# NTSB WPR22LA314: Beech F33A, N4133S, Wilder, ID, August 21, 2022 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Class 3 · Limited · Final report - Date: August 20, 2022, 18:00 local (Aug 21, 2022, 00:00 UTC) - Place: Wilder, ID · Open field - Coordinates: 43.705708, -116.9131 - Nearby events: https://openairdocs.org/map.md?lat=43.7057&lon=-116.9131&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Defining event: [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) - Highest injury: Minor injuries - Injuries: 2 minor - Status: Completed - Report: Approved by Office Director - Investigation class: Class 3 - NTSB office: Western Pacific Region - Parties: Federal Aviation Administration FSDO - NTSB case key (mKey): 105790 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=WPR22LA314 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/105790/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=105790 - Page: https://openairdocs.org/ntsb/WPR22LA314 ## Probable cause Catastrophic engine failure during the initial climb due to an incorrectly installed crankshaft counterweight retaining ring. ## 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: [Beech F33A, 1 case](https://openairdocs.org/ntsb-findings/01058540/cases.md?model=1151425), [All aircraft, 42 cases](https://openairdocs.org/ntsb-findings/01058540/cases.md) - [Maintenance: scheduled/routine maintenance](https://openairdocs.org/ntsb-findings/02062010): Personnel issues › Task performance · Maintenance personnel (probable cause); cases with it: [Beech F33A, 1 case](https://openairdocs.org/ntsb-findings/02062010/cases.md?model=1151425), [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. - [Initial climb: Loss of engine power (total)](https://openairdocs.org/ntsb-events/341) (defining event); cases with it: [Beech F33A, 14 cases](https://openairdocs.org/ntsb-events/341/sequence.md?model=1151425), [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: [Beech F33A, 21 cases](https://openairdocs.org/ntsb-events/470/sequence.md?model=1151425), [All aircraft, 10,189 cases](https://openairdocs.org/ntsb-events/470/sequence.md) ## Analysis The airplane sustained a catastrophic engine failure shortly after takeoff due to a separated crankshaft counterweight. The pilot performed a forced landing, during which the airplane sustained substantial damage. The engine had been overhauled about 14 years and 950 flight hours before the accident. Examination of the remaining counterweights revealed that, during that overhaul, some of their retaining pins had been installed back to front. According to the engine manufacturer, such installation has been known to cause failure of the counterweights and the catastrophic damage observed. The correct installation is documented in the engine maintenance manual and reiterated in a service bulletin that was published 5 years before the engine was overhauled. ## Factual narrative On August 20, 2022, about 1800 mountain daylight time, a Beech F33A, N4133S was substantially damaged when it was involved in an accident near Wilder, Idaho. The pilot and passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot and a mechanic had been performing maintenance, attempting to resolve a problem where the engine would intermittently shudder during flight. After checking the cylinder compression, replacing a set of spark plugs, cleaning the fuel injectors, and confirming the engine timing, they decided to perform a test flight. The engine runup and takeoff were uneventful, and during the initial climb they monitored the engine instrument gauges, and all indicated nominal values. A short time later, the engine shook violently, and stopped producing power. They performed a forced landing into a field, and the airplane sustained damage to the lower forward fuselage and both wings. The airplane was powered by an IO-520-BA engine manufactured by Continental Motors, and overhauled by T.W. Smith Engine Company in 1998, about 950 flight hours before the accident. During the 14-year period leading up to the accident, routine maintenance was performed on the engine, with no work that would have required opening the crankcase or removing any cylinders. The engine was equipped with two sets of moving counterweights mounted to crankshaft blades adjacent to the journals of cylinder Nos. 1 and 2, and 3 and 4. Each counterweight was attached to their respective crankshaft blade by two pins housed within bushings and held in place at their ends with retaining plates and internal retaining “snap” rings. Examination of the engine revealed a large hole in the upper rear section of the crankcase, next to the Nos. 1 and 2 counterweights. Both counterweights had separated from their respective blades and showed similar damage signatures, with one counterweight mounting hole intact with its bushing in place, and the other split open with its material formed outwards. The Nos. 1 and 2 connecting rod caps had detached, and the rods remained attached to their respective pistons. Remnants of the connecting rod caps and bolts, along with two counterweights, fragments of counterweight bushings, a single counterweight pin, and four retaining rings and plates were found in the oil sump. Examination of the fracture surfaces of the remnants revealed features consistent with ductile overload, including granular and rough separation areas, bolt necking along with smear and bending damage consistent with impact. There was no evidence of scoring or heat distress to the rod journals or rod bearings contact surfaces for cylinder Nos. 1 and 2. The engine was then completely disassembled, and although the two counterweights for cylinder Nos. 3 and 4 were intact and essentially undamaged, one retaining ring, retainer plate, and pin were missing. The Continental Maintenance Manual applicable tothe engine gives specific instructions for the installation of the counterweight assembly. It states that the retaining rings, which are stamp-cut, have a sharp side and a beveled side, and should be installed with the sharp side out. The retaining ring ears should be installed towards the crankshaft centerline, and to confirm proper fitment after installation the gap between the ears should be no less than 0.179 inches (Figure 1). Figure 1 – One of the counterweights with its retaining plates and rings, showing the incorrectly installed ring on the right. Examination of the engine revealed that one retaining ring on each of the remaining counterweights was installed incorrectly with the sharp side in, and both had ear-gaps of 0.11 (Figure 1) and 0.14 inches respectively. Continental Service Bulletin (SB) M93-4, issued in February 1993, reiterates the importance of thorough inspection and proper assembly of crankshaft counterweights during engine overhaul, or any time the crankshaft is removed from the engine. It warns that improper installation of the bushings, retaining plates, or retaining rings will cause engine failure. The SB also states that the retaining rings should be fully seated in the bushing bore grooves with the sharp edge facing out. ## Aircraft - Registration: [N4133S](https://openairdocs.org/deregistered/N4133S-2023-08-07), registration cancelled 2023-08-07, S/N CE-591, built 1975 (OpenAirDocs) - Reported make and model: BEECH F33A - Registry model: [Beech F33A](https://openairdocs.org/model/beech-f33a) (registry code 1151425) (OpenAirDocs) - Registry engine: [Continental IO-520 series](https://openairdocs.org/engine/continental-io-520-series) (registry code 17032, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: CE-591 - Year built: 1975 - Airframe hours: 2460.88 - Engines: Continental IO-520-BA 285 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Airworthiness certificate: Standard, Normal - Last inspection: Annual, June 21, 2022, 25 hours before - Departed: 50S, Parma, ID - Airport: 50S, Parma, runway 12/30, 2,700 × 50 ft, asphalt - Equipment: Stall warning system, ADS-B ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 43; injuries: minor; private; airplane ratings: single-engine land, multi-engine land; medical: class 2, with waivers/limitations; seat: left; flight hours: 200 total - Pilot; age 64; injuries: minor; commercial, flight instructor, airline transport; airplane ratings: single-engine land; instrument ratings: airplane; medical: class 2, with waivers/limitations; seat: right; flight hours: 10,000 total ## Weather - Conditions: Visual (VMC), Day - Wind: 260° at 6 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 97 °F, dew point 55 °F - Altimeter: 29.85 inHg - Observed at: KEUL, 13 nm away - METAR: KEUL 202356Z AUTO 26006KT 10SM CLR 36/13 A2985 RMK AO2 SLP081 T03560133 10361 20289 56014 ## 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 20220820014849A](https://openairdocs.org/incident/20220820014849A), Aug 20, 2022: Beech F33A, Parma, ID, Substantial damage. The aircraft was found oriented to the north in a field. It appears to have come in from the west and slid approximately 230 feet from the initial point of… ## Other investigations on N4133S (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 NYC98LA052](https://openairdocs.org/ntsb/NYC98LA052), Dec 24, 1997: Beech BE-33A (N4133S), Lancaster, PA, substantial damage. Probable cause: Passenger control interference which resulted in pilot's failure to maintain control of the airplane during landing. ## Docket (8 files) The files NTSB released with the investigation on April 25, 2024, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=105790. 7.0 MB in all. - Pilot/operator aircraft accident report, NTSB form 6120.1 (item 1, PDF, 9 pages, 2.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16418265&FileExtension=pdf&FileName=r_6120_Redacted-Rel.pdf - Memorandum of record - pilot (item 2, PDF, 2 pages, 77 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16429470&FileExtension=pdf&FileName=MOR-Rel.pdf - Initial engine disassembly report (item 3, PDF, 1 page, 638 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16417736&FileExtension=pdf&FileName=r_TCM%20IO520BA%20Teardown%20report_Redacted-Rel.pdf - Logbook excerpts (item 4, PDF, 6 pages, 2.1 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16418482&FileExtension=pdf&FileName=r_Logbook%20Excerpts_Redacted-Rel.pdf - Teledyne Continental service bulletin M93-4 (item 5, PDF, 2 pages, 111 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16418452&FileExtension=pdf&FileName=M93-4-Rel.pdf - Maintenance manual excerpts (item 6, PDF, 2 pages, 227 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16418275&FileExtension=pdf&FileName=MM%20Excerpt-Rel.pdf - NTSB photos (item 7, PDF, 3 pages, 1.4 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16417540&FileExtension=pdf&FileName=NTSB%20Photos-Rel.pdf - FAA photo (item 8, PDF, 1 page, 254 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=16418410&FileExtension=pdf&FileName=Photo%20FAA-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.