Flight History
On February 10, 2011, about 2027 eastern standard time, a Piper PA-31-350, registration N31NW, owned and operated by Laboratory Corporation of America Inc., was substantially damaged during a routine medical specimen transport flight. The certificated airline transport pilot was not injured. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed and activated. The flight originated from Burlington-Alamance Regional Airport, Burlington, North Carolina (BUY), and was destined for Baltimore-Washington International Airport (BWI), Baltimore, Maryland. The flight was conducted under Title 14 Code of Federal Regulations Part 91.
According to the operator, the flight departed BUY about 1850. Approximately 30 minutes into the flight, while cruising at 7,000 feet with the autopilot engaged, the airplane's nose pitched down slightly. The airplane then pitched up slightly followed by another downward pitch that resulted in a 200-foot altitude deviation. The pilot disengaged the autopilot, re-leveled the airplane at 7,000 feet, and re-engaged the autopilot. Several minutes later, the autopilot turned the airplane toward the next navigational fix. At that time, the pilot noticed a vibration in the control yoke, described as a "buzzing," and observed that the airplane was flying in a slight sideslip to the right. The pilot trimmed the rudder and noted no further vibration. The remainder of the flight was uneventful.
Upon landing and exiting the airplane, the pilot noted that the outer portion of the left elevator was bent down, just outboard of the outermost hinge point.
Aircraft Information
The pilot held an airline transport pilot certificate with numerous ratings, including airplane multiengine land, and had accumulated 16,835 total flight hours, with 7,936 hours in the accident airplane make and model.
The airplane's most recent annual inspection was completed on July 30, 2010, at 11,338 total hours. According to maintenance records, the left elevator had been replaced with a serviceable part on May 17, 2010, at an aircraft total time of 10,910 hours, due to cracking observed in the previously installed elevator. At the time of the accident, the airplane had accumulated 12,351 total flight hours, of which 1,441 hours were accumulated since the left elevator replacement. The total flight hours the accident elevator had accumulated prior to installation could not be determined.
Damage Examination
A Federal Aviation Administration (FAA) inspector examined the airplane after the flight. Photographs showed that the outboard-most portion of the elevator forward of the elevator hinge line was deformed downward at an angle near perpendicular to its normal position. The elevator was removed for disassembly and detailed examination. The forward elevator spar remained intact and had not fractured but was deformed and bent about the elevator hinge line, consistent with the observed external damage. The inboard rib of the balance weight rib tip structure was deformed and bent beginning about 7 inches aft of its leading edge to its aftmost point where it attached to the forward front spar, about 10.5 inches aft of the rib's leading edge. The rib was also fractured from its upper to lower chord, about 9 inches aft of its leading edge. The fracture features were consistent with overload separation and exhibited no evidence of fatigue failure. No evidence of any preexisting damage was observed.
Additional Information
On July 7, 1980, Piper Aircraft released Service Bulletin Number 690, detailing an inspection of the installed elevator balance weight to ensure the correct weight was installed. Upon completion, the elevator part number was to be re-identified. Examination revealed that the accident elevator's part number had been changed, signifying compliance with the service bulletin. Examination of the accident elevator and its sub-components by an NTSB aircraft structures specialist confirmed compliance with all other relevant manufacturer's service bulletins and FAA airworthiness directives.