Consequences of stalling while sideslipping in a glider? In a glider, sometimes it's useful to do a side slip with crossed controls. However, when that happens, the pitot tube angle is out of line and the ASI goes to zero, therefore losing any indication of the current airspeed until the sideslip is interrupted.

During this maneuver, what would happen if I were not to keep proper control of the attitude, and thus airspeed, and were to stall the wings? would the glider spin, or would the unusual attitude prevent it?

Edit: The duplicate question does not necessarily responds as it seems to address powered airplanes, where other factors may be in play. My question targets specifically gliders.

Yes if you were to stall the airplane while in a side slip it will probably depart, or start to depart, into a spin.  How aggressively would depend on the glider's actual stall behavior, some being more benign than others, but say you were in a glider with an abrupt stall with minimal warning and a sharp nose drop.  That sort of glider would spin if you didn't initiate recovery right away.

This isn't such a big problem, because the nice thing about gliders is you don't have power to confuse things when it comes to pitch attitude vs speed.  For a given configuration (weight/CG etc), if attitude X gives speed Y than you can be certain that any time you pitch to attitude to X you will get speed Y, with or without an airspeed indicator.

So, if you are on final at 50 kt, and want to side slip, just make sure you lower the nose a couple of degrees during the slip and control the pitch attitude, so that you will maintain somewhere around 50kt with the additional drag and there is very little risk of stalling and spinning. Easy peasy.

You also have the other impending stall cues, like softening controls, noise dying off, and such, so if you are aware and on top of things there shouldn't be a problem and it would take some ham fisted flying to really mess up.

If you are getting trained well, there should be dedicated no-airspeed instruction and practice and once you are considered a proficient pilot you should have no problem with flying safely with no airspeed for all maneuvers (if you sent me out in a power plane on some kind of wacky challenge, and told me I could only have one operating flight instrument, my choice would be a compass).


Is there a better solution than the U-shaped tailplane for this Airbus concept? Image source: airbus.com
This U-Shaped tail is from a concept aircraft from Airbus, I was wondering if there is an alternative but just as good solution to the U-shaped tail. Using a canard in the front for pitch and winglets on the wingtips?

In airplane empennage design, there is a thing called Tail Volume Coefficient. Mind you, there are no volumes here, but you are working with $m^3/m^3$. It is calculated as follows:
Horizontal tail volume:
$V_{HT} = \cfrac{ l_{HT} \cdot S_{HT} }{ c_{REF} \cdot S_{REF} }$
Vertical tail volume:
$V_{VT} = \cfrac{ l_{VT} \cdot S_{VT} }{ b_{REF} \cdot S_{REF} }$
here

$c_{REF}$ - mean geometric chord (~MAC)
$b_{REF}$ - wingspan
$S_{REF}$ - reference wing area
$l_{HT}$ - horizontal tail arm
$l_{VT}$ - vertical tail arm
$S_{HT}$ - horizontal tail area
$S_{VT}$ - vertical tail area

Now, with that in mind, you can have a perfectly reasonable cruciform solution, U-tail, H-tail, or triple-tail solution, or whichever.
However, freely choosing empennage configuration is not the only condition in design. Engineers likely have other requirements. These two vertical stabilizers (VS) look relatively slender. Perhaps a single VS would be too slender and cause structural issues, perhaps flight dynamics department required better yaw or sideslip control, in which two VSs would maybe be proved better. I think Russians designed An-225 with an H-tail to carry extreme payloads (like Buran), whereas Americans didn't modify 747's empennage for Space Shuttle carrying. There are a number of considerations here. One of which, mind you, is also aesthetics, especially for a passenger airliner.
So, is there a better solution than the U-shaped tailplane for this Airbus concept? It depends. There is no single universally best solution in these things.

Equations from S. Gudmundsson: General Aviation Aircraft Design


What keeps certified GA aircraft from being affordable? A personal (pipe) dream of mine is to own a new aircraft, but the costs for certified GA aircraft is borderline outrageous. A new Cessna 172, considered an entry level aircraft, can go for well over \$250,000 new. The Icon A5, an entry level light sport goes for about \$190,000 for the base model.

Not discounting the engineering process or tooling required, but what really keeps the price of these aircraft so high? Is it possible that a company could bring an aircraft to market that is comparable to the A5 below the \$100,000 mark? I find it hard to imagine that a company couldn't take an aircraft like the SeaRey, certify it, and get it out for a reasonable price.

So the question is, what are the factors that make certified GA aircraft so expensive, especially for established companies like Cessna, Piper, or others? Does the mere presence of an FAA certification command a premium price?

Low volume, high liability, and the overhead of certification all contribute to the high price of factory-new aircraft.

Certification

The process to design, build, and test an aircraft to receive a type certificate from the FAA adds time and cost to any new clean-sheet design (substantially more cost if the design is novel in some way).
The design and construction techniques must conform to the requirements in the FARs, and you have to demonstrate conformance to FAA inspectors (who will also want to see you assemble a few planes under their oversight before issuing you a production certificate to go ahead and make them on your own).

Volume

50+ year old designs like the Piper PA-28 and Cessna 172 that are still in production on an approved type certificate avoid that cost, but are still a low-volume high-touch product: Here's a wing being assembled.
Because of the relatively low demand (and thus low sales volume) the cost of the skilled personnel to build aircraft isn't spread out the way it is with cars (and the investment in large-scale low-touch automation isn't economically feasible). That drives up the manufacturing cost, and the price goes up with it to ensure the manufacturer is still making a profit.

Similar economies of scale affect all the third-party parts going into new planes as well: radios, instruments, lights, etc. that conform to applicable FAA Technical Standard Orders (TSOs) are rather expensive.

Liability

Finally, any new aircraft starts a new 18-year liability period for the manufacturer. Any accident that results in whole or in part from manufacturer errors, omissions, or negligence in a new aircraft can come back to haunt that manufacturer in the form of a lawsuit, so the cost of product liability insurance is baked into the price of every new aircraft. (After 18 years the manufacturer is off the hook thanks to the General Aviation Revitalization Act.)

All of these factors take the Searey from being a \$50,000 kit (airframe, engine, and propeller) to a \$150,000 factory-built Light Sport aircraft, and that is putting it on the market as a Light Sport aircraft under "consensus industry standards". Producing it as a Part 23 certificated aircraft would add the additional cost and requirements of FAA certification.
(I'm using the Searey as a convenient example since you mentioned it in your question and I could find kit and factory-built pricing easily, but other light sport aircraft available in both kit and factory models seem to stack up similarly. I don't know of any that have been subsequently "upgraded" to a Part 23 aircraft: Only a few manufacturers have successfully launched that sort of product, and those command rather substantial prices on the new market.)


What are the FAA regulations on operating UAVs in class E airspace above FL600? What are the regulations on flying UAVs (commercial or experimental) above FL600, i.e. in class E airspace above class A? I want to make a HAPS (High Altitude Pseudo Satellite) and operate it in the higher altitudes.

Is there a way to do this without a pilot's license (I don't know if I can pass TSA background checks)? How high do I have to fly to be above class A and in the class E airspace? Would you recommend launching from international waters? And how high should I fly to be in space or in completely unregulated and uncontrolled airspace?

The FAA limits drone operations to 400 Ft. so getting to FL600 is not really possible.

  Cannot be flown higher than 400 feet above ground level (AGL), unless
  flown within a 400-foot radius of a structure and does not fly higher
  than 400 feet above the structure’s immediate uppermost limit;

The FAA does offer a waiver process for flying drones beyond the regular part 107 rules. You can find all the info on that here. The request to operate in controlled airspace form does ask for a max altitude so its possible it can be requested.

However someone in Russia appears to have flown their drone up to FL330 so it may be allowed there.


Why would there be flight restrictions when the barometric pressure exceeds 31 inHg? FAR 91.144 states that flight restrictions may be issued by notam when barometric pressure exceeds 31" Hg.  Why would such a restriction be necessary?

It is because standard altimeters are not adjustable beyond this range. The AIM 7-2-2 contains information on how to handle it:

  When the barometric pressure exceeds 31.00 inches Hg. The following procedures will be placed in effect by NOTAM defining the geographic area affected:

  (a) For all aircraft. Set 31.00 inches for en route operations below 18,000 feet MSL. Maintain this setting until beyond the affected area or until reaching final approach segment. At the beginning of the final approach segment, the current altimeter setting will be set, if possible. If not possible, 31.00 inches will remain set throughout the approach. Aircraft on departure or missed approach will set 31.00 inches prior to reaching any mandatory/crossing altitude or 1,500 feet AGL, whichever is lower. (Air traffic control will issue actual altimeter settings and advise pilots to set 31.00 inches in their altimeters for en route operations below 18,000 feet MSL in affected areas.)

  (b) During preflight, barometric altimeters shall be checked for normal operation to the extent possible.

  (c) For aircraft with the capability of setting the current altimeter setting and operating into airports with the capability of measuring the current altimeter setting, no additional restrictions apply.

  (d) For aircraft operating VFR, there are no additional restrictions, however, extra diligence in flight planning and in operating in these conditions is essential.

  (e) Airports unable to accurately measure barometric pressures above 31.00 inches of Hg. will report the barometric pressure as "missing" or "in excess of 31.00 inches of Hg." Flight operations to and from those airports are restricted to VFR weather conditions.

  (f) For aircraft operating IFR and unable to set the current altimeter setting, the following restrictions apply:

     (1) To determine the suitability of departure alternate airports, destination airports, and destination alternate airports, increase ceiling requirements by 100 feet and visibility requirements by 1/4 statute mile for each 1/10 of an inch of Hg., or any portion thereof, over 31.00 inches. These adjusted values are then applied in accordance with the requirements of the applicable operating regulations and operations specifications.

  EXAMPLE-
  Destination altimeter is 31.28 inches, ILS DH 250 feet (200-1/2). When flight planning, add 300-3/4 to the weather requirements which would become 500-11/4.

     (2) On approach, 31.00 inches will remain set. Decision height (DH) or minimum descent altitude shall be deemed to have been reached when the published altitude is displayed on the altimeter.

  NOTE-
  Although visibility is normally the limiting factor on an approach, pilots should be aware that when reaching DH the aircraft will be higher than indicated. Using the example above the aircraft would be approximately 300 feet higher.

     (3) These restrictions do not apply to authorized Category II and III ILS operations nor do they apply to certificate holders using approved QFE altimetry systems.

  (g) The FAA Regional Flight Standards Division Manager of the affected area is authorized to approve temporary waivers to permit emergency resupply or emergency medical service operation.

  b. At or above 18,000 feet MSL. To 29.92 inches of mercury (standard setting). The lowest usable flight level is determined by the atmospheric pressure in the area of operation as shown in TBL 7-2-1.

So because most altimeters do not have this kind of range, the altitude readout will be inaccurate. This is especially problematic for IFR operations where you do not have visual reference to the ground.


What safety features prevent jets sucking in ground staff or equipment? There have been some gruesome deaths involving ground staff being sucked into jet engines, presumably because the engine thrust was set well above idle. Are there safety features (besides prudence on the flight deck) that are designed to mitigate this risk?

No, there are no safety features. Only safety procedures on the flight deck and on the ground.

Basically it all boils down to that nobody may go near any aircraft (jet or prop; they are both similarly dangerous) that may have engines running. When starting the engines, the pilots first turn on the beacon (the red flashing lights on the belly and tail), then check the ground crew has left and only then start the engine(s). And similarly upon landing, the pilots shut the engines down, wait a bit to let them spool down and turn off the beacons; then the ground crew should ask (via radio or the wired intercom connected to a socket at the nose) whether the engines are indeed off and only then they may start working.

Since start-up normally only happens after push-back, so away from the terminal, there is usually no risk then. Upon arrival however the ground crew needs to come to the aircraft relatively quickly and insert chocks to the wheels, so the correct procedures are important.

Here see a recent accident where ground worker was injured because the procedures were not followed (he was coming from the rear, so he was only blown away, not sucked in).

In that incident, the engines were at idle. They are still very dangerous in that case. I found an Airbus document which shows danger areas, for A320 with CFM56 engines, at idle as:

suction danger 2.2m (7.2ft) from engines (semicircle forward and to the sides of the engine and back to 1.5m behind the inlet) and
exhaust danger to 55m (180ft) behind the nozzles with 30° spread with exhaust velocity exceeding 105km/h (65mi/h) for 17m (55ft) aft of the nozzles.

At full power the suction area grows to 5.9m (19.5ft) radius and the exhaust danger to 275m (900ft) with velocity over 105km/h down to 150m (500ft) aft.


Does the F-16 have a movable inlet? Does the F-16 have a movable inlet? Everything else like the f15 has it does the f16?

No it does not. Simple oval shaped tube.

{Image from Wikimedia}


Is it possible to get permission for a GA flight to land at Reagan National Airport? If it is possible for a General Aviation flight to land at Reagan National Airport, what would you have to do?

If it's not, what kind of security clearance do commercial carriers and their pilots have to go though in order to land there?

The TSA operates the DCA Access Standard Security Program (DASSP), which allows general aviation flights originating at designated gateway airports to fly into DCA, however there are many restrictions in place, some of the most significant being:

You will need an FAA "reservation slot" to fly in to DCA
(This is required for all unscheduled flights into DCA)
You will need to submit a flight manifest & undergo TSA passenger/baggage screening
The flight crew will need to be cleared by the TSA (fingerprint/background check)
You will need to carry an Armed Security Officer onboard

So the answer is "Yes, you can do it, but you probably don't want to."
It also makes no sense to do it in something like a Cessna 172 as you're giving up at least one seat for the security officer. The program is really geared toward larger aircraft (business jets, etc.) transporting executives with a business reason to be in DC, like testifying before Congress.


Are there multiple reasons for the decrease in pressure over a wing? I'm aware that the decrease in pressure over the wing is due to the curvature of the airfoil which causes a pressure loss due to the spreading of the air as it is redirected.

But is it also due to the increase in velocity from the squeezing of the streamlines at the leading edge, like in a converging duct there is no redirection of flow but there is still a decrease in pressure where there is an increase in velocity?
Is this down to a reduction in the number of collisions per unit time?

The laws of physics don't work in isolation. They always apply all at the same time¹.

Most of them don't describe causality, but relations that are known to be always satisfied². If you know the speed increased, you can conclude the pressure decreased, but if you know pressure decreased, you can similarly conclude the speed increased. Neither is the reason for the other, rather the properties of fluids are reason both always happen together.

And last but not least the laws of physics as we normally use them are not fundamental, but are various perspectives on the underlying properties of the universe and as such have a lot of overlap. Therefore you can usually arrive at the same conclusions in many different ways (provided you properly account for approximations involved).

In this case, the air following the surface of the wing, pressure dropping, the flow accelerating and the streamlines squeezing are all aspects of the one behaviour of fluids—for which there is no simpler way to quantify than calculating the full set of Navier–Stokes equations (there are some simpler models like Kutta–Joukowski theorem, but can't start from the wing shape, but need some experimentally-determined characteristic values of it).

On the low level, pressure is the total momentum imparted by the collisions per unit time and area. So obviously if lower pressure is seen, the collisions must be fewer or weaker. In practice they are both³. However, there is no simple explanation for it on the molecular level either. It is a result of the complex dynamics that averages out to the Navier–Stokes equation on the macroscopic level.

¹ School lessons often fail to teach this by discussing each in isolation and never synthesizing. However, lift is surprisingly complex phenomenon, which requires applying many of them to model.

² Well, at least not observed not to be satisfied, because positive proofs are not possible.

³ The enthalpy decreases, which means the particles move slower and that means they hit both less often, and with less force. The density also decreases a bit, so there is a bit fewer of them per unit volume too. However, this is all easiest to derive from the macroscopic thermodynamic laws. We do have microscopic explanations for them now, but trying to compute anything directly at the low level is futile due to the vast numbers of particles involved.


What extreme measures might a pilot take to avoid extreme weather? What kind of extreme weather would justify a pilot of a commercial airliner taking avoidance measures to the point of likely stall?

Any which the pilot thinks is more dangerous than the avoidance measures?

If you were driving at 100mph towards a wall which you reckoned had a 90% chance of a head-on collision, or could attempt to turn which had a 50% chance of throwing you off a cliff, which would you choose?

Any decision the pilot makes will be made on the basis of "Taking this action is a better option than not taking it".

The main weather which would likely cause this would be high enough levels of icing to be dangerous, or such severe turbulence that the pilot believes the plane will be "upset" enough to throw it out of the performance envelope. A combination of these may be present in a severe storm.


How should one fly the entry procedure to an approach when the hold is not aligned with the outbound course? Consider the following NDB DME approach into runway 08 at Jersey (EGJJ):

Let's assume we are coming in from the North and are currently cleared direct to the JW NDB flying inbound on a 180° track. Now we are cleared for the NDB DME approach. How should the entry into this approach be flown:

When reaching the NDB, immediately turn right to intercept the 246° outbound course. This seems to be prohibited by ICAO PANS-OPS because the difference between my inbound course and the outbound course is larger than 30°:

  Unless the procedure specifies particular entry restrictions, reversal procedures shall be entered from a track within ±30° of the outbound track of the reversal procedure. However, for base turns, where the ±30° direct entry sector does not include the reciprocal of the inbound track, the entry sector is expanded to include it.

(ICAO Document 8168, Vol 1 §4, 3.3.3.1)
Enter the hold with a direct entry and immediately follow the Alternative procedure by extending the outbound leg of the hold. This seems to be the best option, but I'm not sure if this would be expected without being explicitly cleared for the alternative procedure.
Enter the hold with a direct entry and after one racetrack when crossing JW fly a course reversal / alignment turn to the left. As far as I understand, this would be the normal procedure if the hold were aligned with (or within 30° of) the outbound course since no course reversal would be required any more. But in this case, it seems weird since there is nothing in the chart about an alignment turn.
Or maybe something else?

Here is what I imagine the options 1-3 to look like:

I flew many of these types of approaches in northern Canada from 1980 to about 1990. In my opinion Option "2" is the best, followed by option 1, but all three are possible.

It is my understanding that when cleared for an approach, you own the airspace, and as long as you stay in the "protected" airspace, you can do almost anything you like.


Are HUD systems available for light GA aircraft? Some other questions about HUDs and how they work got me thinking. Military aircraft have had reflector sights since before WWII, and full HUDs since the mid-70s. The very same display layout, sans targeting recticles, is fairly familiar to pilots of glass-cockpit aircraft, the primary difference being the representation of the artificial horizon (which, because the display is not a HUD and so not transparent, uses the blue/brown background from the analog instrument).

True HUD systems are starting to make their way into commercial airliners, and the technology is even seen in various cars (primarily luxury brands) as a situational awareness tool. So the question is, what types of reflector-sight flight display systems are available for light singles? I would assume a glass cockpit is a prerequisite to generate the digital display, but given that concession, it seems fairly straightforward to have a monochrome version of the PFD projected onto a glass plate instead of or in addition to the display on the LCD monitor. Has anyone marketed this? Are there disadvantages of having a HUD in a GA aircraft that I'm not thinking about? This sounds like a natural next step now that even entry-level LSAs are foregoing the traditional analog 6-pack for glass displays.

It looks like there have been several attempts at coming up with viable HUDs for light singles but none have, well, taken off (business jets are a different story):

The VirtualHUD company mentioned in this article doesn't exist any more
The G-HULP exists and you can buy it but I couldn't find any useful information about it or even the manufacturer's website

Since there's really nothing much out there, it suggests that HUDs for light singles are too expensive for typical pilots and/or just not useful.

Cost is always relative, but the standalone G-HULP costs USD 6,000 and that has to be compared to other, potentially more useful things like avgas (i.e. flying time!), avionics upgrades, ADS-B or just general maintenance.

But even if a GA pilot has nothing better to spend his money on, it isn't clear that HUDs are actually as useful as you might think. This article looks at a new Honeywell system for business jets that overlays a HUD view on the PFD, and they compared the landing precision of 'heads-up' (traditional HUD) vs. 'heads-down' (HUD on the PFD) pilots:

  A chart that showed landing points at the end of approaches flown by
  pilots using the two systems showed scattershot points with no
  apparent bias toward either system. Both systems allowed their pilots
  to fly very accurate approaches.

  This result, Ververs says, surprised the pilots in the study who had a
  lot of HUD time going into the testing. They had all assumed, she
  says, that the HUD would be the better technology. As far as the
  testing experience could show, it wasn’t better [...]

Of course that's only one specific testing scenario, but it's a very critical one because landings are when you really need to see and react quickly. Personally, I'm not convinced that focusing my eyes on the HUD for airspeed and then through the HUD to the runway would be any quicker or easier than just flicking my eyes between the airspeed indicator and the runway centerline. (Jan Hudec made the comment that focusing shouldn't be an issue with a "good" HUD, so this may not be an issue at all, at least in theory.)

And there are probably other issues with a HUD too, like making an instrument scan more complex; making the pilot focus his vision on the HUD rather than into the distance; or just being a general distraction.

There is an interesting alternative concept to a fixed HUD, by the way: wearable tech. Whether it's any more successful remains to be seen.


What are some first-order drag approximations for airframe/propwash interactions? What are some first-order drag approximations for airframe/propwash interactions, both for dynamic flight and for static thrust, in a traditional tractor configuration?

There is surprisingly little literature on that. This answer by @xxavier lead me to a very interesting paper in which the drag of a Luscombe 8b with and without thrust was compared. A very thoughtful way was used to arrive at zero-thrust numbers, and the result showed that the additional drag from the propeller effects was about 30% of the total zero-lift drag without thrust.

In the paper, the prop efficiency is 81% while the overall efficiency drops to 62% due to slipstream losses.


What throttle setting does an airliner use while cruising? As a passenger, I have always felt like the engine are not kept at take-off thrust/full throttle a few (tens of) seconds after take-off, and so for obvious reasons as fuel efficiency, engine wear prevention, noise control for population in airport area, and so on.

I have also read on this site or on excellent Twitter account of the A380 captain Dave Wallsworth lots of explanation about how to reduce the take-off thrust (eg. flex temp).

But I cannot find any information about the throttle level (N1 percentage may be more accurate) during cruise. My guess is it is not constant because of weight decreasing during flight due to fuel comsumption, but this is only a guess.

I know Airbus airliners have a "CLIMB" position on throttle which allow the autopilot to set N1 automatically to reach cruise speed, but I would like to know how N1 value evolves during cruise.

A320 throttle quadrant with lever at CLIMB position, with auto-throttle range:

(Above is the max cruise limit in standard ISA for the A320.)

It's 80.4% - 86.5% for the different weights and altitudes. Do note that 81% does not mean 81% of the available thrust. The maximum continuous thrust (MCT) at standard temperature is between 86% and 89% for the different cruise flight levels.

The colder the air, the lower the values, and vice versa for hot temperatures. If too hot above ISA, max flight level is limited for the higher weights due to MCT being the limiting factor.

For the A320 example, the thrust levers remain in the CLimb detent from thrust reduction to just before landing in normal operations.

For the 777-200, the range varies from 69% - 96.8% depending on the flight level and weight (with 86.8% - 94.7% being the optimum range). The wider range is due to the 777's wider payload/fuel range when compared to the smaller A320.


How does the FAA define fuel capacity for ultralights? Ultralights under FAR 103 are regulated to a capacity of 5 gallons. I'm wondering how exactly fuel capacity is defined, does it include fuel in the lines, and in the carburetor bowl or elsewhere or just the tank feeding the engine?

FAA Advisory Circular AC 103-7, Paragraph 19 has this to say:

  MAXIMUM FUEL CAPACITY OF A POWERED ULTRALIGHT VEHICLE.

  The maximum fuel capacity for a powered ultralight vehicle is 5 U.S.
  gallons. Any
  powered  ultralight with fuel tank(s) exceeding this capacity is
  ineligible for operation as an ultralight vehicle.

  a. Determination of Fuel Capacity.

  The total volume, including all  available space for
  usable and unusable fuel in the fuel tank or tanks on the  vehicle is
  the mtal fuel capacity. The fuel in the lines, pump, strainer, and
  carburetor is not considered in a calculation of total volume.


Why is air accelerating over the wing surface? I know that there are dozens of questions about lift generation here but after reading them I still don't understand everything. My question is: why does air accelerate over the (upper side) wing? I know that it accelerates because there is pressure differential etc. but why wouldn't the air just flow over both sides of the wing with equal speed?

The Abdullah's answer is correct to it's level of approximation, but I'd like to expand on why the pressure is reduced on the leeward side.
As the air encounters the leading edge, it is pushed out of the way. Due to first law of motion, it would like to continue moving outward from the wing and avoid the area just above the wing. But besides inertia, air also has viscosity, which prevents sharp changes in air velocity, so the incoming air trying to pass high above the wing drags the air near the wing along. But when the air just above the wing is pulled out aft, there is shortage of air just over the wing, which means low pressure.
This low pressure causes the air bend around the wing, and since it pulls air from all sides, accelerate as it enters the low pressure region over the leading edge and decelerate again as it leaves it over the trailing edge.
Without viscosity (e.g. in liquid helium) the pressure would not be reduced, because the oncoming fluid would just continue straight over the highest point and the area over the receding part of the upper surface would be filled with stagnant fluid moving with the wing. In fact that's exactly what happens in stall – as the curvature increases (due to higher angle of attack), at some point the viscosity is no longer enough to keep the air moving, the area over the wing gets filled with air just whirling around and not moving away, so there is no longer shortage of air, the sucking of oncoming air stops and the generated lift rapidly decreases – just the lower surface still generates some.


What is the difference between nautical air miles and nautical ground miles? What is a simple way to understand the difference between the nautical air mile (NAM) and the nautical ground mile (NGM)?
How does the wind affect the net displacement of the aircraft as that is the only differentiating factor between NGM and NAM? (NAM by definition does not include the vertical displacement or the altitude gained by the aircraft.)

For further reference to mathematical formulae defining the above terms:
https://www.theairlinepilots.com/forum/viewtopic.php?t=320
From my deep dive in the quest to unravel the mystery of NAM and NGM, with inspiration from the BELOW answers I'm able to conclude with a couple of points:

NAM and NGM are same if wind is still

NAM measurement is independent of the wind and depends solely on the movement of the aircraft relative to the air around it. NGM is a dependent quantity which solely depends on the wind ie. With a Headwind component NGM is lower than NAM and vice versa for tailwind condition.

The usage of NAM was most prevalent in older flight planning systems for long range cruise before the age of FMCs which do the same thing electronically, NAM provides a database of performance of an aircraft in various phases of flight independent of the wind, to which the wind correction maybe applied to determine the practical value.

A nautical ground mile is one nautical mile over the ground.  A nautical air mile is one nautical mile through the air mass.  This distance can be different because of wind.
For example:
If you are flying at 100 knots true airspeed in a zero wind condition, nautical ground miles will equal nautical air miles.
However, if you are flying at 100 knots true airspeed into a 100 knot headwind, your nautical ground miles will alway be zero, regardless of how many nautical air miles you fly for (at 100 knots).
Anything in between will result in some variance affecting the “net displacement of the aircraft”.  This variance can be calculated using the basic wind triangle.


What kind of warranty comes with a commercial aircraft? Just wondering what the warranty is like. Can an airline simply decide to give every single aircraft back for the money they paid? Assuming they were unhappy with the results.

Will the manufacturers cover any repairs and regular service of the aircraft for x amount of time after the delivery?

I have had direct experience with this and yes new aircraft are sold with a warranty like a car, say for 3 years or 5 years and x hours.  The OEM may maintain local service centers, and a/c under warranty may be sent there for moderate fixes, although most of the time the airline fixes the problem itself and charges back the OEM for labour and gets parts provided by Spares free of charge (to the extent it's worth their while to do so for labour chargebacks; sometimes the administrative hassle to recover, say, 5 manhours at an overhead allowance of 50 or 60 bucks an hour isn't worth the trouble).

In extreme cases problem aircraft have been known to have been taken back by the OEM to prevent an angry operator from canceling a large ongoing order, or some such situation where it's important to mollify the customer.

Sometimes the OEM will use in-house product support teams to go out and do more significant work on aircraft under warranty, especially if the airline doesn't have the resources in-house, for free.

The OEM's program office will have a warranty administration group that manages all this.  A significant sum of money is budgeted by the OEM to cover warranty reimbursements and you could say this is built into the price (I dimly recall that on the Regional Jet program there was a budgeted warranty allowance of about a quarter or half a million $ per aircraft, but it may have been more than that).

Once it's out of warranty, well, you're on you own buddy.  You'll pay for spares, and for support from the OEM beyond basic help desk advice.  Major mods may or may not be provided free of charge to out of warranty a/c, depending on how nearly broke the OEM is budget-wise, or how much the bad publicity will hurt.  An airline may get satisfaction, on old out-of-warranty costs it was unhappy about, as part of a package negotiated on a new aircraft sale.  This is common on re-orders where airlines add more aircraft to an existing fleet.

Airlines may also negotiate (if they're smart) "AD clauses" where the OEM agrees to pay parts and labour for work required under a mandatory AD, with it's own, later, expiry date.


How does a large cargo plane like the C-130 Hercules take off and land in such a short distance? So I was at an air show and saw a C-130J Super Hercules showcasing its capabilities.

The take-off distance it covered was amazingly short (I guess equal to fighter jets), even though it uses propeller based engines. The landing was also super short.

My questions are:

How does such a massive plane manage to take off in short distances ? Is it because it has four engines?
During landing, I couldn't see any thrust reverser (as in commercial jets) in play. What tech does it use to stop so quickly?

Assault Takeoff/Landing Technique

This is a significant reason for the C-130's performance that you witnessed. "Assault" takeoff/landing speeds are lower than normal speeds, and closer to stall speed. Also there are some weight limitations. Further, the crew must be specifically trained.

Stopping Quickly

Any idea of a smooth landing is thrown out the window. The intent is to "plant" the wheels at about 300 feet down the runway. That is, transition immediately from approach attitude to actually landing rather than assuming a touch-down attitude and letting the aircraft float down to the runway.

The nose gear is pushed to the ground and the instant the wheels are on the ground the props are thrown into full reverse, now pushing air forward. At the same time the pilot puts all his might into mashing the brakes. He would "stand on the brakes" as we say. The yoke is also pushed full forward which puts as much weight as possible on the landing gear. The anti-lock brake system is critical here, preventing skidding out of control and blown tires.

In Vietnam, in combat conditions, 130 pilots would put the props in reverse before touching down. If you've seen the video on YouTube of a C-130 landing on an aircraft carrier, they did it there too.

J's Props are a Huge factor

The performance boost of the J models thanks to the new prop and engine is amazing vis-a-vis the older models. But fundamental airframe limitations are still there. Nonetheless more blades (6 vice. 4) and the "un-ducted fan" design simply pushes more air.

Show Off Configuration

An empty airplane with a light fuel load of course maximizes the short takeoff and landing performance.

C-130 Has Fowler Flaps

Not blown flaps. Just because the props push air over the wing does not make it blown flaps. Otherwise, yes, the C-130 was given lots of flapage precisely for this purpose.


How much force is produced by control surfaces? Context:

For some context, I'm a game developer and I'm building a flight sim game. My goal is to have realistic -- not arcade -- physics. The game is in Unity. Unity handles the actual application of the forces -- I just calculate the numbers.

The forces applied to the plane are:

$F_T = \text{Thrust}$ applied to both engines directed forward relative to the plane
$F_L = \text{Lift}$ applied to the center of lift directed perpendicular to velocity
$F_{RR} = \text{Rolling Resistance}$ applied to the center of mass and directed opposite to velocity
$F_W = \text{Weight}$ applied down at the center of mass
$F_{AR} = \text{Air Resistance}$ applied to the center of mass and directed opposite to velocity

The center of mass is positioned slightly forward of the rear landing gear. The center of lift is slightly behind and above the center of mass.

I use a constant thrust directed forward relative to the plane, a constant weight force directed down (world), lift calculated with the below equations directed perpendicular to velocity, and drag directed opposite to velocity. I also have a down force provided by the elevators.

My plane is loosely based on an A320 using a wide variety of figures found online. The mass is $72,000 kg$, wing span is about $35m$, wing area is about $122m$, engine thrust is $110,000N$ each, rolling friction coefficient is $0.04$. The lift coefficient is taken from a table graphed against angle of attack. It looks something like the Cessna graph shown here. The drag coefficient is calculated based on the lift coefficient (formula shown here).

Here is a screenshot of the plane and the forces. Pretent it's an A320 -- it's just a placeholder for now. At the time of the screenshot the plane was travelling at $150kn$.

Issue:

When I apply full throttle to the engines, the plane accelerates as normal. However, upon reaching a typical airliner rotation speed of $150kn$, precisely nothing happens. The plane doesn't lift off the ground until reaching almost $300kn$ where $F_L$ finally overcomes $F_W$. The way I see it, there are two possible causes. First is that my lift maths is wrong, and second is the force provided by the elevators is wrong. I calculated lift as shown here in my other question.

This begs the question, how much force do the control surfaces provide? In particular, the elevators. I know the horizontal stabilizer acts essentially as an upside down wing where the elevators act like flaps/spoilers. I tried using the same lift equation but the force was much to high and the plane would spin uncontrollably on the spot. I also tried calculating (estimating) by hand the torque required to overcome the torque lift of the wing due to the center of lift being behind the center of mass, and then a bit extra to make the torques unbalanced causing rotation. However this was not enough force.

Similarly, how do I calculate how much force is provided by the ailerons, flaps and spoilers -- how do I model this mathematically? Does it just modify the coefficients of lift/drag or do I apply a whole new force?

From the OP, it seems like you are treating the aircraft as a point mass. As a point mass, you don't get the rotational degrees of freedom, so control surface can't be accurately modeled. In the case of takeoff, rotation is achieved via elevator up force, resulting in aircraft pitching up, increasing its angle of attack, resulting in increased the overall lift and achieving the initial vertical acceleration. In summary, you can't model it from first principle without the rotational degrees of freedom.

There are a few things you can do.

You can continue to assume point mass. You can assume some simplified parametric model for takeoff rotation. That is, the trajectory is a parametric relationship of airspeed, time and elevator. It's not a physical model and it won't be accurate to the magnitude of elevator application, but it may suffice. Once in the air, you can do the same thing with banked turn for aileron applications, and airspeed changes with elevator. Essentially, you are working with a performance model (see performance equations of motions), with artificial relationships for control surfaces.

The above may suffice if all you want to do is GTA style flying (as an aside, its takeoff behavior is terrible). It'll look like a plane flying, but won't feel like a plane flying to anyone who's flown a plane.

You can move up to six degrees of freedom. In that case, you'd need more than just lift, drag and thrust; you'll need moment relationships as well. I recommend you to give Etkins, Dynamics of Flight a read. You can skip directly to Chapter 4. You'd be in very good hands once you've read Chapter 4 and 5.


Can I log time in a Cri-Cri twin-engine aircraft? I was looking at potential experimental projects when I read this fascinating website about a tiny aerobatic-capable twin-engine airplane. It's light enough to be an ultralight, but much too fast:

Aside from the obvious fun of flying this little plane, I wondered whether:

I'd be able to log time in the Cri-Cri as multi-time? My guess is yes.
Assuming I'm MEL-IFR, could I log multi-IFR with a two-way radio, altimeter, Dynon-type AI, HI and at least one cert. VOR & glide slope? An approach cert. GPS setup would be too heavy I assume. My guess is this is wishful thinking...

What a positively delightful looking aircraft!

I see no reason you couldn't log time in this as multi-engine time - it clearly has two engines, with two separate sets of controls (at least throttles, from what I can see).

Similarly I see no reason you couldn't fly it IFR as an experimental aircraft, provided it's "properly equipped" (consult the FARs for all the details on what you need), passes an IFR pitot/static test, and has appropriate radios (Transponder which you'd likely need anyway, Com, and Nav).
Whether you'd want to take it up in real weather is another matter though :-)

For that matter if you want GPS you could certainly have it without much weight penalty: throw in a Garmin GNS 430W and cover the Nav/Com and GPS in one ~7-8lb box.  Whether or not that kind of investment in what's basically a single-seat super-ultralight is "worth it" is a judgment call only you could make, but it definitely seems possible.


What Makes G1000 NXi Different From G1000? The new displays are installed on the brand new Cessna aircraft and upgrade plans are ready.

But what is the difference from the G1000 that was there from the early 2000s? Is the tablet/phone compatibility (Which can be used for charts) what makes it different? I cant find comparisons on the internet.

In short. What makes G1000 NXi better than G1000?

The official Garmin announcement lists all new features.

The new hardware features are:

faster processors resulting in faster start-up, map rendering, etc.
more modern animations
a new design with better readability
LED back-lighting (increased display brightness, clarity and better dimming)
lower power consumption

The new software features are:

wireless connectivity (database updates, flight plan transfer and information shared with a mobile device running the Garmin Pilot or ForeFlight apps)
flight path for visual approaches (both for visualization and auto-pilot)
full map overlay on the HSI on the PFD
SurfaceWatch (similar to a RAAS)
full ADS-B compatibility

Further features listed are:

  Advanced Doppler weather radar capabilities, including ground clutter suppression and turbulence detection as options.
  COMM frequency identification displays the station ID, as well as frequency type.
  Display of sectional charts, as well as IFR low/high enroute charts on the MFD.
  NEXRAD weather radar imagery can be overlaid on the moving map and animated on the MFD, as well as the HSI map.
  Vertical Situation Display (VSD) incorporates terrain profile view on the MFD, taking into consideration the active flight plan, altitude constraints and winds aloft.
  Pilots can preview departure and arrival procedures on the MFD prior to loading and activating the procedures.
  Pilots can optionally overlay European Visual Reporting Points (VRPs) on the moving map, as VRPs are standard within the navigation database.
  Three-color terrain shading incorporates green, yellow and red contouring, which depicts the aircraft is 2,000, 1,000 and 100 feet above ground level (AGL) respectively.
  Aircraft maintenance personnel experience faster system software upgrades and streamlined equipment replacement.


RNAV (RNP) Approach Height Loss Question? While viewing the following approach chart, which is an RNAV(RNP) CAT C Approach, there are several landing minima, stating a HEIGHT LOSS OF 50' AND 150', what does that specifically mean?

The approach above appears to be associated with the Antonio Marino Airport, Colombia, South America: (I don't know if it is current or proposed)

Descent below the published DA/H is not permitted due to obstacle clearance requirements. Therefore, a "height loss" (amount of altitude expected to be lost during a go-around [missed approach]) is added to the minimums to account for this.

The first minimum on the chart is 6240 ft. with a 50 ft height loss added and assumes a missed approach climb gradient of 5%.  The second minimum is 6340 ft. with a 50 ft. height loss added and assumes a climb gradient of 4%.

The 50 ft. added for the height loss is based on the use of a "radio altimeter."

The third minimum on the chart is 6340 ft. with a 150 ft. height loss added and assumes a missed approach climb gradient of 5%. The other minimums, all with a 150 ft. height loss added, assume missed approach climb gradients as low as 2.5%.

The 150 ft. added for height loss is based on the use of a "pressure altimeter."

The chart below is from an advanced version of "Required Navigation Performance Authorization Required (RNP AR) Procedure Design Manual" ICAO Doc 9905-AN/471

NOTE: the added height loss for "radio altimeter" use (category C aircraft) shows 71 ft on the chart below.  The published height loss on the OPs IAP plate shows 50 ft.  I do not know why there is a difference unless the requirements are country localized or the ICAO document has been modified.


How does a UFO fly so fast? Now, we have seen the UFOs by US Navy's onboard cameras, they are so fast and they do change their directions very quickly. How do they do so almost breaking the laws of physics?

This is about 3 videos released by the Pentagon. The vehicles in those videos don't fly extraordinarily fast. The 3 videos in question show normal aircraft and a balloon. The reported speeds are incorrect due to imperfections in the equipment used and optical illusions.


Is it safe to fly on airplane with lithium batteries in cargo hold? Lithium-ion batteries have the tendency to go on fire.

I checked baggage policy of European low cost carriers (easyJet, Ryanair, WizzAir), and while spare batteries are banned from cargo hold, it seems that batteries in devices are allowed (also hand baggage could be placed in hold if there is no place in cabin).

If spare batteries are dangerous, aren't batteries in devices too?

A few incidents happended when lithium-ion battery exploded, and the fire has been extinguished by cabin crew.

Such fire could also happen in cargo hold. What's happens then? I've seen people question the ability of halon fire suppression systems to extinguish lithium battery fire, because it works by blocking oxygen from fire, while lithium-ion batteries do not need oxygen to burn:

  Halon basically works by displacing the oxygen that is feeding the
  fire - and won't work when the material that is burning can provide
  its own oxidizer. Li-O batteries fall into that category, along with
  things like ammonium perchlorate (used to make solid rocket
  propellant), gunpowder, and oxygen generation canisters. Once ignited,
  they will continue to burn until the fuel is exhausted....
  (http://www.pprune.org/australia-new-zealand-pacific/538637-melbourne-airport-737-cargo-hold-fire-poss-due-lithium-ion-battery-2.html)

Also this:
https://batterybro.com/blogs/18650-wholesale-battery-reviews/19673027-plane-safety-systems-are-confirmed-to-not-stop-lithium-ion-battery-fires

On the other hand in comments to this question: What safety differences exist between carrying laptops in checked versus carry-on baggage? people suggest that it will keep fire from spreading until battery extinguishes on its own.

Moreover checked baggage is not always handled gently by airport employees, which can damage electronic devices - and batteries in them, which makes them more likely to catch fire.

For me it seems like any airplane carrying electronic devices could go on fire at any moment, and each flight is as safe as the batteries it carries. On the other hand aviation has stringent regulation about using electronic devices on board out of fear of interfering with airplane systems. I guess that if lithium batteries were so dangerous as I think then they would be banned from cargo hold.

So is airplane crash due to lithium battery fire a real danger, or do I worry too much?
(I guess I'm a little nervous - I'm going to fly a third time in my life so far.)

No, it is not safe to fly on an aircraft that has lithium-ion batteries in the hold.  There is a commentary on FAA Safety Alert for Operators (SAFO) 10017 here, which was issued after the crash of UPS Flight 6.

Admittedly, this was a bulk load of 81,000 batteries on a cargo flight.  However a search for 'battery' on AV Herald shows between one and two incidents each month, of lithium ion batteries/devices igniting in the cabin.  These are only the ones reported on that website, we don't know how many may go unreported

The ICAO also considers Li-ion batteries a risk but as Simon Hradecky points out, there is a conflict between this safety advice and the security requirements that force passengers to check-in laptops, tablets etc on some flights.

Personally, I think that, whatever the ICAO, FAA and airline requirements, there are going to be some of these devices that get into the hold (people will forget that they left a battery bank in a bag and security will not recognise it on the scanner). We know that they regularly catch fire.  There are almost certainly going to be airliners brought down by this, it may have already happened - the EgyptAir MS804 fire hasn't been explained yet.


Why does the 737 Original have an explicit hydraulic-quantity indicator for only the A hydraulic system? The 737 (Original, Classic, NG, and MAX) has two primary hydraulic systems (A and B),1 which provide power to the aircraft’s flight controls and other aircraft components (like the wheelbrakes, landing-gear extension/retraction, and nosewheel steering).
On all 737s, the cockpit instrument panels have gauges which provide a readout of the pressure available in both of the primary hydraulic systems.2  Hydraulic quantity, however, is a different matter; on the 737 Original, the cockpit instrumentation features a quantity gauge only for the A hydraulic system, with the B system having to make do with a mere low-quantity warning light (the same type of indicator as with the standby hydraulic system, although on a different one of the instrument panels):

(Diagram originally by the National Transportation Safety Board, page 11 [page 29 of the PDF]; cropped and imageified by me.)
In contrast, the later 737 Classic has quantity gauges for each of the two primary hydraulic systems:

(Diagram originally by the National Transportation Safety Board, page 17 [page 41 of the PDF]; cropped and imageified by me.)
Why doesn’t the Original have quantity gauges for both main hydraulic systems, rather than just for the A system?

1: A third, standby system is unpressurised in normal flight, but can be activated by the flightcrew (or, in a few critical situations, automatically) in the event of a primary hydraulic failure; the 737 also has manual-reversion capability for the ailerons and elevators in the event of a complete hydraulic failure, one of only a few jetliners to still include this capability.
2: The standby hydraulic system, which is normally unpressurised anyways, merely has a warning light that comes on if the pressure within an active standby system falls too low.

Your question: Why doesn’t the Original have quantity gauges for both main hydraulic systems, rather than just for the A system?
On the B737 100/200 airplanes the system B hydraulic reservoir is filled from the system A reservoir.  So, when the system A gauge displays a normal quantity the system B reservoir quantity would also be normal (separate B quantity gauge not required).
If the B hydraulic reservoir "low quantity" warning light illuminated then the A hydraulic reservoir would be at a level of about 1.8 gals (balance line between the A & B reservoirs leaves fluid in the A reservoir if only the B system leaks) and its quantity gauge would indicate so. (and there would be a low quantity or total depletion of the B system reservoir also)
B737-300 airplanes and later models have a differently designed hydraulic system in this regard.


What are the visual differences between the F/A-18 Hornet/Super Hornet and the EA-18G Growler? I was looking at the Northrop Grumman website and came across the EA-18G Growler, which looks very similar to the F/A-18. What are the visual differences between the two?

You asked about visual differences. The main visual difference is that there are no guns on the EA-18G, just AIM-120 AMRAAM or AGM-88 HARM missiles. Other than that the visual differences are minimal. The airframe is still a F/A-18F Super Hornet, where -F stands for twin-seat. Engines are also the same General Electric F414-GE-400, however I suspect there could be some differences in regards to the engine auxiliary equipment, such as the electrical generator. I also suspect there is additional equipment added for the sole purpose of conditioning the electrical power and insulating everything to keep interference minimal. It is even possible that there are optical fibers in areas where on the F/A-18F copper cables are still used.

Main differences:

Dedicated electronic attack equipment, e.g. what makes the aircraft an EA-18G, has been put in the place of the cannon.
The EA-18G has one extra protruding antenna on the back, along with the satcom antenna behind it.
The missile launch rails on the ends of the wings seem to be permanently modified to support the ALQ-218 Tactical Jamming Receiver, which is the same pod as on the EA-6B Prowler.

Here is an image of the EA-Growler showing some of the external modifications and what they’re for:

Source: airforce.gov.au/Archive.org


How does the particular piece of flap behind an engine on a B777 work? On several B77 photos, I notice that flaps just behind the engines are not always coordinated with the others flaps. On this photo flaps are extended but not behind the engine whereas on this photo all flaps are extended. Given the position of this particular flap, I suppose there is something to do with the interaction between flaps and engine. Given the difference between the two photos, it may also have something to do with spoiler extension.

EDIT: OK the two photos are not the same plane, but I find a video where it is obvious this piece of flap is not always coordinated with the rest of the flaps. When looking at the video I first thought it was a flaperon, but after the flaps are extended, it deflects upward several times without making the plane banking.

It is called "inboard aileron" or "high-speed aileron" and is actually a flaperon. It will deflect with the flaps but not extend backwards. At high speed, the outboard ailerons are locked and all roll control is achieved by deflecting the inboard ailerons (and spoilers, if needed). This helps to reduce wing torsion and twist.

Background: Since the trailing edge's sweep angle has a break at the wing station of the engine, and since in Boeing aircraft the flaps extend perpendicularly to the hinge line, there must be a gap between inboard and outboard flaps, otherwise they would collide during extension. This gap is best placed in the station of the engine blast, and is filled with a simple hinged flap. Note that Airbus aircraft have rear-sliding flaps, which stay at a constant span location and can be adjacent to each other even at the wing station of the sweep change.

Boeing 767 from below. Picture by Adrian Pingstone (source)

The picture is of a Boeing 767, but shows the flap arrangement nicely. Note the offset of the forward and rear part of the Küchemann bodies which house the flap tracks.


Do rotorcrafts like helicopters have autopilots? Years ago, I had the opportunity to board a Bell 407 for a long distance flight and put every question related to helicopters that crossed my mind to the pilot when we were forced to land due to visibility issue and also while we refueled.

I realize now that I've missed something important: do rotorcraft including helicopters have autopilots like fixed wing aircraft do, or is that ruled out due to their peculiar flight mechanics?

Yes, helicopters can be fitted with autopilots. Some are very simple, others are quite advanced. The more advanced ones can, for instance, follow a pre-programmed route, climb/descent to a pre-selected altitude, fly an ILS approach, perform a go-around automatically.

They are not ordinarily found in small helicopters due to cost and lack of necessity. All modern offshore helicopters that I've encountered have them and they are used extensively. Usually they are engaged shortly after take-off and disengaged shortly before landing.


What is done to prevent the tail hook from bouncing off the carrier deck? At 2:20 of this video, it appears that the tail hook of the F7U-3 bounces off the flight deck a couple of times before catching a wire. Does this still happen with more modern fighters or has something been done to prevent this from happening?

Note: at some point after this, there is a fatal ramp strike incident.

The tailhook assembly on a modern carrier or terrestrial fighter has a hydraulic damping assembly which forces the hook to stay extended and dampens the impact of the hook into the runway or flight deck.  Without it the hook would bounce off the deck on impact and potentially strike the tail of the aircraft.

This was a major problem during early ship trials of the F-35C airplane the first time it went out to the boat, resulting in an unacceptable 30% boarding rate due to a faulty tailhook design.  The tailhook assembly has since been redesigned and worked well during later sea trials of the jet.

This damping assembly is quite powerful and can injure or kill careless personnel should the uplock accidentally disengage, hence the DANGER TAILHOOK markings on the aft fuselage of some navy aircraft.

The system will handle most landings; on occasion a pilot slams the jet down hard enough that the hook will jump off the deck missing all of the wires.  This is called a hook skip.  It is handled just like any other bolter: Full power at touchdown and go around to enter the bolter pattern for another try.


What's the speed callout by the PNF on airliners for? On all Airliners, there is a speed callout by the PNF at some point during take-off, usually at 80 or 100 KIAS.

Whats the reason for those callouts? And why are some at 80 KIAS and some at 100 KIAS?

This call serves two main purposes. The first is to verify that both airspeed indicators are showing the same speed. Since airspeed = life, it's best to find out that one of them is faulty on the ground rather than in the air.

The second purpose is to distinguish a high-speed rejected takeoff from a low-speed one. Below 80kts (or 100kts or another speed set by the manufacturer and/or airline), a takeoff would be rejected for almost anything out of the ordinary.

But rejecting a takeoff at high speed carries a lot of risk - like brake fires, tyres exploding, directional control difficulty, etc. So above 80 or so knots, a takeoff will only be rejected in the case of major failures. Some modern aircraft even inhibit minor warnings from appearing after 80kts until the aircraft is airborne, because rejecting the takeoff is not worth the risk, so don't saturate the pilots with unnecessary information.

This page goes into some detail about what you would reject a takeoff for at low speed vs high speed. The criteria may vary slightly amongst airlines but the general themes are the same.


About how many aborted takeoffs are there each year in commercial aviation? Watching this sim of a 777 engine failure on takeoffs got me wondering about RTOs, and how often they occur.

The interest was further driven after reading a comment by N1755L that might underline jeopardy in the process:

  If anything is to go wrong with the engines at close to the
  "not-enough-runway-left-to-safely-stop" point, the pilots have only
  10s of thousands of seconds of time to assess the situation and decide
  which decision is the correct one (attempt a stop, or continue the
  takeoff and get into the air).

Perhaps that's exaggeration.  And surely the majority of rejected takeoffs occur at safer speeds.  There appears to be a few similar questions about emergency landings, but nothing on RTOs?

I did find this article from an Aero (Boeing) magazine indicating:

  Historically, the RTO maneuver occurs approximately once each 3,000 takeoffs. Because the industry now acknowledges that many RTOs are not reported, however, the actual number may be estimated at 1 in 2,000 takeoffs.

The article appears to rely on data a couple decades old.  But wondering if that would be a reasonable estimate today.  And, even better, if there's any data on the breakdown of RTOs by speed.

Whatever you've got will be of interest, whether the dataset is confined to specific countries or even airlines.

As off today (March 21st), Aviation Herald lists 26 rejected take-offs, in 2018.

It's 110 days since the start of the year. So that's 110/365ths, or 0.31 of the year. So, the whole year will have 26/0.31, or about 84 rejected or aborted take-offs.

This assumes, all are reported in Aviation Herald, which is probably not true, so the real average number is likely to be higher. But that's a rough starting point, and probably the best estimate you will get.


Do dark conditions due to high-altitude smoke prevent ultralights from flying? According to FAR103, you have to operate ultralights between sunrise and sunset, or between the times laid out in the Air Almanac (if you're in Alaska.) This means that the FAA has determined that certain lighting requirements exist for ultralight pilots, but has laid them down in a time-defined manner, instead of a lighting-involved one. Under normal situations, this is fine - you don't get enough eclipses, volcanic eruptions, or alien invasion fleets blocking the sun to make rules based upon luminosity.
At the moment, there are a number of arguments breaking out about whether Ultralights can fly in my area. It's just after noon, but because of the fires in California, high-altitude smoke and clouds are bringing lighting conditions to being comparable to 30 minutes post-sunset.
If the sun is up and pilots stay clear of clouds (and smoke plumes), and - of course - we're not violating a TFR, is the assumption that we can fly without a 3-mile visible light, or is there something in the FAA regs that deal with this situation?
To reiterate - we're not flying anywhere near the fires, we're not flying in a TFR zone or other controlled airspace, and we're not flying within a mile of a cloud or smoke plume.
Thanks...

The only regulations that apply to ultralights are in part 103. Apart from the obvious visibility and cloud clearance (103.23) and daylight (103.11) ones I see two others that could apply:
103.9(a):

No person may operate any ultralight vehicle in a manner that creates
a hazard to other persons or property.

This seems to be the part 103 equivalent of 91.13 (careless and reckless operations) and it's also written broadly. If you do go flying and something goes wrong, the FAA might argue that flying in marginal conditions was creating a hazard to other pilots or - if you lost control of the aircraft - to people on the ground. Whether or not that's plausible would depend heavily on the specific situation, of course.
103.21:

No person may operate an ultralight vehicle except by visual reference
with the surface.

In low light conditions with a lot of cloud and smoke around, it could be difficult maintaining visual reference.
So, if you're flying at noon, maintaining the required flight visibility, maintaining visual reference with the surface, staying out of TFRs, and not doing anything dangerous, your flight is probably legal.
But the important question here is "is it safe?", not "is it legal?".


How much rudder input does a Cessna 172 require during the take off roll? I am part of an open-source project developing a simulation of a Cessna 172P. We are tweaking our flight dynamic model at the moment and we are looking for feedback from people with real life experience on the 172. In particular, we would like to know how much rudder input does this aircraft require during a take off roll (with no winds) in order to keep it centred on the runway.

With several hundred hours logged on multiple variants of the 172, I would give the relative answer of ‘not much’.  In my experience a C-172 tracks pretty straight with only slight right rudder pressure needed on the ground roll.  It is much less than what is required for a C-182, 206, 210 or other high performance single engine Cessnas and much less that a lot of tailwheel airplanes I’ve flown.

It seems like in a 172 when you are brakes off and rolling, I usually rest my heels on the cockpit floor and apply a slight pressure on the base of the right rudder pedal with the ball of my right foot.  It is necessary as the plane will waltz to the left during the takeoff roll if you don’t.  But the force applied and the deflection of the right rudder pedal is light and limited, if you do it right.

A recommendation might be to send a developer down to a local flight school operating the C-172 and arrange to practice takeoffs and landings with a CFI so they can get an empirical sense for what rudder input is needed on a takeoff roll.


Weather Reporting of wind direction General weather reporting for wind direction in Australian Standard the degrees in wind direction identifies where the wind is coming from.

Is it the same around the world?

Yes, it is generally used that the broadcast wind is the magnetic heading for the direction the wind is coming from. This is because standard runway numbering is magnetic direction and pilots can easily determine the most appropriate runway given the wind.


Why do we use pylons to mount the engines on jetliners? This question focus on jet airliners.

The De Havilland Comet's engine were mounted inside the wing, the Concorde's engines were mounted underwing (as many jet engines) but without pylon. It seems jet airliners' engines are now mounted on pylon. That assumption goes wherever the engine is mounted (underwing or at the rear of the aircraft).

What are the advantages of doing so (aerodynamic, maintenance, safety,...)? Is there some drawback (must be minimal as this design is dominant)?

Note: I don't want discussion about where to mount engine (underwing as for the B747, overwing as for the VFW-Fokker 614, at the rear as for the MD-80, ...), I'm curious about why we use pylons for all this designs.

Engine placement was a tricky question when jets were introduced, and much has been learned since then. The initial idea was to mount them inside the fuselage or wing root. When they grew too big, they were closely mounted to the wing ("underslung" position, like in the Me-262, the Il-28 or the early Boeing 737).

However, the underslung position has two disadvantages:

More of the leading and trailing edges is obstructed, blocking space that would otherwise be used for slats and flaps. Consequently, an underslung position reduces maximum lift.
The center of gravity of the engine is too far back. Moving it more forward helps to place the center of gravity of the wing ahead of its elastic line. Bending will now create an opposing inertial moment, which is very helpful to dampen flutter.

Starting to move the engine downwards away from the wing initially increases drag, because now a narrow slot opens between both with a tendency to separated flow. Only when the engine is moved downwards enough, the drag of the wing-engine arrangement reaches its minimum. This placement was chosen in the next generation of jets like the B-52 or the Boeing 707.

Moving it still further down makes the pylon longer and thus increases the total drag again.

The big diameters of modern high-bypass ratio engines make it impractical to move it down enough to reach the drag minimum, but by moving it forward, the engine can again be lifted up, so a shorter landing gear becomes possible. Vortex generators are added if that pesky separation between engine and nacelle cannot be avoided.


What are the particular challenges faced when landing at Bristol airport (UK)? Earlier this year I returned to Bristol on flight TOM-6633, and like most landings at Bristol the passengers found the experience physically immersive, attention grabbing, and at least a little exciting - enough for the odd gasp and finally some small amount of scattered cheers and claps.

In layman's terms - the approach was characterised by the plane apparently hitting a very large number of considerable bumps, while wagging the wings up and down/rolling from side to side all the way in (trying to avoid the bumps, maybe?). Finally we got near the tarmac and the plane touched down "decisively", enough to make all aboard thankful for buttock fat.

So what are the particular challenges typically facing a pilot coming into Bristol (UK) airport?

Are these challenges considered fun by those folks in the front seats with the fancy hats and scrambled egg (ie: Pilots)?

I have flown into Bristol quite a lot, as I live near there. Most landings are boring, but with good views on a clear day.  Most landings are also from the east, on 27 as the prevailing wind is from the west.

On the fairly rare occasions when you come in from the west on 09 it tends to be in unsettled weather, as that correlates with easterly winds.  You're also coming in over the Bristol Channel (not renowned for good weather, at least at sea level). Final approach from both directions is over some low but lumpy hills, more noticeable to the west of the airport.

"Earlier this year" written in April suggests late winter/early spring, when we had some interesting weather brought in from the NE. With the exact date it might be possible to narrow things down.

Overall it's nothing special but it's perfectly possible for a few things to come together to make it more interesting.


What is the difference between redundancy and fault tolerance? What is the difference between redundancy and fault tolerance in the context of aviation ?

Redundancy is when there are multiple ways of doing the same thing; quite possibly by having multiple gadgets, or ways of interconnecting gadgets, that can perform the same function with the same or at least very similar fidelity even if a non-zero number of them fails. One likely effect of this is that there is no single point the failure of which will cause the failure of the entire system (no "single point of failure").

Fault tolerance is when the overall system can tolerate the failure of a component without going into a dangerous state, but it won't necessarily maintain the safe state by having full functionality or fidelity. The system may operate in a degraded state, but it won't immediately be in a dangerous state.

Redundancy can be a way of providing fault tolerance in the larger system, but redundancy on its own does not guarantee fault tolerance, particularly against all kinds of faults. It's only redundancy if each separate way of accomplishing a goal can function without the other ways of accomplishing the same goal. Fault tolerance is a result; redundancy is one way of achieving that result.

For example, there are two basic ways by which you can cause an airplane to assume a new heading; either by using the ailerons to bank, or by using the rudder to skid. Normally these are used together in a coordinated turn, but if you're really in a pinch, either one can be used to turn (but watch that stall speed). This is one crude example of fault tolerance, since either the ailerons or the rudder can fail and you are still able to make a turn (other effects of the failure, or other effects from the cause of the failure, notwithstanding). — Redundancy, on the other hand, would be more like if you had multiple independent sets of rudders and ailerons, each with its own, independent control system.

Commercial aircraft often have two or three of each flight-critical instrument; one for each (of two) pilot, and one backup instrument. For example, each pilot will have their own attitude indicator ("artificial horizon"), and they will have a shared instrument that can be used to, for example, determine which instrument is faulty if there is a disagreement between the two main instruments. This is an example of redundancy, because if designed right, any one of them can be used fully independently of the others to determine the aircraft's current attitude; the ability of the instrument to carry out the intended function at full fidelity does not depend on the others functioning properly, and there is hopefully no single failure which will cause two or three to fail in the same way, or at all.

An example where having redundancy doesn't necessarily provide fault tolerance can be having multiple hydraulic systems to control deflection of control surfaces. If all hydraulic systems are routed through a single location, and that location is damaged, there exists a possibility that you will lose all hydraulic systems at once due to that single failure. Therefore the hydraulic system is redundant but not necessarily fault tolerant.


What makes a smokeless jet engine? I was recently reading about the MiG-29 and its many upgrades, one of which (MiG-29M) was to smokeless engines.

What makes a smokeless jet engine? Is it just the fuel, or something about the way the engine works itself?

I've observed smokey engines were more common in the past and I'm wondering why that is too. Were they just easier to build for some reason?

Generally, smoke comes from incomplete burned fuel.

Normally, a jet engine burns a very lean mixture (due to turbine temperature constraints). Nevertheless, getting all the fuel to burn is a considerable challenge, primarily because the air/mixture flows faster in the engine than the flame front. So in order to provide stable burn, many tricks come into play: the combustion chamber expands after the compressor; there are special vortex generators that force the mixture to backflow and circulate; the air may be fed in stages along the chamber, etc.

This complicated gas dynamics is difficult to optimise, especially in the 70s when MiG-29's engines (RD-33) were designed. What usually happens is that there are pockets of over-rich mixture in the combustion chamber, and the extra fuel decomposes due to high temperature before it has an opportunity to burn.

From what I know, RD-33MK got a redesigned combustion chamber (amongst other things), but what exactly the changes are is hard to say. I can speculate that the source of the original problem was that RD-33 had an early example of the annular combustion chamber, which was not well studied then. But the problem was bad enough to make MiG-29 more easily detectable in visual fight.


How are aircraft separated at high altitude? When cruising at high altitude, a fixed-wing aircraft has less margin for adjusting its speed, due to the convergence of the stall "speed" and the overspeed limit:

If and aircraft has to be separated to prevent it to get close to a preceding, and ATCO asks to the second aircraft to slow down a bit, this may result in speed lower than the stall speed. On the other hand asking it to descend to a lower level may be costly due to fuel rate increasing.

What is the usual way to fulfill such separation need?

First of all, there is no such thing as a stall speed, but that is a topic of its own.

The ATC system has numerous ways of dealing with keeping aircraft separated, even at high levels. Let me try to summarize some of the most important ones, starting with the planning that happens when planes are still at the ground at their departure airport, working our way towards what happens when they do get (too) close.

Aircraft flying en-route will follow pre-defined routes (known as airways or RNAV-routes). Airways are like highways in the sky, and ensure that air traffic will fly in predictable patterns. This makes it a relatively simple task of predicting potential conflicts (a conflict in this denotes a situation where two or more aircraft get closer than the prescribed separation minima), because every flight will send a flight plan in advance, detailing the planner route, level and speed to fly.

In addition to just specifying lateral paths, airways also have vertical restrictions. This means that, when following a certain airways, you have to be flying in a certain range of vertical levels. It is quite typical for airways to limit traffic to fly at either “even” or “odd” levels. An even level in this case could be 34,000 feet, 36,000 feet, 38,000 feet and so on, while an odd level could be 33,000 feet, 35,000 feet etc. The general rule in most parts of the world is that airways going east will force traffic to fly odd levels, while airways going west will force traffic to fly even levels. This acts as a fall back procedures, which in principle means that two aircraft flying in opposite directions (one heading west, the other east) will never fly at the same level. Of course, it is easy to realise that this rule cannot cover every potential conflict.

We have now looked at some of the permanent infrastructure in the sky, but let’s zoom in further and look at the tactical aspect of flight planning, specifically, air traffic control.

Air traffic controllers, whose job is it to “maintain a safe and expeditious flow of air traffic”, use various means of technology to keep aircraft in the sky separated. In many parts of the world, their job is achieved by processing large amounts of information received in real time about air traffic using radar technology, and communicating with planes using radio. In places where no radar coverage exists, such as over large oceans, only radio is used. If no radar is available, pilots have to periodically call up on the radio and make a detailed position report, stating the location, level, speed and planned route of the aircraft.

Using either radar or pilot position reports, air traffic controllers will predict potential conflicts and try to solve them. (This is really where the essence of your question will be answered).

There are a few different separation minima. For the sake of simplifying the answer slightly, let’s assume we are working with only three:

vertical separation (the vertical space required between two aircraft who pass each other at (almost) the same position
horizontal separation (the horizontal distance required between two aircraft passing each other at the same, or near the same level)
time based separation (the minimum time required between aircraft following the same route, at the same level)

The vertical separation minima is generally 2,000 feet, however, as aircraft altimeters and radars have gotten more accurate, this has been reduced to 1,000 feet in many areas of the world (called RVSM airspace). Considering the fact that most commercial aircraft cruise in a level band between 30,000 feet and 40,000 feet, this gives you 10 different levels to work with (30,000, 31,000, 32,000 and so on). That actually means, that using vertical separation alone, it is possible to have 10 different aircraft at the same position, at the same time, while they are still separated.

Of course, forcing an aircraft to fly at a non-optimum level is not the perfect solution in terms of fuel efficiency, but it can often be the lesser evil (as opposed to forcing speed changes etc.)

Horizontal separation is achieved by (temporarily) changing aircraft routes. This might sound like a big deal, but in fact, potential conflicts are usually detected early enough that only very small adjustments are required. For two aircraft on intersecting tracks, if you detect the conflict between them 10-15 minutes in advance, it will often be enough to instruct either of the aircraft to adjust their heading by as little as 5 degrees to prevent the conflict. Once they are passed, you simply instruct them to return to their planned routes. This will only result in marginally longer flight paths, and so will only cause a small impact on fuel consumption.

Time based separation using speed control is probably the last resort in most cases. Instructing an aircraft to change it speed for a long period can have a serious impact on fuel efficiency. However, there is no need to worry about aircraft being forced to slow down enough to risk a stall (or speed up enough to risk damage to the aircraft). For starters, the pilot would never accept such instructions from air traffic control, and ATC would have to come up with another plan. In addition, air traffic controllers have been trained thoroughly, and are well aware of the performance limitations of different aircraft.

As with heading adjustments however, it might surprise you how little it takes to ensure separation using speed control. This is because most modern airliners actually fly at very similar speeds (usually between 75% and 85% the speed of sound). Changing the speed of an aircraft by just 1% will have a huge impact over a long distance, such as a flight across the North Atlantic Ocean. And so, as with levels, where in principle you have around 10 usable levels, considering 1,000 feet minimum vertical separation, you might also have about 10 different speeds to work with.

Overall, speed control is a very efficient way of maintaining separation that already exists (e.g. two aircraft following each other on the same route, at the same level), because instructing them to fly at the same speed will ensure that the latter aircraft never catches up with the former. Horizontal and vertical separation can be applied when separation needs to be established, for example between aircraft on intersecting or opposite routes.

Finally, let’s briefly discuss what happens if the system fails. That is, if air traffic control, for one reason or the other, fails to provide the required separation between two aircraft.

All modern commercial aircraft are equipped with airborne collision avoidance systems (ACAS), the most common form being the TCAS. TCAS equipment of two different aircraft in proximity to each other communicate directly to determine a) if there is going to be a conflict and b) how to best solve it. I won’t go into details here, but basically, if two aircraft are predicted to get too close, the TCAS systems will work out how to solve the conflict, typically by instructing one aircrew to descend while instructing the other one to climb. The fact that the TCAS systems communicate ensures that the same instruction is not issues to both different aircrews (imagine the airplanes flying toward each other at the same level, both being instructed to climb …). If the TCAS goes off, all instructions received from the TCAS system takes precedence over air traffic control instructions (much like air traffic control instructions take precedence over the general airways rules we covered earlier).

So to sum it all up – aircraft separation comes down to planning. If it is predicted, based on flight plans received from hundreds of different aircraft, that a certain route or level will be very busy for a certain period of time, then the system will simply not allow more aircraft to fly this way. They will be re-routed or their planned level changed, even before they leave the gate (allowing them to bring extra fuel, if required, to fly a slightly longer route or at a non-optimum level). Once in the air, air traffic control will make use of vertical, horizontal and time based separation, and, if all else fails, on-board computer systems will ensure that no collisions actually occur.

Edit:

A few references for further reading:

Mid-Air Collision - On the consequences of losses of separation, and how to prevent them

Conflict Detection - On detecting potential conflicts in the ATC system

ATM Sector Management - On predicting capacity and responding to demand in the ATC infrastructure

Flight Plan Filling - On ATC flight plans and their content

Guidelines for providing Radar Separation - A few example calculations

Airborne Collision Avoidance System (ACAS) - On ACAS, the last resort, when all else fails

Reduced Vertical Separation Minima (RVSM) - On the parts of airspace where the minimum vertical separation is reduced from 2,000 feet to 1,000 feet


Do modern aircraft have sensors to determine weight of the aircraft? Do ALL modern aircraft, particulary airliners and private jets, have weight sensors on all landing gear to determine take off and landing weight in real time so as to determine take off speed and approximate landing distance?  If so were are they installed and if not why not? Are there any attempts to install these on older jet airliners?

No, the 737 does not have such sensors installed because it is less expense to compute the zero-fuel weight (and thus takeoff and enroute and landing weights, by adding fuel on board) by taking the known aircraft empty weight and adding to that the weights of the people and things that are on board.

I've never heard of any attempt to install any such sensors on a 737. Some FMC software can use in-flight performance data to estimate gross weight and alert the pilots if that estimate varies too much from the computed weight, but that is an entirely different approach.


Did Hamilton Sundstrand Corporation fix this GPWS problem? So I was reading about Garuda Indonesia Flight 152 and one of the reason it crashed was for a GPWS malfunction. Here is the Wikipedia article about the crash and GPWS: Garuda Indonesia Flight 152

  The plaintiffs alleged that the GPWS was defectively designed, that the manufacturer was aware of its deficiencies in mountainous terrain for over a decade, and had the system worked as designed the accident could have been avoided.

Was this problem ever fixed? Did Hamilton Sundstrand Corporation fix the problem? Also I was wondering if anybody knows what company makes the GPWS for an Airbus A350 and an Airbus A320?

EGPWS/TAWS is the fix for this problem...

The original Ground Proximity Warning Systems were indeed quite limited due to their inability to know anything about anything besides what was under the plane at the time.  While one could theoretically use ground-mapping radar techniques similar to military terrain following radar for this, that would be dancing in a minefield of classification and relatively advanced signal processing, making it impractical for use in the civil aviation environment.

Instead, EGPWS (enhanced ground proximity warning system)/TAWS uses the aircraft's idea of its own position (from the onboard navigation systems) along with a database of terrain info to generate forward looking warnings in addition to the more straightforward radio-altimeter warnings generated by GPWS.  This is what is found on basically all aircraft in mainline airline service these days, as well as many more modern business jets and commuter-type aircraft as well.

but even TAWS won't save you if you're getting lied to about where you are!

Nonetheless, it's still possible to have a non-pilot-error CFIT in an EGPWS/TAWS equipped aircraft -- on one fateful day in Ethiopia, a British Mediterranean Airlines A320 nearly became a crater twice over thanks to the ADS VOR/DME providing bad bearing information to anyone who tried to use it as a navaid -- without GPS, the only thing the TAWS had to go on was the VOR-updated IRU position, which was being thrown off by the bad data from the ADS VOR.  Luckily for the passengers, the crew had their wits about them and caught the situation before smashing into the ground, but even with GPS being nearly universal in airliners compared to its prevalence in 2003, interference, spoofing, or jamming of GPS signals is still a threat, as this year's Red Flag exercises are reminding us quite vividly by taking out GPS service across much of the western CONUS.


Re old (1993) US VFR sectional charts-- when did the term "Class E" first appear? When did the phrase "Class E" or "Class E airspace" first appear on the legend of US VFR sectional charts, to identify the meaning of the thin dashed magenta line?  I'd like to narrow down the date as precisely as possible. Currently I'm aware that this phrase DID appear on the legend of a sectional chart (Hawaiian Islands) effective November 11, 1993, and did NOT appear on the legend of a sectional chart effective August 19 1993.  Please post the "effective date" of any US VFR sectional chart that you are aware of before November 11 1993 in which the phrase "Class E" or "Class E airspace" does appear on the legend, or the "effective date" of any US VFR sectional chart that you aware of after August 19 1993 in which the phrase "Class E" or "Class E airspace" does not appear on the legend.

Basically this question is just asking when the current "alphabet" system of airspace classification first appeared on US VFR sectional charts-- presumably the terms "Class A", "Class B", "Class C", "Class D", and "Class E" were all introduced at the same time.

When answering this question please disregard any reference to foreign (e.g. Canadian) airspace on the legend of the US VFR sectional chart-- the transition to the "alphabet" system of airspace classification may not have been simultanous between the US and all bordering countries.

According to this AOPA article, the change was made in Sept, 1993

  In a move to simplify airspace classification, the FAA will rename the different airspace categories on Sept. 16, 1993. In order to fall in line with ICAO (International Civil Aviation Organization) practices, it will replace descriptive titles, such as Terminal Control Area, with alphabetical designators, such as Class B Airspace. This change will be phased in gradually. Charts and references will carry both designations until pilots get used to the transition.

https://www.aopa.org/members/ftmag/article.cfm?article=1054

And some more background

  A Brief History of Aeronautical Charting

  To understand the change that GIS has brought to the National Geospatial-Intelligence Agency (NGA), it is helpful to be familiar with the history of aeronautical charting.

  Shortly after the Wright brothers made their historic first flights, the skies began to fill with aircraft. Visibility was the key navigational tool at that time. Aircraft were limited to short flights in clear weather and used transportation routes to navigate by, flying low to the railroads during reduced visibility. Early pilots began making personal notes to help them navigate to and land at increasingly distant airports, and enterprising pilots sold these notes to other pilots, but air travel remained limited by visibility.

  In the 1930s, radio technology made it possible for pilots to navigate farther distances through unfamiliar surroundings in reduced visibility. In 1941, the first instrument approach and landing charts were developed, serving pilots with the need to land in low visibility.

  By this time, aviation was a matter of interest worldwide. Many organizations began drafting standards for aviation-related maps, charts, and information. During World War II, the demand for charts increased dramatically. By 1943, production had increased from around 500,000 per year to more than 11 million. The U.S. Army and Navy air forces each built their own custom charts to fit their wartime needs.

  By the end of the war, it was clear that standardized products and symbology were needed to support international air travel. The following years saw the establishment and maturity of many of the aeronautical- and aviation-related agencies and associations that we see today, such as the U.S. Federal Aviation Administration and the United Nations International Civil Aviation Organization (ICAO), each mandated to ensure the safe, efficient, and orderly evolution of international civil aviation.

  Today, these organizations and others drive the look and feel of aviation products worldwide. They have also mandated an update cycle to ensure that all aircraft are flying on the same data. Depending on the region of the world, this cycle is effective every 28 days or multiples of 28 days. It is easy to see how a map of the world's airports and airways, updated every 28 days and limited by international standards, can become a huge challenge. This challenge is the mission of NGA's Aeronautical Division.

http://www.esri.com/news/arcnews/summer07articles/a-brief-history.html


Does the A320's FMC automatically adjust the rate of descent on a non-precision approach? Does the A320's FMC automatically adjust the rate of descent on a non-precision approach? Like a back course approach for example if the distance to altitude is (or can be) programmed in?

Your mentioning of LOC BC is interesting.

The answer is yes except for LOC or LOC BC approaches.

When the FMGS guides the plane down an approach, it is called managed. If manually selected (e.g. vertical speed or FPA), then it's called selected.

An A320 can fly a fully managed (lat/vert) NPA if it is VOR, VOR/DME, RNAV, or NDB (given that the approach is correctly intercepted and GPS primary is available or the navigational accuracy is good). If all engagement conditions are met, the 2nd and 3rd columns of the FMA will merge and read FINAL APP (you can watch this switch here), and will be flown down to the MDA, after which (by 50 feet) the AP disconnects.

Note: the coded approach needs to be validated and approved by the operator.

If the NPA is LOC, the official SOP is to fly it in LOC mode for lateral and selected for vertical – while calling out the raw data. That's because in a LOC approach the vertical deviation (that appears on the PFD in place of the glide slope) must be ignored because the MAP (missed approach point) could be before the runway.*

* No other reason is given, which may hint at a database limitation (possibly for safety reasons). Boeing's flavor, IAN (which is newer), allows G/P vertical guidance for LOC and B/CRS approaches.

Reference: A320 FCOM, SOP § 3.03.19.

I checked the A380, and its newer FLS (FMS Landing System) allows vertical guidance for LOC and LOC BC approaches, but with a caveat similar to the A320 (but in a more clear manner):

  However, the FLS function is not available, if the NPA is as follows:

  The Missed Approach Point is before the runway threshold, and
  The difference between the final approach course and the runway course is more than 50°.

  When the flight crew selects an NPA, and if the FLS function is not available for this NPA, the NO FLS FOR THIS APPR message appears on the FMS message area. [A380 FCOM § 22-FG-70-80-30]


does a semi sphere have more drag in comparison to a flat plane with equal surface area? What the title says, some things to know is that these aren't solid shapes, think of a bowl and a sheet of wood.

No it doesn't. This chart explains how.
https://www.researchgate.net/figure/Typical-drag-coefficients-for-regular-3-D-objects_tbl2_273771608