Aircraft design What is FADEC

Community / Comments on current news / Swiss-Boeing lands in cold chamber ...

Post from 02/03/2017 - 12:18 am
@ kaktus100:
If there is ash, the engine stops, there is a lack of air (oxygen ...)

More precisely: There are many small silicate particles in an ash cloud and since the combustion temperature in the engine is higher than its melting point, they melt there in order to solidify again in the colder engine parts. There they interfere with the air throughput, so that in the best case scenario the engine only loses power, but it can also go out and in the worst case it is destroyed by several stalls.

But back to topic ...
Post from 03.02.2017 - 01:52
@ Boeing757767: Oops, I actually misread it and typed something in a hurry, sorry for that ...
@fbwlaie: As I said, there is no auto-shutdown when there is vibration. With the A320, if vibrations are the only problem, the engine does not have to be switched off at all (the procedure provides - if icing can be ruled out - to pull out the gas and then to continue operating the engine below the warning level). The philosophy behind this is that if there really is a more serious engine problem there will be other indications that, if necessary, should cause the crew to shut down the engine. By the way, depending on the cause of the error, the vibrations of a shutdown engine that rotates in the air flow without a drive (windmilling) can be significantly worse than those of a running engine, due to resonances etc. (luckily no personal experience with it, but makes sense ... .)
Post from 03.02.2017 - 07:53

In my opinion, a 747 entered an ash cloud over Indonesia.

Right, that was the 747 (1982, BA 9, B747-200).

At Mt St Helens it was a B727 and your DC 8.

I messed up.

Post from 03.02.2017 - 09:19 o'clock
Short question to the experts.
How long can a passenger plane sail from cruising altitude if all engines have failed?
Post from 02/03/2017 - 09:20 am
Short question to the experts.
How long can a passenger plane sail from cruising altitude if all engines have failed?
about 180 km
Post from 02/03/2017 - 10:29 am
Short question to the experts.
How long can a passenger plane sail from cruising altitude if all engines have failed?

It depends a lot on how heavy the aircraft is and how high it flies. Cruising altitude can actually be anything from FL300-FL410. The wind also has an influence on this.

The longest glide flight was achieved by Air Transat 236, which covered about 120km in 19 minutes.
Post from 02/03/2017 - 12:55 pm
Short question to the experts.
How long can a passenger plane sail from cruising altitude if all engines have failed?
about 180 km

The question was addressed to experts and flydc9 answered .......

Its value would be correct, from FL 500! No airliner can go that high.

As marwol writes, this depends on a number of factors. Also e.g. what I do after the engine failure, first dive to have the optimum relight speed (ca 280-300kts IAS) or whether I go straight to a best guild speed.

As a rule of thumb you can take FL by 10 times 2, then you get the nautical miles that you can still sail. In other words about 2 NM per 1000ft. At heights it tends to be less, and more at medium heights. From FL200 you can count on 2.5 NM / 1000ft.

And of course the NM here are NAM (nautical air miles).
Post from 02/03/2017 - 2:05 pm
Post from 02/03/2017 - 2:09 pm

Your contribution sounds convincing, but an article on the British Airways incident at Jakarta is also quite convincing:

"Without engine thrust, a 747-200 has a glide ratio of approximately 15: 1, meaning it can glide forward 15 kilometers for every kilometer it drops. The flight crew quickly determined that the aircraft was capable of gliding for 23 minutes and covering 91 nautical miles (169 km) from its flight level of 37,000 feet (11,000 m). "

Since two GE90 engines generate significantly less drag than 4 RB211 engines and if one also assumes that an airplane design from the nineties is more aerodynamically sophisticated than a humpback design from the sixties, then flydc9's statement should even be conservative.

Post from 03.02.2017 - 14:44
At the very end of this thesis you will find some commercial aircraft with calculated glide ratios. A 320 is otherwise better than A 321:
Post from 02/03/2017 - 3:45 p.m.
@Muck and FW190

Thank you for the two contributions. The thesis is not uninteresting. In my opinion, the most important is on page 22, chapter 5:

"Depending on the flight condition, an aircraft has different glide ratios." I doubt whether it makes sense to calculate with the maximum glide angle from cruising altitude to landing / impact.

Likewise the BA9 with its 15: 1. They only had that until the engines were on again. I do not think that this is relevant in practice over the entire height, so to extrapolate it to a fictitious range.

Again from practice:

When all engines are off, a distinction has to be made: fuel remaining, no fuel remaining.

No fuel remaining: I go to minimum speed. Airbus, for example, specifies Green there and looks for a landing place for me. Glide about 2.5 NM / 1000ft. In the end it gets steeper again because you want to land as slowly as possible and therefore extend the flaps and probably also the landing gear. This doubles the glide angle at the end, i.e. just over 1NM / 1000ft.

Fuel remaining: I try to decrease with opt relightspeed (depending on the aircraft between 250 and 300kts) so that one or more engines come on again. I do this up to the height at which the APU can be started (on many aircraft around FL250-FL200). From there on I do green dot and APU assisted starts. So first steep, a little less than 2NM / 1000ft, then more, about 2.5NM / 1000ft and at the end, if it did not work with starting, see above, very steep.

If I read 15: 1 and Wikipedia explains that this is 15km forward for every 1000m altitude, then you can see how relevant such information is in practice. You can see the foot on my altimeter and the rings on my NAV display are in NM. Likewise, a DME to a place VOR, which I might want to reach, shows in NM. I would like to see who is counting on km and 1000m. Or do all Tupoley fly here?

So let's go back to practice: All ENG out, look at the altimeter, take height times 2, look for a landing place in the distance, depending on the wind arrow +/-, or less. Then you have a real chance. Have flown the buck empty, then you can do a little more.

This post was edited on 03.02.2017 15:59.
Post from 03.02.2017 - 16:27

After looking at the link from FE190 (1000 thanks for that !!!), I know where the different numbers come from:

In practice, the Schippi Airbus can only roughly multiply the height on the altimeter by 2, while for an A330, A340 or the Boeing it is better to take the height times 3 from this article.

And so, 70NM in the A320 on the B777 become 105NM when you are traveling in FL350 and both FADECs call it a day.
Post from 03.02.2017 - 16:33
At the level of the experts discussed here, I cannot keep up. So please forgive me that I, as a non-aviation enthusiast and for all equally "poorly poor" people, calculate faithfully in meters in German.

According to the Wiki, Transat had an engine failure at an altitude of 39,000 feet or 11,887 m, whereupon a descent to 30,000 feet = 9144 m was initiated. The second engine failed 13 minutes later. Since the 30,000 feet have already been reached, I now assume.

After that, the glider flight lasted 120 km from an altitude of 9144 m and the landing speed was 370 km / h. That would be 13.2 km / 1000 m altitude. That is not so far removed from the rough calculation 15: 1 of the British Airway, especially since a defined goal and not a range record was strived for here.

However, it is clear that depending on the load / load, fuel supply, aircraft type and other parameters, different results will come out. We hope that these theoretical calculations remain and that no pilot has to calculate them more precisely in real time.
Post from 02/03/2017 - 6:06 pm
@runway what
@schippi calculates here as a rule of thumb but also fits your example well:

FL 300 = 30,000 feet through 10 times 2 = 60 NM = ± 110 km. Maybe they could have flown a few km (or NM) further. But we don't know (don't feel like looking for that) what the wind component was like.
How does the Austrian say "it fits"
Post from 02/03/2017 - 6:38 pm
Despite all the arguments, I find an auto shutdown more than dangerous. Finally, the "shaft break" fault can also be a sensor fault. Ultimately, this results in a completely different situation for the crew, who then no longer "have the final decision-making authority".

Concerning the argument "Nobody wants the B748 and the A340 can only be scrapped", business graduates should read the TCOs. The maintenance of the 4 A340 engines on the A340-600 is cheaper than the maintenance of the 2 engines on the Dreamliner. Scrapping the machines makes no sense at all in the age of cheap fuel. And maybe that's one of the reasons why Emirates took over most of the passenger traffic between Europe and Asia / Africa. I always choose the A380 if there is a carrier on the route (or occasionally 747 or still existing A340s) if there are longer distances over water.

When it comes to how long an aircraft can fly without engines, that depends to a certain extent on the glide ratio (which is slightly different depending on the aerodynamics and weight of the machine), but in general the calculations of the pre-posters are of course correct, you get there depending on weight and altitude / Airspeed on 100-150km which corresponds to about 20 minutes.