A320 reverse

[NoJoke]

I have been told that the main reason for deploying reverse thrust immediately after landing is to ensure that the lift spoilers deploy.
"After touchdown, when reverse thrust is selected (on at least one engine) and one main landing gear strut is compressed, the ground spoilers partially extend to establish ground contact. The ground spoilers fully extend when both main landing gears are compressed. A small nose down term on the elevators is introduced by the control law."

It also says in the FCTM
"DRY RUNWAY The landing distance calculation does NOT include the effect of thrust reversers."
which seems to back this up. Any ideas?

[TO MEMO]

That`s correct, if spoilers for some reason do not deploy after landing, using reverse will override spoilers logic and make them deploy. Even if you don`t want to use reverse, you should select idle reverse, 2 reasons for that:

- ensure spoilers deploy
- engines will remain at flight idle, so if you see the red lights approaching, you can always select full reverse and thrust will come straight away.

:ok:

[NoJoke]

Thanks for that - safe flying

[divinehover]

You will get partial spoiler deployment once at least one reverser has been selected and one main landing dear strut is fully compressed. You will get full spoiler deployment once both main landing gear struts are fully compressed

This was taken from the A319 FCTM.

[mutley320]

One other reason i can think of; spoilers feed logic to autobrake ( if your using it) So ensuring deployment ( by selecting at least Rev idle) is good belts and braces.

[NoJoke]

Do you mean that the rev thrust will activate the auto-brakes, and or that if rev thrust is not selected the auto-brakes may not function properly? Can you expand a little more please?

[Bill Smith]

From my understanding of the Auto-Brake logic, it activates when the spoilers extend. On Medium there is a 2 second delay before pressure is sent to the brakes and 4 seconds on low.

I believe the reason for selecting reverse is a protection so if the spoilers have inadvertently not been armed they will deploy as soon as reverse is selected on one engine, provided the other is still at idle.

Note: The RTO situation is slightly different

If ground spoilers are armed and GS exeeds 72 Kts, the spoilers will extend when the thrust levers are set to idle.

If the spoilers are not armed and the speed exceeds 72 Kts, the spoilers will extend as soon as reverse is selected.

If the RTO is executed at less than 72 Kts the spoilers will not extend.

Note: As the autobrake looks for a signal from the spoilers, it will not activate in the 3rd case as the spoilers do not deploy!

[Chris Scott]

The trouble with long-winded text descriptions of systems logic - in FCOMs and elsewhere, including PPRuNe - is that the "AND" gates and "OR" gates can so easily become confused by the often unavoidable limitations of syntax, grammar and punctuation. That's why design engineers comunicate their proposals and requirements by mathematics or logic diagrams, I believe.

Bill Smith has given us the best analysis so far, and certainly in line with my fading memory of the A320.

There's just one other point about the desirability of selecting reverse idle, in preference to forward idle, which has not been mentioned. Although these fan-only reversers are fairly ineffectual, in comparison with the old-fashioned buckets of my youth, what is sometimes forgotten is that they do at least eliminate the forward-idle thrust that helped the Iberia A340-600 overrun the runway at Quito recently. [Yes, it was also stuck in flight-idle, instead of ground-idle.]

[TO MEMO]

correct, with one gear touchdown, spoilers deploy partially to help the airplane settle down and also give lateral control. It wasn`t always been like that, actually. That feature was introduced, when spoiler logic was changed after the lufthansa A320 overrun the runway at Warsaw.

cheers

safe flying!

[mutley320]

No Joke.
Have a look at your MEL for dispatch with 1 or both reversers inop. Look up the operations section, interesting reading. Recently highlighted by that runway over-run in South America. rgds, M.

[NoJoke]

Mutley320 I will have a gander at the MEL today, but by going by what TO MEMO has pointed out, the main reason seems to be to have the Rev immediately available. Actually what was the old logic? The reverse thrust selection still activated the LDs but when both maingear were on the ground?