BETHEL, AK, USA
N9956M
Cessna 207
During climb to cruise while passing 2,000 feet msl, the engine lost total power. The airplane nosed onto its back during the subsequent forced landing in marshy tundra. Postaccident inspection revealed wear between the throttle arm and the connecting hardware bushing. The throttle control lever had disconnected from the throttle arm. Service Bulletin SEB95-15R1, 'Throttle Lever Inspection,' that required a visual inspection for wear between the arm and bushing each 50 hours or 12 months, had been complied with 56 hours, 163 hours, and 268 hours prior to the accident by company mechanics. The newly overhauled engine was installed 334 hours prior to the accident.
On May 29, 1998, at 1557 Alaska daylight time, a Cessna 207 airplane, N9956M, sustained substantial damage during a forced landing 10 miles south of Bethel, Alaska. The solo airline transport pilot was uninjured. The flight was operated by Arctic Transportation Services, Inc., of Anchorage, Alaska, as an on-demand cargo flight from Bethel to Tununak, Alaska. Visual meteorological conditions prevailed at the time of the accident, and a company VFR flight plan was filed. The pilot reported to the NTSB Investigator-In-Charge during a telephone interview on May 30, 1998, that during the initial climb to cruise, passing 2,000 feet msl, the engine power dropped to idle. He indicated that manipulating the engine controls did not result in power above idle. During the subsequent forced landing in marshy tundra, the airplane nosed over onto its back. Postaccident investigation revealed that the throttle control lever, manufactured by Teledyne Continental Motors, and assigned Cessna part number 632555-31, became disconnected from the engine throttle. Metallurgical investigation conducted at the NTSB metallurgical laboratory on July 9, revealed wear between the attaching hardware bushing and the throttle arm. Cessna Aircraft Corporation, Inc., issued Service Bulletin SEB95-15 on June 30, 1995, requiring a repetitive inspection every 50 hours or 12 months, on the Throttle Lever Control part number 632555-31. This procedure is a visual inspection for wear, loose bushings, or worn attachment holes. If wear is found, the throttle arm is to be replaced with part number 632555-65. Aircraft with part number 632555-65 do not require repetitive inspection. The Teledyne Continental Motors IO-520F engine, serial number 286404-R, was overhauled 334 hours prior to the accident, and installed by company mechanics on November 21, 1997. Service Bulletin SB95-15R1 ("Throttle Lever Inspection") was complied with on January 28, 1998, at 11,342 airframe hours; on March 23, 1998, at 11,447 airframe hours; and on May 7, 1998, at 11,554 airframe hours. This last inspection was 56 hours prior to the accident. All of these inspections were performed by company mechanics.
The throttle arm disconnecting from the throttle linkage to the engine as a result of inadequate inspection by company maintenance personnel. Factors associated with this accident were the company maintenance personnel not following the repetitive Service Bulletin inspection, and the inadequate design of the throttle arm by the manufacturer.
Source: NTSB Aviation Accident Database
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