# NTSB WPR19LA207: Stinson 108, N6642M, Klamath Falls, OR, July 9, 2019 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: July 9, 2019, 13:20 local (20:20 UTC) - Place: Klamath Falls, OR - Coordinates: 42.132778, -121.71971 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=42.1328&lon=-121.7197&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Defining event: [Takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) - Highest injury: No injuries - Injuries: 2 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration - NTSB case key (mKey): 99984 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR19LA207 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/99984/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=99984 - Page: https://openairdocs.org/ntsb/WPR19LA207 ## Probable cause The mechanic’s failure to identify an engine performance issue, which led to a partial loss of engine power. Contributing to the accident was the pilot’s decision to operate the airplane with a known mechanical deficiency. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Action: incorrect action selection](https://openairdocs.org/ntsb-findings/02041010): Personnel issues › Action/decision · Pilot (probable cause); cases with it: [Stinson 108-3, 1 case](https://openairdocs.org/ntsb-findings/02041010/cases.md?model=9230408), [All aircraft, 397 cases](https://openairdocs.org/ntsb-findings/02041010/cases.md) - [Engine (reciprocating)](https://openairdocs.org/ntsb-findings/01058500): Aircraft › Aircraft power plant · Malfunction (probable cause); cases with it: [Stinson 108-3, 1 case](https://openairdocs.org/ntsb-findings/01058500/cases.md?model=9230408), [All aircraft, 497 cases](https://openairdocs.org/ntsb-findings/01058500/cases.md) - [Maintenance: scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Stinson 108-3, 1 case](https://openairdocs.org/ntsb-findings/02062010/cases.md?model=9230408), [All aircraft, 320 cases](https://openairdocs.org/ntsb-findings/02062010/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Takeoff: Loss of engine power (partial)](https://openairdocs.org/ntsb-events/342) (defining event); cases with it: [Stinson 108-3, 6 cases](https://openairdocs.org/ntsb-events/342/sequence.md?model=9230408), [All aircraft, 1,858 cases](https://openairdocs.org/ntsb-events/342/sequence.md) - [Emergency descent: Collision with terr/obj (non-CFIT) ](https://openairdocs.org/ntsb-events/470); cases with it: [Stinson 108-3, 15 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=9230408), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The pilot had departed on a cross-country flight. About 1,000 ft above ground level, the engine lost partial power. The pilot made a forced landing in an open field, during which the left wing sustained substantial damage as it contacted the ground. The airplane had a recurring engine performance deficiency that the pilot was aware of, and he used a temporary fix to work around the issue. The mechanic who performed maintenance on the engine before the accident thought that the issue involved the carburetor. Postaccident examination of the carburetor revealed no malfunctions that would have precluded normal operation. Postaccident examination of the engine revealed multiple incorrectly set valve clearances and multiple cylinders with lower-than-acceptable compression. Thus, the mechanic who performed maintenance on the engine failed to identify the engine’s out-of-adjustment valves or the low-cylinder compression. ## Factual narrative On July 9, 2019, about 1320 Pacific daylight time, a Stinson 108-3 airplane, N6642M. was substantially damaged when it was involved in an accident near Klamath Falls, Oregon. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that he and a passenger were relocating the airplane to Alaska. The airplane departed from Red Bluff Municipal Airport (RBL), Red Bluff, California, and landed at Crater Lake-Klamath Falls Airport (LMT), Klamath Falls, Oregon, for a refueling stop. The accident occurred after the takeoff from LMT. The pilot stated that the takeoff was normal but that the engine lost partial power when the airplane was at an altitude of above 1,000 ft above ground level. The pilot initiated a forced landing to a nearby field, where the left wing contacted the ground. The pilot stated that he had experienced previous problems with the carburetor. He stated that, after the carburetor underwent an overhaul, the engine ran better but that it would occasionally not get up to full engine speed, so the airplane would not have top end power. To work around the issue, the pilot used a procedure of slowly advancing the throttle to the first three-quarters of travel and then applying the remaining throttle rapidly to attain full power. The pilot stated that this issue did not occur during the first leg of the trip. The mechanic who worked on the airplane before the accident flight stated that the owner, who was not the accident pilot, reported the maintenance problem. The mechanic also stated that he checked the timing, valve lash, induction system, and fuel line to the airframe fuel filter and found no problems, so he determined that the carburetor was the issue. The mechanic temporarily replaced the carburetor with another one and detected a noticeable increase in engine power, which confirmed that the maintenance problem was due to the original carburetor. The carburetor was then provided to the facility that had previously performed an overhaul, and repairs were made. Afterward, the carburetor was reinstalled on the airplane. Postaccident examination of the carburetor revealed no malfunctions that would have precluded normal operation. The engine rocker box covers were removed, and valve clearance on the right-side intake and exhaust valves (Nos, 2, 4, and 6) was found to be within acceptable limits. Valve clearance on the left-side cylinders (Nos. 1, 3, and 5) were found to be greater than 0.20 inch. According to the manufacturer’s engine service manual, the valve clearance is 0.04 inch. A compression test was conducted on each cylinder. Each cylinder held 80 pounds per square inch (psi). Cylinder No. 1 held 62 psi and leaked air past the exhaust valve. Cylinder No. 2 held 48 psi and leaked air past the piston rings and from the exhaust valve. Cylinder No. 3 held 73 psi and leaked air past the piston rings. Cylinder No. 4 held 56 psi and leaked airpast the piston rings. Cylinder No. 5 held 58 psi and leaked air out of the intake valve. Cylinder No. 6 held 33 psi and leaked air out of the intake valve and past the piston rings. No other anomalies were noted that would have precluded normal operation. ## Aircraft - Registration: [N6642M](https://openairdocs.org/aircraft/N6642M), registered now, S/N 108-4642, built 1948 (OpenAirDocs) - Reported make and model: Stinson 108 (3) - Registry model: [Stinson 108-3](https://openairdocs.org/model/stinson-108-3) (registry code 9230408) (OpenAirDocs) - Registry engine: [Franklin 6A4165 series](https://openairdocs.org/engine/franklin-6a4165-series) (registry code 27025, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 108-4642 - Year built: 1948 - Engines: Franklin 6A4165 SERIES 165 horsepower reciprocating - Damage: Substantial damage - Fire: Unknown - Flight: Personal, Part 91 - Airworthiness certificate: Standard, Normal - Departed: LMT, Klamath Falls, OR - Airport: LMT, Klamath Falls - Equipment: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 52; injuries: none; private; airplane ratings: single-engine land; medical: class 2, with waivers/limitations ## Weather - Conditions: Visual (VMC), Day - Wind: 110° at 3 knots - Visibility: 10 statute miles - Lowest ceiling: 12,000 ft broken - Temperature: 75 °F, dew point 32 °F - Altimeter: 30.07 inHg - Observed at: KLMT - METAR: SPECI KLMT 092021Z 11003KT 10SM BKN120 24/05 A3007 RMK AO2 T02390050 ## 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 20190709004379A](https://openairdocs.org/incident/20190709004379A), Jul 9, 2019: Stinson 108-3, Klamath Falls, OR, Substantial damage. The aircraft departed lmt (Klamath Falls). PIC described a procedure he has been using to work around an issue with the carburetor, acceleration and full… ## Docket (5 files) The files NTSB released with the investigation on May 4, 2022, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=99984. 3.3 MB in all. - Pilot's statement (item 1, PDF, 1 page, 113 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13315225&FileExtension=pdf&FileName=Memo%20for%20Record%20Pilot%27s%20Statement-Rel.pdf - Interviews (item 2, PDF, 1 page, 131 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=12947406&FileExtension=pdf&FileName=Memo%20for%20Record%20Mechanic%20Interview-Rel.pdf - Airframe and engine examination report (item 3, PDF, 10 pages, 1.3 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13575796&FileExtension=pdf&FileName=Airframe%20and%20Engine%20Examination%20WPR19LA207-Rel.pdf - Service manual excerpt (item 4, PDF, 2 pages, 296 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13575293&FileExtension=pdf&FileName=Memo%20for%20Record%20Franklin%20Engine%20Service%20Manual%20Excerpt-Rel.pdf - Photos (item 5, PDF, 3 pages, 1.5 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=13316204&FileExtension=pdf&FileName=WPR19LA207%20Photos-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.