RED BLUFF, CA, USA
N6636R
BEECH C23
THE PILOT SAID THAT WHEN HE TRIED TO MAKE A THROTTLE ADJUSTMENT IT HAD NO EFFECT ON THE ENGINE RPM. AFTER ENTERING DOWNWIND ABEAM HIS TOUCHDOWN POINT, HE SHUT DOWN THE ENGINE AND ATTEMPTED TO GLIDE THE REMAINDER OF THE DISTANCE. THE AIRCRAFT TOUCHED DOWN SHORT OF THE RUNWAY AND STRUCK AN EMBANKMENT. AN INSPECTION OF THE AIRCRAFT REVEALED THAT THE THROTTLE LINKAGE HAD SEPARATED FROM THE CARBURETOR THROTTLE ARM. THE BOLT, CASTELLATED NUT, AND WASHER WHICH SECURES THE ASSEMBLY TOGETHER WERE NOT PRESENT. THE ENGINE WAS REINSTALLED IN THE AIRCRAFT FOLLOWING A MAJOR OVERHAUL, 1 MONTH AND 2 OPERATING HOURS PRIOR TO THE ACCIDENT. AN ANNUAL INSPECTION WAS ALSO COMPLETED AND SIGNED OFF AT THAT TIME. THE MECHANIC WHO PERFORMED THE ENGINE REINSTALLATION SAID THAT THE BOLT HAD BEEN REINSTALLED AND THAT A COTTER PIN HAD ALSO BEEN INSTALLED IN THE PROCESS. THE MECHANIC WHO PERFORMED THE ANNUAL INSPECTION REPORTED THAT HE HAD NOT LOOKED THAT CLOSELY AT THE ENGINE SINCE IT HAD JUST BEEN INSTALLED AND INSPECTED BY ANOTHER MECHANIC. THE MANUFACTURER REPORTED THAT THE DESIGN OF THE ASSEMBLY DOES NOT PLACE LOADS ON THE BOLT THAT WOULD BE SUFFICIENT TO PRODUCE AN OVERLOAD FAILURE.
On May 2, 1995, at 1136 hours Pacific daylight time, a Beechcraft C23, N6636R, sustained substantial damage during a landing approach at Red Bluff, California. The aircraft was owned and operated by the pilot and was on a cross-country flight. Visual meteorological conditions prevailed at the time, and a VFR flight plan was filed for the operation. The certificated commercial pilot and his pilot-rated passenger both sustained serious injuries. The flight originated from the Half Moon Bay airport in Half Moon Bay, California, at 1000 on the day of the accident. The pilot reported that when he attempted to make a throttle adjustment, he was able to move the throttle control, however, it had no effect on the engine rpm. He reported that he was about 8 to 10 miles from the Red Bluff airport at the time, and continued on to his destination. After entering downwind for runway 15 and abeam his touchdown point, the pilot shut down the engine and attempted to glide the remainder of the distance on the approach. The aircraft touched down short of the airport boundary and struck an embankment. A postaccident inspection of the aircraft by a Federal Aviation Administration (FAA) airworthiness inspector revealed that the throttle linkage between the throttle lever and the throttle rod end was separated. The connecting bolt (AN3-6), with a castellated locking nut (M21042L3), and smooth spacer (AN960-10), were all missing. On April 20, 1995, the engine was reinstalled in the aircraft after a major overhaul. The engine controls were rigged and an operational check of all powerplant systems and controls was performed. According to an entry in the aircraft logbook, the aircraft was test flown and returned to service with total time on the airframe of 2,220 hours, and an engine tachometer reading of 2,220 hours. On May 1, 1995, the aircraft completed an annual inspection and was found to be airworthy. An airframe and powerplant mechanic with inspection authorization, made an airworthiness entry in the aircraft logbook with total time for the airframe and engine of 2,220 hours. At the time of the accident, the engine tachometer read 2,223 hours. The mechanic who performed the reinstallation reported to FAA inspectors that the bolt had been reinstalled and that a cotter pin had also been installed in the process. The mechanic who performed the annual inspection reported to FAA inspectors that he had not looked that closely at the engine since it had just been installed and inspected by another mechanic. The manufacturer reported that the design of the assembly does not place loads on the bolt that would be sufficient to produce an overload failure.
the separation of the throttle linkage due to improper installation, and the pilot's misjudgement of the glide path necessary to reach the runway prior to shutting down the engine.
Source: NTSB Aviation Accident Database
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