Mechanic reporter claims deferral of altimeter write up procedures vague and controversial.

Attributes
ACN	322095
Time
Date	199511
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz
State Reference	US
Altitude	agl bound lower : 0 agl bound upper : 0
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Person 1
Affiliation	company : air carrier
Function	other personnel other
Qualification	other other : other
ASRS Report	322095
Person 2
Affiliation	company : air carrier
Function	other personnel other
Qualification	other other : other
Events
Anomaly	non adherence other other anomaly other
Independent Detector	other other : unspecified
Resolutory Action	none taken : detected after the fact
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

On the night of the occurrence I was working as a maintenance controller when a flight crew from a company aircraft called to report that the #1 encoding altimeter was flagged. However, the altitude was indicating normally to the crew. After researching the maintenance manuals, wiring diagrams and consulting with avionics, it was determined that the encoding sources (a function of the altimeter) was the cause for the flag. The MEL for this aircraft allows for maintenance on the encoding source to be deferred. So I proceeded to defer maintenance on this item in accordance with the aircraft MEL and the company general maintenance manual. When the aircraft arrived back at a maintenance station, inspection personnel began to question the legalities of the deferral. They claimed that since the instrument was flagged the altimeter is considered failed. I felt comfortable deferring this item. The encoding altimeter provides visual altitude information to the crew and it is also the encoding source for the xponders. Since the altitude information was operating normally I deferred the encoding source (the #1 encoding altimeter). I do not feel that this action was illegal. If the inspection department feels that the action taken was illegal they should revise the MEL pertaining to the encoding source.

Original NASA ASRS Text

Title: MECH RPTR CLAIMS DEFERRAL OF ALTIMETER WRITE UP PROCS VAGUE AND CONTROVERSIAL.

Narrative: ON THE NIGHT OF THE OCCURRENCE I WAS WORKING AS A MAINT CTLR WHEN A FLC FROM A COMPANY ACFT CALLED TO RPT THAT THE #1 ENCODING ALTIMETER WAS FLAGGED. HOWEVER, THE ALT WAS INDICATING NORMALLY TO THE CREW. AFTER RESEARCHING THE MAINT MANUALS, WIRING DIAGRAMS AND CONSULTING WITH AVIONICS, IT WAS DETERMINED THAT THE ENCODING SOURCES (A FUNCTION OF THE ALTIMETER) WAS THE CAUSE FOR THE FLAG. THE MEL FOR THIS ACFT ALLOWS FOR MAINT ON THE ENCODING SOURCE TO BE DEFERRED. SO I PROCEEDED TO DEFER MAINT ON THIS ITEM IN ACCORDANCE WITH THE ACFT MEL AND THE COMPANY GENERAL MAINT MANUAL. WHEN THE ACFT ARRIVED BACK AT A MAINT STATION, INSPECTION PERSONNEL BEGAN TO QUESTION THE LEGALITIES OF THE DEFERRAL. THEY CLAIMED THAT SINCE THE INST WAS FLAGGED THE ALTIMETER IS CONSIDERED FAILED. I FELT COMFORTABLE DEFERRING THIS ITEM. THE ENCODING ALTIMETER PROVIDES VISUAL ALT INFO TO THE CREW AND IT IS ALSO THE ENCODING SOURCE FOR THE XPONDERS. SINCE THE ALT INFO WAS OPERATING NORMALLY I DEFERRED THE ENCODING SOURCE (THE #1 ENCODING ALTIMETER). I DO NOT FEEL THAT THIS ACTION WAS ILLEGAL. IF THE INSPECTION DEPT FEELS THAT THE ACTION TAKEN WAS ILLEGAL THEY SHOULD REVISE THE MEL PERTAINING TO THE ENCODING SOURCE.

Data retrieved from NASA's ASRS site as of July 2007 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.