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TACA aircraft crashed in Honduras

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TACA aircraft crashed in Honduras

Old 7th Jul 2008, 05:55
  #281 (permalink)  
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Always the soul of cordiality, Lemurian.

Thanks anyway for clarifying the calls.

Originally Posted by Lemurian
You cannot derive anything from that spoiler position as it is very easy to restow them ( one T/L above idle is sufficient).
Didn't know that either, thanks. About the A320 dual-purpose levers - I know that to engage reverse you pull them both back against the stops, then press the side-catches to move them into 'reverse idle,' then pull them back further for reverse thrust.

How does it work as you cancel reverse? Presumably it's the same process the other way round? Trip the catches, push the levers forward, then pull them firmly back against the stops once again to make sure that you're back in 'forward idle'?

Would it be possible, in a pressure situation, to be a bit careless, and not retard one or both levers fully after cancelling reverse thrust? Thus ending up with the ground spoilers retracted, and maybe some (highly unwanted) forward thrust as well?
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Old 7th Jul 2008, 06:28
  #282 (permalink)  
 
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Spoilers

RWA

I don't think the spoilers retract until the speed brake lever is depressed, normally as you leave the active, regardless of thrust lever position (but I shall confirm by looking it up).

To come out of (idle) reverse thrust and into the forward (idle) thrust range, simply move the TLs with enough 'force' to overcome the resistance at the gate.

Cheers

Shaker.
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Old 7th Jul 2008, 10:13
  #283 (permalink)  

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Shaker One,

For the "five" call to be generated, you may well have an extended floater on your hands.
The flare is normally started at 20 ft. from the recording, six seconds elapsed between that auto call and the touch-down. That's a longish flare or a short floater (at my speed assumptions, that's also some 500 m of runway gone).
If there was any danger of an extended landing roll, why does the CVR record the engines spooling down 'early' indicating that reverse thrust had been cancelled? You'd keep them in full reverse until the fullstop if necessary.
Good point. It looks, till that instant that for the handling pilot, everything was quite normal ; he even anticipates the 70 kt call by cancelling the reverse thrust.
Does 'decal' on the CVR mean decel? If so, this was given after the 'manual breaking' call. That's the wrong way round isn't it? The decel light will extinguish once manual braking is applied.
Good point, again. The "DECEL" light is on each switchlight of the autobrake system. My only explanation is that the F/O referred to *some deceleration* achieved and my gross computation of that deceleration value is in fact superior to the norm achieved with "MED" auto brakes (3.4 m/s/s iso 3 m/s/s ).
I don't think the spoilers retract until the speed brake lever is depressed,
One T/L forward at more than 20° will retract the ground spoilers.
We'll wait for the official investigation to be concluded.
Agreed.

RWA,
I know that to engage reverse you pull them both back against the stops, then press the side-catches to move them into 'reverse idle,' then pull them back further for reverse thrust.
You know wrong. Pull T/Ls back to the idle stop / Reach in front of T/Ls and lift the reverse *pallets* that unlock the stops / Pull T/Ls into reverse range / Modulate.
The gesture is very similar to another set-up but is more precise.
How does it work as you cancel reverse? Presumably it's the same process the other way round? Trip the catches, push the levers forward, then pull them firmly back against the stops once again to make sure that you're back in 'forward idle'?
Just push them out of the reverse range. The little *pallets* will click back down, thus preventing another ingress into reverse. Confirm the idle stop.
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Old 7th Jul 2008, 13:01
  #284 (permalink)  
 
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Re deceleration; DECEL light. Surely this only indicates that the system is engaged (and working), and presumably ‘without a gauged’ measure, the system does not indicate how much of the demanded deceleration is achieved? Furthermore, if such a quantitative system measured the decal, or more likely, the crew who normally has to judge the amount of achieved deceleration, it is difficult to differentiate between decal provided by the auto brake (brakes) and that from reverse.
Thus in this accident, reverse might have been providing the majority of the decal – poor runway friction, and when reverse was cancelled (habit) the brakes were not able to replace the demanded deceleration value, whether from auto or manual braking.
The position on the runway when reverse was cancelled (touchdown area for the other direction) may have be more susceptible to a wet slippery surface (rubber deposits), all of which add up to the crew having difficulty or insufficient time to detect the change in deceleration due to the lack of adequate braking; apart from running out of runway due to other contributing factors.
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Old 7th Jul 2008, 13:50
  #285 (permalink)  
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Re deceleration; DECEL light. Surely this only indicates that the system is engaged (and working), and presumably ‘without a gauged’ measure, the system does not indicate how much of the demanded deceleration is achieved?
Actually is does, the 'decel' light tells the crew that 80% of the commanded deceleration rate is being achieved.

However, your point remains very valid as there is no way of differentiating between the deceleration provided by the reversers and that which is being provided by the brakes.
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Old 7th Jul 2008, 14:12
  #286 (permalink)  
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Originally Posted by Lemurian
You know wrong. Pull T/Ls back to the idle stop / Reach in front of T/Ls and lift the reverse *pallets* that unlock the stops / Pull T/Ls into reverse range / Modulate.
Thanks again, Lemurian. To impart my full knowledge of airliner throttles so far (though I did occasionally fly powered aircraft as well as gliders! ):-

1. Boeing 737 - (and presumably other Boeings - from sitting on the jumpseat) - separate throttle and reverser levers (the latter higher up on the pedestal). You pull the throttles right back, then reach for and pull the reverser levers (which won't move unless the throttle levers are in 'idle'). To cancel reverse, you just 'return' the reverser levers - as far as the main throttles are concerned, they've been 'finished with engines' ever since you brought them right back.

2. Airbuses (A330 on - from photographs) - similar setup, except that the reverser levers, though separate, are mounted on the front of the main throttle levers. Same principle, though - once you've pulled the main throttles back, they 'stay where they're put,' and you reach over them and work with the reverser levers only. To cancel reverse thrust, all you do is push the separate, auxiliary, reverser levers fully forward/down.

3. Airbus A320 (again from photographs etc.) - the same levers do both jobs, much like the gear lever on an automatic car. You pull the levers back to the 'stop' (which is in fact called the 'Idle Detent'); and then, to engage reverse thrust, you lift the latches and pull the SAME two main levers back into the reverse thrust quadrant. To cancel reverse thrust, you push the levers forward again into the idle 'detent.'

In both cases, 'retarding' and 'cancelling reverse,' having moved the levers into 'Idle,' you have an extra job to do, compared to the other aeroplanes I've described. You have to make extra sure that you actually HAVE got the levers to 'idle,' and not anywhere in front of it or behind it. Which you do by giving them a further firm pull back to make sure that they're hard against the stops?

YouTube - Airbus A320 landing Ilha da madeira

Originally Posted by Lemurian
Confirm the idle stop.
For further reference, please see the above video of a (really good) A320 landing at Madeira.

Have I got it right now?

Last edited by RWA; 7th Jul 2008 at 14:25.
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Old 7th Jul 2008, 14:56
  #287 (permalink)  

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the 'decel' light tells the crew that 80% of the commanded deceleration rate is being achieved.
your point remains very valid as there is no way of differentiating between the deceleration provided by the reversers and that which is being provided by the brakes.
OK, but there is no way that the reversers alone could achieve the 2.4 m/s/s required for the MED setting, and I say again, the deceleration achieved -from the moment the reversers have been announced "active" by the F/O and the 70 kt call, that is to say before auto-brake application- is in fact superior to the requirement.
On the same subject, the influence of the reversers is limited, certainly not as important as the brakes'.

On the subject of that value of deceleration, had it continued, the airplane would have come to a stop some 12 seconds after the 70 kt call ( 42m/s diveided by 3.4 m/s/s equals 12 + ). that means some 252 m later than the 70 kt point.
Going back to my figures, the distance from 40 ft (rad-alt call to a complete stop would have been 1580 m + 252 m = 1802 m.
Though still a ball-park figure, it tells me two things :
1/- Their landing technique, all things going normal would have used most of the runway...
2/- As they were so close to achieving a stop on the runway, the excess speed they had was very low, which explains the survivability of the crash, even after the drop over the cliff.
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Old 7th Jul 2008, 16:17
  #288 (permalink)  
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OK, but there is no way that the reversers alone could achieve the 2.4 m/s/s required for the MED setting
I agree. But there was also no way for the crew to know if the brakes/wheels alone had sufficient grip to achieve the required deceleration on that wet runway.

I agree that reversers are a distant second to brakes when it comes to slowing down the aircraft but in wet conditions their importance increases markedly.
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Old 7th Jul 2008, 17:29
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Not that it really matters, but I thought the Flight Warning Computer (FWC) does most of the callouts, not the EGPWS. Our Simulator does it that way, and the FCOM supports it. Comments?

Just kind of wondering how many different set ups there is out there. Thanks.
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Old 7th Jul 2008, 19:30
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0-8, thanks for the info.
The DECEL light could be an interesting example where crews might inappropriately associate an ‘aircraft’ indication (total deceleration) with a particular system (auto brake) either due to the way it has been taught or from its location – false association, a problem of training/automation.
For interest, does the DECEL light work with manual braking – identifying the level selected on auto brake?

Lemurian, accepting that reverse alone could not archive the required deceleration. However, with some effective braking and aerodynamic drag there was apparently enough deceleration to achieve 80% of the target (DECEL light).
Is the light ‘latched’ ON even if the required decel level is not maintained? If it is, and the brake effectiveness reduces and/or aerodynamic component reduces (slowing down), then the thrust reverse contribution becomes a significant proportion of the total (remaining) deceleration. Unfortunately the decel level probably isn’t enough in the prevailing conditions and the crew are unlikely to determine this until it’s too late. However, there could have been some feedback from foot force when manual braking was used.
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Old 7th Jul 2008, 22:44
  #291 (permalink)  
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If you chaps will excuse a non-pro question, is there any sense in which the use of reversers alters the (aero-)dynamics of the situation such that the brake application is more effective *in itself* than when used on its own? I.E. is there a sense in which the reversers do not just contribute to retardation but also assist the working of the brakes in themselves, such that when removing reversers from the equation the brakes, particularly with a less than perfect runway surface, contribute less even than the contribution they were making previously to the joint braking effort?

Do the reversers, for instance, cause the aircraft to "sit down" more, assisting the wheels to "bite" under braking?
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Old 7th Jul 2008, 23:09
  #292 (permalink)  

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Lemurian, accepting that reverse alone could not achieve the required deceleration. However, with some effective braking and aerodynamic drag there was apparently enough deceleration to achieve 80% of the target (DECEL light).
It's a mystery to me. There is no trace of an auto-brake setting in the transcripts we saw, but it is generally discussed by the crew during the descent/approach briefing.
here I am assuming that the auto-brakes were selected and that the captain cancelled them with a foot pressure on the pedals, causing the "Manual braking" call-out from the F/O.
But in this case, the A/B (MED, I guess) light would have been out and also the "DECEL"" light. So the *DECAL* annunciation is not related to an instrumental indication...
Unfortunately the decel level probably isn’t enough in the prevailing conditions and the crew are unlikely to determine this until it’s too late. However, there could have been some feedback from foot force when manual braking was used.
The kind of deceleration we are talking about here will be felt, I can assure you and you'd feel your shoulderr straps on your collar bones.
That said, a few researches on foot-brake usage have revealed that pilots, in general, do not achieve max braking...The reason is not well identified.
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Old 7th Jul 2008, 23:21
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fyrefli,

is there a sense in which the reversers do not just contribute to retardation but also assist the working of the brakes in themselves, such that when removing reversers from the equation the brakes, particularly with a less than perfect runway surface, contribute less even than the contribution they were making previously to the joint braking effort?
Not really. See it as the T/R add themselves to the drag of the airplane by contributing with a force opposed to the trajectory.
What aids braking by putting most of the aircraft weight on the wheels is the spoilers.
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Old 8th Jul 2008, 01:15
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The 70 knot call was 7 seconds before hitting the fence and going off the cliff. He was reducing reverse before the 70 knot call so must have thought all was well at that time. Why at 70 knots couldn't he stop in that 7 seconds or go back to max reverse thrust if rubber deposits reduced his braking? I know nothing except what I have learned here on Airbus 320 logic but it seems he lost all braking shortly after that call of 70 knots. I landed on that runway many times and always made sure I could turn off on the taxiway 1000 ft short of the end before I would relax reverse and braking. I said it before but that last 1000 feet should be for emergency stopping only. Once slowed down to a safe speed use it to save brake wear and temp. He was in manual braking then so autobrakes would not be the problem at that time.
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Old 8th Jul 2008, 01:47
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Someone sent me a picture of the A340 some arab country was buying that decided to go out and do a full power runup before delivery. They left the flaps up to do the run but to put the take off warning horn out someone pulled the air/ground circuit breaker and the brakes released and they destroyed the aircraft. Could that breaker cause the brakes to fail on the ground in the A320? It is installed to make sure you can land with the brakes on and they won't be locked on touchdown. Does anybody do that?
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Old 8th Jul 2008, 02:23
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Originally Posted by Lemurian
It's a mystery to me. There is no trace of an auto-brake setting in the transcripts we saw, but it is generally discussed by the crew during the descent/approach briefing.
I think one thing we can possibly all agree on is that there is plenty missing from the two versions of the transcripts that we have so far seen.

Also please note that the 'decal' - presumably 'decel' - call does not occur until AFTER the First Officer called 'manual braking.' Could that mean that the call for manual braking was because the autobrakes weren't working?

Alternative explanation of what might have happened below. Please note, Lemurian, that it even gives a possible alternative explanation for the 'En ambar...' call at 1,000 RA :-

"The approach was uneventful until, passing 1,000 feet, the aircraft's status page changed from Cat III DUAL to CAT III Single. This downgrade meant that any single system failure would terminate the automatic approach. Simultaneously, an amber STEERING caption was noted on the ECAM's WHEEL page. A cycling of the A/SKID & N/W STRNG extinguished the caption and a restored status of Cat III DUAL then showed. Neither pilot could recall re-selecting autobrake after cycling the switch. After touchdown and idle reverse selection, the copilot noted that the autobrake was not functioning and called out "Manual Braking." The pilot selected full toe-braking, but gingerly and over a period of 10 seconds. Eventually recognizing "no joy on the braking front," he applied full reversing and instructed the copilot to cycle the A/SKID & N/W STRNG switch. This had nil effect, so he ordered the switch turned OFF in order to access stored hydraulic pressure in the accumulator. Braking was now available, and he urgently brought the aircraft to a halt. With three tires burst and a fourth damaged, the runway was blocked until the tires were changed."

Nothing to do with this accident, though. It refers to an A320 that overran the runway (luckily for them, a fairly long runway) at Cardiff in 2003.

A Very Halting Affair to Remember | Air Safety Week | Find Articles at BNET
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Old 8th Jul 2008, 02:48
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I thought recent procedures associate the decel call with an indication of deceleration on the PFD, not the decel lights.
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Old 8th Jul 2008, 03:05
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The Taca crash about 10 years ago at TGU report said that the captain used manual braking about 500 meters from the end of then runway 01 because autobrakes were not functioning. He ended up in the ditch in a new A310 right before the cliff backwards between the runway and taxiway. I taxied by it many times while they were repairing it in our 757. We use autobrakes but once landed I go manual to make sure on that critical airport we have absolute braking control. I can not imagine flying an airliner that by a glitch in the system could take away the brakes so am sure airbus doesn't either.
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Old 8th Jul 2008, 03:22
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Originally Posted by bubbers44
Someone sent me a picture of the A340 some arab country was buying that decided to go out and do a full power runup before delivery. They left the flaps up to do the run but to put the take off warning horn out someone pulled the air/ground circuit breaker and the brakes released and they destroyed the aircraft
I’m afraid it is pure disinformation as there is no such CB on the 340 overhead reset panel.
On that subject, more information available here

Another Beauty from BEA / Airbus communication service …
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Old 8th Jul 2008, 05:15
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Originally Posted by bubbers44
I can not imagine flying an airliner that by a glitch in the system could take away the brakes so am sure airbus doesn't either.
That appears to have been the position up to 2005, bubbers44. Though one hopes that it has been sorted out by now. To quote, Prof. Ladkin (from that report on the Cardiff/Ibiza incidents I linked to):-

"What will have then happened is that the hot channel, Channel 2, will have relinquished control to the standby, Channel 1, which will have logged the same fault, but cannot relinquish control since it is operating without a standby. On sensing touchdown ("Weight on Wheels"), four seconds after the spoiler deployment signal, the Autobrake function of the BSCU calls the command function to apply current to open the Normal Selector Valve. The COM/MON disagreement fault becomes a failure; the Normal Selector Valve is not opened, the Autobrake function is lost and the Normal braking system is left inoperative. This is recorded in the CFDIU as a failure in the NSVs (although the actual failure was upstream), yet it is sent to the ECAM as a "BRAKES AUTO BRK FAULT" message, which is inhibited from display during landing until engine shut down (but is recorded for post-flight replay). So the crew never saw it --it was not there to be seen."

As far as I can work out (such technical knowledge as I have is in another field) at that time any problem with the 'Anti-Skid and Nosewheel Steering' showed up only as a 'STEERING' warning. Cycling the switch removed the warning; but it ALSO cancelled the autobrake setting, and there was no warning message about that.

So the pilots, on discovering that the autobrake wasn't working, went for manual braking - but, as Prof. Ladkin says, "The COM/MON disagreement fault becomes a failure; the Normal Selector Valve is not opened, the Autobrake function is lost and the Normal braking system is left inoperative."

The solution (which the pilot at Cardiff realised just in time) was to turn off the 'Anti-Skid' as well - but, given that the systems at that time did not provide any sort of warning, it's just as well that he had enough runway left finally to brake to some sort of halt.

As I said, though, you'd hope that any such possible 'glitch' would have been sorted out by now?
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