Jondc9
A few answers for you:
A couple of pages back you asked why sometimes you can see traffic but it isn't displayed.
Its certainly possible that there may not be line of sight to antenna, although less likely now that an upper antenna is required as well as a lower. Much more likely is "Interference Limiting Mode" where in, as part of the overall design strategy of reducing the ammount of ssr transmissions (to decongest the frequencies), TCAS does not continuously interrogate all intruders. Unless the aircraft is in full time tracking, it is not displayed. TCAS may, for distant traffic, or medium range traffic that is closing slowly, and even for fairly nearby traffic that the range is opening on, decrease the interrogation rate. Interference limiting mode is invoked when the TCAS reckons the ssr freqs are becoming congested, so typically in higher traffic densities. If you've ever seen more than 1 blip disappear at once, thats probably interference mode kicking in. [reference - manufacturers bulletin - TCAS: Common causes for traffic disapearance]
I recall when TCAS first came out I asked: what if you get a TCAS RA that says climb and you are already at your max altitude?
a good answer was never forthcoming
pull up into a massive stall/upset?
I ought to be surprised that a good answer was never forthcoming, but sadly I'm not. It seems that a sizeable part of the community feel "TCAS - if you get an RA, follow it" meets the necessary knowledge level and neatly ticks the box in the training requirement.
Firstly, TCAS has inbuilt performance based inhibitions. Based on possibly several inputs, increase climbs and climb RAs can be inhibited.
However, these inhibitions are not comprehensive and ultimately the Pilot has an overriding requirement to protect the aircraft. The answer to your question is the same as to any other RA that presents Hazard: Get as close as you can to the RA, and whatever you do don't manoeuvre opposite. Even if you can only get another couple of hundred feet, its worth doing. Bear in mind RAs only nudge you a few hundred feet from your original flight path (unless the other guy manoeuvres towards you). We are not in the realms of zoom climbing thousands of feet.
As Dr Red quotes in fact.
etrang,
Can anyone explain what possible reasons a pilot might have for switching off a transponder?
Apart from when being naughty of course. Still seem to be a few folk around that turn to standby when changing code, not sure if that practice has been stamped out yet. The other reason will be as per anything else electrical - if it, or some other box nearby, has got smoke pouring out of it.
I hasten to add that non of the above is intended to be comment on this accident, but rather answering TCAS related questions that have been raised.
pb