Can you file a flight plan to an airport whose runway is NOTAMed closed? We're planning a flight (under IFR) to an airport where the runway is notamed closed until 1900L.  The airport authority has said it will likely be open much earlier, so we're hoping to to take off and have the runway open by the time we arrive.

Is it acceptable under part 91 or 135 to file a flight plan to an airport whose runway is NOTAMed closed?
I can't find anything relevant in the FARs or the AIM.

With the added info in the comment, I'm going to say that it should be okay.

  IFR. Runway is notamed closed until 1900L(our ops don't allow landing on taxiways if there are other options and grass is no good for a jet). Airport authority has said it will likely be open much earlier. Wanting to take off and hopefully it will be open by the time we get there.

My reasoning is: you can file to airport (A) that has an instrument approach that will get you down below the weather (say a 3000' overcast), fly the approach until you're in VMC, cancel IFR, and proceed VFR to airport (B), which is where you actually intend to land (but which has no instrument approach to get you below the weather -- and no radar coverage).  This plan works even if airport (A) couldn't accommodate your aircraft for some reason -- runway closed/shortened, weight bearing capacity, whatever.  (Obviously you'd need alternate plans if the weather didn't cooperate with going VFR from A to B, but let's assume that you have a place to go land and plenty of gas to get there for a case like that.)  What matters is that you have an approach you can fly at Airport A, not that you can actually land there.

Worst case, perhaps you could file to airport A where you want to land, and then after that file routing to airport B which is where you'll go if the runway doesn't open up in time.  Thus your filed flightplan is simply "I'll fly an approach at A then go land at B" and that's a perfectly workable plan even with the NOTAM as written.  Then, in flight, if the runway opens early as expected, you tell ATC to amend your destination to airport A and you're all set.

Disclaimer, IANAL (I am not a lawyer), but this seems entirely workable to me.  I know in the 121 world, we explicitly ARE allowed to file to an airport below our mins, with the hope that it comes up (better than forecast) above mins by the time we get there.  It requires extra alternates and such, but just because we "won't" be able to land there based on things as we see them at this moment doesn't mean we can't be dispatched to go there.  And if things get better (weather comes up better than forecast, runway reopens sooner than NOTAM'd), you get to do what you'd hoped for all along.  Just have a sound plan for what you'll do in the scenario where things don't.


What are the differences between the MiG-15 and MiG-17? Apart from the extra wing fence and angled leading edge of the MiG-17, what are the differences visually between the two aircraft?

I'm surprised no-one's mentioned the length - the MiG-15 has a much stubbier appearance than the MiG-17, because it was rather shorter (10.10m vs 11.26m)

The wings of the MiG-17 are angled at 45°, rather more than the MiG-15 (helpful to identify from above), and the tailplane is has a small amount of extra rake too.

Overall, the MiG-17 has a longer, sleeker profile than its older cousin. Here's a comparison, 15 in blue, 17 in red.


What does Phase 3A mean for avionics? I've learned about Phase 1, Phase 2, and Phase 3 electrical systems. But recently I've faced an issue about replacement of Phase 3 Common Display System (CDS) Display Units (DUs) with new Phase 3A CDS DUs.

My question is what does it mean actually regarding Phase 3A? And what are the differences between Phase 3 and Phase 3A?

It is just a matter of technology, it turned out that phase 3 are subject to interferences from wireless devises, resulting in disappearance of displayed data.

We have been alerted of this some years ago and as long as several similar equipments are simultaneously  functional, it is probabilistically nearly impossible to loose the parameters on all these equipments simultaneously.

I found something about this on the following website, but may be on Honeywell website you will get more details

https://www.ainonline.com/aviation-news/2014-10-01/faa-orders-replacement-737-and-777-display-units

So the  trouble of interferences is specific to phase 3 DU, phase 3A corrects this effect.


Is freezing of windows normal in airlines? Recently I was flying on an Airbus A320. While cruising around 37,000 feet, I noticed half of the glass on the window had frozen. But it was a thin layer of ice.

Was it anything to be concerned about? Should I have brought it to the notice of the airline crew?

Edit: Ice formed on the inside of window with a small hole in it. I guess it was the middle layer of glass.

Was it anything to be concerned

No

  Should I have brought it to the notice of the airline crew?

Yes, but not because it is a safety issue. Tell them so they can deal with it to give the next passenger a nicer experience.

What is happening is no different than a glass of ice water sitting on your kitchen counter. The warmer side of the glass (the outside) becomes cooler because of the cold on the inside and it transfers that coolness to the surrounding air. That surrounding air cools enough to cause the moisture it contained to condense into liquid that sticks to your glass. If the glass were cold enough, it would freeze that condensation. The window on the aircraft is that cold so the condensation freezes.

There is a mechanism under the window to keep this from happening. It is a jar of desiccant that absorbs all moisture (dries the air) in the window area so that there is no moisture to condense in the first place. Often, there is a tiny bit still.

As the desiccant absorbs moisture from the air, it retains it. So periodically, it gets saturated to the point it can't absorb anymore and the desiccant needs to be changed.

Either the desiccant in your window needed to be changed or moist air is bypassing the desiccant on its way to the inside surface of the window. Normally there is a seal between the outside window and that thin plastic window you can touch and the only way for air to get in or out of that inter-window area is through the desiccant. Your window may have a broken seal allowing moist air to bypass the desiccant.

Either way, it is a system designed only to keep the window from forming ice so the passengers can look out the window, it has no safety or structural consequences.


Did/do any commercial passenger aircraft have showers for passenger's use? The Emirates A380 has a shower unit for use by First class passengers (previously discussed here), but it got me thinking about the many passenger comforts present in the "golden age" of aviation (pre-US airline industry deregulation, especially when piano lounges were a thing in 747 aircraft) - did any other commercial passenger aircraft (jets or otherwise) have onboard showers for the benefit of passengers?

If not, it seems surprising, because a toilet room could easily be converted to a wet-room shower unit - and aircraft have a ready supply of potable water. Showers could be time-limited to a few minutes - enough to freshen-up after a long-haul flight and I can see it would be popular with business travelers who might not have the luxury of time to use their airlines' business class lounge's showers.

On Emirates or Etihad long haul flights, they do have showers available only to certain passengers. Here you can find a link to an article about the showers. After those two airlines, as for inflight showers go, I do not know of any other inflight showers.
The 777 has inflight showers as well. The airline can request the systems necessary to have the showers. So technically any plane can have it.


Why can't I exactly match the same points on different VFR sectional charts? I am taking a trip from somewhere on the Phoenix sectional up to the grand canyon.  I wanted to just splice the two sectionals together on my computer and then print them out.

I picked a coordinate to align (as you can see in the first image), and with that coordinate aligned, almost nothing else on the map matched up.

Why aren't the sectional maps standardized to people can do this more easily?  I would have loved to make a "custom" map out of the Phoenix sectional, Vegas sectional, and Grand Canyon map, but it's virtually impossible without modifying them further, which I don't want to do in case of messing up the scale and/or orientation.

This is by no means specific to aviation charts. Most likely it's simply general property of local maps.

Maps are flat, but earth surface is (approximately) spherical. So to represent ground features on the flat map a projection is needed and this projection can't preserve all relations—angles, distances and areas—precisely. So there are many different projections that distort different properties.

Small area maps are usually drawn in azimuthal projection with the central point in the centre (or significant point near the centre) of the mapped area. While such projection does not preserve exactly any properties out of the centre, the distortion grows with distance from the centre, so for small areas it's appropriate.

This however means, that each section uses different projection and that near the edges the maps will be distorted each in a slightly different way. That's why the maps can't be easily laid out to form a bigger map. You would have to lay them out on a sphere.

You could try using some software for stitching panoramatic photos (here is one such you can use for free). That should be able to apply suitable transformation to make the maps match. At the cost of increasing the distortion.


How do thrust reversers in high-bypass turbofan engines counteract initial thrust? I've been searching the internet for awhile and haven't really come across a good answer for this question. So:

I have a basic understanding of the principles of flight (thrust, lift, drag, etc). But one thing that has been confusing me is how exactly a thrust reverser on a high-bypass turbofan engine works. So from what I understand, the large fans at the front of the engine will provide the majority of the thrust. Air coming through the inlet nozzle produces an action-reaction pair on the fan blades to produce this forward thrust. So upon deploying the thrust reversers, the air that has already produced a forward thrust on the fan blades now moves back through the bypass duct to strike the thrust reverser, thus redirecting the air forward by creating another action-reaction pair to slow the aircraft.

So it just kind of seems to me that the thrust reverser just cancels out the thrust from the fan blades. Or is the air coming off the fan blades is accelerated so that by the time it hits the thrust reverser the forward directed thrust is greater than the thrust generated from the fan blades, thus producing a net reverse thrust?

Or maybe I'm just looking at this wrong and need to think of the entire engine as a closed system so that the air pushed backward from the fan doesn't produce an action-reaction pair (and thus thrust) until it exits the engine?

I'm just kind of confused on the specifics of the physics of the thrust reverser (where the action-reaction acts).

There are several ways to describe thrust, which amount to the same thing. Very broadly, it's described by Newton's third law: if A moves forward, B moves backward with equal momentum. On a closer level, it comes from pressure differences across the surface of a body. Even closer, you'd be looking at viscosity and velocity, laminar and turbulent flow, boundary layers, analytical equations.

But all these ways come to the same result: if one, applied correctly, predicts result X, the rest can't predict an opposite result. In the most basic view, the reverser's thrust comes from pushing air forward. As long as the ultimate result is air being accelerated in some direction, however it happens, the thrust will be in the opposite direction.

If you want to get into the mechanics (which isn't quite necessary), the exhaust produces high pressure between the engine and the thrust reverser. This pressure acts on the thrust reverser's inner surface. The resulting backwards push is indeed greater than the fan's forward thrust.


What is this fairing on a Cessna 421? What's the purpose of the fairing on fuselage, near leading edge of the wing?

That “fin” is not there on a stock Cessna 421. It's part of the RAM modification  as pointed out by Mike Sowsun. That fin corrects airflow over the wing (probably at high angle-of-attack conditions) which is perturbed by the presence of the fuselage and thereby delays the stall for that portion of the wing near the root. In essence, it "tricks" the portion of the wing near the fuselage into thinking that the fuselage isn't there.

I invite anyone else with information on the RAM mod package to add more detail in a comment and I will edit this answer accordingly.


Is specifically indicating "uncontrolled airfield, student handling radios" by writing "uncontrolled" in a student's log book necessary? I'm a student pilot with 52 flight hours.  I've had multiple lessons at the same uncontrolled airfield handling the communications on each leg while doing touch and goes.  The last lesson my instructor wrote "uncontrolled" in my log book.  I spoke with the chief flight instructor she said that it was to indicate that I was flying in an uncontrolled airfield and handling all the radios.  Is it necessary to reflect radio communications for the private pilot exam with the DPE?
As I indicated above all my flight training for touch and goes (except one) has been at one uncontrolled airfield.  After the first lesson on calling postions in the pattern I've handled all radio communications.  Is writing "uncontrolled" necessary for logging progress?

Thank you.

You need to specify that the requirements of training are met.

For a private pilot under the FAA system, you need to have completed three solo landings at a controlled airport.  Otherwise, radio communication is a required line-item for training.  You should always log the airport of departure and arrival as well as the date.  If someone wants to know whether it was controlled or uncontrolled, they could look up the airport and see if it had a tower on that date, but they shouldn't need to since the required solo with an operating control tower should be specified in your training remarks.

Any examiner in the area would likely know whether any given airport is controlled or not simply from memory, being familiar with the area you're in. The examiner must check to make sure you meet the minimum requirements for the certificate or rating.

Beyond the three landings with a tower and the required standard communications training, there is no need to specify controlled vs. uncontrolled airport operations.


Why don't aircraft have DME that can automatically convert the slant range to ground range? Knowing that $a^2 = b^2 + c^2$ where $a = \text{slant range},\ b= \text{ground range},\ c = \text{height}$.

Why can't the DME equipment which calculates the slant range then just convert it to the ground range? Surely for navigation and position fixing knowing the actual ground range would be more useful? Is there a practical reason why the slant range has stuck?

There's no accurate and simple way to know the height above the station in order to do the calculation with the existing equipment. Altitude is not an indicator as the DME station may be above sea level. If your airplane is at 15,000ft and the station is at sea level you'll get one answer, if the station is at 10,000ft you'd get a completely different result, and mistakes could compromise safety.

The only way your proposed system would work is if the DME device had a complete database of every station height and altimeter readings, which would require upgrading the DME devices at great expense. I don't think anyone is interested in that when you can have GPS for a lot less money.


What happens to the transponder, FDR and CVR in case of an explosion? Will the above mentioned equipment still work and transmit data/location information if an explosion occurs inside the aircraft?

As ratchetfreak noted, the recorders don't transmit data, attached to them is a location beacon that operates for up to 30 days.
This location beacon isn't always successful in enabling searchers to find the recorders. In the case of AF447, it took two years before a search located the aircraft debris field on the sea floor and recovered it's recorders.
As for withstanding the stresses of an explosion, it obviously depends on the strength of the explosion and it's location in the aircraft. In the case of Pan Am 103, destroyed in flight by explosives, the recorders were recovered and data extracted.

A DFDR must obviously have a high degree of ‘crashworthiness.’ The first units were required to withstand a momentary shock force of 1,000gs, the latest test standards now call for a test to 3,400gs for a duration of 6.5 milliseconds. The units also have to withstand a static crushing force at all of its six axis points of an applied load force of 5,000lbs for 5 minutes on each axis. Third, it must withstand a 500lbs piercing force test conducted by dropping it onto a ¼ inch steel pin from 10 feet. Lastly it must withstand a 1,100°C fire test for 60 minutes, and a 260°C oven test for 10 hours.
It is also required that these units are mounted within the tail area of an aircraft, away from the potential crushing force of any engines mounted nearby. The DFDR must be watertight to a depth of 20,000 feet in sea water, and survive at this depth for 30 days - and it must be fitted with an underwater locator beacon which will act like a sonar transmitter, by ‘pinging’ a signal through the medium of water that it might be laying in.

From http://www.avbuyer.com/articles/detail.asp?id=1858

1G is the force you feel on your feet standing up.
12G is the most a fighter-jet pilot normally experiences in combat.
16G sustained for 1 minute will kill you.
25G for an less than a second will hospitalize a fit racing car driver

350G results in total body fragmentation

In a 727 crash landing

Impact forces at the front of the plane peaked at 12 G (12 times the force of gravity), in the centre the force was less, 8 G, at the rear it was 6 G, half that at the front and no greater than being hit in a fairground bumper car.

In a 720 crash,
the maximum force was 14 G vertically for 0.8 seconds

This F4 phantom striking a concrete block at 480 MPH produced average peak forces of less than 60 G (see fig 7). The most solid elements (the engines) experienced forces of up to 700 G (fig 11).

3400G is therefore a lot.


Do helicopters use static wicks? Fixed-wing aircraft (just about all of them!) have static wicks to dissipate static charge buildups before they can become obnoxious or shocking.  Are helicopters fitted with them? This answer suggests they are not.

Static wicks are mostly found on aircraft that fly in Instrument Meteorological Conditions because static charges typically build up when flying in precipitation, not in clear air.

So you won't find static wicks on helicopters that are certified only for visual conditions, like the R-22, R-44, Bell 206, piston Enstroms, etc., but you will find static wicks on helis that are certified for IFR.

  [Static wicks] are used on aircraft to allow the continuous
  satisfactory operation of onboard navigation and radio communication
  systems during precipitation (p-static) conditions. Precipitation
  static is an electrical charge on an airplane caused by flying through
  rain, snow, ice, or dust particles. When the aircraft charge is great
  enough, it discharges into the surrounding air. http://en.wikipedia.org/wiki/Static_discharger


What is the best combination of airfoil shape for flight in ground effect over water? What is the best airfoil shape for flight in ground effect over water?

There are three considerations for this design:

Airfoil shape
Aspect ratio
Dihedral/Anhedral

Airfoil shape: high lift undercambered thick and very forgiving - good idea near the ground
      Gottingen 436, NACA 4412

Low aspect ratio: lower stall speed, better compression lift from ground effect, more
     stable in pitch

Anhedralled wings:  this actually provides more roll stability in ground effect as the
      LOWER wing has more lift.  Anhdralling also helps "trap" more air underneath the wings
      for greater lift.

Ground effect designs would be similar for travel over flat land or water.  Good info in links
provided by @mins and @Juan Jimenez.


Why is there an altitude limitation on operating the slats/flaps on the A320? As per the FCOM limitations chapter there is an altitude limitation of 20000 feet for operating the flaps/slats on the A320?
Why this specific altitude?

Why would you want to deploy high lift devices at any juncture except for departure and arrival?
Holding is the predominant scenario.
Above 20,000ft ICAO holding speeds are higher thus allowing clean configuration.
Above 20,000ft, at slower speeds, the likelihood of encountering icing on the wings when moisture exists is also a very real consideration (upto about 28,000ft) and ice accretion is not what you want with high lift devices hanging out.
Extending slats/flaps in typical cruise or when we are flying in the Mach regime of flight, say about 29,000ft and above, is something that would cause much grief to the average Airliner, a possible jet upset scenario.
If other reasons already cited such as aircraft certification/cost of certification are a factor - most operators would not need a change from the 20,000ft figure.


If you depressurize an aircraft at FL340, will the temperature inside fall to match the temperature outside? Assuming you’d have an oxygen mask on before hand, and you depressurized the aircraft at FL340, would the inside and outside temperatures quickly become the same?

This depends entirely on how you depressurized it.

Depressurizing the aircraft by fully opening the outflow valve will lower the temperature somewhat, but will not bring it to that outside.

The expansion process will be closest to free (Joule) expansion, which causes only small decrease in temperature, not an adiabatic one that corresponds to the atmospheric lapse rate. And while some energy will be lost through the air's initial expansion as it escapes, it will quickly be replaced by new warm air coming in through the packs (cabin pressurization and air conditioning system).

That air supply is quite reliable, as it's bled from engines at about $200\ \mathrm{^\circ C}$ – it then needs to be air-conditioned so as not to roast the passengers. The packs will automatically maintain set temperature, putting less effort into cooling the air if the cabin gets too cold.

If you also disable the engines, so no new air can come in, the airplane will lose some heat. Still, in all other regards, the fuselage will remain a well-insulated vessel with some heat sources on the inside. Also, the less-dense air is much less effective at heat transfer, and has much less heat capacity, so it will get chilly, but the passengers aren't going to freeze to death or even get a frostbite.

The heat capacity of air at ambient pressure will be about $280\ \frac{\mathrm{J}}{\mathrm{m}^3\cdot\mathrm{K}}$. A 737 encloses about $200\ \mathrm{m}^3$, giving a total of $56\ \frac{\mathrm{kJ}}{\mathrm{K}}$. For comparison, the plane's passengers have a specific heat capacity of $3.5\ \frac{\mathrm{kJ}}{\mathrm{kg}\cdot\mathrm{K}}$, giving, for 120–160 of them, about $40\ \frac{\mathrm{MJ}}{\mathrm{K}}$. So a $\sim70\ \mathrm{^\circ C}$ one-time drop in air temperature can technically match the outside, but it can only cool the passengers by at most $0.1\ \mathrm{^\circ C}$.

In practice, the cooling won't be instant, and it has to compete with heat exchange with the still-warm interior. Passenger bodies producing $12{-}18\ \mathrm{kW}$ of waste heat (at rest) will also restore cabin air temperature by $\sim1\ \mathrm{^\circ C}$ every 4 seconds. The larger the hole, the lower the temperature minimum that will be reached. With a broken window, the effect of this one-time expansion heat loss will have been mostly undone before anyone notices it, amidst the chaos.

Tearing the top of the fuselage off, on the other hand, will most definitely let the passengers feel the cold outside. But it will be the powerful wind blowing in, not the air leaving the airplane, that will chill its interior.

Breaking a single window or making a lot of bullet holes (really a lot - it will take a crate of ammo to overcome the packs' air inflow) is about the same as fully opening the outflow valve. It will produce some cooling effect, but it will definitely not bring the interior to the outside temperature, as the cooling effect is one-time, and will be rapidly compensated for.

This kind of event has happened a few times in aviation history. It has caused some fatalities – a person sitting right next to the broken window has been killed by the mechanical force of the escaping air. No one has been frozen to death, not even in the Aloha Flight 243, which represents about the worst possible case for depressurization (which still leaves survivors and not just a debris field).


Do rivets on airframe need special sealant to be airtight on pressurized airliners? Do rivets on airframe need a dedicated sealant, e.g. epoxy, to be really airtight on a pressurized airliner, or is the expansion of the rivet shaft already sufficient?

As a side note, how are carbon fiber panels joined with aluminum or titanium panels?

I banged rivets on a production line long ago.  The countersunk rivets used in the pressure hull depend on expansion of the shaft, but some rivets also have a slightly larger radius where the shank flares out into the head compared to a standard flush rivet, which forms a tighter seal when the rivet is set.

You don't actually apply sealant to the rivet itself. The sealant, which is a crazy-sticky goo stuff (not epoxy, it cures to a hard rubber consistency), gets everywhere when you are shooting rivets on the pressure hull because the faying surfaces (the overlapping metal to metal surfaces) are coated in sealant before assembly, which gets in the rivet holes (the sealant is a pain in many ways; it acts like a lubricant if it gets on the skinny end of the rivet and makes it easy to dump the rivet over when you buck it).

Carbon fiber panels are usually joined to metal with bolts or Hi Lites or similar rivets, with some sort of insert or doubler of stainless or titanium in the carbon to distribute the loads.  Sandwich floor panels for example, typically use a titanimum insert bedded into the sandwich with epoxy resin, through which the fastener goes.  Carbon against titanium is fine, but if joining carbon to aluminum, you MUST have an insulating material to separate them because they live at opposite ends of the galvanic scale.  Carbon touching aluminum = lots of corrosive fun.


How can a passenger tell if a flame-out / engine failure has occurred? Reading this page, a retired American Airlines pilot quotes:

  We tell passengers what they need to know. We don’t tell them things that are going to scare the pants off them. So you’ll never hear me say, ‘Ladies and gentlemen, we just had an engine failure,’ even if that’s true.

Given this, how can an observant passenger sitting over wing (seeing most likely very little of the engine), determine if a flameout or shutdown has occurred from observation?

This is applicable to an aircraft not unlike the Boeing 737 (which I fly on often).

Mainly by the soon to happen descent and landing, probably at a place you weren't expecting to go.  :)

If you are seated behind the wing, you might be able to see smoke or flames coming out of the engine, but other times it will just quit with no visible indicaion, depending on the cause of the failure.

Sometimes (usually just after takeoff when the airplane is slow) it is obvious and you can tell by the change in the sound of the airplane (one side suddenly gets quiet or there might be a loud bang depending on why it failed), a sudden yaw in one direction (the nose pulls to one side), and an abrupt pitching down of the nose (done by the pilot to maintain flying speed).

Other times (like during a descent with plenty of speed and the engines at idle, or when the center engine of a three engine airplane fails) it can be hard for even the pilot to tell without looking at the instrumentation, so you probably won't notice it.

Another major clue would be when the seatbelt sign unexpectedly coming on, without an announcement or indication of turbulence, and the flight attendants suddenly putting things away and getting ready for landing, especially when you aren't close to your destination. Being briefed for an emergency landing is also a dead giveaway (no pun intended).


Should the type of plane influence my travel choice? With those many websites that compare flights we usually have the opportunity to chose between different paths to reach the final destination.

Should the type of plane influence the decision? Ex. If I see that one company uses a Boeing 787 instead of a Boeing 767 or an Airbus A330-300, does that influence the travel experience in a perceivable way (In terms of turbulence attenuance, noise reduction, smoothness of flight, different types of landing/take off)?

As a general rule, not really, though there may be some factors that could cause you to consider it as part of your decision-making.

Some short-haul routes may be served by aircraft of significantly different sizes. For instance, some flights between San Francisco and Los Angeles may be on a Boeing 737, while others are on a CRJ Regional Jet. Still others may be offered on a turboprop like the Dash 8 or the even smaller Beechcraft 1900 (or even smaller aircraft, especially serving remote areas). Even those who aren't afraid of flying may be uncomfortable on small "puddle jumper" aircraft, as the seats and headroom are usually physically small and they can be more impacted by turbulence. Such aircraft can also require standard carry-on bags to be checked at the gate (they are usually returned to you at the gate on arrival), as lack large overhead bins.
The Boeing 787 Dreamliner can be pressurized to a lower cabin altitude and has a higher level of humidity than is typical. Efforts were made to lower cabin noise as well. This can lead to a more comfortable flight. Many of these enhancements may be carried over into future next-generation aircraft.
There may be differences in the cabins depending on the aircraft model, especially in premium classes. For instance, first class passengers on Lufthansa may have a separate bed on Boeing 747 aircraft, while those on Lufthansa's A340 will have to make do with sleeping on bedding atop their luxurious seat. Emirates business class is supposedly far better on the A380 (which includes a bar in the back) than the 777, though which you get mostly depends on your route. In other cases, an airline may be rolling out a new premium seat design, which is only available on some aircraft types. While the differences are less pronounced in economy, there may be variations in seat pitch (legroom) and configuration (2-5-2 vs 3-4-3 for example) that can make a significant difference in comfort.
Some people prefer newer aircraft. This can be difficult to guarantee by type alone though, as many aircraft have been produced over a period of decades. Even older aircraft have to go through a rigorous inspection and maintenance procedure though.

That said, most people are choosing their flights based on factors like price, route/time, and frequent flyer membership. Type of aircraft is usually pretty low on the priority list unless you're an enthusiast determined to fly a certain new model.

Also note that aircraft type is never guaranteed, and carriers reserve the right to make substitutions for operational reasons without notice.


Could I build an airship (rigid dirigible) that used a vacuum rather than lifting gas? There are other questions (c.f. What gas is used in airships to give them buoyancy?) that discuss the use of lifting gasses such as Helium and Hydrogen in airships. Helium is rare and Hydrogen is flammable.

If one could build a light-enough and strong-enough rigid outer frame, then couldn't one use a vacuum rather than lifting gasses?  At ground level, the frame would only have to withstand 15psi (100,000 pascals), which isn't a tremendous amount of force. Theoretically, a vacuum should provide even greater lifting force than any gas.

Have there been any attempts at vacuum based rigid-dirigibles -- and if not, what are the technical or mechanical limitations to doing so?

what are the technical or mechanical limitations to doing so?

There is no known material that has a sufficient combination of lightness and strength to support a vacuum that would support the weight of the container on Earth at sea-level.

There was a similar question with a good answer on Physics.se

Beryllium Vacuum Sphere Boat/Aircraft

  Is it possible to make a solid rigid evacuated "balloon" out of Beryllium or other elements or alloys?

The currently first answer runs through the maths

  calculated it over a database of almost 3700 materials including all common aerospace composites, metals and alloys.

and concludes

  So in short, the best materials fall short of achieving our aim by a factor of just over 2. It is conceivable we might push up the stiffness / density ratio by perhaps developing some kind of Beryllium foam. For example, a closed cell foam of this Beryllium with a relative density of 0,041 would give a value of about 920 at the expense of lowering the Young's modulus to about 600MPa - however, I have no idea if such a foam is even possible. Alternatively it might be possible to come up with some clever engineering of the envelope geometry to overcome the buckling constraint. However, I suspect the effort is unlikely to pay off with a better boyancy ratio than is already achievable by conventional balloons.

Other related questions

Is it possible to create a vacuum ballon using concentric partially pressured spheres?


Whats the difference between a paragliding rescue chute and a parachute? Whats the difference betweem a paragliding rescue chute and a parachute and could I use a parachute as a paragliding rescue chute and what would be a disadvantage/advantage?

At least these points are imortant: Stablity, descent rate, manoeuvrability, opening speed, reliablity.

I'm asking because I've found articles (in german) which make the argument that the current rescue systems for paragliders are a mistake and that "BASE systems" are starting to beeing used in the acro scene. However I could not find details.

dhv.de -> Rettungsgeräte
x-dreamfly.ch -> Retterproblematik

Paragliding rescue chutes are typicly round canopies but there are also other special forms.

Military troop parachutes are also round canopies.

So are chutes used for space exploration.

While parachutes are rectangular.

And also paragliders are rectangular.

Round canopies are said to have a slower descent rate, are more stable then other forms, are simple and open faster and are small but they are not feasible to manoeuvre but I could not find references to back up those claims.

Drawbacks of a skydiving emergency reserve parachute compared to a paragliding emergency parachute would likely include excess bulk and weight, and possibly a longer time to complete the opening sequence-- though perhaps the latter point would not apply to a parachute intended for BASE jumping.  If one has room for the skydiving emergency reserve parachute in their harness, and one is engaged in a high-risk style of flying such as aerobatics, it might make some sense to consider flying with it rather than a purpose-designed paragliding emergency parachute.

For more see related answer Can a paraglider rescue chute and its pilot handle terminal velocity?

It sounds like you have a more than merely academic interest in this topic; if so I'm sure you'll do further research, and we'll look forward to seeing a detailed self-answer to one or both of these questions in the future.


What is the tailhook on naval aircraft made out of? What is the tailhook that enable naval aircraft to land on aircraft carriers, it must be made out of a strong metal to not bend or 'snap' under the force of the thrust that the plane is expelling, as they land then put thrust to full.

Image Source—PACIFIC OCEAN (Dec. 22, 2011) Landing signal officers supervise the arrested recovery of an F/A-18C Hornet on the flight deck aboard the Nimitz-class aircraft carrier USS Carl Vinson (CVN 70).

They're made of alloy steels that have ultra-high strength, high fracture toughness, excellent fatigue resistance, and high resistance to stress corrosion cracking.

Based on one of the manufacturers—QuesTek—the steel's grade is AMS 6516.

The 6xxx grade is a chromium-vanadium steel:

  Chromium-vanadium steel refers to steel alloys incorporating carbon, manganese, phosphorus, sulfur, silicon, chromium, and vanadium. Some forms can be used as high-speed steel. Chromium and vanadium both make the steel more hardenable. Chromium also helps resist abrasion, oxidation, and corrosion. Chromium and carbon can both improve elasticity.

Elasticity is important because you wouldn't want a deformable tailhook.

Other applications for it are:

  Landing gear, rotorshafts, driveshafts, arresting tailhooks and hookshanks, actuators, armor, munitions, gun barrels, and blast-resistant or impact containment devices.


Can a CFI give required instruction and endorsements on a 3rd class medical? Let's suppose a CFI can no longer qualify for a 1st or 2nd class physical, or maybe her/his 2nd class physical was 18 months ago. Can she/he still give required instruction and endorsements as long as they don't charge for their time and are not paid for it in any other way?

A CFI with a third class medical can provide any kind of instruction that they are qualified for (and be compensated for it), per 14 CFR 61.23(a)(3)(iv) and (v). The FAA's position in these scenarios is that you're being compensated for the transference of knowledge, not the operation of the aircraft.

For completeness, A CFI can provide instruction WITHOUT a medical if they are not flying PIC or acting as a required crew member. In this scenario training can be provided for certain additional ratings (e.g. commercial) or flight reviews AS LONG AS the student can PIC during that flight AND the CFI is NOT a required crew member (i.e. safety pilot for insturment training).  Additionally, the FAA has made a legal interpretation that a CFI can provide instruction to a pilot that is not current to carry passengers, as long as all other requirements for the student to be PIC can be met.

The specific regulations that allows this are 14 CFR 61.3(c)(2)(viii) and 14 CFR 61.23(b)(5)


Is certification required to conduct runways repairs? I know that you need a certain certification to fix a plane, but are you required to have a certification to fix a runway?  Or can anyone with the proper equipment be paid to do it?

To the best of my knowledge, you do not require any certification to fix a runway/taxiway, and anyone with a proper equipment can do that. But to facilitate the process, the FAA has published a few checklists which have to be filled while doing this repair job. These checklists can be found Here. FAA also provides assistance in guiding the construction jobs and identifying risks, the link to which is in the same website as mentioned above.


How does the range of a single- and twin-engine for small aircraft compare? I know that one difference between these two types of small aircraft are that in a twin engine, one engine can continue working if the other suddenly fails.

Wouldn’t a single engine plane weigh less and thus can fly longer on a specific amount of fuel comparative to a twin engine plane?

(Cessna 185 Skywagon and Cessna 340)

See here for the major points: What are the pros and cons of single-engine vs. twin-engine? Regarding your specific question:

Wouldn’t a single engine plane weigh less and thus can fly longer on a specific amount of fuel comparative to a twin engine plane?

Both airplanes above are powered by the same 300 hp engine, so yes the twin will be heavier. But it can also lift more weight (i.e. more fuel), and cruise at a higher speed for the same power setting, or cruise at the same speed for lower power setting.

Either the higher speed or lower power, combined with the more fuel, gives the twin a longer range.

In fact, double. 2,603 km compared to 1,333 km.

If you wanted to compare the twin to a single with a 600 hp engine, then there is no weight advantage. Only the bigger engine is harder to maintain.

On a technical note, weight is not a big issue in cruise. The power to overcome the induced drag from the lift (which counters the weight), decreases with speed, i.e., it takes less power to create lift in cruise, than at slow speeds. (See graph below for the induced drag.)

Same fuel

Twins are designed to fly on one engine, which means half the power potential is enough, which is helped by the bigger span wing. So the same fuel load will give the same or more range for the twin. Unless, you want 600 hp vs 2x300 hp, in that case the single will win because of its smaller form.

Some numbers:

For the two planes above, here are the gallons-per-hour and cruise speeds:

             gph             cruise speed kts
Twin         26.0-34.0       202-229
Single       11.7-15.5       122-140

As you can see, the higher fuel consumption is offset nicely by the speed, and note that the twin will reach the cruise altitude in less time as well.

Sources: Cessna 185, Cessna 340

If we compare a twin-piston to a single-turbine then it won't be an apples-to-apples comparison, but the single-turbine plane will be faster, and will have longer range, but that's mainly due to the different engine types (combined with different cruise speeds). For the Cessna Caravan, the turboprop engine (minus the accessories) weighs as half as a single 300 hp piston engine, which can allow for 200-400 kg more fuel, but the turboprop engines are very, very expensive. So depending on the operation, a fuel saving here might be overdone by the initial cost.

(wikimedia.org)


What is the function of a skew sensor in an aircraft? I was trying to understand Slat and Flap control Unit and came across the term "skew sensor". Can anyone explain it to me?

Skew is essentially when the flap doesn't extend or retract straight back.
Picture a situation where you have a 1 meter wide board you're pushing down a track that's slightly wider than the board.  Your left hand is about a quarter of the way in from the left edge, and your right hand similarly in from the right edge.  As long as you push straight down the track, evenly, with both hands, the board slides along and doesn't contact the edge.  Now suppose that your right hand pushes harder than your left hand: the board will start to turn, and the edges of the board will contact the edges of the track.
The skew sensor detects that this sort of misalignment is starting to happen, and causes the flap drive to stop.  Ideally, this takes place before the flap makes physical contact with any other hardware, so nothing is damaged!
Edit:
Video of flaps being extended & retracted on the ground.  You can see that there are multiple flaps on each wing, and while normally everything moves in synch, you can envision how if one actuator stopped working, the errant flap could get turned pretty far out of alignment, make contact with other hardware, and cause some significant damage.  So before this happens, the skew sensor sends the command back to stop everything from moving.
From Boeing's Aero Magazine:

The 757-300 has incorporated a flap skew detection system. Flap skew occurs when either the inboard or outboard edge of the flap moves farther than the rest of the flap. The flap skew detection system monitors, detects, and shuts down the flaps if a skew condition occurs. The heart of this system is the flap slat accessory module (FSAM), taking the place of the flap slat electronic unit (FSEU) number 3. The new LRU was introduced because the existing configuration of the FSEU would not accommodate the addition of the flap skew circuits.
The flap skew sensors are mounted on the trailing edge of the flap jack screws (fig. 4a). The sensor (fig. 4b) is fixed to the flap track, and a target (which contains magnets) is mounted to the jackscrews. As the jackscrew begins to turn, the target also turns. This will pulse the sensor, and a signal (distance traveled) is sent to the FSAM, which compares this signal with the opposite side of the same flap. If the distances traveled by either side of the flap differ by a predetermined amount, the FSAM will shut down the flap system to help eliminate damage to the flap and surrounding structure and the possible loss of a flap in flight. The alternate flap mode will override the normal flap skew detection function, allowing maintenance personnel to move the flaps after maintenance has been performed. Maintenance personnel must verify the flap fault and also ensure that moving the flap will not cause any damage.


What is the proper phraseology for a clearance with a named obstacle departure procedure? The Phoenix Mesa-Gateway Airport (KIWA) has a named obstacle departure procedure - the Phoenix Departure.

What's the correct phraseology for when clearance assigns it to you? Is it "N123AB, cleared to XXX, via the Phoenix Obstacle Departure"?

Items in parentheses on these charts are not said when referring to them by name. It's the same for other departures/arrivals that are RNAV, and for approaches that may be GPS or RNP.


Why did this plane fly in a zigzag pattern? I was tracking flight NKS739 from LAX to SEA this morning and saw that it made some some odd turns. If you look at the track from FlightRadar24.com you can see that it was heading toward SEA then it took a large turn to the right then to the left then returned to its original course.

This does not look like the usual technical glitch from Flightradar24, and FlightAware shows the same track. There was no weather anywhere in the area. There were many aircraft in the area at the time and none of them made any unusual turns. There are no MOA's in the area (most of it is over a national forest) and none of the other aircraft seem to be avoiding anything in the area. I tried to see if LiveATC.net had a recording but that's Seattle center's area and they don't appear to have a feed for ZSE.

I can't come up with any reason for such an odd deviation. The aircraft arrived in SEA and there didn't seem to be any problem. It immediately turned around and made another flight which was uneventful.

Is there anything that might explain this deviation? Is it just a glitch?

Alrighty then, that took some detective work.
Here's another flight around the same time, SkyWest 4458, which arrived 2 minutes later. Notice it's one deviation, compared to two deviations in your example.

Weather seemed fine, but KSEA has TBFM (Time Based Flow Management) since Aug 2013. If the ATC asks a plane to delay its arrival time, the way it's done is to deviate from the route, then get back on it again—that's if slowing down alone won't meet the time target.
Pilots then use the RTA (Required Time of Arrival) function of the FMC. Initially the function was rarely used, but now with NextGen in the U.S., SESAR in Europe, and similar systems elsewhere, it is frequently used.
It can be arranged way ahead of the airport, i.e., it can be ordered by the approach controller, yet the center controller of another ARTCC delivers the message.
It looks exactly like that. Deviate, if not enough, deviate the other way.
Behind the Scenes
The system is called ERAM (En-Route Automation Modernization).
ERAM detects future conflicts, and based on that, traffic is asked to speed up, slow down, or deviate to slow down further. It reduces/eliminates hold time.
Europe—the first to use it in 2012—refers to it as initial 4D trajectory management. Planes arrive at waypoints at agreed times.
For whatever reason—most probably sudden traffic influx—they were asked to slow down.

The difference between this, and the regular vectoring/doglegging in the terminal area, is the way it is predicted, coordinated, and then relayed to airplanes far from the airport.
Below you can see as the jet turned, it slowed down as well. The initial upward spike is just the tailwind when the plane turned.

Source: flightradar24.com


How does density altitude affect Taxi-Out Time? To keep things brief, for a data exploration project, I calculated density altitude for a couple airports and used flight statistics from https://www.transtats.bts.gov/ONTIME/Departures.aspx.

I was under the assumption that a higher density altitude is bad for performance and would involve things like longer takeoff time which can prolong taxi out time(from gate to runway) since a plane in line would have to wait longer for earlier planes to takeoff. Is this true?

Or is there pretty much such a minuscule difference that density altitude shouldn't matter in the context of taxi out time?

The time between takeoffs on a given runway is a function of wake turbulence separation from the preceding aircraft, though wake turbulence avoidance times can often be waived by the pilot in command (depending on operating procedures).  Takeoff separation time is calculated based on aircraft type/weight.

An increase in density altitude could determine whether or not the aircraft can do an intersection takeoff, which in some cases could increase taxi time.


How does the airfoil pitching moment relate to center of pressure? I've looked everywhere to find the answer and it's still unclear to me.

How does pitching moment relate to center of pressure? Does it relate to coefficient of lift?

I have made a carbon fiber wing (Eppler E423) and the CM of that wing is around -.22 where i'd be running it on my racecar.
Where is the center of pressure so I can put my main mount directly under?

PS: let me reword, I want to calculate where my center of pressure is along the chord.
I'd rather use CM to calculate that(if possible), but any other method aside from hand measuring it from a CP plot would be nice.

The pitching moment probably has little (if any) relevance in the case of an airfoil attached to a race car.

In particular, the pitching moment is related to the fact that with a cambered airfoil, the center of pressure will forward and backward depending on the angle of attack at which the airfoil is operating.

In the case of a race car, the angle of attack won't normally vary much, so the pitching coefficient probably isn't very relevant.

I'm not sure it's really relevant, but the aerodynamic center is normally taken as being at 25% of MAC. The Cm basically then defines a torque that's exhibited at the aerodynamic center.

One other point: I'd at least assume that on a race car, the airfoil is mounted upside down compared to an aircraft--that is, it's intended to produce pressure downward, not upward. To the (I think minimal) extent that pitching moment is relevant at all, it'll be positive (whereas it's normally negative for the main wing of an aircraft). That is to say, on an aircraft the pitching moment leads to a force pushing the nose downward, but in your case it'll be a force tending to push the nose up (and the tail down).

Okay, so based on the comment, what's really desired in this case is to compute the location of the center of pressure. To do this, we really need two things: the Cm and the CL.

For the moment, I'm going to assume a Reynolds number around 500,000 or so. For an E423, your quoted Cm of -0.22 corresponds to an Alpha (angle of attack) of around 5 degrees. With Re = 500K and alpha=5, it looks like the CL is about 1.6.

The formula we need is:

hcp = hac - Cmac / CL.

Plugging in the numbers, we get: 0.25 - (-0.22)/1.6.

Running that through the calculator, we get 0.3875. So your center of pressure should be approximately 38.75% of MAC. Of course, you'll need to adjust if you're actually basing your number for Cm on a different combination of angle of attack and Reynolds number.

As noted above, in your case the airfoil is (presumably) upside-down, so that should really be a Cm of +0.22 and a lift of -1.6, but the signs cancel so we get the same result either way (exactly as you'd expect).

References:

Airfoil data
Computation


What does I1001 mean in a METAR remarks? Here is an actual METAR example:

KOMA 190352Z 36017G26KT 3SM -SN OVC012 M08/M11 A3014
RMK AO2 PK WND 36027/0302 FZDZE37SNB27 SLP220 P0000 I1001 T10831111 $

What does the I1001 mean? I have also seen I1000, I1002, I1003, and I1004.

It indicates ice accretion (buildup). This seems to be very obscure, I finally found it in some NOAA release notes for ASOS software v3.07:

  (S01126) ADD ICE ACCRETION REMARK TO METAR/SPECI REPORTS

  Discussion: The amount of ice accreting on a flat surface (planar
  icing) as estimated by the data from the freezing rain sensor, will be
  included in the remarks section of the METAR / SPECI reports. The
  remark will have the format of “Ihnnn,” where “h” is the hourly time
  period, i.e., 1, 3 or 6 hours. The value “nnn” is the ice thickness
  accumulated to the nearest 0.01 inch.

  Please Note: In situations when FZRASN is manually entered in the
  Present Weather field, an inappropriate trace accretion amount (I1000,
  I3000, I6000) might be entered in the remarks section of the METAR /
  SPECI reports. This is a known issue and will be addressed at a later
  time.

Based on that, "I1001" means ice buildup of 0.01 inches in the last 1 hour.

And thanks to Jimmy for finding a more official source: FCM-H1-2017, Federal Meteorological Handbook No. 1 - Surface Weather Observations and Reports (p. 12-18) from OFCM, the Office of the Federal Coordinator for Meteorology.


Is it usual for a first officer not to know how to taxi? According to this article on afspc.af.mil, the first officer of the 737 the pilot in the story was flying with had never taxied a 737. Is this normal?

The exact quote in the article:

  After landing, the first officer turned to Gongol and asked if he knew
  where to taxi, she had never been to the Omaha airport before. Taken
  aback by how cool, calm and collected the first officer had acted
  without knowing the airport, Gongol remembered landing at the airport
  before pilot training.

  "Surprisingly, taxiing was the most stressful part of the day for the
  first officer," said Gongol. "She had never taxied a 737 before and
  the ATC had no idea that the pilot was the reason for the emergency.
  We had to make a quick decision that her switching to the pilot's seat
  and taxiing the aircraft without the training was necessary to save
  the captain's life."

After reading that article carefully, here's what appeared to have happened:

Pilot collapses
Passenger-with-pilots-license comes to flight deck (with both elitist and sexist chip on his shoulder)
First officer moves to left seat, PwPL takes right seat, runs the radios and checklists, maybe drops the gear.

First Officer is a right-seat qualification, on 737s (and many others) the steering handle is on the left side.

So it's quite possible that the FO has never steered a 737 on the ground. It's quite IMpossible that the FO has never taxied an aircraft of any kind before. And there's a huge difference between driving a Gulfstream around and driving a 130-passenger jet around.

If you don't take a corner just right, the main gear ends up in the ditch, the wing hits the ground, the engine inhales grass, gravel and maybe the taxiway sign and a couple of gophers. Trashing a Ferrari is cheaper.

The FO moving to the left seat and flying the plane was the correct action - the B-1 pilot was no more qualified to fly a 737 than I am. But radios are radios, and even the greenest flight attendant can read a checklist.


Who controls VFR flights in class B airspace in Europe? I was reading about this incident where a near miss occurred in class B airspace between IFR and VFR flights that were in contact with different controllers.

So I would like to know which controller normally gives the clearance to enter class B airspace to a VFR flight? When entering from class E, does the area controller provide the clearance or the approach controller of the airport whose class B it is? And is the flight then handed off to the appropriate approach controller? And when the aircraft then crosses from one class B airspace to another?

That particular incident happened

at 4000 ft amsl. This chart does not list frequency for that airspace, but it is clearly airspace of the (Danish) Kobenhavn/Kastrup (EKCH) airport. But it is in Swedish airspace and Sweden area (ESAA). The VFR flight was flying from east to west, so must have crossed from other class B sector that apparently belongs to Malmo (ESMS) about 5 nm earlier. So does it make any sense it was (still) talking to Swedish controller (the article is not absolutely clear, but seems to say it was Sweden area, not Malmo approach) while the other flight was talking to Kobenhavn approach?

Obviously I am not trying to find what happened; the investigation will hopefully eventually explain that. I'd just like to understand what the normal procedure in such situation is.

I'm assuming you're referring to this where a Cessna 172 had a near miss with a 737: http://www.havarikommissionen.dk/~/media/Files/Havarikommissionen/Havarirapporter/Luftfart%202014/Preliminary%20ATI%20Bulletin%20HCLJ510_2014_273.ashx

Regarding who the VFR pilot should have been talking to, that depends. For example if you're flying in Los Angeles you might get clearance into the bravo for LAX from SoCal Approach if you're taking the "coastal route" through the bravo, or you might get clearance from LAX tower if you're flying the lower altitude "mini route" which directly overfly's LAX runways and tower and you'd be talking to whoever you got clearance from until they handed you off.

It really depends how they've set it up. The  terminal area chart (TAC chart) for the bravo airspace contains VFR flyways and procedures including who to contact for clearance. So if you're interested you can get the TAC chart for Kobenhavn and look (usually) on the back of the physical chart where it has more info.

However, having said that: I think this VFR pilot accidentally flew into bravo airspace and will probably lose his/her license. Here's why:

Pilot did not have a Mode C altitude reporting transponder which is REQUIRED to fly in to Bravo.

From the report:

  Aircraft B was reported to fly at 4000 feet with no radar presented altitude readout.

I'm not sure how "Sweden control" hands off to Denmark, but if he's flying to bravo in Denmark you'd expect him to be talking to someone in Denmark, either the bravo airport's tower or Copenhagen Approach which is who the Boeing 737 involved in the incident was talking to.

If he was in Bravo legally he should have been assigned an altitude, heading and squawk code and ATC should have maintained separation between those two aircraft and the bravo controllers are the best in the world at doing exactly that. So I think he accidentally flew into bravo and was talking to the wrong controller.

Edited: To remove irrelevant detail about VFR altitudes above 3000ft AGL.


Does ATC react to pilot position reports? Following previous questions on position reporting:

When do pilots have to submit position reports?
What are pilot position reports?

Does Air Traffic Control somehow react to pilots submitting position reports, are they acknowledged or even repeated by ATC?

What is the exact phraseology of such an acknowledgement / confirmation (voice, CPDLC, and ADS-C)?

Edit & Update: The background of this question is commercial oceanic operations. As pointed out in the answers, there are multiple different position reports. This question mainly focuses on oceanic position reports via voice & CPDLC.

I controlled non-radar airspace for about 2.5 years.

On your end, we’ll probably just say “roger.” We may add instructions to report a future point, or a control instruction.

On our end, we would be using that information for any required separation. For example, we may update a flight strip with your groundspeed, recalculate how we anticipate bring traffic across that same point, or change how we are protecting airspace or altitudes according to where you are. It varies depending on the environment and traffic, but the general concept is ATC is protecting the entire block from where we last knew you were - your previous position report or where you were last in radar contact - and your next reporting point. Your position report allows us to modify that protected area.

But little to none of that information will be relayed to the pilot, unless it is operationally necessary. Even then, it will probably just be in the form of a control instruction.


How is directional control during takeoff and landing maintained in tailwheel airplanes equipped with skis? Reading this question got me wondering: From what I've heard and read about taildraggers, brakes are needed during takeoff and/or landing rolls to maintain directional control and prevent a ground loop. At low airspeeds rudder authority is insufficient to keep the plane going in a straight line.
How is this achieved when skis are mounted instead of wheels? Is there anything special about skis that makes them more controllable  than wheels in these situations?

I have a fair amount of ski time on Cessna 180s and Citabrias. It's a bit like flying floats. The main thing is, you have no brakes.
For lateral control, the skis have varying amounts of lateral compliance depending on the snow compaction, so you slip and slide more or less for each situation, but generally, the laggy reactions makes it easier to control direction on takeoff and landing compared to wheels.  The compliance is like being on wheels on wet grass; instead of darting to the side when the plane swings, it just kind of sashays laterally giving you more time to make corrections.
You may have a ski on the tail, which provides a limited amount of steering control to the extent that the ski design is able to bite sideways (a little skeg on the bottom really helps).  A decent tail ski on lightly compacted snow provides pretty good steering control without having to use large blasts of power to blow the rudder.  Otherwise, you are dependent on large blasts of power to blow the rudder to turn.
On ice or very deep powdery snow, you will be depending more on power to turn, and this is quite a challenge because the shot of power to get the tail to swing to turn also accelerates you forward, and remember, you have no brakes.
Bottom line is you can't really maneuver in tight spaces when on skis without using huge bursts of power, and annoying the local owner whose airplane may be in your prop wash, so it requires a lot more preplanning and thinking things through.
Some airplanes do without a tail ski, keeping the normal tailwheel, and this makes it easier to maneuver on compacted snow where the tire has some bite.  On deep loose snow, the tailwheel becomes an anchor, and you have to lift it out of the snow with shots of power and elevator, on top of lots of rudder to try to maneuver.  That can get exciting.  A tailwheel-only ski plane in deep snow is a pain.  For aircraft with wheel-skis, you normally see a tail ski with a penetrating wheel to do double duty.
So, you have no brakes. So you have to do run-ups on the move, either in a big circle if you have the space, or on the takeoff "roll" if you don't.
Then there's landing at the end of a sunny warm day on a compacted runway and the temperature drops below freezing in the late afternoon as the sun sets, and the runway has a bit of a downhill slope to it, and it's essentially compacted snow with an ice glaze.  Did I mention that you have no brakes?  Been there, done that.


Hydro-pneumatic fuel controls and hydro-mechanical fuel controls What are the advantages and disadvantages of the hydro-pneumatic controls against the hydro-mechanical controls?

They are actually the same thing. Hydro mechanical fuel controls often include the use of pneumatic pressure to regulate the fuel flow. Here’s an example of a simple one: http://blog.covingtonaircraft.com/wp-content/uploads/2015/08/fuel-control-unit-pt6a.gif

The mechanical part is the input of rpm by a shaft connected to the compressor spool. The pneumatic part is the P3 (compressor exit pressure) input.


IFR Currency with a safety pilot who has a BasicMed Here’s my situation and question.  For my IFR currency, I’ve asked a friend to be the Safety Pilot.  He’s aptly qualified BUT he does not have the traditional Medical, but rather he has BasicMed.  My question is; Can I still use him as a Safety Pilot, without jeopardizing my IFR Currency?  If he’s deemed PIC, can I still claim the time and use the IFR work (approaches, hold, tracking, etc…) for my IFR currency?

FAR 61.113(i) authorizes flight as PIC when using BasicMed. Therefore, your buddy can act as safety pilot if he is also acting as PIC.

If you were acting as PIC, that would make your buddy SIC (as a required crew member), which still requires a traditional medical certificate.


Is it possible and effective to perform a forward slip in a large commercial jet? I'm wondering if it's possible to forward slip a large commercial aircraft, like the A320 or even B777, and if so:  is effective or useful, since most small aircraft which I gather do it have no spoilers for instance which large aircraft do?

It's it possible?  Yes, you would do it the same way as in any other airplane.

Is it effective?  Yes, just look at all of the fuselage area that is exposed to the relative wind.

Is it useful?  Not really.  With all of the other drag devices, you shouldn't really need it.

Is it recommended?  You would have to check the AFM.  I looked in the A320 Flight Crew Training Manual and there is no limitation against it, but if you need to slip then that's a strong indication of poor planning and an unstabilized approach which would require a go around.  Even at higher altitudes, it isn't very comfortable for the passengers!


What are the fatigue regulations in the US and Australia for military transport helicopters/rotorcraft? For transport category military helicopters, what are the fatigue regulations as specified by the US and Australian regulatory bodies?

I've managed to find that FAA has 14 CFR 29.571 (Fatigue Tolerance Evaluation of Metallic Structure) but this could just be for civil helicopters.

The US Federal Aviation Administration does not regulate aircraft owned and operated by the military services. I suspect that is the same situation with Australia's CASA.

Parameters for aircraft service life for military aircraft are defined by the manufacturer. The aircraft is designed to meet the requirements specified by the agency requiring the aircraft. This is usually expressed in flight hours, cycles or a combination of that and possibly other parameters.


Why are there so few high-wing jetliners? So far, we have only seen a few civilian jet transports with high wings. All of them BAe 146, Do 328JET, seem to be regional jets. Yet military jet transports are almost completely high-wing. Why aren't we seeing high-wing large jetliners?
Some advantages of high wings:

shorter landing gear
easier access to the fuselage
a better location for the center-of-thrust.
better stability
better ground clearance for upcoming high-bypass turbofans. Lack thereof caused the design changes that ended in 737 MAX crashes
Increased flap efficiency
better able to take advantage of strut-bracing, if any.

Some disadvantages:

less efficient location of landing gear. (probably not mounted on the wings)
more likely to tailstrike
passengers may mock
belly landings could be tricky
water landings may be even more tricky

I don't know how these pros and cons add up though. Can someone give some more info?

Large commercial aircraft have low wings

to easily stow away their long landing gears in the wing root,
to hide the wing spar carry-through below the passenger deck,
and to improve the accessibility of wing-mounted engines.

Long gears make it possible to stretch the fuselage and still be able to rotate during take-off. Stretching makes it possible to tailor one basic design to a wide range of sizes, lowering the development cost of a single aircraft.
Pressurized fuselages need to have their passenger floor a bit below the center of the fuselage tube, leaving ample space below for cargo, systems and structure. Placing the wing high would produce a hump on the fuselage, which adds wave drag at the transsonic cruise speed of typical airliners.
The low position of the wing-mounted engines makes them much better accessible for maintenance; a major reason this configuration was selected in the early jet transports. Civilian freighters use mostly converted passenger planes, and their small number precludes custom designs. Initial concerns about foreign object damage (which resulted in a number of early jetliners with tail-mounted engines) proved to be unfounded.
Large high-wing airplanes with their low fuselage position are easier to load and unload, at the price that the fuselage taper has to start shortly aft of the landing gear, so no stretching is possible. The military doesn't mind and prefers the high-wing variety. Also, the high wing reduces the risk of engine damage by foreign objects on improvised runways. That Lockheed likes to stretch their transports (C-130, C-141) anyway is the exception that proves the rule.
Turboprop-powered civilian airplanes may have a high wing in order to provide more space for the propellers. Here, the fuselage-mounted landing gear can be made short and light (which is how the Do-328 JET evolved). Still, both versions exist. And the ones where the engineers did not know how to attach a jet close to the wing*.
Aerodynamically a mid-wing position would be best. This is used when the payload is compact and needs little space, or is hung externally. In bombers, in other words. Civilian transports will always either have a low or a high wing since nobody wants their passengers to climb across a wingspar carry-through on their way to their seat. At least since 1933.

*  To be fair to the Avro engineers: The high wing position gives that airplane a very high maximum lift coefficient without requiring slats.


What's the difference between a TSO Authorization and a letter of TSO design approval? FAA can issue two types of approval for a TSO part application: TSO Authorization and letter of TSO design approval. What's the difference?

Does it relate to the approval being design-only or production only?

Also, do other Airworthiness Authorities have a similar difference?

According to 14 CFR 21 Subpart O §21.601:

  (2) A TSO authorization is an FAA design and production approval
  issued to the manufacturer of an article that has been found to meet a
  specific TSO;

  (3) A letter of TSO design approval is an FAA design approval for an
  article that has been found to meet a specific TSO in accordance with
  the procedures of § 21.621;

  (4) An article manufactured under a TSO authorization, an FAA letter
  of acceptance as described in § 21.613(b), or an article manufactured
  under a letter of TSO design approval described in § 21.621 is an
  approved article for the purpose of meeting the regulations of this
  chapter that require the article to be approved;

I don't know much about this, but it looks like a TSO Authorization is for domestic (US) manufacturers, and a letter of TSO design approval is for foreign manufacturers who want to import their products into the US. See 21.621:

  §21.621   Issue of letters of TSO design approval: Import articles.

  (a) The FAA may issue a letter of TSO design approval for an article—

  (1) Designed and manufactured in a foreign country or jurisdiction
  subject to the export provisions of an agreement with the United
  States for the acceptance of these articles for import; and

  (2) For import into the United States if— [...]

And the FAA's page on it says:

  What is a letter of design approval?
  An FAA design approval for an article manufactured outside the United States that meets a
  specific TSO.

I have no idea about other aviation authorities, but I assume there are similar regulations in other countries because the same general issue exists everywhere: how do you ensure that both manufactured and imported aviation components meet all required standards?


What are the differences and benefits between/of time-based vs distance-based separation? This video suggests a time-based approach to landing aircraft separation is preferable to the distance-based standard commonly used.  It advertises a greater arrival volume at airports, as strong headwinds can delay the time between aircraft landing.

What are the pros and cons for a change in standard?  Under TBS, aircraft would be spaced more closely (distance-wise) on approach during strong headwinds.  Does this present a possible hazard to trailing aircraft if something goes wrong late in the approach (like this runway incursion?)

There is more information available from NATS on the website on Time Based Separation [TBS] and from a very descriptive Infographic on TBS PDF. While Heathrow (EGLL) is the first airport where this is being researched and tested, there are als other works, such as a research paper called Potential Benefits of a Time-based Separation Procedure to maintain the
Arrival Capacity of an Airport in strong head-wind conditions PDF which applies TBS at Charles Des Gaulles (LFPG).

The main focus of using TBS is to increase airport capacity during strong headwind operations, which significantly decrease groundspeed and therefore traffic flow.

None of the papers I have found speak of hazards related to decreasing the lateral distance between flights. The general idea seems to be that the minimal safety gain accompanying lower groundspeeds due to strong headwinds (lower GS means lower closure rate to objects / stationary traffic on ground) can be partially sacrificed and offset by TBS to maintain airport capacity or reduce the impact of the strong headwinds on airport capacity. This sacrifice becomes available since stronger headwinds also aid the dissipation of wake vortex.

The below table is based on own calculations, assuming constant approach speeds.
It should show you how the time to cover a set distance increases with decreasing ground speeds, which means that e.g. it takes longer to cover 3nm to reach the runway threshold. Reducing the lateral separation (the values chosen are deliberately a bit extreme, as none of the papers mentioned a formula to calculate TBS distances) reduces time to cover the distance, but covering 2.5nm at 130 GS is becoming quite close to 3nm at 150 GS.

+-----+-----+-------+-----+
| GS  | 3nm | 2.5nm | 2nm |
+-----+-----+-------+-----+
| 150 |  72 |    60 |  48 |
| 140 |  76 |    64 |  51 |
| 130 |  83 |    69 |  55 |
+-----+-----+-------+-----+


If an aircraft has two altimeters what is the allowed difference between them? If an Altimeter must be within +/- 75 of known field elevation, and the aircraft has two altimeters, one could be +74 while the other could be -74 and both would be within 75 of known field elevation, but 148ft apart from each other.
I've heard some people say the two altimeters must be within 75 feet of each other, but if this is the case, then the first rule can't be correct.
If ALT1 was -74ft from field elevation and ALT2 was -148ft, then they would be within 75ft of each other, but it would violate the first rule as ALT2 would be -148ft from known field elevation.
It has to be one or the other, it can't be both rules.  I think the second rule of within 75 feet of each other is just made up, but I wanted to check to see if anyone has a source for that rule.

In flight, where there is no field elevation to compare to, tolerances are specified as "between the 2 altimeters." On the ground, they also must both be within 75' of the known field elevation.
Different systems may specify different in-flight tolerances, which may also vary somewhat with altitude.
See also, What is the maximum allowed difference between two altimeters for flying in RVSM airspace?


What is required to fly over Cuba enroute to another country? I understand that you need to get an overflight permit before entering Cuban airspace, even if you aren't landing there.  How do you go about getting permission to overfly them enroute to another country?

Updated now that flights to Cuba are allowed by US operators.  What has changed, and what are the requirements now?  Can we pay them directly yet?

The IACC navigation fees are approximately $170 for a small jet, plus there is a service fee to issue. There is a full list at World Air Operations and you can in fact order the permit for Cuba online there too.


Which airliners could survive an EMP pulse? The incredibly bad, postapocalyptic tv series Revolution begins with a mysterious event that causes all electrical systems to fail all over the globe.  Even batteries don't work anymore.

In the first episode, after the "event" airplanes immediately start falling out of the sky in flat spins.

This had me thinking: which airplanes could survive an EMP-type event (FN1) that fries all electronics and renders electrical systems unusable?  This means that even RATs would not be a viable choice.

Piper cubs and other single-engine planes with purely mechanical linkages could still keep on gliding and land safely.

I don't think any large airliner currently flying could make it. Could even a B-17 or DC-10 make it with no powered electrical systems -- just on unpowered hydraulics alone?

Bonus question: if they did fall out of the sky, I'm assuming it would be in lawn dart mode and not in flat spins?

Footnote 1: While the apocalypse event in Revolution turns out to not be an EMP, you can assume it was something similar for the purpose of this question.

Older airliners use hydraulics and cables attached to the pilot controls. Some RATs power the hydraulics directly as well so limited control is still possible then. The pilots would get a workout but the plane would safely touch down.

However planes with entirely fly-by-wire systems (no current airliner is completely fly-by-wire) will be completely uncontrollable apart from shifting weight and would glide to the ground. They are made stable so they won't just enter a spin and pancake into the ground.


Do stealth airplanes need to limit contrail generation? Stealth aircraft have low visibility on radar.

I assume that they strive to achieve low visibility optically as well, e.g. spend some effort to not stand out too much visually from the surroundings.

A condensation trail (during daytime against a bright sky) could definitely make an invisible aircraft visible.

So what do stealth aircraft do against condensation trails?

Do they have technology aboard to avoid or minimize them?  Or it just a matter of choosing the right conditions (clouds, humidity, altitude, temperature) to fly?

Do stealth airplanes need to limit contrail generation?

Not just stealth aircraft, most military aircraft are required to avoid contrails. Contrails form due to moisture in the aircraft's exhaust. A tried and tested method by NASA is NOT to fly in regions of air that support contrail formation.

Ophir's Pilot Alert System which is used by the B-2 stealth bomber uses LIDAR (light detection and ranging) to differentiate contrails from clouds and tells the pilot to change his altitude as/when necessary.

That being said, it is essential to remember that though contrails are visible to the naked human eye they are NOT visible to Radars. Ergo, until the stealth aircraft is really close (assuming it is on a SEAD/DEAD mission) one cannot see the contrails and by the time they do, it is too late. Moreover, stealth aircraft generally operate during night when contrails are less visible.

  Stealth aircraft have low visibility on radar.

Not necessarily. VHF radar should be able to detect them at long range. Moreover, RCS of aircraft is a complex phenomenon, depending on many stuff (frequency, aspect angle, polarization of signal etc). You will never find a "static" figure for this.


Could the Concorde reliably land with all engines out? The Concorde was designed to fly at supersonic speeds; because of this its delta wings produce more drag at subsonic speeds. My understanding is that delta wings can produce a large amount of lift at high angles of attack. But is this enough to overcome the other obvious difficulties of an all engine out case caused by, for example, fuel leak?

In theory yes.  The loss of the engines will mean you also lose the generators and hydraulic pumps, but Concorde was equipped with a RAT which drove it's secondary and emergency hydraulic systems, so control would be possible.

Having never flown Concorde, but familiar with the flight characteristics of supersonic, high performance aircraft, I would guess such a forced landing would be flown at a steep angle of descent and at higher speeds say around 220-230 kts with leveling out in a shallow descent and roundout at or very near the threshold, placing the aircraft down at Vref in 1000-1500 feet thereafter.


Why do compressors constrict flow if this decreases pressure? An axial compressor (and a ramjet intake, for that matter) is commonly depicted as decreasing the volume of air travelling through as we move closer to the combustion chamber. In axial compressors, either the rotor shaft / cone diameter expands the further along we go (Fig. 1), or the compressor housing squeezes in towards the shaft (Fig. 2).

Intuitively, this makes sense—if a gas is forced into a smaller volume, then it must have a higher pressure. Yet, doesn't the Venturi effect play a role here, as well? Shouldn't the static pressure decrease when the flow is constricted, as it is in these compressors? If so, why are they designed this way? Why not have the compressor diffuse air by increasing the volume instead?

Your understanding of Bernoulli's equation is correct, but the situation in a compressor is more complex, because energy is being added by the rotating blades.

When subsonic flow decreases in speed, and no energy is being added, the total pressure remains the same. This means the static pressure must increase,  because the LHS of Bernoulli's equation isn't changing:

Pt = Ps + 1/2 x rho x velocity ^ 2

But, in the compressor, the rotating blades are adding energy from the mechanical work they are doing on the fluid, and hence the total pressure increases. So, while the above equation still holds, the LHS is now increasing. The static pressure is then given by the isentropic compressible flow equation:

Pt = Ps x (1 + 0.2 x Mn^2).

When someone talks about "pressure" changing, they need to be very clear if they mean static or total pressure.

What the compressor is doing, is increasing the total pressure. Total values are the measure of energy in the flow. But because the Mach number stays about the same from compressor inlet to exit, the static pressure goes up also. But, this isn't really important, increasing the total pressure is the significant factor. Total values represent the energy content of a fluid, because as you can see in Bernoulli's equation, the energy content can be traded between the velocity term and the static term as the fluid speeds up or slows down, but this is just shifting energy from one form to another, it's not changing the total energy content.

As the air in the compressor is being compresssed, it actually needs less space, as your intuition would suggest. A complicating factor is the air temperature is also increasing, so it's not just the same volume of air at only a higher pressure. But, if the compressor expanded as you suggest, the velocity would decrease too much, and then the air flow over the rotor and stator blades would be too slow. This would cause them to loose their aerodynamic performance. The rotating blades would be ineffective in adding energy, and the blades would stall, as the rotational velocity would be too high in comparison with a low axial velocity. A high rotational velocity of the blades and low axial velocity of the air makes the angle of attack of the air on the blades increase. They stall like a wing on an aircraft going slow at a high angle of attack. When the air in the compressor stalls, it no longer wants to flow in the direction of increasing pressure towards the combustor. It reverses direction, and flames can even come out the front of the engine. Not good!


Why is a rectangular wing with winglets not better than an elliptical wing? Why is a simple rectangular wing with winglets not better than an elliptical wing in terms of induced drag and produced lift?

If using Prandtl's lifting line theory, then mathematically/analytically, ignoring issues of wing weight that lead to bell shaped lift distributions and other sorts of intrusions of reality (e.g., stall behavior) the elliptical wing with the elliptical lift distribution is optimal for minimizing induced drag given a fixed wing area.

You can get an elliptical distribution of lift from a rectangular wing via twist, winglets, or other mechanisms, but it will only be elliptical at one cL value. At other values, it will not be elliptical, and thus suboptimal.


What are advantages and disadvantages of Rotax and Lycoming engine designs? I am wondering what are advantages and disadvantages of these two designs, e.g. Rotax 912 vs Lycoming O-235, compared to each other. At first glance they are pretty similar (both are 4-cylinder, horizontally opposed, with carburetors, naturally aspirated, with similar horsepower output etc.) but there are also some differences (engine displacement, maximum RPM, preferred fuel, oil system and consumption etc.) Can someone explain pros and cons of both designs?

The biggest difference between these two engine designs is that the rotax contains a reduction gearbox which allows it to turn faster and hence develop more power per cubic inch of displacement, and the lycoming is a direct drive engine limited to a rotating speed that maintains the  prop tips subsonic. This gives the rotax better power-to-weight ratio  but causes it to run hotter and shortens its time-between-overhauls. In addition, the gearbox itself requires overhauling which adds to the overhaul costs. In practical terms, air-cooled & geared engines for GA aircraft have not proven as popular as direct-drive engines in similar applications; in fact it is common to replace geared engines with direct drive engines with larger displacement to improve reliability and reduce rebuild costs.


Under what circumstances is an FAA accident report required? Under what circumstances is an FAA accident report required?  For example, if two planes are pushing back from a terminal and their wings collide is an accident report always required or does it depend upon damage done to the aircraft?

Generally you do not notify the FAA, you notify the NTSB (the relevant regulations are in 49CFR, specifically 49CFR830).

If you notify the FAA they will contact the NTSB, because the NTSB is the agency charged with investigating aircraft accidents.

If you crash in a cornfield somewhere and notify the NTSB they will probably ask the nearest FSDO to send an investigation team (unless you're a major airline or a fairly high-profile incident).

So ultimately it doesn't much matter which agency you call, but you should be calling the NTSB.

With the administrative stuff out of the way, the reporting requirements are also in that same section of 49CFR. Basically they say:

You are required to notify the NTSB "immediately, and by the most expeditious means available" of any aircraft accident, which is defined as:

  …an occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight and all such persons have disembarked, and in which any person suffers death or serious injury, or in which the aircraft receives substantial damage.

You are also required to notify the NTSB (again, "immediately, and by the most expeditious means available" of any incident (something that's not an accident as defined above) which meets the following criteria:

  Flight control system malfunction or failure;
  Inability of any required flight crewmember to perform normal flight duties as a result of injury or illness;
  Failure of any internal turbine engine component that results in the escape of debris other than out the exhaust path;
  In-flight fire;
  Aircraft collision in flight;
  Damage to property, other than the aircraft, estimated to exceed $25,000 for repair (including materials and labor) or fair market value in the event of total loss, whichever is less.
  Specific requirements for aircraft with a takeoff weight above 12,500 pounds
  Release of all or a portion of a propeller blade from an aircraft, excluding release caused solely by ground contact;
  Specific requirements for "glass cockpit" displays.
  Specific requirements for TCAS advisories.
  Damage to helicopter tail or main rotor blades, including ground damage, that requires major repair or replacement of the blade(s);
  Specific requirements for air carrier blunders like landing on the wrong runway.

"Immediately and by the most expeditious means available" basically means pick up the telephone and call them: They don't want you dispatching a letter via Pony Express that's going to take a week to get to the NTSB's headquarters while the aircraft is sitting in a field exposed to the elements with evidence literally washing away in the rain.


Do landing strips suffer from landing wheel tire tracks? I've now seen several landing strips up close and there are lots of tire tracks from planes' landing wheels. I wonder if it somehow modifies the properties of landing strips to make for poorer landing conditions.

Do landing strips suffer from lots of tire tracks?

It does indeed degrade performance, and runways (and their lights) have to be routinely cleaned of rubber. The FAA specifies safe friction levels.

Wikipedia has this to say:

  The build up of rubber affects the level of friction of the runway, most noticeably as a reduction in braking and ground handling performance. This can lead to incidents such as runway overrun or a lateral slide off the runway.

Some runways are particularly poor:


Should you read back the QNH from an ATIS broadcast? A typical ATIS broadcast includes the QNH ("altimeter" for the cousins).

My habit is to read this back since I have effectively been given the setting by ATC and it is required for my startup. For example:

  Finden 37 with information Delta, the QNH 1022.

I can't find any reference on whether this is required or not.  Additionally, do any CPLs or ATCOs on here consider this to be good or bad practice?

If someone wants me to tag with a jurisdiction, then it would be UK CAA since that is where I fly but I am interested in all responses.

Uk CAA CAP493 Section 3 Chapter 1 Paragraph 11.4 states :

  In the case of a departure ATIS, controllers must obtain a read-back of all relevant altimeter settings contained in the broadcast, unless the setting will also be passed in association with start-up or taxi clearance.

So from the point of view of the controller you are doing a good thing because you are saving him the expense of having to confirm that you have the right QNH on board.


How do engineers log airplane maintenance? Is there an encoding system that replaces the vagueness of natural language when it comes to logging aircraft problems or repairs that took place at a specific site on the airplane?

So, instead of someone having to enter a description like:
"Hydraulic fluid change at system ABC"
Which would be in their own native language and filtered by their own personal level of awareness, they could enter something like:
"GF65Z ABC"

Therefore, internationally, GF65Z could correspond to exactly that type of intervention with some hydraulic system and that would also make further investigation, in the case of some problem, easier.

Anywhere I can find more information about something like this?

Natural language is concrete enough for this purpose, the logs aren't meant for machine parsing but instead for pilots, inspectors and other mechanics.

Having such a code system requires mechanics to memorize all of the codes or have a massive list handy when filling out the logs.

Also making such an international code system requires agencies of all countries/manufacturers to sit together and set those codes for all possible maintenance actions. There is a very high chance an action will be missed so a natural language box for "additional comments" is still required. It also needs to be rolled out to the actual mechanics filling out the logs.


Is it possible to determine the approximate climb rate of an aircraft knowing its top speed, engine power and weight? Is it possible to determine the initial climb rate of a craft with a few key pieces of data such as top speed, engine power and weight?

For example the XB-42 was an experimental bomber design from the WW2 era.

Its top speed was 660 km/h at 7,145 meters.

Its empty weight was 9,475 kg and maximum weight was 16,194 Kg.

Its twin engines produced a total of 2,498 kW at takeoff and 2,834 kW using war emergency power.

Is that enough information to determine the approximate climb rate?  Thanks so much for any help!

Yes, but the process will be indirect. For a rough estimate, the engine power- which is the rate at which it can perform work- can be thought of as lifting the mass of the aircraft upwards against gravity. Since the units of power are foot-pounds per second and velocity is in feet per second, the engine power and the aircraft's mass can be used to solve for the climb rate in feet per second (be sure to use the right units for mass). this ignores airframe drag and propeller efficiency losses and as such yields an absolute upper limit for the maximum possible rate of climb. Your mileage will be lower!

Note that engine power depends on density altitude, and hence this estimate holds only for the density altitude at which the engine's power rating was measured & specified.


Is Part 91 Instrument currency for SIC similar to Part 135 requirements? Part 135 instrument currency in a jet aircraft requiring two pilots, requires both pilots to be instrument current. But how about the same situation for a Part 91 flight? Does the SIC need to have his 6 approaches with tracking, intercepting, holding etc... in the last 6 months?

Only if you fall under the Fractional rules (Subpart K).  Otherwise SIC currency requirements for turbojet airplanes are specified in 14 CFR 91.531, which requires you to be current via 14 CFR 61.55 and has no instrument currency requirement (although you do need your instrument rating to fly under IFR).


How can an aircraft’s maximum design operating speed be greater than its never-exceed speed? According to this AAIB report on a June 2009 mid-air collision between an RAF Grob Tutor and a glider, the Tutor’s maximum design operating speed (VDO) is greater than its never-exceed speed (VNE):

(5) In the case of aerobatic category aeroplanes, allow each occupant to abandon the aeroplane at any speed between VSO and VDO10;  [Quoting the applicable certification requirements for aircraft emergency exits; footnote in source.]

[...]
10 VDO is the maximum design operating speed which for the Tutor is 1.1 VNE or 205 kt.  [The report’s explanation of the aforementioned footnote.  The bolding is mine.  Everything I have quoted from the report comes from page 62 (numbered as page 52).]

The point of the never-exceed speed is, as indicated by its name, that this speed should never be exceeded in this aircraft for any reason whatsoever; as such, aircraft are generally designed and certified with maximum operating speeds well below VNE.  How can the Tutor’s design maximum operating speed be greater than its never-exceed speed?

Maximum design operating speed means "we calculated the aircraft will break apart at that speed". It's obviously higher than the never-exceed speed, which means "you can safely operate the aircraft up to that speed".

Key here is the word "design". It always means something along the lines of "we calculated it to break at that load, please never try". The quotient of design load and maximum expected/allowed load is called safety factor. In this case, the safety factor is 1.1.