Airbus A320 Reverse thrust operation procedure

[Syckes]

Hi.

I would like to know if someone knows why the following is apparently true.

First. I got to thinking about my question after watching a program on the crash of TAM Flight 3054 at Congonhas (SBSP) in Sao Paulo on 17 July 2007. According to the program the pilot did not retard both throttles and then activate the reverse thrust on the engine (#1) on which it was serviceable. He only retarded #1 to idle, leaving #2 with power on and then activated reverse on #1 This was apparently caused by the pilot wanting to slow down as quickly as possible (I believe to be as safe as possible) because of bad WX and RWY conditions in conjunction with SBSP's reputation. He was known to have used the new procedure for applying reverse thrust with one engines reverse system de-activated (retarding both throttles to idle and then applying reverse on BOTH even though only one would activate). The old procedure was to retard both to idle and ONLY apply reverse on the engine that has the system active. According to the program the new procedure was implemented to prevent an accident like this (not retarding one engine to idle). Apparently the old procedure would stop the aircraft better (in a shorter distance) compared with the new. Is this really true? With only one engine's reverse system active, if you apply reverse on both engines or only the active, what is the difference? And why the difference in stopping distance?

Thanks for the info.
Syckes

[Bus Driver Man]

Apparently the old procedure would stop the aircraft better (in a shorter distance) compared with the new. Is this really true? With only one engine's reverse system active, if you apply reverse on both engines or only the active, what is the difference? And why the difference in stopping distance?

Thanks for the info.
Syckes

When you apply reverse on the engine where reverse is inop, the thrust will increase (A320, don't know for other aircraft).
If the reverser doors don't open, this thrust counteracts your braking force. Hence the greater stopping distance.

So yes, the old procedure has a smaller stopping distance, but if you leave the lever in CLB, your autothrust will increase thrust to try to keep the speed at Vapp. The result is the TAM crash.

The new procedure is to prevent a wrong selection of reversers. The safety of this procedure outweighs the slight increase in stopping distance.

[911slf]

I seem to remember Flight magazine saying that if you select reverse thrust on both engines, but thrust reverser locked out on one (which I think was the case):



engine with thrust reverser operating normally gives reverse thrust (up to maximum)

other engine increases power to 'idle reverse' setting - but gives forward thrust, a bit more than 'forward idle'

selecting reverse idle gives no less forward thrust on the engine with reverser inoperative, but of course less reverse thrust on the other one - hence forward idle on both is supposed to be better than reverse idle on both


On a night landing on a short slippery runway with a not previously practised engine configuration one can imagine scope for error.

Did they ever get the runway surface grooved, and/or put any exotic friction material on the end?

[poss]

I saw this one recently also, they did eventually get it grooved, straight after the incident I believe.

Quick question from someone yet to operate a jet - On reverse thrust and LDA, from what I remember reverse thrust isn't taken into account on LDA charts so why is it the captain felt that he needed to use the old method of applying reverse thrust as opposed to the recent method? Surely either would have stopped the aircraft in a safe distance because of the factors applied in the LDA charts?

[IFixPlanes]

Best way to understand an accident is:
Read the Final Report (http://www.cenipa.aer.mil.br/cenipa/paginas/relatorios/pdf/3054ing.pdf).

[Swedish Steve]

When you apply reverse on the engine where reverse is inop, the thrust will increase (A320, don't know for other aircraft).
If the reverser doors don't open, this thrust counteracts your braking force. Hence the greater stopping distance.

Moving the thrust lever from fwd idle to reverse idle selects thrust reverser. But with reverse selected the idle is flight (or approach) idle, not ground idle. There is not a lot of thrust at reverse idle, whether it points back or sideways.
The reason is that the acceleration from ground idle to high power can be protracted, so the engine is powered up to flight idle while the reversers are deploying. Power above reverse idle is inhibited until the reversers are deployed.

[Syckes]

Thanks for the replies guys. I thought that if reverse was de-activated through the FADEC system it would prevent the engine from spooling up to flight idle when reverse is selected on that engine and remain at ground idle but I see now. Thanks.

@911slf. The planned grooves on the runway was completed in September 2007. Sad it was not completed with the RWY overhaul.

[Bus Driver Man]

Moving the thrust lever from fwd idle to reverse idle selects thrust reverser. But with reverse selected the idle is flight (or approach) idle, not ground idle. There is not a lot of thrust at reverse idle, whether it points back or sideways.
The reason is that the acceleration from ground idle to high power can be protracted, so the engine is powered up to flight idle while the reversers are deploying. Power above reverse idle is inhibited until the reversers are deployed.
Didn't know exactly how much thrust the engine produced at idle reverse or full reverse without deployment of the doors. (Didn't had time to look in the FCOM)
Thanks for clarification.

[Slasher]

The extra 55M for the new procedure is purely nominal. Land
me on a short contaminated runway and I'll be going for the
old one.

On Boeings the reverse lever of a deactivated system is totally
inhibited. Why couldn't the Frogs've done the same with their
original design?

[porch monkey]

Actually Slash, had exactly the same thought! 737 just has the lever lock wired down and unable to be lifted. Seemed simple enough! Never flown an airbii tho, so maybe there's more to it.......

[Slasher]

Yep that's the 737 Porch. On a Pratted 747 the lever couldn't
be physically moved even if the lockwire was broken I recall.

SOP was for the PNF to call "REVERSER #...ONLY" on t/down.
That and the lockwire worked very well esp in a high workload
situation on the 737.

And yeh there's definitely more to it. Off the top of my head
Airboos's toy plastic-throttle design is probably part of it, but
again why couldn't they have incorporated a similar system in
the original design... :ugh:

[rudderrudderrat]

Hi Slasher,
why couldn't they have incorporated a similar system in
the original design...
I think the problem lies with the design of the thrust levers being in the climb gate position when autothrust is active. The Thrust Levers are used by some to rest their hands on most of the time. Since there is no intuitive movement as the thrust changes, they can be forgotten as doing something quite important.

It was determined that the crew of TAM Flight 3054 at Congonhas had forgotten about closing the other "plastic thrust lever thingy" because they were in the mind set of only moving one lever into REV.