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A line aircraft maintenance technician (amt) questions how a digital flight control system (dfcs) test for a dual channel mach trim system could have passed with all four mach trim circuit breakers (C/bs) 'open' (pulled). The B737-700 flight crew returned to the gate after noticing the C/bs were still pulled; even though a mach trim MEL had been signed-off.
| Attributes | |
| ACN | 1087322 |
| Time | |
| Date | 201304 |
| Local Time Of Day | 0601-1200 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | B737-700 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Parked |
| Component | |
| Aircraft Component | Mach Trim |
| Person 1 | |
| Function | Technician |
| Qualification | Maintenance Airframe Maintenance Powerplant |
| Experience | Maintenance Technician 30 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy |
Narrative:
B737-700 aircraft came in on MEL for dual channel mach trim failure. I pulled maintenance manual (M/M) and performed digital flight control system (dfcs) built-in test equipment (bite) check. Dfcs passed all tests; verified by lead mechanic; and on the next day [verified] by the line maintenance manager. I have cleared write-ups like this before; but did not know there were [mach trim] circuit breakers (C/bs) pulled; the dfcs passed all tests with [mach trim] circuit breakers out (pulled). When I got home; I thought about the situation and called dayshift line lead on shift and he verified before aircraft left that the [mach trim] C/bs were pulled. Unfortunately; the aircraft returned to the gate during this time. Maintenance went out and found that there were circuit breakers pulled and collared. The only circuit breakers I knew about were stab cutout [switches] to perform this test. MEL write-ups should have circuit breakers (C/bs) listed that are pulled for any MEL. Graveyard [shift].
Original NASA ASRS Text
Title: A Line Aircraft Maintenance Technician (AMT) questions how a Digital Flight Control System (DFCS) Test for a Dual Channel Mach Trim System could have passed with all four Mach Trim Circuit Breakers (C/Bs) 'Open' (pulled). The B737-700 flight crew returned to the gate after noticing the C/Bs were still pulled; even though a Mach Trim MEL had been signed-off.
Narrative: B737-700 aircraft came in on MEL for Dual Channel Mach Trim failure. I pulled Maintenance Manual (M/M) and performed Digital Flight Control System (DFCS) Built-in Test Equipment (Bite) Check. DFCS passed all tests; verified by Lead Mechanic; and on the next day [verified] by the Line Maintenance Manager. I have cleared write-ups like this before; but did not know there were [Mach Trim] Circuit Breakers (C/Bs) pulled; the DFCS passed all tests with [Mach Trim] Circuit Breakers out (pulled). When I got home; I thought about the situation and called Dayshift Line Lead on shift and he verified before aircraft left that the [Mach Trim] C/Bs were pulled. Unfortunately; the aircraft returned to the gate during this time. Maintenance went out and found that there were circuit breakers pulled and collared. The only circuit breakers I knew about were Stab Cutout [Switches] to perform this test. MEL write-ups should have Circuit Breakers (C/Bs) listed that are pulled for any MEL. Graveyard [shift].
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.