TCAS mode selector TA single engine

[MD83FO]

on single engine drift down, will an intruder TCAS calculate its own RA based on my TA selection?

thanks

[Goldenrivett]

will an intruder TCAS calculate its own RA based on my TA selection?
Affirm. http://www.skybrary.aero/bookshelf/books/104.pdf
"When operated in TA-only mode, collision avoidance is still maintained by the TCAS II of the other aircraft."

[RAT 5]

To my best knowledge, if you select TA Only it is advertising that you can not manoeuvre and thus you are declaring that everyone else needs to avoid YOU. This has been debated before in that the QRH does not instruct you in all necessary scenarios to select TA Only. If you are a wounded bird, for any reason, and can not follow ALL RA's, then broadcast TA Only.

[Capn Bloggs]

Always wondered about that but was too afraiiid to ask!!!...

[FE Hoppy]

Going to TA only reduces your sensitivity level as well as inhibiting RA so the other guy will get a TA before you and may even get his RA before you got your TA. It's no problem.

I read a statistic that 80% of the time RA's were only issued to one of the two aircraft. This was due to either: mode A/C only transponder; TA Only selected or Geometry making one manoeuvre early enough that the other didn't have to resolve.

In the worst case the RA enabled aircraft may get a strengthening RA after the initial one.

[Capt Pit Bull]

Either TCAS will generate sufficient separation with one exception which is if you have a encounter where both aeroplanes have an inhibition in the same sense.

e.g. if neither aircraft can climb, or neither aircraft can descend. (the later is pretty unlikely... but hey, so are mid airs)

In these cases one aircraft gets a preventative RA whilst the other gets a corrective.

e.g. say you managed to meet another aircraft at very low altitude and neither could descend. One would get a 'Monitor Vertical Speed' with a 'don't climb' set of red. The other would get a 'Climb Climb'.

If the aircraft that gets the Climb is engine out and can't do it, or can't fully comply, then you won't get the target ammount of separation. This is a shame because the other aircraft could have done it.

By going TA only the encounter is no longer coordinated. The other aircraft will definitely gnerate a 'Climb' for itself.

[No Fly Zone]

I think @ RAT 5 got it right... if you are disabled and not up to optimum performance, use TA only. You should also be sending some alternate transponder code. Not all SOPs include this, but perhaps they should. One more step at a critical time...

After you're stable with one, consider other actions. If you are heavy and cannot move quickly, TA may be a reasonable choice. Your call, but getting a RA that you cannot comply will not make your day. As far as I know, limited performance is not embedded in the TCAS system.

[Oktas8]

As far as I know, limited performance is not embedded in the TCAS system.

TCAS II may well be aware of aircraft performance limitations. For example, my turboprop will not generate "climb" RAs during engine-out flight. (This effectively instructs the other aircraft to do a climb, instead of me, if the geometry requires one of us to climb to avoid collision.)

It is possible for TCAS to be programmed with aircraft ceiling limitations as well, which would be relevant to a drift down situation.

Hopefully your FCOM or flight manual contains instructions about when to use "TA only". I certainly would not do it just for a simple engine failure.

[27/09]

I certainly would not do it just for a simple engine failure.

Whereas some might. Not all TCAS II can tell if you are single engine.

[Pontius]

I certainly would not do it just for a simple engine failure.

Because:

......my turboprop will not generate "climb" RAs during engine-out flight.

Clever and as it should be nowadays. However, all the Boeings I've flown don't have this function, so it is written in the QRH to select TA in the event of the loss of an engine.

[tom775257]

Same on the 320 party bus. TCAS to TA is an action line on ECAM with eng fail.

[RAT 5]

Remember there are may more scenarios, other than engine out ops, where you will be unable to comply with an RA. I will not list some here for want of not opening a can or worms as was done by some when discussing the use of TCAS during EM Desc's. IMHO if you have any reason to expect to be unable to follow an RA then TA only is the selection. I hate to think what would have happened if AF 447 (A330) had received an RA. However, in mitigation I suspect their attention was elsewhere other than their transponder.