Boulderman
'Climb' and 'Increase Climb' RAs are inhibited based on altitude / config parameters. These inhibitions are gross only, the crew must protect the flight envelope. E.G. lets say you've got some ice on the airframe. TCAS can't account for that, so you might get an unachievable climb.
Crews should be trained to do the best they can. E.G. manoeuvre in the correct sense as much as possible. Even doing nothing (say engine fails as you go to pull up) is safer than thinking 'can't climb! I'll have to dive under him....'.
Incidentally, at low rad alts, 'descend' and 'increase descent' RAs get ihibited as well.
Sponix,
Granted the media are saying b757 descended after the t154, but thats not consistent with the RA alerting time at that altitude versus the report of the t154 leaving at 25 seconds.
The RA alerting time is at that level, if memory serves, 35 seconds, which incuding 5 seconds reaction time put the b757 out of its level just before the t154...
Findo,
No, the message is 'Never manoeuvre opposite to an RA', which is quite different to 'Never choose not to follow an RA'.
Whippersnapper
TCAS does not take precedence to GPWS.
GPWS warnings have higher priority than TCAS. TCAS Aurals are inhibited by GPWS activation.
Rationale - Most potential collision scenarios would be a horizontal near miss even without TCAS. Better to risk that than to hit terrain.
Nigel On Draft
The London Terminal Control trainers have been teaching this for several years (they were kind enough to help us out with ATC procedures for our TCAS course, so that the crew would know what was going on at the other end of the radio).
The intermittent contacts on your traffic display are caused by your TCAS going in and out of 'Interference limiting mode'. It is quite normal - only traffic in full time tracking is shown, which any threat will be. Remember, the traffic display is not really designed to give you SA, but only to get your eyes on the target in the event of a TA. Anything else is a bonus, and must be viewed with caution. If you want more info about Interference limiting mode, drop me an email.
Everyone.
On the topic of the Mk 1 eyeball, can I please draw your attention to this post I have made on Tech Log. I don't claim it is a factor in this terrible accident, but I hope people may find it of interest / use.
http://www.pprune.org/forums/showthr...threadid=58559
CPB