Baltimore, MD, USA
N31NW
PIPER PA-31-350
While cruising at 7,000 feet with the autopilot activated, the pilot reported that the airplane's nose pitched down slightly, then 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 pilot noticed a vibration in the control yoke, which he described as a "buzzing," and noticed that the airplane was flying in a right slight sideslip. 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 downward, just outboard of the outermost hinge point and at an angle nearly perpendicular to its normal position. Detailed examination of the elevator showed that its forward spar had deformed but had not fractured. The inboard rib of the balance weight rib tip structure was deformed and fractured from its upper to lower chord aft of its leading edge. The fracture features of the rib were consistent with overload separation, and exhibited no evidence of a fatigue failure. No evidence of any preexisting damage was observed. The total number of flight hours the elevator had accumulated prior to being installed on the accident airplane could not be determined, although examination of the elevator and its sub-components confirmed that it complied with all relevant manufacturer's service bulletins and FAA airworthiness directives.
HISTORY OF FLIGHT On February 10, 2011, about 2027 eastern standard time, a Piper PA-31-350, N31NW, owned and operated by Laboratory Corporation of America Inc., was substantially damaged during a routine flight. The certificated airline transport pilot was not injured. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed and activated for the flight that originated from Burlington-Alamance Regional Airport, Burlington, North Carolina (BUY), and was destined for Baltimore-Washington International Airport (BWI), Baltimore, Maryland. The business flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. According to the operator, the flight departed its base at BUY about 1850 for a scheduled medical specimen transport flight. About 30 minutes into the flight, while the airplane was cruising at 7,000 feet with the autopilot activated, 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 then 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 along the route of flight. About this time, the pilot noticed a vibration in the control yoke, which he described as a "buzzing," and noticed 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. PERSONNEL INFORMATION According to the operator, the pilot held an airline transport pilot certificate with numerous ratings, including airplane multiengine land. The pilot had accumulated 16,835 total hours of flight experience, 7,936 hours of which were in the accident airplane make and model. AIRCRAFT INFORMATION The airplane's most recent annual inspection was completed on July 30, 2010, and at that time the airplane had accumulated 11,338 total hours of operation. 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, 1,441 hours of which had been accumulated since the left elevator had been replaced. The total number of flight hours the accident elevator had accumulated prior to installation on the accident airplane could not be determined. METEOROLOGICAL INFORMATION At 1954, the weather reported at BWI included clear skies and calm winds. The pilot reported that visual meteorological conditions prevailed along the entire route of flight and that the airplane did not encounter any structural icing during the flight. WRECKAGE AND IMPACT INFORMATION A Federal Aviation Administration (FAA) inspector examined the airplane following the flight. Examination of photographs provided by the inspector showed that the outboard-most portion of the elevator forward of the elevator hinge line was deformed downward at angle near perpendicular to its normal position. The elevator was subsequently removed from the airplane 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 damage on the exterior of the elevator. The inboard rib of the balance weight rib tip structure was deformed, and bent beginning about 7 inches aft of the its leading edge, to its aft most point where it was 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 of the rib were consistent with overload separation, and exhibited no evidence of a 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 insure that the correct weight was installed. Upon completion of the service bulletin, the elevator part number was to be re-identified. Examination of the accident elevator revealed that its 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 that the accident elevator was in compliance with all other relevant manufacturer's service bulletins and FAA airworthiness directives.
An in-flight overload failure of the left elevator inboard balance weight rib for undetermined reasons.
Source: NTSB Aviation Accident Database
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