# NTSB ANC21LA068: Stinson 108-1, N8656K, Sterling, AK, August 2, 2021 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: August 2, 2021, 14:58 local (22:58 UTC) - Place: Sterling, AK - Coordinates: 60.528637, -150.82989 - Nearby events: https://openairdocs.org/map.md?lat=60.5286&lon=-150.8299&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Defining event: [Initial climb: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 4 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Alaska Regional Office - Parties: FAA - NTSB case key (mKey): 103616 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC21LA068 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/103616/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=103616 - Page: https://openairdocs.org/ntsb/ANC21LA068 ## Probable cause Insufficient available power as a result of low compression in three engine cylinders. Contributing to the accident was the pilot’s decision to takeoff with a slight quartering tailwind. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Ignition system: spark plugs/igniters](https://openairdocs.org/ntsb-findings/01057421): Aircraft › Aircraft power plant · Related maintenance info; cases with it: [Stinson 108-1, 1 case](https://openairdocs.org/ntsb-findings/01057421/cases.md?model=9230404), [All aircraft, 38 cases](https://openairdocs.org/ntsb-findings/01057421/cases.md) - [Power plant](https://openairdocs.org/ntsb-findings/01057100): Aircraft › Aircraft power plant · Not specified (probable cause); cases with it: [Stinson 108-1, 2 cases](https://openairdocs.org/ntsb-findings/01057100/cases.md?model=9230404), [All aircraft, 198 cases](https://openairdocs.org/ntsb-findings/01057100/cases.md) - [Engine (reciprocating): recip eng cyl section](https://openairdocs.org/ntsb-findings/01058530): Aircraft › Aircraft power plant · Not specified (probable cause); cases with it: [Stinson 108-1, 1 case](https://openairdocs.org/ntsb-findings/01058530/cases.md?model=9230404), [All aircraft, 373 cases](https://openairdocs.org/ntsb-findings/01058530/cases.md) - [Info processing/decision: decision making/judgment](https://openairdocs.org/ntsb-findings/02041520): Personnel issues › Action/decision · Pilot; cases with it: [Stinson 108-1, 2 cases](https://openairdocs.org/ntsb-findings/02041520/cases.md?model=9230404), [All aircraft, 3,098 cases](https://openairdocs.org/ntsb-findings/02041520/cases.md) - [Wind: tailwind](https://openairdocs.org/ntsb-findings/03034015): Environmental issues › Conditions/weather/phenomena · Contributed to outcome; cases with it: [Stinson 108-1, 2 cases](https://openairdocs.org/ntsb-findings/03034015/cases.md?model=9230404), [All aircraft, 594 cases](https://openairdocs.org/ntsb-findings/03034015/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Initial climb: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Stinson 108-1, 2 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=9230404), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) ## Analysis The pilot was conducting a local flight with friends onboard. He estimated the airplane’s takeoff weight to be about 76 lbs under maximum gross weight. The pilot stated that during the initial climb, the engine did not feel like it was producing full power and the airplane descended into trees, which resulted in substantial damage to the fuselage and wings. A video of the takeoff and initial climb revealed that the sound of the engine was consistent throughout the length of the video with no audible anomalies noted. A windsock that was visible in the video showed a slight right-quartering tailwind at the time of the takeoff. A postaccident examination revealed that the top spark plug from the No. 6 cylinder was mostly unscrewed and exhibited external signatures consistent with exposure to high heat, which indicated hot gas was leaking out of the cylinder through the spark plug hole. When the cylinders were checked for compression using the thumb check method, the Nos. 2 and 3 cylinders produced low compression. It is likely that the loose spark plug in combination with the two weak cylinders resulted in the engine producing less than full power. Additionally, the pilot’s decision to takeoff with a slight right-quartering tailwind likely contributed to the airplane’s lack of climb performance. ## Factual narrative On August 2, 2021, about 1458 Alaska daylight time, a Stinson 108-1 airplane, N8656K, was substantially damaged when it was involved in an accident near Sterling, Alaska. The private pilot and three passengers were uninjured. The flight was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he was taking some friends for a local flight. The useful load of the airplane was 766 lbs, and he estimated the takeoff weight was less than 690 lbs, which included the passengers and about 120 lbs of fuel. He stated the takeoff roll took longer than normal; however, the airplane seemed to climb normally with one notch of flaps until about 100 ft above ground level. The pilot said that at that point, the engine did not feel like it was producing full power; the airplane would no longer climb; and it began a descent toward trees located off the departure end of the runway. The airplane subsequently impacted the trees and came to rest at an estimated 45° nose-down angle. The airplane sustained substantial damage to both wings and the fuselage. A video of the takeoff taken by witnesses near the runway showed the airplane from the start of the takeoff roll until just before impact. The main landing gear were airborne just before the tailwheel, and the airplane entered a nose-high attitude and ascended to about tree top level. About 6 seconds after takeoff, the airplane began to descend and continued to descend in a nose-high attitude until the recording stopped. The sound of the engine was consistent throughout the length of the video with no audible anomalies noted. Additionally, the windsock visible in the video indicated a slight right-quartering tailwind at the time of takeoff. Figure 1. Airplane during takeoff During a postaccident engine examination of the Franklin 150-B4 engine, all bottom spark plug ignition wire caps were found to be finger tight. The top spark plug from the No. 6 cylinder was finger tight and exhibited signatures consistent with exposure to high heat on the outside of the plug. The crankshaft was manually rotated, and the cylinders were checked for suction and compression. The Nos. 2 and 3 cylinders exhibited weak compression, and it was difficult to detect suction on these cylinders. When the oil sump was removed, a small metal gear, a portion of a cotter pin and pieces of metallic debris were found in the sump. The camshaft displayed scoring consistent with foreign debris inside the engine. When the fuel strainer was removed, organic material/debris was located within the screen and in the bottom of the bowl. The small metal gear was later determined to be from the original mechanical tachometer, and it fell into the oil sump when the original tachometer was replaced with a digital tachometer. ## Aircraft - Registration: [N8656K](https://openairdocs.org/deregistered/N8656K-2022-03-05), registration cancelled 2022-03-05, S/N 108-1656, built 1947 (OpenAirDocs) - Reported make and model: STINSON 108-1 - Registry model: [Stinson 108-1](https://openairdocs.org/model/stinson-108-1) (registry code 9230404) (OpenAirDocs) - Registry engine: [Franklin 6A4150 series](https://openairdocs.org/engine/franklin-6a4150-series) (registry code 27024, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 108-1656 - Year built: 1947 - Engines: FRANKLIN 6A4150 SERIES 150 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: Stinson Aviation Company LLC - Registered owner: Stinson Aviation Company LLC - Airworthiness certificate: Standard, Normal - Destination: Same as departure - Airport: AK84, Scooter'S Landing Strip, runway 08/26, 2,400 × 80 ft, gravel ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 59; injuries: none; private; airplane ratings: single-engine sea, single-engine land; medical: class 3, with waivers/limitations; seat: left ## Weather - Conditions: Visual (VMC), Day - Wind: 250° at 12 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 73 °F, dew point 57 °F - Altimeter: 30.05 inHg - Observed at: PASX, 7 nm away - METAR: PASX 022256Z AUTO 25012KT 10SM CLR 23/14 A3005 RMK AO2 SLP184 T02280144 ## 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 20210802012339A](https://openairdocs.org/incident/20210802012339A), Aug 2, 2021: Stinson 108-1, Sterling, AK, Substantial damage. On August 2, 2021 at approximately 2:58 pm local time, N8656K, a Stinson 108-1, was substantially damaged during an emergency Landing following a partial… ## Docket (4 files) The files NTSB released with the investigation on January 30, 2023, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=103616. 7.4 MB in all. - Pilot's statement (item 1, PDF, 3 pages, 248 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13407774&FileExtension=pdf&FileName=Pilot%20Statement-Rel.pdf - Examination summary (item 2, PDF, 4 pages, 502 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13408160&FileExtension=pdf&FileName=Examination%20Summary-Rel.pdf - Photos (item 3, PDF, 3 pages, 938 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13407936&FileExtension=pdf&FileName=Photo%20Array-Rel.pdf - Accident video (item 4, MOV, 5.7 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13406384&FileExtension=MOV&FileName=Takeoff%20Video-Rel.MOV 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.