TCAS Again
Thanks for the TCAS block diagram on post 2650, PJ2. It confirms that airspeed is not an input to TCAS, hence not a reason for the NAV TCAS Fail on the ACARS list.
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From Graybeard:
Quote:
"In one instance, (Delta/NW) it was noted the altitude indicated a drop of 300 feet, meaning the ADR was still outputting valid altitude calculation, but perhaps without airspeed trim. "
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DJ77 replied:
"Right, an uncorrected altitude has an error magnitude of a few hundred feet. That may be considered unacceptable for TCAS since RAs occur for an anticipated vertical separation of only 700 ft (above 20,000 ft)."
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Altitude on the PFD was still valid during the Delta/NW event, so the altitude to the TCAS would still have been valid. The ADR will not send different altitudes to these two destinations, except below the QNH transition level.
The TCAS Fail message from AF447 remains unexplained, and not in concert with the other reported failures that can all be explained by erroneous airspeed.
GB