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A line mechanic reports how a change in their air carrier MEL procedures from a maintenance procedure to a flight crew MEL placard deferral procedure; contributed to a 'good' left engine CSD/generator being disconnected on an MD80 aircraft. Lack of troubleshooting under the flight crew placarding procedures prevented the flight crew from isolating the APU auxliary electrical relay that was stuck in the 'on' position.
| Attributes | |
| ACN | 1022929 |
| Time | |
| Date | 201206 |
| Local Time Of Day | 1801-2400 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Light | Dusk |
| Aircraft 1 | |
| Make Model Name | MD-80 Series (DC-9-80) Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Parked |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | APU Electrical |
| Person 1 | |
| Function | Technician |
| Qualification | Maintenance Powerplant Maintenance Airframe |
| Experience | Maintenance Technician 16 |
| Events | |
| Anomaly | Aircraft Equipment Problem Critical Deviation - Procedural Published Material / Policy |
Narrative:
APU aux relay was stuck closed; which caused the left electrical bus to be powered no matter what position the switch was in. When the flight crew started the left engine; the left engine generator failed to pick-up the bus because it was stuck; being [electrically] powered by the APU. The flight crew assumed they had a bad left generator and disconnected it; and installed a crew placard. This situation would not allow the [flight] crew to isolate the left bus and remove power in an emergency (relay stuck on) and also caused them to disconnect a good CSD. This MEL was previously a non [flight] crew placardable item and was recently changed. I believe it requires troubleshooting to determine why the generator is not coming online. The item should be a maintenance MEL only; to accommodate trouble shooting.
Original NASA ASRS Text
Title: A Line Mechanic reports how a change in their Air Carrier MEL procedures from a Maintenance procedure to a flight crew MEL placard deferral procedure; contributed to a 'good' Left Engine CSD/Generator being disconnected on an MD80 aircraft. Lack of troubleshooting under the flight crew placarding procedures prevented the flight crew from isolating the APU Auxliary Electrical Relay that was stuck in the 'ON' position.
Narrative: APU Aux relay was stuck closed; which caused the Left Electrical Bus to be powered no matter what position the switch was in. When the flight crew started the left engine; the Left Engine Generator failed to pick-up the Bus because it was stuck; being [electrically] powered by the APU. The flight crew assumed they had a bad Left Generator and disconnected it; and installed a crew placard. This situation would not allow the [flight] crew to isolate the Left Bus and remove power in an emergency (relay stuck on) and also caused them to disconnect a good CSD. This MEL was previously a non [flight] crew placardable item and was recently changed. I believe it requires troubleshooting to determine why the generator is not coming online. The item should be a Maintenance MEL only; to accommodate trouble shooting.
Data retrieved from NASA's ASRS site as of July 2013 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.