PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Maintenance Powerplant; Maintenance Airframe; Maintenance Inspection Authority
Maintenance Inspector 23; Maintenance Technician 29
Aircraft Equipment Problem Less Severe
Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft
Pa28-161 Piper Warrior. Total time in service is over 10;000 hours. The forward trim cable failed at the trim servo. The 1/16 inch cable to my knowledge is original and approximately 35 years old. This aircraft is in a high use and training environment and based close to the coast. The trim cable and servo is accessed behind the rear baggage panel and is visible for inspection. At the last 100 hour inspection I found no frayed cables. The trim cable in this area makes several full reversal turns through the trim servo pulleys and capstan. Following the incident; I found that the trim servo solenoid was not disengaging the motor in the manual trim mode which causes significant tension on the trim cable when the trim wheel is operated manually. I believe that the cable had a catastrophic failure which caused the 1/16 inch cable to break. The pilot made a safe return to the airport and no injury and no additional mechanical damage resulted from the incident.
The reporter indicated that following the cable replacement; the system would not run.  At that point he identified that the trim switch had failed.  When he opened the switch; he found a broken part that appeared to have caused a runaway condition.  He also added that this could have been the cause of the cable failure.
An Aircraft Maintenance Technician (AMT) reports about a forward trim cable that had a catastrophic failure inflight at the trim servo motor on a Piper PA28-161 Warrior aircraft. The trim servo solenoid was not disengaging the motor in the manual trim mode; causing significant tension on the trim cable when the trim wheel is operated manually.