View Full Version : TCAS RA's and ALT CAP.

24th Aug 2002, 12:51
Since the tragedy over S. Germany, I've read much about the conflict between TCAS and ATC instructions. What crews will do as told by their SOP's, and what ATC expect them to do are not necessarily the same. Hopefully that matter will soon be sorted out and cross all boundaries.

Out of this came comments about what some crews do to stop TA's becoming RA's due to high closer rates. There have been suggestions from the authorities the companies might need to publish SOP's about the use of V/S etc. when approaching cleared altitudes/FL's. to avoid unnecessary RA's.

In the dark distance of memory I have an idea that in the USA it was specified that in the last 1000' closing a cleared level, you should restrict ROD/ROC to 500fpm. This was an FAA SOP.

I've only flown USA produced a/c and never has one of there own autopilots done this. Even the latest NG has over 2000fpm ROC when only 500' from the level. It captures very smoothly, but that's not the point. If it will become a recommendation for crew intervention in this last 1000', I'm not sure this is a good thing. It goes in the wrong direction of increasing workload and distraction.

If this has been an FAA SOP for years why was it not incorporated in the USA designed and certified autpilot programming? It can't be rocket science to do so.:rolleyes:

24th Aug 2002, 13:23
In the european RVSM airspace it's SOP to limit you climb/descent rate to 1000fpm within the last 1000 ft if another aircraft is within 2000ft of the cleared level and within 5 NM laterally. You have to do that in VS Mode because VNAV isn't programmed to do that.

24th Aug 2002, 13:52
Or do it in VNAV just holding the throttles back a bit.. Easy as that..

24th Aug 2002, 15:20
Brenoch - not if you have an autothrottle as well (eg) B737. I just tend to monitor TCAS on approaching the cleared level. If a target is 1000' feet above the cleared level, then I will endeavor to put it in VS, and use 1000 fpm. Honeywell recommend 1500 fpm or less in its pilots manual, although I find 1500 fpm can still trigger a TA.

The problem is if you have a very rapid ROC of say 4000 fpm or more, then ALT ACQ will occur at possibly 2000' or more below the level. It is then not possible to engage VS. The only option is to over-ride the A/P and reduce the pitch using Control wheel steering.

RAT 5 - I don't thing crew intervention is a problem in the last 1000', in fact it actually encourages people to pay attention to what they are doing. Before TCAS some people had there head buried in a newspaper as soon as reaching FL100, and didn't bother monitoring the climb too much. At least this raises the awareness of the cleared level.

Our SOPs are the same as Denti's, which I think is sensible. If there's nobody else about, there's not really any need.

24th Aug 2002, 21:37
Prophead.. I assume you have enough muscle to override the autothrottle.. ;) It's really not all that powerfull..

Pilot Pete
24th Aug 2002, 22:41
Quite Brenoch. Although I guess the engineers would eventually protest if everyone started over-riding the autothrust all the time! (wear on clutches or some such I was once told!)

Our SOP's shy away from the use of vertical speed, especially in the climb as there is no speed protection. Another method which I find works well in the 757 when being re-cleared to climb another couple of thousand feet to cruise is using FLCH, whereas VNAV puts the levers straight up to climb thrust and starts a 'zoom' FLCH does not initially take such a big 'chunk' of thrust and hence the climb is much gentler.


24th Aug 2002, 22:47
I know it's perhaps not the best way of doing it but i prefer it to V/S.. Or just kick out the A/T for the last bit, works equally fine..

25th Aug 2002, 09:53
Brenoch, depends if I'm on my 4th early or not! ;) Seriously though, that does knacker the clutches, and I remember being told off by a trainer for doing that. Not something I've ever seen people do in my company.

Whilst I agree VS has no speed protection as such in the climb, this will never be a problem in this case. If the climb rate is less than 1000 fpm then there is no need to use VS (such as climbing to the max alt.), and if the VS is, say, over 1500fpm, then there is an excess of performance, and the a/c will certainly be able to maintain 1000fpm without any significant loss in speed. I tend to monitor the a/c in the last 1000 ft of a climb anyway, so any speed deviation would be picked up and corrected, plus low speed protection would kick in with anything more than a 5kt underspeed (revert to level change).

Therefore I can see no real drawbacks to using VS, it is much better than disconnecting the A/T - thereby increasing your workload much more than if you were to simply press VS and reduce ROC to 1000fpm if required.

FLCH sounds good, we would only have that if you kept resetting the FMC cruise altitude, so useful for an unplanned, or step climb, but not available for a normal climb.

Agaricus bisporus
28th Aug 2002, 10:00
What to do if you are at the a/c's cieling and get a TCAS "CLIMB!"
Do you obey it and fly your aircraft into an uncertificated part of the flight envelope, thus invalidating your C of A, insurance and so on, or do you...well, do what?

Capt Pit Bull
28th Aug 2002, 13:28
You won't get one.

Clim and Increase Climb RAs have performance based inhibitions.

There is always the possibility that a demanded RA can not be met (perhaps an engine just failed or you are covered in ice), so ultimately the pilot must protect the flight envelope of the aircraft.

Nevertheless, all aircraft should be inhibited at the top of their envelope.

If you should get a climb RA that you can not achieve, for whatever reason, do the best that you can, even if this means just flying level rather than descending.

See other TCAS threads to differentiate between the concept of being permitted to disregard an RA, versus the concept of a manoeuvre opposite.


31st Aug 2002, 02:24
Boeing checklist says for an engine failure select TA only

31st Aug 2002, 10:14
The post about using FLCH and it only giving +/- 1000fpm for step climbs was true for a PIP equiped B767-300 I flew. I don't know about the NG, 737 or any other type a/c.
All the ideas of how to overcome the various autoflight systems are whizz-bang, but that's not the point. Introduction of company SOP's sound good, but standardisation across the industry? I doubt it very much. Even standarsation within one company about how to cheat the a/c autoflight will not work.
I had this discussion about V/S versus FLCH for step climbs, especially in TMA's. It was stamped on by the head of training, along the lines of it being too complicated to teach the new boys. FLCH was safer and simpler. I would have thought it better to teach the corerect use of a system rather than ban it, except for non-precision approaches.

However, I still can't fathom why the AFDS can not be programmed to do this as SOP. In the Boeings the AFDS has lots of other similar possibilities:
CRZ descent
ALT ACQ mode with smooth level off.
Step climb in FLCH with PIP, but not all models.

It would not be beyond the wit of the engineers to include a ROC/ROD limit once in the ALT CAP mode. That way all type a/c in all companies would comply.

The point about being alert, in the loop and intervening is valid, but not everybody is of the same behaviour. It would seem to be such a simple technical introduction into the AFDS. When you consider all the other goodies and add-ons that have been done over the years, this one, which should go a long way to preventing another bang, would seem to have strong merits.

Anyone from BALPA, or other, technical committees out there; or anyone from the certification authorities care to comment?

And I don't want to come back as an A/T clutch on Brenoch's a/c.

Thanks for the ideas, though.

31st Aug 2002, 13:43
HEEY!! Thats wasn't called for.. :D

1st Sep 2002, 21:01
What about using Climb 2 (or 1) to decrease roc approaching cleared level?

1st Sep 2002, 21:04
Brenoch, sorry. Said with smile on my face and kind heart.

L1011; wouldn't work on B767 as it is in full climb above 12000'. I don't know about other types, and that's the point. It needs to be all a/c.:cool: