TCAS alert action

[Olympic260]

Hi all,

A quick question. I was told from a 767 crew that when you have a Tcas alert you have to disconect both AP and AT. Is that the case? If yes is this also the procedure in a 744 or anything changes?

Thx in advance

[wysiwyg]

TA - If VMC start looking for the conflict, if IMC get ready to take control
RA - Disconnect autopilot and fly the indications on the screen (HSI, VSI or PFD). I would leave the autothrottle engaged throughout.

regards
wizzy

[NorthernSky]

Yes, those are normal airline SOP reactions to TA and RA respectively.

However, may I suggest a couple of things?

First, when you get a TA other than in level flight, immediately select VS mode and a low (500-750fpm) rate of climb or descent. In the vast majority of cases this will elliminate the possibility of an RA. You should be close enough to your cleared level for performance concerns not to be an issue, and in any case this will be so as the cause of the TA will probably have been your high rate. However, if you fly a turboprop or a jet without performance limit reversion of some sort, then all the usual caveats about climbing in VS apply.

A lot of nuisance RAs occur in busy airspace because pilots insist on climbing and descending at high rates, and whilst TCAS does not know the MCP altitude it assumes you will keep going up or down. Thus two aircraft which will never get closer than 1000ft are suddenly taking action to 'miss' each other.

As an aside, NATS scientists have been investigating the value of including MCP altitude in TCAS software, the concern being that if there is a danger of the aircraft not levelling off at MCP altitude, then a necessary RA would not be generated until too late.

Now, the actions described above for dealing with an RA introduce the risk of a level bust where none is required by TCAS, and this is quite likely to occur: This is a typical scenario...

You are climbing to FL90 at a high rate, and passing FL80 you receive a TA followed by an RA, for example, 'Monitor Vertical Speed'. Your SOPs say 'disconnect', but the flight path required to satisfy the RA is already being achieved by AFCAS. Disconnecting will raise workload at a critical time, and will remove the protection of ALT ACQ.

In this situation, if you disconnect, you will be expecting to fly away from the FD bars, and will do so happily, and may very possibly lead to flying through the cleared level unnecessarily. Aircraft with strong pitch/power couples are even more tricky to handle here, as suddenly flying a manual raw data level-off with the A/T engaged is not something everyone will do well.

Two conclusions then: (i) If you can easily achieve what the RA requires using AFCAS, then do not disconnect; (ii) Pilots should practise raw data flying on a regular basis - situations such as TCAS RAs are not the time to find your skills are rusty. One ILS every six months does not keep you competent.

[ 05 August 2001: Message edited by: NorthernSky ]

[moleslayer]

For AIRBUS A320/1 :

TA - Monitor Only.

RA - Disconnect A/P & A/THR
Manually Fly The VSI Instructions.