COOPER LANDING, AK, USA
N7541K
CESSNA 180
THE PILOT REDUCED POWER BY RETARDING THE THROTTLE. THE ENGINE RESPONDED AND CONTINUED TO LOSE POWER. THE PILOT APPLIED THROTTLE AND THE ENGINE DID NOT RESPOND. HE ATTEMPTED TO LAND ON RUNWAY 03 BUT WAS UNABLE TO REDUCE POWER AND OVER SHOT THE RUNWAY. HE WAS TURNING TO REVERSE COURSE AND LAND ON RUNWAY 21. DURING THE TURN THE ENGINE BEGAN TO LOSE MORE POWER AND AIRPLANE DESCENDED AND CRASHED INTO TREES. EXAMINATION OF AIRPLANE SHOWED THAT THE THROTTLE ARM WAS NOT SAFETIED TO THE CARBURETOR THROTTLE STOP IAW THE AIRWORTHINESS DIRECTIVE AND HAD SEPARATED FROM THE CARBURETOR.
HISTORY OF FLIGHT On September 11, 1993, at 1510 Alaska daylight time, a wheel equipped Cessna 180 airplane, N7541K, registered to and operated by the Pilot-in-Command, lost power after takeoff and was forced to crash into the trees just beyond the departure end of the runway at Quartz Creek Airstrip, Cooper Landing, Alaska. The air taxi sightseeing flight, operating under 14 CFR Part 135, was departing the Quartz Creek Airstrip for sightseeing over Harding Glacier. A visual flight rules flight plan was filed and visual meteorological conditions prevailed. The commercial certificated Pilot-in-Command and two passengers received serious injuries and one passenger received minor injuries. The airplane was substantially damaged. According the Pilot-in-Command, he reduced power when he reached 300 feet above the ground after takeoff. The engine continued to lose power and he applied full throttle, but the engine did not respond. He then flew a traffic pattern to return to land on runway 03. During his final approach, he was unable to reduce power and lose altitude. He over shot the runway and was attempting to reverse his turn to land on runway 21 after over shooting runway 03. During the turn the airplane began to lose more power and altitude so the pilot stopped the turn and landed straight ahead into the trees. WRECKAGE AND IMPACT INFORMATION The wreckage was located approximately 3/4 of a mile past the departure end of runway 03 on a magnetic bearing of 025 degrees. The area was covered with spruce trees averaging 50 to 75 feet in height. The ground was covered by moss and low growth and was generally level except for an occasional depression from an old stream bed. The airplane was found to be nosed into the ground. The empennage and cabin were standing vertically. The engine was bent 90 degrees toward the cabin top and resting on the ground. The engine compartment was pinned to the ground by two 10 to 12 inch diameter spruce trees. Access to the engine compartment was not attained at the accident site. Both wings remained attached to the airplane and showed crushing damage and tree impact damage. The vertical fin and rudder were not damaged. The horizontal stabilizers and elevators were bent and pieces of metal were torn away. The cockpit switches were secured and were not recorded. However, the throttle was moved in and out of the instrument panel and easily pulled out of the outer housing until the throttle arm obstructed the inner cable's passage through the outer housing. The engine compartment could not be examined to see if the throttle arm or throttle cable had become disconnected from the carburetor. Subsequent examination of the engine compartment, after the airplane was recovered, showed that the throttle cable remained connected to the throttle arm, but the throttle arm was not connected to the carburetor. TEST AND RESEARCH Subsequent examination of the carburetor and throttle are showed the following: 1. That the internal splines of the throttle arm were worn to a knife edged condition. 2. There were two distinctive wear steps on the splines. 3. The retention bolt was secured with a castellated nut instead of the normal self locking nut. 4. The retention bolt compressed the slot at the splined end so that no clearance existed. Additional tightening of the bolt would not result in increased torque. 5. There was no impact damage or mechanical damage to the throttle assembly. 6. Visual examination of the throttle arm, throttle shaft, and throttle stop assemblies showed no evidence or signature of a recent safety wire installation as required by AD-72-06-05. Microscopic examination of the components, accomplished by R.J. Waldron & Co. LTD., of Richmond, British Columbia, Canada, confirmed the visual observation. ADDITIONAL INFORMATION Airworthiness Directive (AD) 72-06-05, effective March 24, 1972, required compliance within 30 days. The AD required that the throttle arm be seated against the shoulder on the throttle stop, that full throttle be attained, that the retention bolt be torqued to 20-28 in-lbs and that the slot on the throttle arm have clearance. The AD specifically states "If the slot has closed so that no clearance remains, replace the arm and retorque to the above specifications." The AD further states that once the specific torque is established, the throttle arm and clamping screw should be safety wired to the throttle stop as depicted in "illustration A." The opening statement of the AD states that this must be complied with to prevent looseness or separation of the throttle arm and that this procedure or any equivalent procedure approved by the Manager, New York Aircraft Certification Office, FAA, New England Region may be used. Examination of the airplane records did not reveal any other equivalent approved procedure. The airplane had undergone extensive repairs caused by a previous accident approximately 2 years earlier by Air Parts Inc., and an Annual inspection was completed May 10, 1993, 83 hours before the accident, by T & B Aircraft Repair. Both businesses are located in Anchorage, Alaska, on Merrill Field. According to the Federal Aviation Administration, if an operator places a new aircraft on his 14 CFR Part 135 Operations Specifications, the aircraft can be inspected by the FAA, but it is the Operator's responsibility to ensure that the airplane meets all the requirements of the Federal Aviation Regulations including compliance with Airworthiness Directives. The Operator, also the Pilot-in-Command, had been operating the airplane in accordance with his 14 CFR Part 135 certificate and operations specifications for 2 years.
THE SEPARATION OF THE THROTTLE ARM FROM THE THORTTLE SHAFT, THE FAILURE OF THE MAINTENANCE PERSONNEL TO COMPLY WITH THE AIRWORTHINESS DIRECTIVE, AND THE COMPANY MANAGEMENT'S FAILURE TO ADEQUATELY ENSURE COMPLIANCE WITH THE AIRWORTHINESS DIRECTIVES.
Source: NTSB Aviation Accident Database
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