How is device control software checked for quality? Many, many reports on the now infamous MCAS suggest a software patch is forthcoming in the next several weeks that will address the confounding single point of failure with the two AOA sensors that probably contributed to at least one 737 MAX crash.

As a software developer (of a much different variety than a Boeing engineer), I am very curious:

What do regulators and the public know about the actual code that flies planes (and sometimes crashes them)?

I've been looking for an hour and can't locate a single patent application that even mentions what language it's written in, though I imagine it's a complex network of machine languages and so forth. I tend to doubt the 737 runs on JavaScript...

More importantly:

Is there any procedure for QA'ing an airline manufacturer's code?
Does someone at the FAA get invited to Boeing's private Github account?

I'm mostly being facetious, but you get the idea. I ask because every day it sounds more and more like a freshman error in code cost 300+ lives.

Is there anywhere I can look for descriptions of this mysterious code and its forthcoming patch?

I've worked on some certified software in a different domain (and slightly less strict); the principle would be similar here.

Basically the certifying authority will want to make sure that proper risk analysis was done on the system—both software and hardware—and risks were mitigated to get to certain level of reliability.

The authority does not have programmers to actually review the code. They will be checking the requirements, the test coverage, records that all procedures were followed. All code must be traceable to requirements that caused it to be written, tests that cover it, there must be records it was reviewed, that all the tests passed.  All requirements must have their tests, then there have to be various stress tests, exploratory tests, the test plans have to be reviewed. There will be various static checks too and guidelines to follow. It is a massive amount of paperwork to make sure risks were not missed.

And then the required estimated mean time between failures for critical systems is so insanely low—IIRC for critical systems the mean time between critical failures must be (estimated) at least 10⁹ hours—that there is simply no way to demonstrate it by tests alone. Even the hardware won't have that reliability—it is hundred thousand years. So the system has to be designed so that it can fail safe and fail over to a backup and then the mean time between failure of all the systems during single flight is what gets above the target.

So there is procedure, but the maker does it and the certification authority only verifies that it was followed.

The safety critical code is indeed usually written in C, or sometimes C++ or Ada. However, safety critical, and any other hard real-time, code must be written with use of static memory only. This eliminates large class of problems that C code is normally known for, and the simplicity of C makes it easier to statically check—and the makers of critical software have powerful advanced tools for doing it—, so it is actually quite good fit.

The code still actually tends to be pretty ugly. It is hammered heavily with the tests, but when fixing issues found, preference is to do smaller changes to avoid breaking other parts that already passed the tests, which adds to its ugliness. Nobody thinks its perfect either, but that's not the point. The hardware is not perfect either, so the backups, fail-safes and fail-overs are designed to handle both kinds of failures.

And note that the current Boeing issue is actually a problem with the requirements. The trim system may run away for example if the switch gets stuck, which is always a risk with mechanical switch, so there must be a cut-off switch to disconnect it. And, judging from the public information only, it seems whoever designed this system argued that that cut-off switch is sufficient to handle failure of the new addition too, so the system was not considered critical and fault detection was not included in the requirements for it. But in doing so they apparently underestimated the human factors involved—specific details will be subject to analysis in the investigation and it is what usually takes so long.

Update: The article about the recent B38M crash (ET-302) links to an FAA document FAA and Industry Guide to Product Certification that gives overview of the whole process. It is not particularly about software, but the general process still applies to that.


Can ailerons be used for pitch change in the event of elevator failure? On standard fixed-wing aircraft that have both ailerons and elevators, can ailerons function as elevators for pitching movement if the elevators fail? Technically it should be possible if both ailerons can rotate in the same direction simultaneously.

If so, what are the key differences and problems if the center of gravity of the aircraft was forward of the ailerons or behind the ailerons?

To my understanding, the farther back the control surface (which causes the pitching) is to the center of gravity, the bigger the pitching moment which results in a more stable configuration.

If the ailerons could be moved in the same way on both wings, the linkage between both is broken and they would float up near their maximum negative (trailing edge up) deflection angle. Even a hydraulic aileron booster would not help, since here still an interlink between both ailerons exists to keep actuation forces down. Only in a fly-by-wire aircraft with fully powered aileron actuators could the control system be programmed to allow symmetric deflection.

The effectivity of such a means of pitch control is very low, and only wing sweep can help to make it useable. Any pitch control input will change lift on the outer wing, and pitching up would mean a loss of lift and result in a plunging motion of the aircraft. If that happens on landing, when the pilot uses to pull the stick to raise the nose gradually, the resulting ground contact will be rather early and bumpy. Pilots of flying wings know this; they are very careful with their pitch control during a flare.

When an ASW-20 glider had crashed a couple of years ago because the pilot had forgotten to connect the elevator linkage, Gerhard Waibel flew to the glider club and demonstrated how to fly the ASW-20 with flaps for pitch control alone. The downside is a much reduced speed range and a high landing speed, because you need to reduce camber in order to pitch up, but it works. Since the flap span is higher than the aileron span, I would strongly recommend to rely on the flaps for pitch control when your elevator stops working if flaps are installed. They also do not need any modification to work as pitch controls since they are rigged to move symmetrically.

If the engines are mounted low or high, their thrust can also be used for pitch control. This was used on several occasions to bring an airliner down after all hydraulic circuits had failed.

EDIT:
Mike Dunlavey insists I should mention flaperons. He is right, they are possible with mechanical linkage only, but you will find them only on wings which have flaps anyway. All modern gliders with flaps will also move the ailerons in sync with the flaps.

But they are the worst choice for pitch control. For one, they are on the part of the wing with the smallest chord. Their lift change will go with the smallest pitch moment change of all controls except the rudder, so it would be much better to use the flaps for pitch control. That the ailerons do move with the flaps will have little effect. Besides, well designed flaperons will have less deflection change for a given flap change so the spanwise lift distribution will stay close to the optimum. This will make them even less effective than the flaps.

I choose not to mention them to make the answer concise. But I'm afraid short answers are not appreciated anymore.


How can one fly a stabilized approach when the final approach path is curved? Some approaches, like the KMTN VOR/DME RWY15 depicted below, have a final approach segment that is curved (in the case below, the entire leg from FAF to RWY is one big DME arc, but this could also happen in RNAV approaches using Radius-to-Fix instead).  However, it is said that one cannot be in a turn in order for an approach to be considered "stabilized" (this is most often stated in the context of circling approaches, but is still applicable for straight-ins of course).  What does one do when stuck with an approach that cannot be flown within stabilized approach criteria?

Perhaps my thinking is now considered outmoded (retired in 1999), but for me the definition of a stabilized approach doesn't preclude turning, but only that the turning (when necessary) is accomplished at a stabilized rate. The idea was to be setup in landing configuration, at your stabilized final approach speed, sink rate, and power and tracking whatever the approach path is from the FAF down to the landing flare.

For tracking DME arcs, we were taught to find that angle of bank that (given our final approach speed) produced the desired turn rate. We would hold that bank, just as we would hold wings level for a straight final approach path.

If the DME started in increase, steepen the bank a little. If it started to decrease, lessen the bank a little.


What do these explanations for propellor RPM increases mean? I have read in a book that if the engine RPM increases while descending, the probable causes are:

Engine transfer bearing leaking excessively
Excessive friction in blade bearings

I am not able to understand these reasons.

Can someone explain "engine transfer bearing" and what these two reasons mean?

The troubleshooting section from the Hartzell Propeller Owner's Manual No.411 states:

B. Engine Speed Varies with Flight Attitude (or Airspeed)
   (1) Small variances in engine speed are normal and are no
       cause for concern.
   (2) Increase in engine speed while descending or increasing
       airspeed:
       (a) Non-feathering ( )(A,B)1 series propeller:
           1 Governor is not increasing oil volume in the
             propeller.
           2 Engine transfer bearing leaking excessively
           3 Excessive friction in the blade bearings or pitch
             changing mechanism

Reasons 1-3 relate to the propellers inability to adjust its blade angle to maintain a constant RPM when descending and airspeed is increased on non-feathering propellers.

The transfer bearing allows governor controlled oil into the crankshaft interior then to the propeller hub. If the bearing is leaking excessively the oil may be leaking back into the crankcase and there may not be enough oil pressure going into the hub to increase the propeller blade pitch and slow the engine down.

If there is excessive friction in the blade bearings the propeller blades may not move freely within the hub even when adequate oil pressure is supplied by governor and oil system.


How do I calculate fuel reserves for IFR and VFR flight plan? I am trying to figure out how to calculate for IFR and VFR for a flight plan example. So from my basic understanding, VFR means you have to add extra 30 minutes to your fuel reserve, and 45 minutes for IFR. So if I wanted to make a flight plan, would I do distance/speed + .5 (for VFR) or + .75 (for IFR)? For instance, if I am calculating that I need an hour's worth of fuel to go a distance of 100 miles at 100 MPH, how would I figure out how much fuel I'd need taking VFR/IFR into consideration?

For FAA regulations:

Once you've gotten everything planned and it's time to add on the fuel reserve, it is based on the airplane's fuel burn rate from a regulatory standpoint.

If the airplane burns ten gallons per hour, you can easily calculate that you need an extra five gallons, which is 30 minutes of flight duration at ten gallons per hour, for day VFR, and you would need 7.5 for night VFR under FAA regulations, which is 45 minutes of duration, so you would just add those to the total that you calculated that you would need to get to your destination, and you have successfully planned your reserve.

For IFR, you would have to select an alternate if the weather conditions require one, plan your flight to your destination, then to the alternate, and then add on 45 minutes worth of fuel after reaching the alternate, which would be 7.5 gallons after reaching the alternate airport.

This is the regulation for IFR reserve: 91.167


How does stall depend on angle of attack but not speed? Everyone says that the angle of attack is what determines a stall, not the speed. I understand the theory and understand that it is separation of the airflow that matters for stalling.

However, I don’t understand in a practical sense. Let’s say you’re in a Citabria going at 100 knots. If you pull up extremely fast, you can get a high angle of attack, beyond what you’d need to stall at 60 knots, yet you wouldn’t stall straight away. If you stayed at that angle of attack, you’d quickly slow, then stall. But if I’m right that you wouldn’t stall straight away, then it seems like the angle of attack is not the only thing that matters.

What am I missing? What’s wrong in my argument?

I believe you are confusing the wing angle of attack with the pitch of the aircraft.  Aircraft moving at a slow, near-stall speed, despite pointing the nose up, will still be traveling more or less horizontally.  Their VSI instrument will read near zero.  Whereas, if you take an aircraft moving quickly and pull the nose up to the same angle, the aircraft will, obviously, climb rapidly.

Why does this matter?  The angle of attack is defined based on the wing's motion through the relative wind.  The wing's orientation relative to the ground isn't involved in the definition in any way.  When the aircraft as a whole is climbing, the relative wind is coming down from above.  As a result the angle of attack is reduced, compared to what it would be if the plane were not climbing.

Just to show some quick numbers, suppose you took an aircraft moving at 100 kts in still air and pulled the nose up so that you are now climbing at 3,000 FPM (most aircraft will lose speed doing this, but the math is valid until the airplane slows down).  $1knot\approx100FPM$, so you'll now have an upward vector of 30 knots.  Your 100 kt airspeed is now moving up at an angle.  A little trigonometry:

$$\sin(x)=\frac{30}{100}$$
$$x=17.46°$$

So, your angle of attack is 17.46 degrees farther away from stalling when climbing at 3000FPM than it would be if your aircraft had the same pitch but was in level flight.

However, few aircraft have the engine power to sustain a climb at this rate.  The aircraft will bleed off speed, and as the speed bleeds off, the aircraft will slow, the climb rate will decrease, the aircraft's velocity will become closer to horizontal, and, eventually, the aircraft will stall if the pitch is held constant.


Piloting as a perishable skill - what skills go first and how to self-assess and mitigate skill loss? I know that in accident reports they will typically say the total number of hours the pilot had, but also the total hours in type and total hours in the last 90 days.  I know from personal experience that landing an airplane can be a perishable skill (I recently went 60+ days since flying and my landings were not the picture-perfect examples they usually are...don't get me wrong, nothing unsafe, just wasn't proud of them...drifting off centerline, excessive float, etc :)

The FAA seems to know this with the 90-day passenger carrying requirement (3 take-offs and landings within 90 days to carry passengers during the day and 3 to a full-stop for night passenger carriage).

All this to say flying doesn't seem to be "just like riding a bike - you never forget it."  But in what sense?  The muscle memory goes? The "seat of the pants" sensation starts to feel foreign?  I know charts can change, regs can change, but do you really "forget how to fly," or just "lose the touch?"

What skills go first, and what is the best way to self-assess your skill quality and mitigate the loss of it?

I have no hard data answers to your questions. Perhaps others will. I can, though, offer some personal observations.

My last two jobs were at 747 carriers. At the first we had two weeks on, two weeks off. At the second, we had 12 days off a month, which, with a little seniority, you could arrange to have as a block.

For me, the first thing to go was my instrument scan, and I used to joke that it took only 4 days of inactivity to lose that. The joking aside, I did notice a slight degradation the first day or two upon returning to work after time off. I should note that my habit was to hand fly the airplane to the first cruise level, and then to hand fly from the top of descent, so I perhaps would notice a bit of degradation more so than those who used the autopilot as soon as possible and until as late as possible.

I retired 15 years ago, and it had been 30 years since I had flown a light single engine airplane when, a few weeks ago, I decided to check out in a Cessna 172. After three sessions, the instructor said he was satisfied. I wasn't and we went out a four time, and he signed me off for my first-ever BFR.

In general, I did a little better than I had expected. In one area, landings, I did a worse. The problem was the sight picture I had in my head from 10 years of landing 747s. On the first landing, knowing that I'd want to flare high, I delayed rounding out until my gut way saying, "if you don't flare, you will crunch the airplane." When I started the flare, the instructor said, "No, you're way too high." I delayed again, then started again, and the instructor said I was still too high." I delayed again, then absolutely had to start again, at which time the instructor said something like, "Well, you're still high but go ahead." That landing was followed by three sessions of nothing but takeoffs and landings. Each session I improved, but, frankly, I have yet to get a really good landing. My next session will be solo and will be nothing but takeoffs and landings.

So, for me at least, I conclude that we don't forget how to fly, but we definite do lose the touch.

After I get the solo takeoff and landings session in, I'm going to go out with the instructor and shoot a couple of ILSs. I'm expecting my instrument scan to be terrible.


What happens if an aircraft goes above maximum altitude? We all know what happens when a plane goes overspeed... but what happens when a plane goes above their max. altitude? And why are planes certified maximum altitudes anyway? Is it because there won't be enough lift to keep them at that altitude? I know it's not because they don't want the aircraft to get lost in space, because the max. alt. of the Airbus A350 is at FL420, which is not even close to space. Anyone ave an answer?

There is a variety of reasons for a maximum altitude:

Most common is insufficient engine performance to climb any higher. Then your question never arises. The aircraft simply cannot go higher.
For more powerful aircraft the partial pressure of the oxygen supply in an unpressurized cabin would drop below the value to keep the pilot(s) alert. For GA aircraft without supplemental oxygen this would be 15,000 ft (short term) or 12,500 ft (long term).
For many airliners it is the pressure limit of the cabin which is certified for a maximum differential to outside pressure. If the airplane climbs higher, the internal pressure must be reduced to less than what is deemed the acceptable minimum for the passengers.
For special subsonic high altitude aircraft with sufficient engine power the limit is the coffin corner when minimum speed and maximum Mach fall together. When that height is exceeded, the aircraft stalls and exceeds its Mach limit at the same time. The result is a shallow dive which can only be recovered a few thousand feet lower.
In some cases the limit is given by minimum combustion chamber pressure inside the engine to keep the flame burning. There are cases when aircraft climbed too high, suffered a flame-out and could not restart.
With supersonic aircraft the limit might be set by maximum flight Mach number, when higher speed means stagnation heat exceeds structural limits. The high Mach number is needed to sustain minimum dynamic pressure to produce enough lift.


How is an aircraft with a stabilator trimmed? Many supersonic fighters have a stabilator to control pitch. My question arises when I cannot see any trim-tab on the stabilisator (e.g. on the F-16 or on the F-22). Other means to trim an aircraft without trim-tab and without using the stabiliser as a trim must exist. What are those means?

Trim is simply a force that offsets the neutral position of the control surface. On aircraft with mechanical controls it is provided aerodynamically via trim tab, but it can also be provided by springs, hydraulics, or simply by adding the selected offset in the fly-by-wire computer. Since F-16, F-18 and F-22 are all fly-by-wire, the last option is most likely.

In fact, all these fighters are aerodynamically unstable, which requires using “cooked” controls where centred stick commands the computer to maintain straight flight and the computer then adjusts the stabilators accordingly, doing small corrections all the time since the flight path would quickly diverge without that. So there is no trim in the traditional sense at all.


What are the ICAO PANS? What are their contents? There are how many I.C.A.O. PANS? What are their basic contents? I have tried a lot in internet, but could not find out.

ICAO Procedures for Air Navigation Services (PANS) are documents approved by the ICAO counsel and recommended to states for worldwide application. As such they attempt to make air navigation services uniform across the world.

There are five PANS:

Procedures for Air Navigation Services - Air Traffic Management (ICAO document 4444, a.k.a. PANS-ATM)

Specifies the actual procedures to be used by air traffic service units in providing the various air traffic services to air traffic.

Procedures for Air Navigation Services - Aircraft Operations  (ICAO document 8168, a.k.a. PANS-OPS)

Lays down rules for designing instrument approach and departure procedures. Such procedures are used to allow aircraft to land and take off when instrument meteorological conditions (IMC) impose instrument flight rules (IFR).

Procedures for Air Navigation Services - Abbreviations and Codes  (ICAO document 8400, a.k.a. PANS-ABC)

Is a list of abbreviations and codes commonly used in aviation.

Procedures for Air Navigation Services - Aerodromes  (ICAO document 9981, a.k.a. PANS-ADR)

This details aerodrome licensing and Aerodrome Manuals

Finally there is the PANS Training which details ISD (instructional Systems Deisgn and Systems Approach to Training (SAT) which enables criterion based and material dependent methodical learning


What are the symptoms of vortex ring state? What are the signs and symptoms a pilot can recognize, that the helicopter is approaching vortex ring state (VRS) and measures should be taken?

A related question discusses how to prevent or recover from VRS, but it does not address the recognition technique. Similar to stalls (which happen unintentionally), being able to identify a worsening situation before the stall fully develops is better than stall recovery.

Vortex ring state is characterized by rapid descent and reduced effectiveness of control inputs. At the onset, it is characterized by increased vibration and buffet of the airframe, with uncommanded changes in helicopter attitude. Also, any increase in the collective is ineffective and counterproductive.

From skybrary.aero:

  Incipient vortex ring conditions are typically:

  increased vibration and buffet,
  the onset of small amplitude ‘twitches’ in pitch and evidence of longitudinal, lateral and directional instability.

  Established vortex ring conditions are characterised by:

  a very rapid increase in rate of descent towards and beyond 3000fpm,
  reduced effectiveness of cyclic inputs in roll or pitch
  the application of collective pitch failing to arrest the rate of descent and usually increasing it.

From FAA Helicopter Flying Handbook- Helicopter Emergencies and Hazards:

  A fully developed vortex ring state is characterized by an unstable condition in which the helicopter experiences uncommanded pitch and roll oscillations, has little or no collective authority, and achieves a descent rate that may approach 6,000 feet per minute (fpm) if allowed to develop.

The best measure against vortex ring state is quite simple- go forward i.e. increase airspeed. Basically, you enter into forward flight so that the rate of descent doesn't oppose the induced flow. You need 'undisturbed' airflow over the rotor disc. Power is to be applied after gaining sufficient airspeed. From skybrary:

  Incipient Stage ... Keep the collective position unchanged and apply forward cyclic to achieve an accelerative (nose down) attitude so as to increase forward airspeed quickly. As soon as a steady increase in airspeed is indicated, and above 30 KIAS, more power can be applied if necessary without waiting until the best rate of climb speed is reached.

  If this action does not resolve the situation rapidly then it is best to treat the condition as established and take the actions below.
  Established Condition. Recovery can only be effected by changing the airflow around the rotor and will inevitably lead to significant loss of height, which makes recovery from a low level occurrence impossible.

  There are two theoretically possible actions: Moving the cyclic forward and lowering the collective. Combining these actions is likely to produce the quickest recovery with the least height loss.

  Application of forward cyclic should increase airspeed but a large input held for several seconds may be required before significant pitch attitude and consequent speed change is achieved, with a significant nose down attitude resulting. Lowering the collective to reduce power towards auto-rotation, so unstalling some of the inboard portion of the blades, may also be effective but forward airspeed must be gained before power is re-applied during recovery.

Autorotation has also been suggested as a measure for overcoming the vortex ring state (by the FAA handbook, for example), but it may lead to further loss of height, which has to be taken into account. Another issue is that there are some variations between the different helicopter types- in case of tilt-rotor aircraft like V-22, the only way is to go into forward flight.


What is the recommended procedure to land a taildragger in a crosswind? Almost 20 years ago I helped a friend (who recently passed away from an unfortunate home accident) ferry a 1948 Stinson from Córdoba, Argentina, to Buenos Aires. We had to make several stops to refuel (while classifying them by how many dogs and cats came out to greet us), and at one of the fields the crosswind component was rather strong. I can handle just about anything thrown at me when flying a tricycle gear aircraft, and went through taildragger endorsement training in a Citabria, but it was a challenge to get this bird safely on the ground.
Thinking about that today, I thought it would be good to gather guidance from experienced taildragger drivers on what is the recommended procedure to safely land a taildragger in a crosswind.

My favoured technique in strong crosswinds, perfected in many hours of glider towing in Super Cubs, Citabrias and Pawnees, is to wheel it on tail high, wing down, and balance it like that until the speed drops enough to lower the tail, then put the tail down and plant it firmly with aft stick.

In those conditions it's desirable not to have the wing at high AOA when ground contact and especially tailwheel contact (traction) is marginal, as you get when you do a 3 point landing.  By wheeling it on (wing down obviously), you get firm mainwheel contact right away, AOA is low so gusts won't pop you back into the air, and you still have air rudder authority.  The technique keeps the transition from air rudder authority to tailwheel ground traction as short as possible.

Wheel landings seem difficult but are actually easier than 3 point once you learn the trick (For the trick to be revealed, send 10$ to my Paypal @...).  Actually, the trick is simply that you PUSH when the main wheels are a foot or two in the air. You'll go plop and won't bounce or skip.  In a crosswind, it's a little trickier because you have to push while holding a sideslip and you find yourself balanced on the one into-wind tire, with your feet and hands going a mile a minute.  As you slow down the other main wheel will come down, then as soon as you slow enough to be able to plant the tailwheel without becoming airborne again, you plant the tail and full aft stick.

Also, be ready to use brake during the rollout in case rudder and tailwheel authority are both insufficient to stop a swing (this can happen on wet grass for example).

Takes some practice, but once you perfect this technique you will have much more confidence in strong X winds.


What is the reason for this route while flying from USA over Cuba? I was flying from Canada to Jamaica, and just past Florida the plane turned 90 degrees towards Nassau. It then continued over Cuba. Is this because of the situation between Cuba and the United States? It appears the plane must enter Cuban airspace from international airspace. But I have heard some planes can enter Cuba via corridors from the US. I am confused over this situation.

This was flight TS0373 on 17Jan2016.

There are two large warning areas there, W-465 A and B. Both are active "intermittently" up to 70,000ft. It seems likely that the route was taken to avoid those areas.


What is the difference between a navigation database and an airport mapping database? What is the difference between "navigation database" and "airport mapping database"? Are those both required by flight management software for flight planning?

Navigation databases are typically targeted at FMS based systems, usually using the ARINC-424 standard.  These are ASCII database files that describe aspects such as approach procedures, flight plans, spacing, etc.  It would also provide basic runway information such as heading and altitude of touchdown points - enough to navigate but not enough to paint a completely pretty picture.
By contrast Airport Mapping Databases provide a detailed layout of the entire airport in question - runways, taxiways, vertical structures such as buildings, etc.  The industry standard is ARINC-816 for the databases themselves, but the content is based on DO-272's parameters.  They are usually installed into systems with displays, e.g. Electronic Flight Bags (EFBs) - this may include Class 2 EFBs that are simply iPads for ground-only operation.
Moving maps of this type provide situational awareness, especially when coupled with Cockpit Display of Traffic Information (CDTI) and its associated applications utilizing ADS-B/TIS-B: these provide awareness as to other aircraft that might be in the vicinity, threat level, etc.
Side note: additional CDTI applications that utilize ADS-B are enumerated in DO-317.  These include airborne procedures, e.g. decreased spacing for in-trail procedures (ITP).


How would the FAA catch people without licenses? It is know that the FAA conducts ramp checks at airports. However, is it likely to be caught flying without a license from uncontrolled airports or grass strips? If so, how would one be caught?

If they are conducting a ramp check and you don’t have a license, the chances of getting caught are 100%.  The size of the airport, the presence of a control tower, or the surface of the runway is immaterial - if it is a public airport the FAA could be there.
If they are not conducting ramp checks, you would only be caught if there were a reportable incident that brings your activity to their attention.  (airspace violation, noise complaint or tip, mishap, etc.) Otherwise, how would they know?
I’m not sure how it might work at a private airport, but I would imagine the FAA would be held to the same standards as law enforcement; i.e. they would require either consent, probable cause, or a warrant to enter your property.


What does the “test result indicator” indicate on a cockpit voice recorder? I am really curious as to what the “green/red” strip of led indicate and the numbers below it. Having read around the web, i speculated that it could be an audio quality rating scale. Would help alot of someone could please help explain the “numbers” and why there is so many led blocks on the strip...

I could not find the exact model you showed, but the A330 and A340 FCOM on SmartCockpit shows a similar one. Unfortunately the description of the test is rather short:

The Overhead Pushbutton explanation on SmartCockpit is equally short:

My best guess would be that it shows the recorded volume from low on the left to high on the right and it is considered OK (test passed) if it reaches into the green LEDs, therefore making sure the CVR can pick up voices clearly enough. I hope someone working with these CVRs can provide a more accurate answer!


How is notification of UAV flight handled in an area with multiple heliports? I'm trying to get up to speed on drone licensing and regulation. I'm in central Houston, well away from either of our major airports; but there are literally 50 heliports listed on B4UFLY as being in my immediate area. AirMap shows 32 of them actually overlapping my current position. Houston did just get the brand-new shiny "Low Altitude Authorization and Notification Capability", but of course only for the two major airports.

I'm absolutely not interested in doing anything wrong; but does this mean I can't legally fly a drone in circles around my back yard at eye level without calling 32 different helicopter operators to let them know? If I managed to find a nearby spot where only, say, four or five areas were overlapping, could I actually call them and notify them, and would that make me properly compliant?

Answers relating either to Section 336 or Part 107 are appreciated. At the moment I'm just a hobbyist; but I do plan to get a remote pilot certification, because my ultimate use is academic research, which falls under commercial rules. Thanks!

Tl;dr: Yes, you are required to contact all airports and heliports within a 5-mile radius.

Unless you have a part 107 certificate you are operating under the rules of 14 CFR Part 101, Subpart E - Special Rule for Model Aircraft. Since the FAA is generally prohibited from setting rules for hobbyist operations, the only specific regulations are under this subpart. They are frustratingly unclear and refer most rulemaking to undefined “nationwide community-based organizations.” Although which organizations, or even what such an organization consists of, are not defined, the FAA works closely with the Academy of Model Aeronautics which publishes a handbook for safe operation.

One of the few specific regulations subpart E does include is the following.

  14 CFR § 101.41 (e) When flown within 5 miles of an airport, the operator of the aircraft provides the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport) with prior notice of the operation.

This means that to be in compliance you must notify all 32 heliports in your area. Note that it does not say you must get permission, only that you must provide prior notice. It also doesn’t say what kind of notice, nor how far in advance, nor if you must notify them every time you fly or if it can be an ongoing situation.

Mongo’s suggestion of mailing a letter to each one would be a good approach. Make sure you keep a copy of the letter sent and a record of who you sent them to. That way if a problem arises you have documentation that you did make the required notification.

Beyond notification, there is no mention of airspace classes, flight restrictions or anything else. It only specifies that:

  14 CFR § 101.41 (d) The aircraft is operated in a manner that does not interfere with and gives way to any manned aircraft

That’s not to say that you don’t have to follow flight restrictions. That would fall under the elastic clause:

  14 CFR § 101.43 Endangering the safety of the National Airspace System.
  No person may operate model aircraft so as to endanger the safety of the national airspace system.

If you are planning to fly for research then you should certainly get a part 107 suas pilot certificate. Part 107 regulations are much more well-defined. If operating under part 107 there is no requirement to notify the airports and heliports. An suas license requires you to know how to read charts and know what type of airspace you are operating in. By default part 107 is restricted to uncontrolled airspace (class G). To operate in controlled airspace you must apply for a waiver and follow the rules of the waiver. Once you have a waiver for controlled airspace the requirements for getting permission depend on the specific airspace you need to fly in. Under part 107, in class G airspace there is no requirement to notify anyone.


Why didn’t the Me 163 experience the serious handling problems suffered by other similarly-designed semitailless aircraft? Although the Messerschmitt Me 163 rocket-powered interceptor had a number of frequently-lethal features (its extremely-toxic, violently-reactive, enthusiastically-explosive hypergolic propellants; its few-minutes-brief endurance in powered flight, allowing enemy fighters to wait and then pounce on it as it glided home; its skid landing gear, which rendered it an immobile sitting duck upon landing until it could be towed to safety), its handling characteristics were not one of these; despite its unusual semitailless design (a vertical tail, but no separate horizontal tail), it was extremely docile at both low and high speeds (despite its excellent manoeuvrability, something more usually found in conjunction with very un-docile handling), being difficult to stall or spin even deliberately and showing no untoward changes in stability characteristics even at very high speed.
In contrast, other similarly-configured semitailless aircraft (DH 108, X-4, F7U) were uniformly beasts to fly, being prone to severe pitch oscillations at high speed, yaw and roll oscillations as well at slightly higher speeds, and generally poor handling characteristics overall.
What kept the Me 163 free of the handling difficulties that plagued all those other semitailless aircraft?

Firstly, the Me 163 is classed as tailless, not semi-tailless. The fin does not count.
Secondly, its characteristics were not wholly benign but they were acceptable by the standards of the moment for a high-speed fighter. Its lateral stability was marginal and it could behave unpleasantly in the stall. When Junkers developed it further, they found it necessary to make the leading-edge slots automatically variable and to increase the area of the landing flaps. But on the whole, yes, it was better than most tailless types.
So, why was this particular plane adequate? You will have to bear with me. A long trail of aerodynamic refinement begins with JW Dunne's tailless swept monoplanes and biplanes of the pioneer era. His D.10 biplane became the first aircraft ever to be officially certified as stable. The finless monoplanes could at least be stalled, but simply pancaked down rather than dropping a wing. Around thirty Dunne machines were flown in the UK and US and none ever had a fatal accident, a staggering safety record for that era. Dunne's secrets were many and subtle, expounded to the Aeronautical Society of Great Britain in 1913.
In the 1920s an ex RAF Captain, GTR Hill, took up the unstallable challenge once more and refined Dunne's aerodynamics, developing among other things the mathematics of the constant centre of pressure via reflex camber. A German visitor whose name I forget took it back to Germany where it was further enhanced and there Alexander Lippisch discovered it. He had the luxury of ten years' single-minded research and experimentation on one prototype after another, from glider to propeller to rocket, until the Me 163 emerged. But neither Hill nor Lippisch could get rid of the fin.
Meanwhile the detailed technical work of Dunne received only voice plaudits from others, while that of Prandtl in the early 1930s went unnoticed. Reimar Horten trod the path for himself to arrive at the finless Horten/Gotha flying-wing fighter which also handled well but came too late for wartime production.
What Dunne intuited and tested in hundreds of models, Lippisch half-grasped and Horten rediscovered and calculated, never made it over to Northrop or General Aircraft or any of the others. When Dunne's trademark conical leading-edge droop was rediscovered and used on the Convair deltas to make them flyable at low speeds, the path to it lay through quite another labyrinth. Back in the UK, Dunne and de Havilland renewed their old friendship, for DH had been Dunne's successor at Farnborough and both had trod the corridors of the RAeS together. DH wrote to Dunne that during the development of the DH.108 he would tease his staff that Dunne had got it right all those years ago, so they better had too. But like Lippisch, even he had to keep the fin. And despite also being informed by both Lippisch and the Hortens, his DH 108 was described by one test pilot as "malignant".
The real questions must be; why did so many designers turn a blind eye to the tailoring of span loading and sideways flow to eliminate adverse yaw and the need for a tail fin? and how did they manage to introduce appalling stall characteristics when Dunne's original breakthrough was to tame the stall? The key lessons had been in print since 1913, for those who had eyes to see, and Horten at least had proved capable of finding them for himself. Simple ignorance, preoccupation with conventional design issues and "not invented here" are my best guess. Prandtl's and Horten's contributions are only now beginning to receive wider acknowledgement. The epilogue must go to General Aircraft, whose GAL.56 was described by the ubiquitous Winkle Brown as the most badly-behaved aircraft he had ever flown, before it went on to kill the most experienced tailless aircraft test pilot in the world and who had consequently flown many Lippisch creations, Robert Kronfeld.
For those who want provenance and more detail I fear that you will have to wait until I can get quite a backlog of stuff past our Covid-coma'ed publishing industry. Or you may tread the Science Museum Archive's Dunne Collection for yourself, all 30,000 documents and boxfuls of artefacts of it.


What is the exhaust from the end of jet wing prior to landing? What is the exhaust from the end of jet wing prior to landing ? My guess,excess fuel from powering down engines.

The only places where any fluid leaves a flying jet aircraft are the engine tail pipes, outflow valves and air cycle machine exhausts, and the auxiliary power unit exhaust, but that is usually only used on the ground.

None of these exhausts usually leaves any visible trail at low altitudes. The engine (and apu, if running; it is a small engine) exhausts contain a lot of water, but are very hot, so it remains a vapour; it only condenses at high altitudes where there is very cold. And the air from outflow valve—excess air leaving cabin—and from air cycle machine—air used for cooling—do not have any more water in them than the ambient air.

What on the other hand might leave visible trail is condensation is vortices behind wing-tips and sometimes end of flaps. This is just fog forming in very humid air due to decrease in temperature, like it might in the coldest hours around dawn, except here the cooling is local, caused by decrease of pressure that accompanies generation of lift by wings (this is called adiabatic cooling).

Regarding fuel, when the engine power is reduced, less fuel is simply pumped to the engines, so more of it stays in the tank. There is absolutely no reason to waste it by venting it anywhere—except for very, very rare case where the aircraft needs to return due to some malfunction, and needs to get lighter to avoid more damage on landing; but this intentional fuel dumping is always done at high altitude so the fuel evaporates before it could get to the ground and contaminate it.


Where can aircraft carriers carry out air operations? I'm interested in any military or civil airspace regulations about where aircraft carriers are allowed to launch and retrieve aircraft.

For example, are fixed wing aircraft allowed to take off from an aircraft carrier while it is docked in port?

I would imagine (though could be wrong) land-based ATC and airspace conflicts have to be managed, amongst other issues.

I don't know what permissions are required (guessing a fair bit of paperwork, involving not only the FAA but also port authorities), but taking off in port (in this case, a museum ship) has been done.  The USS Midway was stationary, looks like minimal wind, but on the other hand an acrobatic plane with lots of power. (Youtube)


What does METAR show when actual RVR is below the reporting minimum? RVR is measured between 50m and 1500m (ICAO). When the actual RVR is below 50m, what does METAR show?

If the RVR is less than the minimum value that can be measured , M will precede this value e.g. R24L/M0050.

If measured in ft, then FT will follow. For example: R24L/M0200FT

For greater than can be measured and trends:

  If the RVR is greater than the maximum value that can be measured, P will precede this value e.g. R24L/P1500.
  If RVR trends can be measured then U, D, or N will follow the RVR value to indicate increasing, decreasing or no change respectively.

Source: https://www.skybrary.aero/index.php/Meteorological_Terminal_Air_Report_(METAR)


Can a zero hour pilot actually launch a Bombardier Q400 with only simulator experience? The thief of the Bombardier Q400 at SEATAC stated that he had a lot of simulator flying (I'm guessing like Flight Simulator for the PC?) Some "experts" stated that he must have had more than that to get the Bombardier off of the ground and flying 'stunts' like loops and rolls. Can a zero hour pilot pull off what apparently did happen or did the thief have to have had much more knowledge? I assume that just starting up the plane to taxi would be a complex procedure, is this easily learned in a PC Game?

You don't even need your own simulator. Here is a good video of how to start a Q400 (taken from a sim game) and here is one from a tech going through an actual cockpit. There is even a chance there were checklists in the aircraft when he arrived.

To get off the ground he really just needed to know how to gun the throttles and roughly when to pull back on the yoke to get airborne. These numbers can be found pretty readily around the web. Considering his fuel and cargo load and depending on the trim of the aircraft it may have even started flying with almost no control inputs.

Whats important to understand about some of the maneuvers he did was the fact that the aircraft was empty and flying on a partial fuel load which will make it easier to do some of those things. I will refrain from diving deep here until the NTSB report is out but at full throttle planes are capable of quite a bit. Rolling an airliner is not out of the question in the right scenario.


When airspaces adjoin vertically, which airspace class does the shared flight level or altitude belong to? Airspaces have a lateral and vertical boundary, which results in airspaces adjoining other and thus having a shared vertical boundary. Which airspace class do these shared vertical boundaries belong to?

Example:
Dortmund's (EDLW) control zone is a class D from GND/SFC to 2500ft MSL, on top of this control zone is a TMA airspace class D from 2500ft MSL to 4500ft MSL thereafter class E from 4500ft MSL to FL100and above that we have class C airspace from FL100 to FL660.

(Image Source: www.skyvector.com - Map Data: skyvector, ARINC, OpenStreetMap)

If an aircraft wants to occupy 2500ft MSL, 4500ft MSL or FL100, which airspace class are they in?

According to ICAO Annex 11 - ATS (Air Traffic Services)PDF, the less restrictive airspace is in effect on shared boundaries:

  Note.— Where the ATS airspaces adjoin vertically, i.e. one above the other, flights at a common level would comply with
  requirements of, and be given services applicable to, the less restrictive class of airspace. In applying these criteria, Class B
  airspace is therefore considered less restrictive than Class A airspace; Class C airspace less restrictive than Class B
  airspace, etc.

Unless national regulations in the country's AIP are in contradiction or the national AIP does not list any information on this, the ICAO regulation will apply.

In the above example, the altitudes or flight level would be considered:

2500ft MSL: Class D airspace
4500ft MSL: Class E airspace, since class E is less restrictive than class D
FL100: Class E airspace, since Class E is less restrictive than class C

Related questions:
What is the difference between “flight level” and “altitude”?
What is the difference between the airspace's classes (for non-pilots)?


Are electronic copies of aircraft logbooks acceptable for reconstruction? This question about a pilot losing the logbook for an aircraft got me thinking about acceptable means to reconstruct logbooks. Reconstructing the logbooks is not a trivial process (or a cheap one). Aircraft logbooks can be lost, misplaced, or destroyed for many different reasons.

There is a big focus on electronic flight bags (EFB's) with electronic logbooks, some sites dedicated to providing electronic logbook services for pilots, but nothing about the airframe/engine logs themselves.

So the question is, would the FAA and potential buyers accept electronic copies of the airframe/engine logbooks as legal record equal in value to the paper copies?

Edit
I'm curious if digitizing old records (scanning) is acceptable for electronic records. The AC for digital records has a lot of emphasis on digital signing by the original signatory, but isn't so clear on the use of a scanned copy of a signature being an acceptable backup for paper records.

According to FAA's advisory AC 120-78A, it is perfectly acceptable to maintain electronic records for airframe/engine.


What causes the "growl" of some large turbofans at takeoff thrust? There are some (all?) large turbofans which emit a distinct "growl" (some people call it a "buzzsaw" sound) at takeoff thrust. What causes it? I've seen it explained (as in this question) as the fan blade tips going trans sonic, but it doesn't account for the pitch, or so I believe. A main fan has something like 20 or 30 blades, and must be spinning at several thousand RPM at takeoff power (maybe on the order of 4,000); a blade tip would then be passing a given fixed point at around 80,000 (or more) per minute or 1,300 (or more) per second.

The musical middle C is only around 260 Hz, so any blade noise should sound like a high-pitched whine, not a low-pitched growl. You can often hear "beat" sounds due to two or more engines running at almost the same speed, but the buzzsaw growl is distinctly different. So what causes that sound at that pitch?

There is a wide range of harmonics generated by the fan, descending all the way into the lower sound spectrum. This article is about sound insulation of a turbofan shroud, and contains sound measurements of an actual turbofan in a ground installation at full TO power:

The article seems to be Google translated into English from Russian, but the observations made are very valid:

  At power regimes with Mach number M>1 at the periphery of blade wheel there is a well- observed shock wave noise appeared on harmonics of rotor frequency that could be seen at fre- quency range between the first rotor frequency and fan BPF. Shock wave noise has a high sound power level due to the used lemniscate inlet duct without lining and waisting.

We presume that "waisting" is meant as in: application of a varying cross-sectional shape (waist). The blue lines in the plot are the harmonics of the rotor frequency. There are 16 of them in the first 1200 Hz, in a linear scale this implies that the distance between blue lines is 75 Hz.

Significant sound peaks can be found at intervals of 75 Hz, immediately starting at the first harmonic line of 75 Hz. Note that the fan Blade Passing Frequency is at around 2,500 Hz, but that the frequency spectrum below the fan BPF is quite densely populated. The dominant sound that is observed on ground from an aircraft turbofan is of course dependent upon the position, distance, inlet shape, acoustic insulation measures etc etc. It makes a lot of sense if most sound insulation efforts are invested in the loudest spectrum, and that the low buzz sounds are regarded as a low priority for suppression since they are not very disturbing.


Why are fuel tanks in the wings filled first, and why are they used last? When fueling airliners, why is fuel filled first in the tanks in the wings and then the center tanks? And why do they use fuel from the center tanks first and then from the tanks in the wings?

From my research I've found the purpose is not to give too much stress to the structure of the wings, but I don't understand exactly how it works. How does having fuel first in the wings and leaving it last in the wings help protect the structure of the wings?

It's for wing bending relief (for cantilevered wings). As the generated lift bends the wings upward, the weight of the fuel will counter that.

As the plane loses weight in-flight due to burning fuel, so does the need for wing bending relief (less weight → less lift), that's why the wing tanks are the last to be used.

For context, a Boeing 777-200ER can hold 29 tonnes of fuel in each wing, and each wing measures ~27 metres and is self-supported.

Example:

Let's say in our airliner each wing tank holds 100 units (200 total for both tanks), and the center tank holds 200 units, and you have a flight that needs 200 units of fuel.

Correct scenario: By filling only the wing tanks, the weight of fuel in the wings will counter the bending of the lift.
Incorrect scenario: By filling only the center tank, the wings will bend a great deal (maybe even beyond their design limit). This is not good, and even if it is within the design limits, the repeating [avoidable] stresses will shorten the plane's lifespan.

Example for order of use (schedule):

Our flight needs 300 units, based on the above, we will fill the wing tanks, and fill half the center tank.

Correct order: By emptying the center first, we have extended the duration of the wing bending relief.
Incorrect order: By emptying the wings first, we lose the wing bending relief, while the plane is still heavy.

Related: How is fuel stored and routed on a trijet with one engine at the tail?


What is the wing angle of attack of a Boeing 737 in cruise? I would like to know the angle of attack that a 737 flies at during cruise. I am specifically interested in the wing angle of attack (if you know the cruise nose-up attitude and the wing incidence angle, that would be good too).

First, let's assume that all lift is created by the wing, and that the plane is flying in ideal conditions, where fuel flow per distance flown is minimal. This point is given by $$c_L = \sqrt{\frac{1-n_v}{3+n_v}\cdot c_{D0} \cdot \pi \cdot AR \cdot \epsilon}$$ Please see this post for more background on this formula.

Nomenclature:
    $c_L \:\:\:$ lift coefficient
    $n_v \:\:\:$  thrust exponent, as in $T \sim v^{n_v} $
    $\pi \:\:\:\:\:$  3.14159$\dots$
    $AR \:\:$  aspect ratio of the wing
    $\epsilon \:\:\:\:\:$  the wing's Oswald factor
    $c_{D0} \:$  zero-lift drag coefficient

The $n_v$ I would estimate to be -0.4, the $c_{D0}$ is somewhere around 0.016, the aspect ratio can be taken from this source and the Oswald factor is 0.8. This gives you an optimum lift coefficient of 0.445. Now we need to know what angle of attack is needed for this lift coefficient. If we look at the midspan airfoil of the 737, this angle of attack is around 2.8 degree.

This source is for model airplanes, so their Mach and Reynolds numbers are much too low for the real thing, and we need corrections for both. Using the Prantdl-Glauert rule for Mach effects, we need to correct by dividing with $\sqrt{(1-Ma^2) \cdot (1 + tan\varphi)}$ = 0.693 at Mach 0.82. Please note that this increment must be applied to the zero-lift angle of attack, which is -1°. Now our angle of attack is only 1.63°. The flight Reynolds number of the 737's MAC is 22 million, so the angle of attack is even less, maybe 1.5°. Now we need a correction for the 737 wing sweep of 25 degree, which is computed by dividing the angle of attack by 0.9, the cosine of the quarter chord sweep angle. This gives about 1.8° as the corrected value.

So my quick-and-dirty answer is 1.8 degrees. Other sections of the wing have slightly different values, according to the wing's twist. Please note that the wing area of the 737 is roughly constant since the Sixties, while the mass has increased considerably. It is safe to assume that it is operating at higher angles of attack than the optimum for best range.


What are the two blisters on F-35 upper wing surface? For all of the F-35 models you can find pictures with and without a blister on the upper wing surface. I'm guessing that it is sensors for the missile warning system that were retrofitted later on, but I couldn't find any information supporting that.

Those are Luneberg Reflectors.

They enhance the radar cross section of the aircraft.

For two reasons; to be more safe around civilian traffic due to being easier spotted by traffic control radars, and where they do not want adversaries to train their radar systems on it to gain knowledge of its strengths and weaknesses.

Not sure if those on the picture is retractable, or has to be fitted/removed by mechanics.

There are many sources for this, here is one:
https://www.businessinsider.com/f-35-luneberg-radar-cross-section-russia-estonia-2017-5?r=US&IR=T


What methods are used to make a turbofan engine spool up quicker? In cases such as a low altitude stall the quick application of power might get a pilot out of a sticky situation, but turbofan engines are fairly sluggish in increasing thrust. If throttle is applied to quickly it can even cause a surge. I'm assuming the problem is the inertia of the fan and compressor. What things do engine manufacturers do to make the engines more responsive? What are the tradeoffs? Do other types of engine (turboprop, turbojet, etc.) suffer from the same problem of delayed response?

Several things come to mind, but they will all reduce efficiency and/or cost money, so they will not be popular with engine users:

For turbofans: Reduce the rotational inertia of the spinning parts by reducing the bypass ratio. Inertia is mass times distance, so making the engine diameter smaller should have the biggest effect.
Increase temperature margins for the turbine. Today, the electronic control (called FADEC for Full Authority Digital Engine Control) will limit the amount of fuel that can be injected into the combustion chamber to limit the temperature in the turbine. By running the turbine hotter for a few seconds the turbine torque can be increased, at the cost of a reduction in the lifetime of the turbine.
For turboprops: Reduce blade pitch momentarily to unload the propeller, so more torque is available for spooling up the engine core. This, however, reduces thrust when it is needed most.
Reduce secondary loads by disconnecting generators and closing bleed valves. This is already done by todays engine control, however.

The best way of dealing with the slow engine response is operational: Avoid situations where the need for a rapid spool-up might arise or enter those situations not with engines set to idle, but to some medium power setting. Carrier pilots do this routinely by spooling up the engine shortly before touchdown, so they will have the required thrust at their disposal if the tail hook fails to catch any of the arrestor cables.

Thanks to RalphJ for pointing out that turboprops use the same tactic. Helicopters never let the engine run in idle while in flight. If less thrust (turboprops) rsp. lift (helicopters) is needed, both adjust pitch to set the desired thrust/lift and keep engine RPM up. Now the mass flow through the engine core is the same as at full thrust, only the amount of heating in the combustion chamber is reduced to adjust the power output of the engine. When more thrust/lift is needed, the pilot adjusts pitch and fuel flow to set the desired thrust/lift level. Since the engine is already running at top speed, the change is not delayed by inertial effects.


Where can the highest air density be found on Earth? I would like to see if there is any possibility of testing, validating and actually demonstrating a potential design for drag-mediated rapid braking of an ultralight plane - possibly a solar plane. In reality, a drag coefficient is not really a constant - it varies with both density and speed.

Tests at low density can be done using altitude, but for the highest density points, I am not sure even what densities are ever available anywhere, and how to go about finding these locations.

At first I thought - Death Valley or the Dead Sea area at night, but they can still be fairly warm.

Then I thought the south pole is really cold but then I realized the altitude is quite high.

Then I thought flying over some arctic or antarctic area near sea level would be the highest density, but water can warm the air a bit.

Is there a known place where one could fly through the highest density air on Earth? Is there a world's record? I suppose one could at least analyze historical airport data, but you'd need temperature, pressure and humidity and synthesize a density.

Assume the craft is actually flying and has a pilot on board - no environmental chambers, wind tunnels or mine shafts.

Any place in the arctic near sea level on a cold day would be much lower than the dead sea on a cool day.

Density Altitude Calculator


What is the EASA definition of night time? EASA requires pilots to log separately night time and night landings in the personal logbook. Now, I'm not sure in which period of time a landing is a night landing and flight time is night flight time. I would appreciate your answer, maybe also with a trustworthy source.

According to this handy document from EASA, night is defined as:

  …the period between the end of evening civil twilight and the beginning of morning civil twilight, or such other period between sunset and sunrise as may be prescribed by the appropriate authority, as defined by the Member State.

(The FAA and ICAO use a similar definition.)

You can get the Civil Twilight times from a convenient astronomical calendar, but ignoring the specifics, the same rule of thumb the FAA uses for purposes of night currency will likely work for you too:

Night starts one hour after sunset
(Sunset being when the last of the visible sun disc drops below the horizon.)
Night ends one hour before sunrise
(Sunrise being when the first of the visible sun disk breaks the horizon.)

This actually cheats you out of a few minutes of "night" on either side of the calculation, but it's conservative guidance if you're conservative in what you log you won't accidentally mess up and give yourself more night time than you're really entitled too (i.e. you won't make yourself "night current" when you really aren't).

Note that I'm a US pilot -- since all my flying and training is based on FAA regs in the US if I'm completely off the mark and any European pilots or CFIs want to set me right it would be much appreciated :-)


When airplanes first got windows, what material was used? When airplanes were first introduced they were open cockpit - but soon enclosed cockpits were developed. What were the first materials in use for airplane windows? I don't believe plexiglass existed back then.

Polymethyl methacrylate (Plexiglas)

The material was developed in 1928 in several different laboratories by many chemists.
Historically, PMMA was an important improvement in the design of aircraft windows, making possible such iconic designs as the bombardier's transparent nose compartment in the Boeing B-17 Flying Fortress.

From early on Plexiglas found a market in aviation, as the alternatives were either flammable or too heavy:
History (albeit short) of aircraft windows

The largest impediment to having closed cabins was the material the windows were to be made of. Prior to [Plexiglas] becoming available in 1933, windows were either safety glass, which was heavy, or cellulose nitrate (i.e.: guncotton), which yellowed quickly and was extremely flammable.

(wikimedia.org) B-17 nose Plexiglas.


What causes the nose landing gear knocking noise on a Boeing 777 while taxiing? The NLG knocking noise heard on taxi-in to stand, what could cause this knocking noise?

(source)

That's a pilot taxiing perfectly on the centerline, which makes one of the two nose landing gear tires hit all the taxiway centerline lights.

Just like the sound the tires of a car make when they hit the cat's eyes on a road at speed.


How does a single engine tail wheel landing gear airplane turn when it is on the ground? Say Cessna 140 as in this video, look like no additional device to make it turnable when it on the ground. It is a single engine and a tail wheel landing gear. Then, how does it turn?

The rudder cable circuit is also connected to the steerable tailwheel through springs that provide a compliant connection.  When you push a pedal it also creates a turn in that direction on the ground.

However the arrangement is unstable in the rolling plane.  The main traction elements, the two front wheels, are ahead of the center of mass so the thing wants to switch ends, like pushing a shopping cart backwards.  So there is no rolling self-aligning tendency like with a tri-gear and you have to actively provide "artificial stability" with your feet.

That, plus the kind of laggy response when the little wheel in the back is turned, with a springy connection, means there is usually a little foot dance going on while you are rolling.  When necessary, you use differential braking to help things along if a steering input (a stab on the rudder) isn't having the effect you want.

Once you are rolling above about 30 mph, the rudder itself starts to provide most of your steering control.

Taildraggers take quite a bit more attention and skill to control while rolling, which gives them a bit of cachet that trigears don't, among pilots that are into that sort of thing (like me).

How it all works:  In the exploded image below, Item 6, the steering horn, is connected to the rudder itself and it turns Item 26, the steering fork (or half fork in this case), which has the wheel on it (the springs are to provide some give to the connection to avoid over stressing things when the wheel touches down unaligned with the surface).

The interconnection between 6 and 26 has various parts that make it work a bit like a breakout clutch; 6 can turn 26, but if 26 is turned by an outside force above a certain point, its connection to 6 releases and it can caster or swivel freely until they line up again and re-engage.

So when you are rolling and work the pedals, the pedals/rudder turn the steering horn (Item 6) and it turns the fork (Item 26) with the tire as if they were a single unit and the airplane turns.  If you are nearly stopped and want to spin around to park, you lock one of the brakes and this puts so much side load on the tailwheel it breaks the fork out of its connection to the steering horn and it's free to swivel.

Later when you are rolling straight and the steering horn and tailwheel are lined up, they lock together again and you have steering control back. The internal breakout mechanism has to be set up so the breakout force required isn't too high (hard to make swivel) or too low (starts swiveling freely when you don't want it to).  You don't want it to start swiveling while you are still rolling at speed and using it for steering, or, like shoving a shopping cart backwards, around you go! (It's called a ground loop)

This is a "steerable/free castering" tailwheel and variations of this type of system are used on probably 95% of GA tailwheel airplanes out there.  When steering with this system, brake can be used as required to assist with steering because the steering authority is limited compared to a nosewheel but you generally only  apply brakes if you really have to, to avoid wearing the brakes out (the springy nosewheel connection in a Cessna 150 is similar).


How does a pilot receive weather information when overflying the oceans? As the aircraft is too far from antennas and units, how do they be aware of weather changes or weather information along their route, or on the destination and alternate airports?

It depends on what info you're after: During cruise I'm mainly interested in threats to the aircraft which normally manifest as echo on the weather radar (clear air turbulence being one famous exception) or by looking out of the window.

Do you want info on your destination and alternate airport you listen to a HF VOLMET station or ask ATC via HF (cumbersome and annoying due to often poor reception).
In our shiny new world we could also ask ATC via an CPDLC free text message. The controller simply uplinks you a message with the requested information.
Depending on your operator there might be a plethora of other information available via ACARS which - when equipped - can communicate via satellite. At my company we can get:

Updates on the winds aloft (important for fuel calculation)
Airport weather information (ATIS, METAR, TAF)
Sigmets

In general, the weather you really need is readily available. An ocean crossing is only a couple of hours. This timeframe is covered by the TAFs. So you shouldn't be too surprised when you don't have all that fancy stuff mentioned above and ask ATC once VHF COM is reestablished or you can receive a VHF VOLMET station.


Why aren’t multiengine general-aviation aircraft required to be capable of sustained single-engine flight? While perusing the See How it Flies website, I came across this alarming statement regarding multiengine general-aviation aircraft:

You must not allow yourself to think that just because airliners can climb with an engine out, your favorite light twin can climb with an engine out.
It is legal to operate a light twin with anemic or nonexistent single-engine climb performance. In such cases, engine failure at low altitude is perhaps the most critical situation that arises in general aviation with any appreciable frequency. Like a single-engine aircraft with partial power failure, you need to make a forced landing.

Given that the main point of having multiple engines is the ability to maintain flight if one of them kicks the bucket in midair, why are GA aircraft with more than one engine allowed to be incapable of maintaining single-engine flight when all this does is double (or triple, or quadruple) the likelihood of a forced landing subsequent to an engine failure?

It is legal to operate a light twin with anemic or nonexistent
single-engine climb performance.

No, and technically it would not be certifiable as airworthy as per § 23.67 Climb: One engine inoperative. Aircraft that were certified at a different point in history may subscribe to different regulations.

(a) For normal, utility, and acrobatic category reciprocating engine-powered airplanes of 6,000 pounds or less maximum weight, the following apply:
(1) Except for those airplanes that meet the requirements prescribed in § 23.562(d), each airplane with a VSO of more than 61 knots must be able to maintain a steady climb gradient of at least 1.5 percent at a pressure altitude of 5,000 feet with the -
(i) Critical engine inoperative and its propeller in the minimum drag position;
(ii) Remaining engine(s) at not more than maximum continuous power;
(iii) Landing gear retracted;
(iv) Wing flaps retracted; and
(v) Climb speed not less than 1.2 VS1.

In other words if you can get to ~5000 Ft. you need to be able to maintain a nominal climb in a light twin.
The regulation for aircraft over 6000 lbs. is similar as well depending on where you draw the line for "light". There is also more information on how the testing occurs in this AC.


What is the CLmax of the CF-100 Canuck? I've been struggling to find specifications for the CF-100 Canuck. What is the CLmax of the CF-100 Canuck and how can I find it?

The CF-100 had a symmetrical NACA 0010 airfoil, which had a Clmax of just under 1.4. according to Airfoil Tools.com (Xfoil).  Is that what you are looking for?


If the airport reported BKN002, would that prevent performing a DH 259' approach? According to this Instrument Approach:

The published Minimums are a Visibility of 1300 m, and a DH of 259 feet.

In accordance with ICAO, would the Visibility and Ceiling be above the Published Minimums to be able to execute the approach or only the Visibility?

For example, if the airport reported BKN002, would that prevent from performing the approach?

On this approach, Jeppesen explicitly states "CEILING REQUIRED", would that Mean that Both Visibility and Ceiling (Broken or Overcast) must be met to execute the approach?

Since you ask about ICAO, I have checked ICAO's PANS-OPS and Manual of All-Weather Operations.

"Ceiling Required" is not an ICAO term.

Since you tagged one of the plates SBAO (a Brazilian FIR; Atlantico ACC), I found a blog post from 2017, Brazil drops Ceiling requirement. From which, only 10 countries use that term, and ICAO hasn't used it since 1979 when PANS-OPS (8168) was released. My only guess is that your Jeppesen screenshot predates this 2017 change (the copyright says 2016).

You need to refer to the local AIP if this term is used locally.


Has the United States Air Force used Contra-rotating Propeller Aircraft? I recently saw a picture of a Russian Bear(TU-95) intercepting one of our(US) military aircraft over the Pacific Ocean.

Many years ago, when I flew in reconnaissance aircraft, we were frequently intercepted by Bears which surprisingly flew at 500+ mph airspeed.

Yet no US Military Aircraft uses contra-rotating props(to my knowledge).
Why is that?

In short, the US didn't need one.

The main reason for the development of Tu-95 was the rather unique situation existing after WWII, when the Soviet Union needed a heavy bomber to carry the (then very heavy) nuclear weapons. Due to the lack of bases anywhere near contiguous United States, the Soviets were at a significant disadvantage when it came to nuking the US before the ICBMs came into picture (US had bases in Europe and in Pacific). At that time, heavy bombers were the only way to deliver a nuclear payload and it required the aircraft to be fast, have a intercontinental range and be able to carry a reasonable payload.

The first attempt in developing a long range bomber during the last days of WWII by the Soviets didn't work out and as a result, they simply reverse engineered USAAF B-29s which had 'landed' in Russia into the Tu-4 'Bull', which lacked the necessary range. In a way, the B-29 was the forefather of Tu-95. Further development continued on this airframe, culminating in the Tu-80 'Barge', which had the necessary range, but was considered unsuitable as it lacked speed, which would be fatal against jet interceptors.

The Tu-95 was developed at the same time of the B-52 'stratofortress'. Actually the Soviet Air Force preferred the jet powered Myasishchev M-4 and Tupolev had to convince Stalin about the Tu-95's suitability. During the initial design phase, the Tupolev bureau considered two versions- one with four turbojets and another one with turboprops. The turbojet version was discarded as it would've lacked range due to the fuel hungry turbojets (Tupolev turned out to be right about that as the M-4 was sidelined due to lack of range).

The payload and speed requirements required a very powerful engine (the Kuznetsov NK-12 is the most powerful turboshaft engine ever) and the contra-rotating props were selected to overcome the problems associated with the large diameter of the propellers.

Western countries also did a lot work with contra-rotating props, but the advent of jet engines and the complexites associated with the counter-rotating props meant few graduated from the prototype stage. The Huges XF-11, for example had counter rotating props initially; they were changed to conventional ones after Huges crashed in it. The Fairey Gannet and Avro Shackleton were among the few western contra-rotating aircraft to see regular service (both were used in ASw roles, which highlight the increased endurance offered by them). A number of contra-rotating aircraft were tested during the end of WWII, but the advent of jet engines meant that the required speed could be achieved in a far better way.


Which small, light aircraft are suitable for operating at very high elevations? I live in Jammu and Kashmir, in an area with an average elevation of 4,500m / 14,700ft MSL . I would like to know what would be a good and cheap light aircraft to carry 3-4 people for a 3-4 hour flight in that location for heights upto 23000ft as mountains are at least this high?
Runway length is 3700ft and asphalt.
Budget is aroung $1 million to 1.5 preowned

Yeah that location is going to present you with a lot of problems, most notably with density altitude and mountain flying.  This is also going to depend on the airports and runway lengths available as well as obstacle clearance altitudes for the area in question.  Most likely it's going to be a turbine powered aircraft which is pressurized for comfort and features good Short Takeoff and Landing (STOL) characteristics and soft field operations.

This question will probably be put on hold shortly, primarily because it is opinion based, but I would recommend a Quest Kodiak or a Pilatus PC-6 for the role due to meeting most of that criteria minus being non-pressurized.  You would just need to provide supplemental oxygen for the crew and passengers during the flight.  Another aircraft which would be recommended is a Pilatus PC-12 or the soon to be released Cessna Denali as they meet all of these needs albeit is a bit larger and less capable as a STOL aircraft.


Where can fuel consumption data by aircraft type and route be found? I am interested in building a data analytics platform for fuel consumption by aircraft type and route. I imagine this kind of information is readily available to airlines thanks to ACARS data. I need the data to build CO2 emissions models.

Are they any freely-available datasets or do I need to get this information from an airline directly?

Thanks!

I am providing an answer to my own question. However, hopefully, someone will be able to expand further on this.

For US Airlines, the bureau of transportation statistics is a reliable source. And the data is free!


During which part of the flight the effect of air resistance is more important? Her teacher asked this question to my niece (8 years old)? However I couldn't find a solid answer either. In which part of the flight, the effect of the air resistance (drag) is more important? Takeoff, cruise, descent or landing?

The answer they are looking for is probably cruise. This is generally the longest part of the flight, so the losses from drag will add up. Most aircraft are optimized as much as possible to have good performance in cruise to save fuel and meet range requirements, so having low drag is more important in this part of the flight than others. This is also generally the section where the aircraft is traveling fastest. As Peter Kämpf showed, drag is highest at higher speeds, other than periods where landing gear, flaps, etc., are extended and add more drag.

As Jay Carr explained, drag is important at every point while the aircraft is in the air, affecting different areas of performance. During takeoff, drag will affect the runway distance needed, and initial climb performance. Low drag during descent is helpful, unless you need to get down faster, like in an emergency descent. Drag is probably highest during landing, because the emphasis is placed on having as much lift as possible at slower landing speeds, and this lift is created at the expense of higher drag.


For flight planning must the forecast weather be above minima one hour before, after or at ETA? (EU-OPS) Citing EU-OPS:

  CAT.OP.MPA.185 Planning minima for IFR flights — aeroplanes

  (a) Planning minima for a take-off alternate aerodrome

    The operator shall only select an aerodrome as a take-off alternate aerodrome when the appropriate weather reports and/or
    forecasts indicate that, during a period commencing one hour before
    and ending one hour after the estimated time of arrival at the
    aerodrome, the weather conditions will be at or above the applicable
    landing minima specified in accordance with CAT.OP.MPA.110. The
    ceiling shall be taken into account when the only approach operations
    available are non-precision approaches (NPA) and/or circling
    operations. Any limitation related to OEI operations shall be taken
    into account.

  (b) Planning minima for a destination aerodrome other than an isolated destination aerodrome

    The operator shall only select the
    destination aerodrome when:

      (1) the appropriate weather reports and/or
      forecasts indicate that, during a period commencing one hour before
      and ending one hour after the estimated time of arrival at the
      aerodrome, the weather conditions will be at or above the applicable
      planning minima as follows:

        (i) RVR/visibility (VIS) specified in accordance with CAT.OP.MPA.110; and

        (ii) for an NPA or a circling operation, the ceiling at or above MDH;

      or

      (2) two destination alternate aerodromes are selected.

  (c) Planning minima for a destination alternate aerodrome, isolated aerodrome, fuel en-route alternate (fuel ERA) aerodrome, en-route alternate (ERA) aerodrome

    The operator shall only select an
    aerodrome for one of these purposes when the appropriate weather
    reports and/or forecasts indicate that, during a period commencing one
    hour before and ending one hour after the estimated time of arrival at
    the aerodrome, the weather conditions will be at or above the planning
    minima in Table 1.

  [...]

On the other hand:

  CAT.OP.MPA.245 Meteorological conditions — all aircraft

  (a) On IFR flights the commander shall only:

    (1) commence take-off; or

    (2) continue beyond the point from which a revised ATS flight plan
    applies in the event of inflight replanning,

  when information is
  available indicating that the expected weather conditions, at the time
  of arrival, at the destination and/or required alternate aerodrome(s)
  are at or above the planning minima.

  (b) On IFR flights, the commander shall only continue towards the
  planned destination aerodrome when the latest information available
  indicates that, at the expected time of arrival, the weather
  conditions at the destination, or at least one destination alternate
  aerodrome, are at or above the applicable aerodrome operating minima.

  (c) On VFR flights, the commander shall only commence take-off when
  the appropriate weather reports and/or forecasts indicate that the
  meteorological conditions along the part of the route to be flown
  under VFR will, at the appropriate time, be at or above the VFR limits

  CAT.OP.MPA.246 Meteorological conditions — aeroplanes

  In addition to CAT.OP.MPA.245, on IFR flights with aeroplanes, the commander shall only continue beyond:

    (a) the decision point when using the reduced contingency fuel (RCF)
    procedure;

    or

    (b) the pre-determined point when using the pre-determined point (PDP)
    procedure,

  when information is available indicating that the expected
  weather conditions, at the time of arrival, at the destination and/or
  required alternate aerodrome(s) are at or above the applicable
  aerodrome operating minima.

So, should a commander of an operator's flight opt to commence a flight when the forecast at the ETA is above the minima, or the forecast needs to be above the minima for the period from one hour before the ETA till one hour after the ETA?

Weather above planning minima one hour before and after ETA for flight planning and for determining alternate requirements (2 alternates vs 1).
Weather above planning minima at ETA for commencing flight.
Weather above operating minima at ETA for continuing flight.

One way you can think of it: in the cockpit weather at ETA. In the briefing room weather one hour before and after.


Is multi element wing good option for slow flight airplanes? Can we use  multi element wing  for slow flight planes, like F1  multi element rear wing?
If we know that pressure act prependicular to the surface why this two upper elements are "almost" vertical?
It seems to me that they produce "tons" of drag instead lift.Resultant  force point to far back,instead down!

Excellent application inverted on the drag racer, which brings home the point perfectly.  If you have enough excess thrust, devices like these can dramaticly increase Coefficient of Lift, but at the cost if loss of lift efficiency, or lower lift to drag ratio.
In the case of the dragster, more propulsion efficiency is lost if tires break loose from the pavement, so the drag of the "inverted Fowler flap" is an acceptable trade-off to the downlift increasing traction.
As mentioned in comments, this is why the Fiesler Storch requires 240 HP to achieve its legendary STOL performance.
And just as flaps 10 is better for lift than flaps 30 for taking off, one might question the need for the second and third flap on a lifting wing, but heavy airliners love them when coming in to land as Fowler flaps.


Can confirmed passengers preview or request flight plans before the flight? Can a passenger who has booked a flight wants to learn about the filed flight plan of their flight, prior to boarding it? I'm aware that the flight plan can change, or an aircraft can deviate from it, but still desire a rough map.

I'm aware of websites like Flightaware.com, but I think they only start tracking after departure?

For example, in the future, I'd want to see beforehand whether the aircrew decides to fly near a no-fly zone or dangerous area.

Yes, and you don't even have to be a confirmed passenger (that would be kind of weird). There are probably several sources for this, but FlightAware includes filed route information for upcoming flights. Note that this link won't work very well in a week, since it's datestamped to the future. However, they show the route on the map, and also print out the current planned route:

UAL1
KIAH STYCK1 DOLEY ADM J21 IRW HYS LBF RAP GGW YEA YEG 5600N 12000W BINGA NCA11 COHIL WUXAN 6000N 16000W 5900N 17000W 5700N 18000E ONEIL R580 OPAKE R580 OLCOT R580 OATIS Y802 ARMOR Y810 KETAR Y811 VEPOX Y811 MELON RJAA


What does "Where AOC requirements are redundant to AAC requirements, or more detailed, the AOC requirements will be followed." on Part 7 of CAR Does it mean, The requirements for AOC are no longer useful to AAC, AOC will be used?

It means that if the AOC is more detailed, or contains the same thing as the AAC, then whatever is written in the AOC should be used.


Air quality monitoring devices for a320 I looking for the air quality monitoring devices for a320. How do they look, where they located?
thank you for the help

Far as I can tell, there are no passive or active air quality monitoring devices on the A320. The cabin air systems on modern airliners are designed against an air quality standard, and their performance is tested with equipment that is installed on the test aircraft for that specific purpose.

EASA published the results of an air quality campaign test program in 2017.

  In total, 69 measurement flights were performed between July 2015 and
  June 2016 on 8 types of aeroplane/engine configurations. This included
  61 flights on aeroplanes equipped with engine bleed air systems, and 8
  flights on Boeing 787 which is equipped with electrical compressors
  (‘bleed free’ system). For all flights, measurement equipment was
  installed in the cockpit and in the cabin.

  The results show that the cabin/cockpit air quality is similar or
  better than what is observed in normal indoor environments (offices,
  schools, kinder gardens or dwellings). No occupational exposure limits
  and guidelines were exceeded. Special attention was paid to
  organophosphates, in particular TCP (Tri Cresyl Phosphates) with the
  use of high sensitivity analysis techniques. Only traces of TCP meta-
  and para-isomers were sometime detected in all aeroplane types, but no
  ortho-isomers were detected.


Why do new engines have a case with a triangular tiling pattern? Take a look at the case of new engines such as the F-135:

or the F-119:

Why do they have a case with a triangular tiling pattern? Is this a new technology? A new material?

This type of structure is called isogrid structure. Solid walls are usually very heavy and therefore engineers use more weight-efficient structures such as sandwich structures or stiffened structures with stringers and frames. A downside is the huge manufacturing cost compared to other options.
As you can see from NASA Report CR-124075 "Isogrid Design Handbook", which was written 50 years ago, it is not a new type of structure.


What is this part of an aircraft (looks like a long thick pole sticking out of the back)? On the website of Kenn Borek Air (an airline specializing in Arctic / Antarctic operations), on this page at the bottom, you can see the following picture:

It looks like a long thick pole sticking out of the aircraft (likely from the back?)
What is it?

That is called a Survey Tail Boom and includes sensitive instruments that need to be mounted away from the aircraft body for clean measurements.
You can see the name of the manufacturer LCAS printed on the boom. In this case, it seems to be a tail boom for magnetic field measurements installed on a Douglas DC-3, which is used for Survey according to Borek Air's fleet information. The LCAS website has a detailed description of the tail boom:

LCAS’ fully certified (Supplemental Type Certificate) tail-mounted transition and boom assemblies carry the magnetometer sensor and requisite electronics. The aft part of the boom system contains the provisions for the magnetometer sensor, the mid section houses the amplifier and flux gate and the transition assembly can house optional electronics such as pressure/temp sensors. The transitions or forward boom assemblies can also be modified for installation of optional video cameras.  The orientation of the sensor is adjustable, to provide optimum coupling with the earth’s magnetic field. This innovation eliminates the traditional towed bird system and offers significant advantages in data quality, pilot work load reductions, survey flight efficiencies, and safety in all types of terrain.
The mod kit includes all the necessary doublers, support assemblies and attaching hardware, as well as new ‘end cap’ with Nav. light provisions, this allowing the aircraft to be flown without the tail boom and the OEM tail cone assembly to remain un-altered.

(lakecentral.com)


How can avionics detect tailwind? We can see the effect of the tailwind on the plane's flight direction on the modern military fighter jet huds. I wonder about how can the avionic systems detect tailwind and which sensors using in the process.

This can be sensed by means of either an INS or GPS to determine a ground velocity and both the data from the pitot static system and a magnetometer to determine the true air velocity.  The local wind velocity is the difference between the ground velocity and the true air velocity.


Why do most fighter craft have a center stick? Is there a specific reason why in most fighter planes, the control column is between the pilots legs instead of on the sides like Airbus airliners? I know the F-16 has sidesticks, but most of the others have it in the middle.

F-16 Cockpit with sidestick

F-15 with centerstick

Images from Wikipedia

At present, it appears to be a design choice rather than any other thing.

Most of the present generation fighters are transitioning to side-mounted sticks from center sticks. Almost all of the US combat aircraft have side-sticks. In Europe, it's somewhat of a mix- Typhoon (and Gripen) have center sticks, while Rafale has a side stick. The Russians are sticking to a center stick in the T-50.

The location of the control stick depends on a number of factors:

Ergonomics- Side stick is better in this regard, limiting the display area in the center; this might be a problem in smaller cockpits.
One of the reasons for using side stick in F-16 was that it (the hand-rest) supported the Pilot's hand during high 'g' maneuvers, along with the inclined seat (which is also being used in a number of aircraft).
There is also the personal choice- some pilots may prefer using a center stick, and others, the other way around (there seems to be little problem in transitioning from one to another).

Historically, combat aircraft have had center sticks. Side sticks have come about after fly-by-wire controls. Eurofighter has the following to say in this regard:

  Every military aircraft cockpit design has to be something of a compromise, but in a small cockpit, a center stick can cause particular ergonomic difficulties, perhaps limiting the size of the display area for the instruments and/or screens ... That is when options are considered, and one of those would be the sidestick as used in the F-16. However, if the cockpit is sufficiently large and the geometry of the seating position is correct, there is no reason to have anything other than a center stick—and the pilots of the four partner nations agreed. The choice between center sticks and sidesticks is 40% personal—the balance being on technical grounds. We find that F-16 pilots convert easily and naturally to a center stick.


Do I have to declare an emergency if I cut into fuel reserves? In another question, I wrote

You only need to plan for regulatory reserves. You don't actually have to land with them

and @Jan replied:

you have to declare emergency if you do cut into them though and that will quite probably get you an investigation

I have never heard that you must declare an emergency if you cut into your reserves (regardless of the stage of flight), and I'm wondering if there is any regulation to back it up.
The only reg that I could find that comes close is NTSB 830, which lists a set of criteria for notifying the NTSB within 10 days:

(a) An aircraft accident or any of the following listed serious incidents occur:
(1) Flight control system malfunction or failure;
(2) Inability of any required flight crew member to perform normal flight duties as a result of injury or illness;
(3) Failure of any internal turbine engine component that results in the escape of debris other than out the exhaust path;
(4) In-flight fire;
(5) Aircraft collision in flight;
(6) Damage to property, other than the aircraft, estimated to exceed $25,000 for repair (including materials and labor) or fair market value in the event of total loss, whichever is less.
(7) For large multiengine aircraft (more than 12,500 pounds maximum certificated takeoff weight): (a bunch of other things)

I'm interested in the answer for Parts 91, 135, and 121, under FAA regulations.

There seems to be no regulations that require decleration of emergency in case of using reserve fuel. US DoT InFO 8004 specifically discusses this:

  Emergency Fuel. Although not defined in the AIM or Federal aviation regulations, the  industry-wide connotation typically associated with the
  term “Fuel Emergency” is:

  The point at which, in the judgment of the pilot-in-command, it is necessary to proceed directly to the airport of in tended landing due to low fuel. Declaration of a fuel emergency is an explicit statement that priority handling by ATC is both required and expected.

Noting that pilot declaring minimum fuel is not an emergency,

  The act of using a portion of the reserve fuel assigned to a flight is not,  in its self a cause to declare a minimum fuel state with the controlling agency. Regulations require reserve fuel to enable aircraft to maneuver, due to unforeseen circumstances. Many aircraft safely arrive at their destination having used a portion of the fuel designated as reserve. There is no regulatory definition as to when, specifically, a pilot must  declare “minimum fuel” or a fuel emergency. Air carriers typically develop such guidance for their pilots and include it in their General Operations
  Manuals; such guidance generally  falls along the following lines:

  •Declare “minimum fuel” when, in your best judgment, any additional delay will cause you to burn into your reserve fuel.

  •Declare a fuel emergency at the point at which, in your judgment, it is necessary for you to proceed directly to the airport at which you intend to land. Declaration of a fuel emergency is an explicit statement that priority handling by ATC is necessary and expected.

(Emphasis mine)