# NTSB ANC13LA029: Cessna 207, N1704U, Bethel, AK, March 6, 2013 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: March 6, 2013, 17:30 local (21:30 UTC) - Place: Bethel, AK - Coordinates: 60.965557, -161.429168 - Nearby events: https://openairdocs.org/map.md?lat=60.9656&lon=-161.4292&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed, report June 11, 2014 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - Parties: Yute Air, Continental Motors, FAA, FAA FSDO-03 - NTSB case key (mKey): 86380 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC13LA029 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/86380/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=86380 - Page: https://openairdocs.org/ntsb/ANC13LA029 ## Probable cause The failure of the engine’s No. 1 piston connecting rod retaining bolts due to fatigue fracturing, which resulted in a loss of engine power during cruise flight. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating): recip eng cyl section](https://openairdocs.org/ntsb-findings/01058530): Aircraft › Aircraft power plant · Failure (probable cause); cases with it: [Cessna 207, 1 case](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=2073602), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Cessna 207, 3 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=2073602), [All aircraft, 3,820 cases](https://openairdocs.org/ntsb-events/341/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Cessna 207, 9 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=2073602), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis Shortly after departure on the commercial passenger/cargo flight, the airplane's engine lost power. The pilot conducted a forced landing on a snow-covered, sparsely treed, tundra area. Just before touchdown, the left stabilizer struck treetops, and the airplane sustained substantial damage. A preliminary examination of the engine revealed a crack in the crankcase. A subsequent examination of the No. 1 piston assembly revealed fatigue fractures in both connecting rod retaining bolts. Additional internal engine damage was found to be consistent with damage caused by the release of the connecting rod from the crankshaft. ## Factual narrative On March 6, 2013, about 1730 Alaska standard time, a Cessna 207 airplane, N1704U, sustained substantial damage during a forced landing on snow-covered tundra about 16 miles northeast of Bethel, Alaska. The airplane was operated as Flight 595, by Yute Air Alaska, Anchorage, Alaska, as a visual flight rules, scheduled passenger/cargo flight under the provisions of 14 Code of Federal Regulations Part 135. The airline transport pilot and the two passengers were not injured. Visual meteorological conditions prevailed at the time of the accident, and the airplane was operating on a company VFR flight plan. The flight had departed Bethel about 1718, en route to Kalskag, Alaska. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge on March 6, the director of operations for Yute Air Alaska reported that the flight originally departed Bethel destined for Kalskag. The pilot reported that about 15 minutes after departure, the engine made a "very loud and unusual whining" noise, which was followed by a partial loss of engine power. He reported the problem to his dispatcher via the company radio frequency, and began a turn toward a frozen pond for an emergency landing. During the turn, all engine power was lost. He then selected a closer area of snow-covered terrain, with small trees, as a forced landing site. Just prior to touchdown, the left stabilizer struck the tops of the trees, resulting in substantial damage to the horizontal stabilizer. After touchdown, the nose tire and fork broke free of the airplane. The airplane was equipped with a Continental Motors IO-520 series engine. A preliminary examination of the engine by company maintenance personnel revealed a crack in the crankcase. The airplane was recovered to a company facility where the engine was removed and shipped to Alaska Aircraft Engines, Anchorage for further examination. The engine was subsequently crated and shipped to Continental Motors, Inc. Analytical Department, Mobile, Alabama for disassembly and inspection. On May 15, 2013 under the supervision of an FAA District Office MIDO Safety Inspector, the engine was disassembled and examined at Continental Motors. The examination revealed that most of the engine's major internal damage was associated with the number one piston assembly. According to a report prepared by the manufacturer's investigator, the number one piston was fractured at the piston pin bore, releasing the number one rod and piston pin assembly at the small end. The unsupported number one rod and piston pin assembly caused damage to the rear section of the crankcase and camshaft. The number one rod had released from the crankshaft, and exhibited extreme mechanical damage. The number one rod was found in the oil sump. There were no signs of lubrication distress. Portions of the piston skirt were recovered from the oil sump and inspected in the CMI lab. The number one cylinder, piston, rod, and sump contents were retainedin bonded storage. The number one piston assembly, connecting rod, and associated pieces were shipped to the National Transportation Safety Board Materials Laboratory, Washington, DC. An examination of the number one piston assembly at the NTSB laboratory on February 12, 2014, revealed fatigue fractures in both connecting rod retaining bolts. Damage to the piston and wrist pin were consistent with damage following the release of the connecting rod from the crankshaft. A copy of the NTSB laboratory report is in the public docket for this case. ## Aircraft - Registration: [N1704U](https://openairdocs.org/aircraft/N1704U), registered now, S/N 20700304, built 1975 (OpenAirDocs) - Reported make and model: CESSNA 207 - Registry model: [Cessna 207](https://openairdocs.org/model/cessna-207) (registry code 2073602) (OpenAirDocs) - Registry engine: [Continental IO-520 series](https://openairdocs.org/engine/continental-io-520-series) (registry code 17032, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 20700304 - Year built: 1975 - Airframe hours: 31641 - Engines: CONT MOTOR IO 520 SERIES 285 horsepower reciprocating - Damage: Substantial damage - Flight: Part 135 - Operator: Flight Alaska Inc., doing business as Yute Air Alaska - Registered owner: Maritime Sales & Leasing Inc - Airworthiness certificate: Standard, Normal; Standard, Utility - Last inspection: 100 hour, January 29, 2013 - Departed: PABE, Bethel, AK - Destination: PALG, Kalskag, AK - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 56; injuries: none; airline transport; airplane ratings: multi-engine land, single-engine sea, single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review September 28, 2012; seat: left; restraint: 3-point; flight hours: 30,000 total, 20,000 in this make and model, 230 in the last 90 days, 102 in the last 30 days, 3 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 30° at 11 knots - Visibility: 10 statute miles - Lowest ceiling: 16,000 ft broken - Temperature: 30 °F, dew point 25 °F - Altimeter: 28.43 inHg - Observed at: PABE, 16 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 20130306003259A](https://openairdocs.org/incident/20130306003259A), Mar 6, 2013: Cessna 207, Akiachak, AK, Substantial damage. Aircraft N1704U fifteen minutes out of bet on flight to klg in cruise at 1000 feet. Engine made very loud whine noise and started losing power. PIC called bet… ## Other investigations on N1704U (1) 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. - [NTSB ANC86LA106](https://openairdocs.org/ntsb/ANC86LA106), Jul 14, 1986: Cessna 207 (N1704U), Ekuk, AK, substantial damage ## Docket (2 files) The files NTSB released with the investigation on May 16, 2014, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=86380. 1.4 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 242 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40412391&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Master.PDF - Materials Laboratory Factual Report 14-012 (item 2, .PDF, 1.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40412392&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report%2014-012-Master.PDF 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.