OMAK, WA, USA
N7836V
MOONEY M20C
THE PILOT, WHILE ON FINAL APPROACH AT 500 FEET AGL, LOST ELEVATOR CONTROL WHEN THE ELEVATOR PUSH ROD SEPARATED DUE TO BENDING FATIGUE. THE MONOBALL BEARING WAS FOUND TO BE FROZEN AND CORRODED. THE AIRCRAFT HAD UNDERGONE AN ANNUAL INSPECTION WHEN PURCHASED 108 HOURS PRIOR TO THE ACCIDENT, AND THE FLIGHT CONTROLS HAD BEEN SIGNED OFF AS LUBRICATED. NO AD LISTING WAS FOUND, HOWEVER, TO VERIFY WHETHER AD 73-21-01 HAD BEEN COMPLIED WITH AT THE ANNUAL INSPECTION. THE AD, WHICH REQUIRED LUBRICATION OF THE FLIGHT CONTROLS EVERY 100 HOURS, WAS 8 HOURS OVERDUE AT THE TIME OF THE ACCIDENT.
On March 3, 1995, approximately 1510 hours Pacific standard time (pst), a Mooney M20C, N7836V, being flown by a certificated private pilot, was substantially damaged during collision with terrain following a loss of control while on approach to runway 35 at the Omak Airport, Omak, Washington. The pilot was uninjured. Visual meteorological conditions prevailed and no flight plan had been filed. The flight, which was personal, was to have been operated under 14CFR91, and originated from Electric City, Washington, approximately 1450. The pilot reported that while on approach and at an altitude of approximately 500 feet above ground he lost elevator control and the aircraft began a series of pitch up and nose down maneuvers. The aircraft impacted the ground in a flat, wings level attitude and slid to rest (refer to NTSB Form 6120.1/2 and Okanogan County Sheriff's Report). Post crash examination by FAA Inspector Ken Ziemer revealed a fracture and separation of the threaded end of the elevator push rod eye bolt. Metallurgical examination of the push rod separation surfaces by the NTSB's Material Laboratory revealed topography typical of high stress reverse bending fatigue. Additionally, the monoball bearing at the end of the rod was found to be frozen and corroded (refer to attached metallurgical report). The aircraft's airframe log was examined and an annual inspection was signed off on July 27, 1994, (tach time 1141.4 hours) at which time the pilot purchased and took possession of the aircraft. The annual entry reported among other entries "Lubed all flight controls" (refer to ATTACHMENT I). Two additional airframe log entries followed the annual, the first documenting a transponder test, and the second documenting the replacement of a belly strobe. No list of current Airworthiness Directives could be located and the pilot reported that he never received such a listing. The tach time on the aircraft at the time of the accident was 1249.32 hours as reported by the FAA inspector on site. This yielded a total of 108 hours time transpired since the last annual inspection. FAA Airworthiness Directive 73-21-01, which applies to Mooney M20C, serial number 2871, references the prevention of "corrosion and/or misrigging in the flight control and landing gear systems." Specifically, the AD requires that all flight controls should be lubricated every 12 months or 100 hours time in service, whichever comes first (refer to ATTACHMENT II). It was not known whether this AD was complied with at the July 27th annual.
THE ELEVATOR PUSH ROD SEPARATION DUE TO FATIGUE. FACTORS CONTRIBUTING TO THE ACCIDENT WERE THE PILOT IN COMMAND'S FAILURE TO INSURE COMPLIANCE WITH THE AIRWORTHINESS DIRECTIVE AND THE FROZEN PUSH ROD BEARING.
Source: NTSB Aviation Accident Database
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