Narrative:

I received a call from [a maintenance technician]. He explained that the airplane was at departure time and that an issue which had occurred previously had re-occurred. He mentioned that both the overhead 'pack off' light and the EICAS message for rh pack were showing. He suggested that we defer the item per MEL. I read through the MEL and agreed that it was an allowable deferral. I remember checking the existing mels boarded on [the aircraft] to verify that all of the components listed in the MEL were operational; and [the technician] agreed that they were. Therefore at this point there was no reason for me to not issue the MEL. Subsequent to the flight crew's needing to don O2 masks and operate the rh pack in spite of the MEL; it was discovered that both the avionics supply fan and exhaust fan had suffered considerable FOD (foreign object debris) to the fan impellers. On the 767; the air conditioning packs and the equipment cooling systems are separate and independent. Failure of the pack and failure of both of the fans at approximately the same time appears to be coincidental. There was history for fwd equipment ovht; and the crew had performed a btb (bus tie breaker); but that issue had been signed off as an intermittent fault. The airplane had performed 3 flight legs without another fwd equipment ovht message. The rh 'pack off' issue was addressed by replacement of the flow control valve.

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Original NASA ASRS Text

Title: Maintenance technicians reported deferring the right air-conditioning pack on a B767-300 and that an equipment cooling system failure on the subsequent flight led to the flight crew donning oxygen masks and using the deferred pack.

Narrative: I received a call from [a Maintenance Technician]. He explained that the airplane was at departure time and that an issue which had occurred previously had re-occurred. He mentioned that both the Overhead 'PACK OFF' light and the EICAS message for RH PACK were showing. He suggested that we defer the item per MEL. I read through the MEL and agreed that it was an allowable deferral. I remember checking the existing MELs boarded on [the aircraft] to verify that all of the components listed in the MEL were operational; and [the technician] agreed that they were. Therefore at this point there was no reason for me to NOT issue the MEL. Subsequent to the Flight Crew's needing to don O2 masks and operate the RH Pack in spite of the MEL; it was discovered that both the Avionics Supply Fan and Exhaust Fan had suffered considerable FOD (Foreign Object Debris) to the fan impellers. On the 767; the Air Conditioning Packs and the Equipment Cooling systems are separate and independent. Failure of the Pack and failure of both of the Fans at approximately the same time appears to be coincidental. There was history for FWD EQUIP OVHT; and the crew had performed a BTB (Bus Tie Breaker); but that issue had been signed off as an intermittent fault. The airplane had performed 3 flight legs without another FWD EQUIP OVHT message. The RH 'PACK OFF' issue was addressed by replacement of the Flow Control Valve.

Data retrieved from NASA's ASRS site 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.