What constitutes a flight review for the purposes of eligibility for a remote pilot certificate under 14 CFR 107.61(d)(2)? An applicant for the Remote Pilot Certificate who already holds a pilot's license can forgo the knowledge test required by 14 CFR 107.61(d)(1) if they have a current flight review. The regulation states that an applicant must be able to demonstrate aeronautical knowledge by satisfying one of the following conditions:

  14 CFR 107.61(d)

  (1) Pass an initial aeronautical knowledge test covering the areas of knowledge specified in §107.73(a); or

  (2) If a person holds a pilot certificate (other than a student pilot certificate) issued under part 61 of this chapter and meets the flight review requirements specified in §61.56, complete an initial training course covering the areas of knowledge specified in §107.74(a) in a manner acceptable to the Administrator.

14 CFR 61.56 specifies that a flight review is:

  (a) Except as provided in paragraphs (b) and (f) of this section, a flight review consists of a minimum of 1 hour of flight training and 1 hour of ground training.

  [...]

  (b) Glider pilots may substitute a minimum of three instructional flights in a glider, each of which includes a flight to traffic pattern altitude, in lieu of the 1 hour of flight training required in paragraph (a) of this section.

  [...]

  (f) A person who holds a flight instructor certificate and who has, within the period specified in paragraph (c) of this section, satisfactorily completed a renewal of a flight instructor certificate under the provisions in §61.197 need not accomplish the one hour of ground training specified in paragraph (a) of this section.

Are these definitions to be understood as the definition of a flight review, or might the following flight review exemptions also count for the purposes of §107.61(d)(2)?

  (d) A person who has, within the period specified in paragraph (c) of this section, passed any of the following need not accomplish the flight review required by this section:

  (1) A pilot proficiency check or practical test conducted by an examiner, an approved pilot check airman, or a U.S. Armed Force, for a pilot certificate, rating, or operating privilege.

  (2) A practical test conducted by an examiner for the issuance of a flight instructor certificate, an additional rating on a flight instructor certificate, renewal of a flight instructor certificate, or reinstatement of a flight instructor certificate.

  (e) A person who has, within the period specified in paragraph (c) of this section, satisfactorily accomplished one or more phases of an FAA-sponsored pilot proficiency award program need not accomplish the flight review required by this section.

For the purpose of initial certification under §107(d)(2), is a flight review to be understood strictly as the training defined by 14 CFR 61.56 (a), (b), or (f), or do the exemptions to the requirement for a flight review—14 CFR 61.56 (d) or (e)—also count as a flight review?

You have to take into account the intent of the regulation.  I think the regulations intent is to ensure the pilot has been evaluated on his knowledge within the previous two years by either a CFI or examiner.

With that in mind, a flight review by a CFI or passing a practical test by an examiner satisfies the requirement for the remote operator to take the full initial knowledge test.

From the preamble to the Part 107 final rule.

  The FAA proposed that a certificated remote pilot must also pass a recurrent aeronautical knowledge test every 24 months. Like the flight review requirement specified in §61.56, the recurrent knowledge test provides the opportunity for a remote pilot’s aeronautical knowledge to be reevaluated on a periodic basis. The FAA adopts this provision as proposed, with one change. As discussed in III.F.2.i, the FAA exempts part 61 pilot certificate holders from the requirement to complete recurrent knowledge tests as long as they satisfy the flight review requirements of §61.56 and complete an online training course every 24 months

Page 6 paragragh g.

  The FAA agrees with commenters who suggested that requiring part-61- certificated pilots who satisfy the flight- review requirements of §61.56 to take an initial or recurrent knowledge test is unduly burdensome. Through initial certification and subsequent flight reviews, a part-61-certificated airman is required to demonstrate knowledge of many of the topic areas tested on the UAS knowledge test. These areas include: Airspace classification and operating requirements, aviation weather sources, radio communication procedures, physiological effects of drugs and alcohol, aeronautical decision-making and judgment, and airport operations. Because a part 61 pilot certificate holder is evaluated on these areas of knowledge in the course of the part 61 certification and flight review process, reevaluating these areas of knowledge on the initial and recurrent knowledge tests conducted under part 107 would be needlessly duplicative.

Page 13 paragraph I


Could the filming of the 747 in "Awakenings" have taken place during the 747 flight testing? In the 1990 film "Awakenings", the main character Leonard awakens after suffering from a catatonic illness for 30 years.

There's a scene where Leonard watches a 747 landing in New York at JFK. This is considered to be an anachronism/continuity error in the film, as the film takes place in the summer of 1969 and the 747 didn't enter revenue service with Pan Am until early 1970.

However, I know that the prototype 747 first flew in late 1968, and my guess is that by the summer of 1969 several aircraft had been produced, and flight testing was ongoing.

My question is if there's any 'plausibly deniable' way Leonard, in the world of this "based on a true story" yet finally fictional movie, could have actually spotted a non-revenue service test flight 747 landing at JFK in the summer of 1969?

I'm more wondering along the lines of if I were transported back in time to the summer of 1969 and hung around JFK, did pre-revenue 747s ever land there? Or did all testing prior to its introduction with Pan Am occur in controlled environments where it wouldn't be observable by the public?

Nope. It wasn't filmed during testing.

When Dr. Sayer takes Leonard out into the city for the first time, they see (among other things) an aircraft landing - a Boeing 747. The movie takes place in 1969 and the first revenue flight of the Boeing 747 was January 21st, 1970. Additionally, the 747 is in El Al livery that was used around 1990 (IMDb).

(airliners.net) Photo date: October 27, 1991.
Could the 747 have been filmed while landing at JFK in the summer of 1969?
It's plausible, because during the flight testing the 747 flew to Paris and it could have very well used JFK (runways were upgraded in the late 60s):

[Boeing took] a test aircraft to the 28th Paris Air Show in mid-1969, where it was displayed to the public for the first time (Wikipedia).

and

[JFK] was designed for aircraft up to 300,000-pound (140,000 kg) gross weight and had to be modified in the late 1960s to accommodate Boeing 747s (Wikipedia).


How long before a Medivac should the pilots be ready? If you are on home reserve how long is it required that the operator notify you of a flight before required Take off time?
Is there a regulation or documentation to support this or is it operators discretion

Medivac pilots (at least the ones in my city) are at the hanger/pad 24/7.

My home field (KPNE) happens to be where some of the medical choppers are stored and dispatched from. In Philadelphia they tend to not be stored at the hospitals. I have met some of the pilots and one of the crew nurses. Where I am the facility is staffed 24/7 much like a road ambulance facility so that as soon as a call comes in they are ready to fly. The helicopters them selves are kept in a hanger, always fueled and alway ready to fly, on these neat rolling carts so that a tug can pull them out as the pilots are getting things squared away in the cockpit.

One of the hospitals in the suburbs keeps their chopper at the hospital (which is fairly close to KDYL) and is avalible 24/7 as well.

I also happen to over look one of the 4 hospital helipads in the city from my home. The pad is generally kept open for arrivals and on a decent weather day that can mean upwards of 10 landings (I have no idea what they are transporting).

I had the pleasure of meeting one of the guys that helped design the Philadelphia Class B. The airspace is specifically designed so that all of the hospitals sit under shelves such that the helicopters can come and go without needing a bravo clearance to expedite their travel times.

Its worth mentioning that ready to fly and will fly are not the same thing and the latter is at the operators discretion. Ultimately the pilots make the go no-go decision and if the weather is dicy rescue teams generally will not fly.


Would better location tracking for airliners improve safety? Once in a while an airliner just up and disappears -- typically over ocean -- and lengthy and expensive search efforts have to be launched in order to find it. The most famous cases in recent years were of course AF447 and MH370.

It is hard for the bemused public to understand how something as large and technologically advanced as a wide-body jet can just go missing. Some people end up on websites like this one, asking why we can't just do such-and-such to make sure planes can always be found. The answers typically center around how such-and-such would actually be very expensive, and probably not 100% effective anyway. This doesn't really seem to convince most questioners, who wonder how important a bit of cash ought to be when there are lives at stake.

The purpose of this question is to clarify whether lives are actually at stake.

Suppose we had a magical technology which at negligible cost could give us reliable access to the exact flight path of an airliner in trouble anywhere on Earth. How much safer would that make flying?

For definiteness, let's assume that the magical technology gives us position samples at 1-minute intervals at a one-hour delay, so it won't be useful for real-time purposes such as ATC.

Would better location tracking for airliners improve safety?

Very simply, no.... us knowing where AF447 was would have made exactly zero difference to the fact that it crashed into the ocean at 400+ knots.

Would we have had a better idea of where to find it? Most probably. Would it have saved any lives? Absolutely not.

As always, these things come down to cost-benefit, and the simple fact is that GPS tracking would prevent very, very few accidents. The only possible benefit would be that it may help us find the black box or wreckage, assisting in the investigation which may just possibly reduce the chances of a similar accident occuring in future. Note that of the two examples you gave, though, only MH370's black box hasn't been found (yet)... so even this benefit is tentative.


Is a destination airport necessary for cross-country VFR departure clearance? New flyer here. When you’re requesting departure clearance for a cross-country VFR, do you have to specify the destination airport to the controller, or can you just specify a direction (eg. “VFR to the south”)?

Just say direction of flight.

If they need more info, they'll ask:

  N12345: Say destination.

I've almost never heard that, except if they think you might be headed towards weather or a TFR.

Examples:

  Understand you're headed to the south.  Be aware of Stadium TFR in effect.

or

  Understand you're headed to the south; have had reports of severe weather in that direction.


What are the pros and cons of wingtip tanks? I am looking into the aerodynamic pros and cons of wingtip tanks. Let's assume they're perfectly streamlined, optimally placed and sized for a given airframe.

I am aware of the purpose of fuel storage on a wing that's too thin or otherwise inadequate for 'wet wing' fuel storage and as a means of permanent fuel storage, but how do tip tanks interact with airflow on the end of the wing?

What are the pros? Are tip tanks effective as 'winglets' or drag-reducing tips, controlling spill and cleaning up vortices? Do they contribute to useful lift and if so what percentage and what is the overall effect on the wing?

And what are the cons, aerodynamic, structural and general? Do they require heavy modifications to the spar or wing in general to attach?

Overall, if a wing design can include bladder or wet wing storage, would it be better not to employ tip tanks?

I happen to own a homebuilt with tip tanks for ALL of the fuel supply (Pazmany PL-2), and while they look really cool, I'd prefer the fuel was in the wing leading edges mid span.

There is no aerodynamic benefit.  The tuna fish shaped tank doesn't function like a winglet (it has to be a wing to work like a winglet) and is too small to have any kind of end plate effect of significance (an end plate has to extend for a full chord to do any good that exceeds its own drag).  The flattened and canted tanks you see on twin engine Cessnas was intended to produce a bit of vertical lift and an enhanced dihedral effect to offset some of the inertial issues in roll that the fuel mass creates; which leads to...
Inertial issues in roll.  The mass of the fuel way outboard in the wings is a total pain.  It deadens the aileron response.  The inertia magnifies roll and yaw disturbances. My airplane is much more snappy with minimum fuel vs full fuel, and wags its tail in turbulence much less. I prefer to fly it with about 1/2 fuel if I'm just going out for an hour or so.  The  mass also kills a lot of the roll-yaw couple and amplifies adverse yaw.  If I skid the airplane with rudder, the roll into the yaw is very mild, in spite of significant dihedral.
Significant form drag. On my plane there is about a 8kt speed penalty from having the tanks taking up space in the airstream (based on the performance of other PL-2s modified to tankless wet-wing).
Fuel imbalances have a huge impact because the arm is so long.  If I ran one tank all the way down with the other nearly full, I'm sure it would use up an unpleasant amount of my aileron authority at low speed (I don't really want to find out how bad - at minimum, it would take probably 10lbs plus of side pressure on the stick to keep wings level). Having no trim tab or bungee, I use the fuel balance as my lateral trim, and when solo, have to achieve about a 2-3 gal right side differential to get the plane to fly hands off.  Then I have to remember to switch back and forth every 10 minutes or so to keep the balance.  I know if I forget because the airplane starts to wander off toward the heavy side, like a horse that suddenly remembers where the barn is while you're riding it.
Structural issues are minor.  You are adding mass at the opposite end of the most highly stressed part of the wing, but you need to make the outer spar structure able to handle the local bending, so some minor reinforcement would be required at the attachment.
One plus is the fuel supply is far away from you, say if you flipped over.  I like that.
One minus is the fuel supply is far away from you, at the first point to touch the ground in any kind of landing excitement.

All that being said, the PL-2 is a delightful airplane even with the tip tanks, and dammit they look awesome.  If I was building one from scratch however, I would do leading edge tanks like the Van's RVs.  Just way more efficient in every way.  As a long range fuel supply add-on however, they can make sense, but I think most designers will just extend the wet wing volume instead, until they run out of that.

On airplanes like the Lear, they made sense because with the super thin wings they were the most practical way to put in a large fuel supply.  But you will notice that they did away with them in later models because other than a handy place to stick tanks that don't get in the way of something else, it's mostly negatives. I shudder to think about how to control a tip-tank Lear with one side nearly empty and one side nearly full, if that were to happen somehow.

A former colleague was an old F-101 Voodoo driver who also had a lot of time in T-33s and he recounted to me once that the T-33's really large tip tanks were a pain due to the flywheel effect of the fuel mass. A little bump would start it rolling, and with the big weights out there, it took more than the normal input to stop the roll and if the conditions were rough you were fighting that constantly.


Is there anywhere I can pick up raw flight data recorder information? We were plotting flightpaths as practice in programming class but unfortunately that was limited to some recordings from a research aircraft.

I'm wondering if I can pick up the raw data files from (accident) Flight Data Recorders somewhere to see if I can plot them as well?

(Like a file with rows listing time, position, altitude, airspeed etc.)

Unlike the AAIB, the NTSB does release FDR data dumps (adjusted for engineering units and culled to the same parameters as the graphs) as part of the docket release for a given accident -- no FOIA pestering needed!

See these examples from the Bedford, MA Gulfstream overrun crash, for instance (they're CSV files).  You'll be able to find more by looking through the dockets associated with recent major NTSB accident reports.


What are the advantages of a forward-swept wing over a rearward-swept wing? What are the advantages of a forward-swept wing vs. a rearward swept one?

Image credit: NASA

Image credit: Paul Maritz / Wikimedia

There have only been a few aircraft built with forward-swept wings. Most notably was the X-29, which you have pictured above. Russia/USSR built one more recently in 1997, the Sukhoi Su-47. One of the biggest claims as to the superiority or an advantage of a forward-swept wing was increased maneuverability. However, in the case of the X-29, as noted in the Flying Qualities Evaluation of the X-29A Research Aircraft,

  The high pitch instability of the airframe led to wide predictions of extreme maneuverability. This perception has held up in the years following the end of flight tests. Air Force tests did not support this expectation. For the flight control system to keep the whole system stable, the ability to initiate a maneuver easily needed to be moderated. This was programmed into the flight control system to preserve the ability to stop the pitching rotation and keep the aircraft from departing out of control. As a result, the whole system as flown (with the flight control system in the loop as well) could not be characterized as having any special increased agility. It was concluded that the X-29 could have had increased agility if it had faster control surface actuators and/or larger control surfaces.

The Su-47 was indeed a highly maneuverable aircraft, capable of pulling 9 Gs, however, its immediate predecessor, the Sukhoi Su-37, was capable of pulling 10 Gs. So it's not clear whether a forward swept wing has any real positive impact on maneuverability.

However, stall characteristics are very different. Air tends to travel towards the rearmost end of the wing. On a standard configuration (Rear-swept wing), this of course moves from the wing root to the wingtip. On a forward-swept wing, however, this moves from the wingtip to the wing root.

  As a result, the dangerous tip stall condition of a backwards-swept design becomes a safer and more controllable root stall on a forward swept design. This allows full aileron control despite loss of lift, and also means that drag-inducing leading edge slots or other devices are not required. With the air flowing inwards, wingtip vortices and the accompanying drag are reduced, instead the fuselage acts as a very large wing fence and, since wings are generally larger at the root, this improves lift allowing a smaller wing. As a result maneuverability is improved, especially at high angles of attack. At transonic speeds, shockwaves build up first at the root rather than the tip, again helping to ensure effective aileron control.

Because of the capability of the X-29 to have the tips of its wings bend down when at high angles of attack, the X-29 remained controllable at an angle of attack of 67 degrees. However, thanks to modern advances in thrust vectoring, the F-22 Raptor is capable of sustaining an angle of attack over 60 degrees.

With inherent instability and problems with extra stresses on the airplane for only moderate or supposed but not observed gains in instability, it is unlikely we will see combat aircraft with forward swept wings any time in the near future. Other technologies have enabled similar or enhanced performance without the need for novel concepts.


Aclad sheet metal P/N 22024T3 I am looking for aclad sheet metal  P/N 22024T3   2MM, 1.2MM AND 1.6MM 1 SQM each. Anyone could help me locate those? I sent requestes to MROs etc, most do not recognize the P/N which is taken from the AIRBUS A320 AMM.  Help, anyonme. I would porefer to find it in Europe if possible.

You have an extra 2 in the P/N. Check 2024T3 ALCLAD ALUMINUM SHEET on aircraftspruce.com.

Double check the AMM and recontact your suppliers.


How is a missile lock detected? How can a fighter aircraft involved in a face-off detect a missile lock from a trailing aircraft so that it can make evasive maneuvers?

To add some data to Matthew's answer:
Anti aircraft missiles come in basically 4 types (some others have been tried but aren't in common use).

Active radar homing
Passive radar homing
Infrared homing
Laser guided

Active radar homing has a radar in the missile sending out signals. Those signals can be detected and classified by the target aircraft.
Passive radar homing has a receiver in the missile reacting to specific signals bounced off of the target by the launching system. These too can be detected and classified by the target aircraft.
Infrared missiles are completely passive and can't be detected this way.
Laser guided missiles are like passive radar homing missiles, except they react to reflections of a laser beam rather than a radar signal. These too can of course be detected and classified with appropriate sensors.

There have been some attempts at detecting missiles by their own infrared signature, typically their engine exhaust. But this is problematic because most of that is of course blocked from the missile's target by the missile body, and also many missiles will spend a lot of their flight towards the target in an unpowered glide state, thus not having a hot engine exhaust.

Other systems generally can't be detected by the target either. Think optical guidance using a radio link with the missile (while you might be able to detect the link, you can't readily know what it's doing or that you're the target if you do recognise it as a missile guidance link).

Optical guidance using control wires is not generally used with anti-aircraft missiles, but sometimes anti-tank missiles using these systems are used against slow flying aircraft. These are utterly impossible to detect.


Is the route which takes the least time always the one with least fuel-burn? Geographically longer paths may require less fuel than the shortest (great circle) path. But what about time ?

Is the most fuel efficient route always the one that has the aircraft in the air for the shortest amount of time (assuming equal speed setting, e.g. LRC) , or not ?

Users here seem split on this question:

  « The most fuel efficient route is the one that has the aircraft in
  the air for the shortest amount of time. » (source)

and:

  « It's possible that the route that results in the smallest fuel burn
  is not the necessarily the route that takes the least time. That's true
  more often than not, but if to get the most favorable winds you had to
  stay low, you might burn more fuel. » (source)

So which one is it ?
And, if possible, please provide a clear explanation why.

Generally, the least time in the air the better, but it's mostly a maximum miles per gallon over the earth thing and this depends on winds.  In the time/fuel burn equation, there is always a "sweet spot", a speed/power configuration that gives the most miles per gallon for "air distance" traveled, but how this translates to a maximum distance covered for a given amount of fuel depends on the headwind/tailwind component.

If headwinds are strong, the most efficient speed may be faster than what is optimal for winds that are light or there is a tailwind.  It's easy to see if you take it to the extreme; imagine you are in an airplane that cruises most efficiently at 50 mph and can go 80 mph.  Most miles per gallon air distance is at 50, but if you have a 50 mph headwind, you aren't going anywhere are you, and your actual miles per gallon is 0.   Dial that ridiculous example back to something more reasonable and you can see that there are subtle variations with winds that have to be taken into account.

Generally speaking if there is nil wind or a tail wind, you would fly at the most efficient miles per gallon speed but with a really strong tailwind it might be better to slow down even more for best earth miles per gallon.  If there is a headwind, the optimal speed might be little faster than the max air miles per gallon speed to use the least fuel to get there.

There was an incident once where an RJ crew had to do an IFR diversion with the flaps stuck at 45 degrees and the crew had to decide what speed to fly at, limited to flap extension speed and with all that drag, taking into account whatever headwind/tailwind they had.  They landed at their alternate with 500 lbs on board, about 10 minutes worth.  Talk about pressure to get your calculations right...


Is there really anything to be gained by placing the propeller at the top of the vertical stabiliser? I am currently designing an electrically powered RC plane with one propeller. The wingspan is c. 2.5 m and the length c. 1.6 m.

Right now the plan is to put the propeller at the top of the VS where the HS is also situated. However, as I've advanced further with my design, it has become clear that it is hard in all possible ways, starting from the structural traits (foam covered with fibreglass) to fitting the 40 mm engine along with the elevator servos.

So, should I just move the propeller + engine down to the aft of the fuselage or is there something about the performance that this move might adversely affect?

E: As mentioned in the comments, moving the motor would affect the pitching moment characteristics of the A/C. "Luckily" I have the option of changing the battery placement within the fuselage to counter this effect so the pitching moment consideration is made void by this.

To place a heavy mass, part of which is even rotating, on a long, flexible beam is generally not a good idea. The engine mass will reduce the eigenfrequency of the vertical tail, inviting early flutter, and any imbalance in the propeller will provide the initial excitation which flutter needs to develop. Also, placing heavy masses away from the center of gravity increases the moments of inertia and makes the handling of the aircraft needlessly sluggish. The designers must feel some pain to pick this unattractive engine position.

Reasons for this unusual engine placement could be:

Better aerodynamic control for ground handling. With the control surfaces squat in the propeller's slipstream, ground handling of seaplanes on water is much improved.
Better visibility for the pilot: Instead of a center engine placement in the nose, a tail location gives much improved visibility.
Less FOD (foreign object damage): The raised prop position makes it less susceptible to being damaged by debris kicked up from the ground.

The first reason explains why most designs with tail-mounted engines are seaplanes. The engine location on the Trislander, the three-engined version of the Britten-Norman Islander, was picked for the last two reasons and because the designers felt that flutter was not much of an issue with that compact, slow utility aircraft.


How much does the FAA private pilot's license checkride cost? I can't find a strong number for this and I would like to know. I'm compiling a list of total cost for each part of getting a private license (training, study material, headset, medical exam, etc), but I can't find how much the checkride will cost.

There's no standard fee for the checkride because each Designated Pilot Examiner (DPE) is free to set his or her own price. I've seen numbers for a private checkride in the \$400-600 range depending on the location, but your instructor should know the local examiners and what they charge. Or just ask the DPE directly, of course. Bear in mind that you might have to pay extra if you have specific requirements like needing a checkride at short notice, on an awkward date, or at a particular location.

This question might be useful too, and see this one for the (unusual) option of using an FAA examiner instead of a DPE.


Why does this regional jet have its air brakes wide open before touchdown? I was looking at a detailed picture of a plane while following its path on Flightradar24.com. Here is the Avro RJ45 I am talking about:

I wonder why its aerobrakes at the empennage seems wide opened before touchdown. What I remember from all the planes I took is flaps are at maximum before touchdown and aerobrakes (sometimes automatically) opens when landing gears touch the runway.

Is it due to special constraints for this particular aircraft?

(Source) F-15 landing with airbrake extended.
(Source) Airbrakes on the Fokker 70.
1. It allows steeper approaches
From Wikipedia:

The engines [on the Avro] lack thrust reversers due to their perceived reduced effectiveness in anticipated conditions. Instead, the plane features large airbrake with two petals below the tail rudder at the rear of the fuselage, which has the advantage of being usable during flight and allowing for steep descent rates if required.

... also...

Airbrakes on the Fokker 70's tail section – similar to that found on the BAe 146 / Avro – allows it to conform with the 5.5° glide slope at London City Airport.

2. It allows better speed control
Some aircraft are overpowered with high power-to-weight ratio. The thrust lever range alone won't be enough to hold the approach speed.
The thrust-to-weight ratio for the RJ100 is 0.28:1, compared to 0.16:1 for the comparable Boeing 717. It's even higher for the smaller RJ's.
Low power and the plane loses speed, some power and the plane gains speed. So, more power is used in conjunction with airbrakes, such as the F-15 shown above.

Once on the ground, they help slow down the plane, same as spoilers.
(Source) Spoilers.
Spoilers have the added benefit of spoiling the lift–transferring more weight to the tires for increased braking capability.

Related: Why do some aircraft (e.g. Avro RJ85) have rear-mounted air brakes?


Why is there no 100% power in the POH power setting table? I've flown a piper cadet arrow. The airplane has an engine of 200 horsepower at 2700 RPM. According to the power setting table in the POH, the maximum power we can set is 75% horsepower. With 100% power, we could fly faster (more fuel would burn though). Why doesn't the manufacturer provide the 100% power setting?

There are no 100% power setting tables because it is impossible to cruise at 100% power with a normally aspirated engine.

100% power is rarely available, even at takeoff.

It is only available at sea level when the temperature is 15C and the altimeter setting is 29.92".


Is there a formula to calculate take off runway distance for commercial planes? I want to be able to calculate the take off runway distance that a plane needs depending on factors such as weight and plane size, etc. I know that graphs exist in the pilot handbook to do this but is there a specific formula that I could perhaps put into a program?

These calculations are quite complex because they take into consideration a lot of different variables, just off the top of my head:

Take off weight, which includes FOB
Runway length
Runway condition
Field elevation
Air temperature
Air pressure
Wind
Engine type and airplane configuration

Based on those (and I am sure many more), you have to calculate at minimum V1, VR and V2, and possibly others.

These calculations are looked up from a table.


Can the lift equation be used for the Ingenuity Mars Helicopter? I am currently working on a basic simulation of the Mars Helicopter Ingenuity, and I am having trouble interpreting the outputs I am receiving from the lift equation. The equation reads as follows:
L = Cl * A * .5 * r * V²
L is lift in newtons, Cl is the coefficient of lift, A is the area of the circle traced by a blade in one rotation, r is atmospheric density, and V is the velocity of the blade. Ingenuity has two rotors 1.2 meters across, each with two blades. For this example, let's assume a rotation rate of 2400 rpm. The coefficient of lift is 0.4, the average for small helicopters. Atmospheric density on Mars is 0.020 kg/m^3. The velocity is taken 1/2 way down the blade and is found by using ((1.2/2)π * rpm / 60). Plugging in the values for Ingenuity gives:
102.871 = 0.4 * π(0.6)² *.5 * 0.020  * 5684.858 * 4
The 4 at the end is added because Ingenuity has four blades, each generating its own lift in accordance with the lift equation.
Dividing the lift by the mass of Ingenuity (1.8 kilograms) gives an upward acceleration of 57.15 m/s². Unfortunately, this number is too large to be accurate. Martian gravity is only 3.711 m/s², and whatever drag that will be generated by the thin atmosphere is likely to be insignificant in relation to such a large upwards acceleration.
So, the question is, how should lift be calculated in this case? Am I using the lift equation incorrectly, or is it simply not applicable to small drones like Ingenuity? If you have any resources for calculating lift more accurately in this case, please share them.
Thank you.

The formula is correct, but you're measuring the wrong area.
A is the area of the wing, i.e., rotor blade, not the area of the rotor disc.
When π(0.6 m)² is replaced with the correct value, about 0.6 m * 0.05 m, then the final number for lift drops by about 40 times, as does the upward acceleration, to a more plausible 1.4 m/s².
(This error is also committed by the first google hit I got for lift equation rotor.)
The next step to improve accuracy would be to not ignore that the root of the blade moves much more slowly than the tip, and conversely that (for Ingenuity at least) the root has greater chord and greater angle of attack.  But the math for that is much more involved.


In the US, is there a way for a pilot to legally "maneuver at will" in actual IMC? In the US, is there a way for a pilot to legally "maneuver at will" in actual IMC?   Let's say you want to practice a series of reversing 360-degree turns and not have to communicate every change in heading to a controller or follow a controller's step-by-step instructions.

For example, is there such a thing as an IMC "practice area" where only one aircraft at a time is allowed to operate under IFR?

Also, is there a distinction between controlled and uncontrolled airspace in this regard?

You don't have to have permission to fly in IMC in uncontrolled, class G, airspace. However, you must have an instrument rating and be in an IFR-certified aircraft. In uncontrolled airspace, you may fly into IMC as you like and perform whatever maneuvers you want. It's a very good idea to get flight following in order to receive traffic warnings from ATC if you decide to fly within IMC in uncontrolled, class G, airspace.

You do need to get permission to fly in controlled airspace (all classes except for G) if you are operating under IFR, regardless of actual meteorological conditions.

Note: Classes A-D require permission under both IFR and VFR; classes E and G do not require permission under VFR.

If you want to practice in IMC within controlled airspace, you must explain your mission to ATC and obtain a clearance to operate under IFR. If ATC has the space and the time, they may give you a clearance for a specific area and perhaps a block altitude if you want to climb and descend. There aren't officially designated areas for practice, but if you ask local instructors, they will tell you where they usually go. Most of the time, the preference is to get out of controlled airspace if possible; it's just easier.


Why must some aircraft get permission to start their engines? Some larger airliners must get ground control permission before starting their engines.

Is this based on size? Does a Learjet need permission?
Is this just turbines? For example does a DC3 or DC6 need permission?
How would a pilot find out? Does the airport supplement or some other document show when it is required?
Are there exceptions such as jets parked on remote ramps, not at gates, non-commercial?

I know from flying small recips that I never needed permission anywhere in the US or Canada - but certain airliners did.

This airport in Australia says they enforces their right for the engine start. Part of the authorization comes from environmental noise control.  townsvilleairport (Australia).

Van Nuy - US, "All  aircraft  with  engines  capable  of  producing
more  than 14,750  lbs.  of  thrust must  be  pushed  back  or  towed  onto  the  taxiway  prior  to  engine  start." (Airport ops) (Of course you need ground approval prior to entering a taxi way...)

When working at Anchorage International, Alaska with Continental 737-757, we had to contact ground control. We could start the engines at the gate while doing maintenance; there were no ground crew around. We started the onboard APU, turned on the red strobes, got permission from ground, then started the engines. I never read a document, this info was relayed to me by my supervisors.

Airliners usually push back from the gate and then start their engines when well clear.

If the aircraft has an unserviceable APU, a ground based power supply must be used at the gate for the start. Permission(coordination) is required so that their are no hazards for ground crew and vehicles in the gate area.

After one engine is started at the gate, the aircraft is pushed back. The next start, still needs permission(coordination) because the operating engine usually has to increase it's thrust above idle in order to have enough bleed air pressure for the "Cross Bleed Start".

EDIT:  "Permission" may be not be mandatory at many airports, so "Coordination" with Apron Control, Ramp Control, or Ground Control may be a better description.


Who else is using electro-thermal wing anti-/de-icing apart from the 787? I am researching into deicing technologies for the future, but apart from Boeing with Ultra/GKN, no one seems to be picking this technology up and being competitive. Any one know why this is? Is it an expensive development? Risky?

Is it on any aircraft manufacturer's roadmaps?

I fail to see what is exactly new in the B787 de-icing system, except for the way it is manufactured (spraying metallic layers onto the composite structure).

Electric heating is the most obvious and straightforward method of de-icing, and the least energetically efficient at that. It is much more efficient to break the ice rather than to melt it - in terms of the energy required. Even B787 with its sheer electric supply can't afford anti-icing (that is, constant heating to prevent ice formation), and de-icing power consumption is 45-75 kW.

Perhaps most Russian (larger) aircraft had electrical wing de-icing system: from Tu-95 (1952) to Il-18 (1957) to Tu-154 (1968) (I could give specific links but they are in Russian). Typically, they work in sections to reduce power demand, and consist of heating wires (rather than layers like on 787) that melt the ice.

Later aircraft such as Il-86 (1976) and -96 had a more advanced electric impulse system, which creates mechanical impulse on the leading edge with induction coils. This deforms the skin for a very brief moment to break the accumulated ice.


On SEP airplanes, why does the fuel consumption decreases with temperature, pressure and airspeed being equal? Looking at the cruise performance tables in the POH of the C150, C172 or C182, one can see that for the same pressure altitude, the same RPM and the same true airspeed, the fuel consumption is reduced at higher temperature.

For example, a 1976 C150 POH indicates, at 2500 RPM, at 2000 ft pressure altitude,

at -5°C: 97 KTAS, 5.3 GPH
at 15°C: 96 KTAS, 4.9 GPH
at 35°C: 95 KTAS, 4.6 GPH

(yes, there is a 1 kt difference each time, but interpolating the values gives very similar results)

But thermodynamics tells us that the efficiency is proportional to the difference of temperature between the isothermal expansion at Th and the isothermal compression at Tc in the Carnot cycle, thus efficiency = (Th-Tc)/Th.

I cannot reconcile the consumption data with that theory, since apparently the output power is the same (true airspeed, with identical parasitic and induced drag forces) for an apparently higher efficiency at higher Tc temperature.

What other factor am I missing?

In the examples cited, there is a slight increase in Density Altitude (DENALT), which results in a slightly higher TAS.  As the air becomes thinner, fewer molecules pass by the aircraft per mile, resulting in a lightly less loss due to drag.  Increased temperature does not have the same range of change as altitude, however, it is nonetheless a higher DENALT, which is thinner air.

As an aside, in practice, you will note that the throttle becomes wider open with less dense air, until it is fully open. (Note that RPM is not the primary measure of power, rather fuel burn is. RPMs will become higher at higher DENALT for the same power.) At that point there will be no more available power, and any increase in temperature or altitude cannot be compensated for by increasing the throttle setting.

You will also note that less energy is expended per mile at higher DENALT, not factoring in the cost of a climb to that altitude.

Finally, a different practical example of this: When flying in icing conditions, conditions (and the POH) may call for continuous carburetor heat at altitude. When this is done, the engine should be releaned, as the DENALT will be higher, and if uncompensated for, will result in a rich mixture which could foul spark plugs.


Why there is no wake turbulence right after touch down or before rotation? It is said that wake turbulence occurs when an aircraft generates lift and there is no wake turbulence after touch down or before take off. That's how we avoid wake turbulence. However, I've thought we have lift while on landing roll or take off roll because there is the angle of incidence and at least a certain amount of speed, just not enough lift to be airborne. Based on my idea, I don't really understand why does wake turbulence suddenly disappear like a magic when we land.
Can someone explain this please?

Well there may be vortex formation on the ground under certain conditions, but it doesn't stick around long enough to really be measured or cause trouble.

Any time a wing is producing lift it will generate a wake. This happens even if the wing generates just enough lift to make the aircraft "lighter" but not enough to get it off the ground: Vortices will still start to form at the wingtips, but as they begin their rotation (downward and outward) they will quickly hit the ground and be dispersed.
If the runway were a narrow strip with the wingtips hanging out in free air you would still see vortex formation in these edge cases, but pilots generally don't like to take off on a tightrope.

Airplanes also usually don't stay in that kind of edge case situation where the wing is generating lift but the wheels are still on the ground for very long: Either they're taking off (soon after the wing starts producing some lift it's producing enough lift and the airplane begins flying), or they're landing (within a few seconds after you touch down you've slowed to a point where the wing's lift production, and thus vortex formation, is negligible). Thus for practical purposes of wake turbulence avoidance the wake begins when the airplane rotates, and ends where it touches down.

It's also worth noting that if you happen to be following close enough for the incipient wingtip vortices to cause trouble on the ground you'll probably be experiencing other issues (jet blast, prop blast, etc.) which will remind you that it's prudent to maintain a safe separation distance from other aircraft on the ground.


What is the range of amplitude of vibration in a helicopter? Vibration in helicopter can be caused by many different reasons. I am interested to know what is the range of amplitude of vibration?

I am interested to know how amplitude varies with frequency of vibration? I am looking for an answer in terms of distance from a reference or equilibrium  or stopping condition. For example does the maximum distance (amplitude) from the reference is 2 cm or less or more when helicopter moves?

I understand that it would depend on the helicopter type. So any reference to such analysis would be appreciated.

This is similar/extention to the question What is the range of frequencies of vibration in a helicopter due to the main rotor alone? where it asked about frequency of rotor.

The amplitude of the vibration depends on the frequency and the acceleration: at a given acceleration, only at low frequencies do we get any significant displacement. If displacement is taken as the intensity indicator, the frequency plot is weighted towards low frequencies - the higher frequencies have a higher energy contents, that is why often a logarithmic relative scale is used (dB).

This document gives good information and background on measuring th severity of vibration. It can be done with an accelerometer: integrating acceleration yields velocity and displacement as well. From the document:

  Experience has shown that the overall RMS value of vibration velocity measured over the range 10 to 1000 Hz gives the best indication of a vibration's severity. A probable explanation is that a given velocity level corresponds to a given energy level so that vibration at low and high frequencies are equally weighted from a vibration energy point of view. In practice many machines have a reasonably flat velocity spectrum.

The vibration frequency plot in the previous answer is in dB acceleration, an earlier slide shows the reference. If it is displacement of a particular frequency in the plot you are after:

Read dB acceleration at the particular frequency
Convert into m/s$^2$ to get acceleration $a$
Amplitude = $\frac{a}{(2 \pi f)^2}$


Why did the design of the Boeing 247's cockpit windows change for some models? Have a look at this article on a famed example of the 247.
The image at the top is the aircraft during its flights with the RAF, likely some time in 1944. Note the reverse-slope windows that are a hallmark of the 247.
Now look at the other aircraft in the same article. They have conventional style slope-down windows. Those two images are from before 1944, one in the 30s and the second around 41/42.
Does anyone know what's going on here? Were certain batches one way or the other?

From the Boeing 247 article (emphasis mine):

The cockpit windshield of the first 247s was angled forward, instead of the conventional aft sweep. This was the design solution (similar to that adopted by other contemporary aircraft that used a forward-raked windscreen) to the problem of lighted control panel instruments reflecting off the windshield at night, but it turned out that the forward-sloping windshield would reflect ground lights instead, especially during landings and it also increased drag slightly.[13][14] By the introduction of the 247D, the windshield was sloped aft in the usual way, and the night-glare problem was resolved by installing an extension (the glarescreen) over the control panel.[15]


Are solar / geomagnetic storms real risks for commercial aviation? Background

Solar storms/flares are solar events sending particles in space that are potentially dangerous on Earth. From Wikipedia:

  Solar flares strongly influence the local space weather in the
  vicinity of the Earth. They can produce streams of highly energetic
  particles in the solar wind, known as a solar proton event. These
  particles can impact the Earth's magnetosphere (see main article at
  geomagnetic storm), and present radiation hazards to spacecraft and
  astronauts. Additionally, massive solar flares are sometimes
  accompanied by coronal mass ejections (CMEs) which can trigger
  geomagnetic storms that have been known to disable satellites and
  knock out terrestrial electric power grids for extended periods of
  time.

Source

They are rated by the US NOAA on a scale from 1 to 5. For instance, level 3 events occur about once a year:

  S3 (Strong) - Biological: radiation hazard avoidance recommended
  astronauts on EVA. Passengers and crew in commercial jets at high
  latitudes may receive radiation equivalent to approximately 1 chest
  x-ray.

There are also geomagnetic storms listed on the same page.

Question

Is this a real risk for commercial aviation, if so how do airlines treat this risks on affected routes, e.g.:

How are airlines informed?
Are pilot-in-command informed and allowed to veto a flight?
What do they do regarding exposed crews and passengers?

A pilot in command can always veto, scrub, or divert a flight. Per the Federal Aviation Regulations FAR 91.3(a), "The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft." This applies to airline operations (air carriers, FAR Part 121), air taxis and charters (FAR Part 135), and general aviation (FAR Part 91) operations.

A much bigger issue than than the radiation exposure for the people will be the atmospheric effects of the radiation, and how the radiation affects, e.g., satellite navigation. A very strong solar flare can require shutting down some on-orbit satellites to avoid damage—including navigation satellites, such as GPS. A very strong solar flare can ionize the atmosphere to the point it interferes with communications, especially in the HF band used for transoceanic communications.


What is NASR, The FAA's System for Managing Aeronautical Information? I've googled this question, and know:

  The National Airspace System Resource (NASR) System provides the Federal Aviation Administration (FAA) with the means for storing and maintaining a reference database with descriptive details of the National Airspace System's (NAS's) infrastructure and the operational status of all components

But what I'm asking is, what does that mean? Is this where companies like AirNav, Jeppesen, and foreflight get their data? When I update my foreflight database, is it downloading new charts and nav data from NASR, or am I misunderstanding the above quote?

Also, related, when Jeppesen makes their own charts, updates them, etc. are they getting their data from NASR, or somewhere else?

NASR contains the current information upon which Air Traffic Control and other FAA activities depend. NASR supports the management of NAS data used by the FAA, chart producers (including Jeppesen), military and other Government entities to produce a variety of aeronautical publications. Downloads from Foreflight use this data, but may be reformatted to suit the application and would not come directly from any NASR database.

In addition, NASR data is accessed by commercial air carriers, flight planners, and flight systems developers as required by FAA regulation to support the safety-of-flight mission.

The data is available on a 28 day subscription basis. Legacy flat files show the data content, though other forms are available. Definitions for each table are here. The tables are:

Airports and Other Landing Facilities (APT)
ARTCC Boundary Descriptions (ARB)
ARTCC Facilities (AFF)
ASOS/AWOS(AWOS)
ATC Tower and Satellite Airport Communications (TWR)
ATS Non-Regulatory Airways (ATS)
Coded Departure Routes (CDRs) (CDR)
Country Codes
Enroute National Fix Program
Significant Points (NATFIX)
Fix/Reporting Point/Waypoint (FIX)
Flight Service Station Communications Facilities (COM)
Flight Service Stations (FSS)
High Altitude Redesign (HAR)
Significant Points (HARFIX)
Holding Patterns (HPF)
Instrument Landing Systems (ILS/MLS) (ILS)
Location Identifiers (LID)
Miscellaneous Activity Area (MAA)
Military Training Routes (MTR)
Navigation Aids (NAV)
Parachute Jump Area (PJA)
Preferred Route / Tower Enroute Control (TEC) Routes (PFR)
Regulatory Airways (AWY)
Standard Terminal Arrival / Standard Instrument Departure (Complete Set) (STARDP)
State Codes
Standard Terminal Arrival / Standard Instrument Departures (AFSS Subset) (SSD)
Weather Reporting Locations (WXL)


Why divide the blades of a 9 blade propeller into 3 groups? In a youtube video an airboat is featured with two contra-rotating propellers, each holding nine blades. Interestingly those nine blades are not spaced evenly, but grouped into three groups. I've never seen such an arrangement before, and I expected an evenly spaced configuration to be more efficient. What could be a reason to prefer this grouped configuration?

If there was a technical reason beyond "it looks cool", I would guess it would be some benefit noise wise, where it may sound more like a 3 blade prop than a 9 blade, and the resulting lower beat frequency of one prop, interacting with its counter-rotating mate, was less objectionable.

I went on a mangrove airboat tour in Forida once in a 454 V8 powered boat and it was earplugs PLUS ear muffs together for me, so I can imagine that anything that helps with noise levels while absorbing all that power would be very sought after.


What could cause an inadvertent squawking of 7700? I get alerts whenever a plane squawks 7700, using a popular flight tracker application. It happens quite frequently that the aircraft, reported to squawk 7700, in actuality squawks 7550 or some other benign number.

What would cause this? Are the instruments such that it starts on 0000, and allows setting each digit with a dial you can turn both left and right?

A transponder in most planes look something like this

(source)

The code is changed by turning the knobs beneath the numbers. Lets say you are assigned 5700 as your code but your previous code was 7456. If you are careless or start from the right most knob your transponder will briefly be set in 7700 until the most significant digit is changed. If the radar does a pass (interrogation) at that time ATC will momentarily receive a 7700. Some people say you should put your transponder in standby (SBY) mode when changing codes to avoid this happening.

Some GA planes (and even some larger planes) have newer digital interface transponders like this one,

(source)

These make it a bit harder to pass through the codes since you are not turning knobs but in bumpy air you could accidentally double tap a number. For example lets say you are assigned 7003 in bumpy air. You go to hit the 7 and accidentally double tap the button. Then you type in the 00 and your code is complete by the time you hit the 3.

After some looking it seems that larger aircraft user a transponder like this one,

(source)

In this case you will see a similar case to the first transponder listed. If its not in STBY while switching you inevitable have to pass over 7700, 7600 or 7500 to get to some codes. If an interrogation happens at that time it may cause the results you mention.

In terms of switching to STBY mode, the only documentation I can find about keeping the transponder in altitude reporting mode is this document which states

  operators and pilots of the need to ensure that transponders are in the
  altitude reporting mode whenever their aircraft is on an airport movement area at all airports.

This was issued in May of 2015 and seems to be related to the ground surveillance systems being installed at airports.

The FAA FAR touches on transponder operation in S91.215 and part C reads

  (c) Transponder-on operation. While in the airspace as specified in paragraph (b) of this section or in all controlled airspace, each person operating an aircraft equipped with an operable ATC transponder maintained in accordance with Sec. 91.413 of this part shall operate the transponder, including Mode C equipment if installed, and shall reply on the appropriate code or as assigned by ATC.

This section simply states that you must "operate" the transponder on the code assigned while in required airspace. That seems a little vague and does not completely exclude putting it in STBY mode to switch codes.


What causes fuel gauges to be untrustworthy? I went on my first flight yesterday (Cessna 152), and I was told not to trust the fuel gauges and to check fuel levels manually. The instructor said that the only fuel gauge reading that I can trust is a 0.

Why is that exactly, and what can be done (or what has been done/studied) to improve their accuracy? Is there some fundamental technical limitation that makes better accuracy difficult to achieve?

Do automobiles have more or less the same issue, or is the inaccuracy more prevalent in aircrafts?

The problem is small airplanes use automotive style rheostat (variable resistor) fuel senders, with the float in the tank, and these just aren't reliable enough to be trusted with something potentially life or death like fuel quantity, and they aren't particularly accurate in the first place.

Here's the thing... In a car you just drive around going past gas stations constantly until the gauge is low.  Imagine you were operating a car in some remote place where the gas stations were 300 miles apart and if you run out of gas short of the next gas station, the road is full of hungry alligators equipped with Slim Jims, making your door locks useless, and you, dinner.

Well, your tank is good for 600 miles and it's half full on the gauge.  Maybe good for 300 miles, maybe not. Are you willing to trust the automotive gauge now?  This is what faces you as pilot any time the tanks are not full, in an airplane with 40 year old fuel senders, that maybe sits around for extended periods.

Bigger airplanes use fuel quantity measurement systems that use "Capacitance Probes", hollow tubes with a center rod, and a current is passed through and the capacitance measured by the fuel level in the tube that completes the circuit between the outer tube and the inner rod.  A computer will monitor the levels from several probes arranged around the tank and they provide a very precise and reliable fuel reading.

There are capacitance probe senders available for homebuilt aircraft, but I'm not aware of any certified units that can be installed in something like a 152.  If available, that would be a good solution, although I'd probably still not be willing to trust it 100%.

Best thing is to use a dipstick and be aware of your fuel consumption/time. During training and renting airplanes, people get into the habit of always going somewhere with full tanks, but later on, especially if you are flying commercially, you are going to have to fly a lot with intermediate quantities, excess fuel being unwanted ballast, so you need to get into the habit of knowing and tracking fuel quantity.

Impress your instructor by showing up with something like this and you will always know exactly how much fuel you have.  If you're cheap and refuel the plane yourself you can make your own with a wood stick if you have a way to get all the useable fuel out of the tank, then add 5 gal at a time and marking your stick appropriately at each level.


How does the FAA BasicMed affect the safety pilot for somebody flying under the hood? When one pilot is practicing instrument flying with a view limiting device (a "hood"), a licensed pilot needs to be along to watch for traffic (the safety pilot). There are several scenarios where none, either, or both are instrument rated, and the flight could be held in IMC or VMC. In this case neither pilot is instrument rated and are just following VORs in visual flight rules.

BasicMed applies to certain aircraft, so lets assume we are talking about your ordinary general aviation IFR capable aircraft with 4 seats and 150 knot cruise speed, while flying VFR.

The FAA states this in their FAQs:

  Q25:  Can I use BasicMed to act as a safety pilot, rather than holding
  a medical?
  A: Only if you’re acting as PIC while performing the
  duties of safety pilot.  The statutory language prescribing BasicMed
  said it only applies to people acting as PIC. BasicMed cannot be
  exercised by safety pilots who are not acting as PIC but are required
  crewmembers.

I find this confusing, aren't safety pilots acting as PIC because they are required crewmembers?

This question suggests that a BasicMed pilot can only be a safety pilot in VMC:Logging PIC time during IFR flight in VMC.

So my question is this (because it pertains to my present situation): Can I be a safety pilot for a non-instrument rated pilot when I have my BasicMed physical, as long as the flight is in VMC? Can I log PIC time while the pilot under the hood is flying? I should, because I am the PIC as safety pilot.

It would be nice if the FAA gave more clarification, and examples for all the practical scenarios pilots would experience. The safety pilot issue itself confuses a lot of people, now we have BasicMed regulations to add to the confusion.

Short answer: the safety pilot with BasicMed must be acting as PIC, but all other regulations and considerations are the same (i.e. as if the safety pilot had a regular medical).

You have quite a lot of points in your question, but I'll try to break it down.

"[...] aren't safety pilots acting as PIC because they are required crewmembers?"

Not always. Being a required crewmember is not necessarily the same as being PIC, e.g. a typical airliner requires two pilots but only one of them is PIC. When you fly with a safety pilot there are two ways to do it:

The safety pilot acts as PIC; the pilot under the hood is a required crewmember
The pilot under the hood acts as PIC; the safety pilot is a required crewmember

As you (and the FAA FAQ) said, BasicMed only allows pilots to act as PIC, not as non-PIC required crewmembers. Therefore only scenario 1 is possible for a safety pilot with BasicMed.

Practically speaking, scenario 1 is what most people do anyway, because it allows both pilots to log PIC time; remember that acting as PIC and logging PIC time are two different things. (In scenario 2 the pilot under the hood would log PIC time but the safety pilot would log SIC time.)

"a BasicMed pilot can only be a safety pilot in VMC"

The concept of a safety pilot only applies to VMC; in IMC you're in real instrument conditions, not simulated ones. Perhaps you meant VFR, not VMC? This question (which you already found) is about acting as a safety pilot under IFR.

"Can I be a safety pilot for a non-instrument rated pilot when I have my BasicMed physical, as long as the flight is in VMC?"

Yes, if you act as PIC, as described above. And again, a safety pilot is only needed in VMC.

"Can I log PIC time while the pilot under the hood is flying?"

Yes, and this has nothing to do with BasicMed. Because simulated instrument flight requires a safety pilot (91.109), that means that if you're the safety pilot and acting as PIC, then you can log PIC time as described in 61.51(e)(iii) (emphasis mine):

  When the pilot acts [...] as pilot in command of an aircraft for which more than one pilot is
  required under the type certification of the aircraft or the
  regulations under which the flight is conducted


What is this button (pressed during approach) on the Airbus A320? I was watching a YouTube video of a cobalt air a320 landing and I seen as he was about 2000 ft AGL he pressed a button on his right hand side just beside the Navigation display. The button illuminated green and 10 seconds later he pressed it again to 'disengage' it.

Does anyone know what this could be and why it is used?

This is the TERR ON ND button, or Terrain on Navigation Display. An EGPWS feature that paints the ND screen with the terrain. The color coding indicates if the surrounding terrain would pose a hazard if flown close to. The push button operation is:

At 46:10 in the video the TERR mode was off, the captain turned it on, pointed something out to the first officer, and turned it off. Zurich (the destination) has areas of high terrain around the airport.
(Source) Click to view.
The color coding and example:
Click to view.


Why would aircraft take-off in the opposite direction as landing despite wind direction? I have visited and flown out of Harare International Airport, Zimbabwe a number of times and the thing that always baffles me is: Why do aircraft use runway 23 to depart, but runway 05 to land?

At first I've thought that it may be a wind change, but it appears it's not the case. Is it because wind is limited at the airport and therefore direction does not matter? Or is there some special procedure for 'hot/high' airports?

Apparently, only the 05 runway has precision approach markings and (Medium Intensity) Approach Lighting System (MALS). Runway 23 has non-precision approach markings and no Approach Light System.

So, the aircraft only land on runway 05.


Why can't I hang glide in NYC? I was stopped by NYPD for attempting to hang glide in an uncongested area by Midland Beach, Staten Island. They called their Legal Bureau and came back with "Illegal Navigation" and if I was to continue I would be arrested and my hang glider would be seized. I called the NYPD Aviation Unit to ask about the legality of my attempted flight and told me to call back again later since this was an unusual request. When I called them back they generically stated that it's not legal under FAA regulations within the NYC area, but did not refer to any specific law and suggested I go to Long Island or Jersey.

What is meant by a "congested area of a city/town/settlement" in FAR 103?

If it's not illegal, then it's legal. So if I can prove that it's not, then I should be legally good to go.

There are (at least) two general points to consider. First, hang gliders are ultralights and the regulations in 14 CFR 103 apply to them. 103.17 says:

  No person may operate an ultralight vehicle within Class A, Class B,
  Class C, or Class D airspace or within the lateral boundaries of the
  surface area of Class E airspace designated for an airport unless that
  person has prior authorization from the ATC facility having
  jurisdiction over that airspace.

If you look at a sectional chart, most of the airspace over NYC is class B, including to the surface in many places:

In a class B surface area ultralights require ATC's permission to operate; whether or not the area was congested is a separate issue and nothing to do with the airspace class itself.

Second, as a general statement the FAA regulates what happens in the air but not what happens on the ground. States and counties can make their own rules about launching and recovering aircraft, and national parks have their own rules too. In other words, you need to make sure that wherever you fly your hang glider, it's both legal to launch and legal to operate in that airspace.

Now, let's look at Midland Beach, Staten Island specifically. I've marked the approximate location on the chart with a red dot. It's hard to see because the chart is so crowded, but that part of the coast is depicted as a "special conservation area" and there's also a comment that it's part of the Gateway National Recreation Area, which is a national park.

The airspace there is class B from 1500ft upwards, meaning that if you stay below that altitude then you're OK from the airspace point of view. It's true that the FAA discourages flight over parks, but it's mostly about noise (not a concern in a hang glider) and there's no actual regulation anyway.

However, it seems likely that you were launching from a national park and that does require permission from whichever authority runs it. I have no idea whether or not that's what the NYPD were talking about.

(My personal suspicion is that the NYPD officers just decided "that can't be legal" and made up something on the spot. But there are still actual regulations that do apply, whether or not the officers were fully informed/trained on them or not. I also don't know why the NYPD would want to enforce FAA regulations, but that's a topic for another site.)


Why is there a difference between military parachutes and those used for skydiving? A couple hours ago I was watching a youtube video where skydivers jump using the skydive parachute, and after that, a military training where the soldiers jump using "old" type parachute, the dome shaped one.

Why is the military using the dome shaped one?

The skydive parachute is smaller, and more compact, and has manoeuvrability (as I can see, I'm not an parachute expert).

Is it because of protection against enemy fire? Since it's larger it can take more damage of enemy firepower, or what?

From what I learned, different types of parachutes don't make them 'old' or 'new'. They are used for different purposes.

For example the dome shape parachute is usually used for static line jump where no maneuverability is really required. They drop vertically relatively to the plane path when air friction is negligible.

The other kinds are usually used for special forces because they always do jumps like HAHO (High Altitude [Jump] High [Altitude] Open) when the location they jump is outside their country's territory, and infiltrate by air so the plane is out of the radar/SA missile range. They have to have the ability to glide on a long distance.

Another case is they have to have the ability to change the trajectory or precisely land in the drop zone. So maneuverability is a must.

Size differs for different manufacturer and different specs. Even though the dome type parachute is relatively larger, the chance of getting hit is similar with other types as you don't have much speed and you can't do crazy high G turns. You really can't avoid any attack towards you unless you have superhuman reactions and the sixth sense.

To conclude, different types of parachutes are used for different purposes in different scenarios.


What aircraft broke the most [total] world records? In the early 1930's aircraft were breaking records each week because the performance needed was quite low. As technology advanced the performance needed to break a record also became higher. Which causes us to ask if it was easier to break records early in the century, or later with the aid of technology.

Howard Hughes built many airplanes specifically for breaking records, yet even today the Russian and American fighter manufactures often strip down their latest fighter prototype and set new world records.

Addendum: There seems to be some confusion over what the question is asking... "most" means "total" as "aeroalias" has supplied below. The basis for the question was a YouTube video that stated the F4 Phantom had broken the most records of any aircraft, but the video was circa 1980 without specifics and it seemed there was a high probability that other aircraft had superseded it. (I would have guessed some aircraft in the 30's, therefore my keen interest in the answer)

At this point "aeroalias" is right on track...

So, what aircraft broke the most (total) world records?

I'm not exactly sure what type of recored you are looking for (civil, military etc.), but a specially modified Su-27 claimed 41 records for altitude and rate of climb between 1986 and 1990. As globalsecurity.org notes:

Between 1986 and 1990, using a specially configured prototype aeroplane T10-15, which became known as P-42, the design bureau's test pilots established 41 IAF-registered world records of rate-of-climb and flight altitude, some of the records being absolute.

P-42 Streak Flanker; image from su27flankerfamily.wordpress.com
Some of these records are given here,

On October 27 and November 15, OKB test pilot Viktor Pugachev added eight climb-to-altitude time records to the table of world achievements in just in two flights-four absolute records for land based aircraft and four records for aircraft with takeoff weight up to 35,274 lb (16,000 kg). Pugachev climbed to 9,843 ft (3,000 m) in 15.573 seconds and to 19,685 ft (6,000 m) in 37.05 seconds.
On March 10, 1987, and on March 23, 1988, test pilot Nikolai Sadovnikov flew the Sukhoi P-42 to 25,528 ft (9,000 m) in 44 seconds, 39,370 ft (12,000 m) in 55.2 seconds and 49,213 ft (15,000 m) in 70.329 seconds.
On June 10, 1987, Sadovnikov claimed a world record for a N category level flight altitude of 63,435 ft (19,335 m).

In some other publications, a number of 27 records have been reported; in either case, it is quite impressive.


Do any airports have runways or taxiways that cross active rail lines at grade? Gibraltar has a runway which crosses an active road at grade (which, due to the peninsula’s geography and the resulting constraints on the airport’s location, happens to be the main road connecting Spain and Gibraltar, thus bringing traffic between the two to a halt whenever the runway is in use), which got me wondering: are there any airports with runways (or, for that matter, taxiways) which have grade crossings with active railroad lines?

There is at least one:

In Gisborne, New Zealand, there is a freight rail line which crosses the south end of runway 14/32 at Gisborne Airport (GIS). It appears to still be an active line for freight (logging) haulage, as well as occasional passenger excursions.

Image source: Google Maps, plus own annotation.

This article has some additional pictures and info as well.


Which FAA regulations apply to the Stratolaunch? (Image source)

Which FAA regulations apply to the Stratolaunch being built by Vulcan Aerospace and Scaled Composites?

Do they follow the same regulations for the type cert, production and CofA (Certificate of Airworthiness) just like a commercial airplane built by Boeing?

That would be under Title 14 CFR, Chapters 400-460.

A lot of this stuff really hasn't been finalized yet and these vehicles are considered only experimental and regulated similar to homebuilt aircraft.  Passengers are required to sign waivers advising them of their risk and that they understand this and hold the organization indemniable to any and all liabilities involved with using this system.


What is a typical ratio of aircraft in air vs. total aircraft per airline? While commercial airlines have a fleet of x aircraft, not all x aircraft will be in the air at any given time. Typically, several aircraft are in the air, some are on the ground (turnaround, loading, unloading, etc.), and some are in maintenance (not active).

What is a typical ratio of aircraft in air vs. total aircraft of an airline? I would be interested in airlines like Southwest, Hawaiian, Alaska Airlines, or FedEx. Can anyone provide some ballpark numbers on such a ratio?

(I assume this heavily depends on the type of airline, ratio of long- to shorthaul flights, budget vs. full-service vs. cargo vs. regional airline, number of total aircraft, route network, and obviously time of day (as some airlines do not operate flights during the night, or at least reduce flights during the night), etc.)

Well here's one way to approach it:

Excluding transatlantic and transcontinental red-eye flights, most airplanes are running between 6 am and about 10 or 11 pm and are down overnight.  Let's just say 18 operational hours per day, or 6570 operational hours per year (we could define operational hours as an aircraft "available for duty").

The average airliner flies between 2 and 3000 hours per year, so lets use 2500.

Being airborne 2500 hours out of 6570 operational hours means the airplanes are airborne about 38% of operating hours.

Allow for aircraft that are in the fleet but are non-operational because they are down for more than overnight; A checks, C checks, D checks, and also dispatch delays.  We could adjust the percentage number down somewhat, say several percent, to allow for that.

We are left with roughly (very roughly, there will be a lot of scatter no doubt) 1/3rd, or slightly better, of a fleet airborne at any one time during the operational day, if you surveyed across a national fleet.


How did a Soviet SA-3 missile manage to shoot down the F-117 Nighthawk? This question is about the F-117A that was shot down in 1999. How did an obsolete missile like the SA-3 shoot down such an advanced aircraft for its time? This question has nothing to do with how aircraft have become more stealthy. It is specific to the 1999 incident. I am just curious as to how an aircraft this stealthy could have been shot down.

"Stealth" does not mean invisible. In fact, there are photographs of F-117s, so clearly, they are visible.

Stealth means less observable than a comparable non-stealth design. A stealth aircraft still has a radar signature, it still generates heat, it still generates noise, and it is still visible … just less so than a non-stealth aircraft.

In this particular case, there was a combination of several factors:

The F-117 was the first production stealth aircraft. A lot of things weren't known by then, for example how to integrate sensor pods, radomes, etc. into the faceted hull in such a way as to not negate the stealth characteristics. As a result, the F-117 was pretty starved for sensor data, for example, it didn't have a radar warning system. The pilot literally didn't even know that he was overflying a missile station until he saw the missiles coming at him through the clouds.
The F-117s were flying exactly the same route at more or less exactly the same time night after night. That's just shoddy mission planning.
The bomb bay is a huge radar reflector, with the doors open, the plane is no longer stealthy. (This is still true for the B-2, BTW.)

So, since they flew the same route every night, it was likely that someone, somewhere would just simply spot or hear them by accident. No matter how stealthy your aircraft is, if someone looks up and you pass between them and, say, the moon, they will see you. Since the route was known, the Yugoslav Army could move their missile station right into the flight path. Since they were also repeatedly bombing the same targets, the Yugoslavs could even make an educated guess at which point the bomb bay doors would be open. They also only had to turn on their radars for short periods of time (again, since they already knew roughly when and where the airplane would be), making it harder to detect them.

And once the missile hits you, it doesn't really matter how old it is. Kaboom is kaboom, regardless of age.

So, to summarize, it was a combination of

bad mission planning
limited sensor capabilities of the F-117
a very clever missile commander (credit where credit is due!)


Why is a rectangular wing planform less efficient than others? I read somewhere that a rectangular wing is inefficient compared to other wing planforms. Can someone clarify why this kind of wing planform is inefficient compared to other planforms and what causes this "inefficiency"?

For the same wing span, an elliptical wing planform is the most aerodynamically efficient compared to any other flat wing planform because it has the lowest induced drag. Note that we are comparing only aerodynamics here. Things get much more nuanced once you couple structural weights, stability & control for a global efficiency (also see @Peter's answer).

1. Induced drag

So restricting to aerodynamics, elliptical wing planform is the most efficient because it has the lowest induced drag. Induced drag is produced because wings have finite span, and therefore one section of the wing distorts the flow on another section, creating downwash. This downwash distorts the lift vector on each wing section, thereby converting what otherwise would be lift into drag.

2. Downwash

Now that you understand induced drag has to do with downwash on each span section, you must appreciate that the distribution of downwash over the span is important to the induced drag generation. Distribution of downwash is dictated completely by the lift distribution over the wing (and vice-versa), which is in turn, dictated by the shape of the wing planform.

3. Lift distribution

For an elliptical wing planform, we can prove that it also generates an elliptical lift distribution. When you do the math of integrating all the sectional induced drag from the downwash and sectional lift, elliptical lift distribution has the lowest induced drag.

The following figures show the distributions of elliptical wing, rectangular wing (taper = 1) and tapered wing (taper = 0.5), with aspect ratio 8 and all producing a total $C_L=0.4$. Here, Ref Cl is the actual lift coefficient distribution that we've talking about, but multiplied by span length; Local Cl is the lift coefficient produced at each wing section, as if it's standalone airfoil; $\alpha_i$ is the downwash distribution in deg. The data are generated from Lifting Line Theory.

As you can see, elliptical distribution maintains a constant downwash, compare that to a wider and more varied one for a rectangular wing. Also, a taper of 0.5 gets you fairly close to the elliptical lift and downwash distributions, especially when you consider the $\frac{C_L}{C_{D_i}}$, which is 62.8 for elliptical and 61.8 for tapered.


How do a helicopter's cyclic and collective transfer commands to the swash plate? I understand the function of the cyclic and collective, and I am specifically wondering if anyone has a good image/video showing the mechanism of how the flight control "mixer" works! I can't seem to find many good illustrations of the mechanisms themselves, even a simple example.

Perhaps something like this but clearer, or something filmed in real life?

Edit: I circled the area in question in the picture below. Basically I understand how the cyclic and collective sticks move, and how the swash plate moves, but how do the stick movements move the swash plate actuators correctly?

I think I generally understand what is going on, and I understand what the swash plate is supposed to do, and which direction the swashplate actuators are supposed to move for a given maneuver. But what does this look like in real life? Is it typical to have just two actuators to the swash plate?
And in this system it seems like adjusting the collective would make the pilot's control column move? Is it common?

For example, I can understand in this picture that the cyclic stick can move forward and aft (circled in blue), which moves a control rod around a pivot, which lifts the forward actuator on the swash plate. I guess I am mostly confused as to how the collective plays in, and would like other diagrams or images to understand.

This is an image of a mirrored cyclic linkage as I understood it from @Pilothead:

Thanks!

The mixer is mainly found in larger helicopters where their expense is not such a large part of the purchase price. This answer explains more of the function of the flight control mixer: it de-couples degrees of freedom from the control inputs.

The helicopter in OP picture shows unmixed inputs into the swash plate: tilt swashplate forward for longitudinal control, sideways for lateral control, pedals connected to tail rotor only. Picture below is from Principles of Helicopter Aerodynamics by Leishman, and shows a schematic of the cyclic longitudinal

Three actuators are connected to the Non-Rotating Plate, which can be tilted and lifted. The Rotating Plate follows the fixed plate, and cyclically pitches the rotor blades so that they adjust their circular path up/down. The swash plate arrangement is quite complicated, as shown in the photo below, from the same book.

The mechanical linkage from the cyclic and collective sticks to the main rotor actuators does have some input summation involved, as the picture below shows (from this source, which indeed calls it a mixer).

There are always three swashplate actuators. The collective stick always deflects all three simultaneously so that the swashplate lifts, while cyclic stick movement deflects one or two in such a way that the swashplate tilts.


What are the design parameters for airliner safety? Airliners designed to carry multiple airfare paying passengers are regulated by CFR 14 Part 25, and by EASA CS-25. The design regulations are such that the probability of a catastrophic failure with multiple deaths is extremely remote or extremely improbable.

How is that defined? Can it be quantified at all?

Extremely improbable is defined as 10$^{-9}$ per flight hour, or one in a billion flight hours. For instance, from EASA CS-25 Detail Design Requirements 4.3:

  The actuation system minimum requirements should also be continuously met after any combination of failures not shown to be extremely improbable (occurrence less than 10$^{-9}$ per flight hour).

For aircraft systems and structures, that means we need to consider the following:

What is the probability that failure of function causes a catastrophe?
What is the exposure time to the failure condition?
What is the failure rate of the hardware?

Flight control systems are flight critical: without it functioning, we may assume that a catastrophe will occur. NASA-TM-72860 depicts the accumulated failure analysis factors for flight control systems like this:

If we take the cruise autopilot as an example:

When it fails, it just means that the pilot will hand-fly the aircraft, and the probability of its failure causing a catastrophe is set to one in a million flying hours. Pretty remote.
During cruise, the autopilot is on all the time. Exposure is pretty close to 100% (= 1)
That requires the cruise autopilot system to have a reliability of 1 failure per thousand flying hours.

The reliability demand is for system functionality, including sensors, processors, electronics, power supply etc. One way to meet functionality demand is to duplicate the system, so that if one system fails, one or more remaining systems will still carry out the function. Not really necessary for the cruise autopilot 10$^{-3}$ demand, but for instance the auto land system must be 1000 times more reliable: it is only functional during landing, but the probability of function loss causing a catastrophe during landing can be quite high due to proximity of the ground and very short reaction times.

That is why the CAT III auto land systems are up to triple redundant - the complete system is duplicated three times - if we only need one functional system and we have three, the functionality failure rate is $f(sys)^3$ Each individual system can then have a failure rate of 10$^{-2}$ per flight hour.

To put these numbers into perspective: the average B777 now flies 12 hours per day, that is 4,380 hours per year. It would have to fly for 228,000 years in order to experience a catastrophic failure with a chance of 1 per 10$^{-9}$ flying hours.

EDIT

Some very good questions from the comments. I'm answering them here, since all comments may be removed once the tally is 20 or more.

@Michael But how are those probabilities determined? Verification through testing gets harder with increasing safety: in order to get any statistical relevance, one would have to subject a safety critical system to 10 billion operational hours and track if there are indeed 10 functional failures. Operational records of all aircraft throughout history provide a frame of reference. Most design changes in aircraft are incremental for this reason, build up operational history of the aircraft first. Design parameter restrictions for military aircraft are much lower, and that is where most revolutionary design changes come from.

@James S:It appears all of these p(Catastrophes) are in isolation. Is there any attempt to calculate chance of catastrophe when there are multiple failures, or chance of failure when one item has already failed?
Yes:

Common mode failures, for instance EMD after an atomic blast that stops all electronics from functioning.
Hidden failures from back-up systems, or systems not in use at the moment. Redundancy is always better because it is always known that the system is operating.
Cascade failures, where one blade tears through all three hydraulic systems.

All of these failure modes may not result in more than 10$^{-9}$ per flight hour. For instance the Gust Load Alleviation: it is only required during an actual gust, but the status of the system since the last test or operation is unknown. Therefore the system reliability used in these failure calculations will have to include all possible failures since the last time the equipment was tested.

@Michael Kjörling Wikipedia claims that 1,526 Boeing 777 aircraft (all models) have been delivered. ... There have been six hull losses, minus one due to criminal act, or one non-criminal hull loss per about 31 million (about 10^7.5) flight hours. The estimates seem to be off by at least one order of magnitude. A hull loss without multiple deaths is not defined as a catastrophe. The design parameters only account for systems functionality and structural integrity, not acts of war. ...error conditions arising from system failures which did not result in a hull loss. are not defined as catastrophic, if a procedural change can fix the situation then the reliability requirements are less strict. The 10$^{-9}$ is a lower limit design parameter: for the B-777 case, divide the actual catastrophes as defined by authorities by the actual flying hours of the fleet, and it becomes apparent how excellent the safety numbers are. But they only start to gain statistical accuracy now, up to 5 - 10 billion flying hours accidents could all be flukes.

Then again: multiple similar catastrophic failures of a new fleet within a short time period may not be coincidental.


What is the significance of 104% for throttle power and rotor speed? I noticed this initially when learning to fly Robinson Helicopters but fail to remember the reason my instructor gave me; this again came up when watching a video about the ISS.

In helicopters (Robinson R22/44), the main rotor typically operates at 104% RPM.
On the space shuttle, after max q, they throttle back up to 104%.

What is the significance of 104%? If this is the maximum, why is this not called 100%, and everything scaled back to fit? This seems the most fit place to ask this, as I have only seen this in aviation / aerospace.

This happens when the maximum output was changed after design.

100% is simply a reference to a certain value. In the space shuttle's case, the engine output was increased after the initial design. Instead of updating the engine value everywhere, they decided to simply keep the initial value constant.

The same goes for N1 in turbo engines. 100% N1 is simply referencing a certain datum defined by the manufacturer. Going over 100% is not necessarily unsafe.


Air to air Missile Guidance vs countermeasures How do missiles successfully hit an air target despite the fact that nearly all Military aircraft are equipped with countermeasures.

Heat Seeker/Infrared missiles : IR Flares as countermeasure

Radar guided missile : Chaff dispersal as countermeasure

Laser guided missile : Flood Laser to blind missile as countermeasure

Which guidence system has most probability in hitting the target even when enemy deploys countermeasures, is there any guidence systems known which don't have a countermeasure?

Basically, the missiles are engaged in a (deadly) game with the aircraft every time a missile is fired. All countermeasures are based on 'confusing' the missile homing systems to a certain extent, usually in the terminal stage. Missiles (or AD systems in general), use a number of methods to overcome this.

The general term for overcoming the countermeasures used by the aircraft is called counter-counter measure (CCM); in case of electronic warfare, electronic counter-counter measure (ECCM) is used.

In case of IR missiles, the aircraft should first know it is being targeted. The usual method is to use a Missile Approach Warning Sensor (MAWS), which detects the missile plume. However, this is not a foolproof method. As far as IR missiles are concerned, the target is usually unaware of the missile lock. The problem with laser guided short range missiles is also quite similar.
A number of newer missiles have dual/multi mode seekers (like IR/UV in Stinger), which helps it differentiate better between the target and decoy. Though decoys can mimic the target in one band (for e.g. IR), it cannot mimic in both the bands (flares have different UV signatures compared to the aircraft).
The missiles can be programmed to ignore the decoy (for e.g chaff) and lock only onto the target signature (rather than locking on to the strongest signal return).
The missiles can differentiate between the target and decoy using the differences in their trajectory.
The missile can discriminate between the target and decoy by using a higher resolution seeker.

It is quite difficult to have a system that couldn't be fooled. Though a video/TV guided missile would come quite close, it is quite impractical in real world. Some laser guided missiles are touted as 'unjammable', but this claim is questionable. Best option is to have a multi-mode seeker that locks onto the target in different regions of the electromagnetic spectrum, though this would make the missile too expensive (again, countermeasures are possible).


Which kind of display are used on commercial aircraft? There are many kinds of display (LED, LCD, PDP...).
Which type is used in the in-flight entertainment system on commercial aircraft?
And which kind of display is used in the electronic flight instrument system?

Traditionally, it was almost only movie projectors in the cabin, since Cathode Ray Tubes (CRT) were too bulky and impractical to fit. It was also very expensive. I think only with the arrival of LCD displays seatback displays that we know now were made possible.

As for cockpit displays, the CRTs were widely used until LCDs were introduced and offered better performance.

You can compare the 737 Classic with retrofitted CRT displays with those of the 737 Next Generation.
Compare the 747-400 to the 747-8 which had LCD in place of CRT.

I can't find pictures, but have been told that the old CRT modules were huge, very deep (which you can't see) and heavy, compare to the thin panel that now is available.

You can still backwards order CRT for aircraft. I was flying with one airline that had done on a very new A320 to maintain commonality with the rest of the fleet. The pilots didn't appreciate it though, since it was bad for the eyes, needed to be dimmed and had (I believe) inferior resolution.

Page 9 of this document gives some details on the display type tradeoff.


What is the meaning of R88/70D in this METAR from Ashgabat International airport? The following METAR is from Ashgabat airport (UTAA)

  UTAA 071300Z 13006KT 9999 FEW050CB BKN050 BKN100 15/06 Q1013 R88/70D
  NOSIG

What does R88/70D mean, I couldn't find any references?

I assume it was a typo, as R88/70D is not a correct METAR format. According to this website with historical METARs the METAR of today at 1300Z at UTAA was:

  METAR UTAA 071300Z 13006KT 9999 FEW050CB BKN050 BKN100 15/06
             Q1013 R88/CLRD70 NOSIG=

All other METARs from UTAA today contain "R88/CLRD70 " as well.

R88/CLRD70 means: all runways are cleared (no more deposits), and a friction coefficient of 0.70.


What are the margins used to avoid a stall while slipping near the ground? Similar questions have been asked before, but in life-and-death questions like this, I want to be certain. This question is about airplane behavior close to the ground in normal and/or near slow flight.

I know that based on the angle of attack, a stall can occur at any airspeed. Alas, what should/does the IAS measure?  Presumably, it is from a pitot tube extending from the wing, straight into the relevant wind that is to fly over the wing, so if the angle of attack becomes very high, presumably the IAS dives, too.

For a small 2-seater or 4-seater with a modern wing (like a Diamond or Cirrus or Flight Design), is an indicated airspeed of 10 knots above stall speed a sufficient guarantor for not stalling?

For example, in a slip near the ground, if my configured stall speed is 60, and I fly it so that my IAS steadily drops down to 70 in my uncoordinated slip (at which point I relax back pressure to keep IAS at 70), am I then assured that the airplane cannot enter a stall?

When I side slip my glider "correctly" the airspeed indicator drops to zero or at least shows large fluctuations between 30 to 90% of the actual airspeed. So the airspeed indicator essentially becomes worthless during a large side slip and can't give any estimate whether the aircraft is approaching a stall or not. And I wouldn't rely on it to judge if the aircraft is approaching a stall.
I can somewhat judge the speed from the sound of the wind and also how much rudder input creates what kind of side slip (slow usually creates more slip angle for full rudder deflection) and also the back pressure needed but the best indicator for the approaching stall is still the elevator buffeting or an angle of attack indicator or angle of attack warning. If you're planning on doing short field landings with low approach speeds then an angle of attack indicator is probably a good investment.

From a physical standpoint the indicated airspeed in a side slip condition should always be less than or equal to the airspeed that you're actually flying. So if you see an airspeed indication in a side slip configuration you're going to have at least that figure as actual airspeed. This is because the airspeed indicator just shows the difference between atmospheric pressure and total pressure (sum of dynamic and atmospheric pressure). And if you rotate your pitot tube from 0 degrees to 90 degrees off the direction of incoming air it will show less and less dynamic pressure and work more like the static port, thus the readout drops. But it can never show more than what the dynamic pressure actually is (disregarding small vibrations due to unstable inflow). So if you look at the airspeed indicator and judge by the speed it reads you should be on the safe side.

Whether or not the 10kt increment is enough depends on how steep your side slip is and what you are flying. Ground effect could also influence how much angle of attack is left before the stall. Only a numerical simulation would give you an exact number here.

But you can always experiment high up in the air, do a side slip down to what feels as low as you would want to go for a safe landing and then pull up even more and see how far you can go without it stalling or see how it departs (relax controls immediately to avoid any nasty spins) if it actually does anything. Maybe it will show some significant buffeting before it actually stalls (great indicator!), maybe it will just lower the nose (not ideal close to the ground but still safe) or maybe it drops a wing (not so good, add more safety margin).