Why couldn't my aircraft depart fully fueled on a 44C day? My flight from Abudhabi to SFO was postponed. Official reason given to us was outside temperatures were too high - around 44+ degree Celsius and aircraft can not take off with full fuel loads at such high temperatures.

While sitting at terminal I saw other flights taking off. When I asked staff about those flights, answer was they are short haul - around 4-5 hours distance.

How does out side temperature affect these flights? Does it have anything to do with fuel volume changing with higher temperatures and hence wrong fuel consumption calculations?

There are two problems:

First, at higher temperatures, the air is less dense; therefore there is less oxygen (by mass) in every cubic metre of it; therefore more air must be ingested by the engine (by volume) for the same quantity of fuel to be completely burnt. If the intake flow rate of air is fixed, then less fuel can be burnt and less power developed compared to a colder air temperature.

The second problem is that the lower density of air reduces the lift generated by the aircraft's wings at any speed. To make up for this the aircraft can travel faster.

In practise this means that aircraft operating in "hot and high" conditions—altitude also affects air density—will require longer runways to take off.

If it gets too hot then the aircraft might not have enough runway to get airborne.

For safety reasons the runway must be long enough for the aircraft to come to a stop if the commander decides to reject the take off at the last moment. But fast, heavy aircraft take a long time to stop; so this means the runway must be even longer.

If the aircraft is lightly loaded then it is not such a problem; there is less mass to accelerate and a lower speed must be obtained for take off. Thus a short flight simply takes a bit longer but still gets off the ground. But for AUH-SFO, this is a very long flight and will require a great deal of fuel to be taken onboard (at a guess I would imagine something on the very rough order of 80 tons). The specifics will vary by aircraft, and by how much is on them.

https://en.wikipedia.org/wiki/Hot_and_high


Have contrails ever occurred at low altitudes, such as at takeoff? Contrails form from the exhaust of jet engines condensing to water-ice. Has this ever happened at low altitudes, especially during or immediately after takeoff?

This is entirely possible if it's cold enough and has also happened. Here's a video of a Tu-204 taking off from Yakutsk at -45°C.

Source


Where can I get test samples for Assistant Air Traffic Controller Officer exam? A few days ago, I applied for the position of Assistant Air Traffic Controller Officer (AATCO), for CAA in Pakistan. The next step is a written test.

What am I supposed to prepare specifically?

My background is in software engineering. Any help/reference will be appreciated.

Based on the country you are looking for the certification, rules may be slightly changed. For India following syllabus is applicable (Source: atcguild.com)

At present it is a year-long ab-initio training (Under revision to make it in two sections of six months each)
Modules:

Air Traffic Services
Aerodromes and Ground Aids
Air Legislation
Meteorology
Communication Procedures
Technical
Search and Rescue
Air Navigation

The selection shall be made on the basis of a

Written test
50% questions on subjects relating to educational qualifications
prescribed
50% on General Knowledge, General Intelligence, General Aptitude,
English etc. Voice test
Personal Interview
Medical fitness as per ICAO Annex-1

I Googled for the subject, but didn't find much information on the paper patterns or example papers.


Do you need to fill out the MedXPress form every time you renew your medical? In the US, to get a 3rd-class medical certificate I know that you have to fill out this form on the FAA's website, get a confirmation number, then take that confirmation number to the medical examiner. My question is, do I have to do that every time? Or is the one confirmation number good forever?

Each time you renew you will need to complete the medical history questionnaire on the MedXPress website and obtain a fresh confirmation number.


How to improve engine-out handling on a multi-engined aircraft? Hypothetically, if I wanted to create a multi-engine airplane with the best single-engine handling characteristics/lowest Vmc, would moving the vertical stabilizer far back be beneficial (even if it looked weird)?

My school of thought is that: At low airspeeds, the rudder is less effective. If I can't increase the amount of airflow over the rudder, will giving the rudder a massive arm allow the plane to have more directional control at lower airspeeds with the increased torque?

Yes providing a longer vertical tail arm is very beneficial for control in case of engine failure.

During the pre-design phase of an aeroplane the Tail Volumes are determined: area of horizontal and vertical tail, times the moment arm. This answer gives more info on some statistical data and methods.

Of course, optimal dimensioning is paramount since we're dealing with aerodynamics and we want to limit drag. The tail arm is usually limited to the useful fuselage length, leaving the tail area to be the main design parameter.


Why is it harder to maintain laminar flow on larger aircraft? I am told that on larger aircraft, suction will be needed to maintain laminar flow because of the larger leading edge radius. Why so? Is it because the air has to travel over a longer distance on the skin, so slows more, and thus piles up toward the trailing edge, causing adverse pressure?

Sort of interesting that very slow, lower Reynolds number airfoils, such as models, actually have to trip the airflow to form a boundary layer.

Surface friction causes the air near the wing surface to move at the wings speed.  In a wind tunnel this is slower than the free stream, in the air, the moving wing speeds up the air around it.  In relative terms, the effect is the same.

Boundary layers are draggier than laminar flow, but much less draggier than turbulent flow.  The boundary layer is like "grease", helping reduce drag and create lift.

At higher subsonic Mach numbers, early efforts at a "laminar flow wing"  for long range escort fighters  resulted in something resembling an airfoil flown backwards, with a sharp leading edge, a very gently increasing thickness (to keep laminar flow), maximum thickness further back towards the trailing edge, and a much shorter taper to the trailing edge.
This is reminiscent of the blunt "boat tail" approach being tried these days, also found in bullets.

Though successful, low speed handling and stall characteristics led to some needed modifications.

But chord length, and airspeed, as well as airfoil type and surface smoothness, are very important parameters in predicting airflow around a wing.  Airfoil Tools, on the web, is a great place to begin to explore airfoil types for various applications.  Particularly of interest are Coefficient of Lift vs AOA, and Lift/Drag ratio.


What qualifies a UAV as an MAV? Micro aerial vehicles are a special class of UAVs that have gained a lot of attention and research focus in the past few years. These are generally smaller in size ranging from 3m to 15 cm depending on where you look.

So, is there a clear, recognized or accepted definition of an MAV in terms of size and power? I am interested in the upper limits i.e. the line classifying a UAV as an MAV.

Currently, there seems to be little official definition, and the term MAV appears is relatively new. The only paper on the topic I could find that specifically approached the area defined it as:

  "small enough to be practical for a single-person transport and use." (Galiński and
  R. Żbikowski, 2007)

Delft University of Technology section on MAV research provide no clear definition in their documents.

I think the definition seems to more subjective to the flying properties to the UAV, which might make the definition more difficult. Since they are not carrying people but sensors, they will be much more varying in weight, especially in with time.

One example, the british army's MAV has a flight time of 25 minutes.  This one is a very small but has a respectable flight time. This will not simplify definition. I think the term coined by Galiński and Żbikowski is the most useful in a practical sense.

Update:
University of Texas page on the DARPA competion says:

  The definition employed in DARPAs program limits these aircraft to a
  size less than 15 centimeters (6 in.) in length, width, or height.
  MAVs must have a weight of 50 grams or less and must be capable of
  staying aloft for 20 to 60 minutes for a distance of 10 kilometers.

The pure source for this this, while not avaliable any longer, I believe I found to be

  The definition employed in DARPA's program limits these craft to a
  size less than 15 cm (about 6 inches) in length, width or height. Source

There are currently no civilian classifications for UAVs from the FAA or EASA, hence the legal problem with these. Most army and air force drones operate under military exceptions if I'm not mistaken.


What inspection packages commercial airliners follow which make them more reliable than a C-130? The Hercules C-130 get unserviceable often due to various technical issues. This causes the flight to be aborted (ground or air abort) due to avionics, propulsion, airframe or electric problems. I know that the three level of maintenance include 'O' (organizational or 1st level), 'I' (intermediate or 2nd level), and 'D' (depot level). USAF work cards are followed in all these inspections/maintenance.

I was wondering why commercial airliners, which no doubt are flying more than the C-130s, are rarely seen aborting a mission and diverting to a place other than the destination. Is there a different procedure or plan or work package followed by the commercial airliners which make the flight more reliable?

As mentioned, factors like a different mission are much more likely to be a reason for any difference in reliability. Military aircraft often fly a harsh mission, the pilots don't fly to extend life, they use max power on every takeoff, fly at a high power setting, and run the engine closer to its temp limit. They aim to get there fast, and the C-130 flies into dirt strips, where the dirt gets ingested into the engines. In comparison, commercial airlines operate with a very close eye on the bottom (financial) line. They take-off derated if they can, and fly with a very simple cruise profile. They do not perform high speed tactical descents that a military C-130 would, into an airport possibly surrounded by hostile forces with air to ground weapons.


Do quadcopter propellers break the sound barrier? I recently bought a quadcopter and noticed every time I fly it there is this weird buzzing noise. I have heard this noise on other quadcopters around the same size as mine(4in by 4in). On an airliner turbofan engine you can sometimes hear this weird buzzing sound from the engines, which this sound is the n1 fan spinning faster than the speed of sound and resulting in this loud buzzing sound. So is my little quadcopter motors going supersonic or is it something else?Source:(dynomodels.co.uk)

Almost certainly not. Given the comments specifying a $0.5$ inch radius (blade length,) that means the circumference of the path of the blade tips would then be

$$2 \pi \cdot 0.5 \, \text{inches} \approx 3.1415 \, \text{inches} \approx 0.2618 \,\text{feet}$$

To get to the speed of sound (which is approximately $1,126 \,\frac{\text{ft}}{\text{s}}$ at sea level,) that means you'd need to have the fan spinning at

$$\frac{1,126}{0.2618} \approx 4,301 \,\text{Hz} \approx 258,060 \,\text{rpm}$$

Needless to say, that's not happening unless you have one seriously expensive quadcopter.

The buzzing you hear is probably either the frequency at which the motor is spinning or, perhaps, the frequency of some oscillation of the fan blades. Most likely, though, it's just the frequency of the motor/fan.


Is it possible to build an ultralight helicopter with electric motors as its main engines? So I'm trying to make an electric ultralight helicopter, but I'm not sure if it will work. Is it possible to use electric motors to make it fly? If yes, I'm going to need some advice.
I'm expecting the aircraft to be able to lift a 200kg load, with the maximum rotor blade diameter of 7m in coaxial rotor configuration.

From a quick Google search, you can find that Sikorsky Firefly and Tier One R44 are two examples of eHelos, conventional helicopters converted to electric propulsion. They both fly around 20-30 minutes (though the Firefly never flew).
As for building an electric helicopter, I believe off-the-shelf components (such as Tesla motors and batteries, available from parts breakers) have enough performance for an eHelo. The actual configuration of the aircraft (single main, coaxial, multicopter etc.) depends on the manufacturer's expertise on rotor blade hubs and/or distributed electric propulsion. So unless you work for Kamov, a coaxial rotor hub will be prohibitively complex (thus expensive) for a prototype ultralight helicopter.


How can OAT and SAT differ? From YouTube.

I always thought SAT (Static Air Temperature) and OAT (Outside Air Temperature) were the same thing. So does this answer, so does Wikipedia:

  [The] outside air temperature (OAT) or static air temperature (SAT) refers to the temperature of the air around an aircraft.

So, what is the difference based on that video capture?

From the manual:

So it appears that this instrument's terminology is a little non-standard.

Additional information:

From the Youtube video, you can see that they are moving at a fair pace:

If you take these numbers and plug it into the equations from this question,

$$Ram~Rise=SAT\times0.2\times{M}^2$$

(remembering that SAT needs to be in degrees Kelvin)

You come up with

$$Ram~Rise=(273-33)\times0.2\times{0.491}^2 \approx 11.6C_{rise}$$

Which is pretty close to what you see in the video.

Additional, additional information:

Here is the conversion chart of OAT to SAT in the POH for that (or similar) airplane.

No other qualification is given, but my assumption is that OAT is not TAT, and would be wrong to label it that... it is just the raw temperature sensor value.


What is the ratio of actual flight time to simulator time on type for airline pilot training? I know that training flying time on large commercial aircraft is awfully expensive but I'm just curious how much training time a typical scheduled passenger airline pilot gets on the real craft these days? In particular I'm motivated by investigation reports that reveal that current simulators may have flaws and shortcomings in realistically simulating some parts of the flight envelope.

I'm sure this varies  a lot by pilot, airline etc. so I'm not at all looking for an exact answer, just a approximate figure.

e.g. Say, I'm flying on a A-320 or a B-787 commanded by a newly type-certified first-officer, what could be the bare minimum actual flight time (not simulator time) on an A-320 / B-787 that he could have had?

PS. What is the type-rating process? Does that have no need for flight time? Can you get Type rated with 100% sim time on type?

Zero hours in type.

The first time a new FO flies the actual airplane could be their first revenue flight with a training captain in the left seat.  Technically, these flights are still considered training, specifically "initial operating experience" (IOE) and a few trips will be flown with training captains before the new FO is released to fly with regular line captains.  IOE is conducted on revenue flights though, so its entirely possible that the before your flight leaves the gate that the FO has exactly 0 hours in type.

The initial training (leading to either a full type or an SIC type) and the upgrade training (full type ride if you only had an SIC type) are 100% in FTD and level D FFS (full flight simulators) and the checkride is in the FFS.


Does an airport need to have at least one instrument approach that I can use in order to fly IFR to it? Half Moon Bay (KHAF) does not have any instrument approaches into the airport that I can use. All the approaches require RNAV but my aircraft is not RNAV-capable. Can I fly IFR to it?

I'm thinking that if weather is good, ATC can clear me for the visual approach.

If weather is bad, I'm thinking that they wouldn't be able to clear me and would ask me for an alternate airport to land at?

Under Part 91, you can file IFR to any point in space, including an airport without an instrument approach. But that doesn't mean you'll be able to land there.

FAR 91.175(a): "Unless otherwise authorized by the FAA, when it is necessary to use an instrument approach to a civil airport, each person operating an aircraft must use a standard instrument approach procedure prescribed in part 97.."

What ATC can do is clear you to that point in space at their lowest vectoring altitude there. If, when you arrive, the conditions are VFR, you can cancel your IFR and land. If not, you have to go somewhere else, possibly the alternate airport you would be required to have filed in your flight plan. And it's that alternate airport that MUST not only have instrument approaches, but have weather forecasts and reports high enough to meet the alternate minimum requirements of 91.169(c).


For calculating $V_{stall}$, why should be used $C_{L,max}$ and not $C_{L,min}$ (that would be more prudent)? Premise: In level unaccelerated flight we have relation $W=L=\frac{1}{2}\cdot\rho\cdot V_{stall}^2\cdot S\cdot C_{L,max}$ (taken from book Daniel P Raymer "Aircraft Design: A Conceptual Approach" equation (5.5) at page 85).

Question: Why $C_{L,max}$? Why not $C_{L,min}$? In fact in case the $C_L$ in use is not $C_L,max$, and speed is little more than $V_{stall}$ (valued for $C_{L,max}$), it happen that Lift is not enough and anyway stall happens on aircraft. If using $C_{L,min}$ the calculation is more cautious.

The stall speed is the speed at which you can still fly the plane in level flight. This is important, because strictly speaking, stall happens at a certain angle of attack, not at a certain speed. In other words, you can safely fly a plane way below stall speed - the problem is that you'll be doing it nose-down in order to keep the angle of attack to a minimum (and that as such you will quickly exceed the stall speed again - hey, we just did a stall recovery maneuver!)

So, let's see what happens when we approach stall speed from a higher speed, while flying level. As we slow down, we must increase our angle of attack to maintain level flight - this way, we are increasing the $C_L$ of the wing, as to keep the lift $L(=W)=\frac{1}{2}\rho VSC_L$ constant when reducing our $V$. Ideally, we'd like to keep increasing our $C_L$ as we reduce our $V$ - however, this means we keep increasing our AoA (angle of attack) until it gets past a critical point, where the airfoil stalls due to flow separation at the suction side of the airfoil.

So really, using $C_{L,min}$ would be nonsensical - if your wings would have a lift coefficient so low at such a low speed, I can guarantee you that $W>L$, i.e., you plummet from the skies. We need to increase our $C_L$ to maintain level flight, and the stall speed is exactly the point where we can no longer increase our $C_L$, or in other words, we arrived exactly at $C_{L,max}$.


There's an airfield somewhere in the United States with a metal runway. Where is it? Somewhere in the United States, there's an airfield (probably military) with a runway made entirely out of metal.  I've seen the approach plate for it, but I can't remember the identifier.

What airfield am I thinking of?

You are thinking of Bogue Field (KNJM). It is a Marine Corps auxiliary landing field, currently mocked up to look like a carrier deck, and last I heard it was still active and in use to practice carrier landings.

The runway surface is Perforated Steel Planking (PSP - actually I believe the new stuff isn't "steel" anymore but the name remains) - discrete sections that can be laid out to quickly construct temporary landing strips in forward combat zones.

A search on AirNav for "pierced steel plaking" came up with a couple more military fields:

KNXP   Twentynine Palms SELF Airport (Strategic Expeditionary Landing Field) -
Twentynine Palms, California, USA

2CA9   Castle Dome Army Heliport -
Yuma Proving Ground (Yuma), Arizona, USA

2CA9 says it's a helipad but it's 3000x65. The rest of the results were all (reasonably sized) helipads.


Is there a minimum weight requirement for an commercial aircraft? For an aircraft to be approved for commercial usage (like Boeing 747s or Airbus 320s), is there any minimum weight requirements, just the aircraft (without passengers and crew).

While there is a minimum weight to be defined as Transport Category, 12500 lbs for jets and 19 seats/19000 lbs for propeller driven airplanes, that's a "minimum maximum weight" you could say, to meet a category definition, which determines the certification standards you have to meet.
There is no minimum weight for certification in any category.  You define the mission you are designing for, payload, range, speed etc., and design it to be as light as you can possibly make it and still meet certification requirements for structural strength and performance (while allowing fudge factors for mistakes and flaws), while meeting your design goals.
So if you could design a 747 with new miracle materials, so its empty weight is 300,000 lbs instead of 400,000 lbs, and it meets all the Transport Category requirements for strength and performance, and it can still do what you want it to do in terms of speed/payload/range, you're good to go.


Compering between ILS / BARO-VNAV my question concerning the Comparisons between the ILS/ Baro-VNAV approaching system
from the view points of safety, technician ( infrastructure, installation,maintenance and ..eg) relation efficiency, capability, accuracy and functionality?

thanks to your good sides..
best regards

ILS provides both lateral and vertical guidance with high precision, which means aircraft using an ILS are allowed to get very close to the ground and each other without visual contact; in theory, a Category IIIC ILS is precise enough to land with zero visibility, but so far no examples actually exist.  Where ILS approaches exist, they're usually preferred.

Baro-VNAV provides only vertical guidance; it would be used for RNAV procedures in conjunction with some form of lateral guidance such as DME/DME/IRU.  Due to the pilot having to manually enter the altimeter setting and the general accuracy of altimeters, the margin of error is much higher and aircraft are not allowed to get nearly as close to the ground (or each other) as they would be with ILS.  Also, Baro-VNAV systems are known to be inaccurate at extreme temperatures (either high or low), so they aren't always available, whereas other vertical guidance systems are immune to that.

The other main difference is cost.  ILS requires both localizer and glideslope equipment on the ground for each runway served; installing and maintaining those systems is quite expensive, whereas the on-board equipment is relatively inexpensive.  In contrast, Baro-VNAV is already installed on many airliners and requires nothing on the ground, just minor modifications to RNAV procedures already being developed for GNSS-equipped aircraft.  The accompanying lateral guidance systems also already exist for other reasons, so there's little or no cost there either.  The combination allows airlines to more reliably and more safely serve the public at more airports with minimal cost to everyone, so it's a reasonable compromise for airports (or individual runways) that don't have enough traffic to justify the high costs of ILS.


What Kind of airfoil configuration is preferred for an hyper sonic plane? I am trying to design a hyper sonic aircraft in line with X-15 for my Aircraft design project. This requires me to figure out the preferred airfoil shape for the wing.

At hypersonic speed the local drag grows with the inclination of the local surface against the free stream. Thus, the best shape is a thin wedge. Drag will scale with the cube of the thickness ratio of the wedge.

Depending on the maximum tolerable heat load, you should choose a pointed leading edge (highest heat load, smallest drag) or a blunt leading edge, where the separated shock will reduce local heat loads, albeit at the price of much higher drag.

Ideally, past its maximum thickness the airfoil tapers down towards a thin trailing edge, and again a wedge shape will cause the least amount of drag.

In the picture below (source) you can barely see the tip airfoil of the X-15:

It used a simple, blunt wedge at the vertical tails because the vacuum at the rear face provided additional directional stability. However, for lowest drag, a double wedge of the smallest thickness possible should be used.


What does unmixed mean? For a unmixed turbofan engine what does ‘unmixed’ mean in regards to the flow of air?  How does this differ from ‘mixed’ also in terms of air flow ?

I believe this refers to the cowling design where a mixed flow the fan and gas core streams mix inside the cowling whereas in unmixed streams the fan air excites the cowling without mixing with the gas core exhaust gases.


What is the correct IATA airplane designator for the Boeing 787-10? Wikipedia claims 781, most other sources say 78J.  I can't find anything authoritative, and IATA has the gall to want US$578 for the answer.  Which one is it?

Update for clarity: Everybody agrees that the four-letter ICAO code is B78X. I'm interested in the three-letter IATA code.

I looked it up in the corresponding IATA document and I can confirm it is 781.

Sadly I think I am not allowed to attach any kind of proof from the document but the source of my information is IATA document 8803 - Aicraft Types in version no. 28.


Why do passenger jets accept input that will cause the aircraft to perform dangerous maneuvers it was not designed for? Examples:

A bank angle > 45 degrees is considered an “upset,” putting the plane in a position that can lead to a loss of control.
A pitch > 20 degrees can possibly be dangerous and cause the aircraft to stall (depends on many factors or course).

These are just a few examples of limits that most passenger jets have. Now why is it that the plane actually accepts input that will cause the aircraft to go beyond these limits? What possibly use could “diving” straight towards the ground or towards the sky have? Or having a high bank angle that will almost certainly cause stalling and loss of control?

Generally speaking, pilots don't like it when a computer interprets or limits their actions. They want final control. They don't always get their way on this but that's their preference.

If I recall correctly, Boeing tends to stick with the philosophy that "the pilot is the final arbiter." Airbus is more likely to preempt pilot inputs and modify them.

Although the majority of crashes and incidents wind up being pilot error, there is a serious flaw to modifying pilot inputs. That flaw is in the case of systems failure.

By definition, failure modes involve things going wrong.  When things go wrong it's effectively impossible to plan, in automation, for all contingencies. People are much better at responding to the unknown than automation systems are.

Take for instance the rule that "bank angles > 45 degrees are dangerous, and are therefore prohibited". How does the plane know that the bank angle is > 45 degrees? Well it's a sensor of course, but what if the sensor has failed? A failed sensor will either signal to take action when none is needed or fail to signal when action is called for. What if the control surfaces have failed and the plane cannot correct the bank angle?

The usual answer to that is redundant systems, high reliability parts and design, etc.  All those are great of course and certainly help a lot. However we still have incidents and accidents.

In the end the question is: Who do you trust more? A pilot or a machine? And statistics and science only help you part-way here. A person's experience, biases and feelings will have a lot to say about how they answer. And by "person", understand that I'm including the customers, the paying public.


Impact of centre of gravity position on stall recovery Can somebody explain what is the impact of CoG position on stall recovery. I heard that stall speed is higher with forward CoG comapared to aft CoG, but does it have influence on stall recovery? Is it more or less difficult with some CoG position?

It sure does, and that is the reason we don't abuse aft CG limits.
An excessively aft CG shortens the torque arm of the tail pitch down forces and lengthens the torque arm of pitch up forces ahead of CG, including more of the wing.
As a full stall develops, the nose of the fuselage will also generate lift in addition to its area drag as the plane sinks, making it harder to "bring the nose down" and unstall the wing by reducing its AOA to the relative wind.
By design, a larger tail adds safety if one is foolish enough to test aft CG limits. A speed brake or parachute is another line of defense.
The effect of forward set CG on stall speed may arise from the need to generate a bit more lift with the wing to counteract increased tail downforce but remember most tail "downforce" is used to set wing AOA, only a little more is needed for forward CG.
Forward set CG will also make it harder to lift the nose in slow flight, which may actually drop the nose before it stalls if elevator is small or travel is limited and the horizontal stabilizer is large.  The B-52 was designed in this manner for obvious reasons.
Each plane is different, and even a docile trainer like the Cessna 152 can be dangerous if aft CG limit is exceeded.


How to interpret the N and R sections in SNOWTAM I am trying to decode this snowtam for 2 days now and I followed this Snowtam Guideline.

So N is taxiway state and multiple taxiway states can be combined. R is apron state and multiple apron states can be combined. But in the example below, I cannot see how it makes sense. For example in R, are 1,2,3,4,6,7,East,North all apron names?

SWES0698 ESSB 12261815 COR
(SNOWTAM 0698
A) ESSB
B) 12261815 C) 12 F) 1/1/1 G) XX/XX/XX H) 5/5/5
N) G1 R S T Y Y1 Y2 Y3 Y4 Y5 YU YW/1/GOOD.
R) 1 2 3 4 6 7 EAST NORTH/1/GOOD
T) RWY 12 BA 67/72/67. RWY 12 COVER 100 PERCENT. APRON SANDED.)
CREATED: 26 DEC 2019 18:32:00
SOURCE: EUECYIYN

Yes, those are all apron names. You can see where they are on the airport chart.


Is it safe to use a propeller plane to fly commercially over the Tibetan Plateau? I saw this youtube video today: Flying over Mt Everest. A lovely view of stunning nature - quite spectacular. However, I looked up the plane - or at least what I think is the plane - and found that it might be a propeller plane: 9N-AHV (I saw this registration number in the video).
The plane appears to be a BAe Jetstream 41 - check that link for details - it is Wikipedia.
Of particular interest (maybe):

Service ceiling: 26,000 ft (7,900 m)
Service ceiling on one engine: 15,000 ft (4,572 m)

Tibetan Plateau: "...average elevation exceeding 4,500 metres (14,800 ft)".
So it sounds like an engine failure for this plane type means that it  can not descend to the acceptable service ceiling? The service ceiling is the maximum usable altitude of an aircraft.
This seems unsafe?
I am not a pilot, but I hear it is rare to fly over Himalaya / Mount Everest / Tibet because planes can't go low enough for passengers to breathe without oxygen if there is an emergency? If they lose an engine they have to descend I read. There is also a lot of turbulence. Why Planes Don't Fly Over Himalayas.
Airports: Lhasa and Kathmandu - short runways - not many places for emergency landings due to medical emergencies and such. And they wrote "the place is desolate with little people around". That sounds a bit funny seeing as the area is situated between China and India :-). Remote it is though. And China has 94% of its population in the eastern part of the country (towards the sea).
Links:

https://www.quora.com/Why-don%E2%80%99t-planes-fly-over-Tibet/answer/Paul-Oroborust

Maximum altitude limit where propellers can propel?

How high can propeller airplanes fly?

The video starts with Mt Everest straight ahead while in a left turn. And based on the video description, the flight took off from Kathmandu. The Nepalese AIP depicts this Mountain Flight Route, shown in red below, and the turn we see is the video would be the turn going back to Kathmandu.

— https://e-aip.caanepal.gov.np

Note that the Tibetan Plateau is north of the Himalayan range. If something goes wrong, a safe altitude less than the Jetstream's 15,000 feet limitation is within reach to the south or on the way back to Kathmandu:

— skyvector.com


How does a taildragger steer (taxi) differently to tricycle gear? I'm aware that there is a difference of some sort. Does a taildragger inherently require more room than a nose gear to taxi around a corner?

It very much depends on the tail-dragger. Many vintage aircraft don't have wheel brakes at all and steer using the rudder, which has the tail wheel or skid attached to it. On these aircraft, steering is ineffective at low speeds, just like when steering a ship with a rudder. Unlike on a ship, you can increase your steerage by adding a burst of power and using the slipstream over the rudder to push it sideways. Very experienced pilots can turn almost on the spot at very low speeds this way, but in a tricky situation it's a judgement call whether to make a wider turn at low speed or add power and risk speeding up. For this reason it's good to have a little extra room, to make sure you can stop completely at any point and still have room to make the turn.

Dan Pichelman makes a good points in the comments. If you take a tricycle and a tail-dragger with the same turning circle, and look at the tyre marks on the ground, the tail-dragger's marks will be much bigger. That tail wheel right at the aftermost point traces out a huge circle, while the tricycle's wheels are very close together. For this reason, you need the whole turning circle to be free from obstacles such as edge markers and lights, while a tricycle can do a full turn with its tail overhanging any obstructions.

One more taxiing issue is visibility. Tail-draggers (again, especially earlier ones) are nose-high on the ground, and the engine cowling tends to prevent the pilot seeing straight forward. There have been many incidents of tail-draggers taxiing right onto smaller aircraft or obstructions straight ahead of them. (It used to be very common with Spitfires.) To avoid this, pilots are taught to weave as they taxi, so they can always check the ground ahead by looking either side of the nose. (Think of it like the clearing turns you make on a long climb.) While a tricycle might go straight along a taxiway it can only just fit into, a tail-dragger wants a much wider taxiway so that it can weave like this. You also need to plan how you're going to make the weave go into a turn when you reach a corner: if you got to the corner as you'd weaved right over to its inside, pointing towards the outside of the corner, you'd need much more room to make the turn.

For all these reasons, while it's entirely possible for a good pilot on a good day to make turns just as tight as a similar-sized tricycle aircraft, it's a good idea to allow a larger unobstructed space on straights and corners if you're expecting tail-draggers, especially students.


What control surfaces do I need to move to do a roll in a model aircraft? Figured that this was the better site to ask than drone SE, but if I'm wrong just let me know.
I'm making a spitfire model and was just wondering how do I do a roll? I have elevator, rudder, and two connected ailerons.
What control surfaces do I move to do a roll?

The ailerons should be connected so that they move opposite each other. When one aileron moves up, the other one must move down, and vice versa. In fact, in full-size aircraft, the ailerons are connected so that it's actually impossible to move them in the same direction*. So, to answer your question, to roll to the right, the right aileron must move up and the left must move down.
*Well, certain airplanes have "drooping ailerons": when the flaps are deployed, it causes both ailerons to tilt downward slightly. But this is about increasing lift at low airspeeds, it doesn't affect how the ailerons control.


Why is C-5 Galaxy not used for commercial airlines while Boeng 747 is? For a layman like I am, both the planes look massive and similar in size and shape, as if a near copy of each other. Do the similarity only end in the size and shape? Do they not perform equally well in similar roles? While Boeing 747 is used for commercial airlines, why isn't Lockheed C-5 Galaxy? Similarly, why is C-5 galaxy popular for Military and 747 isn't?

C-5 Galaxy was designed to military requirements that for cargo aircraft include:

operating from unpaved runways (I am not sure in case of C-5, but probably yes)
operating from airfields without much support
operating from short runways
paradrop capability

These basically imply a high-wing design so that engines are high (to minimize risk of foreign object damage) and the deck is lower for easier loading, front and rear cargo door with loading ramps so loading is possible without any ground infrastructure and some excess thrust for sufficient performance on short fields.

However that design is less efficient. It has higher operating cost. The air force is willing to pay it, because it needs the capabilities it requested. But commercial operations don't need those things, because it has enough well equipped airports to operate from. So the higher cost of operating an L-500 (as civil version of C-5 would be called) makes it uninteresting.

B-747 only shares one design feature with C-5, the raised cockpit that allows full-height (well, almost) cargo door in the nose, but otherwise it is optimized to minimize operating cost, making it great cargo plane for operations between airports.

On a side note, there is some commercial demand for transporting heavy or large cargo to less equipped airports. These are currently covered by ex-soviet-military An-124 aircraft that look very similar to Galaxy, are a bit larger, are certainly able to land on unpaved runways and were simply available when Soviet Union collapsed.


What are the requirements for aircraft marker cones? What are the requirements on aircraft marker cones (a.k.a. safety cones) according to IATA IGOM-96, i.e. size & weight?

According to IATA Airport Handling Manual, safety cones should

be conical in shape
be of a minimum height of 750 mm (22.2″)
have a minimum base weight of 4.53 kg (10 lbs)
be orange in color with reflective striping.


What happened to the power plants after an aircraft is retired? Few weeks ago, there was a Boeing 747 belong to an airliner retired in our country. I am not sure what series is that, but seems it is 747-200. What then will happen immediately to the power plants after it decided to be retired? Is the power plants will be reused, at least for another purpose?

They'll go on another airplane, or go into inventory as spares, or maybe go for overhaul if they are becoming or close to becoming worn out (the can be run until the Inter Turbine Temperature at takeoff or oil consumption becomes excessive, or they fail an internal inspection, or suffer excessive vibration etc).  Engines are changed all the time, every few years, and can be thought of as a separate asset from the individual aircraft.


Why don't short runways use ramps for takeoff? Say you had a runway for light aircraft, but only 700 meters or so of runway. Wouldn't it help to end the runway with a ramp that is ~40 meters above ground and slightly facing the sky at a gradient of 5%. Imagine the runway below was 700 meters long:

The point is to put the plane in a position where it is off the ground and in an upwards trajectory so it doesn't have to raise it's own pitch (but still travelling at near-takeoff speed), I think this could be useful with gliders (maybe with some sort of winch to launch it).

If money were no object, what would the flaws be in this sort of contraption? Is there a reason most runways are flat? Is this sort of thing used on any aircraft carriers or other remote-takeoff locations?

V1.

There are other valid reasons, as have been listed - cost, bidirectional runway use, etc. These would still not completely disqualify ramps, just limit them to very special circumstances. But the one disqualifying factor is that a ski jump takeoff removes the necessary element of safety airliners depend on during takeoff.

Up to a certain airspeed, called V1, an aircraft on a sufficiently sized flat runway can decide to abort. Using all available means, mostly brakes, an aircraft can halt its takeoff run and stop by the end of the runway. With a ski jump takeoff, you don't get that luxury - go off the ramp too slow and you fall off the end, nose first into the ground.

This is not a concern for carrier takeoffs. Every takeoff or landing on a carrier is a close call as it is. There's no spare runway for second thoughts. If things go wrong enough, the pilot has to pull the eject handle before he plunges into the water. In that situation, a ramp adds safety, giving a few more seconds on that ballistic trajectory.

So ski jump ramps are used on carriers that don't have much more expensive and complicated catapults. They are extremely effective there; just a 3 meter tall ramp can cut the takeoff roll in half for a fighter. But this comes at the cost of committing to it completely, do or die (which is the case on carriers anyway).

Since there's no eject handle on airliners, every takeoff has to be a safe one. This means being able to abort the takeoff if you develop a problem on the runway, such as your engines not spinning up to takeoff thrust.

The only way you could get a safe enough V1 with a ski jump is by having a runway of normal length, and then some, before the ramp, which removes the whole point of installing a ramp. You'd never reach it except on aborted takeoffs.


Does weather radar scare off birds? I was told a long time ago that having the weather radar turned on when at low altitudes helps to scare birds out of your way because the can sense/feel the radar.  Casey also mentioned this in another answer of his.

Is there any evidence that weather radar actually scares off birds, or is this another "urban aviation legend"?

My guess is it is an urban legend. Ground based weather radar have been used track and analyse behaviour of birds. Part of this research was done with the radar in fixed beam mode to record individual wing beat frequencies for species identification, keeping the bird in the radar beam. If the birds would be scared away by the beam this research would be almost impossible (and invalid as well). Of course, that's no hard evidence that the birds aren't scared. Also the distance between the bird and radar plays a role of course.

The radar used for that research was operating in the C-band, which is also the frequency band that most aircraft weather radars operate in. Newer aircraft weather radars operate in the X-band, which is a higher frequency band. My gut feeling is that the higher frequency is even less likely to bother birds, but then again, I am not a bird so what do I know?

jwenting suggested in a comment that this myth might have been started because of incidents where animals and humans have been harmed and killed by high power radar transmissions.

The FAA has published an Advisory Circular on recommended practices and precautions for operating weather radar on the ground. While not concerned with birds, it provides an example calculations of the output power and safe distance of a weather radar. It the example, the safe distance is less than 4.5 meter. That is too close for a bird to avoid a mid air collision.


What should a pilot flying IFR in IMC and on final, do if the vacuum system fails? Talking about small aircraft here, assuming the pilot is stable and ready to land, they’re flying IFR and the visibility is nonexistent, but that’s alright because he’s currently IFR! But then the vacuum system fails. The pilot loses:

 Attitude Indicator

 Heading Indicator

 Turn Coordinator

With a very poor visibility I can see how this could end up fatal. What is the do’s and don’t here? I can easily see that with every scenario there can be an argument for both “do” and “don’t”. Pilot could go around, but at the same this may not be smart because you don’t know the pitch of the plane, at the same time I see it being okay because you know airspeed.

I can also see a reason to continue on, to try and see if you can visualize the runway and land, seeing you know your altitude, at the same time I can see how that can be disastrous. So what’s the correct way to go about this type of failure in horrible conditions?

Your scenario isn't really realistic, the turn coordinator and the AI are almost always on different sources of power to protect against this very event. The TC is almost always electrically driven because it gives an alternate source of information.

A loss of an instrument or even a whole suite of instruments is something instrument rated pilots train for, and should practice once they have their rating. We call it partial panel, where you use your other instruments to make up for the loss. If you lose your vacuum driven instruments you fall back on your electrical and non powered instruments like the altimeter, airspeed gauge, VSI and magnetic compass.

Addressing your question, if I experienced a loss of vacuum on short final when I was established on an instrument approach I would most likely simply continue the approach and land. A loss of vacuum doesn't immediately cause those instruments to keel over and die, they keep working for awhile, getting less accurate as they spin down. Heck, if I'm on a short final I may not even recognize the failure!

If I'm on a longer final and I lose my vacuum powered instruments I would also continue the approach unless there was alternative with better conditions or less hazards nearby. Your vacuum instruments aren't going to fix themselves, so there's no point in flying around waiting for something else to go wrong.

The exact situation you describe in your question would be extremely unusual to say the least, this would most likely be caused by something pretty catastrophic that would mean continuing the approach is impossible. If I had a total powered instrument failure but somehow my ILS and radio stayed up I would continue the approach using the residual momentum of the gyros to keep situational awareness as long as possible, then fall back to my working instruments. I'd also declare an emergency, and ask for ATC to give me surveillance radar data, they can give me a running commentary of which direction I'm turning.

Of course, if it was me I'd activate emergency AI app I have on my tablet GPS or my phone. Both use the phone/tablet sensors to produce a pretty reliable picture.


As a contractor for an FBO, is it okay for us to transmit Internet signals right above the tarmac? I have been looking for the FAA Regulations on this with no luck, we are contracted IT with a local FBO and they want to provide internet to all their hangers. The easiest way would be to put a line of sight connector for the network so we can pass the internet over it, HOWEVER it will shoot over the TARMAC and I am not sure if FAA prohibits that. It is only for ground operations the Airplanes won't be using it but I just wanted to cover myself before I did it.

There are no FAA restrictions on setting up WIFI transmitters and receivers at an airport in the United States.

WIFI transmissions do not interfere with the frequencies used by airplanes for operational purposes.


What can disqualify an airport to be used as an alternate? As a military pilot, our regulations listed things that disqualified airports as being alternates.  I have not been able to find a reference to these same items listed in the 14 CFR Part 91.  Does anyone know where to find the regulatory references for the list of things that disqualify an airport as an alternate for an IFR plan?  For example, an airport cannot be used as an alternate if the instrument approach at the airport you plan to use is listed as "Radar Required."  Is that a consideration in General Aviation?  Likewise, I was trained that if a navaid is unmonitored or if the airfield only has GPS approaches, again disqualifies the airfield as an alternate.  However, I don't know where that is written in the FARs.  Does anyone know where I should look?

As far as Part 91 ops go, paragraph 91.169 is the only IFR alternate requirement to my knowledge.

*Unless otherwise authorized by the Administrator, no person may include an alternate airport in an IFR flight plan unless appropriate weather reports or weather forecasts, or a combination of them, indicate that, at the estimated time of arrival at the alternate airport, the ceiling and visibility at that airport will be at or above the following weather minima:

(1) If an instrument approach procedure has been published in part 97 of this chapter, or a special instrument approach procedure has been issued by the Administrator to the operator, for that airport, the following minima:

(i) For aircraft other than helicopters: The alternate airport minima specified in that procedure, or if none are specified the following standard approach minima:

(A) For a precision approach procedure. Ceiling 600 feet and visibility 2 statute miles.

(B) For a nonprecision approach procedure. Ceiling 800 feet and visibility 2 statute miles.

(ii) For helicopters: Ceiling 200 feet above the minimum for the approach to be flown, and visibility at least 1 statute mile but never less than the minimum visibility for the approach to be flown, and

(2) If no instrument approach procedure has been published in part 97 of this chapter and no special instrument approach procedure has been issued by the Administrator to the operator, for the alternate airport, the ceiling and visibility minima are those allowing descent from the MEA, approach, and landing under basic VFR.*

**If you look in the front of the approach book (DOD or JEPP) it will list the 600/800' limitation for alternate designation.  I guess it's not in the UPT syllabus because the 11-214 (and the DOD for that matter) doesn't honor that specific alternate limitation.  FAR Part 135/121 ops might list other limitations that look like the "RVSM reqd, Wx reporting, GPS only, etc.)

-the queep monster....**


How realistic was the airplane scene in Terminator Dark Fate? In the movie Terminator Dark Fate, the C-5 Galaxy Grace (Mackenzie Davis) is flying gets hit by another plane (I think it's a KC-10 Extender) piloted by the Rev-9 Terminator.

What I want to know is how realistic (or not realistic) is this scene. Wouldn't wake turbulence cause an issue?

Part 1 of the scene:

Part 2:

Completely and utterly ridiculous. Let me count the ways:

First video:
0:22 That collision would have destroyed the bigger plane as well, rendering the entire rest of the scene impossible.
0:35 As you mentioned, the wake turbulence would have knocked the trailing airplane down and away.
0:46 There's no way that collision lasted for that amount of time.
1:11 The autopilot would not have been able to function with that level of damage. It wouldn't have even attempted to activate.
1:19 The front of the plane isn't damaged, so the only wind would be from eddies from the hole in back. Which would be pretty strong, don't get me wrong, but not nearly strong enough to pick up a full-grown woman.
1:33 Gravity doesn't just "go away" when you lose two engines. Not to mention the wind described earlier would still be a factor.

Second video:
1:22 Having one parachute open would have slowed the fall of the Humvee quite a bit. It wouldn't still be in freefall.

Note that I'm only covering the aviation-related ridiculousnesses in that scene. There are quite a few other ways it fails basic physics as well.


What is the difference between a non-directional signal and an omidirectional signal from a radio aid? NDB's are non directional and VOR's are omnidirectional.

What is the difference between a signal that is non directional and a signal that is omidirectional, if any?

"Omnidirectional" may not be the most descriptive word for the actual radio signal emitted by a VOR, as contrasted with the signal from a NDB.  We could note that a VOR and a NDB actually both share the characteristic of broadcasting in all directions, as opposed to the narrow beam emitted by a landing approach aid, or the characteristic pattern emitted by the "four course" radio ranges of long ago.

But as for the difference between the radio signals emitted by a VOR and a NDB--

Think of the signal from a VOR as a collection of beams radiating out from the transmitter.  Each beam carries data: it is encoded with the azimuth from the station.  You can easily find more information about how this done: in actual practice the azimuth information is encoded in a phase shift between two different signals.

With a NDB, we also have beams radiating in all directions from a transmitter, but all the beams are the same.  That's why you can only get a relative bearing from a NDB.


Has there even been a case of pilot incapacitation due to food poisoning? On commercial flights, pilots are usually required to have different meal, to reduce the chance of food poisoning affecting both pilots.

Is this just a precautionary measure, or has this actually occurred?

Pilot incapacitation due to food poisoning does appear to have occurred.

The linked question, Is it true that the pilot and co-pilot are required to eat different meals? contains this New York Times article, which describes one incident:

In Australia in 1980, the pilot of a twin-engine commuter airliner suffered from food poisoning and collapsed at the controls. A passenger revived the unconscious pilot, who then was able to land the plane safely.

(However, this may not be quite what you're looking for, as being a single crew plane, it's unlikely he consumed the meal on-board).

The article also describes a number of near misses:

In 1975 luck may have prevented a catastrophe aboard a Japan Air Lines flight  when 143 of the 364 passengers and crew flying from Tokyo to Paris became severely ill just as the plane landed for a fuel stop at Copenhagen. They had eaten omelets that were contaminated with staphylococcal bacteria. The pilots, who had boarded in Anchorage, did not become ill because it was time for their supper, not breakfast. Instead of eating the omeletes, they chose steaks.
In 1982, 10 crew members of an Overseas National Airways DC- 8, including the pilot, co-pilot and flight engineer, became ill about 35 minutes out of Boston on a flight from Lisbon. After the plane landed safely at Logan Airport in Boston, Jo Ryan, a spokesman for the Massachusetts Port Authority, which operates Logan Airport, said, ''The crew all eat different things, but the one thing they had in common was tapioca pudding.''
In 1976 West German health officials reported that two people died and 385 others were sickened by contaminated mayonnaise served aboard a Spantax flight.
In 1976 at least 29 passengers were admitted to a hospital in Australia for treatment of gastro-enteritis after they became sick from a meal served aboard a British Airways flight from Hong Kong to Sydney.

Note the NYT article is dated 1984, so there could have been lots more incidents since then. For example, a search of the Aviation Herald for "food poison"  brings up a number. While you need to read each one and determine if the food poisoning came from the food on board, prior to the flight, or was unconfirmed as the cause, an incident of an inflight meal incapacitating the first officer occurred in a Boeing 737-800 as recently as Nov 18, 2016, flying from Spain to Denmark. In this incident, it is stated that the crew were served different meals.

It says: A chef subsequently informed the first officer that a part of her flight crew meal (cabbage stew) most likely was the source of the food poisoning. Because the cabbage grows in contact with soil, and since it most likely was only heated and not cooked during preparation, live microbiological bacteria might have been present in the hot meal.


Why are rules regarding the use of oxygen masks by commercial pilots often ignored? I was reading an article recently on the effects of rapid depressurization when I came across this tidbit:  According to FAR 135.89.2, aircrews of part charter craft flying pressurized aircraft above 35,000 MSL are required to have one member of the aircrew on oxygen at all times.

I've seen a few videos of charter pilots flying planes around FL410 and I don't recall any where they had masks on (admittedly, there are not a lot of small business jet charter flight videos out there.) In general, though, it seems the rule is ignored.

So, why isn't the rule followed?  Why don't pilots seems to wear oxygen masks in situations the regulations say they are supposed to?

Addendum:

In the original, unedited, version I made the mistake of thinking FAR 135 applied to airliners, when that's clearly 121 that applies to airliners...

Still, in FAR 121.333 it states that the rules around airmasks for commercial airline aircraft (over 30 passengers) require that pilots always have oxygen when they are either a) over FL410 or b) over FL250 and one of the flight crew leaves the flight deck.

Of these conditions, it seems condition A is followed by default (flying under FL410), but condition B is often ignored.  So I'd be curious why that part of the rule isn't followed as well.

Basically, I'm asking why pilots generally don't wear oxygen masks when regulations require that they are supposed to.

A big thanks to Zach Lipton for pointing out my error to me.

The rule you've found is under part 135 of the FARs, which generally governs commuter and on-demand operations like many charter flights. Most commercial airlines, such as those flying large passenger jets on regularly scheduled routes, are part 121 operators, which follow different rules.

For part 135 operators, there are a few caveats. First, above 25,000 MSL, there is an exception to the oxygen requirement if "each pilot has an approved quick-donning type oxygen mask." If the aircraft is so equipped, masks are only required above 35,000 MSL or when one pilot has left the cockpit.

The rules for part 121 operators are a bit different and can be found in 14 CFR 121.333. Under these rules, if quick-donning masks are available and the aircraft has more than 30 seats or a payload capacity of more than 7,500 lbs, oxygen is not required at or below FL410 unless one pilot has temporarily left the controls.

Since the majority of videos you may see online probably involve two pilots flying a large part 121 airliner (or one under a foreign regulatory regime, where different rules apply), oxygen masks would not be required in most of the situations where cockpit films are released.

That said, I found this article, which may be of some interest: Study: Pilots Ignore Oxygen Regulations. It cites the results of a survey conducted as part of a student's master's thesis which concludes that the rules are ignored quite often and that there really aren't effective ways to enforce them either:

  The compliance numbers for Part 121 respondents were higher, with 39
  percent reporting always using oxygen when required above 25,000 feet
  and 48 percent above 41,000 feet.

  Part 135 respondents were nearer the Part 91 results, with 21 percent
  saying they always use supplemental oxygen when only one crewmember is
  at the controls above 25,000 feet and 18 percent continuously using
  oxygen when flying above 35,000 feet.

So for part 121 operators, the primary time when the regulation is relevant is when one pilot has left the cockpit above FL250. The article goes on to discuss some of the reasons pilots may not follow the regulation and whether the regulation makes good sense. Some pilots on the PPRuNe Forums discussed the rules here (before they were changed to FL410) and also here. One author notes, with regard to donning masks during bathroom breaks, that "there is probably no more violated FAR in US operations than this one." Several reasons are posited in those threads, among them:

Some non-military pilots do not receive decompression chamber training, and so do not have an appreciation for the effects of severe hypoxia and its dangers
This practice would use up much of the cockpit oxygen supply, especially on long-haul flights, leaving less available in the event of an emergency (some information on how long oxygen supplies tend to last)
The expense and time involved in topping off oxygen tanks all the time if they were routinely used.
A desire to reduce the complexity of single-pilot operations during breaks, not wanting the remaining pilot to complicate things by donning the mask and adjusting audio settings accordingly instead of focusing on the aircraft
In some cases, restowing the masks may require maintenance personnel after the flight, which is impractical
The same rules do not apply under many other regulatory regimes, which leads people to conclude they are unimportant

Note that some pilots discuss using the masks routinely, both to ensure that their operations are as safe and legal as possible, and to give the crew practice and experience in donning and using the masks so they will be comfortable with them in the event of an emergency.


Why aren't the undersides of military aircraft painted bluey-grey to camouflage them against the sky? Why aren't military aircraft painted a bluey-grey colour to camouflage them against a bluey-grey sky?

(I researched this but couldn't find a clear answer)

Shades of Blue-grey you say? So.......
The F15

(source: boeing.com)
The Mig21

The AWACS

(source: airforce-technology.com)
The Eurofighter

(source: ausairpower.net)
To name a few I could think of from the top of my head. Almost every military aircraft has a variant that has been painted along the blue-grey spectrum at some point or another.


What is the reason for KSFO PRM approaches being decommissioned? In the latest terminal procedures packet dated April 22nd all San Francisco PRM approaches have been deleted.  I haven't seen any notice from the FAA on the decommissioning and am curious what the reason is.  Is there any official documentation on the decommissioning?
Thanks

PRM approaches require recurrent crew training, additional ATC personal (you monitor a PRM controller in addition to the tower controller), and don't increase efficiency into SFO or PHL (which decommissioned their PRM years ago) that much.  Today's airports are being built with runways separated enough to allow simultaneous ILS approaches.
In short - Training cost + Personal cost > operational savings.


How are military aircraft numbered? Can someone describe the numbering system used by the military and how it has changed over the years?  I know that there are fighter aircraft such as the F-15, F-16, F-22, etc but why are there aircraft numbered like the F-117?  and why is the B-2 a B-2 when we have had B-17s in the past?

At present, all US military aircraft follow the 1962 United States Tri-Service aircraft designation system. The first letter ('F' or 'B') denotes the mission of the aircraft, while the number denotes the design number. The designation system produces a Mission-Design-Series (MDS) designation. From Designating and Naming Military Aerospace Vehicles:

4.1. Designator Definition:
4.1.1.The  MDS designator is an official DoD recognized alpha-numeric symbol designation of a military defense aerospace vehicle. .... The designator describes the aerospace vehicle in two components where the components are separated by a hash.The first component, comprised  only  of  alpha characters, describes the mission of the vehicle.The second component, comprised of both alpha-numeric characters, describes the design number and design series of the vehicle.
4.1.2. Standard  aircraft MDS designators are comprised of the following: status prefix(optional), modified mission(optional), basic mission(required), design number (required), design series (required).

The document also gives some examples of this implemenatation:

Both tables from Designating and Naming Military Aerospace Vehicles
The 1962 system replaced the earlier system, where each service had their own systems in place for naming of aircraft.

From 1924 - 1962, the USAF (and the USAAF before them) used the 1924 United States Army Air Service aircraft designation system.

During the same time, the USN used the 1922 United States Navy aircraft designation system.

Once the USAF was formed from the USAAF in 1947, the US Army followed the 1956 United States Army aircraft designation system till 1962.

Before all of these was the 1919 United States Army Air Service aircraft designation system.

More details about the aircraft designation can be found in this page.
Basically, the counters were reset while the 1962 sytem was adopted, leading to unrelated sets of aircraft numbering. As for individual aircraft numbering, there has been a number of cases where the system was not followed, like the F-117 Nighthawk.
Adherence to this system has been patchy at best. So, you have B-1 Lancer and B-2 Spirit after B-52 Stratofortress (this was due to the counters being reset), while the next bomber has been named B-21 Raider.


Why is stabilizer trim often controlled by electric motor while other surfaces are mostly hydraulically controlled? What is the rationale behind the use of electrical motors instead of Hydraulic actuation for the stabilizer which I have seen in most aircraft like Boeing 787.

Weight, cost, reliability and maintenance.

See ACTUATION SYSTEM DESIGN WITH ELECTRICALLY POWERED ACTUATORS

Safety

See THE A380 FLIGHT CONTROL ELECTROHYDROSTATIC ACTUATORS, ACHIEVEMENTS AND LESSONS LEARNT

  In terms of safety several aspects can be
  highlighted: As far as power source redundancy
  is concerned the number is increased from 3 to 4
  since 2 electrical systems replace 1 hydraulic
  system. Furthermore an additional margin of
  safety results from the introduction of the
  hydraulic/electric dissimilarity in the power
  sources: This provides further protection against
  common failures, such as maintenance errors,
  which may affect all the hydraulic systems,
  whatever their number. Moreover the electrical
  power provides flexibility in routing, resulting
  in an easier segregation of power distribution
  routes against engine burst and other “particular
  risks”, and an isolation and reconfiguration
  capability that hydraulic systems cannot offer.

  The reduction in the total number of hydraulic
  components results in improvements of the
  MTBF and dispatch reliability, by elimination
  of potential leakage sources.

  The elimination of the generation and
  distribution components associated to one of the
  hydraulic systems (pump, reservoir, filters,
  plumbing…) and the replacement of the
  associated hydraulic actuators by electrically
  powered actuators results in weight savings.


Why do VTOL aircraft (F-35 or Harrier) have only one engine? Why do VTOL aircraft (F-35 or Harrier) have only one engine? Is it because it is simpler and less expensive? Or what are the reasons?

VTOL aircraft can have more than one engine. It is just that the design process of the Harrier and F-35 led to a situation where only one engine was required.

The main challenge in any VTOL aircraft is to have the engine produce thrust in two different phases of flight: during cruise and during takeoff/landing. This basically requires the powerplant on the aircraft to have two different characteristics at those two phases, because

The direction of the thrust vector is different in TO/Landing and cruise
Amount of thrust required is different; for vertical TO, the thrust should be more than the weight while in cruise, the required thrust is (comparatively) pretty low.

A number of approaches have been tried to solve this problem:

Takeoff the aircraft vertically (aka the tail sitter), like Ryan X-13 Vertijet, and then transition to horizontal flight. However, one major problem is the pilot has severe disorientation problems during transition
Put extra fans, like the Ryan XV-5 Vertifan. The problem was the large (wing) area taken up by the fan and weight penalties. Ironically, a similar concept has been used in F-35
Put extra engines specifically for vertical lift (aka the 'Rolls Royce Concept'), used in Dassault Mirage Balzac. Though this offered (theoretically) better safety, the weight penalty was too much.
Optimise the main engine for cruise and deflect the thrust for takeoff and augment with (small) lift engines (aka the tiltjet concept), like the German EWR VJ 101. This reduced the weight penalty and complexity, but reduced safety in the event of an engine failure.

In order to avoid the weight penalty, the best approach is to have no extra engines at all, with the thrust deflected down at take off and landing. This was called 'vectored thrust' (a term attributed to Theodore Von Karman). This concept was tested in the Bell X-14, which had fixed eingines and thrust vectoring vanes that deflected the exhaust to achieve vertical lift.

Source: history.nasa.gov

In case of the Harrier, the engine, the Bristol Siddeley Pegasus was first developed (as BE.53) and the Hawker aircraft decided to develop an aircraft around it.

During the design proces, the aircraft was redesigned around the Hawker modified BE 53 which the rear jet was split into two, like the Hawker Sea Hawk, which had a similar arrangement. This lead to the 'four poster' thrust vectoring system in the  Harrier.

Source: www.aerospaceweb.org

This is the reason, the Harrier had a single engine.

The case of F-35 is different. The F-35 was designed to replace aircraft operated by a number of US services, and as such had conflicting design requirements. At one end, the USAF wanted a conventional fighter while the USMC wanted a VTOL aircraft. The USN requirements were somewhere in the middle.

Lockheed designers decided that the best way to meet these requirements is to have a separate fan for lifting the aircraft in VTOL, which can simply be eliminated in the USAF and USN variants. This led to the lift fan arrangement (eerily similar to the Vertifan arrangement).

"F-35B Joint Strike Fighter (thrust vectoring nozzle and lift fan)" by Tosaka - Own work. Licensed under CC BY 3.0 via Commons.

So, in case of F-35 the use of a single engine was the best way to meet the requirements. The engine used, the Pratt & Whitney F135 is the most powerful fighter jet engine in service, which helps in making F-35 the first supersonic VTOL aircraft.


In an aircraft with tab-flown control surfaces, how can a jammed surface be detected during preflight examinations or flight control checks? Some aircraft use control surfaces that are driven indirectly through a flying tab system -- this is used to aerodynamically boost control forces, and works well enough in the normal case.  However, it is possible for such a system to mechanically fail in a way such that the flight control and the tab are both capable of free movement throughout the control range, but the control surface does not respond to the tab's movement correctly, causing a reduction or loss of control authority.

How can a pilot catch this type of failure in a preflight or during a flight control check? "Full and free" clearly isn't enough to catch such a failure, since the tab will move freely throughout the entire control range even if the actual surface is frozen in place.  Is it the case that the only way to catch this sort of failure is to disengage the gust locks and then try to move the control surfaces by hand through their full movement range?  Should the control surface position be fed back to cockpit instruments in these aircraft, or is that already a requirement/feature on such types?  Is it common practice or required in a "full and free" check to verify surface followup on such cockpit instruments when they are fitted?

The system you describe was used on large aircraft before hydraulic actuation became standard. The proper name is servo or Flettner tab.

The preflight check would ideally have one mechanic move the cockpit controls and a second mechanic walk around the aircraft and command control movements. While the actual control surface would not move, the servo tab would, and the second mechanic would hold on to the tab to check if it does so against moderate resistance. Then he would manually move the control surface to check if it moves freely through the full deflection range. This might require climbing on a ladder for the second mechanic, but would be the only way to ensure proper function of the control system.

One pilot by himself would not be able to properly check the airplane.


Can experts identify the model using this part (FOD prevention purposes)? We found this part of an aircraft recently and, in order to improve the safety levels at our airport, we would like to know what possible aircraft model (or models) are compatible with this cover so we can locate it.

This is a Military Standard fuel cap, part number MS29525-1.

Here is the DOD page for the products: MS29525-1. It is most likely from a military aircraft or some kind of private ex-military warbird.

There really isn't much to say on it, other than it is used by the Air Force and Navy, as well as some British aircraft. It is a universal part used on many different types. It is a serialized part, you could try calling a local airbase and see if you can get records for it, but they will probably not care enough to track it down.

By the way, whoever is missing it, if a private party, paid a dear price for losing it. The cost of these caps in the private market range from \$600 to \$800.


Is it possible to design a GA plane with a 5' -10' wing span? We see sparrows with 6" wing span land on a dime, yet it seems there no GA planes you can buy or build from a kit with short bodies, short wing spans,
something with a 20' landing/takeoff roll, something with folding wings you can drive out of your garage, take off from your driveway ( if you live in a non built up area) and land almost anywhere at 20mph.

It seems like GA is dying, but I think a lot more people would be interested in flying if GA planes were way more useful.

Yes, there was the BD5 which was nice and small, not STOL though, the Alaskan bush pilots are taking off/landing in 10' ( yeah!!) in their super cubs, a standard Zenith 701 STOL which can take off in 25' with a good headwind, but all have large spans

Using the Cri Cri as an example

Cri Cri Monoplane: , I think it has a span of 15’ and a chord of 2’ for a wing area of 30 ft2.
Cri Cri biplane: Now imagine  converting it into a biplane with a span of 1/2 or 7.5’, same chord.
Cri chi triplane: Now take the Cri Cri monoplane and reduce the span to 1/3, or 5', same chord.

Why can't we have planes with 5-10' wing spans.

Is it impossible to design roll stability into a plane with such a short wing span?

Is there any other reason, like 50% effectiveness, etc. at low span due to span wise flow, instead of chord wise flow, etc.

Looking at Selig's work on multi element racing car wings, their spans are only 5', with a cl of up to 4.5!!  He does mention they need huge end plates to avoid span wise flow.

They can, its just not a very efficient size for one that needs to cary people. The simple answer is that everything comes with a trade off, there are plenty of planes with small wing spans like this one, and this one and some planes that don't have wings at all... But smaller wing spans means a thicker wing, at some point you will run into a drag issue, a roll stability issue or both.

When it comes to aircraft people tend to be concerned with efficiency as air travel has always been about going far, fast, and for a similar cost to what you can on another means of transport. As such efficient designs win out over novel ones or ones that provide some means of limited added benefit.

On any note most of the supporting infrastructure has been designed for planes with substantial wing spans so aircraft width in the GA market is not really a huge issue. Saying a narrower wing is "way more useful" depends on your use case.


How come sonic booms only occur once at the speed of sound and not multiple times? Fighter aircraft today are capable of flying several times the speed of sound. Why is it that the sonic boom only occurs at the moment the plane crosses Mach 1?

Your question is:

  Why is it that the sonic boom only occurs at the moment the plane crosses Mach 1?

The answer is: It doesn't. Sonic boom first occurs when the plane crosses Mach 1 and the plane continues producing sonic boom as long as the speed stays above Mach 1.

Another part of your question is:

  How come sonic booms only occur once?

And the answer is: because the plane flew over you once. If the plane were to turn around and fly over you a second time you'd hear two sonic booms.

When you hear a sonic boom it doesn't mean that that boom was generated at Mach 1. It only means that the boom was generated at speeds equal to or greater than Mach 1. For example, a plane travelling at Mach 3 would still produce a sonic boom but you'd still only hear it once because the "boom" would only reach your ear once.

To understand this you need to understand what a sonic boom is.

Various parts of the airplane generate sound. Form the roar of the jet engines to the whistle of the skin of the aircraft moving through the air.

When travelling at normal subsonic speed. These sounds travel normally through the air and what you hear is a continuous sound of an airplane flying.

When travelling at or faster than the speed of sound, all these sounds arrive at your ear simultaneously. That is to say, if normally you'd be able to hear a plane passing overhead over a period of 10 seconds (for example) then at supersonic speeds all those 10 seconds of sounds (engine roar, woosh of the wings etc.) arrive at your ear at the same moment.

Since all the sounds you'd ever hear from the airplane arrive at the same time, the result is a very loud boom (all the 10 seconds or more of sound added together).

That's why you only hear it once typically.

There are exceptions though. If the plane is long enough, and the nose and tail generate loud sounds, it is possible to experience a double sonic boom caused by the tail generating a second boom. But generally, even a very long plane like the 747 or A380 (or Concorde) would take only a very tiny fraction of a second to travel the length of their body at supersonic speeds. You'd probably need a plane a mile long to experience a proper double boom.


What is difference between TAA and MSA? I know the 'TAA' usually used in RNAV chart, but sometimes it can be used in ILS chart as well. (When defining an IF, GPS is solely methods)

but While I'm studying, I can't find exact difference between TAA and MSA.

Can you let me know ?

BEST

From the FAA Chart User's Guide

  Minimum Safe Altitude (MSA)

  MSAs are published for emergency use on IAP charts. MSAs appear in the
  planview of all IAPs except on approaches for which a Terminal Arrival
  Area (TAA) is used. The MSA is based on the primary NAVAID, waypoint,
  or airport reference point on which the IAP is predicated. The MSA
  depiction on the approach chart contains the identifier of the
  NAVAID/waypoint/ airport used to determine the MSA altitudes. MSAs are
  expressed in feet above mean sea level and normally have a 25 NM
  radius; however, this radius may be expanded to 30 NM if necessary to
  encompass the airport landing surfaces.  Ideally, a single sector
  altitude is established and depicted on the planview of approach
  charts; however, when necessary to obtain relief from obstructions,
  the area may be further sectored and as many as four MSAs established.
  When established, sectors may be no less than 90° in spread. MSAs
  provide 1,000 feet clearance over all obstructions but do not
  necessarily assure acceptable navigation signal coverage.

  Terminal Arrival Areas (TAAs)

  The TAA icons will be positioned in the planview relative to their
  relationship to the procedure. The icon will not have feeder routes,
  airways, or radar vectors depicted. The TAA provides a transition from
  the enroute structure to the terminal environment with little required
  pilot/air traffic control interface for aircraft equipped with Area
  Navigation (RNAV) systems.  A standard TAA has three areas:
  straight-in, left base, and right base. The arc boundaries of the
  three areas of the TAA are published portions of the approach. A TAA
  provides minimum altitudes with standard obstacle clearance when
  operating within the TAA boundaries. TAAs are primarily used on RNAV
  approaches but may be used on an ILS approach when RNAV is the sole
  means for navigation to the IF; however, they are not normally used in
  areas of heavy concentration of air traffic.

  Non-standard TAAs may also be published; i.e., one base leg, no base
  legs.

To summarize:

MSA's are referenced to a primary navaid, waypoint or airport reference point associated with the IAP. They show safe altitudes for a 360 degree area around the reference.

TAA's are referenced relative to their relationship to the procedure.  Generally, that means one reference diagram for each IAF placed near the IAF depiction.


Could drag in a turn be twice the drag of that encountered in straight and level flight? I Just wanted to see if my understanding of drag is correct, as I am unsure.
I understand that during straight and level flight, the drag can be calculated as:

With the first term being the parasitic drag component and the second term being the induced drag component.
However, in a coordinated turn with the same angle of attack at the same airspeed, I have been told that the total drag can be expressed as:

And because the angle of attack is the same, the lift to drag ratio is the same. In this scenario the load factor is 2.
However, since in straight and level flight L = W. So does it follow that the total drag in this turn is double the total drag in the straight and level flight?
i.e.

I don't know why but I feel that this is wrong.
If this is correct, however, the question says that the parasitic drag of the turn is equal to the parasitic drag of the straight and level flight; so would it correct to follow that the induced drag is equal to the following equation?

Could drag in a turn be twice the drag in straight and level flight?

Yes, but this will be a rater steep turn.

…  in a coordinated turn with the same angle of attack at the same airspeed …

No, this is impossible. Either angle of attack or speed have to be higher so the higher lift required for turning can be generated.

… angle of attack is the same, the lift to drag ratio is the same. In this scenario the load factor is 2

And in order to create twice the lift of straight flight, the speed has to be higher by a factor of √2. In this case, L/D is indeed the same, but speed is higher so twice the dynamic pressure is available for creating the required lift. Since both lift and drag are proportional to dynamic pressure, creating twice the lift at the same L/D means that also drag will double.
In order to turn with a load factor of 2g, the bank angle has to be 60°. That is rather steep.


Is the number of private pilots increasing or decreasing? My interest into aviation grows by every day and I seriously start thinking about working in the industry later, as I am very interested into avionics and pilot supporting devices in the general aviation field.

However, what's the trend in general aviation at the moment? Is the number of PPL stagnating, rising or even decreasing. It would be nice if you have data about Europe, the US and International.

The statistics for the number of pilots in the US is fairly easy to come by, The Aircraft Owners and Pilots Association published a report on the number of FAA certified pilots. This shows a general static trend over the 10-or-so years preceding the report in 2011

Year    | Total Pilots
======================
2011    |   618,660
2010    |   627,588
2009    |   594,285
2008    |   613,746
2007    |   590,349
2006    |   597,109
2005    |   609,737
2004    |   618,930
2003    |   625,011
2002    |   631,762
2001    |   612,274

The graph shows the total number of pilots since 1929.

For Europe, this statistic is a little harder to come by. In general, Aviation in Europe is controlled by the European Aviation Safety Association to which pretty much all European countries are members, with a few having a working arrangement to sync up their procedures/licensing. The EU, and its associated agencies are typically bureaucracies at their best (worst!) and so there is unlikely to be a single register of the number of pilots.

For example, some elements of aviation (although NOT Licensing) is still managed by the UK Civil Aviation Authority. With all the various european and intra country agencies involved in European Aviation it will be tougher to get figures for the number of pilots.

Internationally your problem is moreso. With tens of different agencies involved in the Flight Crew Licensing, you may find it harder still to get some accurate figures.


Does TC holder of aircraft need to be notified by the PART 21 DOH that they are making a major mod STC to their product? Can someone confirm if a part 21 design organizations has to inform the TC holder or not? This is because I am on a part 66 course at the moment and the text is as follows in one of the books, but I'm not sure if It is true.
“The Supplemental Type Certificate will not be issued unless the type certificate holder has been informed and has expressed no technical objections to the proposal and has agreed to collaborate with the STC holder in matters affecting continuing airworthiness".

Thanks

I was many years at an OEM, in tech support engineering, and I'm not aware of any requirement to notify the OEM when someone applies for an STC.  You have to remember that many STCs are for airplanes who's manufacturers disappeared long ago, so you really can't make that a basic requirement.  It's possible however, that the FAA may request OEM input like an NTO for a proposed change on a case by case basis, depending on the scope of the mod, and if OEM cooperation is not forthcoming, it could stymie the STC project.

Certainly there is no requirement for the OEM to support an STC for continuing airworthiness, except perhaps where an STC causes an incident or incidents that generate activity toward an Airworthiness Directive and the OEM's Airworthiness Engineering Department has to get involved.  Operators use to come to us for help with issues on a subsystem installed under an STC, and we'd tell them sorry, we have nothing to do with it.

An OEM that is still in business may, or may not, participate in development of an STC.  One of the difficulties for the STC developer is obtaining engineering Source Control Drawings, which the FAA may require as part of the STC data package.  However, a lot of the time the OEM will want nothing to do with the STC, because it implies (to the OEM's customers) that the OEM will be obligated to help support the mod.

The linked Advisory Circular covers the STC application process and there is no mention of No Technical Objection letters from OEMs or requirements for OEMs to support STCs.  OEMs will sometimes discover STC mods done on their fleet that they had no idea existed until they start to get visibility in service.

STC Application Advisory Circular


What front is going to form after a cold air mass meets a warm air mass? What front is going to form after a cold air mass meets a warm air mass -- I think it will form a cold front or an occluded front, but I'm not sure.
Today I learned that different fronts gives different weather conditions for flights and I saw the question that I asked and I thought that it will form a cold front because the moving cold mass will collide with the warmer one and it will force the warmer mass to go up. However, I also learned that a cold air mass is moving faster than a warmer one and in the definition of an occluded front it says that the cold one will overtake the warm mass.
Will it form a cold front or an occluded front, or does it depend in what direction the masses are moving?

Weather awareness certainly is a very important part of pretrip planning before even a short local flight.
While cold air masses usually are of higher density than warmer air, wind direction and pressure play key roles.
What makes it a "front" is movement over the ground one way or the other.  Cold fronts are usually sharply defined because the denser air moves underneath the warm air and pushes it away.  Precipitation can be intense, but short lived, followed by rapid clearing.
If the wind direction is right, such as ahead of a low pressure area (in the northern hemisphere), warm air will advance across the ground.  These fronts ride up over the colder air, sometimes for hundreds of miles.  They bring lowering and thickening clouds, "showery precipitation", and fog before finally moving through.
Warm fronts are notorious for creating freezing rain under the right conditions and must be approached with caution when flying.  Cold fronts primarily carry the risk of severe weather and turbulence.
When cold and warm sit side by side with little movement, or are moving in the same direction (as near the middle of a low), they are said to be occluded.
Another type of front is a "dry line".  Humid air is less dense than dry air of the same temperature.  Dry lines should be watched as they also can produce severe weather and turbulence (as would that second diagram!).
Generally, the cold front and warm air wind directions are more perpendicular to each other.


Is it likely that an aircraft could have been near 10° 08' north at local midnight August 26/27, 2003? Edit: The astronomical data turned out to be different. I'm keeping the constraints below as they where, but those are not relevant to finding the closest person to Mars.
This is part of an effort to determine which human has been closest to Mars. As Apollo astronauts and ISS space station crew are ruled out, this someone must have been on Earth
That's why I'm turning to you. Planes are frequently flying 10km or higher, much higher than any mountain on Earth, and passengers and pilots are therefore higher up than any people on the ground.
There are some rather delicate restrictions:

The aircraft must have been very close to 10° 08' north. There's a quickly growing altitude penalty for being far from this..

The aircraft must have been at this latitude at local solar midnight

The longitude is not overly important. For the western hemisphere, the date is August 26/27, for the Eastern hemisphere, it's August 27/28. Africa can be either, but has a 700m altitude penalty be default.

Is night-time air traffic dense enough for this place to exist?
From initial research, busy airports such as Singapore and Kuala Lumpur are south of this line

Yes, it is very likely that an aircraft would be near that position/time/date as there are many aircraft that fly overnight flights from North American airports to and from South American airports, between Europe and Africa, and also between Asia and Australia.
For example, Air Canada has daily night fights from a Toronto, Canada to Santiago, Chile and both the outbound flight, and return flight, would often pass each other in that very same area and time. I would often operate those flights and we would chat with the crew of the opposite flight to exchange reports on flight conditions.
There are MANY other airlines with similar north-south routes operating overnight flights all over the world.


What is the correct use of the verb "to leave," for exiting the runway? What's the correct way to say, according to the phraseology;

I will leave the runway; I will vacate the runway; or I will exit the runway?

The correct term is to vacate a runway. The term is used several times in the ICAO Manual of Radiotelephony (Doc 9432), including the following example (among many):

  4.9 After landing
  Unless absolutely necessary, controllers should not give taxi instructions to pilots until the landing roll is completed. Unless otherwise advised, pilots should remain on tower frequency until the runway is vacated.

  Pilot: Georgetown Ground Fastair 345 runway vacated
  ATC: Fastair 345 taxi to stand 27 via taxiway alpha

And a relevant note from the same document:

  Note.— The runway is vacated when the entire aircraft is beyond the relevant runway-holding position.


Is there no warning if landing gear is not retracted during flight? I know that most aircraft have a warning system which makes beeping sounds if an aircraft tries to land without the gear down. After reading this news article about an Air India flight 676 flying without retracting the landing gear, I was wondering if there is a reverse mechanism which warns the pilots if the landing gear is not retracted during flight?

If its not there, why?

It's not there because it's like driving with the handbrake on.

  [The flight] was climbing out of Kolkata, however achieved an unusually poor climb rate, was not able to accelerate to normal cruise speeds and leveled off at FL200 after a continuous climb for about 30 minutes (avherald.com).

And because the flight crew should have run the 'after takeoff' checklist, which includes checking that the landing gear is up and locked.

(Source) A typical Airbus A320 checklist.

Related: How much extra drag does landing gear incur?


What are the major causes of parachutes failing to work? What are the top causes of a parachute failing to work?

For "parachute", I mean primarily sporting parachutes, such as used in skydiving, but information about military (paratroop) chutes, ejector seat chutes, etc., would be useful.

For "failing to work", I mean "fails to prevent the sudden stop at the bottom", whether this is through failing to deploy properly, getting tangled, structural failure or whatever.

Inspired by the following comment on this answer:

  maybe you could add something about why sometimes chutes don't open. –  rbp

Hello - your Friendly Neighborhood Parachute Rigger here.

Sport chutes are pretty reliable, have been since the mid 90s to the point where more accidents happen under fully functional canopies.

If we disregard rank stupidity like tying the flaps shut1 or incompetent packing we find that the leading cause of malfunctions is bad body position on deployment. You are supposed to be face down, shoulders level before opening the thing. If you are on your back or tumbling you can have various parts wrap around you. High-performance canopies are somewhat more sensitive to the shoulders being level and can open in a decently fast spin. Depending on the spin direction and your altitude you may not be able to recover2.

The emergency chutes are built differently, emphasizing (obviously) reliability over being able to land at 100km/h. This means that twisted lines are either recoverable or not an issue.

If the jumper isn't paying attention to where he is, you may find that a leading cause of going splat is not using the perfectly good canopy on your back. Automatic activators have more-or-less eliminated this as a common cause3, but if the jumper thinks that the houses look a bit too big and deploys the main at the same time as the reserve opens they may decide to wrap each other up. Ram-air canopies are like badgers - they don't like each other very much and having two open at the same time is a rather delicate situation.

If we turn to landing accidents, we find that there are all kinds of ways to injure or kill yourself with a fully functional canopy overhead. The aforementioned 100km/h landing speed is no joke - hit an obstacle on the ground going that fast and it's exactly the same as jumping out of a car on the highway. Buildings, trees, power lines, vehicles, running propellers etc. have all claimed their sacrifices. And don't try to land on both sides of the fence at the same time. Or in the alligator farm across the road.

Mechanical failure of the system is very rare - riggers won't pack worn-out reserves, and if they are concerned about someone's main they will tell the dropzone management who will usually decline to provide services until it's fixed.

Many jumpers will tie various handles to the pack before travelling. Prevents the pack accidentally opening when curious security or customs pick it up by what looks like the carry handle. Remove before Flight!
Happened to me twice - the first time I looked up, then down, decided I didn't have enough time to fix it. The second time it was spinning the other way and I fixed it in 2 seconds.
Automatic activators fire at 750-1000 feet. If you are in freefall below that altitude you're usually done.


Why did Boeing choose to give the Boeing 720 such a designation? The Boeing 720 was a modification of the Boeing 707. Why was it given the unusual number of "720" instead of a "707-xxx" or "7x7" designation?

Because the launch customer, United Airlines wanted it. From Boeing frontiers:

  The 720 was a ... first marketed to the airlines as the model 707-020. United Airlines was very interested in the 707-020 but had previously decided to go with Douglas and the DC-8. To help United avoid any negative public relations for going back to the 707, Boeing changed the name of the 707-020 to the 720.

According to aviationweek, the name change was at the behest of William ‘Pat’ Patterson, the president of launch customer United Airlines.


Are all tires on an aircraft replaced at the same time? On cars, it is often to replace all four tires at the same time. Is this true also for aircraft?

I imagine the nose gear and main gear probably can be replaced at different intervals. However, are tires within the same gear assembly replaced together? What about left and right gears? For example, is it ok to replace all tires on the left gear only while keeping old tires on the right?

Nope.. they are replaced 'on condition'. Exception is when one tyre has deflated before landing (cockpit indication and later confirmed) then the good tyre on the same axle has to be replaced irrespective of condition.

Tyres have a hard life and get damaged by rubbish on the runway and stand. Also airplanes don't always hit the ground straight .. when they come in at an angle  it wears the side of the thread more on that tyre.