TCAS RA CLIMB on max a/c Celling

[Capt Pit Bull]

The search facilty is your friend:

http://www.pprune.org/tech-log/138138-tcas-climb.html

http://www.pprune.org/tech-log/34578...d-ceiling.html

http://www.pprune.org/tech-log/35445...de-cruise.html


For the original poster:

In summary, if you get an RA you should be following it unless to do so is itself hazardous. For most aeroplanes, a climb of a few hundred feet above ceiling is a minimal risk, so the RA must be followed.

However, if you cannot fully comply with the RA then you must get as close as possible. So if you're in an ice covered turboprop and TCAS asks for +1500, do the best you can, as long as you manouevre in the SAME SENSE as the RA, you will be increasing the vertical distance between you and the other aircraft. If you can only manage +500 then this is still going to help, all that will happen is that the other aircraft RA will be maintained a little longer before it weakens.

The thing you must NOT do is manouevre in the opposite sense to the RA. This is far riskier than doing nothing (in a 'mostly TCAS' environment)

Some FCOMs state that TA can be selected when performance limited to avoid performance limiting RAs.

I had heard this was being suggested. I'm amazed to hear its actually happened. It's so crazy it's beyond belief imho.

pb

[Overheat]

Well, tks guys for all your answers.
I did followed the TCAS, because as you all know we are trained to do so, but... later it get me thinking:
- If we don't follow it, and Murphy is on board, we do not need to fill the ASR
- If we do follow it, and at FL396 a pax gets injured by the manouver will the insurence cover it? You will have some paper work to do...
- If we stall the BUS.... yes, in normal law we can't stall the BUS, but we may not also be able to climb (a floor/TOGA LOCK at FL390 does not make any difference at all...) so if Murphy is on board... should try it on an A321...

Well... as a conclusion... If we have no luck in life what are we doing in aviation after all????

And I never saw anything regarding selecting TA when limited on performance. When should we consider that situation? FCOM you said??? never read anything about that. Can you please tell us the chapter?


Thanks guys.

[Capt Pit Bull]

And I never saw anything regarding selecting TA when limited on performance. When should we consider that situation? FCOM you said??? never read anything about that. Can you please tell us the chapter?

Some situations require TA only. In some cases, for parallel runway ops. Also for Engine Out or certain other malfunctions. There are solid reasons behind these situations.

However, due to this issue (Climb RA at ceiling) it seems some operators have come up with the concept of TA only during high altitude cruise. This is (imho) a deeply stupid idea that could only be thought up by someone that doesn't understand how TCAS works and is incapable of assessing the relative risk.

In coordinated encounters, the outcome is still highly likely to be safe even if one aircraft does not (is unable) to follow its RA. In a high altitude encounter, if you are receiving a climb then the other aircraft is getting a descend (or an 'adjust' to reduce climb). So although performance is an issue for you, it isn't for the other aircraft. The size of the RA and the alerting time is sufficient that compliance by either aircraft is sufficient. (contrary to common opinion, not following an RA does not lead to a large increase in risk, as long as you don't manouevre in the opposite sense to it).

But if you go TA only, and every other aircraft is also at TA only, then you'd better hope that you don't meet another aircraft with the same ceiling. In this case you'll both be at TA only!

If you're at TA only and the other aircraft is at TA/RA, what happens if the other aircraft gets a descend RA, but ATC are giving you a descent for avoiding action* ? You'll follow it, which invalidate the other aircrafts RA. Yes, the other TCAS can strengthen or reverse its RA, so the situation may be salvaged, but clearly this is a riskier situation.

(* or you decide to descend based on visual contact)

So what's different about this and TA ONLY at engine failure? The rationale sounds similar - we can't climb, so set TA only.

The issue during engine failure is the low level possibility where descent RAs are inhibited by radio altitude. In this case BOTH aircraft involved in the encounter are inhibited in one sense (down). In these situations, in a coordinated encounter, one aircraft will get a Climb RA and the other, instead of getting a descend, will get a preventative to NOT climb. But if that aircraft can not climb, due to engine failure, then a collision is possible.

Whereas, if the engine out aircraft is at TA only, the encounter is not coordinated. This means the serviceable aircraft will definitely generate a Climb RA and the encounter should be safe.

So, really, these situations are quite different. With engine out, we are worried about the aircraft being unable to manouevre in either sense, so we set TA only. At high altitude, we only have a problem in one sense, so all aircraft should stay ay TA/RA.

pb

[Graybeard]

TCAS max altitude strapped into the aircraft is the altitude above which the plane cannot achieve 1500 fpm climb for 30 seconds.

I was involved with original TCAS cert on the MD-80, and McDouglas left the altitude limit strap open, as it could hold 1500 fpm climb for 30 seconds at max cruise altitude.

Riding SLF on Jetblue A320, KLGB-KORD two weeks ago, the map display on the seatback tv showed us at 41,000 feet. I thought, Boy, Airbus bragging about Higher Faster Farther was right! Now you tell me 390 is max. The SLF altitude display is GPS derived, huh?

It showed 37.4 on the return Saturday.

GB

[WindSheer]

Any commercial a/c is going to have a max ceiling safety buffer built in.

So you are safe at 41000ft, but climb to 41300 and you stall.....I don't think so.
A bit like sell by dates, you can have something in a cupboard for 2 years, in date, but don't eat it 1 day after its expiration...it will kill you..

[JAR]

EMB195 - No Climb commands or Increased Climb commands are issued at or
above 34000 ft MSL.

[cloud-surfer]

the max enviromental envelope for the A320 family varies depending upon the aircrafts MSN. Some allow 39100, others 39800 pressure altitude (FCOM 3.01.20), so you many not even bust the max altitude limit.

This can be especially usefull when flying in metric airspace as it is possible to climb to 12100 meters, FL397ish.