# NTSB ANC98LA059: Cessna 207, N9956M, Bethel, AK, May 29, 1998 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: May 29, 1998, 15:57 local (23:57 UTC) - Place: Bethel, AK - Coordinates: 60.809993, -161.850723 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=60.8100&lon=-161.8507&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report February 15, 2001 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - NTSB case key (mKey): 3147 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC98LA059 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/3147/pdf - Page: https://openairdocs.org/ntsb/ANC98LA059 ## Probable cause 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. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power, climb - to cruise - throttle/power lever,linkage - disconnected (cause) - maintenance,inspection - inadequate, company maintenance personnel (cause) - maintenance,service bulletin/letter - not followed, company maintenance personnel (contributing factor) - maintenance,design change - required, manufacturer (contributing factor) - acft/equip,inadequate design, manufacturer (contributing factor) - Forced landing, descent - emergency - Nose over, emergency descent/landing ## Analysis 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. ## Factual narrative 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. ## Aircraft - Registration: [N9956M](https://openairdocs.org/aircraft/N9956M), registered now, S/N 20700763, built 1983 (OpenAirDocs) - Reported make and model: Cessna 207 - Registry model: [Cessna 207A](https://openairdocs.org/model/cessna-207a) (registry code 2073605) (OpenAirDocs) - Registry engine: [Continental IO-520-F](https://openairdocs.org/engine/continental-io-520-f) (registry code 17237, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 20700763 - Airframe hours: 11610 - Engines: Continental IO-520-F 300 horsepower reciprocating - Damage: Substantial damage - Flight: Part 135 - Registered owner: Arctic Transportation Service - Airworthiness certificate: Standard, Normal - Last inspection: AAIP, May 8, 1998, 56 hours before - Departed: BET - Destination: AK45, TUNUNAK, AK - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 24; airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, valid medical--no waivers/lim.; seat: left; flight hours: 4,050 total, 1,770 in this make and model, 3,875 as pilot in command, 220 in the last 90 days, 85 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 90° at 13 knots - Visibility: 40 statute miles - Lowest ceiling: 6,500 ft broken - Temperature: 59 °F, dew point 45 °F - Altimeter: 29.00 inHg - Observed at: BET, 10 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19980529014859A](https://openairdocs.org/incident/19980529014859A), May 29, 1998: Cessna 207, Bethel, AK, Substantial damage. Engine power dropped to idle on climb to cruise. Nosed over landing in marshy tundra. (From .4) during climb to cruise while passing 2,000 feet MSL, the engine… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.