PALMER, AK, USA
N7966B
Cessna 172
The student pilot was departing on runway 15, on his first solo flight. He stated that during the initial climb, the engine developed a severe vibration followed by a 'very loud bang'. He made a forced landing on a golf course at the southeast end of the airport. During the landing roll, the airplane's right wing struck a small hill, and sustained substantial damage. After landing, the pilot discovered that the entire propeller, propeller flange, and the forward end of the engine crankshaft were missing. They were later located near the midpoint of the departure runway. An FAA airworthiness inspector's review of the engine log book discovered that the accident engine had previously sustained two propeller strikes. He reported that the log book failed to reflect any inspection following the prop strikes. An NTSB metallurgical examination of the propeller flange assembly revealed multiple clamshell marks, typical of fatigue cracking. The engine is the subject of a Lycoming Engine Service Letter, L163C, that recommends that any engine involved in a sudden stoppage event be removed, dissembled, and inspected prior to returning the engine to service.
On August 15, 1998, about 1415 Alaska daylight time, a wheel equipped Cessna 172 airplane, N7966B, sustained substantial damage during an emergency landing after takeoff from the Palmer Municipal Airport, Palmer, Alaska. The airplane was being operated as a visual flight rules local area instructional flight under Title 14, CFR Part 91, when the accident occurred. The airplane is registered to, and operated by, Mustang Air, Inc., Palmer. The solo student pilot was not injured. Visual meteorological conditions prevailed, and company flight following procedures were in effect. The flight originated at the Palmer Municipal Airport, about 1413. In his written statement to the National Transportation Safety Board (NTSB), the student pilot reported that he was conducting his first solo flight. He said that while departing runway 15, about 450 feet above the runway, the engine developed a severe vibration followed by a "very loud bang". The pilot stated that he made an emergency landing on a golf course at the southeast end of the airport. During the landing roll, the airplane's right wing struck a small hill, and sustained substantial damage. The pilot's postaccident inspection revealed that the entire propeller, propeller flange, and the outboard end of the engine crankshaft were missing from the engine. The missing propeller components were later located near the midpoint of the departure runway. A Federal Aviation Administration (FAA) airworthiness inspector, Anchorage Flight Standards District Office (FSDO), reviewed the engine and airplane log books. He reported that the engine had accumulated a total time in service of 1,737.0 hours, and that no major overhaul had been accomplished since being installed in the accident airplane. The FAA inspector added that the accident airplane's engine had sustained two propeller strikes since being installed in the accident airplane. He said that the engine log books failed to document any postaccident inspection or corrective maintenance following the propeller strikes. The propeller flange assembly was retained by the NTSB investigator-in-charge, and sent to the NTSB Materials Laboratory for examination. A Safety Board metallurgist reported that a stereo microscope examination revealed multiple clamshell marks, typical of fatigue cracking. The engine is the subject of a Lycoming Engine Service Letter, L163C, dated May 20, 1991. The service letter addresses the inspection criteria for an aircraft engine that has been involved in a sudden stoppage accident or incident. The service letter states, in part: "...in the case of a sudden engine stoppage, propeller strike, loss of propeller blade or tip, the safest procedure is to remove and dissemble the engine and completely inspect the reciprocating and rotating parts including crankshaft gear and dowel parts. Any decision to operate an engine which was involved in a sudden stoppage incident/accident without such an inspection must be responsibility of the agency returning the aircraft to service."
Fatigue of the forward end of the engine crankshaft resulting in separation of the propeller assembly, and the operator's failure to comply with a required maintenance procedure. A factor was uneven terrain.
Source: NTSB Aviation Accident Database
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