# NTSB WPR17LA119: Paul R Seipt Sonex, N255BZ, Garfield, WA, June 3, 2017 - Type: NTSB accident investigation - Classification: Accident · No injuries · Class 3 · Limited · Final report - Date: June 3, 2017, 11:30 local (18:30 UTC) - Place: Garfield, WA - Coordinates: 46.99139, -117.12722 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=46.9914&lon=-117.1272&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Defining event: [Enroute-cruise: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Sonex Aircraft - NTSB case key (mKey): 95292 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR17LA119 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/95292/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=95292 - Page: https://openairdocs.org/ntsb/WPR17LA119 ## Probable cause The pilot’s improper torque of screws that attached the flywheel mounting flange to the crankshaft during engine assembly, which resulted in heavy vibrations and the subsequent in-flight loss of the propeller. ## Findings NTSB's coded findings; those marked are part of the probable cause. - [Engine (reciprocating): recip eng rear section](https://openairdocs.org/ntsb-findings/01058540): Aircraft › Aircraft power plant · Incorrect service/maintenance (probable cause); cases with it: [Paul R Seipt SONEX, 1 case](https://openairdocs.org/ntsb-findings/01058540/cases.md?model=05634JI), [All aircraft, 42 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md) - [Action: incorrect action performance](https://openairdocs.org/ntsb-findings/02041015): Personnel issues › Action/decision · Pilot (probable cause); cases with it: [Paul R Seipt SONEX, 1 case](https://openairdocs.org/ntsb-findings/02041015/cases.md?model=05634JI), [All aircraft, 1,386 cases](https://openairdocs.org/ntsb-findings/02041015/cases.md) ## Sequence of events The events NTSB coded, in order, by phase of flight. The defining event best describes what happened. - [Enroute-cruise: Powerplant sys/comp malf/fail](https://openairdocs.org/ntsb-events/340); cases with it: [Paul R Seipt SONEX, 1 case](https://openairdocs.org/ntsb-events/340/sequence.md?model=05634JI), [All aircraft, 820 cases](https://openairdocs.org/ntsb-events/340/sequence.md) - [Enroute-cruise: Part(s) separation from AC](https://openairdocs.org/ntsb-events/338) (defining event); cases with it: [Paul R Seipt SONEX, 1 case](https://openairdocs.org/ntsb-events/338/sequence.md?model=05634JI), [All aircraft, 563 cases](https://openairdocs.org/ntsb-events/338/sequence.md) - [Landing-landing roll: Collision during takeoff/land](https://openairdocs.org/ntsb-events/490); cases with it: [Paul R Seipt SONEX, 1 case](https://openairdocs.org/ntsb-events/490/sequence.md?model=05634JI), [All aircraft, 1,309 cases](https://openairdocs.org/ntsb-events/490/sequence.md) ## Analysis The pilot reported that, during cruise flight, the airplane began vibrating, followed by a loud bang. The pilot saw the propeller separate from the airplane and he subsequently performed a forced landing to a road. During the landing roll, the left wing impacted a guy wire, resulting in substantial damage to the left wing. Postaccident examination revealed that the crankshaft separated at the forward main bearing journal. The area of separation exhibited beach marks propagating from the woodruff key area throughout most of the separated surface area. The flywheel mounting flange attached to the crankshaft and the flywheel mating surface showed material deformation at several screw holes and two fractured screw shafts that remained in their holes in the mount. A 1/4-inch wide area of fretting was noted around the outer circumference of the mounting flange and flywheel mating area. The trigger shaft, which was attached to the flywheel, displayed scuffing and material deformation at the locations of the flywheel mounting flange screw heads. The pilot/builder reported that he found no torque values in the manufacturer’s assembly manual during assembly of the flywheel and he was uncertain of the torque that he applied to the screws, although he thought that it was sufficient. It is likely that he did not adequately torque the screws during installation of the flywheel, which allowed the screws to loosen over time, resulting in elongation of the screw holes and fretting on the flywheel mounting flange and flywheel mating surface. The loose flywheel assembly would have increased vibration throughout the engine, along with torsional loads that ultimately resulted in the separation of the forward crankshaft and propeller assembly. A Federal Aviation Administration (FAA) Advisory Circular shows the recommended torque to be used for a specified fastener. Builders can also contact the manufacturer, who can supply them with a general torque table. The maintenance history of the airplane was not obtained during the investigation. ## Factual narrative On June 3, 2017, about 1130 Pacific daylight time, an experimental, amateur-built Sonex, N255BZ, was substantially damaged when it was involved in an accident near Garfield, WA. The private pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot, who was also the builder of the airplane, reported that, during cruise flight at 4,000 ft mean sea level, he experienced an increasing vibration followed by a loud bang. He subsequently saw the propeller separate from the airplane and he performed a forced landing to a paved road. During the landing roll, the airplane impacted a power pole guy wire, resulting in substantial damage to the left wing (see Figure 1). Figure 1. Accident site. Examination of the airplane revealed that the propeller assembly and forward section of the crankshaft separated from the engine. The propeller and separated crankshaft section were not located. An examination of the engine crankcase and crankshaft was conducted at the aircraft manufacturer. The crankshaft separation surface was located at the forward main bearing journal and exhibited beach marks propagating from the woodruff key slot and extending through most of the separated surface area. (see Figure 2.) The flywheel mounting flange attached to the crankshaft and the flywheel mating surface showed material deformation at several screw holes, and two fractured screw shafts remained in their holes in the mount. (see Figure 3.) A 1/4-inch area of fretting was also noted around the outer circumference of the mounting flange and flywheel mating area. The trigger shaft, which is attached to the flywheel, displayed scuffing and material deformation at the locations of the flywheel mounting screw heads. Figure 2. Crankshaft separation surface area. Figure 3. Flywheel mounting flange. The pilot reported that he found no torque values in the manufacturer’s assembly manual during assembly of the flywheel. He was uncertain of the torque that he applied to the screws, although he thought that it was sufficient. The pilot further reported that it is his common practice to apply Loctite to all critical fasteners, and he could not specifically remember adding it to the fasteners during the assembly. According to the AeroVee 2.0 Assembly Manual, the trigger shaft is installed on the flywheel with four screws and Loctite 242 applied to the screw threads. No torque value is stated in this step. The flywheel and flywheel mounting flange are preassembled for the engine kit. Federal Aviation Administration (FAA) Advisory Circular 43-13-1B Table 7-1 shows the recommended torque to be used for a specified fastener. Builders can also contact the manufacturer, who can supply them with a general torque table. The maintenance history of the airplane was not obtained during the investigation. ## Aircraft - Registration: [N255BZ](https://openairdocs.org/deregistered/N255BZ-2017-08-14), registration cancelled 2017-08-14, S/N 0255, built 2016 (OpenAirDocs) - Reported make and model: PAUL R SEIPT SONEX (UNDESIGNAT) - Registry model: [Paul R Seipt SONEX](https://openairdocs.org/model/paul-r-seipt-sonex) (registry code 05634JI) (OpenAirDocs) - Registry engine: [Aerovee 2.0](https://openairdocs.org/engine/aerovee-2-0) (registry code 01403, 4 cycle) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 0255 - Year built: 2016 - Airframe hours: 92.4 - Engines: AeroVee 2180 80 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Operator: Seipt Paul R - Registered owner: Seipt Paul R - Airworthiness certificate: None - Departed: SFF, SPOKANE, WA - Destination: PUW, PULLMAN/MOSCOW, WA - Equipment: Electronic flight bag or handheld device, Handheld GPS ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 70; injuries: none; private; airplane ratings: single-engine land; last flight review August 16, 2015; seat: left; restraint: 4-point; flight hours: 269 total, 93 in this make and model, 269 as pilot in command, 38 in the last 90 days, 18 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 180° at 8 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 73 °F, dew point 50 °F - Altimeter: 29.95 inHg - Observed at: KPUW, 15 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 20170603007949A](https://openairdocs.org/incident/20170603007949A), Jun 3, 2017: Paul R Seipt SONEX, Garfield, WA, Substantial damage. Aircraft departed spokane, felts field enroute to pullman, WA. While in cruise flight at 4000' MSL over Garfield WA, pilot noticed small vibration in engine… ## Docket (5 files) The files NTSB released with the investigation on January 5, 2021, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=95292. 8.0 MB in all. - NTSB engine examination summary (item 1, PDF, 9 pages, 9 photos, 1.2 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11753335&FileExtension=pdf&FileName=WPR17LA119%20Engine%20Examination%20Summary-Rel.pdf - Aircraft builder notes and photos (item 2, PDF, 13 pages, 5.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11631213&FileExtension=pdf&FileName=Owners%20Notes%20and%20Photos_Redacted-Rel.pdf - FAA advisory circular ac 43.13-1B excerpt (item 3, PDF, 1 page, 12 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11631203&FileExtension=pdf&FileName=AC%2043.13-1B%20-%20Acceptable%20Methods,%20Techniques,%20and%20Practices%20Aircraft%20Inspection%20and%20Repair%20(w_Change%201)-Rel.pdf - Statement of party representatives to NTSB investigation-sonex aircraft (item 4, PDF, 1 page, 910 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11633469&FileExtension=pdf&FileName=NTSB%20Party%20Form-Sonex_Redacted-Rel.pdf - Photo array-accident site (item 5, PDF, 4 pages, 469 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=11753325&FileExtension=pdf&FileName=Photo%20Array-Accident%20Site-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.