PDA

View Full Version : TCAS RA CLIMB on max a/c Celling


Overheat
16th Sep 2009, 21:22
Hello mates.
On my latest check ride I was amazed with one issue.
We're flying an A320 with at FL390 (max). We get a TCAS climb. What do we do?
We climb and maintain the V/S on the green or.... The hell with it, do not risk a high alt and speed stall and hope the other traffic gets and complies with the TCAS descent???

Thanks guys.

Overheat :mad:

763 jock
16th Sep 2009, 21:29
So what did you do?

Runaway Gun
16th Sep 2009, 21:35
Coupla hundred feet aint gonna hurt much, surely?

NigelOnDraft
16th Sep 2009, 21:46
Anybody who is willing to climb to FL390 to cruise, and then think following a TCAS RA "Climb" is a problem, surely has their priorities / risk management understanding somewhat adrift :ooh:

After all, what is the buffet margin at Max Rec Cruise there for :ugh:

NoD

Runaway Gun
16th Sep 2009, 21:48
To allow for increased load factor due to a turn at x.x G ?

763 jock
16th Sep 2009, 22:03
Follow the RA and miss the oncoming/climbing/descending hardware. Stall at FL410 if you have to, recover by 29000' and you'll still clear Everest.

GrandPrix
16th Sep 2009, 22:06
"cover by 29000' and you'll still clear Everest."

Amen, brutha. (or sista)

singpilot
16th Sep 2009, 22:30
Maybe one of the boffins can clarify, but I think latest S/W has MAX ALT in your TCAS Loaded S/W.

Bummer if the other guy is also at MAX ALT. Maybe one gets the -2000 cue and the other gets the 0 cue.

Someone knows.

But as said, I'd certainly find a way to squeak out a few hun up if that's what the RA cue was.

aristoclis
16th Sep 2009, 22:46
TCAS RA orders must be followed even at max ceiling altitude with CLIMB orders.
Stall warning must be respected.

In alternate law it is not wise to be at FL390. In normal law stall warning does not apply. Alpha protection and Alpha floor do. Get the best your airplane can give you and pray...

singpilot
16th Sep 2009, 22:58
Funny, I wasn't thinking of a Bus.

I was thinking of say.... G4. Civilian Svc Ceiling is FL450. Military ceiling is FL510. Depending on the version, service ceilings can be quite different in 'normal' airplanes.

Yes, the Bus gives you a little more 'help' if you want to call it that with Alpha floor and Alpha Prot. But even that will bite if there is a pax onboard named Murphy.

Cardinal
16th Sep 2009, 23:06
At light weights the Bus can provide your buffet margin well above FL390. The limitation stems from her (in)ability to get down. Even if you had hardly any margin, for whatever reason, pull till she shakes. As Nigel said, priorities.

singpilot
16th Sep 2009, 23:53
Thanks, Cardinal for reminding me of that. Most service ceilings are derived from several performance factors. Newer planes almost always have a dive time problem cuz they are so clean (limiting the altitude that the dive starts at). Or the max number is where you cannot climb by more than some vertical rate.

In a Bus, yes, pull and let the computers do the work.

galaxy flyer
17th Sep 2009, 00:04
NoD

My current plane has about 1.6G at FL450, so your point is? Probably something about larger planes.

GF

Thai Pom
17th Sep 2009, 02:00
I believe the Max Ceiling is pin programmed on the TCAS Processor mounting tray at installation. You should not recieve a RA to climb above this programmed value.

Cheers, TP

singpilot
17th Sep 2009, 02:45
Thanks TP, I was pretty sure that was the case.

NigelOnDraft
17th Sep 2009, 05:38
My current plane has about 1.6G at FL450, so your point is? Probably something about larger planes.My point is that with 1.6g available, you have plenty of potential to follow the RA.

I might not have expressed it well? To clarify, my point is your priorities are somewhat adrift if you have climbed to a FL where your performance would be so limited that following an RA gives you any concern. You would surely also be considering turbulence, windshear (it terms of W/V altering quickly), engine failure etc. all of which require some tolerance to IAS/M altering somewhat.

And the absolute (rather than current) Max Ceiling will often have pressurisation / fatigue as a factor, which are not applicable here.

Summary: At FL390 in a 320 series Airbus, I am much happier explaining to my Flt Mgr why I went to FL395 following an RA, than ignoring the RA and all the consequences of that :{

NoD

Clandestino
17th Sep 2009, 06:09
Have a look here. (http://www.skybrary.aero/bookshelf/books/96.pdf) Though they deal with B737, events 5 & 6 are of some relevance to thread.

FL390 is pressurization limit on 320family. If you exceed it, cabin alt will climb as the pressurization controller keeps max diff pressure but that's about it. If sector length wasn't a factor, I never had problems reaching it on 319 with CFM56-5B engines. 320s with -5A were somewhat different story, cruising at FL350 when heavy. Vls is about 1.28 Vs1g when clean, so bus doesn't stall immediately below Vls mark - its the black/red stripe on speed tape that shows your stall margin, not orange one.

I believe the Max Ceiling is pin programmed on the TCAS Processor mounting tray at installation.

Definitively dependent on aeroplane and TCAS computer model. See link above.

The limitation stems from her (in)ability to get down.

Hmmm... I really doubt it. There are no speed or alt limitations on use of speedbrakes and with boards out at Vmo, she dives almost like SB2C. There is a recommendation about not using speedbrakes above FL250 IIRC, for pax comfort though.

Thai Pom
17th Sep 2009, 06:16
Thanks for the link. You are correct there are various ceiling altitude options that can be programmed dependant on Aircraft type.

FE Hoppy
17th Sep 2009, 09:22
This doesn't really take much thinking does it?

Follow RA, miss conflict, explain to fleet chief why you broke a limit.

Ignore RA, So does other guy, hit conflict, no need to explain anything.

If you are at 390 it's because you have the performance to be there.

captjns
17th Sep 2009, 09:30
Some FCOMs state that TA can be selected when performance limited to avoid performance limiting RAs.

Capt Pit Bull
17th Sep 2009, 10:39
The search facilty is your friend:

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

http://www.pprune.org/tech-log/345780-tcas-ra-aircrafts-certified-ceiling.html

http://www.pprune.org/tech-log/354450-tcas-taonly-high-altitude-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
17th Sep 2009, 23:08
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???? :8

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
18th Sep 2009, 09:11
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
21st Sep 2009, 14:37
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
22nd Sep 2009, 17:22
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..:eek:

:ok::ok:

JAR
22nd Sep 2009, 17:45
EMB195 - No Climb commands or Increased Climb commands are issued at or
above 34000 ft MSL.

cloud-surfer
22nd Sep 2009, 17:52
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.