A crj-900 flight crew failed to note the improper deferral of both radio altimeters when only one sh...

Attributes
ACN	953280
Time
Date	201105
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	Regional Jet 900 (CRJ900)
Operating Under FAR Part	Part 121
Flight Phase	Parked
Flight Plan	IFR
Component
Aircraft Component	Radio Altimeter
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 13 Flight Crew Total 10000 Flight Crew Type 300
Person 2
Function	First Officer Pilot Flying
Qualification	Flight Crew Commercial
Experience	Flight Crew Last 90 Days 13 Flight Crew Total 3600 Flight Crew Type 2400
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural MEL Deviation - Procedural Maintenance Deviation - Procedural Published Material / Policy

Narrative:

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.

Original NASA ASRS Text

Title: A CRJ-900 flight crew failed to note the improper deferral of both radio altimeters when only one should have been.

Narrative: 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.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

A crj-900 flight crew failed to note the improper deferral of both radio altimeters when only one should have been.