2011-05 · NASA ASRS report 953280
A CRJ-900 flight crew failed to note the improper deferral of both radio altimeters when only one should have been.
During the approach; we received a radio altimeter horn when the First Officer reduced the throttles to idle. Knowing that the #1 radio altimeter had been deferred; I thought this was the cause for the horn. We completed the flight and the following turn to ZZZ without incident.I received a call from a Manager today concerning these flights. At that time he told me that the aircraft had not only the #1 radio altimeter deferred; but also the #2 radio altimeter. There had been a misunderstanding between Maintenance Control and the Line Mechanic who actually completed the deferral that only the #1 radio altimeter should have been deferred.I feel that the main cause of this problem is the aircraft MEL. I have found this document to be very confusing and poorly written. The MEL in question said that the #1 'or' #2 radio altimeter should be deferred; but the Mechanic misread this as #1 'and' #2 were to be deferred. Pending a re-write of the MEL; we need some type of document to tell the first crew after a deferral exactly what has been done and what indications to expect as a result would be very helpful. I know in theory; this should be apparent in the maintenance log and MEL; but often the log is in Maintenance jargon; abbreviated; or illegible.
Everything appeared normal to us both; since the write up matched the release and we followed those crew procedures....during the approach phase on our arrival into ZZZ; I noticed that the radio altimeter horn would go off every time the thrust levers were left in idle. I quickly realized that having the thrust levers a few percent above idle N1 would discontinue the radio altimeter horn/distraction. Also; there were no audible call outs from 100 FT until touchdown.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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