What was found
MACH TRIM FAILED IN-FLIGHT, AIRCRAFT WOULD NOT DESCEND USING PRIMARY TRIM. CREW HAD TO USE SECONDARY TRIM TO RETURN TO DEPARTURE AIRPORT. AFTER COMPLETING CHECKLIST, CREW WENT BACK TO PRIMARY TRIM.
As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
MACH TRIM FAILED IN-FLIGHT, AIRCRAFT WOULD NOT DESCEND USING PRIMARY TRIM. CREW HAD TO USE SECONDARY TRIM TO RETURN TO DEPARTURE AIRPORT. AFTER COMPLETING CHECKLIST, CREW WENT BACK TO PRIMARY TRIM.