How does the Space Shuttle slow down during re-entry, descent, and landing? Yesterday, my little brother asked me to help him build his new Space Shuttle Lego set.

When we finally finished building it, he started to play with his new toy and asked me to be the "Mission Control". After some time playing, he told me that he had to re-entry and land, so I gave him "permission to re-entry". Then he started to play as if he was coming back to Earth and told me that the Space Shuttle was too hot and moving too fast to land. And that got me thinking:

How does the Space Shuttle reduce speed during the re-entry process?
Does the Space Shuttle have flaps, spoilers and reverse thrust capabilities?
Can the Space Shuttle make a go-around?
Where does it land?

I know that when it is on the ground the Space Shuttle can deploy parachutes to reduce speed.

If you're interested in a more visual, and less technical, explanation of Space Shuttle reentry and landing, I gave a talk titled How to Land the Space Shuttle... from Space at the Stack Overflow meetup in October 2016.

I didn't notice this question until a couple of days ago, but as someone with an unhealthy obsession with specifically the entry and landing phases of shuttle flights, I can say there is a lot of factually incorrect information in the other answers here. Let me see if I can explain it better.

First, the two easy questions, which were answered well by other questions, but I'll include here as well for completeness:

Could the shuttle perform a go-around? No. The OMS engines are too weak to make a difference in the atmosphere, and the main engines (which would be powerful enough) are only fueled by the orange external tank which is jettisoned after launch.
Where did it land? 78 missions landed at the Kennedy Space Center, 54 (including the first) at Edwards Air Force Base, and 1 at White Sands. There were other landing sites designated for emergencies, but none were ever used.

Now, for the really big question of how the shuttle reentered and landed.

  The primary source I'm going to cite in this answer is the Entry, TAEM, and Approach/Landing Guidance Workbook 21002 which was a workbook used for training astronauts. Sadly, I don't have a link to it, but it can be obtained from nasaspaceflight.com via an L2 subscription if you're really interested. I'm going to abreviate this source as ETAGW.

Orbital Mechanics

First, a real quick lesson in orbital mechanics. In order to change the altitude of your orbit you make a change in velocity ($\Delta v$). If you increase velocity, you'll increase altitude, and if you decrease velocity, you'll decrease altitude. However, this effect is most pronounced 180° from the position where you made the change. After a complete 360° orbit, you'll be at approximately the same altitude you started at.

This illustrates the effect:

Starting from the circular orbit (black), if you slow down at point A, you might end up with something like the red orbit, and if you speed up you might end up with something like the blue orbit.

Deorbit Burn

Because of the nature of orbital mechanics, as described above, you want to perform your deorbit maneuver on the opposite side of the planet from your intended landing site. This typically occurred over the Indian Ocean for a landing at Kennedy Space Center in Florida.

The burn itself was performed with the shuttle flying tail first and white (top) side facing towards the Earth (heat shield/black side facing towards space). The two OMS (orbital maneuvering system) engines were used to accomplish the required $\Delta v$ (anywhere between 200 and 550 ft/sec depending on the starting altitude). The burn typically took around 2.5 to 3 minutes. This would lower the perigee (lowest point in an orbit around Earth) to within a few miles of the ground (having a hard time finding a source, but I seem to remember it being around 30-40 miles), which was enough to ensure the orbital path would take them into thick atmosphere.

 Image Source

The OMS engines are essentially larger versions of RCS (reaction control system) jets. RCS jets were used for rotation (attitude) and small translation (velocity in a given direction) changes. The OMS were used for making orbital changes.

Both systems burned the same hypergolic mixture (monomethylhydrazine (MMH) and dinitrogen tetroxide (N2O4)). If the OMS had failed, the RCS jets could have, in theory, been used to slow the shuttle enough for reentry.

Nose Flip

Some answers have said that the orbiter would pitch down 140° for the flip. This is incorrect. After the deorbit maneuver was completed, the orbiter would pitch up about 220° until it reached a 40° nose-up angle of attack (referred to as the "EI -5 attitude" because they must be in that attitude by at least five minutes prior to entry interface).

They have about 20 minutes between the deorbit burn and EI-5, so there's plenty of time to pitch in either direction. Nose up was likely preferred because the APU exhaust vents point up near the tail. This naturally causes the orbiter to want to pitch up when the APUs are running.

During this pitch-up, they would fire the forward RCS jets to dump all the forward fuel, unless it was required for center-of-gravity reasons. The forward RCS jets weren't used during reentry, and dumping the fuel reduces potential hazards to the astronauts.

Once in position, open-loop entry guidance would begin, holding the orbiter at 0° roll (wings level), 0° yaw, and 40° angle of attack (alpha).

Entry Interface

NASA defines the entry-interface (EI) as an altitude of 400,000 feet. There's no hard-edge to the atmosphere, but this is around the altitude where its effects start to become directly detectable.

S-Turns

Some answers have claimed that the shuttle used S-turns for the purpose of slowing down. This is a very common, but over-simplified and arguably inaccurate, explanation.

  "The next time you hear someone talk about the shuttle doing roll reversals to bleed off energy, do not listen. The shuttle does roll reversals because it has a very small alpha envelope." - ETAGW 2.8.1 (emphasis is from original source)

As with any airplane, the shuttle's wings generate lift. As the atmosphere gets denser, the wings are going to generate more lift, and this upward lift will cause the descent rate to slow. In fact if the shuttle maintained a wings-level attitude, it would eventually start to gain altitude causing it to "skip" across the atmosphere several times until it was slow enough to fall through. And while technically a skipping reentry would be possible, it would be very difficult to control with any precision.

So, instead, when the decent rate starts to slow, the shuttle goes into a bank. By controlling the bank angle, they're able to control how much upward lift the wings are generating, and, by extension, control their descent rate.

ETAGW Figure 2-5 illustrating lift vector.

Or course, with the lift vector pointed sideways instead of upwards, the shuttle is going to start to turn. Due to the incredible speed, the turn radius is enormous, but it does gradually turn nonetheless, and the orbiter develops an azimuth error (the difference between the orbiter's current direction and the direction to the landing site).

ETAGW Figure 2-3 illustrating azimuth error.

To correct this azimuth error ($\Delta z$), the orbiter performs "roll reversals". In other words, it turns in the other direction. These turns create the distinctive S-turn reentry track.

The first reversal always occurs at 10.5° $\Delta z$. Subsequent reversals occur at 17.5° until Mach 4 when it starts ramping down to 10° at Mach 3.

  Note: all mach numbers given anywhere in this answer, or referenced anywhere in Space Shuttle materials, aren't true mach numbers. NASA uses 1000 ft/sec as an approximation of Mach 1, and all mach numbers are multiples of that velocity.

Ranging

Obviously, the ultimate goal of reentry is to reach your intended runway at an appropriate speed for landing. While the orbiter doesn't have any engines to help accomplish this, it does have a tremendous amount of orbital energy. Therefore the goal becomes energy management, and more specifically, drag management.

The orbiter has two ways to affect drag during entry: changing angle of attack (alpha), and changing bank angle.

Angle of attack is the quickest way to increase or decrease drag, but the orbiter was only allowed to deviate ±3° from the nominal alpha (40° for most of entry). This is the "very small alpha envelope" referred to earlier. The limitation is designed to ensure proper heat protection and maintain vehicle control.

Changing bank angle, as described above, allows you to control your descent rate. A steeper bank angle will result in reaching thicker air faster, and will therefore result in increased drag. A shallower bank angle will keep the orbiter in thinner air for longer, and result in less drag. However, it takes a little longer to see the effect of a bank change than an alpha change.

There are also bank angle limitations because, again, you don't want to skip out of the atmosphere, and you don't want to fall into thick air so fast that it exceeds the maximum drag the vehicle can handle, but it is a larger envelope than the alpha limits. In fact, in early stages of entry, the orbiter could have even flown upside down (with its lift vector pointed towards Earth) if necessary due to an under-burn as the result of a malfunction during the deorbit burn.

Entry Guidance Phases

I'm not going to go into detail about entry guidance, but I will say that the primary considerations change as speed and altitude changes, and the entry guidance is broken up into phases to reflect this.

ETAGW

In the chart above, the middle line represents the nominal profile. The lowest line is the "equilibrium glide" profile which is the minimum amount of drag that the orbiter must maintain to avoid gaining altitude and skipping. The line at the top left represents a thermal limit (if the orbiter exceeds it, it might burn up). The line at the upper right represents a dynamic pressure limit (if the orbiter exceeds it, it might break up due to aerodynamic forces).

Preentry: This is considered open-loop guidance because all it does it maintain 0° yaw, 0° roll, and 40° alpha until the total load factor becomes 0.132g (approximately 3 ft/sec2 of drag), at which point closed-loop guidance begins.
Temperature Control: Begins at closed loop guidance and ends at a velocity of Mach 19. Tries to maintain a constant temperature within the design limits of the orbiter.
Equilibrium Glide: Simply provides a bridge between temperature control and constant drag phases. It ends when drag reaches 33 ft/sec2. It's named as such because its shape is similar to that of the equilibrium glide profile.
Constant Drag: Maintains a constant drag rate of 33 ft/sec2 until velocity reaches Mach 10.5.
Transition: Designed to transition from the high drag and high alpha of entry to the lower drag and lower alpha required for the orbiter to fly more like an airplane. This phase terminates at Mach 2.5 when TAEM begins.

TAEM

TAEM stands for Terminal Area Energy Management. The objective in this stage is to get the orbiter lined up with the runway with the correct amount of energy to make its final approach. Again, I'm not going to go into a ton of detail (feel free to ask other questions if you want), but here's the gist:

If all went well in the entry stage, TAEM will begin at about 82,000 feet and 60 nautical miles from the runway (intended ground track, not straight-line distance).

Whereas Entry guidance primarily uses bank angle to manage energy, TAEM primarily uses angle of attack. Below Mach 1, the speedbrake (a split rudder) also helps with energy management.

Source: NASA

Phases of TAEM:

S-Turn: Usually not required, but the shuttle will perform S-turns if it is too high on energy at the start of TAEM (too high, or too close to the runway).
Acquisition: Turns the orbiter towards a point of tangency on the heading alignment cone (HAC) and then flys wings-level until it intercepts the HAC. The tangency point is referred to as "waypoint 1" (WP1). During this phase, the orbiter slows to below Mach 1, at which point the commander takes CSS (control-stick steering), which is the closest thing the shuttle has to a "manual" mode.
Heading Alignment: Guides the orbiter around a virtual "cone" (see diagram below) until it is in alignment with the runway. It's not really a cone, mathematically speaking, but it's the easiest way to visualize it.
Prefinal: Establishes the orbiter on the outer glide slope.

ETAGW Figure 3-13 illustrating the HAC.

Approach and Landing

The final guidance phase is called "Approach and Landing". It begins when the orbiter is below 10,000 feet and established on the outer glide slope (OGS), but no later than 5000 feet regardless of glide slope.

The OGS was a 20° glide slope for "light" orbiters (gross weight less than 222,000 pounds) or 18° for "heavy" orbiters (by comparison, normal airplanes use a 3° glide slope). Heavy or light depended on what was in the payload bay. The nominal aim point for the OGS was 7500 feet short of the runway threshold, but there was also a "close-in" aim point at 6500 feet which was used in the event of a strong enough headwind.

The speed brake was used to maintain 300 KEAS (knots equivalent airspeed - it's effectively the same as indicated airspeed) on the OGS until 3000 feet, at which time it calculated how much speed brake should be required for landing, and moved to that position. It would re-calculate once more at 500 feet.

At 2000 feet, the orbiter would begin a "preflare" maneuver designed to transition from the OGS to the shallow 1.5° inner glide slope (IGS). This was accomplished with a circular pull-up followed by an exponential decay onto the IGS.

ETAGW Figure 4-8 illustrating the preflare geometry.

In reality, the IGS is not followed for long, and is more of a guide for making sure you cross the runway threshold on the proper trajectory and get into position to begin the final flare, which is essentially the same as a conventional landing flare in a normal aircraft, except that the shuttle lands at a much higher angle of attack (about 8°) due to its delta wings (more similar to Concorde).

Landing gear was deployed at 300 feet, and if you're interested in landing gear, I wrote a whole answer on landing gear deployment once.

The targeted touchdown point was 2500 feet down the runway at an airspeed of 195 knots for light orbiters, or 205 knots for heavy (within +5/-10 knots).

The drag chute (an addition made in the early 90's) would be deployed shortly after main gear touchdown, but not faster than 195 knots, and sometimes they would wait until nose gear touchdown if there was a crosswind. It would be jettisoned at 60 knots to ensure the chute attachment mechanism didn't hit and damage the main engines.

Control

(e.g. how was the shuttle able to make attitude changes?)

In early entry, the orbiter is still controlled like a spacecraft, using RCS jets to control attitude. As dynamic pressure (q-bar) increases, the aerodynamic surfaces begin to become active and the RCS jets shutdown as follows:

q-bar = 0.5 pounds/ft2 (psf), the elevons begin to act as trim.
q-bar = 2 psf, elevons begin to act as active control surfaces.
q-bar = 10 psf, RCS roll jets are disabled.
q-bar = 40 psf, RCS pitch jets are disabled.
Mach 10, the speedbrake opens on a pre-programmed schedule to act as pitch trim.
Mach 5, rudder becomes active, initially acting primarily as aileron trim.
Mach 1, RCS yaw jets are disabled.

Navigation

(e.g. how did the shuttle know where it was at?)

Navigation, in NASA terms, basically means knowing where you are (guidance answers the question "how do I get where I want to go?"). During entry, the shuttle primarily used inertial navigation units, which were aligned using a star tracker prior to the deorbit burn. As it got closer to the landing site it could also incorporate GPS and/or TACAN signals into the nav data. OV-105 (aka Space Shuttle Endeavor) had a three GPS units installed and no TACANs, whereas the other orbiters had three TACANs and one GPS unit.

On the HAC, anywhere from about 15k to 20k feet in altitude, the orbiter would pick up the microwave landing system (MLS), which acts sort of like a very high precision ILS. From this, they're able to determine their position with high precision and accuracy. Once acquired, this becomes the primary source of nav data for the remainder of the flight.

On landing videos, you can actually see exactly when they pick up MLS because the altitude tape goes from being sort of jerky, then jumps a little bit and becomes smooth. For example, watch here at about the 20k mark (altitude tape is the one on the right).

Below 5000 feet, the orbiter was also able to use a radar altimeter for altitude information.

That's probably more information than you were looking for, but if you have questions about things I didn't cover, or didn't go into enough detail on, feel free to ask separate questions for those.


What is the 0-60mph time of an aircraft carrier catapult? Tesla's new Roadster is giving a 0-60mph time of 1.9 seconds. Truly ludicrous acceleration.

I was wondering how a fighter jet released from a steam catapult compares.

According to Wikipedia https://en.wikipedia.org/wiki/Aircraft_catapult an American carrier type Kitty Hawk has a catapult capable of accelerating a mass of 35000 kg to 139 knots (71,51 m/s), and the system's stroke is 76 m.
From the terminal speed and the stroke, a simple calculation gives a mean acceleration of 33,64 m/s/s. Hence, and assuming the acceleration constant along the stroke, the time needed to reach 60 mph = 26,81 m/s is
t=v/a => t=26,81/33.64 => t=0,796 seconds...


What was the first production jet engine to use a semiconductor based control system? What was the first operational jet engine to use a control system containing semiconductors? This would include analog systems as well as digital ones. I am assuming that analog ones came first.

This would have to be a component used for normal operation of the engine, it would not include any equipment used for maintenance or diagnostic of the engine while on the ground.

Additionally it would have to be an aviation jet engine actually installed in aircraft that flew. Not just an engine used for R & D purposes on the ground.

The RB211 as found on the L-1011 (first flight Nov 16, 1970) had a fuel control amplifier that, while it was not the primary control of the engine, was capable of controlling fuel flow.


Are three airports or four required for private pilot cross country? The cross country requirement for the private pilot certificate says that I need to complete a cross country flight of over 150 nm with full stop landings at three points and one leg at least 50 nm.  Does that mean three full stop landing points other than the primary airport, or three including the primary airport?  So if I take off from Airport A, fullstop land at Airport B, fullstop land at Airport C, then return to Airport A, is that good enough?  Or do I also need to visit Airport D for a total of three fullstop landings away from my primary airport?

The regulation means you need to land at three separate airports.  This should include landing at your original departure airport at the end of the flight.

§61.109(a)(5)(ii)
One solo cross country flight of 150 nautical miles total distance, with full-stop landings at three points, and one segment of the flight consisting of a straight-line distance of more than 50 nautical miles between the takeoff and landing locations


What's the difference between setting auto brakes to MAX vs. RTO in Boeing Aircraft? On Airbus aircraft, before taxiing and before take off, pilots turn auto brakes to MAX.

But on Boeing aircraft, they will set auto brakes to RTO.

Why does Boeing not use auto brakes MAX instead of RTO?

For the 737:

RTO is used for takeoff, and puts full hydraulic system pressure to the brakes. The other autobrake settings, 1, 2, 3, and Max, are used for landing, and brake to achieve a specified deceleration rates. In autobrakes Max, you get very firm brake application, but it's still something less than unmetered system pressure to the brakes.

In all cases, the anti-skid system will prevent a wheel from locking up by reducing (modulating, actually) hydraulic pressure to a particular brake.


Why did this A320 stall protection demo not hold Valpha max? This video is about the Airbus A320 High angle of attack protection

At 4:54 - 5:13 why did it pitch down? I know it is  trying to maintain Valpha max but if it would have stopped following Valpha max it was at around 200 knots and could have kept climbing at a very good rate. Instead it maintained Valpha max but when it maintained Valpha max the speed decreased and and it pitched down and thus the vertical feet per minute started to decrease.

I thought it was suppose to maintain the highest possible lift and if it stayed at 200 knots with the pitch up the aircraft was climbing at a very high rate but it pitched down and slowed the aircraft so it wasn't climbing at its max performance.

You need to look earlier in the video. At 3:59 the sidestick goes full back and full left. The aircraft exceeds the 33deg bank limit on automatic maintenance of pitch and bank, requiring the pilot to hold pitch and bank.

The pilot is in command from 4:54-5:13, not choosing Valpha max. He hits the bank angle and stall limits to demonstrate flight envelope protection, the point of the video.


What short-term alternatives do airlines have to replace their grounded Boeing MAX 8s? The MAX 8 fleet is grounded: what are the other practical aircraft platform options available to AA, SWA or Continental that ensures that ticketed summer 2019 passengers arrive at their destinations safely?

Airlines really don't have a lot of options to carry through with the flights they planned with the grounded airplanes.

Older models of the 737 aren't much of an option. Most of the MAXes weren't intended to replace retiring aircraft, and even if they were, various costs of bringing the older aircraft into service for just a few months would be too expensive to make sense in the long run. The A320 would be the most direct replacement, but even then the situation is similar. New aircraft are ordered years in advance, so they can't just go buy an A320neo and get it right now.

It's possible to use a larger aircraft like the 757, but they would have to be pulled off another route and would burn more fuel.

The summer is peak travel season, so there just isn't any spare capacity out there that's economical to bring on board on short notice for just a few months. Even if they did, once the hundreds of MAXes return to service, the excess capacity is a liability.

Aircraft are a very expensive asset. Fleet needs are planned well in advance to have only as many as they absolutely need. Even an unexpected increase in maintenance time causes cancellations. The downside to this is that they're in trouble if a large disruption hits. The cheapest option is to just cancel a lot of the flights.


What are the numbers in boxes on an A320 ND when terrain is shown? When the TERR On ND button is pressed on the Airbus A320 Cockpit, the TERR information apears on the ND, and 2 boxes in yellow appear.

What do the numbers 146 and 073 mean respectively?

14600 ft and 7300 ft.

A320 FCOM DSC-31-45 :

  Minimum and maximum elevations encountered ahead of the aircraft, within the selected ND range.


What route should I fly in this lost comms scenario? As I've studied, when a pilot faces a lost comm situation the pilot considers two things which are 'fly to altitude' and 'fly to route'.

For 'fly to route', the pilot follows or chooses the route following the orders Assigned-Vectored-Expected-Filed. It is a little hard for me to understand this concept.

For example, take a clearance like this:

  555AZ is cleared to Grand Canyon Airport via DVT One departure PHX VOR
  vectors to DRAKE, Altitude 10000', Frequency 120.7, Transponder 3435

If my comms fail before I arrive at the PHX VOR how can I manage this situation? Do I have to go to Grand Canyon Airport directly? Or go to Drake and hold there?

Rule of thumb:  Whenever a clearance has an instruction to proceed from point X to point Y, where the path between those points is at the controller's discretion (such as vectors), and you have declared a comm failure by squawking 7600, you are to use your own judgement to proceed between those points by the most logical and reasonable path.

So if my clearance told me to expect vectors between two fixes and I now had a comm failure, I would just navigate my own way between them using whatever route keeps me clear of obstacles (probably direct), at or above the minimum charted altitude appropriate to the area (vectoring altitudes can be lower - you are expected to climb to the minimum published altitude following 7600 if it happens while on vectors).

On an arrival, if there is a comm failure on an arrival that involves radar vectors to final, you are expected to navigate yourself to the final approach course by the most reasonable and logical path, not lower than the charted altitude for the airspace you are in.

It's similar with the matter of timing; you are expected to start an approach at the last mutually confirmed or flight planned or expected time, so say if you arrive at a clearance limit early following a comm failure, you are expected to hold on your own as necessary so that you can proceed to the approach when you are supposed to.

The objective is that when the controller is notified of your comm failure when you squawked 7600, he/she will expect you to find your own way between any points that are discretionary at charted minimum altitudes, following a logical route and with timings that the controller can anticipate so the controller can route other traffic around you, confident you'll be able to avoid hill tops or tv towers on your own.

Much of the IFR rules structure is designed to ensure that an airplane with no communication capability can complete a trip maintaining its own obstacle clearance and proceeding in such a way that the controllers can anticipate where you are going with reasonable certainty.  The key thing is to maintain  a safe altitude and avoid going off in directions that make no sense to the controller as you find your way around.


Is there a tank priority sequence for using the fuel tanks? Is there a tank priority sequence for using the fuel tanks, or does the pilot decide?

Which fuel tanks are used in order of priority in aircraft?

What you're talking about, in large aircraft, is often referred to as the fuel burn schedule. Light aircraft generally do not have a fuel burn schedule though they may have have minimal requirements.

The fuel burn schedule is dictated by the aircraft design and is thus different for different aircraft designs.

  Is there a sequence of priority?

Yes, and if you don't observe the fuel burn schedule you risk exceeding the structural limitations of the aircraft, and in particular wing bending moments.

  Or the pilot decides?

No, the pilot does not decide usually. While there may be some leeway in the fuel burn schedules of large aircraft, the pilot or a flight engineer (old aircraft) or an automated system does not decide but rather implements a preset protocol.

As an example, here's a general outline of the fuel burn schedule for 747-100/200 aircraft. This is from memory so might not be entirely correct but is sufficiently so for example purposes:

On start, taxi, and takeoff burn tank to engine. In other words, route the fuel from main tank 1 to engine 1, main tank 2 to engine 2, etc.
Once you're established in your cruise climb, all engines burn out of the center tank if there is fuel in the center tank until the center tank fuel is exhausted (but don't burn any fuel in the center tank that is there for ballast).
Burn engines 1 & 2 from main tank 2 and engines 3 & 4 from main tank 3 until the amount of fuel in main tank 2 matches that in main tank 1 and the amount of fuel in main tank 3 matches that in main tank 4. Main tanks 2 & 3 are larger than 1 & 4. When parity is reached, burn tank to engine.
At some point transfer the fuel in reserve tank 1 to main tank 1 and reserve tank 4 to main tank 4. Likewise, if you have them, from reserve tank 2 to main tank 2 and reserve tank 3 to main tank 3. Most 747-100/200 aircraft didn't have reserve tanks 2 & 3. You have to get the fuel out of the reserve tanks before landing.

Be aware that just as there is a fuel burn schedule, there may also be a fuel loading schedule. In the 747-100/200 that schedule dictated that no fuel goes into the center tank until all other tanks are full. As I remember, the largest center tank available held 114999 lbs of fuel at 6.7 lbs/gal fuel density. Center tank size varied as ordered by the airline and changed through the production run of the aircraft.


Is there an engine thrust level limit for deploying thrust reversers? Does an engine have to be at idle thrust for the reversers to deploy? If the engine is at higher than idle thrust, will it slow down to deploy the reversers and then speed up again, or can it just deploy the reversers at the higher thrust?

I am also asking about turboprops going into beta range.

I had this question based on the discussion on this question:

What to do when you accidentally land on a runway thats borderline long enough to land on?

Engines must be at idle thrust to enter reverse thrust.  This may not be 100% true of the physical action of engine entering reverse thrust (opening the buckets or translating the cowling), but it is required by the thrust levers.  In all airplanes I'm familiar with the thrust levers must be at idle to enter the reverse regime,  In the EMB-145 the reversage was below idle (i.e. you keep moving the levers aft) through a gate.  Even if the engine is capable of entering reverse thrust not at idle, there is no way to command it without first being at idle.


Is DAL-A required for twin-engine helicopters with FADEC? When operating Twin Engine helicopter with FADEC controls, is is necessary to certify at DAL-A?  If so, why? Is it related to the FADEC certification or is this required for an aircraft potentially roling into a military platform?

With no reversion to a direct mode, ie retaining control of the engine possibly with limitation after fadec failure would imply DAL A since that fault results in loss of ability to maintain flight.

With some form of control reversion, the authorities would accept a much lower dal.

You cannot claim credit for the second engine since both engines use common. Software and hardware. So any common cause, common mode fault could take out both engines.

For part 29 helicopters  I would expect Dal A, part 27 probably B..


Can anyone explain what are the apron taxiway and aircraft holding taxiway with an illustration, please? Note: There are 3 types of taxiway

1) Apron taxiway

2) Aircraft holding taxiway

3) Rapid exit taxiway

Apron taxiways are just taxiways, except they are on the apron. They help planes on the apron connect to the main taxiways or the planes on the main taxiways connect to the apron.

I don't know what you meant by holding taxiways, but I assume you meant runway threshold or runway holding point. In that case, here's your illustration:

Notice how the apron taxiways are only on the apron and how they lead to the main taxiways! Also, the blue circled areas are runway holding points.

Legend:
Yellow lines: Apron Taxiways;
Red line: Runway;
Blue circles: Runway holding points;
Orange lines: Main taxiways and high speed taxiway;

Oh, and the high speed taxiway I just mentioned is the slanted taxiway connecting the rwy and taxiway without a holding point. That would answer your Rapid Exit Taxiway question.

Yes your terms are clear, but they are not the exact terms that we use in aviation. I guess that was why that guy said your terms weren't clear. But, I do understand them. It's just you wouldn't use them if you were an actual pilot.


What is the typical climb angle (versus the ground) of a single engine piston plane? What are the normal climbing angles against ground on a SEP (single engine piston) plane and an airliner?

(no wing-air angles in here, but the climb angle when watched from the side of the plane)

(Source: user11961 - Own Work)

That depends on wind speed and the aircraft's thrust-to-weight ratio.

Here are some values, all valid for sea level

GA aircraft: 4 m/s climb speed, 36 m/s airspeed. In calm air, this becomes a climb angle of 6.3°. If the wind blows with 36 m/s, the aircraft will climb vertically relative to earth if it flies straight into the wind.
Airliner: 20 m/s climb speed, 120 m/s. In calm air this becomes a climb angle of 9.5°.
Empty airliner: 30 m/s at 100 m/s. In calm air this becomes a climb angle of 16.7°. At airshows this is used to dramatic effect.

Note that the spectacular angles at airshows involve the conversion of airspeed to altitude, so these maneuvers are instationary.

If you want to know more on computing the optimum climb angle, consider reading this answer.

The main influence on climb speed is the thrust-to-weight ratio of the airplane. Since thrust depends on flight speed, ambient temperature and air density, those factors control the attainable climb speed in combination with the aircraft's weight.

For an observer, the next important influence is wind speed, since the aircraft climbs relative to the air mass it is flying through. If this air mass makes the aircraft appear to fly more slowly, a steeper climb angle can be observed.

Climb performance over airspeed and thrust-to-weight ratio for an idealized turbofan engine. The blue lines show thrust (right Y-axis) and the green lines the resulting climb speed. The two black lines show how the optimum flight speed for best climb speed and best climb angle (steepest climb) vary over thrust loadings. They are easy to find graphically: Just measure the angle of a line from the origin to the point on a green line at the desired flight speed and the right thrust loading (thrust-to-weight ratio). If the scales of the two speeds on the X- and Y-axis would be the same, you could directly take the angle from the plot.

With lots of excess thrust, the optimum is limited by the stall speed (the black line bends into a vertical trend), while with no excess thrust both optimum speeds vx and vy converge. This makes sense: If thrust is just sufficient to keep the airplane from descending at one speed, this speed will both give the best flight path angle and the best vertical speed (unfortunately, both will be 0 at this point). It also helps to reduce induced drag, so aircraft with a high aspect ratio wing will climb steepest at a higher lift coefficient (= lower speed).


Why doesn't condensation form on the inside of airliner windows? If outside the aircraft is pretty cold and inside the cabin the air temperature is different, why don't the windows become fogged up on the inside?

The humidity at the altitude airliners fly at is VERY low. However, a tiny bit of moisture does build up - if you look closely you'll see little ice crystals on the window (it's also very cold up there - in the negative degrees F usually). On top of that - airliners have multiple air conditioning "packs" that dehumidify the cabin air so there would be indeed by very little moisture to condense on the inside of the windows. Also, if you look at the windows - they are often two or three layers with quite a bit of space separating the outside of the window from the inside (often multiple inches). Some of this is for pressurization and some of this is for thermal insulation. The VERY cold outdoor air is not in direct contact with the inside cabin pane.


Can pilots tell if a cloud or fog is made out of water droplets or ice crystals when flying through it? I understand that clouds can be made out of water droplets or ice crystals. And that fog is nothing else than low-lying clouds.

However, I've experienced fog in a wide ranges of temperatures. I like mountaineering and you often get fog high in the mountains. I've been lucky enough to visit the high mountains of Antarctica and I've also experienced fog there at very low temperatures.

This answer (in the comments) and the fog wikipedia article mention that ice fog happens only at extremely low temperatures (-35 or -40 C). But I think I've experienced fog at those temperatures too. Some times, with the right light I've seen the air filled with tiny crystals, but I wouldn't call that "fog", because it is very thin.

Then, as far as I can tell, all thick fogs/clouds feel and look the same. No matter if they are made out of ice crystals or water droplets. Is that right? Or is there a way to differentiate between ice/water fogs?

Or maybe contrary to what I think, I've never experienced frozen fog.

But, would I notice the difference if I were to ever experience it? How would they feel/look different?

Other sources, like the UK meteorological office say that water always remain in liquid state in fog, no matter how low the temperature is. Is that true? Is it true for clouds too? In that case there would be no such thing as "ice clouds".

One possibility is that ice or water clouds would give rise to different optical phenomena, like sun dogs that are produced by ice crystals, but usually in conditions were they are not dense enough to be considered fog, like in this image:

(Image from Wikipedia page for sun dogs)

So I wonder what's the experience of pilots, as they go through clouds?. When they do so, they know also the external air temperature, which is a plus. Do they see sun dogs or other optical phenomena that differentiate water from ice clouds?

Boeing provides some decent notes on this in their powerpoint which you can find in full here. Their sections on pilot reports and the summary section have some good notes for identifying ice crystals in flight/clouds/fog

  Pilots have reported rain, sometimes ‘heavy rain’ on the windscreen, Sometimes at impossibly cold temperatures. This is
  believed to be the result of these small ice crystals melting on
  impact with the heated windscreen
  No observations of significant airframe icing
  Turning on landing lights at night and seeing reflective precipitation .It is likely they were seeing the larger particles even
  though they make up a smaller fraction of the population
  Hearing a different sound from rain. Ice crystals hitting the airframe sounded different than rain or hail
  Light to moderate turbulence
  No significant airframe icing
  TAT probe frozen
  Ice detector not detecting ice (when installed)
  Appearance of rain on the windshield

The same powerpoint also discusses that satellite imagery can be used to see ice crystals. A lot of planes even small stuff have the ability to receive feeds of this data which can be used to identify sections of ice crystals in flight.

According to various sources the threat is particularly dangerous due to the fact that there is no hard and vast way to visually identify the crystals and in many cases the effects are similar to other events and may lead the pilot to belive something else is happening.

For pilots we can only go by look, unless you are flying slow in a 172 you cant exactly pop the window open at altitude and feel the cloud. Simply put pilots can not reasonably tell if a cloud is vapor or crystal prior to flying into it and observing the above noted actions.


Why do most radial engines use an odd number of cylinders? To help suppress vibration, most 'V' and 'horizontal' engines use an even number of cylinders as closely opposed as possible. Radial engines are well known for excessive vibration. For some reason they nearly always use a staggered odd number of cylinders that would seem to promote vibration, why?

An odd number of cylinders is required by the combination of the single-crank radial design, the four-stroke (Otto) work cycle, and the desire to keep the power strokes evenly spaced in time.
To keep the design simple and lightweight, a single-bank radial airplane engine has one crank, which means that the pistons must reach the top of their travel in rotation order. But the four-stroke cycle requires that a piston must reach the top of its travel twice for each power stroke. The only way to promote evenly timed power strokes is to fire every other cylinder in rotation order.
With an even number of cylinders this would require a hesitation or skip in the firing sequence on every rotation as the engine switched between the odd and even cylinders. With an odd number of cylinders the timing is quite naturally smooth. For example, the firing order of an eight-cylinder radial would be
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
*   *   *   *     *   *   *   * *   *   *   *     *   *   *   *

while the firing order of a nine-cylinder radial is
1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9
*   *   *   *   *   *   *   *   *   *   *   *   *   *

If you could watch a radial airplane engine in slow motion you would see that when a cylinder is in its compression stroke, the cylinders on either side of it are in their exhaust strokes, and when a cylinder is beginning its power stroke, the cylinders on either side of it are near to beginning their intake strokes.
Two-stroke radial engines do not need to have an odd number of cylinders.


BLEED FAULT lamp illumination under various conditions In lots of commercial and defence aircrafts, bleed fault is annunciated because of mainly the following reasons:

Overpressure/Overheat
shut-off valve disagreement (i.e. failed open, failed closed)
pressure regulator shut-off valve fails
Precooler fails
Computer failure

However, when there is an emergency condition e.g. engines are lost/off/unavailable (i.e. no generators) and also no APU possible, should there be any bleed fault? Given that the aircrafts are only running on batteries, should there be a bleed fault because your sensors and computers aren't powered up completely?

I know that you have things like built-in autotest stuff that goes on before the computers are powered, but surely when the aircraft is on batteries/emergency power, should there be any bleed faults?

The question is quite broad but here's my understanding..

  However, when there is an emergency condition e.g. engines are lost/off/unavailable (i.e. no generators) and also no APU possible, should there be any bleed fault?

No, since there is no fault (as you've listed). The bleeds are in the correct config and there is no disagreement between the valve and the switch. There is just no pressure to the system. You will get a 'Bleed Off' indication if your switch is on with no pressure to the valve(type dependant). Also you will get a pack off indication - if you've got the bleeds set to feed the packs.

  I know that you have things like built-in autotest stuff that goes on before the computers are powered, but surely when the aircraft is on batteries/emergency power, should there be any bleed faults?

As I said above you wont get faults, but you may get indications that the bleeds are off.


Is the term "small" applied differently between piston engine planes and jet engine planes? My understanding was that "small" covered planes up to 12,500 pounds, no matter the engine type.

Would that be gross weight/max takeoff weight?

Brought to mind by the two recent Cessna Citation crashes (Cessna 560, Cessna 680A), and head lines of "Small  jet crashed during takeoff"  and "Small jet crashed during landing". Pretty sure their gross weights, 15900 lbs and 30800 lbs would push them out of the small category.

Luckily, all crew and passengers were able to walk away in both accidents.

I wouldn't expect press headlines to adhere to the FAA or ICAO definitions of "small", "large", "heavy", etc. This would be a public vernacular definition of "small", which would distinguish from the big airliners most people think of when hearing about jet planes.


How, typically, do passengers and crew behave in a real-life airliner evacuation? Two parts to this:

Do passengers tend to behave in ideal ways?
How do the cabin crew behave?

We know what's supposed to happen: the passengers are supposed to follow instructions, leave possessions behind not inflate their life-jackets inside the aircraft, and so on.

To what extent does this actually happen?

I know for example that passengers have inflated their life-jackets inside the aircraft (with tragic results, in the case of Ethiopian Airlines 961, where some passengers became trapped inside and drowned as a result). I can bet that some passengers will inevitably want to insist on gathering some tremendously important belongings.

I assume also for example that the management of the emergency exits isn't simply left in the hands of the passengers sitting next to them, but that the crew as far as possible take charge, and that generally they become ferociously assertive and intolerant of any nonsense from recalcitrant passengers.

In the emergency landing of Emirates Boeing 777, EK521, 300 souls including 282 passengers successfully evacuated an aircraft that landed with only the left side of the main undercarriage extended, and was already on fire before it had stopped moving.

The aircraft was severely tilted over to one side, which must have made movement inside very difficult. Within a few minutes an explosion threw large pieces high into the air (possibly a slide or wing part) and the fuselage was gutted by the fire.

So at least in one case where one might expect very frightened passengers packed into a burning airliner to panic dangerously, it appears that they did not, and evacuated safely (one crew member was apparently hospitalised).

It's only one case, not enough to describe what typically happens, but please add to this answer with further examples to make it so.


How to calculate the thrust of a piston or turboprop engine? This spawns from a related question. Propeller-drive engines (piston/turboprops) seem to always list their output in horsepower or kilowatts, which are units of power.

I want to know the engine's thrust instead.

How to calculate this?

I know propeller thrust depends on airspeed. What I want is an equation where we input engine power and airspeed (and maybe other parameters), and output thrust.

The simplest equation uses an assumed propeller efficiency $\eta_{Prop}$and converts power P into thrust T like $$T = \frac{P}{v}\cdot\eta_{Prop}$$
The tricky thing is to get $\eta_{Prop}$ right. Use 85% for lightly-loaded* propellers working at their design point. And make sure you subtract the power offtake from the engine for driving the accessories, so you only use the effective power at the propeller, not the rated engine power.

The equation only works if the propeller is in motion, so airspeed $v$ is not zero. For covering the static case, please see this answer.

*The load on a propeller can be expressed by the ratio of thrust to the propeller disc area, made dimensionless by dividing by the dynamic pressure $\frac{\rho}{2}\cdot v^2$. If $T$ is thrust and $d$ is the diameter, the dimensionless thrust loading coefficient $c_T$ is
$$c_T = \frac{T}{\pi\cdot\frac{d^2}{8}\cdot\rho\cdot v^2}$$
Sometimes this is simplified to
$$c_T = \frac{T}{\pi\cdot\frac{d^2}{4}\cdot v^2}$$
Note that this definition needs the propeller thrust at a specific speed. A different way of expressing the propeller loading, which lends itself to using the easy to measure static thrust, is by dividing thrust by the disc area and the dynamic pressure of the propeller tip at rest, with $n$ as the RPM of the prop:
$$c_T = \frac{T}{\frac{\rho}{2}\cdot\left(\frac{n\cdot\pi\cdot d}{60}\right)^2\cdot\pi\cdot\frac{d^2}{4}}$$
and again a simplified form of this can be found in literature:
$$c_T = \frac{T}{\rho\cdot\left(\frac{n}{60}\right)^2\cdot d^4}$$

Generally, a lightly loaded prop has a big diameter and flies at low to moderate speed. While WW II warbirds are still in the lightly loaded realm, all large turboprops (C-130, P-3) are firmly outside of it.


Why aren't runways lit from overhead, like highways? Why don't runways have overhead high-mast lights like roads? YouTube videos substantiate that

aircraft landing lights and runway edge lights are too faint to illuminate the whole runway, and
the runway is dark at night. But then how can pilots spot any physical obstacles on it?

Because the planes might hit them and it's not great for your vision at night. Runway edge lights are not intended to illuminate the runway they are intended to outline it. Proper runway lighting very clearly outlines a runway at night

(source)

Generally speaking there is nothing saying that a planes wingspan needs to be narrower than the runway and at some smaller airports the wings may very well be wider than the runway. This means you would need to put any high mast lights far enough away to allow aircraft clearance. In turn they would need to be quite bright due to the distance.

Another key reason and perhaps more important is to preserve the pilots "night vision". Generally when flying at night its advised to not expose your eyes to any bright lights prior to flying and to ensure that no flash lights or other bright lights go off in the cockpit while flying. This can cause your pupils to constrict making it harder to see in a dark environment. Entering a very bright runway environment all of a sudden would be strenuous on your eyes, in the event of a go around you would then have night vision issues due to the exposure in the brightly lit runway environment. As per the FAA's suggestion:

  Before and during night flight, the adaptation process of the eyes
  must be considered. First, adapt to the low level of light and then
  stay adapted. After the eyes are adapted to the darkness, avoid
  exposing them for more than one second to any bright white light as
  that causes temporary blindness. If exposed to a bright light source,
  such as search lights and landing lights, remember that each eye
  adapts to the dark independently. By closing or covering one eye when
  exposed to light, some night vision acuity is retained in the closed
  eye.


Why doesn't ADS-B use satcoms like ADS-C? With ADS-C, in the middle of remote areas (like ocean), we can send position report via satellite data link.  So, why ADS-B systems on airplane uses ground based stations (VHF datalink) rather than Geostationary Satellites for data transfer?

It's already here, but it's private

Your proposed geostationary orbits are very high, and since aircraft are the transmitters, that means high power antennas are required from the aircraft.

However, low Earth orbits (LEO) are more forgiving. By using 72 ADS-B receiver-equipped satellites in LEO (icao.int), Aireon will provide 100% global coverage by Q3 2018 (aireon.com).

This requires no change to the existing ADS-B technology as long the antenna is top-mounted and capable of 125 watts (most airliners already support 200 W). But it is not a free service to ATC units. Interested ANSPs can use Aireon's data to supplement their own surveillance for a fee. NAV CANADA will use their services for the North Atlantic region by Q4 2018, for example.

The power demand and the provider being a private entity, explains the why not. If surveillance is meant to be publicly owned by each government to be in control of the data source, then each country will need its own constellation of satellites – sort of like the countries and regions that are launching their own GNSS constellations.

Slide 16 (shown below) is from the linked icao.int presentation. The presentation also explains how ADS-C is different:

  ADS-C is an Alternative, But Has Limitations

  ADS-C tracking is not comparable to ADS-B surveillance
  Slower ADS-C update rates results in higher separation (mins vs. sec)
  Barrier to entry: ADS-C requires costly installation and subscriptions
  Multiple providers require individualized equipage on aircraft
  Several commercial aircraft types can’t be retrofitted
  Almost no coverage over polar regions for certain providers
  No service is provided to unequipped aircraft


What is the best design to stack wings of a triplane? I would like to design an ultralight airplane, which probably the total mass will be around 400kg. The speed should not exceed 200km/h. Forget about what the engine I will use. I intend it can land and take off in a small road and/or in a common road, which the road line not more than 2.5m each direction. If I have to occupy both direction, mean the road width is just around 5m, plus small space beside the road in both side. Beside the road, normally many electrical poles. So, not many space available.

To tackle the situation, I need to change wings design without reduce the wing area (A in m2). Was discussed earlier here some of the triplanes that were used during the WWII. If they were used during the war, that mean that such design was safe enough. But, I have a bit confusion regarding how to place the wings' stack? Here are the three options design.

The wings stack are lean to the tail.
The wings are stacked exactly over another.
The wings are lean to the nose.

Another thing. We know that the closer wing to the ground will produce what is called earth deflection (CMIIW about the terminology) during take off. That will make the plane requires longer time to take off. In my opinion, the same effect will occur if we stack the wings too closed one to another, especially if the wings are stacked lean to the nose, the deflection will hit the lower trailing edge if there is no enough space. So what is the best design in this case? And what is the best space?

Wing stagger was mostly chosen to improve pilot vision: In single-seaters, a positive stagger would allow to place the upper wing ahead of the pilot, improving the field of view.

Large bi- and triplanes had no stagger. Here the pilot sits ahead of the wing and large aircraft fly mostly straight, reducing the need for the pilot to observe the airspace around him.

However, if you look for a proven design of a very compact triplane, I would like to suggest the Italian Pensuti triplane. It had a wingspan of only 4 meters and a total weight of just 230 kg. Emilio Pensuti, a test pilot with Caproni during WW I, designed it as an easy to fly aircraft for the common man. Therefore, it is sometimes also called the Caproni-Pensuti triplane. The first version was powered by a 35 HP Anzani engine while a later development, the Breda-Pensuti 2, used a 80 HP engine.

Of course, its wings had no stagger.

Drawing of the Pensuti triplane (picture source). Yes, it did fly!

Pensuti triplane in flight (picture source)

If you build one, I would strongly suggest to change the wing airfoil to a thicker one with the same amount of camber.


Why do lower molar mass rocket exhaust products give higher specific impulse? I tried to work this out.  My thinking is as follows.  If the same amount of energy is given to a low mass particle and a high mass particle, the low mass particle is faster.  A particle with a mass of 1 will be twice as fast as a particle with a mass of 4 but the momentum of the particle with a mass of 1 will be twice that of the particle with mass 2, which seems to go against what is seen with regards to molar mass and specific impulse.

Your question is slightly confusing. What you seem to ask is why, given that momentum is proportional to the energy, and speed increases only with the square of the energy input, a heavy rocket fuel is so much worse than a light fuel.

For a rocket, the speed of the burnt gases exiting the nozzle is important. Heavy molecules need more energy for the same acceleration, so the lighter the rocket fuel is, the higher are the nozzle speeds. Momentum is less important, because the mass of the fuel is on both sides of the equation: Heavy fuel in the rocket's tanks needs more energy for the same acceleration, and the chemical energy of the fuel is not proportional to its molecular mass.

Thrust is mass throughput times exit speed. For a given mass, thrust can be increased if the exit speed can be maximized. Since this mass must be accelerated, the total fuel mass needs to be as small as possible, not the number of fuel molecules (as your question implies). As you say, using lighter molecules helps to achieve this. The only problem is that lighter fuels need more volume, so a hydrogen rocket is bigger than one using alcohol (V-2) or Kerosene (Vostok).

To get the best specific impulse, the mixture in a hydrogen rocket engine is not stoichiometric, but uses only as much oxygen as required to heat up the gases up to their dissociation temperature. Adding more oxygen would set free more energy, but this would only be used up to ionize the combustion gases, not to heat them up more (Oberth effect).


What's the technique for landing without one set of wheels? A Boeing 747-400 recently made an emergency landing without the wheels under the right wing:

News story
Photo of the undercarriage
Video of the landing from the end of the runway

What's the standard technique for carrying out such a landing?

What might go wrong? Does it require more runway? Is there a significant risk of dragging one wing on the ground?

The techniques vary slightly aircraft to aircraft, and also based on what landing configuration you have.  However, the general gist is to hold off the malfunctioning side from the runway for as long as possible, slowing the aircraft in the process, until forced to put it down on the deck.  This minimizes the contact between the wings and/or fuselage with the ground.

The single greatest danger with these types of landings is the risk of fire. The friction between the runway surface and the aircraft is tremendous generating an enormous amount of heat.  This is particularly problematic when you consider that the fuel is stored in the wings.

Fuel may be pumped to the opposite wing to counter-balance weight and move the fuel away to the fuselage with the highest possibility to have contact with the ground. This technique will shift weight away from the missing wheels and consequently reduce the possibility of fire.


Is there a standard time zone for flight schedules? I was reading a question on Travel.SE. The asker was asking whether the time on his ticket was in Daylight Savings Time or in standard time. I would imagine flight schedules are supposed to be time-zone/DST agnostic so as to avoid any potential confusion and timezone conversions.

A commenter mentioned UTC time, which makes sense to me.

So my question is: is there a standard time zone or other time standard used for tickets and/or flight schedules?

Customer facing documents like boarding passes and itineraries typically show local times for ease of use.  Just use airport clocks.  I would not trust the flying public to compute UTC.  It would be chaos.

Crew facing documents will usually be set to UTC, or zulu time.


Why do eastbound transpacific flights fly at lower latitudes than their westbound counterparts? I’ve seen some routes for flights from Asia (mainly Hong Kong and Shanghai) to the west coast of North America, which fly at lower latitudes than flights in the other direction (which they fly closer to the North Pole). From what I know, the jet streams go eastward, and are stronger near the poles. So why don't flights from Asia to western North America fly closer to the pole to take advantage of stronger tailwinds? Or did I get it wrong?

The different routes are due to the enroute winds created by the jet stream. The following map shows the current winds over the Pacific:

(map from skyvector.com)

You can see strong winds from the West in the central Pacific region of up to 150 knots (see here for a legend on how to read wind barbs). A flight from Hong Kong to Los Angeles benefits from these winds. A flight in the opposite direction would experience this as a headwind though and will therefore try to avoid the region. You can see that the winds are much weaker in the North.

In order to organize traffic in the Pacific, a track system has been established: Pacific Organised Track System (PACOTS).

  The Pacific Organised Track System (PACOTS) is a flexible set of aircraft route tracks that primarily link commercial air transport gateways of Japan and Southeast Asia and the gateways of Hawaii and the North American West Coast, as well as those in Texas.

(skybrary.aero)

The following map shows the current PACOTS tracks:

(map from skyvector.com)

The green tracks are for westbound flights and the blue ones for eastbound flights. Due to the changes in the jet stream, these tracks are re-defined twice a day:

  The tracks are developed twice daily by the Japanese Air Traffic Management Centre (ATMC) in coordination with Oakland ARTCC. Eastbound tracks are valid from between 0500Z and 1000Z (depending on origin) to 2100Z (with specified crossing time windows for 160E) and are given a numeric designator. The opposite direction westbound tracks are valid from 1900Z to 0800Z (with specified crossing time windows for 160E) and are designated alphabetically.

(skybrary.aero)


What airfoil type is used on the B727-200F? What airfoil type is used on the Boeing 727-200F? Is it a NACA profile or something else?

My favourite book for questions like this is Obert’s Aerodynamic Design of Transport Aircraft. It shows pressure distribution on the 727 wing and gives some AIAA papers as sources. If you track these down, that might reveal more. Unfortunately no airfoil reference is given; however it is very likely that the 727 uses a proprietary Boeing airfoil.

Posting as answer despite not really answering, as it is still more than a comment...


Difference between general, airframe and power plant concentration courses Trying to enrol for an aircraft maintenance technician course but the options are three that’s general, airframe and powerplant concentration. With the general being an affordable course to pursue, will it be advisable if I choose that than airframe or powerplant and would it be enough to prepare me for FAA exams ?

The US Mechanic certification has two components, Airframe and Powerplant. The license is generally known as an "A&P" license because most candidates choose both. There are, however, three exams. The third is the General knowledge exam. You have three choices for licensing:

Airframe only
Powerplant only
Airframe & Powerplant

For all three options, you must take the General exam as well. Taking a general course will only prepare you for that exam, which does not lead to any license or certification.


Shouldn't the upwash on an airfoil increase the effective angle of attack? From what I understand, induced drag comes from a reduction of the effective angle seen by the airfoil.

However, from wind tunnel smoke visualization, we can see that the streamlines at the leading  edges and stagnation point tend to "go upward'. Which is the opposite of what the effective relative wind is supposed to be and do.

Is this "upward tilt angle" of the streamlines, the result of suction from the upper surface minus the induced angle?

I've included two pictures:

The problem is the true AOA varies depending on where in the flow you measure it.  So what point do you use?  An inch forward of the LE?  Farther forward?  Higher? Lower?

Better to use a consistent value that is independent of the local flow variations in the upwash by using the angle of the chord line to the free stream.


How strong would a servo motor need to be to power the control surfaces of a fixed wing ultralight aircraft? I'm looking to build an ultralight aircraft.

The video above shows a good example of how one is controlled with wires or with metal fulcrums/levers, but I am interested if they can be controlled electronically.

My idea of this is that it would work exactly like an R/C plane, but instead of being controlled with a radio, it will be controlled with a joystick through a wired or wireless signal.

I saw the other post that talked about a wireless fly-by-wire system and they said it could be unreliable, but that's not exactly what I'm wondering. I want to know how I can get the supplies to do it and look at the options.

How strong do the servos need to be for such an application? Obviously the rudder, elevators and ailerons will be light, but not as light as an RC plane's, so I can't use servos from a local hobby shop.

First I'd like to say you are thinking outside the box, not a bad thing...

However for an ultralight aircraft this is impractical. The first problem you have is that most ultralight aircraft don't have electrical systems. Adding one may put you over the weight class for an ultralight. Servo's, batteries, joysticks, etc are also not very "ultralight".

The second thing you need to think about is that R/C's work because a single servo controls two surfaces in the case of ailerons, so they are synchronized. The aerodynamic forces become much, much larger as you scale up, so you will need individual (or multiple) servo's per control surface. Then you need to think about how to synchronize them, and calibrate them.

Next comes in a question of failure modes. If your elevator servo fails, what do you do? What about your electrical system? Dead battery? These FBW systems work on large aircraft because they have multiple redundancies (including traditional cable controls). You won't have the space or weight budget to do that.

It just comes down to trying to shove a complicated system into an uncomplicated aircraft.

And for a little note about "large scale" FBW systems. Usually these systems use hydraulic servo valves, which means that the aircraft includes a hydraulic system (or 3), which are electrically or cable actuated. These can provide sufficient force (along with heavy counterweights) to move the control surfaces. The servo's that you would need would not be available in electrical form since they would need to be powerful, long stroke, and fast. There are servo's that are used in some aircraft for things like flaps, but they are not fast.


What does a jet engine technician do? I know that they repair everything that concerns engines, but what is the actual day for them. Do they sit in the factories or work in airports?

You ask a very broad question. Jet engine technicians can work in various capacities depending on the job they are hired to do.

In my experience, I worked on the flight-line directly on aircraft removing/installing, performing operational checks, troubleshooting and servicing engines and other systems.

Some technicians work on engines out of the aircraft and in a controlled environment like the factories where engines are made. Others work in repair shops tearing down and rebuilding existing engines.


Why are crop dusting spray booms not integrated into the wing? All crop dusting aircraft seem to have an externally mounted spray boom for distributing their pesticides, I imagine this significantly increases drag & therefor performance.

What gives? why not integrate the spray system into the wing?

I have read that crop dusters spray booms remain short of the wing tip to prevent interaction with the wingtip vortices, perhaps another aerodynamic interaction along the main span of the wing prevents this integration?

thanks for considering my question!

Different chemicals use different nozzles and delivery systems.  Many of the spray agents are very corrosive.  Turbulence by the sprayer can be a good thing, as it aids in mixing.

Additionally drag is not a big issue as crop dusters fly slow, and tend to have good power to weight ratios, so the drag of a spray assembly at 70 knots or 60 knots, is not a big concern.  Mixing (with air of) chemicals, reduction of airframe corrosion, and ease of removal are larger concerns.


How do you calculate the vertical and horizontal tail volume if you have Vvbar and Vhbar? I know the general formulas for calculating the horizontal and vertical tail volumes. Unfortunately, I only have Vvbar and Vhbar. I’ve checked through multiple textbooks and I don’t know why I can’t find an expression for Vvbar.

This is what I have.

The 'bar' volumes are the same volumes but taken with respect to the wing-body aerodynamic centre (AC) rather than CG. This is more convenient because this is a constant reference, whereas CG may move.

The difference between them is only the arm: $\overline{c}(h-h_{n_{wb}})$, which leads to your last expression for $V_H$.

For the yaw motion, the aerodynamic centre of the wing is much less relevant(*), and thus the 'plain' $V_V$ (with respect to CG) is commonly used. This is why you can't find an expression for $\overline{V_V}$.

Nevertheless, if we want to relate it to the same wing-body AC as for $V_H$, we can do it. However, in lateral motion the generic reference is the wing span $b$ rather than the MAC $\overline c$ (as you can see from your first two definitions). Thus $\overline c$ is not eliminated, and we have an uglier expression:

$$\overline{V_V} = V_V + \frac{S_{VT}} S \frac {\overline c} b (h-h_{n_{wb}})$$

(*) It could be related to AC of the body alone (which is typically near the very front of the fuselage), but this is also not very sensible: the wing (and the wing-body interaction) does play a major role. I've never seen $\overline{V_V}$ defined like that for airplanes.


What are the Area Control Center (ACC) frequencies for Germany? I'm looking for the frequencies of all Area Control Centers (ACC) in Germany. What are they, or where are they published?

The radio frequencies used by German ACC sectors are listed in AIP Germany ENR 2.1 (page 36 onward). This is the standard place to find ACC frequencies for any country in the world.

There are too many frequencies to list here, but you can find the full document here. Below is a screenshot of page 36. Column 1 contains the sector name and dimension, column 4 contains the frequency(ies) used by that sector.


What is this aircraft, and what country makes it? What is this aircraft and what country produces it?

Source: Google Images

This is a Raytheon Sentinel R1, which is produced by Raytheon (US) and Bombardier (Canada). The aircraft in your picture is operated by the Royal Air Force.

(Image Source: WikiPedia - Author: Alan Radecki)


Did Southwest airlines retire flight 1380 following the accident, and with what number? Just wondering if Southwest Airlines flight 1380 was retired and replaced with a different flight number following the uncontained engine failure and depressurization accident in April 2018?

According to FlightAware, Southwest has not operated a flight with flight number 1380 since the accident flight on April 17. The flights with that number for several weeks after the accident were all been marked as cancelled in the FlightAware database; other flight numbers were used:

Southwest uses the same flight number for many flight segments in a day, but their flight schedule shows that flights from LGA to DAL leaving at around 10:30am are using the flight numbers 5227 (Sundays, 10:35) and 237 (weekdays, 10:45).


What makes spiral instability less harmful than Dutch roll? The FAA Pilot's Handbook of Aeronautical Knowledge says on page 5-20:

  Because it is more desirable for the aircraft to have “spiral
  instability” than Dutch roll tendencies, most aircraft are designed
  with that characteristic.

What are the grounds for that?

Because spiral instability is easier to address by the pilot than Dutch Roll tendencies.

Spiral instability is instability about the longitudinal axis. For example, spiral instability means that if the right wing tip moves down, it continues to move down rolling the plane to the right. Its simple to detect and address with left aileron.

Additional information on spiral instability available here: http://www.faatest.com/books/FLT/Chapter17/SpiralInstability.htm

Dutch Roll causes cross-control-type movements across two axes, the vertical and longitudinal axis, such that when the airplane rolls right, it yaws to the left, then it swings back the other way and rolls left, while yawing to the right. This movement is difficult for the pilot to counteract and the inputs from the pilot can actually amplify these movements.

Additional information on Dutch Roll tendancies available here: http://www.faatest.com/books/FLT/Chapter17/FreeDirectionalOscillations.htm


What is the pressure distribution around a supersonic wing? In subsonic flight the lift manifests itself at 25% of chord, but shifts to 50% of chord when the airplane goes supersonic.

Wondering about that made me think that the reason might be that there is high-pressure in front of the wing´s top-point like there is at the bottom in front of the low-point, and low pressure behind the low-point of the wing like there is behind the top-point.

Assuming a symmetrical biconvex wing profile, that would put the centre of lift the 50% of chord.

A symmetrical biconvex wing going straight forward would produce no lift, so it has to be put at an angle to compensate for the weight of the airplane and the Mach-tuck, but still the lift would manifest itself at 50% of chord "seen my way" - and that gets more and more the faster the plane goes as the AoA gets closer to 0.

A couple of extra questions: at what AoA is a fighter (F-16/18/22/35/Rafaele/Typhoon/Gripen) flying with in low (M 1.3) and high (M 1.8) supersonic flight?

Do fighters have symmetrical biconvex wings or do their wings have a camber?

Normally, supersonic fighter wings for which airfoil information is published use a very thin NACA 6-digit section with very little camber, such as
Aircraft                root airfoil      tip airfoil
McDonnell Douglas F-15  NACA 64A006.6     NACA 64A203
General Dynamics F-16   NACA 64A204       NACA 64A204
Lockheed-Martin F-22    NACA 64A?05.92    NACA 64A?04.29

This information is from The Incomplete Guide to Airfoil Usage by Dave Lednicer. As you can see, the F-16 uses camber throughout, indicated by the 0.2 design lift coefficient of the airfoil, while the F-15 uses an uncambered root airfoil.
Those airfoils are chosen because flow around them at supersonic flight speed is still heavily influenced by subsonic flow characteristics as long as wing sweep allows for a subsonic leading edge. This produces nose suction, and flow around the wingtips disturbes the pure supersonic flow characteristics even when the leading edge is supersonic.
How the idealised flow around a supersonic airfoil looks is explained in this answer.
The angle of attack in supersonic flight depends on air density and load factor, but generally is only a few degrees because drag increases with the square of angle of attack. In other words, if the plane flies at high angle of attack, it decelerates to subsonic speed quickly.
The angle of attack in straight flight depends on altitude, wing loading and aspect ratio and grows with decreasing air density. Normally, at low level the maximum dynamic pressure limit and engine thrust will only allow very low supersonic speeds around Mach 1.1 to 1.3. Only above 20.000 ft will the envelope expend enough to make flight at Mach 1.8 possible.
For a typical wing loading of $\frac{m}{S}$ = 300 kg/m² and Mach 1.3 at 10.000 ft (air density $\rho$ = 0.9 kg/m³, speed of sound $a$ = 330 m/s) the angle of attack is $$\alpha = \frac{2\cdot m\cdot g}{\rho\cdot (Mach\cdot a)^2\cdot S\cdot c_{L\alpha}} \approx 0.5°$$ with a typical lift curve slope of a supersonic wing of $c_{L\alpha}$ = 4.


Do any companies offer 'ejection' experiences? Most airlines now offer fear of flying courses, most airports provide flying lessons and some specialist companies offer zero-gravity flight experiences.

Are there any companies that provide 'ejection' experiences, where you can fly an aircraft and eject from it at a pre-determined location?

Please note, I'm not talking about sky-diving. I want to actually use an ejection seat.

No, there are no companies offering ejection seat experiences, for many reasons:

Cost: Ejection seats are expensive, base costs are somewhere around $100,000 per seat. Seats can't generally be re-used, therefore the cost of an experience is going to be well over that
No platform: There are airplanes that are designed to eject someone and keep flying safely, they are used exclusively for seat testing and not open to the public. Someone would have to develop and build an airplane designed to give a "fighter plane ejection" experience
Ejection is incredibly dangerous: the chances of injury or death are very high. Ejection seat companies have used test dummies instead of humans for decades for this reason
Ejection can lead to life changing health issues: the G forces on a modern seat are at least 12G, and go up from there - they can't be any less or you won't clear the airplane. This compresses the spine and can lead to debilitating, life lasting injury. If your ejection position isn't right you can break or lose a limb
Ejection isn't fun: there's not a pilot or crew member in existence who has used an ejection seat and said "Whoopee! Let's do that again!" Instead they say, if they are capable of speech, "Ow!" or "Please get me clean underwear."

So a company would have to spend tens of millions to develop a system that only rich people would be able to use, still less would want to, and a very precious few would be crazy enough to try.


What's the benefit of this long flight (apart from marketing)? The post Do promotional flight routes have a historical precedent? asks about previous occurrences.

I'm guessing this flight (shown below) was a test flight, as well as being a marketing attempt.

For a test flight, what would the benefit be?

From the this link:

  At 15:38 local time N7874, the fourth 787 built, departed Boeing Field in Seattle for an 18-hour, 22 state test flight. The crew spent the overnight hours above the United States performing ETOPS testing on the new Rolls Royce Trent 1000 TEN engine, which will power the 787-10.

Also this video from the above flightradar blog link.

The 18-hour flight was to test ETOPS, and there's no harm in some marketing as well. Also since the flight will be coming back to Seattle, it makes sense to keep the flight above the US, and near airports. Compared to venturing out in the ocean on a test.


Quadcopter: would putting 3 blades on the same level and the other blade below the first three work? Most quadcopters have their propeller blades all on the same level, or in some cases, a pair of blades placed a little above the other pair.

However, I was wondering if three propellers of a quadcopter can be put on the same level and the other propeller a little lower. Would it just make the quadcopter inefficient?

There are designs with overlapping blades. It's all a tradeoff on space, structure, clean aerodynamics, efficient aerodynamics, etc. This is the Malloy Hoverbike, for example.

So you can definitely have them at different levels, and you can even definitely have them overlap. If the 3 rotors' flow is not involved substantially with the 4th rotor's (not too big a difference in height), it should be no big deal.


What does the PBY Catalina's APU look like? I found some specifications of the PBY Catalina that mention an APU, but I did not find any other references to this APU. It seems  logical that such a plane has an APU, and that this APU is not like modern gas turbine that may be fitted on airliners.

What does the APU look like in this aircraft? Where is it located?

The link you provided is for a Canadian PBY-5A which were called "Canso" in Canada. I flew these aircraft in water bombing operations during the early 1980's.

In your link it describes the 1955 installation of a 28v Homelite APU. It was installed on the left (port) side of the aircraft in the "living quarters" compartment behind the landing gear. The Homelite APU was powered by a 1 cylinder 2 stroke engine, and were often referred to as a "Putt Putt".  They were only used if the Main batteries were weak or discharged.

This is a photo of a Homelite APU from a B-17. They were also used on B-24s and other large WWII aircraft.  It is nearly identical to the ones we used in the civillian PBYs that I flew.

The original military PBY-5A APU installation looks a little different. It appears to be located on the starboard side in the central compartment near the landing gear. It would have been removed when the water bomb tanks were installed.


How would you brief passengers who will try flying your plane? Following up on this question about pilots letting passengers fly the plane, suppose you’re in a Cessna 172 with passengers and you have your PPL. If you want to let a friend try flying the plane, you might climb to 3,000' AGL and get clear of other traffic. You’d probably get to $V_A$ or a little less and trim for level flight. Then, you might let them try some shallow turns. You’d probably say:

Don’t fight me on the controls
If I say let go, let go immediately
Don’t move any of the controls very rapidly
Don’t move any of the controls to their limits

What else might you say? Are these things correct? What else might you let them try?

I find that virtually all the passengers I've let fly for the first time were already so scared of the controls that no "safety briefing" of that sort was necessary.

  Don't fight me on the controls.

  If I say let go, let go immediately.

If you suspect there's even a remote chance of either of these problems, maybe you shouldn't be letting this person fly your plane.

  Don't move any of the controls very rapidly.

  Don't move any of the controls to their limits.

In most small airplanes without hydraulics, it takes quite a bit of force to deflect any of the controls rapidly to their limits. And as soon as your first-time passenger starts to push on the controls, they're going to feel increasingly strong g-forces as the plane responds. For first-timers, this is usually a pretty intimidating feel. If someone is pushing too hard, they're going to feel it, and almost certainly back off or let go entirely.

"Positive transfer of control" using 3-step acknowledgment such as "You have the controls" / "I have the controls" / "You have the controls" is a good idea for flight training, or for flights with 2 pilots taking turns at the controls; but in my opinion it's not necessary for a joyride with a friend. As the PIC, and the only licensed pilot in the cockpit, you need to be monitoring the situation at all times anyway. If you decide the situation requires you to reassert control, you can simply ask them to release the controls. If you can't trust the person to do this promptly, you probably shouldn't be letting them fly your plane anyway; a preflight safety briefing isn't going to solve that.

To be as safe as possible, you can take the following steps before allowing your passenger to fly (some of these you already stated):

Select a location away from controlled airspace, busy airway/routes, or other special-use areas like drop zones.
(Optionally, if you don't mind the extra radio chatter) Tune a nearby ATC radar facility (approach/center) and request radar advisories. Tell them you'll be maneuvering in a certain area.
Climb to a sufficient altitude to allow good clearance from all terrain and obstacles (antennas, etc.), and to allow enough altitude for recovery if your passenger should somehow manage to stall or enter a steep dive or something.
Trim for straight & level flight at $V_A$ for your current weight (lower than the gross-weight $V_A$ you get out of the book).
Make a set of clearing turns and scan for any traffic in the area.
Give your systems a once-over and verify you have sufficient fuel.
Hand over the controls!

You didn't specifically ask about this, but I've flown with a lot of first-time passengers, people who have never been in an airplane. Both children and adults. Many of them are understandably quite nervous. Here are some things I try to do to make it as easy, fun, relaxed and stress-free as possible for them:

Give them a simplified, plain English description of the flight. Tell them exactly what you plan to do and what order things will happen in. E.g.

  First we're going to start the engine. I'll get on the radio and get clearance from the control tower. Then we'll taxi out to the runway and stop for a few minutes while I go through some checks to make sure the plane's in good shape. Then we'll take off and head out to the east to do some sightseeing. While we're up there, if you're comfortable and would like to try your hand at the controls, we can do that. When we're done with that we'll turn around and head back to the airport, land, and taxi back in.

Don't use fancy words or terms that a non-pilot wouldn't understand.
Help them enter the airplane. Show them how to open and shut the door. Show them how to buckle and unbuckle their seat belt.
Ask them if they have any questions.
Do your normal preflight safety briefing, again using simplified English and avoiding pilot terms. Limit it to points that are relevant to a passenger (avoiding the controls, staying quiet if asked, opening the door). They do NOT need to hear about what you're going to do if you have an engine failure on climbout. If this is a normal part of your preflight / before takeoff briefing (as it should be), say it to yourself mentally, not out loud.

During the flight:

Talk your way through everything you're doing. When you're ready to do your run-up, tell them:

  I'm about to run the engine up to power to make sure everything's running smoothly. I'm holding the brakes so we're not going to go anywhere, but the engine will get pretty loud for a minute.

When you're doing your magneto / prop governor checks:

  Now I'm going to do some things to the engine to make sure it's running right. It's going to make some pretty funny noises, but it's perfectly normal.

Talking through everything accomplishes a few goals:

Avoids startling the passenger with something unexpected. A prop governor check sounds really bad to somebody who knows about engines but nothing about planes. A stall horn in the flare may be perfectly normal to you but a loud buzzing alarm is the last thing the first-timer will be expecting to hear. Tell them about it ahead of time.
Makes the passenger feel like they're a part of the flight and not just dead weight in the plane.
Keeps you focused on your tasks as PIC and discourages you from getting distracted in conversation with your passenger.

Make the flight as smooth as possible. Don't overcontrol the airplane. If you drift 100' from your intended altitude, don't pull 2 g's to get back up to it. Make it slow and gentle. They're not a pilot, chances are they're not going to know you drifted 100 feet. They will know if you jerk the thing around. DO NOT hot dog the airplane. You may be bored with slow, gentle flight, but your passenger isn't.
Speak slowly, clearly and confidently.
Smile and try to look like you're having fun. Your first-time passenger is probably feeling pretty vulnerable. When people are vulnerable they feed on the emotions of the people around them. If you look like you're having the time of your life, they're probably going to have fun too. If you look angry, ticked off or scared, you're going to scare them too even if the flight is perfectly smooth. This is especially true and critically important with children!

If/when they're ready to take the controls:

Show them how the yoke controls pitch and roll. Do some (very) gentle climbs and rolls to illustrate what various control inputs do.
Tell them to look outside and not to worry about all the fancy intimidating lights and dials in the cockpit. Tell them that the only tool a pilot needs to fly the plane in good weather is their eyes.
Tell them to relax and have fun! Assure them that they aren't going to crash the plane or break anything and that you're there watching and won't let them do anything unsafe.
After a few minutes, once they get the hang of basic control inputs, you can start to tell them about sight references: show them how to look at the horizon and tell if they're banked, climbing or descending. After 15-30 minutes you should be able to get virtually any passenger to be able to hold straight & level attitude and make gentle turns. Being able to accomplish this is very rewarding for your passenger and makes them feel like they achieved something. It encourages their excitement about aviation and makes them want to fly again.
Don't forget to do your job: scan for traffic. Monitor your engine gauges. Listen for ATC calls. Don't stray into controlled airspace. "Maintain situational awareness."

I've had a great deal of success using these tips when flying with first-timers and children. In 16 years of flying I have had only one bad experience, with an adult passenger who had an unknown (to me) and pretty severe anxiety problem and had a panic attack shortly after takeoff. A couple of kids have fallen asleep on me (which I took as a compliment). Everyone else had the time of their life. And let me tell you... if you're someone who loves flying, there is no better feeling than sharing that with someone else and watching their excitement. It's the closest you'll ever come to reliving your own first flight, which hopefully you remember fondly because somebody cared as much as you do about being the best possible ambassador for aviation!


What is the ICAO equivalent of a "point out"? In FAA air traffic control, when we have an aircraft that is transitioning through someone else's airspace that we want to talk to we do a "point out":

  Point Out. A physical or automated action taken by a controller to transfer the radar identification of an aircraft to another controller if the aircraft will or may enter the airspace or protected airspace of another controller and radio communications will not be transferred. - source

Can anyone please tell me what the equivalent of a point out is in ICAO (with a reference to ICAO Doc 4444 if possible)?

We have an aircraft that is transitioning through someone else's airspace that we want to talk to we do a "point out".

Basically you want to grab the attention of the other controller wrt a particular plane that they are controlling (or unaware of), in ICAO 4444 lingo that's a General Point message:

  11.4.2.5.19 GENERAL POINT MESSAGES The General Point message shall be transmitted to draw the attention of the controller receiving the message to a flight to support voice coordination. The General Point message shall include details of a flight that may have been previously unknown to the receiving unit, to permit it to be displayed if required. This may include, for example, a flight that had planned to operate in airspace under the control of one ATS unit requesting climb or diversion into airspace controlled by another ATS unit which has no details of the flight.


How does the G1000 differ from an airliner’s avionics? I'm going through my multi-engine rating, and my flight training has always been on the G1000. I've had a simple system course on the CRJ-200.
In terms of IFR flying, I really don't see much difference between the two avionics in terms of procedural functionality, except for the FMS.
Anyone can point out what are some of the major differences between the two?
This question is only out of curiosity.

The CRJ's Rockwell Collins FMS-4200 as used in the CRJs is a 1980s design and is far "cruder" than the G1000.  You have a little control head with a small display screen and keyboard where you interface with it.  The G1000 is more like using any modern computer application where much is presented on the main screen with trackball or mouse selectable commands and data with a fairly intuitive presentation.  On the FMS-4200, you have keys on the side of the display to select options that appear next to each key, keys to select various modes on the control head, and you have a one-line "scratchpad" where you can type in text commands or other data.
You could say it's a bit like the difference between using the icon based Windows operating system and the older direct key entry MS DOS.  With a system like the 4200 you have to learn the selections and menus and keystrokes directly, instead of just knowing how to find your way around a pictorial presentation on a large screen that you use like any modern computer application.
If you've mastered the G1000 and you later find yourself on a CRJ type course having to figure out its 1980s FMS system, your G1000 skills probably won't help you that much and you'll just have to figure out the "old school" interface as something new.  To get though the type course in one piece, mastery of the FMS is critical, so if the opportunity to go on that course comes along, get hold of the training material as early as you can to get as much of a head start as possible.


Is the airport capacity related to number of runways? Lets say two different airports have the same number of runways, and terminals capable of handling any number of passengers. I realise that year round climate may have an effect on the number of days that planes may be able to land. But are there any other major factors which are able to make a big difference to the number of passengers those airports would be able to process?
For example, do the placement of runways interfere with air traffic control?

If both make maximum use of their capacity, is it likely that both would have very similar numbers of annual passengers?

Airport Capacity

At major airports the capacity of the system of runways is the most restricting element. While it is usually possible to increase capacity of the other airport elements or adding a new runway (plus associated taxiways) is very expensive and takes a very long time to complete.

The runway capacity is the principal cause of most extreme instances of delays that lead to widespread schedule disruptions, flight cancellations and missed flight connections. The runway capacity varies greatly from day to day and changes are difficult to predict (even a few hours in advance).

Factors:

The capacity of the runway system depends on several factors, the most important ones:

Mix of aircraft classes using the airport: the aircraft mix indicates composition of aircraft fleet that is using any particular runway (e.g. 25% S, 60% L and 15% H).
Separation requirements imposed by the ATM system: due to wind tip vortices, leading aircraft and trailing aircraft must be separated by a determined distance (Heavy aircraft are the ones that produce more wake turbulence).
Type and location of exits from the runway: trailing aircraft of any pair cannot touch down on the runway before leading aircraft is clear of the runway. High-speed runway exits (also well placed runway exits) reduce runway occupancy times for arriving aircraft.
Mix of movements on each runway and the sequencing of the movements: specified for all combinations of consecutive operations (arrival-departure). There's an important trade-off between maximum arrival and departure rates that an airport can achieve.
Lateral separation: (especially in bad weather) between aircraft approaching the same airport on parallel runways.
Sequencing and separation of departing and landing aircraft on runways that intersect.
Sequencing of aircraft approaching airports located in close proximity to one another, where one aircraft must cross the path of another aircraft landing at a nearby airport.
Direction and strength of winds.
Noise-related and other environmental considerations and constraints.

Conclusion:

It is difficult to predict the capacity of the runway system of an airport, so it is difficult to compare two airports with similar runway characteristics, since the factors depending on the airport capacity involve different design and operational parameters. Furthermore, everything is subject to the important probabilistic factor, the weather, which makes the prediction and comparison of airport capacity even more difficult.


Why are aircraft of Russian origin not subject to frequent weighing and CG calculations like western aircraft? Western miltary a/c maintenance requires routine weighing of the plane yearly or during major inspections.Whereas Russian miltary a/c maintenance does not insist on this kind of weighing,so much so that weighing is not part of any maintenance  schedule after initial manufacture ! Can some one give any plausible reason for this anomaly ?

Western doctrine is to keep all aircraft of one type in identical conditions. Once you change one thing, you do it for all aircraft of this type at the same time (or create a subtype). Routine weighing makes sure that the individual aircraft conforms to the type certificate.

Russian doctrine sees every airplane as an individual, and if something is changed, it needs to be documented, but not necessarily done on all other planes of that type. To every airplane belongs a (mostly) metal box with all documents, and they should tell you exactly what has been modified since it was produced. Weighing is now part of maintenance, but needs not be done if nothing has been modified.


What is the maximum holding time? When arriving at a busy airport, airliners may be stacked in holding patterns, increasing flight time. I know airliners are required to carry extra fuel in case of rerouting (including a safety margin).

Once in holding pattern, aircraft may be reordered (not as simple as a FIFO), thus some aircraft may stay longer in their holding pattern.

Is there a legal maximum time an aircraft can stay in an holding pattern? If needed, the question may be narrowed to EASA and FAA regulations.

No, there is no limit. Aircraft stay as long in holding patterns as they have fuel on board.


Are task cards still used in aircraft maintenance? I used to work for a company making maintenance software for the shipping industry. Each component, from a cylinder in an engine to the furnace has to be inspected after (e.g.) 10,000 running hours, or every 2 years, etc.

My question is:

Are task cards like the one below still used in aviation, or is there a more up-to-date way of working nowadays? (The PDF I got this from is 10,000 pages long)
What must airlines do to ensure their planes are maintained according to schedule?

I just watched Engineering Giants - Jumbo Jet Strip-Down, following a British Airways 747 on its D-Check in 2012.

At least for BA, it would seem that paper task/job cards are still heavily used. Apparently there are over 12,000 individual jobs.

I've taken a short (7 secs) clip from the episode, showing walls full of task cards:


What is the function of a sweep cable? This is Goat3 ultralight with sweep cables,what is the fuction of these sweep cables?

To keep the wings straight.

If you remove them there is very little to prevent the wing from rotating around the vertical axis.

All the other cables are attached to the king post or the seat. This cannot provide the leverage needed to counteract the wing yawing relative to the seat.