# NTSB ANC21LA094: Dehavilland DHC-3, N560TR, Bettles, AK, August 21, 2021 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: August 21, 2021, 13:25 local (21:25 UTC) - Place: Bettles, AK - Coordinates: 68.07526, -155.83897 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=68.0753&lon=-155.8390&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Alaska Regional Office - Parties: FAA - NTSB case key (mKey): 103927 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC21LA094 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/103927/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=103927 - Page: https://openairdocs.org/ntsb/ANC21LA094 ## Probable cause The seizure of the engine during flight for undetermined reasons, which led to a total loss of engine power. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Not determined](https://openairdocs.org/ntsb-findings/05000000): Not determined › Not determined · Unknown/Not determined (probable cause); cases with it: [Dehavilland DHC-3, 2 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md?model=2802412), [All aircraft, 2,247 cases](https://openairdocs.org/ntsb-findings/05000000/cases.md) - [Engine (reciprocating)](https://openairdocs.org/ntsb-findings/01058500): Aircraft › Aircraft power plant · Unknown/Not determined (probable cause); cases with it: [Dehavilland DHC-3, 1 case](https://openairdocs.org/ntsb-findings/01058500/cases.md?model=2802412), [All aircraft, 497 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340) (defining event); cases with it: [Dehavilland DHC-3, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=2802412), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) ## Analysis The pilot reported that, while on the base leg approach, he heard a “loud bang,” and the engine lost total power. The pilot determined that the airplane would not be able to reach its intended destination, so he turned the airplane into the wind and made a forced landing on tundra-covered terrain, which resulted in substantial damage to the fuselage. The airplane’s maintenance records were unremarkable. Postaccident examination of the engine revealed that it had seized and sheared the propeller spline into two pieces. The accessory wall could not be removed because of the extensive internal damage to the engine. As a result, the investigation was unable to determine the reason that the engine seized during the flight. ## Factual narrative On August 21, 2021, about 1325 Alaska daylight time, a float-equipped de Havilland DHC-3 Otter airplane, N560TR, sustained substantial damage when it was involved in an accident near Bettles, Alaska. The pilot and two passengers were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 commercial flight. The pilot reported that, while on the base leg approach for a landing at a remote lake, he heard a “loud bang,” and the engine lost total power. The pilot determined that the airplane would not be able to reach its intended destination, so he turned the airplane into the wind and made a forced landing onto an area with tundra-covered terrain, which resulted in substantial damage to the fuselage. A review of the airplane’s maintenance records was unremarkable, and no evidence of regulatory noncompliance was found. Postaccident disassembly and examination of the engine found that it had seized and that the propeller spline had fractured into two pieces. A substantial amount of metal fragmentation was found in the oil screen. The engine was subsequently examined using a lighted borescope, and fragments of broken internal engine pieces were visible, preventing the removal of the aft accessory wall. ## Aircraft - Registration: [N560TR](https://openairdocs.org/aircraft/N560TR), registered now, S/N 141, built 1956 (OpenAirDocs) - Reported make and model: DEHAVILLAND DHC-3 - Registry model: [Dehavilland DHC-3](https://openairdocs.org/model/dehavilland-dhc-3) (registry code 2802412) (OpenAirDocs) - Registry engine: [Pezetel ASZ-621R-M18](https://openairdocs.org/engine/pezetel-asz-621r-m18) (registry code 49800, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 141 - Year built: 1956 - Airframe hours: 16402.4 - Engines: PEZETEL ASZ-621R-M18 967 horsepower reciprocating - Damage: Substantial damage - Flight: Business, Part 135 - Operator: Sourdough Air Service, Inc., doing business as Brooks Range Aviation - Registered owner: Jespersen Aircraft Services Inc - Airworthiness certificate: Standard, Normal - Last inspection: Annual, June 13, 2021 - Departed: Issygok Lake, AK - Destination: Jobe Lake, AK - Flight plan: Company VFR - Equipment: Handheld GPS ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 49; injuries: none; airline transport, commercial; airplane ratings: single-engine sea, single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; last flight review June 18, 2021; seat: front; restraint: 3-point; flight hours: 17,000 total, 600 in this make and model, 16,500 as pilot in command, 300 in the last 90 days, 150 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 240° at 10 knots, gusting 17 - Visibility: 10 statute miles - Lowest ceiling: 4,600 ft broken - Temperature: 48 °F, dew point 37 °F - Altimeter: 29.93 inHg - Observed at: PAKP, 91 nm away - METAR: PAKP 212056Z AUTO 24010G17KT 10SM BKN046 09/03 A2993 RMK AO2 SLP162 60000 T00940033 56010 ## 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 20210821011419A](https://openairdocs.org/incident/20210821011419A), Aug 21, 2021: Dehavilland DHC-3, Kobuk, AK, Substantial damage. For unknown reasons the aircrafts engines seized in flight resulting in an emergency landing on the tundra. Aircraft was recovered and further engine analysis… ## Docket (3 files) The files NTSB released with the investigation on September 27, 2023, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=103927. 2.2 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120 (item 1, PDF, 9 pages, 1.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15833033&FileExtension=pdf&FileName=6120_Redacted-Rel-Rel.pdf - FAA inspector's statement (item 2, PDF, 1 page, 125 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15956390&FileExtension=pdf&FileName=ANC21LA094%20MFR%20FAA%20Inspector-Rel.pdf - Photos (item 3, PDF, 3 pages, 454 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=15833212&FileExtension=pdf&FileName=Accident%20Pictures-Rel.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.