ACAS alert

[south coast]

Question.

If you have an RA to descend and you inform ATC with, 'ACAS descent' and then they tell you to continue the descent to FL X.

After clear of conflict, should you level off, climb back to initial FL or continue the descent to the cleared level?

Thanks.

[Capt Pit Bull]

Well, once you've 'acas descent' the controller should not issue you with a revised clearance.

If they do, they either are acting contrary to procedure or your 'acas descent' call wasn't heard for some reason.

Technically you are supposed to return to your last cleared and acknowledged level once clear of conflict. Standard RT phraseology is to call "returning to [cleared level]" so in effect that prompts the controller to reissue the revised clearance if it is still considered suitable.

pb

[GlueBall]

After you are clear of the ACAS/TACAS Resolution Advisory maneuver you follow ATC instructions.

[south coast]

Just trying to remember how it goes.

If there is a conflict, there is a RA by means of the green area on the VSI telling you what rate of climb or descent is required, descent in this example.

What I cant remember is, once the conflict is over, does the green on the VSI just disappear, it doesnt give you info to return to your original level/altitude, so, if once the green has gone, the conflict is no longer, and during the manoeuvre a clearance was given to descend, then you could quite safely continue to the descend to the new cleared level/altitude?

I guess it is hypothetical as it has been said there should be no clearances given while involved in a RA.

[Capt Pit Bull]

If there is a conflict, there is a RA by means of the green area on the VSI telling you what rate of climb or descent is required, descent in this example.

Not always. Some preventative RAs are red arc only.

What I cant remember is, once the conflict is over, does the green on the VSI just disappear, it doesnt give you info to return to your original level/altitude,

Well, the RA is likely to soften first, assuming its a coordinated RA, before clear of conflict.

Correct, there is no guidance from TCAS back to your original flight path. However your flight director will do, assuming its still on (some companies turn it off) and assuming its still programmed correctly.

so, if once the green has gone, the conflict is no longer, and during the manoeuvre a clearance was given to descend, then you could quite safely continue to the descend to the new cleared level/altitude?

I believe the idea is that a new clearance given in haste is considered to be risky (i.e. deconflicts you against the RA but sets you up for another one imminently) and should therefore be re-evaluated (by atc) once the RA is over and reissued if appropriate. Hence you should return to your last cleared and acknowledged level. Which, given ATC shouldn't be issuing a new one and even if they do the crew shouldn't be following it, has to be the cleared level prior to the RA.



pb

[south coast]

Thanks pit bull

[low n' slow]

My thoughts are that if ATC manouvered you into that situation, it's some kind of evidence that the controller is not in control over the situation. Accepting a clearance during the actual event I feel is a good foundation for a latent error. Let the clear of conflict sound and then ask what they want you to do. That would be my line of action. But Capt pitbull said it first and in a better way...

/LnS

[earnest]

My thoughts are that if ATC manouvered you into that situation, it's some kind of evidence that the controller is not in control over the situation

That's unfair. It could have been a level bust. It often is.

[low n' slow]

And thus per definition the controller is no longer in control over the situation. It might not be his fault, I'll give you that, but he/she is no longer the one running the show...