Air France 296

[Horatio]

Saw an interesting documentary on this 1988 crash last night. The pilot claimed that the black boxes recovered from the plane were switched out with other ones, which lead to him being solely blamed for the crash. Just wondering what folks on this board thought about this:

http://www.airdisaster.com/investiga...96/af296.shtml

[Evan]

A few things:

OEB 19/1: Engine Acceleration Deficiency at Low Altitude
This OEB noted that the engines may not respond immediately to throttle input at low altitude.

I'm not sure what actual issue was being addressed in the OEB, but high-bypass turbine engines do not produce effective thrust immediately upon throttle input if they have been at flight idle for a certain period of time. No pilot should expect them to. The report states that the engines had been at flight idle for an extended period of time, thus normal thrust-lag followed and the descent could not be arrested.

OEB 06/2: Baro-Setting Cross Check
This OEB stated that the barometric altitude indication on the A320 did not always function properly.

Firstly, at 100ft AGL, the pilot must be flying visually and using visual references for altitude. Secondly, he must be monitoring the radar altitude, which was correct, not the barometric. Thirdly, the radar altitude was triggering the EGPWS altitude callouts. They are on the CVR.

[3WE]

Originally Posted by Evan

high-bypass turbine engines do not produce effective thrust immediately upon throttle input if they have been at flight idle for a certain period of time.

Awfully sweeping generalization there.

The error is that they did not follow the paramaters that they were supposed to when doing the flyby.

[Evan]

Originally Posted by 3WE

The error is that they did not follow the paramaters that they were supposed to when doing the flyby.

Where did you get that? I'd like to see those parameters. From what I've read, they didn't have the proper planning for this demonstration.

[Evan]

Originally Posted by 3WE

Awfully sweeping generalization there.

Not really.

Here's a sweeping generalization from NASA Technical Memorandum 104238:

Thrust Response

Most turbine engines respond faster at higher thrust levels than at lower thrust levels. In particular, high-bypass turbofans may be very slow in response at flight idle. For example, a typical high-bypass-ratio engine takes as much as 3 sec to go from flight idle to 30-percent thrust, then 3 more sec to go from 30- to 100-percent thrust.

Now watch that video and count to six...

[orangehuggy]

i have always had my suspicions about this one, mostly because when an airliner crashes into a forest, burns and breaks up, even at lower speed, the likelihood of 133 of the 136 on board surviving is miraculous, see the Polish president flight or a dozen more we could research to compare

[Evan]

Originally Posted by orangehuggy

i have always had my suspicions about this one, mostly because when an airliner crashes into a forest, burns and breaks up, even at lower speed, the likelihood of 133 of the 136 on board surviving is miraculous, see the Polish president flight or a dozen more we could research to compare

Suspicions of what?

Polish 101 crashed inverted. This one remained wings level and sunk into the trees at low speed in a fairly controlled fashion (thanks to alpha protect). Look at the Turkish 1951 crash. Plenty of survivors there.

[Gabriel]

Originally Posted by orangehuggy

i have always had my suspicions about this one, mostly because when an airliner crashes into a forest, burns and breaks up, even at lower speed, the likelihood of 133 of the 136 on board surviving is miraculous, see the Polish president flight or a dozen more we could research to compare

Please, don't compare smoothly landing on thick tree-tops at about stall speed with rolling inverted and falling nose first into the ground.

That said, they were lucky. The thick and relatively smooth tree-tops slowed the airplane down a good bunch before sinking into the thicker trunks, and the fuselage missed hitting thick trunks.

And all that said, what do you propose? There are several amateur videos taken from different angles showing the accident. The accident DID happen. Do you think that everybody on-boar died and the families didn't complain while at the same time there was a fake load of crew and passengers to act as survivors?

[orangehuggy]

Turkish did not crash into a forest or burn, i think there is a small chance that families were paid off, not that i'd bet on it or anything

[Gabriel]

Originally Posted by Evan

A few things:

I'm not sure what actual issue was being addressed in the OEB, but high-bypass turbine engines do not produce effective thrust immediately upon throttle input if they have been at flight idle for a certain period of time. No pilot should expect them to. The report states that the engines had been at flight idle for an extended period of time, thus normal thrust-lag followed and the descent could not be arrested.

I don't know what was in that OEB either, but in FADEC engines it is possible to optimize the response in time of several engine elements (fuel metering valve, variable angle vanes, surge bleed, etc.) to minimize the spool-up lag, which will still be significant (minimize means as short as possible, not shorter than that).

[Gabriel]

Originally Posted by orangehuggy

Turkish did not crash into a forest or burn

Turkish stalled at 400 or 500ft and crashed with little forward speed but a lot of vertical speed, which is the most dangerous because you cannot slid "down" (as you slid forward) and the spine is quite sensitive to compresion loads. And, most people survived too.

Regarding the "burn" part, that there is an explosion or fire isn't a synonym of people being burned. The fuselage is quite resistant to the penetration of flames. I don't know how it happened, but if the wings were ripped by trees and left behind, and that is what ignited, I can imagine most people not being affected by the heat.

[orangehuggy]

i'm quite sensitive when a tree is coming at me at 150mph, but i digress

[3WE]

Originally Posted by Evan

Where did you get that? I'd like to see those parameters. From what I've read, they didn't have the proper planning for this demonstration.

AJ Goes Airbus thread:

Originally Posted by Gabriel

...
-They made the flyby too low (it was supposed to be done at 100 ft).
-They made it too slow.
-The engine thrust was set too low.
-They started to go-around too late.
...

[Evan]

Originally Posted by 3WE

AJ Goes Airbus thread:

Those are just the facts after the fact, not planned parameters. The pilot WAS trying to make the flyby at 100 ft but arrived there without the energy to stabilize (too slow, no thrust available). The attempted go-around was obviously not part of the plan...

The altimeter issue is pure smoke.

Staging this flyby should have involved a good bit of planning by the pilots on how to execute it, and I have seen no evidence that this planning was done. Just good old basic airmanship alone should do the trick....

"Hey, I'm pushing the throttles... why doesn't it go?"

[3WE]

Originally Posted by Evan

The pilot WAS trying to make the flyby at 100 ft but arrived there without the energy to stabilize (too slow, no thrust available).

If you don't have the energy to stabilize at 100 ft, how do have energy to stabilize at 50 feet? (Not saying it can't happen, but that is a very difficult trick and I want to see the data that allows you to say that.)

The video suggests he had energy to level off higher AND had a lot of extra energy to fly level for a good long way.

If he had leveld off at 100 feet, it very well could have "changed the course of events" slightly, but just enough to get him to power up sooner, AND THEN have some buffer to settle towards, but not into, the trees while the engines spooled up slowly (as they generally do).

Then he could still bitch about how strange the Airbus FBW acted, but we wouldn't be trying to figure out if he had a valid complaint or not.

[Evan]

I think he started the descent late, came in too slow with too much vertical speed and engines at prolonged idle, could not arrest the descent to level off at 100ft, fell through, firewalled the throttles to go around but the spool-up lag ruined that plan. None of this has anything to do with FBW or the aircraft systems (the CFM56 is a common Boeing appliance as well). He must have known he was below his MDA because the radalt was spot on and the annunciations were calling out altitude.

This scenario seems desperately familiar doesn't it?