N972NA
AEROSPATIALE ATR-42-300
PLT STATED AUTOPILOT ENGAGED AT 1,000 FEET AFTER T/O. AILERON TRIM WAS USED AFTER AUTOPILOT ENGAGEMENT. FLT WAS GIVEN HEADING CHANGE TO RT. AUTOPILOT HDG BUG DID NOT TURN A CFT. HE DISCONNECTED THE AUTOPILOT AT 2,200 FT AND THE ACFT IMMEDIATELY ROLLED INTO A LEFT 60 DEGREE BANK AND BEGAN DESCENDING. HE THEN ACTIVATED AILERON TRIM TO THE RT AND ALONG WITH THE COPILOT ON THE CONTROLS THEY RECOVERED. POST CRASH EXAMINATION OF THE ACFT STRUCTURE, FLT CONTROLS, AND AUTOPILOT SYSTEM REVEALED NO EVIDENCE TO INDICATE PREINCIDENT FAILURE OR MALFUNCTION OF THESE. THE DFDR AND RADAR DATA INDICATED THE EVENT OCCURRED AT 3,300 FEET AND THAT FOR 45 SECONDS BEFORE THE EVENT OCCURRED THE AILERONS WERE DEFLECTED TO THE RT 2 TO 5 DEGREES. AFTER THE DESCENDING LEFT TURN BEGAN PLTS DID NOT REDUCE POWER FOR 60 SECONDS AND ACFT SPEED EXCEEDED 250 KNOT VNE SPEED. AFTER THE INCIDENT THE ACFT MFG RESTRICTED USE OF THE AILERON TRIM TO 1 DOT WITH AUTOPILOT ENGAGED, NOT THREE DOTS AS HAD BEEN PREVIOUSLY ALLOWED.
THE IMPROPER USE OF AILERON TRIM AND THE IMPROPER PREPARATION FOR AUTO PILOT DISCONNECT BY THE FLIGHT CREW COMBINED WITH EXCESSIVE FORCES APPLIED BY THE AILERON TRIM SYSTEM RESULTING IN A DEPARTURE FROM CONTROLLED FLIGHT. CONTRIBUTING FACTORS TO THE INCIDENT WERE INADEQUATE AND MISLEADING AUTOPILOT WARNINGS, LACK OF CONSPICUITY OF THE AILERON TRIM INDICATOR, LACK OF FAA REGULATION GOVERNING CONTROL AUTHORITY IN MISTRIM CONDITIONS, AUTOPILOT SYSTEM MASKING OF MISTRIM CONDITIONS, AND THE LACK OF FAA REQUIREMENT FOR RECURRENT PILOT TRAINING IN AUTOPILOT USE.
Source: NTSB Aviation Accident Database
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