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Apparently faulty engine start switch allows the left engine of B737-300 to motor when the APU powers the pneumatic system.
| Attributes | |
| ACN | 792847 |
| Time | |
| Date | 200806 |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : iah.airport |
| State Reference | TX |
| Altitude | agl single value : 0 |
| Aircraft 1 | |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | ground : parked |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Experience | flight time total : 14000 flight time type : 5100 |
| ASRS Report | 792847 |
| Person 2 | |
| Affiliation | other |
| Function | other personnel |
| Events | |
| Anomaly | aircraft equipment problem : less severe |
| Independent Detector | other other : 2 |
| Resolutory Action | none taken : anomaly accepted |
| Supplementary | |
| Problem Areas | Aircraft Flight Crew Human Performance |
| Primary Problem | Aircraft |
Narrative:
While sitting at the gate in iah; about 5 mins before departure; the captain started the APU. As the ground air was being disconnected; the ground crew called up to me; said the #1 engine fan was motoring. Looking up at the starter switch; it was slightly turned to the 'ground position' (engine motoring position); engine was motoring. The only conclusion we came to as to how this could have happened; is that when the previous crew turned off the igniters (on the shutdown checklist) they went 'over center;' passed the 'off' detent; the switch was slightly in the 'ground position.' then; when I started the APU (switch next to igniter); I must have bumped the igniter switch more to the ground position -- enough to start the motoring of the engine. We were very baffled by this as the switch falls into a 'detent' when off; normally would not be able to go to the 'ground position' unless the switch is pushed in first. We tried the detent position; it was in fact working fine. No one was injured during this episode.
Original NASA ASRS Text
Title: APPARENTLY FAULTY ENGINE START SWITCH ALLOWS THE LEFT ENGINE OF B737-300 TO MOTOR WHEN THE APU POWERS THE PNEUMATIC SYSTEM.
Narrative: WHILE SITTING AT THE GATE IN IAH; ABOUT 5 MINS BEFORE DEP; THE CAPT STARTED THE APU. AS THE GND AIR WAS BEING DISCONNECTED; THE GND CREW CALLED UP TO ME; SAID THE #1 ENG FAN WAS MOTORING. LOOKING UP AT THE STARTER SWITCH; IT WAS SLIGHTLY TURNED TO THE 'GND POS' (ENG MOTORING POS); ENG WAS MOTORING. THE ONLY CONCLUSION WE CAME TO AS TO HOW THIS COULD HAVE HAPPENED; IS THAT WHEN THE PREVIOUS CREW TURNED OFF THE IGNITERS (ON THE SHUTDOWN CHKLIST) THEY WENT 'OVER CTR;' PASSED THE 'OFF' DETENT; THE SWITCH WAS SLIGHTLY IN THE 'GND POS.' THEN; WHEN I STARTED THE APU (SWITCH NEXT TO IGNITER); I MUST HAVE BUMPED THE IGNITER SWITCH MORE TO THE GND POS -- ENOUGH TO START THE MOTORING OF THE ENG. WE WERE VERY BAFFLED BY THIS AS THE SWITCH FALLS INTO A 'DETENT' WHEN OFF; NORMALLY WOULD NOT BE ABLE TO GO TO THE 'GND POS' UNLESS THE SWITCH IS PUSHED IN FIRST. WE TRIED THE DETENT POS; IT WAS IN FACT WORKING FINE. NO ONE WAS INJURED DURING THIS EPISODE.
Data retrieved from NASA's ASRS site as of May 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.