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Tcas ra at aircraft service ceiling

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Tcas ra at aircraft service ceiling

Old 18th Sep 2014, 18:21
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Tcas ra at aircraft service ceiling

Hi folks
I was wondering if someone can point me in the direction where to find some documentation regarding an RA at the aircraft service ceiling.
I know that the climb can be inhibited in response to discrete indications if the aircraft climb performance prevents it to climb at at least 1500fpm - likewise at its service ceiling.
Any more inputs - in the specific regarding tcas 2 version 7.0 - where to find official data and if the tcas that a specific airframe is mounting has such inhibition?

Many thanks.
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Old 18th Sep 2014, 19:13
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See FAA advisory circular AC 20-151A, "Airworthiness Approval of TCAS II, Versions 7.0 & 7.1 and Associated Mode S Transponders":


In particular sections 2-16 "Aircraft Performance Considerations", 2-17 "Evaluating Aircraft Performance" and the bottom of Table 1 Maneuvers on page 16.

This is the text from 2-17 paragraph G:

"g. If Table 1, Maneuver A causes operation at airspeeds below the minimum, then inhibit the CLIMB RA. If Table 1, Maneuver B or C causes operation at airspeeds below the minimum, then inhibit the INCREASE CLIMB RA. However, early recovery of 1 to 2 seconds is of little or no consequence on the collision avoidance maneuver and a higher overall level of safety will be achieved if inhibits are not provided under these circumstances, as previously discussed in paragraph 2-16."

A summary of system inhibits is listed in Table 2, page 18.
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Old 18th Sep 2014, 20:36
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Thanks very much for such a well structured answer. I knew about the features, but never really managed to look for a reference. I promise to pass them along, if anybody asks.

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