What effect does wing loading (high and low) have on aircraft performance? I've read that stalling speed is partly determined by wing loading. Correct me of I'm wrong - "Aircraft with high loading have more weight relative to their wing area hence the stall speed is increased (as the requirement for lift is increased)".

Also I've read that "faster aircraft have higher wing loading". I didn't quiet understand that statement.

And is wing loading weight/wing area, or mass/wing area?

Wing loading is, as a North American industry standard, defined as weight/wing reference area (W/S). But then again, there is nothing wrong to define it as mass/area; so be careful of comparisons against literature.

As you have correctly cited in your OP, a large wing loading inversely affects performance, this includes takeoff performance and turning performance, all due to increased stall speed. Assuming a constant maximum lift coefficient, the larger the wing loading, the higher the stall speed:

$$V_{{s}}=\sqrt{\frac{W}{S}\frac{2}{\rho C_{L_{max}}}}$$

Large wing loading, however, is beneficial from a ride comfort perspective and offers structural benefit (i.e. weight saving) when considering gust loads. Assuming the same level of gust, the faster an airplane flies, the higher vertical acceleration (G) it experiences. A particularly salient and approximate relationship can be found in 14 CFR 23.341 (pre Admt 64), whereby the load factor from gust is given by:

$$n_z=1+\frac{K_gU_{de}Va}{498(W/S)}$$

In the above, $K_g$ is the gust alleviation factor which increases with W/S, $U_{de}$ is the gust speed in ft/s (found in 23.333 and decreases with altitude), $V$ is equivalent airspeed in kt, $a$ is the lift curve slope. As you can see, the load factor decreases with increasing wing loading and increases with increasing airspeed.


Does any USAF fighter jet use surfaces near the front for pitch control? Some European fighters like Eurofighter use frontal surfaces for pitch control. Does any US fighter use this configuration? And what are these surfaces called?

These surfaces are called canards.
To my knowledge no canard equipped fighter ever entered service with the armed forces, though there were a few experimental prototypes such as the CCV/AFTI F-16 or the F-15 ACTIVE which made use of canard foreplanes.

The Grumman X-29, Rockwell X-31, and Boeing X-36 are other examples of US technology demonstrators which made use of canards for extreme maneuvering, none of which were ever pursued further for development into a fighter aircraft.


Do airliners adjust altitude for latitude? According to this NASA article, the troposphere extends from about 5 miles at the poles to about 9 miles at the equator. Though the height of the troposphere is defined by the height of the tropopause as per this Aviation SE question.

I'd expect that the air pressure at the top of the troposphere would be similar at 5 miles above the poles as it would be at 9 miles above the equator.

As the altitude of an airliner increases, the angle of attack necessary to produce the same amount of lift also increases. Eventually an altitude is reached where the angle of attack necessary to produce sufficient lift is also the stall angle of attack. This pretty much defines an airplane's service ceiling. (Certainly, there are other factors, but this is a pretty big one.)

This suggests that the service ceiling would be lower at the poles than at the equator. Does this mean that an airliner flying a polar route would fly at a lower altitude than one staying in the temperate or tropical regions?

(aviationweather.gov) Significant weather chart.

Note the numbers in boxes. They decrease as the latitude increases: 450 → 400 → 350 → 250.

Note: those values change day to day and season to season, they're not fixed.

Those are the tropopause heights. 450 is FL450, i.e., 45,000 feet at a standard altimeter reading.

This figure is very important in flight planning. Jets typically fly around this figure for optimal aircraft/engine performance.

So yes, you're right, the farther you fly from the equator, the lower you should fly. However, the following two statements are incorrect:

I'd expect that the air pressure at the top of the troposphere [be the same regardless of latitude.]

The pressure gradient is still the same. See: Why is the troposphere 8km higher at the equator than the poles?

As the altitude of an airliner increases, the angle of attack [also increases.]

As the altitude increases, so does the speed, to counter the thinner air. Until you end up in a coffin corner.

Also, for high latitude polar flights, an airline can do away with the optimal performance, because the rise in temperature helps keep the fuel from freezing, however I may stand corrected on that.


What's for the "smoke fittings" in this muffler? Just was reading this manaul => DLE-120 engine User Manual
In this page (pg 4), saw this part:

What's for the "smoke fittings" or "fuel tubing"in this muffler?

It is indeed so that you can generate smoke from the exhaust, typically for airshows. The general idea is that you introduce oil or specific liquids that have been created for specific colours to the hot muffler, which will create smoke. This is how skywriting works, the pilot can turn the system on and off, like lifting their pen from the paper.
If you're not using it, it does need to be plugged as otherwise exhaust (and sound!) will exit the hole rather than the correct exit at the end of the muffler. The "fuel tubing" mentioned in the manual is simply the same tubing used for fuel supply, as the diameter is suitable for it to slot over the nodule, and for the 8-32 screw to fill the inside diameter of the tubing completely, as the diagram indicates.


How are ejection seats tested? How does a company like Martin Baker, evaluate the safety of their ejection seats. Are there any standard metrics or tests that exist? If not, what would be the suggested tests to be performed before they release the seat.

Edit: I am more interested in the type of data they collect from the tests. If I were to create a ejection seat on my own, what quantities would I use it to compare it against Martin Baker's seat?

Martin-Baker tests their seats in an actual aircraft. They have, for some time now, used a Gloster Meteor to test their designs as discussed in this question. They also have a high speed sled at their facility for such tests.. 0-0 tests are easier to pull off since there is no moving component.

Individual components like explosive bolts or handles are likely tested like any other engineering component, in a test facility.


Which commercial aircraft can perform a parallel engine start? In various Youtube videos, e.g. this one, one can see that the Boeing 787 is capable of a parallel engine start (both engines are started at the same time). Are there any other commercial aircraft around that allow for a dual (or multiple parallel) engine startup?

What is the reason the Boeing 787 can perform parallel engine starts? What is the difference with other aircraft that cannot perform a parallel startup?

The main reason behind this capability is that the Boeing 787 starts its engines entirely on electrical power generated by the APU's VFSG (Variable Frequency Starter Generators) vs relying on APU bleed air to start the engines. Thus there isn't the typical drop in pneumatic pressure caused by the pneumatic starters on regular jetliners.
See 787 No-Bleed Systems for reference.

The Airbus A-340 can start both engines on a wing at the same time (1 & 2 then 3 & 4) as described here.


Do aircraft engine intakes require air filters? I see helicopters which have air filters in their engine intakes, but jet fighters and commercial turbojet airliners don't seem to have any filters in their air intakes.

Isn't it true that even tiny particles can damage the turbofan's blades, especially since they rotate at such high speed?

What if the aircraft has to fly through a dusty area?

In addition to Rachet Freak answer I'll add that helicopter engines are subject to much dirtier air. Aircraft operate from runways which are relatively clean. Due to their speed, most dust and debris that is kicked up is behind the engine inlet so it is not sucked in.

Helicopters hover and land vertically and therefore their engines ingest air contaminated with kicked up dust. Especially when operating outside paved surfaces this results in considerable pollution. A filter is much more useful here.


How can a helicopter be designed without a tail rotor? How will the main rotor torque be balanced if a helicopter doesn't have a tail rotor?

The torque in a helicopter is generated by the engine driving the main rotor in one direction, which causes the fuselage to spin in the other direction. The tail rotor shaft is horizontally mounted and hence creates it own 'lift' to provide anti-torque. The pitch of the tail rotor gives directional control.

Common ways to design a helicopter without a tail rotor:

Tandem rotors : Two main rotors mounted one in front of the other. The rotor discs spin in opposite directions. All power from the engines is used for lift. Example: CH-47

Transverse rotors : Two main rotors mounted side-by-side. Example: Kamov Ka-22

Co-axial rotors : Two rotor discs are mounted one on top of the other. The engine units power both rotors. This structure requires a very complex swashplate mechanism. Example: Kamov Ka-25

Intermeshing rotors :  In this main rotor assembly, the two set rotor masts are installed at a slight angle to each other, in a transversely symmetric manner, so that the rotor blades intermesh without colliding with each other. Example: Kaman K-MAX

Tip jet : This is an interesting solution to the no-tail-rotor problem. Instead of driving the rotors with a turboshaft engine, compressed air is sent through nozzles installed at the tips of rotor blades. The engines effectively push against the air rather than the helicopter fuselage. The rotor spins just like a Catherine wheel. Example: Hiller Hornet

NOTAR : NOTAR - NO TAil Rotor uses a fan inside the boom to build a high volume of low-pressure air, which exits through two slots and creates a boundary layer flow of air along the tailboom utilizing the Coandă effect. The boundary layer changes the direction of airflow around the tailboom, creating thrust opposite the motion imparted to the fuselage by the torque effect of the main rotor. Example: MD-900

Refer to Wikipedia for more!


What is the exact meaning of "attitude", does it include translational movement? Reading documentation it is clear to me that "attitude" means the study of orientation of a body. However sometimes it seems to be used loosely for the motion tracking of a body (both translational and rotational, not rotational only).

Is it a mistake or a common abuse of language?

Your assumption is correct, attitude is orientation in space and it excludes translation.

Object orientation in space can be defined using multiple systems. The one used in aviation uses three angles:

heading or yaw (around the yaw axis)
pitch (around the lateral axis)
roll or bank (around the longitudinal axis).

Source.

Attitude is usually understood as orientation relative to the horizontal plane, that is only two angles:

pitch
roll/bank.

In the common definition heading is not taken into account. For example, in no wind condition, "level flight" is usually obtained by maintaining a constant attitude, that is constant pitch and roll angles. We'll find this sense in the expression flying by attitude, nose-up attitude or unusual attitude.

Attitude is visualized using an attitude indicator (aka artificial horizon):

Attitude indicator, indicating 5° right roll and 10° down pitch

In some applications attitude may include heading as well, and thus becomes a synonym for orientation in space using the three angles:

heading/yaw
pitch
roll/bank.

This use is more often found in flight dynamics and astronautics than in aviation. In this sense attitude and speed help determine the velocity vector. More on that in attitude reference frames.

Heading reference must be specified. In aviation heading reference can be geographic or magnetic North and has its own instrument, the horizontal situation indicator or directional gyro (or the compass as a backup instrument):

Directional gyro, indicating a heading of 113°. Source

The three angles can be combined into a single instrument, this is often the case for head up displays:

Source.

3-angles attitude can be quantified as a quaternion or a matrix of angles, usually Euler's angles (actually Tait–Bryan's angles).

It can be visualized using a spherical attitude indicator (more at Space Exploration):

Orbiter attitude indicator, source


Can the Master Caution illuminate without the System Annunciator Panel on the 737NG? Does the master caution light illuminate only with the System Annunciator Panel?
Or is the master caution illumination also connected to the related system panels?
I mean if there is an indication on a system panel and the System Annunciator Panel is inop due to some issue, does the master caution illuminate alone?

If everything is working as designed then the Master Caution is always accompanied by one of the 12 annunciator lights (or more than 1, depending on the situation).
If things aren't working as designed, then what you'll see depends on the nature of the malfunction. If it's as simple as a burned-out bulb in the annunciator panel, then you could get the Master Caution without an accompanying light. That's usually followed by a disgruntled "oh, great" followed by heads swiveling around to find what individual amber light is illuminated. And/or pressing the Recall function (see what fails to light up, or comes on now), and/or using the Lights Test switch.


What is the difference between being instructed to land "as soon as possible" or "at nearest suitable airport"? On commercial airliners, the FCOM (Flight Crew Operating Manual) sometimes gives instructions to the pilots to land sooner than planned, following various in-flight failures or emergencies. For instance, for serious emergencies (e.g. in-flight fire), the pilots would be instructed to LAND ASAP (as soon as possible), as there is a real danger to the aircraft and its occupants if they stay in the air any longer.

For less severe situations, the pilots would be instructed to LAND ANSA (at nearest suitable airport), which gives them more leeway in deciding where to land.

My question is: other than the fact that LAND ASAP is obviously more urgent than LAND ANSA, could anyone go into more details as to how a pilot would interpret these instructions, and how they differ? (for instance, does LAND ASAP mean "land on the nearest reasonably smooth surface", or is it less extreme than that? Are there guidelines on approximately how long you should keep flying after receiving a LAND ANSA instruction?)

I would interpret them as:

ASAP means the plane is going to kill you. Soon. So land before that happens. Short runways, military airports, abandoned airfields, a decent highway, dry lakes (e.g. Edwards AFB), calm bodies of water (e.g. the Hudson River) are all possibilities. Do not concern yourself with operational issues like taking off again, and bureaucratic formalities like immigration will be summarily ignored. Obviously if you are near the Hudson you would try very, very hard to reach JFK, Teterboro or Newark, but sometimes that doesn't work out.

ANSA means try for a real airport considering immediate operational and bureaucratic requirements, but not beyond immediate. this could include turning around and landing at Goose Bay. Basically I'm going to punch "Nearest" on the Nav panel and make an educated choice. Most Nav sets will only show open airfields that can accommodate your aircraft. For example, Gimli would not have appeared for Air Canada flight 143, assuming they had a suitable unit back then and the power hadn't gone out.

The terms are deliberately unclear to give the pilot some flexibility - you can't predict and write a procedure for everything.


When do the LNAV and VNAV NPS pointers appear in the PFD of a B737NG? I am pretty sure the LNAV NPS pointer should appear from after takeoff, if LNAV is armed.
But I am not sure about the VNAV NPS pointer. A VNAV climb is based on Speed, not Path, so I assume there is no NPS Pointer visible during a VNAV Climb.
When will it first come on? Once cruise altitude is reached? What happens if one has to level-off before reaching his CRZ FL? Will the NPS pointer appear at that time?

The lateral NPS will be present if there is a defined LNAV track active, and the APPROACH mode (i.e. to track an ILS) is not active. The vertical NPS is inhibited until the FMC-computed Top-Of-Descent point, so it won't be present during an intermediate level-off during an RNAV departure. It's also inhibited after GS Capture, since the ILS glideslope is then primary & having the NPS would be distracting & unhelpful.


What do the tail numbers on aircraft mean? Could someone please tell me the meaning of the alphanumeric numbers on aircraft's tails?

What exactly does the SB 023 mean for this Indian Sukhoi-30 MKI aircraft?

TL:DR, SB-023 means it is airframe number 23 of the SU-30 model MKi. It is flown by the Indian Air Force.

The small rectangle is what is known as a fin flash. It generally identifies the country of origin of the aircraft and sometimes the garrison or command within that country. In this case it indicates India (not to be confused with the Irish Fin Flash. We can be sure it is India because the roundel further forward is that of the Indian Air Force.

The letters and numbers above are likely to be the "tail code" Which is a USAF term. I'm sure this term has a unique name in Indian military parlance but I can't find it. The Tail code usually describes the either the home base or  manufacturer of the aircraft as well as sequence number of the aircraft. Note that sequence number and serial number are not identical and multiple air frames may share the same sequence number as air frames are retired or refitted.

On a USAF Aircraft a two-letter code generally indicates its home base. The plane would then have a numerical code indicating year built and sequence number.

I've had a look through google images and every SU-30MKi I can find has an SB prefix to its tail code so I am going to guess that it is an indicator of manufacture and/or sub-type. Interestingly, all SU-30s and Mig-29s bear the same prefix within type (SB and KBU, respectively) but Mig-21s have a variety (I've seen UI, CI, CII, and CUI.) Which makes sense since India has fielded multiple variants of the 21 but only one variant of the 30 or 29. My observations are based on a survey of the first 4 pages of google images for each aircraft so are hardly exhaustive.

The Sequence numbers come up in discussions among enthusiasts for example.

It is worth noting that India's military designation system evolved while the country was part of the commonwealth during WWII, the time when most of the world's modern designation systems were conceived. Despite that, India employs many Warsaw pact and a few home-grown systems, resulting in a unique combination of designation system and technologies.


Why isn't there a single best airfoil for subsonic flight? Why does airfoil used by modern subsonic aircraft (this is true for transonic airliners too) vary from plane to plane?

Haven't we figured out a single best airfoil shape, with the highest lift to drag ratio?

For the same reason why we do not have one single type of aircraft flying all commercial and military missions worldwide: flight has many variables, and there is no single optimum solution.

First off, you mention transonic flight in your question, which usually involves sonic flow at over at least part of the airfoil, which significantly alters the desired properties of the airfoil. To follow with this example, have a look at supercritical airfoils. They exhibit good qualities for their typical flight regime, albeit at substantial development and manufacture cost. A simpler NACA airfoil would be more cost-effective for applications that do not require high-subsonic cruise efficiency as one of their main points.

Additionally, there are more specific situations, like flying wings, that usually use reflex camber to deal with the lack of horizontal stabilizer. Again, this modification is rendered into pointless weight and cost if used outside this particular scenario.

Now, to specifically address your Lift-to-Drag requirement: that is simply not a good way to decide "the best airfoil for subsonic flight". High efficiency is important for aircraft with a mission that emphasizes endurance. This category is populated by gliders, and is indeed full of highly optimized designs ($C_L / C_d \approx 50$ is not unheard of) with little differences, mostly due to structural considerations.

Now take another subsonic aircraft with an emphasis on endurance: the maritime patrol aircraft, the best known example here is probably the P-3 Orion. A glider airfoil would be terrible because of the need for thickness to accommodate a spar that can carry the engines without breaking under a bad gust. Instead it uses a NACA 0014-1.10 at the root, transitioning to a NACA 0012-1.10 at the tip, meaning the designers had to compromise between two airfoils even within the same wing.


What is the process for requesting flight following in Canada? In US, the process to get flight following is pretty straightforward. You call the approach/center frequency, request a flight following and you get it.

On a recent flight originating from a Canadian airport (Lachute, CSE4), I contacted Montreal approach after takeoff and requested flight following. They asked me if I had filed a flight plan. I said no, and they asked me to speak to Quebec radio so that a flight plan could be filed, Quebec radio will then give me a number and I am supposed to call Montreal approach again with that number. I contacted Quebec radio and the lady asked me a number of flight plan related questions and then asked me to standby. She never came back. Can someone elaborate on this?

What is the general process to get flight following in Canada?
Is a flight plan required to get flight following?
On another flight originating in Canada (CYKZ - KFRG), I was able to get flight following via Ground Control. So I am guessing a flight plan is not always required. What is so special about Montreal? How am I supposed to know which centers insist on a flight plan before they will provide flight following?

The general procedure in Canada is the same as in the USA: to contact the nearest ATC unit and ask for a radar service.

For any VFR flight beyond 25nm from the point of departure it is mandatory in Canada to file either a flight plan or a flight itinerary before departure - (CAR602.73(2)).

The provision of radar service to VFR traffic is typically at the controller's discretion and dependent on workload.

VFR Traffic in the Montreal area is generally expected to follow the suggestion published in the Canada Flight Supplement to contact the Montreal ACC 30 minutes prior to departure to obtain a discreet squawk code. This procedure becomes mandatory if you hope to penetrate the Class C airspace.

Generally it's worth reading the appropriate national publications and/or getting advice from an FBO at your point of departure when flying in a foreign country (Canada).


Why/How does the Pilatus PC6 Approach nose-down? How is it possible, and why?
Why is the aircraft not overspeeding?
I understand it has beta thrust, so would that be an explanation? What are the advantages to such a steep approach?

How: With flaps out and the engine at idle that is the pitch for this aircraft that will yield its maximum decent speed.

Why: Max rate decent are commonly trained to be used in emergency situations but in this case its likely being used to save time since jump planes make money jumping. In most situations passenger comfort and airspace organization limits decent rates and keeps them controlled. Jump planes simply serve the purpose of getting passengers to jumping altitude and then getting back on the ground to scoop up the next load so max decent is used to save time.


What is the speed of a standard airliner during the different phases of the flight? I would like to know how does the speed of an airliner vary as a function of time.

Ballpark:

At the gate, 0 knots
Taxi, 5-30 knots (usually 10-20)
Takeoff, 150 knots (rough ballpark)
Climbout below 10,000', 250 knots
Climbout above 10,000', 270-320 knots
Climbout above 28,000', Mach .78 (ballpark)
Cruise, Mach .78 (groundspeed ~450 knots +/- wind)
Descent above 28,000', Mach .78
Descent 28k to 10k, 280 knots (up to 330 knots, if ATC requests)
Descent below 10k, 250 knots
Traffic pattern,200 knots
Final approach, 140 knots
Taxi in, 10-30 knots
At the gate, 0 knots

Edit: these are fairly typical 737 numbers; other aircraft will have differences. Regional jets will typically be slower; 747 and 777 will often be faster (especially for takeoff and cruise).


Can I measure induced drag with a simple wind tunnel test? Device can measures total drag force  and lift of wing for given AoA and airflow speed.
Wing both wingtips are far away from side walls.
Airflow speed is constant all the time:50m/s
TOTAL DRAG=MEASURED DRAG
TOTAL DRAG =ZERO LIFT DRAG + INDUCED DRAG
TOTAL DRAG=PROFILE DRAG +INDUCED DRAG
profile drag=skin friction drag + pressure drag
Step 1.
•First I put  wing at zero-lift angle: it show 500N drag force
Step 2.
•Then I put wing at 15° AoA:it show 700N drag force
Results:
So for 15° AoA and 50m/s:
"Profile drag"(Skin friction + pressure drag) is 500N and induced drag is 200N(700-500).
Is this correct calculation?

Yes, by the textbook definition $C_D=C_{D_0}+KC_L^2$.
Your measurement at AoA=0° gives $C_{D_0}$, 500 N.
Your measurement at another AoA=15°, by subtraction, gives $KC_L^2$, the induced drag at that AoA, 200 N.
If measurements at many AoA's yield a consistent $K$ and $C_L$,
then you gain confidence in those values.
If the airfoil is strongly cambered, a better fit to the equation is made if you add another term proportional to $C_L$ (not squared).


What information does Mode S provide? What information about own aircraft does TCAS Mode s( all call) send in the interrogation?
What information does Mode S transponder(intruder)replay to TCAS interrogation?

Mode-S provides altitude and identification data, with Automatic Dependent Surveillance Broadcast (ADS-B) adding global navigation data typically obtained from a Global Positioning System (GPS) receiver. The position and identification data supplied by Mode S/ADS-B broadcasts are available to pilots and air traffic controllers.


Why was F-18 chosen to escort Space Shuttle Endeavour? This question is kind of a continuation to Why does NASA have F/A-18s?

The accepted answer states that

  "NASA uses them for pilot training and as chase planes for research
  aircraft."

So, why was F/A-18 chosen for the Space Shuttle, among ton of other options available (all aircraft with 2 seats)? Also, I would like to know why NASA got F/A-18 in the first place, out of the rest.

Because it's what they had at the time and it's what the astronauts were flying. Only one of the NASA F/A18's is actually a two seater:

  The aircraft were obtained from the U.S. Navy between 1984 and 1991.
  One has a two-seat cockpit while the others are single-seat aircraft.
  NASA research support aircraft are commonly called chase planes and
  fill the role of escort aircraft during research missions.

Their main purpose is to keep an eye out for external issues with the carrier. This podcast covers most of the nitty gritty details of that operation.

  Chase pilots are in constant radio contact with research pilots and
  serve as an "extra set of eyes" to help maintain total flight safety
  during specific tests and maneuvers. They monitor certain events for
  the research pilot and are an important safety feature on all research
  missions.

As for why they have them:

NASA has a long history of using high performance jet trainers to keep the astronauts sharp. Since many of the older generation of shuttle pilots came out of the Navy or were test pilots, choosing former Navy aircraft is only logical. For much of the Apollo era as well as the shuttle era they actually used T-38's for training and keeping the astronauts current. NASA likes high performance, safe, simple jets for astronaut training as there are things you encounter actually flying that you just don't in the simulator.

  "It's actually our most important training that we do as astronauts,"
  said Terry Virts, who flew as the pilot of STS-130 aboard shuttle
  Endeavour. "It’s the one place where we're not in a simulator. It's
  real flying and if you make a mistake, you can get hurt or break
  something or run out of gas. There are a lot of things that happen
  real-world in a T-38 that don't happen in the simulator."

The actual shuttle trainer is a GII that flies with the gear down, full flaps, and thrust reversers to simulate the descent of the shuttle.


When does the FMS in the 737NG switch to approach mode? I fly a B737-800, and we talk about when the FMS enters "Approach mode". At this point, the FMS will command the Vref (plus additive) at the appropriate flap setting. This is helpful to know especially when there is a flap malfunction.
When does the FMS switch to "approach mode" for calculating speeds, and where do I find this information? I haven't seen it in the FCOM.

If the 737 is like most other FMS installations you will find the approach will activate at the capture fix.  It is typically the waypoint just before the FAF.  If you were flying into KMEM RNAV RWY 36C the capture fix would be NESBT and the FAF would be GINIE.
In the FMS that I use, the capture fix is typically loaded twice into the flightplan.  Once from the enroute structure and once again for the approach after the approach name.

NESBT
** RNAV 36C **
NESBT
GINIE


Have jet engines ever "Sheared" off? I have read that jet engines, at least the under-wing ones, are attached to the airplane by shear nuts and bolts so that in case of unstable forces in or on the engine, the engine would fall off to prevent further damage to the airframe. Have there been any incidents and or accidents where the engine has fallen off the plane in accordance to this design feature?

Engine shearoff, though rare, has happened in a number of cases.

Boeing 747F experienced a number of engine falloffs:

On Dec 1991, China Airlines flight 358, a 747-200F, lost an engine near Taiwan and crashed.
On October 1992, a El Al 747-200F crashed after takeoff due to engine separation, at Amsterdam, the Netherlands.
Another 747F from Evergreen Airlines lost an engine over Anchorage, Alaska soon after.
On October 2004, a Boeing 747-132SF of Kalitta Air lost an engine while climbing and landed without further incident.

Engine separation has been reported on 737s too:

In November 2007, Flight CE723, a Nationwide 737-200 lost an engine during takeoff; the aircraft was landed without further incident.
On December 1987, USAIR FLT 224, B737, lost an engine during climb; the aircraft was landed successfully.

There are cases where engine separation has occurred in B707, B727, and DC-10. aviation-safety.net has a list of engine separation incidents.


Do the stabilators on the F/A-18 also have a roll function similar to the F-22? I'm curious about the F/A-18C. I know it has ailerons, but they seem too small to be greatly effective at low speeds. Do the stabilators have a roll function as well? If so, is there a speed at which one or the other becomes inactive?

Yes it has differential stabilators. Below is a description from the F/A-18's (A/B/C/D) NATOPS flight manual. Almost every surface including the flaps and leading edge devices are used in rolling the aircraft (fly-by-wire magic):

2.8.2.8 Control Augmentation System (CAS).
The lateral control system uses ailerons, differential trailing edge flaps, differential leading edge flaps, differential stabilator, and rudders to achieve the desired roll characteristics. Scheduled air data roll rate feedback is used to augment inherent airframe roll damping. At high airspeeds, aileron travel versus stick movement is reduced and the ailerons do not deflect above 600 knots. Differential stabilator and differential trailing edge flap travel is reduced at high speed to prevent exceeding structural limits. The leading edge flaps deflect differentially up to ±3° when below 30,000 feet and above Mach 0.7. Differential flaps are not used in the takeoff or land modes nor above 10° AOA in the auto flaps up mode. At low airspeeds, aileron and differential stabilator travel are reduced with increasing AOA to minimize adverse yaw. Differential stabilator may also be limited due to a pitch command which has priority. With lateral stick deflection, the rolling-surface-to-rudder interconnect (RSRI) schedules increasing rudder deflection as a function of decreasing airspeed and increasing AOA for roll control, coordination, and to reduce adverse yaw.


How does the traffic pattern at a large airport affect nearby, smaller airports? Do the landing and takeoff directions for a smaller airport (GA and bizjet traffic) change when the traffic direction at a nearby large airport changes?

Specifically, I'm wondering about how traffic at FTY and PDK would be affected by the direction of traffic to/from ATL.

Generally speaking when airports like this are close together the airspace is designed to allow operations at both airports to occur without interfering with each other.

Broadly speaking if one airport changes approach direction it may be the result of a wind change. Assuming the local prevailing winds shifted its likely the other airport will change approach direction as well due to the wind shift.

The VFR sectional actually sheds some light on your specific area in question

(source)

In other words, if your flying VFR its likely that IFR aircraft from the outer airfields will initial be assigned to 3000 ft. (so keep your eyes on the lookout) and if we look at the Class B floors around that area 3000 keeps you under them in most places. In a round about way you can infer that controllers are going to assign and vector you under the class B to keep you out of the ATL area. Runway turnarounds or not.


Do large aircraft accumulate water in their tanks? Do large aircraft accumulate water in their tanks?

If so, how is it drained? How often is it drained? At what rate per hour does it accumulate? If not what was done to circumvent the problem?

AFAIK all aircrafts accumulate water in their tanks. Since you ask for large aircraft acccording to wikipeadia:

FAA definition of large aircraft

  The US Federal Aviation Administration defines a large aircraft as any
  aircraft with a certificated maximum takeoff weight of more than
  12,500 lb (5,700 kg)

EASA definition of large aircraft

  The European Aviation Safety Agency (EASA) defines a large aircraft as
  either "an aeroplane with a maximum take-off mass of more than 5,700
  kilograms (12,600 pounds) or a multi-engined helicopter."

Here is Airbus A340 draining process with explanations on youtube

Here you can find EASA regulations about draining https://www.easa.europa.eu/download/etso/ETSO-C76b_CS-ETSO_11.pdf

Here is FAA regulations about water draining
https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC20-125.pdf

On FAA AC 20-125 p.7 states

  WATER REMOVAL/PREVENTION. Water is best removed from jet fuel by
  passing the through approved filtration/separation equipment. A
  two-hour settling period and the use of floating suction to drain fuel
  from the top of a storage tank are also recommended to help prevent
  water from being introduced into a fuel system. Water will readily
  settle-out of aviation gasoline; therefore, filters/separators are not
  required for water removal, however, they are necessary for removal of
  solids. The best means to minimize the amount of water entering a fuel
  system is the inspection and proper maintenance of equipment and the
  training of ground and flight personnel.

Also FAA AC 20-125, Water In Aviation Fuels, para 7 c suggests that it may be necessary to gently rock the wings of some aircraft while draining the sump in order to completely drain all the water.


How many pilots does an airline hire for each new plane they purchase? I guess this would depend if the airplane is narrow body or wide body because wide body airplanes make longer trips. Another way to ask this question is what is the ratio of airplanes and pilots in an airline company for wide body and narrow body passenger jets respectively.

The answer depends greatly on the airline's operations, as the constraints are very different between long-haul and short-haul trips, whether relief crews are required, layover times, need and distribution of reserve pilots, and other factors: some pilots employed by an airline will be performing management duties, on leave, training, etc.

Assuming the numbers on airlinepilotcentral.com are accurate, we can look at some averages:

Emirates: 4,300 pilots, 258 aircraft: 16.7 pilots/aircraft
Delta: 14,600 pilots, 881 aircraft: 16.6 pilots/aircraft
United: 12,491 pilots, 763 aircraft: 16.4 pilots/aircraft
Southwest: 96,14 pilots, 748 aircraft: 12.9 pilots/aircraft
SkyWest (US regional airline): 4,621 pilots, 453 aircraft: 10.2 pilots/aircraft


If an aircraft is not IFR-equipped nor the pilot IFR rated, is it possible to get a border country to grant access from their CAA authority? This could also apply to neighbouring countries that are just over water like UK-France, Canada-US (Lakes).

Basically, a VFR flight only with permission granted from that country (if that's possible?).

And if so, then how would it work?

(Obviously you'll need: en route charts, passport, aircraft papers, PPL license.)

Note: A flight plan (FP) is needed for crossing a border, even for VFR.

For US-Canada, the answer is yes to VFR-only planes/flights/pilots. Note: for crossing the ADIZ, that would require DVFR (Defense VFR).

For UK-France, also yes. Note: even a mixed FP is possible (VFR-IFR-VFR). Below are excerpts from UK AIP:

  1.11.1 Pilots undertaking Cross-Channel flights are reminded that a flight plan MUST be filed for all flights to or from the United Kingdom which will cross the United Kingdom/France FIR Boundary.

  1.11.2 Specific FPL addressing requirements are detailed in paragraph 2 VFR Flight Planning.

  2 VFR Flight Plans

  2.7.1.1 The CAA have received reports that some VFR flight plans, filed for flights between France and the United Kingdom, have not been received at the UK destination aerodrome. Although these reports are infrequent, they nevertheless identify a significant safety aspect of cross-channel flight planning. The ability of the Air Traffic Service Unit at the destination aerodrome to be aware of an inbound flight is a key factor to alert search and rescue services, when appropriate.

  2.7.3.1 Additionally, for flights to/from France, the French Authorities require the frontier crossing point (the UK/France FIR boundary position) to be included in Item 15 (Route) of the FPL. To assist pilots, the UK now includes the ATS route reporting points on the Southern England and Wales 1:500 000 chart. These can be used as a frontier crossing point. A position may also be shown as LAT/LONG, or as a bearing and distance from a route reporting point or navigation aid.

  Example:

  Cap Gris Nez - RINTI
  Cap Gris Nez - 51N00130E
  Cap Gris Nez - RINTI23005
  Cap Gris Nez - DVR16010

As for how that would work, by checking the AIP (1.6  Mechanisms for Filing a FPL), it will be done via 'flightplanningonline' (a fax option is available too).

Also worth submitting, even if not required for a flight to France, is the general aviation report (GAR).

As for the minimum navigation equipment, it is found in GEN 1.5 of each country's AIP. As an example for the UK:

  All aircraft (except gliders and SLMGs) under IFR within Controlled Airspace below FL 245.

  VOR receiver, DME and automatic DF (except aircraft with Special VFR clearance).

Assuming a single-engine plane flying VFR and not for the purpose of public transport and below FL 245, there doesn't seem to be any special requirement for navigational equipment, except for ILS if flying into "certain aerodromes within Control Zones".

In short, you can fly a bare-bones plane across the Channel if you wish, but since weather can and does quickly change, you need to have an exit strategy if faced with visibility below 5 km and/or lots of unanticipated clouds.


What are the duration of TAFs? TAFs (terminal aerodrome forecast) have different durations. Some forecasts 30 hours into the future while others forecasts only 24 hours.
But what is the shortest and longest TAFs? and how often are TAFs updated?

First you will need to learn to decode the TAF's validity period.

TAF YMAY 022230Z 0300/0312 35010KT CAVOK
FM030800 31018KT 9999 SHRA BKN025 OVC100
INTER 0308/0312 31020G40KT 3000 +TSRA BKN010 SCT040CB
RMK FM030600 MOD TURB BLW 5000FT
T 23 24 28 33 Q 1012 1013 1014 1009

The validity of this TAF (in bold) is formatted as ddhh/ddhh.

  Validity period of TAF is from 0000 to 1200, on the 3rd day of the
  month UTC

From here we can see that it's valid for 12 hours.

Another example:

TAF COR YMLT 212240Z 2200/2218 31015G28KT 6000 -RA BKN010 OVC100
TEMPO 2209/2218 2000 +TSRA BKN005 SCT040CB
RMK
T 25 21 18 15 Q 1014 1013 1013 1011

  Validity period of TAF is from 0000 until 1800 on the 22nd of the month UTC

This one is valid for 18 hours.

You may check your country's AIP for how often they are updated.

For instance, in Australia, GEN 3.5 - 5 describes the routine TAF service based on airport size.

A International:  Issued 6 hourly, valid for 24 or 30 hours.
Commencement times 00, 06, 12 and 18 UTC.

B Large: Passengers > 150 000 or Movements > 75,000
Issued 6 hourly, valid for 12 or 18 hours. Commencement times 00, 06, 12 and 18 UTC.

C Medium:
Passengers > 50,000 or Movements > 10,000
Issued 6 hourly, typically valid for 12 hours.
Commencement times are 02, 08, 14 and/or 20 UTC, except in Western Australia where commencement times are 04, 10, 16 and/or 22 UTC.

D Small:
Aerodromes meeting passenger and movement thresholds, or other operational criteria.
Issued 6 or 12 hourly, valid for up to 12 hours.
Commencement times are typically 20 and/or 02 UTC, except in Western Australia where commencement times are typically 22 and/or 04 UTC.


Why do some Airbus jetliners at full thrust sound like turboprops? When riding an A3xx I always noticed the unique "turboprop" like sound when close to full throttle. Why is that so?

I'm assuming you mean that buzzing/growly/deep humming sound.
That is the tips of the fan blades in the first stage fan disc approaching the speed of sound, and getting close to forming shock waves. Their noise generation becomes strong at that point.


What does "still air" mean when planning alternative airports? When planning for a takeoff alternate, according to 14 CFR 121.617

  (1) Aircraft having 2 engines. Not more than one hour from the departure airport at normal cruising speed in still air with one engine inoperative.

What does "still air" mean?

Is it because of the performance tables for Aircraft?

Or just don't take the effect of winds on aircraft range?

The latter - it means you don't need to take winds into account for that portion of the takeoff alternate selection.


What exactly happens when I try to maintain the flare when coming to a hover? I've been considering this question.  I believe myself to be an average pilot but I'm embarrassed to say that I could not figure out the answer to the following question:

I flare and use power to maintain height, for example coming into the hover.  As I slow, I must keep increasing power.  I have enough power to hover out of ground effect.

If I attempt to continue maintaining the flare, attempting to come to a stop, I will sink and if I don't do anything about it, I will hit the ground. Why?

I've been trying to think through all of the key aerodynamic effects but keep hitting a brick wall.

P.S.  Fixed wing pilots - if you don't have a good understanding of helicopters, please try to resist the temptation to guess.  A helicopter in this flight regime is similar to a fixed wing in that it's a powered, heavier than air flying machine. End of list.

If I attempt to continue maintaining the flare, attempting to come to a stop, I will sink and if I don't do anything about it, I will hit the ground. Why?

if you continue to maintain aft cyclic after the flare, you will hit the ground because some of the lift which is being generated will be used to fly the helicopter backwards, and you won't have enough power in to both maintain altitude and also maintain backwards flight (which is what you are commanding with aft cyclic). This is why we level off after the flare: to use all the lift in the vertical direction.

Its the exact opposite of take-off: if you are in a hover on the runway, and push the nose over to the 60KIAS nose-down attitude, you will descend into the runway.

Although I have never tried it, I imagine that at the peak of the flare, if I add (a lot?) of power without changing the attitude (much:), I will not descend into the runway, but rather I will start to fly backwards.


Did DB Cooper's aircraft land safely with the aft stairs open? I've never seen a 727's aft stairs open, but presumably, based on an Wikipedia image and common sense, they do reach the ground when the aircraft is on the ground. Furthermore, (as I understand it), airliners land with a positive pitch, which means that assuming a level runway, the rear of the aircraft will touch down first. However, this suggests that if the aft stairs of the 727 were open during landing, they would impact the ground during landing and, given the pitch, do more than scrape the ground and cause damage to the aircraft.
However, DB Cooper's jump left the aft stairs open, and (as far as I can tell) it seems that the landing was uneventful besides the stress of having a hijacker potentially on board (although it's quite understandable if no one made any record of it, given there were slightly more important things to deal with).
If DB Cooper's flight did land without damage, why is that—did the 727's aft stairs not fully touch the ground? If the stairs did impact the ground, was there sufficient damage to require repairs?
(I meant this question to be more about the 727 than DB Cooper, but since his was the only landing with stairs open, there wasn't much room for speaking in general terms).

The aft airstair was partially deployed for the duration of the approach and landing.
The transcripts of ATC communications between NW305 and various ground stations are freely available (and a fascinating read). The relevant communications (with Reno) begin on PDF page 87 (numbered 213). Below are the mentions of the airstairs from that point on, with times given in PST, 1971-11-24. I added the text in brackets for clarity.

22:35, NW305: OKAY AH WE'RE TRYING TO MAKE CONTACT WITH [Cooper in] THE BACK [of the airplane] NOW AND AH WE'RE GOING TO GET THESE
STEPS UP BEFORE WE CAN MAKE OUR LANDING...
22:43, RENO: NORTHWEST THREE ZERO FIVE WHAT'S THE STATUS ON THE STAIRS NOW SIR
22:43, NW305: AH WE HAVEN'T BEEN ABLE TO GET AHOLD OF ANYBODY [in the back of the plane] YET UH TRYING TO CONTACT HIM AND THEY'RE STILL
DOWN SO I WE HAVEN'T DECIDED YET AH WE MIGHT COME IN AND LAND WITH
THEM DOWN THERE'D BE SOME SPARKS SO
22:48, NW305: APPROACH AH THREE ZERO FIVE WE CAN'T SEEM TO RAISE HIM BACK THERE WE KIND OF HATE TO WE'D JUST AS SOON LAND WITH THE
THING HANGING DOWN IT ISN'T ALL THE WAY DOWN AND THEN PROBABLY WON'T
HAVE ANY PRESSURE ON IT SO WE HOPE IT'LL (unintelligible) FREE...
22:57, NW305: ...WE'RE NOW MARKER INBOUND AND UH AH WE'RE GOING TO BE LANDING WITH THE AIR STAIR IN THE DOWN POSITION AH WE DON'T SEEM TO
GET ANY RESPONSE FROM OUR FRIEND IN THE BACK
[The aircraft touches down and is taxiing.]
23:03, NW305: SEE ANY SPARKS COMING OFF THE TAIL AT ANY TIME ON AH TOUCHDOWN
23:03, RENO: NEGATIVE NONE AT ALL THE ONLY THING THAT'S VISIBLE ON THE TAIL IS LIGHT AH APPARENTLY ON YOUR RAMP
23:03, NW305: ROGER UNDERSTAND STAIR LAMPS AH STAIR LIGHTS
23:03, RENO: I DO SEE SOME AH SPARKS NOW JUST A FEW AH TRAILING YOU AH AS YOU'RE TAXIING IN
23:03, NW305: OUR AH PASSENGER TRIED TO DISEMBARK
23:03, RENO: I STILL DON'T AH GETTING A FEW SPARKS NOT VERY MANY AT ALL
23:03, NW305: OKAY WE'LL TRY TO SLOW OUR TAXIING HERE AS MUCH AH IT PROBABLY IS DRAGGIN AH

Why did the crew not retract the airstair before landing?
The airstair can only be operated from two positions: one in the main cabin and one on the exterior of the aircraft. It cannot be operated from the flight deck. The testimony of Tina Mucklow, the flight attendant whom Cooper interacted with almost exclusively, reveals that

Approximately four minutes after takeoff, [Cooper] stood up, told [Mucklow] to go to the cockpit and close the first-class curtains, and for no one to come out from behind the curtains.

It should be noted that the airstair was still closed and locked at this point. In fact, it was Cooper himself who performed the deployment:

...he asked her to demonstrate to him the procedure for opening the rear door and extending the stairway. She did this and was under the impression that he understood how to do it. She commented that it occured to her at this time that this was the only function of the aircraft which she had discussed with the hijacker during the time she had been with him which he did not seem to be fully aware of.

Even though before Mucklow left Cooper in the cabin "...she pleaded with him to take the bomb with him and he said he would take it with him or disarm it...", nobody could be sure, so complying with his demand for no one to enter the cabin was the obvious choice. Even after the crew suspected he had jumped, there was still some chance that he was present. That—on top of the clearly dangerous situation of being unrestrained in an airborne jet transport with a door open—compelled the crew to sit tight in the cockpit and land with whatever configuration they could control from there. Indeed, third officer and right-seater on the flight Bill Rataczak stated that

...no member of the crew departed from the cockpit to check on the presence of the hijacker following the arrival in the compartment of hostess Mucklow, who had locked the door behind her.

How did the airstair remain partially deployed on its own?
The airstair is in contact with the tarmac when deployed on the ground. In fact, it's designed to essentially wedge itself against the ground and act as a tail stanchion to keep the airplane from tipping backward during loading and unloading. Early 727s such as N467US had mechanical locks for the airstair in both the extended and retracted positions to accomplish this function.
However, the crew had evidence that the airstair was not locked, as Mucklow "observed the red indicator light go on the [flight engineer's] panel indicating that the stairs had been lowered." On the 727-100, that light would be de-energized only if the airstair was locked either up or down. (On the -200, a green light was added to indicate a fully extended and locked position.) The ATC transcript indicates the captain's later belief that the airstair wasn't "all the way down", so it's reasonable to assume the warning light remained illuminated.
That the airstair didn't lock down when deployed indicates that it never fully extended. It is likely that the air loads simply prevented full extension. The airstair hydraulic actuators were not designed with the strength necessary to overcome a 170-knot airstream, especially on early 727s. The extension was limited by the airspeed and subject to fluctuations with changes in the airstream and the weight of Cooper upon the stair.
The inability to fully extend the airstair in flight was even known on the ground beforehand, as the transcript of communications between NW305 and the airline's base at MSP reveal (I cleaned these up):

18:38, MSP: DON'T KNOW OF ANY WAY TO LOCK STAIRS IN AN INTERMEDIATE POSITION.
18:40, NW305: ...STAIRS WILL OPEN ABOUT 20 DEGREES AT 120 KNOTS. IS THAT ENOUGH FOR AN INDIVIDUAL TO ESCAPE THE AIRCRAFT?
18:40, MSP: WITH HIM ON STAIRS WILL OPEN POSSIBLY ENOUGH FOR HIM TO GET OUT. REMAIN UNPRESSURIZED. BE IN LANDING CONFIGURATION WITH
FLAPS. SLOW TO [APPROACH] SPEED BEFORE TRYING TO EXTEND STAIRS.

As it turns out, the stair could not be opened much if at all at 170 knots during a climb, and the captain had to "have 'er about down to a hundred and sixty knots" and level off at 7,000 feet to get the resistance low enough. It makes sense that a higher angle of attack would cause a greater air load on the door due to the increased frontal area. It also makes sense that the airflow alone would be insufficient at any speed to completely re-close the door due to the geometry of the empennage, the weight of the stair, and some hydraulic damping. Once the door was open, the crew were able to climb again to 10,000 feet and keep the airspeed "in the vicinity of one seventy, one eighty [knots]".
Although the hydraulic actuators would have provided damping, the swirling wakes from the landing gear and flaps—not to mention the aircraft turbulence inherent when flying low and slow over mountains in a storm—undoubtedly wrenched the stairs up and down considerably. Cooper's exit has been romanticized as a high-dive into the unknown, but it was more like trying to exit a springboard during an earthquake, with his own weight just exacerbating the problem. We know as much from Richard McCoy, Jr., a copycat hijacker who survived his jump (at the same airspeed) and was later captured and interviewed:

...[McCoy] stood geared up in the open doorway for a very long time before
descending the aft stairs. It was almost midnight, the sky was black,
and the wind was freezing, yet his hands were sweating. Finally, he
was able to collect his wits, take a deep breath and step outside onto
the stairs.
As he stepped out, the entire stairway dropped two feet under his
weight. Knocked off balance with his 70-pound duffle bag between his
legs, he grabbed the right handrail and wrapped both arms around it,
desperately holding on. The stairs shook and vibrated. The noise from
the jet engines on either side of him was horrendous.

In fact, it was cabin-pressure fluctuations caused by Cooper descending and exiting the airstair that allowed for the determination of exactly when he jumped (8:11pm PST):

Crew reported oscillation of cabin rate-of-climb indicator. This probably due to [Cooper's] weight now on stairs, stairs extended further, resultant effect on cabin pressure.

The FBI's analysis was that "When [Cooper] jumped, the air stairs were forced closed (by outside air pressure) causing an increase in air pressure similar to shutting a car door with the windows up". Although we've established that the door was not forced completely closed and locked, it's clear that the airstair was able to hang somewhat freely in the airstream, its deflection affected by air loads, the weight of Cooper, its own weight, and any dampening provided by the actuators.
What was the risk of landing with the airstair deployed?
The crew knew from the cockpit indication that the airstair was neither down and locked nor up and locked. But they had prepared somewhat for the idea of landing with a deployed airstair before they even departed Seattle:

19:27, MSP: IT WOULD PREVENT ANY SUBSEQUENT TAKEOFF IF YOU LAND WITH [THE AIRSTAIR] DOWN.

Mucklow advised Cooper more than once of this fact, given that Cooper had stated intentions to get to Mexico and that Reno was just a necessary refueling stop along the way due to Cooper's wanting to be flown low and slow.
Landing with a deployed airstair could have a range of consequences that had never been investigated or analyzed, so most likely the airline was playing it safe. At the very least, a detailed inspection would need to be carried out before the airplane flew again. If the stair were downlocked, the results of a landing would depend on what failed first. If only the latch failed, you might get away with just dragging the stair, which would cause some exterior damage but overall that'd be a relatively minor fix. If nothing on the airstair failed, I suppose you could bend the entire fuselage. I'd also worry about bits and pieces of failed components being rocketed around the empennage or into the cabin.
Fortunately, at this point the crew was safe from the worst outcomes because the stair was not downlocked. In fact, as we've seen, the crew knew that even at 120 knots the airstair would not be deployed far enough to strike the ground upon touchdown. That speed is in the ballpark for an empty 727 on landing, but even at a lower speed it's entirely plausible that the airstair did not strike the ground on touchdown, and was only able to fully extend once the aircraft was at taxi speed.
What damage did the aircraft sustain?
Given everything we've covered so far, the damage was probably not extensive. Dragging the stairs along at taxi speed would mean not much more than some sheet-metal repair. Looks like some of the railing paneling sheared away, probably in the air:

There's also the placard found in the forest a few years later that got ripped away at some point during the flight.
In any case, the crew was able to easily deplane via the deployed aft stairs:

23:14, NW305: ...WE'LL GO DOWN THE BACK STEPS AND AH AH WE'LL BE TAKING LEAVE OF THE AICRAFT AND SHUTTING IT DOWN AT THIS TIME...


What DAL level is IFE software certified at? An inflight entertainment (IFE) system has software for the computers and for the seatback displays. What DAL level is the software classified at?

DAL is specific to a design and installation. It's a flow down from the aircraft system requirements and design and the safety assessment process.

These processes are defined in SAE ARP4754A Guidelines for Development of Civil Aircraft and Systems and ARP4761 Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.

ARP4754A is the more relevant to this question. A summary of the process is to start with a Functional Hazard Assessment which identifies hazards associated with failure modes of specific functions. Based on the severity of the failure condition a Functional DAL (FDAL) assignment is made.

The next step is to assess the architecture for functional and item independence. This allows for setting Item FDAL for each of the components of the system.

It can get complicated, but for a simple example: If you have an FDAL B and FDAL E function combined into a single item with no independence, the IDAL of both becomes Level B. If they are functionally independent and also independent items, the IDAL would match the FDAL for each.

Back to the question: An old colleague of mine worked much of the certification effort for the B777 IFE when he was at Boeing. As he explained, the highest criticality function in the IFE is the PA override function which is FDAL C. The rest of the IFE system was set at Level D. (you could argue for Level E based on the argument that losing it has no safety effect, but the Level D is based on the requirement that you show non-interference with any other system.)

The question as posed, is about the software which means we're asking about IDAL. If the IFE SW architecture is a single application or multiple applications that lack independence from the PA override code, the IDAL for the IFE SW will be Level C.

It may be possible to architect the SW with proper hardware or software partitioning to provide independence of the functions and items. In that case, the independent items could be developed at the lower IDAL level.


Pay for your Training What are the pros and cons for "paying for your training"?  Specifically, there are companies out there that will sell the right seat for so many dollars an hour for those aspiring pro pilots to build hours.  Is this a bad thing?  Are there benefits to this approach.  Is it simply a function of the competition new pilots face (not considering the rumors of pilot shortages we are about to face)?  Is it unethical?

Pay for training (PFT) is a bad thing.  I am specifically referring to operations in which you pay to go through initial aircraft training and fly right seat.  Yes, you not only pay for 121 initial (BAD!), you also pay to fly from the right seat.  The bottom line is you are occupying a seat that the company should be paying you to be in!

Part 121 pilots are in a constant struggle over wages.  Companies paint a picture that the only reason they take quarterly losses is that they pay the flight crews too much.  Negotiating capital has to be spent to combat this.  These pay for job (PFJ) operations hurt our negotiating positions on wages, as do the pilots that come out of these programs who some might argue are more likely to support concessions (after all, they'll fly for free!).

It is hard to combat these kind of programs because flying is more than a job for a lot of people. It is a dream and a passion and some of these people are more than happy to pay for the "privilege" of flying a beech 1900 from the right seat.

You asked for Pros and Cons, so:

Pros

You learn an aircraft and log some SIC and TT, maybe even turbine.

Cons

You are helping depress wages across the industry.
You are enabling the company to avoid paying a wage to half of its pilots.
You will probably carry a stigma when you move up in the 121 world, at least at the regional level (FO's I flew with were very reluctant to name their former operation if it happened to be [REDACTED])

Don't go the PFJ route.  Find something to do that will pay you a wage to fly and build hours to get into a regional 121 seat.  Once you have your commercial (and cfi) certificates, you shouldn't be paying to fly any more.  You'll also find once you get into the 121 world that paying to accelerate your way there  perhaps wasn't worth it.


Plane that always flies into the wind? Suppose that you dropped an uncontrolled, dummy glider into the air. You want it to always face into the wind by design. Would it be possible? If so, what would such a plane look like?

The short answer is no.
All the glider feels is its flight relative to the air. What the ground is doing beneath it is not relevant, the wind could be blowing a hundred kilometers an hour and the glider would just be carried along without feeling a thing. This is why unpowered balloons always drift with the wind.
To detect and respond to ground speed requires a sophisticated control system.


Are aircraft being fitted with brighter anti-collision lights? I live and work near to DFW airport. Yesterday, I noticed an inbound jet with obviously brighter strobes (anti-collision lights) than any other jet I've seen before. (I believe this was an American Airlines Jet with an engine under each wing.) Does anyone know if aircraft are being fitted with brighter anti-collision lights? This particular aircraft was really noticeable against the low overcast clouds.

Its possible they are just fresh halogen bulbs and brighter than others you have seen but your key line is:

  against the low overcast clouds

Low clouds, fog, and the like give strobes something to reflect off of so they seem brighter in a localized way. I cant find a great image of it but this video showing the graphics updates in X-Plane 11 show the phenomenon
fairly well. On a cloudless night the strobes (an most aircraft lights) have little to reflect off of so they seem darker when looking at them. If you watch departures and arrivals in similar conditions you will also see the landing light throw a similarly "visible" beam. This is all somewhat similar to how laser light is visible in fog.


How unusual is it for remotely piloted aircraft to fly through commercial or general aviation airspace? According to the Phys.org article NASA flies large unmanned aircraft in public airspace without chase plane for first time:

Flights of large craft like Ikhana, have traditionally required a safety chase aircraft to follow the unmanned aircraft as it travels through the same airspace used by commercial aircraft. The Ikhana flew in accordance with the Federal Aviation Administration's (FAA) Technical Standard Order 211—Detect and Avoid Systems—and Technical Standard Order 212—Air-to-Air Radar for Traffic Surveillance.
[...] The Ikhana aircraft was equipped with detect and avoid technologies, including an airborne radar developed by General Atomics Aeronautical Systems, Inc., a Honeywell Traffic Alert and Collision Avoidance System, a Detect and Avoid Fusion Tracker, and an Automatic Dependent Surveillance-Broadcast capability – a surveillance technology where the aircraft determines its position via satellite navigation and periodically broadcasts this information so other aircraft can track it.
The flight took off from Edwards Air Force Base in California and entered controlled air space almost immediately. Ikhana flew into the Class-A airspace, where commercial airliners fly, just west of Edwards at an altitude of about 20,000 feet. The aircraft then turned north toward Fresno, requiring air traffic control to be transferred from the Los Angeles Air Route Traffic Control Center to the Oakland Air Route Traffic Control Center. On the return trip, the pilot headed south toward Victorville, California, requiring communication control to be transferred back to Los Angeles.
During the return flight, the pilot began a gentle descent over the city of Tehachapi, California, into Class E airspace—about 10,000 feet—where general aviation pilots fly. The pilot initiated an approach into Victorville airport at 5,000 feet, coordinating in real time with air traffic controllers at the airport. After successfully executing all of these milestones, the aircraft exited the public airspace and returned to its base at Armstrong.
"We are flying with a suite of sophisticated technology that greatly enhances the safety capabilities of pilots flying large unmanned aircraft in the National Airspace System," said Scott Howe, Armstrong test pilot. "We took the time to mitigate the risks and to ensure that we, as a program, were prepared for this flight."
Tuesday's flight was the first remotely-piloted aircraft to use airborne detect and avoid technology to meet the intent of the FAA's "see and avoid" rules, with all test objectives successfully accomplished.

At the end of the article:

More information: For more information on NASA's Unmanned Aircraft Systems Integration in the National Airspace System project, visit go.nasa.gov/2sx9VCn.

Question: While this was the "...first remotely-piloted aircraft to use airborne detect and avoid technology to meet the intent of the FAA's 'see and avoid' rules, with all test objectives successfully accomplished", (without a chase plane?) how rare is it for remotely-piloted aircraft to fly through US airspace where commercial or general aviation also flies without all those extra qualifications? Has this happened several times, several hundred, daily? Is it even more infrequent without a chase plane?

Click images for full size.
above left: "Aircraft maintenance crews at NASA‘s Armstrong Flight Research Center prepare the remotely-piloted Ikhana aircraft for a test flight June 12, 2018. The test flight was performed to validate key technologies and operations necessary for the Federal Aviation Administration's approval to fly the aircraft in the public airspace without a safety chase aircraft." Credit: NASA/Ken Ulbrich
right: "NASA’s remotely-piloted Ikhana aircraft, based at the agency’s Armstrong Flight Research Center, is flown in preparation for its first mission in public airspace without a safety chase aircraft." Credit: NASA/Carla Thomas

In the US, the main operators of large UAS (i.e. non CFR Part 107 aircraft) are Air National Guard (MQ-9) and the Department of Homeland Security (Customs and Boarder Protection, also MQ-9). Here is a table from the Pentagon on how many missions UAS flew domestically in FY2018. (Note that these are "missions" and do not include other types of operations such as training or flight test, see below.)

A report from OIG published in 2014 lists a total of 5,102 flight hours by CBP in FY2013 (which is supposed to be closer to 26,000+, hence the OIGs investigation). Air National Guard also operates MQ-9 domestically for frequent training missions and contractors such as General Atomics Aeronautical Systems, Inc. and Northrop Grumman operate a fleet of capital aircraft at their respective training centers (e.g. Grand Forks). Lastly, of course, NASA also flies UAS. An example of how such missions are executed is described in this NASA report on the Western States Fire Missions starting on page 30.

So on your question about frequency: Assuming that the sum of all those aircraft result in ~5x number of flight hours, you'd be looking at something like 25,000 yearly flight hours in the US National Airspace System of large Remotely piloted aircraft. This is likely on the low side given the OIGs observation about the operational tempo of the CBP fleet.

So Why Is This Demonstration Relevant?

You may ask: if we're already operating these aircraft without chase planes, what was so special about this flight? It was the ability to fly a UAS without a chase plane without first having to climb to Class A airspace.

FAA Notice 8900.227 stipulates the requirements for how to obtain operational approval for an unmanned aircraft; specifically, it states:

  ... compliance with the see-and-avoid requirement [is a] primary concerns in UAS operational approvals leading to [...] the use of observers [to maintain] flight separation and collision avoidance or ‘segregation’;

In the case of a flight with a chase aircraft, that visual observer is onboard the chase aircraft. This is also where the "Visual Line of Sight Requirement" comes from - the observer/pilot must be able to see the aircraft during the operation.
There is one exception in N8900.227 for the visual observer (VO) requirement:

  VOs are not required in Class A airspace [...]

As a result, so far operations of the above-mentioned agencies occur almost exclusively in Class A airspace; i.e. above 18,000ft. Since those entities are either government agencies or contracting with a government agency, access to restricted airspace is straight forward where these aircraft can circle up or down to and from Class A airspace. In the case CBP and Global Hawk operations in Grand Forks there is a Temporary Flight Restriction that enables this access to Class A airspace without the need of a chase aircraft below 18,000ft.

This type of operation is incredibly inefficient though (imagine if manned aviation had to operate like that). As a result, and that is what makes this NASA flight unique, the ability to use an onboard system to detect and avoid other aircraft (i.e. a Detect and Avoid System) when operating in airspace other than Class A, in particular Class E below 10,000ft where "non-cooperative" aircraft operate removes a list of operational limitations. From N8900.227 again:

  b. Risk Mitigation. While considerable work is ongoing to develop a certifiable detect, sense, and avoid system as an AMOC with the see-and-avoid aspect of §§ 91.113 and 91.115, no current solution exists.

The "considerable work" mentioned refers to this NASA project - and the flight was the capstone demonstration to show equipment in fact can serve as an Alternate Means of Compliance (AMOC) when operating outside of Class A airspace.


How do I get an FAA okay for a private runway? The county I'd like to put a private runway (for my use only) in doesn't require any special permits because the property is zoned Agricultural, BUT they do require some form of acknowledgement from the FAA that the FAA doesn't have a problem with it being in that location.  How do I go about getting something like that from the FAA?  Who do I contact?

You're probably already aware that the FAA itself does not require the operator of a private airfield to receive any kind of approval from the FAA. However, there is a process in place to register a private airfield, and indeed the notice (not approval) is mandatory. The result of that process might satisfy your local authority.

The three FAQs starting here are pertinent. You need to file FAA Form 7480-1, either by mail or via the OE / AAA system.


Can a dual-engine aircraft take off with only one engine? When a dual-engine aircraft (such as the B737, A320, A330, B777 or B787) has reached the point where it is too late to abort a take off, can it take off if one engine fails?

It is a regulatory requirement (EASA CS 25) that commercial aircraft can safely fly should one of the two engines fail at any point of the flight, including takeoff at speeds beyond $V1$. (the maximum speed at which it can still stop before the end of the runway).

  Control Following Engine Failure  1 An acceptable means of showing
  compliance with CS 25.143(b)(1) is to demonstrate that it is possible
  to regain full control of the aeroplane without attaining a dangerous
  flight condition in the event of a sudden and complete failure of the
  critical engine in the following conditions:

  a. At each take-off flap setting at the lowest speed recommended for
  initial steady climb with all engines operating after take-off, with –
  i. All engines, prior to the critical engine becoming inoperative, at
  maximum take-off power or thrust;  ii. All propeller controls in the
  take-off position;  iii. The landing gear retracted;  iv. The
  aeroplane in trim in the prescribed initial conditions; and

  b. With wing-flaps retracted at a speed of 1.23 VSR1 with – i. All
  engines, prior to the critical engine becoming inoperative, at maximum
  continuous power or thrust;  ii. All propeller controls in the
  en-route position;  iii. The landing gear retracted;  iv. The
  aeroplane in trim in the prescribed initial conditions.

Source

For a clip of this happening just as the aircraft is rotating, take a look at this video:

A simulator video of the procedure is also available:


What's the purpose of partial autopilot disengagement after applying certain force to the control wheel? Aeroflot Flight 593 crashed after the autopilot was partially disabled by applying certain force to the control wheel but the only function which was disabled was controlling the ailerons. This partial disengagement went unnoticed for a number of reasons.

I'm reviewing the official accident report (text is in Russian, linked to from the Wikipedia article) and here're my findings from there so far.

The flight manual (cited in the report) is claimed to say that manipulating the control wheel to contradict the autopilot is definitely abnormal and should be avoided. The mechanism for overriding the autopilot is a safety device that engages outside normal operational conditions.

So it looks like there some functionality that allows to override the autopilot and partially disconnect it (so that only ailerons are no longer controlled) and it is claimed to be a safety measure.

What's the purpose of this functionality?

The autopilot will disconnect on large control inputs because this is the most intuitive way to control the plane. On Boeing planes, the controls will physically move along with the autopilot. If the plane starts doing something you don't want it to do, the instinctive action is to grab the controls to correct it. While the autopilot button would normally be the way to disconnect the autopilot, it may not be the instinctive way in an emergency, and it can be helpful to already have both hands on the controls when the autopilot disconnects, rather than having one hand disconnecting the autopilot.

The reason for only disconnecting one part of the autopilot could be to help the pilot. Maybe there is a problem with the elevator controls, or an upset that affects the aircraft primarily in pitch. Maybe the TCAS gives a "climb" command. The pilot wants to take over pitch control to address this situation, but other controls are fine. While the pilot now has control of just pitch, the autopilot is still taking care of the other controls. The autopilot only gives the pilot control of the modes that are being overridden, instead of just turning off and requiring the pilot to deal with all control modes.


How is it safe for helicopters and Ospreys to refuel in mid-air? How do military helicopters like the Blackhawk and CH-53, as well as the V-22 Osprey, perform mid-air refueling without their rotor blades (periodically and accidentally) contacting the drogue or fuel hose and causing a major accident?

I imagine that if the rotor blades did make contact with the fuel hose, either the fuel would be released and be sparked and ignite, or ingested by the helicopter turbines, or the rotor would break, or all of the above!  When a helicopter is refueling, its rotor is nearly above the fuel hose, or at the maximum, maybe 20 feet away?  It's easy to imagine a bit of turbulence or a few centimeters of cyclic movement (a sneeze perhaps?) is all that it would take for the rotor to dip and come forward and contact the hose.

For the Osprey the propellers / rotors are behind the nose of the aircraft and thus farther away from the fuel hose, but still, like a helicopter the Osprey's rotors are very large, and are exposed as opposed to the concealed compressor blades of a jet turbine.

That photograph distorts the perspective.  Just Google for "helicopter air-to-air refueling" and look at the image results.  Many show other perspectives from which you can see that it is not possible for the blades to contact the hose or basket - the probe is longer than those on a fixed-wing craft for exactly that reason.

This video shows a CH-53E Super Stallion chopping off it's own probe through over-controlling the cyclic, but that particular mishap would be possible in other flight phases too.


What is the typical value of maximum lift coefficient for aerobatic aircraft? I'm working on a conceptual design phase project for aerobatic aircraft (for university) and I can't seem to find any statistics about key aerodynamic properties (such as in the question), so I hope somebody here does know something about this subject?

First, don't take the two-dimensional value from an airfoil chart and use it for the full aircraft. Subtract 15-20% for wingtip margin and fuselage influence. Wingtip margin means that the wing is less loaded towards the tips to keep a lift margin for aileron control and to avoid a tip stall.

Next, aerobatic aircraft have lower maximum lift coefficients than GA aircraft. Their wing loading is lower, so they can afford this. A symmetric airfoil mounted at zero incidence has proven to be the best choice, and while some older aerobatic aircraft use cambered airfoils, the camber creates a distinct disadvantage in transitions from normal to inverted flight and vice versa.

And last, the maximum lift coefficient depends on quite a list of parameters. If you need a value for the calculation of structural loads, make sure you add enough strength to cover the increased lift possible with high pitch rates.

If you need a figure for a single-seater piston-powered aerobatic aircraft without flaps for the estimation of minimum speed, use a lift coefficient of 1.3.


Why is a TFR issued when barometric pressure exceeds 31.00 InHg? Why does a barometric pressure above 31.00 InHg trigger a TFR?

That is because most of the legacy altimeter setting barometers cannot handle such high pressures. Most of them, like the one pictured below has a range from 28 to 31 inches of mercury.

Kollsman Altimeter Setting Indicator, image from analogweather.com
From Aeronautical Information Manual:

7-2-4.  High Barometric Pressure
a. Cold,  dry  air  masses  may  produce  barometric pressures in excess of 31.00 inches of Mercury, and many  altimeters  do  not  have  an  accurate  means of being adjusted for settings of these levels.

As a result, the TFR is triggered by 14 CFR 91.144

(a) Special flight restrictions. When ... barometric pressure on the route of flight currently exceeds or will exceed 31 inches of mercury, no person may operate an aircraft or initiate a flight ...


Are there downloadable versions of the Canadian VNC and VTA charts? Are there PDF versions of Canadian VNC and VTA charts available for download? I fly in Australia where airservices lists them on their website so I was hoping to find something similar for Canada.

There is a plan to produce electronic versions but they don't seem to be available yet and you can still only order paper ones.  Go here:

http://www.navcanada.ca/EN/products-and-services/pages/aeronautical-information-products-charts.aspx


What is the maximum altitude of barometric altimeters? An altimeter works by sensing static air pressure. As altitude goes up, the pressure decreases.

If I take a barometric altimeter up to space (e.g. up to satellite orbit), at what altitude does its reading become useless, i.e. the reading can no longer be trusted as a measurement of the height above sea level?

(While altimeter reading is different than GPS altitude even at low altitudes, it is still a very good measurement of height. I'm asking at what height, the air becomes so thin that it is implausible to measure altitude based on static air pressure?).

It depends on the altimeter's design and certification. An example for a  modern analog (aneroid) altimeter is this $5,000 Mid-Continent model.

Its certified range is -1,000 to +20,000 feet, this is a reading you can depend on. The actual mechanical range is -15,000 to +50,000 feet.

An RVSM altimeter working off multiple sources and an air data computer can take you higher. And an altimeter on an F-104 is probably even better.

A cheaper $150 model shows a certified range of 10,000 feet for one of the variants.


How often are drop tanks actually dropped? I know drop tanks are used to extend the range on many fighter jets, but how often are they actually detached from the plane once empty? A lot of WWII movies and documentaries show tanks being dropped before entering combat, but I'm curious about more modern planes and non-combat conditions. Does the increased air resistance offset the cost of dropping the tank on say, a standard patrol, or are they landed and recovered with the plane and if so, are they re-used or simply scrapped?

In general, unless it's an emergency or needed for certain flight operations, the tanks are retained and flown back to base.

There are maneuvering limitations for carriage of certain stores on some aircraft.  The F-16C/D for example limited maneuvering to +6.5/-3 Gs with stores on the inboard two pylons and/or centerline drop tank installed.  If the aircraft was attacked by an offensive flight of enemy fighters, one of the first items prior to commencing ACM with the threat was to jettison stores on these stations.  This allowed the aircraft to maneuver up to a maximum of +9 Gs as the fight commences.


What is the temperature of flap linkages during takeoff and landing in passenger and fighter aircraft? During takeoff and landing, what is the temperature of flap linkages in passenger or fighter jet aircraft?

Components like linkages on a wing flap system can be considered to be the local ambient temperature, subject to some lag if the plane is moving between large temperature changes, because of the time for the components to soak.
So a plane descending from 40000 ft after a cruise at that altitude may have components cold-soaked to ambient, say -40C, and if the airplane descends to 3000 ft to start an approach, where the temperature is +10C, by the time the airplane is at 3000 ft the components can be expected to be a bit cooler than ambient because of the lag time for the components to fully absorb the heat of the warmer lower temperatures.  How much lag would depend on a lot of factors, like the amount of exposure to the freestream, and things like heat being drawn toward cold fuel just ahead of the component.
This was a significant problem in fact on the CRJ200 program, because the screw jack flap actuators were sensitive to extreme cold and like to jam, and a good cold soak at high altitude followed by a quick descent and extension at low altitude, where it was still really cold down low (winter), could leave them still cold enough to have the system fail while still at zero.  There was a big AD related to it.


Is it possible to control an aircraft on the runway if the nose gear collapses? I have read and seen some articles in which, for various reasons, the aircraft's nose gear collapsed after landing during the roll out. This resulted in the aircraft going off the runway.

Is it possible to still control the aircraft during this weird event? Or is it more or less inevitable that the aircraft will run off the runway?

Most aircraft are steered on the ground by pivoting the nose gear. If the nose gear collapses, you therefore lose your primary method of directional control on the ground.

Additionally, parts of the aircraft contacting the ground that are not supposed to contact the ground can cause unwanted yaw, which can contribute greatly to the runway excursions you've noticed in articles regarding gear collapse incidents. This is probably the largest contributing factor to runway excursions in cases of nose gear collapse. However, if it's known that the nose gear did not deploy properly before the landing, the pilots can intentionally hold the nose gear off the ground as long as possible in order to minimize this effect. Holding the nose gear off the ground as long as possible minimizes the time that the contact between the nose and runway surface will be potentially applying yawing forces to the aircraft and also minimizes the speed of the aircraft while those forces are being applied. This gives the pilots more time to respond with differential braking and/or rudder, helping to prevent the nose from moving too far away from the direction of travel and a resulting loss of directional control due to skidding. Of course, this doesn't help if the gear collapse was unexpected, as the pilots wouldn't know to hold the nose gear up.

There are a few additional methods of directional control available to airplanes on the ground, though most are not as effective as pivoting the nose gear and their effectiveness varies with speed:

Rudder - While the aircraft still has high airspeed when rolling down the runway, the rudder will still provide some directional control. This control will diminish very rapidly as the aircraft slows down, though.
Asymmetric braking - Most airplanes allow the pilots to control the brakes on the left and right main gear independently, allowing them to brake harder on one side of the aircraft than on the other. This is more useful for taxi speeds than for high speeds down a runway, though, and can easily cause even more directional control problems if used without proper care at high speeds.
Asymmetric thrust - Multi-engine aircraft almost always allow the pilots to control the thrust (either forward or reverse) of each of the engines independently. However, in the case of a collapsed gear, this is unlikely to be very helpful, due to the large delay between when a thrust change is commanded and when it happens as well as that the engines may now also be striking the ground themselves.


Can a commerical jet fly into a tropical cyclone? There is little doubt on whether planes can fly over a tropical cyclone as clearly demonstrated by this video of a Gulfstream jet flying over hurricane Katrina in 2005 to drop weather instruments.

I do not know the intensity of cyclonic wind at 10km above sea level, but my limited understanding on the subject suggest that the wind is strongest near the surface and weakens with height. If a small plane with high service ceiling can fly over such a powerful storm. Is it possible for a larger plane with a lower service ceiling to fly into a cyclone unscathed?

Considering that most pilots would try to go around a cyclone and that safety regulations may also forbid pilots from putting their passengers in any kind of risk that airlines do not want to bear, by just strictly looking at the aerodynamics and aeronautics of the aircraft, is it feasible for large commercial planes like 747 to fly into a tropical cyclone?

If the wind shear (sometimes called wind gradient, which in my opinion is the better term) encountered in that part of the cyclone the aircraft is penetrating is less than what the aircraft can handle, then, yes, an aircraft can safely fly into a cyclone.

What the aircraft can handle varies greatly depending on the speed at which it is being flown. Large aircraft have a recommended turbulence penetration speed, both in terms of knots and mach. In the absence of such a recommendation, V speeds that are relevant are Va, Vb, and Vo. http://en.wikipedia.org/wiki/V_speeds is a good V speed terminology reference.

I do not know what typical wind gradient values within a cyclone are or what their distribution within the cyclonic area is. However, I would be surprised if they were significantly greater than gradients within tropical thunderstorms, and aircraft do penetrate such.

In season there's a roughly north-south line of thunderstorms that regularly develops between Sumatra and Sri Lanka with tops greater than 50,000 feet. Lacking the fuel to go around the line, we would regularly go through it using radar to avoid the worst. However, with those old radars (back in the 1990s in 747s), it was not uncommon for us to wind up in a cell.


Can you mount a net between 2 helicopters for search and rescue? During situations where multiple people are in danger, I am wondering whether you can have a huge net mounted between 2 helicopters on a device with 2 arms on each helicopter, and when need to rescue, both devices would extend the arms to provide 4 points to connect a huge net, drop it down and then people in danger can just jump on it. Possible applications could be in firefighting or rescue offshore.

Could you? Well - technically, yes. For a little while anyway... Would you actually do it to enact effective rescue operations? No.
There's countless issues with the idea that would make it rather impractical, but I had fun thinking of some of the challenges.
For starters, the net would end up being rather rectangular. The short edges would be as long as the arms on the helicopters could be (which couldn't get too long before they get in the way of landing, flying, etc.), but then you'd need to be able to keep good separation between the two craft so the net would be quite long and thin. The shorter the net was between the two craft, the more responsive it would be to changes in altitude, distance, etc. between the two craft, making the ride even worse. So you'd want it to be long.
You can try this at home - grab a scarf or something similar, and try and hold it out fairly flat between your outstretched arms, with a little action man or barbie doll sitting on it, while going for a walk around the house. You'll be constantly adjusting your arms to keep it flat while in motion and it's still going to be a bouncy ride for your passenger.
The longer the net is, the more drag it will experience, further exacerbating the ride as the drag would be tugging the helicopters around. It wouldn't be very long before the net is pulled tight, at which point the weakest link will fail - the net might tear, but lets pretend it's very strong - the net would be pulled off the arms, the arms might be pulled off the helicopter, or a helicopter might be pulled out of the air.
I did have an idea to help reduce drag... once you've got your passengers on the net (I'll come back to challenges with that), you could have one or both helicopters execute a series of rolls or loops (depending on whether the arms are mounted to a side, or to the front) in order to twist the net up to reduce its surface area! This would have the added benefit of snugly securing your passengers inside the twists of the net.
As for people boarding the net - you'd have to lay it carefully on a flat, open stretch of ground or water. The helicopters would need to either land or very carefully hover, coordinating the entire time in order to not tangle or crash. At which point the person boarding the net could just go for a short jog (or swim) over to one of the helicopters, and board that instead (winched up in the case of water). I'm a bit of a daredevil so I might actually still opt for the net, but in my final seconds (which began counting already when I made that decision) I'd feel pretty guilty about likely destroying two helicopters, the lives of the pilots and crew, and their families.
But oh boy it would be one heck of a ride!


Why does Turkish airlines still fly over Iraq, is it safe? I realized that Turkish Airlines have a lot of flights over Iraq. For example, here is a flight from Istanbul to Maldives (TK 730).

Do you know if it is safe to fly there? Till today I thought that flight space over Iraq was closed for commercial flights.

Flying over conflict zones has been a common practice at all times. However after MH17 was destroyed over Ukraine some changes occurred.

From an overall standpoint, EASA, the safety agency for the European Union, has an active information bulletin dated March 31, 2017, which is the extension of one issued on December 23, 2015:

  Iraq airspace, all altitudes.
  This CZIB applies to operators.
  This CZIB is valid until 30 September 2017

  Due to the hazardous security situation, with the presence of
  terrorist organisations and ongoing high intensity military
  operations, there is a risk of both intentional targeting and
  misidentification of civil aircraft. The presence of a wide range of
  ground-to-ground and dedicated anti-aviation weaponry poses a HIGH
  risk to operations at all flight altitudes.

  Recommendation(s):

  Operators should take this information and any other relevant
  information into account in their own risk assessments, alongside any
  available guidance or directions from their national authority as
  appropriate.

It must be noted that Turkey while not a member of the EU, is still a partner of EASA and Eurocontrol.

On their side, the Iraqi Civil Aviation Authority states the sky over Iraq is safe.

Bottom line, operators have been informed of a high risk, and must evaluate their individual situation based on this warning and all other elements they can get on their own.

As mentioned by EASA, operators must comply with national directives if any.

For French operators, the situation is clear. DGAC, the national aviation agency has purely and simply forbidden Iraqi airspace (FIR ORBB) since July 2014, in an AIC valid for several conflict zones.
A similar order for Turkey would be issued by DGCA, but I was
not able to find such document.

In addition of Air France, many airlines have stopped flying in Iraqi airspace: press articles mention e.g. KLM and Qantas, Lufthansa and Royal Jordanian, and many other similar information can be found online.

The situation of Turkey is a little bit complex. Their have a southern border with Iraq and Syria, and the Sinai peninsula is also a conflict zone.

This may push operators to take more risks than others with southward routes.

About conflict zones, see also: Apart Kenya, what are the current dangerous / unsafe airspaces?


What is "Director" in ATC? On this question SentryRaven gave the following list of ATC stations:

Delivery (if available)
Apron/Ground (if available)
Tower
Departure (if available, sometimes handled by Approach)
Enroute ACC/Center (multiple stations along the route)
Arrival/Approach
Director (if available / in use)
Tower
Ground (if available)

I am not familiar with Director. What does this ATC position do and when is it used?

Some TMA arrival sectors can be further split up into an arrival/pickup part and a director/feeder part.
The arrival controller is responsible for getting aircraft separated either onto downwinds or onto transitions, where they are handed off to the director. The director is then only responsible for turning these aircraft onto the approach, in most cases the ILS.
Essentially, the arrival or pickup tries to get everyone onto the correct separation and speeds, so the director or feeder can turn and clear the aircraft onto their approaches, i.e. feeding the ILS with aircraft.

(Source: SentryRaven - Own Work)
The above picture shows the TMA airspace of Frankfurt (EDDF). The TMA arrival controller would clear aircraft onto the transition or a vectored downwind and hand them over to director.
The director position would then vector the aircraft onto the ILS for a handoff to tower.


What does shimmy in nose landing gear mean? While I was reading a small article on "Reasons for RTO", I came across a situation where the pilots aborted takeoff because of "landing gear shimmy". What does that mean?

the nose gear support strut contains a bearing which allows the nose wheel to swivel like a caster so the plane can turn on the ground. the nose wheel assembly itself is turned either via a hydraulic cylinder or a mechanical linkage connected to pads on the upper tips of the rudder pedals, or in some cases it freely turns on its own during the application of asymmetrical braking to the main gear.

But whatever the details of the nosewheel design are, "shimmy" occurs when the wheel assembly wobbles rapidly back and forth (left-right-left-right) as the plane is rolling down the runway at speed. this is called castering instability and occurs when there is excessive play or looseness in the caster bearing or the support strut or the wheel bearings, or slop in the steering control circuit, or improper inflation of the nose wheel.

The shimmy action sets up strong vibrations in the airframe that the pilot can feel and if strong enough can hear as well. Those vibratory stresses are acting to wiggle loose any bolted connections in the entire nosewheel assembly and can also seek out and activate any fatigue stress raisers present there- in addition to making the airplane difficult to accurately steer.


What does ATC mean when they say "no longer a factor"? During radar vectors, the ATCo informed to the pilot, "no longer a factor." Please, can you clarify to me what this radio transmission means?

This one is usually replied in relation to other air traffic around a particular flight which at one point may have posed a collision risk but is no longer in a position to do so.  Example
ATC: “United 2410, traffic is two miles at your ten o’clock at 5,700.  Cessna.  Report them in sight.”
If it appears the other aircraft will no longer cross paths with the aircraft being directed, the controller may say something like:
ATC: “United 2410, the Cessna traffic no longer a factor.  Turn right heading 340.  Descend and maintain 3,800, slow to 160 knots.”