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At FL260; center asked flight crew of a PC12 to change altitude to FL250. When FL250 was selected in altitude selector; the airplane nosed down in a runaway condition. Control was regained at FL240.
| Attributes | |
| ACN | 668806 |
| Time | |
| Date | 200508 |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | airport : atl.airport |
| State Reference | GA |
| Altitude | msl bound lower : 25000 msl bound upper : 26000 |
| Environment | |
| Flight Conditions | VMC |
| Weather Elements | Thunderstorm |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | artcc : ztl.artcc |
| Operator | general aviation : corporate |
| Make Model Name | PC-12 |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise : enroute altitude change |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : corporate |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 100 flight time total : 30000 flight time type : 500 |
| ASRS Report | 668806 |
| Person 2 | |
| Affiliation | company : corporate |
| Function | flight crew : first officer |
| Events | |
| Anomaly | aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : published procedure non adherence : far other anomaly |
| Independent Detector | aircraft equipment other aircraft equipment : altimeter other flight crewa other flight crewb |
| Resolutory Action | aircraft : automation overrode flight crew flight crew : overcame equipment problem flight crew : returned to assigned altitude |
| Consequence | other |
| Supplementary | |
| Problem Areas | Chart Or Publication Flight Crew Human Performance Aircraft |
| Primary Problem | Aircraft |
Narrative:
We were at 26000 ft just south of atlanta. Atl center asked us to change altitude by 1000 ft. We chose 25000 ft. We put 25000 ft in the altitude selector and started down. We had a pitch trim runaway; the trim went full nose down. By the time we got the aircraft under control; we had descended to around 24000 ft. The rest of the flight was uneventful and we reported the problem to pilatus. Callback conversation with reporter revealed the following information: the reporter stated this runaway trim has occurred 4 times to the reporter and not all in the same airplane. The reporter indicated the problem appears to be in two components; the altitude selector and the autoplt pitch trim system. A service bulletin has reportedly been published addressing this problem. The reporter stated the fix on this airplane was accomplished at a service center and was replacement of the altitude selector. The airplane has been flown about 5 hours and is operating normally. Reporter stated that unofficial talk around operations of this airplane is that there are around 40 reports of trim problems.
Original NASA ASRS Text
Title: AT FL260; CTR ASKED FLT CREW OF A PC12 TO CHANGE ALT TO FL250. WHEN FL250 WAS SELECTED IN ALT SELECTOR; THE AIRPLANE NOSED DOWN IN A RUNAWAY CONDITION. CONTROL WAS REGAINED AT FL240.
Narrative: WE WERE AT 26000 FT JUST S OF ATLANTA. ATL CTR ASKED US TO CHANGE ALT BY 1000 FT. WE CHOSE 25000 FT. WE PUT 25000 FT IN THE ALT SELECTOR AND STARTED DOWN. WE HAD A PITCH TRIM RUNAWAY; THE TRIM WENT FULL NOSE DOWN. BY THE TIME WE GOT THE ACFT UNDER CTL; WE HAD DSNDED TO AROUND 24000 FT. THE REST OF THE FLT WAS UNEVENTFUL AND WE RPTED THE PROB TO PILATUS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THIS RUNAWAY TRIM HAS OCCURRED 4 TIMES TO THE RPTR AND NOT ALL IN THE SAME AIRPLANE. THE RPTR INDICATED THE PROB APPEARS TO BE IN TWO COMPONENTS; THE ALT SELECTOR AND THE AUTOPLT PITCH TRIM SYSTEM. A SERVICE BULLETIN HAS REPORTEDLY BEEN PUBLISHED ADDRESSING THIS PROB. THE RPTR STATED THE FIX ON THIS AIRPLANE WAS ACCOMPLISHED AT A SERVICE CENTER AND WAS REPLACEMENT OF THE ALT SELECTOR. THE AIRPLANE HAS BEEN FLOWN ABOUT 5 HOURS AND IS OPERATING NORMALLY. RPTR STATED THAT UNOFFICIAL TALK AROUND OPS OF THIS AIRPLANE IS THAT THERE ARE AROUND 40 RPTS OF TRIM 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.