Incident Overview
On August 31, 2013, about 1345 eastern daylight time, a Piper PA-28RT-201, registration N2091W, experienced a pitch control failure during takeoff at Hampton Roads Executive Airport (PVG) in Chesapeake, Virginia. The airplane was undamaged and the two pilots were uninjured. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight, which was conducted under Title 14 Code of Federal Regulations Part 91.
The purpose of the flight was to familiarize the pilots with the airplane. During takeoff, as they increased the angle of attack, they heard a loud "pop" and lost pitch control. The airplane became airborne momentarily then touched down in a three-point attitude.
Examination Findings
Examination of the airplane revealed that the aft lower stabilator flight control cable's turnbuckle assembly had broken at the aft cable terminal fitting. The NTSB Materials Laboratory examined the turnbuckle and cable terminal. The cable terminal had fractured in the shank region about 0.25 inches from the wrench flats. Areas of the turnbuckle were covered with white crystalline material, and the shank adjacent to the fracture exhibited reddish orange deposits. Examination under a 5X to 50X binocular zoom stereomicroscope showed a rough fracture surface with crack branching, consistent with stress corrosion cracking. Cleaning with acetone and a scouring pad removed some deposits, but reddish orange deposits remained in crevices. Isolated small pits were observed, with higher density on the outer diameter at the wrench flats. A longitudinal crack was discovered at the end of the terminal adjacent to the cable; reddish orange deposits remained after cleaning.
Regulatory Background
Review of Federal Aviation Administration (FAA) records indicated that the turnbuckle assembly was the subject of FAA Airworthiness Directive (AD) 2013-02-13, prompted by reports of cable assembly failures leading to loss of pitch control. The AD required inspection of the stabilator control system and replacement of parts as necessary.
Maintenance History
The airplane was manufactured in 1979. It had recently been purchased and was intended for rental and pilot training. An annual inspection was performed on July 21, 2013, at which time the aircraft had accrued 6,100.3 total hours. At the incident, total flight hours were 6,106.
According to the mechanic's logbook entry for the annual inspection, AD 2013-02-13 (effective March 11, 2013) had been complied with by inspecting the cables per Piper Service Bulletin (SB) 1245A. The inspection required disassembling the turnbuckle assembly and cleaning it with a solvent such as acetone; a Scotch-Brite general purpose green scouring pad was also permitted. A 10x magnifier, mirror, and light source were used to inspect the turnbuckle, terminal, and cable segment. Any evidence of cracks, cable fraying, or corrosion remaining after cleaning was cause for replacement.