What is the daytime visibility from within a cloud? I ask this question from the context of formation-flying, such as during WW2. What is the visibility in a typical cloud during daytime? Can you lose your wingman right away? Were you at serious risk of mid-air collision when this happened?

The answer is that visibility varies depending on the density of the cloud.  And it can vary significantly.
Flying in formation in IMC is very common in the military.  Sometimes it will be dense enough that all you will have is a wingtip or light.  In those cases it can be very disorienting and difficult to maintain position because you need more than a single point to discern relative motion.  The stress level can go up too since the denser the cloud the closer want you fly to keep sight.  But generally those sort of conditions are relatively brief, and within 10-15 seconds you will likely have the wing and fuselage back in sight.
For reference, in close formation the wing tip might be 10-20 feet from your canopy, with the lead's fuselage another 20 feet beyond that.  So, the worst visibility I have seen (when I lost sight) could have been anywhere from 0-20 feet.  If you see the lead clearly the visibility could be anywhere 50 feet to a mile or more.  You just don't know, all you see is another airplane and gray...  There is certainly no absolute or standard number.
Every formation flight brief should cover lost sight procedures in case it becomes dense enough to require a break away.  I have only ever lost sight and had to break away once.


What determines a plane's range? When a planes maximum range is specified, is fuel [capacity] the only constraint or what else is taken into account?

Would it always or ever be the case that a greater fuel capacity will increase range?

Interesting long-flight story of 64 days in the air, but it doesn't get too technical: https://jalopnik.com/how-a-slot-machine-mechanic-flew-150-000-miles-over-64-5971433

As also stated in this answer:

Range is a function of MTOW and empty weight, according to the Breguet Equation for a jet:
$$R=\frac{V}{c_T} \cdot \frac{L}{D} \cdot ln\frac{W_i}{W_i-W_f}$$

with ${c_T}$ = specific fuel consumption, $W_i$ = initial weight, $W_f$ = fuel weight, $L$ = lift, $D$ = drag.

What increases range if other factors remain constant:

Higher speed $V$
Lower specific fuel consumption.
Higher lift/drag ratio.
Higher TakeOff/Landing weight ratio.

The weight ratio can be because of fuel weight used during the flight, but of course chucking ballast overboard helps as well.


When a large commercial jet touches down, is it committed to stopping? I was reading about flight RWAF9268 earlier today when a questions popped into mind.  When a large commercial jet touches down, is it required to try and come to a complete stop?  Or is it allowed to take off again if part of the craft fails (like the braking system, for example)?  And what factors would make a pilot decide to stay one the ground, or just abort the landing?

When a large commercial aircraft touches down, it is not committed to stopping.

However, it is committed to stopping when the thrust reversers are selected. This is because they take different time to stow and adding power while stowing would likely cause significant asymmetric thrust. And even if they don't, they take their time to stow and you are unlikely to have enough speed and runway when they finally do.

When thrust reverses are not selected, the pilots of course have to consider whether it is more likely that they can stop or lift-off again on the remaining runway. And they sometimes do choose to lift off. There are many incidents where planes went around after tail or even wing strikes or bounces as it's often easier to get the plane under control by adding power. But once thrust reversers are selected, stowing them again means loosing a lot of time and is risky, so go-around is considered out of question afterwards.


If ELAC 1 is under MEL why is it a NO GO item when carrying out EDTO on the A320? In the MEL for the A320 it is mentioned that ELAC 1 is a NO GO if carrying out EDTO operations. Why is ELAC 1 specifically for EDTO? In that case shouldn't it be for non EDTO operations also.

This somewhat contradicts ELAC 2 being a NO GO. Could someone please clarify this with an official reference.

Basically, operating ETOPS/EDTO takes into consideration worst-case scenario situations (EMER ELEC CONFIG) where you will only have ELAC1 working.
In addition, its mentioned that ELAC2 in MEL is a NO-GO item due to the logic behind the system operation where it will allow ELAC2 to work first always, and in case ELAC2 fails ELAC1 will take over.
According to :

A320 FCOM ATA (27-10-20) Architecture (Pitch control). In normal operations, ELAC2 controls the elevator and the horizontal stabilizer, if a failure occurs in ELAC2 the system shifts pitch control to ELAC1.
A320 QRH ABN-18 ELEC (ELEC EMER CONFIG SYS REMAINING), In the emergency electric configuration the ELAC2 wouldn't be available when the emergency generator is running and ELAC1 will be the only available.
A320 FCOM ABN PRO (ELEC EMER CONFIG), ELAC2 is written within the INOP SYS table to confirm what happens when the aircraft goes into the emergency electric configuration.


How can investigators trust flight instrumentation from aviation accidents? I encountered the original question here; I tried to improve the prose by editing it:

  Secondly, about all air disasters involving high-speed impact with terrain, how can investigators trust results from testing instrumentation that hit the ground? In Copa Air Flight 201 they tested the captain's gyro and found it faulty. It probably was, but isn't there the possibility that the gyro was damaged as a result of the impact? I'd really like to hear from an investigator on how it is they determine that test results are so reliable that they can come to a definitive conclusion as to why the accident occurred.

  [User 'bonmec101' writes,  week of 2015 Feb 3]

    +[user] Marvin Kitfox "If you test an instrument from a crashed plane, and it works, you can be pretty dang sure it worked before the crash."

  you haven't seen "Hidden Danger" then [which examines USAir Flight 427). One of my most favorite episodes.

User 'diegus012' answers here, on 2015 Feb 21.

Investigators have experience in inspecting damaged equipment. Over the years they develop an understanding of what kind of damage comes from crashes. Based on this experience they can determine whether the damage is consistent with a crash or just typical operation.

As raptortech97 commented, the gyro from Copa 201 had a wire nearly severed. This is exactly the kind of normal damage that could happen to a gyro in operation, but not the kind of damage that would happen inside a gyro during a crash.

Of course there are many instances where investigators are unable to determine whether equipment was damaged before the crash. Items may be too badly damaged to determine this.

The comment about USAir 427 is also relevant. See also British Airways 38. Some failure modes leave no evidence behind, and thus are difficult to diagnose afterwards.

The investigation will take all of these factors into account along with all other evidence they have. They will not claim a definitive answer based on uncertain test results alone. In the case of Copa 201, the data from the FDR matched the behavior of a gyro with a loose connection, which matched the circumstances of the crash. In the case of the 737 PCU (USAir 427) and RR FOHE (British Airways 38), once the failure mode was tracked down, it was tested in the lab to confirm that such a failure was possible and could cause the expected effects, and to determine the best method to prevent it in the future.


What exactly is an FBO and what services are provided? To most non-U.S. pilots who have little or no experience flying in the U.S., the concept of a FBO is not very well understood.

What exactly is a FBO and what are the services that it can provide? I've heard that they can refuel your plane, move it to a hangar, clean it, provide preflight planning facilities, etc.

Is there a charge for these services (I guess so) and if so, what can be expected? I've also seen many airports with multiple FBOs. How does that work?

All I know is that FBO stands for "Fixed Base Operator".

This may seem like a very stupid question but in Europe there's no such thing. If you need fuel you either taxi to the pump and fill up or call up the fuel provider (if you're lucky because they usually only serve private jets).

A Fixed Base Operator (FBO) is an entity - usually a commercial company - which provides "aviation services" at an airport. One of the main services they provide is fueling, either full service or a self service pump.  They don't all provide both 100LL and JetA, but most do.

Larger ones provide other services, such as catering, lavatory service, pre-flight briefing computers and wifi access, ground power units, and tie down or hangar space for parking.  Charges vary from place to place, most large FBOs will charge a fee for aircraft parking, but sometimes waive a day or so of that if you purchase fuel.  They can often assist in arranging ground transport or hotels as well.

Most are open hours like 7AM - 8PM, but that varies as well.  Most self-service pumps can be used 24 hours a day.

Some have a "crew car" available to borrow for a short trip to get lunch or run an errand, though calling ahead to check on that is important.


How can one quickly estimate interference drag for a configuration? I'm doing some work on streamlining my process for designing new aircraft, and in the process creating/looking for rules of thumb and shortcuts one can use when designing. I'm currently in the process of creating a way of quickly estimating L/D of an aircraft in conceptual design stage. I'm looking for something that doesn't involve a ton of CFD or windtunnel time, and can be incorporated into a spreadsheet. It needs to be +/- 10% of the actual L/D achieved.

I've been able to figure out lift and drag of individual components pretty easily. However, I'm having trouble with figuring a quick way of estimating interference drag. What shortcuts do experienced designers use for estimating interference drag quickly?

Use Sighard Hoerner's Fluid Dynamic Drag. It lists tons of wind tunnel and flight test data for a wide variety of configurations and flight regimes.

Interference drag has several sources:

Flow separation due to the coincidence of the pressure rises of two bodies. Each of them by itself would show attached flow, but in the vicinity of a similar body with its own pressure rise, the flow separates. This is most pronounced at low speed.
Addition of the accelerated flow of two bodies in transsonic flight. While each of the single bodies has no supersonic pocket around it, both in combination will cause a local supersonic area with a subsequent shock.
Disturbance in the spanwise lift distribution, such as wings interrupted by the fuselage or engine nacelles.

Look for areas where one of these conditions is fulfilled, and then try to find a similar case in Horner's book to estimate its severity. Note that all interference drag varies with speed and angle of attack. Doing so carefully will bring you within 10% of the real drag, but needs some experience.

In the end, drag estimation is like bookkeeping. You need to carefully add each component and make sure to avoid double-counting or mixing up reference areas. Sorry, but if you want a good result there are no shortcuts.


Is "Pull up and be ready" standard phraseology? I was next in line (making IFR departure) just after a Bonanza departed, with about a dozen aircraft behind me. Tower called my number and said "pull up and be ready".  I'm accustomed to "line up and wait", changed from the old "position and hold", so I was expecting "line up and wait".  We're always taught to get clarification if we don't understand, but the tower guy seemed disgusted with me for asking, as if "pull up and be ready" is "duh"... standard phraseology.  I've never heard it before, or since, so am I needing to study the AIM a little bit more?

After the fact, I can guess that he meant, "Pull up to the runway hold short line, staying on the taxiway, and be ready for immediate takeoff when cleared".

But his phrasing was non-standard, and definitely confusing.

I think the proper way to say it would have been, "N12345: Hold Short; You are #1 for departure; be prepared to go without delay."

The key parts being:

"Hold Short" is an unambiguous instruction
Informing you that you are next in line.
Informing you what is expected, using the official term "without delay"

Even that is slightly risky, as the "without delay" could be misinterpreted if the pilot misses the initial "hold short" instruction.

I think the proper responses available to the pilot are one of:

"Holding short.  Ready to go without delay"
"Unable"  (I'm not ready yet, perhaps in part because I don't understand)
"Please Clarify" (You used confusing terms; Spell it out for me like I'm 5)


How can opening of a door on small plane cause a drop in altitude? Last week in Ecuador I was on a flight in a small plane (twin engine prop, full with pilot and 5 passengers). The passenger door opened in flight. I was in a position to grab the door and pull it back to the plane and hold it (against a very strong pull) until I could slam it partially shut and then hold it in place until we landed. It didn't seem like that big of a deal except when the door first flew open the plane seemed to drop about 50 feet. What caused the drop in altitude?

In an unpressurized plane the door opening is less of an issue than in a pressurized plane but there are still some issues it presents. Its common for planes to have multiple latching mechanisms to try to prevent this from happening. In some cases they system is not perfect like this AD issued for the DA40 relating to the doors coming off in flight (due to improper closing it appears). Being able to run with out a door or open it in flight is even key for things like para-trooping and skydiving

Depending on the orientation of the door the biggest issue I would foresee is the door shearing off and damaging part of the empennage. This could a have serious if not potentially fatal impact on the plane.

Physically speaking the open door will create drag on the plane which may have been related to the decent you felt. It could also have been an inadvertent reaction by the pilot to the possibly loud noise.

On somewhat of a side note, most aircraft doors are oriented in such a way that the airflow will more or less push them shut (on small GA planes/non pressurized planes). Thus most doors open forwards like the ones on many pipers

Or vertically up so gravity will close them (note the baggage hatch). I would assume this is intentional but it may just be coincidence as that is also how car doors open. Along the opening lines, it is standard emergency procedure in small airplanes to unlatch the door before a forced landing incase the accident mangles the door locks.

For what its worth some planes are even flown with the hatch open most the time (pictured on the ground here but flown in the same config)

Here is a nice article written by a pilot about why it would be very hard (basically impossible) to do on a pressurized plane.


How can I find the CG of a model aircraft based on its dimensions? Given the dimensions and gross weight of an RC model aircraft, how can I find the center of gravity? Can I calculate it, or perhaps there's some way to approximate it?

You cannot.

Assuming that by 'dimensions' you mean the values for length, width and height, there is no way to calculate CofG from it. Two planes with exactly the same dimensions, but one with a thicker wings or tail, will have different C of G.

Even if you know the precise shape of the plane, the C of G cannot be calculated. Replacing a wooden tail with a heavier metal one with the same shape would shift the C of G. So would replacing the engine with a heavier one.

You need either the plane itself, or exact plans showing all the components and their weights (and a lot of maths).


Why would a commercal flight circle while enroute? While selecting random flights to learn about FlightRadar24, I came across AC7311 flying from Toronto, ON (CYYZ) to Indianapolis, IN (KIND), and saw that it flew a couple of circles southwest of Lima, OH (near KAOH).

What are some of the reasons Air Traffic Control would direct the pilots to do that?

As others have noted, this is called a holding pattern, which is used to delay an aircraft while in the air. Of course, this takes time and fuel, so the system works to prevent this from being necessary.

The primary use of holding patterns is by ATC to delay arrivals. This could for traffic reasons, to delay the aircraft until it can join the line of arriving aircraft. It could also be for facility reasons. Bad weather can reduce the rate at which an airport can accept aircraft, meaning some will have to enter a hold. An airport can also be closed for weather, or for another reason, in which case all aircraft must enter a hold, or land at an alternate airport.

Pilots sometimes need to use holding patterns as well. If they have an issue with the plane, they may need time to follow their checklists and diagnose the problem. ATC will give them a place to hold for this time.

Standard arrival procedures generally have holding points published for these cases.  When a holding pattern isn't defined, one can be created. The aircraft will fly for a standard time before turning around, and repeating as necessary.

A better FlightRadar example is perhaps the following image, showing three aircraft in the stack and one leaving it

Source


How can I compute the minimum possible bank angle for a turn with a given radius? I know that I can find an upper bound for the bank angle for a plane, if I know the maximum sustained load factor of that plane because the roll angle and the load factor $n_z$ in a turn are directly related:
$$tan (\varphi) = \sqrt{n_z^2 - 1} \;\; \text{or} \;\; \varphi = arctan\left(\sqrt{n_z^2 - 1}\right)$$
And also I known that the bank angle would not be more than 30° for civilian and 75° and more for military aircraft.

But my question is :

How can one get the minimum possible bank angle an airplane can use to perform a turn with a given radius before reaching the stall speed?

Also I want to know if the stall speed is known, can we use the formula :

$$ W = V/R $$

to calculate the angular rate of turn (of course considering the level turn)?

Given a radius $R$ and a velocity $V$, the bank angle can be computed by:

$\phi = \textrm{atan}\left(\frac{V^2}{R\cdot g }\right)$,

where $g$ is the acceleration by gravity. This shows that the lower the speed becomes, the lower the bank angle becomes. The lowest attainable speed is the stall speed, however we have to take into account the load factor during the turn.

The load factor $n$ during the turn is:

$n=\frac{1}{\cos \phi}$

Due to the increased load factor, the stall speed increases in the turn:

$V_{stall,turn} = V_{stall} \cdot \sqrt n $

The minimum bank angle for a turn with radius R will occur when the speed is equal to the stall speed for that angle.

Solving this mathematically for $\phi$ results in:

$\phi_{min} = \textrm{atan}\left(\frac{V_{stall}^2}{\sqrt{R^2g^2-V_{stall}^4}}\right)$

Note that is the theoretical approach; in practice you would not fly at the stall speed, especially not during turns.

Units are all in SI, you have to apply conversion factors if you want to use aviation units.

Example:

$V_{stall}$ = 50 m/s (approx. 97 knots)
$R$ = 400 m
$\phi_{min}$ = ~39.6 degrees
$V$ = ~57 m/s (approx. 111 knots)


Why didn't early jetliners use turbofans? For subsonic operation, high-bypass turbofans seem to have essentially only advantages for efficiency, noise and takeoff thrust, at least until they reach the size where ground clearance or LP/fan speed mismatch become major issues. Yet early jetliners first used turbojets then only very low-bypass turbofans, despite the existence of turboprops meaning that using gas turbines for indirect propulsion was evidently understood.

Did they not fully realise the potential benefits at the time/thought they wouldn't work well, or was it just very difficult to build a jet with useful excess turbine power (to drive the fan) at the time?

Production turbofans just weren't available. Once they came on the market and were mass-produced, jetliners switched to them.

While turboprops did exist at the time, they were (and are) a turbine engine driving a propeller in place of a piston engine, a straightforward combo of two techs. Turbojet engines were fairly complex machines for the era on their own.

A turbofan involves a large diameter fan, similar in design to an axial compressor, which is more difficult to build than simpler centrifugal compressors used in the first jets and most turboprops. It spins at higher rpm than a prop, and needs to be built and balanced to jet engine tolerances, with the fan tips very close to the casing, but not quite touching it.

The fan also needs to be driven by a core that has enough net power left to produce both thrust and torque, and to do so at low enough rpm to keep the fan (mostly) subsonic. This combination only brings considerable efficiency gains with a two-spool core, using a low-speed shaft to match the fan's optimum rpm, fitted inside a hollow high-speed shaft driving the compressor (unless an aft fan is used). A two-spool with its extra seals is a much more complex engine than a single-spool turbojet or centrifugal flow turboprop.

All of this was done and turbofans quickly became the norm, but it took a few years to develop and ramp up production.


Is there a viable alternative to liquid hydrogen as a fuel for scramjets? Given the difficulty and complexities of storing liquid hydrogen for commercial flight and the high velocity of air passing through  a scramjet, do other types of fuel provide a feasible alternative or solution for scramjets to achieve their maximum theoretical speed of Mach 24? are there any better alternatives?

To list possible alternatives, it is helpful to know why hydrogen is used for scramjets today. The key is the speed of propagation of a combustion in the hydrogen-oxygen mixture.

In order for combustion to take place, the fuel needs to mix with the air and then the ignition needs to propagate fast enough through that mixture in order to allow the combustion to stay stationary relative to the engine. Combustion which happens after the fuel-air mixture has exited the nozzle of the engine is not helping in propulsion.

Therefore, to be suitable as a scramjet fuel, the candidate has to

mix with air really quickly,
have a flame front speed higher than the flow speed in the scramjet, and
achieve complete combustion as quickly as possible.

In all points hydrogen is hard to beat. It is so good that scramjet designers have decided to accept it as their favorite fuel despite of all its disadvantages, which are well known:

Low volumetric efficiency, even in liquid form.
Storage in a cryogenic or high pressure tank.
Small molecular size, so it diffuses into and leaks through many materials, even metals.

All bullet points can more or less directly be traced back to the small size of the hydrogen molecule. Any other scramjet candidate would also benefit from a small molecular size, and acetylene would be the next best candidate, with a flame front speed of 168 cm/s at room temperature (compared to the 364 cm/s of hydrogen).

The difference in speed makes clear that no other fuel comes close to hydrogen.


Is there a way for an aircraft to tell a ground station when the gear is down? Is there any way that someone on the ground can be informed if the landing gear is down? It could be an ACARS message sent to the ground center, or a specific light (sequence) from the aircraft that someone can see visually, or something else. If there is nothing today, is there something that could work in future for all aircraft?

AFAIK, ACARS reports the block time and flight time already. That consists of parking brake release and parking brake set (block time), and weight off wheels to weight on wheels (flight time). These are to help airline maintenance keep track of when they need to do inspections, etc. It would certainly be possible to program it to report wheels up and down, but currently there's no reason to have it report those times.

I'm not sure if you're talking about having this reported in real time or not, but automatic ACARS reports are not exactly in real time. They can transmit things right away (such as text messages from the crew) as long as they have a network connection. But the automated messages are queued for transmission as a block and some types of messages are prioritized over others.

If you're talking about just collecting this data for later analysis, many aircraft are equipped with a quick access recorder (QAR) which records numerous flight parameters. I'm fairly sure wheels up and down times are usually collected. QARs are intended to give information about the flight that can be collected after a flight lands, either by USB, cellular or removable memory cards/disks/tapes. These are collected periodically, such as when the plane returns to the airline hub. This data is used by airlines as part of their flight data monitoring program which looks for incidents that exceed defined thresholds or trends that are occurring to help identify possible safety risks. So the airlines already have a method to collect gear position data.


How do exhaust cones affect the performance of turbine engines? I've seen explanations stating that it creates uniform stream of exhaust gas towards the exhaust duct, however without the cone wouldn't it still be considered a uniform stream?

Also since a divergent duct is formed between the outer duct, and the exhaust cone, does that slow the air down so it reduces turbulence?

(Source)
This is looking into the tail-pipe of a Rolls-Royce Trent 772B.
The purple circles mark the shape of the exhaust, it's ring shaped, also called annular.
If there was no cone, the exhaust will want to fill the gap, creating drag, the cone helps a smooth transition from annular to circular without this drag. As far as I know, every jet engine has one, it's a cheap solution.
Regarding the speed of the exhaust, if the cone is housed in a converging shape, then from start to finish it will be an equal area transition with no loss in velocity. If it is exposed, then some loss in velocity will happen. But more thrust loss would happen if there was no cone.
And as this excerpt below shows, a small reduction in velocity is beneficial:

EXHAUST GAS FLOW
Gas from the engine turbine enters the exhaust system at velocities from 750 to 1,200 feet per second, but, because velocities of this order produce high friction losses, the speed of flow is decreased by diffusion. This is accomplished by having an increasing passage area between the exhaust cone and the outer wall.
The cone also prevents the exhaust gases from flowing across the rear face of the turbine disc. It is usual to hold the velocity at the exhaust unit outlet to a Mach number of about 0.5, i.e. approximately 950 feet per second. Additional losses occur due to the residual whirl velocity in the gas stream from the turbine. To reduce these losses, the turbine rear struts in the exhaust unit are designed to straighten out the flow before the gases pass into the jet pipe.

AgentJayZ on YouTube explains it here (starts from 3:30).
Thanks to @mins for finding the linked exhaust system page.


How do barometric altimetry systems compensate for nonstandard pressure lapse rates? Barometric altimetry relies on atmospheric pressure dropping at a steady rate with altitude, starting from a measured ground-level pressure.  This, in turn, relies on atmospheric density dropping at a constant, steady rate with altitude, which it does not always do:

For instance, if the air close to the ground is much more humid (and, thus, less dense) than the air higher up, then the atmospheric density will drop at a slower-than-standard rate with altitude as the increasing rarefaction of the air is partially compensated by its decreasing humidity, causing the atmospheric pressure to fall off more slowly with altitude than it “should”, and causing an uncorrected altimeter to read falsely low.
Conversely, in a industrial area, with heavily-polluted low-level air containing high concentrations of dense gasses such as carbon dioxide, sulfur oxides, nitrogen dioxide, hydrogen chloride, sulfuric and nitric acids, and heavy hydrocarbons, plus lots of soot and tar particulates which raise the air’s mass significantly while adding very little additional volume, atmospheric density falls off faster with altitude than in a standard atmosphere, as one rises out of the pollution-densified lower layers; this causes the atmospheric pressure to lapse at a higher-than-standard rate, which would cause an uncorrected altimeter to read falsely high.

How do barometric altimeters compensate for nonstandard pressure lapse rates resulting from nonstandard atmospheric density profiles stemming from variations in atmospheric composition with altitude?

This is different from How does an altimeter deal with the non-linear pressure gradient?.  That question is about how an altimeter is designed to match the non-linear ISA model; my question is about how one deals with situations where the ambient air isn't the ISA.

They don't.

Since all aircraft in an area are (or at least should be) having roughly the same error, the errors cancel out and there is no practical effect on vertical separation.

Falsely low readings result in more terrain or obstacle clearance than needed, so that's not a problem either.

Falsely high readings do potentially create a problem, but the minimum clearance is deliberately large to account for the accepted range of altimetry error plus some additional buffer. For example, it doesn't matter if you're 100ft lower than you think when you're still 900ft (rather than 1000ft) above any hazards.


Which company manufactures the air data system on the Boeing 787-9 'Dreamliner' I'm asking specifically about the manufacturer and model of the Pitot probes/tubes that provide the pilots with current air speed readings.

Pretty sure it's either UTC or Honeywell but can't find anything definitive online.

P.S - Is there any evidence of this technology being improved? Especially since Air France flight 447, and more recently Lion Air 610, where in both cases the pilots lost control of the aircraft due to inaccurate airspeed measurements.

Boeing procured the avionics for the B787 in "packages". Air data was part of the "Navigation Package" which included in addition to air data, IRUs, nav radios, GPS sensors, and the FMS software.

Honeywell was selected as the supplier for the Nav package. So they provided the air data system.  I don't know what specific system they supplied.


Is the "Red two standing by" dialog in Star Wars: A New Hope sensible for real fighter pilots? This SFF.SE question: " Why did Red Squadron give their call signs in random order? " raises a good point: for some reason, the "Standing by" responses Red Squadron pilots give before attacking the Death Star in Star Wars Episode IV: A New Hope are out of order:

  Red Leader: All wings report in.
  Red Ten: Red Ten standing by.
  Red Seven: Red Seven standing by.
  Biggs Darklighter: Red Three standing by.
  Porkins: Red Six standing by.
  Red Nine: Red Nine standing by.
  Wedge Antilles: Red Two standing by.
  Red Eleven: Red Eleven standing by.
  Luke Skywalker: Red Five standing by.
  Red Leader: Lock S-foils in attack position.

(to top off the mis-ordering, Red Eight and Red Four never respond).

This was of course answered in-Star-Wars-Universe, but I'd like a perspective of real aviation experts on this:

Is this protocol (all fighters in a group should report in by their call signs) based on something real fighter pilots would do (either WWII era pilots - since Star Wars fighter combat was famously based by Lucas on WWII - or 1970s era).
What is the main purpose of such a protocol? Communications check? Verifying who's flying? Verifying if someone has an issue? Team morale?
In light of #2, does the real life protocol have a specific order of responses, or is it as "whoever responds whenever" as in the Star Wars example?

Tactical call signs are typically given in the format "word" "number" - "number".  For example, Camel 1-1.  In this example Camel 1-1 is the lead Camel in the Camel flight.  As you may have guessed, instructions are always acknowledged in order.  This helps the lead aircraft determine who may not have received the instruction (and some instructions are extremely time critical), or worse, in the event of an accident, determine (by lack of communication) who might be involved.  If someone does miss a comm, then typically the flight waits a few seconds and the next guy in line makes his radio call with the lead noting the person that was skipped.

Tactical call signs change with each flight, and may or may not have any real significance to the event being flown.  Funny ones are usually best; i.e., Camel works really well if you want to Alpha check a point called "Toe".

Here's a typical scenario: While practicing a 2v1 in the MOA (military operating area), Camel 1-2 gets a HYD caution, and has to stop the fight.

Camel 1-2 initiates with, "Camels knock it off, knock it off."

Next the flight reports back in order:

"Camel 1-1, knock it off."
"Camel 1-2, knock it off." (Even though Camel 1-2 initiated it, he still reports in order)
"Camel 1-3, knock it off."

I would say that Lucas came pretty close to replicating the actual sequence.  Sure, they're out of order and they're missing the "# - #" format, but its a decent attempt for Hollywood.


How are the 747-400 rudder pedals and tillers connected to the nose wheel? The Boeing 747-400 Before Taxi Procedure says (emphasis mine):

[...]
Flight controls .............................................. Check C
[...]
Hold the nose wheel tiller during rudder check to prevent undesired nose wheel movement.
Move the rudder pedals to full travel in both directions and verify:

freedom of movement
that the rudder pedals return to center
correct flight control movement on the EICAS display

The FCOM (14.20.3 Landing Gear - System Description) further says:

Nose Wheel and Body Gear Steering
Nose wheel and body gear steering is powered by hydraulic system 1.
Primary low speed steering control is provided by a nose wheel steering tiller for each pilot. Limited steering control is available through the rudder pedals. The tillers can turn the nose wheels up to 70 degrees in either direction. A pointer on the tiller assembly shows the tiller position relative to the neutral settings. The rudder pedals can be used to turn the nose wheels up to 7 degrees in either direction. Tiller inputs override rudder pedal inputs.

I wonder how the rudder pedals and the tillers are connected. How can the tiller override the pedal input? I assume the tillers would move when the pedals are used, but do the pedals also move when the tiller is rotated?

Both steering methods work via a clutch (12) that engages only when the nose wheel is loaded. So in the air, the nose gear won't turn by either input, whether still extended, or retracted.

The pedals' input to the clutch is a pivot, and is therefore more limited, whereas the tiller's (15) interface is cables.

Now based on my understanding:

The pedals move the tiller but not the full range since the cables/clutch/pivot move in that scenario*
If the tiller is held in place, the cables that activate the hydraulic power steering actuators cannot move, and the pedals' input will simply pivot freely (clutch slip)
The tiller overrides the pedals for the same reason in 2.

For completeness, the main body gear steering starts only when the steering input is big thanks to a cool looking cam (29) that pivots the quadrant (23 around 31).

For double completeness, Terry once told me the linked steering is not on a minority of the -1/200 variants, so for those it was either company option, or disabled.

* You can watch it here. Note how the bumps on that takeoff bump the tiller as well.

Sources:

Nose gear steering – Boeing patent (most definitely the 747's judging by the approval date)
Main body gear steering – Boeing patent (definitely the 747's).


Why was there no thrust from the engines in the TACA Flight 110 incident? I have just watched Mayday episode 11, season 11, "Nowhere to Land" about TACA Flight 110 incident. Most key issues of the incident are clearly explained in the episode:

Why both engines turned itself off,
Why there was an overheating alert after restarting the engines (and they had to be shut off).

But, there was a short period of time between restarting the engines and manually shutting them off when pilots were claiming that (based on instruments) both engines are working (spinning), but there is no power / thrust being generated by them (i.e. plane has no power).

Either I missed something or this small issue was not explained.

What does it mean that engines are working (spinning?), but not generating any power? Does this refer to situations where only compressor fans are spinning in the cold section, but there is no fuel burnout in engine's hot section? Or is it something else?

And what can cause such situation? If I am not mistaken or not missing anything -- episode explains issues with heavy rain and hail that damaged fans, but says nothing about fuel distribution system, engine ignition or any other issue that could cause spinning engine to not generate any thrust.

To generate thrust, engines need fuel and air: a spark will ignite fuel (by getting heat, above the ignition point), which burn with the oxygen in the air.

On this (and other incidents), together with air, also rain (and hail or snow) in the engine, so the spark is not enough to ignite the fuel, and so the engines stop working. So, this is the important factor: air and rain enter in the combustion chamber. It is not a problem of fuel distribution, it is just a problem of not being able to ignite fuel. [On car you have air filters, and air compressors, but also a very different cycle compared to jet engines]

The continuous restart means that the engines will continuously add some sparks, so that if ignition fail one, at next turn the the ignition should start again.

The spinning means literary: the engines were spinning, but this doesn't mean they can get enough energy. The article in Wikipedia tell us that they never reached IDLE power. I think the problem is that rain has blocked many of the sparks in the engines, so the engines ignited only some time, enough to get the engine spinning, but not enough to get power.


Where can I find accident statistics on zero gravity flights? I am investigating the option of booking a zero gravity flight with a commercial airline. But I am a nervous flyer.

Do any of the airlines offering this have a 0% accident / fatality record?

A reduced gravity flight is just as a normal flight but doing some stuff at a high altitude, typically between 24,000 and 32,000 feet. The stuff they do is this:

Image Source

Regarding the safety, FAA spokesman said:

  Asked whether these parabolic flights will be as safe as normal
  commercial flights, [FAA spokesman], “If they operate within the
  parameters that we set out, yes, they will be safe.”

There have not been any accidents occurred for a commercial reduced gravity flight.


Tiny margin between VFR cruise and over Class C? Our class C airspace at KRDU has a 4400 ceiling. If I fly Westbound above the airspace at VFR cruise, I'm expected to be at 4500. Since this is a tiny margin and I don't want to bust into the airspace by accident, do some pilots fudge on the cruise altitude and create a larger margin for themselves, flying at say 4600? I'm a lower hour pilot and while that's no excuse to bust minimums, just asking what you all think. Yes yes, flying at 6500 is also an option but this was a rather short XC scenario, plus let's assume a cloud layer at say around 6000MSL. :-)

I had a similar situation flying over the Class C at Albuquerque New Mexico.  Albuquerque's Class C goes up to 9,400 and I was flying VFR at 9,500.  In this case I was using flight following going from Las Cruces NM to Santa Fe NM and was handed off to Albuquerque Approach.  Albuquerque Approach simply told me to notify them if I needed to make any altitude changes to remain VFR.

I think most pilots would simply call Approach in this situation and let them know they are flying over their airspace.  You would need to know the correct altimeter setting anyway to make sure you are at the right altitude.


Identify an USAF transport aircraft in Greenland around 1960 Could anybody help me identify this aircraft?
It was photographed in Greenland around 1960.
Thanks in advance.

That is the Douglas DC-6 / C-118/R6D Liftmaster.

This specific plane was built in June 1947 with modifications for presidential use. It is well known for flying US President Truman. It was the first presidential aircraft that received a distinctive exterior.

It actively served USAF until 1965 when it was transfered to an USAF museum. It is now on display at USAF museum in Dayton, Ohio, USA.

[Source]

[Image Source]


How to calculate the Lift Coefficient for the A320? I'm trying to figure out the lift coefficient of an A320.

What I'm doing is the following: during cruise, the lift is equal to the weight of the aircraft ($mg$) so that I used the cruise table taken from the FCOM to get the speed, the wing area is known ($122.6 m^2$) and I calculated using a tool online the air density at FL290 (29,000 ft).

The result is that the lift coefficient is $0.03029$. Is it right for the assumptions given above?

Next, if I want to relate the $C_L$ with the Angle of Attack, what is the formula and the procedure?

I found a  different number for $C_L$, please check your calculation:

$C_L=\frac{2 m g}{\rho V^2 S}$

substitute:
$
m = 50000 \textrm{ kg}\\
g = 9.81 \textrm{ m}/\textrm{s}^2\\
V = 462 \textrm{ KTAS} = 237.67\textrm{ m/s}\\
S = 122.6 \textrm{ m}^2\\
\rho = 0.475 \textrm{ kg}/\textrm{m}^3
$

This will give:
$C_L = 0.298$

Note that this lift coefficient is for the total aircraft. It includes the lift of the wing, the fuselage lift and also the negative lift of the vertical stabilizer. There is also a small vertical component of thrust that is neglected.

Now that we have an estimate of the lift coefficient, we can estimate the angle of attack. Normally the lift coefficient is assumed to vary linearly with the angle of attack:

$C_L = \frac{\textrm{d}C_L}{\textrm{d}\alpha}\cdot (\alpha-\alpha_0)$

$\alpha_0$ is the zero-lift angle of attack, the angle of attack at which the wing does not generate any lift. For symmetric airfoils, $\alpha_0 = 0$, for chambered airfoils $\alpha_0 < 0$.

I don't know what that angle is for the A320, it will be difficult to obtain. Let's assume for now it is -1.2 degrees.

For infinite long wings in incompressible flow the lift slope $\frac{\textrm{d}C_L}{\textrm{d}\alpha}$ is $2\pi$.

$(\alpha-\alpha_0) = \frac{C_L}{2\pi} =0.0474 \textrm{ rad} \approx 2.72^\circ$

This would result in an angle of attack of $\alpha \approx 1.52^\circ$

Because the wing of the Airbus A320 is not infinitely long but has a span of about 30 meters (excluding the fuselage) we need to correct for that. The reason we need to correct for the finiteness of the wing is that the circulation will cause the local angle of attack of the wing to be lower than the free stream angle of attack. The effective angle of attack $\alpha_{eff} = \alpha - \alpha _i$

The induced angle of attack $\alpha_i$ is given by:

$\alpha_i = \frac{C_L}{\pi AR} = \frac{C_LS}{\pi b^2}$

substitute:
$
S = 122.6 \textrm{ m}^2\\b = 30 \textrm{ m}
$

gives $\alpha_i = 0.0129 \textrm{ rad} \approx 0.74^\circ$

Adding this to our earlier angle of attack results in:

$ 1.52 + 0.74 = 2.26^\circ$

This may not be very accurate as

a) the zero-lift angle of attack may be very different,

b) the lift slope may be flatter due to compressibility effects


What are these lights above the panel in a Blue Angels cockpit? I found the following picture on the Blue Angels Facebook page:

What is the purpose of the lights over the pilot's panel? (The two on the top are green)

I'm not absolutely sure but I think they are the indicators for the inverted fuel pump. From arcforums:

  I finally spoke to a friend of mine who used to fly with the Blue Angels during the 2000/2001 show season. He said the lights on the glare shield were for the inverted pump indicator. The BA fly inverted longer than what is normally permitted for the Hornet so the Blue Angels aircraft are modified with a boost pump mounted to the top of the fuel tank. When they fly an inverted manuver for an extended period that pump is truned on, and while inverted fuel is pumped from the main tank to the feed tank. As fuel in the feed tanks is burned, the light would turns from green to yellow to red. When the light turns red it's time to roll back to a normal flight attitude.

So the three sets of lights should be for the tanks on both the wings.

I think this is the answer because the angle of attack indexers are found to the left of the HUD and look like this:

Also, it appears that they (aoa indexers) are found in carrier aircraft (for e.g. A-4 Skyhawk) as approaches are flown at a specified angle of attack rather than at particular airspeeds.

I believe that these lights are Blue angel specific mod as I'm not able to find them in any other versions.


Why is it common to speak of "Concorde" rather than "the Concorde"? Suppose you researching a book on the history of Boeing B-17.

Suppose you researching a book on the history of the Boeing B-17.

Which of those sentences sounds more complete and correct?

OK, so why on an hour-long PBS documentary on the Concorde, were people constantly talking about "Concorde" this and "Concorde" that, as opposed to "the Concorde" this and that?

It is easy enough to find similar examples on Aviation SE.  Just start to enter any proposed new question with "Concorde" in the titlea and you'll see what I mean, in the long list of "Questions that may already have your answer".

Ultimately it was the chosen name for the project and since it was a bi-lingual project the name was used in by both french and english sides working on it (7:40 into the video), as such the Definitive Article is commonly dropped when talking about it. It also derives from the word agreement and prior to the actually aircraft being built everyone was simply working on an undersigned agreement to build a plane.

  The name Concorde was chosen as, in both French and English (as
  "Concord"), the word means agreement. The plane was to be called
  Concorde in both France and Britain. However British Prime Minister
  Harold Macmillan, decided to remove the "e" from the end, as he was
  annoyed that his French counterpart, Charles de Gaulle, cancelled a
  meeting with him due to having a cold. The British government's
  Minister for Technology, Tony Benn, later replaced it, claiming that
  the "e" stood for Excellence, England, Europe and the Entente Cordial.


Do two stroke engines for small aircraft suffer from degradation between overhauls? Do two stroke engines for small aircraft suffer from degradation between overhauls?

For an automotive engines you can usually expect it to retain most of it's power between services for a long time until a specific failure occurs. During the time between overhauls on a small two stroke aircraft engine like a microlight, does the power available drop noticeably over time and increase after an overhaul/rebuild? Seeing as these only have a small power available to them to the begin with, as in 20-60hp, and this is in turn reduced with altitude, you would have to adjust your flight planning to compensate.

The other option is to have the TBO set to make sure things are changed before power loss becomes an issue, but this would necessarily involve changing out components while they still have usable life in them.

Don't overthink this stuff.

If the rings are good and there are no other abnormalities, there's no reason a 2 stroke shouldn't put out rated power over its service life.  And you would confirm this with a compression test periodically and a quick run at full throttle, while tied down, to check the static RPM.  With a fixed pitch prop, if the power output is down, the static RPM at full throttle will be down, assuming temperature and altitude are more or less the same each time.

Engines like the Rotax 582 were typically overhauled frequently by 4 stroke standards, something like 300 hours, due to potential fatigue on the crankshaft, not from performance degradation.  Possibly the newer versions are being run longer than that.  I've heard that some guys are running them to 500 or more.

So if you maintain the engine, don't allow it to overheat, do a compression test periodically, say every 25 or 50 hours along with a static RPM check at full throttle, you can assume the engine is making rated power and overhaul it only if it fails those tests or has reached the recommended rebuild interval.

And in your flying, don't put too much trust in those engines. It's not the power degradation from wear that'll get you, it'll be the thrown rod or seized piston at the worst possible time.  They are much more highly stressed than 4 stroke aircraft engines, which live a much easier direct-drive life and have really beefy components.  I would NEVER fly a 2 stroke beyond gliding distance of a landing spot.  The saving grace of ultralights is the fact that you can put them into very small spaces when the unreliable 2 stroke lets you down.


What wing spacing is best for a tandem wing configuration? I want to build an airplane but I have limited power(25-28hp). This means that I have to build a power efficient airplane and I finalised on building a tandem airplane. I've read that the wing spacing(distance between the trailing edge of front wing and leading edge of aft wing) should be about 30-50% of the wing span.
So my question is, what wing spacing is best?
I suppose that will help me estimate the length of the aircraft from prop spinner to rudder as intend using wing tip rudders

A tandem wing is never the most efficient planform, but makes for a compact airplane. A case in point is the French design Pou du ciel ("sky louse") which was a very popular homebuilt in the 1930s. The closely coupled wings and the short wing span made it one of the smallest man-carrying designs, but since the rear wing could act like a slotted flap, producing nonlinear lift increases, the aircraft needed careful handling.

Pitch control was achieved by changing the incidence of the forward wing, and a trailing edge down movement normally created a pitch-up moment. Once the gap between the forward wing's trailing edge and the rear wing became too small, the rear wing would show a nonlinear lift increase and add a nose-down movement which became stronger when the pilot pulled the stick further aft. In this condition the aircraft would dive into the ground unless the pilot counter-intuitively moved the stick forward again.

Mignet HM 14 Pou du Ciel (picture source). The initial type flew with a motorcycle engine of 17 HP.

Your idea of moving the wings apart is sound. However, in order to make the plane statically stable, the rear wing needs to produce less lift per area relative to the forward wing, making it less efficient. If you now run an optimizer which varies wing area and minimizes overall drag, you will invariably end up with a conventional design in which the rear wing has 15% - 20% of the area of the main wing.

What is the optimum distance between the wings? This depends entirely on your preferences. You need to know that stability increases linearly with wing-tail distance while pitch damping increases with the square of it. If you want an agile aircraft, keep both close together. If you want to reduce the tail surface and don't intend to fly aerobatics, move both apart. The key figure for stability is the tail volume, which is the product of tail surface area and the distance between wing and tail. Look at airplanes you think are worth emulating and try to match the tail volume of your design to theirs. But don't use a magic number.

In order to minimize engine power, reduce speed. The power need of an aircraft scales with the third power of speed, and many designs of the 1920s successfully used motorcycle engines. A high aspect ratio and a low wing loading, like in a glider, will help to get airborne with just 25 HP. Successful designs with such small engines were the Daimler L 20 or the Messerschmitt M 17.

Messerschmitt M 17 (picture source)


What is the general process for flying a private aircraft to another country? Let's say I want to fly a private airplane to another country. How does one arrange such a flight? Of course this might vary between states, but in general do you need a special permit to fly in with a particular airplane, other than a permit to enter the country? Do you schedule a landing with the airport of destination?

It really depends on the laws of the country you are planning to flight to.

If you want to fly between states in the US, there is no requirement to do any paperwork. Federal Aviation Regulations allow you to fly any distance domestically without filing a flight plan, assuming you are flying under visual flight rule (don't need ATC service), and don't need to fly through any restricted airspaces (most of the US airspace isn't restricted).

Canadian laws require flight plans for all flights longer than 25 nautical miles. However, filing a flight plan doesn't necessarily involve paperwork. Most people do it over the phone.

Flying in Western Europe is similar, but since most airports in Europe require advanced notice (and payment of a landing fee), you'll also have to call the destination airport. Technically you can still fly anywhere you want without doing that... you just won't be able to land.

I don't know much about flying in Eastern Europe, Middle East, or Asia, though if you are in a place like China, where the entire national airspace is restricted and you need a clearance from the military for every take-off... I am guessing there will be paperwork involved.

If you are flying between US/Canada/Mexico, in addition to filing a flight plan (5-10 minutes), you'll also need to notify customs of the destination country so they can expect your arrival to clear you. That also just takes a short phone call.

If you are flying in/out of the US, you'll also need to file eAPIS (electronic advance passenger information system) online. Basically just have to give them names, day of birth, and passport numbers of everyone on the flight, and they will email you a preliminary clearance. You still have to clear customs normally once you land.


How does a pilot file a PIREP? For what reasons would a pilot want to file a PIREP?

If a pilot wanted to file a PIREP, how would he/she go about filing one?

I'll tackle the "How" first - you call up Flight Service (either on the radio or on the phone after you land) and tell them you have a pilot report.  There's a standard format for pilot reports, and if you give all the information in the order it appears on that form it's faster for you and the person taking the report.
If you're filing a pilot report on the ground for conditions you encountered enroute you need to specify the (Zulu) time of your observation (or tell the briefer "20 minutes ago"). In the air it's generally assumed your report is for "now".

Pilots are requested to provide pilot reports for significant deviations from the forecast weather, or for hazardous conditions. Basically we provide them as a courtesy and service to our fellow pilots (like flashing your lights at other cars on the highway if you know there's a speed trap).

Some pilot reports you may want to file in flight are if the Winds Aloft differ from the forecast. If the forecast told you you should have a 10 knot tailwind and you actually have a 5 knot headwind that's pretty significant, and if you tell Flight Service they will pass it along to the weather forecasters and they'll factor it in to their next Winds Aloft calculation. It will also appear in the next pilot's briefing so they'll know the winds in the forecast aren't correct.
Another example is turbulence: If you're encountering continuous moderate chop at 7,000 feet but smooth air at 9,000 feet providing that information could be useful to the next pilot flying through the same area.

A classic example of a PIREP you file after you're on the ground is icing: If there was no icing in the forecast but you've encountered some you should report these conditions. If you're under ATC control you'll obviously tell them, but when you're on the ground you should call Flight Service and file a formal pilot report. Again, the information will be passed to the weather forecasters and the icing AIRMET will be updated, and your PIREP will be passed along to other folks in their briefings to keep them out of the ice.


What are stick position stability and stick force stability? What are stick position stability and stick force stability?
What are the difference between them?
How will changing trim of an aircraft affect them?

Stick position stability.

In its broadest definition, stick position stability means: a larger aft stick deflection is required to maintain a lower constant airspeed. Or in an equation: $d\delta_e/dV > 0$, with $\delta_e$ being the elevator deflection, + = Trailing Edge Up

An aeroplane with stick position stability is easy and safe to control. If the pilot wishes to fly at a lower velocity, they only need to deflect the stick further aft in order to reach the larger Angle of Attack required to maintain lift. An aeroplane with stick position instability will react with an ever increasing nose-up deflection, requiring corrective opposite stick action.

Stick force stability.

An aircraft has stick force stability if deflecting the stick further away from trimmed position, requires a larger force: the stick feels as if it is loaded by a spring. Easy to achieve with irreversible flight controls, which are loaded by a mechanical spring. More difficult with reversible flight controls, where the airforces are directly fed back to the stick: at lower airspeeds the force gradient must be high enough to result in clear stick trim conditions (friction in the control loop plays a role here), at higher airspeeds the aircraft must still be controllable.

Stick position stability is a necessary condition for stick force stability, and stick force stability is an additional requirement for safe and easy control. And it is this stick force stability in a turn that required the implementation of MCAS in the B737MAX: stick force stability must be demonstrated in all flight states in order to obtain certification.


Diamond DA42 - Do you need the electric master on to extend landing gear? For the Diamond DA42 (TDI)
Learning my electric fire emergencies. Would it be wise to extend the landing gear before electric master is turned off?
Does the (hydraulic) gear power pack require the electric master to be on to extend the gear?
I presume if the electric master is switched off, could still extend manually using emergency gear extend lever?

In general you should always follow the emergency procedures described in your POH.
The emergency procedure for an Electrical Fire in Flight does not ask to extend the landing gear:

EMERGENCY SWITCH . . . . . . . . . . . . . . . . ON, if installed
AVIONIC MASTER . . . . . . . . . . . . . . . . . . . . OFF
ELECT. MASTER . . . . . . . . . . . . . . . . . . . . . OFF
Cabin heat & defrost . . . . . . . . . . . . . . . . . . . OFF
Emergency windows . . . . . . . . . . . . . . . . . . . open if required
Land at the next suitable airfield

CAUTION
Switching OFF the ELECTRIC MASTER will lead to total
failure of all electronic and electric equipment. [...]

(DA-42 POH - Emergency Procedures)
In case of a complete electrical failure, the electrical hydraulic pump will no longer function:

In case of a failure of the electrical pump, which is driving the
landing gear actuators, the landing gear can be extended
manually [...]

Even if there is still pressure left in the system, the gear lever will no longer open the valves without electrical power:

The hydraulic pressure for the landing gear operation is provided by an electrically powered
hydraulic pump, which is activated by a pressure switch, when the required pressure is
too low. Electrically actuated hydraulic valves, which are operated with the gear selector
switch, provide the required hydraulic pressure for the movement of the landing gear.

(DA-42 POH - 7.5 Landing Gear)
The checklist for Complete Failure of the Electrical System says:

NOTE
The landing gear uplock is no longer ensured. The landing
gear may slowly extend.
The landing gear can be extended manually according to
3.6.2 - MANUAL EXTENSION OF THE LANDING GEAR.

So it's possible that the gear will already extend without electrical power, but you can always follow the manual extension procedure.


How can civil ATC maintain safety with military aircraft around? I've been asking myself for a while how ATC can maintain air traffic safety with regard to military aircraft - or if they just don't.

As I understand it, all bigger planes (let's for now focus on commercial airliners) have mandatory transponders and warning systems like TCAS and similar. By usage of such systems, ATC knows their position, altitude, heading etc. which is used for planning of take-offs and landings just as well as air traffic safety. Also, systems like TCAS allow pilots to directly respond to unsafe situations even if ATC "didn't see it coming". In short, lots of regulations and techniques to make flying safe.

Now I know even less about military aircraft, but I do know they have transponders, too. I suppose, since enemies would have it a bit easy, those transponders don't operate the same way civil transponders do; or at least they use different frequencies, encryption and what-not. I don't know if they have TCAS but, I suppose, even that could possibly be exploited by enemies.

If I assume correctly, civil ATC cannot necessarily see military aircraft. I've read in another question that FAA doesn't have much power over military but that's just the US anyways. Also, the answer in yet another question suggests that military aircraft do not have to maintain separation.

So, what's the verdict? Do military aircraft assume civil regulations while not in "combat mode"? Or are civil ATC indeed oblivious of military air movements and the military has to provide safety by regulating military and watching civil traffic?

Military aircraft do have transponders that can reply to civil ATC radar and TCAS interrogations. Normally military aircraft operating in civil airspace are visible to civilian ATC and also will trigger TCAS advisories and alerts if they are getting close to airliners.

During  wartime operations, and sometimes during combat practice in dedicated airspace, the transponder is operated in a different mode and will not be replying to civil radar interrogations.

Typically when operating in civil airspace, military aircraft will fly under the civil regulations for that airspace. Training flights are usually conducted in dedicated airspace under military traffic control.

In some cases the military ATC assumes responsibility over military aircraft in otherwise civil ATC controlled airspace. In such a case the military ATC will be responsible for the separation between the military aircraft themselves and between military and civilian aircraft.

In other cases military aircraft may be allowed to maintain their separation from each other on their own, without civil ATC interfering in their operations. This allows for operations where military aircraft flying close to each other like formation flying and aerial refuelling outside the dedicated military airspace. In the USA these operations are called MARSA (Military Assumes Responsibility for Separation of Aircraft). Civil ATC is responsible for keeping Instrument Flight Rules (IFR) aircraft separated from MARSA operations. Visual Flight Rules (VFR) pilots have to maintain separation visually from MARSA flights and vice-versa. If VFR pilots are in contact with ATC they will be advised of ongoing military operations.


What causes airliner tyres to burst as often as they do? Tyres burst - not just fail - remarkably often. The Aviation Herald lists 26 tyre-related incidents this year.

I'd expect fast landings or overweight landings and heavy braking to be implicated, but often, tyres burst during the take-off roll:

Nordica CRJ9 at Kiev and Tallinn on Jun 4th 2019, burst tyre
American B738 at Kingston and Miami on May 7th 2019, tyre damage on departure
American B738 at Vancouver on Apr 19th 2019

Some other failures also appear very regularly (cabin pressurisation, flaps, landing gear). However, these are of complex systems that have many interacting parts, and they also exhibit multiple ways of failing.

Car tyres, which are maintained much less well than aircraft tyres and travel far greater distances over much harsher surfaces, very rarely burst, even when they fail.

Why do the tyres of these large aeroplanes burst rather than fail in other ways? What is it about the way that aircraft tyres are made, or the conditions that they are subjected to, that cause them to burst as often as they do?

Car tires aren't really comparable.

Car tires:

make a lot of miles, but in mostly benign circumstances. Low speeds mean little heating (and slow changes in temperature).
failures are often caused by debris in the road rather than structural failure of the tire itself. (Although on trucks, structural failure is more common)
must be replaced when the tire profile reaches a minimum depth, which means you can't keep using the tire until structural failure happens.
are generally thrown away when the profile reaches minimum depth, because car tires are cheap enough that retreading is not necessary

Airplane tires:

rapidly go through temperature cycles (in-flight: -50 ºC, and on touchdown they rapidly heat up to several hundred ºC)
are kept at much higher pressures (13 bar versus 2 bar for car tires), so if there's a failure it's more likely to be catastrophic.
need to run at high speeds (300 km/h and more)
carry a lot of weight (up to 38 tons, vs. 500 kg for a car tire and 5 tons for a truck tire), which explains why they need such high pressures.
have to be lightweight
are often refurbished


Do all A320-family planes have leading edge high lift devices? I keep seeing pictures of A320/321 planes with slats or some other form of leading edge high lift devices. However, on all my flights in the last years with A320s/321s I never noticed anything changing on the leading edge during approach (from my pax window point of view).

So my question is: Is that an option airlines can choose, if they want to have leading edge high lift devices? Or are they in all aircraft of the family? If so, are operators flexible in using them for approaches?

Unless something broke mid-flight -- which you would have probably been told about as a passenger because of the faster landing speed -- leading edge devices (slats) are used for takeoff, approach, and landing on the A320-family.

For takeoff the slats are put in position 18 or 22, and for landing in position 22 or 27, as the table below from an A320-family flight crew operating manual shows:

If you are sitting well ahead of the wing, you may not notice a change if you don't know what to look for. Here are the 4 positions:

(YouTube) Slats 0, 18, 22, and 27. Also note the arrow showing the 3 extended position markers.

One of the few jetliners built without slats is the DC-9 Series 10.

  The Series 10 was unique in the DC-9 family in not having leading edge slats. The Series 10 was designed to have short takeoff and landing distances without the use of leading edge high-lift devices. Therefore, the wing design of the Series 10 featured airfoils with extremely high maximum lift capability in order to obtain the low stalling speeds necessary for short field performance.

The rationale would have been weight and maintenance cost saving, which was helped by the short range of the plane. For faster cruise speeds and longer range, high-speed tailored wings with slats for low-speed are better than low-speed tailored wings.


What are the pilot responsibilities for "maintain visual separation" clearances? ATC will sometimes give pilots the instruction to maintain visual separation from nearby traffic.

I have a couple questions about this:

There is a related question here about traffic separation.
Is the required separation in this case different, and how can they judge this? (I would like a bit more detail for this specific case than was provided on the answer there)
Normally pilots will follow their flight plan and ATC instructions. What actions should pilots take to maintain separation? I mean, obviously whatever is necessary, but is there any standard method? Should they anticipate an issue and ask ATC if they need to change course?

This is mostly focused on IFR traffic, but how different would VFR be? The situation could be that ATC clears you for a certain maneuver, and other traffic interferes.

It is my understanding that for IFR traffic the controller would expect that there would be no conflict, but things don't always go as planned.

Visual separation is addressed specifically in the AIM (see below).  It is an ATC instruction sometimes given when the pilot reports another aircraft in sight.   ATC is then able to instruct the pilot to "maintain visual separation" from the other aircraft, and it doesn't matter if they are IFR or VFR.

Then it becomes quite simple:

Don't hit the other airplane!

Do whatever you have to do in order to avoid them.  (Usually this is nothing since you just get closer than ATC is allowed to let you otherwise.)
If you are on a specific ATC clearance, then notify ATC immediately if you have to do something contrary to that clearance.

Keep the other aircraft in sight.

Immediately report to ATC if you lose sight of them.

Avoid the wake turbulence of the other aircraft.

Standard radar separation no longer applies since the pilot has accepted separation responsibility from the one specific aircraft that the clearance applies to.  This allows ATC to let aircraft fly more efficient routes (not having to turn to avoid the other aircraft) and also lets more aircraft land in a given amount of time because they can be closer together on final.

Pilots have to use good judgement as to how close they get to the other aircraft, but it is done visually.  They can use any tools at their disposal to help (TCAS, asking ATC how far away they are, etc.) but it all comes down to "that looks good enough for me".

  Section 5. Pilot/Controller Roles and Responsibilities

  5-5-12. Visual Separation

  a. Pilot.

  1. Acceptance of instructions to follow another aircraft or to provide visual separation from it is an acknowledgment that the pilot
  will maneuver the aircraft as necessary to avoid the other aircraft or
  to maintain in‐trail separation. Pilots are responsible to maintain
  visual separation until flight paths (altitudes and/or courses)
  diverge.

  2. If instructed by ATC to follow another aircraft or to provide visual separation from it, promptly notify the controller if you lose
  sight of that aircraft, are unable to maintain continued visual
  contact with it, or cannot accept the responsibility for your own
  separation for any reason.

  3. The pilot also accepts responsibility for wake turbulence separation under these conditions.

  b. Controller. Applies visual separation only:

  1. Within the terminal area when a controller has both aircraft in sight or by instructing a pilot who sees the other aircraft to
  maintain visual separation from it.

  2. Pilots are responsible to maintain visual separation until flight paths (altitudes and/or courses) diverge.

  3. Within en route airspace when aircraft are on opposite courses and one pilot reports having seen the other aircraft and that the
  aircraft have passed each other.

More info is here:

  4-4-14. Visual Separation

  a. Visual separation is a means employed by ATC to separate aircraft in terminal areas and en route airspace in the NAS. There are
  two methods employed to effect this separation:

  1. The tower controller sees the aircraft involved and issues instructions, as necessary, to ensure that the aircraft avoid each
  other.

  2. A pilot sees the other aircraft involved and upon instructions from the controller provides separation by maneuvering the aircraft to
  avoid it. When pilots accept responsibility to maintain visual
  separation, they must maintain constant visual surveillance and not
  pass the other aircraft until it is no longer a factor.

  NOTE-   Traffic is no longer a factor when during approach phase the other aircraft is in the landing phase of flight or executes a
  missed approach; and during departure or en route, when the other
  aircraft turns away or is on a diverging course.

  b. A pilot's acceptance of instructions to follow another aircraft or provide visual separation from it is an acknowledgment that the
  pilot will maneuver the aircraft as necessary to avoid the other
  aircraft or to maintain in-trail separation. In operations conducted
  behind heavy jet aircraft, it is also an acknowledgment that the pilot
  accepts the responsibility for wake turbulence separation.

  NOTE-   When a pilot has been told to follow another aircraft or to provide visual separation from it, the pilot should promptly notify
  the controller if visual contact with the other aircraft is lost or
  cannot be maintained or if the pilot cannot accept the responsibility
  for the separation for any reason.

  c. Scanning the sky for other aircraft is a key factor in collision avoidance. Pilots and copilots (or the right seat passenger)
  should continuously scan to cover all areas of the sky visible from
  the cockpit. Pilots must develop an effective scanning technique which
  maximizes one's visual capabilities. Spotting a potential collision
  threat increases directly as more time is spent looking outside the
  aircraft. One must use timesharing techniques to effectively scan the
  surrounding airspace while monitoring instruments as well.

  d. Since the eye can focus only on a narrow viewing area, effective scanning is accomplished with a series of short, regularly
  spaced eye movements that bring successive areas of the sky into the
  central visual field. Each movement should not exceed ten degrees, and
  each area should be observed for at least one second to enable
  collision detection. Although many pilots seem to prefer the method of
  horizontal back-and-forth scanning every pilot should develop a
  scanning pattern that is not only comfortable but assures optimum
  effectiveness. Pilots should remember, however, that they have a
  regulatory responsibility (14 CFR Section 91.113(a)) to see and avoid
  other aircraft when weather conditions permit.

For even more information, there is an entire section of the Air Traffic Control job aid which the controllers use about visual separation.


Does the Boeing 737 NG have "5" radar altitude callout? So, I was watching a video of a Boeing 737 NG land, and heard the "5" callout. Is that an airline option or something?

EDIT : link to video

The Rockwell Collins EGPWS, that is probably the most widely used system (you can tell right away by the voice that sounds exactly like the character "Data" from Star Trek - Next Generation; I'd swear it's the same actor's voice) comes with the full range of callout altitudes/heights and airlines pick and choose which ones they want by "configuration strapping" settings (connector pin jumper configurations in the mounting tray) when the units are installed in the avionics bay.


Is it feasible to replace brakes on airplanes with electric motor/generator? Would it be feasible to replace the brakes on airplanes with electric motor/generator drive systems?

There are two problems I see with airplanes. When they land, the tires are not spinning to match the ground speed, as the craft touches the ground. So there is a sudden lurch as the tires touch the ground and suddenly begin spinning. The bigger the craft, the more tire mass that must be instantly accelerated.

This disrupts flight stability, and the jolt could be enough to cause a crash or mishap in poor landing conditions. It also causes unnecessary wear and stress to the tires due to the motionless rubber dragging across the runway pavement at first contact.

It would be best for the tires to be spun up to match the ground speed before the craft touches the ground, for the smoothest landing possible.

The second part is just simply the problem of dissipation of heat. It has been discussed elsewhere here that the heat from braking can cause fires and crashes.

As in train locomotives, with a braking motor/generator, the heat could potentially be moved elsewhere to resistive heat coils covering a large area, and cooled using forward thrust or fans.

With a motor/generator unit, the tires can be spun up to either near or matching ground speed, using them as motors powered by the APU, and then switched to be used as generators for braking after ground contact is made.

Has this ever been researched or used on airplanes?

(As a lower middle-class American that is not involved in the airplane industry, I have no hope of doing anything with this or profiting from it, even if it is a practical and potentially patentable new concept that has never been tried before.)

EDIT

I am not talking about regenerative braking or energy recovery into a storage battery. Someone has inferred that though I didn't say anything about it at all.

I understand the storage battery would likely be too much extra weight for a plane to carry, vs the energy recovery of takeoff and landing. (Heh, have a 2000 ft breakaway extension cord on a reel, to drive it down the runway and disconnect right before it lifts off the ground.)

I am only looking at resistive / dynamic braking, dumping the heat in huge resistor banks with a high speed blower, the same as is used on train locomotives. On a plane, air bleed from the engines can blow across the the resistor banks.
Probably should pluralize the title. Rather than a single huge motor/generator, each brake assembly would be replaced by a separate one of these.

So a large plane with say 20 wheels would have 20 motor/generator units, these running at high voltage to keep the amps and wire diameter small. This reduces weight and engineering complexity, eliminating gears and shafts linking all wheels on one set of gear, to one huge motor/gen unit.
This is not two separate devices, but one device that does both functions. Most (but not all) generic electric motors without electronic drive systems can also be a generator.

This could use a permanent magnet motor, or with a powered field coil. Neodymium is capable of extremely high flux density, but loses it when exposed to high heat, so there are density / temperature tradeoffs of permanent vs powered field coils.
Tire hub could potentially be integrated as part of the motor/gen rotor/casing for weight savings (which is very important in aircraft), using a fixed core and a hub that rotates around it in reverse of conventional motor design.

On a hybrid or all-electric car, the motors on the wheels supplement or replace the engine, and by regenerating electricity from the braking, it extends the range of the battery.

On an aircraft, the engines would still be needed for the major part of the working life of the aircraft -- the time while it is in flight.  So unlike the case of a car, you don't get any advantage with the motors themselves by adding the motor/generators to the wheels.

Beyond this, on a large aircraft, electricity is in ample supply when you have jet engines turning, so what's gained by regenerating the electricity from the wheels, during the 60-90 seconds of heavy braking on landing, isn't all that significant when compared to the electricity used and produced over the course of a whole flight.  Not nearly as significant as a drive in the city with many cycles of accellerating to speed then decelerating to a stop, over and over.

Beyond this, the major players then are the added weight and complexity of the motor/generators, vs the gains in terms of (a) tire life, from spinning them up prior to landing, and (b) fuel saved by maneuvering on the ground from the wheel motors instead of the jet engines.  When you consider that the costs of jet fuel are on the order of $1000 to multi-thousands of dollars per flight hour, the costs savings of longer tire life will lose out if the extra weight of the motor generators over conventional brakes means that you're spending more money over the course of the flight to carry the extra weight.  Likewise, the fuel burn during taxi in & taxi our on the motors isn't all that great compared to an hour or many of high-power cruise... power settings for taxi are close to or at idle, so fuel consumption isn't all that high.  Plus, it's common to taxi without all engines running, further reducing fuel burn on the ground.

The big killer for this idea is the weight penalty.  Motor generators are significantly heavier than conventional brakes, and when you consider the amount of energy that brakes have to be able to absorb during a high-speed stop, you'd need some seriously beefy generators to accomplish what aircraft brakes can do.  Or else, you'd have conventional brakes installed to supplement the generators, and the weight goes up further.

As a ballpark, on an hour flight in a 737, an extra 1000 lbs of weight increases the fuel burn by about 10 lbs, or about 1.5 gallons.  Doesn't sound like much, but when you multiply the added weight times every flight hour that the aircraft is operated over the course of a year, it really adds up.  Beyond that, motor/generators are a lot more complex than simple brakes, so they'd be more expensive initially and require more maintenance throughout their service life.  Plus, I suspect, they'd need to be supplemented by conventional brakes that would be used in the event of a high-speed max-effort stop (rejected takeoff, landing on a short runway).

The end result of all of this is, no manufacturer I'm aware of has found that the tradeoffs make this sort of project worthwhile.

The best case is probably one of really long taxi times, but in that case a pushback tug could tow the aircraft to a point close to the runway, saving the fuel burn on the aircraft engines until it was time to start them.  I'm sure this has been considered as well, and again, I'm not aware of any carrier that uses this approach (although outside the U.S., somebody might be).

It's an interesting question, but the costs & the math behind the engineering haven't worked out in its favor, at least thus far.


Does an increase in inlet temperature affect fuel flow and power output? The fuel flow rate decreases as the inlet temperature of the air entering the engine increases. Will the engine produce same amount of power as when the fuel flow was higher?

Most civil aircraft engines are "flat rated". See What is a flat rated engine?

That means, the thrust (power) produced is constant (flat), as ambient temperature increase, up to a certain temperature, and then the turbine inlet temperature limit is reached, and fuel flow and thrust is reduced as the ambient temperature continues to increase.

So, thrust is initially constant as inlet temperature increases, then decreases. It's a bit harder to predict what fuel flow will need to do to achieve this behaviour. It will certainly reduce in the temperature range where thrust is reducing, but in the cooler temperatures before that, it is probably increasing to keep thrust constant. As the chart shows, in this region EGT and N1 rpm are increasing. I expect fuel flow is probably showing the same behaviour as N1.

Thrust cannot actually be measured in flight, so most engines use either N1 rpm, or engine pressure ratio, (turbine exit perssure/engine inlet pressure) as a way to predict thrust. GE typically uses N1, whereas Pratt & Whitney and Rolls Royce usually use EPR. Using EPR is technically better, beacuse it will account for engine deterioration, where as using N1 assumes the fan mass flow remains the same for a given rpm as the engine degrades. But EPR requires 2 pressure measurements, which are less reliable, so most engines that use EPR have N1 control as a backup mode.  See
What is the difference between EPR and rotor speed as thrust setting parameter?


Could the SR-71 Blackbird be used for nearspace tourism? The Blackbird had two seats onboard. Could it be reactivated for nearspace tourism, placing a paying tourist in the other seat? If no, why not or why isn't it being proposed? In leveled flight, the Blackbird flew up to 90,000 ft (27 km) MSL and faster than Mach 3. In a ballistic parabola it could probably reach an even much higher altitude, and on the parabola's top you'd start to experience weightlessness, go above most of the ozone layer, see a black sky with some stars in daytime and the thin blue atmosphere of Earth. An exceptional experience for many.

Significant issues with the concept: the SR-71 lacks RCS, so you'd lose attitude control if you got significantly above normal operating height.  I originally wrote that it doesn't handle in-flight restarts well, but apparently it has the opposite problem -- it needs them all too frequently in normal operation.  It's also not an aircraft built for near-vertical climbs or high-G maneuvers, so a zoom climb is outside its normal operational envelope.
So, you can't demonstrate long (> 1 minute) periods of microgravity without the likelihood of loss of aircraft, crew, and paying passenger.  Beyond that, however, there's virtually zero visibility from the rear seat.  Who'd pay $100,000 for a "near space experience" with no zero G and no view of the black sky and curved horizon?
Never mind the fact that the SR-71 doesn't run on standard jet fuel (JP-1 or Jet-A); the engines could be retuned to do so, but then wouldn't continue to operate at 80,000 feet ASL or push the aircraft to around Mach 3 at that height -- in other words, it wouldn't do what an SR-71 is famous for doing.  And the special fuel the SR-71 requires hasn't been manufactured since the aircraft were retired -- it would probably cost more to restart production of that fuel than you'd make back in a reasonable twenty-year "space tourism" operating life (never mind cost of refurbishing an aircraft, pulling still-classified equipment out of at least the passenger seat, training new pilots -- oh, right, you'd have to refurb one of the trainers, that would at least solve the passenger visibility issue)...
Bottom line: no chance.  You'll get a better experience with the Russians; at least they can do a zoom climb and have RCS to point the nose back down so they don't wind up in a flat spin like the one Yeager had back in the day.


What are all the US airports where E4 "extensions" change to E2 and become part of a larger E2 "surface area" when the tower closes for the night? Of all the US airports with part-time control towers and with E4 "extensions", in which cases are the airspace definitions written so that the E4 "extensions" change to E2 and become part of a larger E2 "surface area" -- which also includes the airspace that was Class D during the daytime -- when the tower closes for the night?

With these 21 airports,  the airspace definitions are written so that the E4 "extensions" change to E2 and become part of a larger E2 "surface area" - which also includes the airspace that was Class D during the daytime -- when the tower closes for the night.

The page number references are for the FAA's "Airspace Designations and Reporting Points" document, FAA JO 7400.11C.  The page numbers listed are for the E4 airspace designation, the E2 airspace designation, and Class D airspace designation.

KENA or PAEN
AAL AK Kenai, AK
Kenai Municipal Airport
E-158, E-7, D-5
KGCK
ACE KS Garden City, KS
Garden City Regional Airport
E-159, E-17, D-7
KJEF
ACE MO Jefferson City, MO
Jefferson City Memorial Airport
E-162, E-21, D-11
KNHK
AEA MD Patuxent River, MD.
Patuxent River NAS (Trapnell Field)
E-165, E-28-29, D-15
KITH
AEA NY Ithaca, NY
Ithaca Tompkins Regional Airport, Ithaca
E-167, E-30-31, D-19
KPOU
AEA NY Poughkeepsie, NY
Dutchess County Airport, Poughkeepsie
E-167, E-32, D-19-20
KCXY
AEA PA Harrisburg, Capital City Airport, PA
Capital City Airport, Harrisburg
E-169, E-35, D-22
KLNS
AEA PA Lancaster, PA
Lancaster Airport
E-170, E-35, D-23-24
KRDG
AEA PA Reading, PA
Reading Regional/Carl A. Spaatz Field, Reading
E-170, E-36, D-24
KUNV
AEA PA State College, PA
University Park
E-171, E-35, D-25
KIPT
AEA PA Williamsport, PA
Williamsport-Lycoming County Airport
E-171, E-37, D-24
KLYH
AEA VA Lynchburg, VA
Lynchburg Regional-Preston Glenn Field Airport
E-172, E-38-39, D-26
KNTU
AEA VA Oceana NAS, VA
Oceana NAS (Apollo Soucek Field)
E-172, E39-40, D-28
KAPN
AGL MI Alpena, MI
Alpena County Regional Airport
MI E-176, E-45, D-36
KMKG
AGL MI Muskegon, MI
Muskegon County Airport
E-177-178, E-48, D-39
KRST **
AGL MN Rochester, MN
Rochester International Airport
E-178, E-54, D-41
KSTC **
AGL MN St. Cloud, MN
St. Cloud Regional Airport
E-178, E-54-55, D-41
KGFK
AGL ND Grand Forks, ND
Grand Forks International Airport
E-179, E-56-57, D-42-43
KILN **
AGL OH Wilmington, OH
Wilmington, Wilmington Air Park
E-181, E-59, D-46
KRAP **
AGL SD Rapid City, SD
Rapid City Regional Airport
E-181, E-61, D-47
KPRC
AWP AZ Prescott, AZ
Ernest A. Love Field
E-210, E-129, D-140

** means that in these 4 cases, no limit on the effective hours is given for the E4 airspace - apparently it is simply assumed that the E4 will be superseded by the E2 whenever the E2 is in effect.

Among airports with part-time control towers and with E4 "extensions", the style of airspace designation that is much more common over the nation as a whole is for the E4 airspace to be in effect 24/7, and for only the Class D airspace to change to E2 when the tower closes for the night.  Here's an example of such a designation:

KMFR
ANM OR Medford, OR
Rogue Valley International-Medford Airport
E-189, E-80-81, D-64

Note that there is no way to tell one style of designation from the other just by looking at the sectional chart or the Airport/ Facility Directory.  Perhaps this may be taken as a hint that the distinction rarely matters in actual practice.

Note the uneven distribution of the airports in the list above among states and regions.  For some reason, in some regions such as the northeast, the style of airspace designation that we're discussing here is actually more common than the style that we see at KMFR.

To understand why the distinction between the two styles of airspace designation might matter, at least in theory, to pilots flying at first light before the tower is open for the day, including ultralight flight, aerobatic practice, non-recreational sUAS (drone) activities, and possibly now that the FAA is implementing some new regulatory changes, recreational sUAS (e.g. RC model airplane) activities, see the first two links below.  Whether this distinction has ever yet mattered in actual practice is an open question-- perhaps in actual practice the airspace in these extensions is simply treated as E4 airspace 24/7 in relation to FARs 91.303c, 103.17, and 107.41.  Nonetheless, pilots of such aircraft would undoubtedly hope that this unusual style of airspace designation is avoided in the future.

It is interesting to note that on the FAA's LAANC map for authorization for sUAS (drone, model airplane) flight, these projecting E4 extensions that change to E2 when the tower is closed at the 21 airports listed above are NOT covered by the grid squares that indicate the areas where pre-authorization is required.  This supports the idea that these extensions are simply treated as E4 airspace 24/7, at least in relation to FAR 107.41.

Unlike what is implied by the actual language of FAR's 91.303c and 9.155c, it seems unlikely that the distinction between the two different styles of airspace designation has ever mattered in actual practice to a pilot seeking to obtain a Special VFR clearance, or planning to fly beneath a cloud ceiling below 1000' AGL without obtaining a Special VFR clearance.  See the third and fourth link below for more.

For more, see these related question or answers:

Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?
What is the primary reason that the non-towered airports KACV and KTLV have E4 extensions to E2 airspace?
In actual practice, do ARTC Center personnel generally follow the rule that a SVFR clearance may be granted in E2 airspace but not E4 airspace? (US)
In the US, is there much variation among the various ARTC Centers as to where a SVFR clearance may be granted?
Does an SVFR clearance extend to Echo surface extensions?
Does an SVFR clearance extend to Echo surface extensions?
Does FAR 91.155c apply to class E surface extensions?


What does ''NAV ILS OUT OF SERVICE'' mean? Just curious about the NOTAM below:

  !SMF 01/045 (KSMF A0080/19) SMF NAV ILS RWY 16L OUT OF SERVICE
  1901180419-1901262359

Does that mean only the glideslope is broken so we can still do a LOC approach, or are both the localizer and glideslope broken?

It means exactly what it says. The ILS is out of service, so you can't use it.

An ILS can consist of several different elements, for example localizer, glidepath, DME, inner/middle/outer markers as well as a bunch of technical monitoring equipment, ATC control panels, warning systems and backup power supplies. Should any of these components fail, it may be required to take the entire system out of service. The NOTAM doesn't say exactly which part of the ILS is broken, but that doesn't matter, since the entire ILS is listed as unavailable. So no, you cannot expect to use the localizer.


How long is the training to get a Boeing 777 rating if one has a 737-200 rating? I was wondering if anyone knows how long the training for a 777 takes if one already holds a 737-200 rating.
I've looked it up online and didn't find an adequate answer.
According to this site, the course for 777 PIC initial certification takes 21 days (48 h) and the course for 777 PIC recurrent certification takes 4 days (16 h), but there's no mention of anything regarding previous ratings.
Here, someone says they think that to go from the 737NG to the 777 would only take 3/4 sim sessions, and someone else says that the course to go from 737NG to 777 is shorter than the course to go from 737-200 to 777.

Does anyone know how many days the "conversion" course would take?

Am I correct to assume one doesn't have to take the full 777 initial certification course if one holds a current 737-200 rating?

And what if the 737-200 rating is no longer valid... does one have to take the full 777 initial certification course?

Thanks a lot

A flight school can offer an "abbreviated type rating course" which takes into account skills from previous type ratings, assuming you have flown an adequate number of flight hours on those ratings.

Boeing also offers a shortened type rating course, details are halfway down their page. To answer your question, Boeing claims 13-15 days for their training and requires 1,000 hours of experience, but it does not depend on a specific rating. There is an even shorter 777-787 conversion as well, that requires a 777 rating.

I think their assumption is that they can skip a lot of basic handling, CRM, checklist type training and focus on the technical aspects. A training provider with the proper approvals could offer a similar class.

Also, for reference, there is the Airbus A320-A330-A340-A380 conversion training which uses the proprietary term "cross crew qualification", and takes less than 2 weeks versus 6 for a full rating. This is done under a EASA approved syllabus, which allows you to do it at any qualified school. Here the requirements are 150 FH on the appropriate Airbus type, and 3 months of experience.


What are the requirements for foreigners to join the RAAF as a fighter pilot? What are the requirements for a foreigner (personally I'm from Cyprus) to join the Royal Australian Air Force to become a fighter pilot?

Only citizens of a country can apply in the government jobs (including armed forces) of that country. There can be some exceptions but I hardly doubt that a foreigner can be hired or trained for any position in military which has access to classified information. Being a fighter pilot even has more restrictions.

Royal Australian Air Force does not hire any foreigner:

  Can I apply if I am not an Australia Citizen?

  To be eligible to join the Air Force, you must be an Australian
  Citizen.

According to Recruitment Centre of Australian Defence Force, this page lists the proofs required for citizenship.


What is this intake at the back of a 737? I've circled an intake in red on the images below. I am working on a 737 NG and I don't know what it's for. I am thinking it's a pressure probe for APU control but I am not sure.

Source

Front view: comparing location to aft door confirms it's the same "device." (Full image.)

The APU insulation panels are not easily damaged, however, it the panels are punctured, you should repair the damaged panel as soon as possible. If you do not repair a puncture immediately, the panel can store fluids in the insulation. If fluids get into the insulation material, you must replace the panel. The air inlet scoop replaces the foam and support insulation (egg crate) that were installed between the APU insulation panels and the bulkhead. During an airplane operation, the air inlet scoop supplies forced outside air through the empty space between the APU insulation panels and the bulkhead for ventilation and for the removal of flammable or unwanted fluids. The location of the air inlet coop is behind the forward insulation panel and adjacent to the forward right side of the APU cowl door.

Source: Boeing training manual