TCAS RA

[Barronflyer]

Can someone please advise the protocol to be followed if dispatching with TCAS RA U/S and subsequently receiving a TCAS TA.

Assumption is that ATC has been advised and avoiding action requested, however considerations?

It's a gamble IMHO to allow the intruder aircraft to take the appropriate action and to do nothing but without RA guidance what to do?

Thanks

[Intruder]

I've had a legitimate RA, coasting out of Japan at cruising altitude.

First priority: If you see an apparent TA conflict, query ATC to find out if they are in contact with him.

Second priority: Follow ATC instructions until you get an RA. If you get no RA...

Third priority: Monitor the traffic, and take evasive action as necessary if none is apparent on his end.

[de facto]

If you receive a TCAS TA,switch all your lights on and look for the traffic while requesting ATC information.

[RAT 5]

It's a gamble IMHO to allow the intruder aircraft to take the appropriate action and to do nothing

I'm not sure about all the tricks of TCAS, but are you suggesting that you expect both a/c in an R/A scenario each to receive an RA and both to manoeuvre? Is this indeed true? More learned friends can perhaps enlighten us.

I'd always thought that if you were broadcasting TA only any other a/c would receive the RA and clear off. Some QRH scenarios tell you to select this mode. Therefore I assume it works. Why would a u/s RA mode not operate in the same manner as TA only?

[Superpilot]

Which a/c type are we talking about here? TCAS RA U/S implies to me that the RA part of the system is distinct and perhaps even powered independently. There is no such failure on the Airbus. You only get a NAV TCAS Fault on the Airbus. Not sure about Boeing.

As you know Mode C is required for RA to work (for both aircraft). If the other aircraft's Mode C is working but TCAS RA is "U/S", I still see no change as RAs are the result of a mutually agreed action plan (You descend, I climb OK?). If that mutual confirmation of what the other aircraft needs to do isn't there, the working TCAS's RA will not be made, that's a basic design feature I thought.

What to do? Exactly as has been suggested as above. Equipment has failed, do what's necessary to avoid a collision without it. TCAS is not a mandatory requirement for most airspace in 95% of cases though some AIPs ask you to have the problem fixed within the next x amount of days if you want to use their airspace. The MEL for A320 gives us 3 days to fix TCAS as a whole.

[NigelOnDraft]

Can someone please advise the protocol to be followed if dispatching with TCAS RA U/S and subsequently receiving a TCAS TA.

Difficult to say there is a "protocol" - down to the Capt to decide if it is acceptable?

If the other aircraft's Mode C is working but TCAS RA is "U/S", I still see no change as RAs are the result of a mutually agreed action plan (You descend, I climb OK?). If that mutual confirmation of what the other aircraft needs to do isn't there, the working TCAS's RA will not be made, that's a basic design feature I thought.

Not sure I agree? TCAS in 1 ac, and Mode C in other means the TCAS equipped aircraft will avoid by itself.

As above, I think it "improbable" that you would know, or could even have, TCAS RA U/S but TA working? Since you do not avoid on a TA alone, you are left with ATC and visual avoidance as your tools in the box. The airspace environment might lend itself to the probability the other ac is TCAS equipped - and indeed, whether the Capt deems the MEL item acceptable in the first place.

[Denti]

As you know Mode C is required for RA to work (for both aircraft). If the other aircraft's Mode C is working but TCAS RA is "U/S", I still see no change as RAs are the result of a mutually agreed action plan (You descend, I climb OK?). If that mutual confirmation of what the other aircraft needs to do isn't there, the working TCAS's RA will not be made, that's a basic design feature I thought.

No, it doesn't work that way. TCAS can and does generate RA's without having to have a mutually agreed action plan. Otherwise it would be useless against pretty much all GA airplanes which were a main reason why TCAS was developed in the first place. Additionally all TCAS installations i know do have the TA ONLY setting which has to be used in case of performance limitations like OEI for example. In that case the other aircraft will still generate an RA if needed.

Even if both TCAS are working they will not always generate an RA in both aircraft, especially with the LEVEL OFF RA it is quite often just one of both aircraft that will use that.

[Superpilot]

I stand happily corrected so thanks for that. I was worried about the small chance that an RA could end up asking a pilot to fly the same manouvre as the other pilot, as he would have a 1/2 chance of doing the same (up/down). But then, the working RA would detect the change and re-advise accordingly. Back to the original question I still think TCAS RA U/S implies a lack of mode C and therefore no RA at all.

[NigelOnDraft]

Back to the original question I still think TCAS RA U/S implies a lack of mode C and therefore no RA at all.

No - apart from anything else the MEL items differ... you likely won't be flying in RVSM airspace without Mode C working.

Even almost every GA aircraft has Mode C - few proper TCAS.

[NZScion]

Originally Posted by Barronflyer

Can someone please advise the protocol to be followed if dispatching with TCAS RA U/S and subsequently receiving a TCAS TA.

Some TCAS units have the ability to have RA inop (RA flag on TCAS display) but still provide TA alerts. In this situation, our MEL directs us to operate the TCAS in TA Only mode, preventing any spurious RA warnings despite or because of the failure. RA inop is not necessarily related to mode C being inop.

Should the entire TCAS be inop, then the MEL directs us to disable the entire system for similar reasons.

The protocol to be followed following a TA is unchanged.