What does 'in-trim speed' mean with respect to Boeing 737 mis-trimming correction? This question was prompted by discussions of the recent Boeing 737 MAX crashes, but it is not specifically about that variant.

In Boeing's 737 NG Flight Crew Training Manual, in Chapter 8 (Non-Normal Operations), under the heading 'Manual Stabilizer Trim' on page 8.16, it states:

  Excessive airloads on the stabilizer may require effort by both pilots to correct the mis-trim. In extreme cases it may be necessary to aerodynamically relieve the airloads to allow manual trimming. Accelerate or decelerate towards the in-trim speed while attempting to trim manually.

In this context, does 'in-trim speed' mean the speed it is mis-trimmed to, the speed it would be trimmed to when put back in trim, or something else? For example, if the airplane is mis-trimmed nose down, and therefore, presumably, for a higher speed than intended, what action would relieve the airloads on the stabilizer, and why?

Additional information about what 'extreme cases' might require the airloads to be relieved in this manner would also be appreciated.

"In-trim" speed means whatever speed the airplane will naturally seek if you let go of the controls.  If you set the stab to position X, the airplane will naturally seek speed Y, for a given weight, thrust, flaps, and C of G condition.

So say the stab is at position X and this makes the airplane want to pitch to 240kt.  It will seek and maintain that speed if you don't touch the controls.  If you want to fly slower, you can add up elevator by pulling the column back, increasing the tail's downforce and pitching the nose up, until it slows to a speed where the forces are back in balance with the elevator held fixed at that position.  Say it's 200kt.

You are now 40 kt below trim speed, and having to hold the elevator displaced to keep it there.  If you want to be able to let it fly hands off at 200kt, you have to move the stab itself so that the tail's downforce with the elevator at neutral is the same as when the elevator was being displaced.  So you trim out the elevator displacement (by applying trim and easing the column back to neutral in little trial and error inputs) and now you're in trim at 200kt, hands off.

The 737 has a stab screw jack with a manual operation feature with a cable circuit between the screw jack and the trim wheels in the cockpit that let the crew turn the jack directly with the trim wheel, with no electric input, when in manual trim mode.

If you are way out of trim, that is, holding a lot of elevator to make the airplane fly slower or faster than its trim speed, it puts a large rotational moment within the horizontal tail which increases the up or down load on the screw jack itself.  These jacks are usually acme screws with dual load path threads that have a fair bit of internal friction under load, and the effort to drive the screw when it's highly loaded can be more than you can apply with your hand on the little wheel on the sides of the center console.

So say you're in manual trim and the airplane is trimmed to 280 kt and you want to slow to 200kt, and pull the nose up with elevator to slow down and you don't retrim as you're slowing down.  At some point, if the out of trim condition and resulting the load on the screwjack is high enough, you can't move the trim wheel because you can't apply enough force to turn the jackscrew.  To avoid this, you should be retrimming the stab as you slow down.

Their procedure is to try to offload some of the out of trim load on the stab jack by moving the elevators back toward the original trim speed.  If you were holding the column way back to slow to 200kt while the airplane was still trimmed for 280kt, you'd release some of the pull, letting the airplane pitch over a bit and accelerate, while trying to move the trim wheel.  At some point you'll have unloaded the stab screw jack enough to make the wheel move.  You don't want to pitch over any more than you have to so you just relieve the elevator enough to get the wheel to move, and keep working it along until it works normally.

In this context, "extreme cases" refers to the case of a large difference between existing speed created by elevator input and existing trim speed.


Can I get a 20/40 requirement waiver after cataract lens replacement? I have had lens replacement surgery and now one eye is focused at 16” (close, reading distance)and the other eye is focused at a distance. I have 20/20 vision both at 16” and at distance as long as both eyes are open.

I have a third class private Pilots license and my medical is due. Can I get a waiver because I don’t meet the 20/40 requirement with either eye closed?

For example when my left eye is closed I can not meet the 20/40 requirement with my right eye when it comes to the 16” test and the same goes for my other eye when it comes to the distance test.

If you are a member of or join AOPA I recommend consulting AOPA member services for help with questions like this. I have consulted them multiple times and they always get a good answer for me or set me in the right direction.

Of course you can consult an Aviation Medical Examiner (AME) first but I recommend you figure out what you need to do and go into your AME knowing you’ll pass the medical exam... once you’ve failed it can be a nightmare to get your medical back and take a long time (and cost lots of money).

Source: I’m a pilot who has used this service of AOPA before


What is the feasibility of converting an F-22 to carrier use? I read that the Navy originally considered to use the ATF(Advanced Tactical Fighter) Programme aircraft (Now known as the F-22) as carrier aircraft but declined to do so when it came out. How feasible is it now to convert an F-22 to carrier use? (I kind of want to know because it is a better plane than the F-35 but is not used on carriers even though it was originally planed for)

In general, land based aircraft do not lend themselves well to carrier conversion. On the other hand, conversion in opposite direction is (relatively) easy, as shown by F-4 and F-18.

Conversion of aircraft to carrier use require a number of modifications:

Tail hook has to added and rear fuselage reinforced for arrested landings.
Landing gear has to be strengthened for high sink rate (~24 ft/s).
Atleast in USN, the front landing gear and fuselage has to be strengthened for catapult launches.
Also, it requires additional equipment, like th Carrier Landing system, redesigned refueling system (pretty much everyone use a system different from USAF).
Carrier based aircraft usually are expected to have better low speed capabilities as they have to fly slower approaches and wave-off (go-around) at lower speed compared to the land based aircraft. This dictates the wing loading, resulting in increased wing area and/or high lift devices.
There are also issues in corrosion prevention etc.

The weight penalty due to these reasons can be non negligible. For example, the naval Rafale M version weighs nearly 500 kg more than the Air Force Rafale C variant (which has ~10 ton empty weight). USN calculated that the NATF (Naval Advanced Tactical Fighter) will be around 1800 kg heavier than the Air force version (ATF was supposed to weigh ~15 ton).

Another thing is that the USAF and USN had different requirements, for example, the USAF wanting a single seater and USN wanting a double seater, requirement of different sensors (for fleet defence) etc. in the end, the aircraft proposed for the NATF looked nothing similar to the one that finally became the F-22 and the project was quietly buried.

F-22 NATF proposal, image from aerospaceweb.org

Note that the design has swing wings, as the aircraft was being proposed for replacing F-14 Tomcat. Another important result of the navalization of the aircraft is the reduction in the number of planform alignments, and their negative impact on the stealth characteristics.

Carrier conversion of F-22 could have been done if it was considered early in design. Doing it now (note that NATF was considered due to the insistence of Congress; it is doubtful if USN ever wanted it). Doing so later in the design process will result in another F-111B fiasco. As for doing it now, it is better to design a new aircraft (which was what the F-35 is).


What happens in a stall during a slip? In flight training we're warned against skidding turns since they have a higher potential for a stall/spin (the classic example being the stall/spin on the base to final turn).

However, how does the airplane behave during a stall entered from a slip?

It's a cross-controlled condition, but since the rudder input is opposite to what it would be in a skid, is it more difficult, or not possible, to spin from such a situation?

In order for a spin to develop, you need two things from the airplane:

it must be stalled
it must be yawing.

Since the airplane is not yawing while in a slip (it is actually flying straight ahead, although uncoordinated), the airplane simply won't spin.  Instead, when the stall occurs the higher wing (which has the higher angle of attack) will stall first, the wing will drop, and the wings will tend level.

That being said, it is still a stall and can be dangerous at low altitudes.  It can also turn into a spin if you leave the rudder applied as the wings level and you come out of the slip (and into a skid).

The best protection for all of this is to watch your airspeed and angle of attack to make sure that you always have sufficient airspeed so that you never stall in the first place.

Additional Information

Since this has generated some debate, here is additional information:

Spin

According to Wikipedia (emphasis added by me):

  Spins can be entered intentionally or unintentionally, from any flight
  attitude and from practically any airspeed—all that is required is
  sufficient yaw rate while an aircraft is stalled.

Yaw

So this brings us to Yaw - Wikipedia:

  The yaw axis is defined to be perpendicular to the body of the wings
  with its origin at the center of gravity and directed towards the
  bottom of the aircraft. A yaw motion is a movement of the nose of the
  aircraft from side to side.

Skid

Skid - Wikipedia actually covers this exact scenario:

  The skid is more dangerous than the slip if the airplane is close to a
  stall. In the slip, the raised wing — the left one if the airplane is
  turning to the right — will stall before the lowered one, and the
  airplane will reduce the bank angle, which prevents the stall. In the
  skid, the lowered wing will stall before the raised one, and the
  airplane will tighten the turn, and the stall can develop to a spin.

Slip

Slip - Wikipedia says:

  A slip is an aerodynamic state where an aircraft is moving somewhat
  sideways as well as forward relative to the oncoming airflow or
  relative wind. In other words, for a conventional aircraft, the nose
  will be pointing in the opposite direction to the bank of the wing(s).
  The aircraft is not in coordinated flight and therefore is flying
  inefficiently.

Note that the aircraft is moving sideways.  The nose of the aircraft is not moving, and it is therefore not yawing.  It also says:

  Often, if an airplane in a slip is made to stall, it displays very
  little of the yawing tendency that causes a skidding stall to develop
  into a spin. A stalling airplane in a slip may do little more than
  tend to roll into a wings level attitude. In fact, in some airplanes
  stall characteristics may even be improved.


Is there any plane that has wing of both aerodynamic and geometric twist? For the proper lift distribution, afaik either of the twist are used? Is there any significant difference having one over another and both? Thank you. The above question has one line answer and both questions can be merged into one.

A wing has geometric twist when, from root to tip, its chord line changes angle, typically without changing the airfoil shape.  This is colloquially known as washout when the root stalls before the tip (or, much more rarely, its opposite, wash-in).
A wing has aerodynamic twist when, from root to tip, its airfoil changes in camber and thus in shape, typically without changing its chord line's angle.
Both twists have a similar effect, in that the zero lift axis changes angle from root to tip, commonly to inhibit tip stalling.
Of these two, geometric twist is easier to design, construct, and analyze, because there's only one airfoil instead of a (possibly continuous) blend of multiple airfoils.
Adding geometric twist to aerodynamic twist might, for example, let you avoid a nonconvex airfoil shape where the camber is large.  Convex shapes are easier to build strongly and stiffly, so that would lighten the wing.


What were to happen if deicing fluid went in to the jet-engine? What were to happen if deicing fluid went in to an engine. I have heard that deicing fluid is somewhat flammable. What were to happen if it went in to the engine? Would it combust like fuel?

Deicing fluid is inhaled by jet engines nearly every time the truck is called out. The question is how much deice can the engines tolerate?

Turbine engines can accept a rather staggering amount of water, to the point that testing them becomes an exercise in water handling instead of engine handling. The fire department can empty their trucks into an idling engine and not affect it.

Deice does contain various flammable liquids, but the overall mixture is not flammable - rather dangerous although fire would be a quick way to clear the ice.

So, unless you find a way to empty the truck into the engine in less than a few seconds it's simply not an issue.


Does a constant power prop exist? What are the tradeoffs compared to a constant speed prop? Variable-pitch props allow pilots to adjust the angle of attack of the propeller to change the load on the engine.
The most common implementation of this is a constant speed prop where the prop governor adjusts pitch to maintain the chosen RPM.
From a pilot's perspective, we only really care about two things:

Power output
Fuel economy

Using a constant speed prop, you can't directly set the output power - you set the throttle and prop speed and observe the power output.
Using a constant speed prop, you also can't directly set the fuel flow rate - you set the throttle and prop speed and observe the fuel flow (or look up the POH).
Using a constant power control law instead the pilot could set the desired power and have the prop pitch adjusted automatically to maintain that (or if impossible, fail in a similar way to a constant speed prop going off the governor).
It is also possible to pick the most fuel efficient RPM for a given engine load which means that the two inputs (throttle + prop speed) get reduced to one: desired power.
The benefits I see are:

Reduced workload
Increased efficiency

The drawbacks I see are:

Inability to operate the engine at anything other than best efficiency for a given power - but I don't actually know what use case that would be useful in.
System complexity
Certification cost

Has a constant power control system ever been used in aviation? Are there other drawbacks that I'm missing?

There are some aircraft that indeed have just power lever and set the RPM on schedule, e.g. the Pilatus PC-7, PC-9, PC-21 line of trainers. Since they are primarily designed for training future jet pilots, and jet aircraft only have power levers, it makes sense to skip the complexity of separate propeller and condition controls.
However normally there are some cases where you do want to set other than most efficient RPM for current power and true airspeed:

The most common is descent and approach. These are flown with high RPM because

the engine is already spinning fast, so it does not have to spool up if you need to add power to go around and
with retarded power it produces more drag, allowing to expedite the descent when needed (the Pilatus PC-7/9/21 have a ventral speed brake; most turboprops don't).

Failure modes, though for most a feather switch would probably be sufficient.


What can the Flight Attendant Panel do? I've noticed that on some airlines (I may have seen it on SAS) the cabin crew had a small touchscreen at the front of the plane which they were using to select recorded audio messages etc, in both their language, and English.
Searching the internet, I found out it's called a Flight Attendant Panel — here are some photos I found:

So I gather they can control the lighting, and movies; but what else can these panels do?

I also found a FAP trainer, which says:

This virtual training environment generates a realistic FAP representation including OBRM, CAM and PRAM

What are OBRM, CAM and PRAM? What is being displayed above?

Here is an interesting presentation that discusses most of the communications systems on the A320 family (looks like the pictures you have and should apply in general). The CIDS (cabin intercommunication data system) starts about halfway through on page 21. The FAP is part of this system and can control:

Passenger reading lights
Passenger call buttons
Cabin lighting controls
Cabin system monitoring/testing
Passenger entertainment system
Passenger address (PA)
Automatic announcement and boarding music
Cabin/Service interphone and calls
EVAC signal
Emergency light
Door bottle pressure monitoring (either oxygen or escape slide?)
Door proximity sensors (doors closed properly)
Smoke detection
Water and waste tank quantities

The acronyms you listed are:

Cabin Assignment Module (CAM)

All the software for specific customer layouts and defined parameters in the FAP (same as OBRP).

On Board Replaceable Module (OBRM)

This is a generic term for any module that is easily replaceable. In this case it refers to the module that contains all the information used by the FAP (same as CAM).

Prerecorded Announcement and Music (PRAM)

A good list of Airbus acronyms including these can be found here.


Aviation theory for fighter pilots Background:

I'm an 18-year-old Finn and so I'll be starting my military service next summer. I'm currently applying to the Air Force to become a fighter pilot, but I don't have any previous training in aviation. I have studied a bit of theory from the internet but I just want to ask what would be the most relevant information for someone trying to become a fighter pilot.

So the quistion...

What should someone, who's wanting to become a fighter pilot, try to learn and in what order? And what are good resources for learning those things?

Thank you in advance!

My experience is with US students who have joined the US Air Force, Navy or become Army Aviators.

My non-flight study guide includes:

Critical thinking
Physics problem solving
Math problem solving
argumentation (related to critical thinking)
FAA Private Pilot and Instrument Pilot training material
where possible visits to towers, TRACON, etc.
volunteering at:  glider club, medvac company
public speaking
STEM college degree, not necessarily in aeronautical science

In college there will be more opportunities, and additional guidance.  Many high school students have learned to fly.  It's nice to have former students who are flying F-16s in various parts of the world.  Some who wanted to be fighter pilots ended up doing things like B-2s, tankers, etc.

Since most pilot jobs involve being an officer, leadership skills are important, and help differentiate applicants. You will always have to somehow differentiate yourself, to be competitive. Every former fighter pilot I know is very competitive.

Best.


How much does an air data module cost? Curious how much Air Data Module and Angle of attack sensor costs, such that is used on commercial airliners.

For airliners, a lot of money, in the tens of thousands or more. Thales Aerospace is one of the manufacturers of AOA's for transport and military aircraft -- the word "cheap" does not exist in their vocabulary and "inexpensive" is a matter of opinion. For GA aircraft they are significantly less expensive, about US\$2000 or less. For aircraft with other than standard airworthiness certificates (experimental, homebuilt, etc.) the cost falls well under US\$1000. Sometimes manufacturers don't call them AOA's, and instead refer to them as "Lift Reserve System." For a general idea of the cost of GA AOA systems, check Aircraft Spruce and search for "AOA".


What is "(CFMCC)" on an ILS approach chart? I'm studying the ILS or LOC RWY 3 approach chart for KMKC. I'm trying to figure out what "(CMFCC)" at the runway means.

Is it a computer navigation aid?

A point shown in parentheses like this is called a Computer Navigation Fix (CNF). If it didn't fall right at the end of the runway, it would be marked with a small X. It's defined in the legend on page 39 (page 41 of the PDF) of the Terminal Procedure Publication User's Guide.

These points are only used to define the navigation track in the flight computer. They should not be used by ATC, but pilots could use them for reference if their FMC or GPS shows them. There is a short AOPA article about them, arguing they should be removed from the charts. Here is a much longer PDF that has a bit more detail on their purpose and a lot more detail about making sure their usage and distinction are clear.


Why are inlet vanes used instead of variable geometry inlets to prevent compressor surge/stall? Jet engine core axial compressors (that of subsonic turbofans anyway) are designed to keep air flowing the right way at max RPM(or close to it). Below that, the airflow slows more and more, and becomes unstable.
In other words, the compressor can no longer compress the large air volume flowing into it. To prevent this, variable inlet vanes are used to reduce the airflow volume into the compressor at low RPM.

My question is: why was this method chosen? When you're running the engine at low power/RPM, the closed vanes will create drag by presenting their blunt face to the air. So why not use a streamlined variable geometry inlet which can forespill the excess air with less drag? such as the following:

TOP: low RPM, a sliding annular door narrows the annular gap

BOTTOM: high RPM, the door slides back, widening the annular gap

What you propose is used as a dust filter for helicopter engines, but even there the plug is not variable. Instead, air spills over the rounded edges of the intake if less is needed.

Intake vanes never close to a point where they would block the intake; instead, they direct the flow such that it hits the compressor blades at the desired angle of attack. They can be moveable to adjust flow to a range of compressor speeds but they never block the flow. Flow control is simply achieved by pumping more or less air into the compressor by means of varying compressor speed. If less air is pumped, more ram pressure builds up in the intake and forces more air to spill over the intake lips. If no separation occurs, this causes little drag and is preferred over something that adds more mass and complexity.

A variable intake body similar to what you propose is only used on supersonic intakes when the shock originating from the tip of such a spike needs to be positioned close to the intake lips in order to achieve uniform flow conditions at the intake face and high precompression efficiency.


What do Turnaround Supervisors do before departure? Before the plane is able to take off, what calculations do Turnaround Supervisors have to do and what do they have to check before the plane departs?

It depends on the airline and their specific procedures. Turnaround supervisors are in charge of ensuring all ground services are performed correctly and safety. The turnaround supervisor is also responsible to verify the load placed onboard the aircraft matches what was specified on the loading instruction report. Calculations can vary between cargo and passenger flights, but usually cargo involves more calculation and observation to ensure the load is adequately secured. The turnaround supervisor may need to crosscheck the information on the loading instruction report and the loadsheet received in the cockpit to ensure the flight crew received accurate information necessary to calculate takeoff speeds.

The National Airlines crash in Afghanistan highlights a serious case where the training of the individuals responsible for securing and calculating the necessary amount of load restraint was grossly inadequate.


How does a pilot switch from IFR to VFR mid-flight? I had a pilot tell me that a rude ATC controller was making him fly way off route and through clouds and turbulence. So he switched to VFR and climbed out of the mess and towards the direction he wanted to go. Without getting into who was right or wrong in this particular situation, how does one cancel IFR mid-flight?

You simply tell ATC your request:

  A: DEXPL, request cancel IFR.
  R: DEXPL, roger, report VMC.
  A: DEXPL, we are VMC.
  R: DEXPL, IFR cancelled at 20. Squawk VFR, approved to leave frequency.


Can a turbofan engine have less noise so that it doesn't disturb our ears? A few years back I have seen that Pratt and Whitney 's Geared Turbofan Engine(GTF) has reduced it's noise levels to about 50%. But recently I was having a discussion with a friend and he told me that there is an engine which has the noise levels reduced to about 10%.I tried searching on the net couldn't find any such engine .Is that even possible?
Considering the fact that the most of the noise is from the engine main exhaust.
 Thanks in advance

Turbofans already produce much less noise than the turbojets used in the 1960s. In general, the higher the bypass ratio, the lower the noise level.

It's difficult to silence a jet engine: any silencer impedes the airflow which means a significant power loss.

Noise levels are usually expressed in dB rather than %, a reduction by 90% is a 20 dB difference, which is huge.
To give an impression: from 1992 to 2000 NASA ran a technology development program aimed at reducing noise by 6 dB.

This chart shows various noise sources in an engine:

Here is an overview of the noise regulations currently in effect:

So Stage 3 is a reduction by 10 dB compared to Stage 2, Stage 4 is a reduction by 7 dB. The quietest aircraft are already at 17 dB below the Stage 4 limit.

So an engine that 'has the noise levels reduced to about 10%' seems plausible (depending on what you're comparing to), and the graphic identifies a few candidates.


Is there a fixed-wing aircraft that uses a scissor propeller configuration? (Source: primeportal.net)

Has there ever been a fixed-wing aircraft whose propeller is in a scissor configuration? Like the Apache's tail-rotor seen here: What are the benefits of a non-orthogonal (scissor) tail-rotor?

This configuration improves the thrust and reduces the noise. If not, what are the drawbacks for such configuration when used for forward thrust?

The nearest match I could find was a stacked non-counter-rotating propeller. Not being coplanar is the only matching feature. It was on a modified Junkers W 34:

(Source)

The tandem-engine Rumpler-Loutzkoy-Taube airplane.

Above is the closest thing to a scissor propeller I could find. As @PeterKämpf notes, unlike a tail-rotor, a tractor propeller is not in a rotor's downwash and its axis of rotation is aligned with the free stream.

The photo shows the world's first co-axial propeller. And it was non-contra-rotating, that is, both propellers rotated in the same direction, like the Apache's.

That, and not being co-planar, are the matching features. Each propeller was powered by a different engine, and they could run at different speeds. Long before variable pitch propellers, it was envisioned (and patented) that the second propeller could have a gearbox to reverse its direction for braking (aircraft at the time didn't have brakes).

Source: oldmachinepress.com


Is there still a minimum height required for becoming a Lufthansa pilot? basically what the title says. Do I still need to be at least 165 cm to become a pilot or has this changed? There is no limit stated at their website but they also don't tell you that there is no limit.

This page for pilot applications shows a 165cm number.
I didn't translate to see what it's for

https://career.be-lufthansa.com/index.php?ac=search_result&search_criterion_activity_level=107

4 pilot jobs listed, only the first 3 show the 165cm.


Why does the DHC-6 have only one set of elevator cables? Air Moorea Flight 1121 crashed because its up-elevator cable broke, allowing the elevator to blow to its faired position and thus be unavailable to counteract the pitch-down moment caused by the flaps being retracted;1 the DHC-6 elevator control system has two cables (up-elevator and down-elevator, distinguished by what part of the aft-quadrant bellcrank they attach to), and, if one breaks, the tension in both is released and the elevator floats.  No redundancy is provided in the form of a second or third set of elevator cables, unlike how most airliners have double- or even triple-redundant flight controls.  Why does the DHC-6 have only a single set of elevator control cables, rather than two or three?

1: No matter that retracting one’s flaps should not do that.

The Twin Otter isn't certified in a category that requires duplicate control runs with split surfaces.  It's more or less a single engine Otter with two PT-6s and a redesigned tail.  Those requirements apply to heavier aircraft than the DHC-6.


How do aircraft rental companies charge while the plane is not flying? I am looking for some general advice - this is specific to the UK but may be similar else where.

I know it is possible to hire a private aircraft, I see comments like this on club/rental sites all the time:

  Fly ASG members can experience affordable personal air travel for the Channel Islands, France and beyond. Fly ASG offers their services of non chartered aircraft rental to engage customers with a new streamlined approach to business and leisure travel.

Many sites mention the brakes on - brakes off fee per hour, but say you took that trip to the Channel Islands, France, or beyond: how do these companies usually charge for the bit where you will presumably be parked while you work on your sand castles at the beach for the day?

Just to be clear I'm not asking about airport parking etc. but how the owner of the aircraft will charge when it is not flying.

Flying clubs and aircraft renters generally only charge for the time the plane is actually in use. In the U.S. at least, this is commonly measured using the Hobbs time (actual clock time used, triggered by oil pressure or some other indicator that the plane is "in use"), or by Tach time, which is a bit trickier but can very roughly be thought of as the amount of wear you've put on the engine. (Strictly speaking it's a count of the number of engine revolutions, converted to "hours at cruise RPM".)

For overnight or longer trips, it's common to find a minimum hourly usage per day. For example, if you take a plane on a 3-day trip, and your club/owner requires 2 hours/day, you will be paying for 2 x 3 = 6 hours of Tach / Hobbs / whatever time, even if you didn't actually use the plane that much. You'll pay for the higher of your actual usage or your minimum usage per day.

It's extremely rare in the U.S., but not unheard-of, to encounter an extra fixed fee per day for taking the airplane for more than one day. (I've never personally encountered a fixed fee like this.) I'm not sure if things are different in the U.K.

Hourly rates can also either be "wet" (the rate includes fuel: any amount you pay for fuel will be deducted from your rental fee when you return) or "dry" (the rate includes the airplane only and you must pay for fuel). "Dry" rentals may or may not also require you to pay for oil or other consumables used.

(This is general information. Of course, if your question is specifically about Fly ASG's policies and fee scales, your best bet is to contact them directly. I know nothing about them.)


Is it permitted to land amphibian plane in the ocean on Californian coast? Given the length of the Californian coast, I was surprised to find so few seaplane services.  I would expect air taxis between Long Beach and the coast, for example.

Is it permitted to land seaplanes along the coast at, say, Zuma Beach geo://34.016286,-118.820402 and do whatever local boats do for mooring?

  In California, for example, you will not need to obtain certification of either a landing area or mooring area. Seaplane Pilots Association

There appear to be very few seaplane bases in California. Seaplanebase only lists five.

Seaplane air taxis only work where the logistics situation and market can support a business case for that kind of service.  It's an expensive way to travel, so there has to be some kind of benefit that makes it worth the cost to the traveler.

This works in the Seattle area and the Lower Mainland of British Columbia where you have large city centers with nearby destination locations that require over-water travel to get to, and business travelers willing to pay extra for fast waterfront-to-waterfront travel.

Vancouver BC has a thriving air taxi market because people want to get across to Vancouver Island quickly, especially Victoria BC, the provincial capital, and the business traveler demand supports seaplane operations up to Twin Otter size.

California? Way cheaper to drive, or go taxi-airport-taxi.  In Vancouver BC or Seattle, a seaplane air taxi service is competing with ferry boat service so it has a serious leg up that makes the ticket price worthwhile. Not so much down south on a contiguous coastline where there are both land and air alternatives.

So bottom line is, there's no money to be made doing it.


Is military grade jet fuel more expensive than civilian grade? Is military grade jet fuel more expensive than civilian grade?
Why are governments moving away from military grade jet fuels?

Prices

Relative prices depend on what military fuel you compare to what civilian fuel. The current US Defense Logistics Agency pricing for jet fuels is as follows:

    Fuel type     $/gallon $/barrel
    JP8 & JA1     2.15     90.30
    JAA           2.13     89.46
    JP5           2.18     91.56

JA1 is "Jet A1"--normal, internationally available civilian jet fuel.
JAA is "Jet A with Additives". It's Jet A (which is slightly less expensive than Jet A1, but available primarily in the US) with some additives added to improve lubrication, reduce corrosion, icing, etc.
JP8 is the jet fuel the US military used for years before (semi-recently) switching to mostly using civilian grades. Basically Jet A1 plus some additives.
JP5 is used primarily aboard aircraft carriers. It has slightly higher density than the others, and a substantially higher flash point (>= 60C, vs. >= 47C for Jet A1/JP8).

Summary

The military designations are mostly slightly more expensive than their purely civilian-grade counterparts. The prices given above are also somewhat higher than the IATA shows for pricing on jet fuels in the general market, at least at this moment1.

Why

Part of the reason for moving to civilian fuels is to reduce costs. Along with that, using something that's widely used and available makes it much easier to manage the supply chain, ensure an adequate supply, etc.

References

Defense Logistics Agency FY 2018 Fuel Prices
JP-8 and other Military Fuels (Warning: PDF)
IATA Jet Fuel Price Monitor

1. At least as I read things, the price given by the DLA is intended to be used for budget estimates, so it presumably reflects their worst-case estimate of the average price during the coming year.


Can a sonic boom produced at 60,000' be heard on the ground? The Concorde normally cruised at an altitude of 55-60,000 feet, but wasn't allowed to fly over populated areas due to the noise it produces. Can the sonic boom of an aircraft at 60,000 feet be heard on the ground?

Yes, a sonic boom produced at 60,000' can be heard on the ground.

First of all, a sonic boom consist in a steep increase of air pressure, followed by a slow, linear decrease below the nominal ambient pressure, and again a steep increase back to the nominal pressure. It is therefore called N-shaped wave or just N-wave. Here is a graph with several sonic booms, measures by NASA and found on Wikipedia:

The same wiki page cites a document from NASA

Aircraft        speed   altitude        pressure
               [mach]   [ft (m)]        [lb/ft² (Pa)]

SR-71           3      80,000 (24,000)  0.9  (43)
Concorde SST    2      52,000 (16,000)  1.94 (93)
F-104           1.93   48,000 (15,000)  0.8  (38)
Space Shuttle   1.5    60,000 (18,000)  1.25 (60)

These measurements are from aircraft with different altitude. As sound pressure depends from distance like  $p\sim\frac{1}{r}$, one may calculate the pressure for a certain altitude as in the following table. However, this assumes that the aircraft causes the same "boom intensity" at that altitude, which you should doubt at least for the SR-71.

Aircraft        speed   altitude        pressure
               [mach]   [ft (m)]        [lb/ft² (Pa)]

SR-71           3      48,000 (15,000)  1.44 (69)
Concorde SST    2      48,000 (15,000)  2.07 (99)
F-104           1.93   48,000 (15,000)  0.8  (38)
Space Shuttle   1.5    48,000 (15,000)  1.5  (72)

As you can see, the Concorde is the loudest aircraft, the most comparable F-104 (speed, altitude) produces just 40% of its sound pressure. But the F-104 is also much much smaller than the Concorde.

The Space Shuttle is very loud for its low speed. However, it looks more like a flying brick than an elegant, streamlined aircraft, so no wonder that it creates strong shock waves.

The SR71 seems to be very quiet for its speed, but as said, I don't think you can pull it down to 48000ft and expect the same behaviour. However, a sonic boom starts to disperse in some (larger) distance, may be this already happened for the SR-71. (Also, it's a spy plane with a very special shape - may be, this reduces the boom, too).

It has to be said that it is hard to translate the numbers into a comparable sound level, because what makes up the loudness is not only the maximum pressure, but also the rise time.
As counter-example, the air pressure changes by 130Pa every meter of altitude (at ground), and you don't hear the change of pressure when standing up from your chair (~100kPa)

Also, a sudden noise appears to be much louder than a noise slowly increasing to the same level - and the bang has the most sudden wave form possible. (Listen loud music with earphones - when the player clips a second, the first moment after really hurts)

However, there is a long table on Wikipedia listing noise sources and their levels. For example:

Trumpet at 0.5m:                63Pa
Jack hammer at 1m:               2Pa  (I'd say: a little quite...)
Loudest human voice at 1 inch: 110Pa

These levels are effective sound pressure. To translate a perfect N-wave with given maximum pressure to effective pressure, you have to multiply the value by $\frac{1}{\sqrt{3}}\approx0.577$.

Thus, the sonic boom of the Concorde has an effective value of 57Pa, which is comparable to the trumpet in 0.5m distance.

(As said, there is still a difference, because the boom is a sharp, short noise, but it gives an idea.)

By the way, I just stumbled on another document, about primary and secondary sonic booms.

It states that you hear a primary sonic boom coming from the aircraft within a lateral distance of ~20nm (solid lines) as well as a secondary boom within a distance of 60-85nm (dashed lines). This secondary waves are a reflection of the upwards travelling shockwaves from the aircraft at the atmosphere.
The secondary boom is not a short, loud bang, but a longer and less intense rumbling, making it difficult to identify the source.


What is the purpose of the string taped to the front of the canopy on gliders? What is the purpose of the piece of string taped to a glider canopy? Is it effectively a turn coordinator, but then what advantages would it have over a gauge such as the ones fitted in powered aircraft?

Yes, the yaw string on the canopy of a glider is there to show you whether or not you are coordinated, especially during turns.  It indicates the relative wind, so will be straight unless the glider is slipping or skidding, in which case it will swing to the left or right.

For those not familiar with them, here is an image that shows one:

According to Wikipedia, they are also used on other aircraft (even jet fighters and the U-2!) although they are used in almost every glider.

Now, the advantages that it has over an actual instrument installed in the panel are numerous:

It is directly in your line of sight while looking outside, so you don't have to look at the instrument panel to see if you are yawing.
It is more sensitive
It reacts faster to changes
It is cheaper
It is lighter
It doesn't require electricity (or even an electrical system on the glider)
It costs far less to maintain
It is easy to recognize when it fails (it's either there or not)


What options are there in Canada for treatment of severe depression and anxiety for pilots? I'm a Canadian commercial helicopter pilot, and I've been struggling with severe depression and anxiety issues since childhood.
I'm very good at faking it, well, good enough that I've been able to lie on my medical in order to get it. Initially I had a 'good reason' to, I thought that my depression issue had something to do with not being fulfilled in life and that maybe following my dreams would sort it out. Because that was the only thing I hadn't tried yet, besides chemical treatment.
Well, it hasn't. In fact, its become abundantly clear to me that its entirely a chemical issue. Its not an issue of environment, job, friends, family, its not an issue I can talk about because there is no reason in the first place. I need actual prescription treatment.
It's entirely independent of my life, which I have no complaints about. Gradually its gotten worse. I took myself off of flying duty when the suicidal ideaton started up again, and have been unemployed since as I cant even get out of bed before 4PM most days, not fit to fly in the least.
Ever since then I've been treating it with cannabis, which has had quite satisfactory results, the daily life-is-pain levels have descended from a steady 8 to a solid 4. But as everybody knows that's not sustainable with aviation drug tests, as well as obviously illegal to continue. I've done lots of research into my options for treatment that wont end up throwing my career away, but maybe its just the depression talking, but all of them see like rather optimistic and shit gambles to me. Every non chemical option i.e, shrinks, supplements, getting outside, exercise, has fallen flat entirely. TC does say on their site that they have some program for treatment, but my interpretation of it is that the goal is to have you off the medication before returning to flight, not to have you able to stably take it during, which in my case sounds like a recipe for disaster as I feel it'll just come back.
I'm seriously considering just hanging up my helmet for good and just accepting that until the issues are sorted out fully, which may be never, that I'll have to pursue another career. I don't want to, I want to be a pilot. I don't want to be a washed up former pilot, because I don't know if I'd ever get over that. But I'm killing myself slowly doing it, so I have to do SOMETHING.
Has anybody ever faced a similar situation before, or have any ideas?
Because all I can see options wise right now is; A, throw away tens of thousands and an entire career to get treatment, and possibly never get over that. Or, B, continue lying on the medical and keep going, but effectively torturing myself.
I don't know what I'm expecting asking an anonymous forum this, but I don't have anyone else to ask aviation related questions and I despise working with shrinks.
PS:
Also, don't be that guy, or any variant of that guy, who goes, "Well you shouldn't have become a pilot in the first place then!", because there's always that guy. I know. Tell me when you've got a time machine to make that piece of advice worth anything.

I'm not going to address the legal aspects of your question, but I will tackle the psychological side as I have a degree in it - although I'm not a practicing psychologist. It sounds like you have been through a bad period and are likely coming out of it into a better period, what you need to do is see a professional and get some help very soon. Everything seems impossible when you're suffering depression, but it's very treatable and you may still be able to fly.
It's in everyone's best interest, especially yours, to have you well and functioning. As you have stated yourself going without treatment is unsustainable whether you are flying or not, so there's two possible outcomes with treatment:

You're better and you can still fly: pilots can fly on anti-depressants in most jurisdictions, including Canada, provided they get medical clearance
You're better and you do something else

Either outcome you're better, which is miles ahead of where you are now. You lose nothing by getting treatment, things can only get better with it.
Drug treatments exist for most types of depression and bi-polar type disorders, and studies show that they are most effective when they are paired with counseling. I would suggest cognitive-behavioral therapy (CBT) as you will learn better coping strategies and thought patterns. Things will get better if you get help, so see your doctor right away.


After a crash, for how long is the airport closed? International airports are busy places. For example, London Heathrow saw an average of 1,290 "air transport movements" per day in 2014. It seems that a crash at the airport, such as BA Flight 38, would cause major disruption.

Yet, according to that same wikipedia page, flight operations were resumed within hours and basically back to normal within a couple of days.

Another more recent example is Turkish Airlines Flight 1878 crashing on landing at Istanbul. Again, the airport "was temporarily closed".

How are airports able to keep disruption to a minimum after (what seems to me to be) a fairly major incident, potentially involving a wrecked plane sitting on the runway? How do they move the wreckage and re-open the airport so quickly?

It completely depends on the accident and airport.

For example if I crash land on 10R at San Francisco, and it's a fairly quiet time of day (eg below the capacity of one runway), the airport could just use 10L and continue operations as normal. Similarly if there was no wind they could just switch to 1/19 L/R instead of 10/28 L/R. I'll discuss this toward the end of this answer.

Even if the crash didn't damage the runway, if the accident didn't damage the runway and the aircraft could be safely moved the airport would be back to normal as soon as the aircraft was moved and the runway had been checked. This could be within an hour.

On the other hand if at a single runway airport, with severe damage to the runway and a need to leave the aircraft in situ to be inspected, it could take several weeks.

In the cases you mentioned, BA 38 landed short of the runway. The airport was closed to arrivals for a few hours, however, and hundreds of flights were delayed, cancelled, or diverted. In the meantime, the runway in question (27L) was closed entirely for arrivals until 3 days later when the aircraft was recovered. However the runway re-opened on the day of the accident for departures only. As Heathrow typically operates with one runway for Departures and one for Arrivals, this had minimal impact on operations: ref

In Turkish flight 1878, the aircraft impacted Runway 5, then again on Runway 35L, but as far as I'm aware no significant damage was done. The other runways were inspected and used until the aircraft was moved. Ataturk is a busy airport, but not so busy that it can't cope with the loss of a single runway. Again a few hundred flights were delayed, cancelled, or diverted.

In neither incident was wreckage left on the actual runway, so once inspected they could be used as normal. There was some disruption in both cases - although no more than that caused by bad weather. If the aircraft had remained on the runway in either case, however, and had the accidents been at a single airport runway (eg London Stansted rather than Heathrow), the airport would likely have been closed for several days.

Another interesting case is Asiana Airlines flight 214 - an accident at San Francisco which closed the Airport for a few hours, and the runway for around a day. The other two runways (1/19 L/R which are perpendicular, as San Francisco has 4 runways arranged as 2 pairs) re-opened after around an hour and meant there was minimal impact, along with the parallel runway (10L/28R) which re-opened 24 hours later. The accident runway (10R/27L) re-opened around a week later.

One thing to note is that in most cases, an airport only needs runways in one direction - so for example at San Francisco there is a lot of resilience in the runways. As long as the accident doesn't cause damage too close to the "crossover" of the runways, San Francisco should almost always be able to operate at near full capacity shortly after an accident, even with a runway closed, due to always having a pair of runways available. Airports such as Heathrow with a single pair of runways are less resilient


How do you catch a runaway blimp? A few hours ago, a rather large (243 feet long) helium blimp owned by NORAD broke loose of its moorings in the Eastern United States and floated away. The news is currently reporting that it's being "escorted" by a pair of F-16's as it floats along at 15,000 feet, and is currently somewhere over Pennsylvania. (Next state over from where it started, at the Aberdeen Proving Grounds in Maryland.)

Given this situation, what are the military's options for recovering this blimp? Do they have to wait for it to crash land somewhere eventually (when it runs out of wind, I suppose?) Or is there some other option for them to "catch" this blimp given its size and the fact it's pretty much under nobody's control?

Here is an article about it: "JLENS blimp has come free of its tether at APG, now floating over Pennsylvania; fighter jets monitoring." The Baltimore Sun. 28 October 2015, 14:34 ET.

Edit: In case anyone is curious, the blimp landed in Pennsylvania a few hours after I posted this question.

Miklaszewski, J. "National Guard to Shoot at Crashed Blimp to Help It Deflate." NBCNews.com. 29 October 2015, 14:32 ET.

Historically, a runaway airship cannot be caught or entered. Eventually it will come down - they all did so far. Only in one case did a Zeppelin fragment of a ship which broke up in a storm make a soft landing so the crew aboard could survive. In all other cases both ship and crew perished or were never seen again.

While the Zeppelins had vertical shafts which allowed the crew to climb to the top of the hull, a blimp can only be entered below the hull. Trying to lower someone James-Bond-style from above will fail, because the big hull will shield the entry points of the gondola very effectively.

Defensive gunner position on a Zeppelin. Note the square hatch at the bottom which leads down to the bottom of the ship.

Also, shooting it down will be an exercise in futility. All it will do is to increase the rate of helium loss, so the flight will be some hours shorter. Helium is inert and will not burn, and those small holes will be tiny relative to the big surface of the hull.

At 15,000 ft it will be hard to try to catch one of the lines most likely hanging from the blimp with a helicopter. Remember that the blimp floats, so the helicopter has to hover at this altitude. Very few are able to do so. Towing will only be possible with another blimp or a helicopter; an airplane will not be able to fly fast enough with a blimp in tow.

The next trick depends on the color of the hull: If it is dark, covering it with something highly reflective will cool it and reduce the blimp's buoyancy. I have, however, no idea how to get a big blanket on that thing. The same will happen when night falls, but first the air will cool and the blimp, which will cool down more slowly, will go up. Later in the night and early in the morning it will sink again.

The wet parts of rain clouds will mostly be below 15,000 ft (water content is proportional to air density, after all), so a shower which drenches the hull and makes it heavier is highly unlikely. There is no obvious way how this thing will come down fast. Except, that is, it climbs further and the hull bursts. This will change the dynamics of this escape in a dramatic way.

The chase planes will help ATC to route traffic around the blimp, and all that can be done is to watch it. With luck the landing will be soft enough that it is not a complete write-off.


What are the ICAO GNSS waypoint naming conventions? I'm curious about ICAO naming conventions regarding GNSS and RNAV waypoints. Would I be correct in assuming that all GNSS area waypoints are 5 letters, and RNAV waypoints are 6?

What about waypoints like CB401? Do these represent a reference to a VOR/DME? If so, why are they included in GPS waypoint databases?

There are no "GNSS waypoints". GNSS is a common position source for RNAV, though not the only one.

All RNAV waypoints, like conventional (e.g. VOR/DME) fixes, have an identifier composed of five alphanumeric characters that is unique within a country. Some countries don't use numbers (e.g. the US); others do.


Why are the cabin inner windows so flexible? A few days ago I flew on an A321. While pointing to something outside my finger touched the window. It made a crackling sound and felt quit flexible.
I was able to push it at least 5mm without any effort (I didn't wanted to push further because I thought I might break it).

On the way back, I flew on a B737 and the same thing applied on its windows as well.

I'm pretty sure it's that thin because of the weight but is there any other reason for such a thin (and probably fragile) inner glass which could be easily damaged by a passenger by mistake?

The inner window is just a plastic protective cover, so that you don't touch the glass, which is probably very cold at altitude. You'll notice on the inner window there is a tiny hole at the bottom to equalize pressure and prevent condensation.

See this article that explains it


Can IPA be used as a FSII with MoGas, particularly with a Peterson STC? This question established a basis for the use of 100% Isopropyl Alcohol (IPA) as a Fuel System Icing Inhibitor (FSII) in aviation gasoline systems. However, this Cessna Service Letter documents that IPA is not to be used as a FSII with automotive gasoline in Lycoming powered Cessna aircraft, or indeed in any Lycoming aircraft whatsoever, in accordance with Lycoming Service Instruction No. 1070R.

Now, Peterson offers their auto fuel STC for many aircraft, including Lycoming powered Cessnas, allowing the use of certain types of non-ethenol automotive fuels. Peterson is known for being outspoken about the problems with ethanol as an additive in automotive gasoline.

My question is twofold:

firstly, is there any documented basis for the use of IPA as an FSII with any type of automotive gasoline in certified aircraft fuel systems (I am thinking part 23 certified aircraft, to exclude non-certified aircraft); and,
secondly, is there any documentation for the allowance or prohibition of the use of IPA as an FSII with a Peterson auto fuel STC?

Oxygenates, which includes alcohol, are not allowed in gasoline used in aircraft even with a special type certificate, not even airplanes certified to use MoGas. MTBE is the one oxygenate that is approved.

Gasoline sized hydrocarbons do not need freeze protection. Up to 1% anhydrous IPA (from a sealed bottle) can be used to clear an acute moisture issue, but the fuel should be consumed asap, IPA should not be a regular blend additive and certainly not be stored after adding to the tank.

The reason alcohol is not allowed is that it creates more far more problems than it solves. Alcohol is strongly attracted to water which helps IPA absorb small amounts of free moisture from the fuel system but it will also absorb moisture from humid air. A very small amount of which (1-2% moisture to total gasoline) will cause the alcohol to separate from the hydrocarbon portion creating an aqueous layer that at low altitudes will cause erratic power surges or completely stop the engine and at higher altitudes is insufficient to prevent ice in the fuel lines.

Meanwhile the octane rating of the remaining hydrocarbon mix will be severely degraded as alcohol containing gasoline is reliant on the alcohol as an anti-detonation additive.
Adding more alcohol to overcome the moisture issue by brute force will reduce the usable energy of the fuel. (joules per kg, alcohol has only 0.6 times the energy of petroleum per Kg) Up to 5% alcohol improves burn efficiency slightly more than it reduces specific energy, plateaus at about 10%, then the reduced energy outweighs any improved efficiency. Of course weight matters to aircraft.

If the plane is stored for a few months, the separated aqueous layer can cause substantial corrosion and schmoo in the system. I wish I had taken pictures of the tank and carburetor of the motorcycle I just rebuilt after sitting in a garage for a year to show what happens with gasohol, and on the flip side I have zero alcohol gasoline that can sit for years.

  NOTICE: Isopropyl alcohol in amounts not to exceed 1% by volume can be
  added only to aviation fuel(not automotive fuel) to prevent ice
  formation in fuel lines and tanks. Although  approved  for use  in
  Lycoming  engines,  do  not  use  isopropyl alcohol in the aircraft
  fuel systems unless approved by the aircraft manufacturer.

Source PDF from Lycoming, which also specifies oxygenates shall be limited to 1%.


Can I get a first class medical with eyesight of -4.25/-1.00 diopters? I'm wondering if I'm able to obtain the FAA 1st class medical certificate with the power of -4.25 and -1 in my eyes. I heard that the difference between the two eyes must not exceed 2 diopters.

From the FAA's website

The key line is "with or without correction". So as long as your vision is correctable to the standards given you are good to go. You can find the full AME guidelines here is you are curious.


Why was the TSR-2 literally burnt down even before its first official flight? The BAC TSR-2 was one of the aviation marvels of the time and the test flights had pretty good records. So why was it cancelled?

The TSR-2 flew quite a few times (24 times); atleast the first prototype did. The mockup was burnt, not the prototype- one of them was shot to pieces for target practice, so pretty much the same fate.

The main reason cited for the cancellation was costs- the rising costs (quite common in new aircraft development), with the expected unit cost triple of original estimates led to the cancellation of the (behind schedule) aircraft by the cash strapped UK govt. The projected replacement, F-111 was also cancelled for the same reason. Note that TSR 2 was the last time the British went solo on combat aircraft development (with the exception of Harrier)- the amount of money required was simply more than what was available.
Strictly speaking, the test flights were not flawless - there were engine and landing gear problems, though these were typical in aircraft development. Though these were not insurmountable, the test flights were fairly typical of aircraft development and nothing special.
The test aircraft was not fitted with the full avionics package; so there is no way measure its performance. However, the entire system was new and would've caused issues with integration and performance (though in all fairness, there was no indication that that would be a great problem), not to mention the effect on cost.
Quite a few of the components developed for the aircraft (The engines, for example) were later used in other aircraft projects, so the program wasn't a total loss.

To a certain extent, development, manufacture and operation of new aircraft requires political will more than technical capability (which can be obtained, given enough time and money); the British govt. didn't have it.


How to get a NOTAM on a Restricted Area? Is there any online service to get restricted area NOTAMS?

For example how can I get NOTAMs related to R-2503-D (intermittent by NOTAM 24 Hrs in advance) on Los Angeles Sectional chart?

I found this website but I am not sure how to find by restricted area name.

For SUA NOTAMs, you can find it via sua.faa.gov, in either map or text format.

If an SUA on a chart has defined hours, stick to those.

Example after downloading the text data:

Map example (layer control is useful):

Color indicates if active or scheduled and how far in the future.


Are two little engines or one big engine more efficient for an ultralight? For an ultralight, should two engines weighing 10kg each and making 7hp each OR one engine weighing 20kg and making 14hp be used?

Normally you have more power relative to engine mass in the bigger engine. If there is no weight advantage (like in your example), other considerations must be added:

Two engines allow to spread the load out. By placing one on each wing, the fuselage weight can be reduced which in turn reduces the wing root bending moment.
If the engines drive a propeller, asymmetric thrust and gyroscopic effects can be eliminated with two engines if one engine runs clockwise and the other runs counterclockwise.
Two engines need twice the number of controls, fuel lines and instrumentation. This is both a cost and a weight issue.
And the obvious one: If one of two engines fails, you still have the other to keep you flying. However, this is only true if your design is capable of flying with the remaining engine only. Now your rudder authority and minimum thrust requirement must be adequate to keep the aircraft flying with the resulting asymmetric thrust.

Note also that with two engines an engine failure is statistically twice as likely.


Is there a rule of thumb to choose an aircraft for long-haul operations? Are there any rule of thumb for a  NEW commercial airliner, maybe 200 seater or more, for long-haul operations ? I imagine it would be -

mostly bigger aircraft as amount of fuel needed would be more
amount of food needed would be more
amount of waste generated would be more
discounts offered by manufacturer

all of which points to having bigger aircraft.

Apart from approximating number of passengers either between A or B or A - hub what sort of other factors influence what sort of aircraft would it be.

I am using long-haul definition from Wikipedia

To make it more precise - 200 or more pax.

Because airplanes are incredibly expensive, using a "rule of thumb" would be extremely foolhardy.

A detailed analysis, likely laid out on a spreadsheet, would be much more appropriate.  You did hit on many of the major points, which also include:

Aircraft Range
Passenger Capacity
Speed
Crew Costs
Fuel Consumption
Cost per hour
Other costs: Insurance, Maintenance, and Leasing
Runway and Weight limitations
FBO services available

Obviously, if a candidate plane cannot fly the desired distance (perhaps limited by range, ETOPS, altitude or runway at takeoff or arrival), then you can't use that plane.  If a candidate plane cannot carry enough pax or cargo, then cross that off.

But once you have planes that can actually complete the mission, then its down to a complex matrix of costs, speed, time, and other benefits, and is a maximization problem without a precise answer.  (Some people will value speed above all else.  Some will value comfort and amenities.)


Can a PPL holder fly family and friends aboard an A380? Would I be able to fly an A380 with a private pilots license and carry family and friends? I know I can fly the A380 with a PPL.

Yes. But you will still need instrument rating and ATPL theory as this is multi crew aircraft. The amount of learning will be the same as to get CPL. Maybe fees for the license will be lower but who cares if you buy an A380?


What type is this aircraft and engine at Munich airport? Please help me to identify the plane and engine.

The fact that it is a single deck, twin engined aircraft with that distinctive wingtip confirm that it is an Airbus A350, operated by Lufthansa. The -900 series is the only A350 in service at this time, and Lufthansa has not ordered the -1000 series.

The A350 is powered by Rolls Royce Trent XWB engines.


Can an Iranian citizen attain ATP in the United States? I know that you can be a pilot in the U.S. as a foreigner. However, are there any special regulations regarding citizens of Iran because of political issues?

The U.S. does not prohibit Iranian citizens entering the United States and remaining here on extended business. It also allows noncitizens to attend flight school, conditional on a review of the candidate by the Transportation Security Administration. So, the U.S. would not categorically prohibit an Iran citizen learning to fly and obtaining a commercial or airline pilot's license.

However, while not impossible, it will be much harder than I just made it sound if you are living in Iran right now, because communications between Iranians and the U.S. State Department have been made difficult by the politics of the past 35 years.

There is, to put it delicately, no functional United States Embassy on Iranian soil. The U.S. maintains a virtual Iranian Embassy online at http://iran.usembassy.gov/ (also in Farsi at http://persian.iran.usembassy.gov/); however it was blocked by Iranian information authorities less than 12 hours after it initially opened and remains blacklisted to this day. Users with a VPN tunnel outside Iran's firewall can access it, but the site is mostly educational; you cannot apply for a visa using the site alone. You'd have to be able to submit your paperwork to a functioning U.S. Embassy or directly to the State Department offices in Washington D.C., which will be a delicate process as the Revolutionary Guard will be monitoring both sides of such correspondence.

Assuming you can establish reliable contact with the U.S. State Department either directly or through an Embassy, you would need an extended visa. There are three basic reasons to stay longer than 90 days, with visa classes for each; work, school, and temporary asylum. If you are coming to the U.S. specifically to learn to fly, an M-1 visa should be what you apply for; it permits entry to the U.S. for "vocational or other non-academic training", including FAA Part 61 and Part 141 flight schools. The Iranian authorities also look most favorably on student visas compared to other types.

In addition to the visa, you would, like any other foreign applicant for flight training, be required to pass a TSA security clearance. This is ultimately discretionary; you cannot force the TSA to grant your clearance (ask any U.S. national; you can't force the TSA to do anything).

While neither the State Department, TSA nor the FAA would categorically prevent you learning to fly based on country of origin, the TSA does list Iran as a country of origin that prohibits the visa holder from "Automatic Revalidation". Essentially, if while attending flight school, you ever left the U.S. (to visit family back home, or even driving north to Canada or south to Mexico for sightseeing) you would be required to go through the full security clearance process again including the TSA check. So, you would have to stay in the United States political borders at all times while in flight school, or you could risk being denied reentry or resumption of your flight training.

While taking flight training and amassing your 1000 hours flight time required for an Airline Transport Pilot license (that 1000 hours number is good only if you're attending a four-year flight school; for most civilians working their way up it's 1,500), there are a number of illegal acts you can unintentionally commit while flying. For citizens, the legal penalty for unintentionally breaking an FAA regulation ranges from nothing to a talking to by air traffic control up to formal hearings with possible suspension or revocation of your pilot certificate. For a non-citizen in the United States for the express purpose of learning to fly, any offense bad enough to get your pilot's license suspended would likely also get you deported (if not for the criminal act, then because you can no longer do what you're here to do). But, you'd usually have to mess up pretty bad several times to get that far.

Once you have your ATPL, your M-1 would no longer be valid as you'd no longer be a student, and so you'd have to leave the U.S. unless you made prior arrangements with the State Department and/or an airline to remain in the country under another status (such as H-1b to work for an airline). If you take your license and leave the country, the FAA ATPL would only allow you to fly "N-numbered" aircraft registered by the FAA. Most other countries have their own registration, and would require you to "convert" your pilot's license to the local regulatory agency's version before you could fly a locally-registered plane. For an ATPL holder this is typically easier than for lower levels, and for the EASA (the largest ICAO-compliant regulatory body besides the FAA) it boils down to a skills test (knowledge and practical), a new medical cert, and being re-rated by the EASA for multi-engine operations (the FAA AMEL class rating does not transfer).


What qualifies as a "takeoff" and "landing" in currency requirements? I just met my night-time currency requirements at KONT.

Landing and taking off from a 12000 foot runway in a Cessna 152 got me to thinking (always dangerous, I know).

There's more than enough room to land to a full stop, take off, climb to (e.g. 50 feet AGL), then immediately land again to a full stop without needing to go around the pattern.

Could doing the above count as two takeoffs and landings?

Perusing FAR 61.57 did not give me an answer.

Now I'm not suggesting that this is a good idea, but brings up a few questions;

1)  Is this a legal maneuver?

2) If so, would it meet currency requirements? (If not, chapter/verse of the regulations kindly requested).

3)  Assuming it's ok with the tower, how would I request such a move?

There's more than enough room to land to a full stop, take off, climb to (e.g. 50 feet AGL), then immediately land again to a full stop without needing to go around the pattern.

50 feet is completely arbitrary. Why not 5 feet? If the wheels leave the ground and touch back down, you took off and landed didn't you?

The regs exist to make sure you're maintaining some basic proficiency. Cutting corners to fulfill the letter of the law without actually refreshing your skills does no one any good — least of all you. Besides, as jwzumwalt pointed out, it most likely wouldn't meet the FAA's definition of takeoff and landing.


Must an instrument approach plate be visible during the approach? Is there any legal requirement to display the approach plate for an IFR approach? Typically it's briefed as part of the descent checks and then kept on display - but I'm struggling to find any legal requirement to keep it visible.

If you can't find any language for that sort of thing there probably isn't any.  At some point the value of regulations ends and you have to let common sense and good airmanship prevail.


What documents/procedures I have to follow to fly my aircraft from the UK to Norway? I'm planning a trip to Norway for when Covid restrictions here in the UK are lifted, and was wondering what documentation is needed to enter Norway. I've already emailed AVINOR, and they simply gave me a link to toll.no, which yields no helpful information.
I'll be flying myself in a British aircraft. I'll be departing from Wick in Scotland and arriving in Kristiansand Kjevik in Norway. I'd like the details as if it were normal, pre-covid times.

Are you flying in your own plane, or as a passenger on an airline?  https://www.udi.no/en/want-to-apply/visit-and-holiday/?resetguide=1 will give you some info, but not everything you need if you're flying in yourself.


A question regarding airfoil parameters If a hypothetical aircraft, which is a tailless straight flying-wing with no fuselage, has the following characteristics:

moderate forward sweep
an aspect ratio = 9
a dihedral angle of 3 degrees
a slight tapering of 5 degrees on each edge
wing twist (10 degrees of total incidence difference between centreline and wing tip)
positively cambered airfoil at centreline, slightly less at the root, minimally positive camber at the inboard section, symmetrical outboard section, negative camber from there towards the wing tips
thickness 10% at the tips, 15% at the root and 20% at the centerline
a low wing loading, i.e. 50 kg/m2
slightly forward CG

And if the required stability in yaw (proverse yaw) is considered to be ensured through sufficient wing twist and symmetrical airfoil/negative camber at the tips,
what kind of airfoil characteristics - or even better - what specific airfoil examples (or at least, a specific airfoil category) would provide both low induced drag and ample lift ability at low speeds of 50KT, but still have low resistance at higher speeds i.e. at 200 KT?
Specifically, how much camber and reflex camber change (in ratio to symmetrical) should be sought for each of the different segments of the wing centreline, root, outboard section and wingtip?
Or, would it be sufficient if the whole planform has an identitical airfoil shape (scaled for chord length due to taper)?
What would be the Centre of Pressure positions (in chord percentage) of such a wing at slow flight or in high-speed cruise?
——
I know it may be a fairly wide question with a myriad of possible answers but I would be grateful to see some examples, so I can have some notion on what the camber/reflex camber for these wing characteristics should be, and to better understand via examples.
Thanks

For a wing to be stable in its own right, its aerodynamic centre must remain static with changes in angle of attack. The usual approach is to sweep the wing and wash-out the outer section. Because your wing is unswept, you have only two choices in creating a stable aerofoil:

A symmetrical aerofoil, i.e. with zero camber.
A cambered aerofoil with reflex camber towards the trailing edge.

The first of these has poor low-speed characteristics and has really only seen use on aerobatic and early supersonic types.
The reflex type offers better low-speed characteristics, thanks to its positively cambered leading edge. RAF 34 provides a good example; it was developed in the 1920s when RAF 33, with even greater reflex, was found to have high drag. RAF 34 had much better performance above 200 kt and was used on several tailless types (usually swept and washed-out as well) such as the Westland Pterodactyls. It would be a good starting-point for your search.
But be aware that your tapered "plank" wing will have abysmal handling characteristics and a vicious, unrecoverable stall. Washout can help a little here, and the CG position will depend on this, as well of course as on your chosen aerofoil. Maybe using it as a hang-glider might be tenable, as the pendulum stability will mask the worst handling issues, but I would not want to take it up in case it stalled!
Addendum
Some remarks have touched on the NASA Prandtl-D experiments led by Albion Bowers, which owe much to Prandtl's "bell-shaped" lift distribution and Reimar Horten's exploitation of it in his flying wings. Prandtl's analysis applied principally to the straight wing and was not concerned with stability or yaw. By contrast the Horten/NASA implementation is applied exclusively to tailless swept flying wings, where stability and proverse yaw in the turn are essential to docile handling. In this latter context, many subtle variations of aerofoil across the span have been tried over the years. JW Dunne anticipated it all, and more, intuitively back in the pioneer era - the Science Museum archive contains boxfuls of his research models - but he was no mathematician. The precise relationships between the various design features and resultant flying characteristics still remain somewhat clouded and contentious, and Dunne's work studiously ignored, so some aspects of the original question here remain unanswerable. But one thing everybody I have mentioned has agreed on; if you do not sweep your wing then you are making life much harder for yourself.


What is the correct formula to calculate propeller efficiency? How to calculate in the right way the efficiency of a propeller?

If we know the engine power, speed of the plane and the thrust of its propeller, what is the correct method, (1) or (2), for calculating the efficiency of the propeller?

Assuming that Method 1 is the correct one, it appears that the efficiency of a propeller must satisfy the inequality:

Update:

It looks like Method 1 is correct and 2 is wrong as long as the page Performance of Propellers, MIT calculates the efficiency on an ideal propeller and gets the same inequality.
If a propeller of diameter, d, delivers the thrust, T, while the plane travels at the speed, V, it always has a maximum possible efficiency that can be calculated, is below 1 and can not be improved. Not even an ideal propeller of diameter, d, has, in general, an efficiency that reaches 100%. The absolute minimum, reference power, is always $TV$ and not something else and the efficiency is always:
$$TV/Power_{absorbed}$$
where the minimum absorbed power is calculated with Froude's Propeller Theory.

Propellers are designed for an optimal tip speed being a certain multiple of the air speed they are flying inside. The angle of the propellers aerofoil shape to the propellers axel changes as you move from the Center to the tip. The more pronounced the blade rotation the higher the intended tip speed.

From memory having the tip speed running at 1-3 times the the air flow speed is not efficient, but at least the propeller works over a wide range of air speeds.

Highly tuned propeller tips are moving at 6x the air speed. However, their effectiveness at moving air disappears rapidly if the air flow is too slow. (The propeller blades are stalled)

The last thing you want on a propeller plane is an efficient propeller.


Why didn't government regulators prevent MH17 from flying the route it took? Why wasn't MH17 prevented by government regulators from flying the route it took?

MH17 wasn't the first case of governments or combatants downing commercial aircraft: Iran Air Flight 655 and Korean Air Lines Flight 007 come to mind.

I find it hard to believe that if an area had an unacceptably high risk for aircraft, that it would be up to the individual airlines to decide not to fly that route, rather than governments being flown over, or the source or destination countries, flat-out forbidding it unless there's no alternative.

Was military aircraft (such as Ukrainian Air Force Ilyushin Il-76 and other incidents mentioned in the Background section of Wikipedia's article on MH17) being shot down in the area a new phenomenon, with regulators not acting fast enough to deal with this new information?

The Airlines can decide for them selves which route to take, however the government has an intelligence operation which can predict events that might happen in political unstable regions of the world. However in the case of MH17 it was not the "army" that shot down a plane but an conflict between rebels and the government.

Routes flown to Kuala Lumpur

While the flight from Amsterdam to Kuala Lumpur from Malaysia airlines have been suspended, one can still retrieve the route flown via flightaware.com:

The KLM flightpath (KL809) 10246km:

The Malaysia Airlines flightpath (MH19) 10855km:

From the plots it can be seen that both Airlines diverted their routes after the accident with MH17. They both avoid Ukrainian airspace.

Would flying these routes prevented the accident? Yes, but at the time intelligence agencies where not aware that the Separatists had acces to such advanced surface-to-air missiles. This also because the nature of the conflict would not suggest that such weapons would be required.


How to choose between BasicMed an a Class III Medical? I'm due for a medical this year, and my last one was before the BasicMed program existed.

I'm a VFR PPL, flying small planes with 6 people or less.

Is there a clear reason to use Basic Med or Class III Medical?

I guess it depends on whether you intend to fly a larger aircraft at higher altitudes at faster speeds or one with a limited number of passengers at lower altitiudes and airspeeds.  If the latter is going to be the only flying you do, then a basic medical will be a good choice.  If you intende to undergo additional training and obtain additional certificates, ratings, or type ratings, I believe you will be required to hold at least a third class medical to do so.


Measuring speed and altitude from personal phone midflight Given that there is no need now for one to swith off their cellphone midflight, inflight wifi is now  a norm and common, Is it possible for me to measure the velocity and altitude of an aircraft using my personal car GPS speed indicator or cellphone app in the case of speed and altitude as a passenger?

Depending on the reliability of the sensors in your phone, yes that sounds completely possible. Most modern aircraft use GNSS for navigation, and your phone relies on the exact same technology.

Be aware that you will get the ground speed - see this question for further details: Why is there a difference between GPS Speed and Indicator speed?


What kind of Chinook helicopter/airplane hybrid is this? I had this question: Could this helicopter's body be a flying wing? and this picture came up.

What kind of helicopter is this?
 What is the extra wing for?

It‘s a BV-347 technology demonstrator:

  In 1969, the Army and then-Boeing Vertol entered into a partnership to improve upon their cargo helicopter fleet, and thus the BV-347 was borne from a CH-47A Chinook that was provided by the Army as a technology demonstrator, according to retired CW5 Jim Kale, who now serves as a tour guide for the U.S. Army Aviation Museum.

Primary objectives as found in above article:

  The BV-347 was tested for more than two years and flew about 350 hours with the intention to meet five primary goals: improve flying qualities with external loads and instrument flight; im-prove stability, control and maneuverability in hover flight and forward flight with high gross weight; reduce rotor noise; reduce vibration stress; and create a modern cockpit environment with improved instrument and navigation displays.

The wing was intended to provide extra lift (works in forward flight only, of course), but apparently didn’t add net benefit:

  The wings were added as a means to improve lift, and although the addition served its purpose, the added weight canceled out any positive effects it provided [...].


What are "ground-based navigation systems which provide vertical guidance" and how do they compare to altimeters? I am a total layman when it comes to aviation but for a school presentation I am trying to understand the reasons why Air Canada 624 crashed while trying to land on runway 05 at Halifax (CYHZ). I have read the investigation report and the press release the Air Canada pilots union have published. The press release says:

  ACPA strongly advocates for all major airports to have the necessary
  equipment to offer both lateral and vertical guidance and high
  intensity lighting to allow pilots to orient aircraft for landing.

  Many runways at Canada’s largest airports lack the ground-based
  navigation systems which provide vertical guidance – that is, the
  distance between the aircraft and the ground – to orient an aircraft
  for landing.

I was under the impression that an altitude reading is always available through the radio altimeter or the barometric altimeter.

Why would such a "ground-based navigation system" that provides "distance between the aircraft and the ground" be needed? What can it provide that the regular altimeters on board cannot provide?

They mean an ILS - Instrument Landing System.

An ILS consist of:

A localizer component, which tells the angle between the aircraft's position and the extended runway centerline. In short, it tells the pilot whether they are left or right.
A glideslope component, which tells the angle between the aircraft's position and the extended runway surface on the ground. Typical glide slope angle is 3 degrees. In short, it tells the pilot whether they are high or low.

An ILS is usually coupled with an DME (Distance Measure Equipment), which tells the distance between the aircraft and the runway threshold. Using the glideslope angle together with the horizontal distance, one can compute the height above runway level.

From page 12 of the report:

  AC624 was then cleared for the straight-in LOC approach ...

Which means only the lateral (left or right) component is available, there is no signal which tells the pilot whether they are high or low relative to the ideal descent path.

A radio altimeter is not very useful when the approach path leading to the runway has uneven terrain. It tells the height above the ground directly under the aircraft.

A barometric altimeter needs to be calibrated by a reading at ground level. It tells the height above sea level.

Both of these altimeters cannot tell the height above runway level. Therefore the pilots must rely on other data to monitor the descent profile, which increases the pilots' workload. In a situation such as low visibility and high crosswinds, this presents a very challenging situation.

If both vertical and horizontal guidance is available, then the pilots can simply follow this guidance all the way to the runway. They can also program the autopilot to follow this guidance, if suitable equipment is installed on the ground as well as onboard the aircraft.

Note the green bars: one is horizontal and one is vertical. They form a cross on the display. If the horizontal bar is up a little bit, the pilot would pull up a bit. If the vertical bar is to the right, the pilot would turn right a bit. These green bars only possible when ILS is used.

It is possible to compute the relative height by using a DME and a barometric altimeter only. For example, I am now 5.5 nautical miles from the runway threshold, and according to the approach chart, I should be at 1,800 feet. Right now my altimeter reads 1,600 feet. That means I am too low and I should reduce my vertical speed to slow down my descent. This calculation has to be done by the pilot himself and not by a computer. Furthermore the pilot must fly the plane, i.e. adjust the control surfaces, run landing checklists, visually verify the alignment with the runway, talk to ATC, set the flaps etc. A pilot is trained to do all this, but increased workload also increases the chance of making an error.


What are the rules regarding (HUD) Head-up displays, especially glasses type? What are the relevant regulations regarding use of HUD displays in non-military aviation?

The specific application in mind would involve providing information to pilots of turboprop survey aircraft flying VFR at about 100m altitude so it's of benefit to have the pilots' focus on what's going on out the window.

You can read about some guidance from the FAA about HUD design in these two Advisory Circulars:

General electronic displays
Enhanced Flight Vision Systems

This handbook is a bit dated but covers certification.

It really depends on what exactly the HUD is supposed to do. Any pilot can bring a handheld GPS along, with the understanding that it is not an "official" navigation instrument. A HUD could be used in a similar way. There are a couple things to keep in mind:

If the HUD is to be used for real navigation or pilot reference, then certification will be an issue. The handbook above talks about this. The HUD would need to be certified just like any other instruments in the cockpit for that use. If a HUD is used for special situations, like low visibility landing, it must be certified in order to be used in those situations. Otherwise you are not allowed to do anything you could not do without the HUD.

Even if the HUD is not to be used for critical flight data, the HUD needs to comply with the FAR 25 sections 25.773 and 25.775, which talk about the windows in the cockpit. The HUD can't interfere with the normal visibility the pilot should have.


What's the point of intercepting an aircraft? I know that it's possible for military aircraft to "intercept" a civilian or foreign aircraft (and I'm well aware of the US interception procedures), but why would they be  doing it in the first place?

What does it actually prevent from occurring?

They can't remotely control the aircraft, so is there anything that they can do once they intercept it?

Military interception usually happens after failure to make the aircraft comply by other means (such as radio, light signals, flares). So, first and foremost it is one way to do visual communications, which is usually hard for the pilot to miss. The messages for follow (wide level turn), land (low pass, landing gear extended), and continue on course (climbing turn) are well established (possibly even internationally?) and all pilots should know them, and are probably enough to defuse most situations. Not to mention that you should try to establish radio communications on 121.5 if you're being intercepted.

I'd wager a guess that the most common cause for interception is that a pilot has strayed into restricted airspace without talking to anyone on the radio, without any malicious intent.

If the pilot ignores the messages, there's always the option of using force, if the risk to occupants and collateral on the ground is acceptable.


How would an aircraft visually signal "in distress"? A ship at sea would fly its flag upside down to signal it's in distress. How does a plane or airliner that has no radio or transponder visually signal that it is in distress?

This question: How do commercial pilots send distress signals? explains how it is done using a radio or transponder, but how could the message "please don't shoot me down" be relayed visually to a fighter pilot?

For the US, the FAA's Intercept Procedures list several things a pilot can indicate without radios:

Acknowledge instructions: rock wings, flash nav lights
Unable to land at indicated airport: flash landing lights
Cannot comply: switch all lights on and off at regular intervals
In distress: switch all lights on and off at irregular intervals


When is squawk 1000 assigned in USA? From Are squawk codes used with ADS-B?:

  Yes, squawk codes are still used and required with ADS-B.

The post is 3 years old though. And from Wikipedia List of transponder codes:

  1000: Used exclusively by ADS-B aircraft to inhibit Mode 3A transmit (USA)

The way I understand that, if the flight will be in complete ADS-B coverage, say a domestic flight, it is assigned 1000.

Is 1000 indeed assigned to ADS-B flights, or are they given discrete* codes still?

* Oops. I didn't mean discrete as in hex discrete, but the 4-digit one that changes from flight to flight.

Currently, FAA's "fusion" software uses discrete squawk codes to merge targets generated by different surveillance systems, i.e. SSR (often several of them) and ADS-B. They plan to upgrade the software so it can merge targets based on Mode S hex code as well, but (as of early 2019) that hasn't been rolled out yet. Once that is in place, ATC will switch to telling Mode S targets to squawk 1000. Mode A/C targets will still need discrete codes, though, including Mode S aircraft in areas that only have Mode C SSR.


How did SR-71 spy, flying at 80,000 ft and 3500 km/h? The SR-71 Blackbird is a famous supersonic reconnaissance/spy aircraft, undoubtedly one of the most amazing flying machines ever. Now, with the capabilities it had:

  Maximum speed: Mach 3.3 (2,200+ mph, 3,540+ km/h, 1,910+ knots) at
  80,000 ft (24,000 m)

How was it used for spying? It must have been difficult to focus on any object on the ground, from such a great height and then many problems are encountered with high speed photography. How were these and many other problems overcome?

The SR-71 Blackbird was equipped with specialized cameras. It would overfly the area of interest and take high-resolution pictures of the ground.

Of particular interest is the Technical Objective Camera (TEOC). It could shoot pictures with a 6'' resolution from the operational altitude of the SR-71. This task was not simple as the aircraft would have moved several hundred feet forwards during the exposure time of the picture which was (depending on the settings) around one or two tenths of a second. Without some kind of correction, this would have resulted in a picture that was blurry in the direction of motion of the aircraft.

To solve this, the velocity over height ratio number was fed to the camera, either manually as computed by the pilot or automatically as computed by the sensors and computer of the SR-71 (and it turns out that the machine did a better job at this than the pilot) and while the picture was taken, the high-precision mirror that directed the camera FOV downwards would rotate in the opposite direction towards which the airplane was moving, thus cancelling it out.


Why do some pilots misuse (troll) the GUARD frequency? When flying I almost always monitor GUARD, VHF 121.5 on my second communications radio. It's almost a daily occurrence that I hear someone transmit the words "work work work" or a long, theatrical "GUUARRDDD!" as a response to someone calling for a ramp taxi clearance on the wrong frequency.

It is interesting that these particular responses are so prevalent.

Has anyone studied this misuse of the guard frequency to determine if there might be a cultural source?

At least in my experience with the last decade of aviation, there hasn't until fairly recently but such common use of the guard frequency for communications which aren't pertinent to its purpose. Has the FAA taken any actions on pilots for misusing the guard frequency in the way mentioned in the first paragraph?

Every field has its bottom 2%, and some of ours regularly self-identify as such on 121.5.

Sigh.

The "work work work" refers to this video (start about 2:55 for the relevant section).


Yellow chevron markings at end of runway, what do they mean? In this YouTube video (link starts video at time of interest), the pilot appears to land in the area marked by the large yellow chevrons, in what appears to me (a layperson) to be a taxi way.

What are the meaning of the yellow markings? Under what conditions can a landing be made before this point?

Those are not chevrons but arrowheads used to mark the start of the runway. So, yes, he did land on the taxiway.

Source: FAA Airfield Standards Quick Reference

He does land slightly before the runway threshold. He even says he is going to land short. Since there was nothing on the taxiway leading to the runway then it seems there is no problem doing that.

screenshot from Google maps of KYKM runway 22 threshold

For comparison, chevrons mark either stopways or blast pads and look like this:

same source as first image

They may include an EMAS bed, so touching down there would not be a good idea.


Why should a test flight be performed when the propellers are changed? From this question I've learned that after a propeller change the plane should go through a test flight. Why is this?

The purpose of the test flight is for the safety of passengers. For most maintenance, in a not-for-hire aircraft, a private pilot can perform the test flight and determine the aircraft is airworthy, but they must do it without passengers.

Title 14 chapter 91.407


Would An-72-like (or any anhedral wing multi-engine aircraft) cruising at high speed, roll counter intuitively right, if left engine suddenly dies? Assuming low angle of attack & anhedral wing configuration. (and as a consequence of natural left yawing moment)

Simple answer: no, it wouldn't, otherwise it wouldn't be certified if it behaved like that :)

The real answer is the same as to why nearly all high-wing aircraft have anhedral. Yes, anhedral angle creates the 'adverse' roll effect, but it is made to counteract the excessive positive effect from all other factors, namely the wing sweep and the high-wing configuration itself. (The latter effect is more complicated than the usually assumed 'pendulum' effect: it has more to do with the added drag and cross-flow effects of the sideslipping fuselage (see, for example, here)).

As always, too much of a good effect is not good at all: excessive static stability causes oscillations, in this yaw/roll case known as Dutch roll, so anhedral is used to reduce the overall effect to a reasonable but still positive level.