Incident Details
On June 3, 2013, at approximately 1520 eastern daylight time, a Piper PA-34-200T, registration N633TC, experienced a trim cable failure during climbout from Tallahassee Regional Airport (TLH) in Tallahassee, Florida. The flight instructor (CFI) and student pilot were not injured, and the airplane sustained no damage. Visual meteorological conditions prevailed, and no flight plan was filed. The airplane was registered to and operated by Florida Flight Training Center under Title 14 Code of Federal Regulations Part 91 as an instructional flight. The flight was originating at the time of the incident.
The CFI reported that the departure from TLH was uneventful. While climbing through 300 feet, the student pilot noticed a problem with the elevator trim wheel. The CFI moved the trim wheel and observed no resistance when turning it. Looking down, he saw the trim cable protruding from the side of the wheel. The student pilot indicated difficulty controlling the airplane, and the CFI assumed control. He advised the tower controller of the emergency and landed without further incident. Post-landing examination revealed that the elevator trim cable had broken and was protruding from the trim wheel housing.
Examination
The elevator trim cable assembly was sent to the NTSB material laboratory for examination. The cable consisted of a 1/16-inch diameter wire rope with a swaged-on ball at one end and a swaged-on turnbuckle fitting at the other end. Visual inspection showed trim cable lubrication along the entire length with no sign of external corrosion. The wire rope had separated about 5 feet 6 inches from the turnbuckle end and 14 feet 6 inches from the ball end. The separation comprised individual wire breaks spread over an approximate 2-inch length of the wire rope. Magnified visual inspection of the cleaned cable revealed that all but a few wires were fractured directly across with no apparent yielding or deformation. Only a few wires, broken or intact, showed internal or external wear. Scanning electron microscope examination of several broken wires indicated features consistent with fatigue progression through the individual wires.
A review of the aircraft logbooks showed that the failure of the trim cable was not detected during the 100-hour and annual inspections on April 25, 2013, nor during compliance with AD 2013-02-13 on April 13, 2013. That airworthiness directive specifies in section 7-149(a) that at each annual or 100-hour inspection, all control cables must be inspected for broken wire strands, and any cable assembly with one broken wire strand in a critical fatigue area must be replaced. The inspection had been completed three months prior to this event.