How is a prevailing wind/average temperature study conducted to determine the runway direction and length for an airport? A popular airport near me (KMYF) has two parallel runways, 28/10 R/L and a crosswind runway, 5/23. Almost always, 28R/L is in use. I'm sure they knew that there was generally a sea breeze in the area, and the wind typically will be right down the runway or within 10-20 degrees of centerline.

I'm sure they do prevailing wind study for the area, and my questions are about the study: What are the specifications for the study? Does the study vary in length depending on location? Is there a standard study battery of tests that they use, and do they test things like average temperature during the study to determine runway length (to maximize utility during high density altitude operations)?

FAA AC 150/5300-13A ("Airport Design") talks a little about this (you want Appendix 2, "Wind Analysis").

Basically you start by figuring out what kind of aircraft you want to operate at the airport, and establishing some basic wind limits (specifically, the maximum crosswind and tailwind components you want to deal with).

Then you call up NOAA's "National Climate Data Center", tell them where you're looking to build your airport, and see if they can have wind data for the location you're looking to build on.

  If NOAA doesn't have data you have a couple of other options -- another nearby airport's wind analysis can be used (if the topography doesn't vary that much and the wind analysis is "recent"), or you may have to perform a wind survey which basically means placing a anemometers on the site to record the wind speed and direction for a year.

Armed with collected wind data you tally up the number of observations in given wind speed ranges and mark them down on a "wind rose".
You then place your runway(s) on the wind rose so that they're aligned with the prevailing winds and determine your "wind coverage" - the amount of time the winds at your site are within your crosswind and tailwind limits.

The advisory circular I linked to shows you how to do this by hand, but there's also software to do this which is how most folks do it. The FAA even has a handy web form which will generate the wind rose and runway/crosswind limit bars for you.

Note that this is just the wind part. As you've alluded to there are a number of other considerations, like terrain: If the prevailing winds favor runway 36, but runway 36 points right at a mountain a mile from the field you might have to align the runway 33 or 03 and sacrifice a perfect headwind for not having pilots fly into the mountain.
Also as ratchet mentioned the airspace around your proposed site may influence your runway layout and types of operations. There's a separate FAA office that deals with "Obstruction Evaluation and Airspace analysis" and a process to go through to ensure that your airport is not deemed "Objectionable".

Also as you alluded to in your question there are other considerations like density altitude (local temperature and humidity trends) which will influence design factors like runway length - there's another advisory circular (AC 150/5325-4B) that talks about runway design criteria, including length considerations.

For even more than you ever wanted to know about airport design you can check out the full 150-series of Advisory Circulars, which all deal with airports in some way (there are ACs on design, construction, markings, lighting, ARFF, and even how to qualify for and obtain federal aid).


In what conditions do airline pilots favor crabbing over de-crabbing for crosswind landings? There are several crosswind landing techniques described on Wikipedia, including crabbing (straightening out after touchdown) and de-crabbing (straightening out just before touchdown).

For airline pilots, are there specific conditions that favor the use of the crab method over the de-crab method for crosswind landings, despite the excessive side load the crab method may incur? When airline pilots use crabbing for crosswind landings, what are the reasons?

(This question is not about the general crosswind landing techniques dealt with in this great post but more about airline pilots' crosswind landing techniques. More specifically, my question addresses some possible conditions where the airline pilots would prefer the crab technique to the de-crab technique.)

First, I would say that the question should be between Crab technique vs sideslip technique. What the wikipedia article describes as De-crab technique is simply a quick transition from crabbing to a momentary sideslip as the wheels touch down. Generally, landing while crabbed is bad form, regardless of type or size of aircraft due to the side load on the landing gear at touchdown.

I was taught that side slip technique (where you fly with the down wind wing slightly elevated and use rudder to keep fuselage and wheels lined up with the centerline) is preferred because you don't have to do any last second adjustments right before touchdown. If you do this correctly, the turning tendency of the aircraft is mostly cancelled out by the cross wind component. Also, if you do this right, you touch down with upwind mains first, then downwind mains.

However, I was also taught that side slip makes passengers feel uncomfortable, and that is why airliners stay in the "crab" until last second.

As to your comment about airliners failing to de-crab, I've seen that too, I argue its just bad technique. Its difficult to properly execute the de-crab, it takes finesse and good timing.


Why are some points shown on a STAR but not attached to the route? I'm looking at the SERFR4 arrival into San Francisco.  There's two waypoints, STOKD and MAKRS, which are shown on the plate but aren't actually connected to the route.  Can anyone help explain why they're there, as there's no mention of either elsewhere in the route.  Thanks!

SERFR4 Arrival: https://flightaware.com/resources/airport/SFO/STAR/SERFR+FOUR+(RNAV)/pdf

Coming from Southern California, you'll often be filed to one of those points, and then on to SERFR for that arrival.  Putting those two points on the page gives perspective of what direction one is coming in from.

It's all RNAV stuff, so is having them on the chart strictly necessary in order to navigate? No.  But it gives a little bit of a picture of what you're expecting to see on the Navigation Display.

Also, as mentioned in the comment, if ATC needs to reroute somebody off of what they filed & over one of those points & then to SERFR, having the point on the page may reduce copying errors when the controller spells out "cleared direct MAKRS, Mike Alpha Kilo Romeo Sierra" -- it at least gives the pilot something to reference when that clearance is being read to him.  Things that reduce the frequency congestion ("Was that Mike Kilo Alpha Romeo Sierra? I don't have that in the database..." "No, it's Mike Alpha Kilo Romeo Sierra" "Oh, okay, Mike Alpha Kilo Romeo Sierra, we'll use that.") are beneficial.


Is it economically viable for Emirates to use a 777 for some of these routes? This question may sound rhetorical or not well posed, but I wonder what the economic viability or sustainability of certain Emirates routes is.

Among its 164 destinations, Emirates is currently serving a whole host of non-major airports (airports which, according to this list, are not among the 30 busiest in the World). Among them are:

Newcastle upon Tyne (NCL)
Prague (PRG)
Bologna (BLQ)
Harare (HRE)

and so forth.

My question: on the majority of these routes, a Boeing 777 is deployed. But how economically viable could it be to fly such a high-capacity plane to destinations where the target market is not so wealthy or not big enough? In some of these instances, Emirates is the sole airline operating the Boeing 777. Also, I speculate that other airlines would probably use another, smaller aircraft to some of these destinations. I am sure Emirates does its market researches with adequate meticulousness before opening any new route, but I am still doubtful - couldn't the people living around Bologna take a train to Milan to get to Dubai, for instance, given their close proximity?

There are many reasons an airline may fly to a given destination and the economics of air travel are complex to say the least. I would like to fist address your question

  couldn't the people living around Bologna take a train to Milan to get
  to Dubai

Sure they could but airlines don't only service locations because of the people that live there they may service them for the very people that don't. I fly both commercially and as a GA pilot to explore new places. I generally fly out of the Philadelphia area which is one of the busiest in the US. From there I head to plenty of tiny airstrips all over the place, none of these airstrips are in towns that are as economically prosperous or busy as Philadelphia but they see my travel because I wish to explore the area. The same goes for foreign airports, simply because a country is less economically prosperous or "busy" than another does not mean it has less to offer culturally and in fact may be a hot bed for tourism.

I have personally been to both Prague and Bologna and they are great cities both with large tourist markets. I can see it being very economical to fly a wide body airliner there full of tourists and maybe only a few locals. While layovers may attract the lower budget fliers there are plenty of people who prefer a direct flight for both the convenience and time savings.

You may be able to find more stats here.


Why do supersonic planes fly higher than subsonic airliners? I saw on wiki that a boeing 737 flys at about 38,000ft and a Concorde flys at 60,000ft. What made it possible, and advantageous, for Concorde to fly so much higher?

It was necessary for Concorde to fly much higher, and not a voluntary decision. A higher cruise altitude increases the demands on the airframe (examples: Combustor size, pressurization) and is only accepted when it comes with sufficient benefits.

An airplane needs a certain wing area for realistic take-off and landing distances. Also, details like the maximum tire speed need to be observed, so the wing area must be large enough to create enough lift at low speed.

Lift is proportional to the square of airspeed and air density. The faster a plane flies, the lower the density can be to create sufficient lift. By flying more than twice as fast as a Boeing 737, the Concorde could fly at a fourth of the density by this reasoning. Air density (symbolized by the Greek letter $\rho$) halves approximately with every 5500 m of altitude increase.

However, the slender wing needed for low supersonic drag is not as efficient as the sub- / transsonic wing of a 737, so a little more density was needed for the Concorde. The 737 is designed for cruise between 8000 m ($\rho$ = 0.526 kg/m³) and 12000 m ($\rho$ = 0.312 kg/m³), and the Concorde flew between 16500 m ($\rho$ = 0.154 kg/m³) and 18000 m ($\rho$ = 0.121 kg/m³).


Do airplanes need brakes in the air? A few days ago I flew on a Boeing 737-900ER. Luckily I was sitting just beside the left wing, seat 26B. I observed that the spoilers were activated (opened) just after the pilot spoke on the Passenger Address System announcing that the airplane was preparing for landing (if I was not mistaken) and began to descend. The spoilers then opened for around 3-5 minutes (picture 1) and then closed again (picture 2) until it touched down. In flight they were not as fully activated/opened as when the airplane landed.

My question:

What is their purpose? Are they brakes?
If they are brakes, does an airplane need brakes in the air?
If they are brakes, is not more efficient to reduce the engine's power rather than to keep it constant power but brake to slow down?

What you saw is called a speed brake, which is one of the functions of the spoilers. From the Boeing 737 NG FCOMv2 (9.20.5 Flight Controls - System Description):

  Flight Spoilers

  Four flight spoilers are located on the upper surface of each wing. Each hydraulic
  system, A and B, is dedicated to a different set of spoiler pairs to provide isolation
  and maintain symmetric operation in the event of hydraulic system failure.
  Hydraulic pressure shutoff valves are controlled by the two flight SPOILER
  switches.

  Flight spoiler panels are used as speed brakes to increase drag and reduce lift, both
  in flight and on the ground. The flight spoilers also supplement roll control in
  response to control wheel commands. A spoiler mixer, connected to the aileron
  cable-drive, controls the hydraulic power control units on each spoiler panel to
  provide spoiler movement proportional to aileron movement.

  The flight spoilers rise on the wing with up aileron and remain faired on the wing
  with down aileron. When the control wheel is displaced more than approximately
  10°, spoiler deflection is initiated.

  Speed Brakes

  The speed brakes consist of flight spoilers and ground spoilers. Hydraulic system
  A powers all four ground spoilers, two on the upper surface of each wing. The
  SPEED BRAKE lever controls the spoilers. When the SPEED BRAKE lever is
  actuated all the spoilers extend when the airplane is on the ground and only the
  flight spoilers extend when the airplane is in the air.

  The SPEEDBRAKES EXTENDED light provides an indication of spoiler
  operation in-flight and on the ground. In-flight, the light illuminates to warn the
  crew that the speed brakes are extended while in the landing configuration or
  below 800 feet AGL. On the ground, the light illuminates when hydraulic pressure
  is sensed in the ground spoiler shutoff valve with the speed brake lever in the
  DOWN position.

You noticed that the spoilers did not extend as much in the air as on the ground. This is intentional to reduce buffeting:

  In-Flight Operation

  Operating the SPEED BRAKE lever in flight causes all flight spoiler panels to rise
  symmetrically to act as speed brakes. Caution should be exercised when
  deploying flight spoilers during a turn, as they greatly increase roll rate. When the
  speed brakes are in an intermediate position roll rates increase significantly.
  Moving the SPEED BRAKE lever beyond the FLIGHT DETENT causes
  buffeting and is prohibited in flight.

The speed brake lever must not be moved above the FLIGHT DETENT while in the air. You can see it in the following image from the FCOM:

To answer your other questions:

  If it is brake, do an airplane need brake in the air?

Yes, sometimes. Ideally a flight profile is calculated that does not require the use of brakes in the air. That means the Flight Management Computer (FMC) calculates a so called Top of Descent point at which you can start an idle descent. So the engines are retarded to idle thrust and the aircraft maintains the target speed by descending. This will get you on final approach at the desired altitude. Two things can happen now:

Air traffic control does not allow you to descend when you want to. This usually happens when there is conflicting traffic and you have to stay at a higher altitude than the idle descent profile for a short while. Afterwards you need to descend faster, which may require the use of speed brakes. You can also try to just increase the target descent speed (since higher speed means more drag and gets you down faster), but if that is not enough speed brakes are needed.
Air traffic control gives you a shortcut. This happens quite a lot. Some Standard Terminal Arrival Routes (STARs) involve some complex maneuvers and turns, but if traffic allows you can get a shortcut. Now your distance to the airport has just been reduced, requiring a steeper descent. Again, use of speed brakes helps here, especially when you are close to the airport already because below 10,000 ft you have to maintain 250 kt or lower, so speeding up is not an option.

  If it is brake, is not more efficient to reduce the engine's power rather than to keep it constant power but brake to make it slower?

The engine will already be reduced to idle on a normal descent profile. Therefore using less power is not an option any more. Use of reverse in flight is usually prohibited for most aircraft, e.g. 737 FCOM:

  Intentional selection of reverse thrust in flight is prohibited.


Do commercial jets ever make 360 in the pattern for separation? It's not uncommon for GA aircraft to circle in the pattern for separation purposes. Does that ever happen to big commercial jets?

Imagine an airliner were cleared for a visual yet forced to execute a go-around and instructed by ATC to take a pattern. When there's another traffic on final, is it a viable option for ATC to instruct the jet to make a left or right 360 for the traffic on final? Does it actually happen in the real world?

Yes, it can happen, but it's pretty uncommon.

Airliners arrive at the destination airport having been sequenced by ARTCC ("Center") and Approach so that they are showing up in an orderly sequence, spaced out so that there is adequate room between them.  They may be set up for an ILS, or they may see the field and accept a visual approach, but either way the flow is generally quite predictable and orderly.  VFR traffic, by its nature, is less controlled and ordered, so it's more likely in that sort of an operation that you'd have two aircraft in positions to arrive at the runway at about the same time, so a solution like a 360 on downwind or on final becomes necessary.  With a flow of airliners (and other IFR traffic) spaced out at 3-5 miles apart, that solution would create as much trouble as it would solve, because now the conflict is with the aircraft behind the one that circled, rather than with the one in front of it.

What does happen more frequently, is the 360 happens much farther out from the airport, and that's called "going into holding" due to traffic saturation.  Maybe the airport is over-loaded with arrivals, or it had to suspend operations while the active runway was changed from 18 to 36 (or whatever they are at a particular field), or there is weather affecting the approaches which slows down the rate at which it can accept arrivals.  The Approach and Center controllers will work to keep the flow of traffic coming into the airport neat & orderly, which means delaying aircraft before they get to Tower's airspace (i.e. the "traffic pattern").  Ideally, they will do this with speed adjustments to get the desired interval, but sometimes the delay needed is more than speed adjustments alone can accomplish.  Then they'll put the arrivals into holding for however long it takes until they can start sending them in again.

That's the more common airline version of a "360 on final"... doing 360's with 10 mile legs on a really, really extended final -- 100+ miles out!

In the case of a go-around that turns downwind, rather than a 360 on final, the typical solution would be to extend turning final out until there is adequate space.  Staying on downwind past a 5 or 10 mile base & final is highly undesirable for a VFR pattern, but for airliners where everybody has an ILS and doesn't really have to maintain sight of the runway, it's no big deal.  For big airports, extending the traffic pattern out to longer finals is highly preferred over having jets circling on final.


Does auto pilot take into consideration the altitude, speed, and the difference in heading change, to calculate the degree of bank? Or is there a “standard” that the auto pilot follows at all times?

By “standard” I mean the aircraft will bank at x amount of degrees each time regardless of the following mentioned? The more you bank, the sharper the turn is, correct?

If your talking about standard rate turns, those are not really practical in large commuter aircraft. As true airspeed increases the maximum turn rate decreases when the bank angle is limited to a comfortable level of less than 30 degrees of bank. So please make this question more specific, which airplane category are you talking about?

Usually the autopilot uses the difference between the target heading and the current heading to generate a bank angle target, often just proportional by a linear factor but limited to, e.g. 25 degrees of bank or the minimum of a 30 degree bank turn and a standard rate turn bank angle or even manually selected like in the Boeing aircraft.
The autopilot then calculates the difference between the target bank angle and the actual bank angle and generates a roll rate target. Based on the roll rate target and current roll rate the autopilot computes a roll acceleration target and finally an aileron deflection target, which could, for example, just be a factor times the roll rate deviation.

The computation from the deviation of any of these parameters to the next lower level control loop target can consider the true airspeed and altitude, yes. But this can't be said for all types of autopilots that ever existed and is too broad of a question.

For certification of an autopilot system it has to be demonstrated that the autopilot remains within a safe enveloped, as specified in the requirements. This could limit the roll acceleration, roll rate, maximum bank angle or demand a response within a certain time frame or a maximum deviation for any of these values, transient allowed overshoots, etc. Since the autopilot has to work throughout the flight envelope the parameters used in the computation of the bank angle, roll rate, roll acceleration, aileron deflection, etc. may require a look-up table for each airspeed and altitude to ensure a stable and safe operation.
This can differ between aircraft types, e.g. a large passenger aircraft should fly less aggressive roll maneuvers because the people sitting on the outside far away from the center are being subjected to major g-forces as the aircraft rolls, which is uncomfortable and potentially hazardous.


Why can't wing-mounted spoilers be used to steepen approaches? In a comment on this answer to my previous question about tail-mounted airbrakes (lack of), @JohnK states:

  You won't see flight spoilers (speed brakes) being used to steepen approaches. You have to be 10kt above Vref to extend them on a CRJ900 and you shouldn't be that hot in the first place, and you aren't allowed to use them at all below 300 ft.

Why do you have to be going abnormally fast to slow down with the spoilers, and why can't they be used at low altitude (especially given that, just like with airbrakes, it would seem to me like spoiler extension would be a safer method of slowing down than pulling the throttle all the way back would be, since, should a go-around become necessary, the spoilers can retract a lot more quickly than the engines can spool up from idle to TOGA)?

They can. The Airbus A318 and Embraer E190 both do this in steep approach mode. You can see spoilers extended in this video of a A318 landing and a similar approach in an E190 at London City Airport.

Going back further, the Lockheed L-1011 did this with a system called Direct Lift Control. When landing flaps were selected, spoilers raised a set amount. Small movements on the yoke raised or lowered the spoilers instead of adjusting the elevators. This made for a very smooth approach and landing.

The common point is that these aircraft use electronics for spoiler control. It's too complicated to do this in a cable flight control system. You need to have the system retract the spoilers quickly in cases like go-around and stalls. As I recall, steep approach mode on the A318 activates a different set of gains on the flight control loops for better handling qualities in that configuration.

Finally, a number of fighters have the same system, and some glider pilots do this manually.


Is this an accurate method to showing how the correct Decision Altitude/Height for an approach has been determined? Here's my method of summarising how the decision altitude/height for an approach was determined:
DH/A =
The highest base altitude/height from the list below +
Altimeter Pressure error +
Altimeter Temperature Error +
Company Operational Procedures Additions

Base altitude/height:

OCA/H
System Minima e.g. ILS 200ft, VOR/DME 250
OCA/H per aircraft category
(Otherwise) Published approach DA/H
Minimum A/H to which the approach aid can be used
Minimum A/H in the Aircraft Flight Manual

Instrument Rated pilots will need an understanding of how the DA was determined, they may be examined on it in theory tests and skills proficiency tests - though whilst actually flying the approach they will use the plate DA.
Is this summary correct, or how would you alter it?

This is USA information. The summary: determine the obstacle clearance surfaces, add the required obstacle clearance buffers to those surfaces, adjust DA for glide slope angle and aircraft speed if not already above the minimum due to obstacle clearance. The procedures are all calculated in true altitude, not indicated altitude. Aircraft that fly IFR in the USA are required to have adjustable precision altimeters based on the ISA atmosphere and barometric altimeter based approaches must have a local weather station that provides the altimeter setting for that airport. The difference in DA based on temperature is not considered significant, however there are low temperature limits placed on baro-vnav approaches due to effects on glide path [not DA].
A typical DA in the USA is determined without altimeter temperature adjustments because a DA is only used with positive vertical course guidance, a three degree slope is the same at any temperature. There may be be a fixed decision-altitude adjustment calculated when a remote weather source must be used, based on potential difference in pressure. There may also be a low temperature limit in some cases for procedures that allow uncompensated baro-vnav systems because this equipment can change the glide path angle.
While there were some old manual calculation standards that could be simplified into the answer you are looking for, the modern method is calculated by computers using rather complex algorithms with multiple intersecting surfaces and measurement-uncertainty adjustments as well as large databases of terrain, obstacles, and local winds. FAA order 8260.3D contains most of the approach design structure, it is 509 pages, but even with all of that in several places it simply references the use of software, an example quote "Increase ROC values by the amount specified by the software." See 8260.3D page 198, 202-203,(cat1 final obstacle surfaces and DA) and appendix C(precipitous terrain adjustments) for some of the formulas.
This is completed with a detailed in flight inspection of the procedure using specialized aircraft to carefully map the navigation signals and controlling obstacles. The FAA also performs this service for many other countries and performs regular flight checks of existing procedures, nav-aids, and airways on a regular schedule. Some basic procedure/airway design requirements can be altered if a flight inspection determines the deviation is safe in that specific case.
As for the core components, they check obstacle clearance of the final approach segment, and recently they also compute the vertical guidance surface.(the part of final between DA and threshold. Note the 34:1 clearance symbol added to new FAA plates, it is related to VGS. Jeppeson omits this piece.) If this requires an increased glide slope angle to meet required clearances the DA may be raised for the faster category aircraft. Then the missed segment is calculated and checked for obstacles, if needed the DA is raised again so that the missed segment has required clearances. The missed segment includes an inertia allowance below DA for aircraft that fail to react until they are at DA,(this is a buffer, not intended for normal use.) this inertia is also why higher speed aircraft are given a higher DA. The difference in height between the navigation equipment in the cockpit, or antenna placement, and the wheels of the aircraft-class expected at that airport is considered for the area between DA and threshold.(A 747 will have its wheels about 30 feet lower than a cessna 172 while following the same glide path.)


How to calculate the real Ground Speed from True Air Speed? In most of the formulas I've found online GS = TAS + Vw, i.e. true air speed plus wind.

However, on the simulator, GS changes drastically if I dive or climb which is obvious because I'm covering 0 ground distance if I dive vertically.

What is therefore a real GS formula from TAS? It has to take into account the wind (Vw) but also the "3D angle of the aircraft" (for the lack of better expression).

First calculate horizontal component of airspeed, then add the wind:

$$v_{GS} = cos(\theta) * v_{TAS} + v_{wind}$$ with $\theta$ being the angle between the horizon and the path of the aircraft in the vertical plane.

Or, if you are unfamiliar with trigonometry (using Pythagora's theorem):

$$ v_{GS} = \sqrt{v_{TAS}^2-v_{verticalSpeed}^2} + v_{wind}$$

Both formulas assume the same units being used for all speeds ($v_{TAS}$, $v_{verticalSpeed}$, $v_{wind}$), and only take horizontal wind into consideration. $v_{wind}$ is only considering the headwind/tailwind component.


Can an F-16 perform Pugachev's Cobra? I know that the F-16 VISTA tech demonstrator incorporated 2D thrust vectoring and could perform this maneuver. I also know that military variants of the F-16 are prevented from intentionally entering such extreme angles of attack via their flight limiters.

However, I also know one more thing; there is a switch just in front of the throttle that allows "manual pitch override". This disables the pitch-plane limiter of the FLCC to allow the pilot to recover from certain types of deep stalls when normally the flight limiters would freeze the control surfaces due to the detected extreme AOA.

The question is, can U.S. military-variant F-16s, with MPO enabled, perform a "Cobra" maneuver like Pugachev's Cobra?

No.

This would require a docile pitch behavior of the airframe up to approx. 110° angle of attack. The design of both the Su-27 and the MiG-29 is based on a geometry that has been carefully optimized by TsAGI to behave nicely over its full AoA range, a care that has not been spent by General Dynamics while designing the F-16. The specifications did not call for it, because the idea was to create a low-cost lightweight fighter to complement the heavy F-15.

However, even the F-15 is AoA limited because less care was spent on its aerodynamic refinement. At higher angles of attack, both the F-16 and the F-15 show a nasty pitch-up which cannot be controlled with the aerodynamic control surfaces - only thrust vectoring can manage this. Contrast this which the Su-27, which shows balanced and slightly negative (nose down) pitch moments over the full AoA range, so the limited control authority coupled with the aircraft's dynamics can make the Cobra maneuver possible.


How can I calculate a gradient using a Jeppesen Student Flight Computer? On a Jeppesen Student Flight Computer (CSG), how does one calculate the gradient in percentage if the ground distance and height above ground level are given?

I can't find anything in the accompanying manual. Apparently this is possible on the E6B and CRP-5.

It works the same way as with the CRP-5. If for example the ground distance and height above ground level is given, then one aligns the ground distance on the inner scale (the B scale) with the height above ground level on the outer scale (A scale). Then look up the number 10 or 10 mark on the inner scale (the CRP-5 has an additional red arrow for this mark), and read the gradient in percentage on the outer scale.


Why does the A350-900 call out to retard at 20 feet above the runway? I watched this video of a delivery of an A350.

at 14:50 there is the sequence I'm interested in: the ground radar normally counts down the distance to the ground, but shortly after the 20 feet mark, it calls the typical "retard" to pull the levers back.

Why is it like this and not like normally at 0 feet?

Why is it like this and not like normally at 0 feet?

Normally is not 0 feet: all Airbus (maybe with the exception of the A380, that might have a longer flare) have a "Retard" call at 20ft, not at 0ft. From the A320 Flight Crew Training Manual:

  As a reminder, the ”RETARD” aural alert will sound. In flare, this aural alert will occur at 20 ft, except in the case of autoland, where it occurs at 10 ft.


Why are the F/A-18 rudders deflected in opposing directions during takeoff? Looking at some videos and photos of F/A-18 Hornets and Super Hornets taking off from carriers and from airfields, I recognised that the left rudder is pointing right, and the right rudder pointing left.

Here's a picture:

Why is that? Are there any aerodynamic advantages?
Is it also used as an airbrake to slow the plane down at landings?
At which point of the flights are the rudders in this position and why? (Takeoff, landing, cruising, or both?)
Does the pilot steer them or is the work done by a computer?

Living Wing

The Super Hornet has a living wing, that is to say, the shape of the wing is constantly in motion throughout every regime of flight. Trailing edge flaps, leading edge flaps, stabs, rudders, and ailerons all move in concert to give the pilot the greatest control during particular phases of flight.

This is evident by the use of the flaps switch. The three flap positions are, Auto (Up), Half, and Full. Up auto means that the flight control system (FCS) will dynamically change the wing based on what it thinks the pilot is trying to do. However, when the flaps switch is placed in the half and full positions the FCS switches to landing mode, and all flight control inputs will be interpreted as such. Even though the flaps switch has been placed to half/full, the pilot has only changed the FCS logic, he has not actually commanded the flaps to a fixed position. There are no fixed gains (flaps positions) like there are in typical commercial aircraft. Instead, the computer adjusts the flaps position to mimic a flaps half/full position, while also giving the pilot the most stable platform it can for landing. The logic has its limits though and if the pilot exceeds 14 AoA in a landing mode (flaps half or full), the FCS may accidently depart the jet. This is obviously bad 200 ft above the ground.  This switch commands the FCS to make flight control decisions and is the toggle between the tactical, and landing modes of flight.

Rudder Toe-In

The particular effect you are referencing is called rudder toe-in. At slower speeds, particularly during high angles of attack, the stabilators may not provide sufficient nose authority to crisply rotate the nose. The massive wing area of the Rhino tends to block the airflow over the stabs. To remedy this problem the Rhino's rudders will automatically bias to the inside and create a downward force, which pitches the nose upwards. While the rudder is toed-in, the pilot can still use the rudders to yaw the aircraft. The FCS selectively moves the rudder position to generate the yawing motion, even while retaining the fared-in position.

Take-off and Landing

During takeoff the rudder will remain in the toe-in position for a fixed 10 seconds after it detects weight off the wheels. This prevents the aircraft from accidentally faring the rudders (and losing nose authority) during one of the most critical phases of flight (AoA probe failures will actually cause the rudders to automatically fare, and this problem is removed by a fixed timing.) During the landing portion of flight, the rudders will also be fared in to give the aircraft more nose authority, and this is handled automatically by the FCS once the pilot commands the aircraft into landing mode by placing the flaps switch out of up auto.

Other Functions

While the Rhino does have small speed brakes that extend during full speedbrake deployment, the primary method of increasing drag to rapidly slow the aircraft is through the use of the control surfaces. The FCS will increase the drag by lowering the flaps, toeing-in the rudders, lowing the ailerons, and deflecting the stabs, all while still giving the pilot a stable platform to fly the aircraft--it's an impressive aircraft.

During high alpha maneuvering, the Rhino will again deflect the rudders to the toed-in position while the flaps switch is in up auto. With the FCS logic in auto, the computers will attempt to retain control of the aircraft during max performance maneuvers, and will automatically schedule the flaps and rudders to compensate for high AoA and slow speed flight. Because the nose is cocked up and the airflow is disrupted over the stabs, the rudders will again create that pitching force that will assist the pilot in maintaining nose authority through any regime of flight.

Emergencies

As stated before, there are times when the rudders may suddenly fare themselves which can have devastating effects during the final portion to land. Rudder failures are serious problems and should be treated as such.  Higher landing speeds and extra caution will be used, and the pilot should understand that wave offs may be impossible due to lack of nose authority in close to the ramp.


What are the essential elements of a control tower? Assuming control towers are essential for large airport operation, what is the minimum needed equipment inside the standard control tower to support airport operation?

The theoretical bare minimum would be a light gun to give light signals to aircraft. A more generally acceptable minimum is a two-way radio to do radio communications with aircraft.

From there up other systems can be added. The list below gives some examples but is not exhaustive.

A telephone. Always useful when you want to get in contact with other parties on the ground (e.g. air traffic control centre) or other parties with you.
Meteorological instruments can provide current wind and visibility at the runway to the tower controller. This is not directly to support the Air Traffic Control function, but to provide information services to pilots.
Airport lighting control: runway (and taxiway) lights are usually controllable from the tower. These systems can become quite complex on larger airports
A display with a feed from an approach radar. This present the air traffic situation around the airport to the controller. Whilst on larger airports the approach controllers are usually not located in the tower itself, smaller airports often combine tower & approach control. Even when approach controllers are physically located elsewhere, the approach radar assists tower controllers as well in building a clear mental picture of the situation.
An emergency button that makes the fire department jump to life.
Surface radar display. This presents the ground traffic situation to the controller. Often not found on small airports, but essential for efficient operations at busy airports, especially in low visibility.
More radio's. To split tower control who do the runways and ground control who do the taxiing aircraft. Further divisions can be made.
A system that shows which runways are active, which are closed for use by the airport authority (e.g. for maintenance)
Electronic flight strip system. The traditional paper strips are now often replaced by a digital equivalent. These E-strip system usually communicate with the whole flight data processing system, correlating strips to radar tracks.
Gate allocation system. It's always nice to now where those arriving aircraft should be directed once they are of the runway.
Gate video systems showing the situation at the gate. (to bust pilots that say they are ready for engine start / pushback whilst they are still loading cargo :-) )
Departure management system. When you have a complex airport with multiple runways and a maze of taxiways, a DMAN may help to get aircraft airborne at the right time in the right sequence in the right direction.
Arrival management system. With many aircraft arriving from all directions, headed for different terminal / gates it helps to have an AMAN to avoid overloading your Terminal Manoeuvring Area with incoming flights competing to be first.
Integration of the Surface radar, DMAN and Gate Allocation System with the lights control system. The level of integration varies. In the most extreme case pilots just have to follow the taxiways that light up green and stop at red stop bars. This avoids a lot of radio communications and confused pilots who didn't exactly remember a taxi clearing involving a dozen of taxiway letters.


Is wheel well overheat detection (not brake temperature sensor) necessary for commercial jet aircraft? Some aircraft do have this detection system (many Boeing aircraft), some do not. Why? What's the main purpose of the wheel well temperature detection system, even though there are brake temperature sensors.

What's the main purpose of this detection system even there are brake temperature sensors.

Far more often than not, the need for brake temperature sensors is after landing to tell you how hot the brakes are. If you had to use heavy braking upon landing, they're going to be hot. How hot they are tells the captain in part how he needs to taxi and whether he should advise ground personnel to stay away from the sides of the tires where the thermal plgus are and possibly to use cooling equipment (typically a huffer) to cool them down.

Wheel well temperature sensors are needed after takeoff. The potential problem here is that you need to keep an eye on how warm the wheel well is getting from the hot tires you have retracted and enclosed in the wheel well.

As an example, let's say you have a 747 freighter loaded to a max takeoff weight of 825,000 lbs or more at Honolulu and taking off on RWY 8R. That's 20,000 feet of taxiing and another 10,000 feet plus of takeoff roll. The flexing of the tires during that taxi and takeoff generates a lot of heat. Once the wheels are in the wells, that heat transfers into the wells and eventually leaves the airplane. However, if for whatever reason, the tires already had a lot of extra heat before the taxi started or a lot of braking was done during the taxi, or the airplane was stuck down low in warmer air after takeoff, whatever, the wheel well temperature might exceed the safe limit.

The solution is usually simple, drop the gear and cool the tires. If you don't you risk a wheel well fire.

  Some aircraft do have this detection system (many Boeing aircraft), some do not. Why?

The short answer is that they have been designed so that they don't need it, which begs the question: why aren't all aircraft designed such that they don't need it. Essentially every aircraft design includes compromises. It's all part of tailoring the design to best accomplish what the aircraft's primary task is to be. Using the 747 example, you could, for example, install a cooling system in the wheel wells to take care of the heat, or you could use heavier tires that didn't flex as much and thus didn't heat up as much, or you could have additional structure able to resist the heat or dissipate it quicker. But whatever means you used, it would mean hauling around more weight and the attendant costs in fuel and loss of payload capability when you didn't need it most of the time. Far better to avoid those high costs, but in the interests of safety install a much lighter system that will alert you to the need to cool off the wheel well by dropping the gear.

Insofar as potential 747 wheel well overheats are concerned, baring mechanical failure, it's generally a problem only when the aircraft is used in a manner that it wasn't designed for. For example, the 747 was designed as a long-haul transport. As such, there would be plenty of time for the wheels to cool down in the wheel wells. As I remember we were told in ground school that 5.5 hours was the cool down time. So, if you have a short leg and then a quick turn with high weights, you might be taking off with tires that have more heat in them than the system was designed to handle.

When JAL decided to use the 747 for high-density, short hauls within Japan, Boeing came up with the 747SR (Short Range) which included a redesign of the undercarriage as well as several other things. The design goal was that that any commuter airliner needs: short legs, frequent takeoffs and landings, and it made sense to optimize the design for that criteria, and that optimization required a decrease in range and payload as I remember.


How is the cockpit rear view of an Airbus A340? Before anything I know this can be sound something stupid and obvious, but I swear I lost 3 or 4 hours searching images and videos before posting this question. So please be mercy with my poor knowledge.
I'm looking for a view of the rear side of the cockpit (when the door is, and the third and four ocuppant seat is).
I only get a very partial views, and the more detailed image is a diagram from the cockpit deck layout (the following is an example from A330, I could get the A340, but I'm not looking for a diagram):

Everyone knows the typical eye-lens shot of the panel, but it was impressive to me that get one of the rear view is really difficult, more even after the tragedy of the Germanian, where a lot of shots has no relevance with I'm looking for.
Any help will be preciated.
Thanks in advance.

I Googled for "a340 360 cockpit view" that returns, with others, this link.

The link is a 360-degree view of the A340 cockpit. Below is a frame grab for one of the angles:


Building optimal RC flying wing I have an EMAX motor that operates at maximum efficiency generating 200g of thurst. This is the only fixed parameter I have.

How do I find the most efficient wing design for this flying wing, considering my motor should push 200g in order to operate on its most efficient range.

I know the bigger the aspect ratio, more efficient the wing will be and more flight time.

I would like to use a KFm airfoil (cause of its simplicity on building it).

How an RC hobbyst (I am a mechanical engineer too), with not much knowledge on drag, lift coefficients... can come up with an optimal design?

EDIT:

Sorry for being too broad. Let's specify better:

1) my electronics weight (motor, esc, battery, servos...) will be at 50g;

2) I want to use a foam board, typical on rc plane community which is thin and lightweight

3) I want to optimize for flight time, not flight distance.

I am really lost at this, even after searching a lot. I know the vector diagram of my plane (weight is down, lift is up perpendicular to the wing, drag parallel to the wing and I know there are many types of drag but I would assume only the most relevant drag which is the one generated by air deflection and thrust is also parallel to the wing pointing forward).

The only vector that I know how to quantify is thrust and weight. The other 2 I am very lost!

EDITED so it can received answers.

You don't need an optimal design to have fun.  General guidelines:  Your model should weigh around 500 - 700 grams.  Wing span around 1.5 meters.  Chord around 0.2 meters.  But you really need to nail down your speed envelope.  Too fast will be difficult to control, too slow and it's an indoor delight but an outdoor nightmare (due to wind).

A good place to start would be a chunky reliable design similar to a Piper Cub or Cessna 152.  Shorter more highly loaded wings should help you find the sweet spot of around 7 to 25 mph, which is good for R/C planes.

Build an engine/battery/servo frame that can easily change out wings and empennage as you fine tune your design with gliding and powered flights.

You may wish to start with a slightly cambered KFm 1.  Slower speed and lower wing loading should give more endurance, but will be blown around by the wind and will actually be less efficient distance wise into the wind.  Go conservative on your first build.

Control surface dimensions can be had from foamies at your local hobby shop or R/C club, and more information is available at the RC Groups website.


What is this metal piece sticking up on the roof of a 182? My CFI and I were stumped as to what the purpose of this metal piece is on the roof of a 182. I couldn't find anything from searching Cessna POHs/docs online... Any ideas?
Here is a close-up:

This appears to be an Outside Air Temperature probe.


If an A320 loses an engine why does the landing category go to CAT3 single? Following an A320 engine failure, why does the the landing category go to CAT3 single even if the APU has been started and is powering the AC bus that was lost by the failed engine?

According to the forums PPRUNE, for A320, taken from here:

  The power supply split function that monitors the electrical segregation of the FMGC's does not consider the APU generator as an independent electrical source. As a consequence, when an engine generator is lost the capability is downgraded to CAT 3 Single.

  The electrical power supply split function monitors......
  -The two BUS TIE contactors
  -The DC TIE contactor (between DC BUS 2 and DC BAT BUS)

  When one of the above contactors is closed, the FMGC considers that the power supply split is lost (independently of the APU generator)

  The A330 does not have this restriction and can be CAT 3 Dual capable even with one engine generator failure as APU is considered an independent electrical source.

Also- if you dig in the FCOMof the plane, you would find that if you perform dual engine cat3 approach, and an engine fails- the buses remain split to prevent the failures from reaching the other side, and it degrades to SINGLE.

If you perform an approcah with the APU online- the electrical system is built that if a failure occurs- the bus ties close and power is managed to the whole aircraft from 1 source only- meaning the buses are not split. Hence the single.


Why are some windows in cockpits made openable? Why do aircraft allow sliding / opening windows in cockpits? What purpose does it serve, and why the same can't be done for passenger windows as well?

The opening cockpit windows do serve some purpose, like providing an additional means of evacuation during an emergency.* There have been instances where the crew had used the cockpit windows to escape during hijackings.
There are other purposes like assisting in crew inspection, signaling ground crew, additional ventilation, smoke egress etc (It can also be used for throwing things out, though it is not generally recommended). One main reason (atleast in the past) appears to be to improve the pilot visibility in case the windshield becomes opaque, for example.
The windows are not found in all aircraft (for eg. 787 doesn't have it) and are not very easy to open (note that it opens inwards). From USAToday Ask the Captain:

First there is a locking mechanism, then either a crank which moves the entire window assembly including the frame, or a lever with which to move the window assembly. When the window is closed and locked, it is sealed shut. When open, it does not separate from the frame as the window in your car does.

Actually, FAR 25 Section 773- Pilot Compartment View requires cockpit windows to be openable (or some other means to have clear windshield during precipitation) :

(b) Precipitation conditions. For precipitation conditions, the following apply:
(1) The airplane must have a means to maintain a clear portion of the windshield, during precipitation conditions, sufficient for both pilots to have a sufficiently extensive view along the flight path in normal flight attitudes of the airplane.
(3) The first pilot must have a window that—
(i) Is openable under the conditions prescribed in paragraph (b)(1) of this section when the cabin is not pressurized;
(4) The openable window specified in paragraph (b)(3) of this section need not be provided if it is shown that an area of the transparent surface will remain clear sufficient for at least one pilot to land the airplane safely in the event of—
(i) Any system failure or combination of failures which is not extremely improbable, in accordance with § 25.1309, under the precipitation conditions specified in paragraph (b)(1) of this section.
(ii) An encounter with severe hail, birds, or insects.

In a pressurized cabin, providing windows is not a great idea. (In addition to the increased weight), if anyone manages to open the window, it would be a recipe for disaster (depressurization -> oxygen masks -> land).

*Many aircraft have escape ropes mounted in a compartment above the window on each side of the cockpit as in this A320:

Photo source
And a video of it being used.


Areodynamics of ancient flying machines. Did they really worked for them? If any modern day aerodynamic scholars by chance  gone through rig vedas of hindu mythology. It has been described like below.

  "jumping into space speedily with a craft using fire and water ...
  containing twelve stamghas (pillars), one wheel, three machines, 300
  pivots, and 60 instruments."

Reference from: https://en.wikipedia.org/wiki/Vimana

Is there any scientifical proofs that those aerodynamic principles would have worked for them or just a myth?

Just a few points:

You are yourself conceding that these are from mythology. If something is from mythology, it is (almost) certainly a myth.
Description of a fictional flying machine and explaining their principles of operation are completely different. To the best of my knowledge, none of these texts even try to explain the principle of operation.
Actually, there was a study carried out on one of these texts, which thoroughly debunked the claims made and concluded,

  ... the planes described above are (at) the best poor concoctions, rather than expressions of something real.None of the planes has properties or capabilities of being flown; the geometries are unimaginably horrendous from the point of view of flying; and the principles of propulsion make then  resist rather than assist flying.


Why barotitis, but only during descents and sometimes? I experience barotitis only during SOME (not all) descents. During takeoffs, my ears feel different, but I feel no pain.

Is the cause pilot's skills, rate of descent, or aviational?

As a plane climbs out, the cabin pressure lowers so that it equals the same pressure as being at about 5,000 feet, the altitude of Denver. What happens inside your ear is that the pressure in the middle ear reduces to match the 5,000 foot cabin pressure, and you might sometime feel your ears "pop," just like going up in an elevator in a tall building.

When the plane descends, the pressure in your middle ear will still be at 5,000 feet, but the pressure in the cabin will go down to sea level (0 feet), and you will feel this pressure on your eardrum, which can cause a lot of discomfort until the pressure equalizes.

The pressure equalizes as air enters the eustachian tubes, which connect your middle ear to your nose and throat. The tube, however, is very narrow and can be blocked by inflammation or mucus due to a cold or other illness, and you won't be able to equalize the pressure. Flying with a cold can be very painful during descent.

The amount of discomfort each passenger experiences is going to vary widely, even from flight-to-flight. For example, if the cabin altitude is 5,000ft and the destination is Denver, then the cabin will not have to further pressurize.  Some other factors are individual physiology (some people will have bigger eustachian tubes than others), illness, ethnicity/gender/gift-of-gab (some are more prone to talking than others, and talking can relieve the pressure), etc.

As a pilot, there are two things you can do:

buy a plane with a lower cabin altitude. I recommend the Gulfstream 650, which has a cabin pressure of 2,765ft at an altitude of 41,000MSL
reduce the rates of your descents, which will give your ears a chance to equalize. ATC, however, expects you to descend at between 500 and 1,500FPM, unless you are given "AT PILOTS DISCRETION."

There are a few different ways to equalize the pressure. The most effective is the valsava maneuver, which is how some scuba divers equalize the pressure as they descend into the water. Alternatively, yawning, chewing gum, sucking on hard candy, or hyperextending your jaw may help. Little children are particularly susceptible to discomfort, and parents will give them gum or candy at the beginning of the descent.


How does rudder lock occur? Citing Wikipedia article on the Vertical Stabiliser:

  Rudder lock occurs when the force on a deflected rudder (in a steady
  sideslip) suddenly reverses as the vertical stabilizer stalls. This
  may leave the rudder stuck at full deflection with the pilot unable to
  recenter it.

But how does this phenomenon occur from an aerodynamics point of view? What does it mean that the force reverses on the rudder? Is pedal force meant here? Furthermore, how can the pilot recover from rudder lock?

Normally, the airflow over the vertical stabilizer is from front to back, which means it hits the front face of the rudder, and acts to centre it. But the vertical stabilizer is actually like a small wing. In a sideslip, the airflow comes more from the side. If you're slipping tail-right, using left rudder, the airflow comes from the right. When the vertical stabilizer stalls, the airflow is no longer acting to centre the rudder: it's just pushing against it, and pushing it away from the centre.


When did the Tu95 first use its armament in combat? When did the Tu95 first use its armament in combat? I know they can carry both missiles and bombs, I'm looking for the earliest date of either one being used in a combat situation.

Last year (!), at least per Wikipedia:

  On 17 November 2015, Tu-95s had their combat debut, being employed for the first time in long range airstrikes as part of the Russian military intervention in the Syrian Civil War.

This seems to have been using the Tu-95 as a missile platform:

  The aircraft launched a total of 34 airborne cruise missiles destroying 13 key targets...


Does True Course, Magnetic Heading, or Magnetic Course determine cruise altitude? Imagine I plot a course on a sectional chart. The straight line plotted reads a 345° course. The nearest isogonic line is 14° W (so +14°). Weather information calls for a wind correction of +2°. Since 345+14+2=1, my magnetic heading would then be 001°.

What course or heading am I to use for choosing my cruise altitude (considering the east/west rule)? Do I use the true course that I plotted on the sectional, the magnetic course, or the magnetic heading?

Magnetic course is to be used in determining the cruise altitude.

From 14 CFR 91.159, "VFR cruising altitude or flight level":

  Except while holding in a holding pattern of 2 minutes or less, or
  while turning, each person operating an aircraft under VFR in level
  cruising flight more than 3,000 feet above the surface shall maintain
  the appropriate altitude or flight level prescribed below, unless
  otherwise authorized by ATC:

  (a) When operating below 18,000 feet MSL and—

  (1) On a magnetic course of zero degrees through 179 degrees, any odd
  thousand foot MSL altitude + 500 feet (such as 3,500, 5,500, or
  7,500); or

  (2) On a magnetic course of 180 degrees through 359 degrees, any even
  thousand foot MSL altitude + 500 feet (such as 4,500, 6,500, or
  8,500).

The same is true for IFR flight: magnetic course determines IFR cruising altitudes. See 14 CFR 91.179, "IFR cruising altitude or flight level".

This is true under FAA regulations. ICAO regulations are similar, but reference magnetic track rather than magnetic course; for these purposes the two terms have the same meaning.


What constitutes "the lights delineating the runway"? ICAO defines RVR as "The range over which the pilot of an aircraft on the centerline of a runway can see the runway surface markings or the lights delineating the runway or identifying its centerline."

What are "the lights delineating the runway" here? Do they just point to runway edge lights? Or do they include approach lighting systems as well?

Presumably it's your runway lighting (edge lights, such as HIRL, MIRL, etc, plus runway end identifier lights - REIL), centerline lights, and touchdown zone lights only, because being able to see the nearest approach light miles away isn't helpful if, by the time I'm at 200' half a mile from the runway (and past that outer-most approach light), I'm inside a dense fog bank with an RVR of 600 feet.

That said, it's a much more common case where the RVR at the runway (where it's measured) is about the same as the in-flight visibility farther out on final, so with an RVR of 4000' you can expect to see the threshold at typical Cat I ILS minimums of 200' AGL (okay, ATDZE for the pedantic & precise), but at 1800 RVR at the same point, you expect to see approach lights but little else.


What happens if you do emergency landing on a US base in middle of the ocean? A theoretical situation.

I fly from Honolulu International to the Bejing but my private jet gets fuel starvation and then I land on the Wake Island airstrip.

What happens next? Would the military give me fuel or they would give me shelter and tell me to stay? Did such things ever happen?

Wake Island has had aircraft divert there before, as it serves as an ETOPS diversion airport.

Per the remarks on AirNav and the NOTAMs:

  RSTD: VERY LIMITED OPERATIONS STATUS, AVBL FOR EMERG LDG AND MIN PRIORITY TFC.

  TRAN ALERT: SVCG FEES RQD. TRAN SVC HRS 2000-0400Z (0800L-1600L) TUE-SAT. CLSD SUN, MON, HOL.

  FUEL: FLIGHT CREW REQUIRED TO ASSIST IN REFUELING. J5(MIL). FLUID - W, SP, PRESAIR.

It's possible you could plan to fly through there with prior permission, as with most military fields. AirNav reports 2% of the average of 49 operations per day are transient general aviation, so it's not entirely military, but government and contractors probably make up most of this.

If your emergency is just that you forgot to have enough fuel, you should be able to get more fuel and depart again, for a fee. If there is a fuel leak or some other maintenance issue, you could be in for a longer stay.

  RSTD: NO AIRCRAFT MAINTENANCE AVBL.

As with the airliner that diverted, maintenance equipment and personnel will have to be flown in for any work that needs to be done.

You should be in contact with Oakland ARTCC through San Francisco ARINC in the oceanic airspace, and can call base operations ahead of time to advise of your needs. If it's outside of their normal staffing hours, they need at least 30 minutes notice to open back up.


How tight should passengers wear the seat belt? How tight should a passenger wear the seat belt?

During takeoff and landing and other moments the seat belt sign is on, I usually pull the belt as tight as possible. This is little uncomfortable, so I loosen it a bit when the seat belt sign is off. I think that one or maybe two fingers might fit between the seat belt and my body.
Is this a good idea? Would wearing the belt as tight as possible give a greater risk of crushing my pelvis bone or something?

Please specify whether there is a difference between a situation where the seat belt sign is on and a situation where the sign is off.

According to this document published by the FAA (about smaller GA planes but the topic is applicable)

  Tests have shown that slack in the restraint system should be minimal.
  In an impact, your body keeps moving until the slack is taken out of
  the restraint, but then must be abruptly stopped to “catch up” with
  the airplane. The restraint should be adjusted as tightly as your
  comfort will permit to minimize potential injuries.

Here is a video of them testing the seats. You can see the waist lines of the dummies does not move very much.

Here is an interesting research paper on the topic, may be worth checking out.

A study was conducted by the DOT "Human Factors Associated With the Certification of Airplane Passenger Seats: Seat Belt Adjustment and Release" on the difference between belt tension (as applied by a passenger) in both a cruise and emergency setting. This looks like the most conclusive numbers I can find on measured tension.

  An analysis of results indicate that most passengers (90%) tighten
  the lap belt to a tension less than 7 lb. during normal flight
  conditions and less than 10 lb. for an anticipated emergency.


Are turns, while under the control of a two-axis autopilot, uncoordinated? Since the two axes of a two-axis autopilot are pitch and roll, when the autopilot executes a turn, is it uncoordinated since the autopilot is not controlling the rudder (yaw)?

Absent other control factors, potentially. It is up to the pilot to maintain coordination with the rudder. However, autopilot turns typically happen at cruise speeds and at gentle bank angles, so the ball won’t get terribly far outside its cage. Even for airplanes with aileron-rudder linkage designed to automatically compensate for adverse yaw, Jan Hudec enumerates other contributors such as P-factor that add slip or skid in a turn.

That’s just for a single-axis autopilot. Your question asks about dual-axis autopilots that have another dimension in which to go “uncoordinated,” viz. pitching up too steeply for the current power setting and causing an aerodynamic stall or pitching down so as to exceed $V_{NO}$, $V_{NE}$, $V_{FE}$, etc.

Being outside sweet spot of the flight envelope is a significant factor behind why many POHs and checklists call for the autopilot to be disengaged below certain altitudes and in critical phases of flight. Cockpit automation when properly understood, used, and monitored is great for reducing pilot workload, but no mechanism should be treated as fool-proof.


Has mod percent changed for Mark-1 glide slopes? Mark-1F glide slopes operate at 80 percent modulation. What was it for earlier versions i. e. Mark-1C, Mark-1D, etc.

The percentage of modulation hasn’t changed, rather the way it is measured. Upon further review the current measurement is 80% SDM (sum), where before the measured value was 40% for 90 & 150 hertz individually. The method of measurement change, may be due to rare case instances where 90 and 150 shouldn’t be exactly equal, but together the sum is always 80%.


What exactly happened with the Flight Computers on XL Airways Germany Flight 888T? I recently saw a documentation about XL Airways Germany Flight 888T. This made some questions rising in my mind:

Two AOA-Sensors failed (freezed) simultaneously. From Wikipedia:

  Two out of three angle of attack sensors have been frozen and rendered inoperative. System logic has been designed to reject sensor values which deviate significantly from the others. In this specific case, this principle led to the rejection of the single operative angle of attack sensor, and to the acceptance of the two faulty ones, which provided similar values, but have been stuck since cruise flight.

The Airbus "shut down" the computers because of unlogic values and displayed USE MAN PITCH TRIM. But as stated above, the Airbus rejected the third sensor and accepted the two working sensors.

What made the computers to deactivate and switch to manual mode?

Is it comparing the outside AOA-Sensors with the gyro data (Thanks to the user "mins" for clarifying the diffeence between AOA-Sensor and Artificial Horizon Data, but maybe the Airbus uses the Gyro-Data as a less ranked AOA reference, which flows into the detection of a faulty AOA-Sensor)

Why aren't Airbus-Computers switching to something like alternate law automatically, instead of deactivating the FBW and displaying a small warning?

It was really hard to form my questions and I'm sure I forgot something. But I would appreciate it if you could answer the questions.

Tl;dr it was in direct law because air data was inconsistent and the landing gear was down.

For a full answer to why the aircraft did what it did I'll answer a few questions one at a time.

Why did the flight computers reject the good sensor and use the frozen ones?

The values of the sensors are fed to the control computers by the ADIRU (air data and inertial reference unit). There are three ADIRU's, each corresponding to three redundant systems of sensors. Part of the ADIRU is the ADR (air data reference). The ADR is responsible for determining the validity of the values coming from the air data sensors (pitot tube, static port and AoA vanes), correcting those values from local AoA to airplane AoA and feeding the values to the control computers. (local AoA at the sensor location is not necessarily the same as the overall airplane AoA due to their positioning on the plane.) Each ADR uses two resolvers for each sensor and compares these values for consistency. Along with the value it also sends to the control computers an indication as to whether the values are valid or not.

The ELAC (elevator/aileron computer), which controls movement of the flight surfaces takes the values from each ADIRU and compares them against the median value. If a sensor deviates from the median value past a certain threshold it assumes sensor failure and rejects the input. It then uses the average value of the other two.

Unfortunately for the crew of XL888t this method anticipates a single sensor failure. When two sensors fail at the same or similar value the system will reject the working sensor. There is really no way to overcome this, but having two sensors fail at the same value is exceedingly unlikely.

Why did the control laws degrade?

This is really the crux of the question. The ELAC is what determines the control laws. It uses information from the aircraft configuration (flaps, slats, air brakes, undercarriage)and the output of the ADIRU to determine how to interpret the pilot's control inputs. It uses this information to determine the α protection speeds (α-prot, α-floor and VLS) and when to engage the automatic envelope protections.

Normally when the aircraft slows the AoA increases unless a nose down input is given. In the case of XL888t the pilots were intentionally trying to put the plane into a stall in order to demonstrate the α protections. The elevator and stabilizer were in full up position and the engines were slowed. The ELAC will allow this position until it reaches the calculated values for α protection. In this case the AoA was not changing. When the parameters the ELAC is using get so far out of their thresholds the ELAC can no longer make the necessary calculations, so the α protections are disabled and control law is degraded to alternate.

So why did it go into direct law?

The test the crew was performing at the time was low  speed  check  in  landing  configuration." Landing configuration obviously indicates that the landing gear be down. In alternate law roll control is in direct law, but pitch control is still as it is in normal law, with automatic trim, etc.,except without α  protections. But when the landing gear is down the pitch control shifts to direct law and autotrim is disengaged. The "USE MAN PITCH TRIM" warning is displayed on the PFD.  It's the pilots' failure to notice this warning that resulted in the crash.

As to why the control laws are designed this way I can't say. Maybe someone else can explain why Airbus made that choice.

Note: All of this information was taken from the BAE final report.


What does "leave clear on its left" mean in UK regulations relating to collision avoidance on non-runway landings? This doesn't seem to be plain English, could someone explain this with a simple example for me please? I'm not sure what 'Leave clear on it's left' means, and it's not clear whether the subject of the sentence is 'A flying machine [etc.]' or 'An aircraft that has landed' (i.e. who's left are we talking about)

  Landing and take-off

  (2) If take-offs and landings are not confined to a runway—

  (a) when landing, a flying machine or glider must leave clear on its
  left any aircraft which has landed, is already landing or is about to
  take off;

  (b) a flying machine or glider which is about to turn must
  turn to the left if the commander of the aircraft is satisfied that
  such action will not interfere with other traffic movements; and

  (c) a
  flying machine which is about to take off must take up position and
  manoeuvre in such a way as to leave clear on its left any aircraft
  which has already taken off or is about to take off.

(CAA:"The Rules of the Air Regulations 2015 ")

I've tried searching for the term online but only seem to be able to find excerpts from the legislation.

Seems understandable to me.
It may be more clear with commas...
"(a) when landing, a flying machine or glider must leave clear, on its left, any aircraft which has landed, is already landing or is about to take off;"

Basically leave enough room between you and any aircraft which may be on your left as you pass them.

The grammar may be a little dated but still perfectly accurate.


How is the TCAS negotation information encoded? As I understand, according to this FAA booklet on TCAS, transponders will engage in cycles of interrogations and responses to establish if a collision may occur.

The next step is for both TCAS systems to negotiate respective resolution advisories. My question is how the negotiation takes place in the TCAS system internally, and in particular what communication protocol takes place for the negotiation.

To elaborate, as an example, a browser can make an HTTP request to a server (like this site) which follows protocols as to what information should be provided and how it should be encoded.

Along the same vein, how is information encoded for TCAS systems to negotiate? Since I don't know of any open source TCAS used in commercial aviation, I can't inspect code.

TCAS air-to-air messages use the same format and frequencies as "Mode S" surveillance radar. They're defined (in great and overwhelming standardesque detail) by a document called "ICAO Annex 10".

ICAO wants serious money for a copy of it -- and of course if you're producing actual avionics nothing less than the official source will do -- but for satisfying idle curiosity it's often possible to find a draft or bootleg by persistent googling.

The Mode S message format is also used for ADS-B broadcasts, so equipment to receive and decode them is relatively easily available to hobbyists. The lower layers of open-source ADS-B software will also be generally relevant.


What are the differences between ADS + INS and ADIRS / ADIRU? What is the main difference and advantage in the Air Data System, between the former architecture (ADS + INS) and the newer one (ADIRS/ADIRU)?

The primary difference is packaging, which saves space and weight. The ARINC 704A IRU is a 4 MCU size LRU. Likewise, the ARINC 706 ADC is also a 4 MCU unit. The ARINC 738A ADIRS combines both functions into a single 4 MCU LRU. Though the ADIRS also includes remotely mounted Air Data Modules (ADM) which reduce the amount of pitot/static plumbing.

Functionally, the ADIRS performs the same functions as the separate IRS and ADS. A big drawback to the older ADS was the need to run the pitot and static lines all the way to the LRU. These lines are a maintenance headache, requiring multiple connections all of which have the potential to leak.

The ADMs can be mounted near the pitot and static sources significantly reducing the plumbing. The ADM converts the pressures to digital signals passed to the ADIRU via ARINC 429 or similar data bus. This simplifies installation, maintenance, and weighs less.

It should be noted that newer aircraft are moving to even newer architectures. The Boeing 787 dispensed with ADIRS and went with the Goodrich SmartProbes for air data and an Earth Reference System (ERS) to replace the IRU.

The Goodrich SmartProbes do away with pitot/static plumbing entirely by incorporating the pressure conversion in the probe base. They also electrically cross-connect the probes to perform the ADC function with no separate LRU.

The ERS addresses the FAA/EASA concerns over common mode faults in the IRU by using an IRU/AHRS mixed sensor architecture. In each of the two ERS, the IRU acts as the primary reference with the AHRS acting as a monitor. The key is that the IRU and AHRS use different hardware and software so that a common design flaw can't affect both and cause an undetected failure.

It's just evolution in the function of the aircraft sensors. They do what they need to do. The big demand from Boeing, Airbus, et al, is to reduce size, weight, power consumption, and cost.


Performance metrics of a propulsion system - optimising a propulsive fan system I'm designing an electric fan propulsion system for a hybrid-electric business jet. The hybrid business jet uses a series hybrid configuration and distributed electric propulsion. The electric fan propulsion system is for the distributed electric propulsion part of the engine and consists of the fan, intake duct and propulsive nozzle. So far, I've designed it so that the efficiencies of each component is as close to 1 and optimising the fan pressure ratio so the mass flow rate is large and the exit velocity is small (to improve propulsive efficiency). I'm currently unsure whether there are any other parameters I'm failing to consider and would like some more insight.

Well, if all you care about is the fan performance by itself, then you've pretty much got it.  Maximize the component cycle efficiency and maximize the propulsive efficiency and that's it.  But if you want to start getting more real-world, then things to think about:

Off design conditions.  You can perfectly optimize efficiency at one condition (i.e. for a large commercial airliner this would be cruise: Mach 0.8 @ 40,000 ft), but the thing still has to have acceptable performance at other conditions (e.g. takeoff, Mach 0 @ 0 ft).  You may have to compromise on cruise efficiency to get acceptable takeoff performance.

Since this is an electric fan, it will be driven by some kind of a motor. That motor will have some speed where it is most efficient.  That may not be the speed at which your fan is most efficient.  You'll need to match the two of them to maximize overall aircraft efficiency.

If you want to go even one step further, that electric motor has to get power from somewhere. Presumably a battery.  To get peak efficiency from the motor might demand X current at Y voltage, but your battery might be optimized for less than X current.  Again, you may need to match the power source to the motor.

If you want to go even further, there are a number of real-world turbomachinery considerations to deal with including: Operability / stall margin, Inlet distortion tolerance (i.e. crosswind), Fan blade aeromechanics (i.e. flutter)


Are there winglet modification regulations? If an already existing fleet (737-800 and 900 without winglets) is thinking of a winglet modification, is that possible without regulations? Or what are the regulations?

In the U.S., changing anything on the wing is considered to be a "Major Repair/Alteration" according to the FAA (FAR Part 43 - Appendix A)

To make those changes, this form - http://www.faa.gov/documentLibrary/media/Form/Form_337.pdf needs to be completed.

As you can see, it requires a certified mechanic to handle the work after which a person with Inspection Authorization would approve the aircraft for return to service.

A little extra reading - Who can perform different maintenance checks?.


Are animals straying onto the runway considered to be a runway incursion? Are animals on the runway defined as a runway incursion?

The FAA defines a runway incursion as:

  Any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft.

So no.


What does the suction gauge actually show? If I recall correctly correctly the vacuum suction gauge in the TB10 has a scale from 3 to 6, with the green range being 4 to 5 (I might slightly off on those numbers though).

It's clearly marked as showing inHg, but unlike the manifold gauge it's on the lower stop when the engine isn't running (rather than the upper stop if, as the manifold gauge, trying to reach ambient pressure). I haven't really paid attention to it's behavior in the aircraft (only checking that it's in the green), and I just looked at it in Xplane right now which might be wrong of course.

Is it showing the negative difference to ambient pressure? Or the difference in pressure before and after the vacuum pump (which may or may not be the same thing)? Or something else completely? :)

According to the diagram below from a TB200 pilots manual the gauge shows the difference between vacuum line and the ambient pressure:

The pressure difference between the ambient and the vacuum line drives the airflow which spins the gyros in you instruments. In the Socata design, there is an implicit assumption that the air filter is not blocked. If the filter would be blocked, the suction gauge would probably exceed the green area unless the vacuum relief valve opens before the red is reached.

If your vacuum pump stops working, the dial will fall to its lower stop. If the air filter is blocked, and both the vacuum pump and the vacuum relief valve working properly, the dial should exceed 5 inHg.

Other designs are a bit more fault tolerant in the sense that they do not make any assumptions on the working of the filter or the relief valve. In the examples below (thanks to voretaq7) the suction gauge indicates the pressure difference over the instrument itself, which is a more robust presentation of how the system is performing.


What is the need for twist along a wing? Why should a wing even have a twist towards its outermost chord? How did that even come about? Why can't it be straight and aligned as it usually is?

Washout or twist is a method to tailor the local incidence to achieve the ideal lift distribution over span independently of the wing's planform.

For example, if you desire to have a wing with minimum induced drag, you choose an elliptic planform. However, when stalling, this kind of wing will show a nasty roll instability because the lift coefficient is constant over span, causing one of the tips to lose lift first. To improve handling, designers learned to add chord near the tips. This by itself would create more lift at those tips than ideal and increase induced drag. So they added twist such that the local incidence decreases toward the tips. Now the wing has again the desired elliptical distribution, but has some margin at the tips to ensure that stall happens there last.

Note that washout will result in the desired lift distribution only at one angle of attack.

Washout is also necessary to adjust the lengthwise lift distribution in flying wings. Here the elevons will adjust local lift in order to trim the aircraft, and in order to avoid excessive trim deflections, washout is added so that deflections can be kept small.


Why was my flight cancelled due to bad weather while other flights were not? I'm stuck in Frankfurt. I missed my connection due to a delay. I was rebooked, but this new flight was also cancelled due to bad weather.

About 30 percent of all flights were cancelled today. However, if the weather is that bad, shouldn't all departures have been cancelled? Why was the weather bad for my flight, but not for other flights that actually departed?

In general, flights get cancelled when arriving flights are delayed or themselves cancelled. Your flight needs three critical things to depart on time, or at all:

an airplane,
flight + cabin crew, and
weather that meets requirements

Aircraft may not arrive due to weather diversions (couldn't land with fuel on hand, etc). If there's no airplane, your flight obviously can't depart. Same goes for bad weather at your departure airport - if it's too bad, you can't go. If the weather at your destination is bad, the flight may also be delayed because the airport can't handle as many aircraft as normal. That's fairly straightforward. Where it gets most complicated is the crew.

Crew have what are referred to as "duty and rest requirements" (at least in the US; other jurisdictions have similar rules, possibly with a different name). A flight crew is "on duty" when they're first scheduled to fly, whether the flight happens or not, and the number of "duty hours" they can have on a given day are limited. The FAA last revised these rules in 2011, as far as I know, but I'm not an airline pilot. With the 2011 rules, "Flight Duty Period limits under the new rules range from nine to 14 hours". These rules exist to prevent fatigue, a major cause of aviation accidents.

What this means is that if weather delays cause crews to overfly their limits, they may be unable to operate the outbound flight. With your example of Frankfurt, there is weather causing delays to arriving flights.

For example...

If a hypothetical crew with a 10 hour duty limit was scheduled to fly, say, three LHR-FRA round trips (call it 3 hours of flight duty time each round trip; this may not be a valid example), but were delayed on their third FRA arrival by 2 hours, they would exceed their duty limits by 1 hour on the return flight (1.5 * 2 + 1.5 * 2 + 1.5 + 2 = 9.5 + 1.5 = 11 > 10). As a result, they would not legally be able to depart.

Normally, airlines plan for this with "reserve" crews that are on call to fill in for missing, sick, overflown, or otherwise unavailable crews so that flights are not seriously delayed. When a huge storm hits, this falls apart as there are not enough reserve crews to operate all the flights, and the situation snowballs out of control.

Our hypothetical crew would be replaced by reserve pilots (and cabin crew) if they were available, and the flight might be delayed by more than the 2-hour flight delay they experienced. If not, the flight would be canceled.


Official way for tower to address all aircraft on frequency for new ATIS? When there's new ATIS info available and the altimiter setting has changed, what's the official phraseology for making the announcement to all the aircraft on the frequency? I'm looking in the FAA ATC phraseology doc FAA order JO 7110.65W, but I don't see it.

My best guess would be something like "Phoenix traffic, information sierra is current, Phoenix altimiter two niner niner eight".

The tower will usually broadcast a note such as “Attention all aircraft: ATIS information Victor is now current. Wind two two zero at seven knots.  Altimeter three zero one four”.  This isn’t official phraseology and really isn’t required of ATC, but is a courtesy call to all pilots operating around the airport to retrieve the latest ATIS broadcast for reference.


What are the names of these aircraft? Part.2 The next part of the group... Can someone help me?

The last one is an Antinov AN-2

(source)

The first one could be the Gee Bee Y Sportster

(source)


What is the definition of "geometric pitch angle" for a propeller? My question is regarding the geometric pitch angle of a propeller. Is it the angle between the rotational/propeller plane and the zero lift line of the particular airfoil at a propeller section? Or is it between the propeller plane and the chord line of the airfoil?

From a variety of online sources (e.g. 1 and 2), the geometric pitch angle is simply the incidence angle between blade reference chord and the plane of rotation.

This makes sense from the definition of blade pitch, which is the distance that a point on the prop would move forward in one rotation, if it's gripping in a solid medium. The conversion from pitch to pitch angle, therefore, has nothing to do with aerodynamics (i.e. lift) and is geometric only.


What flight simulator software did Captain Zaharie Ahmad Shah use? During the investigation of Malaysia Airlines Flight 370, it was revealed that Captain Zaharie Ahmad Shah had a sophisticated home-built flight simulator setup.

(article source)

What flight simulator software is he using here?

Based on the red little strip (notification bar) on the bottom of the instrument panel in the middle, it must be either Microsoft Flight Simulator or Lockheed Martin Prepar3d. The red notifiation bar is specific to Flight Simulator 2004 (FS9) and Flight Simulator X (FSX). Laminar Research's X-Plane uses a different graphics engine and would not have produced a scenery that looks like on the three outside view screens.

The source is not really quotable, but if the name and picture can be taken a proof, then Mr Shah himself writes on the X-Sim.de Forum about FS9 and FSX being used:

  Elo guys,
  zaharie here.... pls to join x-sim. About a month ago I finish assembly of FSX and FS9 with
  6 monitors .... with the latest graphic card ( 2 pieces of asus 7970) on one cpu awesome view on 3 panasonic 32 in. LCD HDMI
  and 3 touchscreen Dell 21 inches for main (MCP) , center pedestal, overhead panel.
  time to take to the next level of simulation.Motion! looking for buddies to share this passion.
  Capt Zaharie Ahmad Shah
  BOEING 777 MALAYSIA AIRLINES

Answer based on own experience with all 3 simulators/publishers.


How does the engine produce aerodynamic lift at high angle of attack? This answer asserts that "at high angle of attack the engine is producing aerodynamic lift". In the context of that answer, we are concerned about the increased torque that raises the nose of the aeroplane with respect to the center of gravity, so we should narrow down our interpretation of the otherwise vague word "lift" as the force component that is perpendicular to the wing or fuselage of an aeroplane. We define the angle of attack as the angle between the fuselage and the incoming airflow direction at infinity (shorthand word for "reasonably far away"). It is very different from the angle of the fuselage makes with the horizontal at high speed while very close to the latter at very low speed. It puzzles me in two ways.

It claims the engine itself produces fuselage-perpendicular force in addition to the thrust parallel to the fuselage and wing, despite the thrust of the engine is directed parallel to the fuselage and thus the wing. How is that perpendicular force produced?
It claims that fuselage-perpendicular force thus produced is dependent on the angle of attack. How does that work?

I would like to see a technical elucidation of this claim or some references supporting or refuting it, best if they come with mathematical derivation.

Edit:

Some answers below observe that when the plane moves, without engine turned on, against the airflow, part of the airflow curves downwards to conclude that a net force perpendicular to the fuselage is exerted. It is not that simple as looking at part of the flow stream, since part of the flow stream goes upwards above the separating point. The net force is the integration of all the pressure on the whole surface, and the pressure on the opposite side of the object presses in the opposite direction. In fact, in a potential flow, the D'Alembert's paradox  shows that the net pressure is exactly zero. Of course, real airflow is not potential flow, but this refutes the overly simple rationale of using downward airflow to derive the fuselage-perpendicular force.

However, when the engine is turned on, especially at high power. The situation may be different so long as the airflow is consistently flowing in the downward direction long after exiting the engine. The momentum of the airflow through the engine may overwhelm other parts of the airflow. But the argument must be more sophisticated than just the downward direction of the airflow.

Anything, even a metal plate creates "lift" when it is under an angle with an air flow. Lift isn't a magical attribute to "wings", it is just a physical consequence of the law of conservation of momentum: when you push a stream of air down, the reactive force is upwards.

the fuselage/engines also act as minor lifting surfaces: when they are under an angle they, inefficiently, redirect the airflow downwards.

For the engine this is also a bit due to the definition of thrust: thrust equations consider an inlet in the same direction of the thrust vector. So the inlet & compressor redirect the flow "downwards" under high angles of attack. - This effect has to show up somewhere: as a lift force generated by the engine.


What is the response time of Pulse Doppler Radar? We have the Airborne Pulse Doppler radar for weather predictions which are I think same as in the A350s and also in fighter jets so, what is the response time of these radars?

For example, if a fighter jet is travelling greater than Mach 1, how much will be the response time of the weather radar and how the response time will affect w.r.t to the speed of the plane?

Edit: Response time means how frequently the data coming from the Radar is getting updated? Like in case of Flight Radars etc, the normal response time or update time for the data varies from 40ms to 100ms.

As Simon alluded, the aircraft's speed (example given Mach 1, approx. 340 m/s) is basically one-millionth the speed of the radar energy (traveling at near-light speed, or 300,000,000 m/s).  It's a non-factor.

Ideally, if you want to radar detect something (water droplets, for instance), the detected object needs to be bigger than one quarter-wavelength of the signal you are bouncing against it.  This alone dictates that the weather radar should operate in the microwave range, typically 8-12 GHz (quarter-wavelength approx. 6-10mm) for most systems.

Radar signals are sent out in pulses a few μs wide.  The pulse frequency is determined by how far out you are scanning.  More distant weather requires a longer "wait" time before a second pulse is sent out.  For instance, a pulse detecting weather 5km out will return about 35μs later (10000m round trip divided by the speed of light), but typically systems scan much further.  100Hz (pulses per second) pulse repetition frequency is not uncommon (i.e. every 10ms).  This is good enough to provide location only.  Pulse-Doppler radars provide an understanding of object movement (i.e. wind speed and direction) as well as location.

We also need to take into account the antenna scan time.  Because the radar signal only returns objects directly in front of the where the antenna is pointing, the antenna needs to be moved around so as to pick up a greater area, and so the scan time is largely affected by the scan pattern.  (Aircraft pitch/roll is also accounted for by most weather radar systems, though depending on the gyros, it is not uncommon for the radar to paint the ground momentarily during a maneuver.)  The Honeywell RDR 2100 takes 3-4 whole seconds to perform a full left-to-right scan (typically 90 degrees or more).

Scan time is also affected by the beam width.  Smaller antennas cannot focus as well as larger antennas, and so will produce a larger beam width, requiring fewer scans to produce a complete picture, at the expense of resolution.

Transferring all this weather data around takes additional time.  Commercial aircraft systems do this over an ARINC 708 data bus at 1mbit/s.  Range data, intensity, antenna azimuth/elevation, transmitter gain, information is all sent to be processed and displayed.  Higher resolutions will take longer to "paint" the screen than lower resolutions.  The actual data transfer time and display processing time is negligible, because your cockpit indicator might only have a refresh rate of around 60Hz, or a full screen update every 17ms, with a pixel response time less than 5ms.  For reference, this is the same refresh rate as a typical flat screen TV.

All told, from the time a radar pulse is sent out, detects weather, returns, is processed, and displayed on the screen, the time elapsed is typically no better than a half second, and typically longer.


It is possible for an airplane to get infested by animals? Is it possible for an airplane to become infested by animals like mice or rats?

Is it possible for them to survive?

Do airliners do anything to prevent a scenario like this?

Has it ever happened before?

Yes, I have personally worked on multiple aircraft that were infested by animals.

All of these aircraft were small planes, single engine Cessnas for example. A typical example would be one or two small mouse nests in the wings. I also found at least one wasp nest in an aircraft wing.

The worst I ever saw was a Mooney that had extensive mouse nests throughout the airframe. That aircraft had been unairworthy for at least a year by the time I saw it.

That Mooney ended up being parted out and scrapped, largely because of extensive corrosion in the wings which was either caused by, or aggravated by, the mouse nests. Urea can induce corrosion in aluminum, and finding a mouse nest or other evidence of rodent activity should prompt closer inspection. All the other instances of mouse nests that I have found in airframes were in aircraft that flew several hundred hours a year and these did not suffer any major damage.

I have also heard stories from many pilots and mechanics of finding birds nests—for example in engine intakes or the empennage—and of rodents chewing into or through electrical wiring. There is also the classic warning to check the pitot tube in case a mud wasp has clogged the intake with a nest. I have never witnessed any of these occurrences myself.

The mud dauber wasp is notorious and is suspected of being a contributing factor in at least one fatal airline accident that I am familiar with: Birgenair Flight 301.

Photo source, courtesy of the FAA

Many means of prevention are available, including typical pest prevention methods such as traps and poisons—in my experience all reserved for use in the storage hanger. The most aviation specific forms are the various covers used to protect pitot tubes, engine inlets, etc.

Photo source, courtesy of the FAA

As far as the possibility of animals surviving, I suppose the odds are low. I have never encountered a live animal in an airplane (pets excepted). For any animal stowing away on a pressurized aircraft operating at high altitude I should think the low oxygen partial pressure and temperature would both discourage survival outside the pressure vessel.

Some flights, particularly international ones, apparently make a practice of spraying some form of pesticide in the cabin to kill mosquitoes and other unwanted creatures.