says that tethered UAVs are not considered balloons or kites (thanks to Steve V. for finding it):

  [...] a small unmanned aircraft that uses powered systems
  for actions such as propulsion or steering is not a balloon or kite
  subject to part 101

And:

  [...] the FAA notes that the definition of small UAS in this rule includes
  tethered powered small UAS

So a UAV is not a kite and it is subject to all the general UAV regulations (I think they'll be published as 14 CFR 107 at some point). There are also a couple of FAA sources that say that if a tethered aircraft of any type is capable of free flight then all the usual regulations apply. This is from the interpretation you quoted:

  Since 1957, the FAA has repeatedly affirmed its position that any
  vehicle designed for tethered operations only, and not for "free
  flight" should be considered a kite.In contrast, if an ultralight vehicle is designed to be tethered only
  until it achieves a predetermined altitude and is released for free
  flight, that ultralight is an aircraft regulated under part 103
  during the entire operation.

There's also a very clear statement on tethered balloons:

  Free and Tethered Flight Considerations. If a balloon is considered an aircraft under one circumstance (such as free flight),
  it must still be considered an aircraft under other operating
  circumstances, including tethered flight. Tethered balloons are
  considered aircraft, and must be operated in compliance with all
  construction, certification, airworthiness, registration, and
  operating regulations applicable to aircraft.

That comment about "operating circumstances" seems to be the general FAA position on tethered aircraft.


Why are bird strikes on approach or landing not as common as on takeoff? I've heard about lots of bird strike incidents that occured during a takeoff roll or the early phase of takeoff climb but hardly heard of bird strikes on approach or landing. Are bird strikes much less common on approach or landing than on takeoff or initial takeoff climb? If they are, why is it?

I've heard about lots of bird strike incidents that occured during a takeoff roll or the early phase of takeoff climb but hardly heard of bird strikes on approach or landing.

This is always a dangerous thing. Only because you hear more bird strikes that occur on takeoff, it does not mean there are more at takeoff.
I found, for example, this report about bird strikes from the year 2000. It says:

[...] 38% of the bird strikes occurred during take-off
and climb, and 56% during approach [...]

That means there are more bird strikes during approach than on takeoff. I assume things haven't changed a lot since then.
This question is even answered in the Wildlife FAQ Section of the FAA:

Q: Do most bird strikes occur while in flight, at takeoff, or landing?
A: About 60% of bird strikes with civil aircraft occur during landing phases of flight (descent, approach and landing roll); 37% occur during take-off run and climb; and the remainder occur during the en-route phase.

A more specific statistic:

Source

Possible reason for subjective perception of bird-strikes happening more often during departure
I thought a little about it and came to following possible reason: After a bird-strike on final, the pilots will continue landing. It would be unwise not to land immediately. For the passengers it will look like a normal landing. If the bird damages the engine, there is only a small change of sound, because the engines are running very low.
However, when a bird-strike occurs while taking off, there is immediate action taken by the pilots. And because the engines are at or near full thrust, the sound of a dying engine can be perceived by the passengers. Last but not least, a departing aircraft has a much higher speed than a landing one, which means more damage.
So, for newspapers, a bird-strike at take-off is more dramatic and drama sells.

More damage to the plane than a bird-strike on final
Passengers not reaching their destination
Dramatic passenger interviews about their "near-death-experience"

A newspaper is not interested in a bird-strike on final, where everything went fine and no passenger noticed anything.
To support my theorem, I googled "bird strike" and clicked on the "News"-tab. I looked through every article that had to do something with an bird-strike incident. 5 out of 6 articles were about a bird-strike on take-off. That's over 80%.


How should I answer this question about measuring airspeed using dynamic pressure? I have come across a question in the PPL Principle of Flight material which I can't understand how to answer:

  Give your opinion on the statement "Measuring dynamic pressure is the
  way to determine the indicated airspeed of an aircraft".

You're confused! Great! Confusion is just an opportunity to learn.

In the spirit of education, I won't answer your question, but I will give you some things to consider.

"Give your argument on the statement" - This usually means you're being asked to support or refute whatever comes next. It will be up to you to decide which is appropriate.
Measuring dynamic pressure - What is dynamic pressure? Are there other kinds of pressure? Is there something else besides pressure that could be measured instead?
is - Is it or is it not?
the way to - the only way? Are there other ways?
determine the indicated airspeed - Is that what is determined? Is anything else determined? Is indicated airspeed the proper thing to determine or do you need something else?
of an aircraft. - Is that correct?

If you can answer all of those, you should have no problem putting them together into a solution. If you're having problems with a specific portion, let us know what's unclear.


Can a normal PASSENGER pilot a plane with no training? This is an extreme question, but I am daring it because I want to.

Situation :

All pilots, officers, die.
just say no crews can pilot a plane
no former pilot in the passenger

Only option is for a normal passenger to pilot a plane. Is this possible?

Without any help, and no prior introduction, it is highly unlikely in a transport or biz jet.  Too much complexity, too much a priori knowledge needed, and too many flight configuration changes to land the plane.  Just an opinion.

There have been lots of attempts to take the uninitiated and have them pilot a simulator to a landing. The outcomes are not favorable, unless there is some previous experience or there is very very active coaching. Every now and then, someone writes a paper or magazine article on this. There have been no large scale studies where more than a handful of lay people have been "tested."

So bottom line, somewhat informed opinion, no it is not likely that the uninitiated would be able to fly to a selected destination and land a plane that is in the transport or bizjet class.


Does density altitude affect actual altitude? Student pilot here, working on my first rating. A lot has been drilled into my head about density altitude as we approach the hot summer months here in the northern hemisphere, and how it causes the plane to act as though it were at a higher altitude—less lift, less power, less thrust—but no one seems to understand when I ask if this also puts the aircraft higher in the sky, as well.

As near as I can understand, the atmosphere actually expands and becomes taller under hot conditions, and the various pressures that we associate with certain altitudes are actually further apart. Is there a flaw in my understanding?

It mystifies me that no one I've talked to seems particularly concerned about something that could potentially throw off your ability to judge your true altitude. Wouldn't you need to be more concerned about cold-weather density altitude when crossing mountain ranges? The mountains don't get shorter just because your pressure levels are closer together . . . right?

(Source)

The basics

Height: absolute height above ground, measured using a radar altimeter (like the helicopter on the right)
QFE: the barometric setting an airport broadcasts that makes an altimeter on ground read zero. This gives height only around the airport if the area is relatively flat. Also known as Above Field Elevation
QNH: the barometric setting an airport broadcasts that makes an altimeter on ground read the airport's elevation (height above mean sea level)
Aircraft using the same QNH below the transition level* in the same area are all flying the same indicated altitudes
Aircraft using QNH 1013 mb (29.92 inHg) are all flying the same pressure altitudes. Above the transition altitude* they're called flight levels

* The transition altitudes and levels vary from place to place. For flying below 18,000 feet in the US, you can ignore flight levels for now.

QNH is good for separation since everyone is using the same measurement system. Even if the temperature's rate of change with altitude (lapse rate) is different from the standard.

Lapse rate

(Source)

On the left is a hotter than usual lapse rate, i.e., it gets colder less slowly. Still, all aircraft using the same pressure setting will still be flying the same indicated altitudes / flight levels.

Pressure altitude (what the altimeter reads when set to 1013/29.92) adjusted for lapse rate deviation is density altitude. It's used for performance calculations.

The answer

You said, "[The] atmosphere actually expands and becomes taller under hot conditions".

Yes, but not for that reason. A hotter than standard day means the air molecules are more jumpy, i.e., they are producing more pressure. That's why 1,000 feet on the left is higher. Think of it this way, air is hot, it's still keeping pressure a bit higher (height).

Remember, a basic altimeter senses only pressure from the static port, it doesn't know the temperature.

Since the pressure is the same for the same altitudes, and the variable is the temperature, it will be lower air density on the left due to the higher temperature (angry molecules don't like to cozy up). That's why engine output and lift are impacted.

For cold weather, usually at or below 0°C (32°F), this deviation can become dangerous in mountainous areas. There are special rules and equipment for that, which are listed on the appropriate charts for airports that usually face such conditions.

Further reading:

Wikipedia: Flight level
SKYbrary: Altimeter Temperature Error Correction
SKYbrary: Transition Altitude/Level
How is non-standard OAT accounted for?
How does altimeter reading vary when departing from ISA conditions?
When calculating takeoff performance why include airport elevation in pressure altitude?
Why is Cessna 172 POH performance chart based on Pressure Altitude and Temperature instead of Density Altitude?


Does the temperature of the body of an aircraft increase its efficiency? I am working on a prototype for an airplane. I was wondering, can the temperature of the body of the plane make it more efficient? If the structure is at 25°C, does it need less energy to maintain a steady state flight than a structure at -20°C?

I had this idea about excess energy that could be collected during the day, and was wondering if there is any chance that when the batteries are fully charged and there's still excess power being generated, I could use it in order to increase the performance of the aircraft.

As your speed increases, your temperature will increase due to fluid friction of the air. When metal gets heated, it becomes weaker and more malleable. Think about when a blacksmith is hammering on a piece of iron over a hot forge. Due to this, your Vne should be reduced so your wings don't fall off.

As far as your initial question, if temperature affects efficiency; not really, unless your body gets so hot and you are going so fast as to alter the shape of the aircraft (which could happen, I suppose.)


In what direction(s) is any debris typically ejected from a jet engine in the case of failure during flight? Has there been evidence of ejected material striking the fuselage or other parts of an aircraft forward of the engine itself?

Which of the various forces acting on rotor blades dominates the trajectory of pieces in the case of a blade failure?

Other than rotor break-up, what kinds of engine malfunction typically cause component separation, and in what direction(s) is material ejected?

For debris ejection out of the engine, the failure of the engine and the failures that follow that create debris; the design criteria is that the failures must be contained in the cowling and the debris exits through the exhaust. Here is the link to the FAA Advisory Circular for designing for catastrophic failure: AC 20-128A

Here is another link that is more devoted to prior uncontained engine failure.


Can one country really ban another from using its airspace? Consider the recent restriction by Saudi Arabia on Qatar Airways flights, which prevents Qatar flights from flying over Saudi airspace. Qatar now has to use longer routes and go fly around the land mass. Does the ICAO not prevent Saudi Arabia from this kind of behavior?

Yes they can.

There was an attempt to allow one to pass over a country freely with the Freedoms of the Air however this is not a blanket thing and not everyone partakes.

  ....As of the summer of 2007, 129 countries were parties to this
  treaty, including such large ones as the United States of America,
  India, and Australia. However, Brazil, Russia, Indonesia, and China
  never joined, and Canada left the treaty in 1988. These large and
  strategically located non-IASTA-member states prefer to maintain
  tighter control over foreign airlines' overflight of their airspace,
  and negotiate transit agreements with other countries on a
  case-by-case basis.:23 Since the end of the Cold War, first freedom
  rights are almost completely universal.:151 Most countries require
  prior notification before an overflight, and may charge substantial
  fees for the privilege (see the wiki article for references)


What are the performance trade-offs in the Icon A5 spin resistant airframe? I've been looking at the website for the Icon A5 amphibian LSA and noticed the wing section clearly has two different cross sections, presumably to facilitate the stall and spin resistance of the aircraft.  One of the videos on the site shows the wing as it stalls and the tell-tales attached to the wing clearly show the flow separation for the inboard section of the wing while the outer section still indicates attached flow.  I would guess that this wing must have either some performance trade offs or else it's a significant cost, otherwise why wouldn't most GA aircraft have this feature?  Perhaps fabrication in sheet metal would be difficult as I believe this aircraft is mostly composite construction.

Though performance details of the aircraft are not available, there seems to be a significant weight penalty associated with making the aircraft spin resistant.
It appears that the aircraft had to get a specific exemption for increased MTOW (1680 lb as against 1430 allowed) due to the incorporation of spin resistant design. Note that the weight given by the manufacturer is 1510 lb, still more than allowed.
As required in the exemption, the aircraft had to be fitted with a ballistic recovery complete-aircraft parachute system, affecting the payload. The engine power is also limited to 135 hp. The range is also low (~300nm).


What to look for in a flight instructor? I want to make the most of my time and budget. There are ton of flight instructors and the quality has to vary widely. Besides being a competent pilot, what should I look for in a CFI? What are the warning signs of a poor CFI?

This is an excellent question and at the same time, very broad. Every student and pilot can give you a ton of advice about what qualities the best CFI must have. I will list a few qualities to look for and then guide you to a few resources which can further elaborate the topic.

I presume you are going for Part 61 (14CFR61.159). I also presume that you have selected a flight school or will choose from a few around your.

Once you get to a flight school, normally you will be assigned a CFI by them. They will interview you and you should do the same.

Ask the CFI why they are teaching and what their goals are
Generally speaking, one half of CFIs are doing it for their future career goals (i.e. to get a job in an airline) and others are doing just because they earned the CFI rating and hence are earning money by teaching.
Once you start flying with a CFI, see how they respond to your mistakes
You are a student and are learning something new. There is no way that you will master everything taught just once. (Maybe you can, I'm not just that smart.) Observe how the CFI will notice your mistake, bring it your attention, rectifies it themselves or gives you instructions to do it, and most importantly, how your mistake affects their mood?
Before and after each lesson, notice how they answer your questions and explain to you what you guys will be doing and have done
Some people (like me) would ask a million questions. Often times, you will find teachers/instructors who don't like to be questioned a lot. All your questions are genuine, you just need to see how they are answered.
Ask your pilot friends to guide you, or check with other students at your flight school.
Your friends can give you a very honest feedback. You can benefit from other students too, but if a CFI works for someone else, they may not work for you. You are the one to judge and make the call.

Naturally, you cannot know about a CFI's style unless you take a few lessons with them. That will definitely cost you money. But spending a little money to learn a valuable lesson is not wasting money. It is an investment.

I am not talking about some other details as they are discussed thoroughly in the references below.

Here are some resources which have answered this same question in more detail.

Pilot Tricks
Ask A Flight Instructor
wiki How
AOPA (AOPA has an article about almost everything aviation-related)
About Money
Flying Mag


How does the head-up display on a spitfire work? It turns out that the Spitfire from World War 2 had a head up display.
Does anybody know how it worked exactly?

All I could find was this picture, but no explanation:

Source

The source does not explain what it does.

Seeing as it is projected, it would only be of use if it were dynamic, that's why I'm asking.

How could they have something like that back in the day?

Edit: Not a duplicate, not all sights were gyro sights.

It's not a head-up display, it's a reflector gunsight. (Follow that link to learn how they work.) It just displays a fixed reticle to aim the cannon, not any flight instrumentation.

Some (but not all) Spitfires had a gyroscopic system to compute target leading and move the position of the reticle appropriately, based on the speed of the aircraft; I suspect that your photo is of this equipment, and that's what the range adjustment visible at the bottom is. More about that can be found at How did the gyro gunsights of WW2 get the range and lead of a target?

  Seeing as it is projected, it would only be of use, if it would be dynamic, that's why I'm asking.

That's not actually true. A "static" reflector gunsight is hugely advantageous over a collimator sight (i.e. a tube that you look through) or iron sights, because the crosshairs still appear in the correct place when you move your head. Early aircraft machine guns used collimator sights, but you have to hold your eye right up to the sight to see through it. This often resulted in injuries if the aircraft jerked at the wrong time. Iron sights were subsequently popular, but you still need to line up with the sights correctly, which is time you don't want to spend in a dogfight. With a reflector gunsight, the image of the crosshairs moves as you move your head, so you only have to glance in the correct direction to line up the shot. That's why they're also popular on small arms nowadays.


Difference between Assessment and Critique? I was reading Aviation Instructor Handbook. I don't know the difference between assessment and critique. That would be great if someone could explain about it! Thank you!
In my understanding, assessment is just comparing student's performance to established standards without saying it was good or bad. And, critique is more like telling the way or process student performs was good or poor without comparing to the standards. But, I'm not completely sure.

My understanding of the difference between assessing and critiquing is this.
Assessing or assessment involves grading a subjects performance or ability against a given standard or ideal. This can involve a letter or numeric grading, or a simple pass/fail grade. When grading against an ideal subject or situation, absent of an accepted standard, can be rather subjective.
Critiquing or a critique is a judgement of the way a subject performs. It is not meant as a way to judge the performance. Rather, it is meant to provide feedback to the subject regardless of the grade against the standard in order for them to improve. This is much like coaching. You would coach both your worst and your best performer for them both to improve. Even if their performance warranted a passing grade.


What is this yellow section around the cockpit window? Saw this while boarding the flight the other day, travelling between HYD (Hyderabad, India) to CCU (Calcutta, India) on Indigo Airlines. Aircraft was an Airbus A320.

There was a yellow patch around the window. Was this because the same was repaired?

You're right. The aft no. 3 fixed window has a reusable retainer with 2 rows of fasteners- one for holding the window glass and another for attaching to the fuselage, as can be seen in this PPG document- this is the two rows of fasteners in the image.

A320 aft window, image from Cockpit Windows Technical Data from PPG Aerospace

My guess is that there was some damage to the area and the airline replaced the whole assembly and sent the aircraft before the primer could be painted over. When painted, it would look some thing like this:

A320 window, image from miles-around.de

Note: The A320 does have an emergency (sliding) window in the cockpit- however, it is in the no.2 window, the details of which can be seen in this document


Why are passenger seats not facing backward on an airplane? In the event of a crash, facing backward sounds much safer:

Forces are applied on a  much larger surface (your whole back is in contact with the seats, instead of just a seatbelt and maybe the opposite seat)
Most passenger are already in position in case of an unpredicted crash.
Passenger without a seatbelt might have higher survival rate

Flying objects would maybe be more dangerous, but

What made designers do it this way ?
Is there any plane with such a configuration ?

You are absolutely correct, backward facing seats are safer.

But tradition and a subjective feeling of being treated better means that people will prefer to be seated facing forward. Some even claim that they develop motion sickness when sitting backwards. This can indeed be the case for some people in trains with their big windows, but much less so in aircraft.

Just note which seats will be occupied last in a train with lounge/mixed seating.

In order to cram the highest number of passengers into their planes, the airlines would need to convert all seats to the backward orientation, and you can be sure there will be some passengers who will complain. If passenger safety would be important to them, airlines could already use better seatbelts, like the 5-point-harnesses used in gliders and aerobatics planes, but they all use the minimum lap belt which is mandated and nothing more. Convenience and cost always win over safety.

Now I need to mention two caveats:

If passengers should be seated backwards, the industry needs to develop new seats. It will not be helpful to turn existing seats around - they would collapse at much lower loads than what a backward-sitting human can sustain. However, to fully support these higher loads, seats will be more heavy and possibly even the floor structure needs to be beefed up.
Backward-facing seating will only help in the fraction of cases where deceleration loads are too high for a forward-facing person, but low enough to make the crash survivable. If the plane flies into a mountain or ditches and sinks before people get out, the better seating will not help.

Some military transports have backward-facing seats. In some crashes, the survivability rate was seven times higher in those than in forward-facing seats. Early air travel also used mixed seating, e.g. on the Zeppelins or the Dornier Do-X. One airline to use mixed seating was Southwest Airlines with their "love seats", and business jets have mixed seating as standard. Thanks to @reirab for pointing out that United Business class also has some backward-facing seats.

Cabin of the Do-X. No seatbelts, seats not bolted to the floor. These were the days ...

Cabin of the Dassault Falcon 7X business jet.


Why new jet aircraft have wider, larger cockpit windshield/windscreen? If you compare aircraft in the same category Boeing 737 with newer Airbus 320 and more recently Comac C919 or Irkut MC-21, it is striking to observe the changes in the cockpit windscreen design.

The trend seems clearly to be wider, larger windscreens. What are the reasons for that?

The area of the windscreen is limited by the structural strength of the materials. The windscreen must withstand the difference between cabin pressure and outside air pressure during cruise. In addition, it must also survive impacts from birds and hail to a certain degree.

As material engineering advanced, we can produce larger windows and windscreen. For example, even though the Boeing 787 has a stronger pressure differential (6,000 feet cabin altitude vs 8,000 feet in traditional airliners), the passenger windows on the 787 are larger than previous productions.


What flight controls should be used to counter asymmetric yaw? How should the autopilot or pilot handle asymmetric yaw, as with one failed engine on a multi-engine turboprop whose engines are not on the centerline?
Should one apply roll control or rudder control?

The details will depend on the exact aircraft type, so I will answer for the Bombardier Dash-8 Q400 as an example.

The autopilot does not have rudder authority on the Dash-8 (source: FCOM Autoflight chapter):

  12.3.7 Autopilot

  The Autopilot (AP) couples the FD commands to the flight control surfaces using pitch and roll servos for automatic control of the aircraft flight path.

If not disengaged, the autopilot would try to maintain heading with roll only.

The yaw damper would not be enough to overcome the yaw asymmetry either:

  12.3.9 Yaw Damper

  The Yaw Damper provides through control of the rudder:

  Damping of the aircraft Dutch Roll mode.
  Turn coordination.

  The Yaw Damper authority is limited to a maximum of ± 4.5 degrees of rudder by mechanical stops. Yaw Damper commands are limited in software as a function of airspeed.

The correct procedure in case of an engine failure would be to hold rudder towards the live engine and then trim the rudder whenever time permits:

(image source: FCOM Flight Controls chapter)

  RUDDER TRIM INDICATOR

  indicates trimmed rudder position

  RUDDER TRIM KNOB (rotary action spring loaded to neutral)
  ROTATE

  trims rudder in desired direction
  first graduation trims slow, second graduation trims fast

The target for the rudder trim should be coordinated flight, i.e. no sideslip indicated on the primary flight display (PFD):

(image source: FCOM Indicating and Recording Systems chapter)

  SLIP/SKID INDICATOR (white)

  the Slip/Skid Indicator shows the lateral acceleration of the aeroplane and is a trapezoid symbol. It turns with the roll pointer
  the maximum deflection indication shows a 0.14 g lateral acceleration. This is equivalent to one and a half the thickness of the upper part of the slip/skid symbol (trapezoid shape)
  the slip skid Indicator is shown to the left when the aeroplane is slipping to the right and to the right when the aeroplane is slipping to the left
  the indicator goes out of view when the aeroplane roll is more than 60 degrees or the related AHRU attitude has malfunctioned


What was the first control room--used for flight test--established in aerospace history? The control room for space missions in Houston is probably the best, most widely known example of a control room.  It is an operations center used in support and execution of flight and space missions.

Historically, what was the first instance wherein a test team used a control room or operations centers for flight operations support?

This question answers why a control room exists, and this question answers who gets to be in there.

This article would seem to suggest that use of radio telemetry started being used sometime during the mid-fifties.

  Then you reduce these rolls of oscillograph readouts and learn to read the data, you will know more about what happened during a flight test than the pilot, the engineer and the designer. These rolls of paper are like novels. It is up to you to get the meaning, then sense the plot and determine whether flight objectives were satisfied.

The quote above is from chapter 5 of "Failure is not an option" by Gene Kranz, describing his first introduction to flight testing in 1954 when he started working for McDonnell Aircraft. As the quote would indicate, data processing happened after the flight was over and that there was no kind of control room monitoring the progress of the flight. An exception was for incidents such as one also described by Kranz, where a B-52 had lowered a missile from the bomb bay in order to fire it. The missile would neither fire or retract, but as the bomber had enough fuel the engineers had enough time to discuss various options.

I suspect that the first form for flight operations support would have been the chaseplane, although this is outside what you are asking.

The next closest thing I've heard about is Mercury Control, which was used to monitor and support flights during the Mercury Program.


Why do jet engine igniters require huge voltages? Wikipedia's Components of Jet Engines has this to say on the igniters:

A high voltage spark is used to ignite the gases. The voltage is stored up from a low voltage (usually 28 V DC) supply provided by the aircraft batteries. It builds up to the right value in the ignition exciters (similar to automotive ignition coils) and is then released as a high energy spark. ...

Most modern ignition systems provide enough energy (20–40 kV) to be a lethal hazard should a person be in contact with the electrical lead when the system is activated, so team communication is vital when working on these systems.

I bolded that part I'm interested in. 20 to 40 kV? That is a huge, huge amount of voltage. Why on Earth would a jet engine need that much voltage to produce a spark? I thought kerosene was relatively easy to ignite.

In short, 40 kV isn't that much voltage for applications that are intentionally creating an electrical arc. Car spark plugs also use voltages in the tens of thousands of volts for the same reason, for example.
As for why that is:
In general, air acts as an electrical insulator. That is, electricity won't pass through air at normal voltages. Which is good because otherwise you'd have a constant arc to ground through the air from any exposed hot conductor and that would cause lots of problems.
As with any insulator, air has a dielectric strength, measured in volts per unit distance. For a given length of air (such as the spark gap in a spark plug,) there exists a breakdown voltage at which point the voltage differential per unit distance exceeds the dielectric strength. When a voltage equal to or greater than the breakdown voltage is applied to conductors on either side of said length of air, the air will suddenly ionize, creating a channel of plasma through the air. The plasma channel now has a much, much, much lower resistance than air normally has, allowing current to flow across the gap and quickly equalizing the potential (i.e. voltage) on each side of the gap.
As you're likely aware, plasma tends to be quite hot. The plasma channel created by the above process is the visible arc that you'll see between the conductors in a spark plug.
For air at normal pressures, the dielectric strength is about 3 MV/m. That is, if you want to create a 1-meter arc, you'd need 3 megavolts of potential across it. Or, in units more suited to creating ignition sparks (which are hopefully not a meter in length,) you need around 3 kV per millimeter. So, for example, in the winter when you take off a fleece coat and then experience a shock the next time you get close to a grounded conductor, the static potential that has built up on you is about 3 kV per millimeter (i.e. 30 kV/cm or around 75 kV/inch) of the maximum length of the arc you can create to such a conductor.
So, in summary, 40 kV really isn't all that much when you're trying to create arcs through air, especially not highly pressurized air, such as in a piston or jet engine. Even relatively small distances require quite high voltages in order to arc. Which is a good thing so that exposed conductors don't just constantly create arcs to ground. Or to grounded people, electronics, etc.
By the way, this ability of an electric field to ionize air is why switches for very high voltage transmission lines have to have much, much longer poles than what you'll find on normal switches. On a 138 kV line, for example, the electricity would simply arc across a switch that created a gap of less than couple of inches or so when open. Perhaps an even larger gap when humidity is high. And these switches do indeed arc while opening and closing. They can also create quite long arcs while opening, since the plasma channel is already in place. Here's an example of what that can look like at 138 kV:

Of course, in this case, you have a more-or-less continuous voltage source, not just a stored-up charge that is suddenly released, so the arc won't just be a brief flash, but will continue until the distance between the conductors becomes too high to maintain the arc.
And, of course, when the potential between the base of a cloud and the ground gets too high, you get lightning. And, yes, that's a very, very high voltage to arc across a kilometer or more. According to the U.S. National Weather Service, a typical lightning bolt involves potentials of around 300 MV. While that actually seems a bit low to arc across the typical distance of a lightning bolt, lightning normally occurs in thunderstorms where the atmosphere is already very humid and, thus, more conductive than normal.

As far as the ease of igniting jet fuel, while that's mostly unrelated to the voltage required to create a spark across a given distance of air, it's actually not that easy to ignite. At standard air pressure, you can drop a lit match in a bucket of jet fuel and it will just extinguish the match. You can also create a raging fire in the fuselage of a Boeing 777 and the fuel remaining in the tanks of said 777 won't burn. This is by design and it's one of the great things about jet fuel for aviation. While the energy density and specific energy of petroleum fuels is very high (by chemical reaction standards,) it actually requires quite high temperatures and/or pressures to ignite jet fuel, making it an ideal fuel for providing lots of energy per unit weight while not tending to randomly burn or explode at inconvenient times.


Why is manoeuvring speed higher in utility category? In a C172P, the manoeuvring speed is 99 KIAS at 2400 lbs, 92 KIAS at 2000 lbs, and 82 KIAS at 1600 lbs. However, it is 102 KIAS at 2100 lbs when in the utility category, which has a more restrictive aft C of G limit.

Why the increase in $V_a$? My guess is that not allowing such an aft C of G in utility category allows the higher manoeuvring speed because this also restricts how low the stall speed could get. Is this correct?

There are three factors: Va speed, weight, and CG limit.

Va is connected to the weight limit, not to the CG limit.  If you look at a typical V/G diagram, you'll notice that Va is defined by the load factor at max gross. Multiplying the load factor times the weight gives the force exerted on the structure at Va.

In the case of the 172, in the normal category at max gross is 3.8G * 2400# = 9120 pounds.

In the utility category 4.4G * 2100# = 9240 (about the same as 9120).

So if the weight is limited to 2100#, the G load can be increased to 4.4, and not exceed the overall structural limits of the aircraft.

The CG limit in the utility category is there to ensure that the CG is forward enough that the pilot can more easily recover from the maneuvers, such as stalls and spins. It probably has a lot to do with the amount of elevator authority, which is necessary to break the stall.


I am licensed as a Private Pilot, Airplane Multiengine Land, what do I need to do to be able to fly as PIC in a Single Engine Land aircraft? I basically got my Multi Engine Rating however not a single engine rating even though most of my training was in ASEL. Now I am curious what I would have to do to be able to fly friends and family in a single engine instead of a twin.

No, you cannot. Just like an ASEL doesn't give you the ability to fly an AMEL, if you have an AMEL that doesn't give you ASEL privileges.
Adding the ASEL shouldn't be that hard though, especially if you've done a majority of your training in one. You will still need to take a check ride.


What is a Certification Flight? After taking a new plane from the manufacturer's factory to its airport base, the plane must undergo a Certification Flight before starting to operate with the airline:

What is a certification flight?
What is the purpose of it?
What are the tasks done on a Certification Flight?
Why doing a Certification Flight if the aircraft has already been tested before?

I believe what you are referring to is an acceptance flight, rather than a certification flight. Certification flights (usually there many) are flights which the manufacturer demonstrates to aviation authorities that a new design of an aircraft is safe. However, just because a design has been tested, does not mean a new aircraft is produced exactly to the design. Acceptance flight is a test flight which make sure the aircraft has been manufactured up to standard.

Acceptance flights are also required after major maintenance work or avionics upgrades. Its purpose is to explore the entire flight envelope and ensure emergency / backup systems work as expected. During a normal flight, only a portion of the systems' functions are used. A test flight is a complete evaluation of all conditions, such that malfunctions or deviations will not go unnoticed.

Of course, the pilots will first examine critical systems (e.g. engines, flight controls) on the ground. Depending on the aircraft, the tests to be completed in the air include:

Engine shutdown and restarts
autopilot roll rates, flap extension speed, engine response etc.
Alternate gear extension
Fuel jettison
Over-speed warnings
Stall protection systems
Ground Proximity Warning System (GPWS)
Auxiliary Power Unit (APU) operation at high altitude
Cabin service systems


How is an off-field landing accomplished at night? Common sense suggests it's much easier to do an off-field landing at day than at night, curious to know how it's accomplished at night.

Off-field landings at night are inherently more difficult and hazardous than in the day because depending on conditions you may have no way to tell what is down there. Unless you have decently strong moonlight all unlit terrain will be completely black, and you won't be able to tell forest from field. This is why it's critical to protect your night vision, it gives you a chance to see what's below you. If there's a highway down there that may be your best option, but if you're in a sparse area on a dark night you have to pick a spot that's into wind and hope it's not badlands. Even then it's still survivable if you have good technique, keep positive control of the airplane and reduce the airspeed as much as you can before impact, without stalling of course.
Aiming for clusters of lights sounds good at first, but that usually means buildings or parking lots which are not good choices.
The best way to de-risk this is through good flight planning. Choose a flight path that goes over friendly terrain: adding 15 minutes of flying time is worth it if it means you are over fields rather than rough terrain or water. Study the terrain using google earth or a similar tool. If you have a GPS you could even put good off-airport landing sites on your map. Give yourself extra altitude, and keep practicing your forced landing technique.


What are the consequences of falsely and/or unnecessarily declaring an emergency? I'm curious as to what would happen to a pilot should they falsely declare an emergency to expedite their landing.

By 'falsely' or 'unnecessarily' I mean that the hypothetical pilot is not experiencing anything abnormal, has adequate fuel onboard, is in perfect VFR conditions, and all souls on board are conscious and in good health. In other words, lying about an emergency status to make their landing more convenient or expedient.

Obviously the absence of a real emergency (and the pilot's knowledge of this) would have to be proven (after all, if the pilot even feels like the safety of the flight is compromised, they can and should declare an emergency and be given full benefit of the doubt), but let's assume for our purposes that the pilot simply admits upon landing that there was no emergency and they were aware of that fact, and that information eventually makes its way to the FAA.

Would the pilot lose their license, be grounded for a time, or face civil punishment? Is it addressed on a case-by-case basis, or is there a prescribed punishment? Has this ever happened before?

I'm interested in the consequences for either private pilots, commercial, or both. Though I'm sure the difference with commercial pilots would be reprimand or termination from the airline, on top of whatever civil punishments exist.

My experience is it is whether ATC files a complaint against you. It has to be pretty serious for them to do that. It works both ways, pilots rarely report ATC mistakes and so there is a gentleman's agreement to not sweat the small stuff. I have had ATC try to kill me at least 4 or 5 times and I never saw the need to report it. I figured the controller already knew the seriousness of it and if a supervisor noticed it, more than enough bad things would happen to them.

Just to be fair, I have screwed up seriously twice. I misunderstood instructions in flying over Vancouver International in  Canada and flew right in front of landing traffic. The second occurrence was when I was flying a twin. I got really busy after the controller unexpectedly routed me to a different runway during approach to Anchorage International, I switched tower frequencies for the new runway and forgot to get "cleared for landing" with the new tower frequency. In both cases the controllers very sternly told me what I had done wrong but never reported it.

In 1975 I had ATC file a complaint with my flight school when I was a student. I turned off the engine when it was obvious I had a 10-15min wait for takeoff. I later found out the FARs require at least one engine running on all ground control areas - no one had told me, Oops.

I have had two very serious problems in my 2500hrs of PIC. I lost an engine in a Cessna-337 (actually I was practicing engine out and one prop accumulator had leaked so the prop would not un-feather). ATC asked if I was declaring an emergency, I said no, and they declared one for me anyway.

The second emergency was when a carb intake became obstructed by an air straightener on a Navion Bendix PS5 pressure carb. Right after taking off I lost about 50% power. I slowly circled back because of "..low fuel pressure.."  , and I said I needed a "precautionary landing". Once again they declared an emergency anyway and I landed safely.

Most pilots don't know the definition of an emergency - In my early years I didn't

One of the possible problems with getting in trouble with the FAA is not knowing what an emergency really is. (They are quite lenient and understand this gap in knowledge. For example I have never seen a FAA definition.)

In about 1985 I discussed my experiences over coffee with a 10,000hr Atlas B747 captain that had been an instructor. He listened attentively, then calmly ask me if I knew when to declare an emergency? I said "if I thought I might die!" He calmly instructed me...

  An emergency is when "safety of flight is in doubt",

  OR when the aircraft is not able to perform as intended,

  OR when the aircraft might not be able to perform as intended.

  It's that simple!!

  Also, a pilot is required to inform ATC (but not report a
  emergency) any time an aircraft is not able to climb at least 500fpm.

Note the emphasis on "might not be able to perform as intended". That may not sound like an emergency but that is how the FAA and ATC see it. And that is pretty low criteria - it gives the PIC lots of legitimate wiggle room.

Once I was told this, it made so much sense and I knew I could defend my actions as PIC in the future. It seems ATC likely has received better training than pilots on what an emergency is, even if the pilot is overly cautious to declare an emergency (as I use to be).

When the prop would not un-feather and I lost partial power, both aircraft would no longer perform "as intended" and I should have declared an emergency.


Is a non-WAAS Garmin 530 certified for an LNAV/VNAV approach? I may not understand all the details of what I'm asking but trying to wrap my head around it.

I am aware that before WAAS, some GPS aircraft were equipped to get vertical guidance by a Barocorrected altitude information sent to the FMS and along with the non-waas GPS could calculate (interpolate) glide path info and were approved to fly LNAV/VNAV approaches.

My question is whether the non-waas Garmin 530 has the ability and necessary FAA approval to perform this and if it is an option?

It seems if used on its own, the 5xx is not capable of LNAV/VNAV approaches.

Source: garmin.com — scroll down to the link that reads: "Garmin Flight Plan Information Excel file".


Are plane's black boxes essentially useless tool in the modern age and how to improve upon it? I am just reading the latest news on the air plane crash that happened couple days ago and it dawned on me that one too many times have I read a story on the NY Times where after black box is obtained, it provided no additional information and almost always resulted in mystery.

MH370 of course demonstrated the failure of a tool such as the black box which has limited battery and no accessibility. Many commented at that time even my own phone can be quickly located once lost, how do they lose a component in a couple million dollar passenger plane?

Air Indonesia crash further demonstrated how due to noise, the recorded data cannot be made out exactly what happened. Yes, that is precisely the problem with a voice recorder - noise is captured as well as speech and if SNR is high enough, you don't hear the speech. You would have thought engineers in this century knew better.

Many have advocated a live video streaming device such as those for CCTV. Other have suggested float on water or a better accessed versions of modern black boxes. What is the technological infeasibility here that is preventing electrical engineers from taking a more active stance towards creating a better black box? What are some of the ways that a better black box can be made?

We have this topic well covered here, here and here (which is the granddaddy of them all).

Basically, it comes down to two issues:

Regulation: It takes a long time for innovations to be approved, especially in safety-related applications.
On long-range flights there are long stretches of no radio contact (except maybe for a satellite connection), so streaming becomes impractical due to the data volume.

Black boxes have been improved a lot since their introduction and they continue to get better. Please let the investigators find and analyze the recordings first before jumping to conclusions.


How to calculate the required motor power and rotor size with respect to the weight of quadcopter? I want to build a quadcopter but don't have any idea about motor and rotor size selection.
Is there a formula or equation to use? What are other things that need to be considered? Trial and error method would be waste of time and money.

The most important thing to remember here is the Purpose. For what purpose do you want to use the Quadcopter?

That being said , let’s start with the very basic .

Required Thrust = ( Weight x 2 ) / 4

In order to choose a motor  you need to determine how much weight you are planning to take, and then work out the thrust required to lift the quadcopter .Also , when purchasing motors  you need to consider Watt’s and Efficiency as well apart from Motor KV and Thrust.The higher the Efficiency, the better it is.The manufacturer/seller of Motors will provide the specifications about the Motor. This will help you to find out the thrust,power, rpm etc of the motor.

http://www.hobbyking.com/hobbyking/store/__28675__D2830_11_1000kv_Brushless_Motor_UK_Warehouse_.html?strSearch=1000kv

Quadcopters have 2 clockwise(CW) and 2 counter-clockwise(CCW) propellers and it has two flight configurations. X config and + config. In X config two arms will face front side while in + config only one arm will face front side. If you are making Quadcopter with plus config you can tune your quadcopter easily by  single axis tuning method .

Single Axis PID Tuning A Quadcopter

Increased propeller pitch and length generally  draws  more current. Also the pitch can be defined as the travel distance of one single prop rotation. In other words, higher pitch means slower rotation, but will increase your vehicle speed which in turn will use more power.If your intention is to do acrobatics, you will need torque propellers which provide more acceleration and it puts less pressure on the power system. Lower pitch propellers will also improve stability.A higher pitch propeller moves greater amount of air, which could create turbulence and cause the aircraft to wobble during hovering. If you notice this with your quadcopter, try to choosing a lower pitched propeller.

http://blog.oscarliang.net/how-to-choose-motor-and-propeller-for-quadcopter/

You may also choose to use this below Quadcopter Calculator. You can dial in everything from motors to props to ESC.

http://www.ecalc.ch/indexcalc.htm


Is there a minimum distance that a pilot is required to fly? Say there are two airports in a city, a large one with a control tower, and a small uncontrolled airport. Say they're only a couple miles apart, such that the small airport is well within the larger airport's controlled airspace. Is anything stopping a pilot from flying directly from one to the other?

There is no rule that says that a flight needs to be at least x miles long. Most training flights don't even leave the vicinity of the airport, and they still count.

The only thing stopping your hypothetical scenario would be that the pilot taking off from the uncontrolled airport needs to obtain an airspace  clearance before taking off. If the bigger airport is busy this could be denied, in which case the pilot would be stuck!


Helicopter mast bumping in low g condition The helicopter shown in the concrete pouring video seems to taking off from a hill and descending down in a way which can be classified as low G with low rotor loading. Although, the helicopter is three-bladed, mast bumping should be less of an issue, but from my understanding still worth considering.
Could a maneuver like this be executed in a similar way with a two-bladed helicopter such as a Bell 206 or Robinson. Furthermore, what is the reason for mast bumping being less of an issue for helicopters with more than two blades?

The famous video of the US Army seems to be describing exactly the condition as shown in the first video as potentially dangerous.

The answer is yes it could be used in that flight profile as the pilot of that AS300 was never in a low G condition with the rotor unloaded during those maneuvers.  Once he dropped the concrete, though he’s descending, he’s also accelerating at a high power setting, which is keeping the rotor loaded.  However, zero G mast bumping is still a risk that must be considered and thoroughly mitigated for during preflight for all helos with a semi rigid rotor system.
Mass bumping only occurs on helicopters with a semi rigid or teetering rotor system. It has to do with how a semi rigid rotor is supported by the mast in an under slung condition, where excess flapping can result in mast bumping.  It will generally occur in conditions like zero-G pushovers at low power settings or when attempting a steep slope landing.  Mast bumping is not possible on rigid, fully articulated, or elastomeric rotor systems where the rotor mounts cannot strike the mast, even with excess flapping.
Here is a pretty good recap on the subject of mast bumping.

Even helos with two bladed semi-rigid rotor systems can be flown through some pretty extreme maneuvers, provided the pilot flies within the design limits and does not unload the rotor.  I remember West Coast JetCopters, who provided the Bell 222 for the television series Airwolf, did some pretty extreme flying on those choppers and a 222 does use a teetering rotor system.  They just had really, really good pilots at the controls.  See 0:57 in the video below where the stunt pilots put a 222 through the helo equivalent of a hammerhead stall.


Why was I getting an uncomfortable feeling in an R22 at 3,000 feet? I was thinking through my flying experiences when I remembered a strange sensation while I was a student.

In a Robinson R22, with about 35 hours experience, I was doing a solo flyout to a nearby airfield for a cup of coffee and a look at the weekend traffic.  To get there, I had to cross a MATZ which included some permanent danger areas up to 2,500 feet.  I'd transited this MATZ several times with a call to the tower but on this particular occasion, I couldn't reach anyone.

Being quite inexperienced, I didn't know if it was just unmanned, I had the wrong frequency or something else so I decided, with no particular place to go, to climb to 3,000 feet and go over the top.  One lesson learned is how long it takes to get to 3,000 feet in a Robbo, especially in a climbing spiral :)

Anyone who has been in an R22 will know that the visibility is superb and as I climbed, the views were spectacular.

As I got to 3,000 feet and leveled off, I had this strange sensation.  It felt as if the aircraft was balanced on top of a tall pole and the cabin had shrunk to really small. I felt as if the aircraft might tip off the top of this pole and plunge.  I also found it difficult to believe the 70kts indicated since the apparent speed over the ground was so low which makes sense given that I'd only ever been that high as a passenger.

I really didn't feel comfortable although I wasn't scared, didn't have any anxiety and felt fully in control of myself but I did abandon the plan, got back down to the 1,000 feet I was more used to and completed a couple of circuits at my home field before landing.

What did I experience?  Has anyone else had anything like this?  I guess that it might be a symptom of vertigo but I have never had problems before or, perhaps something weird in my ear canals following the long spiral climb followed by a level out?

Typical height for helicopters is 500-1,500 AGL, and almost all flights are conducted in this regime.

Below 1,500 AGL the surface is quite close and the ground moves by fairly quickly, so you have a good point of reference.

At 3,000 AGL, you can feel quite disconnected from the earth and can have a bout of altitude fear.

When I had to circle up above out of a valley airport in an airplane, with minimum VFR visibility due to smoke, I felt like I had to keep cross-checking my instruments to maintain airspeed and bank angle. It was an uncomfortable feeling, even having had lots of hood time and actual IMC. So its not unusual for unusual flight regimes to have an unsettling effect.

The circling could have also cause some disorientation.

The most important thing, which you accomplished, is recognizing the signs, not panicking, and you kept flying.


What are some differences that make the new 737 MAX winglets more efficient than a conventional winglet? I was reading this article about the Boeing 737 MAX final assembly and it was saying something about the new winglet generating lift and increasing efficiency. Can you explain to me how this works, and what other changes to the new winglet are made to make it more efficient?

source:Gizmag

The 737 MAX winglet is the latest develpment in the 'winglet war' going in between the Boeing and Airbus.

As it has been described how winglets work and its advantages, I will not go into those. Most of the wingtip devices in use today are there simply to reduce the effect of wingtip vortices i.e. they are more or less vertical to the wing.

For example, the 737-200 winglets produce little lift.

Source: .b737.org.uk

The same goes for 737-800 variants, which use blended winglets which do produce a little lift (redistributing the spanwwise loading).

"A Garuda Indonesia Winglets Boeing 737-800 NG" by FathirLeone - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

And also the 737 NG 'Split Scimitar' wingtips (where do they get these names?).

This adds some weight to the aircraft. For example, the 737 winglet weighs arounf 180 lbs and the total structutal weight increase due to it is around 480 lbs. Obviously, the winglets more than compensate for this increase, that's why we see them used.

With modificaitons, the wintip devices can be used to produce lift and this is the path being taken today with new wingtip device designs, especially with the blended winglet. Boeing took this to the extreme in 787 raked wingtips, which is basically in the horizontal plane, which increased the actual aspect ratio of the wing.

Source: malaysianwings.com

Another idea is to use them to generate lift by changing their angle of installation. This makes the 737 MAX winglet somewhere in between the legacy 737 and 787 winglets. The 737 MAX Advanced Technilogt (AT) winglet has two parts:

An upper part which is at an angle, resulting in some lift being produced.
A lower strake.

The idea is that the winglets also produce some lift in addition to drag reduction. According to Boeing,

  The AT winglet further redistributes the spanwise loading, increasing the effective span of the wing. The AT winglet balances the effective span increase uniquely between the upper and lower parts and therefore generates more lift and reduces drag. This makes the system more efficient without adding more weight.

The AT winglets distribute spanwise loading like this:

Source: b737.org.uk

Note: the first one is the baseline aircraft with no winglet. The second one has the 'blended' winglet, while the third one gives the AT winglet. As can be seen above, some of the lift is generated by the winglets itself.


Does every device/software, developed for use in the cockpit, need to be certified? Every avionic, developed for use in the cockpit has to complete a long and expensive certification process.

Is this only applying for avionics, installed fixed into the aircraft or also for apps like ForeFlight for example?

For example: If I had developed an app similar to ForeFlight to use on the tablet, is there anything I had to do in regards to certification or could I just sell it to pilots?

The answer depends on the functionality and capability of the app. Some basic apps do not need to be certified, whilst more complicated ones will (either by the airline or by the regulator).

Tablets are split into 3 categories (these are the US FAA definitions):
1) Portable devices not mounted to the aircraft with read-only access to aircraft data.
2) Portable devices that can be mounted and can share information with aircraft systems.
3) Permanently mounted devices with access to the flight management computer.

There are also 3 classes of app:
A) Basic apps providing info such as aircraft manuals and procedures.
B) More complex apps providing some navigation info, weather info or exterior views of the aircraft.
C) More complex apps that can provide navigation information and can include 'own ship' position via GPS or the aircraft navigation platform.

Class 1 and 2 tablets can only host type A or B apps. Type A and B apps can be 'self certified' by the airline, providing that documentation on failure modes and usability is available. Some restrictions are in place for type B apps displaying, for example, weather info. Type C apps require regulator approval.

That's a brief summary, but it's very complex. Full details available
in this FAA document. Regulations worldwide vary, but most are broadly similar to those specified by the FAA.


How does the capacity of 2 parallel runways compare to single runway? Under IFR, what is the capacity of 2 near parallel runways and how does it compare to mixed mode single runway?

Definition
There are two key performance indicators that are used to measure the key performance area 'airport capacity':

Peak arrival [declared] capacity
Peak arrival throughput.

What is the capacity of 2 near parallel runways?

It depends if the 2 runways are operated in mixed or segregated mode.

For the US, the two active runway case average value (47) is influenced by the ability to operate in mixed mode with independent runways for Tampa (TPA) and Portland (PDX). Otherwise the grouping is more comparable.

The average is between 40-47 arrivals per hour depending on the mode of operation, the higher value being influenced by the mixed mode operation.

How does it compare to mixed mode single runway?

Single runway is 29-30 arrivals per hour. So we are looking at a 33-50% increase.
Declared and IFR
I'd be careful with the interpretation (since you tagged it IFR), because one of the reasons you see a larger gap between the declared and actual for the US compared to Europe is because in the US the capacity is typically declared based on visual meteorological conditions. This is discussed here:

Why are visual approaches (in the US) preferred by US pilots, but not European pilots?
What are the practical impacts of airports in the US being mostly IATA Level 2?

Source of graph and quotations: Comparison of Air Traffic Management-Related Operational Performance: U.S./Europe, 2015, eurocontrol.int (.pdf inside .zip).


What does steering angle mean? I'm reading the UAVSAR data format and in File Naming Convention section is said that if we take a typical file name:

Dthvly_34501_08038_006_080731_L090HH_XX_01.slc

as the name that follows

Dthvly_34501_08038_006_080731_L  (090)  HH_XX_01.slc

The three digits that are in parentheses, is the steering angle.
And for the above file name, we have:

  Dthvly is the site name, 345 degrees is the heading of UAVSAR in
  flight, with a counter of 01, the flight was the thirty-eighth flight
  by UAVSAR in 2008, this data take was the sixth data take during the
  flight, the data was acquired on July 31, 2008 (UTC), the frequency
  band was L-band, pointing at perpendicular to the flight heading (90
  degrees counterclockwise), this file contains the HH data, this is the
  first interation of processing, cross talk calibration has not been
  applied, and the data type is SLC.

What is steering angle?

Please explain very simply because I'm not very familiar with aviation concepts. I just want to have a sense and intuition about of the aircraft steering angle.

Steering angle, according to the text you bolded:

  pointing at perpendicular to the flight heading (90 degrees counterclockwise)

means the steering angle 090 is the angle, relative to the flight heading counterclockwise, that the data sample was taken.

If the flight heading was 345 degrees, 90 degrees counter clockwise (CCW) is 255 degrees.  This steering angle has no aviation context and is just a relative offset from the aircraft heading for data acquisition (which in this case sounds like a radar sample).


How do designers determine the altitude profiles of neighboring procedures for deconfliction purposes? I am interested in studying ICAO's Continuous Climb Operations design strategy, however I have some trouble understanding how the procedure designers take into consideration the traffic flow from neighboring arrival procedures, in order to avoid conflicts with their proposed departure procedure (optimized for continuous climb).

Doc 9993 (Draft version) states:

  1.1.5.3 Traffic Avoidance. In the most optimum situation, a departure route should be designed in such a way that there is no restriction that prevents an aircraft continuing its optimum flight profile. Both, the arrival (STAR) and the departure (SID) should be de-conflicted laterally or vertically. This optimum situation may not be reachable and therefore a balance must be found between the arrival and the departure routes.

However, even if one makes the assumption that an IAP has a somewhat self-explanatory altitude profile, at least where the glide slope interception begins, this is clearly not the case for STARs. There are charts which do not provide a starting altitude for their depicted arrival procedures, something that makes the estimation of the aircraft's altitude during the route traversal even harder. On top of that, there are arrival procedures that do not have any altitude constraint at all, such as GATBY ONE.

Anything that could point me into the right direction would be more than welcome.

I have some trouble understanding how the procedure designers take into consideration the traffic flow from neighboring arrival procedures

We don't.
We only concern ourselves with terrain and obstacle clearance. Doc 8168 Vol. II I-2-1-1 refers.
Deconfliction is an ATM responsibility, covered in Doc 4444.


Are there statistics showing the relationship between safety and the age of aircraft? Some people seem to believe that some airplanes are less safe to fly just because they are older than others. As a pilot myself who has learned that the safety of aircraft is nothing to do with their age as long as they are properly maintained in accordance with the regulations regarding airworthiness, I take the idea to be wrong and try to talk those people out of their idea whenever I come across them. Some people are persuaded but some are not.

I believe there are nothing better than brute facts in changing one's belief and here is my question: Are there statistics that support the idea that old aircraft are no less safe than new aircraft?

I could not find statistics, so I parsed the data available on https://aviation-safety.net/database. This site does have a statistics page, but it does not have an answer to your question.

I'm not a statistician so I'm sure there are much better ways to crunch and graph this data, but the raw data I found was:

The data includes 5075 crashes from the years 1919 - 2019.
The mean aircraft age is 15.58 years. This age is the age of the particular aircraft involved in the crash, not the "age" of the aircraft's type.

I did not normalize the data in any way, so take it with a grain of salt and except some skews and outliers (for example, a 75 years old DC-3 crashed earlier this year - https://aviation-safety.net/database/record.php?id=20190121-0). On the other hand, crashes in the early years will naturally skew the data, as every aircraft that crashed was new at the time of the crash.


How is data transmitted to CVR and FDR? A recent news item mentioned that "black boxes" are typically stored in the tail section of an aircraft to maximize their odds of surviving a catastrophic incident.

If they're stored in the rear of the aircraft, presumably flight data and cockpit voice data is transmitted via wires which run the length of the aircraft.

Aren't these susceptible to damage during an incident? There have been incidents of explosions and fires which damage flight control cables - aren't the FDR and CVR susceptible in the same way?

You are very correct that this can happen- If i'm not wrong, what happened during the last 6 minutes of Swissair Flight 111 will never be known for this reason.

In general however, by the time the fire would spread to this extent the CVR and/or FDR would probably have picked up some hint of fire and the reason. To increase survivability, the FDR and CVR are connected off separate power buses ('boards'), so I'd imagine the cables for each not exactly next to each other on the fuselage, and if one trips, the other one will hopefully still run for a bit longer.

The cockpit voice recorder operates a simple microphone I believe, so I'd expect that it wouldn't be much more complicated than your computer microphone. The data would probably be converted from analog to digital before being transmitted backwards.

As for the 88 parameters that the Flight Data recorder currently requires, I'd imagine that there would be a serial connection from each relevant part- each flight computer, engine etc. all leading to the back of the aircraft.

Source: FDR Handbook- NTSB


How to best navigate around and land at KPAO (Palo Alto, CA)? Flying VFR into KPAO from the South for the first time in a Cherokee. Any advice on the best way to navigate KSJC and the SFO Bravo?  Thanks.

If you’re coming in VFR from the south, I’d recommend skirting around the San Jose Class C and Moffet’s Class D by flying over the Lexington Reservoir, over Los Gatos and Saratoga and staying just north of the foothills of Palo Alto.  Flown at lower altitudes, you’ll avoid KSFO’s Class B airspace.  Just be aware there’s a lot of GA VFR traffic down in the weeds in that area.  Also be aware of TFRs over Stanford, should they be hosting football games at their stadium.   Typically arrivals and departures from the west are given the Stadium visual arrivals, routing them to Stanford Stadium, thence to a downwind or base entry at KPAO.  Arrivals and departures to the north are given the Bridge visual arrival and departure to the Dumbarton Bridge then entry into KPAO pattern.  Remember as well that “Kung Pao” only has a 2400 ft runway, so be on the ball with you short field ops.  There is extensive flight training going on at that airport and the pattern can be extremely busy on good weather days.  Have a taxi diagram ready to go and be aware of taxi routing via the east loop Taxiway Golf - terminal side - or the west loop taxiway Golf - hanger side.


How can I identify a low flying plane at night over Bangalore? I often see a low flying plane circling over south Bangalore around 00:30-01:00. It circles at least twice and it's not very big, mostly the size of a private jet.

How can I go about identifying it?

On Nov 12 at about 1845 UTC, which would be about 1215 local on Nov. 13, a Vistara A320, reg. VT-TTM, took off from BLR and did several touch-and-go’s at VOBG then returned to BLR.

On Nov. 10, around the same time, another Vistara A320, reg. VT-HYD, did the same thing. Taking off from BLR, doing touch-and-go’s at VOBG before returning to BLR.

According to this article @pondlife found, VOBG airport is open for pilot training.