Incident Overview
On March 14, 2012, at approximately 1545 eastern daylight time, a Piper PA-32R-300, registration N1358H, experienced a loss of elevator control while landing at Warrenton-Fauquier Airport (HWY) in Warrenton, Virginia. The airplane was not damaged, and both the certificated commercial pilot and the certificated flight instructor were uninjured. Visual meteorological conditions prevailed, and no flight plan was filed for the instructional flight, which had departed Manassas Regional Airport (HEF) in Manassas, Virginia, about 1505. The flight was conducted under 14 Code of Federal Regulations part 91.
Flight History
The commercial pilot reported that they departed HEF to the west to conduct practice maneuvers in a local practice area. After completing these maneuvers, they proceeded to HWY to perform takeoffs and landings. The pilot completed one landing and stated that the approach for the second landing was normal but "slightly high." During the landing flare, the pilot heard a "boom," the airplane's nose dropped, and the airplane contacted the runway.
Examination Findings
Post-incident examination revealed that the lower stabilator control cable turnbuckle had fractured. The turnbuckle, manufactured by Bell-Memphis Inc., and the cable were sent to the NTSB Materials Laboratory for further analysis. The examination showed that the turnbuckle fractured in the chamfered transition region between the shank and the wrench flats. The fracture surface was rough with crack branching consistent with stress corrosion cracking. The stainless steel turnbuckle assembly also exhibited areas of corrosion.
Maintenance Background
The airplane's most recent annual inspection was completed on March 13, 2012, and the incident flight was the first flight since that inspection. According to the maintenance logbook entry, the airframe inspection was conducted in accordance with the Piper PA32R-300 inspection report. Item 28 under the Fuselage and Empennage Group states: "Inspect all aileron, rudder, stabilator, and stabilator trim cables; and cable terminals, turnbuckles, guides, fittings, and pulleys for safety, condition, and operation."
Historical Context and Safety Actions
The NTSB issued safety recommendations A-01-6 through A-01-8 in April 2001 to the FAA, suggesting remedial action for the failure of Bell-Memphis stainless steel turnbuckles from chloride-assisted transgranular stress corrosion cracking. These recommendations noted previous failures of control cable turnbuckles and recommended issuance of an airworthiness directive to require inspections of affected aircraft.
In response, the FAA issued a Special Airworthiness Information Bulletin (SAIB) in November 2001 (SAIB number CE-02-05), recommending inspections of all aircraft with 303SE stainless steel turnbuckles installed and advising operators of corrosion and cracking being experienced with control cable terminals. The bulletin recommended inspection of flight control cables and replacement of any cables showing signs of corrosion or cracking.
Additionally, Piper issued a maintenance alert service letter dated March 31, 2003, noting that corrosion may be found on control cable attachment fittings, especially in airplanes in service for 15 years or more. The service letter recommended inspection of cable terminals, turnbuckles, and fittings for corrosion or cracking within the next 100 hours time in service, or to coincide with the next scheduled maintenance event. For airplanes in service for 15 years or more, the letter suggested the use of a 10X magnifier. Any evidence of corrosion or cracking was cause for replacement.
The current revision of the airplane service manual (dated July 15, 2006) included the special control cable fitting inspection for airplanes in service 15 years or more, as outlined in the prior service letter.
In January 2004, the FAA issued a revision to the 2001 SAIB, to include the use of a magnifying glass for the corrosion inspections.
An additional FAA SAIB (number CE-11-01), issued October 4, 2010, advised operators of specific failures related to the horizontal stabilator turnbuckle/control cable assembly on Piper airplanes. The SAIB recommended that operators incorporate the previously issued Piper service letter into their inspection procedures and noted that any evidence of corrosion or cracking was cause for replacement of the cable assembly.
As referenced in the previously issued NTSB Safety Recommendations and the FAA SAIB, as of the date of this report, the NTSB is aware of 15 instances of turnbuckle failures. These failures include 8 in Piper PA-28 series aircraft, 3 in Piper PA-32 series aircraft, 3 in Piper PA-44 series aircraft, and 1 in a Cessna 172.
On August 2, 2012, the FAA issued a Notice of Proposed Rulemaking (NPRM) indicating its intention to adopt a new airworthiness directive (AD) that would require inspections of the stabilator control system and replacement of parts as necessary. The AD would be applicable to PA-28, PA-32, PA-34, and PA-44 airplanes.