Narrative:

After pushback and start it was noted that the 'left CSD oil pressure' and 'left generator off' lights were illuminated. The left generator indicated zero volts and frequencys. A return to the gate was accomplished so maintenance could be accomplished. The decision was made to MEL the CSD system and left generator; with power being provided in-flight via the APU. All maintenance procedures for the MEL were accomplished by air carrier technicians. Particular attention was paid to ensure the CSD was disconnected at the request of the captain. After completion of the MEL procedure; the aircraft was once again able to get underway. After start; during taxi out; it was noted that the 'left CSD oil pressure' light had gone out. A check of the left generator indicated that it was producing normal volts and frequencys. The left generator was placed on the left AC bus and pwred it with completely normal indications. Despite the normal indications it was apparent there was some undiagnosed malfunction with the left CSD or generator system. The aircraft returned to the gate and the flight subsequently canceled. Further attempts to disconnect the CSD by maintenance were unsuccessful and it was replaced. Current MEL procedures pertaining to the CSD and generator system are not appropriate for all failure modes of the CSD. This aircraft very nearly went flying with a defective CSD that was not disconnected from the engine as required; despite correct MEL procedures being accomplished. Once in-flight; it is unlikely the crew could have disconnected the CSD; perhaps leading to more serious problems.

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Original NASA ASRS Text

Title: AN MD80 ON TAXI OUT NOTED L CSD OIL PRESSURE AND L GENERATOR OFF WARNINGS. RETURN TO GATE AND DEFERRED L GENERATOR PER MEL. ON START NOTED L CSD STILL CONNECTED. RETURN TO GATE DUE TO CSD FAILURE.

Narrative: AFTER PUSHBACK AND START IT WAS NOTED THAT THE 'L CSD OIL PRESSURE' AND 'L GENERATOR OFF' LIGHTS WERE ILLUMINATED. THE L GENERATOR INDICATED ZERO VOLTS AND FREQS. A RETURN TO THE GATE WAS ACCOMPLISHED SO MAINT COULD BE ACCOMPLISHED. THE DECISION WAS MADE TO MEL THE CSD SYS AND L GENERATOR; WITH PWR BEING PROVIDED INFLT VIA THE APU. ALL MAINT PROCS FOR THE MEL WERE ACCOMPLISHED BY ACR TECHNICIANS. PARTICULAR ATTN WAS PAID TO ENSURE THE CSD WAS DISCONNECTED AT THE REQUEST OF THE CAPT. AFTER COMPLETION OF THE MEL PROC; THE ACFT WAS ONCE AGAIN ABLE TO GET UNDERWAY. AFTER START; DURING TAXI OUT; IT WAS NOTED THAT THE 'L CSD OIL PRESSURE' LIGHT HAD GONE OUT. A CHK OF THE L GENERATOR INDICATED THAT IT WAS PRODUCING NORMAL VOLTS AND FREQS. THE L GENERATOR WAS PLACED ON THE L AC BUS AND PWRED IT WITH COMPLETELY NORMAL INDICATIONS. DESPITE THE NORMAL INDICATIONS IT WAS APPARENT THERE WAS SOME UNDIAGNOSED MALFUNCTION WITH THE L CSD OR GENERATOR SYS. THE ACFT RETURNED TO THE GATE AND THE FLT SUBSEQUENTLY CANCELED. FURTHER ATTEMPTS TO DISCONNECT THE CSD BY MAINT WERE UNSUCCESSFUL AND IT WAS REPLACED. CURRENT MEL PROCS PERTAINING TO THE CSD AND GENERATOR SYS ARE NOT APPROPRIATE FOR ALL FAILURE MODES OF THE CSD. THIS ACFT VERY NEARLY WENT FLYING WITH A DEFECTIVE CSD THAT WAS NOT DISCONNECTED FROM THE ENG AS REQUIRED; DESPITE CORRECT MEL PROCS BEING ACCOMPLISHED. ONCE INFLT; IT IS UNLIKELY THE CREW COULD HAVE DISCONNECTED THE CSD; PERHAPS LEADING TO MORE SERIOUS PROBS.

Data retrieved from NASA's ASRS site as of January 2009 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.