How else can snowy/icy conditions disrupt airport operations? In casey's fabulous answer here, he identifies several ways snow/ice can disrupt airport operations:

  Continuous heavy snowfall can eventually close an airport if it
  becomes impossible to keep the runways clean, taxi routes become
  unusable due to drifting snow or snow transitions into sustained
  freezing rain (or runs out of de-ice fluid, yes IAH I'm looking at
  you). This is a transient problem and the closure would end as soon as
  conditions ease and the facilities can keep up with it.

Are there other ways that heavy snow (or ice) can disrupt airport operations?  Could it perhaps interfere with lighting or navaids?  Are there other airport functions that stop or slow in snow and ice?

There are multiple ways by which snow can affect the operation in an airport.

Snow (and ice) in runway can affect takeoff by absorbing energy and can impact the aircraft after being kicked up by tires.
During landing, snow or slush in runway can reduce the deceleration rate by reducing friction coefficient, sometimes causing hydroplaning.
The runway length requirements in case of dry and wet conditions are different. This means that some aircraft cannot use the available runway in case of snow/wet conditions.
The requirements to clean the runways (and taxiways) continuously means that the flights will be delayed.
The snow may reduce the visibility of runway and terminal visual markers.
Ramp operations may be affected due to snow/ice.
Beyond a certain level of snow, the airports have to be closed as the aircraft cannot takeoff/land.
Also, it will be snowing in areas around the airport too. This means that there will be difficulty for people in reaching airport in the first place.

Also, see the FAA advisory circulars AC 150/5200-30C - Airport Winter Safety and Operations and AC 91-6A, Water, Slush, and Snow on the Runway


Is it difficult for a GA aircraft to escape a thunderstorm? I live in the midwest, and I'm getting ready to start working on my PPL.  For some reason I find myself really nervous about getting into the air and suddenly seeing a line of thunderstorms rolling in from the southwest.  In my mind it feels like a fast moving front would be difficult to escape...

But I wonder if my fear is wholly unjustified.  So I thought I'd ask:

If I'm in a GA plane (like a Cessna 172) and I see a thunderstorms forming to my southwest (lets say 20 miles away),  how much time, in general, am I going to have to get on the ground before the storm gets to me?  If I turn away from the storm, and start looking for an airport, will I be able to put distance between me and the storm to buy time to get on the ground?

Just to clarify before I get a lot of "that's what preflight briefings are for", this questions assumes there was a preflight briefing.

But thunderstorms have this tendency to show up unannounced where I live (or at least it feels that way to me), and that's what this question is about. What do I do when a thunderstorm, that I wasn't aware was going to be there, suddenly shows up on the horizon headed right for me?

If you take off with a storm 20 minutes away from the airport, it won't have been "unforecast"; the NWS is much better than that. They can pretty accurately predict what's going to happen regarding various fronts at least 24 hours in advance, in turn giving you the advance notice to adjust your flight schedule to ensure you can get around the storm or well away from it.

But let's say someone goofed (probably you), and now you find yourself climbing into the air off the tarmac with the leading wall of a cumulonimbus looming over the horizon, which will be between you and your intended destination before you reach it.

First rule; never fly toward the storm. Cumulonimbus formations are deadly to small craft, and even commercial airliners prefer to stay at altitude in a holding pattern well above the storm and let it pass by before attempting to land. These "thunderheads" produce torrential rains, powerful and frequent lightning, strong updrafts, hailstones ranging from pebbles up to grapefruit, and turbulent cyclonic winds that can culminate in tornadoes. Your Cessna 172 stands no chance.

Flying away from the storm will, at worst, gain you the time between the storm's speed and yours that you can use to find an open airstrip and put down. As Michael Kjorling said in his answer, most Cessna 172 variants cruise at over 100kts, which would require the storm moving across the ground as fast as a Category 2 hurricane rotates, so in most scenarios even if you're flying in still air with the storm moving over the cooler air you're flying in, if you just put the squall line to your rudder you should gain ground. Ideally, the storm will be pushing a mass of air in front of it which will give you a tailwind, and thus you'll be able to put that much more distance between you and the storm front.

Second rule; unless your planned flight is a cross-country flight heading pretty directly away from the incoming front, get on the ground as quickly as you can do so safely, and find a shelter for your aircraft. Obviously, being at your home FBO where you rent your tiedown or hangar is best, but anywhere you can slip your aircraft under a roof or awning for a couple hours will do. Remember that unless you have your instrument rating, the conditions during and after most thunderstorms are IMC and thus illegal (and deadly) for you to fly in.

If you're flying a pressurized aircraft, and/or you have instrument privileges, you have more options, the best of which is to get above the storm and wait it out. However, your Cessna 172 is not pressurized, so unless you have an oxygen bottle aboard (and are endorsed to use it) you're limited to about 12,500 feet and only for a half-hour, well below the top layers of a thunderhead, so you'll have to outrun it, get around it, or put down and shelter in place while it blows over you.


How is a 436 seater A330 fuel efficient? Cebu Pacific is a Philippine low-cost airline , which has 6 A330 in its fleet. The capacity of each of them is 436 . As far as I know, one of the reasons why airlines introduce First Class cabins is because its impossible for them to fly with a huge number of passengers and their luggage. It makes the plane very heavy and less fuel efficient. That's why, we don't have any A380 with more than a capacity of 550 , against its maximum of 853. But, how does Cebu Pacific makes profits from operating a 436 seater A330( which commonly has a capacity of 300 people)?

First of all, keep in mind that the Philippines has one of the shortest average populations on Earth. Their average passenger weighs a lot less than an average American or European, since weight scales roughly with the cube of height. So, 436 Filipinos don't weigh nearly as much as 436, say, Americans or Europeans, assuming average populations from each group. According to Wikipedia, the average Filipino male of age >= 20 is only 5' 3.5" (162cm) and the average female age >= 20 is 4' 11" (150 cm.) Compare those numbers to 5' 9.5" (176 cm) for males and 5' 4" (162 cm) for females for Americans age >= 20. Considering the roughly cubic scale, that's a pretty significant mass difference.

Second, why would putting more passengers on board not be fuel efficient? It will make the aircraft heavier, but it also means that you're carrying that many more people in one trip. My guess would be that you'll burn less fuel per passenger-mile, rather than more. To get a rough estimate, an A330-300 has an operating empty weight of about 274,500 lb. and it can carry about 175,170 lb. of Jet-A. If we assume the average Filipino weighs about 120 lb. (this seems like a reasonable guess based on my experiences in the Philippines,) 436 passengers would come out to 52,320 lb. while the 293 passengers on Delta's A330-300 seat configuration would be 35,160 lb. So, you're increasing mass before fuel by only around 5.5% while increasing passenger count by a whooping 49%. It would be hard to find a scenario in which that does not use less fuel per passenger-mile (unless, of course, you're overweight and can't take off at all.)

Regarding the issue of avoiding being overweight (and, thus, being able to take off,) Cebu Pacific normally doesn't run routes anywhere near the 6,100 nmi range of a fully-loaded A330-300. This means that they won't need to carry a full fuel load. Even a 10% reduction in fuel load from the maximum capacity of an A330-300 would equal the entire added weight of going from 293 passengers to 436. Even at full fuel load, though, judging from the previously-referenced numbers on Wikipedia, we get:

Operating Empty Weight (OEW): 274,500 lb.
Full Fuel Load: 175,170 lb.
436 120 lb. passengers: 52,320 lb.
14 flight + cabin crew x 120 lb. = 1,680 lb.
Total before cargo: 503,670 lb.
Maximum Takeoff Weight (MTOW): 534,000 lb.

So, that still leaves 30,000 lb. for cargo and anything else that's needed, even if they did need to carry a full fuel load for some reason.

The issue of why Cebu Pacific doesn't offer Business/First class cabins was also mentioned. The reasons for this are mostly their target demographic and their route network (combined with the already-explained lack of weight limit.) While there are many business travelers going to and from Cebu City, the routes on which these travelers are typically traveling are already well-served by several high-end airlines that also offer onward connections to Europe and the Americas (e.g. Cathay Pacific to Hong Kong, Korean Air and Asiana to Seoul, Japan Airlines to Tokyo, Emirates to Dubai, EVA to Taipei.) Additionally, Philippine Airlines also already competes in that space (in addition to apparently offering direct flights from Cebu to LAX now, which I think is a rather recent development.)

With their low-cost model and lack of alliance partners for onward connections, it would be difficult for Cebu Pacific to compete for the already well-served premium-cabin demand in Cebu. Instead, their business model is catered to serving Filipinos traveling between islands and to regional destinations where lots of Filipinos work out-of-country. Last I heard, approximately 10,000,000 Filipinos worked outside the Philippines (around 10% of their total population,) so serving that demographic is not a small market. In case it's not obvious, this is an extremely price-sensitive demographic which is well-served by Cebu Pacific's low-cost model.

It should probably also be noted that, while 436 passengers on an A330 is unique to Cebu Pacific, high-density economy-only configurations in general aren't. Lots of regional-service low-cost carriers offer high-density economy-only fleets, even in less cost-sensitive areas like Europe, Canada, and the U.S. In Cebu Pacific's own region, AirAsia and Tigerair also operate similar high-density, economy-only fleets targeting the same demographic (though, admittedly, AirAsia X does have 2 rows of business-class seats in their A330s, but these are on longer routes than Cebu Pacific normally serves, e.g. Singapore-Australia.)


Studying bird flight and insect flight: Would studying aerodynamics of airplanes be useful? Would studying the aerodynamics of airplanes be useful, if one wants to study bird flight and insect flight?

For instance, would studying a gliding paper plane and a gliding unpowered airplane be fundamentally the same?

I've read that aerodynamic laws for airplanes are different from aerodynamic laws governing bird and insect flight, but I forgot where I read this from -- possibly from an academic journal paper, if I remember correctly.

The biggest factor, besides the basic insect ornithopter wing mechanics, is air viscosity effects, or Reynolds Number.  To insects, the air is extremely "thick" with extremely low Reynolds Numbers, and the optimal airfoils are single surface membranes - insect wings. As Rn gets higher, the desired airfoils get thicker (bird wings) and thicker until you are in very high speed flight and the wings have to start getting thinner again.

Anyway, for a basic overview of all of this, I can't recommend the book Miracle of Flight by Stephen Dalton highly enough.  It's a book for the layperson that illustrates flight pretty much up the Reynolds Number range, starting with insects, then birds, then the man-made stuff.


Are there advantages to slotted wingtips? Are there advantages to the way some birds' wingtips end in separate feathers instead of a more solid shape?

As an example, separate-feathered wingtips:

more solid wingtip:

Slotted wingtips provide torsional flexibility.

  A bird’s wingtip feathers must twist in one direction during the upstroke of the wings and in the other direction during the downstroke to keep the local wind striking the wing at an appropriate angle to generate lift and thrust... The turning could be done at the base, with a completely inflexible feather; the aerodynamics are improved and material saved if the local flow forces twist the feather by just the right amount.

-- S. Vogel, Comparative biomechanics: life's physical world, p. 382, 2003.

They also reduce drag.

  The minimum drag of a Harris' hawk gliding freely in a wind tunnel was measured before and after removing the slots by clipping the tip feathers. ... the feathers that form the slotted tips reduce induced drag by acting as winglets that make the wings non-planar and spread vorticity both horizontally and vertically.

-- V. Tucker, Drag reduction by wing tip slots in a gliding Harris' hawk, Parabuteo unicinctus, J Exp Biol 198:775-81, 1995.

They are effective while flapping, not just while gliding.

  We used particle image velocimetry to measure the airflow around the slotted wing tip of a jackdaw (Corvus monedula) as well as in its wake during unrestrained flight in a wind tunnel. The separated primary feathers produce individual wakes, confirming a multi-slotted function, in both gliding and flapping flight.

-- KleinHeerenbrink et al, Multi-cored vortices support function of slotted wing tips of birds in gliding and flapping flight, J R Soc Interface 14(130):20170099, 2017.


What is the limit between lower and higher airways in VFR? On skyvector you see "World high", "world low" and the VFR map.

VFR is always under the clouds, correct?
But how high do you have to be to follow the high/upper and how high for the low/lower airways?

Skyvector uses official charts from the US National Aeronautical Chart Office (NACO) where available. For the rest of the world, it synthesizes maps using the NACO style based on data from each country's Aeronautical Information Publication (AIP). This will not match what local charts look like and is not valid for navigation. Within the US, you can select individual charts by name or the "World" layers that do a clever panoramic blend of all available charts into one seamless worldwide chart.

The "Lo" and "Hi" charts refer to the NACO  "IFR En-Route Low" and "IFR En-Route High" charts. These are roughly equivalent to NACO VFR sectional charts. NACO "IFR Area" charts (only available in a few areas) are roughly equivalent to NACO VFR Terminal charts.

You should look at the NACO chart legends for a full explanation of what all the symbols and numbers mean, but for example, the number above the airway label (without a * or G prefix) is the Minimum En-Route Altitude (MEA), which provides both terrain and obstacle clearance and navaid radio reception. The number below is the length between waypoints in nautical miles.

The NACO "Low" charts show airways with an MEA below FL180, which have labels beginning with V or T, and NACO "High" charts show airways with an MEA of FL180 or higher, which have labels beginning with J or Q. Most other countries use the ICAO naming scheme where all "Upper" airways have a "U" prefix plus some other letter, though what "Upper" means varies by country. Skyvector tends to put "U" airways on the "World Hi" chart and all others on the "World Lo" chart, but it's not consistent across countries, so they may be using other data as well.


What is the difference between en-route delays and airport delays? ANSP performance is gathered an published online on https://ansperformance.eu. They monitor complexity, delays, efficiency and other operational data.

I also noticed they have two ways of describing delays with a formal definition:

En-route delays

  The en-route ATFM delay provides an indication of ATFM delays on the ground due to constraints en-route.

Airport delays:

  The Airport Arrival ATFM Delay provides an indication of ATFM delays on the ground due to constraints at airports.

My question is: What does this exactly mean? Are these different ways of describing the same delays? Or do they describe two different sources of delays.

One reason of my doubt is that both categories use the same classification, from A (accident/incident) - W (weather). Could someone shine some light on this?

The delays you mentioned are imposed by Eurocontrol to manage traffic flow all over Europe:

  Even when an aircraft is ready to depart, it may still be delayed by ‘flow management’ (ATFM). You may well hear that your flight is ‘waiting for its Air Traffic Control slot’ and this is explained in another article. In short, if there is a problem that will delay an aircraft either en-route or on the approach to the destination airport, then it’s safer and cheaper to hold the aircraft on the ground, not burning fuel, and give it a delayed take-off time.

  EUROCONTROL as Network Manager looks at all the flight plans and identifies where and when there are too many flights/too little capacity. This might be as a result of a peak in demand (aviation has rush hours too!), weather problems, limited capacity at the destination airport or many other possibilities. In total, flow management delays account for about 16% of total delays (in 2017), mostly relating to issues at the destination airport.

(Eurocontrol)

  ATFM departure slots are allocated centrally by the European Network Manager upon the request of the local Flow Management Position (FMP), when an imbalance between demand and capacity is foreseen at airports and/or en-route. The purpose of such regulation is to hold aircraft on the ground.

(Eurocontrol ATFM Slot Adherence)

To the pilots, this comes as a so called CTOT (Calculated Take-Off Time):

  A time calculated and issued by the Central Flow Management unit, as a result of tactical slot allocation, at which a flight is expected to become airborne.
  An Air Traffic Flow & Capacity Management (ATFCM) departure slot, forming part of an Air Traffic Control (ATC) clearance, which is issued to a flight affected by Network Management regulations. It is defined by a time and tolerance (-5 to +10 minutes) during which period the flight is expected to take-off.

(Eurocontrol ATM Lexicon)

For each of these delays, there is an associated Reference Location where the reason for the delay is located. This defines, which delay category applies:

En-route delay:

  Delay caused by regulation based on traffic volume which has a reference location classified as AS (Airspace) or SP (Special Point).
  ATFM delay caused by regulations applied by the CFMU at the request of the FMP to protect en-route ATC sectors from overload.

(Eurocontrol ATM Lexicon)
Airport Delay:

  Delay caused by regulation based on traffic volume which has a reference location classified as AZ (Aerodrome Zone) or AD (Aerodrome)

(Eurocontrol ATM Lexicon)

Examples for delaying a departure could be:

enroute weather does not allow to fly the filed route at the moment (En-route delay)
weather at destination is not expected to be good enough to land at the estimated arrival time (Airport delay)
there will be too many aircraft in one air traffic control sector (En-route delay)
there will be too many aircraft arriving at the destination airport at the same time (Airport delay)


How do pilots fight jet lag? Jet lag, medically referred to as desynchronosis and rarely as
  circadian dysrhythmia, is a physiological condition which results from
  alterations to the body's circadian rhythms resulting from rapid
  long-distance trans-meridian (east–west or west–east) travel on
  high-speed aircraft. For example, someone travelling from New York to
  California feels as if the time were three hours later than local
  time. (Source)

As pilots often have to travel between multiple time-zones, especially during long haul flights, with as much as 12 hours of difference between them, how do they fight jet lag?

Crew members each have their own approach to this but in general on the long haul routes, as a pilot you have at least 24h layover, so you can catchup on some sleep, walk outside for a bit (depending on the local time) and then sleep some more so you're fit for the next flight back home. At home you have a couple of days off to recover from the trip.

On the very long flights 13h+ the pilots are with at least 4 so you can do a quick nap on board as well.

As a passenger I cope with the jetlag by looking at the arrival time, do I arrive in the morning I will try to sleep on the plane, will I arrive in the afternoon the I will try to stay awake and go to bed early. By doing so I wake up easily next morning and do not feel jetlagged.


Are the number of unique passengers per airport counted? In airport passenger number statistics, all enplanes and deplanes are added to all direct transfers during a year.

So if I travelled 21 times via Heathrow I was counted as 42 passenger movements at LHR.

Is there anywhere statistics that show the number of unique human beings that travelled via an airport?

Short answer is no, mostly they are not counted. Even if they have this data it is very unlikely that they publish it.

Assuming that you are not a transfer/transit passenger; meaning you have arrived to airport by ground transportation for your departure and you have left the airport via ground transportation when you have arrived; you will be counted as 42 times in the statistics (21 departure + 21 arrival). This is standard counting method.

If you arrive to the airport by a plane, you stay inside the plane and you leave the airport with the same plane; then you are a transit passenger which is counted 1 time.
(You are not a departure or arrival passenger, you are a transit passenger)

If you arrive to the airport by a plane, you leave the plane and you leave the airport with the another plane; then you are a transfer passenger which is counted 1 time.
(You are not a departure or arrival passenger, you are a transfer passenger in this case)

So passengers of an airport are basically; departure + arrival + transit + transfer
(Note: Exact definitions of transit and transfer might change from airport to airport)

Most of the time, especially in smaller airports, airport management does not record passengers on a unique person basis. They simply don't have the unique identifier for each passenger, such as a passport ID number. So they cannot know if a person is travelling first time or fifth time.

However, there are exceptions of course:

There are (very expensive) software that allows airport management to record, filter, manage each passenger data with extreme detail. Its work logic is that it records a special text message that airplane sends to airport before arrival.
For "international" departing/arriving/transfer passengers, this unique traveler information can be obtained from the system of the passport police since they record ID numbers of passports.
Airlines might have this data separately; however this is not a feasible approach since airlines mostly do not share this info.


Is this equation for propeller thrust correct? From dimensional considerations, and assuming that the power $P$ applied to a propeller of diameter $D$ moving at an axial speed $V$ is 100% converted to the acceleration of a mass of air with density $rho$, I have arrived to the following expression for the thrust $F$:

$F=k(P·rho·V)^{1/2}·D$

where $k$ is a non-dimensional constant.

Is that expression basically correct? I'm now editing to include below the derivation, a bit long...

We have a propeller with a diameter $D$, absorbing a power $P$ when moving at an axial velocity $V$ in air of density $\rho$. Let’s assume that there exists a function f such that the thrust $F$ of the propeller is:

$F = f(P,D,V,\rho)$

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

Five variables are too much. The system can’t be solved unless we have four, one dependent and  tree independent…  So, in place of $V$ and $D$, we take the volume $W$ swept by the spinning propeller in the unit of time, dimensions $L^{3}T^{–1}$

$W = π/4 · D^{2} · V$

There is an non-dimensional constant $k$ such that:

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

Switching to the dimensions:

$M^0 L^0 T^0 = (MLT^{–2})^a  (ML^2T^{–3})^b  (ML^{–3})^c (L^3 T^{–1})^d$

Then, the system is:

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

$F$ is the dependent variable, so we make a=1

Solving the system:

$b = –1/2 \\
d = –1/2 \\
c = –1/2$

Inserting in
$k = F^a\cdot P^b\cdot \rho^c \cdot W^d$ where $a,b,c,d$
the values of the exponents, and solving for $F$,

$F = k\cdot P^{1/2}\cdot \rho^{1/2} \cdot W^{1/2}$

But $W = π/4 · D^{2} · V$

Now $k$ may absorb the constant π/4, and we get:

$F = k\cdot P^{1/2}\cdot \rho^{1/2} \cdot V^{1/2}\cdot D$

From the comments:what I want is a derivation of thrust as a function of power absorbed, prop diameter and prop axial velocity..

Power absorbed $P$ is engine torque  times prop angular velocity $\omega$: $P =  \cdot \omega \tag{1}$.
Prop axial velocity at the tip $V_t =\omega \cdot D \tag{2}$

$P$ is the power applied in the axial direction, while thrust is generated in the direction perpendicular to the propeller plane - there must be some function describing the relationship between the forces in both directions. This function would be one describing efficiency and losses, since the primary force application is the engine torque and the thrust is the net resulting force.

If the goal is like is stated in OP ...propeller of diameter  moving at an axial speed  is 100% converted to the acceleration of a mass of air... this means that there are no losses, and we can use the simple impulse theory of the magic disk. This is comprehensively explained in this post, which results in the following equation between thrust and power:

$$P = \sqrt{\frac{F^3}{2\rho A}} \tag{3}$$

If we want $V_t$ in there we need to substitute (1) and (2):

$$\frac { \cdot V_t}{D} = \sqrt{\frac{F^3}{2\rho A}} \tag{4}$$

Since A = propeller disk area = $\frac {\pi}{4} \cdot D^2$, (4) further boils down to:

$$F^{3/2} = k \cdot  \cdot V_t \cdot \rho^{1/2} \tag{5}$$

Note that (3) contains $P$ but no $V_t$, while (5) contains $V_t$ but no P. We could lump the motor torque into the force $F$ dimension, but all my engineering genes scream to not do that because of the origin and effect relationship: no engine torque, no net thrust.

Both (3) and (5) contain $\rho$, which is a must considering that the thrust is obtained by acceleration of a mass of air. The mass flow dimension can disappear into a force dimension as well when multiplied by a velocity, for instance a propeller tip velocity...

This answer shows the relationship between thrust and power of a helicopter rotor in the hover (and therefore of a propeller) using modified momentum theory with losses:

$$C_P = \frac{\kappa \cdot {C_T}^{3/2}}{\sqrt{2}} + \frac{\sigma \cdot {C_D}_0}{8}$$

with $\kappa$ = loss factor and $\sigma$ = blade solidity. So the exponent of the function (induced power) vs. (thrust) is 3/2. Also, there is an additional term that the dimensional analysis cannot catch, which is power required in the propeller plane.


Are lockwires still preferred over self-locking nuts and other ways of bolted joints` safety? I've watched some of the lockwiring videos and if I understood it right then there are two most widely used ways of ensuring that a bolted joint does not get loose:

Lockwire
Self-locking nuts

Difficulties and costs of maintaining the lock-wiring are obvious. My intuition says it only has to be used as a last resort when no other way is available. Nevertheless any aviation junk yard says my intuition is wrong. Lock-wires are everywhere in the old gas turbine engines. My question is:

Do they now use other methods of bolted joints` safety in gas turbine engines (jam nuts and locking washers in particular)?

Difficulties and costs of maintaining the lock-wiring are obvious. My intuition says it only has to be used as a last resort when no other way is available. Nevertheless any aviation junk yard says my intuition is wrong. Lock-wires are everywhere in the old gas turbine engines. My question is:

  Do they now use other methods of bolted joints` safety in gas turbine engines (jam nuts and locking washers in particular)?

Well, maintaining safety lockwire isn't as hard as you think it is: A pair of safety wire pliers will last you a lifetime, and they do about 80% of the work for you (all the maintenance monkey needs to do is cut an appropriate length of wire, hook up the pliers, and twist, making sure the wire is positioned so as to always tighten the fastener).
It is easy to inspect, repairing is simple (just replace the damaged wire), and cost for a spool of wire is minimal compared to using a new self-locking nut every time something needs to be taken apart (safety wire earns its keep for temporary assembly too: You can wire the assembly when you're done, rather than wearing the lock material on a self-locking nut).

Other methods of securing fasteners are used on aircraft (in engines and elsewhere), including cotter pins and self-locking nuts with nylon inserts to prevent them from slipping. The cotter pin is easy to verify (like safety wire), and is widely used.  Self locking nuts on the other hand can slip without much visual indication (torque seal or similar products are often used to mark the nut and fastener to give a visual indication of slip).

A disadvantage to self locking nuts is that they must be replaced any time the fastener is removed (reused nuts will have a lower locking resistance, and may fail to hold), and using them introduces a potential for human error in maintenance operations that does not exist with safety wire, which must be cut to remove it. (There are even folks who try to reuse cotter pins, though normally they are cut to remove them and thus cannot be reused.)


Did A320 NEO need an equivalent to 737 MAX MCAS because of its bigger engines? We read that MCAS on the Boeing 737 MAX was needed because of the new, bigger, heavier engines of the MAX compared to the previous 737 versions.

The closest equivalent to MCAS on the Airbus A320 NEO is the alpha protection even if they are not the same.

But what have been the adaptations to the A320 due to heavier, larger engines?  Can we be sure that A320 does not suffer from issues comparable to those the 737 MAX has, due to their similarities (bigger engines on same airplane)?

The A320 and 737 have very different flight control architectures.

The 737 has physical cables that transmit pilot (or autopilot) input directly to the hydraulic actuators. This was common in the 1960's when the airplane was first designed. This means that the airplane handling comes down to the aerodynamics and the pilot input.

The 737 MAX presented an issue when it was found that certain situations approaching stall could cause the airplane to pitch up, exacerbating the stall, rather than naturally pitching down and recovering as expected. This was due to the larger engine nacelles, which are located ahead of the center of gravity. An aerodynamic change would have taken lots of time and money and had its own drawbacks. Instead, Boeing created MCAS. This applies trim to help to pitch the airplane down when it reaches high angles of attack.

The A320, on the other hand, was designed as a fly-by-wire aircraft. This means that a computer is using sensor inputs to control the airplane all the time, and pilot or autopilot inputs only provide a guide to that computer control.

Fly-by-wire allows some helpful safety features, such as not allowing the airplane to exceed the design envelope, including stall. This means that any A320 in normal conditions will allow the airplane to reach a maximum angle of attack and no higher. Any aerodynamic differences such as a different fuselage length, larger engines, etc, are countered by the flight computer. Other than some possible fine tuning of the control laws of the fly-by-wire system, the A320 neo would not need any special new system to control angle of attack.


How was I able to just plug in my headphones and listen to ATC and pilot chatter? I was travelling from Mumbai to Newark Liberty Intl on United Airlines 49, a Boeing  777-200. I was sitting in the economy section, last row, last seat to the plane's left, basically, I was literally the passenger on the last seat of the aircraft.

When I sat down, I plugged my earphones into the headphone jack and I could hear the conversation between ATC and the pilot, all I had to do was just twist the and hold the jack in a certain position. I could hear them talk to Mumbai ATC, the Islamabad ATC, Kabul ATC, even up to Iceland. My question is, how is this possible? What could have happened? Did the pilot or the airline know about this? Should I have told them about this? Is it illegal to listen to this chatter? Can this happen next time I travel or was I just lucky?

This is a feature offered on some United Airlines aircraft and flights. It's an interesting way to hear what's going on in the cockpit. You can find lots of information by searching for United channel 9.


Are approach and departure procedures based on visual reference points official VFR procedures? Pilots flying VFR follow clearances like the "mall visual" or "east channel departure." These are based on features of the local area that are easy to identify.

Are procedures like this official? Where could a reference be found for these procedures?

Yes, they are official, this is the KSEA MALL VISUAL RWY 34R/C/L approach plate:

I can't find a "East Channel Departure" but if you know what airport it belongs to, you can find it in the Terminal Procedures publication, either in paper form or online.

They are not VFR procedures, but rather visual IFR procedures. The MALL VISUAL would not be assigned to a VFR flight. Some airports do have special arrival/departure procedures which apply to VFR flights; these can be found in the Airport/Facilities Directory (A/FD) or on a website like http://www.airnav.com/ (for the US anyway).


How long does it take for a propeller engine to spool-up? To build further upon the question Why does a turboprop lag?, the following:

Assuming a propeller engine is running in idle and the throttle lever is switched to full thrust instantaneously at t = 0 seconds. How long does it take before the propeller delivers full thrust?

Exact times for a specific engine or range/order of magnitude for a generic one would be appreciated

In my Cessna Cardinal, with 360 cubic inch (~5.9L) carburated engine, I push the throttle in and the response is immediate.  Just like stepping on the pedal in a car with a standard transmission because propeller RPM = engine RPM. I have a constant speed prop, with controllable pitch angle, so it sort of acts like a standard transmission, I can dial it to any 'gear' I want to. For take off and landing, the pitch is flattest, and most responsive. Just like in a car, I can dial the prop pitch flatter and add more throttle for a climb from level cruise, then when at altitude I can dial the prop pitch up and throttle back down for efficient cruising. In planes we generally don't go to full thrust instantaneously, that's rough on the engine, but smoothly push the throttle in, maybe 2-3 seconds from idle to full throttle.  During landing, sometimes a bit of throttle is added to arrest an increasing descent rate, and even that is applied smoothly, and rarely full throttle unless a go-around is needed.

This link shows how the oil pressure, springs, governor, and other bits are used to control the propeller pitch when the RPM has been selected.

http://www.boldmethod.com/learn-to-fly/aircraft-systems/how-a-constant-speed-prop-works/


Are the discrete I/O considered to be part of the ARINC interface? A typical connection used to transmit/receive ARINC data might consist of a cable and a connector similar to the one shown below. Although ARINC transmit/receive channels aren't the only thing this interface can be used for. I've noticed that several different varieties of LRU also use some of the pin connections for I/O discretes.

So, are the I/O discretes considered to be part of the ARINC interface? Or do they just coincidentally share the same connector and have nothing to do with ARINC?

Update

As one of the answers commented on... I am not talking about the discrete bits within an ARINC word but the physical discrete I/O voltage signals that you'd see on an avionics bus.

It depends on which ARINC document you're talking about. ARINC 429 is a digital serial bus standard. Discrete data may be sent in ARINC 429 data words, but that's just bits in a word not the physical discretes you're asking about.

ARINC also has documents that cover standards for other interfaces as well as 'Characteristics' that define specific LRUs such as ARINC 735A for TCAS II.  In these documents ARINC does specify discrete interfaces.  There are two types, open/ground and 28V/open and are defined for both input and output.

So yes, there are discrete interfaces that are part of ARINC standards, just not part of ARINC 429.


What procedures do I have to follow to fly a seaplane from the US to Canada? I work in the States and I'm thinking to go visit my friend in Canada. I have access to an Icon A5 and was thinking to fly from my closest lake in Vermont to his house which is also on a lake. What would be the protocols for doing this? Customs wise. Since I believe I would have to file a flight plan. How would immigration work since I am not planning to land at an airport and I'm also not a citizen of either the US or Canada?

Whenever you land in the US from a departure point not in the US, you have to land at an Airport of Entry as your first US destination airport. It does not have to be a big airport. There are plenty of Class D airports that qualify. You can verify which airports are AOEs in the US Chart Supplement. Some (big ones) are also marked as such on the sectionals.
When crossing the US border, you will need to have arranged customs clearance with the US CBP beforehand if you are landing at a small AOE. You may also need a US CBP DTOPS decal for your aircraft. Then, of course, there is the flight plan. Once you have cleared US CBP, you can fly to any other US domestic destination of your choice.
I would think that when flying into Canada, the TCCA would have similar rules.


Is it legal for a passenger to sit on the jump seat in Part 135 operations? When operating a large turbine aircraft under 14 CFR 135, does the FAA allow a passenger to occupy the jump seat in the cockpit?

Falcon 900 jump seat

Would it matter whether or not they are a company employee (i.e. other than a flight crew member)?

Unlike the airlines, we usually fly with the cockpit door open (if there is even one installed) so it isn't a security issue like the airlines.

Lets start with 14 CFR 135.125, which defines security requirements for part 135 flights:

§135.125   Aircraft security.
Certificate holders conducting operators conducting operations under this part must comply with the applicable security requirements in 49 CFR chapter XII.

We pass the ball to 49 CFR 1544 and make sure we're in the right place:

§1544.1   Applicability of this part.
(a) This part prescribes aviation security rules governing the following:
(1) The operations of aircraft operators holding operating certificates under 14 CFR part 119 for scheduled passenger operations, public charter passenger operations, private charter passenger operations; the operations of aircraft operators holding operating certificates under 14 CFR part 119 operating aircraft with a maximum certificated takeoff weight of 12,500 pounds or more; and other aircraft operators adopting and obtaining approval of an aircraft operator security program.
(b) As used in this part, “aircraft operator” means an aircraft operator subject to this part as described in §1544.101.

For brevity, I'm not posting 1544.101 which defines a host of paragraphs you must comply with depending on your operation.  If we assume a charter operation in an airplane weighing over 12,500 lbs, we get (1544.101(e)(1)):

(1) The requirements of §§1544.215, 1544.217, 1544.219, 1544.223, 1544.230, 1544.235, 1544.237, 1544.301(a) and (b), 1544.303, and 1544.305; and in addition, for all-cargo operations of §§1544.202, 1544.205(a), (b), (d), and (f).
(2) Other provisions of subparts C, D, and E that TSA has approved upon request.
(3) The remaining requirements of subparts C, D, and E when TSA notifies the aircraft operator in writing that a security threat exists concerning that operation.

From here the one we care about is 1544.237, which says:

§1544.237   Flight deck privileges.
(a) For each aircraft that has a door to the flight deck, each aircraft operator must restrict access to the flight deck as provided in its security program.
(b) This section does not restrict access for an FAA air carrier inspector, an authorized representative of the National Transportation Safety Board, or for an Agent of the United States Secret Service, under 14 CFR parts 121, 125, or 135. This section does not restrict access for a Federal Air Marshal under this part.

Which brings us to our answer: YES, a passenger may occupy the jumpseat if you do not have a door, and also if you do have a door as long as your company security program allows it.


What is the ceiling to prohibited space P-47 (or any other P-zone)? On the Dallas-Fort Worth sectional, notice one of the few permanently Prohibited airspace zones west of the Mississippi; P-47, around the PanTex nuclear plant in Amarillo, just northwest of Husband Intl (AMA) and within the outer cylinder of its Class C space.

Now, that zone is directly in the path of AMA's longer runway, 4/22, and Victor routes including V12-280 extend directly away from the PNH VORTAC at AMA right over the top of it.

That leads me to think that either P-47 has a ceiling above which airliners are allowed to operate, or else AMA Approach and Fort Worth Center via Amarillo RCO have a dickens of a time routing incoming traffic when the winds indicate use of runway 4/22. The outer Charlie cylinder begins at 4800 feet, but the chart also clearly states that P-47 is excluded from AMA's class C space where they overlap. That leads me to think that this P-space extends to Jupiter, and all flight traffic including AMA arrivals/departures (it's not a big town, but it's not exactly BFE either in part because of Pantex) have to maneuver specifically to avoid P-47.

So, to confirm, is there any altitude at which you can overfly P-47, or in more general terms any P-zone?

It seems kind of silly for many P-zones, including this one, to extend all the way to space, as beyond a certain altitude if nothing else it becomes impractical to dive straight down into the facility under protection. But, if that's the law...

Special Use Airspace is defined by boundaries in all three dimensions1. The horizontal boundaries are depicted on the chart as you describe. The vertical boundaries are in the sidebar of the chart:

You can see here that P-47 exists from the surface (because there's nothing before the "TO") up to 4800 MSL. KAMA is at at 3607 MSL, so P-47 ends 1200' above the airport surface. At a little more than 5 NM away from the airport (measuring on the sectional), that's about 240 ft/NM climb: well within the performance capabilities of almost every powered aircraft. Overflights on the victor airway obviously have no problem at all.

This is used for allowing traffic where it might otherwise not be possible: Consider P-40 and R-4009, above Camp David in Maryland. When the President is not in residence, R-4009 lies exactly on top of P-40. P-40, from the surface to 5,000, is a no-fly zone. R-4009, from 5,000 to 12,500, can be transited with ATC permission.

(1)There's always an exception: see R-2933, over Cape Canaveral: 5,000 to UNLIMITED.


How do terms apron, ramp, tarmac, taxiway, parking area, gate, hardstand relate to each other? The terms apron, ramp, tarmac, taxiway, parking area, gate, hardstand are used in a way that I cannot understand.

Boeing Everett Factory. Photo by Andrew Hunt at Airliners.net (url unknown). Cropped image from this page

I can't figure out if one is generic and another a part of this set, or if they are well defined by their use (taxiway), or anything else.

Questions I can't answer:

Is this a binary split: Runways vs tarmac?
Is the gate stand part of the tarmac?
Is a parking area different from a ramp?
Is a taxiway considered part of the apron?
Are aprons made of Tarmac (tarmacadam)?
Is a de-icing area part of the ramp?

etc.

In addition I guess this may varies between countries and/or aeronautical jurisdiction.

Can someone provide an accurate view of the lingo and explain whether some are related or synonymous? (filling the blanks if some important term is missing).

Apron and ramp (in US) mean the same, though the official term is apron. FAA Advisory Circular Number 120-57A Surface Movement and Guidance Control System defines it as:

  Apron (Ramp). A defined area on an airport intended to accommodate aircraft for purposes of loading or unloading passengers or cargo, refueling, parking, or maintenance.

Now, the apron includes parking, maintenance and service areas, including taxi lanes.

  The apron area includes the following components:

  (1) Aircraft Parking Positions.  Intended for parking aircraft to enplane/deplane passengers, load or unload cargo.

  (2)  Aircraft Service Areas.  in or adjacent to an aircraft parking position.Intended for use by personnel/equipment for servicing aircraft and staging of equipment to facilitate loading and unloading of aircraft.

  (3)  Taxilanes.  Apron areas which provide taxiing aircraft access to and from parking positions.

  (4)  Vehicle Roadways Markings.  Identified rights of way on the apron area designated for service and Aircraft Rescue and Fire Fighting (ARFF) vehicles.

So,

  Is this a binary split: Runways vs tarmac?

Kinda. Basically, the areas in airport where aircraft are involved are divided (by the FAA atleast) into runway, taxiway and apron.

  i.  Movement Area.  Refers to the runways, taxiways, and other areas of an airport which are used for taxiing or hover taxiing, air taxiing, takeoff, and landing of aircraft,exclusive of loading ramps and aircraft parking areas.

  j.  Non-movement Area.  Refers to taxiways and apron areas that are not under ATC

  Is the gate stand part of the tarmac?

Its part of ramp, so yea.

  Is a parking area different from a ramp?

It is part of the ramp/apron

  Is a taxiway considered part of the apron?

Nope. As already noted.

FAA AC No: AC 150/5300- 13A Airport Design defines runways and taxiways as:

  Runway (RW).  A defined rectangular surface on an airport prepared or suitable for the landing or takeoff of aircraft.

  Taxiway (TW).  A defined path established for the taxiing of aircraft from one part of an airport to another.

  Are aprons made of Tarmac?

Tarmac is a trademark of Tarmac limited, which supplies construction materials for a a number of airports (among others), though most of the aprons are actually made of concrete.

  Is a de-icing area part of the ramp?

As de-icing is part of servicing, it should be part of apron/ramp.

However, it should be noted that though this is the 'official' version, differing local usage means that tarmac is used interchangeably with apron/ramp.


Could you start both A320 engines with APU BLEED on? I've seen some procedures where one engine is started with APU bleed, then APU Bleed is turned off to avoid ingestion of non-desired gases and then the second engine is started with ENG 1 Bleed on.
However, my question would be: Would it be possible to start BOTH engines with the XBLEED Valve in the AUTO position, APU BLEED ON and assuming there are no critical issues (fire, ...)?
To sum up: XBLEED AUTO, APU BLEED ON. Could you start both A320 engines with that configuration?

I have been flying A320s for over two years now and this is the first time I am hearing this. Normally the engines are always started using the APU with its bleed providing air for the air starter motor. So, in normal operations, cross bleed is set at AUTO, APU bleed is turned on and both the engines are started with the help of the APU. Once the engines are started APU bleed is turned off and the APU is shut down. Below is the after start flow of the A320. The green shows the flow of the pilot who starts the engines. As you can see, once the engine mode selector is set to norm, APU is shut down.

The procedure you are talking of is called a cross bleed start which is used when the APU is inoperative for the flight. It is also used by airlines that enforces one engine taxi to save fuel. When APU is not operational, we start one of the engines using an external air source. Once the engine is started the external unit is removed and then to start the next engine we use the bleed from the already started engine. To do that we open the cross bleed and increase the thrust on the running engine until the bleed pressure is sufficient enough for the second engine start up. As soon as both the engines are running we set the cross bleed to AUTO and revert back to normal operation.
As I have told before, I have never heard of any concerns regarding harmful gases coming of the APU bleed. Back when I used to fly Dash 8s we had issues in some of our airplanes smelling of burning oil once engine bleeds are turned on after start up. The airline consulted with Bombardier and they sent a bulletin which said that sometimes oil drippings from engine bearings can fall onto the bleed ducts. Because the duct temperature tends to be quite high, the oil burns off and the smell goes into the cabin. According to them, the lubrication oil used in airplanes is not hazardous or poisonous to human beings. I would say, it applies to all transport category airplanes with gas turbine engines because nearly all of them uses the same type of oil.


Do military aircraft overflying other countries' airspace require special clearance? Is there any special clearance, when military aircraft will overfly other countries' airspace? Are they continuously monitored?

In general, a diplomatic clearance is required for overflight of military aircraft over other countries. The aircraft are considered state aircraft and prior clearance has to be obtained through diplomatic channels. Note that the clearance is usually issued by the defence ministry of the concerned country.
The mode of clearance and monitoring varies from country to country. In case of US:

Foreign governments seeking diplomatic clearance for state aircraft to transit U.S. territorial airspace or land in the United States must obtain a diplomatic clearance number (DCN) issued in advance by the Office of International Security Operations, Bureau of Political Military Affairs (PM/ISO), Department of State. The DCN authorizes the aircraft to transit or land in the United States and/or its territories, in accordance with the approved itinerary.

The overflight permissions are also dependent on agreement between various countries, like India-Pakistan. In some cases, like some EU countries, military transport aircraft can operate without diplomatic clearance.
Some other countries, like Canada give blanket clearance for military aircraft from some countries:

3.2.3 Blanket Diplomatic Clearances to Foreign Military Aircraft

By order-in-council, United States, United Kingdom, and New Zealand military aircraft are exempted from the requirement to have a formal diplomatic clearance (see 3.2.1 above) prior to overflying and/or landing in Canada.

Military aircraft from North Atlantic Treaty Organization countries other than the United States and the United Kingdom are granted clearances on an annual basis. These clearances do not apply to aircraft carrying armed soldiers, armaments and/or other dangerous goods, nor do they apply to aircraft carrying government personnel.

The procedure is usually the same in most of the countries- the overflight request is given through diplomatic channels to the countries' defence ministry, which then evaluates it and approves (or rejects it). The procedure for Canada is given here:

The state of origin will provide full flight details, as outlined in Annex A, in a diplomatic note from its embassy to Foreign Affairs and International Trade Canada (DFAIT). DFAIT will consult with the Department of National Defence (DND) Operations Centre and, if the foreign military aircraft is landing at a civilian airport, with the Foreign Inspection Division to determine whether any pre-conditions should be imposed. After this consultation, DFAIT will reply to the requesting embassy by a return diplomatic note. On advice from DFAIT, the DND Operations Centre officer will then issue the appropriate flight clearance and distribute copies to the interested parties.

In case of India:

For clearance of flights by foreign military aircraft, the concerned diplomatic mission in India or abroad are required to apply to the Ministry of External Affairs with copy to Air Headquaters/Naval Headquaters forclearance of such flights. After clearance given by Ministry of External Affairs, Air Hqrs/Naval Headquaters will issue necessary AOR number for operation of such aircraft, whether it is overflying Indian air space or landing at any Indian airport (civil or defence).

The monitoring of overflying aircraft depends on the country. Civil ATC usually monitors the aircraft carrying transponders, while the military radars (where available), monitor all air traffic and scramble fighters when the aircraft is not identified/responding properly. Overflight without permission may at the very least result in the aircraft being forced to land by authorities.


Which is the smallest available widebody on the market? I'm interested to find out which is the smallest (capacity wise) modern widebody aircraft in production/ operation.

This question is broad enough to try out the new table feature:

Smallest by
All time
In production

MTOW
Airbus A310-200 (144t)
Boeing 767-300F (186.9t)

Length
Airbus A310-200 (46.66m)
Boeing 767-300F (54.94m)

Outside Width
Boeing 767 (5.03m)
Boeing 767 (5.03m)

max. Payload
Airbus A310-200 (32.8t)
Boeing 787-8 (43.3t)

Exit Limit
Airbus A310-200 (275)
Boeing 787-8 (381)

Passengers*
Boeing 767-200 (214)
Boeing 787-8 (242)

Seats Across*
Boeing 767 (7)
Airbus A330neo (8)

* number of seats for typical 2-class layout, seats across for typical economy
(source: Wikipedia)
In summary, the Airbus A310 was the smallest wide-body ever produced by most measures. The smallest wide-body still in production today is the Boeing 767, but only the freighter variant is still produced. The smallest passenger wide-body in production is the Boeing 787 Dreamliner.


Do you need clearance from ATC to switch to a different approach at non-towered airport? When coming in on an instrument approach at a nontowered airport, the approach/center controller will clear you for the approach and approve your frequency change to the CTAF.

Once you're cleared for a particular approach and have changed frequencies, if you later decide you need to deviate from the planned approach (i.e. sidestep or circle instead of straight-in) do you need to get a revised clearance from the approach controller or is clearance for sidestep or circling implied?

Quoted from the Instrument Procedures Handbook, page 4-6:

  APPROACH CLEARANCE

  The approach clearance provides guidance to a position
  from where you can execute the approach, and it also
  clears you to fly that approach. If only one approach pro-
  cedure exists, or if ATC authorizes you to execute the
  approach procedure of your choice, the clearance may
  be worded as simply as “… cleared for approach.” If
  ATC wants to restrict you to a specific approach, the
  controller names the approach in the clearance—for
  example, “…cleared ILS Runway 35 Right approach.”

  When the landing will be made on a runway that is not
  aligned with the approach being flown, the controller
  may issue a circling approach clearance, such as
  “…cleared for VOR Runway 17 approach, circle to land
  Runway 23.”

So if they name the approach, you are restricted to that approach.

I searched the rest of the book for items specifically related to non-towered operations, and found nothing that contradicted that.


Has there ever been a plane not controlled from the nose? Has there ever been an airplane where the pilot, or cockpit were not located near the nose of the airplane?

The de Havilland DH.83 Fox Moth put the passenger cabin and engine in front of the pilot

Author: RuthAS, source: Wikimedia Commons, licensed under Creative Commons Attribution 3.0 Unported licence.


What kind of insulation is used on commercial aircraft? How are commercial aircraft insulated and what kind of fire barrier material is being used?  How much insulation is required in a typical Boeing 747 vs. a Boeing 787?

This article from Boeing describes fire safety on their planes, and they mention "fire-protective insulation blankets." A quick google search suggests that in non-aviation contexts, these are usually ceramic fiber. So it seems likely that at least one form of fire insulation in modern transport-class aircraft is ceramic fiber fire blankets.


Why pilots would leave the cockpit in a short flight? I've occasionally read about pilots being locked out of the cockpit in flight, and was wondering:

Why might a pilot leave the cockpit during a short flight (1-2 hours)?

The cockpit of some airliners lacks a lavatory.

Cockpit layout from AviationKnowledge.wikidot

This is discussed in Skybrary: Flight Deck Security

  Locked Door Flight Safety Issues
  ...
  Physiological Need. Naturally, the need for flight crew to use toilets, access designated crew rest facilities or be supplied with food and drink, requires access through the flight deck door during flight. Procedures for door opening mean that egress and access will take longer with the result that the flight deck crew are not always able to go to the toilet at a time of their exact choice, which may cause them to be distracted and, exceptionally, might exacerbate an existing underlying medical issue in a way that would not otherwise have occurred.
  ...
  Longer term, design change could also ensure that all operating flight crew should be secured on the flight-deck before the passenger boarding doors are closed prior to departure and remain secured on the flight-deck until after the passenger doors are opened at the destination. This would prevent any unlawful entry from the cabin and minimise any unlawful seizure by a single flight crew member.
  To enable this, existing aircraft could be modified and new aircraft designed with all required crew facilities forward of the secure flight-deck door. On short/medium haul aircraft this would require a toilet, safe food & water storage and a reclining crew rest seat. Additionally on aircraft used for long range operations where in-flight relief is required provision of bunk/s.
  This is not a new concept, many long range aircraft already have toilet and crew rest facilities forward of the secure flight-deck door.


Why are heavy flaps better than just a bigger wing? Flaps increase lift during landing and T/O. But when retracted, they do nothing. The space needed to stow the common fowler flaps can't be used for anything else - fuel or structure. Extended flaps are thin, making them need more material to maintain stiffness. Moreover, they transfer their loads through the wing, instead of directly to the fuselage.

So, why do we use flaps instead of just scaling the clean wing up?

Is it because of concerns over cockpit visibility during landing? Can't we use video cameras do display the bottom during high AoA?
Is it because the extra lift - and drag - is unwanted? We can simply increase the cruising altitude without changing the cruise speed.
Is it because (for fowlers) the chord reduction really is that beneficial?  The larger wing volume for fuel leaves more space in the fuselage for everything else. And since the span does not change, induced drag does not increase.
Is it because slotted airfoil, as in many modern flaps, are not good for cruise? Surely we can add slots to the airfoil, and add mechanisms to seal them for cruise.

When flaps are retracted they do nothing, which is the whole point. The byproduct of lift is drag, a larger wing will create more lift, but more drag as well. More drag equals a slower cruising speed, or bigger engines to power past the drag along with higher fuel consumption. Flaps let airplanes cruise faster by getting out of the way.


What are the meanings of these terms related to instrument flight? Please describe and define the following terms:

Homing
0 degree relative bearing
Tracking
Hold
Entry
Holding pattern

What are its uses and purposes?

Any one to suggest a thorough instrument book as well.

Homing & 0° relative bearing

Homing is a technique used with ADF/NDB navigation, where you point the ADF needle at 0° relative bearing, which means that your nose is directly pointed at the navigational aid you are trying to reach. The same technique can crudely be used with VORs and GPS, where homing onto a VOR would be changing the inbound radial every few minutes to establish a new heading to the VOR or using GPS GOTO every few minutes.

This is considered a poor navigational technique, as it purposely neglects wind correction and this the aircraft can get blown off track significantly. You also increase the leg time with this, as you take longer to reach the navaid than with wind correction applied.

(Image Source: navfltsim)

0° relative bearing refers to your longitudinal axis being in line with a navaid, mostly NDB. If something was straigh at your 3 o'clock, it would have a relative bearing of 90°, irrespective of your current magnetic heading.

Tracking

Tracking is technically the same as Homing, however wind correction is applied. Simplified, you account for wind direction and speed and correct your magnetic heading by the wind correction factor, giving you a new corrected heading, which allows you to track to the navaid you are trying to reach.

(Image Source: www.avstop.com)

Hold, Hold pattern and Hold entry

A hold or hold pattern is a racetrack defined by inbound course to a fix, a turn direction and turn time, usually given in minutes. A standard hold will usually be right turns with a timing of 4min for the racetrack, which is 1min for each 180° turn and 1min for each straight legs. Depending on from where you are trying to enter a hold, there will be different hold entry techniques.

(Image Source: www.americanflyers.net)


Why do extra flight crew members sit in the cockpit during takeoff/landing? I have observed this many times for long haul flights where they have extra cockpit crew: during takeoff they all gather in the cockpit and then disperse to their rest areas. They meet again somewhere halfway to hand off flying responsibilities and then gather again before landing. Usually approximately half an hour after/before takeoff/landing.

One way of thinking is, if you are going to rest, rest from the beginning. Just take over your duties when your turn comes up. Why even bother visiting cockpit if you are going to be there only for first 30 minutes or so of the flight.

I understand takeoff/landing are most critical phases of the flight where things can go wrong. But then airline have deemed that whoever is flying the plane at that point is fully capable of flying or in other words fully accredited crew is managing the flight.

Is there any other reason why all the crew has to meet in the cockpit during these phases?

There'a a few reasons for this:

Safety:
During takeoff and landing, everyone should be buckled into a secure seat. They have these seats in the cockpit, and in large aircraft, they're actually very comfortable. Laying down in a crew bed would not be allowed during takeoff or landing (though it happens, off the record). Do note that these beds do indeed have belts that are similar to those on rolling hospital beds, but it's not intended that these be used during takeoff or landing. It would be very difficult to escape the small confined space of the crew bunks during an emergency. Though some crew areas have seats, these are typically not "safe" seats, and they are only meant for resting on while in level flight.

Redundancy:
If something goes wrong with one, or both, of the pilots flying, you would really regret letting the other two qualified pilots go lay down in the back of the plane. Safety comes first in aviation, and the pilots are there to support each other.

Extra Help:
Extra crew sometimes helps the flying crew, whether that be by looking up information, radio frequencies, airport identifiers, and so forth.

Socializing:
Pilots are (usually) pretty friendly to each other. They all share a common interest, and while some of the older pilots may be a bit grizzled, they all got into aviation for their love of aircraft. There's typically some pretty lively conversations in the cockpit. As noted in the comments, this is while on the ground, pre/post taxi. Even during flight operations, additional pilots may be in the cockpit assisting with spotting traffic, birds, and so forth. Conversation is limited somewhat during taxi, takeoff, landing, and all other flying activity below 10,000ft (or until at cruising altitude, if cruising altitude is <10,000ft),


What procedures are used for midair refueling without air supremacy? One of the major themes of the answers to (and comments on) my earlier question about tankers not having ejection seats is that tankers are used only in environments where the threat from enemy aircraft is minimal or nonexistent; for instance:

...Tankers are big, slow, and devoid of defensive measures because they don't need any of that. They're used from a very safe distance, and if there is a risk of enemy air power, friendly air power runs interference...
...Primarily because tankers and transports are being operated in non-combat environments or safely benhind [sic] the front lines of a battlefield so ejection seats are not absolutely necessary for crew survival...
...In the end, it's unlikely a refueler will be shot down. Refuelers are generally only flown in areas where we have control of the airspace, or reason to believe that we are well away from enemy fire...
...A refueler will never be out on it's own. Like I said, they expect aerial supremacy, and have fighters run interference for them. If a fighter is closing on a refueler, full of tens of thousands of pounds of jet fuel, they're already gone...
...For the United States, the assumption is that we will always be able to have air superiority in some area due to overwhelming firepower and technology (though area that may be further away from the battlefield, making the tanker less effective, though still more efficient than landing.) The tanker would never fly directly over the combat zone unless we had air superiority there, as it's quite simply a sitting duck - they have basic defenses though, as you can never guarantee air superiority...
...Tankers are not supposed to be flying in any area where they would be taking enemy fire, so an evacuation situation would essentially be a freak event. Most of the scenarios where a tanker would be attacked have a low survivability anyway...

However, it is quite conceivable that combat aircraft might require mid-air refueling in a situation where air supremacy – or, worse, even air superiority - cannot necessarily be attained (for instance, in a full-scale war between the United States et al and China, or, less likely, Russia), and where restricting tanker aircraft to uncontested airspace would put them so far away from the target(s) being attacked as to be useless.
What are the procedures that are followed for refueling combat aircraft in an environment of mere air superiority or (worse) air parity, rather than air supremacy?  Are the types of tankers used restricted to only those converted from bombers (and thus already possessing both ejection seats and greater maneuverability compared to tankers based off of civilian designs)?  Do aircraft rely solely on buddy tanking (thus tying up most of one’s combat force with tanker duty)?  Are tankers escorted by dense enough swarms of fighters to be able to bull their way through any airspace, no matter how hostile (thus using up most of the tanker’s fuel merely to sustain its own escorts)?  Or do the ministries of war of the countries involved simply resign themselves to having to mass-mail “we regret to inform you” letters?

It's actually a problem the US Navy at least has been considering - with improvements in anti-ship missile capability (such as China's Dong-Feng 21D) meaning that carriers are at risk at ranges approaching 900NMi having to keep the ships out of range is taking a large chunk out of the effective range of aircraft such as the F35C which has a range of 1,200NMi and refuelling a "stealth" aircraft with a conventional tanker plane sort of defeats the point.

As a House Armed Services Committee report noted:

  The committee notes that the aircraft carrier air wing has been optimized for striking power and sortie generation and believes that it may not be configured to support the long-range strike required by current and future threat systems. While the introduction of the F-35C will significantly expand stealth capabilities, the F-35C could require increased range to address necessary targets. The committee believes that several options could be used to address this issue to include developing a stealth tanker capability, improved engine technology, or to develop and procure a strike capability that is purposely built to strike at increased range.

The current proposed answer to this is the MQ-25 development of which was approved by the US Navy earlier this year for service in 2024.

The MQ-25 is intended as an un-manned tanker with stealth capabilities delivering fuel for 4-6 aircraft at a range of ~500NMi, as a) a stealth aircraft itself it will be harder to detect and intercept and b) as UCAV if it does get shot down there's no need to think about ejection seats or any other mechanism to protect the crew.


Can I take friends flying with a private pilot glider license? In the US, will glider clubs let you take up friends in a two-seater if you have a private license? Or do you need a commercial license?

Glider PPL will suffice, did it yesterday and three or four times in the past three months.

That's me in the back seat preparing to take a co-worker for her first glider ride in a Grob-103:


Is it legal/possible to request a flight-path change from Domestic to International minutes after take-off, for a privately owned jet? This is related to the recent escape of Carlos Ghosn from Japan. While we don't know the details yet, M. Ghosn allegedly boarded a private plane from a small airport near Osaka [and probably in a kind of "luggage"!].

In this event, it seems the private plane was aimed to travel internationally. But that brings the question anyway:

Would the pilot of a private plane be authorized to change their destination after take-off, and, more specifically, request to travel to a foreign destination, while initially, (before take-off) the plane was supposed to reach a domestic destination?

Probably not the case in this escape story, but since there is much less passengers verification on domestic flights, allowing the flight-path change (for a private plane) would make things much easier for someone (wealthy) who wants to evade a country.

Generally speaking, ATC doesn't care who you are or where you're going. Their only job is "a safe, orderly and expeditious flow of traffic." If you request to amend the destination on your flight plan, they'll just type it into their computer and give back the new clearance it spits out. Diverting is a fairly routine thing, actually, especially when bad weather is afoot. If they even ask why, it's to make sure it's not due to an emergency or urgency. What (if anything) happens once you're safely on the ground at that new destination is someone else's problem.

That said, the militaries of many countries may take exception to someone flying into their airspace without prior permission, which is a much more complicated topic.


What are the least powerful airplanes that ever flew? What manned airplanes have achieved flight with the least powerful engines (no gliders!), and what was their top speed? Im sure I've heard of an airplane with an 8hp engine capable of exceeding 120 MPH airspeed

There are a number of human-powered aircraft (list here).  For the Gossamer Albatross, we have

  In still air, the required power was on the order of 300 W (0.40 hp),
  though even mild turbulence made this figure rise rapidly.

As far as top speed:

  Allen completed the 22.2 mi (35.7 km) crossing in 2 hours and 49
  minutes, achieving a top speed of 18 mph (29 km/h) and an average
  altitude of 5 ft (1.5 m)


Would all these three things have the exact same effect on the flight duration of a glider? Consider a glider trimmed to fly at some given angle-of-attack, gliding in smooth air (no thermal convection, ridge lift, wave lift, etc.).  If air density is somehow kept exactly constant in all cases, and the glider is launched from the same initial altitude relative to the ground in all cases, would the flight duration be the same in all three cases?  (A yes/no question.)

Extra weight has been added to the glider, exactly at the CG, doubling the glider's weight.
We've increased the value of the gravitational constant from 9.8 m/s/s to a higher value (twice as high).
We've caused the earth (and atmosphere) to steadily accelerate straight “up”, at 9.8 m/s/s, thus creating an apparent increase in the gravitational constant (to an apparent value double the actual value).  (Acceleration starts well before the glider is launched, not mid-flight.  Glider is also accelerating along with everything else at instant of launch, i.e. the atmosphere isn't rushing up past the glider at the instant of launch.  For example the glider could launch by rolling off a ramp mounted on a high tower connected to the ground.)

(Edit: to make this more clear, imagine that a giant rocket engine attached to the other side of the earth is causing this acceleration.  The earth itself is the only thing that is being directly acted on by the accelerating force; the atmosphere and glider each experience the results of this acceleration in a less direct manner.)

Also, if “yes”, then a second question — launched in equilibrium (exactly at its steady-state trim speed for the existing conditions) from a given height, would the glider stay up for a longer duration or a shorter duration after we've made one of these changes?

The intent of the question is to compare the steady-state in-flight dynamics, not some difference  relating to some possible slight variation in the initial kinetic energy imparted at the instant of launch, etc.  In each case, the glider is understood to be launched at its steady-state trim speed in relation to the existing conditions.

Scenarios 2 and 3 would be almost exactly the same. Scenario 1 would be very different. However, the glider would be able to stay up for almost exactly the same amount of time in all three scenarios.

The basic summary of what would happen: In scenario 1, both the weight and the mass would be doubled. In scenarios 2 and 3, the weight would be doubled but the mass would remain the same.

The simplest way to distinguish scenario 1 from the others is to pitch into a vertical climb (or a vertical dive). In scenario 1, the glider will accelerate downwards at $1\ g$, but in scenarios 2 and 3, it'll accelerate downwards at $2\ g$.

Scenarios 2 and 3, on the other hand, are almost completely identical. Specifically:

Scenario 2 simply adds more gravity. Pretty straightforward.

Scenario 3 consists of having the ground accelerate "up" at $1\ g$. We can look at this scenario in a frame of reference where the ground remains stationary. In this frame of reference, everything is just like the real world, except that everything is now experiencing an inertial force equal to $1\ g$ straight down.

How does an inertial force work? Inertial forces feel just like gravity. In fact, the only differences between the extra forces in the two scenarios are:

In scenario 2, the direction of the extra force changes as you move horizontally, because the direction of "down" changes as you move. In scenario 3, the extra force is in the same direction everywhere: namely, the direction opposite the direction of acceleration.
In scenario 2, the extra force gets weaker as you get farther away from the earth. In scenario 3, the extra force is equally strong everywhere.

Both of these differences are probably too small to measure.

Now, finally, I said that the glider will be able to stay up for the same amount of time in all three scenarios. This is because, although the mass of the glider differs between the three scenarios, its weight is the same in all three scenarios. And if the glider is flying at a constant speed in a straight line, weight is the only quantity that matters; mass is now irrelevant, because the glider is not accelerating (in the frame of reference where the earth is stationary).


Does the center of mass for an airplane have to be over the wings? I am designing a model aircraft that will have 4 propellers in a square configuration (think like a quadcopter) so that it can take off and move around like a quadcopter, then transition into plane flight like a VTOL aircraft.

For operating in quadcopter mode, it would be ideal for the center of mass to be in the center of the airframe (behind the main wing) for motor efficiency and agility reasons. If the CG is over the wing the front two motors will have to work harder than the back two, and while the PID controls will stabilize for this, it will decrease throttle headroom.

No.

One relatively trivial example is a tandem wing (or a canard with a very large forward surface, if you will); the center of mass will be between the lifting surfaces, positioned so that the forward surface flies at a higher coefficient of lift than the rear (to give static longitudinal stability).

If you build your model with the motors on short arms, so that they're a bit above the wings when in quadcopter mode, you may be able to manage the CoM shift so that you automatically get the balance right for forward flight in wing lift.


Could this helicopter's body be a flying wing? This question: Could a helicopter fly like a plane this way? asks if a helicopter can turn sideways using additional wings to tip forward to allow the rotor blades to act as a propeller. The tail-setter and other types of planes came up as answers. Similar to the tile Setter their first function of this aircraft would it be to hover then to fly as a plane.

Would this model helicopter with a body shaped of a flying wing be able to fly at a 90 degree angle and at a 90 degree twist transferring lift from the rotor blades to the body?

I have sketched out a picture below on how on might and apologize for imperfections. The body could be longer to create more wing span.

The pilot would need a special seat or controls to adjust for tilt but they would enter it like a normal helicopter. Could this model fly, keep maneuverability and feel of a helicopter foremost?

The pilot would only need to dive Rotor head first to allow the body to serve as a wing.

No, you need sufficient wing span to produce lift without excessive induced drag.

Lifting bodies are only a thing of hypersonic flight where the induced (component of wave) drag is tiny compared to the form (component of wave) drag.

Induced drag is an unavoidable side-effect of producing lift over a finite span. It decreases with wing span, and with dynamic pressure (which in turn grows with density and square of speed; indicated speed is a square root of dynamic pressure). So at slow speed, you need considerable wing span to generate lift efficiently. This applies also to helicopter rotors, which is why they have such large diameters.

Since the other component of drag, form drag, increases with dynamic pressure and cross-section, the optimal wing span decreases with speed. But even jets still have quite high aspect ratio (square of wing span to wing area). Flying bodies without much any wings only become efficient well into supersonic area—and keep in mind that anything resembling a propeller (including tiltrotor) is limited to subsonic.

(At supersonic speeds, the mechanism of drag creation is different, called wave drag, but it still has a form component and induced component and the induced component still depends on wing span and dynamic pressure in the same way.)


Can a small plane be floated off of an aircraft carrier? Would it be possible to float a small plane (say a Cessna 150) off of the deck of an aircraft carrier without the Cessna achieving any forward motion with respect to the aircraft carrier? If not a Cessna 150, is there a standard GA aircraft that could do it?

EDIT:  Per a comment from ratchet freak: the takeoff would be done via lift from the wings, not via an engine duct (VTOL), like a Harrier.

As far as I'm aware this has never been attempted (and I doubt the Navy would let me try - though I'm certainly game if they are!), but:

A Piper J3 Cub stalls at 38mph (33kts).
The USS Enterprise (CVN-65) had a maximum speed of 38.7mph (33.6kts).

So, given a lightly loaded cub and an Enterprise-class carrier at flank speed, it is at least theoretically possible to float that aircraft off the deck (if it were lightly loaded, and thus had a lower stall speed).

Achieving zero relative motion would require a little more effort - specifically you'd have to seek out a headwind, and the Cub would have to be operating at an airspeed above stall, but still pretty close to it.
For example, if the Enterprise were making 30 knots and steaming into a 10 knot headwind the relative wind on deck would be 40 knots. That's enough to lift the Cub, but as soon as it was in the air it would need to pull itself along (via its engine) to maintain that speed. The Cub would have zero relative motion above the deck at an airspeed somewhere around 40 knots).

As a (slightly ridiculous) bonus: The Belite Superlite has a stall speed of 28 mph (25kts). It would be theoretically possible to fly such a plane like a kite from an aircraft carrier. Its advertised takeoff and landing distances (both ~500ft) are also such that it could operate from a carrier deck without need for the catapult to launch or arresting wire to stop.


How do you know ELT's batteries used more than 50% of their capacity? Batteries in ELT need to be replaced or recharged when the transmitter has been used for more than 1 cumulative hour or when 50% of their useful life.

How could I know it's already 50% or more than 1 cumulative hour?

There are two ways:

First, when you test the ELT you should make a note in the aircraft logbook of when it was tested and the results of that test. You can also note how long the transmitter was on during the test. You can then look at all the logbook entries to verify that the cumulative time is less than one hour.
Some ELT's have a self-test feature that presents error codes via an LED or audible beep when they are powered on. For example, here is the self-test page from the Artex 345:

The ELT will beep/flash 7 times when the battery operating time is >1 hour.

As far as the useful life of the battery goes, that is determined during the manufacturer testing for the ELT and will be marked on the ELT as an expiration date. Here is an example:

Source: Aerotechservices.com


Gas Turbine Engine Starting Sequence How to explain the figure above?

I'll use the start sequence of a JT-9D on a 747-200 as an example. It's typical, and since there was no FADEC and since it took two people having to manually do the individual items that will better explain things.

The f.e. turns on the engine ignition switches to energize the igniter that will ignite the fuel when introduced.

The figure doesn't show the next step, that of starting the engine rotating. The f.e. did that by opening the start valve which directed pneumatic air into the starter. Starter operation was confirmed by the f.e. observing N2 rotation—the figure calls that the compressor. Some gas turbines use an electrical starter rather than a pneumatic starter.

At 30% N2 rotation, the captain opens the fuel valve and light-off occurs. The captain and the f.o. monitor the EGT to confirm light-off and to avoid an overtemp—the figure calls that the Peak Starting EGT.

At 50% N2 rotation, the engine can accelerate on its own. The f.e. turns off the igniter and closes the pneumatic vale supplying air to the starter.

The engine continues to accelerate on it's own to idle rpm.

All sorts of things can go wrong, and you practiced those things in the sim, and occasionally you had to contend with them in real life.


What light signals or visual markings indicate that turns should be made to the right at class G airports? FAR 91.126 states:

§91.126 Operating on or in the vicinity of an airport in Class G airspace.
(a) General. Unless otherwise authorized or required, each person operating an aircraft on or in the vicinity of an airport in a Class G airspace area must comply with the requirements of this section.
(b) Direction of turns. When approaching to land at an airport without an operating control tower in Class G airspace—
(1) Each pilot of an airplane must make all turns of that airplane to the left unless the airport displays approved light signals or visual markings indicating that turns should be made to the right, in which case the pilot must make all turns to the right; and
[...]

Are there examples of "approved light signals or visual markings indicating that turns should be made to the right"?

Here's the example from the FAA's Airplane Flying Handbook (chapter 7):

  If there are no other aircraft present, the pilot should check
  traffic indicators on the ground and wind indicators to determine
  which runway and traffic pattern direction to use. [Figure 7-2] Many
  airports have L-shaped traffic pattern indicators displayed with a
  segmented circle adjacent to the runway. The short member of the L
  shows the direction in which the traffic pattern turns are made when
  using the runway parallel to the long member. The pilot should check
  the indicators from a distance or altitude well away from any other
  airplanes that may be flying in the traffic pattern.

Here's what it looks like at Huntsville Executive (KMDQ), which has a right-hand pattern for runway 36:


Why is the critical angle of attack lower in ground effect? Why is the stalling angle of attack lower in ground effect?
Does ground effect more increase pressure on lower side of wing (cushion effect) or more decrease pressure on upper side, or both? So which side of wing more change pressure in ground effect compare to free flight?

(Please don't explain with terms like downwash, tip vortices, wake vortices etc.. I am big supporter of explaining aerodynamics with pressure/pressure fields rather then "past-things"  that happen behind wing.)

Ground effect creates more circulation around an airfoil (either lifting or downforce-ing). Not going into details about how ground effect works, but the 'mirror-vortex' in potential flow explains this very easily.
Increased circulation will manifest in the pressure field as a higher pressure differential between the top and bottom surfaces of the airfoil. An airfoil always has 2 stagnation points, one at the LE and one at the TE. The CP at these points is 1 (the trailing edge stagnation point is lower in real life because of viscous effects). Because the pressure is constrained at the LE and TE, the suction increase happens along the chord, and usually will increase more at the suction peak (~1/4 chord). Now the adverse pressure gradient from the suction peak to the trailing edge is steeper, because we have a higher suction peak, and the same trailing edge pressure. As the adverse pressure gradient becomes steeper and steeper, the airflow will eventually separate from the surface.
Even for the same AOA, ground effect increases the suction on the suction side of the airfoil, which makes the pressure recovery more susceptible to separation.
RE: not using the terms you mentioned, this is a purely 2D effect and can be seen in infinite span wings and has nothing to do with vortices. However just looking at a pressure field without considering anything else is like trying to figure out how a meal is cooked by just looking at the dirty dishes - you need potential flow to explain this.
Regarding what the resultant pressure field looks like, this is very well covered in literature already, and if you want to see the effects for a previously unstudied section, Javafoil will give you useful results - https://www.mh-aerotools.de/airfoils/javafoil.htm


Justification for the 2D cut-out method for determining a rocket's center of pressure I've seen several tutorials on rocket stability where one can empirically obtain the center of pressure by cutting out a 2D imprint of the rocket and balancing the 2D shape as seen in the pictures below:

What is the physical/mathematical justification for this, otherwise, extremely simple method for determining center of pressure?  What are the underlying assumptions behid this method?  In what cases is it applicable?  When it is applicable, what order error should I expect from this method?  In what cases is it not applicable?

I couldn't justify this method more simply than NASA does:

  For model rockets, the magnitude of the pressure variation is quite small. If we assume that the pressure is nearly constant, finding the average location of the pressure times the area distribution reduces to finding just the average location of the projected area distribution.

So the pressure, constant everywhere, "cancels out" leaving you with only area.

And the simplification from a 3-D shape to its 2-D projected area is justified by the shape's relative simplicity and symmetry.  This wouldn't work with a grand piano.


Why would pilots "call the company" after an aborted takeoff? I was skimming through the RealATC videos on YouTube today and watched this one. In it there are two flights taking off from Chicago-Midway (KMDW); Delta flight DAL1328/DL1328 and SouthWest's SWA3828/WN3828. They are each taking off from crossing runways (4R and 31C). For some reason, even though SWA3828 is given clearance to take off, the Delta flight also starts its own rollout.

After the call to abort is given, both aircraft abort takeoff and are able to then safely leave their respective runways in order to taxi back to the proper starting point. One of the aircraft states it will need a few minutes to check for heated brakes. Then both aircraft state they will need to "call company" for some unspecified reason.

Why would both planes need to call company? My guess is to recalculate fuel used to determine if they will have enough fuel to continue the trip. Why else might they need to do so?

An RTO can happen for any reason, mechanical, FOD, ATC error, etc.

The boss (airline operations) will want to know what happened.

Safety

Is everyone safe?

Is anyone in immediate danger?

Prepare documents for the NTSB investigation.

Time

How much time will be lost (e.g. to cool the brakes); this can affect the schedule of this particular plane days ahead. Especially if maintenance is required.

Notify the destination airport of the delay, and also publish the delay for the next flight from said destination airport.

Maintenance

Make sure the airline's maintenance stationed at the airport can deal with the issue.

If not, get on the phone with airlines who can help.

Find a replacement plane and send it over there.

Get the all-clear from an airline engineer that the hot brakes won't affect another attempt. It depends on how hot they are.

If a delay is expected, start the clock, airlines can keep passengers on a stationary plane for so long, I guess it's two hours. Been there, it's awful.

If it will take more, find them a gate, if no gate is available, get the stairs and a bus.

Whose fault was it?

Get a grip on the PR before things get out of hand, i.e. tweet.

If anyone is suspected of not doing their job properly, start an investigation.

If the ATC is at fault, send them the bill.

If it is another airline's fault, call the insurance company.

Fuel

Not really an issue for an aborted take-off after few seconds of take-off thrust, but nonetheless run the numbers again. Both in the cockpit and in the ops center.


Which airplane types never crashed? Is there an airplane that never crashed?

Or more specifically, without any crash history on any database. By crash, let's say any accident / incident which resulted in damage to the airplane and/or injuries to the people on board.

Not including military airplanes, only commercial or general aviation aircraft. Obviously I'm asking about a plane that had multiple flights and maybe is even still flying, not an experimental built that only flew a few times.

As mentioned in this answer: there are seven commercial aircraft types with zero hull loss accidents:

B717
CRJ700, CRJ900, and CRJ1000
A380
B787
B747-8
A350
C-series
A320Neo

Only the first two types have logged more than 1 million departures. The remaining ones are relatively recent types and are still working on statistical significance; especially the long haul aircraft fleet takes a long time to accumulate 1 million departures at 1-2 flights per day per aircraft.


Which 'pusher' propeller aircraft have been used in active military service? The only 'pusher' aircraft I know of that has been used in active military service is the SAAB 21. There are several prototypes out there, but I can't see that any others were used.

Which, if any, other aircraft are there? Maybe the Japanese 'shinden' but if memory serves me that is only a prototype.

If you also count drones, the General Atomics MQ-9 Reaper Drone is a pusher propeller aircraft in active service.

Here are some others:

Convair B-36 Peacemaker
Vickers F.B.5 "Gun Bus"
Airco DH.2
Curtis Model E
Royal Aircraft Factory F.E.2
Royal Aircraft Factory F.E.8
Voisin III Bomber
Boeing GA-1

You may notice that a lot of these aircraft are very old designs. The problem is in 1914 the US Army (there was no US Air Force yet) banned pusher type aircraft after a number of pilots died in them. This mentality carried over on the other side "of the pond" and very few pusher type aircraft entered service after 1916. The SAAB 21 was responsible for the development of ejection seats because a major problem with bailing out was hitting the propeller. Because the prop was behind the pilot, bailing out meant getting pushed through the wood chipper...

The B-36 is a good example of this configuration in its limits. It is a massive aircraft with a 19 foot propeller (second largest propellers in use). Engine fires were common due to mounting the engines backwards and not getting sufficient heat over the carburetors. The aircraft was later modified as the XB-60 with swept wings and 8 jet engines but was inferior to the Boeing XB-52 (later becoming the B-52) and was abandoned.

The other problem is that a pusher type design contributes a lot to the drag of the aircraft and is relatively inefficient compared to tractor designs. By the time swept wings were in fashion (mostly because jet engines pushed speeds higher and higher),  the need for propeller driven military aircraft dropped dramatically in the jet age.


Main structural (and any other) impact of hard landing I was reading this question related to the parts suffering the most G forces. Reflecting about that question I question myself about hard landing, which is not a normal operation.

So, my especific question is: when an airplane is suffering a hard landing event, which are the structural parts (and any other part that might not be structural and I might be forgetting) that are suffering the main damages and why?

Will this answer depend on the airplane vibration mode (i.e. location of engine masses)?

here are the main parts at risk for structural integrity after a hard landing:

the landing gear itself and the attachment points of the gear to the fuselage and/or wings

the fuselage-to-wing attachment structures

the engine-to-wing (pylon) or engine-to-fuselage attachment structures

the main fuselage structure in the immediate vicinity of the wing attachment points

If the hard landing involves a tail strike, then the integrity of the aft pressure bulkhead is at risk.

Note that the structural integrity risk is not simply one of prompt failure due to an overstress impulse load, but also subsequent premature fatigue failure arising from microcracks caused by the hard landing stresses- especially if that cracking occurs in a location which is inaccessible for inspection.


Is it coincidence that the B-2 and YB-49 flying wings have exactly the same wingspan? Development of the Northrop Grumman B-2 Spirit began as far back as 1979; however, this was nearly thirty years after the last flight of Northrop's earlier flying wing the YB-49.

There aren't many apparent similarities: engine position, wing-sweep, shape and control surfaces are all different. Yet they have identical wingspans of 172 feet or 52.4 m.

Is there something special about this particular size? Did Northrop mutate their earlier design (through wind-tunnel testing etc.) from one to the other, or is it purely coincidence?

 B-2 source

 YB-49 source

A random guess without any supporting information. (please edit or delete if this turns out to be inaccurate)

I would guess the logistics of manufacturing. It could the space needed for handling the aircraft in and/or out of manufacturing buildings.
The B-2 program was wildly expensive due to the large number of new technologies involved.

So I guess it was a prudent, maybe even progam-saving decision, to use existing manufacturing facilities are far as possible.