Where is there an FAA source that states that squall lines are non-frontal? There's a question in the FAA commercial question bank that indicates that squall lines are nonfrontal, and the reference for the question points to the Aviation Weather Advisory Circular.
The word, "nonfrontal" (or any variation of it ie "non-frontal") does not appear in that document.  Also, the word "squall" appears four times, and none of those seem to have information that indicates that they are nonfrontal.
Where is the FAA providing this information?  Is it actually correct?

If you go back and look at the previous version of that AC, AC-006A, the index has this definition:

squall line - Any nonfrontal line or narrow band of active
thunderstorms (with or without squalls).

I guess that the question in the question bank was based on AC-006A, which was current until 2016. As for today, chapter 12 of the PHAK has a slightly different definition (p.12-23). It says that squall lines are not necessarily frontal:

Squall Line
A squall line is a narrow band of active thunderstorms. Often it develops on or ahead of a cold front in moist, unstable air, but it may develop in unstable air far removed from any front.

If you need more detailed information on squall lines and fronts you may get a better response on earthscience.SE.


Is there any specific location on airframe for gaining higher drag? I have a model rocket and I want my rocket to reach specific height above the ground level. As soon as desired height is reached, an air brake (umbrella type) is allowed to deploy. In order to have higher drag, what is the best position for the air brake? Will I obtain same drag if the air brake is below or above the Center of Gravity (CG)? Is Cd different for different locations of the air brake (having same surface area)?
Note: Although this question is about a rocket, this really has to do with aerodynamics.

If you want to arrest ascent you put the airbrake behind/below the CG.  Keep in mind the rocket will tend to remain flying "nose first", which may affect parachute deployment (from nose) on the way down.
Notice the Space X Falcon 9 has theirs near the nose allowing the rocket to descend tail first, and are only deployed once the rocket has coasted to maximum altitude, slowed down, and has begun to fall. Nearer to the ground, you use retrorockets and/or parachute.
For a high altitude sounding rocket, it may be preferable to delay parachute deployment, lest the wind carry it too far away from the launch point.


How can I estimate the minimum runway needed to take off with a hang glider? I'm interested in short, or trick, take-offs - such as from platforms, tall trees, etc.

I think that I should have

a wind speed and direction measure
an understanding of my wing surface area

This will let me add to my intuition from regular launches (from sites with known-good launch conditions), and estimate how much velocity I need to add via a run / push.

The methodology to count the wind measure seem a bit more grey, right now.

I can have a sense of the wind where I am, but it may quickly change beyond my launch site.  Since I'm considering how to launch from a stationary position, it would be good to feed my senses / calculations more data like this.

What you need is enough lift to remain in the air. For that, the maximum lift of your hang glider needs to exceed the total weight.

When you know the total weight of the glider (you included), you can derive the theoretical minimum airspeed from the lift formula:

$$L_{max}=\frac12{\rho}V^2C_{max}S$$
$$V_{min}=\sqrt{\frac{2W}{{\rho}C_{max}S}}$$

Where:

$L$ = lift
$\rho$ = air density
$V$ = air speed
$C_{max}$ = maximum lift coefficient
$S$ = wing surface
$W$ = weight

Now you have to know your maximum lift coefficient. Suppose this is 1.2, and for safety and initial manoeuvring, let's add a margin of 40% to the weight.

Let's say your mass is 85 kg, and the glider has a mass of 35 kg. The total weight would be 120 kg — that is about 1,177N weight, which for the sake of safety margin is increased to 1,650N.

I'll estimate the surface of the wing to be $16m^2$. Assume a normal day, the air density will be about $1.225kg/m^3$.

Filling in the numbers is the formula:

$$V_{min}=\sqrt{\frac{2\times1650}{1.225\times1.2\times16}}\approx 12 \textrm{ m/s}$$

Any wind speed you get you can subtract from this figure: what is left you have to achieve by pushing, running or diving.


What is the role of a flight control computer during a steep approach? I am working on a flight control computer (Bombardier) where I got a bunch of requirements for steep approaches. All they do is 'engage steep approach' or disengage it after determining if it is safe to engage the steep approach.

Even after engaging the steep approach, if the pilot does not configure the flight properly (throttle, flap, slat settings) then it disengages the steep mode and informs the pilot.

After carefully going through the requirements, I did not find anything that the flight control computer does during the steep approach.

So is all that the flight control computer does during steep approaches to monitor it and display steep engage or disengage messages?
What would a pilot do if steep approach was to disengage when he reached below 200 ft? (Breaking off from steep approaches, I understand, is the result of losing some of the sensors, jamming of actuators etc..). Can a pilot 'go around' even if the altitude drops below 200 ft (decision height of CAT I landing)?
Is there a possibility for the aircraft to stall while trying to descend steeply?

On the Airbus 318, it appears that the flight control computer does more than just monitor and handle annunciators.

  In March 2006, the European Aviation Safety Agency (EASA) certified a modified control software enhancement to the Airbus A318 designed to allow the aircraft to perform steep approaches. The aircraft is the largest commercial aircraft certified by EASA for steep approach operations. The software modifies the control laws of the aircraft when the steep approach function is selected by the crew, by automatically deploying some of the spoiler panels to provide additional drag when the aircraft is in the landing configuration. It also provides alternative aural alerts to the crew and modifies spoiler deployment automatically below 120 feet (37 m) on landing. The A318 steep approach procedure allows the aircraft to perform approaches at descent angles of up to 5.5°, as opposed to the standard 3° for a normal approach.

A318 Wikipedia

The answer to your question #2 can be found in the aircraft operations manual.

The answer to your question #3 is that an aircraft can stall at any attitude and configuration. A stall is when the critical angle of attack for the wing is exceeded.


Will the Boeing 737 MAX 8's software update require recertification of the aircraft? Will the upcoming software update for the 737 MAX require the plane to go through a new certification like a new plane?

Nope

Updates like this are generally deployed under an Airworthiness Directive ("AD") and in this case will likely be required although not all AD's technically are. AD's are issued against Type Certificates or serial number ranges, or possibly even individual parts. They are publicly published and when it becomes available the FAA will post it here.


What are the process involved in tire rotation during long term storage? During Covid-19 crisis in 2020 a lot of planes are grounded for a long time. Tires of parked planes can develop flat spot hence the need to keep these tire rotate. What are the processes involved regarding tire rotation during this time?
Is the plane towed 100 feet every week or rotate each tire 45 degree every day or something else?

Aircraft with tire marking.

Source: https://www.facebook.com/media/set/?set=a.1908245919474139&type=3

Manufacturers give the manual for storing/parking periodic ground check.

For Airbus A320 family:

  You can ignore this step if you moved the aircraft for the APU start.

  Turn the wheels by 1/4 turn to prevent damage to the tires:

  a) Move the aircraft Ref. AMM xxxx or b) Refer to the jacking for
  wheel change procedures to turn each wheel separately

This is done if storing is more than 15d, and repeated once every 15d.


What is the difference between Boeing 777-31H and Boeing 777-31H(ER)? What exactly is the difference between a B777-31H and B777-31H(ER)? Is ER the latest version of 777-31H?

The 777-31H is a standard Boeing 777-300 manufactured for Emirates (customer code 1H).

The 777-31H(ER) is a Boeing 777-300ER (Extended Range) again for Emirates.

Compared to the standard 777-300, the 777-300ER has:

A longer range due to the extra fuel it can carry (145538 kg compared to 135880 kg for the -300 baseline)
A higher Operating Empty Weight (167829 kg compared to 159570 kg for the -300 baseline)
A higher Maximum Take-Off Weight (351535 kg compared to 299370 kg for the -300 baseline)
A higher maximum structural payload weight (69853 kg compared to 64960 kg for the -300 baseline)
A wider wingspan (64.80 compared to 60.93 m)
A different engine delivering more thrust

The Boeing 777-300ER is always equipped with General Electric GE90-115BL1 engines, while the baseline -300 can be ordered with four different engine models from General Electric, Pratt& Whitney or Rolls Royce. The Emirates Boeing 777-300 aircraft have the Rolls Royce RR Trent 892 engines installed. They deliver 415 kN of thrust, almost 100 kN less than the GE90-115BL1 engines.


How does the aviation industry train and certify English proficiency? How does the aviation industry (pilots and ATC in particular, as opposed to cabin crew) train and certify English proficiency? Do they use classes and examinations associated with general-purpose English training, or ones specifically associated with the aviation industry?

I heard several years ago from Air Crash Investigation that a contributing factor for the Avianca Flight 52 crash was the use of the wrong terminology in communication between the non-native speaking pilots and the ATC.

Proficiency in English is something very much required in aviation. One other major accident I remember is the Charkhi Dadri mid-air collision, which resulted in 349 fatalities, and one of the major reasons was believed to be the poor English of Kazakh Airlines crew.

Keeping such importance of English in mind, and the need to standardize English testing and training, the ICAO  has issued Guidelines for Aviation English Training Programmes.

Training

Candidates are trained for Aviation English in a very similar way to it would be for any other purpose, other than ensuring the following points:

Use of operationally relevant, work-related language.
Exposure to an aviation environment.
Practical training activities such as Listening practice in ATC lab.

Testing

The Test of English For Aviation is a test Developed by Mayflower College in accordance with ICAO's ratings.

Here is how the candidates are tested in TEA:

TEA candidates can score from Level 1 to Level 6 but most candidates score Level 3, 4 or 5. Candidates are awarded a mark from 1 to 6 for each of the 6 skills: pronunciation, structure, vocabulary, fluency, interactions, comprehension.

Read this document


Hypothetical - Basic Med & Insurance I have a friend that needs some info...

He has a Basic Med certification in hand.  He takes a drug that is on the DNI list however it is admissible with a SI (SSRI).  His GP doctor signed his Basic Med form.  His GP doctor obviously knows the drug he is on and knows he is fully functional on the drug.  His GP doctor knows the drug is on the DNI list.

Given that background...

Would he have any possible insurance issues (renters or owners) if he were to ever get into an incident?  Could the insurance company deny a claim if he takes the drug even with a doctor's approval but WITHOUT the SI?

Thoughts?

BasicMed does not completely do away with SI's so your buddy may still need one if he has never had one and has one of the 4 qualifying issues.

To directly answer your question the insurance company may deny a claim on these grounds as they are somewhat free to deny claims as they see fit. There is some more info from the FAA related to SSRI's here. Remember that basic med is about considering yourself fit to fly and being self conscious of your current state it does not set any protections for you that once you deem yourself fit to fly you actual are. Its a fairly new rule so only time will tell how cases play out in the future relating to issues.


What are the consequences of hail damage to a small GA plane? I recently found a Cessna 172 that had been totaled by the insurance company because of hail damage.

The PDF from that page has detailed pictures which show hail-divots all over the the wings, body and empennage.

Can the plane still fly like this?

What effect is this likely to have on the flight characteristic of the plane?

Like anything in aviation, it depends...

There are a lot of discussions on the internet about it you can find

Here (mooney)

Here (cessna)

And Here

It is a case by case situation and depends on the extent of the hail damage and what/where the damage occurred. In many cases the issue crops up that you can not simply bang the dents out you would need to reskin the panel. This can, depending on the aircraft be a costly process.

There are planes out there flying with light hail damage and it causes no problems, in many cases its purely cosmetic. A lot of planes flying out there have other similar damage (tool drops, bird strikes, impacts from rocks etc) and fly just fine.

An good A&P would most likely be able to tell you if the particular Cessna in question is still airworthy.


How can a helicopter show up at 29000ft, 547kts at Flightradar24? Today I observed a strange flight on Flightradar24, a helicopter departing HAM and traveling at altitudes up to 29000ft and speeds up to 547kts which seems to be way beyond the specifications of a helicopter.1

The altitude and speed were quite constant on this level between Hamburg (ATD 16:15) and Frankfurt (about 500km from Hamburg, after 30 minutes flight) and then it began descending and slowing down.

The details in normal resolution for better readability:

About 17:00 the symbol didn't move anymore and the helicopter was now down on 2875ft and 177kts near FKB (Karlsruhe Baden-Baden) and then disappeared.

I checked the registration and is indeed the Agosta Westland AW139 shown on the picture.

Does anyone have an idea how this could be. Usually, the data on Flightradar seems to be reliable, but a helicopter at 547kts seems odd.

1. According to Wikipedia the Agosta Westland AW139 can travel up to 306km/h (165kts) and has a service ceiling of 20000ft.

edit: speed was 547kts, not 247, added image with details.

@mins answer contains good information, however the conclusion that the mistake is in the Flightradar 24 database is not correct.

It is not Flightradar 24 that has a database error:

  30040D IS I-PTFT it is NOT I-MOFI F2TH I-MOFI is miscoded on one box
  and using 30040D incorrectly. I-MOFI is 30047D please change it back!
  Why was it changed in the DB when I-MOFI was correct in the DB, I
  thought miscodes were not allowed anymore?

What this says, is that the 24 bit Aircraft Address (a.k.a. the Mode S address) 30040D belongs to the aircraft with the registration I-PTFT.

The registration I-MOFI has the 24 bit address 30047D, but the quote says it is miscoded on one box (transponder).

Flightradar 24 receives the Aircraft Address with the ADS-B messages from the aircraft and uses the database to find the aircraft associated with the address.

From the screenshot it can be seen that the address they receive is 30040D. In their database, this is correctly linked to the I-PTFT helicopter.

The fault is with the aircraft with registration I-MOFI; it transmits the 24-bit address 30040D while it should have transmitted 30047D. The transponder has the wrong 24-bit address encoded into it.


What are these circles below the wing? There are some circles below the wings of these two aircraft. Look:

Source: Airliners.net (modified)

Source: Airliners.net

On the second picture the circles are clearly visible on the wing. What are they? What is their purpose?

In the US, those are called either "Access Panels" or "Inspection Covers", depending on their function, but many people combine the two terms and call them "Inspection Panels". Based on the comments, other parts of the world apparently refer to them as "Inspection Ports".

We remove both panels and covers to perform routine inspections, but access panels cover system components that may be accessed more often for servicing. Both panels and covers are designed for quick removal, typically fastened with screws, as is the case in the aircraft depicted in the photos above.

Here is an inspection hole with the cover removed. This is on a Cessna 170 that I am in process of rigging. Note the aileron cable turnbuckle visible inside the wing. Through this access panel I will adjust the cable tension, among other things, and once the cable is properly tensioned I will safety wire this turnbuckle. Here the panel is removed for maintenance, but during an inspection I would remove this panel to inspect these same systems.


How is wind direction reported (blowing from or blowing to)? When the tower controller, the ATIS or a METAR says Wind 270, 15 knots does it mean the wind is blowing in the westward or in the eastward direction?

Is there a single convention used to express the wind direction?

As far as METARs are considered, the wind direction gives the direction from which the wind is coming. From METAR definitions:

Wind Direction.
The direction, in tens of degrees, from which the wind is blowing with reference to true north.

So, Wind 270 shows that the wind is coming from west.
The reporting in ATIS and tower is the same, only difference being that the reference is magnetic north, while it is true north for METAR.


Is there a database containing detailed information about airfields and runways? Does an electronic database containing the various civil runways in a given region of the world exists?

Maybe even categorized by type (e.g., grass vs asphalt), length, if controlled or not, etc.

If it does not exists, what would be the effort related to creating one?

As Danny Beckett mentioned in comments, OurAirports has such data, but there is a "use at your own risk" disclaimer. May any source be reliable and trustworthy or will I find such disclaimer on all sources?

The FAA publishes the NASR database. This is an official, authoritative data set that covers all airports, airways, routes and navigation aids under FAA jurisdiction. The data files are not human-readable though and require special software to display.
Other civil aviation authorities in other countries have similar products. Some are available for free, some are not. Many countries claim intellectual property rights on their data and it can be quite difficult to get at/use it.
Some companies like Jeppesen do this collection for you: they have agreements with aviation authorities, obtain each authority's data sets (like the FAA's NASR linked above), and compile all of them into a single large database. This database is then reprocessed in forms usable by avionics like GPS receivers or Flight Management Systems (FMS). These countries charge a significant fee for this service, and there are licensing terms that limit your use of the data. The fee is substantial depending on the format you get the data in (up to thousands of dollars or more for FMS systems for large transport aircraft) and puts the dataset out of reach of a casual user.
The U.S. Department of Defense publishes the DAFIF which is a similar compilation of worldwide data. This database used to be available publicly for free, but is now restricted to Department of Defense personnel (it is not classified but it is not available to the public).
There are many websites based on one or more of the datasets above, but as noted in comments, these websites are not official or authoritative. They also generally have their own license terms that limit the way you can use the information and that prevent you from downloading the database in bulk. This all stems from the intellectual property claims made by many civil aviation authorities. It costs countries a lot of money to maintain the data and they want to be able to generate some revenue from it.
So the bottom line is that for some regions like the United States, official data is readily and freely available; for other regions, not so much. (And among developed countries, the U.S. is the exception; most do not offer their data freely.) To get data for these other regions, or to create a global dataset, would involve a lot of effort and money (beyond the reach of a normal individual). Companies that do this work for you charge hefty fees to provide the data to you.


Why is on-time performance important for commercial flights? From the perspective of an airline, is it just to avoid penalty and also to portray reliable service to the customers?  Or is it just a matter of logistics and scheduling?

I can think of a few:

Any delay in the flight is a waste of valuable resources- the flight, cabin and ground crew who have to be paid and the aircraft itself, which is not generating any revenue but costing money for the airline. Also, the airline may have to pay for the time the aircraft spends in the airport.
There is an economic cost associated with on-time performance- for example, passengers are more likely to take airlines which have better on-time performance over others.
Another case is that of customers taking connecting flights- again, on-time performance could be the difference here. This means loss of business for the lower performing airline.
For airlines operating multiple trips per day, the delay and the associated costs are cumulative; for example, if the first flight of the day is delayed, it snowballs into the day- requires replanning for the rest of the day in other airports and causes further delays.

For the airline industry, the delays cost billions of dollars every year (1 and 2) and can reduce the operating revenues by a few percentage points (3). The table below, taken from the NEXTOR report on Total Delay Impact Study shows the cost to US airlines due to delays.

As can be seen, the the costs due to delay to airlines are quite high.


Do airplanes have sensors to detect landing gear fires? Given that retracting a landing gear that happens to be on fire is a suicidally bad idea, for reasons that should be immediately obvious, do airplanes have temperature sensors on their landing gear in order to detect landing gear fires and prevent burning landing gear from being retracted?

There are fire detection heat sensing loops in the gear well.  If a gear was on fire it would trigger a "GEAR OVERHEAT" message and warning when the gear was up.  There are no retraction prevention systems that are able to detect fires at the gear.  Nationair was a unique series of clusterflarks leading to the accident, on top of the fact that the magnesium wheels started to burn.  Modern magnesium alloys don't do that.


How difficult is it to design a high bypass turbofan given a military derived core? Suppose one of the big-threes is given a military low-bypass turbofan core, how difficult would it be to produce a design centered around this core that matches the competitive performance of a similar brand-new design? What parts are new aside from the fan? Does it need a new LP compressor and LP turbine? Can you safely crank up the overall pressure ratio, confident in the fact that the original design's tolerance for supersonic flight would mean the HP compressor has the ability to take the heat of higher compression subsonic flight and hence needs no modification at all?

As of 2015, the #1 selling jet engine, the CFM56, is exactly that.

The core is from the General Electric F101, which powers the Rockwell B-1 Lancer no less.

The development was shrouded in secrecy, and politics were involved, and at least at one point only the Americans had access to the core details, while the French built around it (the new LP spool – which does include the turbines).

  Engines assembled in France were subject to the initially strict export agreement, which meant that GE's core was built in the U.S., then shipped to the Snecma plant in France where it was placed in a locked room into which even the President of Snecma was not allowed.

The linked Wikipedia featured article is a must read, and trying to summarize it here wouldn't do it any justice. But yes, it's not only possible, it's been done. Judging by the specifications, the civilian CFM56 has higher OPR (a jump from 26.8 to upwards of 27.5–38.3 depending on the variant).

According to the image above and this webpage, technology from the CFM56 fed back into the F110, which went on to power the F-14, F-15, and F-16.


Does one-engine cruise consume less fuel than two-engine cruise? Scenario 1. A two-engine airliner experiences rapid depressurization and makes an emergency descent to 10,000 ft, and diverts to the nearest airport.

Scenario 2. The same two-engine airliner experiences rapid depressurization after it has lost one of its two engines and makes an emergency descent to 10,000 ft, and diverts to the same nearest airport.

In which scenario between the two does the airliner consume a greater amount of fuel, and why?

For an A320, at FL 100 and weight 50 tonnes and ISA, the FF is 1028 kg/h per engine, so two engines is 2056 kg/h.

Now for the same but OEI: the FF is 1891 kg/h (just the one engine).

Scenario 1 is higher fuel flow rate. I'll explain why based on scenario 2.

In scenario 2, with one engine inoperative (OEI), the remaining engine will run at higher power setting, which improves the SFC (see image below), and therefore will improve the endurance (time in the air; how fast the fuel is used).

► It will diminish the range though, as range requires speed, which will be limited with OEI (and also due to the low altitude), i.e., don't mix the improved FF and endurance with why not always fly with one engine (ignoring the safety issues).

Source: Jet Transport Performance Methods, Boeing

(Don't miss the text left of the graph.) That's also why coast guard C-130s orbit with an engine deliberately turned off. Being a turboprop (gas turbine), the SFC relation holds.

Related: Why is max endurance different for jet and props?


Why are most helipads in São Paulo blue coated and identified by a "P"? ICAO Annex 14, Vol II and FAA (AC 5390-2C) standards establishes 'H' and there is no mention to coating TLOF or FATO.
Brazilian National Regulation (RBAC 155 - ANAC) does not provide any guideline for the blue painting.
I would like to know where this common São Paulo helipad pattern comes from.

Examples:

Google Maps (1)
Google Maps (2)
Google Images

According to the Rules for Heliports in Sao Paulo, the P means that it is private heliport. H for public Heliports,  M is for military. Hospitals use the letter H on a red cross, also when they are private or military hospitals. Examples are given in the pictures below.
It seems that the color blue is not required by the regulations; there are various other colors used in Sao Paulo (see a few examples below I found on Google maps).
I think blue is used mostly because it provide good visual contrast with the white or yellow markings. White paint on concrete can be difficult to see under bright sunlight conditions. The blue color also stands out from the urban environment, making the helipads easy to spot from the air. Try it on Google maps; the blue helipads are relatively easy to find on the satellite view.
This video explains the markings (in Portuguese)

Hospital helipad with H marking and red cross

Military helipad with M marking

Green helipad with circular border and 05 Marking

Concrete helipad with circular border and 05 Marking

Red private helipad

Green private helipad
All images are screenshots from Google maps


How much water is carried for jet engine water injection? An answer on a related question stated that water injection was used on some of the early jet planes, for example Boeing 707 and Boeing 747-100/200.

I presume the water is stored in some tank. How much water is typically carried for this? And given the water flow rate, what is the usual water injection time available before water runs out?

This paper here gives a good overview of water injection.

It suggests for injecting water into the compressor, a 300 gallon tank is necessary, for a 2.2% water to core air flow ratio (the historical norm), for injection from take-off to top of climb.

For injecting into the combustor, it suggests a 135 gallon tank, for a 0.5:1 water to fuel ratio, again for injection from take-off to top of climb.

For both of these scenarios, the tank water flow rate was designed to achieve a 50% NOx reduction. The paper gives other water quantities required to acheive different goals (eg different NOx reductions and different turbine temperature reductions).

I don't think the paper indicates how long it takes to get to top-of-climb. I assume these are US gallons, as its a US paper.


Why the use of twin tails? On a number of aircraft such as the:

Antonov 225:

A10:

F35:

Use twin tail designs. I understand for military aircraft that the benefit is it allows for a small tail cross section. Reducing the chance of it being damaged in combat.

In the case of the A225 and other similarly designed cargo aircraft it means the rear of the aircraft can be more easily designed as a cargo hatch.

Are there any other reasons why a twin tail design is preferable over a single tail design?

This constructive solution can be dictated by a number of reasons:

Aerodynamics - for AN 225, 747 Shuttle Carrier Aircraft, A-10 (control surfaces are more effective outside turbulent air);

Some sort of redundancy - for military airplanes F-35, A-10;

Easier construction - since the surface being smaller aerodynamic loads are smaller the structure can be lighter wight;

Radar cross section - F-35, SR-71;

Stability considerations: the arm for the vertical surfaces is a little longer than the arm of a potentially single surface on the longitudinal axis of the aircraft, so the two vertical surfaces combined can have a less surface area than a potentially single surface.


How to compute the change in static temperature using only altitude? I'm given an initial altitude of FL290 in ISA conditions, and the aircaft is said to climb to reach FL310. How can I use this to calculate the change in static temperature between the two flight levels?

I know that the formal term is the lapse rate and generally lapse rate decreases around 2 degrees Celsius per 1000 feet of climb.

Would I use a ISA temperature table to figure out the temperature for the initial altitude and then use the lapse rate to calculate the change in temperature when it climbs to reach FL310?

I found the answer, it's literally looking at ISA temperature table of the initial FL. The lapse rate is 2degrees per 1000 feet of climb. You would see what the initial temperature is for your FL and then you minus the lapse rate for the climb that you are given. So in this case, the lapse rate would be 4degrees as it climbs 2000 feet.


When is aileron trim used? There is an aileron trimmer in some Boeings. When and why should it be used?

P.S. I'm not a pilot, can you answer with less smart words?

Given your request to "answer with less smart words," it's hard to know what knowledge can be assumed, but I'll give it a try.

Let's say you're hand-flying the airplane straight and level, and you find that the right wing keeps wanting to drop, which you prevent by using left-aileron pressure on the control yoke. You can "trim out" the need for that left aileron pressure by rotating the aileron trim to the left (counter-clockwise).

Aileron trim is not often used for the simple reason that in normal aircraft operation, it's usually set where it should be from the previous flight.  In other words, you don't fuss with it unless you notice a need to fuss with it. In 12 years on 727s and 747s, I think I used aileron trim less than a dozen times.

The reasons that I can think of offhand that would make you want to fuss with it include:

The trim wheel was inadvertently moved (or deliberately as a bit of a prank) by someone.
A fuel imbalance has occurred between the fuel in the left and right wings.
You're doing a 3-engine ferry on the 747 or continuing a flight after having lost an engine.

To the best of my knowledge, all Boeing aircraft have aileron trim capability, not just some. Indeed, I would be surprised to find any transport category aircraft that does not have aileron trim capability.

Essentially, aileron trim can be used to to keep and airplane from responding to a situation where one side of an airplane is significantly heavier than the other side.


Can I choose whether hobbyist or Part 107 rules are more advantageous when flying a UAV for fun? According to the FAA's UAS getting started page, if I'm flying a drone for fun within a 5 statute mile radius of an airport, I need to contact the airport and any air traffic control tower before flying. As a Part 107 pilot, I can fly a drone in class G airspace up to 400 ft AGL (or over a structure) without having to contact anyone.

I have a current Part 107 remote pilot license. To me, this makes my ability to fly a drone more flexible.

If I want to fly for fun within 5 miles of an airport and the airspace is class G, I can decide I'm flying as a Part 107 remote pilot and then I don't have to contact ATC or the airport.
If I want to fly for fun within a surface non-class-G area, I can decide that I'm a flying as a hobbyist and contact ATC and the airport if I'm within the 5-mile airport radius, no airspace authorization necessary. This is a no-go if ATC says no, but otherwise a lot faster than applying to the FAA for a waiver to fly in controlled airspace.

In either case, I would ensure that I'm not anywhere near other air traffic, and that I fly safely.

When I'm flying for fun, can I pick and choose as to whether I fly as a hobbyist or a Part 107 pilot?

According to the FAA's own FAQ, you can do either (emphasis mine):

  There are two ways for recreational or hobby UAS fliers to operate in
  the National Airspace System in accordance with the law and/or FAA
  regulations. Each of the two options has specific requirements that
  the UAS operator must follow. The decision as to which option to
  follow is up to the individual operator.

  Option #1. Fly in accordance with the Special Rule for Model Aircraft
  (Public Law 112-95 Section 336). Under this rule, operators must:

  [...]

  Option #2. Fly in accordance with the FAA's Small UAS Rule (Part 107).
  This requires operators to:

  [...]

So, it's your decision. But as always, ask yourself first how you would justify that decision to the FAA if something goes wrong. As a certificated pilot, you actually have something to lose if the FAA decides to take action against you.


Did these pilots break any regulations by hand-flying an A320 for most of the cruise? A couple of days ago, I flew with a popular budget airline within Europe. The aircraft was an A320. It was also a brand new one (only in service since June 2018 and produces 15% less noise and fuel emissions than previous models, or so they told us).

Anyway, onto the question. During the flight, I asked a member of CC if I could meet the pilots after landing, they asked for me and the pilots agreed. They seemed happy to have a chat, I asked them how much hand-flying they had done on the 3 hour flight we had just completed (after reading on here the average for this type is 3 - 7 minutes per flight). The captain sheepishly grinned and pointed at the FO...I turned around and he was laughing. The captain then told me that since the weather was so nice, the FO, who was still fairly new, asked if he could take control. Turns out he ended up hand-flying most of the cruise!

The captain then assured me that pilots don't use passenger flights to 'practice' their skills however, and that it was actually permitted and encouraged by this airline.

I thoroughly enjoyed the 'insider' knowledge of that flight and didn't mind one bit whether the pilots chose to use auto-pilot or not, but my question is - was this actually permitted? I have read, on this site, that the A320 has specific instructions in the manual that pilots must engage auto-pilot after 10,000 ft until approach.

I think they were humouring you Cloud.  Hand flying a jet at level cruise speed is not fun.  It takes a lot of concentration and the novelty quickly wears off, and there is a high risk of getting busted for an altitude deviation due to a little bit of inattention. Even if you are able to find a sweet spot with the trim where it holds altitude perfectly with no stick pressure, making you think you can relax a bit, all it takes is a temperature change or running into a bit of mountain wave and airplane will climb or descend and if you are distracted.. and drift up or down a couple hundred feet... busted.  RVSM legalities aside, I can't believe even a bushy tailed FO would hand fly more than a few minutes in cruise.

Plus with AP on, just one pilot has to be monitoring the AP, and the other one can do paperwork, sleep, do handstands, play video games or whatever.  When hand flying, the pilot not flying has to be monitoring the pilot flying. For an entire hour plus?  No way.  Just too much work and risk to your livelihood.


Do I need a driver's license to get a PPL in Canada? I've been searching on Google but there doesn't seem to be any results confirming or rejecting the requirement of a driver's license prior to PPL. It returns results for the United States, but that is of no use to me.

There is this question, but it doesn't address the having or not having a driver's license prior to PPL.

I have looked at the flight school (a),(b). Unless I am blind, there is no reference to this matter.

It seems like a very obvious question to ask, I'm surprised there is no reference.

If someone could point me to resources, or if someone obtained their PPL prior to driver's license could provide a briefing of whether this is an obvious requirement and I am oblivious to it or is it not a requirement at all.

It does not appear that a driver's license is required. From General information on pilot licences and permits, which details the requirements for getting various kinds of pilot licenses, there is no mention of a driver's license.

Prior to the issue of a permit or licence, an application must be submitted and the following requirements met:

proof of age and citizenship (not required if previously submitted)
proof of medical fitness;
proof of having met the knowledge requirements;
proof of having met the skill requirement;
proof of having met the experience requirement;
payment of the appropriate fees.


Why are geodesic airframes no longer produced? Why are geodesic airframes no longer produced?  Do they cost more than conventional structures?  Are they not as strong as conventional structures?  I assume it is insufficient cost benefit ratio, but how does that work out?

  Wellingtons under construction. Photo: Royal Air Force

Geodesic (sometimes also spelled geodetic) designs were used in aviation as early as 1909, in the Schütte-Lanz SL1 airship. It had a wooden structure with fabric covering, and Professor Johann Schütte, the scientific head of this design, used the most efficient method conceivable. However, planning the shape of all structural members was an enormous amount of work, and stretching an existing ship by inserting a new section was almost impossible. For those reasons, the late Schütte-Lanz airships used aluminum frames with conventional design, just like Zeppelin did from the beginning. Diagonal wire bracing was used to take up shear loads.

Geodesic frames are good in transferring both bending and shear loads. This is helpful when the aerodynamic covering is not stiff enough to contribute any shear stiffness, as in the case of fabric covering. However, when the skin is made from the same material as the frame, it can carry shear loads and a geodesic frame would not improve matters. Now it is better to carry longitudinal loads in longerons and shear in the skin.

But geodesic constructions are not dead. CAD makes the design effort manageable, and in some cases they give a weight advantage. Look at the casing of the EJ200 engine: It uses a geodesic reinforcement to make the casing light and strong and to prevent harmful vibrations. In the end, a jet engine casing is a big pressure vessel and needs to be strong, stiff and light.

photo by Julian Herzog, CC-BY


Why are the windshield wipers in the A320 power-up checklist? I was watching the startup sequence for an A320 and it struck me as unnecessary minutiae to ensure the wipers are off before power on. Is there something important that I'm missing that puts windshield wipers in the same list as thrust and gear levers?

For the same reason you should turn your wipers off when you shut off your car (since very few people go through a power-up checklist in their car...):

Running the wipers on a dry windshield can damage both the wiper and the windshield as the dry blades drag small particles of dirt, grit, rocks, etc across the windshield. These particles can tear up the rubber of the wiper, and they can scratch the windshield. Dragging dirt and rock particles across a wet windshield isn't inherently good for either wiper or screen, but the water acts as a lubricant and significantly reduces the damage potential.

It's far cheaper to print an extra line in the check list and have the pilots take 5 seconds to check it than it is to replace wiper blades and windscreens.


What are the legal requirements to be a "crewmember"? 14 CFR 1.1 includes the following definitions related to crewmembers:

  Crewmember means a person assigned to perform duty in an aircraft during flight time.

  Flightcrew member means a pilot, flight engineer, or flight navigator assigned to duty in an aircraft during flight time.

Some of the regulations (although not all instances) also refer to a required crewmember.

Anecdotaly I have heard of people being assigned as a crewmember on the spot so that they could fly in an aircraft that is limited to "crewmembers only" (i.e. some world war two era aircraft, etc.) by saying something like:

  "If the normal gear extension fails during this flight, then you will be responsible to pull this emergency handle over here.  Okay, got it?"

I'm not sure whether or not that would technically qualify someone as a crewmember, so are there any legal interpretations from the FAA or any guidance on what actually does qualify someone as a crewmember?

I'll take a stab at this one, though I can't guarantee the correctness of my interpretation (the regs don't seem exactly clear on the subject - at least not to me, so there's a lot more "inference" here than I'd normally be comfortable with).

In most cases under Part 91 the only requirement to be a "crewmember" is that the pilot in command says you're a crewmember -- i.e. the PIC determines that a person is qualified to perform a specific duty and designates them to perform it.
In the absence of anything more specific this is the only requirement I can turn up (and it's an inferred requirement - I didn't find anything specifically stating this, but 91.533 regarding flight attendants strongly implies that it's the correct interpretation. There's also a counsel opinion from 2008 - the Schehr letter which talks a little about who is a "crewmember" for purposes of riding in jumpseats that are placarded "For Crew Use Only". That interpretation is based on Part 135, but could be logically extended to Part 91 (and possibly some 121) operations too).

There are frequently more specific requirements though, particularly for positions that are important to flight operations. For example if you buy yourself a nice shiny Lockheed Electra to duplicate Amelia Earhart's trip under Part 91 rules you still cannot simply designate someone off the street to be the Flight Navigator: the FAA has specific requirements for Flight Navigator certification, and someone acting as the flight navigator would need to meet those requirements.

There are also more stringent requirements that are imposed for Part 121 and 135 operators. For example they can't simply designate a person as a flight attendant based on the PIC's determination that they are qualified: There are requirements for filling that crew position which must be met (FAR 121.421 & FAR 135.295 respectively, and possibly other regulations).


If airports with pilot controlled lighting share a CTAF frequency, could the lights be triggered at multiple airports? In the US, CTAF frequencies can be shared between several uncontrolled airports.  That is, a pilot around airport A can hear the transmit of another pilot utilizing airport B.  The question is can a pilot using the shared CTAF frequency and clicking the Pilot Controlled Lighting (PCL) affect the lights of all nearby airports using that same CTAF?

In theory, this could happen.  The consequences may not be severe - wasted power, some light pollution, and a false impression from seeing the lights alone that an(other) aircraft is trying to use the airport when in fact it isn't.

However, it may be less likely than you think.

For one, an aircraft in the air, even at pattern altitude, is going to have a much better path of radio propagation to another aircraft in the air, than an aircraft over one airport may have to a ground antenna at another - in simplistic terms, the radio horizon has doubled.  Ideally (for example in planning towers for a cellular phone network) frequencies are not re-used within the range of expected propagation, but only beyond it - however, in the aircraft-to-aircraft case you have doubled that over the air-to-ground case.

For another, an aircraft receiver is designed to be able to pick up weak signals.  In contrast, the receiver and decider for pilot controlled lighting may have an intentionally high signal threshold, to only trigger on strong nearby transmissions, and not on distant ones, random radio noise, or weak harmonic interference from transmitters on non-aviation bands or unintended emissions from non-radio equipment.


What is the threshold between high Aspect Ratios and low Aspect Ratios? Oftentimes when describing flying organisms and vehicles, their wings are said to have a "high aspect ratio" or a "low aspect ratio". Sometimes the papers (that I read) gave the numbers, but more often, they would just leave the explanation at that.

So I was wondering, in general, what is the minimum ratio that would make it a "high AR" and what is the minimum ratio that would make it a "low AR"? Is there a threshold to be met, or is this analysis of AR rather relative and or subjective?

The boundary depends on the type of aircraft. Fighter wings will be called high aspect ratio when the same aspect ratio in a glider wing will still be called low.

Generally, values below 5 are low, regardless of aircraft type.

With passenger aircraft, the boundary might be around 8.

Gliders will only have a high aspect ratio if it surpasses 20.

Still, there is no defined boundary and in the end the choice depends on the whims of the author.


Which airfoil would be optimum for a glider? The glider I am designing has a mission requirement to fly for as much time as possible. It will fly in the low Re range of about 150,000 to 250,000.

While comparing different airfoils I am looking for a high value of Cl^3/2/Cd to get as high endurance as possible and a high Cl/Cd ratio.

Any other parameters I should consider in selecting the airfoil?
I am currently considering Wortmann FX 63-137, E61, DAE-31 and Fx-74-c15-140.
Any other airfoil suggestions would be appreciated.

For a particular task of optimizing an airplane design for a specific point, you will need to consider the following characteristics, together with the endurance parameter:

The pitching moment of the airfoil, (which will define the tail design, hence will affect weight and CG range and controllability)
Tolerance to contamination and geometric impurities (especially CFD based methods may converge to non-robust shapes)
Stall behavior (does it stall mildly or violently, as a wing)
Wing weight (spar location, spar web thickness)
Aeroelasticity (wing structural modes, static and dynamic aeroelastic properties)
Manufacturability (if somebody will really build it!)

Many of these would require working on a conceptual or preliminary sizing task, where you would design a planform, twist, dihedral, tail volume, CG, mass estimation, aeroelasticity computations etc.

Number 1-2-3 could be more vital and would help pick an airfoil with less efforts than the others.


Why does the DC-9-80/MD-80 have this cusp in its fuselage? The fuselage of the McDonnell Douglas DC-9-80 (also known as the "MD-80") has a pronounced cusp at floor level, as can be seen in this diagram (courtesy of Boeing, eater of McDonnell Douglas - at least, according to @JWalters):

Although the DC-9-80/MD-80's fuselage cusp is nowhere near as extreme as the Boeing 377 Stratocruiser's, it still seems like an unnecessary stress concentrator with no apparent reason for being there; why did McDonnell Douglas put in the cusp, despite its potential for accelerating fatigue damage to the fuselage?

It's not a stress concentrator; it's just the opposite.  What you're missing is that the floor itself at the pinched part forms a tension bridge that allows a more or less 'ovalized' circle while still maintaining tension loading on the skins and frames as if it was a pure circle.

If I had a rubber balloon filled with air and was able to run a string internally from one side to the other, attached to the walls of the balloon, and then drew the string in to pinch the sides of the balloon into a figure eightish profile, I'd have the same thing.  All the loads on the skins are still in tension, as well as the bridging floor beams (the string).


Does a line up and wait instruction clear me to backtrack the runway? I had an interesting occurrence at the start of a recent flying lesson, at an aerodrome with ATC service. We were holding at A and completed our power checks. We hadn't requested nor been offered an intersection departure, and that is not a usual procedure at this aerodrome.

"G-AB ready for departure"
"G-AB via A line up and wait runway 23"
"Via A, line up and wait, runway 23, G-AB"

Following this, I entered the runway and turned to backtrack to the threshold. At this point my instructor said I should have turned the other way to line up at the intersection, because they didn't clear us to backtrack. Was he right to complain, or was I correct to use the full runway length?

Notes

A is only about 20 m from the runway threshold, and this runway is huge, so it makes little practical difference in this case.

At this aerodrome, they usually give LUAW instructions as "via [point], enter, backtrack, line up and wait runway 23". I checked CAP 413, and it doesn't mention "enter, backtrack, line up and wait" as phraseology, so I'd expect a clearance to LUAW entitles you to the whole runway unless you've already agreed an intersection departure. However, it's CAP 413 section 4.24 that introduces the "via A" phrase, and it has this to say:

  When line-up will take place at a position other than for a full-length runway departure the intermediate 'Holding Point' designator shall be included in the line-up instruction. Controllers may include the runway 'Holding Point' designator in any other line-up instruction when considered necessary.

It gives an example, and the only other example with "via" is in the context of an intersection departure. As I said, at this aerodrome they usually include the "via"; maybe they just always consider it necessary. Is not saying "backtrack" here significant, even though it's not a standard part of a LUAW instruction?

Your instructor was correct. According to the CAA Radiotelephony Manual[pdf], since the clearance you received included "via A" your clearance was not for a full length takeoff.

From the Radiotelephony Manual, chapter 4:


Why are HUDs usually green instead of red? Every HUD I've seen, whether photographs or in video games, uses green light to draw the lines and text.

Why green? I thought red was a better color for pilots' eyes so they can stay adjusted for night vision. Do HUD's allow you to switch colors at night?

Note: I'm interested in military aircraft only, especially fighter jets. But if the reason happens to be the same across the military and civilian world, that's fine too of course.

A few thoughts (a bit of personal research):

Eyesight

The eye is most sensitive to green color, as can be seen in this diagram:

  At moderate to bright light levels where the cones function, the eye is more sensitive to yellowish-green light than other colors because this stimulates the two most common (M and L) of the three kinds of cones almost equally. At lower light levels, where only the rod cells function, the sensitivity is greatest at a blueish-green wavelength.

(source: wikimedia.org)

Dotted R line is (night-vision) human rhodopsin 'rods'.

As I understand, any powerful light depletes rhodopsin down requiring that they regenerate, which takes time, just that depletion takes longer with red wavelengths. I think this does not imply that green color 'automatically' screw up night vision if the display intensity is lowered enough.

Technical Limitations

The light has to be collimated to not interfere with depth perception, which complicates having multiple colours. At least in old CRT displays, this would have left you with the choice between blue, red or green. Green and Red is perhaps the color which stands out the most, but this diagram would suggest the red occurs at different wavelengths, perhaps again interfering with collimation:

  Due to the complexity of wide field-of-view reflective HUD optical systems, the optical designer must use all means available to meet display accuracy and parallax error requirements. All certified reflective HUDs today are monochromatic, generally using a narrow-band green emitting phosphor. The addition of a second color to the HUD is a desirable natural progression in HUD technology, however, one of the
  technical challenges associated with adding a second (or third) display color is maintaining the performance standards available in monochrome displays. One method for solving this problem uses a collimator with two independent embedded curvatures, one optimized for green symbology, the other optimized for red symbology, each with a wavelength-selective coating. Avionics Handbook, Chapter 4

Compounding to the previous point, it may be difficult to filter through a single red color through the screen, ending with a rather broad spectrum instead:

Further thoughts:

I think the night vision would be disturbed anyway by the variety of instruments such as maps and radar. I'm also doubting a bit of the importance of night vision in combat situations.
Night vision googles also use monochrome green light, despite having perhaps the greatest benefit of red light should they break and you need to continue without.
Even in a pretty new BMW I drove there was only monochrome green from their own HUD. I read forums accusing systems featuring multiple colours as having inferior display quality.


What is the difference between "R/C", "Drone", "UAV"? Are "remote controlled" aircraft and "drones" the same thing? Are they synonyms for "unmanned aerial vehicle"?

Drones are simply the common name for Unmanned Aerial Vehicles. Representatives from the industry and the military use the term UAV for the aircraft and UAS (Unmanned Aerial System) for the whole system- including communication system, on ground controller etc.

In general, technical publications call them UAVs or usually UAS's and rarely (if ever) drones. On the other hand, the mainstream media refers to them usually as drones as it is easy to communicate.

The ICAO (International Civil Aviation Organization) calls them remotely piloted aircraft. However, there is a subtle difference in using this word as it means that it is being flown by a pilot (controller) on ground.

Though this may be technically true, most of the UAVs, at least those used in the military are capable of highly automated mission profiles (in fact, they depend on the controller only for weapons release) and are on the way to full autonomy.

The choice of wording is one of semantics i.e. about the meaning which is to be conveyed. For example, the nobody wants a system that goes and kills someone without human intervention. So, the USAF calls the MQ-9 Reaper a Remotely Piloted Vehicle in its official page and a UAV in press releases, but not a drone, as it has negative connotations in public mind.


Why scrap an A380 with only almost 10 years? Accordingly to this article "First commercial Airbus A380 turned to dust", first A380 was scrapped.

Apart be a sad news for an aviation fan, it sounds me a bit strange because it was an airplane of only 10-12 years, while generally a plane flights for more than 20.

Ok, I know that A380 was sadly almost a commercial flop but it was not an old plane, I thought that could continue to flight with another airline.

In which way could be more convenient to scrap it instead of sell it flyable to another company?

Well, the article you are referring to quite clearly states the reason for the decision to scrap the plane(s): negotiations with airlines to sell or lease were not successfull, so the only option was to scrap, or rather dismantle the plane.

Furthermore, the article presents the estimate by Dr. Peters Group that it would be able to generate some \$45 million  per aircraft by selling the useable components, and an additional  $480 000 / month by leasing the engines.

As a reference, the list price of a new A380 is (was) something like $ 430 million, the actual prices being, however, much lower. When you consider that a 10 year old plane most likely needs a considerable interior refurbishment, the decision made by Dr. Peters Group does not seem so strange, does it?


Why does the A-4 Skyhawk sit nose-up when on ground? The rear of the plane is nearer to the ground, while the front part of the plane is away from the ground (see image below).

Other planes are more flat.

I think it was for high AoA but these planes are carrier operated so I don't think there is much sense for that.

(wikimedia.org)

This was pretty common on naval aircraft from that era which used the launch bridle catapult interface. It gave the aircraft a high angle of attack during launch and helped the aircraft get clear of the bridle at the end of the launch stroke. It's noticeable on a wide variety of aircraft, including the F7U-3, F4D, A-5, F9F, F8, Super Etendard, Buccaneer, F3H, just to name a few.

Even the F-4 did. The nose landing gear oleo strut could be extended to give a nose high squat for cat shots:

(theaviationgeekclub.com)


Who should handle an emergency when there's both a certificated pilot and a CFI on board? While practicing for my commercial certificate in a T-tail Piper Arrow IV, I put the gear down on downwind, and one green light didn't come on.

In the right seat was a CFII/Multi, who had over 1,000 hours but less than 10 hours in Pipers, whereas I had about 300 hours, and over 200 in Pipers, having done my PPL in stiff-legged Cherokees.

As a certificated pilot, I was PIC, but we talked about how to handle the emergency, and the CFI and I decided that since I had so much more experience in Pipers, I would handle the emergency tasks, while he handled the radios and looked for traffic.

We did the proverbial tower fly by (although they wouldn't say anything except the gear "appeared to be down"), and they cleared me to land on any runway. Our landing was uneventful, and it turned out to be an electrical MX issue.

When we landed, however, the flight school nearly fired the CFI for not having taken control of the aircraft during the emergency.

Did we make the right decision for me to handle the emergency? Or should I have let the CFI/CFII/MEI with over 1,000 take over as PIC and handle the airplane?

From a safety perspective both pilots should be handling any emergency that arises, each working to their individual strengths and expertise to ensure a safe outcome.
This is exactly what you did in the scenario you describe.

In terms of who calls the shots (acts as PIC for the emergency), generally the most qualified pilot onboard should be the one giving the orders. Deciding who that is falls to the pilots onboard (because they're the ones who will arrive at the scene of any resulting accident first).

So in my mind the question really is "How do I determine who is most qualified?" -- Any opinion we can give here comes dangerously close to second-guessing your emergency actions which is something I personally try to avoid, but I'm going to embellish your scenario above for illustrative purposes:

The Instructor
Former air force pilot ATP, CFI/CFII, MEI.
10,000 hours in various jets, 10 hours in an Arrow (doing this instructing gig.) and for the sake of argument no other time in PA-28s.
You
PPL + Instrument Rating, working on your Commercial.
300 hours, 200 in fixed-gear PA-28s and let's say 20 in Arrows.

I'll further assume you both kept your cool and didn't panic (because if either of you turned into a quivering blob that would automatically disqualify them from taking control of the aircraft).

If we go by the certificates, your instructor is certainly "more qualified" - and in 10,000 hours they've probably dealt with more real-world emergencies than you have.

If we go by "time in type" and experience flying PA-28 variants you're clearly more familiar with the general type, and possibly this specific aircraft & systems (like the emergency gear extension system).

Given the above, having you handle the controls seems to be the most logical course of action. The CFI can do "everything else" - communication, traffic scan, calling out checklists & altitudes, etc. - to ensure that you can concentrate on flying the plane and landing as safely as possible.


Aerobatics in "firm" IMC -- how would one do it? Assuming you are aerobatically trained, IFR rated, have an aircraft that is rated for the aerobatic maneuvers you are planning to perform (let us assume that it is acrobatic category, even), and the aircraft in question is type certified and equipped for flight under IFR, how would you plan out and safely execute a set of aerobatic maneuvers in IMC (think solid cloud, but without serious up/downdrafts, icing, or lightning hazards) while flying under IFR?  Can you define a "box clearance" in an IFR flight plan, akin to a VFR aerobatic box, only defined by coordinates or intersections instead of ground reference points?  How feasible is it to carry out the Aresti catalog maneuvers by reference to flight instruments alone?

No - you don't do it.

First and obvious reason, there's no body to see it.

Perhaps much more important is safety though. When pulling a loop, it's not like flight simulator where you just yank the stick aft and watch the attitude indicator (AI). An aerobatic pilot is constantly checking his attitude by looking at his wing tips, quickly glancing the left and right sides back and forth.

In fact, the AI is usually caged (meaning it is locked to prevent rotation) in such violent maneuver. The proper procedure is cage the AI, perform the maneuver, check straight and level (visually), then uncage the AI. If you don't, the gyroscope will tumble quite some time before it settles again, rendering it useless. Meaning, if you perform in IMC, you won't have accurate AI information for recovery.

For nearly vertical maneuvers (e.g. stall turn, rolling while vertical), even a functioning AI wouldn't help, since horizontal direction is undefined in this state. The AI and compass will just flip, yet you have no way to determine which way you go.

Violent G-forces also mean it is much more difficult to read instruments during such maneuver.


How to calculate on ground aircraft yaw rate knowing the longitudinal speed and inferred yaw angle Please consider the following scenario:

a generic aircraft is on-ground taxing at 50 feet per second (~15.25 m/s, ~29.5 knots)
The pilot inferred 20 degrees of yaw

How can I calculate the yaw rate of the aircraft? Do I have enough information to calculate it?

Do I have enough information to calculate it?

No.

Yaw rate is $rad/s$. You have an angle, $rad$ (or degrees), and you have a linear speed, in $m/s$.

You cannot obtain a $rad/s$ value from these two data points.

You need the time interval over which the change in yaw has been observed.


Why aren't Russian jet airliners popular even in Russia? Russia has the proven capability to build large jet airliners.

Ilyushin Il-96
Tupolev Tu-204

But, if we take a look at the major airlines in Russia, they don't appear to have Russian airliners:

Aeroflot
Rossiya
Red Wings

Why aren't Russian jet airliners popular even in Russia?

If there is any reason like X, Y, or Z,  what is Russian government doing to make its home-grown airliners popular?

It all comes down to cost. It is rather easy to build a large jet aircraft. To build an efficient and reliable large jet aircraft is not that easy. If you read the Wikipedia articles you linked carefully you find in the Il-96 article:

  [...] the Il-96-300 had been deemed inferior to counterparts from Boeing and Airbus [...]

and in the Tu-204 article it is indirectly stated that the reliability of the engines isn't that great:

  The PS-90A2 [engine] is expected [to have ...] life cycle cost saving of 35% over the original engine with a simultaneous increase in reliability in the 50 to 100% range.

Your next problem is line maintenance capabilities. That is more or less a chicken and egg problem. The Il-96 is a long range aircraft and you need maintenance on your destination. You need a certified mechanic, tools, and components. Component availability is another problem. If there is only a handful of aircrafts of one type there is no large spare supply around the world thus increasing the cost for the operator.

Another problem is that at least the Tu-204 is not fit for the current airspace structure:

  The Tu-204SM [...] is an upgraded version of the Tu-204-100/300. [... T]here are numerous upgrades, largely aimed at meeting the current and near-future Russian and international standards [...].

And it requires a three man Cockpit Crew. Remember: The Tu-204 is an A321 sized aircraft.

  The new cockpit features allow the Tu-204SM to be flown by a two-pilot crew (as compared with the three-pilot arrangement of the original Tu-204 series).

So far the improved Tu-204SM hasn't materialized so far and likely never will.

  [... There are] currently no orders for the Tu-204SM, and Tupolev has frozen on development work on the aircraft and the UAC will withdraw it from their list of aircraft prices as soon as the Irkut MC-21 comes to the market.

As an airline has to keep the costs under control it is unwise to buy an aircraft which, from the start, is inferior to its competitors. It's a simple calculation: What costs more over the predicted lifespan. Initial costs (unit price) might be lower with one product but you have higher costs for fuel and maintenance. Add in some reliability problems and you get the costs incurred by those on top. Another product might have a higher unit price but the running costs are lower. Now do the math and choose whats best for your airline.

All quotes come from the Wikipedia articles on the Ilyushin Il-96 and the Tupolev Tu-204.


Under what circumstances should the pilot not flying intervene without asking for aircraft control? The communication between the captain and first officer is of great importance, especially when it comes to agreeing who is the pilot flying. This question asks for the procedures regarding taking/handing over control and this is also a related question.

Neither of these question discuss under what circumstances the pilot not flying should intervene without verbally announcing their control of the aircraft.

Are there defined procedures for this?
Is seniority sufficient to immediately intervene in some situations?
Is it up to the crew to decide before-hand that the captain is allowed to "help" a less experienced first officer?

In this video (at about 1:40), the first officer is landing the plane, and immediately after touch-down the captain intervenes by pushing the stick forward, apparently without being the pilot flying at the moment.

This document is also related, although it focuses on when and how to intervene being the less experienced co-pilot. Key quote:

  "You are damned if you ignore a Captain's mistakes!

  You are damned if you do or say something about them!"

There is transfer of control -- "I have the aircraft" / "You have the aircraft."  Then there is intervening -- which may or may not involve a transfer of control... directing "you're getting slow, ADD POWER NOW" may be a more effective example of intervening than taking control, depending on the phase of flight & other circumstances.  (It's easier for a First Officer to intervene with a directive "add power" or "go around" than than for him to take the aircraft!)  And then there is what was shown in the video, which looks like neither of the above -- simply crew duties as @Lnafziger commented. The captain there didn't take over control (yet -- the video ends before he takes over to taxi), they simply both pushed forward on the control column -- put weight on the nosewheel for better steering, perhaps.  Looked perfectly normal & expected.

To answer the question as asked ("Under what circumstances should the pilot not flying intervene without asking for aircraft control?"), there are plenty of times when intervening without taking control could be appropriate -- the directive callout ("ADD POWER!"), or correcting an aircraft system or Flight Management Computer setting, for example.  There are also a smaller set of times when "I have the aircraft!" is appropriate: a disoriented pilot is about to fly into an unusual attitude, or a pilot is incapacitated in a phase of flight where there is no time for "hey, are you okay?" to differentiate between distracted & incapacitated.  The captain always has the prerogative to take over, although there are plenty of times when something else is a better choice -- directing "go around" instead of taking the aircraft at low altitude to try & salvage a bad landing, for instance.  Particularly in cases of incapacitation, the FO also has that option, but realistically, he may have more explaining to do than the captain would have if roles were reversed.

In a pure training situation (initial formation flying in the military comes to mind), there are times when control may transfer back & forth... the student flies as far as he can, starts to get out of position, the instructor takes the aircraft, puts it back into position, the student is given control again, etc.  But that's not really the sort of scenario you'd see in airline operations.  There might be times the pilot-monitoring captain (i.e. he is the pilot not-flying on the FO's leg) might take over the FMC programming rather than talking the FO through the necessary changes -- sometimes it's just better to do it & explain what you're doing rather than talk through each entry and button press.  But that's again not really the same as "I have the aircraft."

With qualified crews in the airline world, it just isn't all that common that a situation arises where one pilot has to assume control outside of the normal transfers (i.e. the normal transfer to the captain on landing if he has the only nosewheel steering tiller).

And, as noted in the comments, every transfer, both expected and unexpected, needs to be verbalized by both pilots: "I have the aircraft."  "You have the aircraft."


Can European (or more generally, non-US) airspace users airfile IFR flight plans? In the US, there are two ways to airfile an IFR flight plan:

Call Flight Service on the radio via the nearest FSS RCO and ask them to file the plan
Ask the ATC entity you're talking to for a "pop up" IFR clearance

Is there any equivalent to either function in European (SES) airspace?  Or is Europe a continent where airfiling IFR flight plans is not possible?  (Bonus points if there's some sort of ICAO standard way of handling airfiling.)

Sure you can. This is from ICAO Doc 4444:

4.4.2.2.1    A flight plan to be submitted during flight should normally be transmitted to the ATS unit in charge of the FIR, control area, advisory area or advisory route in or on which the aircraft is flying, or in or through which the aircraft wishes to fly or to the aeronautical telecommunication station serving the air traffic services unit concerned. When this is not practicable, it should be transmitted to another ATS unit or aeronautical telecommunication station for retransmission as required to the appropriate air traffic services unit.
4.4.2.2.2    Where relevant, such as in respect of ATC units serving high- or medium-density airspace, the appropriate ATS authority should prescribe conditions and/or limitations with respect to the submission of flight plans during flight to ATC units.

And this is from SERA (Standardized European Rules of the Air):

SERA.4001(c) A flight plan shall be submitted, before departure, to an air traffic services reporting office or, during flight, transmitted to the appropriate air traffic services unit or air-ground control radio station, unless arrangements have been made for submission of repetitive flight plans.


What are the historical precedents of today's E2 and E4 airspace? (US) What are the historical precedents of today's E2 and E4 airspace?  From what previous airspace classes did these airspaces evolve?  How do these precedents help us understand the significance of the distinction between E2 and E4 airspace today?

What we now know as Class D and E2 airspaces were once (before 1992) a single type of airspace called a "Control Zone".  "Control Zones" first appeared on charts in the mid-1940's and consisted of a thin dashed circle enclosing an airport-- originally red, later blue. By the time of this 1974 test-prep publication, "Control Zones" had been defined to go up to the overlying "Continental Control Area" at 14,500' MSL.

Originally a "Control Zone" did not indicate a communications requirement for VFR traffic-- many non-towered airports had a Control Zone around them, and a few towered airports lacked them.  Instead, all towered airports were automatically assumed to have an "Airport Traffic Area" around them, 5 miles in radius and 3000' tall, that could not be entered without first establishing radio communications with the tower.  The purpose of a "Control Zone" was simply to impose-- all the way to the surface-- higher VFR cloud clearance and visibility requirements than would exist in "uncontrolled" airspace, for the protection of IFR traffic emerging from clouds.

Around September 1992, changes were made to the markings on the sectional charts in preparation for the upcoming September 1993 "alphabet" airspace reorganization, when the "Airport Traffic Areas" would disappear and the boundary of the communication requirement would be shifted to the edge of Class D airspace.  All "Control Zones" that did not contain a control tower had their depiction changed from a dashed blue line to a dashed magenta line, and were identified on the chart legend as a "Control Zone without communications requirement".  This was the immediate forerunner of today's E2 airspace.  At the same time, to eliminate the future communication burden on VFR traffic (and towers) that would be created in cases where Class D airspace had a projection extending far from a towered airport, some of the projecting portions of Control Zones at towered airports had their borders changed from dashed blue to dashed magenta and were identified on the chart legend as "Control Zone extensions".  These "Control Zone extensions" are the immediate forerunners of today's E4 airspace.  The complete legend on the charts for the new dashed magenta line was "Control Zone at airport without control tower and Control Zone extension without communications requirement".

It is interesting to compare aeronautical sectional charts dating from shortly before the introduction of the dashed magenta markings, to charts effective immediately after the introduction of the dashed magenta markings.  It is interesting to see how the Control Zones at airports with towers changed from their previous shapes. Some were made smaller. On some, any rectangular projections remained part of the blue dashed shape surrounding the airport, while on others, some or all rectangular projections were changed to magenta dashed lines that abutted against the blue dashed shape. The determining factor does NOT appear to simply be how far the projections projected away from the basic inner circular shape.  Clearly, planners were preparing for the communications requirement that would soon be shifted from the old "Airport Traffic Area" boundaries, to the edge of the Class D (or higher) airspace.

Note however that according to the FAR's, the "Airport Traffic Areas" still served as the boundaries of the communications requirement until the September 1993 "alphabet" airspace re-designation.

Therefore it's not clear to me whether or not the distinction between a "Control Zone" and a "Control Zone extension" had any actual practical or regulatory significance in the September 1992 to September 1993 time period.  Could it have simply been a charting convenience to help pilots, chartmakers, and others prepare for the regulatory changes that would go into effect in September 1993?

Certainly FARs 91.155c, 91.157a, 91.303c, 101.33a, and 103.17 continued to simply refer to "Control Zones" with no mention of "extensions" all the way up until the September 1993 airspace re-designation.  Would these FAR's have applied to airspace that was charted as a "Control Zone extension", or only to airspace that was charted as a "Control Zone"?

Diving a little deeper into this question of the significance of the distinction between a "Control Zone" and a "Control Zone extension" prior to September 1993: in the version of the FARs effective Jan 1993, we read "71.1 Applicability The complete listing for all jet airways, area high routes, Federal airways, control areas, control area extensions, area low routes, control zones, transition areas, terminal control areas, airport radar service areas, postive control areas, reporting points, and other controlled airspace can be found in FAA Order 7400.7A, Compilation of Regulations, dated November 2 1992."  Note the lack of the phrase "control zone extension" in this sentence.  Would a careful reading of the November 2, 1992 edition of FAA Order 7400.7A show that the airspace that appeared on the charts as a "Control Zone extension" was still simply considered part of a "Control Zone" from a regulatory standpoint?  Does the phrase "Control Zone extension" appear in this edition of FAA Order 7400.7A at all, or was that airspace simply treated as a completely integral part of the adjoined  "Control Zone"?  So that the distinction between "Control Zone" and "Control Zone extension" essentially existed on the aeronautical charts only, and nowhere in the actual regulatory documents?  I haven't yet been able to obtain a copy of the November 2, 1992 edition of FAA Order 7400.7A, and don't know the answer to these questions.

The actual transition from the "Control Zone"/ "Control Zone extension" terminology to the modern "alphabet" terminology happened in September 1993.  At this time "Airport Traffic Areas" ceased to exist, and all the airspace surrounded by a dashed blue line on the sectional became Class D airspace, and all the airspace surrounded by a dashed magenta line on the sectional became Class E airspace that extended all the way to the surface.  This is when the awkward terminology that we currently find used to describe E2 and E3/E4 airspace in the "Airspace Designations and Reporting Points" document was first applied to what had previously been depicted on the charts as "Control Zones" (around non-towered airports), and what had previously been depicted on the charts as "Control Zone extensions", respectively.  Considering that E4 airspace also goes all the way down to the surface, it's unfortunate that someone didn't come up with a better term than "Designated as Surface Areas" or "Designated as a Surface Area for an airport" to describe the E2 airspace.  September 1993 is also when the language of FARs 91.155c, 91.157a, 91.303c, 101.33a, and 103.17 was changed to its current awkward form.  Regardless of whether or not these FARs had been considered to apply to the airspace of the "Control Zone extensions" during the year or so that they were labelled in that manner on the charts, the language adopted for those FARs in September 1993 clearly matched the E2 airspace description in the "Airspace Designations and Reporting Points" document effective at the time (as well as at the present), and did not match the E3/E4 airspace description.

Addendum--

As a point of related interest, here is a list of activities that require prior authorization (or in the case of aerobatic flight, are prohibited) in E2 airspace but not E3/E4 airspace, along with the relevant FAR or other legislation:

Operating VFR without a SVFR clearance in certain adverse weather conditions -- FAR 91.155c

Ultralight flight-- FAR 103.17

Aerobatic flight-- FAR 91.303c

Operation of an unmanned free balloon below 2000' AGL-- FAR 101.33a

Operation of a small Unmanned Aerial Vehicle (e.g. commercial drone) -- FAR 107.41

Operation of a recreational small Unmanned Aerial Vehicle (e.g. typical hobbyist drone or model airplane) under the "Recreational Exemption" -- language passed by Congress in October 2018

Also, FAR 91.157a allows ATC to grant a SVFR clearance in E2 but not E3/E4

As noted in the links below, the distinction between E2 and E3/E4 airspace is not always observed by ATC in actual practice in relation to the requirement for, and the possibility of granting, a SVFR clearance.

Sources--

Source for FARs as they existed in January 1 1993, also listing the modifications that would become effective September 16 1993

Source for dimensions of "Airport Traffic Area"

Related content on ASE--

What are E2 and E4 airspace?

What are E2 and E4 airspace?

What are E2 and E4 airspace?

Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?

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?

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?

How does the distinction between E2 and E3/E4 airspace affect pilots?


Can an airplane fly with on-off control surfaces? I understand that, at least for remote-controlled model planes, the control surfaces can point to a range of angles, say, from $-30^\circ$ degrees to $30^\circ$. My questions are:

Would the same airplane work if the control surfaces can only point to, say, $-30^\circ$, $0^\circ$, $30^\circ$.
If I rapidly switch the surface on ($0^\circ$) and off ($30^\circ$) like in pulse-width modulation (PWM). Is that equivalent to having the control surface pointing at $15^\circ$?

Theoretically it could work that way. A maneuver that needs a certain control surface deflection for a certain amount of time could be done with full 30 degree deflection in a shorter time.

Fine control and trimming would be more difficult. Small adjustments would require a very short time at full deflection. Control laws would have to take into account the step response of the system to determine how quickly the surface can reach the full deflection. By pulsing a deflection command like with PWM, you could determine a modulation that would keep the surface near some nominal deflection.

For an RC plane's systems this may be fine. With larger aircraft you would need to consider the effect of these large inputs into the control system, and structural effects, including whether 30 degree deflection is possible in the current flight conditions.


How are aircraft wings protected against flutter - aerodynamic oscillations that can break bridges? It's a well known fact bridges can break due to self-amplified oscillations creating excessive loads on their structure, by resonance (galop). It happens from time to time. The Tacoma-Narrows bridge catastrophic failure is popular, but there are modern and less known stories about wind/rain creating a problem which needed to be solved after the bridge opening.

US Tacoma-Narrows bridge collapse in 1940, source (video)

A wing and a bridge roadway have similarities, and they are both exposed to a transverse wind.

Several aircraft in flight with flutter, source (video)

How are wind/rain/resonance-created oscillations (flutter) managed in airplane design? How are these effects tested in flight?

Flutter happens when the eigenfrequencies of two oscillations move close together so their motions can reinforce themselves mutually. When that happens, then the amplitude will increase with each oscillation, up to a point where the amplitude is big enough to break things. That is how bridges are destroyed: Ever more energy is accumulated in the structure, a tiny bit with every oscillation, until the total overwhelms the strength of the weakest part.

If the two eigenfrequencies are not close enough together, both motions will still exist but will normally be damped so they die down quickly after being excited, e.g. by a gust. A typical example is the wing bending motion: When the aircraft flies into an updraft, the wingtips flex up, elastic energy is accumulated and set free once the extra lift from the updraft dies down. The wingtips move down and will very briefly oscillate around their long-term vertical position.

Now add a free-flying aileron (mechanical control system with stick free). This also can oscillate around its long-term deflection angle. As long as the eigenfrequencies of both motions are sufficiently apart, they will not interact. This should be ensured throughout the normal flight envelope. However, flying faster will increase the aileron eigenfrequency, and in this case we should focus on the first antimetric bending motion of the wing. At one point the aileron frequency will come close to the wing bending eigenfrequency, and only then this particular flutter mode will happen.

The glider in the second picture of your question is the SB-9, a longer-span version of the SB-8 (which itself is flutter-free). The added span moved the wing eigenfrequencies down, so they met with the aileron frequency at a lower speed. Now flutter could be observed when flying at the right speed, but it could be stopped simply by gripping the stick.

Therefore, the possible protections against flutter are:

Limit the flight envelope. Prohibit flight speeds at which flutter is possible.
Increase damping. This can be as simple as adding some friction. The rudder cables in gliders are run in PE tubes which add some friction, eliminating rudder flutter.
Increase eigenfrequencies by increasing stiffness. In the SB-13 flying wing glider high modulus carbon fiber was used in the spar to shift the wing's eigenfrequency sufficiently up to avoid a coupling of the wing bending mode with the short period mode of the airplane
Increase eigenfrequencies by mass reduction: When a wing is made lighter especially towards the tips, e.g. by clipping the wing tips, its eigenfrequency will move up, shifting flutter speeds up. Conversely, by adding wingspan to the sound SB-8 design, the eigenfrequency of the SB-9 wing went down.
Change eigenmodes: By running the aileron pushrods near the wing shell, wing bending can effect an aileron deflection which helps to dampen the wing's bending mode.
Cross-coupling of eigenmodes: By reducing the wing spar sweep of the SB-13 by 3° relative to that of the whole wing, the bending motion causes wing torsion which reduces incidence when the wingtips are bent up and vice versa. This is similar to the pushrod trick and is an application of aeroelastic tailoring.

In a similar way, the forward location of the engines on an airliner wing creates an inertial torsion moment when the wing flexes. This increases damping, so this example could had equally appeared in the first point.

To ensure a design is free of flutter, a range of tests is performed prior to first flight and during flight testing. From this answer:

  Since maybe fifty years every new design must go through a static
  vibration test to check which elastic eigenfrequencies exist.
  Analytical methods are used to predict the (speed dependent)
  aerodynamic frequencies and the structure must be modified to remove
  any possibility of resonance. Next, the airframe is tested in flight
  at ever increasing speeds and with exciters at the tips of all
  surfaces (those can be like the vibration motor in your smartphone,
  only bigger, or, in the simplest of cases, the pilot moves the control
  surfaces). At increasing speeds, the exciters are run through a
  frequency sweep (typically from 5 to 60 Hz) and the resulting
  amplitude is measured by strain gages or accelerometers.


How long is the EASA ATPL theory exam valid? I got the JAA CPL and IR and ATPL theory examination in Spain in 2009. They are all expired by now. I didn't renew them until now because I'm flying with the CAAC license and got 3600 hours experience time.
I want to endorse A320 type rating on the EASA license in order to fly in other countrys. They recruiment requirements are EASA CPL(or ATPL) with IR and MEP and (frozen ATPL).

My questions are:

Is the ATPL theory examination expired or is it called the frozen ATPL?
If I hold the valid IR issued by an ICAO member state China,  is the Cross-crediting applicable to RENEWAL of the EASA IR and MEP?

FCL.025 is very clear on that and it says:

  (2) The completion of the airline transport pilot licence (ATPL) theoretical knowledge examinations will remain valid for the issue of an ATPL for a period of 7 years from the last validity date of:
  (i) an IR entered in the licence; or
  (ii) in the case of helicopters, a helicopter’s type rating entered in that licence.

ATPL theory exams are valid for 7 years of the date of expiry of IR, entered in EASA licence. So it depends when your EASA IR expired. ICAO IR unfortunately does not count in this case.

If your ATPL theory exams are not valid anymore, you will have to do them again. It is possible to transfer A320 rating from CAAC (ICAO) licence to an EASA one - depending on your experience. You would need, however, to do LST (licence skill test) on A320 in the simulator and pass all 14 EASA ATPL exams again.


What can a passenger do if (s)he objects to the flight route? Say that after a passenger learns of or views the flight plan, she opposes it (eg due to safety).

She could just refuse to board the flight and forfeit her ticket and costs, but are there less costly and dire and radical options? Despite being only a passenger, could she explain to the flight crew (plausibly via the cabin crew?) her reasons and thus request the reconsideration of the flight route?

Supplementary: I elucidate that I do NOT mean for her to compel or impress a specific route (replete with all the waypoints, VORs, etc...) upon the flight crew, but only a general concern for avoidance.

As an instantiation, if I were a passenger and had apprehended my flight to overfly Ukraine, even outside of the no-fly zone, then I'd remonstrate against it, in favor of a more northern one that would substantively avoid Ukraine.

The passenger can in all likelihood do nothing that is going to change the route.

As you point out, there is always the option to not board.

On long range flights like this, the routing will (depending on winds aloft and other conditions) almost certainly require a fairly direct route to insure that additional fuel stops are not needed. In cases where routes go over warzones or other dangerous areas, they are often rerouted, but in the case of Ukraine the conflict has until now been isolated and military in nature.

Either you trust the flight crew to also be aware of these risks, or you don't. Get on board, or not. I'm sure you could raise the issue with a gate agent, and if you made enough noise or escalated it, you might be able to get a refund (note: I have no idea). However, you also might be perceived as the source of the risk and detained!


How did jet engine aircraft perform compared to the best reciprocating engine aircraft during WW2? How did the performance of jets in World War II compare to the cutting edge propeller planes (e.g. P-51, Zero's, etc) of the day?

Much longer take-off distance and less endurance, but higher speed at all altitudes with jets. The performance advantage of jets widened with increasing altitude and resulted in a higher service ceiling. Both the Me-262 and the Ar-234 would fly at least 100 km/h faster than any propeller airplane, and the Ar-234 could fly reconnaissance missions over France and England in complete impunity. A Me-262 test variant (262 V9) with a low-profile canopy reached 600 MPH in level flight.

This gave jets the possibility to break off combat at will. They could only be engaged with success when they were flying in for a landing with empty tanks or by chance, when the jet pilot was unaware of his opponent. Since the Me-262 was designed to intercept bomber formations, it was not suited for dogfights. The Heinkel He-280, on the other hand, was evaluated in 1943 against a FW-190 and would easily outturn the propeller aircraft, so this was not an engine-related characteristic.

Note that the first kill of a Me-262 was by a de Havilland Mosquito, a very fast propeller aircraft that could outrun almost all other propeller aircraft of its time.


Do aircraft manufacturers have the authority to either approve or disapprove the maintenance procedures of its customers? Having currently read this article in Wikipedia, linked through Reddit, regarding American Airlines Flight 191, which crashed due to maintenance issues.

Inside the article, it says

  McDonnell-Douglas, however, "does not have the authority to either
  approve or disapprove the maintenance procedures of its customers."

Is that the scenario in the current aviation industry, or has it changed. Why would airline companies not listen to the manufacturer and carry out non-approved procedures.

For N-Registered Planes Under FAA regulations... (this may differ elsewhere in the world)

The short answer is No (although some service bulletins may be legally required), the manufacturer can not legally enforce anything per say, however here's how it plays out.

Most makers are at least in some capacity always testing their aircraft and aircraft procedures (at least the models in service). This may be as simple as inspecting the ones out there and looking at used parts for fatigue and what not. This in turn can lead to the company issuing a Service Bulletin which is basically a document that says: "hey here's something we found, you should look at it". This can apply to a any part of the aircraft as well as inspection and maintenance procedures. However service bulletins are not legally required to be complied with when issued by the company (although many may choose to comply).

On the other hand the Service Bulletins may trigger the FAA to issue an Airworthiness Directive which is a legally enforceable document. In this case the owner/operator of the aircraft is legally required to comply and alter their procedures.

In this case of the accident in question I think this is the AD that was issued as a result. You can find a full list of MD-10 AD's Here.

On to the question of why an airline may not listen. This is most likely a cost related issue. If the airlines insurance does not change and the cost to inspect or possibly replace a part that they don't legally need to replace is simply to high, they wont do so until its legally required. Again since every thing in aviation has two sides, manufactures may have the courtesy to replace the part at no cost to the owner. For example, when Porsche dropped the FAA Type Certification for the 3.2 motor in the Mooney M20PFM leaving all the owners somewhat high and dry, Mooney was kind enough to have the 40 odd aircraft updated with Continental motors (although many were destroyed in a hurricane while under going the change). The crux of it also comes down to the fact that only the government and its various organizations (here in US) can legally impose anything on an individual or company. So while it may be a good idea to heed the advice of the maker you may not be required to do so.

--Edit--

To answer the comment below which is somewhat relevant to the original question. My understanding is that yes the FAR's may require you to refer to the manufacturer procedure but at the same time you only must refer to the procedures required (associated with the current certification of the airframe) for your airframe an SB with out an accompanying AD is a manufacturer procedure but is not legally required. So you may refer to it but you may not have to comply with it. Ill dig into the regulations and see if I can find the letter of the law on it.


Why does avgas 100LL smell different than automobile gasoline? Why does avgas 100LL smell differently than automobile gasoline?  And why don't avgas 100LL fumes from a fuel tester located in the cabin make pilots ill?

The sweet smell of 100LL AvGas is due in large part—if not entirely—to the additive Tetraethyllead (TEL). TEL is included in the formulation of 100LL as an anti-detonation additive, octane booster, and lubricant.

A fuel tester stored in the aircraft cabin should not induce crew illness because the tester should be drained of all but residual fuel, that residual fuel will evaporate very quickly—usually long before startup, and aircraft cabins are typically well ventilated.