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BE300 pilot reported an altitude excursion due to an autopilot trim malfunction.
| Attributes | |
| ACN | 1546784 |
| Time | |
| Date | 201805 |
| Local Time Of Day | 0601-1200 |
| Place | |
| Locale Reference | ZZZ.TRACON |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | Super King Air 300 |
| Operating Under FAR Part | Part 91 |
| Flight Phase | Initial Approach |
| Route In Use | Vectors |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Altimeter |
| Person 1 | |
| Function | Captain Pilot Flying Single Pilot |
| Qualification | Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument Flight Crew Multiengine |
| Experience | Flight Crew Last 90 Days 175 Flight Crew Total 5500 Flight Crew Type 1000 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude |
Narrative:
Ferrying aircraft; a diversion was conducted due to an altitude indication fault on the secondary electric altimeter; with no issues on primary. During the final vectors to begin the approach for [the] ILS (guidance only-VMC conditions); an uncommanded pitch trim incident occurred whilst leveling at 4;000 ft MSL. This uncommanded auto pilot trim malfunction caused an unintentional deviation below the assigned altitude of 4;000 ft MSL. As pilot in command; I did what was necessary to control the aircraft and perform the emergency procedure for the event at low altitude; estimating a deviation of 750 ft below my assigned altitude. I communicated after deviating as soon as practicable; requesting an immediate block altitude due to primary control issue; but was unable to advise the approach controller of the event prior to the occurrence; as it was sudden. She was not able to issue me a block altitude; so I then cancelled IFR; maintaining VMC and self terrain clearance at 3;500 ft MSL post recovery. I executed a normal visual approach using the manual trim 'wheel'; and had no further issues. I phoned the approach controller as requested immediately upon securing the aircraft on the ground; and explained the event; and she understood that in no was was my deviation intentional; as I had a stuck trim select switch; and faulty interruption button on the pilots side; which caused the trim to runaway. No attempt was made to use this system for continued flight.
Original NASA ASRS Text
Title: BE300 pilot reported an altitude excursion due to an autopilot trim malfunction.
Narrative: Ferrying aircraft; a diversion was conducted due to an altitude indication fault on the secondary electric altimeter; with no issues on primary. During the final vectors to begin the approach for [the] ILS (guidance only-VMC conditions); an uncommanded pitch trim incident occurred whilst leveling at 4;000 FT MSL. This uncommanded auto pilot trim malfunction caused an unintentional deviation below the assigned altitude of 4;000 FT MSL. As pilot in command; I did what was necessary to control the aircraft and perform the emergency procedure for the event at low altitude; estimating a deviation of 750 FT below my assigned altitude. I communicated after deviating as soon as practicable; requesting an immediate block altitude due to primary control issue; but was unable to advise the approach controller of the event prior to the occurrence; as it was sudden. She was not able to issue me a block altitude; so I then cancelled IFR; maintaining VMC and self terrain clearance at 3;500 FT MSL post recovery. I executed a normal visual approach using the manual trim 'wheel'; and had no further issues. I phoned the approach controller as requested immediately upon securing the aircraft on the ground; and explained the event; and she understood that in no was was my deviation intentional; as I had a stuck trim select switch; and faulty interruption button on the pilots side; which caused the trim to runaway. No attempt was made to use this system for continued flight.
Data retrieved from NASA's ASRS site 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.